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Targeting the PI3K pathway and DNA damage response as a therapeutic strategy in ovarian cancer

Published:April 10, 2020DOI:https://doi.org/10.1016/j.ctrv.2020.102021

      Highlights

      • DNA damage response (DDR) pathways are active drug targets in ovarian cancer (OC).
      • PI3K pathway is involved in DNA replication and genome stability.
      • Inhibition of PI3K pathway augments DDR blockade-induced replication stress.
      • Dual inhibition of DDR and PI3K pathways is a potential therapeutic strategy in OC.
      • Biomarkers are critical for optimal patient selection.

      Abstract

      Ovarian cancer is the most lethal gynecological malignancy worldwide although exponential progress has been made in its treatment over the last decade. New agents and novel combination treatments are on the horizon. Among many new drugs, a series of PI3K/AKT/mTOR pathway (referred to as the PI3K pathway) inhibitors are under development or already in clinical testing. The PI3K pathway is frequently upregulated in ovarian cancer and activated PI3K signaling contributes to increased cell survival and chemoresistance. However, no significant clinical success has been achieved with the PI3K pathway inhibitor(s) to date, reflecting the complex biology and also highlighting the need for combination treatment strategies. DNA damage repair pathways have been active therapeutic targets in ovarian cancer. Emerging data suggest the PI3K pathway is also involved in DNA replication and genome stability, making DNA damage response (DDR) inhibitors as an attractive combination treatment for PI3K pathway blockades. This review describes an expanded role for the PI3K pathway in the context of DDR and cell cycle regulation. We also present the novel treatment strategies combining PI3K pathway inhibitors with DDR blockades to improve the efficacy of these inhibitors for ovarian cancer.

      Keywords

      Introduction

      Ovarian cancer is the deadliest gynecologic malignancy in industrialized countries [
      • Siegel R.L.
      • Miller K.D.
      • Jemal A.
      Cancer statistics, 2019.
      ]. Most women with ovarian cancer are diagnosed at advanced stages and recurrence is common after initial platinum-based chemotherapy leading to incurable disease with limited treatment options [
      • Lheureux S.
      • Gourley C.
      • Vergote I.
      • Oza A.M.
      Epithelial ovarian cancer.
      ]. Therefore, a critical need remains for new effective therapeutic strategies.
      The phosphoinositide 3-kinase (PI3K)/AKT/mechanistic target of rapamycin (mTOR) pathway (referred to as the PI3K pathway) is the most frequently altered signaling, found in ~70% of ovarian cancer [
      • Lheureux S.
      • Gourley C.
      • Vergote I.
      • Oza A.M.
      Epithelial ovarian cancer.
      ,
      • Ediriweera M.K.
      • Tennekoon K.H.
      • Samarakoon S.R.
      Role of the PI3K/AKT/mTOR signaling pathway in ovarian cancer: Biological and therapeutic significance.
      ]. PI3K pathway activation is associated with aggressive phenotypes, chemoresistance and poor prognosis in ovarian cancer [
      • Lheureux S.
      • Gourley C.
      • Vergote I.
      • Oza A.M.
      Epithelial ovarian cancer.
      ,
      • Ediriweera M.K.
      • Tennekoon K.H.
      • Samarakoon S.R.
      Role of the PI3K/AKT/mTOR signaling pathway in ovarian cancer: Biological and therapeutic significance.
      ], making it an important target for treatment. However, only limited clinical activity has been observed with PI3K pathway inhibitors thus far despite the high frequency of PI3K pathway activation in ovarian cancer [
      • Yang J.
      • Nie J.
      • Ma X.
      • Wei Y.
      • Peng Y.
      • Wei X.
      Targeting PI3K in cancer: mechanisms and advances in clinical trials.
      ]. Hence, it is necessary to develop new combination strategies to improve the efficacy of PI3K pathway blockades.
      DNA damage response (DDR) pathways are active therapeutic targets in ovarian cancer. The successful introduction of poly (ADP-ribose) polymerase inhibitor (PARPi) has led to a new treatment paradigm in this disease, particulary for those with BRCA mutations [
      • Mirza M.R.
      • Pignata S.
      • Ledermann J.A.
      Latest clinical evidence and further development of PARP inhibitors in ovarian cancer.
      ]. Also, blockades of ataxia-telangiectasia and Rad3-related (ATR)/cell cycle checkpoint kinase 1 (CHK1) cell cycle pathway are currently being investigated in ovarian cancer [
      • Ivy S.P.
      • Kunos C.A.
      • Arnaldez F.I.
      • Kohn E.C.
      Defining and targeting wild-type BRCA high-grade serous ovarian cancer: DNA repair and cell cycle checkpoints.
      ]. Therefore, an improved understanding of the mechanisms underlying the PI3K pathway and its interactions with other pathways becomes more important to identify the optimal combination treatment candidates. In line with this, emerging preclinical data suggest synergistic cytotoxicity of the combination of PI3K pathway inhibitors and DDR blockades in high-grade serous ovarian cancer (HGSOC) [
      • Huang T.T.
      • Brill E.
      • Thomas C.J.
      • Lee J.M.
      Augmented apoptosis and DNA damage by the combined inhibition of CHK1 and PI3K, mTOR pathways in high-grade serous ovarian cancer (Abstract PB-092). 30th EORTC-NCI-AACR SYMPOSIUM, 13–16; Dublin, Ireland.
      ,
      • Dempsey J.
      • Donoho G.
      • Iversen P.
      • Stephens J.
      • McNulty A.
      • Martinez R.
      • et al.
      Abstract 1761: Inhibition of PI3K/AKT/mTOR signaling by a dual PI3K/mTOR inhibitor (LY3023414) potentiates the antitumor efficacy of the Chk1 inhibitor prexasertib (LY2606368) in models of human high-grade serous ovarian cancer (HGSOC).
      ,
      • O'Neil J.
      • Benita Y.
      • Feldman I.
      • Chenard M.
      • Roberts B.
      • Liu Y.
      • et al.
      An unbiased oncology compound screen to identify novel combination strategies.
      ]. Here, we briefly review the PI3K and DDR pathways with a focus on the relevance to preclinical evidence and clinical development of dual inhibition of these two pathways. We use HGSOC as an example and refer to other rare subtypes, i.e., clear cell or endometrioid ovarian cancer where appropriate this review.

      Alteration of PI3K pathway in ovarian cancer

      Fig. 1 illustrates an overview of the PI3K pathway. Briefly, upon activation, active PI3K phosphorylates PI(4,5)P2 to PI(3,4,5)P3, which consequently activates AKT and its downstream effector mTOR, leading to the entire pathway activation and cell growth. There is a positive feedback loop between AKT and mTORC2 while PTEN and INPP4B negatively regulate the PI3K pathway by converting active PI(3,4,5)P3 to inactive forms [
      • Ediriweera M.K.
      • Tennekoon K.H.
      • Samarakoon S.R.
      Role of the PI3K/AKT/mTOR signaling pathway in ovarian cancer: Biological and therapeutic significance.
      ].
      Figure thumbnail gr1
      Fig. 1An overview of the PI3K pathway. Upon RTK activation induced by growth factors, PI3K phosphorylates PI(3,4)P2 to generate PI(3,4,5)P3. PI(3,4,5)P3 then recruits PDK1 to activate AKT. Individal isoforms of PI3K or AKT are not shown here. mTOR is downstream of AKT. The mTOR complex consists of two components; mTORC1-Raptor and mTORC2-Rictor. AKT directly activates mTOR via phosphorylating mTORC1 or indirectly activates mTORC1 by inhibiting TSC 1/2. mTORC1 phosphorylates the 4E-BP1 and the S6K, which consequently enhances the translation of mRNA encoding proteins, responsible for cell survival (i.e., survivin), proliferation (i.e., Forkhead box O family) and DNA damage response (i.e., BRCA1). There are positive and negative feedback loops for active PI3K signaling. mTORC2 triggers positive feedback on PI3K pathway activation by phosphorylating AKT at Ser473. PTEN and INPP4B negatively regulate the PI3K pathway via converting PI(3,4,5)P3 back to inactive forms, thus impairing AKT activation. Abbreviations: 4E-BP1 = eukaryotic initiation factor 4E binding protein 1; eIF4E = eukaryotic initiation factor 4E; GPCR = G-protein coupled receptor; INPP4B = inositol Polyphosphate 4-phosphatase type II; mTORC = mammalian target of rapamycin complex; PDK1 = phosphoinositide dependent kinases 1; PI3K = phosphatidylinositol 3-kinase; PI3P = phosphatidylinositol 3-phosphate; PI(3,4)P2 = phosphatidylinositol-3,4-bisphosphate; PI(4,5)P2 = phosphatidylinositol-4,5-bisphosphate; PI(3,4,5)P3 = phosphatidylinositol-3,4,5-trisphosphate; PTEN = tumor suppressor phosphatase and tensin homolog; RTK = receptor tyrosine kinase; S6 = ribosomal protein S6; S6K = ribosomal protein S6 kinase; SHP1/2 = SH-2 containing inositol 5′ polyphosphatase 1/2; TSC1/2 = tuberous sclerosis complex 1 and 2.
      The prevalence of aberrant PI3K pathway activations in ovarian cancer varies depending on the histology. The main histologic subtypes are epithelial in origin and include HGSOC (~70%), endometrioid carcinoma (10–15%), ovarian clear cell carcinoma (OCCC, 5–10%), low-grade serous carcinoma (3%), and mucinous carcinoma (2–8%) [
      • Lheureux S.
      • Gourley C.
      • Vergote I.
      • Oza A.M.
      Epithelial ovarian cancer.
      ,
      • Ediriweera M.K.
      • Tennekoon K.H.
      • Samarakoon S.R.
      Role of the PI3K/AKT/mTOR signaling pathway in ovarian cancer: Biological and therapeutic significance.
      ]. PIK3CA mutations and PTEN deletion are more prevalent in OCCC (20–46% and 20%, respectively) and endometrioid carcinoma (12–20% and 40%, respectively) while they occur rarely in HGSOC (2.3–3.7% and 7%, respectively) [
      • Lheureux S.
      • Gourley C.
      • Vergote I.
      • Oza A.M.
      Epithelial ovarian cancer.
      ,
      • Ediriweera M.K.
      • Tennekoon K.H.
      • Samarakoon S.R.
      Role of the PI3K/AKT/mTOR signaling pathway in ovarian cancer: Biological and therapeutic significance.
      ]. Although PIK3CA, AKT or inactivating PTEN mutations are rare in HGSOC, the genomic amplification of PIK3CA (~20%) and AKT isoforms (10–15%), or deletions of PTEN (5%) are not uncommon in HGSOC [
      • Lheureux S.
      • Gourley C.
      • Vergote I.
      • Oza A.M.
      Epithelial ovarian cancer.
      ,
      • Ediriweera M.K.
      • Tennekoon K.H.
      • Samarakoon S.R.
      Role of the PI3K/AKT/mTOR signaling pathway in ovarian cancer: Biological and therapeutic significance.
      ]. Also, approximately one-quarter to one-third of HGSOC express the phosphorylated eukaryotic initiation factor 4E binding protein 1 (4E-BP1) and ribosomal protein S6 kinase (S6K), downstream targets of mTOR, suggesting enhanced active PI3K signaling in subsets of HGSOC [
      • Castellvi J.
      • Garcia A.
      • Rojo F.
      • Ruiz-Marcellan C.
      • Gil A.
      • Baselga J.
      • et al.
      Phosphorylated 4E binding protein 1: a hallmark of cell signaling that correlates with survival in ovarian cancer.
      ]. Accordingly, analysis of the Cancer Genome Atlas data indicates that higher expressions of AKT or MTOR are associated with poor clinical outcome in advanced HGSOC [
      • Ghoneum A.
      • Said N.
      PI3K-AKT-mTOR and NFkappaB pathways in ovarian cancer: Implications for targeted therapeutics.
      ]. Hence, utilizing PI3K pathway inhibitors may have broader clinical applicability in ovarian cancer, regardless of its histological subtypes.
      The initial preclinical studies evaluating PI3K pathway inhibitors demonstrate that chemical inhibition of PI3K pathway induces cell killing in ovarian cancer models, in particular, those with PIK3CA or PIK3R1 activating mutations, or PTEN loss-of-function [
      • Janku F.
      • Yap T.A.
      • Meric-Bernstam F.
      Targeting the PI3K pathway in cancer: are we making headway?.
      ]. However, the clinical application of PI3K pathway inhibitors has been limited in ovarian cancers, even among tumors with PIK3CA-activating mutations, reflecting the complex biology [
      • Banerji U.
      • Dean E.J.
      • Perez-Fidalgo J.A.
      • Batist G.
      • Bedard P.L.
      • You B.
      • et al.
      A phase i open-label study to identify a dosing regimen of the pan-AKT inhibitor AZD5363 for evaluation in solid tumors and in PIK3CA-mutated breast and gynecologic cancers.
      ,
      • Hasegawa K.
      • Kagabu M.
      • Mizuno M.
      • Oda K.
      • Aoki D.
      • Mabuchi S.
      • et al.
      Phase II basket trial of perifosine monotherapy for recurrent gynecologic cancer with or without PIK3CA mutations.
      ]. Currently, work has been focused on identifying selective pathway inhibitors and studying combined treatments to enhance the efficacy of PI3K pathway inhibitors [
      • Ediriweera M.K.
      • Tennekoon K.H.
      • Samarakoon S.R.
      Role of the PI3K/AKT/mTOR signaling pathway in ovarian cancer: Biological and therapeutic significance.
      ]. The focus of this review will be combination therapy of PI3K pathway and DDR blockades.

      Interactions of PI3K pathway with DDR and therapeutic opportunities

      Active PI3K signaling promotes cell survival partly by regulating DDR [
      • Ma Y.
      • Vassetzky Y.
      • Dokudovskaya S.
      mTORC1 pathway in DNA damage response.
      ]. DDR pathway is triggered by DNA damage sensors e.g., PI3K-like kinases (PIKKs). Three PIKKs include DNA-dependent protein kinase (DNA-PK), ataxia-telangiectasia mutated (ATM), and ATR. ATR is activated by DNA single-strand breaks (SSBs), specifically via persistent single-stranded DNA (ssDNA) coated with replication protein A, which is present at stalled replication forks [
      • Blackford A.N.
      • Jackson S.P.
      ATM, ATR, and DNA-PK: the trinity at the heart of the DNA damage response.
      ]. Conversely, ATM and DNA-PK are mainly activated by DNA double-strand breaks (DSBs) via MRE11-RAD50-NBS1 complex and Ku-bound DSB ends, respectively [
      • Blackford A.N.
      • Jackson S.P.
      ATM, ATR, and DNA-PK: the trinity at the heart of the DNA damage response.
      ]. Moreover, preclinical studies indicate that active PI3K signaling is involved in DNA replication, and thus PI3K pathway inhibition induces replication stress [
      • Lamm N.
      • Rogers S.
      • Cesare A.J.
      The mTOR pathway: Implications for DNA replication.
      ]. In support, mTORC1/2 inhibition (PP242) is found to prolong S phase arrest and increase γ-H2AX foci formation in TP53 and BRCA1 mutant SUM149 breast cancer cells [
      • Silvera D.
      • Ernlund A.
      • Arju R.
      • Connolly E.
      • Volta V.
      • Wang J.
      • et al.
      mTORC1 and -2 coordinate transcriptional and translational reprogramming in resistance to DNA damage and replicative stress in breast cancer cells.
      ]. Similarly, the mTOR/PIKK inhibitors (Torin2 and its chemical analogs) and a dual PI3K/mTOR inhibitor (PI3K/mTORi) omipalisib increase replication catastrophe and cell death during S and G2 phases in PI3K-activated triple-negative breast cancer (TNBC) cells [
      • Chopra S.S.
      • Jenney A.
      • Palmer A.
      • Niepel M.
      • Chung M.
      • Mills C.
      • et al.
      Torin2 exploits replication and checkpoint vulnerabilities to cause death of PI3K-activated triple-negative breast cancer cells.
      ]. The following section will describe the roles of PI3K signaling in the context of specific cell cycle phases and DNA repair pathways, and show the preclinical evidence of dual inhibition of PI3K signaling and cell cycle regulators in various cancers including ovarian cancer models.

      DNA replication, cell cycle checkpoints and PI3K signaling

      ATR/CHK1 pathway is essential for successful completion of DNA replication. Cell cycle checkpoints monitor the structural integrity of chromosomes before progression through crucial cell cycle stages. Fig. 2 shows a schematic view of cell cycle control pathways.
      Figure thumbnail gr2
      Fig. 2Cell cycle checkpoints. Checkpoints occur at entry into S phase (the G1/S checkpoint), during replication (intra-S checkpoints) and entry into mitosis (the G2/M checkpoint). For S and G2/M phase checkpoints, ATR activates CHK1 following replication stress-induced SSBs, which subsequently activates WEE1 or inhibits CDC25 phosphatases, leading to deactivation of CDKs. The attenuated CyclinB/CDK1 activity results in the stoppage of G2 to M transition. For G1/S checkpoint, ATM activates CHK2 following DNA DSBs, which in part activates p53. Active p53 transcriptionally induces expression of the CDK inhibitor p21, leading to inhibition of CyclinD/CDK4/6 and CyclinE/CDK2 complexes, thus causing G1 arrest. Proteins contributing to cell-cycle progression are indicated in white boxes, and cell-cycle arrest in gray boxes. Abbreviations: ATM = ataxia-telangiectasia mutate; ATR = ataxia-telangiectasia and Rad3-related; CDC25 = cell division cycle 25; CDK = cyclin-dependent kinase; CHK = cell cycle checkpoint kinase; DSBs = double-strand breaks; SSBs = single-strand breaks.
      The PI3K pathway is important in maintaining genomic stability by involving DNA replication and cell cycle regulation [
      • Lamm N.
      • Rogers S.
      • Cesare A.J.
      The mTOR pathway: Implications for DNA replication.
      ]. Accordingly, PI3K inhibition causes genomic instability and mitotic catastrophe by decreasing the activity of Aurora kinase B, a spindle assembly checkpoint protein, thus increasing the occurrence of lagging chromosomes during prometaphase [
      • Hou H.
      • Zhang Y.
      • Huang Y.
      • Yi Q.
      • Lv L.
      • Zhang T.
      • et al.
      Inhibitors of phosphatidylinositol 3'-kinases promote mitotic cell death in HeLa cells.
      ]. PI3K blockage also increases replication stress and subsequent DNA damage by depleting deoxynucleoside triphosphates (dNTP) in BRCA1-deficient TNBC models [
      • Juvekar A.
      • Hu H.
      • Yadegarynia S.
      • Lyssiotis C.A.
      • Ullas S.
      • Lien E.C.
      • et al.
      Phosphoinositide 3-kinase inhibitors induce DNA damage through nucleoside depletion.
      ].
      Similarly, mTOR inhibition interferes the DNA replication process. The mTOR inhibitor (mTORi) AZD8055 dislodges replication helicase minichromosome maintenance complex proteins 2–7 (MCM2-7) and proliferating cell nuclear antigen (PCNA) from chromatin and reduces the levels of replication factor CDC6, leading to replication stress and consequent ATR/CHK1 activation [
      • Wu X.
      • Li S.
      • Hu X.
      • Xiang X.
      • Halloran M.
      • Yang L.
      • et al.
      mTOR signaling upregulates CDC6 via suppressing miR-3178 and promotes the loading of DNA replication helicase.
      ]. Similarly, a recent study in OVCAR3 and SKOV3 ovarian cancer cell lines shows that a pan-mTORi INK128 decreases the levels of DNA replication-related proteins i.e., POLQ and cell cycle regulators, i.e., FBXW7 [
      • David-West G.
      • Ernlund A.
      • Gadi A.
      • Schneider R.J.
      mTORC1/2 inhibition re-sensitizes platinum-resistant ovarian cancer by disrupting selective translation of DNA damage and survival mRNAs.
      ], causing replication stress.
      AKT also regulates the progression of DNA replication. In response to replication stress, AKT is required for efficient PCNA ubiquitylation, as shown in homologous recombination (HR)-deficient TNBC and colon cancer cells [
      • Villafanez F.
      • Garcia I.A.
      • Carbajosa S.
      • Pansa M.F.
      • Mansilla S.
      • Llorens M.C.
      • et al.
      AKT inhibition impairs PCNA ubiquitylation and triggers synthetic lethality in homologous recombination-deficient cells submitted to replication stress.
      ]. As such, a pan-AKT inhibitor (AKTi) C11 or a pan-PI3K inhibitor (PI3Ki) LY294002 blocks the recruitment of translesion synthesis polymerases at sites of DNA damage, thus hindering the progression of DNA replication forks after UV irradiation, leading to replication stress and cell death [
      • Villafanez F.
      • Garcia I.A.
      • Carbajosa S.
      • Pansa M.F.
      • Mansilla S.
      • Llorens M.C.
      • et al.
      AKT inhibition impairs PCNA ubiquitylation and triggers synthetic lethality in homologous recombination-deficient cells submitted to replication stress.
      ]. Together, these data indicate crosstalk between PI3K signaling and DNA replication process for genomic stability, therefore, the PI3K pathways is an actionable target to induce replication stress and genomic instability in cancer cells.
      AKT has an expanded role in interacting with major cell cycle regulators. Active AKT inhibits CHK1 by directly phosphorylating CHK1 at Ser280 which causes non-functioning cytoplasmic sequestration of CHK1, leading to premature mitotic entry and mitotic catastrophe in BRCA wild-type cell lines including MCF7 breast cancer, human epithelial and mouse embryonic stem cells [
      • Puc J.
      • Keniry M.
      • Li H.S.
      • Pandita T.K.
      • Choudhury A.D.
      • Memeo L.
      • et al.
      Lack of PTEN sequesters CHK1 and initiates genetic instability.
      ,
      • Shtivelman E.
      • Sussman J.
      • Stokoe D.
      A role for PI 3-kinase and PKB activity in the G2/M phase of the cell cycle.
      ]. Similarly, in BRCA1-deficient mouse embryo fibroblasts, AKT1 depletion increases CHK1 nuclear localization and RAD51 foci formation for DNA repair and cell survival following irradiation-induced DSBs [
      • Jia Y.
      • Song W.
      • Zhang F.
      • Yan J.
      • Yang Q.
      Akt1 inhibits homologous recombination in Brca1-deficient cells by blocking the Chk1-Rad51 pathway.
      ]. It appears that AKT has a similar inhibitory role on CHK1 in both BRCA-deficient and -proficient settings, unlike its conflicting function on HR repair in different preclinical models which will be described later.
      AKT also downregulates CDK activity via activating the CDK inhibitors p21 and p27 [
      • Manning B.D.
      • Toker A.
      AKT/PKB signaling: navigating the network.
      ]. AKT directly phosphorylates p21 at Ser146 and further increases the assembly of CyclinD/CDK4 complex for G1/S transition [
      • Manning B.D.
      • Toker A.
      AKT/PKB signaling: navigating the network.
      ]. Separately, AKT phosphorylates p27 at Thr157 thus relocates p27 to the cytoplasm. This relocation of p27 consequently releases the nuclear substrates CyclinE/CDK2 and CyclinA/CDK2 from p27, inducing cell cycle progression [
      • Manning B.D.
      • Toker A.
      AKT/PKB signaling: navigating the network.
      ].
      It is noteworthy that each isoform of AKT (referred to as AKT unless an isoform-specific function is noted) has distinct roles in tumorigenesis. In murine ID8 ovarian cancer cells, AKT1 or AKT3 knockdown shows impaired tumor growth and metastasis, whereas AKT2 knockdown results in increased tumor proliferation and metastasis [
      • Linnerth-Petrik N.M.
      • Santry L.A.
      • Moorehead R.
      • Jucker M.
      • Wootton S.K.
      • Petrik J.
      Akt isoform specific effects in ovarian cancer progression.
      ]. Cristiano et al. also found that total AKT activity for cell proliferation was mainly driven by AKT3. In OVCA429 and DOV13 ovarian cancer cells which have higher total AKT activity, AKT3 but not AKT1 activity is required to induce cell growth by activating CDK1 and G2/M transition [
      • Cristiano B.E.
      • Chan J.C.
      • Hannan K.M.
      • Lundie N.A.
      • Marmy-Conus N.J.
      • Campbell I.G.
      • et al.
      A specific role for AKT3 in the genesis of ovarian cancer through modulation of G(2)-M phase transition.
      ]. The distinct roles of AKT need more mechanistic investigation in various ovarian cancer models as the different AKT isoforms may exert independent, even opposing effects under physiological and pathological conditions.

      PI3K pathway inhibitors in combination with cell cycle blockade as a therapeutic strategy

      Blocking ATR/CHK1 signaling has been hypothesized to promote replication stress, lethal DNA damage and cell death in p53-deficient tumors including HGSOC [
      • Lee J.M.
      • Nair J.
      • Zimmer A.
      • Lipkowitz S.
      • Annunziata C.M.
      • Merino M.J.
      • et al.
      Prexasertib, a cell cycle checkpoint kinase 1 and 2 inhibitor, in BRCA wild-type recurrent high-grade serous ovarian cancer: a first-in-class proof-of-concept phase 2 study.
      ,
      • Murai J.
      Targeting DNA repair and replication stress in the treatment of ovarian cancer.
      ,
      • Brill E.
      • Yokoyama T.
      • Nair J.
      • Yu M.
      • Ahn Y.R.
      • Lee J.M.
      Prexasertib, a cell cycle checkpoint kinases 1 and 2 inhibitor, increases in vitro toxicity of PARP inhibition by preventing Rad51 foci formation in BRCA wild type high-grade serous ovarian cancer.
      ]. As discussed earlier, the PI3K pathway blockades can enhance replication stress. In support, we and other groups found that the CHK1 inhibitor (CHK1i) prexasertib yielded a synergistic anti-tumor effect when combined with a dual PI3K/mTORi LY3023414 in TNBC patient-derived xenografts [
      • Wu W.
      • Donoho G.
      • Iversen P.
      • Dempsey J.
      • Capen A.
      • Castanares M.
      • et al.
      Abstract 3508: Combination of the Chk1 inhibitor (prexasertib) with a PI3K/mTOR inhibitor (LY3023414) induces synergistic anti-tumor activity in triple negative breast cancer (TNBC) models.
      ] and HGSOC cell lines and xenograft models [
      • Huang T.T.
      • Brill E.
      • Thomas C.J.
      • Lee J.M.
      Augmented apoptosis and DNA damage by the combined inhibition of CHK1 and PI3K, mTOR pathways in high-grade serous ovarian cancer (Abstract PB-092). 30th EORTC-NCI-AACR SYMPOSIUM, 13–16; Dublin, Ireland.
      ,
      • Dempsey J.
      • Donoho G.
      • Iversen P.
      • Stephens J.
      • McNulty A.
      • Martinez R.
      • et al.
      Abstract 1761: Inhibition of PI3K/AKT/mTOR signaling by a dual PI3K/mTOR inhibitor (LY3023414) potentiates the antitumor efficacy of the Chk1 inhibitor prexasertib (LY2606368) in models of human high-grade serous ovarian cancer (HGSOC).
      ], possibly by causing greater replication stress compared to monotherapy [
      • Dempsey J.
      • Donoho G.
      • Iversen P.
      • Stephens J.
      • McNulty A.
      • Martinez R.
      • et al.
      Abstract 1761: Inhibition of PI3K/AKT/mTOR signaling by a dual PI3K/mTOR inhibitor (LY3023414) potentiates the antitumor efficacy of the Chk1 inhibitor prexasertib (LY2606368) in models of human high-grade serous ovarian cancer (HGSOC).
      ]. Similarly, the combinations of mTORi AZD8055 with ATR inhibitor AZ20 or CHK1i rabusertib showed synergistic cytotoxicities via inducing replication stress in PI3K-activated TNBC cell models with an activating PIK3CA mutation (H1047R) or low levels of PTEN and/or INPP4B [
      • Chopra S.S.
      • Jenney A.
      • Palmer A.
      • Niepel M.
      • Chung M.
      • Mills C.
      • et al.
      Torin2 exploits replication and checkpoint vulnerabilities to cause death of PI3K-activated triple-negative breast cancer cells.
      ]. In OCCC and HGSOC cell lines, BEZ235, a dual PI3K/mTORi that also targets ATR, decreased cell proliferation and resensitized cisplatin-resistant cells to cisplatin [
      • Oishi T.
      • Itamochi H.
      • Kudoh A.
      • Nonaka M.
      • Kato M.
      • Nishimura M.
      • et al.
      The PI3K/mTOR dual inhibitor NVP-BEZ235 reduces the growth of ovarian clear cell carcinoma.
      ,
      • Santiskulvong C.
      • Konecny G.E.
      • Fekete M.
      • Chen K.Y.
      • Karam A.
      • Mulholland D.
      • et al.
      Dual targeting of phosphoinositide 3-kinase and mammalian target of rapamycin using NVP-BEZ235 as a novel therapeutic approach in human ovarian carcinoma.
      ].
      WEE1 is another key checkpoint at the G2/M transition [
      • Murai J.
      Targeting DNA repair and replication stress in the treatment of ovarian cancer.
      ]. WEE1 inhibitor AZD1775 in combination with mTORi ridaforolimus is synergistically cytotoxic in HGSOC and OCCC cell lines independent of their BRCA and KRAS mutation status [
      • O'Neil J.
      • Benita Y.
      • Feldman I.
      • Chenard M.
      • Roberts B.
      • Liu Y.
      • et al.
      An unbiased oncology compound screen to identify novel combination strategies.
      ]. Similarly, WEE1 serves as an adaptive resistant kinase after PI3K inhibition in glioblastoma cell and in vivo models, where the combination treatment of WEE1 inhibition (AZD1775) with pan-PI3Ki buparlisib caused a synergistic cytotoxic effect [
      • Wu S.
      • Wang S.
      • Gao F.
      • Li L.
      • Zheng S.
      • Yung W.K.A.
      • et al.
      Activation of WEE1 confers resistance to PI3K inhibition in glioblastoma.
      ]. Kuzu et al. also reported that knockdown of AKT3 and WEE1 synergistically inhibited melanoma cell proliferation and xenograft tumor growth [
      • Kuzu O.F.
      • Gowda R.
      • Sharma A.
      • Noory M.A.
      • Kardos G.
      • Madhunapantula S.V.
      • et al.
      Identification of WEE1 as a target to make AKT inhibition more effective in melanoma.
      ].
      Moreover, HGSOC with CCNE1 amplification, which accounts for approximately 20% of HGSOC [
      • Lheureux S.
      • Gourley C.
      • Vergote I.
      • Oza A.M.
      Epithelial ovarian cancer.
      ], may serve as a synthetically lethal model of HGSOC for this dual pathway blockade. CyclinE1/CDK2 complex promotes DNA replication and chromosome segregation by activating S phase-specific genes, i.e., CDC6 and MCM2-7, thus facilitating the formation of DNA replication complexes for S phase entry [
      • Coverley D.
      • Laman H.
      • Laskey R.A.
      Distinct roles for cyclins E and A during DNA replication complex assembly and activation.
      ]. This increased premature S-phase entry leads to replication stress and consequent cell death in HGSOC cell lines [
      • Au-Yeung G.
      • Lang F.
      • Azar W.J.
      • Mitchell C.
      • Jarman K.E.
      • Lackovic K.
      • et al.
      Selective targeting of cyclin e1-amplified high-grade serous ovarian cancer by cyclin-dependent kinase 2 and AKT inhibition.
      ]. As such, AKT inhibition by MK-2206 or GSK2110183 showed synergistic cytotoxicity with a CDK2 inhibitor dinaciclib in CCNE1-amplified HGSOC cell lines [
      • Au-Yeung G.
      • Lang F.
      • Azar W.J.
      • Mitchell C.
      • Jarman K.E.
      • Lackovic K.
      • et al.
      Selective targeting of cyclin e1-amplified high-grade serous ovarian cancer by cyclin-dependent kinase 2 and AKT inhibition.
      ]. Notably, this synergism was not observed with other PI3Ki or mTORi, implying the interaction with CCNE1 may be specific to AKT [
      • Au-Yeung G.
      • Lang F.
      • Azar W.J.
      • Mitchell C.
      • Jarman K.E.
      • Lackovic K.
      • et al.
      Selective targeting of cyclin e1-amplified high-grade serous ovarian cancer by cyclin-dependent kinase 2 and AKT inhibition.
      ] since AKT directly phosphorylates CDK2 and therefore causes a temporary cytoplasmic localization of the CyclinA/CDK2 complex [
      • Manning B.D.
      • Toker A.
      AKT/PKB signaling: navigating the network.
      ].
      Overall, these results support that inhibition of ATR, CHK1, WEE1, or their downstream kinase CDK2 can be a promising combination treatment strategy to increase the efficacy of PI3K pathway inhibitors given its interactions with DNA replication and G2/M cell cycle checkpoints, requiring further evaluation in the clinical setting.

      Roles of the PI3K pathway in DNA repair pathways

      DNA repair process occurs during cell cycle arrest. DSBs are repaired by two major pathways including non-homologous end-joining (NHEJ) and HR repair. HR repair facilitates error-free repair of DSBs primarily during the S and G2 phases, while NHEJ is the preferred DSB repair pathway in the G1 phase [
      • Her J.
      • Bunting S.F.
      How cells ensure correct repair of DNA double-strand breaks.
      ]. The following section will elaborate on the interaction between these two repair signalings and the PI3K pathway. Fig. 3 shows the interactions between PI3K and DNA repair pathways.
      Figure thumbnail gr3
      Fig. 3Crosstalk between PI3K signaling and DNA damage repair pathways. Cytoplasmic PI3K signaling can regulate HR pathway via mTOR-mediated protein synthesis and gene transcription of HR repair while nuclear PI3K signaling can regulate both HR and NHEJ pathways via active AKT. Upon PI3K pathway activation, mTORC1 increases protein synthesis of HR repair proteins e.g., BRCA1, RAD50, RAD51 and FANCD2 by phosphorylating 4E-BP1 and S6K. mTORC2 also increases FANCD2 transcripts by phosphorylating NF-κB which consequently increases its loading onto the promoter region of FANCD2. In addition, PI3K can indirectly downregulate the BRCA1 and BRCA2 transcriptions through compensatory MEK/ERK/EST1 pathway activation. Separately, DNA damage sensors including ATM and DNA-PK induce nuclear AKT activation in response to DSBs. Active AKT blocks nuclear translocation of BRCA1 from cytoplasm leading to impaired HR repair. It also indirectly inhibits BRCA2 via EMSY phosphorylation, resulting in the downregulation of HR pathway. For NHEJ repair, active AKT enhances NHEJ pathway by promoting autophosphorylation of DNA-PKcs. It also stabilizes UBE2S thereby enhances its association with Ku70. Active Ku70 then recruits DNA-PKcs to DSBs sites leading to activation of DNA-PKcs kinase to initiate NHEJ repair process. White boxes represent cytoplasmic proteins, gray boxes are nuclear proteins and black boxes indicate DNA repair proteins. Abbreviations: 4E-BP1 = eukaryotic initiation factor 4E binding protein 1; ATM = ataxia-telangiectasia mutated; DNA-PK = DNA-dependent protein kinase; DNA-PKcs = DNA-dependent protein kinase; DSBs = DAN-double stranded breaks; EMSY = BRCA2-interacting transcriptional repressor; EST1 = transcriptional repressor E26 transformation-specific-1; FANCD2 = Fanconi Anemia complementation group D2; HR = homologous recombination; mTORC = mammalian target of rapamycin complex; NHEJ = non-homologous end joining; PI3K = phosphatidylinositol 3-kinase; S6K = ribosomal protein S6 kinase; UBE2S = ubiquitin-conjugating enzyme E2S.

      HR repair and PI3K signaling

      HGSOC is characterized by universal TP53 mutation and half of them harbors defects in HR repair genes [
      • Lheureux S.
      • Gourley C.
      • Vergote I.
      • Oza A.M.
      Epithelial ovarian cancer.
      ]. The essential role of BRCA1 and BRCA2 proteins in HR repair has been extensively documented [
      • Roy R.
      • Chun J.
      • Powell S.N.
      BRCA1 and BRCA2: different roles in a common pathway of genome protection.
      ]. In brief, BRCA1 acts at an early HR step to promote end resection, and then recruits PALB2 to assist BRCA2 chromatin localization at a later step [
      • Roy R.
      • Chun J.
      • Powell S.N.
      BRCA1 and BRCA2: different roles in a common pathway of genome protection.
      ]. BRCA2 subsequently loads RAD51 recombinase onto the resection site to form a RAD51-ssDNA filament. RAD51-ssDNA filaments are necessary for HR partly by preventing the engagement of the 3′-ssDNA into the deleterious single-strand annealing pathway [
      • Roy R.
      • Chun J.
      • Powell S.N.
      BRCA1 and BRCA2: different roles in a common pathway of genome protection.
      ]. It has been well known that cancer cells including ovarian cancer with deficient BRCA1 or BRCA2 are highly sensitive to PARP1 inhibition or knockdown [
      • Helleday T.
      The underlying mechanism for the PARP and BRCA synthetic lethality: clearing up the misunderstandings.
      ]. Now, PARPis are one of the most active new drug families in the drug armamentarium for ovarian cancer. Good reviews have been published describing PARPi, therefore, it will not be summarized here [
      • Mirza M.R.
      • Pignata S.
      • Ledermann J.A.
      Latest clinical evidence and further development of PARP inhibitors in ovarian cancer.
      ,
      • Slade D.
      PARP and PARG inhibitors in cancer treatment.
      ].
      PI3K inhibition can induce BRCA-deficient phenotype in tumors with BRCA wild-type. Mechanistically, PI3K inhibition triggers a compensatory upregulation of MEK/ERK signaling, as shown in breast and ovarian cancer models [
      • Wang D.
      • Wang M.
      • Jiang N.
      • Zhang Y.
      • Bian X.
      • Wang X.
      • et al.
      Effective use of PI3K inhibitor BKM120 and PARP inhibitor Olaparib to treat PIK3CA mutant ovarian cancer.
      ,
      • Wang D.
      • Li C.
      • Zhang Y.
      • Wang M.
      • Jiang N.
      • Xiang L.
      • et al.
      Combined inhibition of PI3K and PARP is effective in the treatment of ovarian cancer cells with wild-type PIK3CA genes.
      ,
      • Ibrahim Y.H.
      • Garcia-Garcia C.
      • Serra V.
      • He L.
      • Torres-Lockhart K.
      • Prat A.
      • et al.
      PI3K inhibition impairs BRCA1/2 expression and sensitizes BRCA-proficient triple-negative breast cancer to PARP inhibition.
      ]. This activated MEK/ERK signaling induces the binding of the transcriptional repressor E26 transformation-specific-1 to the BRCA1 and BRCA2 promoter regions, resulting in decreased BRCA1 and BRCA2 transcripts and proteins [
      • Wang D.
      • Wang M.
      • Jiang N.
      • Zhang Y.
      • Bian X.
      • Wang X.
      • et al.
      Effective use of PI3K inhibitor BKM120 and PARP inhibitor Olaparib to treat PIK3CA mutant ovarian cancer.
      ,
      • Wang D.
      • Li C.
      • Zhang Y.
      • Wang M.
      • Jiang N.
      • Xiang L.
      • et al.
      Combined inhibition of PI3K and PARP is effective in the treatment of ovarian cancer cells with wild-type PIK3CA genes.
      ,
      • Ibrahim Y.H.
      • Garcia-Garcia C.
      • Serra V.
      • He L.
      • Torres-Lockhart K.
      • Prat A.
      • et al.
      PI3K inhibition impairs BRCA1/2 expression and sensitizes BRCA-proficient triple-negative breast cancer to PARP inhibition.
      ].
      The roles of AKT1 in HR repair are contradictory in literature. In HR-proficient models, AKT1 inhibits HR repair by reducing the nuclear foci formation of BRCA1 and RAD51 following irradiation-induced DNA damages, as shown in BRCA-proficient MCF7 breast cancer cells [
      • Plo I.
      • Laulier C.
      • Gauthier L.
      • Lebrun F.
      • Calvo F.
      • Lopez B.S.
      AKT1 inhibits homologous recombination by inducing cytoplasmic retention of BRCA1 and RAD51.
      ] and hamster ovary cells [
      • Plo I.
      • Lopez B.
      AKT1 represses gene conversion induced by different genotoxic stresses and induces supernumerary centrosomes and aneuploidy in hamster ovary cells.
      ]. However, AKT1 is also reported to promote HR in other studies. AKT1 phosphorylates BRCA1 at Ser694 following hormone stimulation, thus protecting BRCA1 from proteasomal degradation, and also promotes nuclear assembly of BRCA1 complexes in MCF7 breast cancer cells [
      • Nelson A.C.
      • Lyons T.R.
      • Young C.D.
      • Hansen K.C.
      • Anderson S.M.
      • Holt J.T.
      AKT regulates BRCA1 stability in response to hormone signaling.
      ]. AKT1 also increases nuclear RAD51 foci formation at the DSBs, thus inducing HR repair in lung cancer cells [
      • Mueck K.
      • Rebholz S.
      • Harati M.D.
      • Rodemann H.P.
      • Toulany M.
      Akt1 stimulates homologous recombination repair of DNA double-strand breaks in a Rad51-dependent manner.
      ]. In HR-deficient cells, AKT1 partly impairs HR by suppressing CHK1 nuclear localization, which disrupts the interaction between CHK1 and RAD51 [
      • Jia Y.
      • Song W.
      • Zhang F.
      • Yan J.
      • Yang Q.
      Akt1 inhibits homologous recombination in Brca1-deficient cells by blocking the Chk1-Rad51 pathway.
      ]. Furthermore, AKT1 indirectly downregulates HR by activating BRCA2-interacting transcriptional repressor EMSY, resulting in decreased function of BRCA2 [
      • Ezell S.A.
      • Polytarchou C.
      • Hatziapostolou M.
      • Guo A.
      • Sanidas I.
      • Bihani T.
      • et al.
      The protein kinase Akt1 regulates the interferon response through phosphorylation of the transcriptional repressor EMSY.
      ]. More studies are needed to better understand the interactions between AKT and BRCA in HR repair to guide the combination treatment approaches using AKTi.

      NHEJ repair and PI3K signaling

      AKT is also involved in NHEJ-mediated DSB repair. AKT enhances NHEJ repair by forming a complex with DNA-PKcs (DNA-PK catalytic subunit) and stimulating its autophosphorylation [
      • Liu Q.
      • Turner K.M.
      • Alfred Yung W.K.
      • Chen K.
      • Zhang W.
      Role of AKT signaling in DNA repair and clinical response to cancer therapy.
      ]. AKT can also increase the stability of ubiquitin-conjugating enzyme E2S (UBE2S) as well as its association with Ku70 which is essential for the activation of DNA-PKcs kinase [
      • Hu L.
      • Li X.
      • Liu Q.
      • Xu J.
      • Ge H.
      • Wang Z.
      • et al.
      UBE2S, a novel substrate of Akt1, associates with Ku70 and regulates DNA repair and glioblastoma multiforme resistance to chemotherapy.
      ]. Consistently, AKT depletion results in decreased NHEJ repair in non-small cell lung cancer cells [
      • Toulany M.
      • Kehlbach R.
      • Florczak U.
      • Sak A.
      • Wang S.
      • Chen J.
      • et al.
      Targeting of AKT1 enhances radiation toxicity of human tumor cells by inhibiting DNA-PKcs-dependent DNA double-strand break repair.
      ]. Moreover, DNA-PK can act as an upstream signal for AKT activation following genotoxic stress [
      • Liu Q.
      • Turner K.M.
      • Alfred Yung W.K.
      • Chen K.
      • Zhang W.
      Role of AKT signaling in DNA repair and clinical response to cancer therapy.
      ]. Stronach et al. reported that DNA-PKcs specifically phosphorylated nuclear AKT at Ser473 in platinum-resistant OCCC and HGSOC cells but not platinum-sensitive cells [
      • Toulany M.
      • Kehlbach R.
      • Florczak U.
      • Sak A.
      • Wang S.
      • Chen J.
      • et al.
      Targeting of AKT1 enhances radiation toxicity of human tumor cells by inhibiting DNA-PKcs-dependent DNA double-strand break repair.
      ]. There, authors showed that inhibition of DNA-PK (NU7026 and siRNA against DNA-PK) but not mTORC2 (rapamycin and siRNA against Rictor subunit of mTORC2), reversed the activating phosphorylation of AKT at Ser473, thus restoring platinum-sensitivity. This effect appears to be restricted to DNA damage-mediated activation of AKT [
      • Stronach E.A.
      • Chen M.
      • Maginn E.N.
      • Agarwal R.
      • Mills G.B.
      • Wasan H.
      • et al.
      DNA-PK mediates AKT activation and apoptosis inhibition in clinically acquired platinum resistance.
      ]. Notably, the development of platinum-resistance was associated with different AKT isoform activation, i.e., for cisplatin resistance, HGSOC PEO23 and OCCC SKOV3 require AKT1, HGSOC PEA2 requires AKT2, whereas HGSOC PEO4 requires AKT3, respectively [
      • Stronach E.A.
      • Chen M.
      • Maginn E.N.
      • Agarwal R.
      • Mills G.B.
      • Wasan H.
      • et al.
      DNA-PK mediates AKT activation and apoptosis inhibition in clinically acquired platinum resistance.
      ]. Together, these data suggest that the PI3K pathway plays an active role in promoting DNA DSB repair through HR or DNA-PK-dependent NHEJ.

      PI3K pathway inhibitors in combination with DNA repair blockades as a therapeutic strategy

      The initial concept of combining PARPi with PI3K/mTOR pathway inhibitors is based on the reduction of HR repair-related proteins in HR-proficient tumors. In BRCA wild-type HGSOC cell lines, pan-PI3Ki (buparlisib) resulted in attenuated HR repair by downregulating BRCA2 or RAD51, making cells more sensitive to PARPi [
      • Wang D.
      • Li C.
      • Zhang Y.
      • Wang M.
      • Jiang N.
      • Xiang L.
      • et al.
      Combined inhibition of PI3K and PARP is effective in the treatment of ovarian cancer cells with wild-type PIK3CA genes.
      ]. This synergism was seen in both PIK3CA mutant OCCC and wild-type HGSOC ovarian cancer cells [
      • Wang D.
      • Wang M.
      • Jiang N.
      • Zhang Y.
      • Bian X.
      • Wang X.
      • et al.
      Effective use of PI3K inhibitor BKM120 and PARP inhibitor Olaparib to treat PIK3CA mutant ovarian cancer.
      ,
      • Wang D.
      • Li C.
      • Zhang Y.
      • Wang M.
      • Jiang N.
      • Xiang L.
      • et al.
      Combined inhibition of PI3K and PARP is effective in the treatment of ovarian cancer cells with wild-type PIK3CA genes.
      ]. Buparlisib also reduced RAD51 foci formation and sensitizes PTEN mutant endometrial cancer cells to PARPi olaparib [
      • Bian X.
      • Gao J.
      • Luo F.
      • Rui C.
      • Zheng T.
      • Wang D.
      • et al.
      PTEN deficiency sensitizes endometrioid endometrial cancer to compound PARP-PI3K inhibition but not PARP inhibition as monotherapy.
      ]. These data suggest that tumors with PIK3CA mutation alone may not predict the response to PI3K blockade and PARPi combination in the clinical setting reflecting the complex biology. In addition, pan-AKT activity is upregulated at baseline in BRCA-deficient ovarian cancer cells (SKOV3 with BRCA1-knockdown and BRCA2-mutated PEO1) which enhances cell survival despite the absence of HR, making an important target for treatment [
      • Whicker M.E.
      • Lin Z.P.
      • Hanna R.
      • Sartorelli A.C.
      • Ratner E.S.
      MK-2206 sensitizes BRCA-deficient epithelial ovarian adenocarcinoma to cisplatin and olaparib.
      ]. As such, a pan-AKTi MK-2206 and olaparib combination induced synergistic cytotoxicity in BRCA-deficient HGSOC cells [
      • Whicker M.E.
      • Lin Z.P.
      • Hanna R.
      • Sartorelli A.C.
      • Ratner E.S.
      MK-2206 sensitizes BRCA-deficient epithelial ovarian adenocarcinoma to cisplatin and olaparib.
      ].
      Overall, preclinical data suggest PI3K signaling blockades can induce synthetic lethality with DNA repair or cell cycle inhibitors in ovarian cancer. More preclinical studies are necessary for various ovarian cancer models to dissect the interactions between PI3K signaling and HR, and also to develop possible predictive biomarkers to optimize patient selection for treatment.

      PI3K pathway inhibitors in clinical trials

      Several PI3K pathway inhibitors are approved by the United States Food and Drug Administration (FDA) for various cancers [
      • Ediriweera M.K.
      • Tennekoon K.H.
      • Samarakoon S.R.
      Role of the PI3K/AKT/mTOR signaling pathway in ovarian cancer: Biological and therapeutic significance.
      ,
      • Rodrigues D.A.
      • Sagrillo F.S.
      • Fraga C.A.M.
      Duvelisib: A 2018 novel FDA-approved small molecule inhibiting phosphoinositide 3-kinases.
      ,
      • Alpelisib Markham A.
      First global approval.
      ], however, no PI3K pathway inhibitor has been approved by the FDA for the treatment of gynecologic cancers. Here, we will focus on the use of this drug class, either as monotherapy or in combination, in gynecologic cancers.

      PI3K pathway blockade monotherapy in ovarian cancer

      Early trials of single-agent PI3K pathway inhibitors have produced disappointing results despite the high prevalence of PI3K pathway aberrations in ovarian cancer and strong preclinical rationale for their use. Studies have ubiquitously reported overall response rates (ORR; complete + partial responses) of < 10% in advanced or recurrent ovarian cancer and are similarly low across all advanced solid tumor types (Table 1). Few monotherapy trials of PI3K pathway inhibition remain ongoing in this disease (Table 2).
      Table 1PI3K pathway inhibitor monotherapy clinical trials including ovarian and/or endometrial cancer with results.
      DrugMechanismPhasePatientsDose and scheduleEnrollment biomarkerCommon (>10%) adverse eventsORR (RECIST)
      PI3K inhibitor
      Buparlisib
      • Rodon J.
      • Brana I.
      • Siu L.L.
      • De Jonge M.J.
      • Homji N.
      • Mills D.
      • et al.
      Phase I dose-escalation and -expansion study of buparlisib (BKM120), an oral pan-Class I PI3K inhibitor, in patients with advanced solid tumors.
      , Rodon 2014
      Pan-class I PI3K inhibitorIAdvanced solid tumors (n = 83)

      OC (n = 3)
      12.5–150 mg PO qdMutated/amplified PIK3CA and/or mutated/null/low PTEN protein expression (expansion cohort n = 43)G1/2: anorexia, diarrhea, nausea, hyperglycemia, rash, fatigue, stomatitis, asthenia, pruritis, anxiety, depression G3/4: none4.8% overall/0% OC
      Pictilisib
      • Sarker D.
      • Ang J.E.
      • Baird R.
      • Kristeleit R.
      • Shah K.
      • Moreno V.
      • et al.
      First-in-human phase I study of pictilisib (GDC-0941), a potent pan-class I phosphatidylinositol-3-kinase (PI3K) inhibitor, in patients with advanced solid tumors.
      , Sarker 2015
      Pan-class I PI3K inhibitorISolid tumors (n = 60)

      OC (n = 3)
      15–450 mg PO qd for days 1–21/q28

      330–400 mg PO qd for 28/28 days
      NoneG1/2: nausea, diarrhea, vomiting, anorexia, dysgeusia, rash, stomatitis, xeroderma, fatigue G3/4: none1.6% overall/0% OC
      Pilaralisib
      • Matulonis U.
      • Vergote I.
      • Backes F.
      • Martin L.P.
      • McMeekin S.
      • Birrer M.
      • et al.
      Phase II study of the PI3K inhibitor pilaralisib (SAR245408; XL147) in patients with advanced or recurrent endometrial carcinoma.
      , Matulonis 2015
      Pan-class I PI3K inhibitorIIAdvanced or recurrent endometrial carcinoma (n = 67)600 mg capsules or 400 mg tablets qdNoneG1/2: rash, diarrhea, fatigue, nasuea, hyperglycemia, anorexia, G3/4: none6%
      Buparlisib
      • Heudel P.E.
      • Fabbro M.
      • Roemer-Becuwe C.
      • Kaminsky M.C.
      • Arnaud A.
      • Joly F.
      • et al.
      Phase II study of the PI3K inhibitor BKM120 in patients with advanced or recurrent endometrial carcinoma: a stratified type I-type II study from the GINECO group.
      , Heudel 2017
      Pan-class I PI3K inhibitorIIAdvanced or recurrent endometrial carcinoma (n = 40)100 mg PO qd (n = 16*)

      60 mg PO qd (n = 24)
      NoneG1/2: rash, hyperglycemia, mucositis, nausea, vomiting, constipation, diarrhea, abdominal pain, anorexia, dyspnea, depression, anxiety, fatigue, infection, pain, anemia, lymphopenia, hepatic cytolysis, increased ALP, increased GGT hypercholesterolemia, renal toxicity G3/4: rash, hypertension, hyperglycemia0%
      Alpelisib
      • Juric D.
      • Rodon J.
      • Tabernero J.
      • Janku F.
      • Burris H.A.
      • Schellens J.H.M.
      • et al.
      Phosphatidylinositol 3-kinase alpha-selective inhibition with alpelisib (BYL719) in PIK3CA-altered solid tumors: results from the first-in-human study.
      , Juric 2018
      PI3Kα-selective inhibitorIaAdvanced solid tumors (n = 134)

      OC (n = 14)
      30–450 mg PO qd (n = 108)

      120–200 mg PO BID (n = 26)
      PIK3CA mutation (n = 125, 93.3%)G1/2: hyperglycemia, nausea, anorexia, diarrhea, vomiting, fatigue, stomatitis G3/4: hyperglycemia6% overall/0% OC
      AKT inhibitor
      GSK2141795
      • Gungor H.
      • Saleem A.
      • Babar S.
      • Dina R.
      • El-Bahrawy M.A.
      • Curry E.
      • et al.
      Dose-finding quantitative 18F-FDG PET imaging study with the oral pan-AKT Inhibitor GSK2141795 in patients with gynecologic malignancies.
      , Gungor 2015
      Pan-AKT isoform inhibitorIRecurrent/persistent OC (n = 11) or EC (n = 1)50–75 mg PO qdNoneG1/2: nausea, anorexia, vomiting, diarrhea, rash, constipation, lethargy, dizziness, insomnia G3/4: none8%
      Perifosine
      • Hasegawa K.
      • Kagabu M.
      • Mizuno M.
      • Oda K.
      • Aoki D.
      • Mabuchi S.
      • et al.
      Phase II basket trial of perifosine monotherapy for recurrent gynecologic cancer with or without PIK3CA mutations.
      ,

      Hasegawa 2017
      Pan-AKT isoform inhibitorIIRecurrent gynecologic cancer (n = 71)

      PIK3CA mutant OC (n = 5)

      PIK3CA wild-type OC (n = 16)

      PIK3CA mutant EC (n = 7)

      PIK3CA wild-type EC (n = 17)
      600 mg PO day 1 followed by 100 mg PO qdPIK3CA mutationG1/2: anemia, nausea, vomiting, diarrhea, anorexia, malaise, weight loss, hypoalbuminemia, increased creatinine, pain G3/4: diarrhea, anorexia0% overall
      Capivasertib
      • Hyman D.M.
      • Smyth L.M.
      • Donoghue M.T.A.
      • Westin S.N.
      • Bedard P.L.
      • Dean E.J.
      • et al.
      AKT inhibition in solid tumors with AKT1 mutations.
      ,

      Hyman 2017
      Pan-AKT isoform inhibitorIAdvanced solid malignancy in tumors with AKT1 mutations (n = 58)

      OC (n = 7)

      EC (n = 8)
      480 mg BID for 4 days, followed by 3 days off, in 21-day cyclesAKT1 mutationG1/2: diarrhea, nausea, fatigue vomiting, hyperglycemia, rash, abdominal pain, anorexia, pyrexia, dizziness, back pain, elevated AST, cough, dry mouth, headache, edema, congestion, constipation, hypertension, pruritis, myalgia, hypokalemia G3/4: hyperglycemia, diarrhea, rash24% overall/0% OC

      25% EC
      Capivasertib
      • Banerji U.
      • Dean E.J.
      • Perez-Fidalgo J.A.
      • Batist G.
      • Bedard P.L.
      • You B.
      • et al.
      A phase i open-label study to identify a dosing regimen of the pan-AKT inhibitor AZD5363 for evaluation in solid tumors and in PIK3CA-mutated breast and gynecologic cancers.
      ,

      Banerji 2018
      Pan-AKT isoform inhibitorIDose escalation and dose-expansion cohort: advanced solid tumors (n = 90)

      OC (n = 4)

      Expansion cohort: PIK3CA mutant breast (n = 31) and gynecologic cancers (n = 28)

      OC (n = 6)

      EC (n = 10)
      Dose-escalation 80–600 mg BID, 480–640 mg BID 4/7 days, 640–800 mg 2/7 days

      Expansion 480 mg BID for 4/7 days
      PIK3CA mutation (expansion cohort)G1/2: diarrhea, nausea, vomiting, fatigue, anorexia, hyperglycemia, rash, constipation, abdominal pain, pyrexia, headache, anemia, increased creatinine, proteinuria, asthenia, hypomagnesemia G3/4: hyperglycemia0% Dose-escalation and expansion cohorts

      8% PIK3CA mutant gyn cancer expansion cohort
      MK-2206
      • Myers A.P.
      • Konstantinopoulos P.A.
      • Barry W.T.
      • Luo W.
      • Broaddus R.R.
      • Makker V.
      • et al.
      Phase II, 2-stage, 2-arm, PIK3CA mutation stratified trial of MK-2206 in recurrent endometrial cancer.
      , Myers 2019
      Pan-AKT isoform inhibitorIIRecurrent endometrial cancer (n = 36)200 mg PO qwPIK3CA mutation (n = 9, 25%)G1/2: constipation, nausea, vomiting, fatigue fever, hyperglycemia, rash G3/4: rash6% overall (1 PIK3CA mutant, 1 PIK3CA wt)
      mTORC1/2 inhibitor
      MKC-1
      • Elser C.
      • Hirte H.
      • Kaizer L.
      • Mackay H.
      • Bindra S.
      • Tinker L.
      • et al.
      Phase II study of MKC-1 in patients with metastatic or resistant epithelial ovarian cancer or advanced endometrial cancer.
      ,Elser 2009
      mTORC2 inhibitorIIMetastatic or recurrent platinum-resistant OC (n = 21) and advanced EC (n = 21)125 mg/m2 PO BID for 14 days in 28-day cyclesNoneG1/2: fatigue, nausea, anorexia, transaminitis, vomiting, diarrhea, anemia G3/4: neutropenia0% overall
      Everolimus
      • Slomovitz B.M.
      • Lu K.H.
      • Johnston T.
      • Coleman R.L.
      • Munsell M.
      • Broaddus R.R.
      • et al.
      A phase 2 study of the oral mammalian target of rapamycin inhibitor, everolimus, in patients with recurrent endometrial carcinoma.
      , Slomovitz 2010
      mTORC1 inhibitorIIRecurrent endometrial carcinoma (n = 35)10 mg PO qdNoneG1/2: anorexia, constipation, fatigue, mucositis, nausea, pain, rash, anemia, leukopenia, lymphopenia, neutropenia, thrombocytopenia, hypercholesterol, hyperglycemia, hypertriglyceride G3/4: fatigue, nausea, lymphopenia0% overall
      Temsirolimus
      • Behbakht K.
      • Sill M.W.
      • Darcy K.M.
      • Rubin S.C.
      • Mannel R.S.
      • Waggoner S.
      • et al.
      Phase II trial of the mTOR inhibitor, temsirolimus and evaluation of circulating tumor cells and tumor biomarkers in persistent and recurrent epithelial ovarian and primary peritoneal malignancies: a gynecologic oncology group study.
      ,Behbakht 2011
      mTORC1 inhibitorIIRecurrent/persistent epithelial OC or primary peritoneal cancer (n = 54)25 mg IV weeklyNoneG1/2: leukopenia, thrombocytopenia, neutropenia, anemia, fatigue, nausea, gastrointestinal, metabolic, neurosensory, pain G3/4: gastrointestinal, metabolic, pain9.3%
      Temsirolimus
      • Oza A.M.
      • Elit L.
      • Tsao M.S.
      • Kamel-Reid S.
      • Biagi J.
      • Provencher D.M.
      • et al.
      Phase II study of temsirolimus in women with recurrent or metastatic endometrial cancer: a trial of the NCIC clinical trials group.
      , Oza 2011
      mTORC1 inhibitorIIRecurrent or metastatic endometrial cancer (n = 60)

      Chemo-naïve (n = 33)

      Chemo-treated (n = 27)
      25 mg IV weeklyNoneG1/2: fatigue, acne, dry skin, pruritis, rash, diarrhea, anorexia, mouth dryness, nausea, vomiting, cough, lymphopenia, neutropenia, thrombocytopenia, anemia, elevated creatinine, hypokalemia, elevated AST G3/4: fatigue, diarrhea9% overall
      Everolimus
      • Ray-Coquard I.
      • Favier L.
      • Weber B.
      • Roemer-Becuwe C.
      • Bougnoux P.
      • Fabbro M.
      • et al.
      Everolimus as second- or third-line treatment of advanced endometrial cancer: ENDORAD, a phase II trial of GINECO.
      , Ray-Coquard 2013
      mTORC1 inhibitorIIAdvanced or metastatic endometrial cancer (n = 44)10 mg PO qdNoneG1/2: fatigue, nausea, rash, mucositis, vomiting, anorexia, diarrhea, infection, constipation, edema, dyspnea, hemorrhage, anemia, lymphopenia, leukopenia, neutropenia, thrombocytopenia, hypercholesterolemia, hypertriglyceridemia, hyperglycemia, transaminitis, hypercalcemia G3/4: fatigue, anorexia, diarrhea, infection, thromboembolism, anemia, lymphopenia, hyperglycemia9%
      Ridaforolimus
      • Colombo N.
      • McMeekin D.S.
      • Schwartz P.E.
      • Sessa C.
      • Gehrig P.A.
      • Holloway R.
      • et al.
      Ridaforolimus as a single agent in advanced endometrial cancer: results of a single-arm, phase 2 trial.
      , Colombo 2013
      mTORC1 inhibitorIIRecurrent or persistent endometrial cancer (n = 45)12.5 mg IV/day, d1-5 every 2 weeksNoneG1/2: mouth sores, anemia, fatigue, diarrhea, nausea, vomiting, asthenia, anorexia, dysgeusia, anorexia G3/4: anemia11%
      Ridaforolimus
      • Tsoref D.
      • Welch S.
      • Lau S.
      • Biagi J.
      • Tonkin K.
      • Martin L.A.
      • et al.
      Phase II study of oral ridaforolimus in women with recurrent or metastatic endometrial cancer.
      , Tsoref 2014
      mTORC1 inhibitorIIRecurrent or metastatic endometrial cancer (n = 34)40 mg/day; d1-5 of a 7 day cycleNoneG1/2: fatigue, dry skin, nail changes, pruritis, rash, anorexia, diarrhea, mucositis, nausea, dysgeusia, vomiting, edema, dizziness, cough, dyspnea, pneumonitis, weight loss, anemia, neutropenia, thrombocytopenia, lymphopenia, elevated creatinine, elevated ALP, transaminitis, hyperglycemia G3/4: fatigue, weight loss, hyperglycemia8.8%
      Ridaforolimus
      • Oza A.M.
      • Pignata S.
      • Poveda A.
      • McCormack M.
      • Clamp A.
      • Schwartz B.
      • et al.
      Randomized phase II trial of ridaforolimus in advanced endometrial carcinoma.
      , Oza 2015
      mTORC1 inhibitorIIAdvanced endometrial cancer (n = 64 received ridaforolimus)40 mg/day; d1-5 of a 7 day cycleNoneG1/2: diarrhea, mucositis, anorexia, asthenia, nausea, hyperglycemia, vomiting, abdominal pain, stomatitis, fatigue, anemia, rash, pyrexia, hyper cholesterol G3/4: diarrhea, hyperglycemia, anemia0%
      Temsirolimus
      • Emons G.
      • Kurzeder C.
      • Schmalfeldt B.
      • Neuser P.
      • de Gregorio N.
      • Pfisterer J.
      • et al.
      Temsirolimus in women with platinum-refractory/resistant ovarian cancer or advanced/recurrent endometrial carcinoma. A phase II study of the AGO-study group (AGO-GYN8).
      ,

      Emons 2016
      mTORC1 inhibitorIIPlatinum-refractory/resistant OC (n = 22) or advanced/recurrent EC (n = 22)25 mg IV weeklyNoneG1/2: nausea, abdominal pain, diarrhea, stomatitis, constipation, vomiting, fatigue, mucositis, edema, rash, nail disorder, urinary tract infection, dyspnea, headache, neuropathy, anemia, thrombocytopenia, anorexia G3/4: none4.8% OC

      10% EC
      PI3K/mTOR inhibitor
      SF1126
      • Mahadevan D.
      • Chiorean E.G.
      • Harris W.B.
      • Von Hoff D.D.
      • Stejskal-Barnett A.
      • Qi W.
      • et al.
      Phase I pharmacokinetic and pharmacodynamic study of the pan-PI3K/mTORC vascular targeted pro-drug SF1126 in patients with advanced solid tumours and B-cell malignancies.
      ,Mahadevan 2012
      Pan-class I PI3K and mTOR inhibitorIB-cell malignancies (n = 5) and Advanced solid tumors (n = 39)

      OC (n = 5)

      EC (n = 1)
      90–1110 mg/m2/day IV on days 1 and 4 weeklyNoneG1/2: nausea, fatigue, vomiting, diarrhea, pyrexia, anorexia, anemia, pruritis, headache G3/4: edema, diarrhea, weakness, hypoglycemia, anemia, pruritis, hypokalemia, hypersensitivity0% among all solid tumors
      BGT226
      • Markman B.
      • Tabernero J.
      • Krop I.
      • Shapiro G.I.
      • Siu L.
      • Chen L.C.
      • et al.
      Phase I safety, pharmacokinetic, and pharmacodynamic study of the oral phosphatidylinositol-3-kinase and mTOR inhibitor BGT226 in patients with advanced solid tumors.
      , Markman 2012
      PI3Kα/β/γ and mTOR inhibitorIAdvanced solid tumors (n = 57)

      OC (n = 2)

      EC (n = 4)
      2.5–125 mg/day TIWNoneG1/2: nausea, diarrhea, vomiting, anorexia, ftigue, anemia, abdominal pain G3/4: diarrhea0% overall
      PF-04691502
      • Del Campo J.M.
      • Birrer M.
      • Davis C.
      • Fujiwara K.
      • Gollerkeri A.
      • Gore M.
      • et al.
      A randomized phase II non-comparative study of PF-04691502 and gedatolisib (PF-05212384) in patients with recurrent endometrial cancer.
      , Del Campo 2016
      Pan-class I PI3K and mTOR inhibitorIIRecurrent endometrial cancer (n = 18)8 mg PO qdNoneG1/2: diarrhea, fatigue, hyperglycemia, nausea, anorexia, dry mouth, hypokalemia, mucositis, stomatitis, dysgeusia, dyspnea, pneumonitis, rash G3/4: diarrhea, dyspnea, fatigue, hyperglycemia, hypokalemia, pneumonia, pneumonitis, rash, stomatitisTrial terminated early due to AEs
      Gedatolisib
      • Del Campo J.M.
      • Birrer M.
      • Davis C.
      • Fujiwara K.
      • Gollerkeri A.
      • Gore M.
      • et al.
      A randomized phase II non-comparative study of PF-04691502 and gedatolisib (PF-05212384) in patients with recurrent endometrial cancer.
      , Del Campo 2016
      Pan-class I PI3K and mTOR inhibitorIIRecurrent endometrial cancer (n = 40)154 mg IV qwNoneG1/2: nausea, mucositis, anorexia, diarrhea, fatigue, dysgeusia, vomiting, rash, stomatitis, hyperglycemia, asthenia, dry mouth G3/4: fatigue16%
      Apitolisib
      • Makker V.
      • Recio F.O.
      • Ma L.
      • Matulonis U.A.
      • Lauchle J.O.
      • Parmar H.
      • et al.
      A multicenter, single-arm, open-label, phase 2 study of apitolisib (GDC-0980) for the treatment of recurrent or persistent endometrial carcinoma (MAGGIE study).
      , Makker 2016
      Pan-class I PI3K and mTOR inhibitorIIRecurrent or persistent endometrial cancer (n = 56)40 mg PO qdNoneG1/2: hyperglycemia, rash, fatigue, diarrhea, anorexia, vomiting, stomatitis, weight loss, dysgeusia, hypokalemia, hypomagnesemia, abdominal pain, anemia, constipation, dehydration, dry mouth, mucositis, pyrexia G3/4: hyperglycemia, rash, diarrhea9%
      BEZ235
      • Rodon J.
      • Perez-Fidalgo A.
      • Krop I.E.
      • Burris H.
      • Guerrero-Zotano A.
      • Britten C.D.
      • et al.
      Phase 1/1b dose escalation and expansion study of BEZ235, a dual PI3K/mTOR inhibitor, in patients with advanced solid tumors including patients with advanced breast cancer.
      ,Rodon 2018
      Pan-class I PI3K and mTOR inhibitorI/IbSolid tumors (n = 153)

      OC (n = 8)

      EC (n = 5)
      BEZ235 hard gelatin capsule 10–1200 mg/day

      BEZ235 solid dispersion system capsule 400–1000 mg/day
      PIK3CA and/or PTEN molecular alterations (expansion cohort)G1/2: nausea, diarrhea, vomiting, anorexia, fatigue, stomatitis, asthenia, anemia, weight loss, dehydration, dyspnea, abdominal pain, cough, pyrexia, rash, creatinine increase, pruritis G3/4: none0% overall
      LY3023414
      • Rubinstein M.M.
      • Hyman D.M.
      • Caird I.
      • Won H.
      • Soldan K.
      • Seier K.
      • et al.
      Phase 2 study of LY3023414 in patients with advanced endometrial cancer harboring activating mutations in the PI3K pathway.
      , Rubinstein 2019
      Pan-class I PI3K and mTOR inhibitorIIAdvanced endometrial cancer (n = 28)200 mg PO BID in 21-day cyclesLoss of function mutation in PTEN or known activating mutation in PIK3CA, AKT1, PIK3R1, PIK3R2, or MTORG1/2: anemia, hyperglycemia, hyboalbuminemia, hypophosphatemia, transaminitis, leukopenia, hypomagnesemia, thrombocytopenia, nausea, hypocalcemia, hypokalemia, constipation, hyponatremia, increased creatinine, fatigue G3/4: anemia, hyperglycemia, hypophosphatemia, thrombocytopenia, lymphopenia, hypokalemia, hyponatremia16%
      *Trial dose was lowered to 60 mg daily after the first 16 patients experienced high rates of toxicities (cutaneous rash 54%, depressive events 47%, anxiety 40%).
      Abbreviations: ALP = alkaline phosphatase; BID = twice daily; CBR = clinical benefit rate; EC = endometrial cancer; G1/2 = grade 1 or 2; G3/4 = grade 3 or 4; GGT = gamma-glutamyltransferase; gyn = gynecologic; IV = intravenous; OC = ovarian cancer; ORR = overall response rate; mg = milligram; PO = oral; PR = partial response; qd = once daily; qw = once weekly; SD = stable disease; TIW = three times weekly; wt = wild-type.
      Table 2Ongoing monotherapy clinical trials targeting the PI3K pathway including ovarian cancer patients.
      DrugTargetYear openedPhaseNameDiseaseBiomarkerNCT#Status
      GDC-0077PI3Kα selective inhibitor2016IA Phase I, Open-Label, Dose-Escalation Study Evaluating the Safety, Tolerability, and Pharmacokinetics of GDC-0077 as a Single Agent in Patients With Locally Advanced or Metastatic PIK3CA-Mutant Solid Tumors and in Combination With Endocrine and Targeted Therapies in Patients With Locally Advanced or Metastatic PIK3CA-Mutant Hormone-Receptor Positive Breast CancerAdvanced solid tumorsPIK3CA mutant03006172Recruiting
      IPI-549PI3Kγ selective inhibitor2015I/IbA Phase 1/1b First-In-Human, Dose-Escalation Study to Evaluate the Safety, Tolerability, Pharmacokinetics, and Pharmacodynamics of IPI-549 Monotherapy and in Combination With Nivolumab in Subjects With Advanced Solid TumorsAdvanced solid tumorsNone02637531Recruiting
      YY-20394PI3Kδ selective inhibitor2019IA Single-Arm, Open-Label, Multi-Center, Phase I Study of YY-20394 in Patients With Advanced Solid TumorsAdvanced solid tumorsNone04049929Not yet recruiting,as of 12/31/2019
      ARQ 751Pan-AKT inhibitor2016IbA Phase 1b Study of ARQ 751 as a Single Agent or in Combination With Other Anti-Cancer Agents in Adult Subjects With Advanced Solid Tumors With PIK3CA / AKT / PTEN MutationsAdvanced solid tumorsPIK3CA, AKT or PTEN mutations02761694Recruiting
      TAS-117Pan-AKT inhibitor2017IIA Phase II Study of TAS-117 in Advanced Solid Tumors With PI3K/AKT Gene AberrationAdvanced solid tumorsPI3K or AKT aberration03017521Recruiting
      SirolimusmTORC12017IVStudy to Evaluate the Safety and Efficacy of Sirolimus, in Subject With Refractory Solid TumorsRefractory solid tumorsPIK3CA mutation, PIK3CA amplification, PIK3CA-AKT pathway aberration (H1047R, E542K, E545K, PTEN loss)0688881Recruiting
      CapivasertibAKT2015IITargeted Therapy Directed by Genetic Testing in Treating Patients With Advanced Refractory Solid Tumors, Lymphomas, or Multiple Myeloma (The MATCH Screening Trial)Lymphomas, multiple myeloma or solid tumors including ovarian carcinomaAKT mutation02465060Recruiting
      IpatasertibAKTAKT mutation
      SapanisertibmTORmTOR, TSC1 or TSC2 mutation
      GSK2636771PI3KβPTEN mutation/deletion/loss
      BAY 80–6946Pan-class I PI3KPIK3CA mutation, PTEN mutation/loss
      One potential limitation is toxicities leading to suboptimal dosing/schedules or early cessation of trials [
      • Hanker A.B.
      • Kaklamani V.
      • Arteaga C.L.
      Challenges for the clinical development of PI3K inhibitors: strategies to improve their impact in solid tumors.
      ]. In a phase II study of mTORi everolimus in endometrial cancer, 49% (17/35) of patients required a dose reduction and 5 patients were unevaluable after < 1 cycle due to toxicities including stomatitis, hyperglycemia, thrombocytopenia, hypertriglyceridemia, rash and fever [
      • Slomovitz B.M.
      • Lu K.H.
      • Johnston T.
      • Coleman R.L.
      • Munsell M.
      • Broaddus R.R.
      • et al.
      A phase 2 study of the oral mammalian target of rapamycin inhibitor, everolimus, in patients with recurrent endometrial carcinoma.
      ]. Similarly, in a phase II trial of mTORi ridaforolimus, treatment was discontinued in 33% of patients due to adverse events (AEs) predominantly diarrhea, hyperglycemia, and anemia [
      • Oza A.M.
      • Pignata S.
      • Poveda A.
      • McCormack M.
      • Clamp A.
      • Schwartz B.
      • et al.
      Randomized phase II trial of ridaforolimus in advanced endometrial carcinoma.
      ] while another study of ridaforolimus reported dose modifications in 29 of 34 (85%) patients and removal of 7 from the trial for hematologic events, sepsis and most commonly, mucositis [
      • Tsoref D.
      • Welch S.
      • Lau S.
      • Biagi J.
      • Tonkin K.
      • Martin L.A.
      • et al.
      Phase II study of oral ridaforolimus in women with recurrent or metastatic endometrial cancer.
      ]. Moreover, the development of dual PI3K/mTORi PF-04691502 was terminated due to safety concerns including the high rate (22%) of treatment-related pneumonitis observed in a phase II study [
      • Del Campo J.M.
      • Birrer M.
      • Davis C.
      • Fujiwara K.
      • Gollerkeri A.
      • Gore M.
      • et al.
      A randomized phase II non-comparative study of PF-04691502 and gedatolisib (PF-05212384) in patients with recurrent endometrial cancer.
      ].
      The underlying mechanisms of toxicities related to PI3K pathway blockade are partly understood. Hyperglycemia, a common dose-dependent toxicity seen with pan-PI3K, PI3Kα, mTOR and AKT inhibitors (Table 1), occurs because the PI3K pathway mediates insulin-driven glucose uptake [
      • Hanker A.B.
      • Kaklamani V.
      • Arteaga C.L.
      Challenges for the clinical development of PI3K inhibitors: strategies to improve their impact in solid tumors.
      ,
      • Khan K.H.
      • Wong M.
      • Rihawi K.
      • Bodla S.
      • Morganstein D.
      • Banerji U.
      • et al.
      Hyperglycemia and phosphatidylinositol 3-kinase/protein kinase B/mammalian target of rapamycin (PI3K/AKT/mTOR) inhibitors in phase i trials: incidence, predictive factors, and management.
      ]. It occurs in diabetics and non-diabetics, often leading to early discontinuation of treatment. The mechanism of neuropsychiatric effects including anxiety and depression observed with the pan-PI3Ki buparlisib remains incompletely understood but has served to limit its clinical application [
      • Greenwell I.B.
      • Ip A.
      • Cohen J.B.
      PI3K inhibitors: understanding toxicity mechanisms and management.
      ,
      • Matulonis U.A.
      • Wulf G.M.
      • Barry W.T.
      • Birrer M.
      • Westin S.N.
      • Farooq S.
      • et al.
      Phase I dose escalation study of the PI3kinase pathway inhibitor BKM120 and the oral poly (ADP ribose) polymerase (PARP) inhibitor olaparib for the treatment of high-grade serous ovarian and breast cancer.
      ,
      • Heudel P.E.
      • Fabbro M.
      • Roemer-Becuwe C.
      • Kaminsky M.C.
      • Arnaud A.
      • Joly F.
      • et al.
      Phase II study of the PI3K inhibitor BKM120 in patients with advanced or recurrent endometrial carcinoma: a stratified type I-type II study from the GINECO group.
      ].
      Additionally, lack of or poor patient selection may further contribute to unsatisfactory results. Several studies have applied biomarker criteria for improved patient selection to address the low efficacy seen in these trials. However, ORRs have remained low despite application of genomic biomarkers such as PIK3CA mutation, as detailed in Table 1. For instance, the phase I trials of pan-PI3Ki buparlisib and PI3Kα-selective inhibitor alpelisib, which enrolled patients with PIK3CA mutant advanced solid tumors, reported ORRs < 10% overall [
      • Rodon J.
      • Brana I.
      • Siu L.L.
      • De Jonge M.J.
      • Homji N.
      • Mills D.
      • et al.
      Phase I dose-escalation and -expansion study of buparlisib (BKM120), an oral pan-Class I PI3K inhibitor, in patients with advanced solid tumors.
      ,
      • Juric D.
      • Rodon J.
      • Tabernero J.
      • Janku F.
      • Burris H.A.
      • Schellens J.H.M.
      • et al.
      Phosphatidylinositol 3-kinase alpha-selective inhibition with alpelisib (BYL719) in PIK3CA-altered solid tumors: results from the first-in-human study.
      ]. Similarly, a phase II study of pan-AKTi perifosine in recurrent gynecologic cancer recruited PIK3CA mutant ovarian (n = 5), endometrial (n = 7) and cervical (n = 10) as well as PIK3CA wild-type ovarian (n = 16), endometrial (n = 17) and cervical cancer patients (n = 16). No complete or partial responses were observed, regardless of PIK3CA status [
      • Hasegawa K.
      • Kagabu M.
      • Mizuno M.
      • Oda K.
      • Aoki D.
      • Mabuchi S.
      • et al.
      Phase II basket trial of perifosine monotherapy for recurrent gynecologic cancer with or without PIK3CA mutations.
      ]. A multi-arm study of pan-AKTi capivasertib (AZD5363) examined the impact of both PIK3CA and AKT1 mutations (Table 1; NCT01226316) [
      • Banerji U.
      • Dean E.J.
      • Perez-Fidalgo J.A.
      • Batist G.
      • Bedard P.L.
      • You B.
      • et al.
      A phase i open-label study to identify a dosing regimen of the pan-AKT inhibitor AZD5363 for evaluation in solid tumors and in PIK3CA-mutated breast and gynecologic cancers.
      ,
      • Hyman D.M.
      • Smyth L.M.
      • Donoghue M.T.A.
      • Westin S.N.
      • Bedard P.L.
      • Dean E.J.
      • et al.
      AKT inhibition in solid tumors with AKT1 mutations.
      ]. The expansion cohort recruiting PIK3CA mutant gynecologic cancers, including endometrial (n = 10) and ovarian cancer (n = 6), reported an 8% ORR [
      • Banerji U.
      • Dean E.J.
      • Perez-Fidalgo J.A.
      • Batist G.
      • Bedard P.L.
      • You B.
      • et al.
      A phase i open-label study to identify a dosing regimen of the pan-AKT inhibitor AZD5363 for evaluation in solid tumors and in PIK3CA-mutated breast and gynecologic cancers.
      ]. Another arm of this trial assessed whether activating AKT1 mutations enhance sensitivity to direct AKT inhibition with capivasertib. Limited efficacy was again reported, with a 17% ORR among AKT1 mutated gynecologic cancers (2/8 endometrial, 1/3 cervical and 0/7 ovarian cancer partial responses) [
      • Hyman D.M.
      • Smyth L.M.
      • Donoghue M.T.A.
      • Westin S.N.
      • Bedard P.L.
      • Dean E.J.
      • et al.
      AKT inhibition in solid tumors with AKT1 mutations.
      ]. Consistently low response rates (RRs) were also seen with dual PI3K/mTOR inhibition, including a phase I trial of BEZ235 in PIK3CA or PTEN mutated advanced solid tumors reporting a 0% ORR [
      • Rodon J.
      • Perez-Fidalgo A.
      • Krop I.E.
      • Burris H.
      • Guerrero-Zotano A.
      • Britten C.D.
      • et al.
      Phase 1/1b dose escalation and expansion study of BEZ235, a dual PI3K/mTOR inhibitor, in patients with advanced solid tumors including patients with advanced breast cancer.
      ] and a phase II of LY3023414 in advanced endometrial cancer with activating PI3K pathway mutations reporting at 16% ORR [
      • Rubinstein M.M.
      • Hyman D.M.
      • Caird I.
      • Won H.
      • Soldan K.
      • Seier K.
      • et al.
      Phase 2 study of LY3023414 in patients with advanced endometrial cancer harboring activating mutations in the PI3K pathway.
      ]. Insufficient activity of single-agent PI3K pathway targeting despite the application of genomic biomarkers suggests more research is needed to identify improved biomarkers of response [
      • Hanker A.B.
      • Kaklamani V.
      • Arteaga C.L.
      Challenges for the clinical development of PI3K inhibitors: strategies to improve their impact in solid tumors.
      ]. Moreover, it highlights potential pathway redundancy and compensatory feedback loops resulting in resistance to treatment with PI3K pathway inhibitors [
      • Yang J.
      • Nie J.
      • Ma X.
      • Wei Y.
      • Peng Y.
      • Wei X.
      Targeting PI3K in cancer: mechanisms and advances in clinical trials.
      ,
      • Hanker A.B.
      • Kaklamani V.
      • Arteaga C.L.
      Challenges for the clinical development of PI3K inhibitors: strategies to improve their impact in solid tumors.
      ].
      Therefore, combination therapies are currently under investigation as a strategy to address these challenges. There are many active and moderately promising studies looking at the combination of PI3K pathway inhibitors with classic chemotherapies, including carboplatin and paclitaxel, as well as with targeted therapies such as the circulating VEGF antibody bevacizumab, which have been detailed in reviews and studies [
      • Ediriweera M.K.
      • Tennekoon K.H.
      • Samarakoon S.R.
      Role of the PI3K/AKT/mTOR signaling pathway in ovarian cancer: Biological and therapeutic significance.
      ,
      • Yang J.
      • Nie J.
      • Ma X.
      • Wei Y.
      • Peng Y.
      • Wei X.
      Targeting PI3K in cancer: mechanisms and advances in clinical trials.
      ,
      • Gasparri M.L.
      • Bardhi E.
      • Ruscito I.
      • Papadia A.
      • Farooqi A.A.
      • Marchetti C.
      • et al.
      PI3K/AKT/mTOR pathway in ovarian cancer treatment: are we on the right track?.
      ,
      • Schmid P.
      • Abraham J.
      • Chan S.
      • Wheatley D.
      • Brunt A.M.
      • Nemsadze G.
      • et al.
      Capivasertib plus paclitaxel versus placebo plus paclitaxel as first-line therapy for metastatic triple-negative breast cancer: the PAKT trial.
      ]. The focus of this section will be combination therapy with PI3K pathway and DDR inhibitors.

      Clinical benefit of targeting PI3K pathways and DDR

      Therapeutic combinations of PI3K and DDR inhibitors are actively being investigated in clinical trials (Table 3, Table 4). Available results suggest the combinations are generally tolerable and show modestly promising early signs of improved activity compared to single-agent PI3K pathway inhibition, though further research and final reports from ongoing trials are eagerly awaited.
      Table 3Trials of PI3K pathway inhibitors in combination with DDR inhibitors in gynecologic cancers with results.
      DrugsMechanism of PI3K pathway inhibitorPhasePatientsDose and scheduleBiomarkerCommon (>10%) adverse eventsResponse in OC
      PI3K inhibitor
      Buparlisib + olaparib
      • Matulonis U.A.
      • Wulf G.M.
      • Barry W.T.
      • Birrer M.
      • Westin S.N.
      • Farooq S.
      • et al.
      Phase I dose escalation study of the PI3kinase pathway inhibitor BKM120 and the oral poly (ADP ribose) polymerase (PARP) inhibitor olaparib for the treatment of high-grade serous ovarian and breast cancer.
      ,

      Matulonis 2017
      Pan-class I PI3K inhibitorIRecurrent HGSOC, fallopian tube, or primary peritoneal cancer (n = 46); TNBC (n = 24)Buparlisib 40-50mq qd + olaparib 100–300 mg BIDNoneG1/2: nausea, fatigue, hyperglycemia, anorexia, depression, diarrhea, anxiety, mucositis, vomiting, transaminitis, anemia, thrombocytopenia, lymphopenia G3/4: noneORR 29%

      12 PR (8 with gBRCAm), 20 SD (13 with gBRCAm)
      Alpelisib + olaparib
      • Konstantinopoulos P.A.
      • Barry W.T.
      • Birrer M.
      • Westin S.N.
      • Cadoo K.A.
      • Shapiro G.I.
      • et al.
      Olaparib and alpha-specific PI3K inhibitor alpelisib for patients with epithelial ovarian cancer: a dose-escalation and dose-expansion phase 1b trial.
      , Konstantinopoulos 2019
      PI3Kα-selective inhibitorIRecurrent epithelial OC (n = 28); breast cancer (n = 4)Alpelisib 200–300 mg qd + olaparib 100–200 mg BIDNoneG1/2: nausea, hyperglycemia, fatigue, diarrhea, vomiting, anorexia, headache, anemia, constipation, elevated creatinine, thrombocytopenia, rash, increased amylase, abdominal pain, dry skin, dysgeusia, dyspnea, mucositis G3/4: hyperglycemiaORR 36%

      10 PR (3 with gBRCAm), 14 SD (7 with gBRCAm)
      Abbreviations: BID = twice daily; G1/2 = grade 1 or 2; G3/4 = grade 3 or 4; gram = germline BRCA mutation; ORR = overall response rate; PR = partial response; ad = once daily; SD = stable disease; TNBC = triple negative breast cancer
      Table 4PI3K pathway inhibitors in combination with DDR inhibitors under clinical development in advanced tumors including gynecologic cancers.
      DrugsMechanism of PI3K pathway inhibitorYear openedPhaseNameDiseasesBiomarkerNCT#Status
      PI3K inhibitor
      Copanlisib + niraparibPan-class I PI3K inhibitor2018IbA Phase Ib Study of the Oral PARP Inhibitor Niraparib With the Intravenous PI3K Inhibitor Copanlisib for Recurrent Endometrial and Recurrent Ovarian, Primary Peritoneal, or Fallopian Tube CancerRecurrent endometrial, ovarian, primary peritoneal or fallopian tube cancerNone03586661Recruiting
      Copanlisib + olaparib + durvalumabPan-class I PI3K inhibitor2019IbA Phase Ib Biomarker-Driven Combination Trial of Copanlisib, Olaparib, and MEDI4736 (Durvalumab) in Patients With Advanced Solid TumorsAdvanced solid tumorsPTEN mutation; or PIK3CA mutation; or mutation in DDR genes: ARID1A, ATM, ATRX, BARD1, BRCA1, BRCA2, BRIP1, CDK12, CHEK1, CHEK2, FANCA, FANCL, MRE11A, MSH2, PALB2, PARP1, POLD1, PP2R2A, RAD51B, RAD51C, RAD51D, RAD54L, XRCC203842228Recruiting
      AKT inhibitor
      Capivasertib + olaparibPan-AKT isoform inhibitor2014IbA Phase Ib Study of the Oral PARP Inhibitor Olaparib With the Oral mTORC1/2 Inhibitor AZD2014 or the Oral AKT Inhibitor AZD5363 for Recurrent Endometrial, Triple Negative Breast, and Ovarian, Primary Peritoneal, or Fallopian Tube CancerRecurrent endometrial, TNBC, and ovarian, primary peritoneal, or fallopian tube cancerNone02208375Active, not recruiting
      Capivasertib + olaparibPan-AKT isoform inhibitor2015IA Phase I Multi-centre Trial of the Combination of Olaparib (PARP Inhibitor) and AZD5363 (AKT Inhibitor) in Patients With Advanced Solid TumoursBRCA1/2 mutant cancersor TNBC, HGSOC, CRPC, and tumors with somatic mutations or other aberrations known to result in a hyperactivated PI3K/AKT pathwayNone02338622Unknown on CT.govas of 12/31/2019
      Capivasertib + olaparibPan-AKT isoform inhibitor2015IIA Phase II Study of the PARP Inhibitor Olaparib (AZD2281) Alone and in Combination with AZD1775, AZD5363, or AZD6738 in Advanced Solid TumorsAdvanced solid tumorsPTEN, PIK3CA, AKT, or ARID1A mutation02576444Recruiting
      mTORC1/2 inhibitor
      Vistusertib + olaparibmTORC1/2 inhibitor2014IbA Phase Ib Study of the Oral PARP Inhibitor Olaparib With the Oral mTORC1/2 Inhibitor AZD2014 or the Oral AKT Inhibitor AZD5363 for Recurrent Endometrial, Triple Negative Breast, and Ovarian, Primary Peritoneal, or Fallopian Tube CancerRecurrent ovarian, primary peritoneal, or fallopian tube cancer, endometrial cancer, breast cancerNone02208375Active, not recruiting
      Everolimus + niraparibmTORC1 inhibitor2017IA Phase 1 Evaluation of the Safety and Tolerability of Niraparib in Combination With Everolimus in Advanced Ovarian and Breast CancerOvarian cancer, breast cancerNone03154281Recruiting
      PI3K/mTOR inhibitor
      LY3023414 + PrexasertibPan-class I PI3K /mTORC1/2 inhibitor2014IA Study of Prexasertib (LY2606368) With Chemotherapy or Targeted Agents in Participants With Advanced CancerAdvanced or metastatic cancerPIK3CA mutations02124148Active, not recruiting
      Gedatolisib + PalbociclibPan-class I PI3K /mTORC1/2 inhibitor2017IIPhase I Study of the CDK4/6 Inhibitor Palbociclib (PD-0332991) in Combination With the PI3K/mTOR Inhibitor Gedatolisib (PF-05212384) for Patients With Advanced Squamous Cell Lung, Pancreatic, Head & Neck and Other Solid TumorsSolid tumorsNone03065062Recruiting
      Abbreviations: CRPC = castration resistant prostate cancer; ER+ = estrogen receptor positive; HER2- = human epidermal growth factor receptor 2 negative; HGSOC = high grade serous ovarian cancer; TNBC = triple negative breast cancer.

      Combining PI3K pathway inhibitors with DNA repair inhibitors

      To date, only 1 trial has published results of a PI3K pathway inhibitor with a DDR inhibitor, specifically with the PARPi olaparib. In the first arm of this phase I trial (NCT01623349), the pan-class I PI3Ki buparlisib was combined with olaparib. 69 patients with women’s cancers were enrolled, 46 of whom had recurrent HGSOC [
      • Matulonis U.A.
      • Wulf G.M.
      • Barry W.T.
      • Birrer M.
      • Westin S.N.
      • Farooq S.
      • et al.
      Phase I dose escalation study of the PI3kinase pathway inhibitor BKM120 and the oral poly (ADP ribose) polymerase (PARP) inhibitor olaparib for the treatment of high-grade serous ovarian and breast cancer.
      ]. The combination resulted in dose-limiting toxicities (DLTs) of grade 3 transaminitis and depression, consistent with the neuropsychiatric AEs observed with buparlisib monotherapy, requiring attenuation of the buparlisib dose. Moreover, depression and anxiety were observed in 36% and 28% of patients, respectively, prompting future evaluation of α-specific PI3Ki alpelisib (BYL719), which has no known central nervous system (CNS) toxicity, in the second arm. ORR with the olaparib and buparlisib combination was 29% in germline BRCA mutated (gBRCAm) and 12% in germline BRCA wild-type (gBRCAwt) HGSOC patients. Of the 24 patients included in the breast cancer cohort, RRs were 33% and 20% in gBRCAm and gBRCAwt patients, respectively. No difference in RRs was observed based on platinum-sensitivity, as is typically described with PARP inhibition [
      • Gelmon K.A.
      • Tischkowitz M.
      • Mackay H.
      • Swenerton K.
      • Robidoux A.
      • Tonkin K.
      • et al.
      Olaparib in patients with recurrent high-grade serous or poorly differentiated ovarian carcinoma or triple-negative breast cancer: a phase 2, multicentre, open-label, non-randomised study.
      ,
      • Matulonis U.A.
      • Penson R.T.
      • Domchek S.M.
      • Kaufman B.
      • Shapira-Frommer R.
      • Audeh M.W.
      • et al.
      Olaparib monotherapy in patients with advanced relapsed ovarian cancer and a germline BRCA1/2 mutation: a multistudy analysis of response rates and safety.
      ]. However, as RRs to single-agent olaparib in the BRCAm population are approximately 30%, data suggest the combination did not provide added benefit in the BRCAm setting [
      • Matulonis U.A.
      • Penson R.T.
      • Domchek S.M.
      • Kaufman B.
      • Shapira-Frommer R.
      • Audeh M.W.
      • et al.
      Olaparib monotherapy in patients with advanced relapsed ovarian cancer and a germline BRCA1/2 mutation: a multistudy analysis of response rates and safety.
      ,
      • Kaufman B.
      • Shapira-Frommer R.
      • Schmutzler R.K.
      • Audeh M.W.
      • Friedlander M.
      • Balmana J.
      • et al.
      Olaparib monotherapy in patients with advanced cancer and a germline BRCA1/2 mutation.
      ].
      The alpelisib plus olaparib arm of this trial enrolled patients with recurrent epithelial ovarian (n = 28) or breast cancer (n = 4). DLTs included hyperglycemia and neutropenic fever. An expansion cohort was enrolled at the maximum tolerated dose (MTD) of alpelisib 200 mg once daily plus olaparib 200 mg twice daily (BID) [
      • Konstantinopoulos P.A.
      • Barry W.T.
      • Birrer M.
      • Westin S.N.
      • Cadoo K.A.
      • Shapiro G.I.
      • et al.
      Olaparib and alpha-specific PI3K inhibitor alpelisib for patients with epithelial ovarian cancer: a dose-escalation and dose-expansion phase 1b trial.
      ]. Common (>10%) AEs are listed in Table 3; notably, there were no CNS issues. Early signs of clinical activity were observed among ovarian cancer patients, with responses in 4 of 12 (33%) BRCAwt, platinum-resistant patients and 3 of 10 (30%) gBRCAm [
      • Konstantinopoulos P.A.
      • Barry W.T.
      • Birrer M.
      • Westin S.N.
      • Cadoo K.A.
      • Shapiro G.I.
      • et al.
      Olaparib and alpha-specific PI3K inhibitor alpelisib for patients with epithelial ovarian cancer: a dose-escalation and dose-expansion phase 1b trial.
      ], requiring further investigation.
      In light of these findings, several ongoing trials are now investigating the PI3K pathway and PARPi combination (Table 4). Two phase I trials investigating combination therapy with copanlisib, a pan-class I PI3Ki, are actively recruiting patients as of 12/31/2019. One trial is investigating copanlisib with PARPi niraparib in recurrent gynecologic cancers (NCT03586661), while the other is exploring potential for synergy with immunotherapy by testing the triplet of copanlisib, olaparib and anti-programmed death ligand-1 (PD-L1) durvalumab in advanced solid tumors with PTEN, PIK3CA, or DDR gene mutations (NCT03842228; Table 4).
      AKT inhibition is also being combined with PARPi in several ongoing trials (Table 4). A dose escalation (n = 20) and dose expansion (n = 33) phase I trial of capivasertib, an AKTi, with olaparib enrolled 53 patients with advanced cancers, including 19 with ovarian and 16 with breast cancer (NCT02338622). Recommended phase 2 doses (RP2D) were established as 300 mg olaparib BID and 400 mg capivasertib BID for 4 of 7 days or 300 mg olaparib BID and 640 mg capivasertib BID for 2 of 7 days [
      • Michalarea V.
      • Lorente D.
      • Lopez J.
      • Carreira S.
      • Hassam H.
      • Parmar M.
      • et al.
      Abstract CT323: Accelerated phase I trial of two schedules of the combination of the PARP inhibitor olaparib and AKT inhibitor AZD5363 using a novel intrapatient dose escalation design in advanced cancer patients.
      ,
      • Michalarea V.
      • Roda D.
      • Drew Y.
      • Carreira S.
      • O’Carrigan B.S.
      • Shaw H.
      • et al.
      Abstract CT010: Phase I trial combining the PARP inhibitor olaparib (Ola) and AKT inhibitor AZD5363 (AZD) in germline (g)BRCA and non-BRCA mutant (m) advanced cancer patients (pts) incorporating noninvasive monitoring of cancer mutations.
      ], the latter of which are the MTDs of both drugs when used as monotherapy [
      • Banerji U.
      • Dean E.J.
      • Perez-Fidalgo J.A.
      • Batist G.
      • Bedard P.L.
      • You B.
      • et al.
      A phase i open-label study to identify a dosing regimen of the pan-AKT inhibitor AZD5363 for evaluation in solid tumors and in PIK3CA-mutated breast and gynecologic cancers.
      ,
      • Robson M.
      • Im S.A.
      • Senkus E.
      • Xu B.
      • Domchek S.M.
      • Masuda N.
      • et al.
      Olaparib for metastatic breast cancer in patients with a germline BRCA mutation.
      ]. The only DLT was a grade 3 rash, while grade 3 non-DLT toxicities included anemia, diarrhea, vomiting and proteinuria in the 4 of 7 day schedule and transaminitis, nausea, fatigue, anemia, rash, hyperglycemia, and diarrhea in the 2 of 7 day schedule [
      • Michalarea V.
      • Lorente D.
      • Lopez J.
      • Carreira S.
      • Hassam H.
      • Parmar M.
      • et al.
      Abstract CT323: Accelerated phase I trial of two schedules of the combination of the PARP inhibitor olaparib and AKT inhibitor AZD5363 using a novel intrapatient dose escalation design in advanced cancer patients.
      ,
      • Michalarea V.
      • Roda D.
      • Drew Y.
      • Carreira S.
      • O’Carrigan B.S.
      • Shaw H.
      • et al.
      Abstract CT010: Phase I trial combining the PARP inhibitor olaparib (Ola) and AKT inhibitor AZD5363 (AZD) in germline (g)BRCA and non-BRCA mutant (m) advanced cancer patients (pts) incorporating noninvasive monitoring of cancer mutations.
      ]. There was a 27% (10/37) ORR, including responses in platinum-resistant gBRCAm ovarian (n = 2), BRCAwt ovarian (n = 2), gBRCAm breast (n = 4) and BRCAwt TNBC (n = 1) [
      • Michalarea V.
      • Roda D.
      • Drew Y.
      • Carreira S.
      • O’Carrigan B.S.
      • Shaw H.
      • et al.
      Abstract CT010: Phase I trial combining the PARP inhibitor olaparib (Ola) and AKT inhibitor AZD5363 (AZD) in germline (g)BRCA and non-BRCA mutant (m) advanced cancer patients (pts) incorporating noninvasive monitoring of cancer mutations.
      ], although final results have yet to be published.
      Similarly, in an ongoing phase Ib dose-escalation and expansion study for patients with recurrent endometrial, ovarian, or TNBC (NCT02208375), preliminary results from 38 enrolled patients reported DLTs of diarrhea and vomiting, establishing the RP2D as 300 mg BID olaparib and 400 mg BID capivasertib 4 of 7 days as above [
      • Westin S.
      • Phase I.
      Expansion of olaparib (PARP inhibitor) and AZD5363 (AKT inhibitor) in recurrent ovarian, endometrial and triple negative breast cancer.
      ]. Similar AE profiles as described above were observed. A 24% RR was seen in 30 evaluable patients (7/30), including 1 ovarian, 4 endometrial and 2 TNBC patients, with translational studies ongoing. The results of an ongoing phase II trial of olaparib with capivasertib in patients with advanced solid tumors with PIK3CA, AKT, or ARID1A mutations will provide important information regarding the clinical activity of this combination as well as the potential benefits of patient selection based on molecular characteristics (NCT02576444).
      Lastly, several trials are exploring the combination of PARP and mTOR inhibition. An active phase I trial of olaparib with mTORC1/2 inhibitor vistusertib (AZD2014) in recurrent ovarian, endometrial and TNBC (NCT02208375) enrolled 74 patients, predominantly BRCAwt (89%). One arm tested olaparib with continuous vistusertib at 5 dose levels (DL) and the second tested olaparib with 4 DL of vistusertib 2 days on, 5 days off. DLTs included neutropenia, thrombocytopenia, allergic reaction, fatigue, and hyperglycemia. The RP2D of arm 1 was olaparib 200 mg BID with continuous vistusertib 50 mg BID while RP2D of arm 2 was olaparib 300 mg BID with vistusertib 100 mg BID 2 of 7 days. Other common AEs (>40%) included nausea, anemia, hyperglycemia, fatigue, leukopenia, increased creatinine, headache, vomiting, and hypercholesterolemia [
      • Westin S.N.
      • Litton J.K.
      • Williams R.A.
      • Shepherd C.J.
      • Brugger W.
      • Pease E.J.
      • et al.
      Phase I trial of olaparib (PARP inhibitor) and vistusertib (mTORC1/2 inhibitor) in recurrent endometrial, ovarian and triple negative breast cancer.
      ]. ORR was 19% among 64 evaluable patients across all DL, with ORRs of 20% and 27% in ovarian and endometrial cancer patients, respectively [
      • Westin S.N.
      • Litton J.K.
      • Williams R.A.
      • Shepherd C.J.
      • Brugger W.
      • Pease E.J.
      • et al.
      Phase I trial of olaparib (PARP inhibitor) and vistusertib (mTORC1/2 inhibitor) in recurrent endometrial, ovarian and triple negative breast cancer.
      ]. Final results of this trial will help determine if combination with mTOR inhibition can enhance RRs to PARPi among BRCAwt patients and the planned correlative molecular analyses may serve to identify biomarkers of response.
      A phase I trial of mTORi everolimus with niraparib is actively recruiting patients with advanced breast and ovarian cancer (NCT03154281). Together, these ongoing clinical trials of PARPi and PI3K pathway inhibitors and related biomarker work will hopefully pave the way for improved therapeutic options for PI3K pathway blockades.

      Combining PI3K pathway inhibitors with cell cycle checkpoint inhibitors

      The dual PI3K/mTORi gedatolisib is currently being investigated in combination with CDK4/6 inhibitor palbociclib and endocrine therapy (letrozole or fulvestrant) in a phase Ib trial of women with estrogen receptor-positive (ER+) metastatic breast cancer (NCT02684032). Preliminary reports from the dose-escalation arm found DLTs of grade 3 neutropenia, stomatitis, febrile neutropenia, mucositis and abdominal pain, while nausea, stomatitis, fatigue, and neutropenia were the most common AEs overall. Early antitumor activity was reported, with RRs of 33% and 20% in the letrozole and fulvestrant arms, respectively, while the dose-expansion phase remains ongoing [
      • Forero-Torres A.
      • Han H.
      • Dees E.C.
      • Wesolowski R.
      • Bardia A.
      • Kabos P.
      • et al.
      Phase Ib study of gedatolisib in combination with palbociclib and endocrine therapy (ET) in women with estrogen receptor (ER) positive (+) metastatic breast cancer (MBC) (B2151009).
      ]. Similarly, a phase I trial of gedatolisib with palbociclib for patients with advanced solid tumors is recruiting patients (NCT03065062; Table 4).
      Based on promising preclinical evidence of enhanced antitumor activity in TNBC models [
      • Wu W.
      • Donoho G.
      • Iversen P.
      • Dempsey J.
      • Capen A.
      • Castanares M.
      • et al.
      Abstract 3508: Combination of the Chk1 inhibitor (prexasertib) with a PI3K/mTOR inhibitor (LY3023414) induces synergistic anti-tumor activity in triple negative breast cancer (TNBC) models.
      ], a phase I trial in advanced or metastatic cancer is actively investigating the safety of the CHK1i prexasertib with the dual PI3K/mTORi LY3023414 (NCT02124148). 50 patients were enrolled, including 13 in a dose-escalation cohort and 9 in an initial dose-expansion cohort at the MTD of prexasertib 105 mg/m2 every 14 days plus LY3023414 200 mg BID. Although no DLTs were observed in the dose-escalation cohort, 2 patients experienced DLT-equivalent toxicities in the expansion group (anemia, neutropenia, thrombocytopenia, oral mucositis, abdominal pain, fatigue), leading to a reduced LY3023414 dose of 150 mg BID in subsequent cohorts [
      • Hong D.S.
      • Moore K.N.
      • Bendell J.C.
      • Karp D.D.
      • Wang J.S.-Z.
      • Ulahannan S.V.
      • et al.
      A phase Ib study of prexasertib, a checkpoint kinase (CHK1) inhibitor, and LY3023414, a dual inhibitor of class I phosphatidylinositol 3-kinase (PI3K) and the mammalian target of rapamycin (mTOR) in patients with advanced solid tumors.
      ]. The final two cohorts of this trial included 15 participants with PIK3CA-mutated solid tumors and 13 TNBC patients [
      • Hong D.S.
      • Moore K.N.
      • Bendell J.C.
      • Karp D.D.
      • Wang J.S.-Z.
      • Ulahannan S.V.
      • et al.
      A phase Ib study of prexasertib, a checkpoint kinase (CHK1) inhibitor, and LY3023414, a dual inhibitor of class I phosphatidylinositol 3-kinase (PI3K) and the mammalian target of rapamycin (mTOR) in patients with advanced solid tumors.
      ]. Common AE included leukopenia/neutropenia, thrombocytopenia, nausea, stomatitis, vomiting, and anemia. Febrile neutropenia was reported in 25% of patients and dose reductions were common, suggesting the prophylactic growth factor support may be necessary. Of the preliminarily evaluable patients across all four cohorts, 5 achieved a partial response, although final analysis remains pending [
      • Hong D.S.
      • Moore K.N.
      • Bendell J.C.
      • Karp D.D.
      • Wang J.S.-Z.
      • Ulahannan S.V.
      • et al.
      A phase Ib study of prexasertib, a checkpoint kinase (CHK1) inhibitor, and LY3023414, a dual inhibitor of class I phosphatidylinositol 3-kinase (PI3K) and the mammalian target of rapamycin (mTOR) in patients with advanced solid tumors.
      ]. Results from these studies will be the first available clinical data on the safety and activity of PI3K pathway inhibitors in combination with cell cycle checkpoint inhibition.

      Conclusions

      Although the precise mechanisms of oncogenicity of the PI3K pathway and DDR are still under investigation, this signaling cascade is an attractive therapeutic target because of the high frequency of aberrations in ovarian cancers. In this review, we have discussed that DDR inhibition may represent potential synthetically lethal therapeutic approaches with PI3K pathway blockades. While dual inhibition of PARP or cell cycle checkpoint inhibitors with PI3K pathway inhibition represents a promising preclinical anti-tumor effect in ovarian cancers, the therapeutic possibilities for this combination need to be proven. Another concern would be acquired or de novo resistance to these therapies which we did not discuss details here. Understanding more about the molecular abnormalities involved in PI3K pathway-dysregulated tumors, exploring novel therapeutic trial designs and drug combinations, and defining potential predictive biomarkers, are necessary to rapidly advance the field of PI3K pathway inhibitor therapy for ovarian cancer. This is a field rich in opportunity, and the coming years should see a better understanding of which ovarian cancer patients we should treat with PI3K pathway and DDR blockade combinations and where these agents should be best applied during the treatment course of this disease.

      Author contributions

      T.T.H., E.J.L., C.C., and J.M.L wrote the manuscript and made the tables.

      Financial Support

      This work was supported by the Intramural Research Program of the National Cancer Institute (JML, # ZIA BC011525 ), Center for Cancer Research.

      Declaration of Competing Interest

      The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.

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