PARP Inhibitor Therapy Research Articles

PTEN Deficiency in Tubo-Ovarian High-Grade Serous Carcinoma is Associated with Poor Progression-Free Survival and is Mutually Exclusive with CCNE1 Amplification

As a critical tumor suppressor, PTEN has gained much attention in cancer research. Emerging evidence suggests an association between PTEN status and clinical outcome in certain tumors, and may be predictive of response to several therapies. However, the significance of PTEN deficiency in tubo-ovarian high-grade serous carcinomas (HGSCs) is still poorly understood. We evaluated PTEN expression in HGSCs and determined its clinical relevance. A cohort of 76 HGSC specimens was profiled using tissue microarray. Immunohistochemistry (IHC) of PTEN, ER, PR, AR, CD8, FOXP3, and PD-L1 was performed. Targeted gene panel testing by massively parallel sequencing was performed in 51 cases. PTEN deficiency (complete or subclonal loss) detected by IHC was identified in 13 of the 62 HGSCs (21%) and was significantly correlated with reduced expression of ER and worse first progression-free survival (P < .05) but not with PD-L1 expression, the density of intratumoral T lymphocytes, or overall survival. In our cohort, tumor progression within 1 year of PARP inhibitor therapy was found more frequently in PTEN-deficient cases than in PTEN-intact cases (100% vs 52%). Molecular profiling showed that intragenic mutation or deletion was not the predominant mechanism for PTEN inactivation in HGSCs. In addition, CCNE1 amplification was found to be mutually exclusive with PTEN deficiency at both protein and DNA levels. An analysis of the genomic data from 1702 HGSC samples deposited with The Cancer Genome Atlas database obtained from cBioPortal confirmed the low rate of detection of PTEN gene alterations and the mutually exclusive nature of PTEN loss and CCNE1 amplification in HGSCs. These findings indicate that PTEN deficiency defines a distinct clinically significant subgroup of HGSCs with a tendency for ER negativity, wild-type CCNE1 status, inferior clinical outcomes, and potential drug resistance. These tumors may benefit from PI3K pathway inhibitors in combination with other ovarian cancer regimens, which deserves further investigation.

32O 5-year (y) overall survival (OS) with maintenance olaparib (ola) plus bevacizumab (bev) by clinical risk in patients (pts) with newly diagnosed advanced ovarian cancer (AOC) in the phase III PAOLA-1/ENGOT-ov25 trial

In the PAOLA-1/ENGOT-ov25 trial, adding maintenance ola to bev improved progression-free survival in homologous recombination deficiency-positive (HRD+; tumour BRCA1/2 mutation [tBRCAm] and/or genomic instability) pts with newly diagnosed AOC at higher and lower risk of progression by disease stage and surgical status. Greatest benefits were seen in lower-risk pts (Harter et al. Gynecol Oncol 2022). Here, we analysed 5-y OS according to clinical risk and HRD status. Pts in response after first-line platinum-based chemotherapy + bev were randomized 2:1 to ola (300 mg bid; up to 24 months [mo]) + bev (15 mg/kg q3w; up to 15 mo) or placebo [pbo] + bev. This post hoc exploratory analysis evaluated OS in pts classified as higher risk (stage III with upfront surgery and residual disease or neoadjuvant chemotherapy; stage IV) or lower risk (stage III with upfront surgery and no residual disease), and by HRD status. 537 pts were randomized to ola + bev and 269 to pbo + bev (median OS follow-up 61.7 and 61.9 mo, respectively). Of 806 randomized pts, 595 (74%) were classified as higher risk and 211 (26%) as lower risk. At final data cutoff (22 March 2022), OS events had occurred in 377 higher-risk pts (data maturity 63%) and 69 lower-risk pts (data maturity 33%). OS was prolonged with ola + bev in higher- and lower-risk pts with a tBRCAm or who were HRD+. No OS benefit was seen in HRD− pts in any clinical risk subgroup. Subsequent PARP inhibitor therapy was received by 19.5% and 19.6% of ola + bev pts, and 45.9% and 45.2% of pbo + bev pts, in higher- and lower-risk groups, respectively.Table: 32OHRD statusHigher risk (n=595)Lower risk (n=211)No. of events/no. of pts (%)5-y OS rate† (%)No. of events/no. of pts (%)5-y OS rate† (%)Ola + bevPbo + bevOla + bevPbo + bevOla + bevPbo + bevOla + bevPbo + bevFull analysis set249/399 (62)128/196 (65)38.535.339/138 (28)30/73 (41)72.758.3HRD+*82/177 (46)53/89 (60)55.242.211/78 (14)16/43 (37)88.361.3tBRCAm43/109 (39)29/55 (53)65.248.35/48 (10)8/25 (32)91.466.1HRD−116/144 (81)46/62 (74)18.226.324/48 (50)12/23 (52)48.048.5HRD status by Myriad MyChoice HRD Plus assay; tBRCAm status by central labs.*HRD+ defined as a tBRCAm and/or genomic instability score of ≥42 on the Myriad MyChoice HRD Plus assay; †Kaplan–Meier estimates. Open table in a new tab HRD status by Myriad MyChoice HRD Plus assay; tBRCAm status by central labs. *HRD+ defined as a tBRCAm and/or genomic instability score of ≥42 on the Myriad MyChoice HRD Plus assay; †Kaplan–Meier estimates. This post hoc analysis of 5-y OS suggests that adding maintenance ola to bev should be considered for all HRD+ pts with newly diagnosed AOC, irrespective of their clinical risk status. Particular benefit was observed in HRD+ lower-risk pts who achieved 5-y OS rates of 88.3%.

PARP Inhibitor Therapy for Breast Cancer With PALB2 Mutations

PARP Inhibitor Therapy for Breast Cancer With PALB2 Mutations

Interleukin-34 cancels anti-tumor immunity by PARP inhibitor.

Breast cancer susceptibility gene 1 (BRCA1)-associated ovarian cancer patients have been treated with A poly (ADP-ribose) polymerase (PARP) inhibitor, extending the progression-free survival; however, they finally acquire therapeutic resistance. Interleukin (IL)-34 has been reported as a poor prognostic factor in several cancers, including ovarian cancer, and it contributes to the therapeutic resistance of chemotherapies. IL-34 may affect the therapeutic effect of PARP inhibitor through the regulation of tumor microenvironment (TME). In this study, The Cancer Genome Atlas (TCGA) data set was used to evaluate the prognosis of IL-34 and human ovarian serous carcinoma. We also used CRISPR-Cas9 genome editing technology in a mouse model to evaluate the efficacy of PARP inhibitor therapy in the presence or absence of IL-34. We found that IL34 was an independent poor prognostic factor in ovarian serous carcinoma, and its high expression significantly shortens overall survival. Furthermore, in BRCA1-associated ovarian cancer, PARP inhibitor therapy contributes to anti-tumor immunity via the XCR1+ DC-CD8+ T cell axis, however, it is canceled by the presence of IL-34. These results suggest that tumor-derived IL-34 benefits tumors by creating an immunosuppressive TME and conferring PARP inhibitor therapeutic resistance. Thus, we showed the pathological effect of IL-34 and the need for it as a therapeutic target in ovarian cancer.

DDR genes analysis and PARP-inhibitors therapy as tailored management in metastatic prostate cancer: achieved answers, open questions and future perspectives.

article: DDR genes analysis and PARP-inhibitors therapy as tailored management in metastatic prostate cancer: achieved answers, open questions and future perspectives - Minerva Urology and Nephrology 2022 December;74(6):649-52 - Minerva Medica - Journals

The microtubule inhibitor eribulin demonstrates efficacy in platinum-resistant and refractory high-grade serous ovarian cancer patient-derived xenograft models.

Despite initial response to platinum-based chemotherapy and PARP inhibitor therapy (PARPi), nearly all recurrent high-grade serous ovarian cancer (HGSC) will acquire lethal drug resistance; indeed, ~15% of individuals have de novo platinum-refractory disease. To determine the potential of anti-microtubule agent (AMA) therapy (paclitaxel, vinorelbine and eribulin) in platinum-resistant or refractory (PRR) HGSC by assessing response in patient-derived xenograft (PDX) models of HGSC. Of 13 PRR HGSC PDX, six were primary PRR, derived from chemotherapy-naïve samples (one was BRCA2 mutant) and seven were from samples obtained following chemotherapy treatment in the clinic (five were mutant for either BRCA1 or BRCA2 (BRCA1/2), four with prior PARPi exposure), recapitulating the population of individuals with aggressive treatment-resistant HGSC in the clinic. Molecular analyses and in vivo treatment studies were undertaken. Seven out of thirteen PRR PDX (54%) were sensitive to treatment with the AMA, eribulin (time to progressive disease (PD) ⩾100 days from the start of treatment) and 11 out of 13 PDX (85%) derived significant benefit from eribulin [time to harvest (TTH) for each PDX with p < 0.002]. In 5 out of 10 platinum-refractory HGSC PDX (50%) and one out of three platinum-resistant PDX (33%), eribulin was more efficacious than was cisplatin, with longer time to PD and significantly extended TTH (each PDX p < 0.02). Furthermore, four of these models were extremely sensitive to all three AMA tested, maintaining response until the end of the experiment (120d post-treatment start). Despite harbouring secondary BRCA2 mutations, two BRCA2-mutant PDX models derived from heavily pre-treated individuals were sensitive to AMA. PRR HGSC PDX models showing greater sensitivity to AMA had high proliferative indices and oncogene expression. Two PDX models, both with prior chemotherapy and/or PARPi exposure, were refractory to all AMA, one of which harboured the SLC25A40-ABCB1 fusion, known to upregulate drug efflux via MDR1. The efficacy observed for eribulin in PRR HGSC PDX was similar to that observed for paclitaxel, which transformed ovarian cancer clinical practice. Eribulin is therefore worthy of further consideration in clinical trials, particularly in ovarian carcinoma with early failure of carboplatin/paclitaxel chemotherapy.

Inibidores de PARP como terapia de manutenção de primeira linha no câncer de ovário: recomendações de um painel de especialistas do Brasil

To report consensus recommendations on the current role of poly(ADP-ribose) polymerase (PARP) inhibitors in the front-line management of patients with epithelial ovarian cancer (EOC) in the healthcare setting of Brazil. The expert panel convened in March 2021 and comprised 20 medical oncologists focus on gynecological oncology. The panel answered anonymously and based on scientific evidence a total of 67 questions. The panel reached consensus (at least 75% of votes for the same recommendation) or majority vote (50% to 74.9%) for the majority of questions that addressed: (1) who and when to test for BRCA mutations or homologous recombination deficiency (2) what test should be used; (3) when should maintenance PARP inhibitor therapy be indicated; (4) which PARP inhibitor should be used; (5) when should bevacizumab be combined; and (6) toxicity management. The current recommendations may help Brazilian practitioners to improve the use of PARP inhibitors in front-line management of EOC.

Oxaliplatin prior to PARP inhibitor in BRCA-mutated ovarian cancer.

The use of PARP inhibitor (PARPi) has shown a considerable benefit in progression-free survival (PFS) in relapsed, platinum-sensitive epithelial ovarian cancer (OC). Our study aimed to investigate the impact of the last platinum-based chemotherapy treatment in response to PARPi. Retrospective cohort study. The study involved 96 consecutive, pretreated, platinum-sensitive advanced OC patients. Demographics and clinical data were retrieved from clinical records. PFS and overall survival (OS) were calculated from the start of PARPi. Germline BRCA mutation was investigated in all cases. Platinum-based chemotherapy before PARPi maintenance therapy included pegylated liposomal doxorubicin-oxaliplatin (PLD-Ox) in 46 patients (48%) and other platinum-based chemotherapy in 50 patients (52%). During a median follow-up of 22 months from the beginning of PARPi therapy, 57 patients relapsed (median PFS: 12 months) and 64 patients died (median OS: 23 months). During multivariable analysis, receiving PLD-Ox before PARPi was associated with improved PFS [hazard ratio (HR): 0.46, 95% CI: 0.26-0.82] and OS (HR: 0.48, 95% CI: 0.27-0.83). In 36 BRCA-mutated patients, PLD-Ox was associated with improved PFS (2-year PFS: 70.0% versus 25.0%, p = 0.02). Receiving PLD-Ox before PARPi may improve prognosis in platinum-sensitive advanced OC patients and may provide advantages in the BRCA-mutated subgroup.

Development of PARP Inhibitors in Targeting Castration-Resistant Prostate Cancer.

Prostate cancer is a genetically heterogenous disease and a subset of prostate tumors harbor alterations in DNA damage and repair (DDR) genes. Prostate tumor DDR gene alterations can arise via germline or somatic events and are enriched in high-grade and advanced disease. Alterations in genes in the homologous recombination (HR) repair pathway are associated with sensitivity to PARP inhibition in breast and ovarian cancer, and data from recently completed randomized trials also demonstrate benefit of PARP inhibitor therapy in patients with advanced metastatic castration-resistant prostate cancer (mCRPC) and tumor HR gene alterations. PARP inhibitors have been investigated in first-line mCRPC in biomarker-selected and unselected populations, and are currently under study in earlier disease states in patients with DDR gene alterations. This chapter focuses on the current state of PARP inhibitor development in prostate cancer with particular emphasis on biomarkers and combination therapy approaches.

Genetic Mutation Assay in Ovarian Cancer Patient

Ovarian cancer is the third most common cases of cancer among Indonesian women. It has a poor prognosis with a moderate to low 5-year survival rate with conventional therapy. Targeted therapies, immunotherapies, and novel treatment approaches are being explored in clinical trials, offering potential improvements in survival rates and outcomes, unfortunately, not every patient responds to these therapeutic modalities. It takes a molecular assay to predict which patient has a response to this therapy. Genome instability is one of the unique characteristics found in most cancers in humans. Ovarian cancer patients with mutations of BRCA1 or BRCA2, have been found to exhibit high sensitivity to PARP inhibitor therapy. Targeting the Homologous Recombinant Deficiency (HRD) that was caused by BRCA mutations and inhibiting PARP-mediated DNA repair, would result in the death of cancer cells. Conclusion: molecular assay from ovarian cancer tissue would have the benefit to predict response to PARP inhibitor targeted therapy.

IMAGENE trial: multicenter, proof-of-concept, phase II study evaluating the efficacy and safety of combination therapy of niraparib with PD-1 inhibitor in solid cancer patients with homologous recombination repair genes mutation

Previous clinical trials have demonstrated the potential efficacy of poly (ADP-ribose) polymerase (PARP) inhibitors (PARPis) in patients with cancer involving homologous recombination repair (HRR) gene-mutation. Moreover, HRR gene-mutated cancers are effectively treated with immune checkpoint inhibitors (ICIs) with the increase in tumor mutation burden. We have proposed to conduct a multicenter, single-arm phase II trial (IMAGENE trial) for evaluating the efficacy and safety of niraparib (PARPi) plus programmed cell death-1 inhibitor combination therapy in patients with HRR gene-mutated cancers who are refractory to ICIs therapy using a next generation sequencing-based circulating tumor DNA (ctDNA) and tumor tissue analysis. Key eligibility criteria for this trial includes HRR gene-mutated tumor determined by any cancer gene tests; progression after previous ICI treatment; and Eastern Cooperative Oncology Group Performance Status ≤ 1. The primary endpoint is the confirmed objective response rate (ORR) in all patients. The secondary endpoints include the confirmed ORR in patients with HRR gene-mutation of ctDNA using the Caris Assure (CARIS, USA). The target sample size of the IMAGENE trial is 57 patients. Biomarker analyses will be performed in parallel using the Caris Assure, proteome analysis, and T cell repertoire analysis to reveal tumor immunosurveillance in peripheral blood. Our trial aims to confirm the clinical benefit of PARPi plus ICI combination therapy in ICI-resistant patients. Furthermore, through translational research, our trial will shed light on which patients would benefit from the targeted combination therapy for patients with HRR gene-mutated tumor even after the failure of ICIs. The IMAGENE trial: jRCT, Clinical trial no.: jRCT2051210120, Registered date: November 9, 2021.

Therapy of BRCA-associated metastatic breast cancer. Efficacy and safety of talazoparib in the real-world clinical practice

Introduction. PARP inhibitors demonstrated high efficacy in BRCA1/2-associated Her2-negative metastatic breast cancer (BC). They were included in the current standard chemotherapy regimen and recognized as a priority option for the treatment of such tumours following the results of clinical studies.Aim. Review the experience with talazoparib (Talzenna) in the real-world clinical practice of 6 medical centers in Russia.Materials and methods. The review included data from 29 patients with HER2-negative metastatic breast cancer associated with a gBRCA mutation, who have been receiving talazoparib therapy in 6 medical centers of Russia since April 2021. Talazoparib was given at the standard dose 1 mg once daily, the dose was reduced, if any adverse event developed.Results. The median age of the patients was 50 years. 23 patients had a BRCA1 mutation, 5 patients had a BRCA2 mutation and one of the patients had a PALB2 mutation. Prior to starting talazoparib therapy, patients had received up to 9 lines of therapy for metastatic disease, the median was 1 line. The median follow-up period at that time was only 4.6 months. The median recurrence-free survival (RFS) was not reached. Progression was observed in 10 patients with a treatment period of 1 to 7.5 months, 19 patients continued to receive PARP inhibitor therapy without signs of disease progression, with a treatment period of 2 to 18 months. The objective response rate (ORR) was 57.2%, the clinical efficacy was confirmed in 85.7% of cases. The subgroup analysis showed that the lowest efficacy of therapy was reported in the group of patients, who had received prior therapy with platinum-based drugs, the median progression-free time (mPFT) was 4.5 months. (95% CI: 1.79-9.2). While for patients who had not received the prior platinum drug regimens, the median was not reached. Haematologic toxicities were common adverse events (AEs) for the talazoparib therapy, which were reported in 34.5% of cases. Transfusions of blood components were required in 3 patients, one of them required them repeatedly. All dose modifications were due to hematological toxicities. 7 patients (24.1%) required a dose reduction and 3 patients (10.3%) - repeated dose reduction.Conclusions. Testing for BRCA1/2 mutations in Her2-negative mBC should be a mandatory diagnostic procedure. Talazoparib therapy is an effective and safe treatment option for patients with gBRCAmut HER2-mBC.

The BRCAness Landscape of Cancer

BRCAness refers to the damaged homologous recombination (HR) function due to the defects in HR-involved non-BRCA1/2 genes. BRCAness is the important marker for the use of synthetic lethal-based PARP inhibitor therapy in breast and ovarian cancer treatment. The success provides an opportunity of applying PARP inhibitor therapy to treat other cancer types with BRCAness features. However, systematic knowledge is lack for BRCAness in different cancer types beyond breast and ovarian cancer. We performed a comprehensive characterization for 40 BRCAness-related genes in 33 cancer types with over 10,000 cancer cases, including pathogenic variation, homozygotic deletion, promoter hypermethylation, gene expression, and clinical correlation of BRCAness in each cancer type. Using BRCA1/BRCA2 mutated breast and ovarian cancer as the control, we observed that BRCAness is widely present in multiple cancer types. Based on the sum of the BRCAneass features in each cancer type, we identified the following 21 cancer types as the potential targets for PARPi therapy: adrenocortical carcinoma, bladder urothelial carcinoma, brain lower grade glioma, colon adenocarcinoma, esophageal carcinoma, head and neck squamous carcinoma, kidney chromophobe, kidney renal clear cell carcinoma, kidney renal papillary cell carcinoma, liver hepatocellular carcinoma, lung adenocarcinoma, lung squamous cell carcinoma, mesothelioma, rectum adenocarcinoma, pancreatic adenocarcinoma, prostate adenocarcinoma, sarcoma, skin cutaneous melanoma, stomach adenocarcinoma, uterine carcinosarcoma, and uterine corpus endometrial carcinoma.

9 Caged rucaparib: cancer directed delivery of PARPi

Poly (ADP-ribose) polymerase inhibitors (PARPi) have revolutionized the treatment of ovarian cancer, improving progression free survival in the upfront and recurrent setting. Unfortunately, due to side effects patients often require dose reductions or altogether discontinue PARPi therapy. Additionally, due to bone marrow toxicity, PARPi cannot be effectively combined with chemotherapy. Recently, it was demonstrated that a ferrous iron-activated MEK inhibitor can circumvent MEKi related toxicity in non-tumorigenic tissues. Therefore, we developed a ferrous iron-activated form of rucaparib to target cancer cells while mitigating PARPi toxicity. Normal cells maintain a lower concentration of intracellular labile ferrous iron (Fe(II)) as compared with cancer cells. We introduced an Fe(II)-sensitive 1,2,4-trioxolane moiety at a reactive amine in rucaparib, creating a Fe(II)-activatable form of rucaparib (TRX-Ruc). A negative control, Di-Ruc, that cannot be activated by Fe(II), was also synthesized. Both compounds were then tested for their ability to inhibit PARP using a cell-free PARP1 assay. Cellular antiproliferative activity was tested in UWB –/– (BRCA1- deficient ovarian cancer cells) using the CellTiterGlo viability assay, and intracellular inhibition of PARP was evaluated with a parylation Western blot. In the cell free PARP1 inhibitor assay, the IC50 of rucaparib was 2.9 nM while TRX-Ruc had significantly decreased potency, with an IC50 of 92.3 nM. Di-Ruc had no inhibitory effect as expected. UWB –/– viability was decreased by rucaparib and TRX-Ruc with an equivalent IC50 of approximately 300 nM while Di-Ruc only had an effect at very high concentrations. To ensure the mechanism of TRX-Ruc on cell viability was due to PARP inhibition, a parylation western was performed. Both rucaparib and TRX-Ruc inhibited parylation while the negative control, Di-Ruc had only minimal effects. The addition of an Fe(II)-sensitive “TRX” moiety on rucaparib significantly reduces the biochemical activity of rucaparib in the absence of Fe(II). However, in an ovarian cancer cell line, the activity of TRX-ruc is restored leading to decreased cell viability, which we demonstrated was realized through the inhibition of PARP. This new Fe(II)-sensitive compound is an exciting and novel approach to deliver PAPRi specifically to cancer cells, potentially reducing toxicity and allowing effective combinations of PARPi with other cytotoxic therapies.

Differential responses to taxanes and PARP inhibitors in ATM-versus BRCA2-mutated metastatic castrate-resistant prostate cancer.

PARP(poly(ADP-ribose) polymerase) inhibitors (PARPi) are now standard of care in metastatic castrate-resistant prostate cancer (mCRPC) patients with select mutations in DNA damage repair (DDR) pathways, but patients with ATM- and BRCA2 mutations may respond differently to PARPi. We hypothesized that differences may also exist in response to taxanes, which may inform treatment sequencing decisions. mCRPC patients (N = 158) with deleterious ATM or BRCA2 mutations who received taxanes, PARPi, or both were retrospectively identified from 11 US academic centers. Demographic, treatment, and survival data were collected. Kaplan-Meier analyses were performed and Cox hazard ratios (HR) were calculated for progression-free survival (PFS) as well as overall survival (OS), from time of first taxane or PARPi therapy. Fifty-eight patients with ATM mutations and 100 with BRCA2 mutations were identified. Fourty-four(76%) patients with ATM mutations received taxane only or taxane before PARPi, while 14 (24%) received PARPi only or PARPi before taxane. Patients with ATM mutations had longer PFS when taxane was given first versus PARPi given first (HR: 0.74 [95% confidence interval[CI]: 0.37-1.50]; p = 0.40). Similarly, OS was longer in patients with ATM mutations who received taxane first (HR: 0.56 [CI: 0.20-1.54]; p = 0.26). Among patients with BRCA2 mutations, 51 (51%) received taxane first and 49 (49%) received PARPi first. In contrast, patients with BRCA2 mutations had longer PFS when PARPi was given first versus taxane given first (HR: 0.85 [CI: 0.54-1.35]; p = 0.49). Similarly, OS was longer in patients with BRCA2 mutations who received PARPi first (HR: 0.75 [CI: 0.41-1.37]; p = 0.35). Our retrospective data suggest differential response between ATM and BRCA2 mutated prostate cancers in terms of response to PARPi and to taxane chemotherapy. When considering the sequence of PARPi versus taxane chemotherapy for mCRPC with DDR mutations, ATM, and BRCA2 mutation status may be helpful in guiding choice of initial therapy.

Human Metastatic Cholangiocarcinoma Patient-Derived Xenografts and Tumoroids for Preclinical Drug Evaluation.

Cholangiocarcinoma (CCA) is usually diagnosed at advanced stages, with limited therapeutic options. Preclinical models focused on unresectable metastatic CCA are necessary to develop rational treatments. Pathogenic mutations in IDH1/2, ARID1A/B, BAP1, and BRCA1/2 have been identified in 30%-50% of patients with CCA. Several types of tumor cells harboring these mutations exhibit homologous recombination deficiency (HRD) phenotype with enhanced sensitivity to PARP inhibitors (PARPi). However, PARPi treatment has not yet been tested for effectiveness in patient-derived models of advanced CCA. We have established a collection of patient-derived xenografts from patients with unresectable metastatic CCA (CCA_PDX). The CCA_PDXs were characterized at both histopathologic and genomic levels. We optimized a protocol to generate CCA tumoroids from CCA_PDXs. We tested the effects of PARPis in both CCA tumoroids and CCA_PDXs. Finally, we used the RAD51 assay to evaluate the HRD status of CCA tissues. This collection of CCA_PDXs recapitulates the histopathologic and molecular features of their original tumors. PARPi treatments inhibited the growth of CCA tumoroids and CCA_PDXs with pathogenic mutations of BRCA2, but not those with mutations of IDH1, ARID1A, or BAP1. In line with these findings, only CCA_PDX and CCA patient biopsy samples with mutations of BRCA2 showed RAD51 scores compatible with HRD. Our results suggest that patients with advanced CCA with pathogenic mutations of BRCA2, but not those with mutations of IDH1, ARID1A, or BAP1, are likely to benefit from PARPi therapy. This collection of CCA_PDXs provides new opportunities for evaluating drug response and prioritizing clinical trials.

DNAR-12. COMBINING TUMOUR TREATING FIELDS WITH THERAPEUTIC DNA DAMAGE RESPONSE INHIBITORS TO INCREASE POTENCY IN HIGH-GRADE GLIOBLASTOMAS USING CLINICALLY RELEVANT EX-VIVO GLIOMA STEM CELL MODELS

Abstract High-grade gliomas are the most common and aggressive type of primary brain cancer. Despite maximal surgical resection, followed by chemotherapy and radiotherapy, overall survival for patients remains between 10-16 months, with limited improvement in survival rates over the last 40 years. This highlights an urgent unmet clinical need to develop more effective therapeutic interventions for these devastating tumours.Tumour-Treating Fields (TTFields), which deliver low-intensity (1–3V/cm) intermediate-frequency (100–300kHz) alternating electric fields to localised tumour sites, represents an exciting new clinically-approved fourth modality for the treatment of high-grade gliomas, with randomised clinical trial evidence supporting improved overall survival (20.9 vs 16.0 months). Whilst TTFields are primarily thought to mediate their anti-cancer effects by disrupting mitotic tubulin dimer alignment leading to abnormal chromosomal segregation and mitotic cell death, recent data suggests that TTFields may also attenuate DNA damage repair efficiency and replication fork dynamics. We therefore hypothesised that combining TTFields with therapeutic DNA damage response inhibitors (DDRi), to develop next generation multimodal therapy regimes, would enhance TTFields potency in glioma cells either alone, or in combination with current standard-of-care chemoradiotherapy. To assess this, we employed clinically-relevant patient-derived primary glioma stem cell (GSC) models that represent both inter-patient and intra-tumoural heterogeneity, including unique ex-vivo models of post-surgical residual disease. We show that combining TTFields with radiation and clinically approved PARP inhibitor therapy leads to significantly increased amounts of DNA damage with concurrent decreased clonogenic survival in GSCs. Furthermore, we have shown similar impressive potency when TTFields treatments are combined with ATR inhibitors that are currently being assessed in various global clinical trials for other cancers. Overall, these exciting findings support further assessment of TTFields and DDRi combinations to underpin future clinical trials combining TTFields with clinically approved DDRi to improve outcomes for patients with currently incurable high-grade gliomas.

SN-38 Sensitizes BRCA-Proficient Ovarian Cancers to PARP Inhibitors through Inhibiting Homologous Recombination Repair.

As a multifunctional protein posttranslational modification enzyme in eukaryotic cells, Poly-ADP-ribose polymerase (PARP) acts as a DNA damage sensor, which helps to repair DNA damage through recruiting repair proteins to the DNA break sites. PARP inhibitors offer a significant clinical benefit for ovarian cancer with BRCA1/2 mutations. However, the majority of ovarian cancer patients harbor wild-type (WT) BRCA1/2 status, which narrows its clinical application. Here, we identified a small compound, SN-38, a CPT analog, which sensitizes BRCA-proficient ovarian cancer cells to PARP inhibitor treatment by inhibiting homologous recombination (HR) repair. SN-38 treatment greatly enhanced PARP inhibitor olaparib induced DNA double-strand breaks (DSBs) and DNA replication stress. Meanwhile, the combination of SN-38 and olaparib synergistically induced apoptosis in ovarian cancer. Furthermore, combination administration of SN-38 and olaparib induced synergistic antitumor efficacy in an ovarian cancer xenograft model in vivo. Therefore, our study provides a novel therapeutic strategy to optimize PARP inhibitor therapy for patients with BRCA-proficient ovarian cancer.

A Phase 2 study of prexasertib (LY2606368) in platinum resistant or refractory recurrent ovarian cancer

ObjectiveHigh-grade serous ovarian cancer, the most frequent type of ovarian cancer, has a poor prognosis and novel treatments are needed for patients with platinum resistant/refractory disease. New therapeutic strategies targeting cell cycle checkpoints, including CHK1 inhibition with prexasertib, may help improve clinical response and overcome resistance. MethodsPatients with ovarian cancer (N = 169) were assigned to 4 cohorts as part of the Phase 2 multicenter trial (NCT03414047): Cohort 1: platinum resistant, BRCA-wildtype with ≥3 lines prior therapy; Cohort 2: platinum resistant BRCA-wildtype with <3 lines prior therapy; Cohort 3: platinum resistant, BRCA-mutated with prior PARP inhibitor therapy; Cohort 4: platinum refractory, BRCA-mutated, or BRCA-wildtype with any number of prior therapy lines. The primary endpoint was objective response rate (ORR) and secondary endpoints included disease control rate (DCR), and safety. DNA from tumor biopsies was sequenced to identify biomarkers. ResultsThe ORR in platinum resistant patients (Cohorts 1--3) was 12.1%, and 6.9% in platinum refractory patients. In platinum resistant patients, DCR was 37.1%, and consistent across cohorts. In platinum refractory patients, DCR was 31.0%. Consistent with the prexasertib mechanism of action, the most common treatment related adverse events of all grades included thrombocytopenia, neutropenia, fatigue, nausea, and anemia. ConclusionsPrexasertib demonstrated durable single agent activity in a subset of patients with recurrent ovarian cancer regardless of clinical characteristics, BRCA status, or prior therapies, including PARPi. There was no obvious correlation with genomic alterations in responders vs non-responders, emphasizing the need for alternative biomarker approaches for responder identification.

Integrated proteomics identifies PARP inhibitor-induced prosurvival signaling changes as potential vulnerabilities in ovarian cancer

BRCA1/2-deficient ovarian carcinoma (OC) has been shown to be particularly sensitive to poly (ADP-ribose) polymerase inhibitors (PARPis). Furthermore, BRCA1/2 mutation status is currently used as a predictive biomarker for PARPi therapy. Despite providing a major clinical benefit to the majority of patients, a significant proportion of BRCA1/2-deficient OC tumors do not respond to PARPis for reasons that are incompletely understood. Using an integrated chemical, phospho- and ADP-ribosylation proteomics approach, we sought here to develop additional mechanism-based biomarker candidates for PARPi therapy in OC and identify new targets for combination therapy to overcome primary resistance. Using chemical proteomics with PARPi baits in a BRCA1-isogenic OC cell line pair, as well as patient-derived BRCA1-proficient and BRCA1-deficient tumor samples, and subsequent validation by coimmunoprecipitation, we showed differential PARP1 and PARP2 protein complex composition in PARPi-sensitive, BRCA1-deficient UWB1.289 (UWB) cells compared to PARPi-insensitive, BRCA1-reconstituted UWB1.289+BRCA1 (UWB+B) cells. In addition, global phosphoproteomics and ADP-ribosylation proteomics furthermore revealed that the PARPi rucaparib induced the cell cycle pathway and nonhomologous end joining (NHEJ) pathway in UWB cells but downregulated ErbB signaling in UWB+B cells. In addition, we observed AKT PARylation and prosurvival AKT-mTOR signaling in UWB+B cells after PARPi treatment. Consistently, we found the synergy of PARPis with DNAPK or AKT inhibitors was more pronounced in UWB+B cells, highlighting these pathways as actionable vulnerabilities. In conclusion, we demonstrate the combination of chemical proteomics, phosphoproteomics, and ADP-ribosylation proteomics can identify differential PARP1/2 complexes and diverse, but actionable, drug compensatory signaling in OC.