PARP Inhibitor Therapy Research Articles

Comprehensive analysis of somatic reversion mutations in homologous recombination repair genes in a large cohort of Chinese pan-cancer patients.

e15093 Background: Mutations leading to homologous recombination deficiency increases the sensitivity towards platinum-based chemotherapy, as well as the PARP inhibitor. The acquired resistance caused by reversion mutations diminishes the prolonged benefit from the treatment. Herein, we aimed to investigate the prevalence and characteristics of reversion mutations in Chinese population. Methods: The next-generation sequencing data from 23,712 pan-cancer patients (including over 17 cancer types) were retrospectively analyzed for pathogenic/likely pathogenic (P/LP) germline mutations in homologous recombination repair (HRR) genes and possible somatic reversion mutations emerged later. Somatic mutations predicted to restore the open reading frame were identified and further classified into definitive or putative reversion mutations depending on whether the somatic mutation could be confirmed to occur on the same allele as the germline mutation by sequencing reads. Results: From the 23,712 patients, 685 (2.9%) were identified with P/LP germline HRR gene mutations, among which we identified 11 cases with 21 definitive and 4 putative somatic reversion mutations upon treatment, including 8 cases of breast cancer, 3 cases of ovarian cancer, 1 case of pancreatic cancers, and another case of lung cancer. The reversion mutations occurred in 3 genes: BRCA1 (7 cases), BRCA2 (5 cases) and PALB2 (1 case), but not in any other HRR genes in our cohort. Therefore, the incidence of reversion mutations in HRR genes was 1.6% (11/685), with the highest incidence observed in BRCA1 (5.26%) followed by BRCA2 (2.7%) and PALB2 (1.96%). Interestingly, multiple somatic reversion mutations could be observed in 3 patients, indicating heterogeneity in the resistance mechanisms. Among 6 patients with detailed treatment history available, 5 of them had reversion mutations detected after systemic platinum-based chemotherapy and/or PARP inhibitor treatment. The other patient of metastatic breast cancer had 6 prior lines of treatment including 2 cycles of thoracic perfusion of endostatin and lobaplatin before BRCA2 reversion mutation was detected. This patient subsequently received olaparib monotherapy with a progression free survival of only 2 months. Conclusions: This retrospective study demonstrated that the reversion mutations were observed in three HRR-associated genes ( BRCA1, BRCA2 and PALB2) with four cancer types (breast cancer, ovarian cancer, lung cancer and pancreatic cancer) from this Chinese patient cohort. The reversion mutations frequently occurred after resistance to platinum-based chemotherapy and/or PARP inhibitor, and may predict poor outcome from ensuing PARP inhibition therapy. Therefore, monitoring HRR mutation status along the course of the disease could be beneficial especially to informing resistance mechanism and guiding subsequent therapies.

Identification of biomarkers complementary to homologous recombination deficiency for improving the clinical outcome of ovarian serous cystadenocarcinoma.

Ovarian cancer patients with homologous recombination deficiency (HRD) tumors would benefit from PARP inhibitor (PARPi) therapy. However, patients with HRD tumors account for less than 50% of the whole cohort, so new biomarkers still need to be developed. Based on the data from the SNP array and somatic mutation profiles in the ovarian cancer genome, we found that high frequency of actionable mutations existed in patients with non‐HRD tumors. Through transcriptome analysis, we identified that a downstream target of the cGAS‐STING pathway, CXCL11, was upregulated in HRD tumors and could be used as a predictor of survival outcome. Further comprehensive analysis of the tumor immune microenvironment (TIME) revealed that CXCL11 expression signature was closely correlated with cytotoxic cells, neoantigen load and immune checkpoint blockade (ICB). Clinical trial data confirmed that the expression of CXCL11 could be used as a biomarker for anti‐PD‐1/PD‐L1 therapy. Finally, in vivo and in vitro experiments showed that cancer cells with PARPi treatment increased the expression of CXCL11. Collectively, our study not only provides biomarkers of ovarian cancer complementary to the HRD score but also introduces a potential new perspective for identifying prognostic biomarkers of immunotherapy.

NPRL2 reduces the niraparib sensitivity of castration-resistant prostate cancer via interacting with UBE2M and enhancing neddylation

In this study, we explored the regulatory effects of nitrogen permease regulator 2-like (NPRL2) on niraparib sensitivity, a PARP inhibitor (PARPi) in castrate-resistant prostate cancer (CRPC). Data from The Cancer Genome Atlas (TCGA) and Genotype-Tissue Expression (GTEx) program were retrospectively examined. Gene-set enrichment analysis (GSEA) was conducted between high and low NRPL2 expression prostate adenocarcinoma (PRAD) cases in TCGA. CCK-8 assay, Western blot analysis of apoptotic proteins, and flow cytometric analysis of apoptosis were applied to test niraparib sensitivity. Immunofluorescent (IF) staining and co-immunoprecipitation (co-IP) were conducted to explore the proteins interacting with NPRL2. Results showed that the upregulation of a canonical protein-coding transcript of NPRL2 (ENST00000232501.7) is associated with an unfavorable prognosis. Bioinformatic analysis predicts a physical interaction between NPRL2 and UBE2M, which is validated by a following Co-IP assay. This interaction increases NPRL2 stability by reducing polyubiquitination and proteasomal degradation. Depletion of NPRL2 or UBE2M significantly increases the niraparib sensitivity of CRPC cells and enhances niraparib-induced tumor growth inhibition in vivo. NPRL2 cooperatively enhances UBE2M-mediated neddylation and facilitates the degradation of multiple substrates of Cullin-RING E3 ubiquitin ligases (CRLs). In conclusion, this study identified a novel NPRL2-UBE2M complex in modulating neddylation and niraparib sensitivity of CRPC cells. Therefore, targeting NPRL2 might be considered as an adjuvant strategy for PARPi therapy.

The PARP Enzyme Family and the Hallmarks of Cancer Part 1. Cell Intrinsic Hallmarks.

Simple SummaryPoly (ADP-ribose) polymerase (PARP) proteins regulate DNA damage correction, replication, and gene transcription. By controlling pivotal aspects of these processes, PARPs are heavily implicated in cancer development. Inhibitors of PARPs, approved for cancer chemotherapy a few years ago, have achieved great success against tumors of the breast and ovary carrying mutations in the BRCA1/2 genes. The spectrum of the inhibitors is avidly sought to be extended to tumors with different genetic backgrounds and cancers of other origins. This pursuit requires thorough apprehension of PARP-dependent processes affecting cancer development. The hallmarks of cancer are acquired by defining capabilities that differentiate cancer cells from their normal counterparts. Here, in two joint papers, we walk through the connections between these cancer traits and PARP functions. The present review focuses on how PARPs affect the features of cancer that can be attributed to cell-intrinsic changes increasing proliferative potential and survival capabilities. In a kindred paper, we explore the PARP association of cancer hallmarks that derive from tissue-level reorganization in tumors and intercellular interactions of cancer cells.The 17-member poly (ADP-ribose) polymerase enzyme family, also known as the ADP-ribosyl transferase diphtheria toxin-like (ARTD) enzyme family, contains DNA damage-responsive and nonresponsive members. Only PARP1, 2, 5a, and 5b are capable of modifying their targets with poly ADP-ribose (PAR) polymers; the other PARP family members function as mono-ADP-ribosyl transferases. In the last decade, PARP1 has taken center stage in oncology treatments. New PARP inhibitors (PARPi) have been introduced for the targeted treatment of breast cancer 1 or 2 (BRCA1/2)-deficient ovarian and breast cancers, and this novel therapy represents the prototype of the synthetic lethality paradigm. Much less attention has been paid to other PARPs and their potential roles in cancer biology. In this review, we summarize the roles played by all PARP enzyme family members in six intrinsic hallmarks of cancer: uncontrolled proliferation, evasion of growth suppressors, cell death resistance, genome instability, reprogrammed energy metabolism, and escape from replicative senescence. In a companion paper, we will discuss the roles of PARP enzymes in cancer hallmarks related to cancer-host interactions, including angiogenesis, invasion and metastasis, evasion of the anticancer immune response, and tumor-promoting inflammation. While PARP1 is clearly involved in all ten cancer hallmarks, an increasing body of evidence supports the role of other PARPs in modifying these cancer hallmarks (e.g., PARP5a and 5b in replicative immortality and PARP2 in cancer metabolism). We also highlight controversies, open questions, and discuss prospects of recent developments related to the wide range of roles played by PARPs in cancer biology. Some of the summarized findings may explain resistance to PARPi therapy or highlight novel biological roles of PARPs that can be therapeutically exploited in novel anticancer treatment paradigms.

Abstract IA-003: Oxygen dependent resistance to PARP inhibitors

Abstract Severe hypoxia causes resistance to conventional chemotherapy and has been reported to synergize with PARP inhibitors (PARPi) through suppression of homologous recombination (HR). While this synergistic killing is true at oxygen levels less than 0.5%, our study shows that less severe hypoxia (e.g. 2% oxygen) is instead associated with resistance to PARPi in HR proficient cells. Interestingly, we demonstrate that HR deficient hypoxic tumors are significantly less responsive to PARPi, due to limited ROS-induced intrinsic DNA damage. To determine the contribution of hypoxic cells to PARPi, we used the hypoxic cytotoxin Tirapazamine to target hypoxic tumor cells. We found that the elimination of hypoxic tumor cells by Tirapazamine led to a substantial antitumor response with PARPi compared to PARPi treated tumors alone, without enhancing normal tissue toxicity. These studies indicate that tumor hypoxia reduces the efficacy of PARPi to tumor cells and that eliminating hypoxic tumor cells will enhance the efficacy of PARPi therapy. Citation Format: Manal Mehibel, Jimmy Xu, Grace Li, Jung Moon, Kaushik Thakkar, Anh Diep, Ryan Kim, Joshua Bloomstein, Siren Xiao, Julien Bacal, Joshua Saldivar, Quynh Le, Karlene Cimprich, Erinn Rankin, Amato Giaccia. Oxygen dependent resistance to PARP inhibitors [abstract]. In: Proceedings of the AACR Virtual Special Conference on Radiation Science and Medicine; 2021 Mar 2-3. Philadelphia (PA): AACR; Clin Cancer Res 2021;27(8_Suppl):Abstract nr IA-003.

The spectrum of tumors harboring BAP1 gene alterations

Germline mutations in the BRCA1-associated protein (BAP1) gene (MIM # 603089) are associated with a substantially increased risk for developing melanoma, mesothelioma, and renal cell carcinoma. Somatic inactivation of the BAP1 gene was noted in these and other tumors types, including esophageal cancer and cholangiocarcinoma. The favorable response of BRCA1/2-associated tumors to poly (ADP-ribose) polymerase (PARP) inhibitor therapy, raises the possibility that tumors harboring BAP1 mutations may exhibit similar sensitivity to PARP inhibitor therapy. Given the possibility that BAP1 alterations may have therapeutic implications, this study was aimed to describe the spectrum of tumors that harbor BAP1 alterations. The Foundation Medicine database was queried for known or likely pathogenic BAP1 genomic variants through July 2019. Overall, 4982/374,694 (1.81%) tumors harbored pathogenic BAP1 genomic alterations. Highest rates were noted in mesothelioma (45.24%), cholangiocarcinoma (13.37%), renal cell carcinoma (10.52%), thymic cancer (8.16%), salivary gland cancer (6.18%), and melanoma (5.1%). There were 59 unique BAP1 short variants detected in at least 10 samples. More same tissue tumors of squamous cell histology harbored BAP1 alterations than adenocarcinomas. The current study highlights tumor types that display higher than previously appreciated rates of somatic BAP1 genomic alterations.

Molecular and clinical predictors of improvement in progression-free survival with maintenance PARP inhibitor therapy in women with platinum-sensitive, recurrent ovarian cancer: A meta-analysis.

The authors performed a meta-analysis to better quantify the benefit of maintenance poly(ADP-ribose) polymerase inhibitor (PARPi) therapy to inform practice in platinum-sensitive, recurrent, high-grade ovarian cancer for patient subsets with the following characteristics: germline BRCA mutation (gBRCAm), somatic BRCA mutation (sBRCAm), wild-type BRCA but homologous recombinant-deficient (HRD), homologous recombinant-proficient (HRP), and baseline clinical prognostic characteristics. Randomized trials comparing a PARPi versus placebo as maintenance treatment were identified from electronic databases. Treatment estimates of progression-free survival were pooled across trials using the inverse variance weighted method. Four trials included 972 patients who received a PARPi (olaparib, 31%; niraparib, 35%; or rucaparib, 34%) and 530 patients who received placebo. For patients who had germline BRCA1 mutation (gBRCAm1) (N = 471), the hazard ratio (HR) was 0.29 (95% CI, 0.23-0.37); for those who had germline BRCA2 mutation (gBRCAm2) (N = 236), the HR was 0.26 (95% CI, 0.17-0.39); and, for those who had sBRCAm (N = 123), the HR was 0.22 (95% CI, 0.12-0.41). The treatment effect was similar between the gBRCAm and sBRCAm subsets (P = .48). In patients who had wild-type BRCA HRD tumors (excluding sBRCAm; N = 309), the HR was 0.41 (95% CI, 0.31-0.56); and, in those who had wild-type BRCA HRP tumors (N = 346), the HR was 0.64 (95% CI, 0.49-0.83). The relative treatment effect was greater for the BRCAm versus HRD (P = .03), BRCAm versus HRP (P < .00001), and HRD versus HRP (P < .00001) subsets. There was no difference in benefit based on age, response after recent chemotherapy, and prior bevacizumab. In platinum-sensitive, recurrent, high-grade ovarian cancer, maintenance PARPi improves progression-free survival for all patient subsets. PARPi therapy has a similar magnitude of benefit for sBRCAm and gBRCAm. Although patients with BRCAm derive the greatest benefit, the absence of a BRCAm or HRD could not be used to exclude patients from maintenance PARPi therapy.

Tumour Versus Germline BRCA Testing in Ovarian Cancer: A Single-Site Institution Experience in the United Kingdom.

The aim of this audit was to evaluate the usefulness and serviceability of testing for pathogenic mutations in BRCA1 or BRCA2 (BRCA1/2) genes in ovarian cancer (OC) patients. One hundred and thirty-five patients with more common histological sub-types of OC were retrospectively identified between 2011 and 2019. The fail rate of the molecular analysis was 7.4% (10/135). One hundred and twenty-five records were evaluated: 99 (79.2%) patients had wild-type BRCA (both somatic and germline); tumour BRCA1/2 (tBRCA1/2) pathogenic mutations were found in 20 (16%) patients with distribution between BRCA1 and BRCA2 being 40% and 60%, respectively; 13 (10.4%) patients with pathogenic variants had germline mutations; and tBRCA1/2 with variant of unknown significance (VUS), in the absence of pathogenic BRCA1 or BRCA2 variants, was detected in 6 (4.8%) patients. Our data show that expanding the molecular service to the routine first-tumour testing for patients with OC will potentially increase the detection rate of BRCA mutations, thereby providing early benefits of PARP inhibitors therapy. The tumour testing service should continue to be offered to newly diagnosed patients with high-grade epithelial cancers, including high-grade serous carcinoma, but also with carcinosarcomas and poorly-differentiated metastatic adenocarcinomas of unknown origin.

Olaparib tablets as maintenance therapy in patients with platinum-sensitive relapsed ovarian cancer and a BRCA1/2 mutation (SOLO2/ENGOT-Ov21): a final analysis of a double-blind, randomised, placebo-controlled, phase 3 trial

Olaparib, a poly (ADP-ribose) polymerase (PARP) inhibitor, has previously been shown to extend progression-free survival versus placebo when given to patients with relapsed high-grade serous or endometrioid ovarian cancer who were platinum sensitive and who had a BRCA1 or BRCA2 (BRCA1/2) mutation, as part of the SOLO2/ENGOT-Ov21 trial. The aim of this final analysis is to investigate the effect of olaparib on overall survival. This double-blind, randomised, placebo-controlled, phase 3 trial was done across 123 medical centres in 16 countries. Eligible patients were aged 18 years or older, had an Eastern Cooperative Oncology Group performance status at baseline of 0-1, had histologically confirmed, relapsed, high-grade serous or high-grade endometrioid ovarian cancer, including primary peritoneal or fallopian tube cancer, and had received two or more previous platinum regimens. Patients were randomly assigned (2:1) to receive olaparib tablets (300 mg in two 150 mg tablets twice daily) or matching placebo tablets using an interactive web or voice-response system. Stratification was by response to previous chemotherapy and length of platinum-free interval. Treatment assignment was masked to patients, treatment providers, and data assessors. The primary endpoint of progression-free survival has been reported previously. Overall survival was a key secondary endpoint and was analysed in all patients as randomly allocated. Safety was assessed in all patients who received at least one treatment dose. This trial is registered with ClinicalTrials.gov, NCT01874353, and is no longer recruiting patients. Between Sept 3, 2013 and Nov 21, 2014, 295 patients were enrolled. Patients were randomly assigned to receive either olaparib (n=196 [66%]) or placebo (n=99 [34%]). One patient, randomised in error, did not receive olaparib. Median follow-up was 65·7 months (IQR 63·6-69·3) with olaparib and 64·5 months (63·4-68·7) with placebo. Median overall survival was 51·7 months (95% CI 41·5-59·1) with olaparib and 38·8 months (31·4-48·6) with placebo (hazard ratio 0·74 [95% CI 0·54-1·00]; p=0·054), unadjusted for the 38% of patients in the placebo group who received subsequent PARP inhibitor therapy. The most common grade 3 or worse treatment-emergent adverse event was anaemia (which occurred in 41 [21%] of 195 patients in the olaparib group and two [2%] of 99 patients in the placebo group). Serious treatment-emergent adverse events were reported in 50 (26%) of 195 patients receiving olaparib and eight (8%) of 99 patients receiving placebo. Treatment-emergent adverse events with a fatal outcome occurred in eight (4%) of the 195 patients receiving olaparib, six of which were judged to be treatment-related (attributed to myelodysplastic syndrome [n=3] and acute myeloid leukaemia [n=3]). Olaparib provided a median overall survival benefit of 12·9 months compared with placebo in patients with platinum-sensitive, relapsed ovarian cancer and a BRCA1/2 mutation. Although statistical significance was not reached, these findings are arguably clinically meaningful and support the use of maintenance olaparib in these patients. AstraZeneca and Merck.

An Overview of PARP Inhibitors for the Treatment of Breast Cancer.

Loss-of-function mutations in BRCA1 and BRCA2 are detected in at least 5% of unselected patients with breast cancer (BC). These BC susceptibility genes encode proteins critical for DNA homologous recombination repair (HRR). This review provides an update on oral poly(ADP-ribose) polymerase (PARP) inhibitors for the treatment of BC. Olaparib and talazoparib are PARP inhibitors approved as monotherapies for deleterious/suspected deleterious germline BRCA-mutated, HER2-negative BC. Olaparib is approved in the USA for metastatic BC and in Europe for locally advanced/metastatic BC. Talazoparib is approved for locally advanced/metastatic BC in the USA and Europe. In phase 3 trials, olaparib and talazoparib monotherapies demonstrated significant progression-free survival benefits compared with chemotherapy. Common toxicities were effectively managed by supportive treatment and dose interruptions/reductions. Veliparib combined with platinum-based chemotherapy has also shown promise for locally advanced/metastatic BC in a phase 3 trial. Differences in efficacy and safety across PARP inhibitors (olaparib, talazoparib, veliparib, niraparib, rucaparib) may relate to differences in potency of PARP trapping on DNA and cytotoxic specificity. PARP inhibitors are being investigated in early BC, in novel combinations, and in patients without germline BRCA mutations, including those with somatic BRCA mutations and other HRR gene mutations. Ongoing phase 2/3 studies include PARP inhibitors combined with immune checkpoint inhibitors for the treatment of triple-negative BC. Wider access to testing for BRCA and other mutations, and to genetic counseling, are required to identify patients who could benefit from PARP inhibitor therapy. The advent of PARP inhibitors has potential benefits for BC treatment beyond the locally advanced/metastatic setting.

Differences in the genomic landscape of advanced prostate cancer (aPC) patients (pts) with BRCA1 versus BRCA2 mutations as detected by machine learning analysis of the comprehensive genomic profile (CGP) of cell-free DNA (cfDNA).

162 Background: PARP inhibitors (PARPi) provide significant clinical benefit for men with aPC with BRCA 1 and BRCA 2 mutations. However, in clinical trials, pts with BRCA1 mutations appeared to derive less benefit than pts with BRCA2 (De Bono et al., 2020). Probabilistic Graphical Models (PGMs) are artificial intelligence (AI) algorithms that capture multivariate, multi-level dependencies in complex patterns in large datasets while retaining human interpretability. We hypothesize that PGMs can reveal variants in BRCA1 and 2 that co-segregate with other known pathogenic variants and may explain the difference in response to PARPi therapy. Methods: Multilevel gene interdependencies between BRCA1 or BRCA2 were assessed using a Bayesian Network (BN) machine learning approach and Fisher’s exact test. CGP was performed by a validated cfDNA NGS panel that sequenced 74 clinically relevant cancer genes (Guardant360, Redwood City, CA). Only variants of known significance and those of unknown significance with a pathogenic REVEL score were included in the analysis. Results: Of 4671 men with aPC undergoing cfDNA CGP, 1248 men with somatic mutations in BRCA1, BRCA2, ATM, or combinations of the three were included in the analysis. The Bayesian network analysis demonstrated positive interdependencies between pathogenic variants in BRCA1 and 7 other genes. A positive interdependency between BRCA2 and 2 genes was present (table). ATM displayed negative interdependency with both BRCA 1 and 2. Conclusions: Our results demonstrate a decreased association of BRCA2 versus BRCA1 with known or predicted pathogenic variants at other loci. This may explain increased sensitivity of aPC with BRCA2 mutations to PARPi due to fewer concurrent resistance pathways. For example, alteration of ERBB2, which segregates strongly with BRCA1, is known to induce tumor progression and invasion in aPC and is associated with castration-resistance. These hypothesis-generating data reveal differential genomic signatures associated with BRCA1 as compared to BRCA2 and may inform development of future combinatorial treatment regimens for these pts. [Table: see text]

Abstract PS10-11: Associations with response to poly(ADP-ribose) polymerase (PARP) inhibitors in patients with BRCA mutated metastatic breast cancer: Results of a meta-regression analysis

Abstract Background: PARP inhibitors (PARPi), when given as single agents, have modest antitumor activity in patients with advanced breast cancer and mutation in BRCA1 or BRCA2. It is unclear whether some subgroups derive greater benefit from treatment.Methods: Two electronic databases (MEDLINE, CENTRAL) and one registry (Clinicaltrials.gov) were searched from inception to June 2020 to identify trials of PARPi in patients with metastatic breast cancer. Objective response rate (ORR) and disease control rate (DCR) to PARPi were extracted and pooled in a meta-analysis using the Mantel Haenszel random effects model. Analyses were performed for patients with a BRCA mutation exclusively. Meta-regression explored the influence of patient and tumor characteristics and previous chemotherapy on ORR and DCR as reported in individual studies. Analysis comprised of a linear regression weighted by individual study sample size using the weighted least squares (mixed effect) method. Quantitative significance was defined using methods described by Burnand et al. Results: Twenty-two studies comprising 1627 patients were identified and among these 1466 (90%) patients had a germline (n=1451) or a somatic (n=15) BRCA mutation and were included in the analysis. In 7 of these studies (32%; n=680 patients), the PARPi was given in combination with a platinum-based chemotherapy.; 54% of breast cancers were triple-negative. 81% of patients had received at least 1 prior line of chemotherapy in the metastatic setting and 28% were previously exposed to a platinum-based chemotherapy in the metastatic setting. Pooled ORR was 46%; 66% when combined with platinum vs 36% with PARPi alone (OR 3.44, 2.77-4.29, p0.001). Meta-regression results are shown in the Table. Previous chemotherapy in the metastatic setting, especially platinum-based chemotherapy, was associated with highly significantly lower ORR as defined by by Burnand et al. Age and hormone receptor status were not associated with response. Quantitatively similar results were observed for DCR. Conclusion: PARPi therapy is associated with lesser response in patients with prior chemotherapy exposure, especially platinum-based treatment. There was no association between ORR and hormone receptor status or age. Dependent variableVariableCoefficients BêtaSignifianceORR BRCA1/2n = 146645.67 %Age-0.320.34Previous chemotherapy in metastatic setting-0.700.004Previous platinum in metastatic setting-0.620.02Platinum refractory-0.390.22Hormone receptor positive0.190.48Triple negative-0.120.66DCR BRCA1/2n = 126071.47 %Age-0.240.53Previous chemotherapy in metastatic setting-0.740.006Previous platinum-0.420.21Platinum refractory-0.070.83Hormone receptor positive-0.120.69Triple negative0.230.47 Citation Format: Alexandra Desnoyers, Brooke E. Wilson, Michelle B. Nadler, Eitan Amir. Associations with response to poly(ADP-ribose) polymerase (PARP) inhibitors in patients with BRCA mutated metastatic breast cancer: Results of a meta-regression analysis [abstract]. In: Proceedings of the 2020 San Antonio Breast Cancer Virtual Symposium; 2020 Dec 8-11; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2021;81(4 Suppl):Abstract nr PS10-11.

Abstract PD13-03: Genomic profiling of breast cancer leptomeningeal metastasis (BCLM) reveals a divergent evolution and therapeutic targets

Abstract Background: Leptomeningeal metastasis remains a devastating development in breast cancer, with a median survival of 3-4 months, no widely accepted standard treatment, and limited access to trials of novel therapies. In addition, lack of access to leptomeningeal metastatic material hampers the pre-clinical investigation of the disease process and molecular drivers. This project uses CSF as a liquid biopsy to characterise BCLM, through genomic analysis of the cell-free DNA (cfDNA), and the development of pre-clinical BCLM models by the expansion of CSF disseminated tumour cells. Methods: CSF (surplus to clinical requirements) and blood were collected from patients undergoing evaluation of leptomeningeal metastasis. cfDNA was extracted from CSF and plasma, and subjected to ultra-low pass whole genome sequencing (ulpWGS) to assess tumour-derived cfDNA fraction. Samples with &amp;gt;10% tumour fraction underwent whole exome sequencing, along with matched archival primary tumour, archival extra-cranial metastatic site(s) and germline DNA. CSF cells were expanded in vitro (to establish 3D patient-derived organoids (PDOs). Results: Cohort demographics are shown in Table 1. Whole exome sequencing (WES) in 21 patients reveals that 65.2% of variants found in CSF cfDNA were not shared with the primary tumour or other matched samples. Phylogenetic analysis shows a divergent evolution from extra-cranial metastatic sites, represented by plasma cfDNA (n = 12) and/or metastatic site tissue DNA (n = 7). The most frequently mutated cancer-associated genes in CSF were MUC16 (12/21), TP53 (11/21), CDH1 (10/21), and KMT2D (7/21). The common occurrence of CDH1 loss-of-function mutations was in keeping with the large number of lobular cases, however were also discovered in CSF of two cases with E-cadherin positive ductal primary tumours. Furthermore, mutations (including frameshift indels) in JAK family proteins (JAK1, JAK3 and TYK2) were present in 5/21 cases, and were private to CSF in 4/21. Potential actionable gene alterations private to CSF include; IDH2 (3/21), GLI1 (3/21), PIK3CA (2/21) and PTCH1 (2/21). Further, there was an enrichment for somatic BRCA1/2 mutations (5/21, 2 private to CSF) indicating potential for platinum and/or PARP inhibitor therapy in these individuals. Patient-derived organoids (PDOs) were established using CSF tumour cells from 3 ER+/HER2- and 2 TNBC BCLM cases. WES of PDOs revealed high concordance with genomic variants identified in the matched CSF cfDNA. Therapeutic compound testing revealed 3/5 PDOs did not display sensitivity to methotrexate, the most commonly used BCLM intrathecal treatment. Patient-derived xenograft (PDX) models have been established by mammary fat pad, intraductal, intracardiac and intracerebroventricular injection routes. Conclusion/future plans: WES of CSF cfDNA provides insight into genomic changes in BCLM, including the divergent evolution, and BCLM specific alterations, some of which are potentially targetable. Parallel PDO and PDX models are being used to validate potential drivers and therapeutic targets. Treatment options beyond intrathecal methotrexate are urgently needed and in future might be molecularly tailored based on alterations discovered by CSF cfDNA sequencing. Table 1. Clinical demographicsDemographicsMedian, years (range)Age at BC diagnosis45 (24 – 66)Time from primary BC to BCLM4.7 (0.7 – 14.7)Time from first metastasis to BCLM1.2 (0.0 – 6.5)Histological Typen (%)Lobular10 (48)Ductal8 (38)Mixed ductal/lobular3 (14)Immuno-histochemical phenotypen (%)ER+ HER2-13 (62)TNBC5 (24)ER+ HER2+2 (9)ER- HER2+1 (5)Metastatic sitesn (%)No other metastatic sites (BCLM only)3 (14)Bone12 (57)Serosal8 (38)Brain6 (29)Liver4 (19)Ovary4 (19) Citation Format: Amanda Fitzpatrick, Marjan Iravani, Adam Mills, Eleanor Knight, Thanussuyah Alaguthurai, Vandna Shah, Alicia Okines, Nick Turner, Mark Harries, Syed Haider, Andrew Tutt, Clare Isacke. Genomic profiling of breast cancer leptomeningeal metastasis (BCLM) reveals a divergent evolution and therapeutic targets [abstract]. In: Proceedings of the 2020 San Antonio Breast Cancer Virtual Symposium; 2020 Dec 8-11; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2021;81(4 Suppl):Abstract nr PD13-03.

Deep exploration of PARP inhibitors in breast cancer: monotherapy and combination therapy.

ObjectiveNearly 5% of patients with breast cancer carry germline BRCA mutations, which are more common in triple-negative breast cancer (TNBC). Previous clinical trials demonstrated the therapeutic efficacy of poly (ADP-ribose) polymerase inhibitors (PARPis) against BRCA-mutated metastatic breast cancer. The current study conducted a systemic review and meta-analysis of the clinical efficiency and safety of PARPis, either alone or combined with chemotherapy, in patients with TNBC.MethodsWe searched PubMed, EMBASE, and ClinicalTrials.gov to identify randomized controlled trials comparing PARPi therapy with chemotherapy, and comparisons of chemotherapy plus PARPis with chemotherapy alone were included. The study endpoints included the clinical response, progression-free survival, and adverse event rates.ResultsPARPi therapy was revealed to improve progression-free survival in patients with advanced breast cancer, either alone or in combination with chemotherapy. Subgroup analysis illustrated that patients with mutant BRCA1 and mutant BRCA2 and those who had not been treated with platinum-based agents could specifically benefit from PARPis.ConclusionPARPi monotherapy can significantly improve clinical outcomes in patients with advanced breast cancer, especially those with TNBC, those who had not previously received platinum therapy, and those with mutant BRCA1/2. PARPis combined with chemotherapy represent new treatment options for patients with advanced cancer.

Poly(ADP-ribose) polymerase inhibition in pancreatic cancer.

Pancreatic ductal adenocarcinoma (PDAC) is a lethal disease with limited treatment options. Recently, the poly(ADP-ribose) polymerase inhibitor (PARPi) olaparib has been approved for maintenance therapy after successful platinum-based chemotherapy in patients with germline mutations in BRCA1 and BRCA2. Approval was based on the POLO study that has shown a significant improvement in progression-free survival for patients with metastatic PDAC after at least 4 months of platinum-based chemotherapy. Hopefully, this first biomarker-directed targeted therapy for a relevant subgroup of pancreatic cancer patients is only the beginning of an era of personalized therapy for pancreatic cancer. The potential role for PARPi in improving survival in patients with pancreatic cancer containing somatic tumor mutations has yet to be established. Multiple studies investigating whether PARPi therapy might benefit a larger group of pancreatic cancer patients with homologous recombination repair deficiency and whether combinations with chemotherapy, immunotherapy, or small molecules can improve efficacy are currently underway. We here review the molecular basis for PARPi therapy in PDAC patients and recent developments in clinical studies.

PARP Inhibitors in Triple-Negative Breast Cancer Including Those With BRCA Mutations.

Poly(ADP-ribose) polymerase (PARP) is involved in single-strand DNA break base excision repair. PARP inhibition causes synthetic lethality in breast cancers associated with germline BRCA1 and BRCA2 mutations and is routinely used in clinical practice for metastatic breast cancer. Breast cancers with homologous recombination deficiency or BRCAness, most commonly triple-negative breast cancers, may also benefit. Currently, PARP inhibitor use for triple-negative breast cancer with wild-type BRCA does not have definitive efficacy; however, this is an area of active research. Further clinical and translational data may identify additional patient populations that will benefit from PARP inhibitor therapy.

The role of novel poly (ADP-ribose) inhibitors in the treatment of locally advanced and metastatic Her-2/neu negative breast cancer with inherited germline BRCA1/2 mutations. A review of the literature.

The use of the PARP inhibitors (PARPi) in the treatment of breast cancer (BC) with germine mutations has evolved over the years, and further research has been done in order to broaden the horizon of this treatment strategy. Therefore the aim of this paper is to review the efficiency of PARPi in the treatment of BRCA 1/2-mutated locally advanced and metastatic Her-2/net negative BC mentioning their side effects, mechanism of resistance and future directions. Inhibition of PARP transforms single-strand breaks into double-strand breaks (DBS), the accumulation of the latter causing cell death (cell apoptosis). The Olympia AD phase III trial demonstrated a statistically significant progression-free survival rate (PFS) when using the PARPi olaparib in metastatic BC with germline BRCA1/2 mutations without any benefit of the overall survival rate. PARPi therapy is associated with acceptable responsive rates and progression-free survival rates in locally advanced and metastatic BRCA1/2 associated BC through mechanisms that enhance and increase the sensitivity to chemotherapeutic or target agents as they induce a synthetic lethality and cell apoptosis. The side effects are not significant, the most adverse effects being related to the hematological and gastrointestinal systems. Olaparib is currently approved in the first-line treatment of BRCA1/2 mutated Her-2/neu negative metastatic BC at an oral dose of 300 mg twice daily, while Talazoparib represents a category one recommendation in locally advanced and metastatic Her-2/neu negative BC in women with central nervous system metastases.

High-grade serous ovarian carcinoma and detection of inactivated BRCA genes from biopsy material of Slovak patients.

Ovarian cancer is the leading cause of mortality among all gynecological cancers in developed countries and its most common and most lethal type is the high-grade serous ovarian carcinoma (HGSC). At the molecular level, nearly half of all HGSCs exhibit ineffective homologous DNA recombination and disruption of DNA damage/repair pathway inactivation caused often by BRCA1 and BRCA2 gene mutation. Recently, the detection of BRCA1/2 mutations became important for personalized treatment of HGSC patients with the PARP-inhibitors in the defined clinical setting of relapse after positive adjuvant platinum-based chemotherapeutic response. Based on the selection of patients by regional oncologists, we attempted to verify the possibilities of BRCA1/2 mutation testing on archival formalin-fixed paraffin-embedded (FFPE) biopsy material from regional hospitals. In the study we used: a/ FFPE tumor resections of 97 patients sent to our laboratory, originally stored in archives of regional departments for a period of 1-3 years and retrieved on the principle to contain a maximum of non-necrotic tumor tissue, b/ next-generation sequencing (NGS) assay covering all known mutations in the BRCA1/2 genes on MiSeq (Illumina® platform), and c/ Sophia DDM® bioinformatics platform. After processing of FFPE samples, 5 cases were excluded due to the insufficient genomic DNA quantity. Bioinformatics results of NGS analyses of 92 patients' samples indicated 17.39% pathogenic mutations and 32.61% potentially pathogenic mutations in genes BRCA1/2. Overall, 50% pathogenic and potentially pathogenic mutations were detected in the patient's cohort. The relatively high incidence of BRCA1/2 mutations in our series may be influenced by various indicators including the selection of patients based on adjuvant therapy response as well as regional or population heterogeneity in their frequency. Based on the interdisciplinary cooperation, the use of archival biopsy material processed primarily and stored for a longer period in different laboratories without uniformly defined pre-analytical conditions allows identifying the HGSC patients who might better respond to the PARP-inhibition therapy.

Olaparib in the metastatic HER2-negative breast cancer setting

Understanding of cancer biology is at the cornerstone of design of new and effective treatment strategies. Identification of molecular drivers of tumor growth and progression allow identify right patient for the right treatment for personalized treatment plan optimization. Breast cancer (BC) encompasses a heterogeneous collection of neoplasms with diverse morphologies, molecular phenotypes, responses to therapy, probabilities of relapse and overall survival. Molecular and histopathological classification aims to categories tumors into subgroups to inform clinical decisions, to improve long-term treatment results and maintain the quality of life of this group of patients. Germinal mutation in the BRCA1/2 (BRCAm) genes in a tumor determines the hereditary predisposition, disease manifestation, therapeutic options and clinical efficacy. Therefore, patients withBRCAmBCrepresent a special subgroup requiring personalized treatment approach.Olaparib, a poly (ADP-ribose) polymerase (PARP) inhibitor, is a targeted therapeutic agent that acts as inhibitor of single-strand breaks reparation, leading to their accumulation, conversion to double-strand breaks and eventually to cancer cell apoptosis. Olaparib is a first-in-class PARP-inhibitor with an outstanding antineoplastic activity known for some malignant tumors, demonstrates effectiveness and safety of therapy inBRCAmBCas well. The results of OlympiAD and LUCY trials are represented in the article. Subgroup analysis may define the patient population that would benefit from PARP inhibitors therapy.

Myelodysplastic syndrome and acute myeloid leukaemia in patients treated with PARP inhibitors: a safety meta-analysis of randomised controlled trials and a retrospective study of the WHO pharmacovigilance database

Poly(ADP-ribose) polymerase (PARP) inhibitors have shown efficacy and acceptable safety in a range of neoplasms, particularly in ovarian cancers. However, some concerns have emerged regarding rare and delayed adverse events including cases of myelodysplastic syndrome and acute myeloid leukaemia, for which data are scarce. The aim of this study was to estimate the risk of myelodysplastic syndrome and acute myeloid leukaemia related to PARP inhibitors, via a systematic review and safety meta-analysis, and to describe clinical features of PARP inhibitor-related myelodysplastic syndrome and acute myeloid leukaemia cases reported in WHO's pharmacovigilance database (VigiBase). We systematically reviewed randomised controlled trials (RCTs) comparing PARP inhibitor therapy versus control treatments (placebo and non-placebo) in adults (age ≥18 years) treated for cancer in MEDLINE, the Cochrane Central Register of Controlled Trials, and the ClinicalTrials.gov registry with ongoing surveillance up to May 31, 2020. The date range for included studies was not restricted. By a stepwise method to capture all available adverse events, we first extracted data on myelodysplastic syndrome and acute myeloid leukaemia cases from ClinicalTrials.gov. If cases were not available, we extracted them from published manuscripts, or subsequently contacted corresponding authors or sponsors to provide data. RCTs without available data from ClinicalTrials.gov, publications, or corresponding authors or sponsors were excluded. The primary outcome was the summary risk of myelodysplastic syndrome and acute myeloid leukaemia related to PARP inhibition versus placebo treatment in RCTs. We used a fixed-effects meta-analysis to obtain Peto odds ratios (ORs) with 95% CIs. In a separate observational, retrospective, cross-sectional pharmacovigilance study of VigiBase, cases of myelodysplastic syndrome and acute myeloid leukaemia related to PARP inhibitor therapy were extracted on May 3, 2020, and clinical features summarised with a focus on median duration of PARP inhibitor exposure, median latency period between first drug exposure and diagnosis, and proportion of cases resulting in death. Our systematic review and safety meta-analysis were registered with PROSPERO, CRD42020175050. Our retrospective pharmacovigilance study was registered on ClinicalTrials.gov, NCT04326023. For our safety meta-analysis, initial searches identified 1617 citations, and 31 RCTs were systematically reviewed for eligibility. 28 RCTs with available adverse events were analysed (18 placebo and ten non-placebo RCTs), with 5693 patients in PARP inhibitor groups and 3406 patients in control groups. Based on the 18 placebo RCTs (n=7307 patients), PARP inhibitors significantly increased the risk of myelodysplastic syndrome and acute myeloid leukaemia compared with placebo treatment (Peto OR 2·63 [95% CI 1·13-6·14], p=0·026) with no between-study heterogeneity (I2=0%, χ2 p=0·91). The incidence of myelodysplastic syndrome and acute myeloid leukaemia across PARP inhibitor groups was 0·73% (95% CI 0·50-1·07; I2=0%, χ2 p=0·87; 21 events out of 4533 patients) and across placebo groups was 0·47% (0·26-0·85; I2=0%, χ2 p=1·00; three events out of 2774 patients). All 28 RCTs were rated as having unclear risk of bias. In VigiBase, 178 cases of myelodysplastic syndrome (n=99) and acute myeloid leukaemia (n=79) related to PARP inhibitor therapy were extracted. In cases with available data, median treatment duration was 9·8 months (IQR 3·6-17·4; n=96) and median latency period since first exposure to a PARP inhibitor was 17·8 months (8·4-29·2; n=58). Of 104 cases that reported outcomes, 47 (45%) resulted in death. PARP inhibitors increased the risk of myelodysplastic syndrome and acute myeloid leukaemia versus placebo treatment. These delayed and often lethal adverse events should be studied further to improve clinical understanding, particularly in the front-line maintenance setting. None.