PARP Inhibitor Therapy Research Articles

DNA Repair Enzyme Poly(ADP-Ribose) Polymerase 1/2 (PARP1/2)-Targeted Nuclear Imaging and Radiotherapy.

Simple SummaryIn parallel to the successful clinical implementation of PARP1/2 inhibitors as anti-cancer drugs, which interfere with the DNA repair machinery, these small molecule agents have also gained attention as vehicles for molecular imaging and radiotherapy. In this review article, we summarize the development and preclinical evaluation of radioactively-labelled PARP inhibitors for positron emission tomography (PET) for many applications, such as selecting patients for PARP inhibitor treatment, response prediction or monitoring, and diagnosis of tumors. We report on early clinical studies that show safety and feasibility of PARP-imaging in humans. In addition, we summarize the latest developments in the field of PARP-targeted radiotherapy, where PARP inhibitors are studied as vehicles to deposit highly cytotoxic radioisotopes in close proximity to the DNA of tumor cells. Lastly, we look at synthetic strategies for PARP-targeted imaging and therapy agents that are compatible with large scale production and clinical translation. Since it was discovered that many tumor types are vulnerable to inhibition of the DNA repair machinery, research towards efficient and selective inhibitors has accelerated. Amongst other enzymes, poly(ADP-ribose)-polymerase 1 (PARP1) was identified as a key player in this process, which resulted in the development of selective PARP inhibitors (PARPi) as anti-cancer drugs. Most small molecule PARPi’s exhibit high affinity for both PARP1 and PARP2. PARPi are under clinical investigation for mono- and combination therapy in several cancer types and five PARPi are now clinically approved. In parallel, radiolabeled PARPi have emerged for non-invasive imaging of PARP1 expression. PARP imaging agents have been suggested as companion diagnostics, patient selection, and treatment monitoring tools to improve the outcome of PARPi therapy, but also as stand-alone diagnostics. We give a comprehensive overview over the preclinical development of PARP imaging agents, which are mostly based on the PARPi olaparib, rucaparib, and recently also talazoparib. We also report on the current status of clinical translation, which involves a growing number of early phase trials. Additionally, this work provides an insight into promising approaches of PARP-targeted radiotherapy based on Auger and α-emitting isotopes. Furthermore, the review covers synthetic strategies for PARP-targeted imaging and therapy agents that are compatible with large scale production and clinical translation.

Abstract P5-13-02: Serially biopsied BRCA1/2 mutant breast tumors frequently acquire alterations in BRCA1, BRCA2, and CREBBP

Abstract Introduction Tumors with alterations in BRCA1 or BRCA2 (BRCAm) are sensitive to poly ADP ribose polymerase inhibitors (PARPi), with significant benefit in ovary, breast, prostate, and pancreatic cancers. Despite strong early responses on PARPi, many patients eventually exhibit relapse. Previous literature has identified BRCA1/2 reversion as a common class of acquired alteration in the resistance setting; however, additional resistance pathways have not been well characterized. Here, we examined 100 BRCAm patients who were profiled with serial biopsy during clinical care to identify possible therapy resistance alterations. Methods Comprehensive genomic profiling (CGP) was carried out in a Clinical Laboratory Improvement Amendments (CLIA)-certified, CAP (College of American Pathologists)-accredited laboratory (Foundation Medicine Inc., Cambridge, MA, USA). Tissue biopsy CGP was performed on FFPE blocks examining at least 324 genes for all classes of alterations (FoundationOne® and FoundationOne® CDx). Liquid biopsy CGP was performed examining at least 62 genes (FoundationACT®, FoundationOne®Liquid).One hundred breast cancer patients with baseline BRCAm were serially profiled with CGP testing during routine clinical care (n=50 tissue then liquid; n=50 tissue for both tests). As a comparator, we examined 1,294 patients without a baseline BRCAm (BRCAwt) profiled with serial biopsy (n = 585 tissue then liquid; n=709 tissue for both tests). Co-occurrence analyses (Fisher’s exact) were run on the full research dataset, including 12,198 breast-biopsied (local) and 16,586 metastatic-biopsied samples. All classes of genomic alterations were included in the analysis. Results Of the serially biopsied samples, 7.2% (100/1,394) had baseline BRCAm. In patients with baseline BRCAm, acquired alterations were frequently observed in BRCA1/2 (17%), ESR1 (16%), TP53 (15%), MYC (12%), CREBBP (10%), RB1 (9%), PIK3CA (9%), and NF1 (5%). To understand if any of these are specific to the BRCAm population, we compared the milieu of acquired alterations to a serially biopsied BRCAwt cohort (n=1,294). While many of the alterations were common and shared across both cohorts, likely due to endocrine therapy use, acquired alterations in BRCA1, BRCA2, and CREBBP were specifically enriched in the BRCAm population (all p<0.005). Acquired BRCA1/2 mutations were predicted reversion mutations and spanned a range of mechanisms, including large deletion/rearrangement events that remove the exon of the truncal mutation, point mutations that change a nonsense BRCA1/2 to a missense event, upstream indels that revert the frame of the truncal BRCA1/2 event, and splice site mutations that lead to a skipping of the truncal BRCA1/2. Of note, a majority of cases with a reversion involved a rearrangement event (9/17; 53%). For patients with a baseline BRCA1/2 short variant mutation, there was a trend towards a higher rate of reversion in BRCA2 v BRCA1 (23.1% v 18.5%, p>0.05). Acquired BRCAm were never observed in cases with baseline deletion of BRCA1/2. The high rate of acquired CREBBP alterations was specific to the BRCAm population (10% BRCAm v 1% BRCAwt; p = 0.0013), suggesting a possible role for CREBBP in platinum or PARPi resistance. Consistent with this, BRCAm and CREBBP significantly co-occur in the metastatic setting (Odds ratio, OR = 1.6; p = 0.016) but not in the local setting (OR = 1.1; p = 0.68). Conclusions Analysis of serially biopsied BRCAm breast cases revealed frequent acquisition of BRCA1/2 reversion mutations and CREBBP alterations that are not frequently observed in BRCAwt samples. Additional studies are warranted to investigate the possible role of CREBBP in PARPi therapy resistance. Citation Format: Ethan Sokol, Smruthy Sivakumar, Brennan Decker, Jeffrey Ross, Priti Hegde. Serially biopsied BRCA1/2 mutant breast tumors frequently acquire alterations in BRCA1, BRCA2, and CREBBP [abstract]. In: Proceedings of the 2021 San Antonio Breast Cancer Symposium; 2021 Dec 7-10; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2022;82(4 Suppl):Abstract nr P5-13-02.

Abstract P5-16-17: Targeting homologous recombination-proficient triple negative cancer cells with a novel RAD51 inhibitor

Abstract Out of all breast cancers (BC), ~20% are triple negative breast cancers (TNBC) devoid of the three receptors that define breast cancer treatment strategies such as estrogen receptor (ER), progesterone receptor (PR) and ERBB2 (also known as HER2). Unlike other BC, TNBC disproportionally affects younger women and those of African origins and recurs early within 5 years after diagnosis in ~ 40% of the patients. Standard care for TNBC patients includes surgery, ionizing radiation (IR) treatment and chemotherapy. Successful targeting of the poly (ADP-ribose) polymerase (PARP) has revolutionized therapy for cancer patients carrying gmBRCA1/2. However, in TNBC patients optimal clinical usage of PARP inhibitors (PARPi) is stifled by a) only 15-20% of TNBC patients being positive for gmBRCA1/2 and currently receiving PARPi therapy, b) most PARPi-treated gmBRCA1/2 patients developing resistance due to restoration of HR-mediated DNA DSB repair and, c) PARPi treatment-associated toxicities that require dose adaptations or drug discontinuation. Our novel therapeutic approach addresses this clinical unmet need by further advancing a small molecule inhibitor of HR that includes the 80% TNBC patients wild type for BRCA1/2 genes, re-sensitizes patients resistant to PARPi due to restoration of HR-mediated DNA DSB repair and lowers PARPi doses by conferring greater sensitivity to PARPi actions through synthetic lethality approaches.We first defined OA-NO2 ((E)-9/10-nitro-octadec-9-enoic acid), an endogenous electrophilic fatty acid nitroalkene as an RAD51 inhibitor in TNBC. RAD51 is essential in HR-mediated DNA DSB repair, is a highly coveted drug target in cancer and is a revealing functional biomarker for PARPi sensitivity. OA-NO2 reacts with protein thiols via reverse Michael addition reaction and has broad spectrum anticancer activities. OA-NO2 inhibits RAD51 function by selectively alkylating RAD51 on Cys319, a residue essential in RAD51- guided HR. In combination with the PARPi talazoparib, OA-NO2 synergizes the killing of TNBC cells in vitro and in vivo. Two reasons motivated the further development of OA-NO2 as RAD51 inhibitor: 1) X-ray crystal structure modeling predicted superior fitting with the RAD51 C-terminus if the nitroalkene substituent is closer to the carboxylate terminus of the nitro-fatty acid, and 2) OA-NO2 exhibits off target effects by inhibiting c-GAS-STING signaling and activating Nrf2 activity, thus, possibly offsetting anti-cancer activities. To optimize nitroalkene-mediated RAD51 inhibition, a library of >50 compounds was built that expands upon 5 chemical classes. The library was evaluated for structure activity relationships (SAR) and a new lead nitroalkene emerged, CP-23. This electrophilic small molecule kills as a monotherapy TNBC and not benign breast epithelial cells and unlike OA-NO2, has no impact on STING and Nrf2 signaling, or the cell cycle. CP-23 inhibits RAD51 DNA binding, shows potent inhibition of RAD51 nuclear foci formation after ionizing radiation (IR) treatment and HR in a GFP-reporter cell line, and demonstrated drug synergism with PARP inhibition and IR. At present, in vivo tumor growth inhibition, expansion of PARPi-CP-23 synthetic lethality studies and pilot PK/toxicology evaluation are underway. Citation Format: Carola Anke Neumann, John J Skoko, Bruce A Freeman, Francisco Schopfer, Steven Robert Woodcock, Fei Chang, Lisa Hong, Dennis Carl Braden, Crystal Uvalle. Targeting homologous recombination-proficient triple negative cancer cells with a novel RAD51 inhibitor [abstract]. In: Proceedings of the 2021 San Antonio Breast Cancer Symposium; 2021 Dec 7-10; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2022;82(4 Suppl):Abstract nr P5-16-17.

Re-treatment with PARPi in patients with recurrent epithelial ovarian cancer: A single institutional experience

IntroductionWe aimed to evaluate real-life experiences with the re-challenge of poly(ADP-Ribose)Polymerase (PARP) inhibitors (PARPi) after a prior PARPi therapy in patients with recurrent EOC. MethodsA retrospective descriptive study was conducted at a tertiary care center of excellence for ovarian cancer. Demographic, pathological, and therapeutic data were collected for patients with recurrent epithelial ovarian cancer who were re-treated with PARPi in their therapy course. ResultsTwenty-nine patients were included in the study. Twenty-six patients received the second PARPi as maintenance therapy after two different lines of therapy and three patients received the second PARPi as upfront therapy after progression. Most of the patients (57.7%) were exposed to first PARPi after a second-line therapy. The median progression-free survival under the first and second PARPi therapy was estimated at 15 and 7 months respectively. PFS under the second PARPi after platinum-based chemotherapy was better after a complete remission with a median PFS of 8.5 months, compared to patients with partial remission (5.5 months). A better PFS was noted in case of negative BRCA status under the second PARPi therapy (median PFS of 7.4 vs. 4.5 months, p = 0.11). The second PARPi therapy was mainly discontinued due to disease progression (84.6% of the cases). Discontinuation of treatment with the second PARP due to toxicity was needed in one case who developed a myelodysplastic syndrome. ConclusionReal-life data support prospective evidence that patients with recurrent EOC may derive benefit of the re-treatment with PARPi in case of clear response to the last platinum-based therapy.

PARP Inhibitor Applicability: Detailed Assays for Homologous Recombination Repair Pathway Components.

Poly(ADP-ribose) polymerase inhibitors (PARPi) have been in clinical use since 2014 for certain patients with germline BRCA1/2 mutations, but as evidence and approvals for their use in a wider range of patients grow, the question of how best to identify patients who would benefit from PARPi becomes ever more complex. Here, we discuss the development and current state of approved selection testing for PARPi therapy and the ongoing efforts to define a broader range of homologous recombination repair deficiencies that are susceptible to PARP inhibition.

Phenethyl Isothiocyanate Enhances the Cytotoxic Effects of PARP Inhibitors in High-Grade Serous Ovarian Cancer Cells.

While PARP inhibitor (PARPi) therapies have shown promising results in the treatment of high-grade serous ovarian cancer (HGSOC) harboring homologous recombination deficiencies, primary resistance to PARPi frequently occurs and even initial responders may eventually become resistant. Therefore, the development of novel effective combinatorial strategies to treat HGSOC is urgently needed. Here, we report that H2O2-induced oxidative stress sensitized HGSOC cells to PARPi BMN 673. Furthermore, Phenethyl isothiocyanate (PEITC) as a ROS-inducing agent significantly enhanced the cytotoxic effects of BMN 673. Mechanistically, combined use of PEITC and BMN 673 resulted in ROS overproduction and accumulation, enhanced DNA damage, G2/M arrest and apoptosis, all of which were significantly reversed by the ROS scavenger N-Acetyl-L-cysteine. We also showed that while PEITC did not further enhance the ability of BMN 673 on PARP1 trapping in HGSOC cells, the therapeutic effects of the PEITC/BMN 673 combination were at least in part dependent on the presence of PARP1. Importantly, the PEITC/BMN 673 combination potently abrogated the growth of HGSOC tumor spheroids and patient-derived organoid models of HGSOC and cervical cancer. Our findings provide a basis for further investigation of the utility of PARPi combination regimen in HGSOC and cervical cancer through ROS-mediated mechanisms.

Investigation of PALB2 Mutation and Correlation With Immunotherapy Biomarker in Chinese Non-Small Cell Lung Cancer Patients.

BackgroundPALB2, a gene in the homologous recombination repair (HRR) pathway of the DNA damage response (DDR), is associated with the efficacy of platinum-based chemotherapy, immunotherapy, and PARP inhibitor therapy in several tumors. However, the PALB2 characteristics, its correlation with immunotherapy biomarker, and the prognostic effect of immunotherapy in non-small cell lung cancer (NSCLC) were unknown.MethodsTumor tissue samples from advanced Chinese NSCLC patients were analyzed by next-generation sequencing (NGS) (panel on 381/733-gene). Tumor mutation burden (TMB) is defined as the total number of somatic non-synonymous mutations in the coding region. Microsatellite instability (MSI) was evaluated by NGS of 500 known MSI loci. Programmed Cell Death-Ligand 1 (PD-L1) expression was evaluated using immunohistochemistry (Dako 22C3 or SP263). One independent cohort (Rizvi2018.NSCLC.240.NGS cohort) containing genomic and clinical data from 240 patients with advanced NSCLC and two cohorts (the OAK and POPLAR study cohort) containing genomic and clinical data from 429 patients with advanced NSCLC were used to analyze the prognostic effect of PALB2 on immunotherapy.ResultsGenetic mutation of 5,227 NSCLC patients were analyzed using NGS, of which 162 (3.1%) harbored germline PALB2 mutation (PALB2gmut) and 87 (1.66%) harbored somatic PALB2 mutation (PALB2smut). In NSCLC patients with PALB2gmut and PALB2smut, the most frequently mutated gene was TP53 (65%, 64%). PALB2smut (14.52 Muts/Mb) was associated with higher TMB (p < 0.001) than PALB wild-type (PALB2wt) (6.15 Muts/Mb). However, there was no significant difference in TMB between PALB2gmut (6.45 Muts/Mb) and PALB2wt (6.15 Muts/Mb) (p = 0.64). There was no difference in PD-L1 expression among PALB2gmut, PALB2smut, and PALB2wt. In the Rizvi2018.NSCLC.240.NGS cohort, there was no difference in progression-free survival (PFS) (HR =1.06, p = 0.93) between PALB2 mutation (3.15 months) and PALB2wt (3.17 months). The OAK and POPLAR study cohort of NSCLC patients showed that there was no difference in overall survival (OS) (HR =1.1, p = 0.75) between PALB2 mutation (10.38 months) and PALB2wt (11.07 months).ConclusionsThese findings suggest that PALB2 may not be used as a biomarker for determining prognosis on immunotherapy in NSCLC.

AKT Isoforms Interplay in High-Grade Serous Ovarian Cancer Prognosis and Characterization.

Simple SummaryNew therapeutical strategies are needed to improve survival in high-grade serous ovarian cancer (HGSOC) patients. AKT inhibitors are promising agents able to act in synergy with PARP inhibitors and platinum-based therapies, but the subset of patients who could benefit from this approach is still unclear. We analyzed AKT isoforms expression in a retrospective cohort and we identified four AKT expression groups related to patients’ survival, tumor morphology and the BRCA status that could help in stratifying patients for future clinical trials.High-grade serous ovarian cancer (HGSOC) is among the deadliest gynecological malignancies. The acquired resistance to platinum-based therapies and the intrinsic heterogeneity of the disease contribute to the low survival rate. To improve patients’ outcomes, new combinatorial approaches able to target different tumor vulnerabilities and enhance the efficacy of the current therapies are required. AKT inhibitors are promising antineoplastic agents able to act in synergy with PARP inhibitors, but the spectrum of patients who can benefit from this combination is unclear, since the role of the three different isoforms of AKT is still unknown. Here, we study the expression of AKT isoforms on a retrospective cohort of archive tissue by RT-droplet digital PCR (ddPCR) analyzing their association with the clinicopathological features of patients. Based on AKT1/AKT2 and AKT1/AKT3 ratios, we define four AKT classes which were related to patients’ survival, tumor morphology and BRCA1 expression. Moreover, our results show that high AKT3 expression levels were frequently associated with tumors having classic features, a low number of mitoses and the presence of psammoma bodies. Overall, our study obtains new insights on AKT isoforms and their associations with the clinicopathological features of HGSOC patients. These evidences could help to better define the subsets of patients who can benefit from AKT and PARP inhibitors therapy in future clinical trials.

Abstract IA15: Targeting tumor associated macrophages for anti-cancer therapy

Abstract Despite objective responses to poly(ADP-ribose) polymerase (PARP) inhibition and improvements in progression-free survival (PFS) compared to standard chemotherapy in patients with BRCA-associated triple-negative breast cancer (TNBC), benefits are transitory. Using high-dimensional single-cell profiling of human TNBC, here we demonstrate that macrophages are the predominant infiltrating immune cell type in breast cancer susceptibility (BRCA)-associated TNBC. Through multi-omics profiling, we show that PARP inhibitors enhance both anti- and pro-tumor features of macrophages through glucose and lipid metabolic reprogramming, driven by the sterol regulatory element-binding protein 1 (SREBF1, SREBP1) pathway. Combining PARP inhibitor therapy with colony-stimulating factor 1 receptor (CSF1R)-blocking antibodies significantly enhanced innate and adaptive antitumor immunity and extended survival in mice with BRCA-deficient tumors in vivo, and this was mediated by CD8+ T cells. Collectively, our results uncover macrophage-mediated immune suppression as a liability of PARP inhibitor treatment and demonstrate that combined PARP inhibition and macrophage-targeting therapy induces a durable reprogramming of the tumor microenvironment (TME), thus constituting a promising therapeutic strategy for TNBC. This work highlights the importance of a deep understanding the tumor microenvironment (TME) before and after therapy. Citation Format: Jennifer L. Guerriero. Targeting tumor associated macrophages for anti-cancer therapy [abstract]. In: Abstracts: AACR Virtual Special Conference: Tumor Immunology and Immunotherapy; 2021 Oct 5-6. Philadelphia (PA): AACR; Cancer Immunol Res 2022;10(1 Suppl):Abstract nr IA15.

Germline predisposition to soft tissue sarcoma

Soft tissue sarcoma (STS) most often occurs sporadically, but can also arise in the setting of a germline cancer predisposition syndrome (CPS). There is significant diversity amongst STS diagnoses as these tumors exhibit a variety of histologies, occur in all age groups, and can occur in any location in the body. This diversity is also reflected in the many known associated germline cancer predisposition associations. Some STS diagnoses, such as anaplastic rhabdomyosarcoma, are associated with high heritability and other STS, such as Ewing sarcoma, are notably absent from known CPS. Recognizing when a STS is more likely to be hereditary can influence clinical management. Individuals diagnosed with STS due to CPS may be at risk for other malignancies and should undergo additional surveillance for early detection. Additionally, family members should undergo genetic testing as they also may be at risk to develop STS and other CPS-associated malignancies. Some underlying cancer predisposition diagnoses may have implications for the treatment of a concurrent malignancy as in the case of PARP inhibitor therapy in the setting of homologous recombination deficiency. This review summarizes current knowledge of selected STS and their associations with CPS.

Olaparib Use in Patients With Metastatic Breast Cancer Harboring Somatic BRCA1/2 Mutations or Mutations in Non-BRCA1/2, DNA Damage Repair Genes

BackgroundPoly-ADP ribose polymerase (PARP) inhibitors (PARPi) are active in patients with germline BRCA1/2 (gBRCA1/2)-mutated breast cancer, accounting for 5% to 10% of all breast cancers. Another 5% to 10% harbor somatic BRCA1/2 (sBRCA1/2) mutations or mutations in non-BRCA1/2, homologous recombination repair (HRR) genes but until recently, there were no data for the use of PARPi in these patients. This study examines the use of olaparib in patients with metastatic breast cancer harboring sBRCA1/2 or germline or somatic non-BRCA1/2, HRR mutations and demonstrates potential activity of PARPi in this setting. MethodsIn this retrospective, single institution study, patients who were treated with off-label, off-protocol olaparib for metastatic breast cancer harboring sBRCA1/2 or germline or somatic non-BRCA1/2, HRR mutations were identified. The primary aim was to describe these patients’ demographics, tumor characteristics, mutations, safety and tolerability, response rates, progression free survival, PARPi-associated survival and subsequent treatment. ResultsSeven patients were treated off-label, off-trial with olaparib for sBRCA1/2-mutated cancers (n = 4) or non-BRCA1/2, HRR-mutated cancers (n = 3). All patients with sBRCA1/2-mutated cancers responded to PARP inhibition; patients with non-BRCA1/2, HRR-mutated cancers did not respond. The median progression free survival in patients with a sBRCA1/2 mutation was 6.5 months (range 5-9 months) vs. 3 months (range 2-4 months) in patients with non-BRCA1/2, HRR mutations. ConclusionThis single institution experience adds to recent larger reports confirming evidence for PARPi therapy in patients with metastatic breast cancer harboring sBRCA1/2 mutations. No activity was observed in patients with either germline or somatic non-BRCA1/2, HRR-mutated cancers.

Patients' and oncologists' preferences for second-line maintenance PARP inhibitor therapy in epithelial ovarian cancer.

Aim: To understand the preferences of US patients and oncologists for PARP inhibitors as second-line maintenance (2LM) for epithelial ovarian cancer. Methods: A discrete choice experiment was conducted to assess thepreferences of treatment attributes. Results: The most valued attributes were risk of grade 3/4 adverse events (AEs; patients, n=204) and progression-free survival (PFS; oncologists, n=151). To accept a 37% increased risk of grade 3/4 AEs, PFS would need to increase by 27.9months (patients) and 6.3months (oncologists). The least valued attributes were dosing form/frequency (patients) and grade 3/4 anemia risk (oncologists). Conclusion: Patients' and oncologists' willingness to make benefit-risk trade-offs in the 2LM setting suggests that the PFS gains observed in selected studies of poly (ADP-ribose) polymerase inhibitors in BRCA-mutated disease are worth the toxicity risk.

PARP Inhibition Activates STAT3 in Both Tumor and Immune Cells Underlying Therapy Resistance and Immunosuppression In Ovarian Cancer.

Despite the promising activity of poly(ADP-ribose) polymerase (PARP) inhibitors (PARPi) in many cancer types with defects in the DNA damage response the majority of the treated patients acquire PARPi resistance and succumb to their diseases. Consequently, there is an urgent need to identify the mechanisms of PARPi resistance. Here, we show that PARPi treatment promotes STAT3 activation in ovarian cancer cells, tumor-associated immune cells and fibroblasts, resulting in PARPi resistance and immunosuppression. Comparison of ovarian cancer patient-matched tumor biopsies before and after PARPi therapy revealed that STAT3 activity was significantly higher in tumor cells and tumor-associated immune cells and fibroblasts post PARPi treatment. Moreover, one-time PARPi treatment activated STAT3 both in tumor cells as well as diverse immune subsets and fibroblasts. PARPi-treated immune cells exhibited decreased expression of immunostimulatory interferon (IFN)-γ and Granzyme B while increasing immunosuppressive cytokine IL-10. Finally, we demonstrate that the acquisition of PARPi resistance in ovarian cancer cells was accompanied by increased STAT3 activity. Ablating STAT3 inhibited PARPi-resistant ovarian tumor cell growth and/or restored PARPi sensitivity. Therefore, our study has identified a critical mechanism intrinsic to PARPi that promotes resistance to PARPi and induces immunosuppression during PARPi treatment by activating STAT3 in tumor cells and tumor-associated immune cells/fibroblasts.

Efficacy and safety of poly (ADP-ribose) polymerase inhibitors therapy for BRCA-mutated breast cancer: A systematic review and meta-analysis.

To evaluate the efficacy, safety, and potential advantages of Poly (ADP-ribose) polymerase inhibitors (PARPi) in treating BRCA-mutated breast cancer, we performed a meta-analysis of published studies. Four randomized controlled trials (RCTs) were included in the meta-analysis. Data analysis was conducted in Review Manager 5.4. The progression-free survival (PFS) of the patients with triple-negative (hazard ratio [HR] 0.81; 95% confidence interval [CI] 0.74-0.88; P < 0.00001) or hormone receptor-positive (HR 0.83; 95% CI 0.77-0.91; P < 0.0001) BRCA-mutated breast cancer was significantly extended in the containing PARPi therapy arm versus the chemotherapy arm. PFS of the patients who did not receive platinum-based therapy (HR 0.78; 95% CI 0.70-0.86; P < 0.0001) was significantly extended in the PARPi monotherapy arm versus the chemotherapy arm. The objective response rate of patients treated by PARPi monotherapy (risk ratio [RR] 2.51; 95% CI 1.81-3.47; P < 0.00001) was significantly higher than that of patients treated by chemotherapy. The incidence of thrombocytopenia in patients received PARPi combined therapy was obviously increased compared with chemotherapy group (RR 1.36; 95% CI 1.07-1.72; P = 0.01). PARPi monotherapy markedly increased the incidence of anemia (RR 5.83; 95% CI 2.64-12.88; P < 0.0001) versus chemotherapy. However, the risk of neutropenia (RR 0.48; 95% CI 0.29-0.81; P = 0.006) was reduced in the PARPi monotherapy arm. There were no statistical differences in other adverse events among these three groups. PARPi combined therapy and monotherapy improved PFS of patients with BRCA-mutated breast cancer compared with standard chemotherapy, which was unrelated to type of BRCA mutation and status of hormone receptor. PARPi therapy has slightly higher hematological toxicity and better overall safety and tolerance. CRD42020204385.

Abstract P018: Integrative proteomics of PARP1 protein complexes and post-translational modifications implicates DDR and AKT-mTOR signaling in mediating response or primary resistance of ovarian carcinoma cells to PARP1 inhibitors

Abstract Background: About 40-50% of epithelial ovarian cancers (EOC) show defects in DNA repair by homologous recombination (HR), which are mostly associated with BRCA1/2 loss-of-function mutations. The PARP inhibitors (PARPis) olaparib, niraparib and rucaparib were recently approved for treatment of ovarian cancer patients with platinum sensitivity and recurrent ovarian cancer who carry inactivating BRCA1/2 mutations. These targeted drugs produce significant response rates ranging from 40-60% in patients with BRCA-linked advanced EOCs, but resistance is a continuing challenge. Whereas several studies have reported various mechanisms of acquired resistance to PARPis, the mechanisms of primary resistance are still poorly understood. Our goal is to develop predictors of PARPi response and to identify new targets for combination therapy to overcome primary resistance. We apply a novel integrated proteomics approach to develop mechanism-based biomarkers of response or primary resistance and to identify new therapeutic targets for rational combination approaches that can overcome resistance to single agent PARPi therapy. METHODS: The isogenic EOC cell line pair UWB1.289 with BRCA1 deletion (parental; UWB) and reconstituted with ectopic BRCA1 (UWB+B) was used. The effects of FDA approved PARPis on BRCA1-null and BRCA1-reconstituted UWB1.289 cells regarding short- and long-term cell viability were determined by CellTiterGlo and crystal violet assays. Chemical proteomics, global phosphoproteomics and ADP-ribosylation proteomics were used to identify the components of PARP1-based multiprotein complexes as well as protein post-translational modifications in the DNA damage signaling network in BRCA1/2-linked EOC cells. Specific PARP1-engaged protein complexes were further determined by immunoblotting. Frozen BRCA1-proficient and deficient ovarian cancer patient tumor samples collected at the time of debulking were also characterized by chemical proteomics. RESULTS: Cell viability assays confirmed the expected correlation between PARPi response and BRCA1/2 status. Chemical proteomics followed by validation with co-immunoprecipitation revealed differential composition of the PARP1/2-Ku70/Ku80 protein complexes in PARPi-sensitive UWB compared to UWB+B cells. Global phosphoproteomics and ADP-ribosylation proteomics further indicated that rucaparib induced the cell cycle and c-NHEJ pathways in UWB cells, but down-regulated the MAPK pathway in UWB+B cells. In addition, our results showed that inhibition of AKT PARylation and AKT-mTOR signaling may help to preserve cell viability in UWB+B cells after rucaparib treatment. Consistently, synergy with DNAPKi and AKTi was more pronounced in UWB+B cells. CONCLUSION: Ovarian cancers that do not respond to PARPi displayed significant changes in PARPi-engaged protein complexes as well as post-translational protein modifications. The combination of chemical, phospho- and ADP-ribosylation proteomics can generate a systems view of PARP1 complexes and diverse drug compensatory signaling in EOC. Citation Format: Ou Deng, Sweta Dash, Thales Nepomuceno, Bin Fang, Douglas Marchion, John Koomen, Alvaro N. Monteiro, Uwe Rix. Integrative proteomics of PARP1 protein complexes and post-translational modifications implicates DDR and AKT-mTOR signaling in mediating response or primary resistance of ovarian carcinoma cells to PARP1 inhibitors [abstract]. In: Proceedings of the AACR-NCI-EORTC Virtual International Conference on Molecular Targets and Cancer Therapeutics; 2021 Oct 7-10. Philadelphia (PA): AACR; Mol Cancer Ther 2021;20(12 Suppl):Abstract nr P018.

Vitamin C Enhances PARPi Efficacy for the Treatment of AML

Poly-ADP-ribose polymerase inhibitors (PARPi) are currently in clinical trial to determine their therapeutic efficacy for the treatment of acute myeloid leukemia (AML). We have shown that vitamin C (VitC), an essential micronutrient and co-factor of Ten-Eleven translocation (TET) proteins, enhances AML sensitivity to PARPi, potentially due to an increased dependency on base-excision repair (BER) enzymes needed to remove TET-catalyzed oxidized methylcytosine bases via active DNA demethylation. TET2 is the most frequently mutated TET gene in patients with AML, and vitamin C treatment can mimic genetic restoration of TET2 function, leading to DNA demethylation, differentiation, and leukemia cell death. Whether vitamin C efficacy in combination with PARPi depends on the level of TET2 functional alleles is not yet known and may stratify whether TET2 wild-type or mutant patients should be targeted by vitamin C adjuvant therapy.We have generated primary murine AML-ETO9a+ and MLL-AF9+ leukemia models with Tet2 +/+, Tet2 +/- and Tet2 -/- alleles to determine the Tet2-dependent efficacy of PARPi treatment when combined with vitamin C. Furthermore, we have performed CRISPR gene knockout and drug library screening in human AML cell lines in combination with vitamin C treatment, and tested a panel of 10 AML cell lines with titrating concentrations of PARPi (Olaparib, Talazoparib, Veliparib and Rucaparib) alone or in combination with vitamin C (L-ascorbic acid) mimicking physiological to pharmacological in vivo doses. Primary murine AML cells and human cell lines were assayed for colony-forming capacity, differentiation, cell cycling, viability and effects on DNA methylation, levels of oxidized 5-mC and gene expression upon combination treatment in vitro and in vivo. TET2 mutant PDX and primary murine AMLs treated in vivo with L-ascorbate (4g/kg) and Olaparib (50mg/kg) by daily IP injection were also monitored for disease burden, cellular differentiation and survival.Vitamin C is known to drive the TET-catalyzed iterative oxidation of 5-methylcytosine (5-mC) leading to the formation of 5-hydroxymethylcytosine (5-hmC), 5-formylcytosine (5-fC) and 5-carboxylcytosine (5-caC). We show that VitC-PARPi combination treatment causes an accumulation of oxidized 5-mC intermediates in the AML genome that correlates with increased yH2AX formation in mid-S phase and cell cycle stalling. Vitamin C reduces the IC 50 of Olaparib and Talazoparib by greater than 10-fold in human AML cells lines and primary murine leukemia cells, and treatment in combination promotes myeloid differentiation and blocks colony-forming capacity greater than either alone. In both our in vitro and in vivo studies, Tet2 +/- AML cells exhibit increased sensitivity to vitamin C treatment alone or in combination with PARPi compared to either Tet2 +/+ or Tet2 -/- cells, suggesting that patients with TET2 haploinsufficiency, which represents the majority of TET2 mutant cases, could benefit the most from combined treatment.Our findings confirm that vitamin C can act synergistically with PARPi to block AML cell viability, reduce colony-forming capacity, and decrease leukemia burden in PDX and primary murine leukemia models in a TET2 allelic dose-dependent manner. The combinatorial effect works at clinically relevant concentrations of PARPi, and low-pharmacological doses of vitamin C. These studies suggest that vitamin C can be used as a non-toxic therapeutic adjuvant to PARPi therapy for the treatment of AML. DisclosuresNeel: Northern Biologics, LTD: Current equity holder in publicly-traded company, Other: Co- Founder; SAB: Other: Co-Founder; Navire Pharma: Consultancy, Current equity holder in publicly-traded company; Jengu Therapeutics: Consultancy, Current equity holder in publicly-traded company, Other: Co-Founder; Arvinas, Inc: Consultancy, Current equity holder in publicly-traded company; Recursion Pharma: Current equity holder in publicly-traded company.

Utilization of Poly(ADP-Ribose) Polymerase Inhibitors in Ovarian Cancer: A Retrospective Cohort Study of US Healthcare Claims Data.

IntroductionWe aimed to characterize real-world utilization of poly(ADP-ribose) polymerase (PARP) inhibitors (PARPi) in women with ovarian cancer (OC).MethodsThis retrospective observational study of claims data from US MarketScan® Commercial/Medicare Supplemental databases included women with OC initiating olaparib, niraparib, or rucaparib from January 1, 2017, to May 31, 2019. Patients were observed from first outpatient prescription until at least 30 days’ follow-up. Clinical events of interest (CEIs), based on adverse reactions in PARPi prescribing information, were identified from claims using ICD-9/10 codes. Other outcomes included dose modification, persistence, adherence, healthcare resource utilization (HCRU), and cost.ResultsOverall, 303, 348, and 162 women with OC received olaparib, niraparib, and rucaparib, respectively. During follow-up, risk of any CEI was higher with niraparib versus olaparib (odds ratio 3.36 [95% confidence interval 2.00–5.65]) and niraparib versus rucaparib (2.09 [1.10–3.95]), with no significant difference between rucaparib and olaparib (1.61 [0.93–2.79]). PARPi dose decreases were observed in 21.1%, 35.1%, and 30.2% of olaparib-, niraparib-, and rucaparib-treated patients, respectively. Persistence (no treatment gaps of more than 90 days) was significantly higher (P < 0.05) with olaparib (62.2%) versus niraparib (35.9%) and rucaparib (48.7%); adherence (medication possession ratio, MPR ≥ 80%) was 80.2% versus 38.6% and 63.2%, respectively (P < 0.001). Inpatient admissions and outpatient service use were higher with niraparib and rucaparib versus olaparib, reflected in mean (± standard deviation) total medical costs (excluding pharmacy) of $5393 ± 8828 for olaparib, $7732 ± 14,054 for niraparib, and $6868 ± 7929 for rucaparib.ConclusionDifferences between the licensed PARPi were observed in the risk of experiencing a CEI, likelihood of dose modifications, ability to receive continuous PARPi therapy, HCRU, and costs.Supplementary InformationThe online version contains supplementary material available at 10.1007/s12325-021-01959-5.

Integrated, Integral, and Exploratory Biomarkers in the Development of Poly(ADP-Ribose) Polymerase Inhibitors.

In this article, we highlight biomarkers for poly(ADP-ribose) polymerase inhibitor (PARPi) sensitivity and resistance and discuss their implications for the clinic. We review the predictive role of a range of DNA repair genes, genomic scars, mutational signatures, and functional assays available or in development. The biomarkers used for patient selection in the specific Food and Drug Administration-approved indications for breast, ovarian, prostate, and pancreatic cancer vary across tumor type and likely depend on disease-specific DNA repair deficiencies but also the specifics of the individual clinical trials that were conducted. Mutations in genes involved in homologous recombination and/or replication fork protection are synthetic lethal with PARPi. Cancers with homologous recombination deficiency exhibit high genomic instability, characterized by genome-wide loss of heterozygosity, among other genomic aberrations. Next-generation sequencing can identify multiple patterns of genomic changes including copy number variations, single-nucleotide variations, insertions/deletions, and structural variations rearrangements characteristic of homologous recombination deficiency. Clinical trial evidence supports the use of BRCA mutation testing for patient selection, and for ovarian cancer, there are 3 commercial assays available that additionally incorporate genomic instability for identifying subgroups of patients that derive different magnitudes of benefit from PARPi therapy. Finally, we summarize new strategies for extending the benefit of PARPi therapy toward broader populations of patients through the use of novel biomarkers. Ultimately, design of a composite biomarker test combining multiple mutational signatures or development of a dynamic assay for functional assessments of homologous recombination may help improve the test accuracy for future patient stratification.

The Principles and Practice of PARP Inhibitor Therapy.

Yap, Timothy A. MD, PhD, FRCP∗,†,‡,§; Coleman, Robert L. MD, FACOG, FACS∥,¶ Author Information

Next generation sequencing identifies potential PARP inhibitor sensitive mutations

Abstract Introduction/Objective Poly ADP-ribose polymerase (PARP) inhibitors are a novel and important drug class targeting homologous recombination DNA repair defects (HRD) and have been approved for use in breast, pancreatic and ovarian cancers. Originally targeted for loss of function mutations in BRCA1 and BRCA2, many other genes are involved in the HRD pathway; Rimar et al detailed 19 DNA repair genes associated with homologous recombination and PARP inhibitor sensitivity. Our 214 gene NGS panel, Iowa Cancer Mutation Profile, includes BRCA1, BRCA2 and 15 other HRD pathway genes. We reviewed cases from the prior 12 months to determine the frequency of HRD7 pathway gene variants in various tumor types with potential PARP inhibitor sensitivity. Methods/Case Report Iowa Cancer Mutation Profile NGS test results from June 4, 2020 through May 7, 2021 were reviewed for variants involving ATM, ATR, BAP1, BLM, BRCA1, BRCA2, CDK12, CHEK1, CHEK2, FANCA, FANCC, FANCD2, MRE11A, NBN, PALB2, RAD51c and RAD51d, categorized as pathogenic, likely pathogenic or of unknown significance and had the tumor type identified. Additional chart review for PARP inhibitor therapy was performed in cases of breast, pancreatic, and ovarian cancer. Results (if a Case Study enter NA) A total of 599 cases were reviewed with 234 found to have variants in genes with possible PARP inhibitor sensitivity. Of these 2% (n=8) and 11% (n=43) of variants were categorized as pathogenic or likely pathogenic while most (n=334) were categorized as variants of unknown significance. The pathogenic and likely pathogenic variants included mutations in ATM (n=13), BRCA2 (n=12), BAP1 (n=8), FANCA (n=5), BRCA1 (n=4), NBM (n=3), FANCD2 (n=2), ATR (n=1), CDK12 (n=1), FANCC (n=1), and RAD51d (n=1), and frameshift (n=19) and nonsense (n=19) alterations were most common. Non-small cell lung cancer was the most frequent tumor type identified (n=78). At this time no PARP inhibitors were identified for use in cases of breast (n=9), pancreatic (n=3) and ovarian cancer (n=33). Conclusion Review of our institutional results for mutations in HRD pathway genes identified possible PARP inhibitor sensitivity in 8% (46 of 599) of cases during the period of review in a wide variety of tumor types. Our results suggest that variants with possible sensitivity to PARP inhibitor therapy are frequently identified from many tumor types and should be a component of solid tumor mutation profiling.