ADP-ribose Polymerase Inhibitors Research Articles

Research Progress of PARP-1 Related Dual Target Inhibitors

The treatment of cancer has always been based on surgery, radiotherapy and chemotherapy, but the cure rate of these methods is often very low and the side effects on patients are very serious. With the gradual understanding of cancer, targeted drug therapy has gradually attracted the attention of the scientific community. Initially, doctors used some single target inhibitors as targeted drugs for tumor treatment. However, with the increasing of single drug resistance and side effects, the problems of single drug resistance and side effects gradually emerge in clinical practice. Poly ADP-ribose polymerase-1 inhibitor (parp-1i) can inhibit DNA damage and repair in cells, so it is used as a kind of targeted drugs for tumor therapy. At a time when single target drugs are facing challenges, scientists have turned their attention to dual target inhibitors related to parp-1i with stronger effects. In this paper, we focus on the challenges faced by PARP-1 related single target inhibitors and the research progress of HDAC inhibitors or BRD4 inhibitors combined with PARP-1 inhibitors as double target inhibitors. It was found out that some new synthesized dual PARP/HDAC inhibitors and PARP/BRD4 inhibitors have shown great anticancer activities in vitro experiments, including compound I-8 and II-16 Therefore, this review confirmsthat PARP-related dual target inhibitors can be a promising approach to treat cancer cell.

Poly (ADP-ribose) polymerase inhibitors (PARPi) for advanced malignancies with multiple DNA-repair genetic aberrations

ABSTRACT Introduction Poly (ADP-ribose) polymerase inhibitors (PARPi) have been approved for the treatment of advanced tumors with defects in genes involved in homologous recombination repair (HRR), including cancers of the prostate, pancreas, breast, and ovary. In these advanced tumors, PARPi afford ‘synthetic lethality’ by blocking the PARP-associated repair pathway in cancer cells with HRR genetic mutations, resulting in chromosome instability and cellular apoptosis. According to the synthetic lethality theory, patients with a greater burden of genetic alterations, in proportion (relative quantity) or category, would have more satisfactory outcomes after PARPi administration. However, this issue remains obscure based on the existing sporadic evidence. Areas covered We summarize the therapeutic effects of PARPi in advanced tumors with multiple HRR genetic mutations, and attempted to compare these results with those obtained for cancers with a single mutation. Expert opinion Limited evidence has provided a possibly encouraging response to PARPi among patients carrying multiple HRR genetic mutations compared with those with a single mutation (although the treatment effect was negative in some patients). Further research is needed to understand the role of PARPi in tumor cells with multiple HRR genetic mutations.

Combined inhibition of BADSer99 phosphorylation and PARP ablates models of recurrent ovarian carcinoma

BackgroundPoly (ADP-ribose) polymerase inhibitors (PARPis) have been approved for the treatment of recurrent epithelial ovarian cancer (EOC), regardless of BRCA status or homologous recombination repair deficiency. However, the low response of platinum-resistant EOC, the emergence of resistance in BRCA-deficient cancer, and therapy-associated toxicities in patients limit the clinical utility of PARPis in recurrent EOC.MethodsThe association of phosphorylated (p) BADS99 with clinicopathological parameters and survival outcomes in an EOC cohort was assessed by immunohistochemistry. The therapeutic synergy, and mechanisms thereof, between a pBADS99 inhibitor and PARPis in EOC was determined in vitro and in vivo using cell line and patient-derived models.ResultsA positive correlation between pBADS99 in EOC with higher disease stage and poorer survival is observed. Increased pBADS99 in EOC cells is significantly associated with BRCA-deficiency and decreased Cisplatin or Olaparib sensitivity. Pharmacological inhibition of pBADS99 synergizes with PARPis to enhance PARPi IC50 and decreases survival, foci formation, and growth in ex vivo culture of EOC cells and patient-derived organoids (PDOs). Combined inhibition of pBADS99 and PARP in EOC cells or PDOs enhances DNA damage but impairs PARPi stimulated DNA repair with a consequent increase in apoptosis. Inhibition of BADS99 phosphorylation synergizes with Olaparib to suppress the xenograft growth of platinum-sensitive and resistant EOC. Combined pBADS99-PARP inhibition produces a complete response in a PDX derived from a patient with metastatic and chemoresistant EOC.ConclusionsA rational and efficacious combination strategy involving combined inhibition of pBADS99 and PARP for the treatment of recurrent EOC is presented.

DNA Repair Enzymes Promising in Cancer Therapy; Poly (ADP-Ribose) Polymerase Inhibitors

DNA Repair Enzymes Promising in Cancer Therapy; Poly (ADP-Ribose) Polymerase Inhibitors

Abstract 1288: STING agonism enhances anti-tumor immune responses and therapeutic efficacy of PARP inhibition in BRCA-associated breast cancer

Abstract Poly (ADP-ribose) polymerase (PARP) inhibitors exert their efficacy by inducing synthetic lethal effects, as well as cGAS/STING-mediated immune responses in BRCA- and other homologous recombination repair-deficient cancer cells. Here, we investigated whether the immunologic and therapeutic effects of PARP inhibition in BRCA-deficient breast cancer models could be augmented by synthetic cyclic dinucleotide agonists of STING. In in vitro experiments, combined olaparib-mediated PARP inhibition and ADU-S100-mediated STING agonism induced a greater degree of STING pathway activation and proinflammatory cytokine production compared to monotherapies in BRCA1-deficient human MDA-MB-436 cells and mouse triple-negative breast cancer cell lines derived from a genetically engineered model of BRCA-deficient breast cancer. In vivo experiments were conducted in mice bearing completely established tumors derived from the genetically engineered mouse model expanded syngeneically. In this model, the combination also induced an improved immune response compared to either monotherapy alone, evidenced by a greater degree of cytotoxic T cell recruitment and activation, and enhanced dendritic cell activation and antigen presentation. Nanostring mRNA analysis indicated that combinatorial effects were the result of augmented interferon signaling and antigen processing, as well as heightened leukocyte and dendritic cell functions. The combination markedly improved anti-tumor efficacy in vivo compared to monotherapy treatment, with evidence of complete tumor clearance and prolongation of survival. Finally, in mice treated with the combination, tumors could not be re-established upon rechallenge, indicating the induction of immunologic memory. These results support the development of combined PARP inhibition and STING agonism in BRCA-associated breast cancer. Citation Format: Heta Jadhav, Constantia Pantelidou, Aditi Kothari, Renyan Liu, Gerburg Wulf, Jennifer L. Guerriero, Geoffrey I. Shapiro. STING agonism enhances anti-tumor immune responses and therapeutic efficacy of PARP inhibition in BRCA-associated breast cancer [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2022; 2022 Apr 8-13. Philadelphia (PA): AACR; Cancer Res 2022;82(12_Suppl):Abstract nr 1288.

Abstract 5408: Targeting ATR and AKT pathways promotes cell death in PARP inhibitor-resistant ovarian cancer cells by increasing DNA damage and lethal replication stress

Abstract Poly (ADP-ribose) polymerase inhibitors (PARPis) have changed the treatment paradigm in the management of high-grade serous ovarian cancer (HGSOC). However, most HGSOC ultimately develops resistance to PARPi, leading to unmet medical needs for better therapeutic strategies. ATR-mediated G2/M cell cycle checkpoints are important for cell survival and DNA repair, especially in HGSOC due to its dysfunctional p53-mediated G1/S checkpoint, making them an attractive therapeutic target. However, only modest monotherapy activity of ATR inhibitors (ATRis) has been reported in patients with HGSOC, highlighting the need for combination treatment. We conducted a high-throughput drug combination screen of ATRi (ceralasertib) with 1,912 drugs in two PARPi-resistant BRCA2-mutant PEO1 (PEO1/OlaR and PEO1/OlaJR) HGSOC cell lines. In this screen, 234 drugs showed synergistic cytotoxicity with ATRi, including 31 (13.2%) cell cycle checkpoint inhibitors, 27 (11.5%) chemotherapeutic drugs, and 13 (5.6%) PI3K/AKT pathway inhibitors. We prioritized the PI3K/AKT pathway inhibitors for ATRi combination because the PI3K/AKT pathway is upregulated in >70% of HGSOC and associated with an aggressive phenotype. Moreover, PI3K/AKT signaling is found to be activated in HGSOC cells with PARPi resistance. We separately validated that an ATRi (ceralasertib < 1 μM) in combination with an AKT inhibitor (AKTi; capivasertib < 10 μM) yielded additive/synergistic cytotoxic effects (combination index < 1) in various HGSOC cell lines, including acquired and de novo PARPi-resistant (PEO1/OlaR, PEO1/OlaJR, and PEO4) and platinum-resistant HGSOC cell lines (OVCAR3), by XTT and colony formation assays. With clinically attainable concentrations of ATRi (1 μM) and AKTi (10 μM), the combination treatment increased cell apoptosis compared to ATRi (increased 2.1 to 95.2-fold; P < 0.001) or AKTi alone (increased 3.3 to 92.2-fold; P < 0.001) in both PARPi-sensitive and -resistant HGSOC cells. ATRi+AKTi treatment also showed greater DNA damage as evidenced by increased percentage of cells with ≥ 5 γH2AX foci relative to ATRi (increased 1.1 to 7.6-fold; not significant in PEO1 and P < 0.001 in PARPi-resistant cells) or AKTi (increased 2.3 to 6.2-fold; P < 0.001) in both PARPi-sensitive and -resistant cells. Furthermore, ATRi+AKTi treatment augmented replication stress as measured by increased phospho-RPA+/γH2AX+ populations compared with ATRi (increased 1.7 to 4.7-fold; P < 0.001) or AKTi (increased 3.7 to 12.0-fold; P < 0.001). Overall, our results suggest that dual inhibition of ATR and AKT pathways results in greater cell death by increasing DNA damage and replication stress in HGSOC cells with PARPi resistance. Citation Format: Tzu-Ting Huang, Chih-Yuan Chiang, Nitasha Gupta, Kelli Wilson, Ken Chih-Chien Cheng, Jung-Min Lee. Targeting ATR and AKT pathways promotes cell death in PARP inhibitor-resistant ovarian cancer cells by increasing DNA damage and lethal replication stress [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2022; 2022 Apr 8-13. Philadelphia (PA): AACR; Cancer Res 2022;82(12_Suppl):Abstract nr 5408.

Abstract 3494: Characterizing the relationship between genotype and phenotype in DNA damage response-altered pancreatic cancer models

Abstract Alterations in DNA damage response (DDR) proteins are prevalent across cancers and present unique opportunities for the therapeutic induction of synthetic lethality (i.e., two gene deficiencies in the same pathway synergize to kill tumor cells). In pancreatic adenocarcinoma, patients harboring alterations in DDR genes, such as in homology-directed repair (HDR), comprise the 10-20% of patients that may benefit from the recent FDA approval of Olaparib, a poly (ADP-ribose) polymerase inhibitor that disrupts non-homologous end joining (NHEJ). Despite being the best-in-class targeted therapy for DDR-altered pancreatic cancers, a subset of patients fails to respond to Olaparib and those that initially respond eventually go on to develop resistance. The mechanisms underlying resistance are poorly elucidated but suggest that some patients harboring DDR-altered tumors are HDR-proficient or revert to HDR-proficiency during therapy, bypassing the second gene deficiency requisite for synthetic lethal induction with targeted therapy (e.g., Olaparib). Utilizing patient-derived models of cancer, we are actively investigating DDR-altered, pancreatic tumor cell lines and exploring the relationship between DDR-alterations and HDR-deficiency with three goals: [1] To evaluate the prevalence of HDR-proficiency in BRCA-altered tumors, [2] to understand the extent to which patient-derived models of cancer are concordant and predictive of clinical outcomes, and [3] to identify novel therapeutic strategies for resistant patients. So far, we have observed HDR-proficiency by functional assays (e.g., RAD51 foci formation) in DDR-altered patient-derived cell lines that corresponds with poor response to Olaparib in vitro, and resistance to platinum therapy clinically. Whereas DDR-altered HDR-deficient lines had greater sensitivity to Olaparib and platinum therapy. These early data suggest that measures of HDR by functional assay may be more predictive of clinical therapeutic responses than the use of genetic signatures alone. Citation Format: James R. Carroll, Jason M. Link, Jonathan R. Brody. Characterizing the relationship between genotype and phenotype in DNA damage response-altered pancreatic cancer models [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2022; 2022 Apr 8-13. Philadelphia (PA): AACR; Cancer Res 2022;82(12_Suppl):Abstract nr 3494.

Abstract 804: Trapped PARP1 cytotoxicity is modulated by the ubiquitin-dependentsegregase p97

Abstract Poly-(ADP-ribose) polymerase inhibitors (PARPi) elicit anti-tumor activity in homologous recombination defective cancers by promoting cytotoxic, chromatin-bound, “trapped” PARP1. Here we have elucidated a pathway that process trapped PARP1. By exploiting wild-type or trapping-resistant PARP1 transgenes combined with either a rapid immunoprecipitation mass-spectrometry of endogenous proteins (RIME)-based approach or PARP1 Apex2-proximity labelling linked to mass-spectrometry, we generated proteomic profiles of trapped and non-trapped PARP1 complexes. These experiments demonstrated an increase in the SUMO1/2 modifications upon trapping, as well as an interaction with the ubiquitin-regulated p97 ATPase (aka VCP). Subsequent experiments demonstrated that upon trapping, PARP1 is SUMOylated by the SUMO-ligase PIAS4 and subsequently ubiquitinated by the SUMO-targeted E3-ubiquitin ligase, RNF4, events that promote p97 recruitment and p97 ATPase-mediated removal of trapped-PARP1 from chromatin. Consistently, small molecule p97 complex inhibitors, including a metabolite of the clinically-used drug disulfiram, CuET that acts as a p97 sequestration agent, prolong PARP1 trapping and thus enhance PARPi-induced cytotoxicity in homologous recombination defective tumor cells and patient-derived tumor organoids. Taken together, these results suggest that p97 ATPase plays a key role in the processing of trapped PARP1 from chromatin and the response of homologous recombination defective tumor cells to PARPi. Citation Format: Dragomir B. Krastev, Chris Lord. Trapped PARP1 cytotoxicity is modulated by the ubiquitin-dependentsegregase p97 [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2022; 2022 Apr 8-13. Philadelphia (PA): AACR; Cancer Res 2022;82(12_Suppl):Abstract nr 804.

Abstract 1792: FGFR3 mediated PARP1 tyrosine 158 phosphorylation promotes PARP inhibitor resistance

Abstract Poly(ADP-ribose) polymerase (PARP) inhibitors (PARPi), which induce DNA damage by inhibiting PARP1 enzymatic activity and trapping PARP on the damaged DNA, are used to eliminate BRCA1/2-mutated (BRCAm) cancer. However, clinical observations suggest that BRCAm tumors develop PARPi resistance. Current strategies to overcome PARPi resistance include impeding multiple DNA repair pathways to induce excessive DNA damage. Here, we propose a novel strategy targeting oncogenic receptor tyrosine kinases to enhance PARP trapping. By developing triple-negative breast cancer (TNBC) cells with acquired talazoparib resistance, we observed a high prevalence of activated fibroblast growth factor receptor 3 (FGFR3) kinase in these cells through kinase antibody array analysis. Mass spectrometry analysis and in vitro kinase assay suggested that FGFR3 phosphorylated PARP1 at tyrosine residues 158 and 176. Biochemistry studies suggested that only PARP1 tyrosine 158 phosphorylation contributes to PARPi resistance in the cells we developed. We then developed a monoclonal antibody against tyrosine 158 phosphorylated PARP1, and found that high-level PARP1 tyrosine 158 phosphorylation positively correlated with PARPi resistance in breast cancer patient-derived xenograft models. We further demonstrated that the combination of FGFR inhibitor and PARPi delayed DNA repair with prolonged PARP trapping. Moreover, synergy between PARPi and FGFR inhibition was observed in multiple TNBC cell lines with PARPi resistance in vitro. The combination of PARPi and FGFR inhibitor also showed synergism in vivo, and treatment with the combination of PARPi and FGFR inhibitor was tolerated in mouse models. These findings reveal that PARP1 tyrosine 158 phosphorylation facilitates resolving of the PARPi-induced PARP-trapping, and that the tyrosine 158 phosphorylated PARP1 may be an effective biomarker to indicate FGFR3 mediated PARPi resistance. Citation Format: MeiKuang Chen, Yuan Gao, Weiya Xia, Yu-Han Wang, Jennifer K. Litton, Yu-Yi Chu, Funda Meric-Bernstam, Helen Piwnica-Worms, Banu Arun, Jordi Rodon Ahnert, Yongkun Wei, Wei-Chao Chang, Hung-Ling Wang, Coya Tapia, Constance T. Albarracin, Shao-Chun Wang, Ying-Nai Wang, Gabriel N. Hortobagyi, Chunru Lin, Liuqing Yang, Dihua Yu, Mien-Chie Hung. FGFR3 mediated PARP1 tyrosine 158 phosphorylation promotes PARP inhibitor resistance [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2022; 2022 Apr 8-13. Philadelphia (PA): AACR; Cancer Res 2022;82(12_Suppl):Abstract nr 1792.

Abstract 2081: Poly ADP-ribose polymerase inhibition enhances T cell cytotoxicity and anti-tumor function by altering NAD+ levels

Abstract Poly ADP-ribose polymerase (PARP) is an NAD-dependent DNA repair enzyme. Inhibition of PARP in BRCA-mutant cancers has been a clinically approved therapy for several years. While the PARP inhibitor, olaparib, has been approved for the treatment of BRCA-mutant breast and ovarian cancers, it has not been used in other cancers because its mechanism of action relies on synthetic lethality. We have found that olaparib may also have use in other cancers due to its ability to modulate the immune system directly. Specifically, we have found that olaparib is able to increase the proliferation, activation, and cytotoxicity of T cells in vitro and reduce tumor growth in vivo at low doses. Recent papers have proposed that olaparib is able to enhance T cell function through the stimulator of interferon genes (STING) pathway by enhancing antigen presenting cell activity and resulting in more granzyme B expression and enhanced tumor killing. Using purified T cells from both wild type and STING knockout mice, we have shown that olaparib can also cause an increase in granzyme B and perforin expression, an increase in T cell proliferation, and enhanced tumor cell killing in a STING-independent manner. Because PARP is an NAD-consuming enzyme, we examined the role of NAD+ in the activation T cells and the production of granzyme B and perforin. By using an inhibitor of NAD+ recycling, FK866, we show that T cells have reduced NAD+ levels, reduced granzyme B and perforin expression, and even fail to activate in the presence of CD3 and CD28 when NAD+ is limited; however, adding olaparib to these cells rescues the effects of FK866 and allows proliferation and granzyme B production. In vivo we can see that even at olaparib doses that are significantly below those which induce synthetic lethality of tumor cells, olaparib is able to inhibit tumor growth in models of both colorectal and breast cancer. This suggests that olaparib can modulate the activity of T cells directly and has implications for enhancing the anti-tumor activity of these cells both alone and in combination with other forms of immunotherapy. Citation Format: Matthew J. Dean, Liqin Zheng, Phaethon Philbrook, Augusto C. Ochoa, A. Hamid Boulares. Poly ADP-ribose polymerase inhibition enhances T cell cytotoxicity and anti-tumor function by altering NAD+ levels [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2022; 2022 Apr 8-13. Philadelphia (PA): AACR; Cancer Res 2022;82(12_Suppl):Abstract nr 2081.

Real-world effectiveness of first-line maintenance olaparib in women with BRCA-mutated advanced ovarian cancer: U.S. retrospective cohort study.

5518 Background: Following cytoreductive surgery and first-line (1L) platinum based chemotherapy, 70% of patients (pts) with newly diagnosed advanced ovarian cancer (AOC) experience relapse within 3 years. 1L maintenance treatment (tx) with olaparib monotherapy, a poly (ADP-ribose) polymerase inhibitor, extended progression free survival in pts with BRCA mutated (BRCAm) AOC in the SOLO-1 (NCT01844986) randomized controlled trial (RCT). We aimed to describe real world characteristics, tx patterns, and clinical outcomes of pts with newly diagnosed, BRCAm AOC. Methods: Data were collected from 457 pts via electronic case report forms in the US. Pt eligibility criteria were positive BRCAm test result between Jan-June 2019 (6 months post 1L olaparib FDA approval), newly diagnosed AOC (no maintenance tx prior to index), aged ≥18 years, no RCT enrollment, no active neoplasia, no prior tx for metastatic/stage IV cancer. Pt follow up was until July 2021. Kaplan-Meier (KM) estimation was used for time to event analysis using progression proxies: Time to subsequent therapy and discontinuation (or death for both) from initiation of 1L maintenance olaparib monotherapy. Results: Pt mean age (±SD) at index was 62 (±10) years, 64% of pts were white and 18% African American; further clinical characteristics are in the table. 95% of pts received ≥1 pharmacological tx. At 1L, 36% of pts (156/433) received maintenance tx after chemotherapy, with 64% of pts (277/433) receiving routine surveillance (no maintenance tx). Olaparib was the most common maintenance tx (67%, 105/156), with 67% of pts (70/105) prescribed olaparib monotherapy. At 24 months, the KM model estimated 91% of pts (95% confidence interval: 82, 96) would not progress to their subsequent therapy, with a median discontinuation of olaparib monotherapy of 25.0 (interquartile range [IQR]: 21.0, not estimable) months, over a median follow-up of 22.0 (IQR: 20.6, 24.0) months. Conclusions: This real world study complements SOLO-1 RCT data by demonstrating prolonged benefit of 1L olaparib in newly diagnosed pts with BRCAm AOC in terms of lower likelihood of progression (tx switch/death). To assess real world tx effectiveness globally, data collection across further eight countries is due to be completed in 2022. [Table: see text]

Lurbinectedin in patients with pretreated BRCA1/2-associated metastatic breast cancer: Results from a phase II basket study.

1092 Background: Lurbinectedin (L) is a selective inhibitor of oncogenic transcription that leads to cell apoptosis and shows antitumor activity against homologous recombination repair-deficient cell lines. A previous phase II study (Cruz et al. JCO 2018;36:3134-3143) demonstrated antitumor activity in patients (pts) with pretreated metastatic breast cancer (median of 1 prior advanced chemotherapy line) and BRCA1/2-mutated tumors with L 3.5 mg/m2 or 7.0 mg flat dose (equivalent to 4.0 mg/m2) every three weeks [q3wk]). This report focuses on the outcomes in the BRCA1/2-associated breast cancer cohort of a phase II Basket multitumor trial. Methods: This phase II study evaluated L 3.2 mg/m2 1-hour intravenous (i.v.) infusion q3wk in a cohort of 21 female pts with pretreated BRCA1/2-associated breast cancer. The primary efficacy endpoint was ORR according to RECIST v1.1. Secondary endpoints included duration of response (DoR), progression-free survival (PFS), OS and safety. Results: Median age was 45 years (range, 29-73 years). Hormone receptor (HR)+ disease was observed in 76.2% of pts, triple negative disease in 19.0% and HER2+ in 9.5%. BRCA1 and BRCA2 were reported in 47.6% and 52.4% of pts, respectively. Median number of prior lines of chemotherapy for advanced disease was 2 (range, 0-3 lines). Prior poly(ADP-ribose) polymerase inhibitors and platinum compounds had been administered to 23.8% and 47.6% of pts, respectively. Confirmed partial response (PR) was observed in six pts (ORR = 28.6%; 95% CI, 11.3-52.2%). Lurbinectedin was active in both BRCA mutations: four PRs in 11 pts (36.4%) in BRCA2 and two PRs in 10 pts (20.0%) in BRCA1. Median DoR was 8.6 months, median PFS was 4.1 months and median OS was 16.1 months. Stable disease (SD) was observed in ten pts (47.6%), including three pts with unconfirmed response in a subsequent tumor assessment (ORR unconfirmed = 42.9% [95%CI, 21.8-66.0]). Clinical benefit rate (PR + SD≥4 months) was 76.2% (95% CI, 52.8-91.8%). The most common grade 3/4 toxicity was neutropenia (42.9%; grade 4, 23.8%; with no febrile neutropenia). Conclusions: This phase II study met its primary endpoint and confirmed the activity of L in pretreated BRCA1/2-associated breast cancer pts. L 3.2 mg/m2 1-hour i.v. infusion q3wk showed an acceptable, predictable and manageable safety profile. Considering the exploratory aim of this trial as well as previous results in other phase II study, further development of L in this indication is warranted. Clinical trial information: NCT02454972.

Elucidating the Dynamics and Selective Mechanistic Mode of Inhibition of a Novel Poly ADP-Ribose Polymerase-1 Inhibitor

: Poly ADP-ribose polymerase-1 (PARP-1), due to its role in DNA damage and repair, has been identified as a crucial therapeutic target to attenuate cancer development and progression. More so, selective inhibition has remained a focal point in PARP-1 targeting and has led to the development of numerous compounds, including the recently identified Cpd10n, a novel homoerythrina alkaloid derivative. To expound on the selective PARP-1 inhibition mechanisms by Cpd10n, we employed computational simulation methods in this study. Findings revealed that the inhibitor stabilized the characteristic motion of activated PARP-1 as evidenced by reductions in residual deviations and structural flexibility. Findings further revealed that Cpd10n was favorably bound at the active site PARP-1 as supported by the occurrence of strong hydrogen and halogen bonds based on complementarity. These were in addition to aromatic bonds with an enhanced ring to ring stability. Steady and high-affinity interactions between the fluorine atom of Cpd10n and Glu988 could potentiate the selective activity of the compound. Interaction analyses also revealed that inhibitor binding was strongly dependent on electrostatic effects over van der Waal contributions, which were relatively minimal. We believe findings from this study will further contribute to the rational structure-based design of highly selective PARP-1 inhibitors.

Germline Mutational Landscape in Chinese Patients With Advanced Breast Cancer

BackgroundGenetic testing for breast cancer (BC) patients may shift the paradigm towards more personalized management and treatment strategies. While gene alterations may be ethnic-specific in breast cancer, our understanding of genetic epidemiology of BC remains mainly driven by data from Caucasian populations and further limited to selected handful of genes.MethodsWe collected whole blood samples from 356 BC patients at metastatic first line BC and primary stage IV disease at Beijing Cancer Hospital between Jan. 2013 to Dec. 2019. A comprehensive 600-gene cancer panel was used to detect germline variants in the covered genes with a median 300x sequencing depth. Variants were classified into pathogenic, likely pathogenic, variant of uncertain significance, likely benign and benign groups according to the ACMG/AMP Standards and Guidelines. Pathogenic and likely pathogenic variants were considered as deleterious mutations.ResultsThe median age of 356 BC patients was 49 years (range, 21-87 years) at the first diagnosis of BC. Deleterious germline mutations across 48 cancer-related genes were identified in 21.6% (77/356) of the patients. The most prevalent mutations were BRCA1/2 mutations (7.0%), followed by ATM and RAD50 mutations (1.4% each). In addition, patients with family history were more likely to carry BRCA1 mutations (P=0.04). Moreover, patients with triple-negative breast cancer (TNBC) were more likely to harbor BRCA1 mutations than those with HR+ or HER2+ breast cancer (P=0.006). While there was no significant survival difference observed in BRCA1/2 carriers relative to non-carriers, patients with DNA damage repair (DDR) gene mutations (mostly frequently BRCA, ATM, RAD50) had worse disease-free survival (P=0.02).ConclusionsThe most prevalent germline mutations in a large cohort of Chinese patients with advanced BC were BRCA1/2 mutations, followed by ATM and RAD50 mutations. In total, approximately 16.0% (57/356) of patients carry deleterious mutations in DDR pathway. Patients with breast or ovarian cancer family history were more likely to carry BRCA1/2 mutations, and ones with DDR mutations had worse survival. These findings suggest that DDR mutations are prevalent in Chinese BC patients who may potentially benefit from treatment with Poly (ADP-ribose) polymerase inhibitors.

A randomized phase 2 trial to evaluate the antitumor activity of enzalutamide (EZ) and talazoparib (TALA) for the treatment of metastatic hormone-naïve prostate cancer (mHNPC): ZZFIRST.

TPS209 Background: Multiple lines of evidence suggest a crosstalk between androgen receptor (AR) signaling and DNA damage repair (DDR) in prostate cancer. Co-targeting both pathways in mHNPC can result in a clinically relevant synergistic effect. ZZFIRST trial is evaluating the combination of TALA –a poly(ADP-ribose) polymerase inhibitor– and EZ –an AR signaling inhibitor– in mHNPC patients. Methods: This is a multicenter, open-label, randomized, investigator-initiated phase 2 clinical trial. Men aged ≥18 years with histologically confirmed mHNPC, an ECOG performance status of 0-1, and a prostate-specific antigen (PSA) ≥4 ng/mL at enrolment are eligible. Patients must have not received previous systemic treatment for locally advanced or mHNPC. A total of 54 patients will start treatment with EZ 160 mg/day for 2 28-day cycles in addition to standard androgen-deprivation therapy (ADT). Patients are then randomized and stratified based on homologous recombination gene alterations on a 1:2 ratio to either continue EZ 160 mg/day, or to receive EZ 160 mg/day plus TALA 0.5 mg/day. In both arms, patients will continue ADT throughout the trial. Treatment will continue until progressive disease (PD) or unacceptable toxicity. PSA will be determined every 4 weeks and radiological tumor extend will be assessed at screening and every 8 weeks for the 6 initial months of treatment and every 12 weeks thereafter until PD. Primary endpoint is PSA-complete response defined as the percentage of patients with PSA < 0.2 ng/mL at 12 months of therapy. Secondary endpoints include PSA-complete response at any time point and at month 7, PSA response ( < 4 ng/ml) at 7 and 12 months, PSA-progression-free survival (PSA-PFS), radiologic PFS, time to castration resistance based on PSA-PFS and rPFS, and overall survival. Safety will be assessed as per NCI-CTCAE 5.0. Exploratory endpoints include analysis of transcriptional changes in AR and DDR pathways and assessment of genomic signatures on tumor and liquid biopsies collected at baseline, 4 weeks, and PD. An imaging sub-study of whole-body diffusion weighted MRI will help to further study antitumor activity and drug resistance mechanisms. This trial was opened to accrual in July 2020. Currently 44 patients have been enrolled (with 37 randomized by cycle 3 day 1) out of 54 expected. Analysis will be assessed with the exact binomial test. At least 11 patients must maintain PSA < 0.2 ng/mL by 12 months of therapy among 32 evaluable patients in the combination arm to justify further investigation of this strategy. A drop-out rate of 10% has been considered. Clinical trial information: NCT04332744.

Abstract ES3-2: Clinical management of moderate penetrance genes

Abstract Genetic epidemiologic studies have found that germline pathogenic mutations in the following 12 genes confer a substantial (two-fold or higher) increase in breast cancer risk: ATM, BARD1, BRCA1, BRCA2, CDH1, CHEK2, NF1, PALB2, PTEN, RAD51C, RAD51D and TP53. Mutations in several of these genes, including the notable examples of ATM, CHEK2 and PALB2, are classified as “moderate penetrance”: conferring a relative risk of breast cancer that is between two-times and five-times higher than that of the average woman. Next-generation sequencing technology and lower costs have enabled the widespread use of multiplex germline testing panels that contain both high and moderate penetrance genes. Recent studies have reported a relatively high prevalence of ATM, CHEK2 and PALB2 mutations among unselected breast cancer patients (approximately 0.5-1% per gene), including among women diagnosed at older ages. ATM and CHEK2 mutations are associated with elevated risks of hormone receptor-positive breast cancer, while PALB2 mutations are more associated with triple-negative disease. Important recent developments in the clinical management of patients with moderate penetrance gene mutations include model-based estimates of optimal breast screening protocols; evidence suggesting the safety of adjuvant radiotherapy; emerging data on susceptibility to targeted therapy with poly(ADP-ribose) polymerase inhibitors; and characterization of the risks of developing other, non-breast cancers. Ongoing studies and future research priorities will be discussed. Citation Format: AW Kurian. Clinical management of moderate penetrance genes [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 ES3-2.

PARP-remmers bij gemetastaseerde prostaatkanker: een systematische review

PARP inhibitors in metastatic prostate cancer: a systematic review Background. Poly ADP-ribose polymerase (PARP) inhibitors provide a novel therapeutic approach for the treatment of metastatic prostate cancer. They act on the homologous recombination DNA repair mechanism. In metastatic prostate cancer, 20-25% of the patients harbour a homologous recombination repair deficiency. This review investigates the current evidence for the use of PARP inhibitors in clinical practice. Methods. The databases MEDLINE, CENTRAL and EMBASE were searched, as well as the clinical trial registries EudraCT and Clinicaltrials.gov. Randomised controlled trials with PARP inhibitors were included. The outcomes of interest were: overall survival (OS), progression-free survival (PFS), objective response rate (ORR), adverse events and quality of life. The data were analysed according to Cochrane methodology. Results. Three controlled trials were included, all in a castration-resistant setting. Five phase 2 trials were excluded; these data are presented in a narrative form. One study of olaparib in monotherapy versus enzalutamide or abiraterone found a benefit in OS and PFS in patients with a BRCA1, BRCA2 or ATM mutation, though not in patients with other HRD (‘homologous recombination deficiency’) mutations. Two studies investigated a PARP inhibitor in combination with abiraterone versus abiraterone in monotherapy. The combination with olaparib showed a modest PFS benefit, whereas the veliparib combination showed no OS or PFS benefit. Conclusion. At present, the role of PARP inhibitors is limited to BRCA1, BRCA2 and ATM mutation carriers. Combination therapy with other agents could provide a synergistic advantage and is being researched. Fourteen ongoing trials meet the inclusion criteria and will clarify the role of PARP inhibitors in the treatment of prostate cancer.

Abstract P119: Differential sensitivity to poly(ADP-ribose) polymerase inhibitors in patient-derived cell models of breast cancer

Abstract Female breast cancer (BC) became the most commonly diagnosed cancer globally in 2020. One of the hallmarks of BC is both intratumor and intertumor heterogeneity. Efforts have been made to categorize this heterogeneity based on the presence or absence of estrogen receptor (ER), progesterone receptor (PR) and human epidermal growth factor receptor 2 (HER2/ERBB2). Receptor expression patterns are used to stratify BC and the subsequent treatments. Much of the current knowledge of breast cancer comes from in vitro and in vivo studies using well established cell lines, some of which have been cultured since the 1950s. Given that serial passaging over many years has been reported to alter the mutational profile of cell lines and therefore their relevance to clinical decisions on the primary tumour, new near-tumor cell models need to be generated. In this study, tumour biopsies or ascitic fluids were obtained from a local cancer research biobank, as well as directly from metastatic BC patients across the globe. Using mechanical dissociation and cell separation techniques we isolated tumor cells and grew them in proprietary media. The resultant models were subjected to whole exome and RNA sequencing. In addition, the models were tested in a 3-day cell death assay against a library of more than 50 FDA-approved drugs. The models and four BC cell lines (HCC1937, ZR-75-1, MDA-MB-436 and HCC1428) were also tested in a longer term 7-day assay against a panel of four poly(ADP-ribose) polymerase (PARP) inhibitors. A total of 10 patient-derived cell (PDC) models were successfully established from biopsies or ascitic fluids taken from patients with primary (1/10) or metastatic (9/10) BC. Models were established from patients with ER+ BC, HER2+ BC and triple negative BC (TNBC) within an average of 23 days from sample arrival. All models displayed a greater sensitivity to the non-targeted drugs in the library compared with the targeted drugs. Mutations in breast cancer associated 1 (BRCA1) and BRCA2 genes that were not present in BC cell lines were identified in a subset of the PDCs. All models showed some sensitivity to PARP inhibitors, and most were exquisitely sensitive to talazoparib with IC50s of less than 100 nM. Determining cell death responses in near-tumour PDCs should thus be adopted to enable more informed clinical decisions for treatment pathways and in parallel will be promising tools for oncology drug discovery. Citation Format: Immaculate Nalubowa, Subir Singh, Yuen Ngan Fan, Rachel Howard-Jones, Albert Bezman, Dominic I. James, Geoff Muckle, Gareth J. Griffiths. Differential sensitivity to poly(ADP-ribose) polymerase inhibitors in patient-derived cell models of breast cancer [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 P119.

Abstract P068: Different treatment schemes cause distinct PARP inhibitor resistance mechanisms in BRCA2-mutant ovarian cancer cells

Abstract Poly (ADP-ribose) polymerase inhibitors (PARPis) represent a major advance in ovarian cancer management, now as treatment for recurrent ovarian cancer and as a maintenance therapy following platinum-based chemotherapy in the upfront and platinum-sensitive recurrent settings. Yet, a growing number of patients progress through PARPis, creating a need for further understanding on resistance mechanisms. We hypothesized that different treatment dosing/timing schemes would cause distinct mechanisms of acquired resistance to PARPis. To test this hypothesis, we exposed BRCA2-mutant PEO1 ovarian cancer cells to 0.5 μM olaparib, doubling its concentration up to 40 μM over 3–4 months (PEO1/OlaJR). The second PARPi-resistant PEO1 cell line (PEO1/OlaR) was developed using a relatively low initial dose of 5 nM olaparib, and gradually increasing its concentration up to 20 μM over 6 months. To confirm PARPi resistance, cell proliferation and viability were measured by MTT and colony formation assay, respectively. Both cell lines were resistant to two different PARPis beyond clinically achievable concentrations (olaparib IC50 141.7–372.8 μM and rucaparib IC50 37.1–51.2 μM) and demonstrated restored homologous recombination (HR) repair as evidenced by increased HR-reporter activity (1.32 to 1.45-fold compared to PEO1, p < 0.05) and RAD51 foci formation (5.2 to 6.1-fold compared to PEO1, p < 0.001). For PEO1/OlaJR, distinct resistance mechanisms to PARPi were noted: 1) promoting drug efflux confirmed by increased MDR efflux activity (1.92-fold compared to PEO1, p < 0.001) and increased protein levels of an ABCB1 transporter (7.2-fold compared to PEO1); and 2) enhancing HR repair restoration, likely via reduced REV7 protein expression (0.43-fold compared to PEO1). On the other hand, PEO1/OlaR exhibited a mesenchymal cell phenotype with greater invasion ability as measured by transwell invasion assay (2.25-fold compared to PEO1, p < 0.001) and restored HR repair with upregulation of TRIP13 protein (1.85-fold compared to PEO1). PEO1/OlaR also showed increased cell survival, possibly via activation of PI3K/AKT signaling, as evidenced by increased p-AKT (2.12-fold compared to PEO1). No loss of 53BP1 was observed in either PEO1/OlaJR or PEO1/OlaR based on whole exome sequencing and immunoblotting of 53BP1. BRCA2 reversion mutation status is currently under investigation. Altogether, our findings suggest that mechanisms of resistance to PARPis arise differently based on the duration and concentrations of drug treatment, highlighting the importance of appreciating interplay between specific treatment schemes and the downstream consequences. Thus, developing tailored therapeutic strategies should consider various mechanisms of PARPi resistance. Citation Format: Tzu-Ting Huang, Jayakumar R. Nair, Nitasha Gupta, Tomomi M. Yamamoto, Benjamin G. Bitler, Jung-Min Lee. Different treatment schemes cause distinct PARP inhibitor resistance mechanisms in BRCA2-mutant ovarian cancer cells [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 P068.

Abstract P057: The ubiquitin-dependent ATPase p97 removes cytotoxic trapped PARP1 from chromatin

Abstract Poly-(ADP-ribose) polymerase inhibitors (PARPi) elicit anti-tumour activity in homologous recombination defective cancers by promoting cytotoxic, chromatin-bound, “trapped” PARP1. How cells process trapped PARP1 remains unclear. By exploiting wild-type or trapping-resistant PARP1 transgenes combined with either a rapid immunoprecipitation mass-spectrometry of endogenous proteins (RIME)-based approach or PARP1 Apex2-proximity labelling linked to mass-spectrometry, we generated proteomic profiles of trapped and non-trapped PARP1 complexes. This combined approach identified an interaction between trapped PARP1 and the ubiquitin-regulated p97 ATPase (aka VCP). Subsequent experiments demonstrated that upon trapping, PARP1 is SUMOylated by the SUMO-ligase PIAS4 and subsequently ubiquitinated by the SUMO-targeted E3-ubiquitin ligase, RNF4, events that promote p97 recruitment and p97 ATPase-mediated removal of trapped-PARP1 from chromatin. Consistent with this, small molecule p97 complex inhibitors, including a metabolite of the clinically-used drug disulfiram, CuET that acts as a p97 sequestration agent, prolong PARP1 trapping and thus enhance PARPi-induced cytotoxicity in homologous recombination defective tumour cells and patient-derived tumour organoids. Taken together, these results suggest that p97 ATPase plays a key role in the processing of trapped PARP1 from chromatin and the response of homologous recombination defective tumour cells to PARPi. Citation Format: Dragomir Krastev, Shudong Li, Yilun Sun, Yves Pommier, Kristijan Ramadan, Christopher J. Lord. The ubiquitin-dependent ATPase p97 removes cytotoxic trapped PARP1 from chromatin [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 P057.