Combining Poly (ADP-ribose) Polymerase Inhibition Research Articles

Combination Therapy with Trastuzumab and Niraparib: Quantifying Early Proliferative Alterations in HER2+ Breast Cancer Models.

HER2-targeted treatments have improved survival rates in HER2+ breast cancer patients, yet poor responsiveness remains a major clinical obstacle. Recently, HER2+ breast cancer cells, both resistant and responsive to HER2-targeted therapies, have demonstrated sensitivity to poly-(ADP-ribose) polymerase (PARP) inhibition, independent of DNA repair deficiencies. This study seeks to describe biological factors that precede cell viability changes in response to the combination of trastuzumab and PARP inhibition. Treatment response was evaluated in HER2+ and HER2- breast cancer cells. Further, we evaluated the utility of 3'-Deoxy-3'-[18F]-fluorothymidine positron emission tomography ([18F]FLT-PET) imaging for early response assessment in a HER2+ patient derived xenograft (PDX) model of breast cancer. In vitro, we observed decreased cell viability. In vivo, we observed decreased inhibition in tumor growth in combination therapies, compared to vehicle and monotherapy-treated cohorts. Early assessment of cellular proliferation corresponds to endpoint cell viability. Standard summary statistics of [18F]FLT uptake from PET were insensitive to early proliferative changes. Meanwhile, histogram analysis of [18F]FLT uptake indicated the potential translatability of imaging proliferation biomarkers. This study highlights the potential of combined trastuzumab and PARP inhibition in HER2+ breast cancer, while demonstrating a need for optimization of [18F]FLT-PET quantification in heterogeneous models of HER2+ breast cancer.

Abstract SY17-01: The complexities of tumor associated macrophages and the key to effective targeting 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. Macrophages are an innate immune cell that play a critical role in host defense and maintaining tissue homeostasis, however their infiltration into tumors has been associated with disease progression and resistance to therapy. Tumor associated macrophages (TAMs) represent a significant proportion of solid tumors, including breast cancer. TAMs play a major role in tumorigenesis as they can enhance tumor cell growth, angiogenesis and metastasis. In addition, TAMs can inhibit anti-tumor responses of T cells. Our recent work has shown that removal or conversion of TAMs to an anti-tumor phenotype enhances chemo- and immuno-therapy establishing TAMs as targets for anti-cancer therapy. 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. Therefore, targeting TAMs offers great potential to enhance both chemo- and immuno-therapy. Deep analysis of TAMs in solid tumors has revealed the complexity of TAMs and revealed major gaps in our knowledge of the functional and phenotypic characterization of TAM subsets associated with cancer, before and after treatment. Here we will discuss the complexity of TAMs in solid tumors including characterizing TAM subsets, location, and crosstalk with neighboring cells, as well as novel TAM-modulating strategies and combinations that are likely to enhance current therapies and overcome chemo- and immuno-therapy resistance. Citation Format: Jennifer L. Guerriero. The complexities of tumor associated macrophages and the key to effective targeting for anti-cancer therapy. [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2023; Part 1 (Regular and Invited Abstracts); 2023 Apr 14-19; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2023;83(7_Suppl):Abstract nr SY17-01.

Abstract 311: Optimization of treatment schedule for the combination therapy of ATR inhibitor elimusertib and PARP inhibitor niraparib in preclinical tumor models

Abstract Background: Ataxia telangiectasia and Rad3-related (ATR) kinase and poly-(ADP-ribose) polymerase (PARP) are central components of the DNA damage response (DDR) machinery that act via distinct DNA repair pathways whereby combined inhibition of ATR and PARP is expected to be highly synergistic. Elimusertib is a potent and selective ATR inhibitor currently in phase I development in patients with advanced solid tumors carrying DDR defects. Niraparib is an approved PARP inhibitor for the treatment of ovarian cancer. Several different dosing schedules of a combination treatment with elimusertib and niraparib were explored in preclinical tumor model systems to identify a dose regimen that optimally balances safety and efficacy for translation into clinical studies. Methods: Preclinical human mCRPC xenograft model 22RV1 in male immunocompromised (NMRI nude) mice was used. Multiple variations of treatment duration and sequence of drug application were investigated. Both drugs were used at their MTD in the respective combination dosing regimen. Antitumor activity was assessed by tumor area measurement, and safety/tolerability was determined by body weight change and evaluation of hematological parameters. Results: Preclinical data demonstrated strong synergistic antitumor activity resulting from combined blockade of ATR and PARP. In vitro and in vivo data revealed that concomitant inhibition of both ATR and PARP mediated DNA repair is required for maximal synergy. 13 different combination dosing schedules were tested in vivo. Elimusertib was dosed between 20 and 40 mg/kg BID for 3 days on/4 days off, or 3 days on/11 days off. Niraparib was dosed QD continuously or using various intermittent schedules. Overall, best efficacy and tolerability was achieved when PARPi and ATRi were applied concurrently using a discontinuous schedule. The condensed treatment time of both drugs and the extended treatment-free period demonstrated better mitigation of hematological effects, reducing the treatment impact on red blood cell counts in peripheral blood. Conclusion: In preclinical in vitro and in vivo studies it was demonstrated that concurrent inhibition of ATR and PARP resulted in higher tumor cell cytotoxicity than any sequential blockade of ATR and PARP. Evaluating different treatment regimens of combined elimusertib and niraparib indicated that applying both drugs using a discontinuous schedule to balance efficacy and safety in a preclinical mCRPC xenograft model produces an optimal therapeutic window. A non-randomized, open-label trial evaluating the safety and efficacy of elimusertib in combination with niraparib for the treatment of patients with advanced solid tumors is currently ongoing (NCT04267939). Citation Format: Antje Margret Wengner, Gerhard Siemeister, Bart Ploeger, Lisa Ehresmann, Nils Guthof, Gary Wilkinson. Optimization of treatment schedule for the combination therapy of ATR inhibitor elimusertib and PARP inhibitor niraparib in preclinical tumor models [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2023; Part 1 (Regular and Invited Abstracts); 2023 Apr 14-19; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2023;83(7_Suppl):Abstract nr 311.

Abstract F2-3: Immunosuppressive macrophages and PARP inhibitor resistance

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. Macrophages are an innate immune cell that play a critical role in host defense and maintaining tissue homeostasis, however their infiltration into tumors has been associated with disease progression and resistance to therapy. Tumor associated macrophages (TAMs) represent a significant proportion of solid tumors, including breast cancer. TAMs play a major role in tumorigenesis as they can enhance tumor cell growth, angiogenesis and metastasis. In addition, TAMs can inhibit anti-tumor responses of T cells. Our recent work has shown that removal or conversion of TAMs to an anti-tumor phenotype enhances chemo- and immuno-therapy establishing TAMs as targets for anti-cancer therapy. 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. Therefore, targeting TAMs offers great potential to enhance both chemo- and immuno-therapy. Deep analysis of TAMs in solid tumors has revealed the complexity of TAMs and revealed major gaps in our knowledge of the functional and phenotypic characterization of TAM subsets associated with cancer, before and after treatment. Here we will discuss the complexity of TAMs in solid tumors including characterizing TAM subsets, location, and crosstalk with neighboring cells, as well as novel TAM-modulating strategies and combinations that are likely to enhance current therapies and overcome chemo- and immuno-therapy resistance. Citation Format: Jennifer Guerriero. Immunosuppressive macrophages and PARP inhibitor resistance [abstract]. In: Proceedings of the 2022 San Antonio Breast Cancer Symposium; 2022 Dec 6-10; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2023;83(5 Suppl):Abstract nr F2-3.

Combining PARP Inhibition and Immunotherapy in BRCA-Associated Cancers.

Poly (ADP-ribose) polymerase (PARP) inhibitors have significantly improved treatment outcomes of homologous recombination (HR) repair-deficient cancers. While the activity of these agents is largely linked to multiple mechanisms underlying the synthetic lethality of PARP inhibition and HR deficiency, emerging data suggest that their efficacy is also tied to their effects on the immune microenvironment and dependent upon cytotoxic T-cell activation. Effects observed in preclinical models are currently being validated in on-treatment biopsy samples procured from patients enrolled in clinical trials. Although this work has stimulated the development of combinations of PARP inhibitors with immunomodulatory agents, results to date have not demonstrated the superiority of combined PARP inhibition and immune checkpoint blockade compared with PARP inhibition alone. These results have stimulated a more comprehensive assessment of the immunosuppressive components of the tumor microenvironment that must be addressed so that the efficacy of PARP inhibitor agents can be maximized.

Does PARP Inhibition Sensitize Chondrosarcoma Cell Lines to Chemotherapy or Radiotherapy? Results From a Three-dimensional Spheroid Cell Model.

Chondrosarcomas are well known for their resistance to conventional chemotherapy and radiotherapy treatment regimens, which is particularly detrimental in patients who have unresectable tumors. Recently, inhibition of poly(ADP-ribose) polymerase (PARP) by talazoparib was shown to sensitize chondrosarcoma cell lines to chemotherapy (temozolomide) or radiotherapy, irrespective of isocitrate dehydrogenase (IDH) mutation status. Because two-dimensionally grown cell lines have limitations and may not accurately represent the clinical response to drug treatment, we aimed to use a more representative three-dimensional alginate spheroid chondrosarcoma model. It is important to test therapeutic agents in vitro before testing them in animals or humans; therefore, we aimed to determine the effectiveness of a PARP inhibitor in reducing the viability of chondrosarcoma spheroids. Using a more stringent, complex in vitro model refines future therapeutic options for further investigation in animal models, increasing efficiency, reducing unnecessary animal use, and saving time and cost. (1) Does talazoparib treatment slow or inhibit the growth of chondrosarcoma spheroids, and does an increased treatment duration change the drug's effect? (2) Does talazoparib work in synergy with temozolomide treatment to reduce the viability of chondrosarcoma spheroids? (3) Does talazoparib work in synergy with radiotherapy treatment to reduce the viability of chondrosarcoma spheroids? Three representative conventional chondrosarcoma cell lines (CH2879 [IDH wildtype], JJ012 [IDH1 mutant], and SW1353 [IDH2 mutant]) were cultured as alginate spheroids and treated with talazoparib (0.001 to 10 µM), temozolomide (0.01 to 100 µM), or combinations of these drugs for 3, 7, and 14 days, representing different stages of spheroid growth. The cell lines were selected to represent a variety of IDH mutation statuses and were previously validated in spheroid culturing. Temozolomide was chosen because of its previous success when combined with PARP inhibitors, dissimilar to other commonly used chemotherapies. The effect on spheroid viability was assessed using three cell viability assays. Additionally, spheroid count, morphology, proliferation, and apoptosis were assessed. The effect of talazoparib (5 to 10 nM) combined with ƴ-radiation applied using a 137 C source (0 to 6 Gy) was assessed as surviving fractions by counting the number of spheroids (three). The therapeutic synergy of low-concentration talazoparib (5 to 10 nM) with temozolomide or radiotherapy was determined by calculating Excess over Bliss scores. Talazoparib treatment reduced the spheroid viability of all three cell lines after 14 days (IC 50 ± SD of CH2879: 0.1 ± 0.03 µM, fold change: 220; JJ012: 12 ± 1.4 µM, fold change: 4.8; and SW1353: 1.0 ± 0.2 µM, fold change: 154), compared with 3-day treatments of mature spheroids. After 14 days of treatment, the Excess over Bliss scores for 100 µM temozolomide and talazoparib indicated synergistic efficacy (Excess over Bliss scores: CH2879 59% [lower 95% CI 52%], JJ012 18% [lower 95% CI 8%], and SW1353 55% [lower 95% CI 25%]) of this combination treatment. A stable synergistic effect of talazoparib and radiotherapy was present only in JJ012 spheroids at a 4Gƴ radiation dose (Excess over Bliss score: 22% [lower 95% CI 6%]). In our study, long-term PARP inhibition was more effective than short-term treatment, and only one of the three chondrosarcoma spheroid lines was sensitive to combined PARP inhibition and radiotherapy. These findings suggest subsequent animal studies should focus on long-term PARP inhibition, and temozolomide combined with talazoparib has a higher chance of success than combination with radiotherapy. Combination treatment of talazoparib and temozolomide was effective in reducing the viability of chondrosarcoma spheroids and spheroid growth, regardless of IDH mutation status, providing rationale to replicate this treatment combination in an animal chondrosarcoma model.

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

Poly (ADP-ribose) polymerase (PARP) inhibitors exert their efficacy via synthetic lethal effects and by inducing cGAS/STING-mediated immune responses. We demonstrate that compared to monotherapies, combined PARP inhibition and STING agonism results in increased STING pathway activation, greater cytotoxic T-cell recruitment and enhanced dendritic cell activation in BRCA1-deficient breast cancer models. The combination markedly improved anti-tumor efficacy in vivo, with evidence of complete tumor clearance, prolongation of survival and induction of immunologic memory.

A phase Ia/Ib study of talazoparib in combination with tazemetostat in metastatic castration-resistant prostate cancer (mCRPC).

TPS5098 Background: Enhancer of zeste homolog 2 (EZH2) is frequently overexpressed in metastatic castration-resistant prostate cancer (mCRPC), and is linked to lineage plasticity and therapy resistance. In pre-clinical studies, EZH2 directly regulates DNA damage repair (DDR) gene expression, and pharmacologic inhibition of EZH2 sensitizes prostate cancer cells to genotoxic stress as induced by poly-ADP ribose polymerase (PARP) inhibition. The PARP inhibitor talazoparib and EZH2 inhibitor tazemetostat are currently under study in mCRPC, and we are conducting a Phase 1 clinical trial of the combination. Methods: Phase 1a of the study will define the recommended phase 2 dose (RP2D) and Phase 1b will better assess safety and preliminary clinical activity of the combination at the RP2D. Eligible patients must have progressive disease after at least one secondary hormonal therapy and taxane-based chemotherapy (or felt not to be more appropriate for taxane), have disease evaluable for response (PSA ≥ 2 ng/ml or measurable disease by RECIST 1.1) and have a metastatic lesion amenable to biopsy adequate for next generation sequencing. In Phase 1a (n = 9-18), the starting doses are talazoparib 0.75 mg daily and tazemetostat 600 mg BID, with dose escalation/de-escalation of both agents by up to 2 dose levels [DLs] based on a 3+3 design. The RP2D is the maximum tolerated dose (MTD) or DL +2 (talazoparib 1 mg daily + tazemetostat 800 mg BID) if the MTD is not reached. After 6 patients are treated at the RP2D, phase 1b will enroll an additional 20 patients to an expansion cohort. The primary endpoint of safety and tolerability is based on incidence of dose-limiting toxicities [DLTs] and incidence and grade of adverse events [AEs] by CTCAE version 5.0. For the secondary endpoint of overall response rate (ORR; defined as PSA reduction by ≥ 50% OR radiographic response by RECIST 1.1), with a sample size of 26 (6 patients from dose escalation and 20 from expansion), we deem talazoparib+tazemetostat effective if ORR is ≥ 5/26 (19%). The probability of concluding that the treatment strategy effective is 0.11 if its true response rate is 10% and at least 0.93 if the true response rate exceeds 30%. Mandatory pre-treatment and on-treatment (8-week) biopsies will undergo targeted genetic sequencing, transcriptomic profiling, ChIP (Chromatin ImmunoPrecipitation)-seq, and immunohistochemistry (IHC) for DDR and differentiation markers; blood specimens will undergo circulating cell-free DNA and circulating tumor cell profiling – these studies will nominate possible predictive biomarkers for therapeutic response and serve as pharmacodynamic markers of combined PARP and EZH2 inhibition. The goal of this study is to expand treatment options in mCRPC through a novel approach to exploit EZH2 as a therapeutic target through co-targeting the DDR response. Enrollment began in July 2021. Clinical trial information: NCT04846478.

A phase Ia/Ib study of talazoparib in combination with tazemetostat in metastatic castration-resistant prostate cancer (mCRPC).

TPS195 Background: Enhancer of zeste homolog 2 (EZH2) is frequently overexpressed in metastatic castration-resistant prostate cancer (mCRPC), and is linked to lineage plasticity and therapy resistance. In pre-clinical studies, EZH2 directly regulates DNA damage repair (DDR) gene expression, and pharmacologic inhibition of EZH2 sensitizes prostate cancer cells to genotoxic stress as induced by poly-ADP ribose polymerase (PARP) inhibition. The PARP inhibitor talazoparib and EZH2 inhibitor tazemetostat are currently under study in mCRPC, and we are conducting a phase 1 clinical trial of the combination. Methods: Phase 1a of the study will define the recommended phase 2 dose (RP2D) and phase 1b will better assess safety and preliminary clinical activity of the combination at the RP2D. Eligible patients must have progressive disease after at least one secondary hormonal therapy and taxane-based chemotherapy (or felt not to be more appropriate for taxane), have disease evaluable for response (PSA ≥ 2 ng/ml or measurable disease by RECIST 1.1) and have a metastatic lesion amenable to biopsy adequate for next generation sequencing. In phase 1a (n=9-18), the starting doses are talazoparib 0.75 mg daily and tazemetostat 600 mg BID, with dose escalation/de-escalation of both agents by up to 2 dose levels [DLs] based on a 3+3 design. The RP2D is the maximum tolerated dose (MTD) or DL +2 (talazoparib 1 mg daily + tazemetostat 800 mg BID) if the MTD is not reached. After 6 patients are treated at the RP2D, phase 1b will enroll an additional 20 patients to an expansion cohort. The primary endpoint of safety and tolerability is based on incidence of dose-limiting toxicities [DLTs] and incidence and grade of adverse events [AEs] by CTCAE version 5.0. For the secondary endpoint of overall response rate (ORR; defined as PSA reduction by ≥ 50% OR radiographic response by RECIST 1.1), with a sample size of 26 (6 patients from dose escalation and 20 from expansion), we deem talazoparib+tazemetostat effective if ORR is ≥ 5/26 (19%). The probability of concluding that the treatment strategy effective is 0.11 if its true response rate is 10% and at least 0.93 if the true response rate exceeds 30%. Mandatory pre-treatment and on-treatment (8-week) biopsies will undergo targeted genetic sequencing, transcriptomic profiling, ChIP (Chromatin ImmunoPrecipitation)-seq, and immunohistochemistry (IHC) for DDR and differentiation markers; blood specimens will undergo circulating cell-free DNA and circulating tumor cell profiling – these studies will nominate possible predictive biomarkers for therapeutic response and serve as pharmacodynamic markers of combined PARP and EZH2 inhibition. The goal of this study is to expand treatment options in mCRPC through a novel approach to exploit EZH2 as a therapeutic target through co-targeting the DDR response. Enrollment began in July 2021. Clinical trial information: NCT04846478.

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.

Therapeutic potential of the PI3K inhibitor LY294002 and PARP inhibitor Talazoparib combination in BRCA-deficient triple negative breast cancer cells

Poly (ADP-ribose) polymerase (PARP) inhibitors provide a promising therapeutic strategy for triple-negative breast cancers (TNBCs) with BRCA1/2 mutation. However, acquire resistance mechanisms and genetic alterations limit the clinical efficacy of PARP inhibitors. The aberrant activation of phosphatidylinositol 3-kinase (PI3K) is a significant problem for cancer development and thus the inhibition of PI3K by PI3K inhibitors is a novel targeted therapy in advanced breast cancer. Here, we, for the first time, investigated that the combined inhibition of PARP by Talazoparib (TAL) and PI3K by LY294002 synergistically inhibited proliferation of BRCA1 mutant HCC1937 TNBC cells through apoptosis, G0/G1 arrest, oxidative stress and increased DNA damage compared to drug alone. Additionally, TAL and LY294002 combination could be a promising strategy for overcoming TAL resistance. Co-treatment of TAL with LY294002 considerably suppressed the activation of PI3K, Akt1 and mTOR expression and phosphorylated protein levels in TNBC cells and caused changes in the multiple kinase phosphorylation. Our findings revealed that the dual inhibition of PARP and PI3K might represent an effective therapeutic strategy for TNBC and potentially overcome TAL resistance.

Abstract PO-046: Combining PARP inhibition with radiation to sensitize homologous recombination proficient pancreatic cancer to immunotherapy

Abstract Pancreatic cancer is notoriously resistant to most cancer therapeutics including immunotherapy. We have previously shown that inhibition of the DNA damage response (DDR) enhances radiation-induced Type I interferon (T1IFN) and sensitizes pancreatic cancers to immunotherapy. In this study, we investigated the efficacy of radiation in combination with the poly (ADP-ribose) polymerase (PARP)inhibitor olaparib and programmed death ligand 1 (PD-L1) immune checkpoint blockade in otherwise resistant homologous recombination (HR) proficient pancreatic cancer. Initial studies demonstrated, in contrast to olaparib alone, that the combination of olaparib and radiation induced innate immune signaling in HR proficient pancreatic cancer cells marked by increases in pTBK1, T1IFN and pSTAT1. In animal tumor models, we found that the therapeutic efficacy of olaparib and radiation was greater in immune competent versus immune deficient hosts. In addition to the positive immune effects of olaparib and radiation, we also observed increased expression of PD-L1, a negative immune regulatory mechanism that likely restrains T1IFN-mediated innate immunity. We therefore went on to test the combined efficacy of PD-L1 blocking antibody with olaparib and radiation in syngeneic pancreatic tumor models. We found that monotherapy was ineffective in controlling tumor growth while doublet therapy with olaparib and radiation produced an intermediate tumor growth response. Importantly, maximal tumor growth inhibition was achieved following combined treatment with olaparib, radiation, and anti-PD-L1 which was significant relative to doublet therapy with olaparib-radiation or anti-PD-L1-radiation, and associated with a 20% complete response rate. Given that advances in therapy of pancreatic cancer require improvements in both local and systemic disease control, we examined the efficacy of combined therapy against tumors outside of the radiation field. In addition to the effects on tumors in the radiation field, we found that combined therapy with olaparib, radiation and anti-PD-L1 significantly delayed the growth of contralateral tumors outside of the radiation field, suggesting an adaptive immune response. Taken together, these studies illustrate the potential efficacy of combined therapy with olaparib, radiation, and anti-PD-L1 on both local and systemic pancreatic cancer and support our proposed clinical trial in patients with pancreatic cancer. Citation Format: Qiang Zhang, Long Jiang, Yawen Zheng, Theodore Lawrence, Vaibhav Sahai, Michael D. Green, Meredith Morgan. Combining PARP inhibition with radiation to sensitize homologous recombination proficient pancreatic cancer to immunotherapy [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 PO-046.

Combining PARP Inhibition with Platinum, Ruthenium or Gold Complexes for Cancer Therapy.

Platinum drugs are heavily used first‐line chemotherapeutic agents for many solid tumours and have stimulated substantial interest in the biological activity of DNA‐binding metal complexes. These complexes generate DNA lesions which trigger the activation of DNA damage response (DDR) pathways that are essential to maintain genomic integrity. Cancer cells exploit this intrinsic DNA repair network to counteract many types of chemotherapies. Now, advances in the molecular biology of cancer has paved the way for the combination of DDR inhibitors such as poly (ADP‐ribose) polymerase (PARP) inhibitors (PARPi) and agents that induce high levels of DNA replication stress or single‐strand break damage for synergistic cancer cell killing. In this review, we summarise early‐stage, preclinical and clinical findings exploring platinum and emerging ruthenium anti‐cancer complexes alongside PARPi in combination therapy for cancer and also describe emerging work on the ability of ruthenium and gold complexes to directly inhibit PARP activity.

Combined PARP Inhibition and Immune Checkpoint Therapy in Solid Tumors.

Genomic instability is a hallmark of cancer related to DNA damage response (DDR) deficiencies, offering vulnerabilities for targeted treatment. Poly (ADP-ribose) polymerase (PARP) inhibitors (PARPi) interfere with the efficient repair of DNA damage, particularly in tumors with existing defects in DNA repair, and induce synthetic lethality. PARPi are active across a range of tumor types harboring BRCA mutations and also BRCA-negative cancers, such as ovarian, breast or prostate cancers with homologous recombination deficiencies (HRD). Depending on immune contexture, immune checkpoint inhibitors (ICIs), such as anti-PD1/PD-L1 and anti-CTLA-4, elicit potent antitumor effects and have been approved in various cancers types. Although major breakthroughs have been performed with either PARPi or ICIs alone in multiple cancers, primary or acquired resistance often leads to tumor escape. PARPi-mediated unrepaired DNA damages modulate the tumor immune microenvironment by a range of molecular and cellular mechanisms, such as increasing genomic instability, immune pathway activation, and PD-L1 expression on cancer cells, which might promote responsiveness to ICIs. In this context, PARPi and ICIs represent a rational combination. In this review, we summarize the basic and translational biology supporting the combined strategy. We also detail preclinical results and early data of ongoing clinical trials indicating the synergistic effect of PARPi and ICIs. Moreover, we discuss the limitations and the future direction of the combination.

Combined PARP and ATR inhibition potentiates genome instability and cell death in ATM-deficient cancer cells

The poly (ADP-ribose) polymerase (PARP) inhibitor olaparib is FDA approved for the treatment of BRCA-mutated breast, ovarian and pancreatic cancers. Olaparib inhibits PARP1/2 enzymatic activity and traps PARP1 on DNA at single-strand breaks, leading to replication-induced DNA damage that requires BRCA1/2-dependent homologous recombination repair. Moreover, DNA damage response pathways mediated by the ataxia-telangiectasia mutated (ATM) and ataxia-telangiectasia mutated and Rad3-related (ATR) kinases are hypothesised to be important survival pathways in response to PARP-inhibitor treatment. Here, we show that olaparib combines synergistically with the ATR-inhibitor AZD6738 (ceralasertib), in vitro, leading to selective cell death in ATM-deficient cells. We observe that 24 h olaparib treatment causes cells to accumulate in G2-M of the cell cycle, however, co-administration with AZD6738 releases the olaparib-treated cells from G2 arrest. Selectively in ATM-knockout cells, we show that combined olaparib/AZD6738 treatment induces more chromosomal aberrations and achieves this at lower concentrations and earlier treatment time-points than either monotherapy. Furthermore, single-agent olaparib efficacy in vitro requires PARP inhibition throughout multiple rounds of replication. Here, we demonstrate in several ATM-deficient cell lines that the olaparib and AZD6738 combination induces cell death within 1–2 cell divisions, suggesting that combined treatment could circumvent the need for prolonged drug exposure. Finally, we demonstrate in vivo combination activity of olaparib and AZD6738 in xenograft and PDX mouse models with complete ATM loss. Collectively, these data provide a mechanistic understanding of combined PARP and ATR inhibition in ATM-deficient models, and support the clinical development of AZD6738 in combination with olaparib.

A phase Ib/II study of niraparib plus temozolomide plus atezolizumab versus atezolizumab as maintenance therapy in extensive-stage small cell lung cancer (TRIO-US L-06).

TPS9084 Background: Maintenance therapy is a promising therapeutic approach for extensive-stage small cell lung cancer (ES-SCLC), especially in light of IMpower 133 (Horn NEJM 2018). SCLC models of poly (ADP-ribose) polymerase (PARP) protein 1 and 2 inhibition suggested synergy with temozolomide (TMZ) (Wainberg AACR 2016). Combining PARP inhibition and TMZ with atezolizumab after first-line therapy for ES-SCLC may improve disease control. Methods: This is a phase 1b/2, randomized, open-label study of TMZ plus niraparib, a PARP inhibitor, with atezolizumab versus atezolizumab as maintenance therapy in adult patients with ES-SCLC after completion of platinum-based first-line chemotherapy. The primary outcome for phase 1b is the RP2D of TMZ in combination with niraparib, and for phase 2, progression-free survival (PFS). Secondary endpoints include safety, objective response rate, and overall survival. Exploratory endpoints include adverse events and patient-reported outcomes, including health-related quality of life. Phase 1b participants are required to have an advanced and incurable solid malignancy. Part one of phase 1b includes an accelerated lead-in of 12 participants treated in cohorts of 6 with an initial dose level of niraparib 200 mg po daily in 28-day cycles and low-dose TMZ 40 mg po daily on days 1-5 of each cycle. Part two includes a safety lead-in of 6 patients receiving standard-of-care atezolizumab, to which R2PD niraparib and TMZ will be added. For phase 2, participants are required to have ES-SCLC with a complete response or partial response per RECIST 1.1 following 4 to 6 cycles of platinum-based chemotherapy and ability to proceed to randomization within 7 weeks after day 1 of the last cycle of prior chemotherapy. Prophylactic WBRT is allowed prior to study. 52 participants will be stratified by a history of brain metastases and randomized 1:1 to atezolizumab with or without RP2D niraparib plus TMZ. There will be no cross-over between arms. To date, cohort 1 had two DLTs. Enrollment to dose level -1 and an intermediate dose have been completed without a DLT. The atezolizumab safety lead-in begins enrollment in March 2020. Clinical trial information: NCT03830918.

PI3K p110α inhibition sensitizes cervical cancer cells with aberrant PI3K signaling activation to PARP inhibitor BMN673.

Poly(ADP‑ribose) polymerase (PARP) inhibitors have little effect on homologous recombination repair (HRR)‑proficient tumor types, such as cervical cancer. In addition to catalytic activity, the PARP inhibitor, BMN673, traps PARP1 on damaged DNA and induces cytotoxic effects. The aim of the present study was to evaluate the therapeutic effect of PI3K inhibitors and BMN673 on cervical cancer cells. The Chou‑Talalay method was used to assess the synergistic effect of drug combinations on cervical cancer cells. The effect of PI3K inhibitors and BMN673 on cell growth and survival were also assessed via a Cell Counting Kit‑8 assay and three‑dimensional sphere culture. Cell migration and invasion were assessed via Transwell migration and Matrigel invasion assays, respectively. In addition, DNA damage and HRR competency were assessed via immunofluorescent staining analysis of γH2AX and RAD51 foci, and tail moment in a comet assay. PARP1 binding in chromatin was assessed via a cellular trapping assay. Exvivo cultured sections of patient‑derived cervical tumors were subjected to drug exposure followed by histological and immunohistochemical analyses. The results revealed that the PI3K p110α inhibitor BYL719 and the PARP inhibitor BMN673 synergized to inhibit cervical cancer cell proliferation, migration and invasion invitro and exvivo. However, the pan‑PI3K inhibitor BKM120 did not produce the aforementioned effects. Additionally, cervical cancer cells exhibiting aberrant PI3K activation were more responsive to the combined inhibition of PI3K p110α and PARP. Mechanistically, BYL719 co‑operated with BMN673 to increase PARP1 trapping on chromatin, induce severe DNA damage and exert cytotoxic effects. The combined use of BMN673 and BYL719 may serve as a promising therapeutic strategy for patients with cervical cancer exhibiting aberrant PI3K activation.

Combined PARP and Immune Checkpoint Inhibition in Ovarian Cancer

Recent studies have demonstrated that, besides direct cytotoxic effects, poly(ADP ribose) polymerase (PARP) inhibitors (PARPis) exhibit antitumor immunity that occurs in a stimulator of interferon genes (STING)-dependent manner and is augmented by immune checkpoint blockade (CPB). In ovarian cancer, combined PARP and immune checkpoint inhibition has yielded encouraging preliminary results in two early-phase clinical trials and is currently being evaluated in both first-line and recurrent settings.

Abstract 4300: Overexpression of PARP is an independent prognostic marker for poor survival in Middle Eastern breast cancer and its inhibition can be enhanced with embelin co-treatment

Abstract Patients with aggressive breast cancer (BC) subtypes usually don’t have favorable prognosis despite the improvement in treatment modalities. These cancers still remain a major cause of morbidity and mortality in females. This has fostered a major effort to discover actionable molecular targets to treat these patients. Poly ADP ribose polymerase (PARP) is one of these molecular targets that are under comprehensive investigation for treatment of such tumors. However, its role in the pathogenesis of BC from Middle Eastern ethnicity has not yet explored. Therefore, we examined the expression of PARP protein in a large cohort of over 1000 Middle Eastern BC cases by immunohistochemistry. Correlation with clinico-pathological parameters were performed. Nuclear PARP overexpression was observed in 44.7% of all BC cases and was significantly associated with aggressive clinico-pathological markers. Interestingly nuclear PARP overexpression was an independent predictor of poor prognosis. PARP overexpression was also directly associated with XIAP overexpression, with PARP and XIAP co-expression in 15.8% (159/1008) of our cases. We showed that combined inhibition of PARP by olaparib and XIAP by embelin significantly and synergistically inhibited cell growth and induced apoptosis in BC cell lines. Finally, co-treatment of olaparib and embelin regressed BC xenograft tumor growth in nude mice. Our results revealed the role of PARP in Middle Eastern BC pathogenesis and prognosis. Furthermore, our data support the potential clinical development of combined inhibition of PARP and XIAP, which eventually could extend the utility of olaparib beyond BRCA deficient cancer. Citation Format: Maqbool Ahmed, Abdul K. Siraj, Poyil Pratheeshkumar, Sandeep Parvathareddy, Sasidharan Padmaja Divya, Fouad Al-Dayel, Asma Tulbah, Dahish Ajarim, Khawla S. Al-Kuraya. Overexpression of PARP is an independent prognostic marker for poor survival in Middle Eastern breast cancer and its inhibition can be enhanced with embelin co-treatment [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2019; 2019 Mar 29-Apr 3; Atlanta, GA. Philadelphia (PA): AACR; Cancer Res 2019;79(13 Suppl):Abstract nr 4300.

Overexpression of PARP is an independent prognostic marker for poor survival in Middle Eastern breast cancer and its inhibition can be enhanced with embelin co-treatment.

Patients with aggressive breast cancer (BC) subtypes usually don’t have favorable prognosis despite the improvement in treatment modalities. These cancers still remain a major cause of morbidity and mortality in females. This has fostered a major effort to discover actionable molecular targets to treat these patients. Poly ADP ribose polymerase (PARP) is one of these molecular targets that are under comprehensive investigation for treatment of such tumors. However, its role in the pathogenesis of BC from Middle Eastern ethnicity has not yet been explored. Therefore, we examined the expression of PARP protein in a large cohort of over 1000 Middle Eastern BC cases by immunohistochemistry. Correlation with clinico-pathological parameters were performed. Nuclear PARP overexpression was observed in 44.7% of all BC cases and was significantly associated with aggressive clinico-pathological markers. Interestingly, nuclear PARP overexpression was an independent predictor of poor prognosis. PARP overexpression was also directly associated with XIAP overexpression, with PARP and XIAP co-expression in 15.8% (159/1008) of our cases. We showed that combined inhibition of PARP by olaparib and XIAP by embelin significantly and synergistically inhibited cell growth and induced apoptosis in BC cell lines. Finally, co-treatment of olaparib and embelin regressed BC xenograft tumor growth in nude mice. Our results revealed the role of PARP in Middle Eastern BC pathogenesis and prognosis. Furthermore, our data support the potential clinical development of combined inhibition of PARP and XIAP, which eventually could extend the utility of olaparib beyond BRCA deficient cancer.