PARPi Triggers the STING-Dependent Immune Response and Enhances the Therapeutic Efficacy of Immune Checkpoint Blockade Independent of BRCAness

Single-Arm Phases 1 and 2 Trial of Niraparib in Combination With Pembrolizumab in Patients With Recurrent Platinum-Resistant Ovarian Carcinoma

IMPORTANCE

Patients with recurrent ovarian carcinoma frequently develop resistance to platinum-based chemotherapy, at which time treatment options become limited.

OBJECTIVE

To evaluate the poly(adenosine diphosphate-ribose) polymerase (PARP) inhibitor niraparib combined with pembrolizumab in patients with recurrent ovarian carcinoma.

DESIGN, SETTING, AND PARTICIPANTS

The TOPACIO/KEYNOTE-162 (Niraparib in Combination With Pembrolizumab in Patients With Triple-Negative Breast Cancer or Ovarian Cancer) trial, an open-label, single-arm phases 1 and 2 study enrolled women with advanced or metastatic triple-negative breast cancer (TNBC) or recurrent ovarian carcinoma, irrespective of BRCA mutation status. Median follow-up was 12.4 months (range, 1.2 to ≥23.0 months). Data were collected from April 15, 2016, through September 4, 2018, with September 4, 2018, as a data cutoff, and analyzed from September 4, 2018, through January 30, 2019.

INTERVENTIONS

The recommended phase 2 dose (RP2D) was 200 mg of oral niraparib once daily and 200 mg of intravenous pembrolizumab on day 1 of each 21-day cycle.

MAIN OUTCOMES AND MEASURES

The primary objectives of phase 1 were to evaluate dose-limiting toxic effects and establish the RP2D and dosing schedule. The primary objective of phase 2 was to assess objective response rate (ORR; complete plus partial responses). Results from the phase 1 ovarian carcinoma and TNBC cohorts and phase 2 ovarian carcinoma cohort are reported. Because of the similarity in the phase 1 and 2 ovarian carcinoma populations, the data were pooled to perform an integrated efficacy analysis.

RESULTS

Fourteen patients (9 with ovarian carcinoma and 5 with TNBC) in phase 1 and 53 patients with ovarian carcinoma in phase 2 were enrolled, for a pooled ovarian carcinoma cohort of 62 patients (median age, 60 years [range, 46-83 years]). In the integrated efficacy phases 1 and 2 ovarian carcinoma population (60 of 62 evaluable patients), ORR was 18% (90% CI, 11%-29%), with a disease control rate of 65% (90% CI, 54%-75%), including 3 (5%) with confirmed complete responses, 8 (13%) with confirmed partial responses, 28 (47%) with stable disease, and 20 (33%) with progressive disease. The ORRs were consistent across subgroups based on platinum-based chemotherapy sensitivity, previous bevacizumab treatment, or tumor BRCA or homologous recombination deficiency (HRD) biomarker status. Median duration of response was not reached (range, 4.2 to ≥14.5 months). At data cutoff, 2 patients with a response and 1 patient with stable disease continued to receive treatment.

CONCLUSIONS AND RELEVANCE

Niraparib in combination with pembrolizumab is tolerable, with promising antitumor activity for patients with ovarian carcinoma who have limited treatment options regardless of platinum status, biomarker status, or prior treatment with bevacizumab. Responses in patients without tumor BRCA mutations or non-HRD cancers were higher than expected with either agent as monotherapy.

TRIAL REGISTRATION

ClinicalTrials.gov identifier: NCT02657889.

Inhibition of ATM Increases Interferon Signaling and Sensitizes Pancreatic Cancer to Immune Checkpoint Blockade Therapy

Combinatorial strategies are needed to overcome the resistance of pancreatic cancer to immune checkpoint blockade (ICB). DNA damage activates the innate immune response and improves ICB efficacy. Because ATM is an apical kinase in the radiation-induced DNA damage response, we investigated the effects of ATM inhibition and radiation on pancreatic tumor immunogenicity. ATM was inhibited through pharmacologic and genetic strategies in human and murine pancreatic cancer models both in vitro and in vivo. Tumor immunogenicity was evaluated after ATM inhibition alone and in combination with radiation by assessing TBK1 and Type I interferon (T1IFN) signaling as well as tumor growth following PD-L1/PD-1 checkpoint inhibition. Inhibition of ATM increased tumoral T1IFN expression in a cGAS/STING-independent, but TBK1- and SRC-dependent, manner. The combination of ATM inhibition with radiation further enhanced TBK1 activity, T1IFN production, and antigen presentation. Furthermore, ATM silencing increased PD-L1 expression and increased the sensitivity of pancreatic tumors to PD-L1-blocking antibody in association with increased tumoral CD8+ T cells and established immune memory. In patient pancreatic tumors, low ATM expression inversely correlated with PD-L1 expression. Taken together, these results demonstrate that the efficacy of ICB in pancreatic cancer is enhanced by ATM inhibition and further potentiated by radiation as a function of increased tumoral immunogenicity, underscoring the potential of ATM inhibition in combination with ICB and radiation as an efficacious treatment strategy for pancreatic cancer. SIGNIFICANCE: This study demonstrates that ATM inhibition induces a T1IFN-mediated innate immune response in pancreatic cancer that is further enhanced by radiation and leads to increased sensitivity to anti-PD-L1 therapy.See related commentary by Gutiontov and Weichselbaum, p. 3815.

DNA sensing by the cGAS-STING pathway in health and disease

The detection of pathogens through nucleic acid sensors is a defining principle of innate immunity. RNA-sensing and DNA-sensing receptors sample subcellular compartments for foreign nucleic acids and, upon recognition, trigger immune signalling pathways for host defence. Over the past decade, our understanding of how the recognition of nucleic acids is coupled to immune gene expression has advanced considerably, particularly for the DNA-sensing receptor cyclic GMP-AMP synthase (cGAS) and its downstream signalling effector stimulator of interferon genes (STING), as well as the molecular components and regulation of this pathway. Moreover, the ability of self-DNA to engage cGAS has emerged as an important mechanism fuelling the development of inflammation and implicating the cGAS-STING pathway in human inflammatory diseases and cancer. This detailed mechanistic and biological understanding is paving the way for the development and clinical application of pharmacological agonists and antagonists in the treatment of chronic inflammation and cancer.

BRCA2 abrogation triggers innate immune responses potentiated by treatment with PARP inhibitors

Heterozygous germline mutations in BRCA2 predispose to breast and ovarian cancer. Contrary to non-cancerous cells, where BRCA2 deletion causes cell cycle arrest or cell death, tumors carrying BRCA2 inactivation continue to proliferate. Here we set out to investigate adaptation to loss of BRCA2 focusing on genome-wide transcriptome alterations. Human cells in which BRCA2 expression is inhibited for 4 or 28 days are subjected to RNA-seq analyses revealing a biphasic response to BRCA2 abrogation. The early, acute response consists of downregulation of genes involved in cell cycle progression, DNA replication and repair and is associated with cell cycle arrest in G1. Surprisingly, the late, chronic response consists predominantly of upregulation of interferon-stimulated genes (ISGs). Activation of the cGAS-STING-STAT pathway detected in these cells further substantiates the concept that BRCA2 abrogation triggers cell-intrinsic immune signaling. Importantly, we find that treatment with PARP inhibitors stimulates the interferon response in cells and tumors lacking BRCA2.

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.

Inflammatory signaling in genomically instable cancers

Recent studies have shown that genomic instability in tumor cells leads to activation of inflammatory signaling through the cGAS/STING pathway. In this review, we describe multiple ways by which genomic instability leads to cGAS/STING-mediated inflammatory signaling, as well as the consequences for tumor development and the tumor microenvironment. Also, we elaborate on how tumor cells have apparently evolved to escape the immune surveillance mechanisms that are triggered by cGAS/STING signaling. Finally, we describe how cGAS/STING-mediated inflammatory signaling can be therapeutically targeted to improve therapy responses.

Delivering a STINGing Blow to Small Cell Lung Cancer via Synergistic Inhibition of DNA-Damage Response and Immune-Checkpoint Pathways

Small cell lung cancer (SCLC) has demonstrated modest responses to immune-checkpoint blockade despite harboring a high mutational burden. In this issue, Sen and colleagues show remarkable synergy between inhibition of the DNA-damage response and the PD-1 axis, resulting in striking tumor regressions in SCLC mouse models.See related article by Sen et al., p. 646.

Evidence to date: talazoparib in the treatment of breast cancer

Approximately 5-10% of all patients diagnosed with breast cancer have germline BRCA1/2 mutations, which make their disease more susceptible to DNA-damaging agents and a new class of drugs known as poly(ADP-ribose) polymerase (PARP) inhibitors. Talazoparib is a new PARP inhibitor that has been recently approved for use in patients with metastatic breast cancer with germline BRCA mutations after a phase III trial showed superior progression-free survival when compared to standard chemotherapy. In this review, we analyze the development of talazoparib as well as its safety profile and the potential role of the combination therapy with standard cytotoxic drugs and with novel therapies.

PARP-1 inhibitor modulate β-catenin signaling to enhance cisplatin sensitivity in cancer cervix

Cisplatin is a keystone for treatment of both recurring and locally advanced cervical cancer. However toxic side effects and acquired resistance limits its efficacy. Enhanced DNA repair is one of the mechanisms through which cancer cells acquire cisplatin resistance. Inhibitors of PARP, which is a DNA damage repair enzyme, have been approved for use in BRCA mutated cancers like breast and ovary cancer. However little is known about the therapeutic efficacy of PARP inhibitors in cervical cancer, either as a single agent or in combination with cisplatin. We hypothesized that PARP-1 inhibition might improve the sensitivity of cervical cancer cells to cisplatin by diminishing DNA repair. To ascertain this, we determined effect of PARP-1 inhibition on cisplatin cytotoxicity in HeLa and SiHa cell lines. Combination of cisplatin with PJ34, a phenanthridinone-derived PARP-1 inhibitor, augmented cisplatin toxicity in vitro by decreasing cell proliferation, enhancing cell cycle block and cell death, and decreasing invasion and metastasis, when compared with either of the single agent alone. We further show that PARP-1 inhibition inhibited β-catenin signaling and its downstream components such as c-Myc, cyclin D1 and MMPs indicating a possible link between single strand base damage repair and WNT signaling. In conclusion, PARP-1 inhibition might augment cisplatin cytotoxicity in cervical cancer cells by modulating β-catenin signaling pathway. Combining PARP-1 inhibitors with cisplatin might be a promising approach to overcome cisplatin resistance and to achieve a better therapeutic effect.

DNA Repair Deficiency in Breast Cancer: Opportunities for Immunotherapy

Historically the development of anticancer treatments has been focused on their effect on tumor cells alone. However, newer treatments have shifted attention to targets on immune cells, resulting in dramatic responses. The effect of DNA repair deficiency on the microenvironment remains an area of key interest. Moreover, established therapies such as DNA damaging treatments such as chemotherapy and PARP inhibitors further modify the tumor microenvironment. Here we describe DNA repair pathways in breast cancer and activation of innate immune pathways in DNA repair deficiency, in particular, the STING (STimulator of INterferon Genes) pathway. Breast tumors with DNA repair deficiency are associated with upregulation of immune checkpoints including PD-L1 (Programmed Death Ligand-1) and may represent a target population for single agent or combination immunotherapy treatment.

Poly-ADP-ribose polymerase inhibitor use in ovarian cancer: expanding indications and novel combination strategies

The use of poly(ADP-ribose) polymerase (PARP) inhibition is transforming care for the treatment of ovarian cancer, with three different PARP inhibitors (PARPi) gaining US Food and Drug Administration approval since 2014. Given the rapidly expanding use of PARPi, this review aims to summarize the key evidence for their use and therapeutic indications. Furthermore, we provide an overview of the development of PARPi resistance and the emerging role of PARPi combination therapies, including those with anti-angiogenic and immunotherapeutic agents.

Adaptive responses in a PARP inhibitor window of opportunity trial illustrate limited functional interlesional heterogeneity and potential combination therapy options

Poly (ADP-ribose) polymerase inhibitor (PARPi)-based combination therapies are demonstrating efficacy in patients, however, identifying the right combination for the right patient remains a critical challenge. Thus, it is urgent to develop approaches able to identify patients likely to benefit from specific combination therapies. Several groups, including ours, have demonstrated that targeting adaptive responses induced by PARPi increases depth and duration of response. In this study, we instituted a talazoparib (PARPi) monotherapy window of opportunity trial to identify informative adaptive responses in high grade serous ovarian cancer patients (HGSOC). Patients were treated for 7 to 14 days with PARPi monotherapy prior to surgery with tissue samples from multiple sites being collected pre- and post-treatment in each patient. Analysis of these samples demonstrated that individual patients displayed different adaptive responses with limited interlesional heterogeneity. Ability of combination therapies designed to interdict adaptive responses to decrease viability was validated using model systems. Thus, assessment of adaptive responses to PARPi provides an opportunity for patient-specific selection of combination therapies designed to interdict patient-specific adaptive responses to maximize patient benefit.

The DNA Damaging Revolution: PARP Inhibitors and Beyond

Cancer-specific DNA repair defects are abundant in malignant tissue and present an opportunity to capitalize on these aberrations for therapeutic benefit. Early preclinical data demonstrated the concept of synthetic lethality between BRCA genetic defects and pharmacologic PARP inhibition, suggesting that there may be monotherapy activity with this class of agents and supporting the early trial testing of this molecularly driven approach. Although the first foray into the clinic for PARP inhibitors was in combination with DNA-damaging cytotoxic agents, clinical development was limited by the more-than-additive toxicity, in particular dose-limiting myelosuppression. As more tolerable single agents, PARP inhibitors are now approved for the treatment of ovarian cancer in different settings and BRCA-mutant breast cancers. Beyond PARP inhibitors, there is now a large armamentarium of potent and relatively selective inhibitors in clinical trial testing against key targets involved in the DNA damage response (DDR), including ATR, ATM, CHK1/2, WEE1, and DNA-PK. These agents are being developed for patients with molecularly selected tumors and in rational combinations with other molecularly targeted agents and immune checkpoint inhibitors. We detail the clinical progress made in the development of PARP inhibitors, review rational combinations, and discuss the development of emerging inhibitors against novel DDR targets, including DNA repair proteins, DNA damage signaling, and DNA metabolism.

PARP Inhibitor Efficacy Depends on CD8+ T-cell Recruitment via Intratumoral STING Pathway Activation in BRCA-Deficient Models of Triple-Negative Breast Cancer

Combinatorial clinical trials of PARP inhibitors with immunotherapies are ongoing, yet the immunomodulatory effects of PARP inhibition have been incompletely studied. Here, we sought to dissect the mechanisms underlying PARP inhibitor-induced changes in the tumor microenvironment of BRCA1-deficient triple-negative breast cancer (TNBC). We demonstrate that the PARP inhibitor olaparib induces CD8⁺ T-cell infiltration and activation in vivo, and that CD8⁺ T-cell depletion severely compromises antitumor efficacy. Olaparib-induced T-cell recruitment is mediated through activation of the cGAS/STING pathway in tumor cells with paracrine activation of dendritic cells and is more pronounced in HR-deficient compared with HR-proficient TNBC cells and in vivo models. CRISPR-mediated knockout of STING in cancer cells prevents proinflammatory signaling and is sufficient to abolish olaparib-induced T-cell infiltration in vivo. These findings elucidate an additional mechanism of action of PARP inhibitors and provide a rationale for combining PARP inhibition with immunotherapies for the treatment of TNBC. SIGNIFICANCE: This work demonstrates cross-talk between PARP inhibition and the tumor microenvironment related to STING/TBK1/IRF3 pathway activation in cancer cells that governs CD8⁺ T-cell recruitment and antitumor efficacy. The data provide insight into the mechanism of action of PARP inhibitors in BRCA-associated breast cancer.This article is highlighted in the In This Issue feature, p. 681.

Exploiting DNA Replication Stress for Cancer Treatment

Complete and accurate DNA replication is fundamental to cellular proliferation and genome stability. Obstacles that delay, prevent, or terminate DNA replication cause the phenomena termed DNA replication stress. Cancer cells exhibit chronic replication stress due to the loss of proteins that protect or repair stressed replication forks and due to the continuous proliferative signaling, providing an exploitable therapeutic vulnerability in tumors. Here, we outline current and pending therapeutic approaches leveraging tumor-specific replication stress as a target, in addition to the challenges associated with such therapies. We discuss how replication stress modulates the cell-intrinsic innate immune response and highlight the integration of replication stress with immunotherapies. Together, exploiting replication stress for cancer treatment seems to be a promising strategy as it provides a selective means of eliminating tumors, and with continuous advances in our knowledge of the replication stress response and lessons learned from current therapies in use, we are moving toward honing the potential of targeting replication stress in the clinic.

Beyond DNA repair: the novel immunological potential of PARP inhibitors

Loss of excision repair cross-complementation group 1 (ERCC1), frequently found in lung cancer, and mutations in breast cancer type 1/2 susceptibility genes (BRCA1/2), often found in ovarian, breast and prostate cancers, confer sensitivity to poly-(ADP-ribose) polymerase inhibitors (PARPi). Our work, and that of others, shows that PARPi selectively trigger tumor cell-autonomous immune phenotypes in ERCC1- or BRCA-defective contexts. This suggests that PARPi, used in appropriately selected populations, might mediate their therapeutic effects by potentiating anti-tumor immunity.

Using Reverse Phase Protein Array (RPPA) to Identify and Target Adaptive Resistance

Tumor cells and the tumor ecosystem rapidly evolve in response to therapy. This tumor evolution results in the rapid emergence of drug resistance that limits the magnitude and duration of response to therapy including chemotherapy, targeted therapy, and immunotherapy. Thus, there is an urgent need to understand and interdict tumor evolution to improve patient benefit to therapy. Reverse phase protein array (RPPA) provides a powerful tool to evaluate and develop approaches to target the processes underlying one form of tumor evolution: adaptive evolution. Tumor cells and the tumor microenvironment rapidly evolve through rewiring of protein networks to bypass the effects of therapy. In this review, we present the concepts underlying adaptive resistance and use of RPPA in understanding resistance mechanisms and identification of effective drug combinations. We further demonstrate that this novel information is resulting in biomarker-driven trials aimed at targeting adaptive resistance and improving patient outcomes.