Abstract B065: Polymerase theta inhibition activates the cGAS-STING signaling pathway and elicits an immune response in homologous recombination-deficient pancreatic adenocarcinoma

Abstract

Pancreatic ductal adenocarcinoma (PDAC) is a highly lethal malignancy that harbors mutations in homologous recombination (HR) repair genes in up to 25% of cases. Defects in HR impart to tumor cells a specific vulnerability to poly-ADP ribose polymerase inhibitors and platinum-based chemotherapy. However, not all patients respond, and some who initially respond develop resistance and progress. Thus, new therapies that are effective against HR-deficient PDAC are needed. Here, we show that inactivation of the HR pathway in PDAC is associated with overexpression of polymerase theta (Polθ, or POLQ), a key enzyme that regulates the alternative non-homologous end-joining (alt-NHEJ) pathway of double-strand break (DSB) DNA repair. Using both human and murine HR-deficient PDAC models, we find that POLQ knockdown is synthetically lethal with mutations in HR genes (BRCA1, BRCA2, and PALB2) as well as the DNA damage repair gene ATM. Further, we present the first findings that POLQ knockdown enhances cytosolic micronucleus formation and activates cyclic GMP-AMP synthase (cGAS)-stimulator of interferon genes (STING) signaling. In an in vivo murine model, POLQ inhibition also leads to STING-dependent recruitment of immune cells and enhanced CD8+ T cell infiltration in the BRCA2-deficient tumor microenvironment (TME). Through its role in the alt-NHEJ pathway, we thus find that POLQ is critical for DSB repair in HR-deficient PDAC, and its inhibition presents a novel synthetic lethal approach to suppress tumor growth while simultaneously stimulating an immune response in the PDAC TME. Citation Format: Grace Oh, Annie Wang, Lidong Wang, Jiufeng Li, Gregor Werba, Daniel Weissinger, Ende Zhao, Surajit Dhara, Rosmel Hernandez, Amanda Ackermann, Despoina Kalfakakou, Emily A. Kawaler, Talia Golan, Theodore H. Welling, Agnel Sfeir, Diane M. Simeone. Polymerase theta inhibition activates the cGAS-STING signaling pathway and elicits an immune response in homologous recombination-deficient pancreatic adenocarcinoma [abstract]. In: Proceedings of the AACR Special Conference on Pancreatic Cancer; 2022 Sep 13-16; Boston, MA. Philadelphia (PA): AACR; Cancer Res 2022;82(22 Suppl):Abstract nr B065.

When DNA-damage responses meet innate and adaptive immunity

“…BRCA2 deficiency induces a high frequency of stalled DNA replication forks that enhance the number of cGAS-positive micronuclei, consequently provoking a cascade of inflammatory cytokine expression [103]. Similar results have been found in DNA polymerase θ (POLQ) knockdown BRCA2-deficient pancreatic ductal adenocarcinoma cells [104]. However, the latest solid research has indicated that the chromatin bridges serve as the direct and strong stimulators of cGAS rather than micronuclei [105].…”

Polymerase θ inhibition steps on the cGAS pedal

“…These two recent studies demonstrate that, in certain HR-deficient settings, Pol θ inhibition has a substantial impact on immune activation through stimulation of the cGAS/STING pathway (14,16). HR-deficient PDAC models, relative to PDAC models that lacked HR-associated gene mutations.…”

“…In the current issue of the JCI, Oh and Wang, et al report findings that reveal the impact of Pol θ inhibition on immune activation (Figure 1) (14). Their study focuses on pancreatic ductal adenocarcinoma (PDAC), motivated by the observations that nearly a quarter of PDAC cases are associated with HR-associated gene alterations and that POLQ overexpression correlates with worse prognosis in two independent cohorts of PDAC patients.…”

“…While BRCA2-deficient tumors seem to be most consistently sensitive to Pol θ inhibition, it's not currently clear whether all BRCA1-deficient tumors will be Pol θ dependent, and even less is known about tumors with mutations in other synthetically lethal gene targets such as PALB2, ATM, or others (17). While Oh and Wang, et al provided evidence that Pol θ inhibition in ATM-mutant PDAC stimulates cGAS/STING activity, in vivo tumor growth effects were not evaluated (14).…”

“…Another important and unresolved question is whether all Pol θ inhibitors will exhibit similar biological effects. Both studies used the same two Pol θ inhibitors in their experiments (14,16). ART558 is a recently identified allosteric Pol θ inhibitor (13,18).…”