Leveraging Vulnerabilities Induced by STING Activation in Pancreatic Cancer

PROJECT SUMMARY/ABSTRACT Stimulator of interferon genes (STING) is an emerging target for the treatment of solid tumors. Investigations of the therapeutic relevance of STING agonists have primarily focused on the immunomodulatory effects mediated by STING-activation dependent induction of type I interferons (IFN) in the tumor microenvironment.

However, how IFN signaling induced by STING agonists impacts malignant cell signaling and metabolism is poorly understood and, whether these effects can be therapeutically exploited has not been investigated. Data are presented showing that STING is highly over-expressed in pancreatic ductal adenocarcinoma (PDAC) and

that its activation in PDAC malignant cells results in impaired tumor growth in an IFN-signaling dependent manner. Thus, elucidating the consequences of STING-driven IFN signaling is particularly relevant in PDAC which is the third-leading cause of cancer-related mortality in the U.S. with an overall survival of less than one

year. Preliminary metabolomic and proteomic analyses point to two major interconnected biochemical processes impacted by IFN signaling in PDAC cells: (i) nucleotide metabolism, which is evidenced by the depletion of deoxyribonucleotide triphosphate (dNTP) and nicotinamide adenine dinucleotide (NAD) pools; and

(ii) activation of the DNA replication stress response signaling pathway mediated by Ataxia Telangiectasia and Rad3-related protein (ATR). This proposal is designed to test the hypothesis that STING-driven dNTP and NAD depletion in malignant cells result from the transcriptional upregulation of SAM domain and HD domain-

containing protein 1 (SAMHD1), a powerful dNTP phosphohydrolase, and of specific members of the poly- ADP-ribose-polymerase (PARP) family (PARP9/10/14) which increase NAD consumption, respectively. It will further test the hypothesis that malignant cells engage specific adaptive mechanisms to counteract these

metabolic alterations and that their inhibition will synergize with STING agonists. Studies in Aim 1 will investigate the consequences of STING activation in orthotopic PDAC cell line and patient-derived xenograft models from a pre-existing repository and will investigate mechanistic links between STING activation and

replication stress. Studies in Aim 2 will test rationally designed combination therapies that block two major co- dependencies elicited by STING activation in PDAC cells: (i) the ATR-regulated replication stress response and (ii) nicotinamide phosphoribosyltransferase (NAMPT)-mediated nicotinamide recycling. Studies in Aim 3

will employ immunocompetent implantation and autochthonous PDAC models to test the concept of targeting co-dependencies identified in Aims 1 and 2 in the context provided by ongoing clinical trials in which STING agonists are combined with immune checkpoint blockade. Collectively, studies proposed in this application are

designed to increase the understanding of the interplay between STING/IFN signaling, nucleotide/NAD metabolism and replication stress in PDAC with the ultimate goal of uncovering critical vulnerabilities to be exploited by new therapeutic approaches against this extremely aggressive and difficult to treat malignancy.