Restoring anti-tumor immunity in chromosomally unstable tumors

Chromosomal instability (CIN)—the frequent missegregation of chromosomes during mitosis—is a genomic hallmark of solid tumors and correlates with immune evasion and resistance to immunotherapies, but underlying mechanisms are poorly understood. CIN leads to release of DNA into the cytosol where it triggers the cGASSTING pathway. While activation of this axis usually results in the expression of type I interferons (I-IFNs), potent immune stimulatory cytokines, we find that in CIN-driven cancers the opposite occurs: CIN-mediated tonic cGASSTING activation suppresses I-IFN production. Understanding and targeting mechanisms underlying this observation may restore immune-mediated elimination of multiple common cancers. We generated rigorous preliminary data, including analyses of human genomic data and tissue samples, a series of sufficiency and necessity experiments, and several in vivo studies across multiple cancers, leading us to the following hypothesis: CIN-induced tonic cGAS-STING signaling drives immune escape through STING depletion resulting in interferon tachyphylaxis, and relief of this tonic signal through cGAS inhibition restores immunogenicity and sensitizes various cancer types to immunotherapies. In further preliminary studies we show that genetic deletion of CGAS restores I-IFN expression in human and mouse models and sensitizes otherwise resistant tumors to either STING-agonist or anti-PD1 therapies in vivo. Using cutting-edge structure-activity-relationship (SAR) analyses, we designed and synthesized putative small molecule cGAS inhibitors. One of these, compound 1 (C1), shows potent (EC50=1.44 nM), durable, and human selective cGAS-inhibitory activity, and favorable in vivo pharmacokinetics without apparent toxicities. In Aim 1, we will perform critical epistasis experiments, elucidate mechanisms of STING depletion and interferon tachyphylaxis, and determine the generalizability of the proposed mechanism(s) using pan-cancer analyses in existing data bases. In Aim 2, we will use human and new murine models with chimeric expression of functional human CGAS and use novel CRISPR-dependent base editing tools to identify precisely map cGAS residues needed for restoring immunogenic output, and to determine which residues are required for C111 activity. In Aim 3, we will use a parallel genetic and pharmacological strategy to test whether catalytic disruption of cGAS sensitizes CIN-driven cancers to individual or combination immunotherapies. We will also dissect changes in the tumor-microenvironment resulting from cGAS inhibition. Completion of this work will resolve a long-standing paradox in cancer immunobiology, provide key mechanistic insights into cancer immune evasion, and offer the rationale and preclinical foundation for developing novel, first-in-class cancer therapies targeting cGAS, suitable for future clinical translation. By informing both fundamental biology of cancer and therapeutic advances, this work will have an important impact. Vertebrate animals are used to study the complex tumor-immune interactions that are difficult to model otherwise. Project Number: 1R01CA312637-01 | Fiscal Year: 2026 | NIH Institute/Center: National Cancer Institute (NCI) | Principal Investigator: Benjamin Izar | Institution: COLUMBIA UNIVERSITY HEALTH SCIENCES, NEW YORK, NY | Award Amount: $681,818 | Activity Code: R01 | Study Section: Mechanisms of Cancer Therapeutics B Study Section[MCTB] View on NIH RePORTER: https://reporter.nih.gov/project-details/11361797