Abstract A010: Epigenetic priming restores tumor-intrinsic cGAS–STING competence in glioblastoma and enables immunogenic DNA damage responses

Abstract The cGAS–STING pathway is a key component of innate antitumor immunity. Cytosolic double-stranded DNA is sensed by cGAS to generate cGAMP, the endogenous substrate for STING, whose activation primes type 1 interferon responses. DNA damage induced by genotoxic therapies should, in principle, activate cGAS-STING signaling. However, glioblastoma (GBM) tumors fail to mount this intrinsic immune response. We have previously shown that STING is epigenetically silenced by promoter methylation in GBM, and that this methylation can be reversed by treatment with the DNA methyltransferase inhibitor decitabine. Here, we hypothesize that epigenetic priming will restore the cGAS-STING pathway and sensitize GBM to STING agonists and therapy-induced DNA damage. We first profiled cGAS and STING expression in GBM tissues using multiplex imaging and found that tumor cells express detectable cGAS but not STING. Treatment of GBM cell lines with decitabine successfully restored STING expression, but robust stimulation of interferon-stimulated genes required the combination of decitabine and the endogenous STING agonist cGAMP. Genetic deletion of STING abrogated this effect, confirming pathway specificity. We next examined whether decitabine-induced STING reconstitution sensitizes GBM to temozolomide-induced DNA damage. Although temozolomide induced DNA damage, it failed to generate cytosolic DNA substrates capable of activating cGAS, as evidenced by minimal cGAS–DNA colocalization, lack of micronuclei formation, and absence of interferon signaling following temozolomide and decitabine co-treatment. Collectively, these data demonstrate that epigenetic reprogramming restores tumor-intrinsic STING competence in GBM and enables potent responses to STING agonists, but that temozolomide-induced DNA damage is insufficient to engage this pathway. These findings define mechanistic constraints on immunogenic DNA damage in GBM and support rational combinations of epigenetic priming with STING-activating therapies, while motivating evaluation of alternative genotoxic modalities such as radiation therapy or tumor-treating fields. Citation Format: Sebastian Ouyang, Virginia Wertman, Michelle Bowie, Matthew Waitkus, Giselle López, Justin Low, David Ashley. Epigenetic priming restores tumor-intrinsic cGAS–STING competence in glioblastoma and enables immunogenic DNA damage responses [abstract]. In: Proceedings of the AACR Special Conference in Cancer Research: Brain Cancer; 2026 Mar 23-25; Philadelphia, PA. Philadelphia (PA): AACR; Cancer Res 2026;86(6_Suppl):Abstract nr A010.