Abstract 4844: Epigenetic reprogramming of the STING pathway as a combination strategy in high grade serous ovarian cancer

Abstract High-grade serous ovarian carcinoma (HGSOC), accounting for 70% of ovarian carcinoma cases, is often diagnosed at an advanced stage and associated with a poor prognosis. A significant clinical challenge is the lack of effective treatments for platinum-resistant OC and non-BRCA-mutated, homologous recombination proficient (HRP) tumors, which represent over 50% of HGSOC. Furthermore, although cancer immunotherapies can produce complete and durable responses, response rates in OC are modest with most patients experiencing only transient therapeutic benefit, underlining the urgent need for novel approaches to enhance antitumor immunity. Our prior research demonstrated that DNMT inhibitors (DNMTis) and PARP inhibitors upregulate ZNFX1, a zinc finger protein that facilitates STING-dependent interferon signaling and antitumor immune responses through a mechanism of pathogen mimicry. We hypothesize that in addition to upregulating ZNFX1 and immune responses, DNMTis restore STING through epigenetic reprogramming, leading to tumor cell intrinsic STING activation mediating anti-tumor response. In this study, we investigated the role of STING in HGSOC and the mechanisms underlying STING pathway activation by DNMTi. Analysis of the TCGA and GTEX database revealed reduced basal STING expression in HGSOC patient tumors, predominantly in TP53 mutant HGSOC. Furthermore, higher STING expression was linked to improved overall and progression free survival. Analysis of STING methylation in normal and HGSOC samples from TCGA database identified 6 hypermethylated sites near the promoter region/transcriptional start site. Our Infinium MethylationEPIC Array v2.0 BeadChip profiling of the HGSOC cell line OVCAR3 showed hypermethylation of these 6 sites. To determine whether this promoter-driven silencing could be reversed, we treated HRP and HR-deficient (HRD) HGSOC cell lines with increasing concentrations of DNMTi (0-100 nM decitabine, DAC). This treatment increased (P<0.01) STING expression in a dose-dependent manner and upregulated (P<0.001) downstream STING targets, CXCL10, TNFα, IL6. To further evaluate STING agonist could restore functional activation of STING signaling in addition to demethylation, HGSOC cells were treated with DAC (10nM), STING agonist (CRD3874; 1μM) and combination and evaluated for downstream STING targets by western and qPCR. The DAC-STING agonist combination increased pSTING1, pTBK1, and pIRF3 and apoptosis-dependent cell death. Additionally, combination treatment markedly reduced proliferation, colony and spheroid formation compared to single drug treatments. Together, these results demonstrate epigenetic regulation of STING expression in HGSOC, regardless of HRD status. Combining a DNMTi with a STING agonist has the potential to enhance the antitumor immune response and represents a promising therapeutic strategy for HGSOC patients. Citation Format: Saranya Rajendran, Elnaz Abbasi Farid, Kaushlendra Tripathi, Ishani Chattopadhayay, Shu Zhang, Stephen B. Baylin, Feyruz V. Rassool, Kenneth P. Nephew. Epigenetic reprogramming of the STING pathway as a combination strategy in high grade serous ovarian cancer [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2025; Part 1 (Regular Abstracts); 2025 Apr 25-30; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2025;85(8_Suppl_1):Abstract nr 4844.