Abstract LB421: Targeting STAT3 in combination with epigenetic therapy induces tumor suppressive IL-24 in non-small cell lung cancer

Abstract Non-small cell lung cancer (NSCLC) is the leading cause of cancer-related deaths worldwide, with 5-year survival rates of less than 30%. Therefore, there is a critical need for novel combinatorial strategies to enhance the efficacy of current approaches. A current approach for the treatment of advanced NSCLC was developed in our lab and others utilizing DNA methyltransferase inhibition (DNMTi) paired with histone deacetylase inhibition (HDACi) to sensitize patients to immunotherapy. However, most patients do not benefit durably from epigenetic therapy alone or in combination with other treatments. We and others have shown that STAT3 activation is increased after epigenetic therapy. Because persistent STAT3 signaling is associated with poor prognosis and promotes cancer cell survival in multiple cancer types, including NSCLC, we treated a panel of 19 human NSCLC cell lines with the STAT3 inhibitor, C188-9, and epigenetic therapy and identified 12 cell lines demonstrating a synergistic reduction in cancer cell proliferation. We further demonstrated a durable reduction in anchorage-dependent and -independent colony formation two weeks post-treatment with STAT3i+epigenetic therapy. Interestingly, cell lines with Ras and KRAS+STK11 mutations were positively associated with response. In addition to phenotypic characterization, we defined the transcriptome consequences of our novel therapeutic paradigm by RNA sequencing. These data showed that STAT3i+epigenetic therapy suppressed cell cycle and activated apoptotic pathways, which we further validated by immunoblotting and flow cytometry. Notably, we observed significant perturbation of gene sets involved in key bioenergetic pathways, namely oxidative phosphorylation, glycolysis, and glutamine metabolism. When considered as a whole, these pathway-level data indicated that glutamine metabolism might be significantly perturbed, and so exogenous glutamine might be conditionally essential in combination-treated cells. Utilizing a glutaminase inhibitor, we confirmed sensitization to glutamate reduction in STAT3i+epigenetic therapy treated cells. Additionally, we observed significant induction of IL-24 in STAT3i-treated groups, with the highest induction (>2000 fold) in the STAT3i+epigenetic therapy group. IL-24, silenced in most cancer cells, is a tumor-suppressive cytokine shown to induce cancer cell death, cancer stem cell differentiation, and sensitization to cytotoxic therapies. Therefore, we hypothesized that the anti-cancer effects of STAT3i+epigenetic therapy are mediated through IL-24 induction. To test this hypothesis, we treated NSCLC cells with exogenous IL-24 and confirmed epigenetic therapy-induced sensitization to IL-24. In summary, we define STAT3 as an actionable target that synergizes with epigenetic therapy to diminish the ability of NSCLC cells to proliferate and survive in anchorage-dependent and -independent conditions, associated with significant induction of IL-24. Citation Format: Julia An, Calvin Chen, Ying-Yu Chen, Jina Park, Stephen Baylin, Michael Topper. Targeting STAT3 in combination with epigenetic therapy induces tumor suppressive IL-24 in non-small cell lung cancer [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2025; Part 2 (Late-Breaking, Clinical Trial, and Invited Abstracts); 2025 Apr 25-30; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2025;85(8_Suppl_2):Abstract nr LB421.