Abstract 3102: Spliceosome perturbation enhances immunotherapy in SCLC by triggering ZBP1-driven necroptosis in cancer-associated fibroblasts

Abstract Small cell lung cancer (SCLC) is the most lethal form of lung cancer with a 5-year overall survival of 5%. Despite advancements in immunotherapy, SCLC is characterized by an immunologically ‘cold’ tumor microenvironment (TME) and the majority of SCLC patients remain unresponsive to these treatment strategies. This combination of poor survival outcomes and limited therapeutic options underscores the critical urgency of identifying innovative strategies to treat SCLC. A potential approach to activate an innate immune response within tumors is by promoting the accumulation of endogenous "virus-like" nucleic acids in cancer cells, thereby initiating an antiviral response, concept known as ‘viral mimicry’. Here, we demonstrated that targeting the spliceosome component SF3B1 is an effective strategy to induce viral mimicry not only in cancer cells but also in cells from the TME, including cancer associated fibroblasts (CAFs). SF3B1 inhibition induced the formation of Z-form RNAs (Z-RNAs), which are unique, left-handed dsRNA species and necroptosis-activating ligands for Z-DNA binding protein 1 (ZBP1). Notably, we found that SF3B1 inhibition triggered ZBP1-dependent necroptosis, a highly immunogenic cell-death, through the RIPK3- ZBP1-MLKL axis in necroptosis-competent cancer cells and patient-derived CAFs. In vivo, SF3B1 inhibition promoted a decreased tumorigenicity and increased immunogenicity, as well as ZBP1-driven necroptosis in CAFs, enhancing response to immune checkpoint blockade (ICB). These findings have significant implications for inducing viral mimicry in immunologically "cold" tumors. Since SF3B1 inhibition can trigger necroptosis by targeting any necroptosis-competent cell, including CAFs within the TME, our results suggest that this approach could create a more immunogenic TME in all SCLC patients, regardless of whether their tumor cells have impaired necroptosis signaling. Thus, SF3B1 inhibitors and potentially other spliceosome-targeted therapies represent a promising strategy with exceptional translational potential for inducing necroptosis and enhancing ICB responsiveness in aggressive “cold” tumors, such as SCLC. Citation Format: Xinpei Jiang, Xueying Ma, Yunyun Zhou, Siddharth Balachandran, Israel Cañadas. Spliceosome perturbation enhances immunotherapy in SCLC by triggering ZBP1-driven necroptosis in cancer-associated fibroblasts [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 3102.