Abstract 6404: NOTCH1 drives immunogenicity through STING and improves survival with immune checkpoint blockade in small cell lung cancer

Abstract Immune checkpoint blockade (ICB) combined with chemotherapy as a first-line treatment for extensive-stage small-cell lung cancer (ES-SCLC) has shown modest survival benefits. While a subset of patients with immune-inflamed tumors respond to ICB, the mechanisms underlying these responses and the lack of predictive biomarkers in clinical practice remain challenges. In this work, we identify high NOTCH1 expression as a key predictor of overall survival (OS) in patients treated with atezolizumab (atezo) plus chemotherapy in both ASCL1-enriched (HR 0.39, P=0.0012) and NEUROD1-enriched (HR 0.44, P=0.024) subsets. Expression of other major NOTCH signaling genes, including NOTCH2, REST, and HES1 showed no association with OS. Using in vitro models, we demonstrate that NOTCH1 upregulates MHC Class I expression and antigen presentation machinery (APM) genes, while REST is not required for these effects. Mechanistically, NOTCH1 promotes epithelial-mesenchymal transition (EMT) and epigenetically enhances STING1 expression by modulating H3K27ac occupancy at the 5’ end of the STING1 locus. Knockout of STING1 in NOTCH1-active cells partially diminishes APM gene expression and HLA-B levels, indicating that STING is critical for NOTCH1-driven immune activation. Concordantly, STING1, AXL expression, and APM signature are enriched in NOTCH1 high compared to low NOTCH1 expressing tumors in IMpower133, validating our proposed mechanisms. Furthermore, using syngeneic mouse models, we show that NOTCH1 activation converts SCLC tumors from immune-excluded to highly inflamed enabling CD8+ T cell-mediated complete tumor regression. Notch1 knockout cells exhibit reduced tumor-intrinsic surface MHC Class I expression, diminished EMT features, and decreased STING expression accompanied by tumor-extrinsic depletion of both total and activated CD8+ T cells, highlighting NOTCH1 as a key driver of tumor immunogenicity. Combining a STING agonist (MSA-2) with ICB results in complete and durable tumor regression specifically in NOTCH1-active tumors. Immunohistochemical analyses demonstrate active NOTCH1 signaling in approximately 30% of SCLC tumors, underscoring its relevance for patient stratification. In conclusion, our results suggest NOTCH1 as a predictive biomarker for ICB and a therapeutic target to enhance anti-tumor immune responses in SCLC and related neuroendocrine cancers in which NOTCH1 is typically suppressed. Citation Format: Yoo Sun Kim, Barzin Y. Nabet, Briana N. Cortez, Nai-Yun Sun, Robin Sebastian, Christophe E. Redon, Anagh Ray, Sivasish Sindiri, Min-Jung Lee, Shraddha Rastogi, Nahoko Sato, Jane Trepel, Noemi Kedei, Thorkell Andresson, Sudipto Das, Suresh Kumar, Alan E. Bers, Hongliang Zhang, Alberto Chiappori, Priyanka Gopal, Mohamed E. Abazeed, Haobin Chen, Mirit I. Aladjem, Yves Pommier, Moises J. Velez, David S. Shames, Nitin Roper. NOTCH1 drives immunogenicity through STING and improves survival with immune checkpoint blockade in small cell lung 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 6404.