Abstract 2599: Trastuzumab deruxtecan reprograms immune response by stimulating cGAS-STING pathway in gastric cancer cells

Abstract Background: The combination approach of antibody-drug conjugates and immune checkpoint inhibitors (ICIs) is being tested to enhance efficacy and overcome resistance in solid tumors. Although trastuzumab deruxtecan (T-DXd) is approved in HER2-positive gastric cancer (GC), its impact on the GC immune microenvironment remains elusive. This study explores how T-DXd modulates the immune response, providing essential insights on the development of T-DXd and immunotherapy combinations. Methods: Comet assays and immunofluorescence assessed DNA damage. RNA-seq delineated the impact of T-DXd on GC cells (NCI-N87 and SNU-484). In vivo complex of enzyme assays and immunostaining of topoisomerase 1-DNA covalent cleavage complex (TOP1cc) were used to determine the action mechanism of T-DXd. RT-qPCR, and ELISA measured cGAS-STING cytosolic dsDNA sensing pathway activation. Further validation included cGAS knockdown and 2’3’-cGAMP addition to confirm the role of cGAS in T-DXd-induced promotion of inflammatory response. In coculture experiments, we utilized THP-1-derived dendritic cells (TDDCs) and PBMCs from healthy donors to prove the effect of T-DXd on immune cells. FACS analyses probed the activation markers of TDDCs and CD8+ T cells. Results: T-DXd-induced DNA damage upregulated PD-L1 expression in GC cells in an IRF1-dependent manner. RNA-seq revealed gene signatures associated with increased antitumor immune response, including proinflammatory response and type-I IFN, following T-DXd treatment. Mechanistically, T-DXd co-localized TOP1cc with γ-H2AX-positive micronuclei, activating the cGAS-STING pathway and triggering a robust IFN-I response. Knockdown of cGAS in cancer cells abolished the T-DXd-induced IFN-I response. T-DXd enhanced HLA-DR and CD86 expression in TDDCs, particularly when cocultured with GC cells. The physical interaction between cancer cells and TDDCs, along with the presence of cGAS in cancer cells, was found to be essential for the upregulation of dendritic cell (DC) activation marker by T-DXd. Furthermore, T-DXd elevated CD69, Granzyme B, and IFNG expression in CD8+ T cells exclusively under coculture setting with NCI-N87. Conclusion: T-DXd exerts immunostimulatory effects in GC cells through the activation of the cGAS-STING pathway, leading to a reprogramming of DC and CD8+ T cell phenotypes. This provides a molecular rationale for combining T-DXd with ICIs for the treatment of patients with HER2-positive tumors. Citation Format: Kyoung-Seok Oh, Ah-Rong Nam, Ju-Hee Bang, Yoojin Jeong, Sea Young Choo, Hyo Jung Kim, Su In Lee, Jae-Min Kim, Jeesun Yoon, Tae-Yong Kim, Do-Youn Oh. Trastuzumab deruxtecan reprograms immune response by stimulating cGAS-STING pathway in gastric cancer cells abstract. In: Proceedings of the American Association for Cancer Research Annual Meeting 2024; Part 1 (Regular Abstracts) ; 2024 Apr 5-10; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2024;84 (6Suppl): Abstract nr 2599.