Abstract 2712: Therapy-induced senescence promotes tumor immunosuppression in cholangiocarcinoma

Abstract Background and Aims: Senescent cells are characterized by high expression of markers including p16INK4A, p21cip1, and production of a senescence-associated secretory phenotype (SASP). Therapy-induced senescence can be triggered by cytotoxic drugs and can promote resistance to further chemotherapy and immunotherapy. Cholangiocarcinoma (CCA) is a highly lethal tumor with an abundance of immunosuppressive cells such as myeloid-derived suppressor cells (MDSCs). We have demonstrated that cancer cells can leverage noncanonical proapoptotic tumor necrosis factor-related apoptosis-inducing ligand (TRAIL) signaling to foster MDSC accumulation in murine CCA (PMID: 38219900). We hypothesize that senescent cancer cells may be an important source of TRAIL. In this study, we aim to dissect the effects of TIS on CCA tumor growth and the tumor immune microenvironment (TIME). Methods: Sequential immunofluorescence (IF) was conducted on resected human CCA specimens. Using murine models of CCA (PMID: 29464042; 38458319), murine CCA cells (SB cells) were implanted into livers of WT C57BL/6J male mice. Mice were treated for two weeks with the potent senescence inducers, alisertib, etoposide, or doxorubicin. Mice were sacrificed and tumor and TIME characterization were conducted. In vitro functional studies employed murine bone marrow (BM)-derived MDSCs treated with conditioned medium (CM) from proliferating or senescent. murine (SB) cells, then co-cultured with CD8 T cells isolated from murine splenocytes. Results: Using IF, we demonstrated the majority of p16+ and p21+ senescent cells in human CCA are cancer cells, rather than stromal cells. Both p16+ and p21+ cancer cells were increased in tumors from patients who have undergone cytotoxic therapy with gemcitabine/cisplatin (Gem/Cis). In vivo senescence induction led to an increase in MDSC abundance and reduced cytotoxic T lymphocyte infiltration in mice. Incubation of BM-MDSCs with CM from senescent cancer cells enhanced MDSC viability and suppressive function. scRNA seq data demonstrated that TRAIL+ human CCA cells have higher expression of a senescence signature compared to TRAIL- cells. Senescence inducing therapy also significantly increased Trail expression in murine tumors in vivo. Mechanistically, incubation of BM-MDSCs with senescent murine CCA cells with deletion of Trail significantly decreased MDSC viability. Conclusion: we have demonstrated that senescent cancer cells accumulate in tumors from patients treated with standard-of-care therapy with Gem/Cis. Senescent cancer cells enhance the abundance and suppressive function of MDSCs via TRAIL. Thus, senolysis has the potential to rewire the TIME, and augment response to systemic therapy. Citation Format: Binbin Li, Meina Cai, Jingchun Yang, Sumera Ilyas. Therapy-induced senescence promotes tumor immunosuppression in cholangiocarcinoma [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 2712.