Abstract 6641: Improving response to bladder-sparing therapies by combining radiotherapy to immuno-potentiating agents in immunologically cold models of bladder cancer

Abstract INTRODUCTION: Radiation therapy (RT) is a promising approach for bladder-sparing in muscle-invasive bladder cancer (MIBC). Despite its efficacy, 30% of patients develop radioresistant tumors necessitating salvage surgery. Combining RT with immune checkpoint inhibitor was reported to have synergic effects on anti-tumor immunity. In addition, activation of the STING pathway induces cell death, cancer cell antigens release and presentation, and promote T cells trafficking into tumors. Previous in vivo results from our team using the immunologically ‘hot’ murine tumor model MB49 demonstrated significant improvement of survival and immune cell infiltration upon STING agonist treatment, when combined with RT and anti-PDL1 treatment. Oppositely, treating the ‘cold’ tumor model UPPL with a combination of RT and anti-PDL1 treatment did not improve survival compared to RT alone. Consistently, UPPL tumors present low T cell and high neutrophil infiltration in vivo. Thus, the main objective of the present study is to evaluate whether combining RT, anti-PDL-1 and STING agonist treatments can improve the immunogenicity of UPPL tumors. METHODS: Male C57BL/6 mice were subcutaneously injected with 5. 106 UPPL cells then randomized into various treatment combinations of RT, anti-PDL-1 and STING agonist. Midpoint and endpoint tumors were harvested for flow cytometry and IHC and stools for 16S-sequencing. RESULTS: We report that RT-combined treatments delayed tumor growth and prolonged survival in vivo. Neighborhood analyses in tissue revealed that response to RT combinations associated with increased macrophages density in the vicinity of infiltrating CD8+ T cells and with gut enrichment in Faecalibaculum, Bifidobacterium, and Candidatus arthomitus. Network analyses showed strong positive correlations between pro-tumor neutrophil recruitment and beneficial gut microbes in non-responders. Network analyses revealed positive correlations between pro-tumor neutrophil recruitment and dysbiotic gut microbes in non-responders. Conversely, these same neutrophil populations were associated to families associated to gut health in responding mice. CONCLUSIONS: Our results suggest combining RT in cold tumors enhances the TME, boosting T cell function via macrophage support. Furthermore, distal gut microbes may impact local anti-tumor immunity by influencing neutrophil polarization. This study contributes to the limited literature exploring immune modulation in a conventionally 'cold' bladder tumor cell lines, which has implications for treating human resistant tumors. Citation Format: Eva Michaud, Sabina Fehric, Gautier Marcq, JiaMin Huang, Fabio Cury, Madhuri Koti, José Joao Mansure, Ciriaco Piccirillo, Wassim Kassouf. Improving response to bladder-sparing therapies by combining radiotherapy to immuno-potentiating agents in immunologically cold models of bladder cancer 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 6641.