Varying Treatment outcomes of small molecule STING Agonist ADU-S100 in intratumoral and intravesical treatment regimens in syngeneic murine MB49 and in the N-methyl-N-nitrosourea (MNU) rat Model of urothelial carcinoma

Abstract Introduction: Intratumoral (IT) delivery of STING agonist ADU-S100 shows strong CD8+T cells-mediated antitumor immunity. However, rapid absorption from IT sites, short terminal half-life and adverse outcomes caused withdrawal of ADU-S100 from clinical trials. We reported development of BCG-STING, a preclinical candidate for non-muscle invasive bladder cancer (NMIBC) that overexpresses a bioactive STING agonist (c-di-AMP) and shows enhanced antitumor efficacy over BCG-WT by increasing tumor infiltrating CD4+ and CD8+ T cells and inflammatory macrophages. The similar mechanism of action prompted us to compare antitumor efficacy of BCG-STING with ADU-S100 in an IT as well as intravesical (IV) dosing regimen. Methods: Syngeneic MB49 flank tumors in C57BL/6 female mice received IT treatment of BCG-WT, BCG-STING (5 x 106CFU) or ADU-S100 (100, 50 or 25 mg). Endpoint involved tumor volume measurement and flow-cytometry based tumor immune infiltrate analyses (at 100 μg). MNU carcinogen rat model of NMIBC and the standard IV administration regimen was used for BCG-WT or BCG-STING (5 x 106 CFU, 6x weekly) or ADU-S100 (25 μg, 6x weekly). Tumor involvement index (TII) and pathological tumor staging tumor involvement index were determined using histopathological analyses of MNU rat bladders. Results: IT administration of ADU-S100 in MB49 tumor remained most-effective immunotherapy as compared to BCG-WT or BCG-STING even at lowest dose (25 μg), consistent with strongest infiltration of TNF-α+MHCII+F4/80+CD11b+ macrophages and IFN-γ+CD8+ T cells as compared to BCG-STING or BCG-WT. Strikingly, we observe a significant increase in immunosuppressive IL-10+ and ARG-1+ Ly6C(hi)Ly6G(-) monocytic myeloid-derived suppressor cells (M-MDSCs) in MB49 tumors treated with ADU-S100 and BCG-WT, but not BCG-STING. In contrast to MB49 model, IV induction course of BCG-STING in MNU rat model showed the greatest antitumor effects with only 5% residual TII compared to 30% in ADU-S100 or 42% in BCG-WT. Tumor staging displayed residual T1 (50%), CIS (25%) and Ta (25%) tumors in ADU-S100 group, while BCG-WT treated group showed a lower degree of invasion to the lamina propria with CIS (50%), T1 (25%) and Ta (25%) residual tumors. BCG-STING IV therapy resulted in 60% of rat bladders showing complete tumor regression while 40% had minimal residual non-invasive tumors. Conclusions: The varying therapeutic outcomes of IT vs IV treatment regimens of ADU-S100 over BCG-STING or BCG-WT in different urothelial carcinoma models suggest the important role of varying tumor microenvironment and dosing regimens on relative antitumor efficacy. Increased percentage of immunosuppressive M-MDSCs specifically in response to ADU-S100 or BCG-WT suggests unique advantages associated with BCG-STING. Citation Format: Alok K. Singh, Kara Lombardo, Monali Praharaj, James Liu, Russel Becker, Kelly Harris, Max Kates, David McConkey, Andres Matoso, William R. Bishai, Trinity Jude Bivalacqua. Varying Treatment outcomes of small molecule STING Agonist ADU-S100 in intratumoral and intravesical treatment regimens in syngeneic murine MB49 and in the N-methyl-N-nitrosourea (MNU) rat Model of urothelial carcinoma [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2022; 2022 Apr 8-13. Philadelphia (PA): AACR; Cancer Res 2022;82(12_Suppl):Abstract nr 3511.