PD53-11: Divergent Therapeutic Outcomes of 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

Alok Kumar Singh*, Kara Lombardo, Monali Praharaj, James Liu, Russel Becker, Kelly Harris, Max Kates, David McConkey, Andres Matoso, William R Bishai, Baltimore , MD, Trinity Jude Bivalacqua, Philadelphia , PA

Introduction: STING agonist ADU-S100 as an intratumoral (IT) therapeutic regimen shows excellent CD8+T cells-mediated antitumor immunity. Rapid absorption from IT sites, short terminal half-life and treatment related adverse outcomes caused withdrawal of ADU-S100 from clinical trials. We developed BCG-STING, a preclinical candidate for non-muscle invasive bladder cancer (NMIBC) that overexpresses a STING agonist (c-di-AMP). BCG-STING confers superior antitumor immunity over BCG-WT by increasing tumor infiltrating CD4+ and CD8+ T cells and inflammatory macrophages. Due to similarities in the mechanism of action, we compared 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 were given IT treatment of BCG-WT, BCG-STING (5 x 106CFU) or ADU-S100 (100, 50 or 25 mg). End-point measurements included tumor volume 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). Histopathological analyses of MNU rat bladders were performed for tumor involvement index (TII) and pathological tumor staging.

Results: IT administration of ADU-S100 in MB49 tumor showed greatest tumor regression over BCG-WT or BCG-STING even at lowest dose (25 µg). ADU-S100 caused strongest infiltration of TNF-a+MHCII+F4/80+CD11b+ macrophages and IFN-?+CD8+ T cells as compared to BCG-STING or BCG-WT. We did 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, lV 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 revealed 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 divergent therapeutic outcomes of IT vs IV treatment regimens of ADU-S100 over BCG-STING or BCG-WT in different urothelial carcinoma models indicate the critical role of tumor microenvironment and dosing regimens on relative efficacy. Induction of immunosuppressive M-MDSCs by ADU-S100 or BCG-WT suggests unique advantages of BCG-STING. The therapeutic targeting of M-MDSCs as combination may improve therapeutic efficacies of BCGs.

Source of Funding: National Institute of Health, Maryland Tedco, Willowcroft Foundation, and Cigarette Restitution Fund