Abstract LB-122: Significant cytotoxic and immumomodulatory effects of continuous low dose intravesical gemcitabine in rodent bladder tumor models

Abstract Traditional gemcitabine bladder instillations (40 mg/mL) exhibit limited efficacy possibly due to micturition and saturable nucleotide uptake limiting tumor exposure. The present study investigates gemcitabine's anti-tumor and immunomodulatory effects after continuous low dose intravesical administration to enhance bladder tumor exposure. The direct effects of low dose gemcitabine at nominal bladder urine concentrations of 0, 20, 40, or 80 µg/ml were studied in athymic nude rats with human MIBC cells, T24-TurboFP635, injected into the bladder. After 3 days tumor growth, gemcitabine or vehicle was perfused into the bladder over 5 days, N=6 per group. Tumor bioluminescence was measured on day 5. A companion study in immunocompetent Wistar rats inoculated with syngeneic NBTII bladder tumors provided tumors for immunocyte analysis. A significant reduction in bladder tumor bioluminescence of 47.6%, 70.5% and 91.2% vs control was observed in the 20, 40, and 80 µg/ml groups, respectively. Flow cytometric analysis of residual tumors in immunocompetent rats demonstrated a significant decrease of 85.2% in the proportion of tumor T regulatory cells to T effector cells. Gemcitabine immunogenicity was studied in immunocompetent rats with NBTII cells injected into the bladder and subcutaneous flank tissue; flank tumors were implanted either simultaneously with bladder tumors or 14 days after bladder tumor implantation. Control groups received only flank tumors, N=15, or bladder and flank tumors with vehicle perfusion, N=10. Treatment groups, N=10, received two 5-day bladder perfusions, yielding gemcitabine urine concentrations of 10, 20, and 40 µg/ml which were separated by 7 days. Flank tumor growth was similar with tumor doubling times of 4.5 days after subcutaneous injections of 1.0, 2.5, or 5.0 x 106 cells and was unchanged with concomitant bladder tumor implantation and vehicle perfusion. During the first gemcitabine perfusion cycle, flank tumor growth was fully arrested, with tumor sizes averaging only 50% of controls in rats with concomitant bladder tumors; this effect was maintained during the 7-day drug free period in the 60 µg/ml group. Initiation of the second perfusion resulted in rapid flank tumor ablation in all but one animal completing the study. A similar priming effect was observed in the 15 and 30 ug/ml groups. Delaying flank tumor implantation to 3 days before the second perfusion not only prevented tumor growth but completely ablated all tumors. The results suggest continuous low dose intravesical gemcitabine inhibits bladder tumor growth, shifts the tumor microenvironment toward effector T cell dominance and induces a systemic immune response sufficient to suppress distant disease. Perhaps for the first time, the results also demonstrate a cytotoxic agent can induce a significant abscopal response when administered under proper conditions. Citation Format: Dennis H. Giesing, Don Reynolds, Vikas Agarwal, Chris Cutie, Balaji Ramachandran, Aravindakshan Jayaprakash, Satheesh Rajendiran, Purnand Sarma. Significant cytotoxic and immumomodulatory effects of continuous low dose intravesical gemcitabine in rodent bladder tumor models [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2018; 2018 Apr 14-18; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2018;78(13 Suppl):Abstract nr LB-122.