Background: Trifluridine/tipiracil (FTD/TPI) is an oral nucleoside antitumor agent that is composed of trifluridine and tipiracil hydrochloride at a molecular ratio of 1:0.5. Checkpoint-blockade immunotherapies are particularly effective in patients with tumor T cell infiltrations. In this study, the antitumor effects of FTD/TPI + anti-mouse PD-1 antibody combination were studied in a syngeneic mouse model and the tumor-infiltrating lymphocyte (TIL) subsets were evaluated. Method: The mouse colorectal cancer cell line CMT-93 was subcutaneously implanted into C57BL/6 mice. Vehicle (0.5% Hydroxypropyl methylcellulose, 10 mL/kg, p.o.), FTD/TPI (75, 100, and 150 mg/kg/day, twice daily, days 1-14, p.o.), anti-mouse PD-1 antibody (clone RMP1-14; 0.1 mg/body; once daily, days 1, 5, and 9; i.p.), and FTD/TPI + anti-mouse PD-1 antibody combination were administered, and inhibitory activity was evaluated according to tumor-volume changes. Single-cell suspensions were prepared from collected tumors. Based on cell marker expression, CD4+ T cells, CD8+T cells, and regulatory T cells (Tregs) were identified using antibodies against CD4, CD8, CD25, and Foxp3, and subsets of TILs were evaluated by flow cytometry. Results: Both anti-mouse PD-1 antibody and FTD/TPI monotherapies were effective in vivo. Tumor-growth inhibition by anti-mouse PD-1 antibody was 81.7% at 0.1 mg/kg/day and that by FTD/TPI was 33.4%, 46.1%, and 59.5% at 75, 100, and 150 mg/kg/day, respectively. FTD/TPI + anti-mouse PD-1 antibody combination using FTD/TPI (75, 100, and 150 mg/kg/day) with anti-mouse PD-1 antibody (0.1 mg/kg/day) inhibited tumor growth at significantly higher rates (P < 0.05; 91.8%, 95.7%, 98.4%, respectively) than monotherapy. Remarkably, the 150-mg/kg/day FTD/TPI + 0.1-mg/kg/day anti-mouse PD-1 antibody combination caused complete tumor regression in four/five mice without body-weight reduction or drug-related deaths; however, none of the monotherapies caused complete tumor regression. Flow cytometric analysis revealed a higher CD8+ T cell percentage among total lymphocytes and a lower Treg percentage in CD4+ T cells after combination therapy compared with the controls. Conclusion: FTD/TPI + anti-mouse PD-1 antibody combination was synergistically effective on CMT-93 mouse colon tumor. This combination increased CD8+ T cell percentages in whole lymphocyte and decreased Treg percentages in CD4+ T cell. This suggests that FTD/TPI + anti-mouse PD-1 antibody combination modulates tumor T cell populations and improves their antitumor activity.

Citation Format: Norihiko Suzuki, Hiroshi Tsukihara, Fumio Nakagawa, Takashi Kobunai, Teiji Takechi. Efficacy of trifluridine/tipiracil + anti-mouse PD-1 antibody combination on mouse colorectal cancer model and related tumor immunomodulatory effects [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2017; 2017 Apr 1-5; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2017;77(13 Suppl):Abstract nr 1071. doi:10.1158/1538-7445.AM2017-1071