Abstract 5547: Synergistic action of sitagliptin and checkpoint inhibition for ovarian cancer therapy

Abstract

Abstract Ovarian cancer is the most lethal gynecological malignancy and treatment options have not improved in decades. Whilst ovarian tumors have an immune-mediated component, emerging immunotherapies (e.g. anti-PD-1, anti-PD-L1) have failed to achieve robust clinical response for ovarian cancer patients. There is an urgent need to develop new therapeutic strategies to improve survival rates in women, particularly those with recurrent, chemoresistant disease. In an ongoing study we are investigating the repurposing of sitagliptin, an anti-diabetes drug, as a novel immunomodulatory therapy in ovarian cancer. Ovarian tumors were generated in C57BL/6 wild-type mice by intrabursal implantation of ID8 murine ovarian cancer cells. Following the formation of primary tumors (~2 weeks), mice received a daily oral dose of sitagliptin (50mg/kg) until ethical endpoint. Anti-tumor immune responses were examined by flow cytometry and immunohistochemical staining according to tumor stage. Mice were assessed for overall survival compared to paclitaxel chemotherapy as standard-of-care. Daily sitagliptin treatment increased circulating Teff:Treg cell ratios in the blood, peritoneal fluid and tumor tissue at an early stage, and this was sustained throughout disease. Sitagliptin also enhanced T effector cell activation and proliferation, indicating that increased Teff:Treg ratios were a positive indicator of the anti-tumor immune response. Treatment with sitagliptin alone increased median survival time by 27% compared to both untreated controls and paclitaxel as standard-of-care, suggesting a beneficial effect mediated by anti-tumor immune responses. Of particular interest, sitagliptin treatment specifically increased the percentage of CXCR3+ T effector cells in the peritoneal cavity. Recent data has suggested that CXCR3+ T cells are functionally required for immune checkpoint inhibitors to exert efficacy. Thus, we hypothesize that sitagliptin may enhance the efficacy of immune checkpoint inhibitor therapies in ovarian cancers. Our ongoing studies are investigating the combination of sitagliptin with anti-PD-1 and anti-PD-L1 antibodies, as a rational approach to improving their efficacy in ovarian cancers. These studies will identify a clinically relevant and directly translatable approach to improve prognosis for ovarian cancer patients. Citation Format: Laura R. Moffitt, Amy L. Wilson, Bashirah Basri, Kirsty L. Wilson, Magdalena Plebanski, Andrew N. Stephens. Synergistic action of sitagliptin and checkpoint inhibition for ovarian cancer therapy [abstract]. In: Proceedings of the Annual Meeting of the American Association for Cancer Research 2020; 2020 Apr 27-28 and Jun 22-24. Philadelphia (PA): AACR; Cancer Res 2020;80(16 Suppl):Abstract nr 5547.