Programmed cell death-1 (PD-1) is an immunosuppressive receptor expressed on T cells upon activation. Once interacting with its ligand, programmed death ligand-1 (PD-L1), the PD-1:PD-L pathway curbs T cell activation and thereby serves as a natural protection mechanism against autoimmunity. However, this pathway has been hijacked by cancer cells in order to evade the immune system. This interface has already been recognized as an effective target for cancer therapy leading to the development of immune checkpoint inhibitor (ICI) immunotherapy. Blocking the PD-1:PD-L axis unleashes T cells from suppression to maintain their effector function against tumor cells. ICI has durable efficacy in many types of cancer; however, colorectal cancer, except for the approximately 4% microsatellite-instable (MSI) colorectal cancer, stands out as one of the few human cancers that does not respond to ICI immunotherapy. One potential mechanism that these tumor cells may be using is resisting cell death, making them insensitive to apoptosis induction by T cells. Ceramide, the central metabolite of the sphingolipid metabolism pathway, plays a critical role in many cell signaling processes, and one of its most prevalent roles can be seen in cell death. Our lab has developed five novel ceramide mimetics (IG4, IG7, IG14, IG17, and IG19) which function to sensitize tumor cells to apoptosis and enhance T cell-mediated cell death. We have previously shown that these ceramide mimetics significantly increase FasL-induced apoptosis by perforin-deficient cytotoxic T lymphocytes. Using the murine colon carcinoma cell line CT26, we show that the ceramide mimetics induce tumor cell death in a dose-dependent manner. Interestingly, the ceramide mimetics appear to be functioning by different mechanisms in vitro. Still, we report here that these five ceramide mimetics exhibit tumor suppression activity in a colon tumor mouse model in a dose-dependent manner in vivo. Also, ceramide mimetic IG19 significantly increased the efficacy of anti-PD-1 mAb immunotherapy in suppressing colon tumor development in vivo. Our data thus indicate that ceramide mimetics are potential effective enhancers for ICI immunotherapy in colon cancer.

Citation Format: Priscilla S. Redd, Chunwan Lu, John D. Klement, Mohammed Ibrahim, Dafeng Yang, Daniela Payne, Iryna Lebedyeva, Kebin Liu. Ceramide mimetics regulation of tumor cell response to immune checkpoint inhibitor immunotherapy [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2019; 2019 Mar 29-Apr 3; Atlanta, GA. Philadelphia (PA): AACR; Cancer Res 2019;79(13 Suppl):Abstract nr 2263.