HIF-PH inhibitors induce pseudohypoxia in T cells and suppress the growth of microsatellite stable colorectal cancer by enhancing antitumor immune responses.

Background: Recent studies have revealed that CD8 T cells can be activated via genetic upregulation of HIF-1α, thereby augmenting antitumor effector functions. HIF-1α upregulation can be attained by inhibiting HIF-prolyl hydroxylase (HIF-PH) under normoxic conditions, termed pseudohypoxia. This study investigated whether pseudohypoxia induced by HIF-PH inhibitors suppresses Microsatellite stable (MSS) colorectal cancer (CRC) by affecting tumor immune response.

Methods: The HIF-PH inhibitors Roxadustat and Vadadustat were utilized in this study. In vitro, we assessed the effects of HIF-PH inhibitors on human and murine colon cancer cell lines (SW480, HT29, Colon26) and murine T cells. In vivo experiments were performed with mice bearing Colon26 tumors to evaluate the effect of these inhibitors on tumor immune responses. Tumor and spleen samples were analyzed using immunohistochemistry, RT-qPCR, and flow cytometry to elucidate potential mechanisms.

Results: HIF-PH inhibitors demonstrated antitumor effects in vivo but not in vitro. These inhibitors enhanced the tumor immune response by increasing the infiltration of CD8 and CD4 tumor-infiltrating lymphocytes (TILs). HIF-PH inhibitors induced IL-2 production in splenic and intratumoral CD4 T cells, promoting T cell proliferation, differentiation, and immune responses. Roxadustat synergistically enhanced the efficacy of anti-PD-1 antibody for MSS cancer by increasing the recruitment of TILs and augmenting effector-like CD8 T cells.

Conclusion: Pseudohypoxia induced by HIF-PH inhibitors activates antitumor immune responses, at least in part, through the induction of IL-2 secretion from CD4 T cells in the spleen and tumor microenvironment, thereby enhancing immune efficacy against MSS CRC.