Targeting macrophage migration inhibitory factor to inhibit T cell immunosuppression in the tumor microenvironment and improve cancer outcomes in head and neck squamous cell carcinoma.

Head and neck squamous cell carcinoma (HNSCC) is the 7th most common cancer globally with a 40-50 % survival rate. Although macrophage migration inhibitory factor (MIF) is overexpressed in most solid tumors and promotes tumor growth and invasion, the therapeutic potential of MIF inhibition in HNSCC is yet to be explored. In this study, we investigated the efficacy of CPSI-1306, a small-molecule MIF inhibitor, on HNSCC cell growth and cancer associated signaling pathways in vitro, as well as its impact on T cells in the HNSCC tumor microenvironment in vivo. CPSI-1306 did not reduce HNSCC cell proliferation in vitro, and mildly decreased VEGF and EGFR expression. However, CPSI-1306 significantly reduced tumor development in two orthotopic mouse oral cancer (MOC-2 and MOC-1) HNSCC models. Interestingly, CPSI-1306 treatment increased T cell infiltration to the tumor microenvironment and completely abrogated immunosuppressive checkpoint markers TIGIT, TIM3, and CTLA-4, but not PD-1 on tumor infiltrating CD8(+) T cells. This was accompanied by increased CD8(+) T cell expression of antitumoral cytokines IFN-γ and TNF-α in the draining lymph nodes and Granzyme B in the tumor microenvironment of CPSI-1306 treated tumor bearing mice. Our studies demonstrate that the small molecule MIF inhibitor CPSI-1306 potently inhibits T cell immunosuppression in the tumor microenvironment and reduces tumor growth in HNSCC. These studies open a novel therapeutic option for modulating anti-tumoral T cell immunity to improve HNSCC outcomes by targeting MIF.