Trametinib Suppresses the Stimulated T Cells Through G1 Arrest and Apoptosis

The development of efficient immunosuppressants may bring significant benefits to patients after organ/stem transplantation and those with allergies or autoimmune diseases. MEK inhibitors were originally developed as anticancer reagents, but recent reports have suggested that they may have the potential to be immunosuppressants. Trametinib is a first-in-class MEK inhibitor. Here, we examined the effects of trametinib on the immune system and revealed its mechanism. Trametinib suppressed both CD4 and CD8 T-cell proliferation and activated T cells, which expressed CD25 and TIM3, in a dose-dependent manner in vitro. Trametinib also suppressed T cell-related cytokine secretion in a dose-dependent manner. Notably, trametinib suppressed T cell proliferation through the induction of G1 arrest and apoptosis in stimulated T cells. In addition, trametinib induced regulatory T cells (Tregs). We confirmed that low concentrations of trametinib (1 and 10 nM) were not toxic toward splenic naïve T cells and normal mouse liver cells. In this study, we demonstrated whether trametinib suppressed CD4 and CD8 T cell proliferation by inducing G1 arrest and apoptosis along with suppression of cytokine secretion.