Novel small molecule IL-6 inhibitor suppresses autoreactive Th17 development and promotes Treg development

Multiple sclerosis (MS) is the leading cause of non-traumatic neurological disability in the United States in young adults, but current treatments are only partially effective, making it necessary to develop new, innovative therapeutic strategies. Myelin-specific interleukin (IL)-17-producing T helper type 17 (Th17) cells are a major subset of CD4 T effector cells (T_eff ) that play a critical role in mediating the development and progression of MS and its mouse model, experimental autoimmune encephalomyelitis (EAE), while regulatory T cells (T_reg ) CD4 T cells are beneficial for suppressing disease. The IL-6/signal transducer and activator of transcription 3 (STAT-3) signaling pathway is a key regulator of Th17 and T_reg cells by promoting Th17 development and suppressing T_reg development. Here we show that three novel small molecule IL-6 inhibitors, madindoline-5 (MDL-5), MDL-16 and MDL-101, significantly suppress IL-17 production in myelin-specific CD4 T cells in a dose-dependent manner in vitro. MDL-101 showed superior potency in suppressing IL-17 production compared to MDL-5 and MDL-16. Treatment of myelin-specific CD4 T cells with MDL-101 in vitro reduced their encephalitogenic potential following their subsequent adoptive transfer. Furthermore, MDL-101 significantly suppressed proliferation and IL-17 production of anti-CD3-activated effector/memory CD45RO⁺ CD4⁺ human CD4 T cells and promoted human T_reg development. Together, these data demonstrate that these novel small molecule IL-6 inhibitors have the potential to shift the T_eff  : T_reg balance, which may provide a novel therapeutic strategy for ameliorating disease progression in MS.