Antagonizing Retinoic Acid-Related-Orphan Receptor Gamma Activity Blocks the T Helper 17/Interleukin-17 Pathway Leading to Attenuated Pro-inflammatory Human Keratinocyte and Skin Responses

The nuclear hormone receptor retinoic acid receptor-related-orphan-receptor-gamma t (ROR gamma t) is the key transcription factor required for Th17 cell differentiation and for production of IL-17 family cytokines by innate and adaptive immune cells. Dysregulated Th17 immune responses have been associated with the pathogenesis of several inflammatory and autoimmune diseases such as psoriasis, psoriatic arthritis, and ankylosing spondylitis. In this article, we describe the in vitro pharmacology of a potent and selective low molecular weight ROR gamma t inhibitor identified after a structure-based hit-to-lead optimization effort. The compound interfered with co-activator binding to the ROR gamma t ligand binding domain and impaired the transcriptional activity of ROR gamma t as evidenced by blocked IL-17A secretion and RORE-mediated transactivation of a luciferase reporter gene. The inhibitor effectively reduced IL-17A production by human naive and memory T-cells and attenuated transcription of pro-inflammatory Th17 signature genes, such as IL17F, IL22, IL26, IL23R, and CCR6. The compound selectively suppressed the Th17/IL-17 pathway and did not interfere with polarization of other T helper cell lineages. Furthermore, the inhibitor was selective for ROR gamma t and did not modify the transcriptional activity of the closely related family members ROR alpha and ROR beta. Using human keratinocytes cultured with supernatants from compound treated Th17 cells we showed that pharmacological inhibition of RORgt translated to suppressed IL-17-regulated gene expression in keratinocyte cell cultures. Furthermore, in ex vivo immersion skin cultures our ROR gamma t inhibitor suppressed IL-17A production by Th17-skewed skin resident cells which correlated with reduced human beta defensin 2 expression in the skin. Our data suggests that inhibiting ROR gamma t transcriptional activity by a low molecular weight inhibitor may hold utility for the treatment of Th17/IL-17-mediated skin pathologies.