Structure-Activity Relationship Studies Of Trisubstituted Isoxazoles As Selective Allosteric Ligands For The Retinoic-Acid-Receptor-Related Orphan Receptor Gamma T

The inhibition of the nuclear receptor retinoic-acid-receptor-related orphan receptor gamma t (ROR gamma t) is a promising strategy in the treatment of autoimmune diseases. ROR gamma t features an allosteric binding site within its ligand-binding domain that provides an opportunity to overcome drawbacks associated with orthosteric modulators. Recently, trisubstituted isoxazoles were identified as a novel class of allosteric ROR gamma t inverse agonists. This chemotype offers new opportunities for optimization into selective and efficacious allosteric drug-like molecules. Here, we explore the structure-activity relationship profile of the isoxazole series utilizing a combination of structure-based design, X-ray crystallography, and biochemical assays. The initial lead isoxazole (FM26) was optimized, resulting in compounds with a similar to 10-fold increase in potency (low nM), significant cellular activity, promising pharmacokinetic properties, and a good selectivity profile over the peroxisome-proliferated-activated receptor gamma and the farnesoid X receptor. We envisage that this work will serve as a platform for the accelerated development of isoxazoles and other novel chemotypes for the effective allosteric targeting of ROR gamma t.