VBY-891

VBY-891 is a small molecule, second-generation cathepsin S inhibitor developed for oral administration. It acts as a potent, competitive, and reversible inhibitor of the cathepsin S enzyme (CTSS), with high selectivity over other human cathepsins such as L, B, F, and K. The drug was initially developed by Virobay and later licensed to LEO Pharma for dermatological indications. Its primary indication has been psoriasis—an inflammatory autoimmune skin disease—but it has also shown activity in preclinical models of autoimmunity and neuropathic pain. The mechanism of action involves inhibition of cathepsin S, which plays a key role in antigen presentation and immune system regulation; thus its inhibition may modulate immune responses relevant to autoimmune diseases[1][2][3][4][5].