Optimization of Potent and Selective Cyclohexyl Acid ERAP1 Inhibitors Using Structure- and Property-Based Drug Design.

Endoplasmic reticulum aminopeptidase 1 (ERAP1) cleaves the N-terminal amino acids of peptides, which can then bind onto major histocompatibility class I (MHC-I) molecules for presentation onto the cell surface, driving the activation of adaptive immune responses. In cancer, overtrimming of mature antigenic peptides can reduce cytotoxic T-cell responses, and ERAP1 can generate self-antigenic peptides which contribute to autoimmune cellular responses. Therefore, modulation of ERAP1 activity has potential therapeutic indications for cancer immunotherapy and in autoimmune disease. Herein we describe the hit-to-lead optimization of a series of cyclohexyl acid ERAP1 inhibitors, found by X-ray crystallography to bind at an allosteric regulatory site. Structure-based drug design enabled a >1,000-fold increase in ERAP1 enzymatic and cellular activity, resulting in potent and selective tool molecules. For lead compound 7, rat pharmacokinetic properties showed moderate unbound clearance and oral bioavailability, thus highlighting the promise of the series for further optimization.