The Discovery and Development of Boceprevir: A Novel, First-generation Inhibitor of the Hepatitis C Virus NS3/4A Serine Protease

An estimated 2-3% of the world's population is infected with hepatitis C virus (HCV), making it a major global health problem. Consequently, over the past 15 years, there has been a concerted effort to understand the pathophysiology of HCV infection and the molecular virology of replication, and to utilize this knowledge for the development of more effective treatments. The virally encoded non-structural serine protease (NS3) is required to process the HCV polyprotein and release the individual proteins that form the viral RNA replication machinery. Given its critical role in the replication of HCV, the NS3 protease has been recognized as a potential drug target for the development of selective HCV therapies. In this review, we describe the key scientific discoveries that led to the approval of boceprevir, a first-generation, selective, small molecule inhibitor of the NS3 protease. We highlight the early studies that reported the crystal structure of the NS3 protease, its role in the processing of the HCV polyprotein, and the structural requirements critical for substrate cleavage. We also consider the novel attributes of the NS3 protease-binding pocket that challenged development of small molecule inhibitors, and the studies that ultimately yielded milligram quantities of this enzyme in a soluble, tractable form suitable for inhibitor screening programs. Finally, we describe the discovery of boceprevir, from the early chemistry studies, through the development of high-throughput assays, to the phase III clinical development program that ultimately provided the basis for approval of this drug. This latest phase in the development of boceprevir represents the culmination of a major global effort to understand the pathophysiology of HCV and develop small molecule inhibitors for the NS3 protease.