Boceprevir

Boceprevir is a peptidomimetic compound (a small molecule designed to mimic a peptide substrate) that acts as a reversible inhibitor of the hepatitis C virus (HCV) NS3/4A serine protease, an enzyme essential for viral polyprotein processing and HCV replication. Approved by the FDA in May 2011, boceprevir was one of the first direct-acting antiviral (DAA) agents for hepatitis C, marking the beginning of a revolution in HCV treatment that would eventually lead to cure rates exceeding 95%.

The NS3/4A protease cleaves the HCV polyprotein at four specific junctions, a process essential for generating the non-structural proteins required for viral replication. Boceprevir covalently but reversibly binds to the active site serine residue of the protease, inhibiting its catalytic activity. By blocking polyprotein processing, boceprevir halts viral replication at a post-translational step.

Boceprevir was approved for use in combination with peginterferon alfa and ribavirin for the treatment of chronic HCV genotype 1 infection. The SPRINT-2 and RESPOND-2 trials demonstrated that adding boceprevir to peginterferon/ribavirin significantly increased sustained virologic response (SVR, effectively cure) rates from approximately 38-40% with peginterferon/ribavirin alone to 63-75% with the boceprevir-containing triple regimen.

Despite this significant improvement, boceprevir's clinical use was relatively short-lived. The drug had substantial limitations including activity restricted to genotype 1, a high pill burden (three times daily dosing of 4 capsules each time), significant drug-drug interactions, and the continued requirement for interferon and ribavirin with their associated side effects. The rapid development of second-generation DAAs — particularly sofosbuvir-based regimens — that offered interferon-free, pan-genotypic treatment with higher SVR rates led to boceprevir's discontinuation by Merck in 2015.