Antiviral Properties and Mechanism of Action Studies of the Hepatitis B Virus Capsid Assembly Modulator JNJ-56136379

Capsid assembly is a critical step in the hepatitis B virus (HBV) life cycle, mediated by the core protein. Core is a potential target for new antiviral therapies, the capsid assembly modulators (CAMs). JNJ-56136379 (JNJ-6379) is a novel and potent CAM currently in phase II trials. We evaluated the mechanism of action (MOA) and antiviral properties of JNJ-6379 in vitro Size exclusion chromatography and electron microscopy studies demonstrated that JNJ-6379 induced formation of morphologically intact viral capsids devoid of genomic material ('primary' MOA). JNJ-6379 accelerated the rate and extent of HBV capsid assembly in vitro JNJ-6379 specifically and potently inhibited HBV replication; median 50% effective concentration (EC50) 54 nM (HepG2.117 cells). In HBV-infected primary human hepatocytes (PHHs), JNJ-6379, when added with the viral inoculum, dose-dependently reduced extracellular HBV DNA levels (median EC50 93 nM) and prevented covalently closed circular DNA (cccDNA) formation, leading to a dose-dependent reduction of intracellular HBV RNA levels (median EC50 876 nM) and reduced antigen levels ('secondary' MOA). Adding JNJ-6379 to PHHs 4/5 days post infection reduced extracellular HBV DNA and did not prevent cccDNA formation. Time-of-addition PHH studies revealed that JNJ-6379 most likely interfered with post-entry processes. Collectively, these data demonstrate that JNJ-6379 has a dual MOA on the early and late steps of the HBV life cycle, which is different to the MOA of nucleos(t)ide analogues. JNJ-6379 is in development for chronic hepatitis B treatment, and may translate into higher HBV functional cure rates.