Future Therapies for Functional Cure of Chronic HBV: Review of Investigational Drugs in Phase 1 and 2 Development

Treating patients with chronic hepatitis B (CHB) infection with long-term oral antiviral therapy or pegylated interferon is the current standard of care (SOC). However, functional cure, defined as sustained hepatitis B surface antigen (HBsAg) seroclearance that is associated with favorable clinical outcomes, is a rarely achieved treatment endpoint with the SOC. Remarkable advances in CHB therapy have been made in the recent years. This review was aimed to describe the different new treatment agents that are in the clinical phase of development. These include two main groups of agents that either target the viral replication cycle or enhance host immune control on the hepatitis B virus (HBV). The former group includes viral entry inhibitor, RNA gene silencers, core protein inhibitors, nucleic acid polymer, and monoclonal antibodies. The latter group includes toll-like receptor agonists, RIG-1/NOD2 agonist, therapeutic vaccines, and apoptosis inducer. While some agents show promise in reduction of HBsAg levels and even HBsAg seroclearance, others are relatively modest in term of additional virological control effected by their different modes of action against HBV. These agents are in general well tolerated. Many upcoming new drugs against HBV are expected to enter phase II clinical trials. New challenge ahead would be the choice and duration of combination therapy to achieve a satisfactory rate of HBsAg seroclearance.