Identification of Retinoic Acid Receptor Agonists as Potent Hepatitis B Virus Inhibitors via a Drug Repurposing Screen.

Currently available therapies for chronic hepatitis B virus (HBV) infection can efficiently reduce viremia, but induce hepatitis B surface antigen (HBsAg) loss in a very few patients and do not much affect the viral covalently closed circular DNA (cccDNA). To discover new agents with complementary anti-HBV effects, we performed a drug repurposing screen of 1,018 Food and Drug Administration (FDA)-approved compounds using HBV-infected primary human hepatocytes (PHH). Several compounds belonging to the family of retinoic acid receptor (RAR) agonists were identified that reduced HBsAg levels in a dose-dependent manner without significant cytotoxicity. Among them, Tazarotene exhibited the most potent anti-HBV effect with an IC50 for HBsAg of less than 30 nM in PHH. The inhibitory effect was also observed in HBV-infected dHepaRG models, but not in HepG2.215 cells, and HBV genotype A to D were similarly inhibited. Tazarotene was further demonstrated to repress HBV cccDNA transcription, as determined by the levels of HBV cccDNA, RNAs and the activation of HBV promoters. Moreover, RNA-sequence analysis showed that Tazarotene did not induce an interferon response, but altered the expression of a number of genes associated with RAR and metabolic pathways. Inhibition of RARβ, but not RARα, by specific antagonist significantly attenuated the anti-HBV activity of Tazarotene, suggesting Tazarotene inhibits HBV in part through RARβ. Finally, a synergistic effect of Tazarotene and Entecavir on HBV-DNA levels was observed. Therefore, RAR agonists as represented by Tazarotene were identified as potential novel anti-HBV agents.