h Hepatitis B virus (HBV) remains a major human pathogen despite the development of both antiviral drugs and a vaccine, in part because the current therapies do not suppress HBV replication far enough to eradicate the virus. Here, we screened 51 troponoid compounds for their ability to suppress HBV RNaseH activity and HBV replication based on the activities of ␣-hydroxytropolones against HIV RNaseH, with the goal of determining whether the tropolone pharmacophore may be a promising scaffold for anti-HBV drug development. Thirteen compounds inhibited HBV RNaseH, with the best 50% inhibitory concentration (IC 50 ) being 2.3 M. Similar inhibition patterns were observed against HBV genotype D and C RNaseHs, implying limited genotype specificity. Six of 10 compounds tested against HBV replication in culture suppressed replication via blocking of viral RNaseH activity, with the best 50% effective concentration (EC 50 ) being 0.34 M. Eighteen compounds inhibited recombinant human RNaseH1, and moderate cytotoxicity was observed for all compounds (50% cytotoxic concentration [CC 50 ] ؍ 25 to 79 M). Therapeutic indexes ranged from 3.8 to 94. Efficient inhibition required an intact ␣-hydroxytropolone moiety plus one or more short appendages on the tropolone ring, but a wide variety of constituents were permissible. These data indicate that troponoids and specifically ␣-hydroxytropolones are promising lead candidates for development as anti-HBV drugs, providing that toxicity can be minimized. Potential anti-RNaseH drugs are envisioned to be employed in combination with the existing nucleos(t)ide analogs to suppress HBV replication far enough to block genomic maintenance, with the goal of eradicating infection.
More than 2 billion people have been infected with hepatitis B virus (HBV) at some time in their lives and up to 350 million remain chronically infected as carriers of HBV (1, 2). Approximately 20% of chronic hepatitis B patients develop liver cirrhosis, leading to hepatic insufficiency and portal hypertension (3). Furthermore, there is a 100-fold higher risk of development of hepatocellular carcinoma in chronic HBV patients than in noncarriers (4). Every year, HBV infection kills more than 500,000 people from cirrhosis, liver failure, and hepatocellular carcinoma (5).The global level of chronic HBV infection still mandates development of new drugs despite the development of excellent vaccines and drugs against the virus. Seven drugs have been approved by the U.S. Food and Drug Administration for treating HBV infection. Interferon alpha and pegylated interferon alpha are immunomodulatory agents. However, the need for subcutaneous administration, the poor long-term responses, the very low cure rates, and the high frequency of adverse side effects make interferon far from an ideal drug (6). The nucleos(t)ide analog drugs lamivudine, adefovir, entecavir, telbivudine, and tenofovir are phosphorylated to their triphosphate derivatives by cellular enzymes and become chain-terminating substrates of the HBV reverse transcr...
