Inhibition of HBV replication by N-hydroxyisoquinolinedione and N-hydroxypyridinedione ribonuclease H inhibitors

We recently developed a screening system capable of identifying and evaluating inhibitors of the Hepatitis B virus (HBV) ribonuclease H (RNaseH), which is the only HBV enzyme not targeted by current anti-HBV therapies. Inhibiting the HBV RNaseH blocks synthesis of the positive-polarity DNA strand, causing early termination of negative-polarity DNA synthesis and accumulation of RNA:DNA heteroduplexes. We previously reported inhibition of HBV replication by N-hydroxyisoquinolinediones (HID) and N-hydroxypyridinediones (HPD) in human hepatoma cells. Here, we report results from our ongoing efforts to develop more potent anti-HBV RNaseH inhibitors in the HID/HPD compound classes. We synthesized and screened additional HIDs and HPDs for preferential suppression of positive-polarity DNA in cells replicating HBV. Three of seven new HIDs inhibited HBV replication, however, the therapeutic indexes (TI = CC50/EC50) did not improve over what we previously reported. All nine of the HPDs inhibited HBV replication with EC(50)s ranging from 110 nM to 4 mu M. Cellular cytotoxicity was evaluated by four assays and CC(50)s ranged from 15 to > 100 mu M. The best compounds have a calculated TI of > 300, which is a 16-fold improvement over the primary HPD hit. These studies indicate that the HPD compound class holds potential for antiviral discovery.