1,4-Dihydroxy-1,8-napthyridinone (DHN) analogs as HIV-1 reverse transcriptase-associated RNase H inhibitors

Reverse transcriptase (RT)-associated RNase H (RNH) remains the only virally encoded enzymatic function of HIV-1 yet to be targeted by any drugs approved or in the development pipeline. We have previously developed 1,4-dihydroxy-1,8-napthyridinone (DHN) analogs as potent inhibitors of orthopoxvirus resolvases which belong to the RNase H-like (RNHL) nuclease family featuring a two-metal-dependent catalytic mechanism. In this work, we have enriched the in-house DHN collection to 82 analogs and tested them in HIV-1 in vitro and antiviral assays. In biochemical assays against RT, most analogs inhibited RT RNH activity with low nM to sub-μM potencies without appreciable inhibition against RT polymerase (pol) activity. Structure-activity relationship (SAR) analysis reveals that analogs bearing a phenyl at C-3 with various substitutions at C-5 position are particularly potent. Removing the N-1 hydroxyl group largely abrogated the RNH inhibition, consistent with a two-metal-chelating pharmacophore. In a cell-based antiviral assay against HIV-1 virus, many analogs exhibited sub-μM antiviral activity without significant cytotoxicity. Finally, most analogs were tested against HIV-1 integrase strand transfer (INST) activity which also belongs to the RNHL family. Although some inhibited INST with IC₅₀ values in the low to mid μM range, the antiviral activity appears to correlate better with RT RNH inhibition.