7-Deaza-7-fluoro modification confers on 4′-cyano-nucleosides potent activity against entecavir/adefovir-resistant HBV variants and favorable safety

We designed, synthesized and identified a novel nucleoside derivative, 4’-C-cyano-7-deaza-7-fluoro-2’-deoxyadenosine (CdFA), which exerts potent anti-HBV activity (IC(50) ~26 nM) with favorable hepatocytotoxicity (CC(50)~56 μM). Southern blot analysis using wild-type HBV (HBV(WT))-encoding-plasmid-transfected HepG2 cells revealed that CdFA efficiently suppresses the production of HBV(WT) (IC(50)=153.7 nM), entecavir (ETV)-resistant HBV carrying L180M/S202G/M204V substitutions (HBV(ETV)(R); IC(50)=373.2 nM), and adefovir dipivoxil (ADV)-resistant HBV carrying A181T/N236T substitutions (HBV(ADV)(R); IC(50=)192.6 nM), whereas ETV and ADV were less potent against HBV(ETV)(R) and HBV(ADV)(R) (IC(50): >1,000 and 4,022.5 nM, respectively). Once-daily peroral administration of CdFA to human-liver-chimeric mice over 14 days (1 mg/kg/day) comparably blocked HBV(WT) and HBV(ETV)(R) viremia by 0.7 and 1.2 logs, respectively, without significant changes in body-weight or serum human-albumin levels, although ETV only slightly suppressed HBV(ETV)(R) viremia (CdFA vs ETV; p=0.032). Molecular modeling suggested that ETV-TP has good nonpolar interactions with HBV(WT) reverse transcriptase (RT(WT))’s Met204 and Asp205, while CdFA-TP fails to interact with Met204, in line with the relatively inferior activity against HBV(WT) of CdFA compared to ETV (IC(50): 0.026 versus 0.003 nM). In contrast, the 4’-cyano of CdFA-TP forms good nonpolar contacts with RT(WT)’s Leu180 and RT(ETV)(R)’s Met180, while ETV-TP loses interactions with RT(ETV)(R)’s Met180, explaining in part why ETV is less potent against HBV(ETV)(R) than CdFA. The present results show that CdFA exerts potent activity against HBV(WT), HBV(ETV)(R) and HBV(ADV)(R) with enhanced safety and that 7-deaza-7-fluoro modification confers potent activity against drug-resistant HBV variants and favorable safety, shedding light to further design more potent and safer anti-HBV nucleoside analogs.