Inhibition of hepatitis B virus DNA polymerase by enantiomers of penciclovir triphosphate and metabolic basis for selective inhibition of HBV replication by penciclovir

Abstract

Chronic hepatitis B virus (HBV) infection has been esti-The deoxyguanosine analog penciclovir (PCV; 9-[4-mated to affect more than 300 million individuals worldwide, hydroxy-3-hydroxymethyl-but-1-yl]guanine), has shown and those affected are unable to benefit from recently develpotent antiviral activity against herpes viruses and hepoped hepatitis B surface antigen-containing vaccines. 1 Atadnaviruses. Efficacy against chronic hepatitis B virus tempts to control chronic HBV disease using antiviral chemo-(HBV) infection has been demonstrated in an animal therapy have, until recently, been relatively unsuccessful. 2,3model and in recent clinical trials of famciclovir, the oral Although early attempts to treat HBV infection with nucleoform of PCV. The antiviral activity of PCV is believed side analogs were often compromised by associated toxicity, 2,3 to be dependent on the intracellular formation of PCVthe discovery that the replication of hepadnaviral genomes triphosphate (PCV-TP) which is presumed to inhibit involves an obligatory reverse transcription step 4,5 has stimu-HBV replication by interfering with viral DNA polymerase activity. The (S)-enantiomer is preferentially formed lated renewed interest in this field. In particular, the many in herpes virus-infected cells, and is the more active nucleoside analogs which have been identified as inhibitors against the herpes simplex virus; however, little is of the human immunodeficiency virus reverse transcriptase, known about the biochemical mechanisms of PCV phos-seem to be generally regarded as potential anti-HBV phorylation or of interference with viral replication in agents.2,3 However, it is becoming increasingly clear that HBV-infected cells. Here, we report that in contrast with there are other HBV-specific enzymatic processes besides reherpes simplex virus, the (R)-enantiomer of PCV-TP is verse transcription which are potential targets for nucleoside a more potent inhibitor of HBV DNA polymerase-reverse analogs. 6,7 transcriptase (pol-RT) in vitro than the (S)-enantiomer.Compound screening using a variety of systems including In assays for HBV DNA pol-RT activity, in which purified cell-free enzyme assays, cell culture, and live animal models viral core particles were the enzyme source, the IC 50 s suggest that apart from (-)-b-L-2,3-dideoxy-3-thiacytidine for (R)-and (S)-enantiomers of PCV-TP were 2.5 mmol/L (lamivudine) and structurally related deoxycytidine anaand 11 mmol/L, respectively. The estimated K i s for (R)-logs, 3,8,9 the most efficacious anti-HBV agents identified to and (S)-PCV-TP were É0.03 mmol/L and É.04 mmol/L, date are deoxyguanosine (GdR) analogs.2,3 Members of the respectively, about 3-fold lower than the K m for deoxy-latter group with proven anti-HBV activity include acyclovir guanosine triphosphate (dGTP) in the same system. In (ACV), 10 dideoxyguanosine, 11,12 ganciclovir (GCV), 13-17 penaddition, we report that PCV metabolism is similar in ciclovir (PCV), [18][19][20][21][22] and the carbocyclic analog of 2-deoxyguaboth control ...

In Vitro Antihepadnaviral Activities of Combinations of Penciclovir, Lamivudine, and Adefovir

“…6). Both specifically inhibit the hepadnaviral DNA polymerase/reverse transcriptase by competing with the corresponding dNTPs for incorporation into nascent DNA and acting as chain terminators after incorporation (11,33,35). Specific interference with the unique dGTP-dependent step which primes hepadnaviral reverse transcription (12) is an additional mechanism by which PCV exerts antihepadnaviral activity and which is not shared by 3TC.…”

In vitro evaluation of hepatitis B virus polymerase mutations associated with famciclovir resistance

“…Previous studies have shown that both the (R)-and (S)-enantiomers can inhibit HBV polymerase; however, the (R)-enantiomer was over 4-fold more potent than the (S)-enantiomer. 15,19 In our studies we used racemic PCVTP, which contains an equal proportion of both enantiomers.…”

“…15 Famciclovir was originally approved for the treatment of herpes simplex virus and herpes zoster virus. 16,17 Later, famciclovir was shown to have activity against human and duck hepatitis B viruses in enzymatic and cell culture assays and in animal models of infection.…”

“…16,17 Later, famciclovir was shown to have activity against human and duck hepatitis B viruses in enzymatic and cell culture assays and in animal models of infection. 15,[18][19][20][21] Clinical studies subsequently showed that famciclovir can reduce serum HBV levels in patients chronically infected with HBV. 5,10,11 In analogous fashion to the treatment of human immunodeficiency virus (HIV) infection, HBV infection also requires prolonged administration of nucleoside analogs to eliminate the virus from patients' sera, and emergence of drug-resistant HBV during extended monotherapy appears to be a factor that may ultimately limit treatment efficacy.…”

Transient selection of a hepatitis B virus polymerase gene mutant associated with a decreased replication capacity and famciclovir resistance

“…3,4 It was further shown that penciclovir triphosphate not only inhibits the DNA dependent DNA polymerase activity of the HBV polymerase, 5 but also the RNA-dependent activity of this enzyme, i.e., reverse transcription, by inhibiting the synthesis of the short DNA primer for reverse transcription. 6 Preliminary evidence suggested that famciclovir may have clinical utility in the treatment of chronic hepatitis B patients 7 and in orthotopic liver transplant patients.…”