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 ...

The Enantioselectivity of Enzymes Involved in Current Antiviral Therapy Using Nucleoside Analogues: A New Strategy?

“…However, in the series of 2′,3′-dideoxynucleoside triphosphates, the introduction of a fluorine atom at position 2′ of the ribose reversed this tendency (Figure 9) (von Janta-Lipinski et al, 1998). The (R)-enantiomer of PCVTP is a more potent inhibitor of human or duck HBV DNA polymerases than the (S)-enantiomer (Dannaoui et al, 1997;Saw et al, 1996). Finally, the interaction of β-L-FMAUTP (Aguesse-Germon et al, 1998;Pai et al, 1996), β-L-FddCTP (Zoulim et al, 1996), or β-L-Fd4CTP (Zhu et al, 1998) with HBV or DHBV DNA polymerases resulted in strong inhibitions of the enzymes in all cases.…”

“…Compared to HIV RT, the difficulty of obtaining pure samples of the enzyme has probably hampered the inhibition studies with nucleoside triphosphate analogues. In vitro assays of enzyme activity generally use human HBV particles isolated from chronic producer lines (for example, 2.2.15 cells) as the source of enzyme (Davis et al, 1996;Saw et al, 1996;von Janta-Lipinski et al, 1998;Zhu et al, 1998), although assays for the expression of enzymatically active duck HBV RT and human HBV polymerase were recently developed (Aguesse-Germon et al, 1998;Li & Tyrrell, 1999). Mechanistic studies of HBV polymerase inhibition by Lnucleoside triphosphate analogues have seldom been performed but, at least in the case of L-3TCTP, it has been suggested that both competitive inhibition by binding to DHBV RT and DNA chain termination occur (Severini et al, 1995).…”

Treatment of chronic hepatitis B: New antiviral therapies

“…Penciclovir is efficiently phosphorylated to the active metabolite, penciclovir triphosphate. It shows promise for the treatment of HBV based on in vitro data demonstrating effective inhibition of HBV replication [70,73]. Clinical experience with famciclovir in the treatment of HBV infection is still limited.…”