Denavir
The guanine nucleoside analog penciclovir is active against chronic duck hepatitis B virus infection in vivo.

Lin E, Luscombe C, Wang YY, Shaw T, Locarnini S.

Victorian Infectious Diseases Reference Laboratory, Fairfield Hospital, Victoria, Australia.

Ducks congenitally infected with duck hepatitis B virus (HBV) were treated with the antiviral guanine nucleoside analog penciclovir for 4 weeks at a dose of 10 mg/kg of body weight per day. The effects of treatment on viremia and intrahepatic viral genome replication, transcription, and translation were examined. In seven of eight penciclovir-treated ducks, viremia was barely detectable after a week of treatment. After 4 weeks of treatment, molecular hybridization studies showed that intrahepatic viral DNA, RNA, and protein levels were significantly reduced compared with those in placebo-treated controls. Synthesis of all viral replicative intermediates, including the normally persistent viral supercoiled DNA species, was inhibited by penciclovir treatment. Examination of liver tissue sections after in situ DNA hybridization or immunohistochemical staining confirmed that viral DNA and protein synthesis had been profoundly inhibited in most hepatic parenchymal cells. However, small subpopulations of cells, in particular the small bile duct epithelial cells, remained strongly positive for duck HBV antigens and DNA despite treatment. There was no evidence of toxicity associated with penciclovir therapy. This study confirms the safety and potent antihepadnaviral activity of penciclovir in vivo but indicates that further improvements in antiviral therapy will be required to completely eliminate HBV infection.

Online source: www.ncbi.nlm.nih.gov/entrez/query.fcgi?cmd=Retrieve&db=PubMed&list_uids=8834889&dopt=Abstract penciclovir Denavir



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

Shaw T, Mok SS, Locarnini SA.

Victorian Infectious Diseases Reference Laboratory, Fairfield Hospital, Australia.

The deoxyguanosine analog penciclovir (PCV; 9-[4-hydroxy-3-hydroxymethyl-but-1-yl]guanine), has shown potent antiviral activity against herpes viruses and hepadnaviruses. Efficacy against chronic hepatitis B virus (HBV) infection has been demonstrated in an animal model and in recent clinical trials of famciclovir, the oral form of PCV. The antiviral activity of PCV is believed to be dependent on the intracellular formation of PCV-triphosphate (PCV-TP) which is presumed to inhibit HBV replication by interfering with viral DNA polymerase activity. The (S)-enantiomer is preferentially formed in herpes virus-infected cells, and is the more active against the herpes simplex virus; however, little is known about the biochemical mechanisms of PCV phosphorylation or of interference with viral replication in HBV-infected cells. Here, we report that in contrast with herpes simplex virus, the (R)-enantiomer of PCV-TP is a more potent inhibitor of HBV DNA polymerase-reverse transcriptase (pol-RT) in vitro than the (S)-enantiomer. In assays for HBV DNA pol-RT activity, in which purified viral core particles were the enzyme source, the IC50s for (R)- and (S)-enantiomers of PCV-TP were 2.5 micromol/L and 11 micromol/L, respectively. The estimated Kis for (R)- and (S)- PCV-TP were approximately 0.03 micromol/L and approximately .04 micromol/L, respectively, about 3-fold lower than the Km for deoxyguanosine triphosphate (dGTP) in the same system. In addition, we report that PCV metabolism is similar in both control (HepG2) and in HBV-transfected (2.2.15) hepatoblastoma cells in vitro, indicating that cellular enzyme(s) catalyze PCV phosphorylation. Peak PCV-TP concentrations of about .4 micromol/L were reached in both cell types in less than 12 hours, and intracellular PCV-TP was exceptionally stable with a half-life of about 18 hours. These observations provide a mechanistic basis for the potent activity of PCV against HBV.

Online source: www.ncbi.nlm.nih.gov/entrez/query.fcgi?cmd=Retrieve&db=PubMed&list_uids=8903366&dopt=Abstract penciclovir Denavir



Denavir
Synergistic inhibition of hepadnaviral replication by lamivudine in combination with penciclovir in vitro.

Colledge D, Locarnini S, Shaw T.

Victorian Infectious Diseases Reference Laboratories, Fairfield Hospital, Victoria, Australia.

Lamivudine ([-]-beta-L-2',3'-dideoxy-3'-thiacytidine [3TC]) and penciclovir (9-[2-hydroxy-1-(hydroxymethyl)ethoxymethyl]guanine [PCV]) are potent inhibitors of hepatitis B virus (HBV) replication. Both drugs have entered phase III clinical trials for treatment of chronic HBV infection. 3TC and PCV are deoxycytidine and deoxyguanosine analogs, respectively, and their modes of action and how they interact are matters of both theoretical and practical interest. We compared the antiviral activities of 3TC and PCV alone and in combination in primary duck hepatocyte (PDH) cultures derived from ducklings congenitally infected with the duck hepatitis B virus (DHBV). 3TC and PCV inhibited DHBV replication to a comparable extent when used alone (50% inhibitory concentrations with 95% confidence intervals were 0.55 [0.50-0.59] micromol/L for 3TC and 0.35 [0.27-0.43] micromol/L for PCV), and in combination, the two nucleoside analogs acted synergistically over a wide range of clinically relevant concentrations. Synergy between PCV and 3TC was also observed in acutely infected cells and in "washout" experiments designed to assess the persistence of antiviral activity after drug removal. Furthermore, the combination was more effective in reducing the normally recalcitrant viral covalently closed circular (CCC) DNA form of DHBV than either drug alone. These results suggest that combinations of 3TC and PCV may act synergistically against HBV in vivo.

Online source: www.ncbi.nlm.nih.gov/entrez/query.fcgi?cmd=Retrieve&db=PubMed&list_uids=9214473&dopt=Abstract penciclovir Denavir



Denavir
In vitro oxidation of famciclovir and 6-deoxypenciclovir by aldehyde oxidase from human, guinea pig, rabbit, and rat liver.

Rashidi MR, Smith JA, Clarke SE, Beedham C.

Pharmaceutical Chemistry, School of Pharmacy, University of Bradford, UK.

Famciclovir, a 9-substituted guanine derivative, is a new antiviral agent which undergoes rapid hydrolysis and oxidation in man to yield the active antiherpes agent, penciclovir. Studies with human liver cytosol have indicated that the oxidation of the penultimate metabolite, 6-deoxypenciclovir, to penciclovir is catalyzed by the molybdenum hydroxylase, aldehyde oxidase. In the present study the oxidation of famciclovir and 6-deoxypenciclovir with partially purified molybdenum hydroxylases from human, guinea pig, rabbit, and rat livers and bovine milk xanthine oxidase has been investigated. Famciclovir and 6-deoxypenciclovir were oxidized predominantly to 6-oxo-famciclovir and penciclovir, respectively, by human, guinea pig, and rat liver aldehyde oxidase. Small amounts of 8-oxo and 6,8-dioxo-metabolites were also formed from each substrate. Famciclovir and 6-deoxypenciclovir were good substrates for rabbit liver aldehyde oxidase but, in each case, two major metabolites were formed. 6-Deoxypenciclovir was converted to penciclovir and 8-oxo-6-deoxypenciclovir in approximately equal quantities; famciclovir was oxidized to 6-oxo-famciclovir and a second metabolite which, on the basis of chromatographic and UV spectral data, was thought to be 8-oxo-famciclovir. Two groups of Sprague Dawley rats were identified; those containing hepatic aldehyde oxidase and xanthine oxidase and those with only xanthine oxidase. These have been designated AO-active and AO-inactive rats, respectively. Famciclovir was not oxidized by enzyme from AO-inactive rats or bovine milk xanthine oxidase although 6-deoxypenciclovir was slowly converted to penciclovir by rat liver or milk xanthine oxidase. Inhibitor studies showed in human, guinea pig, and rabbit liver that xanthine oxidase did not contribute to the oxidation of famciclovir and 6-deoxypenciclovir; thus it is proposed that drug activation in vivo would be catalyzed solely by aldehyde oxidase.

Online source: www.ncbi.nlm.nih.gov/entrez/query.fcgi?cmd=Retrieve&db=PubMed&list_uids=9224775&dopt=Abstract penciclovir Denavir



Denavir
Phosphorylation of aciclovir, ganciclovir, penciclovir and S2242 by the cytomegalovirus UL97 protein: a quantitative analysis using recombinant vaccinia viruses.

Zimmermann A, Michel D, Pavic I, Hampl W, Luske A, Neyts J, De Clercq E, Mertens T.

Universitat Ulm, Abteilung Virologie, Germany.

We used recombinant vaccinia viruses (rVV) containing the UL97 open reading frame (ORF) of the human cytomegalovirus (HCMV) to investigate the UL97-dependent phosphorylation of different nucleoside analogs. The rVV T1 expressed the wild-type UL97 protein whereas rVV A5 contained a 12 bp deletion in the UL97 which had been known to be responsible for resistance of HCMV to ganciclovir (GCV). The rVV T1opal was generated which contained a stop codon at position 1089 of the UL97 ORF and which expressed a truncated UL97 protein. We quantitatively analyzed the capability of these rVVs to phosphorylate GCV, penciclovir (PCV), aciclovir (ACV) and 2-amino-7-[(1,3-dihydroxy-2-propoxy)methyl] purine (S2242) as well as the natural nucleosides deoxycytidine and deoxythymidine. Moreover, we compared their phosphorylating capability with that of herpes simplex virus type 1 strains. In thymidine kinase (TK)-deficient 143B cells infected with rVV T1, the three compounds GCV, ACV and PCV were phosphorylated with different efficiency whereas in cells infected with the rVV A5 a markedly reduced but not completely abolished phosphorylation of these compounds was observed. In rVV T1opal-infected cells no specific phosphorylation of the compounds was detectable at all. Neither S2242 nor the natural substrates of TKs were phosphorylated by any of the vaccinia recombinants. The rVVs proved to be a suitable tool for analysis of UL97-dependent phosphorylation of nucleoside analogs and also allowed to quantitatively study the influence of UL97 mutations on drug phosphorylation.

Online source: www.ncbi.nlm.nih.gov/entrez/query.fcgi?cmd=Retrieve&db=PubMed&list_uids=9330759&dopt=Abstract penciclovir Denavir