Denavir
Use of isotopically chiral [4'-13C]famciclovir and 13C NMR to identify the chiral monoacetylated intermediates in the conversion of famciclovir to penciclovir by human intestinal wall extract.

Vere Hodge RA, Darlison SJ, Readshaw SA.

SmithKline Beecham Pharmaceuticals, Epsom, Surrey, England.

Famciclovir is the oral form of the potent antiherpesvirus agent, penciclovir. Hydrolysis of one of the acetyl ester groups of famciclovir creates a chiral centre leading to the possible formation of (R)- and (S)-enantiomers. During its conversion to penciclovir, famciclovir forms two chiral metabolites, namely monoacetyl-6-deoxy-penciclovir and monoacetyl-penciclovir. The absolute configuration and stereospecificity of the monoacetyl metabolites of famciclovir, produced in human intestinal wall extract, were determined using isotopically chiral famciclovir and 13C NMR spectroscopy of the isolated metabolites. 13C NMR showed that the esterase(s), in human intestinal wall extract, hydrolysed the acetyl group preferentially from the pro-(S)-acetoxymethyl group of famciclovir. The specificity of esterase action in forming monoacetyl-6-deoxy-penciclovir and monoacetyl-penciclovir was about 77 and 72%, respectively.

Online source: www.ncbi.nlm.nih.gov/entrez/query.fcgi?cmd=Retrieve&db=PubMed&list_uids=8305284&dopt=Abstract penciclovir Denavir



Denavir
Use of isotopically chiral [4'-13C]penciclovir and 13C NMR to determine the specificity and absolute configuration of penciclovir phosphate esters formed in HSV-1 and HSV-2 infected cells and by HSV-1-encoded thymidine kinase.

Vere Hodge RA, Darlison SJ, Earnshaw DL, Readshaw SA.

SmithKline Beecham Pharmaceuticals, Epsom, Surrey, England.

Penciclovir is a potent antiherpesvirus agent which is highly selective due to its phosphorylation only in virus infected cells. Phosphorylation of one of the hydroxymethyl groups of penciclovir (PCV) creates a chiral centre leading to the possible formation of (R)- and (S)-enantiomers. The absolute configuration and stereospecificity of the PCV-phosphates produced in cells infected with herpes simplex viruses types 1 and 2 (HSV-1 and HSV-2), as well as by HSV-1-encoded thymidine kinase, were determined using isotopically chiral [4'-13C]PCV precursors and 13C NMR spectroscopy of the isolated metabolites. The absolute configuration of penciclovir-triphosphate (PCV-TP) produced in HSV-1 infected cells was shown to be S with an enantiomeric purity of greater than 95%. However, in contrast fo HSV-1-infected cells in which none of the (R) enantiomer was detected, about 10% of (R)-PCV-TP was produced in HSV-2-infected cells. Phosphorylation of PCV by HSV-1-encoded thymidine kinase was found to give 75% (S)- and 25% (R)-PCV-monophosphate. The proportion of the (S)-isomer appears to be amplified in the subsequent phosphorylations leading to the triphosphate.

Online source: www.ncbi.nlm.nih.gov/entrez/query.fcgi?cmd=Retrieve&db=PubMed&list_uids=8305285&dopt=Abstract penciclovir Denavir



Denavir
Susceptibility of Oka varicella vaccine strain to antiviral drugs.

Shiraki K, Matsui S, Aiba N.

Department of Virology, Toyama Medical and Pharmaceutical University, Japan.

Susceptibility of Oka varicella vaccine virus to antiherpetic drugs was determined by the effective dose for 50% plaque reduction (ED50) using cell-free virus preparation. ED50 values were 3.02 microM for acyclovir, 3.72 microM for vidarabine, 0.0035 microM for sorivudine, and 4.67 microM for penciclovir. Oka varicella vaccine virus was as susceptible to these drugs as wild-type viruses. Sensitivity of thymidine kinase (TK)-deficient virus to penciclovir and of some DNA polymerase (DPase) mutants to sorivudine suggested that these drugs might be used for the treatment of vaccine recipients, even if Oka varicella vaccine became acyclovir-resistant by mutations in the TK or DPase genes, respectively. This result encourages the wider use of Oka varicella vaccine even for immunocompromised hosts because of its attenuation and susceptibility to chemotherapeutic drugs.

Online source: www.ncbi.nlm.nih.gov/entrez/query.fcgi?cmd=Retrieve&db=PubMed&list_uids=8310756&dopt=Abstract penciclovir Denavir



Denavir
Analysis of the thymidine kinase genes from acyclovir-resistant mutants of varicella-zoster virus isolated from patients with AIDS.

Talarico CL, Phelps WC, Biron KK.

Division of Virology, Wellcome Research Laboratories, Research Triangle Park, North Carolina 27709.

Patients with AIDS often experience recurrent infections with varicella-zoster virus (VZV) requiring repeated or prolonged treatment with acyclovir (ACV), which may lead to the development of ACV resistance. The ACV resistance of isolates recovered from such patients is associated with diminished VZV thymidine kinase (TK) function. We determined the nucleotide sequences of the TK genes of 12 ACV-resistant VZV strains purified from nine patients with AIDS. Five VZV strains contained nucleotide deletions in their TK genes, introducing a premature termination codon which is expected to result in the production of a truncated protein. No detectable full-length TK protein could be immunoprecipitated from extracts of cells infected with these virus strains. These TK-deficient strains were cross resistant to the TK-dependent antiviral agents ACV, 9-(4-hydroxy-3-hydroxymethylbutyl-yl)guanine (penciclovir), and 1-beta-D-arabinofuranosyl-E-5-(2-bromovinyl) uracil (BVaraU). The remaining seven strains each contained a nucleotide change that resulted in an amino acid substitution in the TK protein. These substitutions occurred throughout the TK protein, namely, in the ATP-binding site, the nucleoside-binding site, between the two binding sites, and at the carboxy terminus of the protein. We determined the effects of these mutations on the stability of TK protein expression in virus-infected cells and on the sensitivity of mutants to the TK-dependent antiviral agents ACV, BVaraU, and penciclovir.

Online source: www.ncbi.nlm.nih.gov/entrez/query.fcgi?cmd=Retrieve&db=PubMed&list_uids=8380452&dopt=Abstract penciclovir Denavir



Denavir
Comparative activity of penciclovir and acyclovir in mice infected intraperitoneally with herpes simplex virus type 1 SC16.

Sutton D, Boyd MR.

SmithKline Beecham Pharmaceuticals, Epsom, Surrey, United Kingdom.

Penciclovir [PCV; 9-(4-hydroxy-3-hydroxymethylbut-1-yl)guanine; BRL 39123] is a potent and selective inhibitor of herpes simplex virus and varicella-zoster virus in human cell culture. We have compared the activities of PCV and acyclovir (ACV) in DBA/2 mice infected intraperitoneally with herpes simplex virus type 1 SC16 by measuring the amount of virus in peritoneal washings. In untreated mice after an eclipse phase, virus titers are maximum at 48 h after infection and decline thereafter. PCV and ACV reduced virus replication to a similar extent when given ad libitum in drinking water, even though ACV had better oral bioavailability and greater potency in murine cells. Thus, PCV was more active than had been predicted. In dose-response experiments, PCV given as a single subcutaneous dose 24 h after infection was active at a 10-fold-lower dose than ACV (P < 0.01). A single subcutaneous dose of PCV at 5 h after infection prevented virus replication for 3 days and was more effective than three doses of ACV given 1, 5, and 20 h after infection (P < 0.05). The superior activity of PCV following discrete dosing is not due to pharmacokinetic differences but is probably a reflection of the known stability of the intracellular triphosphate. In this model, the maintenance of high concentrations in blood is less important for PCV than for ACV and may lead to less-frequent doses in clinical use.

Online source: www.ncbi.nlm.nih.gov/entrez/query.fcgi?cmd=Retrieve&db=PubMed&list_uids=8388195&dopt=Abstract penciclovir Denavir