Denavir
Emergence of resistance to acyclovir and penciclovir in varicella-zoster virus and genetic analysis of acyclovir-resistant variants.

Ida M, Kageyama S, Sato H, Kamiyama T, Yamamura J, Kurokawa M, Morohashi M, Shiraki K.

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

We have characterized the differential actions of acyclovir and penciclovir against varicella-zoster virus (VZV) in cell culture by comparing the frequency of appearance of resistant viruses followed by their characterization. Cells were infected with cell-free virus and the cultures were successively treated with increasing concentrations of acyclovir or penciclovir. Drug-resistant viruses were selected in the presence of 6 microg/ml of acyclovir or penciclovir. The emergence frequency of resistant viruses was significantly higher following acyclovir exposure than following penciclovir exposure (Fisher's exact test, P<0.0001), possibly reflecting virus growth differences under these experimental conditions. Based on antiviral drug susceptibility and thymidine kinase (TK) activity assays, 11 acyclovir-resistant variants from seven experiments using three virus strains (Kawaguchi strain, Oka varicella vaccine strain and a clinical isolate from a zoster patient) were found to be TK-deficient. Sequence analysis of TK-deficient variants of the Kawaguchi strain revealed deletions that caused frameshifts, resulting in premature termination in the TK gene.

Online source: www.ncbi.nlm.nih.gov/entrez/query.fcgi?cmd=Retrieve&db=PubMed&list_uids=10027650&dopt=Abstract penciclovir Denavir



Denavir
Comparative analysis of DNA breakage, chromosomal aberrations and apoptosis induced by the anti-herpes purine nucleoside analogues aciclovir, ganciclovir and penciclovir.

Tomicic MT, Bey E, Wutzler P, Thust R, Kaina B.

Institute of Toxicology, Division of Applied Toxicology, University of Mainz, Obere Zahlbacher Str. 67, Germany.

Nucleoside analogues have been used in antiviral therapy and suicide cancer gene therapy. Therefore, it is of importance to compare their potential cytotoxic and genotoxic action. Using metabolically competent CHO cells expressing the thymidine kinase gene of herpes simplex virus type 1 (CHO-HSVtk cells) as a model system, the induction of DNA breaks was compared with the induction of structural chromosomal aberrations and apoptosis/necrosis after exposure to the anti-herpes nucleoside analogues aciclovir (ACV), ganciclovir (GCV) and penciclovir (PCV). After continuous treatment of CHO-HSVtk cells with the drugs, LD(10) in a colony-forming assay was 50, 0.5 and 1 microM for ACV, GCV and PCV, respectively, with GCV to be the most potent agent as determined at a given dose level. There was a remarkable difference in the activity of the agents to kill HSVtk expressing and non-expressing cells: the difference in cellular sensitivity of HSVtk(+) versus HSVtk(-) cells at LD(10) level was 7-fold for ACV, 60-fold for GCV and 400-fold for PCV. The drugs were shown to be strong inducers of apoptosis that was analysed as to concentration- and time-dependence; they induced to only very low extent necrosis. The agents were also highly potent in the induction of DNA single-strand breaks (SSBs) and double-strand breaks (DSBs) (as measured by single cell gel electrophoresis (SCGE)) and chromosomal aberrations. Although PCV induced DNA DSBs with a kinetics and frequency similar to that of GCV, it caused mostly condensation defects instead of "typical" structural chromosomal aberrations. For the drugs used, the frequency of apoptotic cells and the induction of abnormal mitoses appear to be related indicating genotoxic effects induced by the agents to be involved in cell killing due to apoptosis.

Online source: www.ncbi.nlm.nih.gov/entrez/query.fcgi?cmd=Retrieve&db=PubMed&list_uids=12175901&dopt=Abstract penciclovir Denavir



Denavir
Penciclovir susceptibilities of herpes simplex virus isolates from patients using penciclovir cream for treatment of recurrent herpes labialis.

Sarisky RT, Bacon T, Boon R, Locke L, Nguyen TT, Leary J, Esser K, Saltzman R.

Department of Host Defense, The Antimicrobial and Host Defense Center of Excellence for Drug Discovery, GlaxoSmithKline Pharmaceuticals, Collegeville, Pennsylvania 19426-0989, USA. robert_t_sarisky gsk.com

The antiherpesvirus agent penciclovir (PCV) shares an identical activation pathway and a similar mode of action with acyclovir (ACV). However, since PCV represents a relatively recent treatment option, the clinical resistance profile to PCV is less well known. A susceptibility program was established to assess the resistance profile for serial herpes simplex virus isolates from immunocompetent patients with recurrent herpes labialis obtained throughout a 4-day period of treatment with topical PCV (1% cream) or a placebo. Two isolates (2 of 1,035 [0.19%]), representing 0.34% of the patients (2 of 585), were confirmed to be PCV-resistant (Pcv(r)) herpes simplex virus type 1 by a plaque reduction assay in MRC-5 cells. These two viruses were highly resistant to PCV (50% inhibitory concentrations [IC(50)s], >55 micro g/ml) and were isolated less than 17 h after the start of patient-initiated treatment. However, subsequent isolates on days 2 and 3 from these patients were completely susceptible to PCV (IC(50)s, <2.0 micro g/ml). Thus, it is not clear whether the resistance to PCV for these two early-treatment isolates was directly associated with the 17 h of PCV treatment; several possible explanations are discussed. In an analysis of the distribution of IC(50) differences between the first and last isolates, there were three patients with minor IC(50) increases in the PCV-treated population and one in the placebo-treated group, although statistically, only the latter was an outlier. No patients were found to have Pcv(r) virus at the end of acute treatment, regardless of treatment group. Overall, the prevalence of Pcv(r) was found to be similar to the 0.3% Acv(r) reported for immunocompetent, untreated populations.

Online source: www.ncbi.nlm.nih.gov/entrez/query.fcgi?cmd=Retrieve&db=PubMed&list_uids=12183237&dopt=Abstract penciclovir Denavir



Denavir
CL1-SR39: A noninvasive molecular imaging model of prostate cancer suicide gene therapy using positron emission tomography.

Pantuck AJ, Berger F, Zisman A, Nguyen D, Tso CL, Matherly J, Gambhir SS, Belldegrun AS.

Department of Urology, Pharmacology and Crump Institute for Molecular Imaging, University of California School of Medicine, Los Angeles, California, USA.

PURPOSE: We developed a prostate cancer tumor model capable of being noninvasively imaged using positron emission tomography (PET) based on expression of the herpes simplex virus thymidine kinase (HSV1-tk) reporter gene. MATERIALS AND METHODS: The androgen independent, metastatic prostate cancer cell lines CL1 and CL1-GFP were stably transfected with the mutant HSV1-tk gene pcDNA3.1/pCMV-sr39tk, which has increased ability to phosphorylate penciclovir. The presence of the sr39tk gene product was analyzed by Western blot analysis and relative thymidine kinase enzyme activity was assessed by a functional thymidine kinase enzyme activity assay. Subcutaneous and orthotopic CL1 and CL1-SR39 tumor xenografts were established in SCID mice. The ability to image CL1-SR39 was assessed using fluorodeoxyglucose and F-penciclovir ( F-FHBG) micro-PET (a rodent PET scanner). To investigate the systemic distribution of intratumoral sr39tk injections established CL1 tumors were transiently injected with first generation adenoviral vectors carrying the sr39tk gene under control of the strong cytomegalovirus promoter Ad-CMV-HSV1-sr39tk and imaged using micro-PET. RESULTS: Transfection of sr39tk into CL1 cells was successful. CL1-SR39 thymidine kinase enzyme activity was greater than twice the activity of the glioma cell line C6-SR39 control and above the threshold necessary for micro-PET detection. Fluorodeoxyglucose micro-PET in SCID mice was positive for CL1 and CL1-SR39 tumors. Selective micro-PET of subcutaneous CL1-SR39 tumors was done using F-FHBG. Micro-PET imaging after systemic and intratumoral injection of Ad-CMV-HSV1-sr39tk revealed significant systemic transgene leakage with significant hepatic expression of sr39TK protein. CONCLUSIONS: Molecular based imaging of sr39tk transfected prostate cancer tumors and adenoviral delivered HSV1-tk suicide gene therapy based on the selective conversion and intracellular trapping of F-FHBG by sr39tk is feasible. Potential applications include noninvasive monitoring of the location, duration and intensity of gene constructs, which may contribute to the safety of clinical gene therapy protocols, and noninvasive imaging of the prostate cancer xenograft response to experimental therapy.

Online source: www.ncbi.nlm.nih.gov/entrez/query.fcgi?cmd=Retrieve&db=PubMed&list_uids=12187266&dopt=Abstract penciclovir Denavir



Denavir
Evaluation of anti-herpesvirus activity of (1'S,2'R)-9-[[1',2'-bis(hydroxymethyl)cycloprop-1'-yl]methyl]- guanine (A-5021) in mice.

Iwayama S, Ohmura Y, Suzuki K, Ono N, Nakazawa H, Aoki M, Tanabe I, Sekiyama T, Tsuji T, Okunishi M, Yamanishi K, Nishiyama Y.

Pharmaceutical Research Laboratories, Ajinomoto Co., Inc., Kawasaki, Japan.

The anti-herpesvirus activity of (1'S,2'R)-9-[[1',2'-bis(hydroxymethyl)cycloprop-1'-yl]methyl]guani ne (A-5021) was evaluated in murine cells and in several murine models of herpes simplex virus (HSV) infection. Against HSV type 1 (HSV-1), A-5021 was 15-30- and 30-60-fold more active, and against HSV type 2 (HSV-2), it was 2- and 8-fold more active than acyclovir and penciclovir in Balb/3T3 cells, respectively. When antiviral compounds were administered orally (once daily) to mice infected intraperitoneally with HSV-1 (Tomioka), A-5021 was more active than acyclovir or famciclovir in spite of its relatively low oral bioavailability. A-5021 was as active as penciclovir when the antiviral compounds were given intravenously (three times daily) to mice infected intraperitoneally with HSV-2 (186). In mice with a cutaneous HSV-1 (KOS) infection, three times daily oral therapy with A-5021 at 25 mg/kg per day produced more significant reduction in severity of skin lesions than equivalent treatment with acyclovir or famciclovir. In mice infected intracerebrally with HSV-1 (Tomioka), complete survival was observed in the group treated intravenously with A-5021 at 25 mg/kg per day (three times daily), while more than 50% of mice died in the groups treated intravenously with acyclovir of up to 100 mg/kg per day (three times daily). Moreover, A-5021 was more effective than acyclovir in clearing infectious virus from the brain. These findings demonstrate that A-5021 has potent anti-HSV activity in several murine models.

Online source: www.ncbi.nlm.nih.gov/entrez/query.fcgi?cmd=Retrieve&db=PubMed&list_uids=10389656&dopt=Abstract penciclovir Denavir