Gene/Protein Disease Symptom Drug Enzyme Compound
Pivot Concepts:   Target Concepts:
Query: EC:2.7.1.21 (thymidine kinase)
 7,561 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

One of the most frequently studied therapeutic strategies in the field of suicide gene therapy is based on the expression by tumor cells of the Herpes simplex virus thymidine kinase gene (HSVtk) followed by a ganciclovir (GCV) treatment. In order to investigate the potential of other enzyme/prodrug strategies, we studied in vitro and in vivo the ability of the Varicella zoster virus thymidine kinase gene (VZVtk) to act as a suicide gene and to kill non-transduced bystander cells, and compared this activity to that of its HSV counterpart. Four different antiviral compounds were tested as prodrugs. Our comparative study demonstrates the superiority of the HSVtk/GCV system among the different combinations tested and underlines the importance of both the tumor cell type and the prodrug in the success of a prodrug/suicide gene strategy.
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PMID:Identification of factors important for the success of suicide gene therapy after a comparative study of Varicella zoster and Herpes simplex viral thymidine kinases efficacy on breast cancer cells. 1617 63

Varicella zoster virus encodes a thymidine kinase responsible for the activation of antiherpetic nucleoside prodrugs such as acyclovir. In addition, herpes virus thymidine kinases are being explored in gene/chemotherapy strategies aimed at developing novel antitumor therapies. To investigate and improve compound selectivity, we report here structure-based site-directed mutagenesis studies of varicella zoster virus thymidine kinase (VZVTK). Earlier reports showed that mutating residues at the core of the VZVTK active site invariably destroyed activity; hence, we targeted more distal residues. Based on the VZVTK crystal structure, we constructed six mutants (E59S, R84V, H97Y/A, and Y21H/E) and tested substrate activity and competitive inhibition for several compound series. All VZVTK mutants tested retained significant phosphorylation activity with dThd as substrate, apart from Y21E (350-fold diminution in the k(cat)/K(m)). Some mutations give slightly improved affinities: bicyclic nucleoside analogs (BCNAs) with a p-alkyl-substituted phenyl group seem to require aromatic ring stacking interactions with residue 97 for optimal inhibitory effect. Mutation Y21E decreased the IC(50) value for the BCNA 3-(2'-deoxy-beta-D-ribofuranosyl)-6-octyl-2,3-dihydrofuro[2,3-d]pyrimidin-2-one (Cf1368) 4-fold, whereas mutation Y21H increased the IC(50) value by more than 15-fold. These results suggest that residue 21 is important for BCNA selectivity and might explain why HSV1TK is unable to bind BCNAs. Other mutants, such as the E59S and R84V thymidine kinases, which in wild-type VZVTK stabilize the dimer interface, give opposite results regarding the level of sensitivity to BCNAs. The work described here shows that distal mutations that affect the VZVTK active-site may help in the design of more selective substrates for gene suicide therapy or as anti-varicella zoster virus drugs.
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PMID:Mutations distal to the substrate site can affect varicella zoster virus thymidine kinase activity: implications for drug design. 1655 72

Varicella zoster virus (VZV), a member of the herpesvirus family, is responsible for a primary infection (varicella, chickenpox) as well as a recurrent disease (zoster, shingles). The course of varicella is generally benign in immunocompetent patients. For zoster, post-herpetic neuralgia is the most common complication. In immunocompromised patients, particularly patients suffering from the acquired immune deficiency syndrome (AIDS), transplant recipients and cancer patients, VZV infections can be life-threatening. For these patients and also for immunocompetent patients at risk, such as pregnant women or premature infants, the current treatment of choice is based on acyclovir (ACV) by either intravenous or oral route. The low oral bioavailability of ACV, as well as the emergence of drug-resistant virus strains, have stimulated efforts towards the development of new compounds for the treatment of VZV infections. Among these new compounds, penciclovir (PCV) and its oral prodrug form, famciclovir (FCV), 882C87, BVDU, BVaraU and the oral prodrug form of acyclovir (valacyclovir) rank among the most promising. Like ACV itself, all these drugs are dependent on the virus-encoded thymidine kinase (TK) for their intracellular activation (phosphorylation), and, therefore, cross-resistance to these drugs may be expected for those virus mutants that are TK-deficient and thus resistant to ACV. However, such TK(-) VZV mutants are still sensitive to the acyclic nucleoside phosphonates (i.e. HPMPC), which for their phosphorylation do not depend on the virus-encoded TK. The molecular targets within the viral replicative cycle, with which these different compounds interact, are discussed, as are the in vitro activity and in vivo efficacy of the most promising compounds. Other aspects, such as vaccination and passive immunization, are briefly mentioned.
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PMID:Chemotherapy of varicella zoster virus infections. 1861 13

Varicella zoster virus (VZV) is usually associated with mild to moderate illness in immunocompetent patients. However, older age and immune deficiency are the most important risk factors linked with virus reactivation and severe complications. Treatment of VZV infections is based on nucleoside analogues, such as acyclovir (ACV) and its valyl prodrug valacyclovir, penciclovir (PCV) as its prodrug famciclovir, and bromovinyldeoxyuridine (BVDU; brivudin) in some areas. The use of the pyrophosphate analogue foscarnet (PFA) is restricted to ACV-resistant (ACV(r)) VZV infections. Since antiviral drug resistance is an emerging problem, we attempt to describe the contributions of specific mutations in the viral thymidine kinase (TK) gene identified following selection with ACV, BVDU and its derivative BVaraU (sorivudine), and the bicyclic pyrimidine nucleoside analogues (BCNAs), a new class of potent and specific anti-VZV agents. The string of 6 Cs at nucleotides 493 to 498 of the VZV TK gene appeared to function as a hot spot for nucleotide insertions or deletions. Novel amino acid substitutions (G24R and T86A) in VZV TK were also linked to drug resistance. Six mutations were identified in the "palm domain" of VZV DNA polymerase in viruses selected for resistance to PFA, PCV, and the 2-phophonylmethoxyethyl (PME) purine derivatives. The investigation of the contributions of specific mutations in VZV TK or DNA polymerase to antiviral drug resistance and their impacts on the structures of the viral proteins indicated specific patterns of cross-resistance and highlighted important differences, not only between distinct classes of antivirals, but also between ACV and PCV.
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PMID:In vitro-selected drug-resistant varicella-zoster virus mutants in the thymidine kinase and DNA polymerase genes yield novel phenotype-genotype associations and highlight differences between antiherpesvirus drugs. 2219 Jul 13


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