Gene/Protein Disease Symptom Drug Enzyme Compound
Pivot Concepts: Gene/Protein Disease Symptom Drug Enzyme Compound   Target Concepts: Gene/Protein Disease Symptom Drug Enzyme Compound

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Query: EC:2.7.1.21 (thymidine kinase)
7,561 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

(E)-5-(2-bromovinyl)-2'-deoxyuridine (BVDU, Brivudin, Zostex, Zerpex, Zonavir), now more than 20 years after its discovery, still stands out as a highly potent and selective inhibitor of herpes simplex virus type 1 (HSV-1) and varicella-zoster virus (VZV) infections. It has been used in the topical treatment of herpetic keratitis and recurrent herpes labialis and the systemic (oral) treatment of herpes zoster (zona, shingles). The high selectivity of BVDU towards HSV-1 and VZV depends primarily on a specific phosphorylation of BVDU to its 5'-diphosphate (DP) by the virus-encoded thymidine kinase (TK). After further phosphorylation (by cellular enzymes), to the 5'-triphosphate (TP), the compound interferes as a competitive inhibitor/alternate substrate with the viral DNA polymerase. The specific phosphorylation by the HSV- and VZV-induced TK also explains the marked cytostatic activity of BVDU against tumor cells that have been transduced by the viral TK genes. This finding offers considerable potential in a combined gene therapy/chemotherapy approach for cancer. To the extent that BVDU or its analogues (i.e., BVaraU) are degraded (by thymidine phosphorylase) to (E)-5-(2-bromovinyl)uracil (BVU), they may potentiate the anticancer potency, as well as toxicity, of 5-fluorouracil. This ensues from the direct inactivating effect of BVU on dihydropyrimidine dehydrogenase, the enzyme that initiates the degradative pathway of 5-fluorouracil. The prime determinant in the unique behavior of BVDU is its (E)-5-(2-bromovinyl) substituent. Numerous BVDU analogues have been described that, when equipped with this particular pharmacophore, demonstrate an activity spectrum characteristic of BVDU, including selective anti-VZV activity.
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PMID:(E)-5-(2-bromovinyl)-2'-deoxyuridine (BVDU). 1538 33

5'-Fluorouracil (5-FU), used in the treatment of colon and breast cancers, is converted intracellularly to 5'-fluoro-2'-deoxyuridine (5-FUdR) by thymidine phosphorylase and is subsequently phosphorylated by thymidine kinase to 5'-fluoro-2'-dUMP (5-FdUMP). This active metabolite, along with the reduced folate cofactor, 5,10-methylenetetrahydrofolate, forms a stable inhibitory complex with thymidylate synthase that blocks cellular growth. The present study shows that the ATP-dependent multidrug resistance protein-5 (MRP5, ABCC5) confers resistance to 5-FU by transporting the monophosphate metabolites. MRP5- and vector-transfected human embryonic kidney (HEK) cells were employed in these studies. In 3-day cytotoxicity assays, MRP5-transfected cells were approximately 9-fold resistant to 5-FU and 6-thioguanine. Studies with inside-out membrane vesicles prepared from transfected cells showed that MRP5 mediates ATP-dependent transport of 5 micromol/L [(3)H]5-FdUMP, [(3)H]5-FUMP, [(3)H]dUMP, and not [(3)H]5-FUdR, or [(3)H]5-FU. The ATP-dependent transport of 5-FdUMP showed saturation with increasing concentrations and had a K(m) of 1.1 mmol/L and V(max) of 439 pmol/min/mg protein. Uptake of 250 micromol/L 5-FdUMP was inhibited by dUMP, cyclic nucleotide, cyclic guanosine 3',5'-monophosphate, amphiphilic anions such as probenecid, MK571, the phosphodiesterase inhibitors, trequinsin, zaprinast, and sildenafil, and by the chloride channel blockers, 5-nitro-2-(3-phenylpropylamino)-benzoic acid and glybenclamide. Furthermore, the 5-FU drug sensitivity of HEK-MRP5 cells was partially modulated to that of the HEK-vector by the presence of 40 micromol/L 5-nitro-2-(3-phenylpropylamino)-benzoic acid but not by 2 mmol/L probenecid. Thus, MRP5 transports the monophosphorylated metabolite of this nucleoside and when MRP5 is overexpressed in colorectal and breast tumors, it may contribute to 5-FU drug resistance.
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PMID:The multidrug resistance protein 5 (ABCC5) confers resistance to 5-fluorouracil and transports its monophosphorylated metabolites. 1589 50

The aim of the present study was to estimate the expression of mRNA, specific for thymidine kinase 1 (TK1), deoxycytidine kinase (dCK), and thymidine phosphorylase (dThdPase), i.e. enzymes involved in pyrimidine and purine metabolism in human papillary thyroid carcinoma (PTC) tissue. Additionally, the expression of dCK was estimated, in medullary thyroid carcinoma (MTC). For control, the RNA expression levels for all the enzymes were measured in macroscopically unchanged thyroid tissue. Reverse transcriptase-polymerase chain reaction (RT-PCR) and densitometry were employed for mRNA expression measurements, with the beta-actin gene as a control housekeeping gene. The levels of mRNA expression for TK1, dCK and dThdPase in human PTC, as well as mRNA expression for dCK in MTC, were significantly higher than mRNA expressions for those enzymes found in macroscopically unchanged thyroid tissue. It is concluded that an increased expression of mRNA, specific for TK1, dCK and dThdPase, may be involved in carcinogenic processes in the human thyroid.
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PMID:Increased expression of mRNA specific for thymidine kinase, deoxycytidine kinase or thymidine phosphorylase in human papillary thyroid carcinoma. 1597 30

As a general rule, enzymes act on only one enantiomer of a chiral substrate and only one of the enantiomeric forms of a chiral molecule may bind effectively at the catalytic site, displaying biological activity. In recent years, some exceptions have been found among viral and cellular enzymes involved in the synthesis of deoxynucleoside triphosphates and in their polymerisation into DNA. Examples are: herpes virus thymidine kinases, cellular deoxycytidine kinase and deoxynucleotide kinases, human immunodeficiency virus type 1 (HIV-1) reverse transcriptase, hepatitis B virus (HBV) DNA polymerase and, to a lesser extent, some cellular DNA polymerases. The lack of enantioselectivity allows herpes simplex virus (HSV) thymidine kinase and cellular deoxycytidine kinase to phosphorylate the unnatural L-beta-enantiomers of D-thymidine and D-deoxycytidine, respectively, or of their analogues to monophosphate. This phosphorylation represents the first and often the rate-limiting step of their activation to triphosphates. The L-triphosphates can then exert antiviral (anti-HSV, anti-Human cytomegalovirus, anti-HIV-1, anti-HBV) and anticancer activities. Although only one L-nucleoside (3TC) has so far gained United States of America Food and Drug Administration (USA FDA) approval for clinical use against HIV-1, other L-enantiomers of nucleoside analogues, which have shown antiviral or anticancer activity in cell cultures are in clinical trials. Their resistance to enantioselective enzymes, such as thymidine phosphorylase, thymidylate synthase, (deoxy)-cytidine and dCMP deaminases, and their lower affinity for the mitochondrial thymidine kinase can ensure a higher selectivity and lower cytotoxicity with respect to those exerted by their corresponding natural D-enantiomers and might be exploited to solve problems arising during chemotherapy, such as metabolic inactivation, cytotoxicity and drug-resistance.
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PMID:Molecular basis for the antiviral and anticancer activities of unnatural L-beta-nucleosides. 1599 31

Pyrimidine antagonists, for example, 5-fluorouracil (5-FU), cytarabine (ara-C) and gemcitabine (dFdC), are widely used in chemotherapy regimes for colorectal, breast, head and neck, non-small-cell lung cancer, pancreatic cancer and leukaemias. Extensive metabolism is a prerequisite for conversion of these pyrimidine prodrugs into active compounds. Interindividual variation in the activity of metabolising enzymes can affect the extent of prodrug activation and, as a result, act on the efficacy of chemotherapy treatment. Genetic factors at least partly explain interindividual variation in antitumour efficacy and toxicity of pyrimidine antagonists. In this review, proteins relevant for the efficacy and toxicity of pyrimidine antagonists will be summarised. In addition, the role of germline polymorphisms, tumour-specific somatic mutations and protein expression levels in the metabolic pathways and clinical pharmacology of these drugs are described. Germline polymorphisms of uridine monophosphate kinase (UMPK), orotate phosphoribosyl transferase (OPRT), thymidylate synthase (TS), dihydropyrimidine dehydrogenase (DPD) and methylene tetrahydrofolate reductase (MTHFR) and gene expression levels of OPRT, UMPK, TS, DPD, uridine phosphorylase, uridine kinase, thymidine phosphorylase, thymidine kinase, deoxyuridine triphosphate nucleotide hydrolase are discussed in relation to 5-FU efficacy. Cytidine deaminase (CDD) and 5'-nucleotidase (5NT) gene polymorphisms and CDD, 5NT, deoxycytidine kinase and MRP5 gene expression levels and their potential relation to dFdC and ara-C cytotoxicity are reviewed.
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PMID:Genetic factors influencing pyrimidine-antagonist chemotherapy. 1604 92

The presence of mtDNA abnormalities inherited as Mendelian traits indicates the existence of mutations in nuclear genes affecting the integrity of the mitochondrial genome. Two groups of nucleus-driven abnormalities have been described: qualitative alterations of mtDNA, i.e. multiple large-scale deletions of mtDNA, and quantitative decrease of the mtDNA copy number, i.e. tissue-specific depletion of mtDNA. Autosomal dominant or recessive (adPEO), progressive ophthalmoplegia and autosomal-recessive mitochondrial neurogastrointestinal encephalomyopathy (MNGIE), are three neurodegenerative disorders associated with the coexistence of wild-type mtDNA with several deletion-containing mtDNA species. Heterozygous mutations of the genes encoding the muscle-heart isoform of the adenosine diphosphate/adenosine triphosphate mitochondrial translocator (ANT1), the main subunit of polymerase gamma (POLG1), and of the putative mtDNA helicase (Twinkle) have been found in adPEO families linked to three different loci, on chromosomes 4q34-35, 10q24, and 15q25, respectively. Mutations in the gene encoding thymidine phosphorylase have been identified in several MNGIE patients. Severe, tissue-specific depletion of mtDNA is the molecular hallmark of rapidly progressive hepatopathies or myopathies of infancy and childhood. Two genes, deoxyguanosine kinase and thymidine kinase type 2, both involved in the mitochondrion-specific salvage pathways of deoxynucleotide pools, have been associated with depletion syndromes in selected families.
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PMID:Inherited Mendelian defects of nuclear-mitochondrial communication affecting the stability of mitochondrial DNA. 1612 Mar 7

A nucleoside analogue 4'-ethynylstavudine (4'-Ed4T) was recently synthesized during chemical studies directed towards the development of a new route to 4'-carbon-substituted nucleosides. This compound was found to be more anti-HIV-1 active than the parent compound stavudine (d4T) and much less toxic to various cells and also to mitochondrial DNA synthesis. It became apparent that 4'-Ed4T is a better substrate for human thymidine kinase than d4T, and very much more resistant to catabolism by thymidine phosphorylase. The study of 4'-Ed4T against various drug-resistant HIV-1 mutants has disclosed its unique activity profile.
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PMID:4'-Ethynylstavudine (4'-Ed4T) has potent anti-HIV-1 activity with reduced toxicity and shows a unique activity profile against drug-resistant mutants. 1613 May 20

The pro-drug 5-fluorouracil (5-FU) exerts its anti-proliferative action after conversion into cytotoxic metabolites. We previously demonstrated that the anti-cancer action of 5-FU could be enhanced by boosting thymidine phosphorylase (TP) activity in cancer cells, the first step of the DNA pathway, that yields the critical anti-thymidylate synthase (TS) fluorodeoxyuridine monophosphate (FdUMP) metabolite. In the present study, we further studied to what extent 5-FU activity could be optimized by overexpressing cancer cell thymidine kinase (TK), the second step of the DNA pathway, for which controversial data have been published so far. Additionally, screening of biochemical modulators likely to contribute to 5-FU activation was also carried out. TK-overexpressing colorectal cells were obtained after designing vectors harboring viral and human cDNA, and performing stable transfection in the human HT29 cell line. Anti-proliferative assays were subsequently performed so as to evaluate change in cell sensitivity to 5-FU, and metabolism monitoring was carried out to follow drug activation and FdUMP formation after cellular uptake. Finally, TS inhibition was assessed as a pharmacological endpoint. Results showed that overexpression of TK led to a marked desensitization of our model. A negative correlation (r = 0.87) was found between the level of TK activity and 5-FU anti-proliferative action - the higher the activity, the lower the sensitivity. Of the various drugs screened as putative modulators, only those involved in TP activity proved to enhance 5-FU efficacy via optimized FdUMP formation. Conversely, genetically increasing TK activity did not modify 5-FU activation pathway nor subsequent TS inhibition in our model. Therefore, our results indicate that TK is not a limiting step in the production of anti-TS FdUMP and that tumor cells overexpressing TK are likely to resist 5-FU-based chemotherapies.
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PMID:Genetic and biochemical modulation of 5-fluorouracil through the overexpression of thymidine kinase: an in-vitro study. 1655 5

Mitochondrial (mt) neurogastrointestinal encephalomyopathy (MNGIE) is an autosomal recessive disease associated with depletion, deletions, and point mutations of mtDNA. Patients lack a functional thymidine phosphorylase and their plasma contains high concentrations of thymidine and deoxyuridine; elevation of the corresponding triphosphates probably impairs normal mtDNA replication and repair. To study metabolic events leading to MNGIE we used as model systems skin and lung fibroblasts cultured in the presence of thymidine and/or deoxyuridine at concentrations close to those in the plasma of the patients, a more than 100-fold excess relative to controls. The two deoxynucleosides increased the mt and cytosolic dTTP pools of skin fibroblasts almost 2-fold in cycling cells and 8-fold in quiescent cells. During up to a two-month incubation of quiescent fibroblasts with thymidine (but not with deoxyuridine), mtDNA decreased to approximately 50% without showing deletions or point mutations. When we removed thymidine, but maintained the quiescent state, mtDNA recovered rapidly. With thymidine in the medium, the dTTP pool of quiescent cells turned over rapidly at a rate depending on the concentration of thymidine, due to increased degradation and resynthesis of dTMP in a substrate (=futile) cycle between thymidine kinase and 5'-deoxyribonucleotidase. The cycle limited the expansion of the dTTP pool at the expense of ATP hydrolysis. We propose that the substrate cycle represents a regulatory mechanism to protect cells from harmful increases of dTTP. Thus MNGIE patients may increase their consumption of ATP to counteract an unlimited expansion of the dTTP pool caused by circulating thymidine.
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PMID:Mitochondrial DNA depletion and thymidine phosphate pool dynamics in a cellular model of mitochondrial neurogastrointestinal encephalomyopathy. 1677 11

Derivatives of 2'-deoxyuridine that contain fluoroalkyl groups at the C5 position and derivatives of thymidine that contain fluoroalkyl groups at the N3 position were synthesized and examined in three in vitro assays designed to evaluate their potential as radiopharmaceuticals for imaging cellular proliferation. Three of the former nucleosides and five of the latter were synthesized. The three assays were as follows: (a) phosphoryl transfer assay, which showed that all three of the former nucleosides and four of the latter ones were phosphorylated by recombinant human thymidine kinase 1 (TK1) and that N(3)-(2-fluoroethyl)-thymidine (NFT202) was the most potent substrate of the eight nucleosides studied; (b) transport assay, which indicated that all eight nucleosides had good affinity for an 6-[(4-nitrobenzyl)thio]-9-beta-d-ribofuranosylpurine-sensitive mouse erythrocyte nucleoside transporter, with inhibition constants in the range of 0.02-0.55 mM; and (c) degradation assay, which showed that all but one of the former nucleosides and none of the latter were degraded by recombinant Escherichia coli thymidine phosphorylase (an enzyme that catalyzes the glycosidic bond of thymidine and 2'-deoxyuridine derivatives). From these in vitro screening assays, we selected NFT202 as a candidate for subsequent in vivo evaluation because this compound met the three minimum requirements of the in vitro screening assays and had the most potent phosphorylation activity as a substrate for recombinant human TK1.
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PMID:Alkyl-fluorinated thymidine derivatives for imaging cell proliferation I. The in vitro evaluation of some alkyl-fluorinated thymidine derivatives. 1693 94


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