title: Relaxed enantioselectivity of human mitochondrial thymidine kinase and chemotherapeutic uses of L-nucleoside analogues.
abstract: Our discovery that Herpes virus thymidine kinase (TK) and cellular deoxycytidine kinase lack enantioselectivity, being able to phosphorylate both D- and L-enantiomers of the substrate, suggested the use of unnatural L-nucleoside analogues as antiviral drugs (Herpes, hepatitis and immunodeficiency viruses). Several L-nucleoside analogues have displayed a short-term cytotoxicity much lower than their corresponding D-counterpart. Since the delayed cytotoxicity of a drug often depends on its effects on mitochondrial metabolism, we have investigated the degree of enantioselectivity of human mitochondrial thymidine kinase (mt-TK). We demonstrate that mt-TK does not show an absolute enantioselectivity, being able to recognize, although with lower efficiency, the L-enantiomers of thymidine, deoxycytidine and modified deoxyuridines, such as (E)-5-(2-bromovinyl)-2'-deoxyuridine and 5-iodo-2'-deoxyuridine. Interestingly, the reported negative co-operativity of mt-TK phosphorylating beta-D-2'-deoxythymidine (D-Thd), disappears when the deoxyribose moiety has the inverted configuration, resulting in the preferential phosphorylation of d-Thd even in the presence of high concentrations of the L-enantiomer. This, coupled with the higher Km for beta-L-2'-deoxythymidine (L-Thd), makes mt-TK resistant to high concentrations of L-Thd and L-Thd analogues, minimizing the mitochondria-dependent delayed cytotoxicity that might be caused by the administration of L-nucleoside analogues as antivirals.
authors.affiliation: Istituto di Genetica Biochimica ed Evoluzionistica, Consiglio Nazionale delle Ricerche, Pavia, Italy.
authors.forename: A
authors.initials: A
authors.lastname: Verri
authors.forename: G
authors.initials: G
authors.lastname: Priori
authors.forename: S
authors.initials: S
authors.lastname: Spadari
authors.forename: L
authors.initials: L
authors.lastname: Tondelli
authors.forename: F
authors.initials: F
authors.lastname: Focher
mesh_terms: D001667:Binding, Competitive; D001973:Bromodeoxyuridine / Q000031:analogs & derivatives / Q000494:pharmacology; D003517:Cyclopentanes / Q000494:pharmacology; D003600:Cytosol / Q000201:enzymology; D003841:Deoxycytidine / Q000031:analogs & derivatives* / Q000378:metabolism / Q000494:pharmacology* / Q000627:therapeutic use; D003842:Deoxycytidine Kinase / Q000378:metabolism*; D003857:Deoxyuridine / Q000031:analogs & derivatives / Q000494:pharmacology; D006367:HeLa Cells; D006801:Humans; D008928:Mitochondria / Q000201:enzymology*; D010766:Phosphorylation; D013237:Stereoisomerism; D013379:Substrate Specificity; D013936:Thymidine / Q000031:analogs & derivatives* / Q000378:metabolism / Q000494:pharmacology* / Q000627:therapeutic use; D013937:Thymidine Kinase / Q000378:metabolism*
chemical_list: D003517:Cyclopentanes; D003841:Deoxycytidine; C020235:brivudine; C063455:carbocyclic 5-iodo-2'-deoxyuridine; D013937:Thymidine Kinase; D003842:Deoxycytidine Kinase; D001973:Bromodeoxyuridine; D013936:Thymidine; D003857:Deoxyuridine