title: Design of species- or isozyme-specific enzyme inhibitors. 1. Effect of thymidine substituents on affinity for the thymidine site of hamster cytoplasmic thymidine kinase.
abstract: 5-(Ethylamino)- and 5-acetamido-2'-deoxyuridine 5'-triphosphates were synthesized; the extent and concentration dependence of their inhibitory action on the title enzyme resembled that of the feedback inhibitor TTP. This and other findings provide a tentative indication that bulk tolerance near C-5 of the thymine ring may be more extensive at the TTP site than at the thymidine site. Enzyme-inhibitor dissociation constants (Ki values) were determined for thymidine derivatives monosubstituted at various positions. Competitive inhibition with respect to thymidine (indicative of substituent tolerance in the enzyme-thymidine complex) was produced by 3-amylthymidine (Ki = 65 muM), trans-5-bromo-6-ethoxy-5,6-dihydrothymidine diastereoisomers (Ki = 180 and 310 muM), 5'-C-(acetamidomethyl)- and 5-C-(propionamidomethyl)thymidine epimers (Ki range 65--1100 muM), 3'-acetamido- and 3'-(ethylthio)-3'-deoxythymidines (Ki = 2.5 mM and 12 muM, respectively), and certain 5'-(alkylamino)- and 5'-(alkylthio)-5'-deoxythymidines (Ki range 180--1200 muM). Evidence indicates that bulk tolerance at some, if not most, of the above atoms of thymidine is found in the enzyme-thymidine complexes of human and other mammalian thymidine kinases; attachment of suitable substituents to such atoms could, in principle, lead to thymidine site directed isozyme-specific inhibitors of human cytoplasmic thymidine kinase, which is a candidate target in the design of antineoplastic drugs.
mesh_terms: D000818:Animals; D006224:Cricetinae; D003593:Cytoplasm / Q000201:enzymology; D003841:Deoxycytidine / Q000031:analogs & derivatives / Q000138:chemical synthesis / Q000494:pharmacology; D003857:Deoxyuridine / Q000031:analogs & derivatives / Q000138:chemical synthesis / Q000494:pharmacology; D006801:Humans; D066298:In Vitro Techniques; D007527:Isoenzymes / Q000037:antagonists & inhibitors*; D007668:Kidney / Q000201:enzymology; D007700:Kinetics; D008722:Methods; D008928:Mitochondria / Q000201:enzymology; D013329:Structure-Activity Relationship; D013379:Substrate Specificity; D013936:Thymidine / Q000031:analogs & derivatives* / Q000138:chemical synthesis / Q000494:pharmacology; D013937:Thymidine Kinase / Q000037:antagonists & inhibitors*; D013942:Thymine Nucleotides / Q000138:chemical synthesis / Q000494:pharmacology
chemical_list: D007527:Isoenzymes; D013942:Thymine Nucleotides; D003841:Deoxycytidine; D013937:Thymidine Kinase; D013936:Thymidine; D003857:Deoxyuridine