title: 5'-deoxy-5'-methylthioadenosine phosphorylase--IV. Biological activity of 2-fluoroadenine-substituted 5'-deoxy-5'-methylthioadenosine analogs.
abstract: 5'-Deoxy-5'-methylthioadenosine phosphorylase (MTAPase) phosphorolyzes 5'-deoxy-5'-methylthioadenosine (MTA) generated during polyamine biosynthesis to adenine and 5-methylthioribose-1-phosphate. Two doubly-substituted, 2-fluoroadenine-containing analogs of MTA, 5'-deoxy-2-fluoroadenosine (5'-dFAdo) and 5'-deoxy-5'-iodo-2-fluoroadenosine (5'-IFAdo), were synthesized and studied as substrates of MTAPase: their reaction with this enzyme resulted in the liberation of the cytotoxic base, 2-fluoroadenine, as well as potentially cytotoxic analogs of 5-methylribose-1-phosphate. The activities of these MTA analogs were compared to that of the singly-substituted analog, 5'-deoxy-5'-methylthio-2-fluoroadenosine (5'-MTFAdo). The cytotoxic action of these MTA analogs depended primarily on their conversion to 2-fluoroadenine-containing nucleotides, as a cell line that contains both MTAPase and adenine phosphoribosyltransferase (APRT) activity (HL-60 human promyelocytic leukemia) readily converted these MTA analogs to 2-fluoroadenine-containing nucleotides (especially 2-fluoroadenosine triphosphate) and was highly sensitive to the growth-inhibitory effects of all three compounds (IC50 values in the 10(-8) M range), whereas cell lines lacking MTAPase (CCRF-CEM human T-cell leukemia) or APRT (HL-60/aprt1 cells) did not form analog nucleotides and were relatively insensitive to these compounds (IC50 values in the 10(-5) M range). The doubly-substituted analogs were not more growth inhibitory than 5'-MTFAdo in wild type HL-60 cells as the potent effects of 2-fluoroadenine may mask the activity of the 5-methylthioribose-1-phosphate analogs generated in the reaction of these compounds with MTAPase. 5'-dFAdo and 5'-IFAdo also were irreversible inhibitors of S-adenosylhomocysteine hydrolase, which may explain in part the weak but observable growth inhibitory action of these compounds against MTAPase-deficient cell lines.
mesh_terms: D000228:Adenine Phosphoribosyltransferase / Q000378:metabolism; D000241:Adenosine / Q000031:analogs & derivatives* / Q000378:metabolism / Q000627:therapeutic use; D002460:Cell Line; D055598:Chemical Phenomena; D002621:Chemistry; D002851:Chromatography, High Pressure Liquid; D003839:Deoxyadenosines / Q000031:analogs & derivatives / Q000378:metabolism / Q000627:therapeutic use; D006801:Humans; D015470:Leukemia, Myeloid, Acute / Q000188:drug therapy / Q000201:enzymology; D010430:Pentosyltransferases / Q000378:metabolism*; D011683:Purine-Nucleoside Phosphorylase / Q000378:metabolism*; D013329:Structure-Activity Relationship; D013872:Thionucleosides / Q000378:metabolism* / Q000627:therapeutic use
chemical_list: D003839:Deoxyadenosines; D013872:Thionucleosides; C008500:5'-methylthioadenosine; C030964:2'-fluoro-2'-deoxyadenosine; D010430:Pentosyltransferases; D011683:Purine-Nucleoside Phosphorylase; C021784:5'-methylthioadenosine phosphorylase; D000228:Adenine Phosphoribosyltransferase; D000241:Adenosine