title: Potent and specific inhibitors of mammalian phosphoribosylpyrophosphate (PRPP) synthetase.
abstract: The monophosphates of the exocyclic amino ribonucleosides, 4-amino- and 4-methoxy-8-(D-ribofuranosylamino)pyrimido[5,4-d]pyrimidine, are potent and specific inhibitors of human erythrocyte and B-lymphoblast PRPP synthetase. The inhibition by MRPP monophosphate is competitive (Ki = 35 microM with the PRPP synthetase cofactor, Pi (Km = 2 mM). The nucleosides are phosphorylated to the active metabolite by adenosine kinase and these nucleoside monophosphates accumulate in the cell. beta-ARPP is a substrate, albeit poor, for adenosine deaminase and solutions of the beta-anomer of this nucleoside and its monophosphate anomerize over time to give alpha- and beta-mixtures. beta-MRPP is more resistant to adenosine deaminase and anomerization of the nucleoside and its monophosphate is negligible. The effect of treatment of cells with the nucleosides is a time-dependent and nearly universal reduction in the nucleotide content which appears to result from a reduction in the availability of PRPP for dependent metabolic pathways. In studies with the WI-L2 lymphoblasts, some of these pathways, de novo and salvage (hypoxanthine and guanine) synthesis of purine nucleotides, are more sensitive to a restriction of PRPP availability than others, i.e. de novo pyrimidine synthesis. The nucleosides have shown promise as therapeutic agents in a mouse leukemia evaluation system but may also have future use in unravelling the complex regulation of PRPP synthetase and the dependent nucleotide synthesis pathways.
authors.affiliation: Department of Biochemistry, Nucleic Acid Research Institute, Costa Mesa, California 92626.
authors.forename: R C
authors.initials: RC
authors.lastname: Willis
authors.forename: L D
authors.initials: LD
authors.lastname: Nord
authors.forename: J M
authors.initials: JM
authors.lastname: Fujitaki
authors.forename: R K
authors.initials: RK
authors.lastname: Robins
mesh_terms: D000818:Animals; D000970:Antineoplastic Agents / Q000494:pharmacology; D002455:Cell Division / Q000187:drug effects; D002460:Cell Line; D002470:Cell Survival / Q000187:drug effects; D006801:Humans; D007939:Leukemia L1210 / Q000188:drug therapy; D051379:Mice; D010770:Phosphotransferases / Q000037:antagonists & inhibitors*; D012263:Ribonucleosides / Q000138:chemical synthesis / Q000494:pharmacology* / Q000627:therapeutic use; D012268:Ribose-Phosphate Pyrophosphokinase / Q000037:antagonists & inhibitors*; D013329:Structure-Activity Relationship; D014407:Tumor Cells, Cultured / Q000187:drug effects
chemical_list: D000970:Antineoplastic Agents; D012263:Ribonucleosides; D010770:Phosphotransferases; D012268:Ribose-Phosphate Pyrophosphokinase