title: Cytotoxicity of a new uridine analog, 4-hydroxy-1-(beta-D-ribofuranosyl)-pyridazine-6-one, and its interaction with uridine kinase.
abstract: A new uridine analog, 4-hydroxy-1-(beta-D-ribonfuranosyl)-pyridazin-6-one (3-deaza-6-azaUrd), inhibited the growth of L1210 cells in culture, with a concentration to reduce growth rate to 50% of control of 7 X 10(-5) M. After treatment for 24 or 48 h with 5 X 10(-4) M 3-deaza-6-azaUrd, 80% of the cells were unable to resume growth when the analog was removed from the cultures; also, 99% of the cells were killed, as determined by colony formation in soft agar. Studies on the prevention of the cytotoxic effects of 5 X 10(-4) M 3-deaza-6-azaUrd showed that uridine or cytidine gave complete protection. 2'-Deoxycytidine also gave partial protection, but orotic acid or thymidine had no effect on the growth inhibition by 3-deaza-6-azaUrd. These results suggested that growth inhibition by 3-deaza-6-azaUrd might be due to interference in pyrimidine biosynthesis. Activation of 3-deaza-6-azaUrd to its 5'-phosphate derivative appeared to be catalyzed by uridine kinase. 3-Deaza-6-azaUrd was shown to complete with uridine for phosphorylation (Ki = 4.7 mM) and, therefore, to be a possible alternative substrate for uridine kinase from mouse kidney (Km for uridine = 82 microM). The enzyme was partially purified by streptomycin sulfate precipitation, ammonium sulfate fractionation, and gel filtration. This preparation was found to be free of pyrimidine nucleoside phosphorylase and uridine monophosphate kinase.
mesh_terms: D000818:Animals; D000964:Antimetabolites, Antineoplastic; D001380:Azauridine / Q000031:analogs & derivatives* / Q000378:metabolism / Q000494:pharmacology; D001711:Biotransformation; D002478:Cells, Cultured; D007668:Kidney / Q000201:enzymology; D007700:Kinetics; D007939:Leukemia L1210 / Q000188:drug therapy*; D051379:Mice; D008970:Molecular Weight; D010770:Phosphotransferases / Q000037:antagonists & inhibitors*; D013329:Structure-Activity Relationship; D014541:Uridine Kinase / Q000037:antagonists & inhibitors*
chemical_list: D000964:Antimetabolites, Antineoplastic; C017852:3-deaza-6-azauridine; D001380:Azauridine; D010770:Phosphotransferases; D014541:Uridine Kinase