title: Mechanisms of drug resistance to inhibitors directed at the individual subunits of ribonucleotide reductase.
abstract: Ribonucleotide reductase consists of two non-identical subunits, non-heme iron subunit (NHI) and effector-binding subunit (EB), that are encoded by different genes and that can be specifically and independently inhibited. L1210 cell lines were selected for resistance to hydroxyurea (HU-7), deoxyadenosine (Y-8), or the combination of pyrazoloimidazole and deoxyadenosine (ED2). The gene for the NHI was amplified in the HU-7, Y-8, and ED2 cell lines; there was no amplification of the gene for the EB. The mRNA for the NHI was increased in the HU-7, Y-8, and ED2 cells, but there was no change in the mRNA levels for the EB. Reductase activity was increased in the HU-7, ED2 cells, but not in the Y-8 cells. The reductase activities in the Y-8 and the ED2 cells were not subject to feedback inhibition by dATP. These data show that the mechanisms of resistance to inhibitors directed at this reductase are varied and do not require increased enzyme activity. Further, gene amplification or increased mRNA levels did not necessarily result in increased levels of cellular enzyme.
authors.affiliation: Department of Internal Medicine, University of South Florida College of Medicine, H. Lee Moffitt Cancer Center and Research Institute, Tampa 33612.
authors.forename: G L
authors.initials: GL
authors.lastname: Carter
authors.forename: D P
authors.initials: DP
authors.lastname: Thompson
authors.forename: J G
authors.initials: JG
authors.lastname: Cory
mesh_terms: D000818:Animals; D000970:Antineoplastic Agents / Q000494:pharmacology*; D002455:Cell Division / Q000187:drug effects; D004273:DNA, Neoplasm / Q000235:genetics / Q000302:isolation & purification; D003839:Deoxyadenosines / Q000494:pharmacology*; D004351:Drug Resistance / Q000235:genetics*; D006918:Hydroxyurea / Q000494:pharmacology*; D007939:Leukemia L1210 / Q000201:enzymology; D046911:Macromolecular Substances; D051379:Mice; D011720:Pyrazoles / Q000494:pharmacology*; D012334:RNA, Neoplasm / Q000235:genetics / Q000302:isolation & purification; D012262:Ribonucleoside Diphosphate Reductase / Q000037:antagonists & inhibitors* / Q000235:genetics; D012264:Ribonucleotide Reductases / Q000037:antagonists & inhibitors* / Q000235:genetics; D014407:Tumor Cells, Cultured / Q000166:cytology / Q000187:drug effects* / Q000201:enzymology
chemical_list: D000970:Antineoplastic Agents; D004273:DNA, Neoplasm; D003839:Deoxyadenosines; D046911:Macromolecular Substances; D011720:Pyrazoles; D012334:RNA, Neoplasm; C019857:CDP reductase; D012264:Ribonucleotide Reductases; D012262:Ribonucleoside Diphosphate Reductase; C000971:2,3-dihydro-1H-imidazo(1,2-b)pyrazole; D006918:Hydroxyurea