title: Mechanisms of acquired resistance to the quinazoline thymidylate synthase inhibitor ZD1694 (Tomudex) in one mouse and three human cell lines.
abstract: Four cell lines, the mouse L1210 leukaemia, the human W1L2 lymphoblastoid and two human ovarian (CH1 and 41M) cell lines, were made resistant to ZD1694 (Tomudex) by continual exposure to incremental doses of the drug. A 500-fold increase in thymidylate synthase (TS) activity is the primary mechanism of resistance to ZD1694 in the W1L2:RD1694 cell line, which is consequently highly cross-resistant to other folate-based TS inhibitors, including BW1843U89, LY231514 and AG337, but sensitive to antifolates with other enzyme targets. The CH1:RD1694 cell line is 14-fold resistant to ZD1694, largely accounted for by the 4.2-fold increase in TS activity. Cross-resistance was observed to other TS inhibitors, including 5-fluorodeoxyuridine (FdUrd). 41M:RD1694 cells, when exposed to 0.1 microM [3H]ZD1694, accumulated approximately 20-fold less 3H-labelled material over 24 h than the parental line. Data are consistent with this being the result of impaired transport of the drug via the reduced folate/methotrexate carrier. Resistance was therefore observed to methotrexate but not to CB3717, a compound known to use this transport mechanism poorly. The mouse L1210:RD1694 cell line does not accumulate ZD1694 or Methotrexate (MTX) polyglutamates. Folylpolyglutamate synthetase substrate activity (using ZD1694 as the substrate) was decreased to approximately 13% of that observed in the parental line. Cross-resistance was found to those compounds known to be active through polyglutamation.
authors.affiliation: CRC Centre for Cancer Therapeutics, Institute of Cancer Research, Sutton, Surrey, UK.
authors.forename: A L
authors.initials: AL
authors.lastname: Jackman
authors.forename: L R
authors.initials: LR
authors.lastname: Kelland
authors.forename: R
authors.initials: R
authors.lastname: Kimbell
authors.forename: M
authors.initials: M
authors.lastname: Brown
authors.forename: W
authors.initials: W
authors.lastname: Gibson
authors.forename: G W
authors.initials: GW
authors.lastname: Aherne
authors.forename: A
authors.initials: A
authors.lastname: Hardcastle
authors.forename: F T
authors.initials: FT
authors.lastname: Boyle
mesh_terms: D000818:Animals; D000970:Antineoplastic Agents / Q000493:pharmacokinetics / Q000494:pharmacology*; D002352:Carrier Proteins / Q000378:metabolism; D003856:Deoxyuracil Nucleotides / Q000378:metabolism; D004351:Drug Resistance; D005260:Female; D058973:Folate Receptors, GPI-Anchored; D005492:Folic Acid / Q000031:analogs & derivatives / Q000378:metabolism; D005493:Folic Acid Antagonists / Q000494:pharmacology; D006801:Humans; D007700:Kinetics; D007939:Leukemia L1210 / Q000188:drug therapy* / Q000201:enzymology* / Q000378:metabolism; D008214:Lymphocytes / Q000187:drug effects* / Q000201:enzymology* / Q000378:metabolism; D008727:Methotrexate / Q000378:metabolism / Q000493:pharmacokinetics; D051379:Mice; D009363:Neoplasm Proteins / Q000378:metabolism; D010051:Ovarian Neoplasms / Q000188:drug therapy* / Q000201:enzymology* / Q000378:metabolism; D010453:Peptide Synthases / Q000378:metabolism; D011099:Polyglutamic Acid / Q000378:metabolism; D011506:Proteins / Q000378:metabolism; D011799:Quinazolines / Q000378:metabolism* / Q000493:pharmacokinetics / Q000494:pharmacology*; D011956:Receptors, Cell Surface; D013876:Thiophenes / Q000493:pharmacokinetics / Q000494:pharmacology*; D013940:Thymidylate Synthase / Q000037:antagonists & inhibitors* / Q000378:metabolism; D013942:Thymine Nucleotides / Q000378:metabolism; D014407:Tumor Cells, Cultured
chemical_list: D000970:Antineoplastic Agents; D002352:Carrier Proteins; D003856:Deoxyuracil Nucleotides; D058973:Folate Receptors, GPI-Anchored; D005493:Folic Acid Antagonists; D009363:Neoplasm Proteins; D011506:Proteins; D011799:Quinazolines; D011956:Receptors, Cell Surface; D013876:Thiophenes; D013942:Thymine Nucleotides; D011099:Polyglutamic Acid; D005492:Folic Acid; C007267:2'-deoxyuridylic acid; D013940:Thymidylate Synthase; D010453:Peptide Synthases; C023103:folylpolyglutamate synthetase; C068874:raltitrexed; C059966:ICI 198583; C024157:thymidine 5'-triphosphate; D008727:Methotrexate