title: Comparison of thymidylate synthase (TS) protein up-regulation after exposure to TS inhibitors in normal and tumor cell lines and tissues.
abstract: Thymidylate synthase (TS) is an important target for cancer chemotherapy. However, several mechanisms of resistance to TS inhibitors have been described. One mechanism that may be relevant to short-term exposure to TS inhibitors occurs as a result of disruption of the autoregulatory loop, which allows TS to control its own translation. This disruption leads to up-regulation of TS protein and is generally thought to decrease efficacy. This study has investigated TS protein up-regulation using a range of TS inhibitors in both tumor and nonmalignant cell lines in vitro and in vivo. Up-regulation of TS protein showed a time-, dose-, and cell-type-specific response to treatment with ZD9331. This response was observed in W1L2 cells treated for 24 h at equitoxic doses of raltitrexed (6-fold), ZD9331 (10-fold), fluorouracil (5-fold), LY231514 (7-fold), AG337 (7-fold), and BW1843U89 (3-fold). Up-regulation was observed over a range of doses. Elevation of TS protein only persisted up to 12 h after removal of drug. The extent of induction does not depend on basal TS levels. Nontransformed human fibroblasts showed significantly greater up-regulation of TS protein than tumor cells exposed to an equitoxic dose of ZD9331. In vivo experiments using the L5178Y thymidine kinase -/- mouse lymphoma implanted into DBA2 mice also showed greater up-regulation of TS protein in normal intestinal epithelial cells compared with tumor cells. These results confirm that TS up-regulation is a common feature of TS inhibition in tumor cells and that it may occur to a greater extent in normal tissues, although the clinical implications of these findings remain to be determined.
authors.affiliation: Cancer Research Campaign Centre for Cancer Therapeutics, Belmont, Surrey, United Kingdom.
authors.forename: S J
authors.initials: SJ
authors.lastname: Welsh
authors.forename: J
authors.initials: J
authors.lastname: Titley
authors.forename: L
authors.initials: L
authors.lastname: Brunton
authors.forename: M
authors.initials: M
authors.lastname: Valenti
authors.forename: P
authors.initials: P
authors.lastname: Monaghan
authors.forename: A L
authors.initials: AL
authors.lastname: Jackman
authors.forename: G W
authors.initials: GW
authors.lastname: Aherne
mesh_terms: D000704:Analysis of Variance; D000818:Animals; D000964:Antimetabolites, Antineoplastic / Q000494:pharmacology; D000970:Antineoplastic Agents / Q000494:pharmacology; D015153:Blotting, Western; D004305:Dose-Response Relationship, Drug; D004797:Enzyme-Linked Immunosorbent Assay; D005260:Female; D005347:Fibroblasts / Q000378:metabolism; D005434:Flow Cytometry; D005472:Fluorouracil / Q000494:pharmacology; D005971:Glutamates / Q000494:pharmacology; D006147:Guanine / Q000031:analogs & derivatives* / Q000494:pharmacology; D006801:Humans; D007211:Indoles / Q000494:pharmacology; D020128:Inhibitory Concentration 50; D054833:Isoindoles; D051379:Mice; D008811:Mice, Inbred DBA; D018613:Microscopy, Confocal; D009368:Neoplasm Transplantation; D000068437:Pemetrexed; D011799:Quinazolines / Q000494:pharmacology; D013876:Thiophenes / Q000494:pharmacology; D013940:Thymidylate Synthase / Q000037:antagonists & inhibitors* / Q000378:metabolism*; D013997:Time Factors; D014407:Tumor Cells, Cultured; D015854:Up-Regulation
chemical_list: D000964:Antimetabolites, Antineoplastic; D000970:Antineoplastic Agents; D005971:Glutamates; D007211:Indoles; D054833:Isoindoles; D011799:Quinazolines; D013876:Thiophenes; C094299:ZD 9331; D000068437:Pemetrexed; C079601:1843U89; D006147:Guanine; D013940:Thymidylate Synthase; C068874:raltitrexed; C099178:nolatrexed; D005472:Fluorouracil