title: Significance of thymidylate synthase for resistance to pemetrexed in lung cancer.
abstract: Pemetrexed (MTA) is a multitargeted antifolate with promising clinical activity in lung cancer. We exposed the small cell lung cancer cell line PC6 to stepwise-increasing pemetrexed concentrations of 0.4, 1.6, and 4.0 microm, and established three pemetrexed-resistant lung cancer cell lines: PC6/MTA-0.4, PC6/MTA-1.6, and PC6/MTA-4.0 cells. To investigate the mechanisms of acquired resistance to pemetrexed, we measured the expression levels of the thymidylate synthase (TS), reduced folate carrier (RFC), and folylpoly-gamma-glutamate synthetase (FPGS) genes. TS gene expression was significantly increased in PC6/MTA-1.6 and PC6/MTA-4.0 cells relative to parental cells in a pemetrexed dose-dependent manner. In contrast, the levels of RFC gene expression in PC6/MTA-0.4 cells and FPGS in PC6/MTA-1.6 cells were significantly decreased, whereas the levels of both genes were restored in PC6/MTA-4.0 cells. Knockdown of TS expression using siRNA enhanced pemetrexed cytotoxicity in PC6/MTA-4.0 cells. The expression level of the TS gene was significantly correlated with the concentration of pemetrexed for 50% cell survival (IC(50)) in 11 non-small cell lung cancer cell lines. These results suggest that the alteration of molecular pharmacological factors in relation with pemetrexed resistance is dose-dependent, and that up-regulation of the expression of the TS gene may have an important role in the acquired resistance to pemetrexed. In addition, TS may be a predictive marker for pemetrexed sensitivity in lung cancer.
authors.affiliation: Department of Medical Oncology and Immunology, Nagoya City University Graduate School of Medical Sciences, Nagoya, Japan.
authors.forename: Hiroaki
authors.initials: H
authors.lastname: Ozasa
authors.forename: Tetsuya
authors.initials: T
authors.lastname: Oguri
authors.forename: Takehiro
authors.initials: T
authors.lastname: Uemura
authors.forename: Mikinori
authors.initials: M
authors.lastname: Miyazaki
authors.forename: Ken
authors.initials: K
authors.lastname: Maeno
authors.forename: Shigeki
authors.initials: S
authors.lastname: Sato
authors.forename: Ryuzo
authors.initials: R
authors.lastname: Ueda
mesh_terms: D000964:Antimetabolites, Antineoplastic / Q000494:pharmacology*; D045744:Cell Line, Tumor; D019008:Drug Resistance, Neoplasm; D004791:Enzyme Inhibitors / Q000494:pharmacology*; D005971:Glutamates / Q000494:pharmacology*; D006147:Guanine / Q000031:analogs & derivatives* / Q000494:pharmacology; D006801:Humans; D008175:Lung Neoplasms / Q000188:drug therapy* / Q000201:enzymology / Q000473:pathology; D026901:Membrane Transport Proteins / Q000235:genetics; D000068437:Pemetrexed; D010453:Peptide Synthases / Q000235:genetics; D058978:Reduced Folate Carrier Protein; D013940:Thymidylate Synthase / Q000032:analysis / Q000037:antagonists & inhibitors* / Q000235:genetics*
chemical_list: D000964:Antimetabolites, Antineoplastic; D004791:Enzyme Inhibitors; D005971:Glutamates; D026901:Membrane Transport Proteins; D058978:Reduced Folate Carrier Protein; C548699:SLC19A1 protein, human; D000068437:Pemetrexed; D006147:Guanine; D013940:Thymidylate Synthase; D010453:Peptide Synthases; C023103:folylpolyglutamate synthetase