title: Significance of thymidylate synthase expression for resistance to pemetrexed in pulmonary adenocarcinoma.
abstract: Pemetrexed (PEM), a multi-targeted antifolate, has promising clinical activity in non-squamous non-small cell lung cancer. However, the majority of patients eventually acquire resistance to PEM. To evaluate the resistant mechanisms, the A549 lung adenocarcinoma cell line was exposed to stepwise increasing PEM concentrations of 1.6, 6.4 and 16 μM to establish three PEM-resistant lung cancer cell lines, A549/PEM-1.6, -6.4 and -16. Growth inhibition was determined by the 3-[4,5-dimethylthiazol-2-yl]-2,5-diphenyltetrazolium bromide assay. Expression of the genes encoding thymidylate synthase (TS), reduced folate carrier (RFC) and folypoly-γ-glutamate synthetase (FPGS) were analyzed by quantitative real-time reverse transcription polymerase chain reaction. The three A549 cell lines showed more resistance to PEM (3.7-, 17.3-and 38.0-fold, respectively) compared with that of the parental cell line, which also showed cross-resistance to cisplatin, but not to docetaxel, vinorelbine and 5-Fluorouracil (5-FU). TS gene expression was significantly increased in three PEM-resistant cells, relative to that of the parental cells, in a PEM dose-dependent manner. Knockdown of TS expression with siRNA enhanced the cytotoxicity of PEM in A549/PEM-16 cells. By contrast, the levels of RFC and FPGS gene expression in A549/PEM-1.6 and -6.4 cells were significantly decreased, whereas the levels of the two genes were restored in A549/PEM-16 cells. In summary, PEM-resistant A549 cells remained sensitive to docetaxel, vinorelbine and 5-FU. TS expression appeared to be associated with resistance to PEM, which may be a predictive marker for PEM sensitivity in lung adenocarcinoma.
authors.affiliation: Department of Oncology, Jiangsu Province Geriatric Institute, Nanjing, Jiangsu 210009, P.R. China.
authors.forename: Min
authors.initials: M
authors.lastname: Yang
authors.affiliation: Department of Oncology, Jiangsu Province Geriatric Institute, Nanjing, Jiangsu 210009, P.R. China.
authors.forename: Wei-Fei
authors.initials: WF
authors.lastname: Fan
authors.affiliation: Department of Oncology, Jiangsu Province Geriatric Institute, Nanjing, Jiangsu 210009, P.R. China.
authors.forename: Xiao-Lin
authors.initials: XL
authors.lastname: Pu
authors.affiliation: Department of Oncology, Jiangsu Province Geriatric Institute, Nanjing, Jiangsu 210009, P.R. China.
authors.forename: Fu-Yin
authors.initials: FY
authors.lastname: Liu
authors.affiliation: Department of Oncology, Jiangsu Province Geriatric Institute, Nanjing, Jiangsu 210009, P.R. China.
authors.forename: Li-Juan
authors.initials: LJ
authors.lastname: Meng
authors.affiliation: Department of Oncology, Jiangsu Province Geriatric Institute, Nanjing, Jiangsu 210009, P.R. China.
authors.forename: Jun
authors.initials: J
authors.lastname: Wang
keywords: folypoly-γ-glutamate synthetase; non-small cell lung cancer; pemetrexed; reduced folate carrier; resistance; thymidylate synthase