Significance of thymidylate synthase for resistance to pemetrexed in lung cancer

Cancer Sci. 2010 Jan;101(1):161-6. doi: 10.1111/j.1349-7006.2009.01358.x. Epub 2009 Sep 10.


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.

MeSH terms

  • Antimetabolites, Antineoplastic / pharmacology*
  • Cell Line, Tumor
  • Drug Resistance, Neoplasm
  • Enzyme Inhibitors / pharmacology*
  • Glutamates / pharmacology*
  • Guanine / analogs & derivatives*
  • Guanine / pharmacology
  • Humans
  • Lung Neoplasms / drug therapy*
  • Lung Neoplasms / enzymology
  • Lung Neoplasms / pathology
  • Membrane Transport Proteins / genetics
  • Pemetrexed
  • Peptide Synthases / genetics
  • Reduced Folate Carrier Protein
  • Thymidylate Synthase / analysis
  • Thymidylate Synthase / antagonists & inhibitors*
  • Thymidylate Synthase / genetics*


  • Antimetabolites, Antineoplastic
  • Enzyme Inhibitors
  • Glutamates
  • Membrane Transport Proteins
  • Reduced Folate Carrier Protein
  • SLC19A1 protein, human
  • Pemetrexed
  • Guanine
  • Thymidylate Synthase
  • Peptide Synthases
  • folylpolyglutamate synthetase