Resistance of colorectal cancer cells to 5-FUdR and 5-FU caused by Mycoplasma infection

Anticancer Res. 2008 Jul-Aug;28(4B):2175-80.


Background: 5-Fluorouracil (5-FU) is an antineoplastic drug that targets thymidylate synthase (TS). Tumour cells can develop resistance to anti-TS drugs by a variety of mechanisms including up-regulation of TS protein and alterations in drug uptake and degradation. The possible mechanisms of the observed rapid development of resistance to the pyrimidine analogs 5-FUdR and 5-FU in cultured HCT116 colon cancer cells were investigated.

Materials and methods: Cell survival was determined in resistant and control HCT116 cells treated with 5-FUdR and 5-FU for 7 days. The ability of the cells to take up and metabolize these drugs was determined by Western blotting and [3H]thymidine incorporation.

Results and conclusion: Resistant HCT116 cells were 5- and 100-fold more resistant to killing by 5-FU and 5-FUdR, respectively, than the parental cells and exhibited impaired uptake. Although the HCT116R cells were initially Mycoplasma free, a low level of Mycoplasma contamination was found in these cells after several weeks in culture. Sensitivity to 5-FUdR was restored by treatment with an anti-Mycoplasma antibiotic. Our observations emphasize the need for frequent testing for Mycoplasma contamination in any cell line under investigation for resistance to anti-TS drugs.

MeSH terms

  • Aminopterin / metabolism
  • Aminopterin / pharmacology
  • Antimetabolites, Antineoplastic / pharmacology*
  • Colorectal Neoplasms / drug therapy*
  • Colorectal Neoplasms / metabolism
  • Colorectal Neoplasms / microbiology*
  • Drug Resistance, Neoplasm
  • Floxuridine / pharmacology*
  • Fluorouracil / pharmacology*
  • HCT116 Cells
  • HT29 Cells
  • HeLa Cells
  • Humans
  • Hypoxanthine / metabolism
  • Hypoxanthine / pharmacology
  • Mycoplasma Infections / drug therapy
  • Mycoplasma Infections / metabolism*
  • Thymidine / metabolism
  • Thymidine / pharmacology
  • Thymidine Kinase / metabolism
  • Thymidylate Synthase / antagonists & inhibitors
  • Thymidylate Synthase / metabolism
  • Tritium


  • Antimetabolites, Antineoplastic
  • Floxuridine
  • Tritium
  • Hypoxanthine
  • Thymidylate Synthase
  • Thymidine Kinase
  • Aminopterin
  • Fluorouracil
  • Thymidine