Increased methotrexate-induced DNA strand breaks and cytotoxicity following mutational loss of thymidine kinase

Int J Cancer. 1991 Apr 22;48(1):92-5. doi: 10.1002/ijc.2910480117.


The cytotoxicity and DNA lesions induced by methotrexate (MTX) were compared in wild-type, hypoxanthine-guanine phosphoribosyltransferase-deficient (HGPRT-) and thymidine-kinase-deficient (TK-) HL-60 cells. TK- and HGPRT- cells were approximately 10 and 3 times more sensitive to MTX than wild-type cells, respectively. Following incubation with 2 microM MTX for 16 hr, TK- cells showed a significantly higher number of DNA strand breaks. Concomitantly, DNA fragmentation at the nucleosomal linker region was detected more prominently in TK- cells. Although MTX tended to decrease TTP pools similarly in all 3 cells types, the initial TTP level in TK- cells was only about one-fifth of that found in the wild type. These results indicate that the thymidine salvage pathway has a pivotal role in mediating MTX-induced toxicity and DNA lesions.

MeSH terms

  • Cell Line
  • Cell Survival / drug effects
  • DNA Damage*
  • DNA, Neoplasm / drug effects
  • DNA, Neoplasm / genetics*
  • Humans
  • Hypoxanthine Phosphoribosyltransferase / genetics
  • Kinetics
  • Leukemia, Promyelocytic, Acute
  • Methotrexate / pharmacology*
  • Methylnitronitrosoguanidine / pharmacology*
  • Mutagenesis
  • Thymidine Kinase / genetics*
  • Thymine Nucleotides / metabolism


  • DNA, Neoplasm
  • Thymine Nucleotides
  • Methylnitronitrosoguanidine
  • Hypoxanthine Phosphoribosyltransferase
  • Thymidine Kinase
  • thymidine 5'-triphosphate
  • Methotrexate