Mechanisms of Natural Resistance to Antifolates in Human Soft Tissue Sarcomas

Wei Wei Li, James T. Lin, William P. Tong, Tanya M. Trippett, Murray F. Brennan, Joseph R. Beitino

Research output: Contribution to journalArticlepeer-review

57 Scopus citations


Efforts to use fresh human sarcoma cells for evaluating antifolate resistance with an in situ thymidylate synthesis assay using 5-[3H] deoxyuridine were unsuccessful because of low thymidylate synthesis activity in enzymatically disaggregated tumors. By incubating tumor cell suspensions in supplemented RPMI-1640 medium with 10% fetal bovine serum for 3 days, activity of the in situ thymidylate synthesis assay markedly increased (1.42 versus 0.03 pmol/h/107 cells), thus allowing 75% of samples to be evaluated for antifolate sensitivity. By criteria developed with a methotrexate-resistant and -sensitive cell line, this assay indicated that most sarcomas are naturally resistant to methotrexate (12 of 15). Natural resistance to 10-ethyl-lO-deazaaminopterin and trimetrexate was also observed in 60% of the samples (nine of 15, respectively). The results from the 3-day in situ assay were confirmed by specific tests for resistance mechanisms in most sarcoma samples. The resistance mechanisms detected were impaired polyglutamylation, an increased level of dihydrofolate reductase, and amplification of this gene. These results encourage further exploration of this assay to predict response to antifolates in individual patients and to evaluate efficacy of new antifolates as candidates for clinical trial.

Original languageEnglish (US)
Pages (from-to)1434-1438
Number of pages5
JournalCancer Research
Issue number6
StatePublished - Mar 1992
Externally publishedYes

All Science Journal Classification (ASJC) codes

  • Oncology
  • Cancer Research


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