Resistance of a human ovarian cancer line to 5-fluorouracil associated with decreased levels of 5-fluorouracil in DNA.
Two human ovarian cancer cell lines were established from a patient before (PEO1) and after (PEO4) the onset of resistance to 5-fluorouracil (5-FU)/cisplatin-based chemotherapy. Using growth inhibition assays, we determined that the PEO4 line was almost 5-fold more resistant to 5-FU than the PEO1 line. The addition of either 1 or 20 microM leucovorin did not enhance the growth-inhibitory effects of 5-FU against the resistant PEO4 line. In characterizing the potential mechanisms of 5-FU resistance, we found no differences in thymidylate synthase activity between the two lines using both the 5-fluoro-2'-deoxyuridine-5'-monophosphate-binding and catalytic assays. A 4-hr exposure to 1 microM 5-FU resulted in greater ternary complex formation in the resistant line, and we observed no differences between the two lines in 5-FU incorporation into RNA. However, a 4-hr exposure to 1 microM [3H]5-FU resulted in a 3-fold decrease in 5-FU accumulation in the DNA of the resistant PEO4 line. Cesium sulfate gradient centrifugation was used to more accurately separate and analyze for DNA-incorporated 5-FU metabolites and confirmed that the absolute level of 5-FU in the DNA of the PEO4 cells was markedly decreased (6.5-fold) compared with that of the sensitive PEO1 cell line. Moreover, time course studies demonstrated that the accumulated 5-FU in the DNA of the PEO4 cells was more rapidly removed compared with that in the PEO1 cells. Our findings suggest that decreased 5-FU levels in DNA, in part due to an enhanced removal from DNA, represent a mechanism by which the human ovarian cancer PEO4 line expresses decreased sensitivity to 5-FU.
Division of Cancer Treatment, National Cancer Institute, Bethesda, Maryland 20892.
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Chu
G M
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Lai
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Zinn
C J
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Allegra
D004260:DNA Repair; D004273:DNA, Neoplasm / Q000187:drug effects / Q000378:metabolism*; D003856:Deoxyuracil Nucleotides / Q000378:metabolism; D004351:Drug Resistance; D005260:Female; D005472:Fluorouracil / Q000378:metabolism / Q000494:pharmacology*; D006801:Humans; D010051:Ovarian Neoplasms / Q000378:metabolism*; D012334:RNA, Neoplasm / Q000378:metabolism; D013940:Thymidylate Synthase / Q000032:analysis; D014407:Tumor Cells, Cultured / Q000187:drug effects / Q000378:metabolism
D004273:DNA, Neoplasm; D003856:Deoxyuracil Nucleotides; D012334:RNA, Neoplasm; C007267:2'-deoxyuridylic acid; D013940:Thymidylate Synthase; D005472:Fluorouracil