[Comparison of in vitro assays for the cytotoxic effect of anticancer drugs].

The cytotoxic effects of three anticancer drugs, methotrexate (MTX), 5-fluorouracil (5-Fu) and oridonin (Rub A), were investigated using a human gastric adenocarcinoma cell line (MGc80-3) and a human esophageal cancer cell line (CaEs-17) by means of colony-forming assay, dye exclusion test, measurement of incorporation of 3H-thymidine into DNA and examination of mitotic index. MGc80-3 cells, exposed for 24 hr to increasing concentrations of MTX (0-1.6 micrograms/ml), 5-Fu (0-12 micrograms/ml) or Rub A (0-25 micrograms/ml), showed different types of dose-survival curves determined by colony-forming assay. It suggests that these drugs have different models of action. The killing effect of MTX and 5-Fu was obviously underestimated by dye exclusion; the cell numbers were reduced to about 30% and 60% of control, while the colony formation showed approximately 2.5 and 3.5-log kill. When CaEs-17 cells exposed for 6 hr to varying concentrations of Rub A (0-15 micrograms/ml), the reduction in cell number (15 micrograms/ml, T/C = 18.0%) was always less than that (15 micrograms/ml, T/C = 3.8%) in colony formation. Under the same condition, the mitotic index, however, increased with increasing dosage first, and then the T/C values, at higher concentrations (5-15 micrograms/ml), reached approximately 200%. Although the drug significantly inhibited the incorporation of 3H-thymidine, the pattern of the dose-response curve differed from the dose-survival curve. These findings in cytobiochemistry and morphology may contribute to explain the cytotoxicity of an anticancer drug, but failed in correlation with the data obtained by colony-forming assay which seems to be the most reliable method for determining drug-induced cell lethality.