[Isolation and properties of methotrexate-resistant choriocarcinoma cells in vitro]

The sensitivity to methotrexate (MTX) of ten kinds of human choriocarcinoma cell lines was studied in vitro. The cell line most sensitive to MTX was HCCM-5 and it was fed with a medium containing increasing concentrations of MTX. A resistant subline (HCCM-5R) which could proliferate in the medium containing 5 X 10(-7)M MTX was obtained after about 80 weeks of feeding. The properties of HCCM-5R cells were compared with those of the parent HCCM-5 cells. i) There were no apparent differences in morphology between the HCCM-5 and HCCM-5R lines. The population doubling time was almost the same for both cell lines. ii) The hCG level in the culture fluid of the HCCM-5R cells was about twice as high as that of the HCCM-5 cells. iii) The concentration of MTX which inhibited 50% of DNA synthesis in HCCM-5R cells was 10,000 times higher than that for HCCM-5 cells. iv) Each X and Y chromosome was identified in 90% of the HCCM-5 cells, while no Y chromosome was detected in the HCCM-5R cells. v) The DNA distribution pattern for HCCM-5R cells consisted of a large fraction of each cell with DNA G1 phase content and distributed in the tetraploid range, whereas that of HCCM-5 showed no particular cell cycle pattern. vi) The incorporation of 3H-MTX in the HCCM-5R cells was one tenth of that in the HCCM-5. vii) The intracellular DHFR activity of the HCCM-5R cells was about 5 times higher than that of HCCM-5. These results suggest that MTX-resistant cells among the HCCM-5 cells were selected in long-term contact with MTX, and sensitivity to MTX was concerned with both the MTX transport and intracellular DHFR levels.