Cytotoxic effect of paclitaxel (taxol) either alone or in combination with irradiation in two rat yolk sac tumour cell lines with different radiosensitivities in vitro.

PURPOSE

To investigate the differences between two rat yolk sac tumour cell lines with different radiosensitivities in paclitaxel sensitivity and in the sensitizing effects of paclitaxel in combination with irradiation.

MATERIALS AND METHODS

NMT-1 is a parent radiosensitive cell line and NMT-1R is a variant radioresistant cell line.

RESULTS

Clonogenic assay demonstrated almost the same paclitaxel sensitivity with Do of 5.15 nM in NMT-1 and 5.02 nM in NMT-1R. Many apoptotic cells and DNA ladder formations were observed at 24 h after exposure to paclitaxel in both cell lines. The incidence of DNA fragmentation after 24 h exposure to 20 nM paclitaxel was 12.4 +/- 3.3% for NMT-1, and 13.0 +/- 1.9% for NMT-1R. Paclitaxel showed a supra-additive effect in combination with irradiation in both cell lines at 12 h after paclitaxel treatment only when the accumulation of cells in the G2/M phase reached its peak.

CONCLUSIONS

Paclitaxel had the same cytotoxic effect in two cell lines with different radiosensitivity due to the induction of apoptosis. A supra-additive effect to radiation was observed with 12 h pretreatment in both cell lines. Paclitaxel may be effective for tumours with a component of different radiosensitivity in combination with irradiation.