In vitro radiosensitisation by trabectedin in human cancer cell lines.

Purpose: To examine the potential radiosensitising properties of trabectedin (ET-743, Yondelis).
Methods and Materials: In vitro chemosensitivity was assessed in four tumour cell lines (DU145, HeLa, HT29, HOP62) by the crystal violet method. IC10s and IC50s were established for 1-h, 24-h and 7-day (continuous) exposure times. Radiosensitisation was evaluated by conventional colony assay. BrdUrd DNA-labelling and flow cytometry were used to analyse cell cycle kinetics. The rate of apoptotic induction was assed by annexyn-V labelling.
Results: Mean IC50s were 18.8 nM (10.5 - 30), 2.5 nM (1.5 - 5) and 0.25 nM (0.2-0.8) for 1 h, 24 h and continuous exposure times, respectively. HT29 and HOP62 were the most sensitive cells lines to trabectedin. Radiosensitisation was observed in DU145 and HeLa cells with a dose enhancement factor (DEF) of 1.92 and 1.77 at IC50 dose level, respectively. Trabectedin induced early S phase arrest in all cell lines studied.
Conclusions: Trabectedin, at pharmacologically appropriated concentrations, harbours a significant in vitro radiosensitising effect and induces cell cycle changes and apoptosis in several human cancer cell lines. Further studies to define the clinical potential of the combination of trabectedin and radiotherapy are needed.