The purpose of this study was to determine, as we did for paclitaxel, the cytotoxic and radiosensitizing potential of docetaxel in human head and neck cancer cells (ZMK-1), and in cervical squamous cell carcinoma cells (CaSki). ZMK-1 cells were incubated with docetaxel for 3, 9 or 24 hr before irradiation and 24 hr after irradiation. CaSki cells were incubated with docetaxel 24 hr before and after irradiation. For ZMK-1 cells, the docetaxel concentrations (0.7, 0.7 and 0.35 nM) were determined to obtain approximately equivalent cell survival at the different incubation times (3, 9 and 24 hr, respectively). For CaSki cells, the necessary concentration of docetaxel was 0.07 nM. Radiation doses were given from 0 to 7 Gy. Cell survival was measured by a standard clonogenic assay after a 9-day incubation. Flow cytometry was used to measure the capacity of docetaxel to accumulate cells in the G2/M phase of the cell cycle. We observed a weak accumulation of cells in the G2/M phase for the ZMK-1 cells and a pronounced accumulation for CaSki cells. For docetaxel incubation before irradiation, the isoeffect enhancement ratios for ZMK-1 cells determined at the 37% survival level were 1.18, 2.01, and 2.40 for pre-incubation at 3, 9 and 24 hr, respectively; for CaSki cells the ratio was 1.44. For a docetaxel incubation of 24 hr after irradiation, the isoeffect enhancement ratios determined at the 37% survival level were 1.54 and 1.17 for the ZMK-1, and CaSki cells, respectively. A radiosensitizing effect of docetaxel could be demonstrated unambiguously in the two cell lines used. In contrast to our previously published results with paclitaxel, docetaxel seems to be a better radiosensitizer than paclitaxel.
Copyright 2001 Wiley-Liss, Inc.