Taxol-enhanced cytotoxic effect of radiation in human promyelocytic leukemia cells: relative resistance of multidrug-resistant HL-60 cells in vitro

Cytotoxic effects of sequential taxol (paclitaxel) and X-irradiation on drug-sensitive human cultured promyelocytic leukemia (HL-60) cell line and its multidrug-resistant sublines were examined using photometric MTT test and flow cytometry. Paclitaxel (at concentrations 1-10 nmol) stimulated the cytotoxic effect of irradiation in HL-60 and to a lesser extent also in HL-60/ADR, but not in HL-60/VCR cells. The stimulation of radiation-induced cytotoxic effect by paclitaxel correlated with its potential to induce cell cycle and viability alterations identified with flow cytometric analysis (i.e. increased propidium iodide staining, increased side scatter, decreased forward angle scatter, accumulation of necrotic cell detritus, apoptotic pre-G0 cells and cells in the G2/M phase of the cell cycle).