Micromolar taxol, with or without hyperthermia, induces mitotic catastrophe and cell necrosis in HeLa cells

Although the mode of action of taxol, when used in nanomolar or micromolar concentrations during long periods, is extensively studied, there are few data available on taxol-mediated cytotoxicity when the drug is applied for a short time alone or in combination with hyperthermia. We studied the effect of taxol and hyperthermia on cell cycle kinetics, proliferation, and mode of cell death in human cervical carcinoma HeLa cells, following a scheme which resembles the one currently used in regional chemotherapy.

Cells were incubated with micromolar doses of taxol for two h under normothermic or hyperthermic conditions and then cultured in drug-free medium for several days. Cell viability was assessed via an MTT assay. Necrotic and apoptotic cell death was determined using Trypan blue staining and TUNNEL assay, respectively. Flow cytometry was used for the analysis of cell cycle kinetics and the counting of apoptotic cells. Mitotic index, nuclear morphology and nuclear envelope organization were analyzed by fluorescence microscopy.

Cells exposed to micromolar doses of taxol for 2 h and then transferred to a drug-free medium for 24 h were arrested at G2/M or M phase. When treated cells were cultured in normal media for longer periods, most of them remained in a tetraploid state, became multinucleated without properly completing cytokinesis and died mostly by necrosis. Hyperthermia alone exerted a cytotoxic effect, inhibited proliferation and caused minor changes in cell cycle kinetics. When combined with taxol treatment, hyperthermia modified the cell cycle-arresting effects of the drug, but did not alter significantly taxol-mediated cytotoxicity.

From these data we conclude that short time incubation of HeLa cells under normothermic or hyperthermic conditions with micromolar concentrations of taxol is sufficient enough to induce extended cell growth arrest and cell death by necrosis.