In vitro cytotoxicity, apoptosis, effects on cell cycle kinetics and schedule-dependent effects induced by paclitaxel on c6 and cho-k1 cell lines

Exposure of C6 and CHO-K1 cells to different concentrations of the antineoplastic drug paclitaxel resulted in a loss of cellular viability. The percentage of surviving cells fell significantly after 48 hours of treatment and IC₅₀ values observed were between 0.5 to 0.75 and 0.25 to 0.75 μg/ml in C6 and CHO-K1 cells, respectively. No significant cytotoxicity was observed after 24 hours of treatment and cells incubated at higher concentrations of paclitaxel showed increased survivability. Paclitaxel induced apoptosis by caspase 3/7 activation and caused accumulation of cells in the G2/M phase of the cell cycle. Upon fluorescent microscopy, both the cell lines lost the morphology, confluence and adherence at 24 hours but effects were much more pronounced at 48 hours of treatment. The in vitro data suggested that paclitaxel is highly effective when there is prolonged exposure of tumor to the drug rather than increasing the intratumoral or biophasic concentration of the drug.