Cell cycle effects of gemcitabine

Gemcitabine (2 ' ,2 ' -difluoro-2 ' -deoxycytidine, or dFdC) is a promising anticancer agent with demonstrated clinical activity in solid tumours curr ently undergoing clinical trials. Despite extensive studies on the biochemi cal mechanism of action, cell cycle perturbations induced by dFdC have not yet been thoroughly investigated, apart from the expected inhibition of DNA synthesis. The aim of our study was to clarify whether cell population kin etics is a vital factor in the cytotoxicity of dFdC in single or repeated t reatments and in the dfdC-cisplatin combination. Ovarian cancer cells growi ng in vitro were treated with dFdC for I hr in a range of concentrations fr om 10 nM to 10 pM. Cell kinetics was investigated by DNA-bromodeoxyuridine flow cytometry, using different experimental protocols to measure either th e time course of DNA-synthesis inhibition or the fate of cells in G,, S or G,M at the time of dFdC treatment or 24 hr later, A modified sulforhodamine B test was used to assess the growth inhibition caused by dFdC given alone or with cisplatin, Although dFdC promptly inhibited DNA synthesis, cytotox icity on proliferating cells was not specific for cells initially in the S phase. DNA synthesis was restored after a G, block of variable, dose-depend ent length, but recycling cells were intercepted at the subsequent checlkpo ints, resulting in delays in the G,M and G, phases. The activity of repeate d treatment with dFdC+dFdC or dfdC+cisplatin was highly dependent on the in terval length between them. These results suggest that the kinetics of cell recycling from a first dFdC treatment strongly affects the outcome of a se cond treatment with either dFdC itself or cisplatin. (C) 2001 Wiley-Liss, I nc.