Search

Background: Paclitaxel (Taxol) is known to act mainly in mitosis, interfering with microtubule dynamics, but effects on the other cells cycle phases have been reported also. However, a comparative picture of perturbation and killing in the G1, S and G2M phases after drug treatment is lacking. The approach developed by our group tackles the problem of the complexity of cell cycle effects with the aid of a computer program simulating cell cycle progression and new quantities measuring cell-cycle arrest and death. Methods: The program generates data that were compared with those given by absolute cell counts and by different flow cytometry techniques, enabling us to follow the fate of G1 and G2M blocked cells either re-entering the cycle or dying, distinguishing cytostatic and cytotoxic effects. Apoptosis was analyzed in order to refine the description of cytotoxic effects. Results: We estimated the number of blocked and dead cells after short-term Taxol treatments in a range of concentrations and post-drug incubation times. G2M block was immediately active at low concentrations but was reversible, becoming irreversible only at the highest concentrations. G1block became active later, allowing cell cycle progression of cells initially in G1, but was still active 48 h post-treatment, at intermediate concentrations. S-phase delay was detected after 24 h. The death rate was much higher within G1than G2M blocked cells. Conclusions: Our analysis unraveled the complexity of cell cycle effects of the drug, and revealed the activity of G1 checkpoint, hidden by a prompter but less cytotoxic G2M block. Cytometry 37:113–124, 1999. © 1999 Wiley-Liss, Inc.

Flow cytometric cyclin expression/DNA content analysis, now commonly used, provides useful information on the mechanisms regulating cell cycle progression. However, this biparametric analysis does not make a clear-cut distinction between G1 and S-early or between S-late and G2M phase cells. This paper proposes a new three-parameter flow cytometric method with which to determine cyclin B1 levels in single cells in different cell cycle phases by coupling bromodeoxyuridine (BrdUrd) immunodetection and DNA content. DNA denaturation by HCl did not alter the level of cyclin B1. Differences in cyclin B1 expression were observed in seven human cancer cell lines of different origin. The percentage of cyclin B1-positive cells and the cyclin B1 content per cell indicated different patterns. In some cases cyclin B1 accumulation preceded the G2M checkpoint, at which its content usually started to rise. Using available easily reproducible techniques, this flow cytometric approach gives details of intracellular variability in cyclin expression. Cytometry