Pharmacometabolomics of docetaxel-treated human MCF7 breast cancer cells provides evidence of varying cellular responses at high and low doses

There is growing evidence that docetaxel, a microtubule-targeting agent like the other taxane paclitaxel, induces dual cytotoxicity mechanism according to dose level. Postgenomics screening technologies are now more and more applied to the elucidation of drug response mechanisms. Proton nuclear magnetic resonance spectroscopy-based pharmacometabolomics was here applied to get further insight into the response of human MCF7 breast carcinoma cells to docetaxel at high (clinical, 5 mu M) and low (1 nM) doses. The global response to both doses was evaluated by nuclear morphology and DNA content, the latter as an index of cell proliferation and DNA ploidy. High dose provoked long-lasting cell cycle arrest in mitosis during the first 48 h of exposure to treatment and severe decrease in DNA content followed by significant amount of cell death. In contrast, at low dose, no long-lasting cell cycle arrest was observed on micrographies, and DNA content was decreased but less than at high dose (P < 0.05), without significant cell death. This response was compared to biochemical alteration assessed by pharmacometabolomics. Thirty metabolites were identified and quantified. Metabolite profiling at clinical dose revealed time-dependent disorders in derivatives of glycolysis, lipid metabolism and glutathione metabolism. Comparison between high and low doses was performed at 72 h and showed common traits including the accumulation of cytidinediphosphocholine (x5.0 and x6.9, respectively, P < 0.03), the decrease in phosphatidylcholine (x0.3 and x0.2, respectively, P < 0.03), and gluthathione (x0.6 and x0.6, respectively, P < 0.03). Despite that, significant dose-dependent differences were found in 12 of 30 measured metabolites. Among them, the most discriminant metabolites were polyunsaturated fatty acids (ratio of high-to-low dose of 14.8, P < 0.05), glutamate, myoinositol, and homocysteine (ratio < 0.4, P < 0.05). In addition, the mechanism for glutathione decrease was different. At high dose, it resulted from extensive consumption with precursor starvation (glutamate: -89%, P < 0.05) and increased glutathione S-transferase activity (x5, P < 0.01), whereas at low dose, it resulted from glutathione biosynthesis blockade with homocysteine accumulation (+144%, P < 0.03) and decreased glutathione S-transferase activity (-70%, P < 0.01). Altogether, this pharmacometabolomics analysis provides further evidence of the varying cellular responses at high and low doses of docetaxel in MCF7 breast cancer cells.