Cell culture and preparation of stock solutions The CT26 cell line (mouse colon carcinoma) was obtained from American Type Culture Collection Cells. Cells were kept in DMEM ((Dulbeccos' modified Eagle's medium, Sigma) with 10% heat inactivated fetal bovine serum (Gibco, Life Technologies) and 1% penicillin streptomycin (Sigma) in a humidified incubator with 5% CO2 at 37 °C. Cells were detached using trypsin-EDTA solution (Sigma), counted, and seeded at the necessary density in plates of the appropriate size. A stock solution of the respective compounds (ca. 1 mM) was prepared with DMSO Hybri-Max TM (Sigma) and stored at -20 °C. Before each experiment, the stock solutions were diluted with the cell culture medium at the desired concentration and then added to the cells. Owing to the inherent toxicity of DMSO, the final concentration of DMSO never exceeded 1-2% after the dilution in DMEM.