5637, T24 and SW780 cell apoptosis was analyzed using an Annexin V-FITC/PI double staining kit (Invitrogen, Carlsbad, Calif, USA) with flow cytometry (FACScan, BD Biosciences, San Jose, CA, USA) as described previously [20 (link)]. Apoptotic cell proportion was calculated using CELL Quest 3.0 software (BD Biosciences).