After exposure to drugs, the viability was determined by the MTT assay following published procedures [15]. Briefly, 40,000–50,000 cells in 500 μl of medium were plated onto each well of 24-well tissue culture plate. After 24 h of culture, ALA (0.5–5 mM), Hemin (8–24 μg/ml) or D-glucose (2–3 mg/ml) dissolved in PBS immediately prior to use, were added to the medium. Cells were cultured for 24 h. After exposure, the medium was aspirated and replaced with 300 μl of fresh drug-free medium containing 0.5 mg/ml (3-[4,5-dimethylthiazol-2-yl]-2,5-diphenyltetra-zolium bromide) MTT. The cells were incubated for an additional 4 h. This medium containing MTT was removed by inverting the plate and 200 μl of dimethylsulphoxide (DMSO) were then added to each well. After 10 minutes of shaking, absorbance in each well was read in a microplate reader at 570 nm. All experiments included untreated control cells, they were repeated three times and each concentration was tested in sextuplicate. Viability was expressed in terms of population growth, as percent of an untreated control population with standard error of the mean (SEM).