colorimetric assay to measure cell cytotoxicity, proliferation or viability. Metabolically active cells are able to convert the dye to a water-insoluble dark blue formazan by reductive cleavage of the tetrazolium ring [28,29]. MTT in PBS (100 ll at 2.5 mg/ml) was added and the cells were incubated for 2 h. The solution was carefully removed and the remaining crystals were dissolved in 100 ll of DMSO after which the absorbance at 590 nm of each well was determined using a BIO-RAD microplate model 550 reader. The growth inhibition was determined relative to untreated controls. Data were used for construction of response curves and determination of the IC50 (concentration of the complex that restricts cell growth to 50% of that compared with the control) values was graphically done by use of GraphPad Prism software, version 3.02, 2000.