Fig. 6 Cell growth, assayed using MTT test, of KB cells treated and untreated with compound 3 (C3) (25 µM) and N-acetylcysteine (NAC) (500 µM) for 72 hrs. Stock solution of the compound 3 was prepared in DMSO and the final concentration of this solvent was kept constant at 0.25%. Control cultures received DMSO alone. Each value represents the mean ± SD of three experiments, performed in quadruplicate. *Significant vs. control untreated cells (p < 0.001). **Significant vs. cells treated with compound 3 (25 µM) (p < 0.001).