Anti-proliferative effect of GBT on human cancer cells. Cell viability was determined by MTT assay. The results are expressed as percentages of viable cells compared to untreated cells (vehicle). Data show the means ± SD of two independent triplicate experiments. (A) Inhibition of cell viability by GBT in several human cancer cell lines for 48 h. (B) Comparison of the effects of GBT on the viability of three squamous carcinoma cell lines: A431, SCC12, and SCC13 for 48 h. (C) Effect of GBT on the growth of A431 and HaCaT cells for 24 and 48 h, respectively. (D) Comparison of GBT-induced cytotoxicity between A431 cells and mouse primary liver cells (as a normal cells) in a dose- and time-dependent manner.