Evaluating the cytotoxic effects of lovastatin on leukemic cell lines using the MTT assay. (A and B) MTT enzyme activity, after exposure to 0 to 150 μmol/L lovastatin for 2 days, of 6 representative ALL and 7 AML cell lines, respectively. The dotted lines are at the level of MTT30. Results shown are the average of two independent experiments performed in quadruplicate, where the error bars represent the standard deviation of the mean. The values obtained were normalized to the solvent controls set at 100 for clarity of presentation. (C) Histogram showing the concentration of lovastatin required to achieve a decrease of MTT activity by 50% (MTT50) in the ALL and AML cell lines examined. MTT50 values for the ALL and AML cell lines were determined by regression analysis by the method of Chou-Talalay as previously described.49 The significant difference (P = .0012) in the MTT50 values between the ALL and AML cell lines was determined by the Wilcoxon test.