FTI-induced inhibition of cell viability and colony formation in normal and CML bone marrow cells measured by colorimetric MTT and methylcellulose colony-forming cell (CFC) assays. Each circle in panels A (colorimetric MTT assay) and B (methylcellulose CFC assay) represents a subject studied and indicates the percentage of inhibition of cell viability and colony formation by each FTI at the IC50 described in “Effects of FTIs on CML cells” (control cultures were considered 100%). Horizontal bars represent the mean; vertical bars, SEM. Cumulative mean inhibition of cell viability and of CFC, ± SEM, for any FTI used: 45% ± 5% and 47.7% ± 7% in CML cells versus 12.3% ± 2% and 15.5% ± 1% in normal cells; P = .03 and P < .001, respectively. (C) FTI effects on CFC from purified CD34⁺ cells of 3 CML patients and 3 healthy donors, measured by methylcellulose CFC assay. SCH at 1 μM (▦) was inoffensive on normal cells while causing more than 50% colony growth inhibition of CML cells; at 10 μM(▪) there was 50% colony growth inhibition of normal cells and 90% colony growth inhibition of CML cells. Error bars represent SEM. Statistical analysis (paired t test) showed P < .05 only in the CML group for no treatment (□) versus 1 μM and 10 μM SCH.