Honokiol induces B-CLL cell death and apoptosis in a dose- and time-dependent manner. (A) B-CLL cells from 19 patients were isolated and treated with varying concentrations of honokiol for 6 or 24 hours. Viability was determined by measuring the level of ATP as an indicator of metabolic activity using a luminescence-based assay. The assay was performed in duplicate, and each sample was normalized to cells incubated without drug to determine the LC₅₀. (B) PBMCs from 19 B-CLL patients or from 7 healthy donors were isolated and treated with the indicated concentrations of honokiol for 6, 24, or 48 hours. Viability was measured as described above. Results were normalized to cells incubated without drug. Error bars represent 95% confidence intervals. (C) B-CLL cells were incubated with the indicated concentrations of honokiol for 16 hours, and then apoptosis was determined by flow cytometric analysis of annexin V-FITC/PI-stained cells. Numbers in each quadrant indicate the percentage of cells labeled with annexin V-FITC (bottom right), PI (top left), annexin V-FITC and PI (top right), or unlabeled (bottom left). (D) PBMCs from 8 B-CLL patients or from 6 healthy donors were isolated and treated with the indicated concentrations of honokiol for 16 hours, and then apoptosis was determined by flow cytometric analysis of annexin V-FITC/PI-stained cells. Apoptosis was determined by the percentage of annexin V-positive cells. Error bars represent 95% confidence intervals.