Effects of flavopiridol (FP) on mitochondrial membrane potential and annexin binding in CLL patient cells. (A) CD19⁺ CLL patient cells were isolated from peripheral blood and treated with 1.5 μM FP for 1, 3, and 6 hours (N = 5) in media with 10% human serum. Mitochondrial membrane potential was quantified by flow cytometric determination using JC-1, and data are given as the percentage treated cells with intact mitochondria (aggregated JC-1) relative to untreated cells at the same time points. Annexin binding was assessed by flow cytometry using FITC-labeled annexin, and data are shown as the percentage of annexin-negative cells in treated samples relative to time-matched untreated samples in each case. Error bars represent ± standard deviation. The average percentage of intact mitochondria at 6 hours in FP-treated cells was significantly less than in untreated cells (*P < .001). Likewise, annexin positivity was significantly less in treated cells at 6 hours relative to untreated (**P < .001). (B) Whole peripheral blood from CLL patients (N = 7) was incubated for 6 hours with or without 3.0 μM FP. CD19⁺ cells were rapidly isolated and assessed as above. Data are shown relative to untreated, time-matched samples in each case. The average percentage of intact mitochondria in whole blood treated with FP was significantly less than in untreated cells (*P = .007). In contrast, there was no significant change in annexin positivity between treated and untreated cells (P = .13).