Flavopiridol effects on respiration in CLL patient cells. Oxygen consumption rate (OCR) of CLL cells was determined using electron paramagnetic resonance (EPR) as described in “Measurement of cellular respiration.” (A) CLL samples (N = 5) were incubated with or without 1.5 μM FP for 3, 5, or 6 hours. Cells (250 000) plus probe were transferred to a sealed microcapillary and analyzed for 20 minutes. Untreated cells (N = 8) were analyzed at several intervals to ensure that incubation alone up to 6 hours had no effect on OCR. Data are presented as mol O₂ consumed per minute per million cells. The average oxygen consumption of CLL cells treated with FP for 6 hours was significantly less than in untreated cells (*P < .001). (B) In an independent experiment, KCN (100 μM, N = 3) and CCCP (50 μM, N = 5) were used as negative and positive controls for oxygen utilization, respectively. The OCR of CLL cells treated with CCCP following 6 hours of FP treatment (N = 5) was significantly increased relative to cells treated with FP alone (**P = .03).