Flavopiridol inhibited RNA synthesis in CLL cells. (A) The impact on the potency of flavopiridol was compared between 10% autologous patient plasma and fetal bovine serum in the culture medium. [³H]uridine incorporation was measured in the presence of 1 μM (♦) and 3 μM (•) flavopiridol in media with autologous plasma, or in the presence of 1 μM flavopiridol in fetal bovine serum (▪). Data are presented as percentages of time-matched controls (mean ± SE; n=4 patients each performed in triplicate). The disintegrations per minute (DPM) values for untreated samples in plasma or fetal bovine serum averaged 70 057 and 39 159, respectively. (B) Time and concentration dependence of inhibition on [³H]uridine incorporation by flavopiridol. Data are presented as percentages of time-matched controls (mean ± SE, triplicate samples) of results from CLL cells from 11 patients incubated with 0.1 (▪), 0.3 (▾), 1 (♦), and 3 μM (•) flavopiridol.