Effect of flavopiridol on cell growth. (A) SUDHL4 cell line. Cultures were exposed to various concentrations of flavopiridol and at the indicated points counted by electronic counter at 24 hours (▪), 48 hours (□), and 72 hours (□). The data are shown as percentage of untreated control. Total untreated control cell number/culture at 24 hours was 104,040 ± 3,750; 48 hours, 183,880 ± 6,687; and 72 hours, 371,670 ± 11,956. (B) PC3 cell line. Exponentially growing cells were incubated with flavopiridol at the indicated concentrations for 48 hours, and cell growth was assessed by the colorimetric SRB assay, as described in Materials and Methods. The data are the mean of four determinations ± standard deviation (SD) and are representative of three experiments for each cell line.