A, Primary cultures of human corticotroph tumor (numbers 1–6) cells treated with vehicle or R-roscovitine for 48 hours. Medium ACTH concentrations in primary cultures were measured by RIA (normalized for viable cell numbers; n = 6 tumors, mean ± SE). *, P < .05. B, POMC mRNA measured by RT-PCR in extracts derived from human corticotroph tumor (numbers 2, 4, 5, and 6) cells treated with vehicle or R-roscovitine. C, Western blot analysis of ACTH expression in primary cultures of human corticotroph tumor (from patient 5 in Table 1) treated with vehicle or R-roscovitine. Tumor numbers correspond to patient numbers in Table 1. RT-PCR was performed in triplicates.