Luteolin abrogates the growth-stimulatory effects of exogenous IGF-I in HT-29 cells. (A) HT-29 cells were plated in 24-well plates at a density of 5 × 104 cells/well. One day later, the cells were serum-starved for 24 h with serum-free DMEM/F12 supplemented with 5 mg/L transferrin, 0.1 g/L BSA, and 5 μg/L selenium for 24 h. After serum-starvation, the cells were incubated in serum-free medium containing 0 or 60 μmol/L of luteolin with or without 10 nmol/L of IGF-I for 24, 48, and 72 h. Viable cell numbers were estimated via an MTT assay. (B) Cells were plated in 96-well plates at a density of 6 × 103 cells/well. Cells were serum-starved and then treated with 0 or 60 μmol/L of luteolin with or without 10 nmol/L of IGF-I for 2 h. [3H]Thymidine was then added, and the incubation was continued for an additional 1 h in order to measure its incorporation into DNA. Each bar represents the mean ± SEM (n = 6). Means without a common letter differ, P < 0.05.