Cyproheptadine alters the expression of cell cycle regulatory proteins. (A) Western blot analysis of the expression of p16, HBP1, p21, p27, Rb, and phospho-Rb in HCC cells treated with 40 μM of cyproheptadine for different lengths of time. As shown in the figure, the levels of p16 and HBP1 increased in HepG2 cells after treatment with cyproheptadine for 1–4 h, followed by a gradual decrease during 6–8 h, but did not change significantly in Huh-7 cells. The levels of p21 and p27 increased in Huh-7 cells after 4–6 h and 1–4 h of treatment, respectively, but did not change significantly in HepG2 cells. The level of phospho-Ser795 Rb decreased in a time-dependent manner after 2–8 h of treatment in Huh-7 cells, but not in HepG2 cells. (B) Western blot analysis of cyclin D1 expression in cyproheptadine-treated HCC cells. The result shows a moderate decrease in the cyclin D1 level in Huh-7 cells after treatment with cyproheptadine for 30 h, but not in HepG2 cells.