We investigated the cytotoxic effects of casticin on normal fibroblast cells (3T3 Swiss Albino and TIG-103) (Fig. 2B and C). 3T3 Swiss Albino cells grew well after the addition of casticin at a concentration between 0.3 and 1.0 μM. There were no significant differences in the growth between the control and the casticin-treated cells on days 2 and 3. Similar results were obtained in TIG-103. The growth of TIG-103 was not inhibited significantly by casticin on days 3 and 4.
KB cells express epidermal growth factor (EGF) receptor molecules on their surfaces much more than normal cells such as fibroblasts [8]. EGF is a potent mitogen controlling the growth of various types of cells through its specific receptor. Next, we examined whether the specific inhibition of KB cells depended on EGF receptors or not. A431 cells are also well known to have a high number of EGF receptors [8], whereas casticin at a concentration between 0.3 and 1.0 μM showed no significant effect on the growth of A431 cells (Fig. 2D). Our data suggest that the growth inhibition by casticin was irrelevant to numbers of EGF receptors