Confirmation of uterotrophic activity of 3-(4-methylbenzylidine)camphor in the immature rat

In this study we found that the ultraviolet sunscreen component 3-(4-methylbenzylidine)camphor (4MBC) is uterotrophic in immature rats when administered by either subcutaneous injection or oral gavage. These data confirm earlier reports of uterotrophic activity for this agent when administered to immature rats in the diet or by whole-body immersion; however, they are in contrast to negative unpublished immature rat uterotrophic assay results. Data also indicate that 4MBC binds to isolated rat uterine estrogen receptors and shows activity in a human estrogen receptor yeast transactivation assay; however, we considered both of these effects equivocal. In this study, we confirmed the original observation that 4MBC was active as a mitogen to MCF-7 breast cancer cells. We evaluated and discounted the possibility that the estrogenic activity of 4MBC is related to its bulky camphor group, which is of similar molecular dimensions to that of the weak estrogen kepone. Uncertainty remains regarding the mechanism of the uterotrophic activity of 4MBC.