Differential effects of esculetin and daphnetin on in vitro cell proliferation and in vivo estrogenicity

Esculetin (6,7-dihydroxycoumarin) and daphnetin (7,8-dihydroxycoumarin) are secondary metabolites of plants used in folk medicine. These compounds have showed great antiproliferative activity in several tumor cell lines and have been proposed as potential anticancer agents. However, the estrogenic potential of these two compounds has to date not been reported. The present study compared esculetin and daphnetin on the inhibition of cell proliferation and cell cycle progression of the MCF-7 estrogen-responsive human carcinoma cell line. In vivo and in vitro estrogenic activity for both compounds was also evaluated. Esculetin inhibited cell proliferation after 72h exposure (IC50=193±6.6μM), while daphnetin evidenced inhibiting effects starting at 24-h exposure (72h, IC50=73±4.1μM). Both effects showed changes in cyclin D1 gene expression. In non-estrogenic conditions (E-screening assay), esculetin produced biphasic response on proliferation of the MCF-7 cells; at 10⁻⁸–10⁻⁶M, concentrations induced proliferative effects as EC50=4.07×10⁻⁹M (E₂=2.91×10⁻¹²M); at higher concentrations (10⁻⁵–10⁻⁴M), cell proliferation was inhibited. Relative proliferative effect at E₂ was 52% (E₂=100), relative proliferative potency was 0.072 (E₂=100). Additionally, esculetin tested in vivo showed estrogenic effects at 50–100mg/kg doses; relative uterotrophic effect at E₂ was 37%, with relative uterotrophic potency registered at 0.003. In contrast, daphnetin did not induce estrogenic effects in vitro or with in vivo models. The low estrogenic activity of esculetin could prove useful in postmenopausal therapy but not as a safe antitumor agent in estrogen-dependent tumors. Daphnetin-based antiproliferative selectivity with MCF-7 cells showed that daphnetin is a promising antitumoral agent also acting on estrogen dependent tumors.