Naringenin and 17β-estradiol coadministration prevents hormone-induced human cancer cell growth



Flavonoids have been described as health-promoting, disease-preventing dietary components. In vivo and in vitro experiments also support a protective effect of flavonoids to reduce the incidence of certain hormone-responsive cancers. In particular, our previous results indicate that the flavanone naringenin (Nar), decoupling estrogen receptor α (ERα) action mechanisms, drives cancer cells to apoptosis. Because these studies were conducted in the absence of the endogenous hormone 17β-estradiol (E2), the physiological relevance of these findings is not clear. We investigate whether the antiproliferative Nar effect persists in the presence of physiological E2 concentration (i.e. 10 nM), using both ERα-transfected (HeLa cells) and ERα-containing (HepG2 cells) cancer cell lines. Ligand saturation experiments indicate that Nar decreases the binding of E2 to ERα without impairing the estrogen response element (ERE)-driven reporter plasmid activity. In contrast, Nar stimulation prevents E2-induced extracellular regulated kinases (ERK1/2) and AKT activation and still induces the activation of p38, the proapoptotic member of mitogen-activating protein kinase (MAPK) family. As a consequence, Nar stimulation impedes the E2-induced transcription of cyclin D1 promoter and reverts the E2-induced cell proliferation, driving cancer cell to apoptosis. Thus, these results suggest that coexposure to this low-affinity, low-potency ligand for ERα specifically antagonizes the E2-induced ERα-dependent rapid signals by reducing the effect of the endogenous hormone in promoting cellular proliferation. As a whole, these data indicate that Nar is an excellent candidate as a chemopreventive agent in E2-dependent cancers. © 2009 IUBMB IUBMB Life, 62(1):51–60, 2010