Relationships Among In Vitro Anti-mastocarcinoma Activity Of Luteolin, IGF-1 Pathway And ERα

Luteolin is a representative of natural flavonoids existing in many natural herbs, vegetables and fruits. Recent studies have shown that luteolin elicits significant anti-proliferative activity against different human cancer cell lines including breast cancer cell. This effect is mainly exerted through blocking signal transduction in cancer cells.There is accumulating evidence implicating insulin-like growth factor-1(IGF-1) mediated signal transduction pathway in development and/or progression of breast cancer.It has been shown to play an important role in regulating normal and malignant cell growth. Studies recently demonstrated that overexpression of IGF-1 and IGF-1R in cancer cells is associated with tumor growth. They are the most powerful predictor of breast cancer prognosis as well as key targets of antitumer drug. Cell signal pathway is a complex network, not linear. Recent studies revealed that IGF-1 pathway is also regulated by ERα. To elucidate the target of luteolin anticancer activity, the current study investigated relationships among IGF-1 pathway, ERαand luteolin anticancer activity.1. MTT assay was used to examine the effect of luteolin on MCF-7 cell proliferation. The results showed that luteolin inhibited MCF-7 cell proliferation in a dose-and time-dependent.2. Flow cytometry was used to determine the effect of luteolin on MCF-7 cell apoptosis. The results showed that luteolin could induce cell apoptosis and promote S arrest.3. MTT assay and Flow Cytometry were used to detect the effect of luteolin on IGF-1-induced breast cancer cell proliferation and apoptosis resistance, respectively.The results showed that IGF-1 could induce MCF-7 cell proliferation and inhibit cell apoptosis. Luteolin exhibited a potent ability to blunt IGF-1-stimulated MCF-7 cell growth and reversed IGF-1-induced apoptosis.4. ELISA and Western blotting analysis were used to detect the in vitro anti-cancer effects of luteolin on IGF-1 signal pathway in MCF-7 cells.The results showed that luteolin-induced decrease of IGF-1 was associated with a concomitant increase of IGFBP-3 in MCF-7 cell culture supernatant; Luteolin markedly decreased IGF-1R and Akt phosphorylation without affecting Erk1/2 phosphorylation. These suggest luteolin primarily acts through IGF-1 mediated PI3K-Akt pathway to exert its anti-breast cancer effect.5. MTT assay and Western blotting analysis were used to detect relationship between ERαexpression and the inhibitory effect of luteolin on IGF-1 induced breast cancer cell proliferation. The results showed that ERαexpression was directly involved in luteolin inhibiting IGF-1 induced MCF-7 cell proliferation.6. Western blotting analysis were used to determine the effect of luteolin on IGF-1 induced Akt phosphorylation with and without ICI182780 and ERαknockdown. The results showed that before treatment with ICI182780 and transfection, compared with IGF-1 control, treatment with luteolin markedly reduced p-Akt level. After treatment with ICI182780 and transfection, luteolin treatment had a p-Akt level similar to control group.These findings indicate that anti-mastocarcinoma activity of luteolin via inhibiting IGF-1 mediated PI3K-Akt pathway is related to ERαexpression. ERαis possibly one of the targets of luteolin.