The Anti-Tumor Effect of Wogonin, a Lipoxygenase Inhibitor, in both Estrogen Receptor-Positive and -Negative Human Breast Cancers

Abstract

Lipoxygenase inhibitors have been reported to inhibit cell growth and/or induce apoptosis in various tumors including hepatic, colorectal, mammary, lung, and gliomas. We tested the effect of wogonin (5,7-dihydroxy-8-methoxyflavone), a lipoxygenase inhibitor, in ER-positive (MCF-7 and T47D) and -negative breast cancer cell lines (MDA-MB-231 and SK-BR-3). Anchorage-dependent cell growth was attenuated by wogonin, independently of its ER status, in a dose- and time-dependent manner. Flow cytometry analysis gave enhanced sub-G1 population by wogonin, which is indicative of augmented apoptosis. Moreover, enhanced nuclear fragmentation was observed by DAPI staining. Furthermore, anti-apoptotic Bcl-2 and Bcl-xL proteins were reduced, while pro-apoptotic Bax was enhanced in wogonin-treated cells. Total and phosphorylated forms of Akt were downregulated by wogonin. Total and phosphorylated forms of GSK-3β were reduced, as well as Cyclin D1 protein, which implies the downregulation of the canonical Wnt signaling pathway by wogonin. In ER-positive MCF-7 and T47D cells, the expression of ER was down-regulated by wogonin, which might have additionally contributed to attenuated cell proliferation. Likewise, the expression of EGFR and c-ErbB2 and their phosphorylated forms were down-regulated by wogonin in ER-negative MDA-MB-231 and SK-BR-3 cells, respectively. Finally, the growth of T47D, MDA-MB-231, and SK-BR-3 xenografts was attenuated by oral administration of wogonin for 4 weeks. As we have shown the inhibitory effect of wogonin both in vitro and in vivo, our novel findings open the possibility of wogonin as an effective therapeutic agent against both ER-positive and -negative breast cancers, particularly against the more aggressive and hormonal therapy-resistant ER-negative, EGFR or c-ErbB2-overexpressing types.