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Introduction
Isoflavones are a flavonoid subclass that includes daidzein (7,4-dihydroxyisoflavone) and genistein (4′,5,7-trihydroxyisoflavone), which are the predominant isoflavones in legumes, such as soybeans, and are commonly found in a variety of human foods (1,2). Several epidemiological studies have revealed an inverse association between isoflavone consumption and the risk of breast cancer in Asians, indicating that dietary intervention may reduce the risk of breast cancer (3–5).
Based on this hypothesis, a number of studies have investigated the pharmacological activities of isoflavones as candidate anticancer agents. Many have reported that isoflavones significantly inhibit breast cancer cell growth in vitro(6–8), and that this growth inhibition stimulates the signal transduction pathway leading to apoptosis. Moreover, our previous studies support the theory that isoflavones, including genistein and daidzein, exhibit anticancer activity against breast cancer both in vivo(9,10) and in vitro(11,12).
Breast cancer is one of the cancers most frequently diagnosed in women. According to a US National Cancer Institute (NCI) report, one in eight women in the US (~13.3%) will develop breast cancer during their lifetime (13,14). Breast cancer is a group of heterogeneous diseases that manifest in several clinical, molecular and histopathological forms; this makes effective chemotherapy difficult. The response to a cancer drug may differ according to biological factors including estrogen receptor (ER) status, progesterone receptor status and c-erbB-2 expression. The present study compared the anticancer activity of daidzein and genistein via their effect on ERα and c-erbB-2 expression in breast cancer cell lines.
Materials and methods
Cell culture
Human breast cancer MCF-7, SK-BR-3 and ZR-75-1 cell lines were purchased from the KCLB (Korean Cell Line Bank, Seoul, Korea) and were used in the present study. Each cell line was routinely maintained in RPMI-1640 medium (Invitrogen, Carlsbad, CA, USA) supplemented with 10% fetal bovine serum (FBS) and antibiotics (50 U/ml penicillin and 50 μg/ml streptomycin; Gibco, Carlsbad, CA, USA) at 37°C in a humidified atmosphere containing 5% CO2. Each cell type was plated at a density of 0.8–1.2×106 cells/well and 2.5–5.0×103 cells/well on 6- and 96-well plates for 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT) and immunoblotting assays, respectively. Daidzein and genistein were purchased from LC Laboratories® (Woburn, MA, USA) and dissolved in dimethyl sulfoxide (DMSO; final concentration 0.1% in medium).
MTT assay
Each...