Combination of methylselenocysteine with tamoxifen inhibits MCF-7 breast cancer xenografts in nude mice through elevated apoptosis and reduced angiogenesis

To investigate the therapeutic effect of methylselenocysteine (MSC) combined with tamoxifen in MCF-7 breast cancer xenograft and the underlying mechanisms. MCF-7 breast cancer xenograft was established in ovariectomized female athymic nude mice and treated with tamoxifen and/or MSC. Tumor size was measured twice a week. Immunohistochemistry and TUNEL assays were used to measure ERα expression, ERα target genes (progesterone receptor (PR) and cyclin D1 expression), Ki-67 index, apoptosis and microvessel density. Combined treatment with tamoxifen and MSC synergistically inhibited tumor growth compared to MSC alone and tamoxifen alone. MSC alone or MSC + tamoxifen significantly reduced ERα, PR and cyclin D1, Ki67 index and microvessel density while increasing apoptosis in tumor tissues. These findings demonstrate synergistic growth inhibition of ERα positive breast cancer xenografts by combination of tamoxifen with organic selenium compounds. Organic selenium may provide added benefit when combined with tamoxifen in adjuvant therapy or prevention.