Effect of dietary β-sitosterol glucoside on the growth of estrogen-dependent human breast cancer (MCF-7) tumors implanted in ovariectomized athymic mice.

B168

Phytosterols (PSs) have been used as dietary supplements due to their ability on lowering cholesterol levels and enhancing immune function.The biological effects of β-sitosterol (BSS) and its glucoside form β-sitosterol glucoside (BSSG) have been described and so far most used to lower blood cholesterol levels. Many studies have also reported the protective effects of the consumption of diet high in PSs against breast and other type of cancers. Previously, we observed the preventive effect of dietary BSSG on estrogen-stimulated human breast tumor growth in vivo. The present study evaluated the effect of dietary BSSG at wider concentration range [125 - 750 parts per million (ppm)] on the growth of 17-β-estradiol E₂-stimulated human breast cancer in vivo. We hypothesize that dietary BSSG intake could inhibit E2-stimulated growth of MCF-7 tumor implanted into ovariectomized athymic mice. To test our hypothesis, we implanted E₂ silastic tubes that produces 100 - 150 pM of circulating E₂, injected MCF-7 cells, and randomly grouped the mice into five treatment groups (E₂, E₂ + 125 ppm BSSG, E₂ + 250 ppm BSSG, E₂ + 500 ppm BSSG, and E₂ + 750 ppm BSSG). After the cell injection, the animals were on treatment diets for 10 weeks. Tumor size and body weight were monitored weekly during the study. At week 10, the average tumor size of the E₂ reached 126 mm² and the study was terminated. At completion of the study, we analyzed tumors for cell proliferation marker (Ki67) using immunohistochemical staining and gene expression in tumors using a real time quantitative reverse transcription polymerase chain reaction (qRT-PCR), and serum E₂ and total cholesterol levels were measured. Dietary BSSG inhibit the E₂-stimulated MCF-7 tumor growth in mice. Dose dependent reduction of tumor suface area, serum estrogen and cholesterol are evident with BSSG treatment. Cell proliferation and relative gene expression data of estrogen responsive markers (pS2, bcl2, TNF-α, MMP2 and MMP9) have also been clearly demonstrated the inhibitory effect of BSSG on the growth of MCF-7 tumor implanted into ovariectomized athymic mice. BSSG at 125 ppm dosage shows a maximum reduction (13.9 ± 0.78 %) in Ki67 expression compared to all other dosages with respect to estrogen treated control (E₂, 48.22 ± 3.6 %) group. Relative mRNA expression of estrogen receptor (ER) - downstream regulated markers, pS2 and bcl2 shown to be down regulated with all the dosages of BSSG treatment compared to the E₂ control . Also, the overexpression of TNF-α and its concomitant influence on the expression of metastasis inducible matrixmetallopriteinases, MMP2 and MMP9 found to be abrogated by BSSG treatment. In conclusion, the consumption of food products high in BSSG may have protective effect on MCF-7 tumor growth in vivo, by altering serum E₂ level, cell proliferation, apoptosis and inhibition of tumor invasion promoting markers.