In vitro and in vivo studies of antioxidant and anti-breast cancer activities of pomiferin

Yang, Raymond X.
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University of Guelph

Reactive oxygen species (ROS) are ubiquitous in the human body and play a pivotal role in many chronic diseases, including cancer. The human body has developed a strong antioxidant defense system. Unfortunately, this system cannot be adequately maintained with ageing. The supply of exogenous antioxidants to help the body fight these diseases is a logical approach. Polyphenols, particularly flavonoids, have been found to be strong antioxidants. In this study, the prenylated isoflavone, pomiferin, from Osage orange, was examined. I found that pomiferin had a much stronger antioxidant activity than soy isoflavones, genistein and daidzein, in three different antioxidant assays including [beta]-CLAMS, FRAP and PCL. By using both estrogen receptor positive (MCF-7) and negative (MDA-MB-435) cancer cell lines, pomiferin showed much lower IC50 values than soy isoflavones in both cell lines (5.2 ± 0.90 vs 5.4 ± 0.72 M) after 24 hr treatment. The selectivity of pomiferin between cancer cells and MCF-10A (spontaneously immortalized human breast epithelial cell line) was high. Microarray techniques were used to find the gene expression changes when all three cells were treated with 5.0 M pomiferin. At p < 0.05, 515, 691 and 59 genes were significantly regulated for MCF-7, MDA-MB-435 and MCF-10A, respectively; and at p < 0.01 cut off, 94, 105 and 1 genes, respectively. Many of these genes are associated with antioxidant enzymes, cell cycle regulation and apoptosis. To confirm the results from microarray, RT-qPCR was used to verify some of the gene expression changes. The expression of 20 out of 21 genes was confirmed. In addition, the xenograft models of MCF-7 and MDA-MB-435 cells were established to find the 'in vivo' anticancer activity of pomiferin. The tumour size was significantly reduced in MCF-7 with 0.2% and MDA-MB-435 with 0.5% of pomiferin in their diet (p < 0.05). Bioavailability of pomiferin was measured and the correlation with tumour sizes was evaluated. Plasma pomiferin level can partially explain the tumour size, but many other factors likely play a role. Further studies are needed to determine the specific mechanism(s) by which pomiferin alters specific gene expression and the differential effects in tumour versus normal cells.

reactive oxygen species, antioxidants, prenylated isoflavone, pomiferin, Osage orange