Abstract 903: Comparison of the citrus flavonoid naringenin and metformin for effects on breast cancer in obese ovariectomized mice

Abstract

Abstract Metformin has been shown to decrease breast cancer incidence in diabetic women, suggesting that improvement of metabolic status may be a useful approach to decrease breast cancer risk. As the putative cellular target of metformin, AMP-activated protein kinase (AMPK) not only regulates energy metabolism in liver, muscle, and adipose tissue but also inhibits protein synthesis and induces cell cycle arrest and apoptosis. Naringenin is a flavonoid abundant in citrus fruits that may have beneficial effects on metabolic health and tumorigenesis. Our in vitro data showed that naringenin inhibited proliferation of E0771 murine breast cancer cells, increased AMPK activity, and reduced expression of cell cycle regulatory proteins Cyclin D1 and anti-apoptotic Bcl-2 protein. In this study, we evaluated whether dietary naringenin acts like metformin to suppress mammary tumor growth in a mouse model of postmenopausal obesity. Ovariectomized female C57BL/6J mice were fed a high-fat diet (60% energy as fat) for 3 weeks to induce obesity. Then mice were randomized to experimental diets of HF (continued the high-fat diet), LN (high fat + 1% wt/wt naringenin in diet), HN (high fat + 3% wt/wt naringenin in diet), and Met (high fat + 180 mg/kg metformin in water) for 5 weeks. After 2 weeks of treatment, 5 × 10(5) E0771 cells were injected into one thoracic mammary fat pad. Mice were maintained on study diets for another 3 weeks. For all mice tumor weight correlated with weight gain in the first 5 weeks prior to cell inoculation (r = 0.51, p < 0.01). There was no difference in fasting glucose levels among the groups on week 8. No difference was observed between the HF and LN groups regarding final body weight, food intake, tissue weights, and tumor mass. HN significantly decreased final body weight, food intake, and adipose depot mass. mRNA expression of two inflammatory cytokines, interleukin 6 and monocyte chemoattractant protein-1 were decreased in perigonadal fat of the HN group. Although tumor growth (cm2) decreased over time in HN mice, there was no significant difference in tumor mass between HF and HN groups at necropsy (p = 0.4). HN did not affect AMPK activity in tumor tissue, but decreased Bcl-2 protein expression. Additionally, dietary naringenin resulted in a dose ­dependent accumulation in plasma, tumor, and mammary fat. In comparison to naringenin enriched diets, metformin significantly reduced tumor growth and final tumor weight, without affecting body weight, food intake, and tissue weights. Metformin decreased protein expression of Cyclin D1 in mammary tumors. However, we did not observe AMPK activation and changes in Bcl-2 protein levels in tumors. Taken together, these data suggest that metformin may inhibit mammary tumor growth without affecting metabolic status as assessed by body weight, adiposity, and fasting glucose. There may be different mechanisms of action for naringenin and metformin to alter mammary tumorigenesis. Citation Format: Jia-Yu Ke, Yung-Hsuan Hsiao, Shana R. Straka, Lisa D. Yee, Martha A. Belury. Comparison of the citrus flavonoid naringenin and metformin for effects on breast cancer in obese ovariectomized mice. [abstract]. In: Proceedings of the 106th Annual Meeting of the American Association for Cancer Research; 2015 Apr 18-22; Philadelphia, PA. Philadelphia (PA): AACR; Cancer Res 2015;75(15 Suppl):Abstract nr 903. doi:10.1158/1538-7445.AM2015-903