Abstract PD09-06: Obesity Promotes Breast Cancer Progression and Tamoxifen Resistance Via Cross-Talk between Growth Factor and Estrogen Signaling Pathways

Abstract

Epidemiological studies indicate that obesity increases the risk of breast cancer by approximately 50% in postmenopausal women. This population most commonly develops estrogen receptor (ER) alpha positive breast cancer, suggesting that elevated estrogen synthesis by the adipose tissue and local mammary epithelia is the primary mediator of breast tumorigenesis in obese postmenopausal women. However, the specific mechanisms by which obesity promotes the development of postmenopausal breast cancer remain unclear. In vitro and animal studies have indicated that obesity-associated growth factor and cytokine signaling also play a role in breast tumorigenesis. Specifically, obesity is accompanied by elevated levels of insulin, insulin-like growth factor 1 (IGF-1), and leptin, and these all have significant tumorigenic effects in the breast. In the current study, we utilize an in vitro model of obesity to examine the effects of elevated circulating hormones and growth factors on breast cancer cells. C57BL/6 mice were randomized at six weeks of age to either a 60% fat diet to induce obesity or a 10% fat diet to produce a lean comparison and maintained on these diets for 12 weeks prior to sacrifice. Sera was obtained from the mice at the time of euthanasia and used to treat ER alpha positive MCF-7 breast cancer cells at a concentration of 2% in serum-free media. Preliminary data indicates that sera from the obese mice induces 31% greater proliferation of MCF-7 cells in comparison to sera from lean animals (p=0.0025). This proliferation is mediated primarily via a phosphoinositide 3-kinase (PI3K) pathway, as evidenced by the ability of LY294002, a PI3K inhibitor, to neutralize the proliferative effect of the obese sera. The addition of LY294002 to MCF-7 cells treated with 2% obese sera decreased proliferation by 43% (p=0.0083). Intriguingly, tamoxifen did not significantly affect proliferation in the cells treated with obese sera (p=0.2425), suggesting that obesity may induce tamoxifen resistance. Consequently, we hypothesize that obesity promotes breast cancer progression and tamoxifen resistance via cross-talk between growth factor and ER alpha signaling pathways. Further studies will be conducted to examine the pathways through which circulating factors mediate obesity-induced breast cancer progression. These will include measurement of the expression and activation of ER alpha, Akt, Erk1/2, IGF-1 receptor, and other proteins in MCF-7 cells in response to treatment with sera from obese and lean mice. By improving our understanding of the mechanisms linking obesity and post-menopausal breast cancer risk, we ultimately hope to develop a rational and effective chemopreventive regimen for this population. Citation Information: Cancer Res 2010;70(24 Suppl):Abstract nr PD09-06.

Body size and breast cancer prognosis in relation to hormone receptor and menopausal status: a meta-analysis

“…Furthermore, obesity has been reported to significantly influence the efficacy of treatment with aromatase inhibitors likely through influencing aromatase availability [12]. Cross-talk between growth factor (e.g., ER) and insulin signaling pathways [13] may also lead to treatment resistance and poor outcomes.…”