P4-03-02: High Fat Diet-Induced Postmenopausal Obesity Promotes Tumor Angiogenesis and Breast Cancer Progression in Age-Relevant Ovariectomized Mice.

Abstract

Abstract Background: Obese postmenopausal women have 50% higher risk of breast cancer than non-obese women. The mechanisms of postmenopausal obesity-induced breast cancer are poorly understood due to lack of the established animal model that mimics postmenopausal obesity related to breast cancer progression. Material and Methods: Using age-relevant C57BL/6 mice, this study determined whether postmenopausal obesity increases VEGF expression, tumor angiogenesis, and breast tumor growth. Ovariectomy (OVX) was performed in 12 sixty week-old female mice (life span is about 140 weeks), then followed by a low-fat (5%, LF, n=6) or a high-fat (60%, HF, n=6) diet for 12 weeks. In the 8th wk of the dietary program, 10^6 E0771 (mouse breast cancer) cells were injected in the left fourth mammary gland. Tumor size was monitored using dial calipers for 4 wk. Body weights were monitored weekly. At the end of the experiment, blood samples, visceral fat, and tumors were collected for measuring VEGF expression using ELISA and intratumoral microvessel density (IMD) using CD31 immunochemistry. Results: Body weight was significantly increased in OVX/HF mice, compared to OVX/LF group (55.3±1.7 vs. 41.5±1.5 g; P<0.01). There was a two-fold increase in the ratio of visceral fat/BW in OVX/HF mice, compared to those in OVX/LF group (0.062±0.005 vs. 0.032±0.003; P<0.01). Postmenopausal obesity significantly increased breast tumor weight over the control (4.62±0.63 vs. 1.98±0.27 g; P<0.01) and IMD (173±3.7 vs. 139±4.3 IM#/mm^2; P<0.01). Tumor VEGF levels were higher in OVX/HF mice, compared to OVX/LF group (73.3±3.8 vs. 49.5±4.3 pg/mg protein; P<0.01). Plasma VEGF levels (69±7.1 vs. 48±3.5 pg/ml) and visceral fat VEGF levels (424.4±39.5 vs. 208.5±22.4 pg/mg protein) were significantly increased in OVX/HF mice, compared to OVX/LF group, respectively (n=6; P<0.01). Interestingly, adipose tissue primary culture showed that subcutaneous fat released more VEGF, compared to visceral fat (6.77±1.14 vs. 0.94±0.16 pg/mg tissue; n=6; P<0.01). The abdominal subcutaneous fat expressed more VEGF proteins than visceral fat in OVX/HF mice (692±72 vs. 431±44 pg/mg protein; n=6; P<0.01). There was a strong positive linear correlation between increased breast tumor weight and visceral fat weight in OVX mice (R2=0.7379; N=12; P<0.01). However, there was no significant difference in heart, or kidney weight/body weight ratio between postmenopausal obesity (OVX/HF) mice and the control mice (OVX/LF). Discussion: Our observations indicate that ovariectomy plus a high fat diet with the inoculation of E0771 (mouse ER+ breast cancer) cells in female wild type >60 week old mice can mimic human obesity-induced postmenopausal breast cancer. The increased tumor angiogenesis in postmenopausal obese mice was correlated with increased breast tumor growth, adipose tissue mass, and adipokines such as VEGF. These findings support the hypothesis that postmenopausal obesity promotes tumor angiogenesis and breast cancer progression, possibly through increased adipose tissue mass and adipokines such as VEGF that could systemically and locally affect breast cancer progression. Citation Information: Cancer Res 2011;71(24 Suppl):Abstract nr P4-03-02.