The adult prevalence of obesity in the United States exceeds 30% and obesity is associated with increased cancer risk and poor prognosis, including postmenopausal breast cancer. p53 is a tumor suppressor gene that responds to diverse cellular stress including DNA damage, oxidative stress and hypoxia. p53 is mutated in most human cancers, including postmenopausal breast cancer, and is involved in the regulation of lipogenic enzymes. However, the links between p53 and obesity in postmenopausal breast cancer are poorly understood. Here we test the hypothesis that the effect of obesity on mammary tumor growth is impacted by p53 status. The aim of this study was to determine how p53-deficient mammary tumor cells (relative to p53 wild-type cells) respond to obesity-driven tumor growth. To test this hypothesis, we used ovariectomized (OVX) C57BL/6 mice randomized to a control diet (n=40) or a diet-induced obesity (DIO) regimen (n=40) for 10 weeks. At the time, DIO mice were approximately 40% heavier (p<0.001) and had 45% greater adiposity (p<0.001) than control mice. Mice were then injected (in the 4th mammary fat pad) with either p53-deficient (p53+/-) or p53 wild-type (p53+/+) MMTV-Wnt-1 mammary tumor cells. Mice were monitored for tumor growth, killed when moribund, and tumors were collected at study end point. We found an interaction between diet and p53 status, with p53+/+ Wnt-1 tumors grown in DIO mice developing the more aggressive morphology compared to p53+/+ Wnt tumors in control mice while the observation was not seen in p53+/- Wnt tumors. From histopathological analysis we also discovered that the DIO regimen promotes local invasion of mammary tumor cells and alters the morphology of MMTV-Wnt-1 p53+/+ mammary tumors. Specifically, p53+/+ Wnt tumors grown in DIO mice displayed disorganized ductal structures characteristic of p53+/- tumors grown in control mice, and DIO exacerbated this aberrant morphology in p53+/- Wnt tumors. Moreover, immunohistological analyses showed that DIO reduces p53 protein expression while elevating Ki-67 expression only in the p53+/+ Wnt mammary tumors. These results suggest that p53 and DIO have interactive effects on mammary tumor growth, as p53+/+ Wnt tumors growing in DIO mice resulted in higher tumor grade similar to p53+/- Wnt tumors. / text

Obesity increases breast cancer risk and progression in postmenopausal women. The Akt/mTOR signaling pathway is activated in tumors in response to increased levels of obesity-related growth factors, including insulin-like growth factor (IGF)-1. Hence, we evaluated energy balance modulation as a mechanism for breast cancer prevention through modulation of Akt/mTOR. Studies suggest that dietary calcium can decrease weight gain, although an exact mechanism is not yet identified. Therefore, we investigated the effects of low-fat (10 kcal % fat) or high-fat (45 kcal % fat) diets containing either calcium phosphate (dairy) or calcium carbonate (supplement) on body weight in ovariectomized (OVX) C57BL/6 mice to determine if dietary calcium could overcome the effects of a high-fat diet. We showed that dairy decreased body weight, with no effect on food consumption. However, it is not known if restoration of normal weight can reverse mammary tumor progression and/or Akt/mTOR pathway activation. To evaluate this, mice were fed a control diet, a calorie restricted regimen, or a diet-induced obesity (DIO) regimen for 17 weeks, after which the DIO mice were switched to the control diet, and this resulted in a 20% weight loss and mice of equal weight to control mice. MMTV-Wnt-1 mammary tumor cells were orthopically injected at week 20, following weight loss. At week 22, mice began placebo or RAD001, an mTOR inhibitor, treatment by oral gavage. Tumor growth and Akt/mTOR signaling were enhanced in formerly obese mice, despite reduction in weight, adiposity and serum hormone levels. RAD001 decreased tumor growth in the CR and control group, but was less effective in the formerly obese mice. In an additional study, we added a DIO gourp which was not switched to the control diet, and found that circulating IGF-1 levels remained significantly elevated in formerly obese mice relative to control and were comparable to levels in the DIO mice. We found that the mechanism of tumor progression was through enhanced Akt/mTOR signaling in both obese and formerly obese mice. Based on the Akt/mTOR activation in MMTV-Wnt-1 tumor growth and progression, we next investigated the anticancer effects of ursolic acid (UA), a pentacyclic triterpene. It was previously shown that UA can affect Akt signaling. Our results showed that UA was effective decreasing tumor growth and Akt/mTOR signaling. Taken together, our findings show that the growth-enhancing effects of obesity on mammary tumor may persist even after weight loss and suggest that a combination of dietary and pharmacologic interventions targeting IGF-1/Akt/mTOR may be an effective strategy in the treatment of postmenopausal breast cancer. / text