Abstract SY11-04: Factors associated with changes in body weight and the protective effect of chronic versus intermittent calorie restriction on mammary tumorigenesis

To date one of the most effective strategies for the prevention of mammary tumor development is calorie restriction. Reduced incidence and/or extended latency for the development of spontaneously and carcinogen-induced mammary tumors have been documented following various degrees of reduced calorie intake. In the majority of these studies chronic calorie restriction (CCR) has been implemented whereby the animals are given the same amount of reduced calories every day. Although this is easy to implement in experimental conditions, such an approach may have limited application to humans. Interestingly, we have reported that periods of intermittent calorie restriction (ICR) consisting of periods of 50% reduced intake followed by ad libitum refeeding resulting in an overall restriction of 20-25% was more protective than the same degree of restriction implemented in a CCR protocol. In three separate studies transgenic MMTV-TGF-α mice fed low-fat AIN93M diets had mammary tumor incidences ranging from 3-15% for ICR mice compared to 27-44% for CCR mice and 68-84% for ad libitum-fed (AL) mice (CEBP 11: 836,2002; Exp Biol Med 232:70,2007; Cancer Prev Res 2:712,2009). In a second strain of transgenic mice also susceptible to mammary tumor development, MMTV-neu, there was no protective effect of CCR while ICR resulted in an ∼50% reduction in mammary tumor incidence (Nutrition & Cancer 44:162,2002). To understand why ICR is superior to CCR we have measured circulating growth regulating factors which have been reported to be related to tumorigenesis. In addition we determined protein expression levels of their corresponding receptors in mammary tissues and mammary tumors. We have found that ICR restriction periods are characterized by reductions in serum IGF-I and leptin and following refeeding neither level reached that of AL mice. Further, ICR restriction is characterized by a large increase in the adiponectin:leptin ratio. These observations indicate an environment conducive to reduced cell proliferation and/or enhanced apoptosis based on in vitro studies using human breast cancer cell lines. In mammary tissue CCR and ICR mice had reduced leptin expression compared to AL mice but only ICR mice had elevated AdipoR1 compared to AL and CCR mice, while leptin receptor expression was reduced. Neither CCR nor ICR affected mammary tissue or mammary tumor adiponectin or AdipoR2 expression. Two proteins associated with IGF-I signaling, IGFBP3 and IGF-IR, were also measured, IGFBP3 was higher in mammary tumors from both ICR and CCR mice while only CCR mice had higher expression in mammary tissue. There was no effect of IGF-IRα in either tissue. We have conducted two recent studies expanding on our earlier experiments. In the first we fed a higher fat diet to MMTV-TGF-α mice to determine if we could overcome the protective effect of ICR. Mice were fed diets to provide the same absolute intake of fat on a daily basis over the course of the study (10-82 weeks of age). Despite the increased fat intake during refeeding the protective effect of ICR was maintained with mammary tumor incidence of 4% obtained for ICR mice compared to 52% for CCR mice and 66% for AL mice. In the second study MMTV-neu mice which were only moderately protected by the ICR protocol in the earlier study were fed reduced calories combined with the addition of the omega-3 fatty acid, eicosapentaenoic acid, EPA, to the diet. This was based on studies that suggested a protective effect of EPA and/or fish oil on mammary tumorigenesis. EPA was included in the diet at 71% of fat calories in a diet where 9% of total calories were supplied as fat. Control diets contained soybean oil as the fat source. Mice were enrolled at 10 weeks of age and followed until 60 weeks of age. EPA included in the AL diet had a modest effect on mammary tumor development resulting in a 28% decrease in incidence from 87% in AL-CONTROL mice to 63% in AL-EPA mice. For the calorie restricted mice CCR-CONTROL and CCR-EPA mice had incidence rates of 47% and 40% respectively while ICR-CONTROL mice had an incidence rate of 59%. EPA combined with ICR reduced mammary tumor incidence to only 15%. Serum and tissue analyses are presently underway including determination of mammary tissue, mammary fat pad and mammary tumor SIRT1 and SIRT3 levels. Although the mechanism of action to explain why ICR is superior to CCR for mammary tumor prevention remains unknown ICR may provide a unique approach for cancer prevention Support: CA101858, DOD17-97-7055, KOMEN for the Cure and The Hormel Foundation.) Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 102nd Annual Meeting of the American Association for Cancer Research; 2011 Apr 2-6; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2011;71(8 Suppl):Abstract nr SY11-04. doi:10.1158/1538-7445.AM2011-SY11-04