A Narrowed Window for Targeting Metabolic Flexibility in Breast Cancer Prevention

描述（由申请人提供）：本项目验证了一个关于绝经后肥胖相关乳腺癌风险出现的新假设，同时研究了以代谢控制为目标的两种相关干预措施——二甲双胍和定期运动——对肥胖相关肿瘤促进的影响。该假说认为，肥胖相关的代谢调节受损建立了对绝经期体重增加的肿瘤促进作用的易感性。基于这一假设，代谢调节受损和正能量失衡是绝经后肥胖相关乳腺癌风险出现的必要条件。将三种具有良好特征的乳腺癌（甲基亚硝基脲）、肥胖（肥胖易感大鼠）和更年期（手术卵巢切除术，OVX）模型合并在一起，为研究绝经后肥胖相关肿瘤的促进建立了一个实验范式。在OVX的作用下，瘦和肥胖的荷瘤大鼠出现一段体重快速增加的时期，在此期间，肥胖大鼠的肿瘤退行较少，肿瘤进展较多，新出现的肿瘤较多。肥胖大鼠较慢、能量效率较低的体重增加预示着OVX后的肿瘤负担和多样性，二甲双胍治疗显著抑制OVX后的肿瘤进展。肥胖患者肿瘤中孕激素受体（PR）的表达在OVX治疗前和OVX诱导的体重增加期间增加。在第一个目标中，我们通过在ovx诱导体重增加的关键窗口期间操纵代谢控制和能量平衡来验证双需求假说。在OVX诱导体重增加的窄窗期，我们将暂时采用两种已知的相关干预措施（二甲双胍和定期运动）来改善代谢控制，以评估它们对长期肿瘤预后的影响。在第二个目标中，我们采用了24小时能量平衡和燃料利用的多示踪研究，以检查肥胖是否会损害ovx诱导的过度喂养的代谢反应，并在肿瘤中赋予“侵袭性”糖酵解/脂肪生成表型。我们将研究二甲双胍治疗是否能使这种代谢反应正常化，并改善肥胖对肿瘤代谢的影响。在第三个目标中，我们研究了肥胖相关的PR表达升高的原因和后果。来自aim 2的组织将用于确定在ovx诱导的体重增加期间过度喂养是否会导致乳腺局部雌激素增加。人类乳腺癌细胞（PR+）和（PR-）不表达PR，将被用来研究在营养丰富或细胞因子丰富的环境中，PR表达对肿瘤细胞代谢和增殖的不依赖配体的影响。总之，这些研究将检验在卵巢功能丧失后，代谢控制不良和已存在的肿瘤受体状态是否会共同促进生存和生长。本项目的观察结果可能指向围绝经期或绝经后不久的关键时间窗口，这将最大限度地提高改善胰岛素敏感性和/或代谢控制的干预措施的预防和治疗效果。

DESCRIPTION (provided by applicant): This project tests a novel hypothesis regarding the emergence of obesity-associated risk for breast cancer after menopause, while examining the impact of two relevant interventions targeting metabolic control, metformin and regular exercise, on obesity-associated tumor promotion. The hypothesis asserts that obesity- associated impaired metabolic regulation establishes a susceptibility to the tumor promoting effects of the menopause-induced weight gain. Based upon this hypothesis, both impaired metabolic regulation and the positive energy imbalance are required for the emergence of obesity-associated breast cancer risk after menopause. Three well-characterized models of breast cancer (methylnitrosourea), obesity (obesity-prone rats) and menopause (surgical ovariectomy, OVX) were merged to create an experimental paradigm for studying obesity-associated tumor promotion after menopause. In response to OVX, lean and obese, tumor bearing rats exhibit a period of rapid weight gain, during which obese rats have fewer tumors regress, more tumors progress, and more tumors newly emerge. The slower, less energetically efficient weight gain of obese rats predicts post-OVX tumor burden and multiplicity, and metformin therapy dramatically suppresses tumor progression after OVX. Tumors in the obese have increased expression of progesterone receptor (PR) prior to OVX, and during OVX-induced weight gain. In the first aim, we test the dual-requirement hypothesis by manipulating metabolic control and energy balance during the critical window of OVX-induced weight gain. Two relevant interventions known to improve metabolic control (metformin, regular exercise) will be employed transiently during the narrow window of OVX- induced weight gain, to assess their impact on long term tumor outcomes. In the second aim, we employ a 24-hr multi-tracer study of energy balance and fuel utilization to examine if obesity impairs the metabolic response to OVX-induced overfeeding and imparts an "aggressive" glycolytic/lipogenic phenotype in tumors. We will examine if metformin therapy normalizes this metabolic response and ameliorates the effects of obesity on tumor metabolism. In the third aim, we investigate the cause and consequences of the obesity-associated elevation in PR expression. Tissues from aim 2 will be used to determine if estrogens are increased locally in the mammary gland in response to overfeeding during OVX-induced weight gain. Human breast cancer cells that do (PR+) and do not (PR-) express PR will be used to examine the ligand-independent effects of PR expression on tumor cell metabolism and proliferation, when challenged with a nutrient-rich or cytokine-rich environment. Together, these studies will examine if poor metabolic control and pre-existing tumor receptor status converge to promote survival and growth after the loss of ovarian function. Observations in this project may point to a critical window of time in peri-menopause or shortly after menopause that will maximize the prevention and therapeutic efficacy of interventions that that improve insulin sensitivity and/or metabolic control.