A Narrowed Window for Targeting Metabolic Flexibility in Breast Cancer Prevention

描述(申请人提供)：这个项目测试了一个关于绝经后乳腺癌出现肥胖相关风险的新假说，同时考察了两种旨在控制代谢的相关干预措施--二甲双胍和定期锻炼--对肥胖相关肿瘤的促进作用。该假说认为，肥胖相关的代谢调节受损建立了对绝经后体重增加的肿瘤促进作用的易感性。根据这一假设，代谢调节受损和正能量失衡都是绝经后肥胖相关乳腺癌风险出现的必要条件。将乳腺癌(甲基亚硝酸脲)、肥胖(肥胖倾向大鼠)和绝经(外科卵巢切除术，OVX)三个典型的模型合并在一起，创建了一个研究绝经后肥胖相关肿瘤促进作用的实验范式。荷瘤大鼠对OVX、瘦身和肥胖的反应是体重快速增长，在此期间肥胖大鼠肿瘤消退较少，肿瘤进展较多，新生肿瘤较多。肥胖大鼠体重增加较慢，能量效率较低，预示着去卵巢后肿瘤的负担和多样性，二甲双胍治疗显著抑制了去卵巢后肿瘤的进展。肥胖者的肿瘤在OVX前和OVX诱导的体重增加期间孕激素受体(PR)的表达增加。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检验双重需求假说。在OVX诱导的体重增加的狭窄窗口期间，将暂时采用两种已知的改善代谢控制的相关干预措施(二甲双胍、定期锻炼)，以评估它们对长期肿瘤结果的影响。在第二个目标中，我们采用了一项24小时的能量平衡和燃料利用的多示踪研究，以检查肥胖是否损害了对OVX诱导的过量喂养的代谢反应，并在肿瘤中赋予了“侵略性”的糖酵解/产脂表型。我们将研究二甲双胍治疗是否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，我们调查肥胖相关PR表达升高的原因和后果。来自Aim 2的组织将被用来确定在OVX诱导的体重增加过程中，乳腺中的雌激素是否局部增加，以回应过度喂养。当受到营养丰富或细胞因子丰富的环境的挑战时，表达PR的(PR+)和不表达PR(PR-)的人乳腺癌细胞将被用来检测PR表达对肿瘤细胞代谢和增殖的配体无关的影响。总而言之，这些研究将检验在卵巢功能丧失后，代谢控制不良和先前存在的肿瘤受体状态是否融合在一起，以促进生存和生长。本项目中的观察可能指向围绝经期或绝经后不久的关键时间窗口，这将使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最大化。

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.