Abstract 2930: Calorie restriction and rapamycin, but not exercise, inhibit MMTV-Wnt-1 mammary tumor growth in a mouse model of postmenopausal obesity

Abstract

Abstract Obesity is an established breast cancer risk factor in postmenopausal women, and calorie restriction (CR) and exercise (EX) are the two most recommended ways to prevent or reverse obesity. The mammalian Target of Rapamycin (mTOR) pathway is a potential mechanistic target underlying the effects of these interventions, and rapamycin (mTOR inhibitor) has been shown to mimic many of the anticancer effects of CR. However, the effects of obesity reversal by CR, EX, or treatment with rapamycin, on mammary tumor development have not been well studied. Therefore, we administered a diet-induced obesity regimen to 60 ovariectomized C57BL/6 mice for 8 weeks to induce obesity. The mice were then randomized into 4 groups (n=15/group): Control (AIN-76A diet ad libitum); CR (30% calorie restriction relative to control); EX (control diet ad libitum + treadmill exercise at 20m/min, 45min/day, 5days/week); and Rapamycin (control diet ad libitum + 5mg/kg injected i.p. every 48 hrs). Body weight and total body fat were measured every two weeks (using MRI). All mice were injected (4th mammary fat pad) with 5 × 104 MMTV-Wnt-1 mammary tumor cells at week 12, and at week 18 tumors were extracted and analyzed by immunohistochemistry (IHC). At the end of the study, mice in the CR group weighed significantly less (27.6 ± 2.6 g) and displayed lower percent body fat (34.7 ± 5.2 %) than mice in the control group (41.7 ± 2.9 g and 47.9 ± 1.8 %). There were no differences in body weigh or percent body fat in the EX (38.3 ± 3.10 g and 45.9 ± 2.6 %) and Rapamycin (37.4 ± 2.7 g and 46.6 ± 5.6 %) groups compared to control. At the end of the study, the CR and Rapamycin groups had comparable tumor weights (0.04 ± 0.02 g and 0.07 ± 0.04 g) that were significantly smaller than those in the control and EX groups (both 0.3 ± 0.2 g and 0.3 ± 0.2 g). IHC analysis showed that Rapamycin significantly reduced p-mTOR, Cyclin D1 and p-S6 Ribosomal Protein (markers of mTOR activation) compared to control, Exercise and CR. Exercise displayed variable levels of p-mTOR, Cyclin D1 and p-S6 and CR displayed no differences compared to control. Rapamycin tumors were bimodal for both p-Akt (upstream of mTOR) and Ki67 (proliferation marker); those tumors displaying high p-Akt (∼50%) also displayed high Ki67 staining, but tumors with low pAkt displayed low Ki67 staining. CR and Exercise had no effect on p-Akt and Ki67 compared to control. There were no differences in Cleaved-Caspase 3 (marker of apoptosis) between the groups. We conclude that CR and Rapamycin reverse the effects of obesity on Wnt-1 mammary tumor growth, but apparently via different mechanisms, while EX does not appear to have anti-tumor growth effects in obese mice. Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 101st Annual Meeting of the American Association for Cancer Research; 2010 Apr 17-21; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2010;70(8 Suppl):Abstract nr 2930.