Polyphenolics from mango (Mangifera indica L.) suppress breast cancer ductal carcinoma in situ proliferation through activation of AMPK pathway and suppression of mTOR in athymic nude mice.

The objective of this study was to assess the underlying mechanisms of mango polyphenol decreased cell proliferation and tumor volume in ductal carcinoma in situ breast cancer. We hypothesized that mango polyphenols suppress signaling along the AKT/mTOR axis while up-regulating AMPK. To test this hypothesis, mango polyphenols (0.8 mg gallic acid equivalents per day) and pyrogallol (0.2 mg/day) were administered for 4 weeks to mice xenografted with MCF10DCIS.com cells subcutaneously (n=10 per group). Tumor volumes were significantly decreased, both mango and pyrogallol groups displayed greater than 50% decreased volume compared to control. There was a significant reduction of phosphorylated protein levels of IR, IRS1, IGF-1R, and mTOR by mango; while pyrogallol significantly reduced the phosphorylation levels of IR, IRS1, IGF-1R, p70S6K, and ERK. The protein levels of Sestrin2, which is involved in AMPK-signaling, were significantly elevated in both groups. Also, mango significantly elevated AMPK phosphorylation and pyrogallol significantly elevated LKB1 protein levels. In an in vitro model, mango and pyrogallol increased reactive oxygen species (ROS) generation and arrested cells in S phase. In silico modeling indicates that pyrogallol has the potential to bind directly to the allosteric binding site of AMPK, inducing activation. When AMPK expression was down-regulated using siRNA in vitro, pyrogallol reversed the reduced expression of AMPK. This indicates that pyrogallol not only activates AMPK, but also increases constitutive protein expression. These results suggest that mango polyphenols and their major microbial metabolite, pyrogallol, inhibit proliferation of breast cancer cells through ROS-dependent up-regulation of AMPK and down-regulation of the AKT/mTOR pathway.

Calorie restriction: effect on growth of human tumors heterotransplanted in nude mice.

The presence of 4 human malignant tumors (1 breast, 1 lung, and 2 colon carcinomas) growing subcutaneously as heterotransplants in nude mice did not significantly affect the body weights of adult animals until the tumors reached very large dimensions (tumor wt greater than 15% of the body wt). However, a colon carcinoma (HT 29) induced a cessation of the natural rate of body weight increase when it grew in young adults (animals weighing approximately equal to 25 g which will gain 6 g or approximately equal to 25% body wt in 1 mo). Calorie restriction at all the levels tested (8, 6, 4, and 2 g/day/mouse) with standard pelletized mouse food produced both weight loss in the animals (with and without tumor) and a lowering of the growth rate of all the 4 tumors tested growing at a subcutaneous site and/or under the kidney capsule. Each tumor responded differently to the calorie restriction. The 4 tumors tested grew equally in both male and female nude mice. Young animals weighing 20 g inoculated with a fifth tumor (MeWo melanoma) exhibited tumor growth inhibition proportional to restriction of calorie intake. Their survival, however, did not improve.