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.