|
|
Back to 2015 Annual Meeting Program
Metformin Decreases Metabolic Activity, Cell Proliferation, and Protein Synthesis in Colon Cancer Cells
Jennifer W. Harris*1, Yekaterina Zaytseva1, Yang-an Wen1, Xiong Xiaopeng1, B. Mark Evers1, 2, Tianyan Gao1, 2
1University of Kentucky, Lexington, KY; 2Markey Cancer Center, Lexington, KY
Background: Metabolic syndrome is strongly associated with changes in the physiologic function of adipose tissue leading to insulin resistance, chronic inflammation, and colorectal carcinogenesis; tumor cell microenvironment strongly influences tumor onset and progression. Metformin is the most widely used drug in the biguanide class for treating Type II diabetes. Previous studies suggest metformin has an anti-tumor effect in colon cancer; however, the direct metabolic implications of the drug have yet to be determined.
Methods: To determine the effect of metformin on AMPK signaling and cellular metabolic responses in colon cancer cells, human colon cancer cell lines, SW480 and KM20, were treated with metformin (0 or 1mM) for 20h, and oxygen consumption rate (OCR) and extracellular acidification rate (ECAR) were measured using Seahorse XF 96 analyzer. Data analysis was performed using Xfe WAVE™ software. To test if colon tissues respond to metformin during ex vivo incubation, the mucosal layer of mouse colon was isolated and treated with metformin; tissues were then homogenized and protein lysates collected. Expression of pACC, pAMPK, pS6K, and cleaved caspase-3 was assessed by western blot. In addition, in pilot study, we collected colon cancer samples from patients with Stage II disease who were either taking metformin (n=2) or were not (n=2); expression of Ki-67,a marker of proliferation, and pS6, a protein synthesis marker, was assessed by immunohistochemistry.
Results: Oxygen consumption rates were significantly inhibited in SW480 and KM20 cells when treated with metformin compared to control, and in contrast, the extracellular acidification rate showed little change in metformin-treated cells, suggesting that metformin is capable of inhibiting mitochondrial respiration and oxidative phosphorylation in colon cancer cells. Treating mouse colon tissues with metformin resulted in an increase in both AMPK and ACC phosphorylation. In contrast, the phosphorylation and activity of S6K, a substrate of mTOR, was decreased. Furthermore, colon cancer patients with a history of recent metformin use demonstrated decreased expression of Ki-67 and pS6, suggesting decreased cell proliferation and protein synthesis, respectively.
Conclusions: Collectively, our data show that metformin is effective at activating AMPK and inhibiting mTOR in colon cancer cells in vitro and in mouse tissues ex vivo. Our study indicates that metformin treatment alters cellular metabolism in CRC cells suggesting that metformin impacts the key metabolic pathways that regulate glucose and fatty acid metabolism and may have beneficial effects on inhibiting cancer cell growth and proliferation.
Back to 2015 Annual Meeting Program
|
