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Metformin Alters Cellular Metabolism of Colon Cancer Cells Co-Cultured With Adipocytes
Jennifer W. Harris*1, Yekaterina Zaytseva2,1, B. Mark Evers2,1, Tianyan Gao3,2
1Department of Surgery, University of Kentucky, Lexington, KY; 2Markey Cancer Center, University of Kentucky, Lexington, KY; 3Department of Molecular and Cellular Biochemistry, University of Kentucky, Lexington, KY
Currently two thirds of the nation's population is considered overweight or obese by measurement of body mass index. Colon and rectal cancers are intimately linked to the development and maintenance of obesity. Obesity is strongly associated with changes in the physiological function of adipose tissue, leading to insulin resistance, chronic inflammation, and altered secretion of adipokines, and carcinogenesis. Metformin, an oral hypoglycemic agent and an activator of AMP activated protein kinase (AMPK), has recently been tested for its anticancer effect. The goal of this study is to determine if using metformin in adipogenic environments alters cellular metabolism that leads to tumor inhibition.
METHODS. (i) Pre-adipocytes, 3T3L1 cells, were differentiated using dexamethasone, 3-Isobutyl-1-methyl-2,6(1H,3H)-purinedione (IBMX), and insulin and were grown in a transwell co-culture system with human colon cancer lines including SW480, HT29, and HCT116. Cell lysates were prepared from co-cultured cancer cells and analyzed using Western blot analysis. (ii) Primary adipocytes were isolated from either epididymal fat of C57/BL6 mice or human mesenteric fat of patients with colon cancer. Conditioned media was collected from cultured adipocytes and incubated with SW480, HT29 or HCT116 cells. Cell lysates were prepared from cancer cells and analyzed by Western blot. (iii) SW480, HT29, HCT116 cells were treated with different concentrations (0 mM, 0.25 mM, 0.50 mM, 1.0 mM, 5.0mM) of metformin for 12 hours. The rates of glucose consumption and lactate production were measured using cell medium. Cell lysates were prepared and analyzed by Western blot.
RESULTS. We found that co-culturing colon cancer cells with differentiated 3T3L1 cells or primary adipocytes from mouse and human altered the activation status of signaling molecules, including mammalian target of rapamycin (mTOR), AMPK, and extracellular signal related kinases (ERK). In addition, metformin treatment resulted in a decrease in cell proliferation and an increase in AMPK activity in colon cancer cells. Significantly, the rates of glucose consumption and lactate production were decreased in a dose-dependent manner in metformin-treated cells.
CONCLUSIONS. Cancer cells grown in adipogenic environments have increased potential for increased growth, metastasis, and invasion. Treating cells with agents that down-regulate pathways common to adipogenesis and oncogenesis may provide therapeutic avenues to decrease cancer development.
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