Metformin induces unique biological and molecular responses in triple negative breast cancer cells

Abstract

Triple negative (TN) breast cancer is more frequent in women who are obese or have type II diabetes, as well as young women of color. These cancers do not express receptors for the steroid hormones estrogen or progesterone, or the type II receptor tyrosine kinase (RTK) Her-2 but do have upregulation of basal cytokeratins and the epidermal growth factor receptor (EGFR). These data suggest that aberrations of glucose and fatty acid metabolism, signaling through EGFR and genetic factors may promote the development of TN cancers. The anti-type II diabetes drug metformin has been associated with a decreased incidence of breast cancer, although the specific molecular subtypes that may be reduced by metformin have not been reported. Our data indicates that metformin has unique anti-TN breast cancer effects both in vitro and in vivo. It inhibits cell proliferation (with partial S phase arrest), colony formation and induces apoptosis via activation of the intrinsic and extrinsic signaling pathways only in TN breast cancer cell lines. At the molecular level, metformin increases P-AMPK, reduces P-EGFR, EGFR, P-MAPK, P-Src, cyclin D1 and cyclin E (but not cyclin A or B, p27 or p21), and induces PARP cleavage in a dose- and time-dependent manner. These data are in stark contrast to our previously published biological and molecular effects of metformin on luminal A and B, or Her-2 type breast cancer cells. Nude mice bearing tumor xenografts of the TN line MDA-MB-231, treated with metformin, show significant reductions in tumor growth (p = 0.0066) and cell proliferation (p = 0.0021) as compared to untreated controls. Metformin pre-treatment, before injection of MDA-MB-231 cells, results in a significant decrease in tumor outgrowth and incidence. Given the unique anti-cancer activity of metformin against TN disease, both in vitro and in vivo, it should be explored as a therapeutic agent against this aggressive form of breast cancer.

The Antidiabetic Drug Metformin Inhibits Gastric Cancer Cell Proliferation In Vitro and In Vivo

“…However, it is important to consider that cells in culture are grown under hyperglycemic conditions (21). Tissue culture medium alone contains high concentrations of glucose, and 5% to 10% FBS is typically added, resulting in excessive growth stimulation.…”

Diet and tumor LKB1 expression interact to determine sensitivity to anti-neoplastic effects of metformin in vivo

“…For example, it has been shown that metformin suppresses polyp formation in ApcMin/ þ mice (Tomimoto et al, 2008), inhibits in vivo growth of p53 null cancers (Buzzai et al, 2007), attenuates tumorigenesis in phosphatase and tensin homolog-deficient mice (Huang et al, 2008) and slows proliferation of triple-negative breast cancer cells (Liu et al, 2009); however, these studies did not investigate the anti-neoplastic effects of metformin in the context of variation of dietary energy intake or insulin levels. This issue is critical as all epidemiological evidence for an anti-neoplastic action of metformin is derived from type II diabetic patients and metformin has important endocrine effects at the whole organism level in the setting of type II diabetes, apart from any direct effects on neoplastic cells.…”

Antiproliferative action of metformin in human lung cancer cell lines

“…Mazzone et al reported that diabetes patients with lung cancer who were previously treated with metformin or thiazolidinediones had a lower incidence of metastatic disease at the time of diagnosis and a reduced risk of death compared to those who did not receive the same treatment (4). Thereafter, the antiproliferative action of metformin was confirmed via in vivo and in vitro experiments in various cancer cell lines including breast (5)(6)(7)(8), prostate (9), pancreas (10), and ovarian cancer (11)(12)(13) as well as lung adenocarcinoma (8).…”

“…Despite these findings, the precise mechanisms of the metformin-induced effects are not fully understood. In particular, controversy remains about whether metformin is apoptotic (6,10) or just cytostatic (5,9) and whether it kills cancer cells synergistically with cytotoxic agents including cisplatin (11,13), paclitaxel (8), and doxorubicin (17), or if it is antagonistic to cisplatin (18,19).…”