Abstract 3567: Metformin suppresses synthesis of pro-survival sphingolipid, sphingosine-1-phosphate, by inhibition of sphingosine kinase-1, in MCF-7 and SK-BR-3 breast cancer cell lines
Authors: Rose Ashley , Wann Daniel , Lightner Janet , Brannon Marianne , Stone William , Palau Victoria , Krishnan Koyamangalath 
Published: July 2016

Abstract
The antidiabetic drug, Metformin, may possess anti-cancer properties. Metformin has been shown to suppress proliferation of breast cancer cells primarily through activation of AMP-activated protein kinase (AMPK) and its suppression of downstream signaling pathways, such as mTOR, involved in cell replication. Other mechanisms may also play a role. Sphingolipids have a role in apoptosis and survival. Sphingosine-1-phosphate (S1P), a bioactive lipid mediator, promotes cell survival, proliferation, migration, angiogenesis, lymph angiogenesis, and immune response. S1P is involved in both intracellular and extracellular functions and regulates proliferation and survival. Blocking S1P synthesis inhibits cellular proliferation. Sphingosine kinase (SphK) is a lipid kinase that catalyzes formation of S1P from the precursor sphingosine. SphK is known to be upregulated in cancer cells, promoting tumor progression. S1P has a critical role in cancer progression and is considered a viable target for cancer therapeutics.
Our previous studies show that metformin has an effect on the synthesis of pro-apoptotic ceramides. We hypothesized that metformin induces cytotoxicity by reducing levels of the pro-survival sphingolipid, S1P. Firstly, MCF-7 and SK-BR-3 breast cancer cell lines were treated with increasing concentrations of metformin, and cytotoxicity was determined by MTT cell culture experiments after 24 hours of drug exposure. Metformin induces cytotoxicity in these breast cancer cells at a lowest concentration of 2.5mM, and percentage cytotoxicity increases in a dose-dependent manner. We utilized liquid chromatography and mass spectrometry and determined that cellular S1P levels are decreased in MCF-7 cells treated with 2.5mM metformin when compared with the control group. Finally, we treated MCF-7 and SK-BR-3 breast cancer cells with metformin, SK I/II (a known SphK inhibitor), and an untreated control group for 2, 4 and 6 hours. The dose of metformin was 10mM, which was chosen from a dose-response curve using MTT assay. The dose of SK I/II was 20uM, chosen based on the IC50 given. All treatments were done using low glucose media. Using the lysates from the harvested cells, gel electrophoresis and western blots using antibodies to SphK and S1P were run. Our results showed that metformin decreased the cellular levels of SphK and S1P. Thus, metformin exhibits anticancer properties via inhibiting the production of pro-survival lipid S1P. This data suggests that the pro-apoptotic effect of metformin may be partly mediated through its disruption of synthesis of S1P in breast cancer cells. Further work is necessary to characterize the sphingolipid content of MCF-7 and SK-BR-3 cancer cells before and after metformin treatment.
Citation Format: Ashley Rose, Daniel Wann, Janet Lightner, Marianne Brannon, William Stone, Victoria Palau, Koyamangalath Krishnan. Metformin suppresses synthesis of pro-survival sphingolipid, sphingosine-1-phosphate, by inhibition of sphingosine kinase-1, in MCF-7 and SK-BR-3 breast cancer cell lines. [abstract]. In: Proceedings of the 107th Annual Meeting of the American Association for Cancer Research; 2016 Apr 16-20; New Orleans, LA. Philadelphia (PA): AACR; Cancer Res 2016;76(14 Suppl):Abstract nr 3567.