Abstract 4427: Multiple cation-selective transporters contribute to the anti-proliferative effects of metformin in ovarian cancer cell lines.
Authors: Everett Ruth S. , Zhang Yunhui , Ononiwu Innocent M. , Bae-Jump Victoria L. , Thakker Dhiren R. 
Published: August 2014

PURPOSE: Recent studies show that the anti-diabetic drug metformin exhibits anticancer effects against a broad spectrum of cancers including ovarian cancer. Because metformin is highly hydrophilic with a net positive charge at all physiologic pH values, it requires cation-selective transporters to enter into cells and interact with its intracellular target 5’ adenosine monophosphate-activated protein kinase. The expression pattern and level of these transporters in cancer cells would determine the intracellular concentrations and subsequently the anti-proliferative activity of metformin. This study aims to investigate metformin transporter expression and the impact of these transporters on metformin uptake and anti-proliferative activity in human ovarian cancer cell lines that are routinely used to assess potential anti-cancer agents against this cancer type.

METHODS: Total RNA from human ovarian cancer cell lines (IG, SKOV3 and HEY) was subjected to real-time PCR to determine expression levels of the common cation transporters organic cation transporter (OCT) 1-3, plasma membrane monoamine transporter (PMAT), multidrug and toxin extrusion transporters (MATE) 1 and 2. Uptake of [14C]metformin (50μM) in the presence or absence of the cation-selective transporter inhibitors famotidine and 1-methyl-4-phenylpyridinium (MPP+) was assessed to determine the contributions of transporters to metformin uptake in these cell lines.

RESULTS: OCT3 mRNA was highly expressed in IG cells, with low levels of OCT2, PMAT and MATE1. Metformin uptake into IG cells was significantly (P&lt;0.05) inhibited by 5mM MPP+ (which inhibits all cation-selective transporters at this concentration), and by 200 μM famotidine (which is a more selective inhibitor of OCT3 than OCT2 at this concentration). In SKOV3 cells where OCT2 was the predominant transporter with low levels of OCT3, PMAT and MATE1, metformin uptake was significantly (P&lt;0.05) inhibited by 5 mM MPP+ and 200 μM famotidine. Cation-selective transporter expression was negligible in the HEY cell line in which metformin uptake was lower than uptake in IG and SKOV3 cells, and was not inhibited by either of the two inhibitors.

CONCLUSIONS: The ovarian cancer cell lines used in this study are utilized as models to test anticancer agents against ovarian cancer. In order to use these cell lines to investigate the anti-proliferative activity of metformin so as to predict its anticancer effects in ovarian cancer, the expression of metformin transporters and metformin uptake in relation to the expression of these transporters needs to be elucidated. Studies on determining the IC50 values of metformin in ovarian cancer cell lines, as well as cation-selective transporter expression studies in human ovarian tumor tissue samples are currently in progress.

Citation Format: Ruth S. Everett, Yunhui Zhang, Innocent M. Ononiwu, Victoria L. Bae-Jump, Dhiren R. Thakker. Multiple cation-selective transporters contribute to the anti-proliferative effects of metformin in ovarian cancer cell lines. [abstract]. In: Proceedings of the 104th Annual Meeting of the American Association for Cancer Research; 2013 Apr 6-10; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2013;73(8 Suppl):Abstract nr 4427. doi:10.1158/1538-7445.AM2013-4427