Abstract LB-345: Differences in metformin transporter expression between breast tumor and breast cancer cell lines: selecting a relevant breast cancer cell model for metformin therapy

Abstract

Abstract Purpose: Recent studies show that the anti-diabetic drug metformin induces significant anticancer effects in several cancers including breast cancer via activation of intracellular AMPK. Because of its hydrophilic nature and net positive charge at physiologic pHs, metformin requires cation-selective transporters such as OCT1-3, PMAT and MATE1-2 to enter cells and activate AMPK. Expression of these transporters in cancer cells would determine the intracellular concentrations of metformin that can be achieved for anticancer effects. Therefore, elucidating metformin transport in breast cancer is central to understanding optimum dosing and transporter-associated inter-subject variability in its anticancer efficacy. However, there is limited information on metformin transport in breast cancer. Studies in our laboratory suggest that cation-selective transporters are expressed at negligible levels in MCF-7 cells, a widely used in vitro breast cancer model, which is not consistent with the robust anticancer effect of metformin in xenograft mouse models and clinical studies. Therefore, this study aims at determining a) metformin transporter expression in human breast tumor, b) if metformin transporter expression in breast cancer cell lines is relevant to that in breast tumor tissue and c) there is differential metformin transporter expression in tumor and non-malignant breast tissue. Methods: Total RNA isolated from breast cancer cell lines MCF-7, SK-BR-3, MDA-MB-231, ZR-75-1, BT-474, MDA-MB-435S, MDA-MB-468, BT-20 and BT-549 and from 14 pairs of human breast tumor and adjacent non-malignant breast tissues was subjected to.real-time PCR to determine relative expression levels of OCT1-3, PMAT, MATE1 and 2. Results: Most cell lines expressed low levels of candidate cation-selective transporters. MDA-MB-468 and BT-549 showed high expression of MATE1 and MDA-MB-231 expressed high levels of OCT3 and MATE1. In tumor and non-malignant breast tissue, the predominant transporters were OCT3 and PMAT. Nine of the total 14 tumor samples showed downregulation of OCT3 by 85% and PMAT by 66% compared to non-malignant tissue. Conclusions: The expression profile of cation-selective transporters is different between tumor and normal breast tissue and between breast tumor tissue and cell lines. Therefore, one needs to use caution in choosing a relevant in vitro cell model for investigating anticancer efficacy of metformin whose uptake is transporter-mediated. Expression data suggest that OCT3 and PMAT may play a major role in metformin intracellular uptake in breast cancer. MDA-MB-231 may be a useful model to assess the metformin anticancer effects in breast cancer. Clearly, genetic variability in metformin transporters may lead to differential responses to metformin anticancer therapy. Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 103rd Annual Meeting of the American Association for Cancer Research; 2012 Mar 31-Apr 4; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2012;72(8 Suppl):Abstract nr LB-345. doi:1538-7445.AM2012-LB-345