title: Cation-selective transporters are critical to the AMPK-mediated antiproliferative effects of metformin in human breast cancer cells.
abstract: The antidiabetic drug metformin exerts antineoplastic effects against breast cancer and other cancers. One mechanism by which metformin is believed to exert its anticancer effect involves activation of its intracellular target, adenosine monophosphate-activated protein kinase (AMPK), which is also implicated in the antidiabetic effect of metformin. It is proposed that in cancer cells, AMPK activation leads to inhibition of the mammalian target of rapamycin (mTOR) and the downstream pS6K that regulates cell proliferation. Due to its hydrophilic and cationic nature, metformin requires cation-selective transporters to enter cells and activate AMPK. This study demonstrates that expression levels of cation-selective transporters correlate with the antiproliferative and antitumor efficacy of metformin in breast cancer. Metformin uptake and antiproliferative activity were compared between a cation-selective transporter-deficient human breast cancer cell line, BT-20, and a BT-20 cell line that was engineered to overexpress organic cation transporter 3 (OCT3), a representative of cation-selective transporters and a predominant transporter in human breast tumors. Metformin uptake was minimal in BT-20 cells, but increased by >13-fold in OCT3-BT20 cells, and its antiproliferative potency was >4-fold in OCT3-BT20 versus BT-20 cells. This increase in antiproliferative activity was associated with greater AMPK phosphorylation and decreased pS6K phosphorylation in OCT3-BT20 cells. In vitro data were corroborated by in vivo observations of significantly greater antitumor efficacy of metformin in xenograft mice bearing OCT3-overexpressing tumors versus low transporter-expressing wildtype tumors. Collectively, these findings establish a clear relationship between cation-selective transporter expression, the AMPK-mTOR-pS6K signaling cascade, and the antiproliferative activity of metformin in breast cancer.
authors.affiliation: Division of Pharmacotherapy and Experimental Therapeutics, UNC Eshelman School of Pharmacy, the University of North Carolina at Chapel Hill, Chapel Hill, NC.
authors.forename: Hao
authors.initials: H
authors.lastname: Cai
authors.affiliation: Division of Pharmacotherapy and Experimental Therapeutics, UNC Eshelman School of Pharmacy, the University of North Carolina at Chapel Hill, Chapel Hill, NC.|Research Center for Drug Metabolism, Jilin University, Changchun, People's Republic of China.
authors.forename: Yunhui
authors.initials: Y
authors.lastname: Zhang
authors.affiliation: Division of Molecular Pharmaceutics, UNC Eshelman School of Pharmacy, the University of North Carolina at Chapel Hill, Chapel Hill, NC.
authors.forename: Tianxiang Kevin
authors.initials: TK
authors.lastname: Han
authors.affiliation: Division of Pharmacotherapy and Experimental Therapeutics, UNC Eshelman School of Pharmacy, the University of North Carolina at Chapel Hill, Chapel Hill, NC.
authors.forename: Ruth S
authors.initials: RS
authors.lastname: Everett
authors.affiliation: Division of Pharmacotherapy and Experimental Therapeutics, UNC Eshelman School of Pharmacy, the University of North Carolina at Chapel Hill, Chapel Hill, NC.
authors.forename: Dhiren R
authors.initials: DR
authors.lastname: Thakker
mesh_terms: D055372:AMP-Activated Protein Kinases / Q000378:metabolism*; D000818:Animals; D000970:Antineoplastic Agents / Q000494:pharmacology*; D001943:Breast Neoplasms / Q000473:pathology*; D045744:Cell Line, Tumor; D049109:Cell Proliferation / Q000187:drug effects; D005260:Female; D008325:Mammary Neoplasms, Experimental / Q000188:drug therapy / Q000473:pathology; D008687:Metformin / Q000494:pharmacology*; D051379:Mice; D008819:Mice, Nude; D027701:Organic Cation Transport Proteins; D038762:Ribosomal Protein S6 Kinases, 70-kDa / Q000378:metabolism; D015398:Signal Transduction / Q000187:drug effects*; D058570:TOR Serine-Threonine Kinases / Q000378:metabolism; D023041:Xenograft Model Antitumor Assays; D000099254:Organic Cation Transporter 3
chemical_list: D055372:AMP-Activated Protein Kinases; D000970:Antineoplastic Agents; D008687:Metformin; D027701:Organic Cation Transport Proteins; D038762:Ribosomal Protein S6 Kinases, 70-kDa; D058570:TOR Serine-Threonine Kinases; D000099254:Organic Cation Transporter 3; C546842:MTOR protein, human
keywords: AMPK pathway; antiproliferative activity; breast cancer; metformin; transporters