title: The phenomenon of acquired resistance to metformin in breast cancer cells: The interaction of growth pathways and estrogen receptor signaling.
abstract: Metformin, a biguanide antidiabetic drug, is used to decrease hyperglycemia in patients with type 2 diabetes. Recently, the epidemiological studies revealed the potential of metformin as an anti-tumor drug for several types of cancer, including breast cancer. Anti-tumor metformin action was found to be mediated, at least in part, via activation of adenosine monophosphate-activated protein kinase (AMPK)-intracellular energy sensor, which inhibits the mammalian target of rapamycin (mTOR) and some other signaling pathways. Nevertheless, some patients can be non-sensitive or resistant to metformin action. Here we analyzed the mechanism of the formation of metformin-resistant phenotype in breast cancer cells and its role in estrogen receptor (ER) regulation. The experiments were performed on the ER-positive MCF-7 breast cancer cells and metformin-resistant MCF-7 subline (MCF-7/M) developed due to long-term metformin treatment. The transcriptional activity of NF-κB and ER was measured by the luciferase reporter gene analysis. The protein expression was determined by immunoblotting (Snail1, (phospho)AMPK, (phospho)IκBα, (phospho)mTOR, cyclin D1, (phospho)Akt and ERα) and immunohistochemical analysis (E-cadherin). We have found that: 1) metformin treatment of MCF-7 cells is accompanied with the stimulation of AMPK and inhibition of growth-related proteins including IκBα, NF-κB, cyclin D1 and ERα; 2) long-term metformin treatment lead to the appearance and progression of cross-resistance to metformin and tamoxifen; the resistant cells are characterized with the unaffected AMPK activity, but the irreversible ER suppression and constitutive activation of Akt/Snail1 signaling; 3) Akt/Snail1 signaling is involved into progression of metformin resistance. The results presented may be considered as the first evidence of the progression of cross-resistance to metformin and tamoxifen in breast cancer cells. Importantly, the acquired resistance to both drugs is based on the constitutive activation of Akt/Snail1/E-cadherin signaling that opens new perspectives to overcome the metformin/tamoxifen resistance of breast cancer.
authors.affiliation: Laboratory of Clinical Biochemistry, Institute of Clinical Oncology, N.N. Blokhin Cancer Research Centre, Moscow, Russia.
authors.forename: Alexander M
authors.initials: AM
authors.lastname: Scherbakov
authors.affiliation: Laboratory of Molecular Endocrinology, Institute of Carcinogenesis, N.N. Blokhin Cancer Research Centre, Moscow, Russia.
authors.forename: Danila V
authors.initials: DV
authors.lastname: Sorokin
authors.affiliation: Laboratory of Cell Death Mechanisms, Institute of Carcinogenesis, N.N. Blokhin Cancer Research Centre, Moscow, Russia.
authors.forename: Victor V
authors.initials: VV
authors.lastname: Tatarskiy
authors.affiliation: Laboratory of Microbial Viruses, S.N. Winogradsky Institute of Microbiology, Russian Academy of Sciences, Moscow, Russia.
authors.forename: Nikolay S
authors.initials: NS
authors.lastname: Prokhorov
authors.affiliation: Laboratory of Molecular Endocrinology, Institute of Carcinogenesis, N.N. Blokhin Cancer Research Centre, Moscow, Russia.
authors.forename: Svetlana E
authors.initials: SE
authors.lastname: Semina
authors.affiliation: Laboratory of Oncoendocrinology, N.N. Petrov Research Institute of Oncology, St, Petersburg, Russia.
authors.forename: Lev M
authors.initials: LM
authors.lastname: Berstein
authors.affiliation: Laboratory of Molecular Endocrinology, Institute of Carcinogenesis, N.N. Blokhin Cancer Research Centre, Moscow, Russia.
authors.forename: Mikhail A
authors.initials: MA
authors.lastname: Krasil'nikov
mesh_terms: D055372:AMP-Activated Protein Kinases / Q000235:genetics / Q000378:metabolism; D018931:Antineoplastic Agents, Hormonal / Q000494:pharmacology*; D015820:Cadherins / Q000235:genetics / Q000378:metabolism; D049109:Cell Proliferation / Q000187:drug effects; D019938:Cyclin D1 / Q000235:genetics / Q000378:metabolism; D019008:Drug Resistance, Neoplasm / Q000187:drug effects* / Q000235:genetics; D047628:Estrogen Receptor alpha / Q000235:genetics / Q000378:metabolism; D005260:Female; D015972:Gene Expression Regulation, Neoplastic; D006801:Humans; D007004:Hypoglycemic Agents / Q000494:pharmacology*; D061986:MCF-7 Cells; D008687:Metformin / Q000494:pharmacology*; D016328:NF-kappa B / Q000235:genetics / Q000378:metabolism; D010766:Phosphorylation; D051057:Proto-Oncogene Proteins c-akt / Q000235:genetics / Q000378:metabolism; D015398:Signal Transduction; D000071250:Snail Family Transcription Factors / Q000235:genetics / Q000378:metabolism; D058570:TOR Serine-Threonine Kinases / Q000235:genetics / Q000378:metabolism; D013629:Tamoxifen / Q000494:pharmacology*
chemical_list: D018931:Antineoplastic Agents, Hormonal; C530104:CCND1 protein, human; D015820:Cadherins; D047628:Estrogen Receptor alpha; D007004:Hypoglycemic Agents; D016328:NF-kappa B; C000604407:SNAI1 protein, human; D000071250:Snail Family Transcription Factors; D013629:Tamoxifen; D019938:Cyclin D1; D008687:Metformin; C546842:MTOR protein, human; D051057:Proto-Oncogene Proteins c-akt; D058570:TOR Serine-Threonine Kinases; D055372:AMP-Activated Protein Kinases
keywords: breast cancer; cell signaling; epithelial-mesenchymal transition; metformin; signal transduction; signal transduction pathways