Metformin enhances cisplatin cytotoxicity by suppressing signal transducer and activator of transcription-3 activity independently of the liver kinase B1-AMP-activated protein kinase pathway

• Published in: American journal of respiratory cell and molecular biology Vol. 49; no. 2; pp. 241 - 250
• Main Authors: Lin, Chien-Chung, Yeh, Hsuan-Heng, Huang, Wei-Lun, Yan, Jing-Jou, Lai, Wu-Wei, Su, Wen-Pin, Chen, Helen H W, Su, Wu-Chou
• Format: Journal Article
• Language: English
• Published: United States American Thoracic Society 01.08.2013
• Subjects: AMP-Activated Protein Kinases - genetics; AMP-Activated Protein Kinases - metabolism; Animals; Antineoplastic Agents - agonists; Antineoplastic Agents - pharmacology; Carcinoma, Non-Small-Cell Lung - drug therapy; Carcinoma, Non-Small-Cell Lung - genetics; Carcinoma, Non-Small-Cell Lung - metabolism; Carcinoma, Non-Small-Cell Lung - pathology; Cell Line, Tumor; Cisplatin - agonists; Cisplatin - pharmacology; Drug Resistance, Neoplasm - drug effects; Drug Synergism; Gene Silencing; Humans; Hypoglycemic Agents - agonists; Hypoglycemic Agents - pharmacology; Interleukin-6 - genetics; Interleukin-6 - secretion; Lung Neoplasms - drug therapy; Lung Neoplasms - genetics; Lung Neoplasms - metabolism; Lung Neoplasms - pathology; Metformin - agonists; Metformin - pharmacology; Mice; Mice, SCID; Protein-Serine-Threonine Kinases - genetics; Protein-Serine-Threonine Kinases - metabolism; Reactive Oxygen Species - metabolism; STAT3 Transcription Factor - genetics; STAT3 Transcription Factor - metabolism; TOR Serine-Threonine Kinases - genetics; TOR Serine-Threonine Kinases - metabolism; Vascular Endothelial Growth Factor A - genetics; Vascular Endothelial Growth Factor A - secretion; Xenograft Model Antitumor Assays
• ISSN: 1044-1549; 1535-4989
• DOI: 10.1165/rcmb.2012-0244oc

Metformin has been used as first-line treatment in patients with type 2 diabetes, and is reported to reduce cancer risk and progression by activating the liver kinase B1 (LKB1)-AMP-activated protein kinase (AMPK) pathway. Cisplatin remains the main drug for treating advanced non-small-cell lung cancer. However, drug resistance often develops through several mechanisms during the treatment course, including one mechanism mediated by the activation of the IL-6/signal transducer and activator of transcription (STAT)-3 pathway, related to the generation of reactive oxygen species (ROS). This study demonstrated a correlation between STAT3 phosphorylation and cisplatin cytotoxicity, using AS2 (PC14PE6/AS2)-derived cell lines (AS2/S3C) that contained constitutively active STAT3 plasmids as a model. A STAT3 inhibitor (JSI-124) enhanced the cisplatin sensitivity in AS2 cells, whereas metformin inhibited STAT3 phosphorylation and enhanced cisplatin cytotoxicity. By contrast, another AMPK activator (5-aminoimidazole-4-carboxamide-riboside) failed to produce these effects. LKB1-AMPK silencing by small, interfering RNA or mammalian target of rapamycin (mTOR) inhibition by rapamycin or pp242 did not alter the effect of metformin on STAT3 activity suppression, suggesting that metformin can modulate the STAT3 pathway through an LKB1-AMPK-independent and probably mTOR-independent mechanism. Metformin also inhibited cisplatin-induced ROS production and autocrine IL-6 secretion in AS2 cells. Both mechanisms contributed to the ability of metformin to suppress STAT3 activation in cancer cells, which resulted in the decreased secretion of vascular endothelial growth factor by cancer cells. The growth of subcutaneous tumor xenografts was significantly delayed by a combination of cisplatin and metformin. This is the first study to demonstrate that metformin suppresses STAT3 activation via LKB1-AMPK-mTOR-independent but ROS-related and autocrine IL-6 production-related pathways. Thus, metformin helps to overcome tumor drug resistance by targeting STAT3.