Abstract 71: Metformin inhibits lung cancer cell growth and angiogenesis in vitro and in vivo: Effect on IL6-Stat3 pathway

Abstract

Abstract The usage of metformin as a first line treatment for type 2 diabetes associates with reduced cancer risk. Animal studies have shown that metformin inhibits breast cancer growth mainly via AMPK-mTOR pathway. Associated clinical trial is conducting. However, the application of metformin in other cancers and other mechanisms remain not clarified. In our previous study, we demonstrated the down-regulation of TSC1 (tuberous sclerosis 1) in lung cancer cells from malignant pleural effusion (MPE) and verified with qRT-PCR and immunohistochemistry. TSC1/TSC2 complex can suppress the mTOR pathway and receive input from LKB1-AMPK pathway and we found that metformin induced TSC1expression in vitro. Previous studies demonstrate that TNFα-sphingomyelinase and IL6-Stat3 contribute the formation of MPE via activating VEGF secretion. TNF-α can also induce IL6 secretion in many tumors. In our recent study, we first investigated the effect of metformin on proliferation of lung cancer cell. Lung cancer lines including PC14PE6/AS2 (AS2), A549 and CL 1-0 were treated with various dosage of metformin. After treatment for 96 hours, metformin inhibited proliferation of AS2, A549 and CL1-0 lung cancer cells dose-dependently. The IC50 of all cells are around 2.5-5 mM, measured by MTT assays. We also investigated the addictive cytotoxicity of metformin to cisplatin. Metformin co-incubation with cisplatin for 72 hr in AS2 cells displayed an increased cytotoxicity as compared to each agent alone. As for the association with angiogenesis, by analyzing the supernatant with ELISA assay, the VEGF secretion also decreased after treatment with metformin in AS2 and A549 cells. And Western blotting was conducted to access the effect on Stat3 and AMPK phosphorylation of metformin. In AS2 cell, not only the phosphorylation of AMPK increased after metformin treatment, the Stat3 phosphorylation was also suppressed. In addition, stimulation with TNF-α led to substantial secretion of IL6, which was inhibited by co-incubation with metformin. In vivo, the AS2 cells were injected i.p. into the unanesthetized nude mice and MQ-water or metformin (1mg) were injected 2 days later. Around 2 to 4 weeks, the mice developed peritoneal carcinomatosis and malignant ascites. In the metformin group, though the same number of mice developed peritoneal carcinomatosis and ascites, the amount of ascites and VEGF level are less than the control group. In conclusion, metformin inhibit lung cancer cell proliferation and angiogenesis in vitro and in vivo. And the IL6-Stat3-VEGF pathway may also involve in the anticancer effect of metformin. Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 101st Annual Meeting of the American Association for Cancer Research; 2010 Apr 17-21; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2010;70(8 Suppl):Abstract nr 71.