Abstract 4542: Regulation of the cell cycle by metformin is p21-dependent in lung cancer

Abstract

Abstract The oral antidiabetic agent metformin has antineoplastic activity that is likely mediated by mechanisms independent of its hypoglycemic effects. Previously reported in human non-small cell lung carcinoma (NSCLC) cell lines, 24 h treatment with metformin induced growth inhibition and G0/G1 phase arrest through induction of the energy sensing kinase AMP-activated kinase (AMPK) and the DNA damage responsive protein ataxia telangectasia mutated (ATM). AMPK and ATM are both known to regulate G0/G1 and G2 phases through modulation of the p53-p21 axis. Therefore, the objective of our study was to elucidate the molecular mechanism of metformin induced cell cycle arrest in NSCLC. Congruent with previous findings, we demonstrate that 5mM metformin treatment for up to 72 h inhibits growth in H1299 and A549 NSCLC cell lines, but not in the non-cancerous fibroblast cell line MRC-9. In H1299 and A549 cells, growth inhibition was associated with an induction of phosphorylation of AMPK and ATM as well as a reduction in phosphorylation of AKT and mTOR. Extending these findings using H1299 cells, metformin consistently induced only a transient G0/G1 phase arrest at 24 h by downregulating cyclin D1 and p27 and upregulating p21 and at 72 h a G2/M-arrest by accumulating cyclin B1 and upregulating p21 and p27. These arrests were associated with ATM and Chk-2 activation and resultant inhibitory phosphorylation of cyclin dependent phosphatase CDC25c. Importantly, p21 knock down in H1299 cells demonstrated the coordinate loss of p27 stabilization, attenuation of the G0/G1 phase arrest at 24 h, and decrease in inhibitory phosphorylation of pan-cyclin dependent kinases. Therefore, we demonstrate for the first time in NSCLC that metformin activates G1 and G2 -checkpoint responses, but the fidelity of the G1-arrest is compromised by the downregulation of p27. However, p21-dependent upregulation of p27 facilitates a G2/M arrest at 72 h. The ability of metformin to control aberrant oncogenic cell-cycle regulation by inducing negative cell-cycle regulators p21 and p27 may provide a novel therapeutic strategy in lung cancer. Note: This abstract was not presented at the meeting. Citation Format: Amanda Templeton, Rajagopal Ramesh. Regulation of the cell cycle by metformin is p21-dependent in lung cancer. [abstract]. In: Proceedings of the 105th Annual Meeting of the American Association for Cancer Research; 2014 Apr 5-9; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2014;74(19 Suppl):Abstract nr 4542. doi:10.1158/1538-7445.AM2014-4542