Introduction: Metformin has been shown to inhibit human cancer cell growth via activation of MAP kinase with resultant inhibition of mTOR signaling pathway. We have reported the over-expression of ornithine decarboxylase (ODC) in human melanoma cell lines. ODC is a key enzyme in polyamine biosynthesis. We determined the effect of metformin in combination with DMFO, an ODC inhibitor, on tumor proliferation and migration, and the possible mechanisms, using human melanoma cells. Methods: Human melanoma cells were treated with Metformin, DFMO, or combination. Cell proliferation assay was performed using Cell Titer Blue proliferation assay. Cell migration assay was performed by seeding melanoma cells in 24-well plate. After overnight incubation, an artificial homogenous wound was created onto the monolayer with a plastic micropipette tip. After wounding, the migration of cells into the wound was observed at 0- and 48-hour time points. Quantitative RT-PCR for ODC1 detection was performed using Assay-on-Demand Hs00159739-ml. GAPDH served as housekeeping control. Western blotting was performed to determine the expression of AMP kinase, mTOR, p70S6K and 4E-BP1, Raf-1 and Raf-B. Data were presented as means ± SD for the three separate experiments. For comparison between groups, the student's t test was used and p< 0.05 was considered to be statically significant. Results: There was dose-dependent inhibition of melanoma cell proliferation and migration with either metformin or DFMO. Synergistic inhibition was observed with the combination treatment on both cell migration and proliferation. There was synergistic inhibition of ODC expression with the combined treatment compared with DFMO alone (p<0.01). The combination treatment also lead to significant enhancement of AMPK activation and increased phosphorylation of AMPKΨ at Thr-172 compared with metformin alone (p<0.01). The combination treatment resulted in inhibition of mTOR signaling with decreased phosphorylation of mTOR, p70S6K and 4E-BP1, Raf-1 and Raf-B in treated cancer cells, when compared with individual drug treatments. Conclusion: We have observed a synergistic effect of AMP kinase activation and polyamine synthesis inhibition on suppressing human melanoma proliferation and migration. The synergism is due to enhanced inhibition of both polyamine synthesis and mTOR signaling pathways.

Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 103rd Annual Meeting of the American Association for Cancer Research; 2012 Mar 31-Apr 4; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2012;72(8 Suppl):Abstract nr 4126. doi:1538-7445.AM2012-4126