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BACKGROUND/AIMS Colorectal cancer is the third leading cause of death in patients with cancers in America. Monensin has represented anti-cancer effect on various human cancer cells. We seek to investigate the effect of monensin on proliferation of human colorectal cancer cells and explore whether IGF1R signaling pathway is involved in anti-cancer mechanism of monensin. METHODS Cell proliferation and migration were assessed by crystal violet staining and cell wounding assay respectively. Cell apoptosis was analyzed by Hoechst 33258 staining and flow cytometry. Cell cycle progression was detected with the use of flow cytometry. Cancer-associated pathways were assessed with the use of pathway-specific reporters. Gene expression was detected by touchdown-quantitative real-time PCR. Inhibition of IGF1R was tested by immunofluorescence staining. Inhibition of IGF1R signaling was accomplished by adenovirus-mediated expression of IGF1. RESULTS We found that monensin not only effectively inhibited cell proliferation, cell migration as well as cell cycle progression, but also induced apoptosis and G1 arrest in human colorectal cancer cells. Monensin was shown to target multiple cancer-related signaling pathways such as Elk1, AP1, as well as Myc/max, and suppressed IGF1R expression via increasing IGF1 in colorectal cancer cells. CONCLUSION Monensin could suppressed IGF1R expression via increasing IGF1 in colorectal cancer cells. It has the potential to be repurposed as an anti-colorectal cancer agent, but further studies are still required to investigate the detailed mechanisms of monensin underlying its anti-cancer motion.Key MessagesMonensin inhibits the cell proliferation and the migration, induces apoptosis and inhibits cell cycle progression in human colorectal cancer cells.Monensin may exert anti-cancer activity by targeting multiple signaling pathways, including the IGF1R signaling pathway.Monensin has the potential to be repurposed as an anti-colorectal cancer agent.