Background: CO is a freely diffusible gas that acts as a physiological mediator of many biological and cellular processes, which has been shown to possess anticancer effect in many kinds of cancers. However, the effect of CO on prostate cancer has not been demonstrated. Therefore, we analyzed the antitumor activities and related mechanisms of CO on prostate cancer in vitro and in vivo. Methods: Cell viability of LNCaP and PC-3 cells after CORM-2 treatment was measured by CCK-8 assay, whereas the ATP production were detected by ATP detection assay. The early apoptosis induced by CO was evaluated by flow cytometry, and the expression level of apoptosis-related molecules (Caspases 3, 8, 9 and cleaved-Caspases 3, 8, 9) was detected using Western blot. Matrigel in vitro invasion assay was used to evaluate the effect of CO on cell invasion. We then evaluated the impact of CO on the expression of several key regulators involved in the LKB1 signaling pathway. At last, xenograft tumor in nude mice was used to further investigate the antitumor effect of CO in vivo. Results: Our results showed that CO could significantly inhibit proliferation and invasion, and induce apoptosis in human prostate cancer cell lines. The expression of LKB1 could be up-regulated after CO treatment, and CO also could increase p-AMPK levels and decrease p-mTOR. Furthermore, LKB1 knockdown could weaken the effect of CO on prostate cancer cells. In vivo, CO treatment significantly suppressed tumor growth and induced apoptosis in xenografts tumor in nude mice. Conclusions: CO possesses striking anticancer effect in human prostate cancer cells in vitro and in vivo, which is largely mediated by LKB1-AMPK-mTOR axis. (C) 2018 Elsevier Inc. All rights reserved.