Monascin accelerates anoikis in circulating tumor cells and prevents breast cancer metastasis

Anoikis resistance has been observed in various types of cancers in which anchorage-independent growth is a crucial step for cancer metastasis. Therefore, agents interfering with this specific cancer cell behavior may be integrated into novel antimetastatic strategies. Monascin (MS), a secondary metabolite found in Monascus species, is a known potent chemopreventive compound used for treating metabolic complications; however, the effect of MS on anoikis resistance has not been investigated. In this study, 4T1 breast cells were treated with MS under either suspension or adhesion conditions. The higher cytotoxicity of MS was more potent against suspended cells than against adherent cells. This selective cytotoxicity was due to the induction of anoikis, which was evidenced by changes in cell aggregation, caspase activity, and Annexin V/propidium iodide binding as well as the results of systemic metastasis in an animal model. Furthermore, MS inhibited E-cadherin and β-catenin expression in the cells; the treated cells formed spherical aggregates, which suggested that anchorage-independent growth was prevented by MS. These results provide new insights into the mechanisms underlying the growth-preventing effect of MS on cancer cells and indicate the potential ability of MS to suppress metastasis.