Harmane induces apoptosis through RRM2B and suppresses colorectal cancer progression

ABSTRACT Colorectal cancer (CRC) is a common malignant tumor of the digestive system, and chemotherapy resistance often leads to poor patient prognosis. Harmane, a natural indole alkaloid, is found in Leguminosae plants (particularly those of the Crotalaria genus), as well as in mammalian tissues and certain food products. It exhibits potential anticancer activities through multiple mechanisms in various cancers, including liver, breast, and thyroid cancers. However, the role of harmane in the treatment of CRC remains unclear. In this study, we demonstrate that harmane induces cell cycle arrest and apoptosis in CRC cells via the p53–RRM2B axis. Furthermore, at the level of the gut microbiota, harmane reshapes microbial composition, thereby contributing to its anti-tumor effects. IMPORTANCE This study is the first to demonstrate a progressive decline of harmane levels in the gut from healthy individuals to advanced adenoma and CRC patients, suggesting its potential protective role in CRC development. We further found that harmane promotes CRC cell apoptosis via RRM2B-mediated regulation, revealing the underlying molecular mechanism. Moreover, in vivo experiments showed that harmane can modulate gut microbial composition and its derived metabolites, and fecal microbiota transplantation experiments indicated that harmane exerts anticancer effects by regulating both the gut microbiota and microbial metabolites. This study proposes a novel therapeutic strategy for CRC, highlighting the importance of incorporating gut microbiota modulation into cancer treatment.