Casticin activates Rheb GTPase by binding to residue Trp141 and induces tumor senescence

Senescence is a state of irreversible growth arrest that can be induced in colorectal cancer (CRC). Developing drugs that can induce senescent CRC cells without promoting stemness can significantly improve treatment outcomes. Our study reveals a unique mechanism by which casticin (CAS) induces senescence in CRC. Importantly, CAS treatment does not induce stemness in CRC, as demonstrated both in vitro and in vivo. Further investigations showed that CAS binds to Rheb protein at residue Trp141, changing the conformation of Rheb protein, increasing its protein stability and activity. Additionally, CAS elevates AMPK activity. Knockdown of Rheb suppresses AMPK activity, indicating that AMPK acts downstream of Rheb. Crucially, inhibiting either Rheb or AMPK completely abolishes CAS-induced senescence in CRC. This study demonstrates that CAS binding to Trp141 activates Rheb GTPase, effectively inducing senescence in CRC through the Rheb/AMPK signaling pathway without promoting cancer cell stemness. This novel discovery highlights the potential for developing herbal-based senescence-inducing agents targeting Rheb for cancer treatments.