Discovery and Structural Optimization of Elephantopus scaber -Derived Sesquiterpene Lactones as Covalent PRDX6 Inhibitors for Colorectal Cancer

Abstract Colorectal cancer (CRC) remains a highly aggressive malignancy, highlighting the need for therapeutic agents with distinct mechanisms of action. Natural products provide structurally diverse and biologically privileged scaffolds for anticancer drug discovery. Building on an anti-CRC germacrane-type sesquiterpene lactone scaffold (SC) isolated from Elephantopus scaber Linn., we identified PRDX6 as a covalent target using a biotinylated probe and covalent mass spectrometry, which revealed engagement of the catalytic residue Cys47. Structure-guided C6 functionalization with a 1,2,3-triazole motif afforded compound 1c, which showed enhanced PRDX6 binding, inhibited PRDX6 enzymatic activity, and promoted intracellular ROS accumulation, leading to potent anti-CRC effects. To improve in vivo developability, a morpholine hydrochloride prodrug, 6c, was designed and synthesized. Compound 6c displayed favorable pharmacokinetic properties, efficient systemic release of 1c, and significant antitumor efficacy in CRC xenograft models. This study establishes SC-derived sesquiterpene lactones as promising natural product-based covalent PRDX6 inhibitors for CRC drug discovery.