Abstract: Lipoic acid is an endogenous disulfide compound capable of suppressing growth of various cancer cell lines via mitochondria-targeted mode of action,while non-transformed primary cells are hardly affected.Coumarin,a natural product with fluorescence,was one of widely used imaging reagents.We present here,the design,synthesis and in vitro biological assessment of a novel lipoic acid-coumarin conjugate.This conjugate is a multifunctional molecule composed of a coumarin moiety as a fluorescent reporter and lipoic acid as a model active drug.After entering tumor cells,the conjugate can release lipoic acid and concomitantly fluorescence intensity increases,due to hydrolysis of ester bonds between lipoic acid and coumarin by hydrolytic enzyme in cancer cells.MTT assay was used to investigate its inhibitory activity on tumor cells.Reactive oxygen species (ROS) removal was detected by DCFH-DA kit.Flow cytometry was used to detect apoptosis.Fluorescence microscopy was used to detect intracellular imaging.The results showed that compared with lipoic acid,the in vitro anticancer activity of the conjugate increased by an order magnitude.Further research revealed that the conjugate can scavenge reactive oxygen species,an important substances for proliferation and growth of cancer cells.Apoptosis induced by the conjugate was significantly stronger than those of other tested compounds.Fluorescence microscopic experiments reveal that the fluorescence intensity reaches its maximum at 6 h,indicating drug release can be readily monitored at the cellular level.

Key words: lipoic acid, coumarin, conjugate, anti-tumor activity