Licochalcone A Derivatives as Selective Dipeptidyl Peptidase 4 Inhibitors with Anti-Inflammatory Effects

A set of 22 analogs of licochalcone A was designed andsynthesizedto explore their potentials as dipeptidyl peptidase 4 (DPP4) inhibitorswith anti-inflammatory effects. The anti-DPP4 effects of these analogswere evaluated using the fluorescent substrate Gly-Pro-N-butyl-4-amino-1,8-naphthalimide (GP-BAN). The nitro-substitutedanalogue 27 exhibited the most potent activity (K ( i ) = 0.96 & mu;M). A structure-activity relationship investigation revealedthat 4-hydroxyl and 5-chloro substituents are essential for DPP4 inhibition,while the 3 & PRIME;-nitro substituent improved both DPP4 inhibitionand microsomal stability. Furthermore, compound 27 demonstratedgood selectivity for DPP4 over other proteases, including dipeptidylpeptidase 9 (DPP9), thrombin, prolyl endopeptidase (PREP), and fibroblastactivation protein (FAP). The cytotoxic effect of 27 wasevaluated in cancer cell lines HepG-2 and Caco-2 and in somatic RAW264.7cells and RPTECs. Compound 27 showed no toxicity to normalcells and weak toxicity to cancer cells. In a living cell imagingassay, 27 blocked the dipeptidase activity of DPP4 inboth Caco-2 and HepG-2 cells. This compound also dose-dependentlysuppressed the expression levels of the chemokines tumor necrosisfactor-& alpha; (TNF-& alpha;), interleukin-6(IL-6), and interleukin-1 & beta; (IL-1 & beta;).