Synthesis and in vitro/in vivo anticancer evaluation of pentacyclic triterpenoid derivatives linked with -phenylalanine or -proline

Extensive research effort has been put in pentacyclic triterpenoids due to their numerous biological activities. However, their poor water solubility and low oral bioavailability limit their antitumor effects in vivo. To address these issues, 37 triterpenoid acid derivatives linked to l-phenylalanine or l-proline were designed and synthesized in this study. Structure-activity relationship (SAR) studies found two promising glycyrrhetinic acid (GA) derivatives 11 and 16. Compound 11 was obtained by C3-OH esterification and C30-COOH modification with l-phenylalanine while 16 was obtained by attaching C3-OH with l-phenylalanine. Compounds 11 and 16 exhibit up to 48- and 120-fold improvement respectively compared with the IC50 values of naturally occurring GA in the cellular assay. Fluorescence microscope and flow cytometric analysis suggested that both compounds 11 and 16 increased the content of ROS and Ca2+ in cancer cells, decreased mitochondrial membrane potential (JC-1), and activated the regulator caspase-3/8/9 to trigger cell apoptosis. RNA-seq analysis and western blot analysis indicated that compounds 11 and 16 may promote apoptosis by upregulating the functions of pro-apoptotic factors while inhibiting the proteasome activity.