Synthesis and antitumor effects of novel betulinic acid derivatives bearing electrophilic moieties.

Betulinic acid (BA) is a kind of naturally occurring lupane pentacyclic triterpenoid, possessing various biological activities including antiviral, anti-inflammatory and antitumor activity. Covalent inhibitors, characterized by electrophilic warheads that form covalent bonds with specific amino acid residues of target proteins, have garnered enormous attention in anticancer agent discovery over the past decade owing to their exceptional selectivity and efficacy. In this study, BA was structurally modified with electrophilic groups, and 23 derivatives of BA were synthesized. Most of these BA derivatives exhibited improved antiproliferative activity against MCF-7, HeLa, MDA-MB-231 cells in MTT assay, especially the compound 15b (IC = 1.09 μM against MCF-7 cells). Further study demonstrated that 15b inhibited the migration and clone formation of MCF-7 cells, induced the apoptosis, autophagy and cycle arrest at G2/M phase in MCF-7 cells, and promoted the production of intracellular reactive oxygen species (ROS). Western blot analysis showed that 15b inhibited AKT/mTOR signaling pathway in MCF-7 cells. In addition, 15b reversed the resistance of JIMT-1 cells to trastuzumab, which might be related to the inhibition of AKT/mTOR pathway. Finally, 15b significantly inhibited the growth of tumor in the breast cancer xenograft mouse model with 36 % inhibition rate of tumor growth and without significant reduction of mouse body weight.