Synthesis, Biological Evaluation of Fluorescent 23-Hydroxybetulinic Acid Probes, and Their Cellular Localization Studies

23-Hydroxybetulinic acid (23-HBA) is a complex lupane triterpenoid, which has attracted increasing attention as an anticancer agent. However, its detailed mechanism of anticancer action remains elusive so far. To reveal its anticancer mode of action, a series of fluorescent 23-HBA derivatives conjugated with coumarin dyes were designed, synthesized, and evaluated for their antiproliferative activities. Subcellular localization and uptake profile studies of representative fluorescent 23-HBA probe 26c were performed in B16F10 cells, and the results suggested that probe 26c was rapidly taken up into B10F10 cells in a dose-dependent manner and mitochondrion was the main site of its accumulation. Further mode of action studies implied that the mitochondrial pathway was involved in 23-HBA-mediated apoptosis. Together, our results provided new clues for revealing the molecular mechanism of natural product 23-HBA for its further development into an antitumor agent.