Abstract. Metal-containing compounds have been extensively studied for many years as potent proteasome inhibitors. The 20S proteasome, the main component of the ubiquitin proteasome pathway, is one of the excellent targets in anticancer drug development. We recently reported that several copper complexes were able to inhibit cancer-special proteasome and induce cell death in human cancer cells. However, the involved molecular mechanism is not known yet. We therefore synthesized three copper complexes and investigated their abilities on inhibiting proteasome activity and inducting apoptosis in human breast cancer cells. Furthermore, we employed molecular dockings to analyze the possible interaction between the synthetic copper complexes and the β5 subunit of proteasome which only reflects the chymotrypsin-like activity. Our results demonstrate that three Cu(II) complexes possess potent proteasome inhibition capability in a dose-dependent and time-dependent manner in MDA-MB-231 human breast cancer cells. They could bind to the β5 subunit of the 20S proteasome, which consequently cause deactivation of the proteasome and tumor cell death. The present study is significant for providing important theoretical basis for design and synthesis of anticancer drugs with low toxicity, high efficiency and high selectivity.
IntroductionMetal complexes have important applications in many aspects of life. In recent years, the successful development of metalbased pharmaceuticals, including copper anticancer agents, has attracted more attention on metal complexes in cancer treatment (1-3). Studies have shown that the copper complexes, such as dithiocarbamate (4,5), 8-hydroxyquinoline (6), clioquinol (7) and some Schiff base copper coordination compounds (8-10), exert promising anticancer activity by targeting the ubiquitinproteasome pathway (UPP) in preclinical trials.The UPP selectively mediates cellular protein degradation which regulates cell cycle progression, signal transduction, differentiation, proliferation and apoptosis (11). The tagged proteins are degraded by the 26S proteasome, a huge cylinderlike protein complex, consists of one 20S core particle and two 19S regulatory particles (12). The 20S core particle comprises four packed rings, and each ring consists of 7 distinct subunits: the outer two rings are α subunits, acting like a 'gate' and controlling which proteins may go through into the cylinder; the inner two rings are β subunits, which form a catalytically active protease and are responsible for protein degradation (13). In proteasome of mammal cells, all α and β subunits are distinct and only subunits β1, β2 and β5 are catalytically active, which are responsible for caspase or peptidyl-glutamyl peptide-hydrolyzing (PGPH)-like activity, trypsin-like and chymotrypsin (CT)-like, respectively (14-16).Previous research has demonstrated that the inhibition of proteasomal CT-like activity is closely associated with tumor cell apoptosis (17)(18)(19)(20). Therefore, it is no surprise that selective inhibition of proteaso...