Schiff base Cu(II) complexes as inhibitors of proteasome in human cancer cells

Background: It has been demonstrated that proteasome inhibitors might be potential anticancer drugs. The copper complexes can be used as specific proteasome inhibitors in tumor cells able to induce apoptosis by the ubiquitin-proteasome pathway. The goal of our study was to test the cytotoxic and proteasome inhibitory effects of five Schiff base Cu(II) complexes - [Cu2(sal-D,L-glu)2(isoquinoline)2] . 2C2H5OH (1), [Cu(sal-5-met-L-glu)(H2O)].H2O (2), [Cu(ethanol)2(imidazole)4][Cu2(sal-D,L-glu)2(imidazole)2] (3), [Cu(sal-D,L-glu)(2-methylimidazole)] (4) on human lung carcinoma cells A549, cervix carcinoma cells HeLa and glioblastoma cells U-118MG.

Material and methods: For the cytotoxic analysis we used MTT test and for monitoring the proteasome inhibition western blot analysis.

Results: We have observed different cytotoxic effects of tested complexes on human cancer cells depending on the ligand present in their structure. Cu(II) complexes 4 and 5 were the most effective against A549 cells; all complexes were cytotoxic against HeLa cells and the complex 4 was the most effective against U-118MG. Moreover, we have detected the inhibition of the proteasome activity in human cancer cells A549 by Cu(II) complexes 1, 2 and 4 at IC50 concentration.

Conclusion: Results of our study suggest that isoquinoline- and imidazole-based copper complexes could be used as inhibitors of the proteasome system in cancer cells A549 (Tab. 1, Fig. 1, Ref. 26).