Synthesis, biological characterization and evaluation of molecular mechanisms of novel copper complexes as anticancer agents

Background: To overcome the hurdles of cisplatin, majorly its toxicity and resistance, there has been extensive search for alternative anti-cancer metal-based compounds. Here, three Cu(II)-complexes, Cu(Sal-Gly)(phen), Cu(Sal-Gly)(pheamine), Cu(Sal-Gly)(phepoxy) are characterized for their interaction with DNA, cytotoxicity and mechanism of action. Methods: The binding ability of the complexes to Calf-Thymus DNA was evaluated by competition fluorescence studies with thiazole-orange, UV-Vis and circular dichroism spectroscopic titrations. Cytotoxicity was evaluated by MTT analysis. The DNA damage was analyzed through cleavage of supercoiled DNA via agarose gel-electrophoresis, and 8-oxo-guanidine and gamma H2AX staining in cells. Apoptosis was detected via DNA condensation/fragmentation, mitochondrial membrane potential, Annexin V staining and caspase 3/7 activity. Formation of reactive oxygen species was determined by DCFDA- and GSSG/GSH-analysis. Results: Binding constants to DNA were evaluated as 1.7 x 10(6) (Cu(Sal-Gly)(phen)), 2.5 x 10(6) (Cu(Sal-Gly)(pheamine)) and 3.2 x 10(5) (Cu(Sal-Gly)(phepoxy)). All compounds induced DNA damage. Apoptosis was the main form of cell death. There was an increase in ROS, which is most likely responsible for the observed DNA-damage. Although the compounds were cytotoxic to all tested cancer cell lines, only Cu(Sal-Gly)(pheamine) displayed significantly lower toxicity towards non-cancer cells, its associated phenotypes differing from the other two Cu-complexes. Thus, Cu(Sal-Gly)(pheamine) was further assayed for molecular changes in response to drug treatment using a custom designed RT-qPCR array. Results showed that Harakiri was significantly upregulated. Presence of p53 was not required for apoptosis in response to Cu-complexes. Conclusions and general significance: These Cu-complexes, namely Cu(Sal-Gly)(pheamine), may be considered promising anticancer agents with activity in cancer cells even with deficient p53 status. Portuguese Foundation for Science and Technology UID/QUI/00100/2013 IST-UTL Center of the Portuguese Mass Spectrometry Networks REM2013 - RECI/QEQ-QIN/0189/2012