Anticancer chiral and racemic ternary copper(II) complexes: Multiple mechanisms and epigenetic histone methyltransferase enzymes as novel targets

Abstract

Copper complexes have the potential to overcome the limitations of platinum anticancer drugs and to provide a solution to difficult to cure metastatic breast cancer. The anticancer properties of a set of ternary copper(II) complex salts, viz. [Cu(phen)(l-ala)(H2O)]NO31, rac-[Cu(phen)(ala)(H2O)]NO32, rac-[Cu(phen)(4MeOCA)(H2O)]NO33 (1,10-phenanthroline, phen; alanine, ala; 4-methyl-oxazolidine-4-carboxylate, 4MeOCA) are reported herein. The main focus is on their potency and mechanism of action towards metastatic breast MDA-MB-231 cancer cells. They were more cytotoxic than cisplatin by 24 fold. The results of a 5-dose screening of 1 and 3 on the NCI panel of 60 human cancer cell lines, and their structure activity relationship (SAR) analysis revealed novel feature of overcoming drug resistance. Other studies include cellular and nuclear morphological studies of 1 – 3 on metastatic breast cancer MDA-MB-231, normal breast MCF10A and Chang Liver cells together with (i) apoptosis and cell cycle analysis, (ii) ROS assays (PNDA and DCFH-DA), (iii) JC-1 mitochondrial membrane potential assay, and (iv) proteasome inhibition assay on MDA-MB-231 cells. In addition, the docking of the L- and D-enantiomers of [Cu(phen)(ala)(H2O)]+ cations in the proteolytic sites of the 20S provided new insight on their mechanism of proteasome inhibition. A preliminary epigenetic study on MDA-MB-231 and T47D breast cancer cells treated with 1 – 3 to monitor their EZH1, EZH2 and H3K27me3 protein expression indicated new mode of action involving histone methylating enzymes. The results showed for the first time the unusual effect of EZH1 and EZH2 knockdown in the two cell lines on apoptosis induced by copper(II) complex 3 to be cell subtype dependent.