Protein binding studies with human serum albumin, molecular docking and in vitro cytotoxicity studies using HeLa cervical carcinoma cells of Cu(ii)/Zn(ii) complexes containing a carbohydrazone ligand.

The interaction of two binuclear mixed ligand Cu(ii) complexes [Cu(o-phen)LCu(OAc)] (1) and [Cu(o-phen)LCu(o-phen)](OAc) (2) (H3L = o-HOC6H4C(H)[double bond, length as m-dash]N-NH-C(OH)[double bond, length as m-dash]N-N[double bond, length as m-dash]C(H)-C6H4OH-o) and a new mononuclear Zn(ii) complex [Zn(HL)(o-phen)(H2O)](OAc)·H2O (3) (H2L = o-HOC6H4-C(H)[double bond, length as m-dash]N-NH-C([double bond, length as m-dash]O)-NH-N[double bond, length as m-dash]C(H)-C6H4OH-o, o-phen = 1,10-phenanthroline, and OAc = CH3COO-) with human serum albumin (HSA) was studied using fluorescence quenching, synchronous and 3D fluorescence measurements and UV-vis spectroscopy. 3D fluorescence studies showed that the HSA structure was altered at the secondary and tertiary levels upon binding with the complexes. This was further supported by the electronic absorption spectral studies of HSA in the absence and presence of the compounds. The average binding distance (r) between HSA and the complexes was obtained by Förster's resonance energy transfer theory. Complex 3 was structurally characterized by X-ray crystallography. Molecular docking studies indicated that all three complexes primarily bind to HSA in subdomain IIA with amino acid residues such as Arg218 and Lys199 which are located at the entrance of Sudlow's site I. The in vitro cytotoxicities of complexes 1-3 against HeLa cells showed promising anticancer activity (IC50 = 3.5, 3.9 and 16.9 µM for 1, 2 and 3, respectively). Live cell time lapse imaging for 1 was done to capture the dynamic behavior of the cells upon treatment with the complex. Cell cycle analysis by flow cytometry with HeLa cells indicated that 1 and 2 induced cell cycle arrest in the G2/M phase while 3 induced arrest in the G0/G1 phase leading to cell death. Compounds 1 and 2 but not 3 induced apoptosis through the mitochondrial pathway as suggested from the relative p53, caspase3 and bcl2 mRNA levels measured by real-time quantitative PCR analysis.

Efficient hydrolytic cleavage of DNA and antiproliferative effect on human cancer cells by two dinuclear Cu(II) complexes containing a carbohydrazone ligand and 1,10-phenanthroline as a coligand.

We report the synthesis, crystal structures and biological activities of two dinuclear Cu(II) complexes [Cu(o-phen)LCu(OAc)] (1) and [Cu(o-phen)LCu(o-phen)](OAc) (2), where o-phen = 1,10-phenanthroline, H3L = o-HOC6H4C(H)=N-NH-C(OH)=N-N=C(H)-C6H4OH-o, and OAc=CH3COO-. Both compounds display strong and broad X-band EPR spectra at RT in their powder state confirming that these are paramagnetic. The intercalative DNA binding of the compounds as revealed from spectrophotometric studies was found to be consistent with the results of fluorescence spectroscopic studies for ethidium bromide displacement assay as well as enhanced viscosity of DNA in the presence of these compounds. The compounds effectively catalyze hydrolytic cleavage of supercoiled pUC19 DNA and show remarkable cytotoxicity toward human lung cancer A549 cell line (IC50 values are 4.34 and 8.46 µM for 1 and 2, respectively) and breast cancer MCF7 cell line (IC50 values are 6.50 and 8.68 µM for 1 and 2, respectively) and are found to be relatively less toxic toward keratinocyte HaCaT normal cell line (IC50 values are 11.19 and 16.01 µM for 1 and 2, respectively). Annexin-V/PI dual staining results analyzed by flow cytometry strongly suggest the induction of apoptotic pathway for the anticancer activity of these complexes. Flow cytometry experiment for cell cycle analysis showed considerable increase in the G2/M phase in both A549 and MCF7 cell lines by these two compounds. On the other hand, compounds 1 and 2 activate reactive oxygen species (ROS) level in A549 cells, but act as scavengers or inhibitors of ROS in MCF7 cell line as analyzed by DCFDA staining using flow cytometry. Two dinuclear Cu(II) complexes exhibit efficient hydrolytic cleavage of DNA and display remarkable cytotoxicity against human lung cancer A549 and breast cancer MCF7cells. The ROS level in A549 cells is activated, but the ROS level in MCF7 cells is decreased in the presence of these complexes. Cell cycle analysis by flow cytometry shows G2/M phase arrest in both these cell lines.