Mononuclear copper(II) complexes with polypyridyl ligands: synthesis, characterization, DNA interactions/cleavages and in vitro cytotoxicity towards human cancer cells

DNA being the necessary element in cell regeneration, controlled cellular apoptosis via DNA binding/cleaving is considered an approach to combat cancer cells. The widely prescribed metallodrug cisplatin has shown interactions with the guanine-N7 center, and a plethora of complexes are continually developed to enhance crosslinking properties as well as covalent and non-covalent interactions. Two pentadentate ligands, L1 (1-(6-(1H-benzo[d]imidazol-2-yl)pyridin-2-yl)-N,N-bis(pyridin-2-ylmethyl)methanamine) and L2 (1-(6-(1-methyl-1H-benzo[d]imidazol-2-yl)pyridin-2-yl)-N,N-bis(pyridin-2-ylmethyl)methanamine), were synthesized together with their respective copper(II) complexes [1](ClO4)2 and [2](ClO4)2, which crystallized in a trigonal bipyramidal fashion. Different analytical and spectroscopic methods confirmed their formation, and their redox behaviour was also examined. The interactions of salmon sperm DNA (ss-DNA) with these two complexes were explored using absorbance spectroscopy, and they both exhibited a binding affinity (Kb) of ∼104 M-1. Fluorescence quenching experiments with ethidium bromide (EB)-bound DNA (EB-DNA) were also performed, and Stern-Volmer constant (KSV) values of 6.93 × 103 and 2.34 × 104 M-1 for [1](ClO4)2 and [2](ClO4)2, respectively, were obtained. Furthermore, DNA conformational changes due to the interactions of both complexes were validated via circular dichroism. We also assessed the DNA cleavage property of these complexes, which resulted in the linearization of circular plasmid DNA. This finding was supported by studying the growth of MDA-MB-231 breast cancer cells upon treatment with both Cu(II) complexes; IC50 values of 5.34 ± 1.02 μM and 0.83 ± 0.18 μM were obtained for [1](ClO4)2 and [2](ClO4)2, respectively. This validates their affinity towards DNA, and these insights can be further utilized for non-platinum based economical metallodrug development based on first row transition metals.

Chromophore appended DPA-based copper(II) complexes with a diimine motif towards DNA binding and fragmentation studies

Mixed ligand copper(II) complexes [Cu(L1)(bpy)](ClO4)21 and [Cu(L2)(bpy)](ClO4)22 (where L1 = 1-(anthracen-9-yl)-N,N-bis(pyridin-2-ylmethyl)methanamine, L2 = 1-(pyren-1-yl)-N,N-bis(pyridin-2-ylmethyl)methanamine and bpy = 2,2'-bipyridine) were synthesised and characterised thoroughly via different analytical and spectroscopic techniques i.e., UV-vis spectroscopy, fluorescence spectroscopy, FT-IR spectroscopy, HRMS and EPR spectroscopy. The molecular structures of the synthesised complexes were obtained using the single-crystal X-ray diffraction technique. Both complexes exhibited penta-coordinated and acquired distorted square pyramidal geometry. The redox behaviour of complexes 1 and 2 was investigated by employing cyclic voltammetry. The DNA binding study was carried out by UV-vis spectrophotometry using double-stranded salmon sperm DNA (ds-ss-DNA). The binding constant (Kb) values of 1 and 2 were 0.11 × 104 M-1 and 1.05 × 104 M-1, respectively, which indicates that 2 has better binding ability than 1. This might be due to the higher conjugative abilities with the extended surface area of the aromatic pyrene ring compared to the anthracene moiety. The fluorescence quenching experiments were also performed with EB bound DNA (EB-DNA) and Stern-Volmer constant (KSV) values were calculated as 1.23 × 105 M-1 and 1.39 × 105 M-1 for 1 and 2, respectively, suggesting that 2 showed stronger interaction with ss-DNA than 1. The molecular docking data support the DNA-binding studies, with the sites and mode of interactions against B-DNA varying with 1 and 2. Evaluation of the DNA binding properties of the complexes to linearized plasmid DNA indicated that 2 had modest DNA binding properties, which is a pre-requisite for a genotoxic agent. The effect of 1 and 2 on cell survival was analysed using HeLa cells by MTT assay and it was observed that the IC50 values of 1 and 2 were 43.7 μM and 18.6 μM, respectively. Our study paves the way for the designing of bio-inspired novel mixed metal complexes, which shows promising results for further exploration of molecular and mechanistic studies towards the development of non-platinum based economical metallodrugs.

Transition metal complexes as self-activating chemical nucleases: proficient DNA cleavage without any exogenous redox agents

Chemical nucleases have found potential applications in the research fields of chemistry, biotechnology and medicine. A variety of metal complexes have been explored as good to outstanding therapeutic agents for DNA cleavage activity most likely via hydrolytic, oxidative or photoinduced cleavage pathways. However, most of these DNA cleaving agents lack their utility in in vivo applications due to their dependence on exogenous oxidants or reductants to achieve successful DNA damage. In view of addressing these issues, the development of metal complexes/organic molecules serving as self-activating chemical nucleases has received growing attention from researchers. In only the last decade, this field has dramatically expanded for the usage of chemical nucleases as therapeutic agents for DNA damage. The present study provides an overview of the opportunities and challenges in the design and development of self-activating chemical nucleases as improved DNA therapeutic candidates in the absence of an external redox agent. The reports on DNA nuclease activity via self-activation, especially with copper, zinc and iron complexes, and their mechanistic investigation have been discussed in this review article.

(8-Hydroxyquinoline) Gallium(III) Complex with High Antineoplastic Efficacy for Treating Colon Cancer via Multiple Mechanisms

A series of (8-hydroxyquinoline) gallium(III) complexes (CP-1-4) was synthesized and characterized by single X-ray crystallography and density functional theory (DFT) calculation. The cytotoxicity of the four gallium complexes toward a human nonsmall cell lung cancer cell line (A549), human colon cancer cell line (HCT116), and human normal hepatocyte cell line (LO2) was evaluated using MTT assays. CP-4 exhibited excellent cytotoxicity against HCT116 cancer cells (IC₅₀ = 1.2 ± 0.3 μM) and lower toxicity than cisplatin and oxaliplatin. We also evaluated the anticancer mechanism studies in cell uptake, reactive oxygen species analysis, cell cycle, wound-healing, and Western blotting assays. The results showed that CP-4 affected the expression of DNA-related proteins, which led to the apoptosis of cancer cells. Moreover, molecular docking tests of CP-4 were performed to predict other binding sites and to confirm its higher binding force to disulfide isomerase (PDI) proteins. The emissive properties of CP-4 suggest that this complex can be used for colon cancer diagnosis and treatment, as well as in vivo imaging. These results also provide a foundation for the development of gallium complexes as potent anticancer agents.

The strong in vitro and vivo cytotoxicity of three new cobalt(II) complexes with 8-methoxyquinoline

Three new cobalt(II) complexes, [Co(MQL)₂Cl₂] (CoCl), [Co(MQL)₂Br₂] (CoBr), and [Co(MQL)₂I₂] (CoI), bearing 8-methoxyquinoline (MQL) have been designed for the first time. MTT assays showed that CoCl, CoBr, and CoI exhibit much better antiproliferative activities than cisplatin toward cisplatin-resistant SK-OV-3/DDP and SK-OV-3 ovarian cancer cells, with IC₅₀ values of as low as 0.32-5.49 μM. Further, CoCl and CoI can regulate autophagy-related proteins in SK-OV-3/DDP cells and, therefore, they can induce primarily autophagy-mediated cell apoptosis in the following order: CoCl > CoI. The different antiproliferative activities of the MQL complexes CoCl, CoBr, and CoI could be correlated with the lengths of their Co-X bonds, which adopted the following order: CoI > CoBr > CoCl. The 8-HOMQ complexes CoCl (ca. 60.1%) and CoI (ca. 48.8%) also showed potent in vivo anticancer effects after 15 days of treatment. In summary, the MQL ligand highly enhances the antiproliferative activities of cobalt(II) complexes in comparison to other previously reported 8-hydroxyquinoline metal complexes.