Investigation of DNA/BSA binding of three Ru(II) complexes by various spectroscopic methods, molecular docking and their antimicrobial activity

Ruthenium Complexes in the Fight against Pathogenic Microorganisms. An Extensive Review

The widespread use of antibiotics has resulted in the emergence of drug-resistant populations of microorganisms. Clearly, one can see the need to develop new, more effective, antimicrobial agents that go beyond the explored 'chemical space'. In this regard, their unique modes of action (e.g., reactive oxygen species (ROS) generation, redox activation, ligand exchange, depletion of substrates involved in vital cellular processes) render metal complexes as promising drug candidates. Several Ru (II/III) complexes have been included in, or are currently undergoing, clinical trials as anticancer agents. Based on the in-depth knowledge of their chemical properties and biological behavior, the interest in developing new ruthenium compounds as antibiotic, antifungal, antiparasitic, or antiviral drugs has risen. This review will discuss the advantages and disadvantages of Ru (II/III) frameworks as antimicrobial agents. Some aspects regarding the relationship between their chemical structure and mechanism of action, cellular localization, and/or metabolism of the ruthenium complexes in bacterial and eukaryotic cells are discussed as well. Regarding the antiviral activity, in light of current events related to the Covid-19 pandemic, the Ru (II/III) compounds used against SARS-CoV-2 (e.g., BOLD-100) are also reviewed herein.

DNA groove-binding and acid-base properties of a Ru(II) complex containing anthryl moieties

DNA groove binders have been poorly studied as compared to the intercalators. A novel Ru(II) complex of [Ru(aeip)₂(Haip)](PF₆)₂ {Haip = 2-(9-anthryl)-1H-imidazo[4,5-f][1,10]phenanthroline and aeip = 2-(anthracen-9-yl)-1-ethyl-imidazo[4,5-f][1, 10]phenanthroline} is synthesized and characterized by elemental analysis, ¹H NMR spectroscopy and mass spectrometry. The complex is evidenced to be a calf-thymus DNA groove binder with a large intrinsic binding constant of 10⁶ M^-1 order of magnitude as supported by UV-visible absorption spectral titrations, salt effects, DNA competitive binding with ethidium bromide, DNA melting experiment, DNA viscosity measurements and density functional theory calculations. The acid-base properties of the complex studied by UV-Vis spectrophotometric titrations are reported as well.

Molecular docking, QSAR properties and DNA/BSA binding, anti-proliferative studies of 6-methoxy benzothiozole imine base and its metal complexes

The molecular and QSAR (Quantitative Structure-Activity Relationship) properties of title compound 2-((6-Methoxybenzo[d]thiazol-2-ylimino)methyl)-6-ethoxyphenol (HL) were evaluated employing HyperChem 7.5 tools. The interaction of the 1a-1e complexes of HL with calf thymus DNA (CT-DNA) was investigated by absorption titrations, Fluorescence quenching and viscosity measurements. The experimental data suggest that these complexes bind to CT-DNA through an intercalative mode, wherein DNA-binding affinity of 1e is found to be greater compared to other complexes. The tryptophan emission-quenching with bovine serum albumin (BSA) experiment revealed stronger binding of 1e than other complexes in the hydrophobic region of protein. The photocleavage of plasmid pBR322 DNA investigated in the presence of the title complexes inferred conversion of supercoiled form of DNA plasmid to circular nicked form. Free-radical scavenging activity studies of HL and its metal complexes determined by their interaction with the stable free-radical DPPH have shown promising antioxidant property. Further cytotoxicity studies with HeLa and MCF-7 cell lines indicated that the compounds can efficiently inhibit the cell proliferation in a dose dependent manner. The DAPI staining assay studies revealed the higher potency of 1e to induce apoptosis. AbbreviationsBSABovine serum albumin proteinCT-DNACalf thymus DNADMSODimethyl sulfoxideDAPI4',-6-Diamidino-2-phenylindole dihydrochlorideESI-MSElectrospray ionization mass spectrometryIC₅₀Half-maximal inhibitory concentrationMBTYE2-((6-methoxybenzo[d]thiazol-2-ylimino) methyl)-6-ethoxyphenolMTT3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromidePBSPhosphate-buffered salineTrisTris(hydroxymethyl)aminomethaneCommunicated by Ramaswamy H. Sarma.

Design, synthesis, in vitro anticancer, antioxidant and antibacterial activity; DNA/BSA binding, photoleavage and docking studies of Cu(II) ternary metal complexes

Three mononuclear, mixed ligand ternary Cu(II) complexes of 3-((Z)-1-(2-hydroxyphenylimino)ethyl)-4-hydroxy-6-methyl-2H-pyran-2-one (HEHMP) viz; [Cu-(Phen) (HEHMP)] (1a), [Cu-(Bpy)(HEHMP)] (1 b) and [Cu-Bpy(NCS)(HEHMP)] (1c) were synthesized and characterized by data obtained from various spectral techniques. The binding affinities of these complexes with calf thymus DNA (CT-DNA) and bovine serum albumin (BSA) protein were explored by absorption and fluorescence quenching titrations. The results indicated strong affinity of the title compounds to bind with both CT-DNA and BSA. The antioxidant properties of the synthesized compounds evaluated by free-radical scavenging method using spectrophotometric technique indicated their affirmative potential activity. Gel electrophoresis experiments revealed the efficacy of metal complexes in resulting the cleavage of pBR322 supercoiled DNA. In vitro cytotoxicity studies of these complexes evaluated by 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT) assay against HeLa and MCF-7 cancer cell lines indicated relatively high effectiveness of the complex 1c. Confocal microscopy signified the potential of the complexes to induce apoptosis in HeLa cell lines. In addition, the antibacterial activity of the compounds carried out by disc diffusion method revealed significantly enhanced antibacterial activity in Cu (II) ternary complexes compared to the activity of ligands in unbound form signifying the implicit role of metal ion in inducing lipophilic character.

DNA binding, photocleavage, antimicrobial and cytotoxic properties of Ru(II) polypyridyl complexes containing BOPIP ligand, (BOPIP = {2-(4-(benzyloxy) phenyl)-1H-imidazo [4,5-f] [1,2]phenanthroline})

A novel ligand BOPIP (BOPIP = {2-(4-(benzyloxy)phenyl)-1H-imidazo[4,5-f][1,10]phenanthroline}) and its mononuclear Ru(II) polypyridyl complexes [Ru(phen)₂ BOPIP]²⁺(1) (phen = 1,10-Phenanthrolene), [Ru(bpy)₂ BOPIP]²⁺(2) (bpy = 2,2' bipyridyl), [Ru(dmb)₂ BOPIP]²⁺(3) (dmb = 4, 4' -dimethyl 2, 2' -bipyridine), [Ru(Hdpa)₂ BOPIP]²⁺(4) (Hdpa = 2,2'dipyridylamine) have been synthesized successfully and characterized by elemental analysis, UV-vis, IR, ¹H, ¹³ C-NMR, and ESI-MS Spectroscopy. The interaction of these complexes with CT-DNA was studied using absorption, emission techniques, viscosity measurements and molecular docking studies. The docking study also supports the binding ability of complexes obtained through the absorption and emission techniques. These studies reveal that the Four Ru(II) polypyridyl complexes bind to DNA predominantly by intercalation. The Antimicrobial activity and cytotoxicity of these complexes are also reported.

Study of the interaction of Co(III) polypyridyl complexes with DNA: an experimental and computational approach

Three new cobalt(III) polypyridyl complexes, [Co(L - L)₂IIP]³⁺ where IIP = 2-(2H-isoindol-1-yl)-2H-imidazo[4,5-f][1, 10]phenanthroline, L = 1) phen (1,10-phenanthroline), 2) bpy (2,2'bipyridyl), 3) dmb (4, 4-dimethyl 2, 2'-bipyridine) have been synthesized, characterized (UV -VIS, IR, ¹HNMR and ¹³C NMR spectroscopy) and screened for their in vitro antibacterial activity against E.coli, Staphylococcus aureus and Bacillus subtilis. The binding of these complexes with calf-thymus DNA (CT-DNA) has been investigated by absorption and fluorescence spectroscopy, viscosity measurements. The experimental studies indicate that complexes bind to CT-DNA by means of intercalation, but with different binding affinities due to differences in the planarity of the ancillary ligand. The complexes promote photocleavage of plasmid DNA from super coiled form I to the open circular form II. The antibacterial activities suggest that the metal complexes are more active as compared to the prepared un-complexed IIP ligand. In addition, a conformational search was carried out by Molecular Dynamics Simulations, and docking revealed that complexes intercalate between base pairs of DNA. The experimental and computational approaches reveal that the length of the intercalator and the nature of ancillary ligand are highly important factors for DNA binding.

Anticancer and antibacterial activity in vitro evaluation of iridium(III) polypyridyl complexes

Three iridium(III) polypyridyl complexes [Ir(ppy)₂(PYTA)](PF₆) (1) (ppy = 2-phenylpyridine), [Ir(bzq)₂(PYTA)](PF₆) (2) (bzq = benzo[h]quinolone) and [Ir(piq)₂(PYTA)](PF₆) (3) (piq = 1-phenylisoquinoline, PYTA = 2,4-diamino-6-(2'-pyridyl)-1,3,5-triazine) were synthesized and characterized by elemental analysis, IR, ¹H NMR and ¹³C NMR. The cytotoxic activity of the complexes toward cancer SGC-7901, Eca-109, A549, HeLa, HepG2, BEL-7402 and normal LO2 cell lines was investigated by 3-(4,5-Dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT) method. Complex 3 shows the most effective on inhibiting the above cell growth among these complexes. The complexes locate at the lysosomes and mitochondria. AO/EB, Annex V and PI and comet assays indicate that the complexes can induce apoptosis in SGC-7901 cells. Intracellular ROS and mitochondrial membrane potential were examined under fluorescence microscopy. The results demonstrate that the complexes increase the intracellular ROS levels and induce a decrease in the mitochondrial membrane potential. The complexes can enhance intracellular Ca²⁺ concentration and cause a release of cytochrome c. The autophagy was studied using MDC staining and western blot. Complexes 1-3 can effectively inhibit the cell invasion with a concentration-dependent manner. Additionally, the complexes target tubules and inhibit the polymerization of tubules. The antimicrobial activity of the complexes against S. aureus, E. coli, Salmonella and L. monocytogenes was explored. The mechanism shows that the complexes induce apoptosis in SGC-7901 cells through ROS-mediated lysosomal-mitochondrial, targeting tubules and damage DNA pathways. Three iridium(III) complexes [Ir(N-C)₂(PYTA)](PF₆) (N-C = ppy, 1; bzq, 2; piq, 3) were synthesized and characterized. The anticancer activity of the complexes against SGC-7901 cells was studied by apoptosis, comet assay, autophagy, ROS, mitochondrial membrane potential, intracellular Ca²⁺ levels, release of cytochrome c, tubules and western blot analysis. The antibacterial activity in vitro was also assayed.