DNA binding, prominent photonuclease activity and antibacterial PDT of cobalt(II) complexes of phenanthroline based photosensitizers

Red and NIR light-triggered enhancement of anticancer and antibacterial activities of dinuclear Co(II)-catecholate complexes

Photoactive complexes of bioessential 3d metals, activable within the phototherapeutic window (650-900 nm), have gained widespread interest due to their therapeutic potential. Herein, we report the synthesis, characterization, and light-enhanced anticancer and antibacterial properties of four new dinuclear Co(II) complexes: [Co(phen)(cat)]2 (Co-1), [Co(dppz)(cat)]2 (Co-2), [Co(phen)(esc)]2 (Co-3), and [Co(dppz)(esc)]2 (Co-4). In these complexes, phen (1,10-phenanthroline) and dppz (dipyrido[3,2-a:2',3'-c]phenazine) act as neutral N,N-donor ligands, while cat2- and esc2- serve as O,O-donor catecholate ligands derived from catechol (1,2-dihydroxybenzene) and esculetin (6,7-dihydroxy coumarin). Their high-spin paramagnetic nature and dimeric identity in solution were confirmed by magnetic susceptibility, UV-visible, emission, and mass spectral data. Co-1-Co-4 exhibited an absorption band within the 600-850 nm range, originating from a charge transfer transition. The electrically neutral complexes demonstrated sufficient solution stability both in the dark and under irradiated conditions. The dppz complexes Co-2 and Co-4 exhibited notable toxicity towards A549 lung carcinoma cells, with potency increasing significantly under brief (5 min) exposure to 660 nm (red) and 808 nm (NIR) laser light (IC50 ∼ 8.9 to 14.9 μM). Notably, their toxicity towards normal NIH-3T3 fibroblast cells was minimal. Cellular assays highlighted that the induced cell death followed an apoptotic pathway, primarily due to mitochondrial damage. Co-2 and Co-4 also demonstrated significant antibacterial potency against Gram-(+) S. aureus and Gram-(-) P. aeruginosa, with effectiveness significantly enhanced upon 808 nm laser irradiation (MIC ∼ 15-142 μM). The increase in the anticancer and antibacterial efficacies was attributed to the generation of cytotoxic singlet oxygen (1O2) species upon red/NIR light exposure. Notably, 808 nm NIR irradiation produced more pronounced effects compared to 660 nm. This study is the first to report on cobalt complexes exhibiting red and NIR light-triggered enhancement of antibacterial and anticancer activities, illuminating the path for the development of long-wavelength absorbing cobalt complexes with enhanced therapeutic efficacy.

Photodynamic Inactivation of Bacteria Using Nickel(II) Complexes with Catecholate and Phenanthroline Ligands

Metal complexes activated by light can combat infections by triggering the photodynamic inactivation of bacteria. Herein, we report six mixed-ligand nickel(II) complexes with the formulation [Ni(NN)2(L)] (1-6), where NN represents an N,N-donor phenanthroline ligand, specifically 1,10-phenanthroline (phen in 1, 2), dipyrido[3,2-d:2',3'-f]quinoxaline (dpq in 3, 4), and dipyrido[3,2-a:2',3'-c]phenazine (dppz in 5, 6), while L is an O,O donor bidentate ligand derived from catechol (cat2-, in 1, 3, 5) or esculetin (esc2-, in 2, 4, 6). The paramagnetic d8 octahedral complexes demonstrated good dark and photostability in the solution phase and exhibited significant light absorption in the visible (400-700 nm) region. When exposed to low-energy visible light, these complexes demonstrated significant photodynamic inactivation activity against both Gram-(+) Staphylococcus aureus (S. aureus) and Gram-(-) Escherichia coli (E. coli) bacteria. This resulted in minimum inhibitory concentration (MIC) values ranging from 0.31-9.49 μM. The activity was caused by the cell-damaging singlet oxygen species produced by the complexes under light exposure. Notably, the complexes showed no bacterial inhibition activity under dark conditions. This study marks the first examples of Ni(II) complexes designed for light-triggered antibacterial activity, illuminating the path for Ni(II)-based non-macrocyclic complexes for antibacterial PDT applications.

Substituted naphthoxy-phthalonitrile derivatives: Synthesis, substituent effects, DFT, TD-DFT Calculations, antimicrobial properties and DNA interaction studies

Herein, substituted-naphthol derivatives 4a-e were synthesized in two steps, namely the Diels Alder cycloaddition and Cu-catalyzed aromatization reactions, respectively. Then, pththalonitrile derivatives 7-12 have been prepared by a nucleophilic displacement reaction of 3-nitrophthalonitrile with the naphthol derivatives 4a-e, 5 and, obtained in excellent yields. Structural characterization of the compounds was identified by different spectroscopic techniques. Antimicrobial properties of the synthesized compounds were determined by the microdilution procedure against Gram-positive, Gram-negative bacteria, and yeast. Furthermore, the DNA interaction of the compounds were determined by gel electrophoresis. One of the most prominent findings is that compounds 9 and 10 have more inhibitory effects on Gram-positive bacteria than Gram-negative bacteria. These compounds especially exhibited the highest antibacterial potency against S. aureus (625 µg/mL) among Gram-positive bacteria. According to the plasmid DNA interaction results, the synthesized compounds caused changes in the structure and mobility of the plasmid DNA. Then, geometry optimizations and frequency calculations were conducted at B3LYP/6-311 G(d,p) level of DFT, and optimized structures were used for further analyses. The NBO results revealed that the π→π * and n→π * interactions were greatly contributed to lowering the stabilization energy of all compounds (7-12). FMO energy analyses showed that compound 9 has the biggest electrodonating power.

Identification of dual-targeted Mycobacterium tuberculosis aminoacyl-tRNA synthetase inhibitors using machine learning

Background: The most serious challenge in the treatment of tuberculosis is the multidrug resistance of Mycobacterium tuberculosis to existing antibiotics. As a strategy to overcome resistance we used a multitarget drug design approach. The purpose of the work was to discover dual-targeted inhibitors of mycobacterial LeuRS and MetRS with machine learning. Methods: The artificial neural networks were built using module nnet from R 3.6.1. The inhibitory activity of compounds toward LeuRS and MetRS was investigated in aminoacylation assays. Results: Using a machine-learning approach, we identified dual-targeted inhibitors of LeuRS and MetRS among 2-(quinolin-2-ylsulfanyl)-acetamide derivatives. The most active compound inhibits MetRS and LeuRS with IC₅₀ values of 33 μm and 23.9 μm, respectively. Conclusion: 2-(Quinolin-2-ylsulfanyl)-acetamide scaffold can be useful for further research.

Macrocyclic "tet a"-Derived Cobalt(III) Complex with a N,N'-Disubstituted Hexadentate Ligand: Crystal Structure, Photonuclease Activity, and as a Photosensitizer

A cobalt(III) complex, [Co(L)]Cl (complex 1, where L = 1,8-[N,N-bis{(3-formyl-2-hydroxy-5-methyl)benzyl}]-1,4,8,11-tetraaza-5,5,7,12,12,14-hexamethylcyclotetradecane) with distorted octahedral geometry has been synthesized and characterized using various spectroscopic techniques. The structure of the ligand has remarkably rich hydrogen intermolecular interactions such as H···H, H···C/C···H, and H···O/O···H that vary with the presence of the metal ion, and the structure of complex 1 has Cl···H interactions; this result has been proved by Hirshfeld surface and two-dimensional (2D) fingerprint maps analyses. The complex exhibits a quasi-reversible Co(III)/Co(II) redox couple with E _1/2 = -0.76 V. Calf thymus DNA (CT DNA) binding abilities of the ligand and complex 1 were confirmed by spectroscopic and electrochemical analyses. According to absorption studies, the ligand and complex 1 bind to CT DNA via intercalative binding mode, with intrinsic binding strengths of 1.41 × 10³ and 8.64 × 10³ M^-1, respectively. A gel electrophoresis assay shows that complex 1 promotes the pUC19 DNA cleavage under dark and light irradiation conditions. Complex 1 has superior antimicrobial activity than the ligand. The cytotoxicity of complex 1 was tested against MDA-MB-231 breast cancer cells with values of IC₅₀ of 1.369 μg mL^-1 in the dark and 0.9034 μg mL^-1 after light irradiation. Besides, cell morphological studies confirmed the morphological changes with AO/EB dual staining, reactive oxygen species (ROS) staining, mitochondria staining, and Hoechst staining on MDA-MB-231 cancer cells by fluorescence microscopy. Complex 1 was found to be a potent antiproliferative agent against MDA-MB-231 cells, and it can induce mitochondrial-mediated and caspase-dependent apoptosis with activation of downregulated caspases. The biotoxicity assay of complex 1 on the development of Artemia nauplii was evaluated at an IC₅₀ value of 200 μg mL^-1 and with excellent biocompatibility.

Antimicrobial Photodynamic Therapy: Latest Developments with a Focus on Combinatory Strategies

Antimicrobial photodynamic therapy (aPDT) has become a fundamental tool in modern therapeutics, notably due to the expanding versatility of photosensitizers (PSs) and the numerous possibilities to combine aPDT with other antimicrobial treatments to combat localized infections. After revisiting the basic principles of aPDT, this review first highlights the current state of the art of curative or preventive aPDT applications with relevant clinical trials. In addition, the most recent developments in photochemistry and photophysics as well as advanced carrier systems in the context of aPDT are provided, with a focus on the latest generations of efficient and versatile PSs and the progress towards hybrid-multicomponent systems. In particular, deeper insight into combinatory aPDT approaches is afforded, involving non-radiative or other light-based modalities. Selected aPDT perspectives are outlined, pointing out new strategies to target and treat microorganisms. Finally, the review works out the evolution of the conceptually simple PDT methodology towards a much more sophisticated, integrated, and innovative technology as an important element of potent antimicrobial strategies.

Discovery of metal-based complexes as promising antimicrobial agents

The antimicrobial resistance (AMR) is an intractable problem for the world. Metal ions are essential for the cell process and biological function in microorganisms. Many metal-based complexes with the potential for releasing ions are more likely to be absorbed for their higher lipid solubility. Hence, this review highlights the clinical potential of organometallic compounds for the treatment of infections caused by bacteria or fungi in recent five years. The common scaffolds, including antimicrobial peptides, N-heterocyclic carbenes, Schiff bases, photosensitive-grand-cycle skeleton structures, aliphatic amines-based ligands, and special metal-based complexes are summarized here. We also discuss their therapeutic targets and the risks that should be paid attention to in the future studies, aiming to provide information for researchers on metal-based complexes as antimicrobial agents and inspire the design and synthesis of new antimicrobial drugs.