Lighting up metallohelices: from DNA binders to chemotherapy and photodynamic therapy

Trinuclear rhenium(I)-based metallocages as anticancer agents towards human cervical cancer cells

The first examples of spherical-shaped trinuclear rhenium(I) organometallic cages displaying cytotoxic, antimetastatic, antiproliferative and DNA-damaging behavior towards a human cervical (HeLa) cancer cell line are reported. The compact design of the metallocages facilitates their interactions with biosystems leading to comparable efficiency to that of the commonly used anticancer drug cisplatin.

Self-Assembly of Rhenium(I) Double-Stranded Helicate and Mesocate from Flexible Ditopic Benzimidazolyl/Naphthanoimidazolyl N-Donor and Rigid Bis-Chelating Hydroxyphenylbenzimidazolyl N∩OH-Donor Ligands: Synthesis, Characterization, and Photophysical and B-DNA Docking Studies

The self-assembly of three rheniumtricarbonyl core-based supramolecular coordination complexes (SCCs), fac-[Re(CO)3(μ-L)(μ-L')Re(CO)3] (1-3) was carried out using Re2(CO)10, rigid bis-chelating ligand (HO∩N-Ph-N∩OH (L1) (where HO∩N = 2-hydroxyphenylbenzimidazolyl), and flexible ditopic N-donor ligands (L2 = bis(3-((1H-benzoimidazol-1-yl)methyl)-2,4,6-trimethylphenyl)methane, L3 = bis(3-((1H-naphtho[2,3-d]imidazol-1-yl)methyl)-2,4,6-trimethylphenyl)methane, L4 = bis(4-(naphtho[2,3-d]imidazol-1-yl-methyl)phenyl)methane) via a one-pot solvothermal approach. In the solid state, the dinuclear SCCs adopt heteroleptic double-stranded helicate and meso-helicate architectures. The supramolecular structures of the complexes are retained in the solution based on the 1H NMR and electrospray ionization (ESI)-mass analysis. The spectral and photophysical properties of the complexes were studied both experimentally and using time-dependent density functional theory (TDDFT) calculations. All of the supramolecules exhibited emission in both solution and solid states. Theoretical studies were conducted to determine the chemical reactivity parameters, molecular electrostatic potential surface plots, natural population, and Hirshfeld analysis for complexes 1-3. Additionally, molecular docking studies were carried out for complexes 1-3 with B-DNA.

Bioinorganic supramolecular coordination complexes and their biomedical applications

The field of Bioinorganic Supramolecular Chemistry is an emerging research area including metal-based supramolecules resulting from coordination-driven self-assembly (CDSA), whereby metal ions and organic ligands can be easily linked by metal-ligand bonds via Lewis' acid/base interactions. The focus of this 'In a Nutshell' review will be on the family of supramolecular coordination complexes, discrete entities formed by CDSA, which have recently captured widespread attention as a new class of versatile multifunctional materials with broad biological applications including molecular recognition, biosensing, therapy, imaging and drug delivery. Herein, we provide a summary of the state-of-the-art use of these systems in biomedicine, with some selected representative examples, as well as our visions of the challenges and possible directions in the field.

Hydrazone- and imine-containing [PdPtL4]4+ cages: a comparative study of the stability and host-guest chemistry

A new [PdPtL₄]⁴⁺ heterobimetallic cage containing hydrazone linkages has been synthesised using the sub-component self-assembly approach. ¹H and DOSY nuclear magnetic resonance (NMR) spectroscopy and electrospray ionisation mass spectrometry (ESIMS) data were consistent with the formation of the [PdPtL₄]⁴⁺ architecture. The cage was stimulus-responsive and could be partially disassembled and reassembled by the addition of dimethylaminopyridine (DMAP) and p-tolenesulfonic acid (TsOH), respectively. Additionally, the stability of the hydrazone cage against hydrolysis in the presence of water and nucleophilic decomposition in the presence of guest molecules was compared to a previously synthesised imine-containing [PdPtL₄]⁴⁺ cage. It was established that the hydrazone linkage was more resistant to hydrolysis. Furthermore, the host-guest (HG) chemistry with a series of drug and drug-like molecules was examined. The hydrazone cage was shown to interact with cisplatin while the smaller imine cage was shown to interact with 5-fluorouracil and oxaliplatin in CD₃CN. No HG interactions were observed in the more polar d₆-DMSO. In vitro antiproliferative activity studies demonstrated both cages were active against the cancer cell lines tested and displayed half-maximal inhibitory (IC₅₀) values in the range of 25-35 μM. Most [PdPtL₄]⁴⁺-drug mixtures tested had higher IC₅₀ values than the hosts. However, the [PdPtL₄]⁴⁺ cages, and [PdPtL₄]⁴⁺:drug mixtures were less cytotoxic than the well established anticancer drugs cisplatin, oxaliplatin and 5-fluorouracil.

Discovery of the Anticancer Activity for Lung and Gastric Cancer of a Brominated Coelenteramine Analog

Cancer is still a challenging disease to treat, both in terms of harmful side effects and therapeutic efficiency of the available treatments. Herein, to develop new therapeutic molecules, we have investigated the anticancer activity of halogenated derivatives of different components of the bioluminescent system of marine Coelenterazine: Coelenterazine (Clz) itself, Coelenteramide (Clmd), and Coelenteramine (Clm). We have found that Clz derivatives possess variable anticancer activity toward gastric and lung cancer. Interestingly, we also found that both brominated Clmd (Br-Clmd) and Clm (Br-Clm) were the most potent anticancer compounds toward these cell lines, with this being the first report of the anticancer potential of these types of molecules. Interestingly, Br-Clm possessed some safety profile towards noncancer cells. Further evaluation revealed that the latter compound induced cell death via apoptosis, with evidence for crosstalk between intrinsic and extrinsic pathways. Finally, a thorough exploration of the chemical space of the studied Br-Clm helped identify the structural features responsible for its observed anticancer activity. In conclusion, a new type of compounds with anticancer activity toward gastric and lung cancer was reported and characterized, which showed interesting properties to be considered as a starting point for future optimizations towards obtaining suitable chemotherapeutic agents.

DNA Interaction, DNA Photocleavage, Photocytotoxicity In Vitro, and Molecular Docking of Naphthyl-Appended Ruthenium Complexes

With the development of metal-based drugs, Ru(II) compounds present potential applications of PDT (photodynamic therapy) and anticancer reagents. We herein synthesized two naphthyl-appended ruthenium complexes by the combination of the ligand with naphthyl and bipyridyl. The DNA affinities, photocleavage abilities, and photocytotoxicity were studied by various spectral methods, viscosity measurement, theoretical computation method, gel electrophoresis, and MTT method. Two complexes exhibited strong interaction with calf thymus DNA by intercalation. Production of singlet oxygen (¹O₂) led to obvious DNA photocleavage activities of two complexes under 365 nm light. Furthermore, two complexes displayed obvious photocytotoxicity and low dark cytotoxicity towards Hela, A549, and A375 cells.

Target-Oriented Synthesis of Marine Coelenterazine Derivatives with Anticancer Activity by Applying the Heavy-Atom Effect

Photodynamic therapy (PDT) is an anticancer therapeutic modality with remarkable advantages over more conventional approaches. However, PDT is greatly limited by its dependence on external light sources. Given this, PDT would benefit from new systems capable of a light-free and intracellular photodynamic effect. Herein, we evaluated the heavy-atom effect as a strategy to provide anticancer activity to derivatives of coelenterazine, a chemiluminescent single-molecule widespread in marine organisms. Our results indicate that the use of the heavy-atom effect allows these molecules to generate readily available triplet states in a chemiluminescent reaction triggered by a cancer marker. Cytotoxicity assays in different cancer cell lines showed a heavy-atom-dependent anticancer activity, which increased in the substituent order of hydroxyl < chlorine < bromine. Furthermore, it was found that the magnitude of this anticancer activity is also dependent on the tumor type, being more relevant toward breast and prostate cancer. The compounds also showed moderate activity toward neuroblastoma, while showing limited activity toward colon cancer. In conclusion, the present results indicate that the application of the heavy-atom effect to marine coelenterazine could be a promising approach for the future development of new and optimized self-activating and tumor-selective sensitizers for light-free PDT.

A new class of anionic metallohelicates based on salicylic and terephthalic acid units, accessible in solution and by mechanochemistry

We present a new class of anionic metallohelicates based on an abundant, industrially relevant salicylic acid derivative, leading to discrete double and triple-stranded architectures based on divalent and trivalent metals (Cu²⁺, Fe³⁺, respectively). The ability to assemble the metallohelicates in a solvent-free environment presents the opportunity to develop an inexpensive and environmentally-friendly design of helicate materials.

Dynamic Stereoselection of Peptide Helicates and Their Selective Labeling of DNA Replication Foci in Cells*

Although largely overlooked in peptide engineering, coordination chemistry offers a new set of interactions that opens unexplored design opportunities for developing complex molecular structures. In this context, we report new artificial peptide ligands that fold into chiral helicates in the presence of labile metal ions such as Fe^II and Co^II . Heterochiral β-turn-promoting sequences encode the stereoselective folding of the peptide ligands and define the physicochemical properties of their corresponding metal complexes. Circular dichroism and NMR spectroscopy in combination with computational methods allowed us to identify and determine the structure of two isochiral ΛΛ-helicates, folded as topological isomers. Finally, in addition to the in-vitro characterization of their selective binding to DNA three-way junctions, cell-microscopy experiments demonstrated that a rhodamine-labeled Fe^II helicate was internalized and selectively stains DNA replication factories in functional cells.