Fluorescent metal-based complexes as cancer probes

Pt(II) Bis(pyrrole-imine) complexes: Luminescent probes and cytotoxicity in MCF-7 cells†

Four Pt(II) bis(pyrrole-imine) Schiff base chelates (1-4) were synthesised by previously reported methods, through a condensation reaction, and the novel crystal structure of 2,2'-{propane-1,3-diylbis[nitrilo(E)methylylidene]}bis(pyrrol-1-ido)platinum(II) (1) was obtained. Pt(II) complexes 1-4 exhibited phosphorescence, with increased luminescence in anaerobic solvents or when bound to human serum albumin (HSA). One of the complexes shows a 15.6-fold increase in quantum yield when bound to HSA and could be used to detect HSA concentrations as low as 5 nM. Pt(II) complexes 1-3 was investigated as potential theranostic agents in MCF-7 breast cancer cells, but only complex 3 exhibited cytotoxicity when irradiated with UV light (λ355nmExcitation). Interestingly, the cytotoxicity of complex 1 was unresponsive to UV light irradiation. This indicates that only complex 3 can be considered a potential photosensitising agent.

Novel half Salphen cobalt(III) complexes: synthesis, DNA binding and anticancer studies

While platinum(II)-based drugs continue to be employed in cancer treatments, the escalating occurrence of severe side effects has spurred researchers to explore novel sources for potential therapeutic agents. Notably, cobalt(III) has emerged as a subject of considerable interest due to its ubiquitous role in human physiology. Several studies investigating the anticancer effects of Salphen complexes derived from cobalt(III) have unveiled intriguing antiproliferative properties. In a bid to enhance our understanding of this class of compounds, we synthesized and characterized two novel half Salphen cobalt(III) complexes. Both compounds exhibited notable stability, even in the presence of physiologically relevant concentrations of glutathione. The application of spectroscopic and computational methodologies unravelled their interactions with duplex and G4-DNAs, suggesting an external binding affinity for these structures, with preliminary indications of selectivity trends. Importantly, antiproliferative assays conducted on 3D cultured SW-1353 cancer cells unveiled a compelling anticancer activity at low micromolar concentrations, underscoring the potential therapeutic efficacy of this novel class of cobalt(III) complexes.

DNA-Targeted Complexes of Tc and Re for Biomedical Applications

Due to their favorable chemical features, Re and Tc complexes have been widely used for the development of new therapeutic agents and imaging probes to solve problems of biomedical relevance. This review provides an update of the most relevant research efforts towards the development of novel cancer theranostic agents using Re and Tc-based compounds interacting with specific DNA structures. This includes a variety of homometallic complexes, namely those containing M(CO)3 (M=Re, Tc) moieties, that exhibit different modes of interaction with DNA, such as covalent binding, intercalation, groove binding or G-quadruplex DNA binding. Additionally, heterometallic complexes, designed to potentiate synergistic effects of different metal centers to improve DNA-targeting, cytotoxicity and fluorescence properties, are also reviewed. Particular attention is also given to 99m Tc- and 188 Re-labeled oligonucleotides that have been widely explored to develop imaging and therapeutic radiopharmaceuticals through the in vivo hybridization with a specific complementary DNA or RNA target sequence to provide useful molecular tools in precision medicine for cancer diagnosis and treatment. Finally, the need for further improvement of DNA-targeted Re and Tc-based compounds as potential therapeutic and diagnostic agents is highlighted, and future directions are discussed.

Sun Light Responsive 2D Covalent-Organic Frameworks Platform as a Catalysts Boost C-H Bond Arylation and Dopamine Regeneration

Photocatalysis is one of the most promising methods for producing organic compounds with a renewable source of energy. Two-dimensional covalent organic frameworks (2D COFs) are a type of polymer that has developed as a potential light-harvesting catalyst for artificial photosynthesis with a design-controllable platform that might be developed into a new type of cost-effective and metal-free photocatalyst. Here, we present a two-dimensional covalent organic framework synthesis technique as a low-cost and highly efficient visible light active flexible photocatalyst for C-H bond activation and dopamine regeneration. 2D COF were synthesized from tetramino-benzoquinone (TABQ) and terapthaloyl chloride monomer through condensation polymerization reaction and the resultant photocatalyst have remarkable performance due to its visible light-harvesting capacity, appropriate band gap, and highly organized π-electron channels. The synthesized photocatalyst is capable to convert dopamine into leucodopaminechrome with a higher yield (77.08%) and also capable to activate the C-H bond between 4-nitrobenzenediazonium tetrafluoroborate and pyrrole.

A Dipeptide-derived Dansyl Fluorescent Probe for the Detection of Cu2+ in Aqueous Solutions

A novel dansyl-based fluorescent probe (DG) was designed via the introduction of a dipeptide, glycyl-L-glutamine. DG showed good selectivity and sensitivity towards Cu2+ in aqueous solutions in the pH span of ~ 6-12. The coordination of Cu2+ with the dipeptide moiety led to the fluorescent quenching of the dansyl fluorophore. The association constant value for Cu2+ was 0.78 × 104 M- 1 in a 1 to 1 stoichiometric ratio. The detection limit in HEPES buffer solution (10 mM, pH 7.4) was 1.52 µM. DG also showed strong anti-interference capability in the presence of other metal ions. It was worth noting that DG maintained the detection ability towards Cu2+ in real water samples and cell imaging, implying the potential application opportunities in complicated environments.

N-Heterocyclic Carbene-Iridium Complexes as Photosensitizers for In Vitro Photodynamic Therapy to Trigger Non-Apoptotic Cell Death in Cancer Cells

A series of seven novel iridium complexes were synthetized and characterized as potential photosensitizers for photodynamic therapy (PDT) applications. Among them, four complexes were evaluated in vitro for their anti-proliferative activity with and without irradiation on a panel of five cancer cell lines, namely PC-3 (prostate cancer), T24 (bladder cancer), MCF7 (breast cancer), A549 (lung cancer) and HeLa (cervix cancer), and two non-cancerous cell models (NIH-3T3 fibroblasts and MC3T3 osteoblasts). After irradiation at 458 nm, all tested complexes showed a strong selectivity against cancer cells, with a selectivity index (SI) ranging from 8 to 34 compared with non-cancerous cells. The cytotoxic effect of all these complexes was found to be independent of the anti-apoptotic protein Bcl-xL. The compound exhibiting the best selectivity, complex 4a, was selected for further investigations. Complex 4a was mainly localized in the mitochondria. We found that the loss of cell viability and the decrease in ATP and GSH content induced by complex 4a were independent of both Bcl-xL and caspase activation, leading to a non-apoptotic cell death. By counteracting the intrinsic or acquired resistance to apoptosis associated with cancer, complex 4a could be an interesting therapeutic alternative to be studied in preclinical models.

Polyoxometalate-based materials in extraction, and electrochemical and optical detection methods: A review

Polyoxometalates (POMs) as metal-oxide anions have exceptional properties like high negative charges, remarkable redox abilities, unique ligand properties and availability of organic grafting. Moreover, the amenability of POMs to modification with different materials makes them suitable as precursors to further obtain new composites. Due to their unique attributes, POMs and their composites have been utilized as adsorbents, electrodes and catalysts in extraction, and electrochemical and optical detection methods, respectively. A survey of the recent progress and developments of POM-based materials in these methods is therefore desirable, and should be of great interest. In this review article, POM-based materials, their properties as well as their identification methods, and analytical applications as adsorbents, electrodes and catalysts, and corresponding mechanisms of action, where relevant, are reviewed. Some current issues of the utilization of these materials and their future prospects in analytical chemistry are discussed.

Chalcogenides-incorporating carbonic anhydrase inhibitors concomitantly reverted oxaliplatin-induced neuropathy and enhanced antiproliferative action

Platinum-based chemotherapy is widely used for the treatment of different tumors but is associated with serious side effects, among which neuropathic pain. Carbonic anhydrase (CA, EC 4.2.1.1) inhibitors have recently been validated as therapeutic agents in neuropathic pain and as antitumor agents. We report the synthesis of new organochalcogenides bearing the benzensulfonamide moiety acting as potent inhibitors of several human CA isoforms and, in particular, against hCA II and VII endowed with potent neuropathic pain attenuating effects. Moreover, in combination with cisplatin or doxorubicin, some of the new CA inhibitors enhanced the effects of the anticancer drugs capability in counteracting breast cancer MCF7 cell viability. The concomitant anti-neuropathic pain and antiproliferative effects of the new chalcogenide-based CA inhibitors represent an innovative approach for the counteraction and management of side effects associated with clinically platinum drugs as antitumor agents.

Metal-Based G-Quadruplex Binders for Cancer Theranostics

The ability of fluorescent small molecules, such as metal complexes, to selectively recognize G-quadruplex (G4) structures has opened a route to develop new probes for the visualization of these DNA structures in cells. The main goal of this review is to update the most recent research efforts towards the development of novel cancer theranostic agents using this type of metal-based probes that specifically recognize G4 structures. This encompassed a comprehensive overview of the most significant progress in the field, namely based on complexes with Cu, Pt, and Ru that are among the most studied metals to obtain this class of molecules. It is also discussed the potential interest of obtaining G4-binders with medical radiometals (e.g., 99mTc, 111In, 64Cu, 195mPt) suitable for diagnostic and/or therapeutic applications within nuclear medicine modalities, in order to enable their theranostic potential.

Metal complexes as optical probes for DNA sensing and imaging

Transition and lanthanide metal complexes have rich photophysical properties that can be used for cellular imaging, biosensing and phototherapy. One of the applications of such luminescent compounds is the detection and visualisation of nucleic acids. In this brief review, we survey the recent literature on the use of luminescent metal complexes (including Re^I, Ru^II, Os^II, Ir^III, Pt^II, Eu^III and Tb^III) as DNA optical probes, including examples of compounds that bind selectively to non-duplex DNA topologies such as quadruplex, i-motif and DNA mismatches. We discuss the applications of metal-based luminescent complexes in cellular imaging, including time-resolved microscopy and super-resolution techniques. Their applications in biosensing and phototherapy are briefly mentioned in the relevant sections.

A multiple acetal chalcone-BODIPY-based fluorescence: synthesis, physical property, and biological studies

Fluorescent probes with outstanding physical and biological properties are superior for functional fluorescent dyes design. However, few studies pay attention to the stability of specific groups in fluorescent probes. The aldehyde group in the fluorescent probe is highly active but unstable under certain conditions. Therefore, we introduced ethoxy groups to realize the conversion to aldehyde groups under acidic conditions and avoid the instability of straightforward aldehyde groups. In this work, two fluorophores based on the multi acetal difluoroboraindacene (BODIPY) units with combination of the pharmaceutical intermediate chalcone have been firstly developed. In the design part, chalcone was introduced as a medium for fluorophore and multiple acetal. The mild synthesis strategy is based on the ligand ((Z)-2-chloro-1-(difluoroboranyl)-5-((4-ethyl-3,5-dimethyl-2H-pyrrol-2-ylidene)(phenyl)methyl)-1H-pyrrole) and connects with chalcone in (2E,2'E)-3,3'-(1,3-phenylene)bis(1-(2,4-bis(2,2-diethoxyethoxy)phenyl)prop-2-en-1-one). The emission wavelengths of the products are around 530 nm with high fluorescence intensity. To highlight the biological characteristics of these novel BODIPY fluorescents, we further demonstrated biological analysis studies on MTT and flow cytometry assays. The IC₅₀ values of BODIPY 5 ranged from 79 ± 6.11 to 63 ± 5.67 μM and BODIPY 6 were found to be 86 ± 4.07 to 58 ± 10.51 μM in tested cell lines. Flow cytometry data analysis shows that the representative agent 6 and reference have similar rational apoptosis rates in first quadrant. Last but not least, 6 shows outstanding biological compatibility and cell imaging potential in live cell imaging and in vivo assay, not only is the fluorescence prominent enough, but also rapidly distributes. Thus, our study reports a mild synthesis strategy and full biological analysis on BODIPY fluorescents, and the subtle modulation of the physical and biological properties by pharmaceutical substituents makes these designed chalcone-BODIPY-based dyes hopeful to realize drug functional fluorescent dyes. Two new highly sensitive BODIPY fluorophores are synthesized based on the ligand ((Z)-2-chloro-1-(difluoroboranyl)-5-((4-ethyl-3,5-dimethyl-2H-pyrrol-2-ylidene)(phenyl)methyl)-1H-pyrrole), which connects with chalcone in (2E,2'E)-3,3'-(1,3/4-phenylene)bis(1-(2,4-bis(2,2-diethoxyethoxy)phenyl)prop-2-en-1-one). Multiple acetals were introduced and the physical and biological properties of BODIPYs are described with MTT assay and in vitro and in vivo imaging.

Synthesis and preliminary evaluation of a PET-FI bimodal imaging agent targeting estrogen receptor

Estrogen receptor is an attractive target for the diagnosis and treatment of breast cancer. This article reports for the first time a dual-modality imaging agent targeting estrogen receptor that can use PET imaging to diagnose breast cancer and utilize fluorescence imaging to achieve intraoperative navigation. Fluorescence experiments show that [^natGa] 1 has typical aggregate induced emission characteristics. Above the critical concentration, [^natGa] 1 can form biocompatible nanomicelles. [^natGa] 1 can quickly light up estrogen receptor positive MCF-7 cells. Cell uptake experiments show that [⁶⁸Ga] 1 is mediated by estrogen receptor. Therefore, [^nat/68Ga] 1 shows the characteristics of highly sensitive diagnosis and visualization of breast cancer, and can be used as a lead compound for the development of a novel PET-FI bimodal imaging agent targeting the estrogen receptor.

Solid-State Structural Transformation and Photoluminescence Properties of Supramolecular Coordination Compounds

The combination of strong coordination bonds and hydrogen bonding interactions were used to generate a series of supramolecular coordination materials (SCMs), which was achieved by reacting a bis-pyridyl amide ligand, namely N-(4-pyridyl)nicotinamide (4PNA) with copper(II), zinc(II), and cadmium(II) benzoates. The SCMs were structurally characterized using X-ray diffraction and the key intermolecular interactions were identified via Hirshfeld surface analysis. The role of solvent molecules on the supramolecular architecture was analyzed by synthesizing the SCMs in different solvents/solvent mixtures. A solvent-mediated solid-state structural transformation was observed in copper(II) SCMs and we were able to isolate the intermediate form of the crystal-to-crystal transformation process. The luminescence experiments revealed that complexation enhanced the fluorescence properties of 4PNA in the zinc(II) and cadmium(II) SCMs, but a reverse phenomenon was observed in the copper(II) SCMs. This work demonstrated the tuning of supramolecular assembly in coordination compounds as a function of solvents for generating SCMs with diverse properties.

Hyperbranched Polymers Modified with Dansyl Units and Their Cu(II) Complexes. Bioactivity Studies

Two new copper complexes of hyperbranched polymers modified with dansyl units were synthesized and characterized by infrared spectroscopy (IR) and electron paramagnetic resonance (EPR) techniques. It was found that copper ions coordinate predominantly with nitrogen or oxygen atoms of the polymer molecule. The place of the formation of complexes and the number of copper ions involved depend on the chemical structure of the polymer. The antimicrobial activity of the new polymers and their Cu(II) complexes was tested against Gram-negative and Gram-positive bacterial and fungal strains. Copper complexes were found to have activity better than that of the corresponding ligands. The deposition of the modified branched polymers onto cotton fabrics prevents the formation of bacterial biofilms, which indicates that the studied polymers can find application in antibacterial textiles.

ISAC Probe Tag Dictionary: Standardized Nomenclature for Detection and Visualization Labels Used in Cytometry and Microscopy Imaging

Since the advent of microscopy imaging and flow cytometry, there has been an explosion in the number of probes, consisting of a component binding to an analyte and a detectable tag, to mark areas of interest in or on cells and tissue. Probe tags have been created to detect and/or visualize probes. Over time, these probe tags have increased in number. The expansion has resulted in arbitrarily created synonyms of probe tags used in publications and software. The synonyms are problematic for readability of publications, accuracy of text/data mining, and bridging data from multiple platforms, protocols, and databases for Big Data analysis. Development and implementation of a universal language for probe tags will ensure equivalent quality and level of data being reported or extracted for clinical/scientific evaluation as well as help connect data from many platforms. The International Society for Advancement of Cytometry Data Standards Task Force composed of academic scientists and industry hardware/software/reagent manufactures have developed recommendations for a standardized nomenclature for probe tags used in cytometry and microscopy imaging. These recommendations are shared in this technical note in the form of a Probe Tag Dictionary. © 2020 International Society for Advancement of Cytometry.