Efficient and Rapid Mechanochemical Assembly of Platinum(II) Squares for Guanine Quadruplex Targeting

Solid-State Self-Assembly: Exclusive Formation and Dynamic Interconversion of Discrete Cyclic Assemblies Based on Molecular Tweezers

In contrast to self-assembly in solution systems, the construction of well-defined assemblies in the solid state has long been identified as a challenging task. Herein, we report the formation of tweezers-shaped molecules into various assemblies through a solid-state self-assembly strategy. The relatively flexible molecular tweezers undergo exclusive and quantitative assembly into either cyclic hexamers or a porous network through classical recrystallization or the exposure of powders to solvent vapor, despite the fact that they form only dimers in solution. The cyclic hexamers have high thermal stability and exhibit moderate solid-state fluorescence. The formation of heterologous assemblies consisting of different tweezers allows for tuning these solid-state properties of the cyclic hexamer. Furthermore, (trimethylsilyl)ethynyl-substituted tweezers demonstrate solvent-vapor-induced dynamic interconversion between the cyclic hexamer and a pseudocyclic dimer in the solid state. This assembly behavior, which has been studied extensively in solution-based supramolecular chemistry, had not been accomplished in the solid state so far.

A G-quadruplex-binding platinum complex induces cancer mitochondrial dysfunction through dual-targeting mitochondrial and nuclear G4 enriched genome

BACKGROUND

G-quadruplex DNA (G4) is a non-canonical structure forming in guanine-rich regions, which play a vital role in cancer biology and are now being acknowledged in both nuclear and mitochondrial (mt) genome. However, the impact of G4-based targeted therapy on both nuclear and mt genome, affecting mt function and its underlying mechanisms remain largely unexplored.

METHODS

The mechanisms of action and therapeutic effects of a G4-binding platinum(II) complex, Pt-ttpy, on mitochondria were conducted through a comprehensive approaches with in vitro and in vivo models, including ICP-MS for platinum measurement, PCR-based genetic analysis, western blotting (WB), confocal microscope for mt morphology study, extracellular flux analyzer, JC1 and Annexin V apoptosis assay, flow cytometry and high content microscope screening with single-cell quantification of both ROS and mt specific ROS, as well as click-chemistry for IF study of mt translation. Decipher Pt-ttpy effects on nuclear-encoded mt related genes expression were undertaken via RNA-seq, Chip-seq and CUT-RUN assays.

RESULTS

Pt-ttpy, shows a highest accumulation in the mitochondria of A2780 cancer cells as compared with two other platinum(II) complexes with no/weak G4-binding properties, Pt-tpy and cisplatin. Pt-ttpy induces mtDNA deletion, copy reduction and transcription inhibition, hindering mt protein translation. Functional analysis reveals potent mt dysfunction without reactive oxygen species (ROS) induction. Mechanistic study provided first evidence that most of mt ribosome genes are highly enriched in G4 structures in their promoter regions, notably, Pt-ttpy impairs most nuclear-encoded mt ribosome genes' transcription through dampening the recruiting of transcription initiation and elongation factors of NELFB and TAF1 to their promoter with G4-enriched sequences. In vivo studies show Pt-ttpy's efficient anti-tumor effects, disrupting mt genome function with fewer side effects than cisplatin.

CONCLUSION

This study underscores Pt-ttpy as a G4-binding platinum(II) complex, effectively targeting cancer mitochondria through dual action on mt and nuclear G4-enriched genomes without inducing ROS, offering promise for safer and effective platinum-based G4-targeted cancer therapy.

Intermediates in Mechanochemical Reactions

Mechanochemical reactions offer methodological and environmental advantages for chemical synthesis, constantly attracting attention within the scientific community. Besides unmistakable sustainability advantages, the conditions under which mechanochemical reactions occur, namely solventless conditions, sometimes facilitate the isolation of otherwise labile or inaccessible products. Despite these advantages, limited knowledge exists regarding the mechanisms of these reactions and the types of intermediates involved. Nevertheless, in an expanding number of cases, ex situ and in situ monitoring techniques have allowed for the observation, characterization, and isolation of reaction intermediates in mechanochemical transformations. In this Minireview, we present a series of examples in which reactive intermediates have been detected in mechanochemical reactions spanning organic, organometallic, inorganic, and materials chemistry. Many of these intermediates were stabilized by non-covalent interactions, which played a pivotal role in guiding the chemical transformations. We believe that by uncovering and understanding such instances, the growing mechanochemistry community could find novel opportunities in catalysis and discover new mechanochemical reactions while achieving simplification in chemical reaction design.

Dual-Emissive Rectangular Supramolecular Pt(II)-p-Biphenyl with 4,4'-Bipyridine Derivative Metallacycles: Stepwise Synthesis and Photophysical Properties

Mixed-ligand tetranuclear supramolecular coordination complexes (SCCs) of Pt(II)-p-biphenyl and bridging ligands derivatives of 4,4'-bypiridine (8)-(10), were synthesized and characterized. The SCCs were synthesized stepwise, starting from the Pt-p-biphenyl -Pt core. The crystal structure of complex {[Pt(2,2'-bpy)]4(μ-bph)2(μ-(4,4'-bpy)2}{PF6}4 (2,2'-bpy = 2,2'-bipyridine, bph = p-biphenyl and 4,4'-bpy = 4,4' bipyridine), was determined using single-crystal diffraction methods. The emission profile of the tetranuclear complexes (8)-(10) was influenced by the length of the bridging ligands and was found to depend on solvent polarity. Dual-emission patterns in methanol-water mixtures were observed only in the cases of complexes (9) and (10), attributed to aggregation-induced emission phenomena.

Induction-heated ball-milling: a promising asset for mechanochemical reactions

While ball-milling is becoming one of the common tools used by synthetic chemists, an increasing number of studies highlight that it is possible to further expand the nature and number of products which can be synthesized, by heating the reaction media during mechanochemical reactions. Hence, developing set-ups enabling heating and milling to be combined is an important target, which has been looked into in both academic and industrial laboratories. Here, we report a new approach for heating up reaction media during ball-milling reactions, using induction heating (referred to as i-BM). Our set-up is attractive not only because it enables a very fast heating of the milling medium (reaching ≈80 °C in just 15 s), and that it is directly adaptable to commercially-available milling equipment, but also because it enables heating either the walls of the milling jars or the beads themselves, depending on the choice of the materials which compose them. Importantly, the possibility to heat a milling medium "from the inside" (when using for example a PMMA jar and stainless steel beads) is a unique feature compared to previously proposed systems. Through numerical simulations, we then show that it is possible to finely tune the properties of this heating system (e.g. heating rate and maximum temperature reached), by playing with the characteristics of the milling system and/or the induction heating conditions used. Lastly, examples of applications of i-BM are given, showing how it can be used to help elucidate reaction mechanisms in ball-milling, to synthesize new molecules, and to control the physical nature of milling media.

Organometallic Pillarplexes That Bind DNA 4-Way Holliday Junctions and Forks

Holliday 4-way junctions are key to important biological DNA processes (insertion, recombination, and repair) and are dynamic structures that adopt either open or closed conformations, the open conformation being the biologically active form. Tetracationic metallo-supramolecular pillarplexes display aryl faces about a cylindrical core, an ideal structure to interact with open DNA junction cavities. Combining experimental studies and MD simulations, we show that an Au pillarplex can bind DNA 4-way (Holliday) junctions in their open form, a binding mode not accessed by synthetic agents before. Pillarplexes can bind 3-way junctions too, but their large size leads them to open up and expand that junction, disrupting the base pairing, which manifests in an increased hydrodynamic size and lower junction thermal stability. At high loading, they rearrange both 4-way and 3-way junctions into Y-shaped forks to increase the available junction-like binding sites. Isostructural Ag pillarplexes show similar DNA junction binding behavior but lower solution stability. This pillarplex binding contrasts with (but complements) that of metallo-supramolecular cylinders, which prefer 3-way junctions and can rearrange 4-way junctions into 3-way junction structures. The pillarplexes' ability to bind open 4-way junctions creates exciting possibilities to modulate and switch such structures in biology, as well as in synthetic nucleic acid nanostructures. In human cells, the pillarplexes do reach the nucleus, with antiproliferative activity at levels similar to those of cisplatin. The findings provide a new roadmap for targeting higher-order junction structures using a metallo-supramolecular approach, as well as expanding the toolbox available to design bioactive junction binders into organometallic chemistry.

FeII 4L4 tetrahedron binds and aggregates DNA G-quadruplexes

Since the discovery of the G-quadruplex (G4) structure in telomeres in 1980s, studies have established the role it plays in various biological processes. Here we report binding between DNA G4 and a self-assembled tetrahedral metal-organic cage 1 and consequent formation of aggregates, whereby the cage protects the DNA G4 from cleavage by S1 nuclease. We monitor DNA–cage interaction using fluorescence spectroscopy, firstly by quenching of a fluorescent label appended to the 5′ end of G4. Secondly, we detect the decrease in fluorescence of the G4-selective dyes thioflavin-T and Zn-PPIX bound to various DNA G4 sequences following the addition of cage 1. Our results demonstrate that 1 interacts with a wide range of G4s. Moreover, gel electrophoresis, circular dichroism and dynamic light scattering measurements establish the binding of 1 to G4 and indicate the formation of aggregate structures. Finally, we find that DNA G4 contained in an aggregate of cage 1 is protected from cleavage by S1 nuclease.

We find Fe^II₄L₄ binds to G-quadruplex and forms aggregates. G-quadruplex in the aggregates is protected from digestion by S₁ nuclease.

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.

Applications of isothermal titration calorimetry in pure and applied research from 2016 to 2020

The last 5 years have seen a series of advances in the application of isothermal titration microcalorimetry (ITC) and interpretation of ITC data. ITC has played an invaluable role in understanding multiprotein complex formation including proteolysis-targeting chimeras (PROTACS), and mitochondrial autophagy receptor Nix interaction with LC3 and GABARAP. It has also helped elucidate complex allosteric communication in protein complexes like trp RNA-binding attenuation protein (TRAP) complex. Advances in kinetics analysis have enabled the calculation of kinetic rate constants from pre-existing ITC data sets. Diverse strategies have also been developed to study enzyme kinetics and enzyme-inhibitor interactions. ITC has also been applied to study small molecule solvent and solute interactions involved in extraction, separation, and purification applications including liquid-liquid separation and extractive distillation. Diverse applications of ITC have been developed from the analysis of protein instability at different temperatures, determination of enzyme kinetics in suspensions of living cells to the adsorption of uremic toxins from aqueous streams.

Mechanochemical methods for the transfer of electrons and exchange of ions: inorganic reactivity from nanoparticles to organometallics

For inorganic metathesis and reduction reactivity, mechanochemistry is demonstrating great promise towards both nanoparticles and organometallics syntheses.

Recent developments in the construction and applications of platinum-based metallacycles and metallacages via coordination

Coordination-driven suprastructures have attracted much interest due to their unique properties. Among these structures, platinum-based architectures have been broadly studied due to their facile preparation. The resultant two- or three-dimensional (2D or 3D) systems have many advantages over their precursors, such as improved emission tuning, sensitivity as sensors, and capture and release of guests, and they have been applied in biomedical diagnosis as well as in catalysis. Herein, we review the recent results related to platinum-based coordination-driven self-assembly (CDSA), and the text is organized to emphasizes both the synthesis of new metallacycles and metallacages and their various applications.

Catalytic Room-Temperature C-N Coupling of Amides and Isocyanates by Using Mechanochemistry

A mechanochemical route is developed for room-temperature and solvent-free derivatization of different types of amides into carbamoyl isatins (up to 96 % conversion or yield), benzamides (up to 81 % yield), and imides (up to 92 % yield). In solution, this copper-catalyzed coupling either does not take place or requires high temperatures at which it may also be competing with alternative thermal reactivity, highlighting the beneficial role of mechanochemistry for this reaction. Such behavior resembles the previously investigated coupling with sulfonamide substrates, suggesting that this type of C-N coupling is an example of a mechanochemically favored reaction, for which mechanochemistry appears to be a favored environment over solution.

A self-assembled Ru-Pt metallacage as a lysosome-targeting photosensitizer for 2-photon photodynamic therapy

Photodynamic therapy (PDT) is a treatment procedure that relies on cytotoxic reactive oxygen species (ROS) generated by the light activation of a photosensitizer. The photophysical and biological properties of photosensitizers are vital for the therapeutic outcome of PDT. In this work a 2D rhomboidal metallacycle and a 3D octahedral metallacage were designed and synthesized via the coordination-driven self-assembly of a Ru(II)-based photosensitizer and complementary Pt(II)-based building blocks. The metallacage showed deep-red luminescence, a large 2-photon absorption cross-section, and highly efficient ROS generation. The metallacage was encapsulated into an amphiphilic block copolymer to form nanoparticles to encourage cell uptake and localization. Upon internalization into cells, the nanoparticles selectively accumulate in the lysosomes, a favorable location for PDT. The nanoparticles are almost nontoxic in the dark, and can efficiently destroy tumor cells via the generation of ROS in the lysosomes under 2-photon near-infrared light irradiation. The superb PDT efficacy of the metallacage-containing nanoparticles was further validated by studies on 3D multicellular spheroids (MCS) and in vivo studies on A549 tumor-bearing mice.

Biomedically Relevant Self-Assembled Metallacycles and Metallacages

Diverse metal-organic complexes (MOCs), shaped as rectangles, triangles, hexagons, prisms, and cages, can be formed by coordination between metal ions (Pt, Pd, Ru, Rh, Ir, Zn, Co, and Cd) and organic ligands, with potential applications as alternatives to conventional biomedical materials for therapeutic, sensing, and imaging purposes. MOCs have been investigated as anticancer drugs in the treatment of malignant tumors in lung, cervical, breast, colon, liver, prostate, ovarian, brain, stomach, bone, skin, mouth, thyroid, and other cancers. MOCs with one, two, and three cavities have also been investigated as drug carriers and prepared for the loading and release of different drugs. In addition, MOCs can target proteins by the shape effect and recognize sugars and DNA by electrostatic interactions, as well as estradiol by host-guest interactions, etc. This Perspective mainly covers achievements in the biomedical application of MOCs. We aim to identify some key trends in the reported MOC structures in relation to their biomedical activity and potential applications.

FeII4L4 Tetrahedron Binds to Nonpaired DNA Bases

A water-soluble self-assembled supramolecular Fe^II₄L₄ tetrahedron binds to single stranded DNA, mismatched DNA base pairs, and three-way DNA junctions. Binding of the coordination cage quenches fluorescent labels on the DNA strand, which provides an optical means to detect the interaction and allows the position of the binding site to be gauged with respect to the fluorescent label. Utilizing the quenching and binding properties of the coordination cage, we developed a simple and rapid detection method based on fluorescence quenching to detect unpaired bases in double-stranded DNA.

Subcellular Duplex DNA and G-Quadruplex Interaction Profiling of a Hexagonal PtII Metallacycle

Metal-driven self-assembly afforded a multitude of fascinating supramolecular coordination complexes (SCCs) with applications as catalysts, host-guest, and stimuli-responsive systems. However, the interest in the biological applications of SCCs is only starting to emerge and thorough characterization of their behavior in biological milieus is still lacking. Herein, we report on the synthesis and detailed in-cell tracking of a Pt2 L2 metallacycle. We show that our hexagonal supramolecule accumulates in cancer cell nuclei, exerting a distinctive blue fluorescence staining of chromatin resistant to UV photobleaching selectively in nucleolar G4-rich regions. SCC co-localizes with epitopes of the quadruplex-specific antibody BG4 and replaces other well-known G4 stabilizers. Moreover, the photophysical changes accompanying the metallacycle binding to G4s in solution (fluorescence quenching, absorption enhancement) also take place intracellularly, allowing its subcellular interaction tracking.

Hydrogen-bonded 3D network of d10-metal halide coordination polymer containing N-(3-pyridinyl) nicotinamide: influence of ligand conformation, halide anions and solvent

The crystal structures of four new d¹⁰-metal halide coordination polymers are determined as one-dimensional (1D) zigzag chains which are in contact with each other by C/N–H⋯X (X = Cl, Br, I) hydrogen bonds.

Visualizing Kinetically Robust CoIII4L6 Assemblies in Vivo: SPECT Imaging of the Encapsulated [99mTc]TcO4- Anion

Noncovalent encapsulation is an attractive approach for modifying the efficacy and physiochemical properties of both therapeutic and diagnostic species. Abiotic self-assembled constructs have shown promise, yet many hurdles between in vitro and (pre)clinical studies remain, not least the challenges associated with maintaining the macromolecular, hollow structure under nonequilibrium conditions. Using a kinetically robust Co^III₄L₆ tetrahedron we now show the feasibility of encapsulating the most widely used precursor in clinical nuclear diagnostic imaging, the γ-emitting [^99mTc]TcO₄^- anion, under conditions compatible with in vivo administration. Subsequent single-photon emission computed tomography imaging of the caged-anion reveals a marked change in the biodistribution compared to the thyroid-accumulating free oxo-anion, thus moving clinical applications of (metallo)supramolecular species a step closer.

Selective parallel G-quadruplex recognition by a NIR-to-NIR two-photon squaraine

Fluorescence imaging probes for specific G-quadruplex (G4) conformations are of considerable interest in biomedical research. Herein, we present the synthesis and the binding properties of a new water-soluble near-infrared (NIR) amphiphilic squaraine dye (CAS-C1) which is capable of selective detection of parallel over non-parallel and non G4 topologies. The striking changes in its linear optical response upon binding to parallel G4s give rise to high fluorescence quantum yields (Φ f ≈ 0.7) and one-photon molecular brightness in the far-red-NIR region. The outstanding recognition process of CAS-C1 for parallel G4s via end-stacking provides binding constants in the nanomolar regime (K b = 107 to 108 M-1) awarding it as one of the most potent parallel G4 binders currently available. Moreover, the CAS-C1-parallel G4 system exhibits large two-photon absorption (TPA) cross-sections and molecular brightness in the second NIR biological transparency window (λ ≈ 1275 nm), making it an ideal candidate for NIR-to-NIR ultrasensitive two-photon procedures.

Anticancer Activity and Cisplatin Binding Ability of Bis-Quinoline and Bis-Isoquinoline Derived [Pd2L4]4+ Metallosupramolecular Cages

New bis-quinoline (L q) and bis-isoquinoline-based (L iq) ligands have been synthesized, along with their respective homoleptic [Pd2(L q or L iq)4]4+ cages (C q and C iq). The ligands and cages were characterized by 1H, 13C and diffusion ordered (DOSY) NMR spectroscopies, high resolution electrospray ionization mass spectrometry (HR-ESIMS) and in the case of the bis-quinoline cage, X-ray crystallography. The crystal structure of the C q architecture showed that the [Pd2(L q)4]4+ cage formed a twisted meso isomer where the [Pd(quinoline)4]2+ units at either end of the cage architecture adopt the opposite twists (left and right handed). Conversely, Density Functional Theory (DFT) calculations on the C iq cage architecture indicated that a lantern shaped conformation, similar to what has been observed before for related [Pd2(L tripy)4]4+ systems (where L tripy = 2,6-bis(pyridin-3-ylethynyl)pyridine), was generated. The different cage conformations manifest different properties for the isomeric cages. The C iq cage is able to bind, weakly in acetonitrile, the anticancer drug cisplatin whereas the C q architecture shows no interaction with the guest under the same conditions. The kinetic robustness of the two cages in the presence of Cl- nucleophiles was also different. The C iq cage was completely decomposed into free L iq and [Pd(Cl)4]2- within 1 h. However, the C q cage was more long lived and was only fully decomposed after 7 h. The new ligands (L iq and L q) and the Pd(II) cage architectures (C iq and C q) were assessed for their cytotoxic properties against two cancerous cell lines (A549 lung cancer and MDA-MB-231 breast cancer) and one non-cancerous cell line (HDFa skin cells). It was found that L q and C q were both reasonably cytotoxic (IC50S ≈ 0.5 μM) against A549, while C iq was slightly less active (IC50 = 7.4 μM). L iq was not soluble enough to allow the IC50 to be determined against either of the two cancerous cell lines. However, none of the molecules showed any selectivity for the cancer cells, as they were all found to have similar cytotoxicities against HDFa skin cells (IC50 values ranged from 2.6 to 3.0 μM).

Multicomponent Mechanochemical Synthesis of Cyclopentadienyl Titanium tert-Butoxy Halides, Cp x TiX y (O t Bu)4-(x+y) (x, y = 1, 2; X = Cl, Br)

Titanium tert-butoxy halides of the formula Cp _x TiX _y (O ^t Bu)_4-(x+y) (x, y = 1, 2; X = Cl, Br) have been prepared thorough milling the reagents without solvent. In the case of the chloride derivatives, Cp₂TiCl₂ is used as a starting material; in the case of the bromides, a mixture of LiCp, TiBr₄, and Li[O ^t Bu] is used. The stoichiometric ratios of the starting materials are reflected in the major products of the reactions. Single-crystal X-ray structures are reported for Cp₂TiCl(O ^t Bu), Cp₂TiBr(O ^t Bu), and CpTiBr₂(O ^t Bu), as well as for Cp₂TiCl(O ⁱ Pr) and a redetermination of Cp₂TiCl(OMe). The tert-butoxy derivatives are notable for their nearly linear Ti-O-C angles (>170°) that reflect Ti-O π-bonding, an interpretation supported with density functional theory calculations.

Heterometallic Ru-Pt metallacycle for two-photon photodynamic therapy

As an effective and noninvasive treatment of various diseases, photodynamic therapy (PTD) relies on the combination of light, a photosensitizer, and oxygen to generate cytotoxic reactive oxygen species that can damage malignant tissue. Much attention has been paid to covalent modifications of the photosensitizers to improve their photophysical properties and to optimize the pathway of the photosensitizers interacting with cells within the target tissue. Herein we report the design and synthesis of a supramolecular heterometallic Ru-Pt metallacycle via coordination-driven self-assembly. While inheriting the excellent photostability and two-photon absorption characteristics of the Ru(II) polypyridyl precursor, the metallacycle also exhibits red-shifted luminescence to the near-infrared region, a larger two-photon absorption cross-section, and higher singlet oxygen generation efficiency, making it an excellent candidate as a photosensitizer for PTD. Cellular studies reveal that the metallacycle selectively accumulates in mitochondria and nuclei upon internalization. As a result, singlet oxygen generated by photoexcitation of the metallacycle can efficiently trigger cell death via the simultaneous damage to mitochondrial function and intranuclear DNA. In vivo studies on tumor-bearing mice show that the metallacycle can efficiently inhibit tumor growth under a low light dose with minimal side effects. The supramolecular approach presented in this work provides a paradigm for the development of PDT agents with high efficacy.

Phenanthroline polyazamacrocycles as G-quadruplex DNA binders

Several phenanthroline polyazamacrocycles are proposed as ligands for c-MYC and telomeric G-quadruplex structures.