Targeting Amyloids with Coated Nanoparticles: A Review on Potential Combinations of Nanoparticles and Bio-Compatible Coatings

Amyloidosis is the major cause of many neurodegenerative diseases, such as, Alzheimer's and Parkinson's where the misfolding and deposition of a previously functional protein make it inept for carrying out its function. The genesis of amyloid fibril formation and the strategies to inhibit it have been studied extensively, although some parts of this puzzle still remain unfathomable to date. Many classes of molecules have been explored as potential drugs in vitro, but their inability to work in vivo by crossing the blood-brain-barrier has made them an inadequate treatment option. In this regard, nanoparticles (NPs) have turned out to be an exciting alternative because they could overcome many drawbacks of previously studied molecules and provide advantages, such as, greater bioavailability of molecules and target-specific delivery of drugs. In this paper, we present an overview on several coated NPs which have shown promising efficiency in inhibiting fibril formation. A hundred and thirty papers published in the past two decades have been comprehensively reviewed, which majorly encompass NPs comprising different materials like gold, silver, iron-oxide, poly(lactic-co-glycolic acid), polymeric NP, etc., which are coated with various molecules of predominantly natural origin, such as different types of amino acids, peptides, curcumin, drugs, catechin, etc. We hope that this review will shed light on the advancement of symbiotic amalgamation of NPs with molecules from natural sources and will inspire further research on the tremendous therapeutic potential of these combinations for many amyloid-related diseases.

Hypochlorous Acid-Activated UCNPs-LMB/VQIVYK Multifunctional Nanosystem for Alzheimer's Disease Treatment

The development of nanosystems, which can photooxygenate amyloid-β (Aβ), detect the Tau protein, and inhibit effectively the Tau aggregation, is increasingly important in the diagnosis and therapy of Alzheimer's disease (AD). Herein, UCNPs-LMB/VQIVYK (UCNPs: upconversion nanoparticles, LMB: Leucomethylene blue, and VQIVYK: Biocompatible peptide) is designed as a HOCl-controlled released nanosystem for AD synergistic treatment. Under exposure to high levels of HOCl, the released MB from UCNPs-LMB/VQIVYK will produce singlet oxygen (¹O₂) under red light to depolymerize Aβ aggregation and reduce cytotoxicity. Meanwhile, UCNPs-LMB/VQIVYK can act as an inhibitor to decrease Tau-induced neurotoxicity. Besides, UCNPs-LMB/VQIVYK can be used for upconversion luminescence (UCL) due to its unexceptionable luminescence properties. This HOCl-responsive nanosystem offers a new therapy for AD treatment.

Synthetic approaches to metal-coordination-directed macrocyclic complexes

Metal-coordination-directed macrocyclic complexes, in which macrocyclic architectures are formed by metal-ligand coordination interactions, have emerged as attractive supramolecular scaffolds for the creation of materials for applications in biosensing and therapeutics. Despite recent progress, uncontrolled multicyclic cages and linear oligomers/polymers is the most likely outcome from metal-ligands assembly, representing a challenge to current synthetic methods. Herein we outlined the state-of-art synthetic approaches to the metal-coordination-directed macrocyclic complexes by using foldable ligands or through assembly of amphiphilic ligands. This mini-review offers a guideline for the efficient preparation of metal-coordination-directed macrocyclic complexes with predictable and controllable structures, which may find applications in many biology-related areas.

Manganese promotes α-synuclein amyloid aggregation through the induction of protein phase transition

α-Synuclein (α-Syn) is the major protein component of Lewy bodies, a key pathological feature of Parkinson’s disease (PD). The manganese ion Mn²⁺ has been identified as an environmental risk factor of PD. However, it remains unclear how Mn²⁺ regulates α-Syn aggregation. Here, we discovered that Mn²⁺accelerates α-Syn amyloid aggregation through the regulation of protein phase separation. We found that Mn²⁺ not only promotes α-Syn liquid-to-solid phase transition but also directly induces soluble α-Syn monomers to form solid-like condensates. Interestingly, the lipid membrane is integrated into condensates during Mn²⁺-induced α-Syn phase transition; however, the preformed Mn²⁺/α-syn condensates can only recruit lipids to the surface of condensates. In addition, this phase transition can largely facilitate α-Syn amyloid aggregation. Although the Mn²⁺-induced condensates do not fuse, our results demonstrated that they could recruit soluble α-Syn monomers into the existing condensates. Furthermore, we observed that a manganese chelator reverses Mn²⁺-induced α-Syn aggregation during the phase transition stage. However, after maturation, α-Syn aggregation becomes irreversible. These findings demonstrate that Mn²⁺ facilitates α-Syn phase transition to accelerate the formation of α-Syn aggregates and provide new insights for targeting α-Syn phase separation in PD treatment.

Artificial Chiral Interfaces against Amyloid-β Peptide Aggregation: Research Progress and Challenges

Alzheimer's disease (AD) is a progressive neurodegenerative disorder characterized by an imbalance between the production and clearance of amyloid-β (Aβ) species. AD not only influences the life quality of the patients but also heavily burdens the families and society. Therefore, it is an urgent mission to research and develop some new anti-amyloid aggregation drugs. In recent years, there were research and development of engineered nanostructures as Aβ amyloid inhibitors have attracted extensive attention and become a new frontier in nanomedicine. The effects of nanostructural surface properties (e.g., morphology, charge, hydrophobicity) on inhibition of Aβ aggregation are modulated by adsorbed Aβ peptides. Nevertheless, chirality has been seldom considered in recognition of Aβ species and modulation of Aβ aggregations. Moreover, a more relevant question for chiral inhibitors is little known about the molecular mechanism of how to interface chiral effects Aβ targeting recognition and effective mitigation of amyloidosis at the molecular level. Herein, we review recent experimental and theoretical results acquired in the specific areas of artificial chiral nanostructure inhibitors. This article will be essential to provide a microlevel insight into the effects of chiral nanointerfaces on amyloidosis processes as well as the development of chiral inhibitor drugs against Aβ fibrillation.

Breaker peptides against amyloid-β aggregation: a potential therapeutic strategy for Alzheimer's disease

Alzheimer's disease (AD) is a progressive neurodegenerative disorder, for which blocking the early steps of extracellular misfolded amyloid-β (Aβ) aggregation is a promising therapeutic approach. However, the pathological features of AD progression include the accumulation of intracellular tau protein, membrane-catalyzed cell death and the abnormal deposition of Aβ. Here, we focus on anti-amyloid breaker peptides derived from the Aβ sequence and non-Aβ-based peptides containing both natural and modified amino acids. Critical aspects of the breaker peptides include N-methylation, conformational restriction through cyclization, incorporation of unnatural amino acid, fluorinated molecules, polymeric nanoparticles and PEGylation. This review confers a general idea of such breaker peptides with in vitro and in vivo studies, which may advance our understanding of AD pathology and develop an effective treatment strategy against AD.

Novel strategies for the fight of Alzheimer's disease targeting amyloid-β protein

Alzheimer's disease (AD), which is recognised as a devastating neurodegenerative disease throughout the world and lack of effective treatments, is a growing concern in modern society with a growing population of elderly patients. A growing number of studies reveal that abnormal accumulation and deposition of Aβ is responsible for AD. Inspired by this, strategies for the treatment of AD targeting-Aβ clearance have been discussed for a long period, exploring new drugs which is capable of destroying soluble Aβ oligomers and unsolvable Aβ aggregates. In this paper, results of recent clinical trials on several anti-amyloid-β drugs are presented and several emerging anti-amyloid AD therapies based on recent studies are reviewed. Furthermore, some of the current challenges and novel strategies to prevent AD are addressed. Herein, this review focuses on current pharmacotherapy of AD targeting-Aβ and intends to design a promising therapeutic agent for AD treatment.

Cavity-Containing [Fe2L3]4+ Helicates: An Examination of Host-Guest Chemistry and Cytotoxicity

Two new di(2,2′-bipyridine) ligands, 2,6-bis([2,2′-bipyridin]-5-ylethynyl)pyridine (L1) and bis(4-([2,2′-bipyridin]-5-ylethynyl)phenyl)methane (L2) were synthesized and used to generate two metallosupramolecular [Fe₂(L)₃](BF₄)₄ cylinders. The ligands and cylinders were characterized using elemental analysis, electrospray ionization mass spectrometry, UV-vis, ¹H-, ¹³C and DOSY nuclear magnetic resonance (NMR) spectroscopies. The molecular structures of the [Fe₂(L)₃](BF₄)₄ cylinders were confirmed using X-ray crystallography. Both the [Fe₂(L1)₃](BF₄)₄ and [Fe₂(L2)₃](BF₄)₄ complexes crystallized as racemic (rac) mixtures of the ΔΔ (P) and ΛΛ (M) helicates. However, ¹H NMR spectra showed that in solution the larger [Fe₂(L2)₃](BF₄)₄ was a mixture of the rac-ΔΔ/ΛΛ and meso-ΔΛ isomers. The host-guest chemistry of the helicates, which both feature a central cavity, was examined with several small drug molecules. However, none of the potential guests were found to bind within the helicates. In vitro cytotoxicity assays demonstrated that both helicates were active against four cancer cell lines. The smaller [Fe₂(L1)₃](BF₄)₄ system displayed low μM activity against the HCT116 (IC₅₀ = 7.1 ± 0.5 μM) and NCI-H460 (IC₅₀ = 4.9 ± 0.4 μM) cancer cells. While the antiproliferative effects against all the cell lines examined were less than the well-known anticancer drug cisplatin, their modes of action would be expected to be very different.

Current Strategies for Modulating Aβ Aggregation with Multifunctional Agents

Alzheimer's disease (AD), as the primary cause of dementia, has seriously affected millions of people worldwide and brought a very heavy financial and social burden. With the growth of population and aging, the situation will worsen unless efficacious drugs are found to reverse, stop, or even slow down disease progression. More and more evidence has demonstrated that amyloid-β (Aβ) aggregation is an upstream causative factor in AD pathogenesis and then triggers a slew of pathological events. Furthermore, the concentrated redox metal ions in the AD brain, especially Cu(II), can significantly exacerbate Aβ aggregation and contribute to the formation of neurotoxic reactive oxygen species (ROS). Therefore, the inhibition of Aβ aggregation and relief of amyloidosis-initiated neurotoxicity play a critical role in AD treatment. Until now, several methods have been proposed to modulate Aβ aggregation, such as developing aggregation inhibitors to interfere with Aβ assembly via noncovalent interactions, copper chelators to cut off metal-accelerated Aβ aggregation and concomitant cytotoxicity, photooxidation to reduce the hydrophobicity and aggregation tendency of Aβ, thermal dissociation to disrupt amyloid aggregates susceptible to temperature, degradation with artificial protease to fracture the Aβ peptide into small fragments, and the clearance of peripheral Aβ to bypass the obstruction of the BBB and reduce the Aβ burden.In this Account, we focus on our contributions to the development of Aβ-targeted multifunctional molecules and nanoparticles, emphasizing the diversified strategies and synergistic therapeutic effects. These therapeutic agents possess the following multifunctionalities: (1) compared with frequently used aggregation inhibitors restricted by intrinsically feeble and sensitive noncovalent interactions, multifunctional agents can efficiently block Aβ aggregation by exploiting two or more Aβ-specific inhibition strategies simultaneously; (2) apart from regulating Aβ aggregation, multipronged agents can also target and modulate other pathological factors in AD pathogenesis, such as increased oxidative stress, abnormal copper accumulation, and irreversible neuron loss; (3) multifunctional platforms with both diagnostic and therapeutic modalities through integrating in situ imaging, real-time diagnostics, a multitarget direction, stimuli-responsive drug release, and the blood-brain barrier (BBB) translocation features are instrumental in improving drug levels at trouble sites, diminishing off-target adverse reactions, evaluating therapeutic effects, and averting overtreatment.Given the fact that amyloid aggregation, local inflammation, and metal dyshomeostasis are universal biomarkers shared by various neurodegenerative disorders, this Account provides a perspective for the evolution of customized therapeutic agents with multiple reactivities for other neurodegenerative diseases. In addition, recent studies have indicated that Aβ aggregates can enter the nucleus and induce DNA damage and anomalous conformational transition. We also explore the influences of DNA on the biological effects of Aβ aggregates.

Investigation on the effect of three isoflavones on the fibrillation of hen egg-white lysozyme

In this paper, the effects of three isoflavones including daidzein, genistein, and puerarin on fibrillation of hen egg-white lysozyme were investigated by various analytical methods. The results demonstrated that all isoflavones could effectively inhibit the fibrillogenesis of hen egg-white lysozyme and destabilized the preformed fibrils of hen egg-white lysozyme in a dose-dependent manner. To further understand the inhibition mechanism, molecular modeling was carried out. The docking results demonstrated that the isoflavones could bind to two key fibrogenic sites in hen egg-white lysozyme through van der Waals force, electrostatic forces, and hydrogen bonding, as well as σ-π stacking. By these means, isoflavones could not only obviously enhance the hydrophobicity of the binding sites, but also greatly stabilize the native state of HEWL, which was able to postpone the fibrosis process of hen egg-white lysozyme.

Metallohelices emulate the properties of short cationic α-helical peptides

Naturally occurring peptides in many living systems perform antimicrobial and anticancer host defence roles, but their potential for clinical application is limited by low metabolic stability and relatively high costs of goods. Self-assembled helical metal complexes provide an attractive synthetic platform for non-peptidic architectures that can emulate some of the properties of short cationic α-helical peptides, with tuneable charge, shape, size and amphipathicity. Correspondingly there is a growing body of evidence demonstrating that these supramolecular architectures exhibit bioactivity that emulates that of the natural systems. We review that evidence in the context of synthetic advances in the area, driven by the potential for biomedical applications. We note some design considerations for new biologically-relevant metallohelices, and give our outlook on the future of these compounds as therapeutic peptidomimetics.

Studies on the effect of a Fupenzi glycoprotein on the fibrillation of bovine serum albumin and its antioxidant activity

In this study, the effect of a glycoprotein obtained from Fupenzi (FPZ) (Rubus chingii Hu.) on the fibrillation of bovine serum album (BSA) was investigated by multi-spectroscopic methods and transmission electron microscopy. Moreover, the cytotoxicity of the glycoprotein and the effect of it on H₂O₂-induced cell viability were investigated by cell counting kit and β-galactosidase kit, respectively. The experimental results indicated that the glycoprotein showed very low toxicity to NRK-52E cells and could obviously delay cell senescence and improve cell viability. Moreover, the glycoprotein could effectively inhibit the formation of BSA fibrils and destroy the stability of preformed BSA fibrils in a concentration-dependent manner. Generally, antioxidant capacities are thought to be related to the anti-amyloidogenic activity of inhibitors; therefore, to reveal the inhibitory mechanism, the anti-oxidative property of the glycoprotein was examined by DPPH and ABTS assays. The results demonstrated that FPZ glycoprotein had a remarkable antioxidant activity and the IC₅₀ values of DPPH and ABTS were 0.249 mg mL^-1 and 0.092 mg mL^-1, respectively. This work suggested that the FPZ glycoprotein had the potential to be designed a new therapeutic agent for attenuating aging and preventing the age-related diseases.

Molecular crowding effects on the biochemical properties of amyloid β-heme, Aβ-Cu and Aβ-heme-Cu complexes

Heme as a cofactor has been proposed to bind with β-amyloid peptide (Aβ) and the formed Aβ-heme complex exhibits enhanced peroxidase-like activity. So far, in vitro studies on the interactions between heme, Cu and Aβ have been exclusively performed in dilute solution. However, the intracellular environment is highly crowded with biomolecules. Therefore, exploring how Aβ-heme-Cu complexes behave under molecular crowding conditions is critical for understanding the mechanism of Aβ neurotoxicity in vivo. Herein, we selected PEG-200 as a crowding agent to mimic the crowded cytoplasmic environment for addressing the contributions of crowded physiological environments to the biochemical properties of Aβ-heme, Aβ-Cu and Aβ-heme-Cu complexes. Surprisingly, experimental studies and theoretical calculations revealed that molecular crowding weakened the stabilization of the Aβ-heme complex and decreased its peroxidase activity. Our data attributed this consequence to the decreased binding affinity of heme to Aβ as a result of the alterations in water activity and Aβ conformation. Our findings highlight the significance of hydration effects on the interaction of Aβ-heme and Aβ-Cu and their peroxidase activities. Molecular crowding inside cells may potentially impose a positive effect on Aβ-Cu but a negative effect on the interaction of Aβ with heme. This indicates that Aβ40-Cu but not Aβ40-heme may play more important roles in the oxidative damage in the etiology of AD. Therefore, this work provides a new clue for understanding the oxidative damage occurring in AD.

A nano-cocktail of an NIR-II emissive fluorophore and organoplatinum(ii) metallacycle for efficient cancer imaging and therapy

A novel NIR-II theranostic nanoprobe, PSY (∼110 nm), was concisely developed, which demonstrated excellent photostability, high tumor uptake, superior S/N ratios and more efficient cancer treatment with minimal side effects than cisplatin.

The scarcity of efficient imaging technologies for precise cancer treatment greatly drives the development of new nanotheranostic based platforms that enable both diagnostic and therapeutic functions, together in a single formulation. Owing to the complicated physiological microenvironment, nanosystems designed with the possibility of noninvasive real-time monitoring of therapeutic progression in the second near-infrared channel (NIR-II, 1000–1700 nm) could substantially improve the current cancer therapies. Herein, we design a novel NIR-II theranostic nanoprobe, PSY (size ∼110 nm), by incorporating organoplatinum(ii) metallacycles P1 and an organic NIR-II molecular dye, SY1030, into the FDA-approved polymer Pluronic F127. Preliminary in vitro and in vivo studies suggest that PSY is capable of being internalized into glioma U87MG-cells with no significant internalization in non-cancerous tissues. In addition, it shows excellent photostability and minimal background for real-time monitoring the process of therapy in the NIR-II region. Furthermore, in U87MG xenografts and orthotopic breast tumor, PSY demonstrat significantly improved anticancer efficacy compared to a clinically approved Pt(ii)-based anticancer drug, cisplatin. The engineered nano-cocktail PSY offers a simple strategy for delivering the organoplatinum(ii) macrocycle P1 and NIR-II fluorophore SY1030 as a cocktail of diagnostic and therapeutic functions and highlights its promising capacity for future cancer treatment.

Chirality-Selected Chemical Modulation of Amyloid Aggregation

Due to the composed α-helical/β-strand structures, β-amyloid peptide (Aβ) is sensitive to chiral environments. The orientation and chirality of the Aβ strand strongly influence its aggregation. Aβ-formed fibrils have a cascade of chirality. Therefore, for selectively targeting amyloid aggregates, chirality preference can be one key issue. Inspired by the natural stereoselectivity and the β-sheet structure, herein, we synthesized a series of d- and l-amino acid-modified polyoxometalate (POM) derivatives, including positively charged amino acids (d-His and l-His) and negatively charged (d-Glu and l-Glu) and hydrophobic amino acids (d-Leu, l-Leu, d-Phe, and l-Phe), to modulate Aβ aggregation. Intriguingly, Phe-modified POMs showed a stronger inhibition effect than other amino acid-modified POMs, as evidenced by multiple biophysical and spectral assays, including fluorescence, circular dichroism, NMR, molecular dynamic simulations, and isothermal titration calorimetry. More importantly, d-Phe-modified POM had an 8-fold stronger inhibition effect than l-Phe-modified POM, indicating high enantioselectivity. Furthermore, in vivo studies demonstrated that the chiral POM derivatives crossed the blood-brain barrier, extended the life span of AD transgenic Caenorhabditis elegans CL2006 strain, and had low cytotoxicity, even at a high dosage.

Supercharging SpyCatcher toward an intrinsically disordered protein with stimuli-responsive chemical reactivity

We report a supercharged, intrinsically disordered protein, SpyCatcher(-), possessing stimuli-responsive reactivity toward SpyTag with tunable yields ranging from 4% to 98% depending on pH, temperature, ionic strength, etc. The CD and NMR studies reveal that the reaction occurs through a folded intermediate formed probably via a different mechanism from that of SpyCatcher.

Stereochemistry and amyloid inhibition: Asymmetric triplex metallohelices enantioselectively bind to Aβ peptide

Stereochemistry is vital for pharmaceutical development and can determine drug efficacy. Herein, 10 pairs of asymmetric triplex metallohelix enantiomers as a library were used to screen inhibitors of amyloid β (Aβ) aggregation via a fluorescent cell-based high-throughput method. Intriguingly, Λ enantiomers show a stronger inhibition effect than Δ enantiomers. In addition, the metallohelices with aromatic substituents are more effective than those without, revealing that these groups play a key role in the Aβ interaction. Fluorescence stopped-flow kinetic studies indicate that binding of the Λ enantiomer to Aβ is much faster than that of the Δ enantiomer. Furthermore, studies in enzyme digestion, isothermal titration calorimetry, nuclear magnetic resonance, and computational docking demonstrate that the enantiomers bind to the central hydrophobic α-helical region of Aβ13-23, although with different modes for the Λ and Δ enantiomers. Finally, an in vivo study showed that these metallohelices extend the life span of the Caenorhabditis elegans CL2006 strain by attenuating Aβ-induced toxicity. Our work will shed light on the design and screening of a metal complex as an amyloid inhibitor against Alzheimer's disease.

Chiral supramolecular coordination cages as high-performance inhibitors against amyloid-β aggregation

A family of chiral tetrahedral Ni₄⁸⁺ coordination cages with tunable size and multiple interaction sites can effectively inhibit Aβ aggregation.

Peptide-Based Polymer-Polyoxometalate Supramolecular Structure with a Differed Antimicrobial Mechanism

Because of the increasing prevalence of multidrug resistance feature, several investigations have been so far reported regarding the antibiotic alternative supramolecular bioactive agents made of hybrid assemblies. In this regard, it is well-established that combinational therapy inherited by assembled supramolecular structures can improve the bioactivity to some extent, but their mode of action has not been studied in detail. We provide first direct evidence that the improved mechanism of action of antimicrobial supra-amphiphilic nanocomposites differs largely from their parent antimicrobial peptide-based polymers. For the construction of a hybrid combinational system, we have synthesized side-chain peptide-based antimicrobial polymers via RAFT polymerization and exploited their cationic nature to decorate supra-amphiphilic nanocomposites via interaction with anionic polyoxometalates. Because of cooperative antimicrobial properties of both the polymer and polyoxometalate, the nanocomposites show an enhanced antimicrobial activity with a different antimicrobial mechanism. The cationic stimuli-responsive peptide-based polymers attack bacteria via membrane disruption mechanism, whereas free radical-mediated cell damage is the likely mechanism of polymer-polyoxometalate-based supra-amphiphilic nanocomposites. Thus, our study highlights the different antimicrobial mechanism of combinational systems in detail, which improves our understanding of enhanced antimicrobial efficacy.

Antifreeze Protein Mimetic Metallohelices with Potent Ice Recrystallization Inhibition Activity

Antifreeze proteins are produced by extremophile species to control ice formation and growth, and they have potential applications in many fields. There are few examples of synthetic materials which can reproduce their potent ice recrystallization inhibition property. We report that self-assembled enantiomerically pure, amphipathic metallohelicies inhibited ice growth at just 20 μM. Structure-property relationships and calculations support the hypothesis that amphipathicity is the key motif for activity. This opens up a new field of metallo-organic antifreeze protein mimetics and provides insight into the origins of ice-growth inhibition.

N-Methyl Mesoporphyrin IX as an Effective Probe for Monitoring Alzheimer's Disease β-Amyloid Aggregation in Living Cells

Formation of amyloid fibrils by amyloid-β peptide (Aβ) is an important step in Alzheimer's disease (AD) progression. Screening and designing of new molecules which can monitor the amyloidosis process especially in cells are diagnostically and therapeutically important. Utilizing Thioflavin T (ThT), the commonly used amyloid dye, is the most standardized way to monitor amyloid. However, with the green fluorescence emission and small Stokes shift, the fluorescence of ThT can overlap with that arising from other intrinsic fluorescent components in the cells, making it not suitable for detection of protein aggregates in vivo. Therefore, it is urgent for developing amyloid probes with large Stokes shifts and red-shifted fluorescence emission to detect Aβ aggregates in cells. In this report, we found that N-methyl mesoporphyrin IX (NMM), a widely used G-quadruplex DNA specific fluorescent binder, can be an efficient probe for monitoring Aβ fibrillation in living cells. NMM is nonfluorescent in aqueous solution or monomeric Aβ environments. However, through stacking with the Aβ assemblies, NMM emits strong fluorescence. Furthermore, the large Stokes shift and stable photoluminescence make it an ideal probe for detecting Aβ aggregates in highly fluorescent environments and cell culture. Our results provide a new sight to design and screen new reagents for monitoring the diseases associated with protein conformational disorders.

Unsymmetrical N-Aryl-1-(pyridin-2-yl)methanimine Ligands in Organonickel(II) Complexes: More Than a Blend of 2,2'-Bipyridine and N,N-Diaryl-α-diimines?

The new organonickel complexes [(R-PyMA)Ni(Mes)X] [R-PyMA = N-aryl-1-(pyridin-2-yl)methanimine; aryl = phenyl, 2,6-Me₂-, 3,5-Me₂-, 2,4,6-Me₃-, 2,6-ⁱPr₂-, 3,5-(OMe)₂-, 2-NO₂-4-Me-, 4-NO₂-, 2-CF₃-, and 2-CF₃-6-F-phenyl; Mes = 2,4,6-trimethylphenyl; X = F, Cl, Br, or I] were obtained as approximate 1/1 cis and trans isomeric mixtures or pure cis isomers depending on the PyMA ligand and X. The [(R-PyMA)Ni(Mes)X] complexes with X = Br or Cl were directly synthesized from the precursors trans-[(PPh₃)₂Ni(Mes)X], while [(PyMA)Ni(Mes)X] derivatives with X = F or I were obtained from [(PyMA)Ni(Mes)Br] through X exchange reactions. Although density functional theory (DFT) calculations show a preference for the sterically favored cis isomers, both isomers could be observed in many cases; in three cases, even single crystals for X-ray diffraction could be obtained for the trans isomers. Possible intermediates for the isomerization were investigated by DFT calculations. All complexes were studied by multiple spectroscopic means, electrochemistry, and spectroelectrochemistry (for the reduction processes). The long-wavelength metal-to-ligand charge-transfer (MLCT) absorptions vary markedly with the R substituent of the ligand and the cathodic electrochemical potentials to a far smaller degree. Both are almost invariable upon variation of X. All of this is in line with Ni-based and π*-based lowest unoccupied molecular orbitals (LUMOs). In line with the unsymmetric character of the N_Py^N_methanimine ligand, electrochemistry and MLCT transitions seem to not correspond to the same type of π* LUMO, making these PyMA ligands more interesting than the symmetric heteroaromatic polypyridine ligands such as 2,2'-bipyridine (bpy; N_Py^N_Py) and N,N-diaryl-substituted aliphatic α-diimines (N_methanimine^N_methanimine) such as the diaza-1,3-butadienes (DAB). First attempts to use these complexes in Negishi-type cross-coupling reactions were successful.

Co-assembly of polyoxometalates and peptides towards biological applications

The synergistic self-assembly of biomolecules with polyoxometalates (POMs) has recently been considered as an effective approach to construct nano-biomaterials with diverse structures and morphologies towards applications in drug delivery, controlled release, tissue engineering scaffolds, and biomineralization, due to the unique features of the clusters in addition to many well-known inorganic nanoparticles. This review presents an overview of recent work focusing on the noncovalent co-assembly of peptides and POMs as well as their biological applications. In the co-assemblies triggered by the interaction between the components significant advantages are observed that POMs or peptides alone do not possess; examples include chiral recognition of hybrid metal oxides, the quick hydrolysis of peptides, and enhanced inhibition of Aβ aggregation. Finally, we outline a brief perspective on possible unresolved issues and future opportunities in this field.

Ruthenium(II) polypyridyl complexes with hydrophobic ancillary ligand as Aβ aggregation inhibitors

The synthesis, spectral and electrochemical characterization of the complexes of the type [Ru(NN)2(txbg)](2+) where NN is 2,2'-bipyridine (bpy) (1), 1,10-phenanthroline (phen) (2), dipyrido [3,2-d:2',3f] quinoxaline (dpq) (3), and dipyrido[3,2-a:2',3'-c]phenazine (dppz) (4) which incorporate the tetra-xylene bipyridine glycoluril (txbg) as the ancillary ligand are described in detail. Crystal structures of ligand txbg and complex 2 were solved by single crystal X-ray diffraction. Thioflavin T (ThT) fluorescence and Transmission Electron Microscopy (TEM) results indicated that at micromolar concentration all complexes exhibit significant potential of Aβ aggregation inhibition, while the ligand txbg displayed weak activity towards Aβ aggregation. Complex 1 showed relatively low inhibition (70%) while complexes 2-4 inhibited nearly 100% Aβ aggregation after 240 h of incubation. The similar potential of complexes 2-4 and absence of any trend in their activity with the planarity of polypyridyl ligands suggests there is no marked effect of planarity of coligands on their inhibitory potential. Further studies on acetylcholinesterase (AChE) inhibition indicated very weak activity of these complexes against AChE. Detailed interactions of Aβ with both ligand and complex 2 have been studied by molecular modeling. Complex 2 showed interactions involving all three polypyridyl ligands with hydrophobic region of Aβ. Furthermore, the toxicity of these complexes towards human neuroblastoma cells was evaluated by MTT assay and except complex 4, the complexes displayed very low toxicity.

Opposing Effects of Cucurbit[7]uril and 1,2,3,4,6-Penta-O-galloyl-β-d-glucopyranose on Amyloid β25-35 Assembly

Alzheimer's disease (AD) is a neurodegenerative disease characterized by extracellular deposits of amyloid β protein (Aβ) in the brain. The conversion of soluble monomers to amyloid Aβ fibrils is a complicated process and involves several transient oligomeric species, which are widely believed to be highly toxic and play a crucial role in the etiology of AD. The development of inhibitors to prevent formation of small and midsized oligomers is a promising strategy for AD treatment. In this work, we employ ion mobility spectrometry (IMS), transmission electron microscopy (TEM), and molecular dynamics (MD) simulations to elucidate the structural modulation promoted by two potential inhibitors of Aβ oligomerization, cucurbit[7]uril (CB[7]) and 1,2,3,4,6-penta-O-galloyl-β-d-glucopyranose (PGG), on early oligomer and fibril formation of the Aβ25-35 fragment. One and two CB[7] molecules bind to Aβ25-35 monomers and dimers, respectively, and suppress aggregation by remodeling early oligomer structures and inhibiting the formation of higher-order oligomers. On the other hand, nonselective binding was observed between PGG and Aβ25-35. The interactions between PGG and Aβ25-35, surprisingly, enhanced the formation of Aβ aggregates by promoting extended Aβ25-35 conformations in both homo- and hetero-oligomers. When both ligands were present, the inhibitory effect of CB[7] overrode the stimulatory effect of PGG on Aβ25-35 aggregation, suppressing the formation of large amyloid oligomers and eliminating the structural conversion from isotropic to β-rich topologies induced by PGG. Our results provide mechanistic insights into CB[7] and PGG action on Aβ oligomerization. They also demonstrate the power of the IMS technique to investigate mechanisms of multiple small-molecule agents on the amyloid formation process.

The effects of a series of carbon dots on fibrillation and cytotoxicity of human islet amyloid polypeptide

Carbon dots can change hIAPP aggregation kinetics and have a potential to reduce the cytotoxicity of the polypeptide.

Anticancer metallohelices: nanomolar potency and high selectivity

New optically pure helicate-like architectures are extremely active against cancer cell lines, with IC₅₀ values as low as 40 nM, but nearly three orders of magnitude less active against healthy cells. There is also low toxicity to microbes and amoeba.

A range of new helicate-like architectures have been prepared via highly diastereoselective self-assembly using readily accessible starting materials. Six pairs of enantiomers [Fe₂L₃]Cl₄·nH₂O (L = various bidentate ditopic ligands NN–NN) show very good water solubility and stability. Their activity against a range of cancer cell lines in vitro is structure-dependent and gives IC₅₀ values as low as 40 nM. In an isogenic pair of HCT116 colorectal cancer cells, preferential activity was observed against cell lines that lack functional p53. Selectivity is also excellent, and against healthy human retinal pigment epithelial (ARPE19) and lung fibroblast (WI38) cells IC₅₀ values are nearly three orders of magnitude higher. Cisplatin is unselective in the same tests. The compounds also appear to have low general toxicity in a number of models: there is little if any antimicrobial activity against methicillin-resistant Staphylococcus aureus and Escherichia coli; Acanthamoeba polyphaga is unaffected at 25 μg mL^–1 (12.5 μM); Manduca sexta larvae showed clear evidence of systemic distribution of the drug, and rather than any observation of adverse effects they exhibited a significant mean weight gain vs. controls. Investigation of the mode of action revealed no significant interaction of the molecules with DNA, and stimulation of substantial cell death by apoptosis.

Chiral Metallo-Supramolecular Complex Directed Enantioselective Self-Assembly of β-Sheet Breaker Peptide for Amyloid Inhibition

Chiral recognition plays an important role for biomacromolecules involved self-assembly and further affects their biological functions. Herein, it is demonstrated that two chiral metal complexes can enantioselectively bind with Aβ15-20, leading to the formation of different self-assembled nanostructures. With the ability of both metal complexes and Aβ15-20 to inhibit Aβ1-40 aggregation, the NiM@P hybrid particles can act as bifunctional Aβ inhibitors.

Biologically active [Pd2L4](4+) quadruply-stranded helicates: stability and cytotoxicity

There is emerging interest in the anti-proliferative effects of metallosupramolecular systems due to the different size and shape of these metallo-architectures compared to traditional small molecule drugs. Palladium(II)-containing systems are the most abundant class of metallosupramolecular complexes, yet their biological activity has hardly been examined. Here a small series of [Pd2(L)4](BF4)4 quadruply-stranded, dipalladium(II) architectures were screened for their cytotoxic effects against three cancer cell lines and one non-malignant line. The helicates exhibited a range of cytotoxic properties, with the most cytotoxic complex [Pd2(hextrz)4](BF4)4 possessing low micromolar IC50 values against all of the cell lines tested, while the other helicates displayed moderate or no cytotoxicity. Against the MDA-MB-231 cell line, which is resistant to platinum-based drugs, [Pd2(hextrz)4](BF4)4 was 7-fold more active than cisplatin. Preliminary mechanistic studies indicate that the [Pd2(hextrz)4](BF4)4 helicate does not induce cell death in the same way as clinically used metal complexes such as cisplatin. Rather than interacting with DNA, the helicate appears to disrupt the cell membrane. These studies represent the first biological characterisation of quadruply-stranded helicate architectures, and provide insight into the design requirements for the development of biologically active and stable palladium(II)-containing metallosupramolecular architectures.

In vivo anticancer activity of rhomboidal Pt(II) metallacycles

The development of novel antitumor agents that have high efficacy in suppressing tumor growth, have low toxicity to nontumor tissues, and exhibit rapid localization in the targeted tumor sites is an ongoing avenue of research at the interface of chemistry, cancer biology, and pharmacology. Supramolecular metal-based coordination complexes (SCCs) have well-defined shapes and geometries, and upon their internalization, SCCs could affect multiple oncogenic signaling pathways in cells and tissues. We investigated the uptake, intracellular localization, and antitumor activity of two rhomboidal Pt(II)-based SCCs. Laser-scanning confocal microscopy in A549 and HeLa cells was used to determine the uptake and localization of the assemblies within cells and their effect on tumor growth was investigated in mouse s.c. tumor xenograft models. The SCCs are soluble in cell culture media within the entire range of studied concentrations (1 nM-5 µM), are nontoxic, and showed efficacy in reducing the rate of tumor growth in s.c. mouse tumor xenografts. These properties reveal the potential of Pt(II)-based SCCs for future biomedical applications as therapeutic agents.

Gold-nanoparticle-based multifunctional amyloid-β inhibitor against Alzheimer's disease

Targeting amyloid-β (Aβ)-induced complex neurotoxicity has received considerable attention in the therapeutic and preventive treatment of Alzheimer's disease (AD). The complex pathogenesis of AD suggests that it requires comprehensive treatment, and drugs with multiple functions against AD are more desirable. Herein, AuNPs@POMD-pep (AuNPs: gold nanoparticles, POMD: polyoxometalate with Wells-Dawson structure, pep: peptide) were designed as a novel multifunctional Aβ inhibitor. AuNPs@POMD-pep shows synergistic effects in inhibiting Aβ aggregation, dissociating Aβ fibrils and decreasing Aβ-mediated peroxidase activity and Aβ-induced cytotoxicity. By taking advantage of AuNPs as vehicles that can cross the blood-brain barrier (BBB), AuNPs@POMD-pep can cross the BBB and thus overcome the drawbacks of small-molecule anti-AD drugs. Thus, this work provides new insights into the design and synthesis of inorganic nanoparticles as multifunctional therapeutic agents for treatment of AD.

Recognition of nucleic acid junctions using triptycene-based molecules

The modulation of nucleic acids by small molecules is an essential process across the kingdoms of life. Targeting nucleic acids with small molecules represents a significant challenge at the forefront of chemical biology. Nucleic acid junctions are ubiquitous structural motifs in nature and in designed materials. Herein, we describe a new class of structure-specific nucleic acid junction stabilizers based on a triptycene scaffold. Triptycenes provide significant stabilization of DNA and RNA three-way junctions, providing a new scaffold for the development of nucleic acid junction binders with enhanced recognition properties. Additionally, we report cytotoxicity and cell uptake data in two human ovarian carcinoma cell lines.

Chiral metallohelical complexes enantioselectively target amyloid β for treating Alzheimer's disease

Stereochemistry is a very important issue for the pharmaceutical industry and can determine drug efficacy. The design and synthesis of small molecules, especially chiral molecules, which selectively target and inhibit amyloid-β (Aβ) aggregation, represent valid therapeutic strategies for treatment of Alzheimer's disease (AD). Herein we report that two triple-helical dinuclear metallosupramolecular complexes can act as a novel class of chiral amyloid-β inhibitors. Through targeting α/β-discordant stretches at the early steps of aggregation, these metal complexes can enantioselectively inhibit Aβ aggregation, which is demonstrated using fluorescent living cell-based screening and multiple biophysical and biochemical approaches. To the best of our knowledge, this is the first report of enantioselective inhibition of Aβ aggregation. Intriguingly, as a promising candidate for AD treatment, the chiral metal complex can cross the blood-brain barrier and have superoxide dismutase activity. It is well-known that chiral discrimination is important for understanding chiral drug action. Generally, one enantiomer is pharmaceutically active while the other is inactive or exerts severe side effects. Chiral discrimination should be important for AD treatment. Our work provides new insights into chiral inhibition of Aβ aggregation and opens a new avenue for design and screening of chiral agents as Aβ inhibitors against AD.

Asymmetric triplex metallohelices with high and selective activity against cancer cells

Small cationic amphiphilic α-helical peptides are emerging as agents for the treatment of cancer and infection, but they are costly and display unfavourable pharmacokinetics. Helical coordination complexes may offer a three-dimensional scaffold for the synthesis of mimetic architectures. However, the high symmetry and modest functionality of current systems offer little scope to tailor the structure to interact with specific biomolecular targets, or to create libraries for phenotypic screens. Here, we report the highly stereoselective asymmetric self-assembly of very stable, functionalized metallohelices. Their anti-parallel head-to-head-to-tail 'triplex' strand arrangement creates an amphipathic functional topology akin to that of the active sub-units of, for example, host-defence peptides and p53. The metallohelices display high, structure-dependent toxicity to the human colon carcinoma cell-line HCT116 p53(++), causing dramatic changes in the cell cycle without DNA damage. They have lower toxicity to human breast adenocarcinoma cells (MDA-MB-468) and, most remarkably, they show no significant toxicity to the bacteria methicillin-resistant Staphylococcus aureus and Escherichia coli.

New insights into Alzheimer's disease amyloid inhibition: nanosized metallo-supramolecular complexes suppress aβ-induced biosynthesis of heme and iron uptake in PC12 cells

Nanosized metallo-supramolecular compounds, [Ni2 L3 ](4+) and [Fe2 L3 ](4+) , can not only strongly inhibit Aβ aggregation but also reduce the peroxidase activity of Aβ-heme. Further studies demonstrate that through blocking the heme-binding site, these two compounds can suppress Aβ-induced biosynthesis of heme and iron uptake in PC12 cells. This work provides new insights into molecular mechanisms of Aβ inhibitors on Aβ-mediated neurotoxicity.

Transition-metal-substituted polyoxometalate derivatives as functional anti-amyloid agents for Alzheimer's disease

Inhibitions of amyloid β (Aβ) aggregation and Aβ-haem peroxidase-like activity have received much attention because these two symptoms can be the primary targets of therapeutic strategies for Alzheimer's disease (AD). Recently, our group found that polyoxometalate (POM) with a Wells-Dawson structure can efficiently inhibit Aβ aggregation. However, the interaction between POMs and Aβ is robust, but still needs to improve Aβ binding affinity. More importantly, it is unclear whether POMs can cross the blood-brain barrier and decrease Aβ-haem peroxidase-like activity. Here we show that our designed series of transition metal-functionalized POM derivatives with a defined histidine-chelated binding site have much better Aβ inhibition and peroxidase-like activity inhibition effects than the parent POM. More intriguingly, we show that these compounds can cross the blood-brain barrier and are metabolized after 48 h. Our work provides insights into the design, synthesis and screening of inorganic metal compounds as multifunctional therapeutic agents against AD.