Rationally designed peptoids modulate aggregation of amyloid-beta 40

Rationally Designed Peptoid Inhibitors of Amyloid-β Oligomerization

While plaques comprised of fibrillar Aβ aggregates are hallmarks of Alzheimer's disease, soluble Aβ oligomers present higher neurotoxicity. Thus, one therapeutic approach is to prevent the formation of Aβ oligomers and reduce their associated harmful effects. We have proposed a peptoid mimic of the Aβ hydrophobic KLVFF core as an ideal candidate aggregation inhibitor due to its ability to evade proteolytic degradation via repositioning of the side chain from the α-carbon to the amide nitrogen. This peptoid, JPT1, utilizes chiral sidechains to achieve a helical structure, while C-terminal addition of two phenylalanine residues places aromatic groups on two sides of the helix with spacing designed to facilitate interaction with amyloid β-sheet structure. We have previously shown that JPT1 modulates Aβ fibril formation. Here, we demonstrate that JPT1 also modulates Aβ oligomerization, and we explore the role of the charge on the linker between the KLVFF mimic and the extended aromatic residues. Additionally, we demonstrate that peptoid-induced changes in Aβ oligomerization correlate with attenuation of oligomer-induced nuclear factor-κB activation in SH-SY5Y human neuroblastoma cells. These findings support the therapeutic potential of peptoids to target early stages of Aβ aggregation and impact the associated Aβ-induced cellular response.

Luteoloside inhibits Aβ1-42 fibrillogenesis, disintegrates preformed fibrils, and alleviates amyloid-induced cytotoxicity

Abnormal aggregation and fibrillogenesis of amyloid-β protein (Aβ) can cause Alzheimer's disease (AD). Thus, the discovery of effective drugs that inhibit Aβ fibrillogenesis in the brain is crucial for the treatment of AD. Luteoloside, as one of the polyphenolic compounds, is found to have a certain therapeutic effect on nervous system diseases. However, it remains unknown whether luteoloside is a potential drug for treating AD by modulating Aβ aggregation pathway. In this study, we performed diverse biophysical and biochemical methods to explore the inhibition of luteoloside on Aβ1-42 which is linked to AD. The results demonstrated that luteoloside efficiently prevented amyloid oligomerization and cross-β-sheet formation, reduced the rate of amyloid growth and the length of amyloid fibrils in a dose-dependent manner. Moreover, luteoloside was able to influence aggregation and conformation of Aβ1-42 during different fiber-forming phases, and it could disintegrate already preformed fibrils of Aβ1-42 and convert them into nontoxic aggregates. Furthermore, luteoloside protected cells from amyloid-induced cytotoxicity and hemolysis, and attenuated the level of reactive oxygen species (ROS). The molecular docking study showed that luteoloside interacted with Aβ1-42 mainly via Conventional Hydrogen Bond, Carbon Hydrogen Bond, Pi-Pi T-shaped, Pi-Alkyl and Pi-Anion, thereby possibly preventing it from forming the aggregates. These observations indicate that luteoloside, a natural anti-oxidant molecule, may be applicable as an effective inhibitor of Aβ, and promote further exploration of the therapeutic strategy against AD.

Modulating the RAGE-Induced Inflammatory Response: Peptoids as RAGE Antagonists

While the primary pathology of Alzheimer's disease (AD) is defined by brain deposition of amyloid-β (Aβ) plaques and tau neurofibrillary tangles, chronic inflammation has emerged as an important factor in AD etiology. Upregulated cell surface expression of the receptor for advanced glycation end-products (RAGE), a key receptor of innate immune response, is reported in AD. In parallel, RAGE ligands, including Aβ aggregates, HMGB1, and S100B, are elevated in AD brain. Activation of RAGE by these ligands triggers release of inflammatory cytokines and upregulates cell surface RAGE. Despite such observation, there are currently no therapeutics that target RAGE for treatment of AD-associated neuroinflammation. Peptoids, a novel class of potential AD therapeutics, display low toxicity, facile blood-brain barrier permeability, and resistance to proteolytic degradation. In the current study, peptoids were designed to mimic Aβ, a ligand that binds the V-domain of RAGE, and curtail RAGE inflammatory activation. We reveal the nanomolar binding capability of peptoids JPT1 and JPT1a to RAGE and demonstrate their ability to attenuate lipopolysaccharide-induced pro-inflammatory cytokine production as well as upregulation of RAGE cell surface expression. These results support RAGE antagonist peptoid-based mimics as a prospective therapeutic strategy to counter neuroinflammation in AD and other neurodegenerative diseases.

Understanding the Molecular Mechanisms of Polyphenol Inhibition of Amyloid β Aggregation

Alzheimer's disease (AD) is highly associated with self-aggregation of amyloid β (Aβ) proteins into fibrils. Inhibition of Aβ aggregation by polyphenols is one of the major therapeutic strategies for AD. Among them, four polyphenols (brazilin, resveratrol, hematoxylin, and rosmarinic acid) have been reported to be effective at inhibiting Aβ aggregation, but the inhibition mechanisms are still unclear. In this work, these four polyphenols were selected to explore their interactions with the Aβ17-42 pentamer by molecular dynamics simulation. All four polyphenols can bind to the pentamer tightly but prefer different binding sites. Conversion of the β-sheet to the random coil, fewer interchain hydrogen bonds, and weaker salt bridges were observed after binding. Interestingly, different Aβ17-42 pentamer destabilizing mechanisms for resveratrol and hematoxylin were found. Resveratrol inserts into the hydrophobic core of the pentamer by forming hydrogen bonds with Asp23 and Lys28, while hematoxylin prefers to bind beside chain A of the pentamer, which leads to β-sheet offset and dissociation of the β1 sheet of chain E. This work reveals the interactions between the Aβ17-42 pentamer and four polyphenols and discusses the relationship between inhibitor structures and their inhibition mechanisms, which also provides useful guidance for screening effective Aβ aggregation inhibitors and drug design against AD.

Recent advances in anticancer peptoids

Since most tumors become resistant to drugs in a gradual and irreversible manner, making treatment less effective over time, anticancer drugs require continuous development. Peptoids are a class of peptidomimetics that can be easily synthesized and optimized. They exhibit a number of unique characteristics, including protease resistance, non-immunogenicity, do not interfere with peptide functionality and skeleton polarity, and can adopt different conformations. They have been studied for their efficacy in different cancer therapies, and can be considered as a promising alternative molecular category for the development of anticancer drugs. Herein, we discuss the extensive recent advances in peptoids and peptoid hybrids in the treatment of cancers such as prostate, breast, lung, and other ones, in the hope of providing a reference for the further development of peptoid anticancer drugs.

Controlled and Selective Photo-oxidation of Amyloid-β Fibrils by Oligomeric p-Phenylene Ethynylenes

Photodynamic therapy (PDT) has been explored as a therapeutic strategy to clear toxic amyloid aggregates involved in neurodegenerative disorders such as Alzheimer's disease. A major limitation of PDT is off-target oxidation, which can be lethal for the surrounding cells. We have shown that a novel class of oligo-p-phenylene ethynylenes (OPEs) exhibit selective binding and fluorescence turn-on in the presence of prefibrillar and fibrillar aggregates of disease-relevant proteins such as amyloid-β (Aβ) and α-synuclein. Concomitant with fluorescence turn-on, OPE also photosensitizes singlet oxygen under illumination through the generation of a triplet state, pointing to the potential application of OPEs as photosensitizers in PDT. Herein, we investigated the photosensitizing activity of an anionic OPE for the photo-oxidation of Aβ fibrils and compared its efficacy to the well-known but nonselective photosensitizer methylene blue (MB). Our results show that, while MB photo-oxidized both monomeric and fibrillar conformers of Aβ40, OPE oxidized only Aβ40 fibrils, targeting two histidine residues on the fibril surface and a methionine residue located in the fibril core. Oxidized fibrils were shorter and more dispersed but retained the characteristic β-sheet rich fibrillar structure and the ability to seed further fibril growth. Importantly, the oxidized fibrils displayed low toxicity. We have thus discovered a class of novel theranostics for the simultaneous detection and oxidization of amyloid aggregates. Importantly, the selectivity of OPE's photosensitizing activity overcomes the limitation of off-target oxidation of traditional photosensitizers and represents an advancement of PDT as a viable strategy to treat neurodegenerative disorders.

A Water-Soluble Peptoid Chelator that Can Remove Cu2+ from Amyloid-β Peptides and Stop the Formation of Reactive Oxygen Species Associated with Alzheimer's Disease

Cu bound to amyloid-β (Aβ) peptides can act as a catalyst for the formation of reactive oxygen species (ROS), leading to neuropathologic degradation associated with Alzheimer's disease (AD). An excellent therapeutic approach is to use a chelator that can selectively remove Cu from Cu-Aβ. This chelator should compete with Zn²⁺ ions (Zn) that are present in the synaptic cleft while forming a nontoxic Cu complex. Herein we describe P3, a water-soluble peptidomimetic chelator that selectively removes Cu²⁺ from Cu-Aβ in the presence of Zn and prevent the formation of ROS even in a reductive environment. We demonstrate, based on extensive spectroscopic analysis, that although P3 extracts Zn from Cu,Zn-Aβ faster than it removes Cu, the formed Zn complexes are kinetic products that further dissociate, while CuP3 is formed as an exclusive stable thermodynamic product. Our unique findings, combined with the bioavailability of peptoids, make P3 an excellent drug candidate in the context of AD.

Bio-instructive materials on-demand - combinatorial chemistry of peptoids, foldamers, and beyond

Combinatorial chemistry allows for the rapid synthesis of large compound libraries for high throughput screenings in biology, medicinal chemistry, or materials science. Especially compounds from a highly modular design are interesting for the proper investigation of structure-to-activity relationships. Permutations of building blocks result in many similar but unique compounds. The influence of certain structural features on the entire structure can then be monitored and serve as a starting point for the rational design of potent molecules for various applications. Peptoids, a highly diverse class of bioinspired oligomers, suit perfectly for combinatorial chemistry. Their straightforward synthesis on a solid support using repetitive reaction steps ensures easy handling and high throughput. Applying this modular approach, peptoids are readily accessible, and their interchangeable side-chains allow for various structures. Thus, peptoids can easily be tuned in their solubility, their spatial structure, and, consequently, their applicability in various fields of research. Since their discovery, peptoids have been applied as antimicrobial agents, artificial membranes, molecular transporters, and much more. Studying their three-dimensional structure, various foldamers with fascinating, unique properties were discovered. This non-comprehensive review will state the most interesting discoveries made over the past years and arouse curiosity about what may come.

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.

Computational Insights into the Binding of Monolayer-Capped Gold Nanoparticles onto Amyloid-β Fibrils

Amyloids-β (Aβ) fibrils are involved in several neurodegenerative diseases. In this study, atomistic molecular dynamics simulations have been used to investigate how monolayer-protected gold nanoparticles interact with Aβ(1-40) and Aβ(1-42) fibrils. Our results show that small gold nanoparticles bind with the external side of amyloid-β fibrils that is involved in the fibrillation process. The binding affinity, studied for both kinds of fibrils as a function of the monolayer composition and the nanoparticle diameter, is modulated by hydrophobic interactions and ligand monolayer conformation. Our findings thus show that monolayer-protected nanoparticles are good candidates to prevent fibril aggregation and secondary nucleation or to deliver drugs to specific fibril regions.

Human Serum Albumin-Inspired Glycopeptide-Based Multifunctional Inhibitor of Amyloid-β Toxicity

In Alzheimer's disease (AD), insoluble Aβ42 peptide fragments self-aggregate and form oligomers and fibrils in the brain, causing neurotoxicity. Further, the presence of redox-active metal ions such as Cu2+ enhances the aggregation process through chelation with these Aβ42 aggregates as well as generation of Aβ42-mediated reactive oxygen species (ROS). Herein, we have adopted a bioinspired strategy to design and develop a multifunctional glycopeptide hybrid molecule (Glupep), which can serve as a potential AD therapeutic. This molecule consists of a natural metal-chelating tetrapeptide motif of human serum albumin (HSA), a β-sheet breaker peptide, and a sugar moiety for better bioavailability. We performed different biophysical and docking experiments, which revealed that Glupep not only associates with Aβ42 but also prevents its self-aggregation to form toxic oligomers and fibrils. Moreover, Glupep was also shown to sequester out Cu2+ from the Aβ-Cu2+ complex, reducing the ROS formation and toxicity. Besides, this study also revealed that Glupep could protect PC12-derived neurons from Aβ-Cu2+-mediated toxicity by reducing intracellular ROS generation and stabilizing the mitochondrial membrane potential. All these exciting features show Glupep to be a potent inhibitor of Aβ42-mediated multifaceted toxicity and a prospective therapeutic lead for AD.

Cyanidin-3-O-glucoside inhibits Aβ40 fibrillogenesis, disintegrates preformed fibrils, and reduces amyloid cytotoxicity

Alzheimer's disease (AD) is mainly caused by the fibrillogenesis of amyloid-β protein (Aβ). Therefore, the development of effective inhibitors against Aβ fibrillogenesis offers great hope for the treatment of AD. Cyanidin-3-O-glucoside (Cy-3G) is a commonly found anthocyanin that is mainly present in fruits, with established neuroprotective effects in situ. However, it remains unknown if Cy-3G can prevent Aβ fibrillogenesis and alleviate the corresponding cytotoxicity. In this study, extensive biochemical, biophysical, biological and computational experiments were combined to address this issue. It was found that Cy-3G significantly inhibits Aβ40 fibrillogenesis and disintegrates mature Aβ fibrils, and its inhibitory capacity is dependent on the Cy-3G concentration. The circular dichroism results showed that Cy-3G and Aβ40 at a molar ratio of 3 : 1 slightly prevents the structural transformation of Aβ40 from its initial random coil to the β-sheet-rich structure. Co-incubation of Aβ40 with Cy-3G significantly reduced the production of intracellular reactive oxygen species induced by Aβ40 fibrillogenesis and thus reduced Aβ40-induced cytotoxicity. Molecular dynamics simulations revealed that Cy-3G disrupted the β-sheet structure of the Aβ40 trimer. Cy-3G was found to mainly interact with the N-terminal region, the central hydrophobic cluster and the β-sheet region II via hydrophobic and electrostatic interactions. The ten hot spot residues D7, Y10, E11, F19, F20, E22, I31, I32, M35 and V40 were also identified. These findings not only enable a comprehensive understanding of the inhibitory effect of Cy-3G on Aβ40 fibrillogenesis, but also allow the identification of a valuable dietary ingredient that possesses great potential to be developed into functional foods to alleviate AD.

Is the p3 Peptide (Aβ17-40, Aβ17-42) Relevant to the Pathology of Alzheimer's Disease?1

Despite the vast heterogeneity of amyloid plaques isolated from the brains of those with Alzheimer's Disease (AD), the basis of the Amyloid Cascade Hypothesis targets a single peptide, the amyloid-β (Aβ) peptide. The countless therapeutic efforts targeting the production and aggregation of this specific peptide have been met with disappointment, leaving many to question the role of Aβ in AD. An alternative cleavage product of the Amyloid-β protein precursor, called the p3 peptide, which has also been isolated from the brains of AD patients, has been largely absent from most Aβ-related studies. Typically referred to as non-amyloidogenic and even suggested as neuroprotective, the p3 peptide has garnered little attention aside from some conflicting findings on cytotoxicity and potential self-assembly to form higher order aggregates. Herein, we report an extensive analysis of the findings surrounding p3 and offer some evidence as to why it may not be as innocuous as previously suggested.

Electrostatic Assemblies of Single-Walled Carbon Nanotubes and Sequence-Tunable Peptoid Polymers Detect a Lectin Protein and Its Target Sugars

A primary limitation to real-time imaging of metabolites and proteins has been the selective detection of biomolecules that have no naturally occurring or stable molecular recognition counterparts. We present developments in the design of synthetic near-infrared fluorescent nanosensors based on the fluorescence modulation of single-walled carbon nanotubes (SWNTs) with select sequences of surface-adsorbed N-substituted glycine peptoid polymers. We assess the stability of the peptoid-SWNT nanosensor candidates under variable ionic strengths, protease exposure, and cell culture media conditions and find that the stability of peptoid-SWNTs depends on the composition and length of the peptoid polymer. From our library, we identify a peptoid-SWNT assembly that can detect lectin protein wheat germ agglutinin (WGA) with a sensitivity comparable to the concentration of serum proteins. To demonstrate the retention of nanosensor-bound protein activity, we show that WGA on the nanosensor produces an additional fluorescent signal modulation upon exposure to the lectin's target sugars, suggesting the lectin protein remains active and selectively binds its target sugars through ternary molecular recognition interactions relayed to the nanosensor. Our results inform design considerations for developing synthetic molecular recognition elements by assembling peptoid polymers on SWNTs and also demonstrate these assemblies can serve as optical nanosensors for lectin proteins and their target sugars. Together, these data suggest certain peptoid sequences can be assembled with SWNTs to serve as versatile optical probes to detect proteins and their molecular substrates.

Discovery of Neuroregenerative Peptoid from Amphibian Neuropeptide That Inhibits Amyloid-β Toxicity and Crosses Blood-Brain Barrier

Development of potential therapeutics for Alzheimer's disease (AD) requires a multifaceted strategy considering the high levels of complexity of the human brain and its mode of function. Here, we adopted an advanced strategy targeting two key pathological hallmarks of AD: senile plaques and neurofibrillary tangles. We derived a lead short tetrapeptide, Ser-Leu-Lys-Pro (SLKP), from a dodeca-neuropeptide of amphibian (frog) brain. Results suggested that the SLKP peptide had a superior effect compared to the dodecapeptide in neuroprotection. This result encouraged us to adopt peptidomimetic approach to synthesize an SLKP peptoid. Remarkably, we found that the SLKP peptoid is more potent than its peptide analogue, which significantly inhibits Aβ fibrillization, moderately binds with tubulin, and promotes tubulin polymerization as well as stabilization of microtubule networks. Further, we found that SLKP peptoid is stable in serum, shows significant neuroprotection against Aβ mediated toxicity, promotes significant neurite outgrowth, maintains healthy morphology of rat primary cortical neurons and crosses the blood-brain barrier (BBB). To the best of our knowledge, our SLKP peptoid is the first and shortest peptoid to show significant neuroprotection and neuroregeneration against Aβ toxicity, as well as to cross the BBB offering a potential lead for AD therapeutics.

High Selectivity and Sensitivity of Oligomeric p-Phenylene Ethynylenes for Detecting Fibrillar and Prefibrillar Amyloid Protein Aggregates

Misfolding and aggregation of amyloid proteins into fibrillar aggregates is a central pathogenic event in neurodegenerative disorders such as Alzheimer's (AD) and Parkinson's diseases (PD). Currently, there is a lack of reliable sensors for detecting the range of protein aggregates involved in disease etiology, particularly the prefibrillar aggregate conformations that are more neurotoxic. In this study, the fluorescent sensing of two novel oligomeric p-phenylene ethynylenes (OPEs), anionic OPE1- and cationic OPE2+, for detecting prefibrillar and fibrillar aggregates of AD-associated amyloid-β (Aβ40 and Aβ42) and PD-associated α-synuclein proteins (wildtype, and single mutants A30P, E35K, and A53T) over their monomeric counterparts, were tested. Furthermore, the performance of OPEs was evaluated and compared to thioflavin T (ThT), the most widely used fibril dye. Our results show that OPE1- and OPE2+ exhibited aggregate-specific binding inducing large fluorescence turn-on and spectral shifts based on a combination of backbone planarization, hydrophobic unquenching, and superluminescent OPE complex formation sensing modes. OPEs exhibited higher selectivity, higher binding affinity, and comparable limits of detection for Aβ40 fibrils compared to ThT. OPE2+ exhibited the largest fluorescence turn-on and highest sensitivity. Significantly, OPEs detected prefibrillar aggregates of Aβ42 and α-synuclein that ThT failed to detect. The superior sensing performance, the nonprotein specific detection, and the ability to selectively detect fibrillar and prefibrillar amyloid protein aggregates point to the potential of OPEs to overcome the limitations of existing probes and promise significant advancement in the detection of the myriad of protein aggregates involved in the early stages of AD and PD.

Genesis of Neuroprotective Peptoid from Aβ30-34 Inhibits Aβ Aggregation and AChE Activity

Aβ peptide and hyper-phosphorylated microtubule associated protein (Tau) aggregation causes severe damage to both the neuron membrane and key signal processing microfilament (microtubule) in Alzheimer's disease (AD) brains. To date, the key challenge is to develop nontoxic, proteolytically stable amyloid inhibitors, which can simultaneously target multiple pathways involved in AD. Various attempts have been made in this direction; however, clinical outcomes of those attempts have been reported to be poor. Thus, we choose development of peptoid (N-substituted glycine oligomers)-based leads as potential AD therapeutics, which are easy to synthesize, found to be proteolytically stable, and exhibit excellent bioavailability. In this paper, we have designed and synthesized a new short peptoid for amyloid inhibition from 30-34 hydrophobic pocket of amyloid beta (Aβ) peptide. The peptoid selectively binds with 17-21 hydrophobic region of Aβ and inhibits Aβ fibril formation. Various in vitro assays suggested that our AI peptoid binds with tubulin/microtubule and promotes its polymerization and stability. This peptoid also inhibits AChE-induced Aβ fibril formation and provides significant neuroprotection against toxicity generated by nerve growth factor (NGF) deprived neurons derived from rat adrenal pheochromocytoma (PC12) cell line. Moreover, this peptoid shows serum stability and is noncytotoxic to primary rat cortical neurons.

Basified Human Lysozyme: A Potent Inhibitor against Amyloid β-Protein Fibrillogenesis

The aggregation of amyloid β-proteins (Aβ) has been recognized as a key process in the pathogenesis of Alzheimer's disease (AD), so inhibiting Aβ aggregation is an important strategy to prevent the onset and treatment of AD. Our recent work indicated that decreasing the positive charges (or introducing negative charges) on human lysozyme (hLys) was unfavorable in keeping the inhibiting capability of hLys on Aβ aggregation. Therefore, we have herein proposed to basify hLys by conversion of the carboxyl groups into amino groups by modification with ethylene diamine. Basified hLys (Lys-B) preparations of three modification degrees (MDs), denoted as hLys-B1 (MD, 1.5), hLys-B2 (MD, 3.3), and hLys-B3 (MD, 4.4), were synthesized for modulating Aβ fibrillogenesis. The hLys-B preparations kept the stability and biocompatibility as native hLys did, whereas the inhibitory potency of hLys-B on Aβ fibrillogenesis increased with increasing MD. Cytotoxicity analysis showed that cell viability with 2.5 μM hLys-B3 increased from 62.5% (with 25 μM Aβ only) to 76.1%, similar to the case with 12.5 μM hLys (75.5%); cell viability with 6.25 μM hLys-B3 increased to 82.0%, similar to the case with 25 μM hLys (80.9%). The results indicate about four- to fivefold increase in the inhibition efficiency of hLys by the amino modification. Mechanistic analysis suggests that such a superior inhibitory capability of hLys-B was attributed to its more widely distributed positive charges, which promoted broad electrostatic interactions between Aβ and hLys-B. Thus, hLys-B suppressed the conformational transition of Aβ to β-sheet structures at low concentrations (e.g., 2.5 μM hLys-B3), leading to changes in the aggregation pathway and the formation of Aβ species with less cytotoxicity. The findings provided new insights into the development of more potent protein-based inhibitors against Aβ fibrillogenesis.

Rapid Growth of Acetylated Aβ(16-20) into Macroscopic Crystals

Aberrant assembly of the amyloid-β (Aβ) is responsible for the development of Alzheimer's disease, but can also be exploited to obtain highly functional biomaterials. The short Aβ fragment, KLVFF (Aβ_16-20), is crucial for Aβ assembly and considered to be an Aβ aggregation inhibitor. Here, we show that acetylation of KLVFF turns it into an extremely fast self-assembling molecule, reaching macroscopic ( i.e., mm) size in seconds. We show that KLVFF is metastable and that the self-assembly can be directed toward a crystalline or fibrillar phase simply through chemical modification, via acetylation or amidation of the peptide. Amidated KLVFF can form amyloid fibrils; we observed folding events of such fibrils occurring in as little as 60 ms. The ability of single KLVFF molecules to rapidly assemble as highly ordered macroscopic structures makes it a promising candidate for applications as a rapid-forming templating material.

Bifunctionality of Iminodiacetic Acid-Modified Lysozyme on Inhibiting Zn2+-Mediated Amyloid β-Protein Aggregation

Aggregation of amyloid β-proteins (Aβ) mediated by metal ions such as Zn²⁺ has been suggested to be implicated in the progression of Alzheimer's disease (AD). Hence, development of bifunctional agents capable of inhibiting Aβ aggregation and modulating metal-Aβ species is an effective strategy for the treatment of AD. In this work, we modified iminodiacetic acid (IDA) onto human lysozyme (hLys) surface to create an inhibitor of Zn²⁺-mediated Aβ aggregation and cytotoxicity. The IDA-modified hLys (IDA-hLys) retained the stability and biocompatibility of native hLys. Extensive biophysical and biological analyses indicated that IDA-hLys significantly attenuated Zn²⁺-mediated Aβ aggregation and cytotoxicity due to its strong binding affinity for Zn²⁺, whereas native hLys showed little effect. Stopped-flow fluorescence spectroscopy showed that IDA-hLys could protect Aβ from Zn²⁺-induced aggregation and rapidly depolymerize Zn²⁺-Aβ aggregates. The research indicates that IDA-hLys is a bifunctional agent capable of inhibiting Aβ fibrillization and modulating Zn²⁺-mediated Aβ aggregation and cytotoxicity as a strong Zn²⁺ chelator.

A Systematic Review of Antiamyloidogenic and Metal-Chelating Peptoids: Two Structural Motifs for the Treatment of Alzheimer's Disease

Alzheimer's disease (AD) is an incurable form of dementia affecting millions of people worldwide and costing billions of dollars in health care-related payments, making the discovery of a cure a top health, societal, and economic priority. Peptide-based drugs and immunotherapies targeting AD-associated beta-amyloid (Aβ) aggregation have been extensively explored; however, their therapeutic potential is limited by unfavorable pharmacokinetic (PK) properties. Peptoids (N-substituted glycine oligomers) are a promising class of peptidomimetics with highly tunable secondary structures and enhanced stabilities and membrane permeabilities. In this review, the biological activities, structures, and physicochemical properties for several amyloid-targeting peptoids will be described. In addition, metal-chelating peptoids with the potential to treat AD will be discussed since there are connections between the dysregulation of certain metals and the amyloid pathway.

Current progress, challenges and future prospects of diagnostic and therapeutic interventions in Alzheimer's disease

The diverse pathological mechanisms and their implications for the development of effective diagnostic and therapeutic interventions in Alzheimer's disease are presented with current progress, challenges and future prospects.

Dihydrochalcone molecules destabilize Alzheimer's amyloid-β protofibrils through binding to the protofibril cavity

Dihydrochalcone molecules destabilize Aβ_17–42protofibrils by disrupting the N-terminal β1 region and the turn region through binding to the protofibril cavity.

Iminodiacetic Acid-Modified Human Serum Albumin: A Multifunctional Agent against Metal-Associated Amyloid β-Protein Aggregation and Cytotoxicity

Metal-induced amyloid β-protein (Aβ) aggregation plays a key role in the pathogenesis of Alzheimer's disease. Although several agents have been recognized to block metal-associated Aβ aggregation, their therapeutic potential is marred due to the high-concentration metal ions in the amyloid plaques. To overcome this problem, we have herein developed iminodiacetic acid-modified human serum albumin (I-HSA) to fight against the aggregation. The multifunctional nature of I-HSA was extensively characterized in inhibiting the Aβ₄₂ aggregation associated with Zn²⁺ and Cu²⁺. The results revealed the following: (1) I-HSA significantly inhibited Aβ₄₂ aggregation and alleviated its cytotoxicity. (2) I-HSA possessed a metal-chelate capacity as high as 31.2 mol/mol, and 25 μM I-HSA could effectively inhibit the influence of 250 μM Zn²⁺ on Aβ₄₂ aggregation. (3) Equimolar I-HSA remarkably attenuated the reactive oxygen species damage caused by the Aβ₄₂ and Cu²⁺-Aβ₄₂ species. (4) I-HSA could remodel metal-Aβ₄₂ fibrils into unstructured aggregates with less neurotoxicity. The cytotoxicity of mature Cu²⁺-Aβ₄₂ aggregates was mitigated from 64.8% to 25.4% under the functioning of I-HSA. In conclusion, I-HSA showed prominent advantages for the high metal-chelate capacity. To our knowledge, I-HSA is the first multifunctional macromolecule for inhibiting high-concentration metal-induced Aβ₄₂ aggregation and remodeling mature metal-induced Aβ₄₂ species.

Hematoxylin Inhibits Amyloid β-Protein Fibrillation and Alleviates Amyloid-Induced Cytotoxicity

Accumulation and aggregation of amyloid β-protein (Aβ) play an important role in the pathogenesis of Alzheimer's disease. There has been increased interest in finding new anti-amyloidogenic compounds to inhibit Aβ aggregation. Herein, thioflavin T fluorescent assay and transmission electron microscopy results showed that hematoxylin, a natural organic molecule extracted from Caesalpinia sappan, was a powerful inhibitor of Aβ42 fibrillogenesis. Circular dichroism studies revealed hematoxylin reduced the β-sheet content of Aβ42 and made it assemble into antiparallel arrangement, which induced Aβ42 to form off-pathway aggregates. As a result, hematoxylin greatly alleviated Aβ42-induced cytotoxicity. Molecular dynamics simulations revealed the detailed interactions between hematoxylin and Aβ42. Four binding sites of hematoxylin on Aβ42 hexamer were identified, including the N-terminal region, S8GY10 region, turn region, and C-terminal region. Notably, abundant hydroxyl groups made hematoxylin prefer to interact with Aβ42 via hydrogen bonds. This also contributed to the formation of π-π stacking and hydrophobic interactions. Taken together, the research proved that hematoxylin was a potential agent against Aβ fibrillogenesis and cytotoxicity.

Modulating amyloid-β aggregation: The effects of peptoid side chain placement and chirality

Alzheimer's disease (AD) is characterized by the buildup of insoluble aggregated amyloid-β protein (Aβ) into plaques that accumulate between the neural cells in the brain. AD is the sixth leading cause of death in the United States and is the only cause of death among the top ten that cannot currently be treated or cured (Alzheimer's Association, 2011; Selkoe, 1996). Researchers have focused on developing small molecules and peptides to prevent Aβ aggregation; however, while some compounds appear promising in vitro, the research has not resulted in a viable therapeutic treatment. We previously reported a peptoid-based mimic (JPT1) of the peptide KLVFF (residues 16-20 of Aβ) that modulates Aβ40 aggregation, specifically reducing the total number of fibrillar, β-sheet structured aggregates formed. In this study, we investigate two new variants of JPT1 that probe the importance of aromatic side chain placement (JPT1s) and side chain chirality (JPT1a). Both JPT1s and JPT1a modulate Aβ40 aggregation by reducing total β-sheet aggregates. However, JPT1a also has a pronounced effect on the morphology of fibrillar Aβ40 aggregates. These results suggest that Aβ40 aggregation may follow a different pathway in the presence of peptoids with different secondary structures. A better understanding of the interactions between peptoids and Aβ will allow for improved design of AD treatments.

Novel C6-substituted 1,3,4-oxadiazinones as potential anti-cancer agents

The insulin-like growth factor 1 receptor (IGF-1R) is a membrane receptor tyrosine kinase over-expressed in a number of tumors. However, combating resistance is one of the main challenges in the currently available IGF-1R inhibitor-based cancer therapies. Increased Src activation has been reported to confer resistance to anti-IGF-1R therapeutics in various tumor cells. An urgent unmet need for IGF-1R inhibitors is to suppress Src rephosphorylation induced by current anti-IGF-1R regimens. In efforts to develop effective anticancer agents targeting the IGF-1R signaling pathway, we explored 2-aryl-1,3,4-oxadiazin-5-ones as a novel scaffold that is structurally unrelated to current tyrosine kinase inhibitors (TKIs). The compound, LL-2003, exhibited promising antitumor effects in vitro and in vivo; it effectively suppressed IGF-1R and Src and induced apoptosis in various non-small cell lung cancer cells. Further optimizations for enhanced potency in cellular assays need to be followed, but our strategy to identify novel IGF-1R/Src inhibitors may open a new avenue to develop more efficient anticancer agents.

TANGO-Inspired Design of Anti-Amyloid Cyclic Peptides

β-Amyloid peptide (Aβ) self-associates into oligomers and fibrils, in a process that is believed to directly lead to neuronal death in Alzheimer's disease. Compounds that bind to Aβ, and inhibit fibrillogenesis and neurotoxicity, are of interest as an anti-Alzheimer therapeutic strategy. Peptides are particularly attractive for this purpose, because they have advantages over small molecules in their ability to disrupt protein-protein interactions, yet they are amenable to tuning of their properties through chemical means, unlike antibodies. Self-complementation and peptide library screening are two strategies that have been employed in the search for peptides that bind to Aβ. We have taken a different approach, by designing Aβ-binding peptides using transthyretin (TTR) as a template. Previously, we demonstrated that a cyclic peptide, with sequence derived from the known Aβ-binding site on TTR, suppressed Aβ aggregation into fibrils and protected neurons against Aβ toxicity. Here, we searched for cyclic peptides with improved efficacy, by employing the algorithm TANGO, designed originally to identify amyloidogenic sequences in proteins. By using TANGO as a guide to predict the effect of sequence modifications on conformation and aggregation, we synthesized a significantly improved cyclic peptide. We demonstrate that the peptide, in binding to Aβ, redirects Aβ toward protease-sensitive, nonfibrillar aggregates. Cyclic peptides designed using this strategy have attractive solubility, specificity, and stability characteristics.

Natural Tripeptide-Based Inhibitor of Multifaceted Amyloid β Toxicity

Accumulation of amyloid beta (Aβ) peptide and its aggregates in the human brain is considered as one of the hallmarks of Alzheimer's disease (AD). The polymorphic oligomers and fully grown fibrillar aggregates of Aβ exhibit different levels of neuronal toxicity. Moreover, aggregation of Aβ in the presence of redox-active metal ions like Cu(2+) is responsible for the additional trait of cellular toxicity induced by the generation of reactive oxygen species (ROS). Herein, a multifunctional peptidomimetic inhibitor (P6) has been presented, based on a naturally occurring metal chelating tripeptide (GHK) and the inhibitor of Aβ aggregation. It was shown by employing various biophysical studies that P6 interact with Aβ and prevent the formation of toxic Aβ forms like oligomeric species and fibrillar aggregates. Further, P6 successfully sequestered Cu(2+) from the Aβ-Cu(2+) complex and maintained it in a redox-dormant state to prevent the generation of ROS. P6 inhibited membrane disruption by Aβ oligomers and efficiently prevented DNA damage caused by the Aβ-Cu(2+) complex. PC12 cells were rescued from multifaceted Aβ toxicity when treated with P6, and the amount of ROS generated in cells was reduced. These attributes make P6 a potential therapeutic candidate to ameliorate the multifaceted Aβ toxicity in AD.

Rapid identification of metal-binding peptoid oligomers by on-resin X-ray fluorescence screening

N-Substituted glycine peptoid oligomers have recently attracted attention for their metal binding capabilities. Due to their efficient synthesis on solid phase, peptoids are well suited for generation of compound libraries, followed by screening for molecular recognition and other diverse functional attributes. Ideally, peptoids could be simultaneously screened for binding to a number of metal species. Here, we demonstrate the use of bench-top X-ray fluorescence (XRF) instrumentation to screen rapidly, on solid support, a library of peptoid oligomers incorporating metal-binding functionalities. A subset of the peptoid sequences exhibited significant metal binding capabilities, including a peptoid pentamer and a nonamer that were shown to selectively bind nickel. The binding capabilities were validated by colorimetric assay and by depletion of Ni(2+) ion concentration from solution, establishing bench-top XRF as a rapid, practicable high-throughput screening technique for peptoid oligomers. This protocol will facilitate discovery of metallopeptoids with unique material properties.

Rationally designed peptidomimetic modulators of aβ toxicity in Alzheimer's disease

Alzheimer's disease is one of the devastating illnesses mankind is facing in the 21st century. The main pathogenic event in Alzheimer's disease is believed to be the aggregation of the β-amyloid (Aβ) peptides into toxic aggregates. Molecules that interfere with this process may act as therapeutic agents for the treatment of the disease. Use of recognition unit based peptidomimetics as inhibitors are a promising approach, as they exhibit greater protease stability compared to natural peptides. Here, we present peptidomimetic inhibitors of Aβ aggregation designed based on the KLVFF (P1) sequence that is known to bind Aβ aggregates. We improved inhibition efficiency of P1 by introducing multiple hydrogen bond donor-acceptor moieties (thymine/barbiturate) at the N-terminal (P2 and P3), and blood serum stability by modifying the backbone by incorporating sarcosine (N-methylglycine) units at alternate positions (P4 and P5). The peptidomimetics showed moderate to good activity in both inhibition and dissolution of Aβ aggregates as depicted by thioflavin assay, circular dichroism (CD) measurements and microscopy (TEM). The activity of P4 and P5 were studied in a yeast cell model showing Aβ toxicity. P4 and P5 could rescue yeast cells from Aβ toxicity and Aβ aggregates were cleared by the process of autophagy.

Methods for the Creation of Cyclic Peptide Libraries for Use in Lead Discovery

The identification of initial hits is a crucial stage in the drug discovery process. Although many projects adopt high-throughput screening of small-molecule libraries at this stage, there is significant potential for screening libraries of macromolecules created using chemical biology approaches. Not only can the production of the library be directly interfaced with a cell-based assay, but these libraries also require significantly fewer resources to generate and maintain. In this context, cyclic peptides are increasingly viewed as ideal scaffolds and have proven capability against challenging targets such as protein-protein interactions. Here we discuss a range of methods used for the creation of cyclic peptide libraries and detail examples of their successful implementation.

Function and toxicity of amyloid beta and recent therapeutic interventions targeting amyloid beta in Alzheimer's disease

Our Feature Article details the physiological role of amyloid beta (Aβ), elaborates its toxic effects and outlines therapeutic molecules designed in the last two years targeting different aspects of Aβ for preventing AD.