Blood-brain barrier peptide shuttles

Nanomaterials-mediated lysosomal regulation: a robust protein-clearance approach for the treatment of Alzheimer's disease

Alzheimer's disease is a debilitating, progressive neurodegenerative disorder characterized by the progressive accumulation of abnormal proteins, including amyloid plaques and intracellular tau tangles, primarily within the brain. Lysosomes, crucial intracellular organelles responsible for protein degradation, play a key role in maintaining cellular homeostasis. Some studies have suggested a link between the dysregulation of the lysosomal system and pathogenesis of neurodegenerative diseases, including Alzheimer's disease. Restoring the normal physiological function of lysosomes hold the potential to reduce the pathological burden and improve the symptoms of Alzheimer's disease. Currently, the efficacy of drugs in treating Alzheimer's disease is limited, with major challenges in drug delivery efficiency and targeting. Recently, nanomaterials have gained widespread use in Alzheimer's disease drug research owing to their favorable physical and chemical properties. This review aims to provide a comprehensive overview of recent advances in using nanomaterials (polymeric nanomaterials, nanoemulsions, and carbon-based nanomaterials) to enhance lysosomal function in treating Alzheimer's disease. This review also explores new concepts and potential therapeutic strategies for Alzheimer's disease through the integration of nanomaterials and modulation of lysosomal function. In conclusion, this review emphasizes the potential of nanomaterials in modulating lysosomal function to improve the pathological features of Alzheimer's disease. The application of nanotechnology to the development of Alzheimer's disease drugs brings new ideas and approaches for future treatment of this disease.

Targeting cerebral diseases with enhanced delivery of therapeutic proteins across the blood-brain barrier

INTRODUCTION

Cerebral diseases have been threatening public physical and psychological health in the recent years. With the existence of the blood-brain barrier (BBB), it is particularly hard for therapeutic proteins like peptides, enzymes, antibodies, etc. to enter the central nervous system (CNS) and function in diagnosis and treatment in cerebral diseases. Fortunately, the past decade has witnessed some emerging strategies of delivering macromolecular therapeutic proteins across the BBB.

AREAS COVERED

Based on the structure, functions, and substances transport mechanisms, various enhanced delivery strategies of therapeutic proteins were reviewed, categorized by molecule-mediated delivery strategies, carrier-mediated delivery strategies, and other delivery strategies.

EXPERT OPINION

As for molecule-mediated delivery strategies, development of genetic engineering technology, optimization of protein expression and purification techniques, and mature of quality control systems all help to realize large-scale production of recombinant antibodies, making it possible to apply to the clinical practice. In terms of carrier-mediated delivery strategies and others, although nano-carriers/adeno-associated virus (AAV) are also promising candidates for delivering therapeutic proteins or genes across the BBB, some issues still remain to be further investigated, including safety concerns related to applied materials, large-scale production costs, quality control standards, combination therapies with auxiliary delivery strategies like focused ultrasound, etc.

Angiopep-2 Grafted PAMAM Dendrimers for the Targeted Delivery of Temozolomide: In Vitro and In Vivo Effects of PEGylation in the Management of Glioblastoma Multiforme

The present study was aimed to synthesize, characterize, and evaluate the angiopep-2 grafted PAMAM dendrimers (Den, G 3.0 NH₂) with and without PEGylation for the targeted and better delivery approach of temozolomide (TMZ) for the management of glioblastoma multiforme (GBM). Den-ANG and Den-PEG₂-ANG conjugates were synthesized and characterized by ¹H NMR spectroscopy. The PEGylated (TMZ@Den-PEG₂-ANG) and non-PEGylated (TMZ@Den-ANG) drug loaded formulations were prepared and characterized for particle size, zeta potential, entrapment efficiency, and drug loading. An in vitro release study at physiological (pH 7.4) and acidic pH (pH 5.0) was performed. Preliminary toxicity studies were performed through hemolytic assay in human RBCs. MTT assay, cell uptake, and cell cycle analysis were performed to evaluate the in vitro efficacy against GBM cell lines (U87MG). Finally, the formulations were evaluated in vivo in a Sprague-Dawley rat model for pharmacokinetics and organ distribution analysis. The ¹H NMR spectra confirmed the conjugation of angiopep-2 to both PAMAM and PEGylated PAMAM dendrimers, as the characteristic chemical shifts were observed in the range of 2.1 to 3.9 ppm. AFM results revealed that the surface of Den-ANG and Den-PEG₂-ANG conjugates were rough. The particle size and zeta potential of TMZ@Den-ANG were observed to be 229.0 ± 17.8 nm and 9.06 ± 0.4 mV, respectively, whereas the same for TMZ@Den-PEG₂-ANG were found to be 249.6 ± 12.9 nm and 10.9 ± 0.6 mV, respectively. The entrapment efficiency of TMZ@Den-ANG and TMZ@Den-PEG₂-ANG were calculated to be 63.27 ± 5.1% and 71.48 ± 4.3%, respectively. Moreover, TMZ@Den-PEG₂-ANG showed a better drug release profile with a controlled and sustained pattern at PBS pH 5.0 than at pH 7.4. The ex vivo hemolytic study revealed that TMZ@Den-PEG₂-ANG was biocompatible in nature as it showed 2.78 ± 0.1% hemolysis compared to 4.12 ± 0.2% hemolysis displayed by TMZ@Den-ANG. The outcomes of the MTT assay inferred that TMZ@Den-PEG₂-ANG possessed maximum cytotoxic effects against U87MG cells with IC₅₀ values of 106.62 ± 11.43 μM (24 h) and 85.90 ± 9.12 μM (48 h). In the case of TMZ@Den-PEG₂-ANG, the IC₅₀ values were reduced by 2.23-fold (24 h) and 1.36-fold (48 h) in comparison to pure TMZ. The cytotoxicity findings were further confirmed by significantly higher cellular uptake of TMZ@Den-PEG₂-ANG. Cell cycle analysis of the formulations suggested that the PEGylated formulation halts the cell cycle at G2/M phase with S-phase inhibition. In the in vivo studies, the half-life (t_1/2) values of TMZ@Den-ANG and TMZ@Den-PEG₂-ANG were enhanced by 2.22 and 2.76 times, respectively, than the pure TMZ. After 4 h of administration, the brain uptake values of TMZ@Den-ANG and TMZ@Den-PEG₂-ANG were found to be 2.55 and 3.35 times, respectively, higher than that of pure TMZ. The outcomes of various in vitro and ex vivo experiments promoted the use of PEGylated nanocarriers for the management of GBM. Angiopep-2 grafted PEGylated PAMAM dendrimers can be potential and promising drug carriers for the targeted delivery of antiglioma drugs directly to the brain.

Drug delivery to the brain – lipid nanoparticles-based approach

The complex structure of the human brain defines it as one of the most inaccessible organs in terms of drug delivery. The blood-brain barrier (BBB) represents a microvascular network involved in transporting substances between the blood and the central nervous system (CNS) – enabling the entry of nutrients and simultaneously restricting the influx of pathogens and toxins. However, its role as a protective shield for CNS also restricts drug access to the brain. Since many drugs cannot cross the BBB due to unsuitable physicochemical characteristics (i.e., high molecular weight, aqueous solubility, etc.), different technological strategies have been developed to ensure sufficient drug bioavailability. Among these, solid lipid nanoparticles (SLNs) and nanostructured lipid carriers (NLCs) are promising approaches thanks to their lipid nature, facilitating their brain uptake, small sizes, and the possibilities for subsequent functionalization to achieve targeted delivery. The review focuses on applying SLNs and NLCs as nanocarriers for brain delivery, outlining the physiological factors of BBB and the physicochemical characteristics of nanocarriers influencing this process. Recent advances in this area have also been summarized.

Peptides as Pharmacological Carriers to the Brain: Promises, Shortcomings and Challenges

Central nervous system (CNS) diseases are among the most difficult to treat, mainly because the vast majority of the drugs fail to cross the blood-brain barrier (BBB) or to reach the brain at concentrations adequate to exert a pharmacological activity. The obstacle posed by the BBB has led to the in-depth study of strategies allowing the brain delivery of CNS-active drugs. Among the most promising strategies is the use of peptides addressed to the BBB. Peptides are versatile molecules that can be used to decorate nanoparticles or can be conjugated to drugs, with either a stable link or as pro-drugs. They have been used to deliver to the brain both small molecules and proteins, with applications in diverse therapeutic areas such as brain cancers, neurodegenerative diseases and imaging. Peptides can be generally classified as receptor-targeted, recognizing membrane proteins expressed by the BBB microvessels (e.g., Angiopep2, CDX, and iRGD), "cell-penetrating peptides" (CPPs; e.g. TAT_47-57, SynB1/3, and Penetratin), undergoing transcytosis through unspecific mechanisms, or those exploiting a mixed approach. The advantages of peptides have been extensively pointed out, but so far few studies have focused on the potential negative aspects. Indeed, despite having a generally good safety profile, some peptide conjugates may display toxicological characteristics distinct from those of the peptide itself, causing for instance antigenicity, cardiovascular alterations or hemolysis. Other shortcomings are the often brief lifetime in vivo, caused by the presence of peptidases, the vulnerability to endosomal/lysosomal degradation, and the frequently still insufficient attainable increase of brain drug levels, which remain below the therapeutically useful concentrations. The aim of this review is to analyze not only the successful and promising aspects of the use of peptides in brain targeting but also the problems posed by this strategy for drug delivery.

Overcoming the blood–brain barrier for the therapy of malignant brain tumor: current status and prospects of drug delivery approaches

Besides the broad development of nanotechnological approaches for cancer diagnosis and therapy, currently, there is no significant progress in the treatment of different types of brain tumors. Therapeutic molecules crossing the blood–brain barrier (BBB) and reaching an appropriate targeting ability remain the key challenges. Many invasive and non-invasive methods, and various types of nanocarriers and their hybrids have been widely explored for brain tumor treatment. However, unfortunately, no crucial clinical translations were observed to date. In particular, chemotherapy and surgery remain the main methods for the therapy of brain tumors. Exploring the mechanisms of the BBB penetration in detail and investigating advanced drug delivery platforms are the key factors that could bring us closer to understanding the development of effective therapy against brain tumors. In this review, we discuss the most relevant aspects of the BBB penetration mechanisms, observing both invasive and non-invasive methods of drug delivery. We also review the recent progress in the development of functional drug delivery platforms, from viruses to cell-based vehicles, for brain tumor therapy. The destructive potential of chemotherapeutic drugs delivered to the brain tumor is also considered. This review then summarizes the existing challenges and future prospects in the use of drug delivery platforms for the treatment of brain tumors.

Peptide Shuttles for Blood–Brain Barrier Drug Delivery

The blood–brain barrier (BBB) limits the delivery of therapeutics to the brain but also represents the main gate for nutrient entrance. Targeting the natural transport mechanisms of the BBB offers an attractive route for brain drug delivery. Peptide shuttles are able to use these mechanisms to increase the transport of compounds that cannot cross the BBB unaided. As peptides are a group of biomolecules with unique physicochemical and structural properties, the field of peptide shuttles has substantially evolved in the last few years. In this review, we analyze the main classifications of BBB–peptide shuttles and the leading sources used to discover them.

Delivering the Promise of Gene Therapy with Nanomedicines in Treating Central Nervous System Diseases

Central Nervous System (CNS) diseases, such as Alzheimer's diseases (AD), Parkinson's Diseases (PD), brain tumors, Huntington's disease (HD), and stroke, still remain difficult to treat by the conventional molecular drugs. In recent years, various gene therapies have come into the spotlight as versatile therapeutics providing the potential to prevent and treat these diseases. Despite the significant progress that has undoubtedly been achieved in terms of the design and modification of genetic modulators with desired potency and minimized unwanted immune responses, the efficient and safe in vivo delivery of gene therapies still poses major translational challenges. Various non-viral nanomedicines have been recently explored to circumvent this limitation. In this review, an overview of gene therapies for CNS diseases is provided and describes recent advances in the development of nanomedicines, including their unique characteristics, chemical modifications, bioconjugations, and the specific applications that those nanomedicines are harnessed to deliver gene therapies.

BBPpredict: A Web Service for Identifying Blood-Brain Barrier Penetrating Peptides

Blood-brain barrier (BBB) is a major barrier to drug delivery into the brain in the treatment of central nervous system (CNS) diseases. Blood-brain barrier penetrating peptides (BBPs), a class of peptides that can cross BBB through various mechanisms without damaging BBB, are effective drug candidates for CNS diseases. However, identification of BBPs by experimental methods is time-consuming and laborious. To discover more BBPs as drugs for CNS disease, it is urgent to develop computational methods that can quickly and accurately identify BBPs and non-BBPs. In the present study, we created a training dataset that consists of 326 BBPs derived from previous databases and published manuscripts and 326 non-BBPs collected from UniProt, to construct a BBP predictor based on sequence information. We also constructed an independent testing dataset with 99 BBPs and 99 non-BBPs. Multiple machine learning methods were compared based on the training dataset via a nested cross-validation. The final BBP predictor was constructed based on the training dataset and the results showed that random forest (RF) method outperformed other classification algorithms on the training and independent testing dataset. Compared with previous BBP prediction tools, the RF-based predictor, named BBPpredict, performs considerably better than state-of-the-art BBP predictors. BBPpredict is expected to contribute to the discovery of novel BBPs, or at least can be a useful complement to the existing methods in this area. BBPpredict is freely available at http://i.uestc.edu.cn/BBPpredict/cgi-bin/BBPpredict.pl.

Liposomes: An emerging carrier for targeting Alzheimer's and Parkinson's diseases

The function of the brain can be affected by various factors that include infection, tumor, and stroke. The major disorders reported with altered brain function are Alzheimer's disease (AD), Parkinson's disease (PD), dementia, brain cancer, seizures, mental disorders, and other movement disorders. The major barrier in treating CNS disease is the blood-brain barrier (BBB), which protects the brain from toxic molecules, and the cerebrospinal fluid (CSF) barrier, which separates blood from CSF. Brain endothelial cells and perivascular elements provide an integrated cellular barrier, the BBB, which hamper the invasion of molecules from the blood to the brain. Even though many drugs are available to treat neurological disorders, it fails to reach the desired site with the required concentration. In this purview, liposomes can carry required concentrations of molecules intracellular by diverse routes such as carrier-mediated transport and receptor-mediated transcytosis. Surface modification of liposomes enables them to deliver drugs to various brain cells, including neurons, astrocytes, oligodendrocytes, and microglia. The research studies supported the role of liposomes in delivering drugs across BBB and in reducing the pathogenesis of AD and PD. The liposomes were surface-functionalized with various molecules to reach the cells intricated with the AD or PD pathogenesis. The targeted and sustained delivery of drugs by liposomes is disturbed due to the antibody formation, renal clearance, accelerated blood clearance, and complement activation-related pseudoallergy (CARPA). Hence, this review will focus on the characteristics, surface functionalization, drug loading, and biodistribution of liposomes respective to AD and PD. In addition, the alternative strategies to overcome immunogenicity are discussed briefly.

Peptide-based delivery of therapeutics in cancer treatment

Current delivery strategies for cancer therapeutics commonly cause significant systemic side effects due to required high doses of therapeutic, inefficient cellular uptake of drug, and poor cell selectivity. Peptide-based delivery systems have shown the ability to alleviate these issues and can significantly enhance therapeutic loading, delivery, and cancer targetability. Peptide systems can be tailor-made for specific cancer applications. This review describes three peptide classes, targeting, cell penetrating, and fusogenic peptides, as stand-alone nanoparticle systems, conjugations to nanoparticle systems, or as the therapeutic modality. Peptide nanoparticle design, characteristics, and applications are discussed as well as peptide applications in the clinical space.

A nanocleaner specifically penetrates the blood‒brain barrier at lesions to clean toxic proteins and regulate inflammation in Alzheimer's disease

Insurmountable blood‒brain barrier (BBB) and complex pathological features are the key factors affecting the treatment of Alzheimer's disease (AD). Poor accumulation of drugs in lesion sites and undesired effectiveness of simply reducing Aβ deposition or TAU protein need to be resolved urgently. Herein, a nanocleaner is designed with a rapamycin-loaded ROS-responsive PLGA core and surface modification with KLVFF peptide and acid-cleavable DAG peptide [R@(ox-PLGA)-KcD]. DAG can enhance the targeting and internalization effect of nanocleaner towards neurovascular unit endothelial cells in AD lesions, and subsequently detach from nanocleaner in response to acidic microenvironment of endosomes to promote the transcytosis of nanocleaner from endothelial cells into brain parenchyma. Then exposed KLVFF can capture and carry Aβ to microglia, attenuating Aβ-induced neurotoxicity. Strikingly, rapamycin, an autophagy promoter, is rapidly liberated from nanocleaner in the high ROS level of lesions to improve Aβ degradation and normalize inflammatory condition. This design altogether accelerates Aβ degradation and alleviates oxidative stress and excessive inflammatory response. Collectively, our finding offers a strategy to target the AD lesions precisely and multi-pronged therapies for clearing the toxic proteins and modulating lesion microenvironment, to achieve efficient AD therapy.

Transportation of Single-Domain Antibodies through the Blood-Brain Barrier

Single-domain antibodies derive from the heavy-chain-only antibodies of Camelidae (camel, dromedary, llama, alpaca, vicuñas, and guananos; i.e., nanobodies) and cartilaginous fishes (i.e., VNARs). Their small size, antigen specificity, plasticity, and potential to recognize unique conformational epitopes represent a diagnostic and therapeutic opportunity for many central nervous system (CNS) pathologies. However, the blood–brain barrier (BBB) poses a challenge for their delivery into the brain parenchyma. Nevertheless, numerous neurological diseases and brain pathologies, including cancer, result in BBB leakiness favoring single-domain antibodies uptake into the CNS. Some single-domain antibodies have been reported to naturally cross the BBB. In addition, different strategies and methods to deliver both nanobodies and VNARs into the brain parenchyma can be exploited when the BBB is intact. These include device-based and physicochemical disruption of the BBB, receptor and adsorptive-mediated transcytosis, somatic gene transfer, and the use of carriers/shuttles such as cell-penetrating peptides, liposomes, extracellular vesicles, and nanoparticles. Approaches based on single-domain antibodies are reaching the clinic for other diseases. Several tailoring methods can be followed to favor the transport of nanobodies and VNARs to the CNS, avoiding the limitations imposed by the BBB to fulfill their therapeutic, diagnostic, and theragnostic promises for the benefit of patients suffering from CNS pathologies.

Development of Polymeric Nanoparticles for Blood-Brain Barrier Transfer-Strategies and Challenges

Neurological disorders such as Alzheimer's disease, stroke, and brain cancers are difficult to treat with current drugs as their delivery efficacy to the brain is severely hampered by the presence of the blood-brain barrier (BBB). Drug delivery systems have been extensively explored in recent decades aiming to circumvent this barrier. In particular, polymeric nanoparticles have shown enormous potentials owing to their unique properties, such as high tunability, ease of synthesis, and control over drug release profile. However, careful analysis of their performance in effective drug transport across the BBB should be performed using clinically relevant testing models. In this review, polymeric nanoparticle systems for drug delivery to the central nervous system are discussed with an emphasis on the effects of particle size, shape, and surface modifications on BBB penetration. Moreover, the authors critically analyze the current in vitro and in vivo models used to evaluate BBB penetration efficacy, including the latest developments in the BBB-on-a-chip models. Finally, the challenges and future perspectives for the development of polymeric nanoparticles to combat neurological disorders are discussed.

An update on actively targeted liposomes in advanced drug delivery to glioma

High-grade glioma is one of the most aggressive types of cancer with a low survival rate ranging from 12 to 15 months after the first diagnosis. Though being the most common strategy for glioma therapy, conventional chemotherapy suffers providing the therapeutic dosage of common therapeutics mostly because of limited permeability of blood-brain barrier (BBB), and blood-brain tumor barrier (BBTB) to anticancer agents. Among various nanoformulations, liposomes are considered as the most popular carriers aimed for glioma therapy. However, non-targeted liposomes which passively accumulate in most of the cancer tissues mainly through the enhanced permeation and retention effect (EPR), may not be applicable for glioma therapy due to BBB tight junctions. In the recent decade, the surface modification of liposomes with different active targeting ligands has shown promising results by getting different chemotherapeutics across the BBB and BBTB and leading them into the glioma cells. The present review discusses the major barriers for drug delivery systems to glioma, elaborates the existing mechanisms for liposomes to traverse across the BBB, and explores the main strategies for incorporation of targeting ligands onto the liposomes. It subsequently investigates the most recent and relevant studies of actively targeted liposomes modified with antibodies, aptamers, monosaccharides, polysaccharides, proteins, and peptides applied for effective glioma therapy, and highlights the common challenges facing this area. Finally, the actively targeted liposomes undergoing preclinical and clinical studies for delivery of different anticancer agents to glioma cells will be reviewed.

Endosomal escape cell-penetrating peptides significantly enhance pharmacological effectiveness and CNS activity of systemically administered antisense oligonucleotides

Antisense oligonucleotides (ASOs) are an emerging class of gene-specific therapeutics for diseases associated with the central nervous system (CNS). However, ASO delivery across the blood-brain barrier (BBB) to their CNS target cells remains a major challenge. Since ASOs are mainly taken up into the brain capillary endothelial cells interface through endosomal routes, entrapment in the endosomal compartment is a major obstacle for efficient CNS delivery of ASOs. Therefore, we evaluated the effectiveness of a panel of cell-penetrating peptides (CPPs) bearing several endosomal escape domains for the intracellular delivery, endosomal release and antisense activity of FDA-approved Spinraza (Nusinersen), an ASO used to treat spinal muscular atrophy (SMA). We identified a CPP, HA2-ApoE(131-150), which, when conjugated to Nusinersen, showed efficient endosomal escape capability and significantly increased the level of full-length functional mRNA of the survival motor neuron 2 (SMN2) gene in SMA patient-derived fibroblasts. Treatment of SMN2 transgenic adult mice with this CPP-PMO conjugate resulted in a significant increase in the level of full-length SMN2 in the brain and spinal cord. This work provides proof-of-principle that integration of endosomal escape domains with CPPs enables higher cytosolic delivery of ASOs, and more importantly enhances the efficiency of BBB-permeability and CNS activity of systemically administered ASOs.

Critical Review of Lipid-Based Nanoparticles as Carriers of Neuroprotective Drugs and Extracts

The biggest obstacle to the treatment of diseases that affect the central nervous system (CNS) is the passage of drugs across the blood-brain barrier (BBB), a physical barrier that regulates the entry of substances into the brain and ensures the homeostasis of the CNS. This review summarizes current research on lipid-based nanoparticles for the nanoencapsulation of neuroprotective compounds. A survey of studies on nanoemulsions (NEs), nanoliposomes/nanophytosomes and solid lipid nanoparticles (SLNs)/nanostructured lipid carriers (NLCs) was carried out and is discussed herein, with particular emphasis upon their unique characteristics, the most important parameters influencing the formulation of each one, and examples of neuroprotective compounds/extracts nanoencapsulated using these nanoparticles. Gastrointestinal absorption is also discussed, as it may pose some obstacles for the absorption of free and nanoencapsulated neuroprotective compounds into the bloodstream, consequently hampering drug concentration in the brain. The transport mechanisms through which compounds or nanoparticles may cross BBB into the brain parenchyma, and the potential to increase drug bioavailability, are also discussed. Additionally, factors contributing to BBB disruption and neurodegeneration are described. Finally, the advantages of, and obstacles to, conventional and unconventional routes of administration to deliver nanoencapsulated neuroprotective drugs to the brain are also discussed, taking into account the avoidance of first-pass metabolism, onset of action, ability to bypass the BBB and concentration of the drug in the brain.

Lipid-Based Nanocarriers for The Treatment of Glioblastoma

Glioblastoma multiforme (GBM) is the most common and malignant neoplasia having origin in the brain. The current treatments involve surgery, radiotherapy, and chemotherapy, being complete surgical resection the best option for the patient survival chances. However, in those cases where a complete removal is not possible, radiation and chemotherapy are applied. Herein, the main challenges of chemotherapy, and how they can be overcome with the help of nanomedicine, are approached. Natural pathways to cross the blood-brain barrier (BBB) are detailed, and different in vivo studies where these pathways are mimicked functionalizing the nanomaterial surface are shown. Later, lipid-based nanocarriers, such as liposomes, solid lipid nanoparticles, and nanostructured lipid carriers, are presented. To finish, recent studies that have used lipid-based nanosystems carrying not only therapeutic agents, yet also magnetic nanoparticles, are described. Although the advantages of using these types of nanosystems are explained, including their biocompatibility, the possibility of modifying their surface to enhance the cell targeting, and their intrinsic ability of BBB crossing, it is important to mention that research in this field is still at its early stage, and extensive preclinical and clinical investigations are mandatory in the close future.

Brain penetrating peptides and peptide-drug conjugates to overcome the blood-brain barrier and target CNS diseases

Nearly one in six people worldwide suffer from disorders of the central nervous system (CNS). There is an urgent need for effective strategies to improve the success rates in CNS drug discovery and development. The lack of effective technologies for delivering drugs and genes to the brain due to the blood-brain barrier (BBB), a structural barrier that effectively blocks most neurotherapeutic agents from reaching the brain, has posed a formidable hurdle for CNS drug development. Brain-homing and brain-penetrating molecular transport vectors, such as brain permeable peptides or BBB shuttle peptides, have shown promise in overcoming the BBB and ferrying the drug molecules to the brain. The BBB shuttle peptides are discovered by phage display technology or derived from natural neurotropic proteins or certain viruses and harness the receptor-mediated transcytosis molecular machinery for crossing the BBB. Brain permeable peptide-drug conjugates (PDCs), composed of BBB shuttle peptides, linkers, and drug molecules, have emerged as a promising CNS drug delivery system by taking advantage of the endogenous transcytosis mechanism and tricking the brain into allowing these bioactive molecules to pass the BBB. Here, we examine the latest development of brain-penetrating peptide shuttles and brain-permeable PDCs as molecular vectors to deliver small molecule drug payloads across the BBB to reach brain parenchyma. Emerging knowledge of the contribution of the peptides and their specific receptors expressed on the brain endothelial cells, choice of drug payloads, the design of PDCs, brain entry mechanisms, and delivery efficiency to the brain are highlighted. This article is categorized under: Therapeutic Approaches and Drug Discovery > Emerging Technologies Therapeutic Approaches and Drug Discovery > Nanomedicine for Neurological Disease.

BBPpred: Sequence-Based Prediction of Blood-Brain Barrier Peptides with Feature Representation Learning and Logistic Regression

Blood-brain barrier peptides (BBPs) have a large range of biomedical applications since they can cross the blood-brain barrier based on different mechanisms. As experimental methods for the identification of BBPs are laborious and expensive, computational approaches are necessary to be developed for predicting BBPs. In this work, we describe a computational method, BBPpred (blood-brain barrier peptides prediction), that can efficiently identify BBPs using logistic regression. We investigate a wide variety of features from amino acid sequence information, and then a feature learning method is adopted to represent the informative features. To improve the prediction performance, seven informative features are selected for classification by eliminating redundant and irrelevant features. In addition, we specifically create two benchmark data sets (training and independent test), which contain a total of 119 BBPs from public databases and the literature. On the training data set, BBPpred shows promising performances with an AUC score of 0.8764 and an AUPR score of 0.8757 using the 10-fold cross-validation. We also test our new method on the independent test data set and obtain a favorable performance. We envision that BBPpred will be a useful tool for identifying, annotating, and characterizing BBPs. BBPpred is freely available at http://BBPpred.xialab.info.

Taking the Myc out of cancer: toward therapeutic strategies to directly inhibit c-Myc

c-Myc is a transcription factor that is constitutively and aberrantly expressed in over 70% of human cancers. Its direct inhibition has been shown to trigger rapid tumor regression in mice with only mild and fully reversible side effects, suggesting this to be a viable therapeutic strategy. Here we reassess the challenges of directly targeting c-Myc, evaluate lessons learned from current inhibitors, and explore how future strategies such as miniaturisation of Omomyc and targeting E-box binding could facilitate translation of c-Myc inhibitors into the clinic.

Incorporation of docosahexaenoic acid (DHA) enhances nanodelivery of antiretroviral across the blood-brain barrier for treatment of HIV reservoir in brain

Although the newer antiretroviral (ARV) drugs are highly active against the human immunodeficiency virus (HIV) in the body compartment, they often fail to effectively tackle the HIV reservoir in the brain because of inefficient penetration to the blood-brain barrier (BBB). In this study, we investigated the potential benefits of incorporating docosahexaenoic acid (DHA), an omega-3 fatty acid essential for brain development, in lipid nanocarriers for facilitating the BBB passage of an ARV darunavir. The resulting nanocarriers (nanoARVs) containing 5-15% DHA were 90-140 nm in size, had high darunavir payload (~11-13% w/w), good stability and minimal cellular toxicity, and could be further decorated with transferrin (Tf) for Tf-receptor targeting. In BBB models of hCMEC/d3 cells, nanoARVs with higher DHA content achieved increased nanocarrier uptake and up to 8.99-fold higher darunavir permeation than free darunavir. In animals, nanoARVs were able to achieve 3.38-5.93-fold increase in brain darunavir level over free darunavir. Tf-conjugated nanoARVs also achieved significantly higher anti-HIV activity than free darunavir (viral titer 2 to 2.6-fold higher in latter group). Comparison of DHA incorporation and Tf-receptor targeting showed that while both strategies could enhance the cellular uptake and brain accumulation of the nanocarriers, DHA was more effective (P < 0.05) for improving BBB permeation and brain accumulation of the darunavir payload. Substituting DHA with another oil noticeably reduced the cellular uptake of nanoARVs. Overall, this proof-of-concept study has supported the development of DHA-based nanoARVs as an effective, safe yet technically simple strategy to enhance brain delivery of darunavir and potentially other lipophilic ARVs for treatment of HIV reservoir.

Lipid Nanoparticles Improve the Uptake of α-Asarone Into the Brain Parenchyma: Formulation, Characterization, In Vivo Pharmacokinetics, and Brain Delivery

Treatment of brain-related diseases is one of the most strenuous challenges in drug delivery research due to numerous hurdles, including poor blood-brain barrier penetration, lack of specificity, and severe systemic toxicities. Our research primarily focuses on the delivery of natural therapeutic compound, α-asarone, for the treatment of brain-related diseases. However, α-asarone has poor aqueous solubility, bioavailability, and stability, all of which are critical issues that need to be addressed. This study aims at formulating a lipid nanoparticulate system of α-asarone (A-LNPs) that could be used as a brain drug delivery system. The physicochemical, solid-state properties, stability, and in vitro and in vivo studies of the A-LNPs were characterized. The release of α-asarone from the A-LNPs was prolonged and sustained. After intravenous administration of A-LNPs or free α-asarone, significantly higher levels of α-asarone from the A-LNPs were detected in murine plasma and brain parenchyma fractions, confirming the ability of A-LNPs to not only maintain a therapeutic concentration of α-asarone in the plasma, but also transport α-asarone across the blood-brain barrier. These findings confirm that lipid nanoparticulate systems enable penetration of natural therapeutic compound α-asarone through the blood-brain barrier and may be a candidate for the treatment of brain-related diseases.

To What Extent Do Fluorophores Bias the Biological Activity of Peptides? A Practical Approach Using Membrane-Active Peptides as Models

The characterization of biologically active peptides relies heavily on the study of their efficacy, toxicity, mechanism of action, cellular uptake, or intracellular location, using both in vitro and in vivo studies. These studies frequently depend on the use of fluorescence-based techniques. Since most peptides are not intrinsically fluorescent, they are conjugated to a fluorophore. The conjugation may interfere with peptide properties, thus biasing the results. The selection of the most suitable fluorophore is highly relevant. Here, a comprehensive study with blood-brain barrier (BBB) peptide shuttles (PepH3 and PepNeg) and antimicrobial peptides (AMPs) (vCPP2319 and Ctn[15-34]), tested as anticancer peptides (ACPs), having different fluorophores, namely 5(6)-carboxyfluorescein (CF), rhodamine B (RhB), quasar 570 (Q570), or tide fluor 3 (TF3) attached is presented. The goal is the evaluation of the impact of the selected fluorophores on peptide performance, applying routinely used techniques to assess cytotoxicity/toxicity, secondary structure, BBB translocation, and cellular internalization. Our results show that some fluorophores significantly modulate peptide activity when compared with unlabeled peptides, being more noticeable in hydrophobic and charged fluorophores. This study highlights the need for a careful experimental design for fluorescently labeled molecules, such as peptides.

Improving Cell Penetration of Gold Nanorods by Using an Amphipathic Arginine Rich Peptide

Introduction

Gold nanorods are highly reactive, have a large surface-to-volume ratio, and can be functionalized with biomolecules. Gold nanorods can absorb infrared electromagnetic radiation, which is subsequently dispersed as local heat. Gold nanoparticles can be used as powerful tools for the diagnosis and therapy of different diseases. To improve the biological barrier permeation of nanoparticles with low cytotoxicity, in this study, we conjugated gold nanorods with cell-penetrating peptides (oligoarginines) and with the amphipathic peptide CLPFFD.

Methods

We studied the interaction of the functionalized gold nanorods with biological membrane models (liposomes) by dynamic light scattering, transmission electron microscopy and the Langmuir balance. Furthermore, we evaluated the effects on cell viability and permeability with an MTS assay and TEM.

Results and Discussion

The interaction study by DLS, the Langmuir balance and cryo-TEM support that GNR-Arg₇CLPFFD enhances the interactions between GNRs and biological membranes. In addition, cells treated with GNR-Arg₇CLPFFD internalized 80% more nanoparticles than cells treated with GNR alone and did not induce cell damage.

Conclusion

Our results indicate that incorporation of an amphipathic sequence into oligoarginines for the functionalization of gold nanorods enhances biological membrane nanoparticle interactions and nanoparticle cell permeability with respect to nanorods functionalized with oligoarginine. Overall, functionalized gold nanorods with amphipathic arginine rich peptides might be candidates for improving drug delivery by facilitating biological barrier permeation.

A ligand-based system for receptor-specific delivery of proteins

Gene delivery using vector or viral-based methods is often limited by technical and safety barriers. A promising alternative that circumvents these shortcomings is the direct delivery of proteins into cells. Here we introduce a non-viral, ligand-mediated protein delivery system capable of selectively targeting primary skin cells in-vivo. Using orthologous self-labelling tags and chemical cross-linkers, we conjugate large proteins to ligands that bind their natural receptors on the surface of keratinocytes. Targeted CRE-mediated recombination was achieved by delivery of ligand cross-linked CRE protein to the skin of transgenic reporter mice, but was absent in mice lacking the ligand's cell surface receptor. We further show that ligands mediate the intracellular delivery of Cas9 allowing for CRISPR-mediated gene editing in the skin more efficiently than adeno-associated viral gene delivery. Thus, a ligand-based system enables the effective and receptor-specific delivery of large proteins and may be applied to the treatment of skin-related genetic diseases.

Newly Discovered Action of HpTx3 from Venom of Heteropoda venatoria on Nav1.7 and Its Pharmacological Implications in Analgesia

It has been reported that Heteropodatoxin3 (HpTx3), a peptidic neurotoxin purified from the venom of the spider species Heteropoda venatoria, could inhibit K_v4.2 channels. Our present study newly found that HpTx3 also has potent and selective inhibitory action on Na_v1.7, with an IC₅₀ of 135.61 ± 12.98 nM. Without effect on the current–voltage (I-V) relationship of Na_v1.7, HpTx3 made minor alternation in the voltage-dependence of activation and steady-state inactivation of Na_v1.7 (4.15 mV and 7.29 mV, respectively) by interacting with the extracellular S3–S4 loop (S3b–S4 sequence) in domain II and the domain IV of the Na_v channel subtype, showing the characteristics of both pore blocker and gate modifier toxin. During the interaction of HpTx3 with the S3b–S4 sequence of Na_v1.7, the amino acid residue D in the sequence played a key role. When administered intraperitoneally or intramuscularly, HpTx3 displayed potent analgesic activity in a dose-dependent manner in different mouse pain models induced by formalin, acetic acid, complete Freund’s adjuvant, hot plate, or spared nerve injury, demonstrating that acute, inflammatory, and neuropathic pains were all effectively inhibited by the toxin. In most cases HpTx3 at doses of ≥ 1mg/kg could produce the analgesic effect comparable to that of 1 mg/kg morphine. These results suggest that HpTx3 not only can be used as a molecular probe to investigate ion channel function and pain mechanism, but also has potential in the development of the drugs that treat the Na_v1.7 channel-related pain.

Liposome delivery systems for the treatment of Alzheimer's disease

Alzheimer's disease (AD) will affect around 115 million people worldwide by the year 2050. It is associated with the accumulation of misfolded and aggregated proteins (β-amyloid and tau) in the senile plaques and neurofibrillary tangles found in the brain. Currently available drugs for AD only temporarily alleviate symptoms and do not slow the inevitable progression of this disease. New drugs are required that act on key pathologies in order to arrest or reverse cognitive decline. However, there has been a spectacular failure rate in clinical trials of conventional small molecule drugs or biological agents. Targeted nanoliposomes represent a viable and promising drug delivery system for AD that have not yet reached clinical trials. They are biocompatible, highly flexible, and have the potential to carry many different types of therapeutic molecules across the blood-brain barrier (BBB) and into brain cells. They can be tailored to extend blood circulation time and can be directed against individual or multiple pathological targets. Modifications so far have included the use of brain-penetrating peptides, together with Aβ-targeting ligands, such as phosphatidic acid, curcumin, and a retro-inverted peptide that inhibits Aβ aggregation. Combining several modifications together into multifunctional liposomes is currently a research area of great interest. This review focuses on recent liposomal approaches to AD therapy, including mechanisms involved in facilitating their passage across the BBB, and the evaluation of new therapeutic agents for blocking Aβ and/or tau aggregation.

Enhanced uptake of gH625 by blood brain barrier compared to liver in vivo: characterization of the mechanism by an in vitro model and implications for delivery

We have investigated the crossing of the blood brain barrier (BBB) by the peptide gH625 and compared to the uptake by liver in vivo. We clearly observed that in vivo administration of gH625 allows the crossing of the BBB, although part of the peptide is sequestered by the liver. Furthermore, we used a combination of biophysical techniques to gain insight into the mechanism of interaction with model membranes mimicking the BBB and the liver. We observed a stronger interaction for membranes mimicking the BBB where gH625 clearly undergoes a change in secondary structure, indicating the key role of the structural change in the uptake mechanism. We report model studies on liposomes which can be exploited for the optimization of delivery tools.

Functionalization of stable fluorescent nanodiamonds towards reliable detection of biomarkers for Alzheimer's disease

Background

Stable and non-toxic fluorescent markers are gaining attention in molecular diagnostics as powerful tools for enabling long and reliable biological studies. Such markers should not only have a long half-life under several assay conditions showing no photo bleaching or blinking but also, they must allow for their conjugation or functionalization as a crucial step for numerous applications such as cellular tracking, biomarker detection and drug delivery.

Results

We report the functionalization of stable fluorescent markers based on nanodiamonds (NDs) with a bifunctional peptide. This peptide is made of a cell penetrating peptide and a six amino acids long β-sheet breaker peptide that is able to recognize amyloid β (Aβ) aggregates, a biomarker for the Alzheimer disease. Our results indicate that functionalized NDs (fNDs) are not cytotoxic and can be internalized by the cells. The fNDs allow ultrasensitive detection (at picomolar concentrations of NDs) of in vitro amyloid fibrils and amyloid aggregates in AD mice brains.

Conclusions

The fluorescence of functionalized NDs is more stable than that of fluorescent markers commonly used to stain Aβ aggregates such as Thioflavin T. These results pave the way for performing ultrasensitive and reliable detection of Aβ aggregates involved in the pathogenesis of the Alzheimer disease.

Electronic supplementary material

The online version of this article (10.1186/s12951-018-0385-7) contains supplementary material, which is available to authorized users.

Peptide Mediated Brain Delivery of Nano- and Submicroparticles: A Synergistic Approach

The brain is a complex, regulated organ with a highly controlled access mechanism: The Blood-Brain Barrier (BBB). The selectivity of this barrier is a double-edged sword, being both its greatest strength and weakness. This weakness is evident when trying to target therapeutics against diseases within the brain. Diseases such as metastatic brain cancer have extremely poor prognosis due to the poor permeability of many therapeutics across the BBB. Peptides can be designed to target BBB receptors and gain access to the brain by transcytosis. These peptides (known as BBB-shuttles) can carry compounds, usually excluded from the brain, across the BBB. BBB-shuttles are limited by poor loading of therapeutics and degradation of the peptide and cargo. Likewise, nano- submicro- and microparticles can be fine-tuned to limit their degradation and with high loading of therapeutics. However, most nano- and microparticles' core materials completely lack efficient targeting, with a few selected materials able to cross the BBB passively. Combining the selectivity of peptides with the high loading potential of nano-, microparticles offers an exciting strategy to develop novel, targeted therapeutics towards many brain disorders and diseases. Nevertheless, at present the field is diverse, in both scope and nomenclature, often with competing or contradictory names. In this review, we will try to address some of these issues and evaluate the current state of peptide mediated nano,-microparticle transport to the brain, analyzing delivery vehicle type and peptide design, the two key components that must act synergistically for optimal therapeutic impact.

From venoms to BBB-shuttles. MiniCTX3: a molecular vector derived from scorpion venom

A monocyclic peptidomimetic version of chlorotoxin, MiniCTX3, was developed as a BBB-shuttle being able to transport nanoparticles across endothelial cells. Our results reveal animal venoms as an outstanding source of BBB-shuttles.

A New Noncanonical Anionic Peptide That Translocates a Cellular Blood-Brain Barrier Model

The capacity to transport therapeutic molecules across the blood–brain barrier (BBB) represents a breakthrough in the development of tools for the treatment of many central nervous system (CNS)-associated diseases. The BBB, while being protective against infectious agents, hinders the brain uptake of many drugs. Hence, finding safe shuttles able to overcome the BBB is of utmost importance. Herein, we identify a new BBB-translocating peptide with unique properties. For years it was thought that cationic sequences were mandatory for a cell-penetrating peptide (CPP) to achieve cellular internalization. Despite being anionic at physiological pH, PepNeg (sequence (SGTQEEY) is an efficient BBB translocator that is able to carry a large cargo (27 kDa), while maintaining BBB integrity. In addition, PepNeg is able to use two distinct methods of translocation, energy-dependent and -independent, suggesting that direct penetration might occur when low concentrations of peptide are presented to cells. The discovery of this new anionic trans-BBB peptide allows the development of new delivery systems to the CNS and contributes to the need to rethink the role of electrostatic attraction in BBB-translocation.