Efficient gene delivery targeted to the brain using a transferrin‐conjugated polyethyleneglycol‐modified polyamidoamine dendrimer

D-bait: A siDNA for regulation of DNA-protein kinases against DNA damage and its implications in cancer

siDNA fragments, also called Dbait and Pbait, are small DNA oligonucleotides of 30-32 base pairs that cause impairment in DNA repair pathways. Like siRNA and miRNA molecules, which lead to the degradation of mRNA molecules through the Argonaute and Drosha machinery, respectively, Dbait molecules act as false DNA damage signals and trigger and exhaust the DNA repair machinery. In normal cells with no significant DNA damage, the influence of these molecules is negligible. However, in cancer, when there is heavy DNA damage due to replication and anticancer therapies, the cancer cell is heavily dependent on DNA repair proteins to keep the genome intact and limit breaks. This phenomenon primarily occurs during radiation therapy, as significant DNA damage surpasses several DNA repair mechanisms, causing an accumulation of unrepaired lesions and ultimately leading to cell death. This review explores the therapeutic capacity of siDNA molecules in cancer treatment by stimulating the repair mechanisms in cells that depend on DNA repair pathways. For aggressive malignancies such as glioblastoma, prostate cancer, and colorectal cancer, the use of siDNA as a radiosensitizer, especially when combined with other treatments, increases the vulnerability of tumor cells to radiation-induced DNA damage, hence potentially enhancing therapy results.

Nanosystems for targeted drug Delivery: Innovations and challenges in overcoming the Blood-Brain barrier for neurodegenerative disease and cancer therapy

The evolution of sophisticated nanosystems has revolutionized biomedicine, notably in treating neurodegenerative diseases and cancer. These systems show potential in delivering medication precisely to affected tissues, improving treatment effectiveness while minimizing side effects. Nevertheless, a major hurdle in targeted drug delivery is breaching the blood-brain barrier (BBB), a selective shield separating the bloodstream from the brain and spinal cord. The tight junctions between endothelial cells in brain capillaries create a formidable physical barrier, alongside efflux transporters that expel harmful molecules. This presents a notable challenge for brain drug delivery. Nanosystems present distinct advantages in overcoming BBB challenges, offering enhanced drug efficacy, reduced side effects, improved stability, and controlled release. Despite their promise, challenges persist, such as the BBB's regional variability hindering uniform drug distribution. Efflux transporters can also limit therapeutic agent efficacy, while nanosystem toxicity necessitates rigorous safety evaluations. Understanding the long-term impact of nanomaterials on the brain remains crucial. Additionally, addressing nanosystem scalability, cost-effectiveness, and safety profiles is vital for widespread clinical implementation. This review delves into the advancements and obstacles of advanced nanosystems in targeted drug delivery for neurodegenerative diseases and cancer therapy, with a focus on overcoming the BBB.

Selective Transfection of a Transferrin Receptor-Expressing Cell Line with DNA-Lipid Nanoparticles

Despite considerable progress in using lipid nanoparticle (LNP) vehicles for gene delivery, achieving selective transfection of specific cell types remains a significant challenge, hindering the advancement of new gene or gene-editing therapies. Although LNPs have been equipped with ligands aimed at targeting specific cellular receptors, achieving complete selectivity continues to be elusive. The exact reasons for this limited selectivity are not fully understood, as cell targeting involves a complex interplay of various cellular factors. Assessing how much ligand/receptor binding contributes to selectivity is challenging due to these additional influencing factors. Nonetheless, such data are important for developing new nanocarriers and setting realistic expectations for selectivity. Here, we have quantified the selective, targeted transfection using two uniquely engineered cell lines that eliminate unpredictable and interfering cellular influences. We have compared the targeted transfection of Chinese ovary hamster (CHO) cells engineered to express the human transferrin receptor 1 (hTfR1), CHO-TRVb-hTfR1, with CHO cells that completely lack any transferrin receptor, CHO-TRVb-neo cells (negative control). Thus, the two cell lines differ only in the presence/absence of hTfR1. The transfection was performed with pDNA-encapsulating LNPs equipped with the DT7 peptide ligand that specifically binds to hTfR1 and enables targeted transfection. The LNP's pDNA encoded for the monomeric GreenLantern (mGL) reporter protein, whose fluorescence was used to quantify transfection. We report a novel LNP composition designed to achieve an optimal particle size and ζ-potential, efficient pDNA encapsulation, hTfR1-targeting capability, and sufficient polyethylene glycol sheltering to minimize random cell targeting. The transfection efficiency was quantified in both cell lines separately through flow cytometry based on the expression of the fluorescent gene product. Our results demonstrated an LNP dose-dependent mGL expression, with a 5-fold preference for the CHO-TRVb-hTfR1 when compared to CHO-TRVb-neo. In another experiment, when both cell lines were mixed at a 1:1 ratio, the DT7-decorated LNP achieved a 3-fold higher transfection of the CHO-TRVb-hTfR1 over the CHO-TRVb-neo cells. Based on the low-level transfection of the CHO-TRVb-neo cells in both experiments, our results suggest that 17-25% of the transfection occurred in a nonspecific manner. The observed transfection selectivity for the CHO-TRVb-hTfR1 cells was based entirely on the hTfR1/DT7 interaction. This work showed that the platform of two engineered cell lines which differ only in the hTfR1 can greatly facilitate the development of LNPs with hTfR1-targeting ligands.

Harnessing nanomedicine for modulating microglial states in the central nervous system disorders: Challenges and opportunities

Microglia are essential for maintaining homeostasis and responding to pathological events in the central nervous system (CNS). Their dynamic and multidimensional states in different environments are pivotal factors in various CNS disorders. However, therapeutic modulation of microglial states is challenging due to the intricate balance these cells maintain in the CNS environment and the blood-brain barrier's restriction of drug delivery. Nanomedicine presents a promising avenue for addressing these challenges, offering a method for the targeted and efficient modulation of microglial states. This review covers the challenges faced in microglial therapeutic modulation and potential use of nanoparticle-based drug delivery systems. We provide an in-depth examination of nanoparticle applications for modulating microglial states in a range of CNS disorders, encompassing neurodegenerative and autoimmune diseases, infections, traumatic injuries, stroke, tumors, chronic pain, and psychiatric conditions. This review highlights the recent advancements and future prospects in nanomedicine for microglial modulation, paving the way for future research and clinical applications of therapeutic interventions in CNS disorders.

Polyamidoamine Dendrimers: Brain-Targeted Drug Delivery Systems in Glioma Therapy

Glioma is the most common primary intracranial tumor, which is formed by the malignant transformation of glial cells in the brain and spinal cord. It has the characteristics of high incidence, high recurrence rate, high mortality and low cure rate. The treatments for glioma include surgical removal, chemotherapy and radiotherapy. Due to the obstruction of the biological barrier of brain tissue, it is difficult to achieve the desired therapeutic effects. To address the limitations imposed by the brain's natural barriers and enhance the treatment efficacy, researchers have effectively used brain-targeted drug delivery systems (DDSs) in glioma therapy. Polyamidoamine (PAMAM) dendrimers, as branched macromolecular architectures, represent promising candidates for studies in glioma therapy. This review focuses on PAMAM-based DDSs in the treatment of glioma, highlighting their physicochemical characteristics, structural properties as well as an overview of the toxicity and safety profiles.

Advancing nucleic acid delivery through cationic polymer design: non-cationic building blocks from the toolbox

The rational integration of non-cationic building blocks into cationic polymers can be devised to enhance the performance of the resulting gene delivery vectors, improving cell targeting behavior, uptake, endosomal escape, toxicity, and transfection efficiency.

siRNA drug delivery across the blood-brain barrier in Alzheimer's disease

Alzheimer's disease (AD) is a progressive neurodegenerative disease with a few FDA-approved drugs that provide modest symptomatic benefits and only two FDA-approved disease-modifying treatments for AD. The advancements in understanding the causative genes and non-coding sequences at the molecular level of the pathophysiology of AD have resulted in several exciting research papers that employed small interfering RNA (siRNA)-based therapy. Although siRNA is being sought by academia and biopharma industries, several challenges still need to be addressed. We comprehensively report the latest advances in AD pathophysiology, druggable targets, ongoing clinical trials, and the siRNA-based approaches across the blood-brain barrier for addressing AD. This review describes the latest delivery systems employed to address this barrier. Critical insights and future perspectives on siRNA therapy for AD are also provided.

Advanced genetic therapies for the treatment of Rett syndrome: state of the art and future perspectives

Loss and gain of functions mutations in the X-linked MECP2 (methyl-CpG-binding protein 2) gene are responsible for a set of generally severe neurological disorders that can affect both genders. In particular, Mecp2 deficiency is mainly associated with Rett syndrome (RTT) in girls, while duplication of the MECP2 gene leads, mainly in boys, to the MECP2 duplication syndrome (MDS). No cure is currently available for MECP2 related disorders. However, several studies have reported that by re-expressing the wild-type gene is possible to restore defective phenotypes of Mecp2 null animals. This proof of principle endorsed many laboratories to search for novel therapeutic strategies to cure RTT. Besides pharmacological approaches aimed at modulating MeCP2-downstream pathways, genetic targeting of MECP2 or its transcript have been largely proposed. Remarkably, two studies focused on augmentative gene therapy were recently approved for clinical trials. Both use molecular strategies to well-control gene dosage. Notably, the recent development of genome editing technologies has opened an alternative way to specifically target MECP2 without altering its physiological levels. Other attractive approaches exclusively applicable for nonsense mutations are the translational read-through (TR) and t-RNA suppressor therapy. Reactivation of the MECP2 locus on the silent X chromosome represents another valid choice for the disease. In this article, we intend to review the most recent genetic interventions for the treatment of RTT, describing the current state of the art, and the related advantages and concerns. We will also discuss the possible application of other advanced therapies, based on molecular delivery through nanoparticles, already proposed for other neurological disorders but still not tested in RTT.

Conjugation, Prodrug, and Co-Administration Strategies in Support of Nanotechnologies to Improve the Therapeutic Efficacy of Phytochemicals in the Central Nervous System

Phytochemicals, produced as secondary plant metabolites, have shown interesting potential therapeutic activities against neurodegenerative diseases and cancer. Unfortunately, poor bioavailability and rapid metabolic processes compromise their therapeutic use, and several strategies are currently proposed for overcoming these issues. The present review summarises strategies for enhancing the central nervous system's phytochemical efficacy. Particular attention has been paid to the use of phytochemicals in combination with other drugs (co-administrations) or administration of phytochemicals as prodrugs or conjugates, particularly when these approaches are supported by nanotechnologies exploiting conjugation strategies with appropriate targeting molecules. These aspects are described for polyphenols and essential oil components, which can improve their loading as prodrugs in nanocarriers, or be part of nanocarriers designed for targeted co-delivery to achieve synergistic anti-glioma or anti-neurodegenerative effects. The use of in vitro models, able to simulate the blood-brain barrier, neurodegeneration or glioma, and useful for optimizing innovative formulations before their in vivo administration via intravenous, oral, or nasal routes, is also summarised. Among the described compounds, quercetin, curcumin, resveratrol, ferulic acid, geraniol, and cinnamaldehyde can be efficaciously formulated to attain brain-targeting characteristics, and may therefore be therapeutically useful against glioma or neurodegenerative diseases.

Nonviral nanoparticle gene delivery into the CNS for neurological disorders and brain cancer applications

Nonviral nanoparticles have emerged as an attractive alternative to viral vectors for gene therapy applications, utilizing a range of lipid-based, polymeric, and inorganic materials. These materials can either encapsulate or be functionalized to bind nucleic acids and protect them from degradation. To effectively elicit changes to gene expression, the nanoparticle carrier needs to undergo a series of steps intracellularly, from interacting with the cellular membrane to facilitate cellular uptake to endosomal escape and nucleic acid release. Adjusting physiochemical properties of the nanoparticles, such as size, charge, and targeting ligands, can improve cellular uptake and ultimately gene delivery. Applications in the central nervous system (CNS; i.e., neurological diseases, brain cancers) face further extracellular barriers for a gene-carrying nanoparticle to surpass, with the most significant being the blood-brain barrier (BBB). Approaches to overcome these extracellular challenges to deliver nanoparticles into the CNS include systemic, intracerebroventricular, intrathecal, and intranasal administration. This review describes and compares different biomaterials for nonviral nanoparticle-mediated gene therapy to the CNS and explores challenges and recent preclinical and clinical developments in overcoming barriers to nanoparticle-mediated delivery to the brain. This article is categorized under: Therapeutic Approaches and Drug Discovery > Nanomedicine for Neurological Disease Therapeutic Approaches and Drug Discovery > Emerging Technologies Nanotechnology Approaches to Biology > Nanoscale Systems in Biology.

Dendrimer Technology in Glioma: Functional Design and Potential Applications

Novel therapeutic and diagnostic methods are sorely needed for gliomas, which contribute yearly to hundreds of thousands of cancer deaths worldwide. Despite the outpouring of research efforts and funding aimed at improving clinical outcomes for patients with glioma, the prognosis for high-grade glioma, and especially glioblastoma, remains dire. One of the greatest obstacles to improving treatment efficacy and destroying cancer cells is the safe delivery of chemotherapeutic drugs and biologics to the tumor site at a high enough dose to be effective. Over the past few decades, a burst of research has leveraged nanotechnology to overcome this obstacle. There has been a renewed interest in adapting previously understudied dendrimer nanocarriers for this task. Dendrimers are small, highly modifiable, branched structures featuring binding sites for a variety of drugs and ligands. Recent studies have demonstrated the potential for dendrimers and dendrimer conjugates to effectively shuttle therapeutic cargo to the correct tumor location, permeate the tumor, and promote apoptosis of tumor cells while minimizing systemic toxicity and damage to surrounding healthy brain tissue. This review provides a primer on the properties of dendrimers; outlines the mechanisms by which they can target delivery of substances to the site of brain pathology; and delves into current trends in the application of dendrimers to drug and gene delivery, and diagnostic imaging, in glioma. Finally, future directions for translating these in vitro and in vivo findings to the clinic are discussed.

Yeast-derived vacuoles as a novel carrier with enhanced hCMEC/D3 cell monolayer penetration

The blood-brain barrier (BBB) is a brain protection structure that restricts drug delivery from the blood to the central nervous system. Thus, we developed a novel drug carrier using yeast vacuoles to overcome this problem. The purpose of this study was to assess the drug transportability of yeast vacuoles using a human cerebral microvascular endothelial cell line (hCMEC/D3) cell monolayer. Here, we used daunorubicin (DNR) as a microtubule-targeting agent with the ability to disaggregate pre-formed fibrils and prevent Tau fibrillization. An in vitro model was developed by culturing hCMEC/D3 cells on Transwell inserts in EBM-2 endothelial basal medium until the cells formed a monolayer. Next, nano-sized yeast vacuoles were loaded with DNR, and the signals inside and outside the hMEC/D3 cell monolayer were detected using the GloMax^® Explorer fluorometer. DNR penetrated the cell monolayer and was regulated by endocytosis via receptor-mediated macropinocytosis on the surface of the cell. Confocal imaging showed a significant increase in intracellular DNR fluorescence when the cells were treated with the vacuole-encapsulated drug. These results indicate that the drug penetrated the hCMEC/D3 cell monolayer via encapsulation into the vacuoles. Overall, yeast-derived vacuoles are promising candidates as drug carriers to the brain.

Directing the Way-Receptor and Chemical Targeting Strategies for Nucleic Acid Delivery

Nucleic acid therapeutics have shown great potential for the treatment of numerous diseases, such as genetic disorders, cancer and infections. Moreover, they have been successfully used as vaccines during the COVID-19 pandemic. In order to unfold full therapeutical potential, these nano agents have to overcome several barriers. Therefore, directed transport to specific tissues and cell types remains a central challenge to receive carrier systems with enhanced efficiency and desired biodistribution profiles. Active targeting strategies include receptor-targeting, mediating cellular uptake based on ligand-receptor interactions, and chemical targeting, enabling cell-specific delivery as a consequence of chemically and structurally modified carriers. With a focus on synthetic delivery systems including polyplexes, lipid-based systems such as lipoplexes and lipid nanoparticles, and direct conjugates optimized for various types of nucleic acids (DNA, mRNA, siRNA, miRNA, oligonucleotides), we highlight recent achievements, exemplified by several nucleic acid drugs on the market, and discuss challenges for targeted delivery to different organs such as brain, eye, liver, lung, spleen and muscle in vivo.

Advances of nano drug delivery system for the theranostics of ischemic stroke

From the global perspective, stroke refers to a highly common cause of disability and death. Ischemic stroke (IS), attributed to blood vessel blockage, preventing the flow of blood to brain, acts as the most common form of stroke. Thus far, thrombolytic therapy is the only clinical treatment for IS with the approval from the FDA. Moreover, the physiology barrier complicates therapeutically and diagnostically related intervention development of IS. Accordingly, developing efficient and powerful curative approaches for IS diagnosis and treatment is urgently required. The advent of nanotechnology has brought dawn and hope to better curative and imaging forms for the management of IS. This work reviews the recent advances and challenges correlated with the nano drug delivery system for IS therapy and diagnosis. The overview of the current knowledge of the important molecular pathological mechanisms in cerebral ischemia and how the drugs cross the blood brain barrier will also be briefly summarized.

Targeting nucleic acid-based therapeutics to tumors: Challenges and strategies for polyplexes

The current medical reality of cancer gene therapy is reflected by more than ten approved products on the global market, including oncolytic and other viral vectors and CAR T-cells as ex vivo gene-modified cell therapeutics. The development of synthetic antitumoral nucleic acid therapeutics has been proceeding at a lower but steady pace, fueled by a plethora of alternative nucleic acid platforms (from various antisense oligonucleotides, siRNA, microRNA, lncRNA, sgRNA, to larger mRNA and DNA) and several classes of physical and chemical delivery technologies. This review summarizes the challenges and strategies for tumor-targeted nucleic acid delivery. Focusing primarily on polyplexes (polycation complexes) as nanocarriers, delivery options across multiple barriers into tumor cells are illustrated.

Overcoming barriers in non-viral gene delivery for neurological applications

Gene therapy for neurological disorders has attracted significant interest as a way to reverse or stop various disease pathologies. Typical gene therapies involving the central and peripheral nervous system make use of adeno-associated viral vectors whose questionable safety and limitations in manufacturing has given rise to extensive research into non-viral vectors. While early research studies have demonstrated limited efficacy with these non-viral vectors, investigation into various vector materials and functionalization methods has provided insight into ways to optimize these non-viral vectors to improve desired characteristics such as improved blood-brain barrier transcytosis, improved perfusion in brain region, enhanced cellular uptake and endosomal escape in neural cells, and nuclear transport of genetic material post- intracellular delivery. Using a combination of various strategies to enhance non-viral vectors, research groups have designed multi-functional vectors that have been successfully used in a variety of pre-clinical applications for the treatment of Parkinson's disease, brain cancers, and cellular reprogramming for neuron replacement. While more work is needed in the design of these multi-functional non-viral vectors for neural applications, much of the groundwork has been done and is reviewed here.

Aqueous Biphasic Systems Comprising Natural Organic Acid-Derived Ionic Liquids

Despite the progress achieved by aqueous biphasic systems (ABSs) comprising ionic liquids (ILs) in extracting valuable proteins, the quest for bio-based and protein-friendly ILs continues. To address this need, this work uses natural organic acids as precursors in the synthesis of four ILs, namely tetrabutylammonium formate ([N4444][HCOO]), tetrabutylammonium acetate ([N4444][CH3COO]), tetrabutylphosphonium formate ([P4444][HCOO]), and tetrabutylphosphonium acetate ([P4444][CH3COO]). It is shown that ABSs can be prepared using all four organic acid-derived ILs paired with the salts potassium phosphate dibasic (K2HPO4) and tripotassium citrate (C6H5K3O7). According to the ABSs phase diagrams, [P4444]-based ILs outperform their ammonium congeners in their ability to undergo liquid–liquid demixing in the presence of salts due to their lower hydrogen-bond acidity. However, deviations to the Hofmeister series were detected in the salts’ effect, which may be related to the high charge density of the studied IL anions. As a proof of concept for their extraction potential, these ABSs were evaluated in extracting human transferrin, allowing extraction efficiencies of 100% and recovery yields ranging between 86 and 100%. To further disclose the molecular-level mechanisms behind the extraction of human transferrin, molecular docking studies were performed. Overall, the salting-out exerted by the salt is the main mechanism responsible for the complete extraction of human transferrin toward the IL-rich phase, whereas the recovery yield and protein-friendly nature of these systems depend on specific “IL-transferrin” interactions.

An Overview of Nanotechnologies for Drug Delivery to the Brain

Drug delivery to the brain has been one of the toughest challenges researchers have faced to develop effective treatments for brain diseases. Owing to the blood–brain barrier (BBB), only a small portion of administered drug can reach the brain. A consequence of that is the need to administer a higher dose of the drug, which, expectedly, leads to a variety of unwanted side effects. Research in a variety of different fields has been underway for the past couple of decades to address this very serious and frequently lethal problem. One area of research that has produced optimistic results in recent years is nanomedicine. Nanomedicine is the science birthed by fusing the fields of nanotechnology, chemistry and medicine into one. Many different types of nanomedicine-based drug-delivery systems are currently being studied for the sole purpose of improved drug delivery to the brain. This review puts together and briefly summarizes some of the major breakthroughs in this crusade. Inorganic nanoparticle-based drug-delivery systems, such as gold nanoparticles and magnetic nanoparticles, are discussed, as well as some organic nanoparticulate systems. Amongst the organic drug-delivery nanosystems, polymeric micelles and dendrimers are discussed briefly and solid polymeric nanoparticles are explored in detail.

Gene Therapy Approach with an Emphasis on Growth Factors: Theoretical and Clinical Outcomes in Neurodegenerative Diseases

The etiology of many neurological diseases affecting the central nervous system (CNS) is unknown and still needs more effective and specific therapeutic approaches. Gene therapy has a promising future in treating neurodegenerative disorders by correcting the genetic defects or by therapeutic protein delivery and is now an attraction for neurologists to treat brain disorders, like Alzheimer's disease, Parkinson's disease, amyotrophic lateral sclerosis, spinal muscular atrophy, spinocerebellar ataxia, epilepsy, Huntington's disease, stroke, and spinal cord injury. Gene therapy allows the transgene induction, with a unique expression in cells' substrate. This article mainly focuses on the delivering modes of genetic materials in the CNS, which includes viral and non-viral vectors and their application in gene therapy. Despite the many clinical trials conducted so far, data have shown disappointing outcomes. The efforts done to improve outcomes, efficacy, and safety in the identification of targets in various neurological disorders are also discussed here. Adapting gene therapy as a new therapeutic approach for treating neurological disorders seems to be promising, with early detection and delivery of therapy before the neuron is lost, helping a lot the development of new therapeutic options to translate to the clinic.

Nanocarriers Call the Last Shot in the Treatment of Brain Cancers

Our brain is protected by physio-biological barriers. The blood–brain barrier (BBB) main mechanism of protection relates to the abundance of tight junctions (TJs) and efflux pumps. Although BBB is crucial for healthy brain protection against toxins, it also leads to failure in a devastating disease like brain cancer. Recently, nanocarriers have been shown to pass through the BBB and improve patients’ survival rates, thus becoming promising treatment strategies. Among nanocarriers, inorganic nanocarriers, solid lipid nanoparticles, liposomes, polymers, micelles, and dendrimers have reached clinical trials after delivering promising results in preclinical investigations. The size of these nanocarriers is between 10 and 1000 nm and is modified by surface attachment of proteins, peptides, antibodies, or surfactants. Multiple research groups have reported transcellular entrance as the main mechanism allowing for these nanocarriers to cross BBB. Transport proteins and transcellular lipophilic pathways exist in BBB for small and lipophilic molecules. Nanocarriers cannot enter via the paracellular route, which is limited to water-soluble agents due to the TJs and their small pore size. There are currently several nanocarriers in clinical trials for the treatment of brain cancer. This article reviews challenges as well as fitting attributes of nanocarriers for brain tumor treatment in preclinical and clinical studies.

Nanomedicine in Hepatocellular Carcinoma: A New Frontier in Targeted Cancer Treatment

Hepatocellular carcinoma (HCC) is the third leading cause of cancer-related death and is associated with a dismal median survival of 2-9 months. The fundamental limitations and ineffectiveness of current HCC treatments have led to the development of a vast range of nanotechnologies with the goal of improving the safety and efficacy of treatment for HCC. Although remarkable success has been achieved in nanomedicine research, there are unique considerations such as molecular heterogeneity and concomitant liver dysfunction that complicate the translation of nanotheranostics in HCC. This review highlights the progress, challenges, and targeting opportunities in HCC nanomedicine based on the growing literature in recent years.

Exploring Pharmacological Mechanisms of Essential Oils on the Central Nervous System

Essential oils (EOs) have been traditionally used as ancient remedies to treat many health disorders due to their enormous biological activities. As mainstream allopathic medication currently used for CNS disorders is associated with adverse effects, the search to obtain safer alternatives as compared to the currently marketed therapies is of tremendous significance. Research conducted suggests that concurrent utilization of allopathic medicines and EOs is synergistically beneficial. Due to their inability to show untoward effects, various scientists have tried to elucidate the pharmacological mechanisms by which these oils exert beneficial effects on the CNS. In this regard, our review aims to improve the understanding of EOs' biological activity on the CNS and to highlight the significance of the utilization of EOs in neuronal disorders, thereby improving patient acceptability of EOs as therapeutic agents. Through data compilation from library searches and electronic databases such as PubMed, Google Scholar, etc., recent preclinical and clinical data, routes of administration, and the required or maximal dosage for the observation of beneficial effects are addressed. We have also highlighted the challenges that require attention for further improving patient compliance, research gaps, and the development of EO-based nanomedicine for targeted therapy and pharmacotherapy.

Transferrin Receptor Targeted Polyplexes Completely Comprised of Sequence-Defined Components

Human transferrin protein (Tf) modified polyplexes have already displayed encouraging potential for receptor-mediated nucleic acid delivery into tumors. The use of a blood-derived targeting protein and polydisperse macromolecular cationic subunits however presents a practical challenge for pharmaceutical grade production. Here, Tf receptor (TfR) targeted small interfering RNA (siRNA) polyplexes are designed that are completely composed of synthetic, monodisperse, and sequence-defined subunits generated by solid-phase supported synthesis. An optimized cationizable lipo-oligoaminoamide (lipo-OAA) is used for siRNA core polyplex formation, and a retro-enantio peptide (reTfR) attached via a monodisperse polyethylene glycol (PEG) spacer via click chemistry is applied for targeting. Improved gene silencing is demonstrated in TfR-expressing KB and DU145 cells. Analogous plasmid DNA (pDNA) polyplexes are successfully used for receptor-mediated gene delivery in TfR-rich K562 cells and Neuro2a cells. Six lipo-OAAs differing in their lipidic domain and redox-sensitive attachment of lipid residues are tested in order to evaluate the impact of core polyplex stability on receptor-dependent gene transfer.

Gene therapy in epilepsy

Gene therapy may constitute a promising alternative to conventional pharmacological tools and surgeries for epilepsy. For primary epilepsy, a single variant leading to a significant effect is relatively rare, while other forms are considered complex in inheritances with multiple susceptible mutations and impacts from the environment. Gene therapy in preclinical models of epilepsy has attempted to perform antiepileptogenic, anticonvulsant, or disease-modifying effects during epileptogenesis or after establishing the disease. Creating gene vectors tailored for different situations is the key to expanding gene therapy, and choosing the appropriate therapeutic target remains another fundamental problem. A variety of treatment strategies, from overexpressing inhibitory neuropeptides to modulating the expression of neurotransmitters or ion channels, have been tested in animal models. Additionally, emerging new approaches of optogenetics and chemogenetics, as well as genome-editing tools will further boost the prosperity of gene therapy. This review summarizes the experience obtained to date and discusses the challenges and opportunities in clinical translations.

Recent Applications of Retro-Inverso Peptides

Natural and de novo designed peptides are gaining an ever-growing interest as drugs against several diseases. Their use is however limited by the intrinsic low bioavailability and poor stability. To overcome these issues retro-inverso analogues have been investigated for decades as more stable surrogates of peptides composed of natural amino acids. Retro-inverso peptides possess reversed sequences and chirality compared to the parent molecules maintaining at the same time an identical array of side chains and in some cases similar structure. The inverted chirality renders them less prone to degradation by endogenous proteases conferring enhanced half-lives and an increased potential as new drugs. However, given their general incapability to adopt the 3D structure of the parent peptides their application should be careful evaluated and investigated case by case. Here, we review the application of retro-inverso peptides in anticancer therapies, in immunology, in neurodegenerative diseases, and as antimicrobials, analyzing pros and cons of this interesting subclass of molecules.

Recent Advances in Preclinical Research Using PAMAM Dendrimers for Cancer Gene Therapy

Carriers of genetic material are divided into vectors of viral and non-viral origin. Viral carriers are already successfully used in experimental gene therapies, but despite advantages such as their high transfection efficiency and the wide knowledge of their practical potential, the remaining disadvantages, namely, their low capacity and complex manufacturing process, based on biological systems, are major limitations prior to their broad implementation in the clinical setting. The application of non-viral carriers in gene therapy is one of the available approaches. Poly(amidoamine) (PAMAM) dendrimers are repetitively branched, three-dimensional molecules, made of amide and amine subunits, possessing unique physiochemical properties. Surface and internal modifications improve their physicochemical properties, enabling the increase in cellular specificity and transfection efficiency and a reduction in cytotoxicity toward healthy cells. During the last 10 years of research on PAMAM dendrimers, three modification strategies have commonly been used: (1) surface modification with functional groups; (2) hybrid vector formation; (3) creation of supramolecular self-assemblies. This review describes and summarizes recent studies exploring the development of PAMAM dendrimers in anticancer gene therapies, evaluating the advantages and disadvantages of the modification approaches and the nanomedicine regulatory issues preventing their translation into the clinical setting, and highlighting important areas for further development and possible steps that seem promising in terms of development of PAMAM as a carrier of genetic material.

Radiolabelling of nanomaterials for medical imaging and therapy

Nanomaterials offer unique physical, chemical and biological properties of interest for medical imaging and therapy. Over the last two decades, there has been an increasing effort to translate nanomaterial-based medicinal products (so-called nanomedicines) into clinical practice and, although multiple nanoparticle-based formulations are clinically available, there is still a disparity between the number of pre-clinical products and those that reach clinical approval. To facilitate the efficient clinical translation of nanomedicinal-drugs, it is important to study their whole-body biodistribution and pharmacokinetics from the early stages of their development. Integrating this knowledge with that of their therapeutic profile and/or toxicity should provide a powerful combination to efficiently inform nanomedicine trials and allow early selection of the most promising candidates. In this context, radiolabelling nanomaterials allows whole-body and non-invasive in vivo tracking by the sensitive clinical imaging techniques positron emission tomography (PET), and single photon emission computed tomography (SPECT). Furthermore, certain radionuclides with specific nuclear emissions can elicit therapeutic effects by themselves, leading to radionuclide-based therapy. To ensure robust information during the development of nanomaterials for PET/SPECT imaging and/or radionuclide therapy, selection of the most appropriate radiolabelling method and knowledge of its limitations are critical. Different radiolabelling strategies are available depending on the type of material, the radionuclide and/or the final application. In this review we describe the different radiolabelling strategies currently available, with a critical vision over their advantages and disadvantages. The final aim is to review the most relevant and up-to-date knowledge available in this field, and support the efficient clinical translation of future nanomedicinal products for in vivo imaging and/or therapy.

Lactoferrin coated or conjugated nanomaterials as an active targeting approach in nanomedicine

A successful drug delivery to a specific site relies on two essential factors including; efficient entrapment of the drug within the carrier and successful delivery of drug- loaded nanocarrier to the target site without opsonisation or drug release in the circulation before reaching the organ of interest. Lactoferrin (LF) is a glycoprotein belonging to the transferrin (TF) family which can bind to TF receptors (TFRs) and LF membrane internalization receptors (LFRs) highly expressed on the cell surface of both highly proliferating cancer cells and blood brain barrier (BBB), which in turn can facilitate its accessibility to the cell nucleus. This merit could be exploited to develop actively targeted drug delivery systems that can easily cross the BBB or internalize into tumor cells. In this review, the most recent advances of utilizing LF as an active targeting ligand for different types of nanocarriers including: inorganic nanoparticles, dendrimers, synthetic biodegradable polymers, lipid nanocarriers, natural polymers, and nanoemulstions will be highlighted. Collectively, LF seems to be a promising targeting ligand in the field of nanomedicine.

Brain Delivery of Nanomedicines: Trojan Horse Liposomes for Plasmid DNA Gene Therapy of the Brain

Non-viral gene therapy of the brain is enabled by the development of plasmid DNA brain delivery technology, which requires the engineering and manufacturing of nanomedicines that cross the blood-brain barrier (BBB). The development of such nanomedicines is a multi-faceted problem that requires progress at multiple levels. First, the type of nanocontainer, e.g., nanoparticle or liposome, which encapsulates the plasmid DNA, must be developed. Second, the type of molecular Trojan horse, e.g., peptide or receptor-specific monoclonal antibody (MAb), must be selected for incorporation on the surface of the nanomedicine, as this Trojan horse engages specific receptors expressed on the BBB, and the brain cell membrane, to trigger transport of the nanomedicine from blood into brain cells beyond the BBB. Third, the plasmid DNA must be engineered without bacterial elements, such as antibiotic resistance genes, to enable administration to humans; the plasmid DNA must also be engineered with tissue-specific gene promoters upstream of the therapeutic gene, to insure gene expression in the target organ with minimal off-target expression. Fourth, upstream manufacturing of the nanomedicine must be developed and scalable so as to meet market demand for the target disease, e.g., annual long-term treatment of 1,000 patients with an orphan disease, short term treatment of 10,000 patients with malignant glioma, or 100,000 patients with new onset Parkinson's disease. Fifth, downstream manufacturing problems, such as nanomedicine lyophilization, must be solved to ensure the nanomedicine has a commercially viable shelf-life for treatment of CNS disease in humans.

Resveratrol Nanoparticles: A Promising Therapeutic Advancement over Native Resveratrol

The importance of fruit-derived resveratrol (RES) in the treatment of various diseases has been discussed in various research publications. Those research findings have indicated the ability of the molecule as therapeutic in the context of in vitro and in vivo conditions. Mostly, the application of RES in in vivo conditions, encapsulation processes have been carried out using various nanoparticles that are made of biocompatible biomaterials, which are easily digested or metabolized, and RES is absorbed effectively. These biomaterials are non-toxic and are safe to be used as components in the biotherapeutics. They are made from naturally available by-products of food materials like zein or corn or components of the physiological system as with lipids. The versatility of the RES nanoparticles in their different materials, working range sizes, specificity in their targeting in various human diseases, and the mechanisms associated with them are discussed in this review.

Tissue-Specific Delivery of Oligonucleotides

From the initial discovery of short-interfering RNA (siRNA) and antisense oligonucleotides for specific gene knockdown at the posttranscriptional level to the current CRISPR-Cas9 system offering gene editing at the genomic level, oligonucleotides, in addition to their biological functions in storing and conveying genetic information, provide the most prominent solutions to targeted gene therapies. Nonetheless, looking into the future of curing cancer and acute diseases, researchers are only cautiously optimistic as the cellular delivery of these polyanionic biomacromolecules is still the biggest hurdle for their therapeutic realization. To overcome the delivery obstacle, oligonucleotides have been encapsulated within or conjugated with delivery vehicles for enhanced membrane penetration, improved payload, and tissue-specific delivery. Such delivery systems include but not limited to virus-based vehicles, gold-nanoparticle vehicles, formulated liposomes, and synthetic polymers. In this chapter, delivery challenges imposed by biological barriers are briefly discussed; followed by recent advances in tissue-specific oligonucleotide delivery utilizing both viral and nonviral delivery vectors, discussing their advantages, and how judicious design and formulation could improve and expand their potential as delivery vehicles.

PEGylated nanocarriers: A promising tool for targeted delivery to the brain

Targeted drug delivery across the blood-brain barrier is an extremely challenging quest in the fight with fatal brain ailments, with the major hurdles being short circulation time, reticuloendothelial system (RES) uptake, and excretion of nanocarriers. PEGylation has emerged as a boon for targeted drug delivery to the brain. It is well established that PEGylation can increase the circulation time of nanocarriers by avoiding RES uptake, which is indispensable for increasing the brain's uptake of nanocarriers. PEGylation also acts as a linker for ligand molecules to achieve active targeting to the brain. Using PEGylation, novel approaches are being investigated to facilitate ligand-receptor interactions at the brain endothelium to ease the entry of therapeutic drugs into the brain. In addition, PEGylation made it simpler to assess the brain tissue for delivering diagnostic molecules and theranostic nanocarriers. The potential of PEGylated nanocarriers is being investigated vastly to boost the therapeutic effect several fold in the treatment of brain diseases. This review sheds light on the contribution of PEGylated nanocarriers, especially liposomes, polymeric nanoparticles, and dendrimers for brain-specific delivery of bioactives.

Dendrimer-Based Drug Delivery Systems for Brain Targeting

Human neuroscience has made remarkable progress in understanding basic aspects of functional organization; it is a renowned fact that the blood-brain barrier (BBB) impedes the permeation and access of most drugs to central nervous system (CNS) and that many neurological diseases remain undertreated. Therefore, a number of nanocarriers have been designed over the past few decades to deliver drugs to the brain. Among these nanomaterials, dendrimers have procured an enormous attention from scholars because of their nanoscale uniform size, ease of multi-functionalization, and available internal cavities. As hyper-branched 3D macromolecules, dendrimers can be maneuvered to transport diverse therapeutic agents, incorporating small molecules, peptides, and genes; diminishing their cytotoxicity; and improving their efficacy. Herein, the present review will give exhaustive details of extensive researches in the field of dendrimer-based vehicles to deliver drugs through the BBB in a secure and effectual manner. It is also a souvenir in commemorating Donald A. Tomalia on his 80th birthday.

H7K(R2)2-modified pH-sensitive self-assembled nanoparticles delivering small interfering RNA targeting hepatoma-derived growth factor for malignant glioma treatment

The lack of effective glioma therapeutics mandates the development of novel treatment strategies. Hepatoma-derived growth factor (HDGF) has been considered as a potential glioma therapeutic target, and its expression level in gliomas is positively related to the malignant grade. Although there are no effective and specific inhibitors against this target, small interfering RNA targeting HDGF (siHDGF)-mediated RNA interference (RNAi) can inhibit the target protein function by knockdown of HDGF expression. However, the application of siHDGF in glioma research and therapy is hampered by the challenge to safe and effective in vivo systemic delivery of siHDGF to gliomas. To address this question, we develop the peptide H7K(R2)2-modified pH-sensitive self-assembled hybrid nanoparticles encapsulating siHDGF (H7K(R2)2-PSNPs (siHDGF)). The acidic glioma microenvironment is beneficial to the membrane penetration of H7K(R2)2-PSNPs and the encapsulated siHDGF. Following systemic administration, H7K(R2)2-PSNPs (siHDGF) can effectively deliver siHDGF into the brain and malignant glioma cells, and therefore can significantly downregulate HDGF expression, inhibit malignant phenotypes of glioma cells, result in reduced tumor volumes and prolonged survival times in nude mice bearing U251 human glioblastoma. Thus, systemic administration of H7K(R2)2-PSNPs (siHDGF) offers an effective way for the targeted delivery of siHDGF and may serve as a practical malignant glioma therapy.

A versatile endosome acidity-induced sheddable gene delivery system: increased tumor targeting and enhanced transfection efficiency

BACKGROUND

Polycation carriers show great foreground in the developing efficient and safe gene delivery; nevertheless, they are cytotoxic and unstable in vivo because of the excess cationic charge. PEGylation improves the biocompatibility and stability of polycation, whereas PEGylation restrains the endosomal escape to some extent.

MATERIALS AND METHODS

To address this issue and promote the transfection in vivo, a pH-sensitive conjugate folate-polyethylene glycol-carboxylated chitosan (shorten as FA-PEG-CCTS) was designed and coated on the surface of PEI/NLS/pDNA (PNDs), forming a versatile gene carrier FA-PEG-CCTS/PEI/NLS/pDNA (FPCPNDs). The novel carrier exhibited a few picturesque characteristics, including (i) neutral surface charge to restrain nonspecific interactions; (ii) folate receptors (FR)-mediated endocytosis to augment cellular uptake; (iii) dual proton sponge effect to realize endosome escape, and (iv) nuclear localization sequences (NLS) to enhance the transfection of pDNA.

RESULTS

FPCPNDs could compress and protect pDNA from degradation. FPCPNDs energetically targeted tumor cells because of their high binding affinity between FA and highly expressed FR on the tumor surface, accordingly enhancing the cellular uptake. In the acidic endosomes, FA-PEG-CCTS segment dissociated from PNDs. Then, PNDs realized endosomal escape through the proton sponge effect of PEI. Furthermore, FPCPNDs showed admirable transfection efficiency with the aid of NLS peptides. What's more, in vivo studies revealed that FPCPNDs had supreme antitumor activity among the whole preparations.

CONCLUSION

In vitro and in vivo assays thus demonstrate that FPCPNDs is a hopeful strategy for gene delivery.

Challenges of gene delivery to the central nervous system and the growing use of biomaterial vectors

Gene therapy is a promising form of treatment for those suffering from neurological disorders or central nervous system (CNS) injury, however, obstacles remain that limit its translational potential. The CNS is protected by the blood brain barrier, and this barrier blocks genes from traversing into the CNS if administered outside of the CNS. Viral and non-viral gene delivery vehicles, commonly referred to as vectors, are modified to enhance delivery efficiency to target locations in the CNS. Still, there are few gene therapy approaches approved by the FDA for CNS disease or injury treatment. The lack of viable clinical approaches is due, in part, to the unpredictable nature of many vector systems. In particular, safety concerns exist with the use of viral vectors for CNS gene delivery. To seek some alternatives to viral vectors, development of new non-viral, biomaterial vectors is occurring at a rapid rate. This review discusses the challenges of delivering various forms of genetic material to the CNS, the use and limitations of current viral vector delivery systems, and the use of non-viral, biomaterial vectors for CNS applications.

Gene Therapy Tools for Brain Diseases

Neurological disorders affecting the central nervous system (CNS) are still incompletely understood. Many of these disorders lack a cure and are seeking more specific and effective treatments. In fact, in spite of advancements in knowledge of the CNS function, the treatment of neurological disorders with modern medical and surgical approaches remains difficult for many reasons, such as the complexity of the CNS, the limited regenerative capacity of the tissue, and the difficulty in conveying conventional drugs to the organ due to the blood-brain barrier. Gene therapy, allowing the delivery of genetic materials that encodes potential therapeutic molecules, represents an attractive option. Gene therapy can result in a stable or inducible expression of transgene(s), and can allow a nearly specific expression in target cells. In this review, we will discuss the most commonly used tools for the delivery of genetic material in the CNS, including viral and non-viral vectors; their main applications; their advantages and disadvantages. We will discuss mechanisms of genetic regulation through cell-specific and inducible promoters, which allow to express gene products only in specific cells and to control their transcriptional activation. In addition, we will describe the applications to CNS diseases of post-transcriptional regulation systems (RNA interference); of systems allowing spatial or temporal control of expression [optogenetics and Designer Receptors Exclusively Activated by Designer Drugs (DREADDs)]; and of gene editing technologies (CRISPR/Cas9, Zinc finger proteins). Particular attention will be reserved to viral vectors derived from herpes simplex type 1, a potential tool for the delivery and expression of multiple transgene cassettes simultaneously.

Design concepts of polyplex micelles for in vivo therapeutic delivery of plasmid DNA and messenger RNA

Nonviral delivery of plasmid (p)DNA or messenger (m)RNA is a safe and promising therapeutic option to continuously supply therapeutic proteins into diseased tissues. In most cases of in vivo pDNA and mRNA delivery, these nucleic acids are loaded into carriers based on cationic polymers and/or lipids to prevent nuclease-mediated degradation before reaching target cells. The carriers should also evade host clearance mechanisms, including uptake by scavenger cells and filtration in the spleen. Installation of ligands onto the carriers can facilitate their rapid uptake into target cells. Meanwhile, carrier toxicity should be minimized not only for preventing undesirable adverse responses in patients, but also for preserving the function of transfected cells to exert therapeutic effects. Long-term progressive improvement of platform technologies has helped overcome most of these issues, though some still remain hindering the widespread clinical application of nonviral pDNA and mRNA delivery. This review discusses design concepts of nonviral carriers for in vivo delivery and the issues to be overcome, focusing especially on our own efforts using polyplex micelles. © 2019 Wiley Periodicals, Inc. J Biomed Mater Res Part A: 107A: 978-990, 2019.

Poly(propylene imine) dendrimers with histidine-maltose shell as novel type of nanoparticles for synapse and memory protection

Poly(propylene imine) dendrimers have been shown to be promising 3-dimensional polymers for the use in the pharmaceutical and biomedical applications. Our aims of this study were first, to synthesize a novel type of dendrimer with poly(propylene imine) core and maltose-histidine shell (G4HisMal) assessing if maltose-histidine shell can improve the biocompatibility and the ability to cross the blood-brain barrier, and second, to investigate the potential of G4HisMal to protect Alzheimer disease transgenic mice from memory impairment. Our data demonstrate that G4HisMal has significantly improved biocompatibility and ability to cross the blood-brain barrier in vivo. Therefore, we suggest that a maltose-histidine shell can be used to improve biocompatibility and ability to cross the blood-brain barrier of dendrimers. Moreover, G4HisMal demonstrated properties for synapse and memory protection when administered to Alzheimer disease transgenic mice. Therefore, G4HisMal can be considered as a promising drug candidate to prevent Alzheimer disease via synapse protection.

Applications of nanotechnology in drug delivery to the central nervous system

In recent years, the researchers and drug designers have given growing attention to new nanotechnology strategies to improve drug delivery to the central nervous system (CNS). Nanotechnology has a great potential to affect the treatment of neurological disorders, mainly Alzheimer's disease, Parkinson's disease, brain tumors, and stroke. With regard to neurodegeneration, several studies showed that nanomaterials have been successfully used for the treatments of CNS disorders. In this regard, nanocarriers have facilitated the targeted delivery of chemotherapeutics resulting in the efficient inhibition of disease progression in malignant brain tumors. Therefore, the most efficacious application of nanomaterials is the use of these substances in the treatment of CNS disease that enhances the overall effect of drug and highlights the importance of nano-therapeutics. This study was conducted to review the evidence on the applications of nanotechnology in designing drug delivery systems with the ability to cross through the blood-brain barrier (BBB) in order to transfer the therapeutic agents to the CNS.

A stabilized retro-inverso peptide ligand of transferrin receptor for enhanced liposome-based hepatocellular carcinoma-targeted drug delivery

The application of tumor targeting ligands to the treatment of cancer holds promise for improving efficacy and reducing toxicity. ^LT7 (_L(HAIYPRH)) peptide, a phage display-selected peptide, exhibited high binding affinity to transferrin receptor (TfR) overexpressed on tumor cells. However, its in vivo tumor targeting efficiency was impaired due to enzymatic degradation in blood circulation. To improve the stability and targeting ability, a retro-inverso analogue of ^LT7 peptide, named ^DT7 peptide (_D(HRPYIAH)), was designed for targeted therapy of hepatocellular carcinoma. The result of computer simulation predicted that ^DT7 bound to TfR protein more efficiently than ^LT7, and this prediction was confirmed experimentally by surface plasmon resonance (SPR). Ex vivo stability experiment demonstrated that ^DT7 possessed stronger ability against proteolysis than ^LT7 in fresh mouse serum. We further prepared ^DT7-, ^LT7-, and transferrin (Tf)-modified liposomes (^DT7-LIP, ^LT7-LIP, and Tf-LIP, respectively). ^DT7-LIP showed a significantly stronger in vitro targeting ability than ^LT7-LIP and Tf-LIP under normal condition and simulated biological condition. In addition, the in vitro antitumor effect of DTX-loaded ^DT7-LIP was markedly enhanced in comparison to DTX-loaded ^LT7-LIP and DTX-loaded Tf-LIP. In vivo imaging indicated that ^DT7-LIP had better tumor accumulation than ^LT7-LIP and Tf-LIP. For in vivo antitumor studies, the tumor growth rate of mice treated with DTX-loaded ^DT7-LIP was significantly inhibited compared to that in mice treated with DTX-loaded ^LT7-LIP and DTX-loaded Tf-LIP. Overall, this study verified the potential of the stable ^DT7 peptide in improving the efficacy of docetaxel in the treatment of hepatocellular carcinoma. STATEMENT OF SIGNIFICANCE: A phage display library-selected ^LT7 (_L(HAIYPRH)) peptide exhibited high affinity to transferrin receptor (TfR). However, its bioactivity was impaired in vivo as L-peptides are susceptible to degradation by proteolytic enzymes. Here, we designed a retro-inverso peptide ^DT7(_D(HRPYIAH)) and demonstrated its increased serum stability and higher binding affinity to TfR. A stabilized targeted drug delivery system was further constructed by modified ^DT7 peptide on the surface of liposomes. The data indicated that ^DT7 peptide-modified liposomes exhibited higher targeting ability in vitro and in vivo. More importantly, ^DT7-modified liposomes demonstrated positive preclinical significance in enhancing the therapeutic effects against hepatocellular carcinoma.

Overcoming the Blood-Brain Barrier: The Role of Nanomaterials in Treating Neurological Diseases

Therapies directed toward the central nervous system remain difficult to translate into improved clinical outcomes. This is largely due to the blood-brain barrier (BBB), arguably the most tightly regulated interface in the human body, which routinely excludes most therapeutics. Advances in the engineering of nanomaterials and their application in biomedicine (i.e., nanomedicine) are enabling new strategies that have the potential to help improve our understanding and treatment of neurological diseases. Herein, the various mechanisms by which therapeutics can be delivered to the brain are examined and key challenges facing translation of this research from benchtop to bedside are highlighted. Following a contextual overview of the BBB anatomy and physiology in both healthy and diseased states, relevant therapeutic strategies for bypassing and crossing the BBB are discussed. The focus here is especially on nanomaterial-based drug delivery systems and the potential of these to overcome the biological challenges imposed by the BBB. Finally, disease-targeting strategies and clearance mechanisms are explored. The objective is to provide the diverse range of researchers active in the field (e.g., material scientists, chemists, engineers, neuroscientists, and clinicians) with an easily accessible guide to the key opportunities and challenges currently facing the nanomaterial-mediated treatment of neurological diseases.