Effective intravenous therapy for neurodegenerative disease with a therapeutic enzyme and a peptide that mediates delivery to the brain

Fructose-2,6-bisphosphate restores DNA repair activity of PNKP and ameliorates neurodegenerative symptoms in Huntington's disease

Huntington's disease (HD) and spinocerebellar ataxia type 3 (SCA3) are the two most prevalent polyglutamine (polyQ) neurodegenerative diseases, caused by CAG (encoding glutamine) repeat expansion in the coding region of the huntingtin (HTT) and ataxin-3 (ATXN3) proteins, respectively. We have earlier reported that the activity, but not the protein level, of an essential DNA repair enzyme, polynucleotide kinase 3'-phosphatase (PNKP), is severely abrogated in both HD and SCA3 resulting in accumulation of double-strand breaks in patients' brain genome. While investigating the mechanistic basis for the loss of PNKP activity and accumulation of DNA double-strand breaks leading to neuronal death, we observed that PNKP interacts with the nuclear isoform of 6-phosphofructo-2-kinase fructose-2,6-bisphosphatase 3 (PFKFB3). Depletion of PFKFB3 markedly abrogates PNKP activity without changing its protein level. Notably, the levels of both PFKFB3 and its product fructose-2,6 bisphosphate (F2,6BP), an allosteric modulator of glycolysis, are significantly lower in the nuclear extracts of post-mortem brain tissues of HD and SCA3 patients. Supplementation of F2,6BP restored PNKP activity in the nuclear extracts of patients' brain. Moreover, intracellular delivery of F2,6BP restored both the activity of PNKP and the integrity of transcribed genome in neuronal cells derived from striatum of HD mouse. Importantly, supplementing F2,6BP rescued the HD phenotype in Drosophila, suggesting F2,6BP to serve in vivo as a cofactor for the proper functionality of PNKP and thereby, of brain health. Our results thus provide a compelling rationale for exploring the therapeutic use of F2,6BP and structurally related compounds for treating polyQ diseases.

Advances in therapies for neurological lysosomal storage disorders

Lysosomal Storage Disorders (LSDs) are a diverse group of inherited, monogenic diseases caused by functional defects in specific lysosomal proteins. The lysosome is a cellular organelle that plays a critical role in catabolism of waste products and recycling of macromolecules in the body. Disruption to the normal function of the lysosome can result in the toxic accumulation of storage products, often leading to irreparable cellular damage and organ dysfunction followed by premature death. The majority of LSDs have no curative treatment, with many clinical subtypes presenting in early infancy and childhood. Over two-thirds of LSDs present with progressive neurodegeneration, often in combination with other debilitating peripheral symptoms. Consequently, there is a pressing unmet clinical need to develop new therapeutic interventions to treat these conditions. The blood-brain barrier is a crucial hurdle that needs to be overcome in order to effectively treat the central nervous system (CNS), adding considerable complexity to therapeutic design and delivery. Enzyme replacement therapy (ERT) treatments aimed at either direct injection into the brain, or using blood-brain barrier constructs are discussed, alongside more conventional substrate reduction and other drug-related therapies. Other promising strategies developed in recent years, include gene therapy technologies specifically tailored for more effectively targeting treatment to the CNS. Here, we discuss the most recent advances in CNS-targeted treatments for neurological LSDs with a particular emphasis on gene therapy-based modalities, such as Adeno-Associated Virus and haematopoietic stem cell gene therapy approaches that encouragingly, at the time of writing are being evaluated in LSD clinical trials in increasing numbers. If safety, efficacy and improved quality of life can be demonstrated, these therapies have the potential to be the new standard of care treatments for LSD patients.

A mouse mutant deficient in both neuronal ceroid lipofuscinosis-associated proteins CLN3 and TPP1

Late-infantile neuronal ceroid lipofuscinosis (LINCL) and juvenile neuronal ceroid lipofuscinosis (JNCL) are inherited neurodegenerative diseases caused by mutations in the genes encoding lysosomal proteins tripeptidyl peptidase 1 (TPP1) and CLN3 protein, respectively. TPP1 is well-understood and, aided by animal models that accurately recapitulate the human disease, enzyme replacement therapy has been approved and other promising therapies are emerging. In contrast, there are no effective treatments for JNCL, partly because the function of the CLN3 protein remains unknown but also because animal models have attenuated disease and lack robust survival phenotypes. Mouse models for LINCL and JNCL, with mutations in Tpp1 and Cln3, respectively, have been thoroughly characterized but the phenotype of a double Cln3/Tpp1 mutant remains unknown. We created this double mutant and find that its phenotype is essentially indistinguishable from the single Tpp1-/- mutant in terms of survival and brain pathology. Analysis of brain proteomic changes in the single Tpp1-/- and double Cln3-/- ;Tpp1-/- mutants indicates largely overlapping sets of altered proteins and reinforces earlier studies that highlight GPNMB, LYZ2, and SERPINA3 as promising biomarker candidates in LINCL while several lysosomal proteins including SMPD1 and NPC1 appear to be altered in the Cln3-/- animals. An unexpected finding was that Tpp1 heterozygosity significantly decreased lifespan of the Cln3-/- mouse. The truncated survival of this mouse model makes it potentially useful in developing therapies for JNCL using survival as an endpoint. In addition, this model may also provide insights into CLN3 protein function and its potential functional interactions with TPP1.

Targeting the central nervous system in lysosomal storage diseases: Strategies to deliver therapeutics across the blood-brain barrier

Lysosomal storage diseases (LSDs) are multisystem inherited metabolic disorders caused by dysfunctional lysosomal activity, resulting in the accumulation of undegraded macromolecules in a variety of organs/tissues, including the central nervous system (CNS). Treatments include enzyme replacement therapy, stem/progenitor cell transplantation, and in vivo gene therapy. However, these treatments are not fully effective in treating the CNS as neither enzymes, stem cells, nor viral vectors efficiently cross the blood-brain barrier. Here, we review the latest advancements in improving delivery of different therapeutic agents to the CNS and comment upon outstanding questions in the field of neurological LSDs.

Elevated levels of tripeptidyl peptidase 1 do not ameliorate pathogenesis in a mouse model of Alzheimer disease

One potential therapeutic strategy for Alzheimer disease (AD) is to promote degradation of amyloid beta (Aβ) and we previously demonstrated that the lysosomal protease tripeptidyl peptidase 1 (TPP1) can degrade Aβ fibrils in vitro. In this study, we tested the hypothesis that increasing levels of TPP1 might promote degradation of Aβ under physiological conditions, slowing or preventing its accumulation in the brain with subsequent therapeutic benefits. We used 2 approaches to increase TPP1 activity in the brain of J20 mice, an AD model that accumulates Aβ and exhibits cognitive defects: transgenic overexpression of TPP1 in the brain and a pharmacological approach employing administration of recombinant TPP1. While we clearly observed the expected AD phenotype of the J20 mice based on pathology and measurement of behavioral and cognitive defects, we found that elevation of TPP1 activity by either experimental approach failed to have any measurable beneficial effect on disease phenotype.

Clinical Development of Cell Therapies to Halt Lysosomal Storage Diseases: Results and Lessons Learned

Although cross-correction was discovered more than 50 years ago, and held the promise of drastically improving disease management, still no cure exists for lysosomal storage diseases (LSDs). Cell therapies hold the potential to halt disease progression: either a subset of autologous cells can be ex vivo/ in vivo transfected with the functional gene or allogenic wild type stem cells can be transplanted. However, majority of cell-based attempts have been ineffective, due to the difficulties in reversing neuronal symptomatology, in finding appropriate gene transfection approaches, in inducing immune tolerance, reducing the risk of graft versus host disease (GVHD) when allogenic cells are used and that of immune response when engineered viruses are administered, coupled with a limited secretion and uptake of some enzymes. In the last decade, due to advances in our understanding of lysosomal biology and mechanisms of cross-correction, coupled with progresses in gene therapy, ongoing pre-clinical and clinical investigations have remarkably increased. Even gene editing approaches are currently under clinical experimentation. This review proposes to critically discuss and compare trends and advances in cell-based and gene therapy for LSDs. Systemic gene delivery and transplantation of allogenic stem cells will be initially discussed, whereas proposed brain targeting methods will be then critically outlined.

Designing peptide nanoparticles for efficient brain delivery

The targeted delivery of therapeutic compounds to the brain is arguably the most significant open problem in drug delivery today. Nanoparticles (NPs) based on peptides and designed using the emerging principles of molecular engineering show enormous promise in overcoming many of the barriers to brain delivery faced by NPs made of more traditional materials. However, shortcomings in our understanding of peptide self-assembly and blood-brain barrier (BBB) transport mechanisms pose significant obstacles to progress in this area. In this review, we discuss recent work in engineering peptide nanocarriers for the delivery of therapeutic compounds to the brain: from synthesis, to self-assembly, to in vivo studies, as well as discussing in detail the biological hurdles that a nanoparticle must overcome to reach the brain.

Therapeutic approaches targeting Apolipoprotein E function in Alzheimer's disease

One of the primary genetic risk factors for Alzheimer’s disease (AD) is the presence of the Ɛ4 allele of apolipoprotein E (APOE). APOE is a polymorphic lipoprotein that is a major cholesterol carrier in the brain. It is also involved in various cellular functions such as neuronal signaling, neuroinflammation and glucose metabolism. Humans predominantly possess three different allelic variants of APOE, termed E2, E3, and E4, with the E3 allele being the most common. The presence of the E4 allele is associated with increased risk of AD whereas E2 reduces the risk. To understand the molecular mechanisms that underlie APOE-related genetic risk, considerable effort has been devoted towards developing cellular and animal models. Data from these models indicate that APOE4 exacerbates amyloid β plaque burden in a dose-dependent manner. and may also enhance tau pathogenesis in an isoform-dependent manner. Other studies have suggested APOE4 increases the risk of AD by mechanisms that are distinct from modulation of Aβ or tau pathology. Further, whether plasma APOE, by influencing systemic metabolic pathways, can also possibly alter CNS function indirectly is not complete;y understood. Collectively, the available studies suggest that APOE may impact multiple signaling pathways and thus investigators have sought therapeutics that would disrupt pathological functions of APOE while preserving or enhancing beneficial functions. This review will highlight some of the therapeutic strategies that are currently being pursued to target APOE4 towards preventing or treating AD and we will discuss additional strategies that holds promise for the future.

Analysis of Brain and Cerebrospinal Fluid from Mouse Models of the Three Major Forms of Neuronal Ceroid Lipofuscinosis Reveals Changes in the Lysosomal Proteome

Treatments are emerging for the neuronal ceroid lipofuscinoses (NCLs), a group of similar but genetically distinct lysosomal storage diseases. Clinical ratings scales measure long-term disease progression and response to treatment but clinically useful biomarkers have yet to be identified in these diseases. We have conducted proteomic analyses of brain and cerebrospinal fluid (CSF) from mouse models of the most frequently diagnosed NCL diseases: CLN1 (infantile NCL), CLN2 (classical late infantile NCL) and CLN3 (juvenile NCL). Samples were obtained at different stages of disease progression and proteins quantified using isobaric labeling. In total, 8303 and 4905 proteins were identified from brain and CSF, respectively. We also conduced label-free analyses of brain proteins that contained the mannose 6-phosphate lysosomal targeting modification. In general, we detect few changes at presymptomatic timepoints but later in disease, we detect multiple proteins whose expression is significantly altered in both brain and CSF of CLN1 and CLN2 animals. Many of these proteins are lysosomal in origin or are markers of neuroinflammation, potentially providing clues to underlying pathogenesis and providing promising candidates for further validation.

TPP1 Delivery to Lysosomes with Extracellular Vesicles and their Enhanced Brain Distribution in the Animal Model of Batten Disease

Extracellular vesicles (EVs) are promising natural nanocarriers for delivery of various types of therapeutics. Earlier engineered EV-based formulations for neurodegenerative diseases and cancer are reported. Herein, the use of macrophage-derived EVs for brain delivery of a soluble lysosomal enzyme tripeptidyl peptidase-1, TPP1, to treat a lysosomal storage disorder, Neuronal Ceroid Lipofuscinoses 2 (CLN2) or Batten disease, is investigated. TPP1 is loaded into EVs using two methods: i) transfection of parental EV-producing macrophages with TPP1-encoding plasmid DNA (pDNA) or ii) incorporation therapeutic protein TPP1 into naive empty EVs. For the former approach, EVs released by pretransfected macrophages contain the active enzyme and TPP1-encoding pDNA. To achieve high loading efficiency by the latter approach, sonication or permeabilization of EV membranes with saponin is utilized. Both methods provide proficient incorporation of functional TPP1 into EVs (EV-TPP1). EVs significantly increase stability of TPP1 against protease degradation and provide efficient TPP1 delivery to target cells in in vitro model of CLN2. The majority of EV-TPP1 (≈70%) is delivered to target organelles, lysosomes. Finally, a robust brain accumulation of EV carriers and increased lifespan is recorded in late-infantile neuronal ceroid lipofuscinosis (LINCL) mouse model following intraperitoneal administration of EV-TPP1.

The inhibition of acetylcholinesterase by a brain-targeting polylysine-ApoE peptide: biochemical and structural characterizations

The in-trans delivery of protein therapeutics across the blood-brain barrier by K16ApoE peptide carrier has been demonstrated to improve the neurological symptoms and increase the life-span of late-infantile neuronal ceroid lipofuscinosis (LINCL) mice. However, acute toxicity of K16ApoE was observed in LINCL mice resulting in a narrow therapeutic index, limiting the potential of translating the K16ApoE into a viable drug delivery system. This study aims to unravel the toxic mechanism of action. We hypothesized that the toxic response towards the peptide was induced by inhibition of acetylcholinesterase (AChE) activity at neuro-muscular junction. Here, results from the dose-response study suggested that AChE activity was inhibited by K16ApoE at either low or high doses but not at the mid-dose where a significant increase in AChE activity was observed. Meanwhile, molecular docking simulations showed that the N-terminus of K16ApoE is capable of binding to the active site gorge of AChE. In addition to a favorable spatial orientation, this docking pose also revealed strong surface charge interactions which may account for the observed inhibitory effect. While statistical analysis of the dose response and survival ratio suggested that AChE is not the primary mechanism of action for the acute toxicity of K16ApoE, both biochemical evidence and structural analysis have assigned indirect but critical roles for AChE in the overall toxicity mechanism of this peptide carrier.

Modulators of IgG penetration through the blood-brain barrier: Implications for Alzheimer's disease immunotherapy

This review serves to highlight approaches that may improve the access of antibody drugs to regions of the brain affected by Alzheimer's Disease. While previous antibody drugs have been unsuccessful in treating Alzheimer's disease, recent work demonstrates that Alzheimer's pathology can be modified if these drugs can penetrate the brain parenchyma with greater efficacy. Research in antibody blood-brain barrier drug delivery predominantly follows one of three distinct directions: (1) enhancing influx with reduced antibody size, addition of Trojan horse modules, or blood-brain barrier disruption; (2) modulating trancytotic equilibrium and/or kinetics of the neonatal Fc Receptor; and (3) manipulation of antibody glycan carbohydrate composition. In addition to these topics, recent studies are discussed that reveal a role of glycan sialic acid in suppressing antibody efflux from the brain.

Blood-brain barrier shuttle peptides: an emerging paradigm for brain delivery

Brain delivery is one of the major challenges in drug development because of the high number of patients suffering from neural diseases and the low efficiency of the treatments available. Although the blood-brain barrier (BBB) prevents most drugs from reaching their targets, molecular vectors - known as BBB shuttles - offer great promise to safely overcome this formidable obstacle. In recent years, peptide shuttles have received growing attention because of their lower cost, reduced immunogenicity, and higher chemical versatility than traditional Trojan horse antibodies and other proteins.

Guanidinylated Neomycin Conjugation Enhances Intranasal Enzyme Replacement in the Brain

Iduronidase (IDUA)-deficient mice accumulate glycosaminoglycans in cells and tissues and exhibit many of the same neuropathological symptoms of patients suffering from Mucopolysaccharidosis I. Intravenous enzyme-replacement therapy for Mucopolysaccharidosis I ameliorates glycosaminoglycan storage and many of the somatic aspects of the disease but fails to treat neurological symptoms due to poor transport across the blood-brain barrier. In this study, we examined the delivery of IDUA conjugated to guanidinoneomycin (GNeo), a molecular transporter. GNeo-IDUA and IDUA injected intravenously resulted in reduced hepatic glycosaminoglycan accumulation but had no effect in the brain due to fast clearance from the circulation. In contrast, intranasally administered GNeo-IDUA entered the brain rapidly. Repetitive intranasal treatment with GNeo-IDUA reduced glycosaminoglycan storage, lysosome size and number, and neurodegenerative astrogliosis in the olfactory bulb and primary somatosensory cortex, whereas IDUA was less effective. The enhanced efficacy of GNeo-IDUA was not the result of increased nose-to-brain delivery or enzyme stability, but rather due to more efficient uptake into neurons and astrocytes. GNeo conjugation also enhanced glycosaminoglycan clearance by intranasally delivered sulfamidase to the brain of sulfamidase-deficient mice, a model of Mucopolysaccharidosis IIIA. These findings suggest the general utility of the guanidinoglycoside-based delivery system for restoring missing lysosomal enzymes in the brain.

Proteomic Analysis of Brain and Cerebrospinal Fluid from the Three Major Forms of Neuronal Ceroid Lipofuscinosis Reveals Potential Biomarkers

Clinical trials have been conducted for the neuronal ceroid lipofuscinoses (NCLs), a group of neurodegenerative lysosomal diseases that primarily affect children. Whereas clinical rating systems will evaluate long-term efficacy, biomarkers to measure short-term response to treatment would be extremely valuable. To identify candidate biomarkers, we analyzed autopsy brain and matching CSF samples from controls and three genetically distinct NCLs due to deficiencies in palmitoyl protein thioesterase 1 (CLN1 disease), tripeptidyl peptidase 1 (CLN2 disease), and CLN3 protein (CLN3 disease). Proteomic and biochemical methods were used to analyze lysosomal proteins, and, in general, we find that changes in protein expression compared with control were most similar between CLN2 disease and CLN3 disease. This is consistent with previous observations of biochemical similarities between these diseases. We also conducted unbiased proteomic analyses of CSF and brain using isobaric labeling/quantitative mass spectrometry. Significant alterations in protein expression were identified in each NCL, including reduced STXBP1 in CLN1 disease brain. Given the confounding variable of post-mortem changes, additional validation is required, but this study provides a useful starting set of candidate NCL biomarkers for further evaluation.

A Basic ApoE-Based Peptide Mediator to Deliver Proteins across the Blood-Brain Barrier: Long-Term Efficacy, Toxicity, and Mechanism

We have investigated delivery of protein therapeutics from the bloodstream into the brain using a mouse model of late-infantile neuronal ceroid lipofuscinosis (LINCL), a lysosomal disease due to deficiencies in tripeptidyl peptidase 1 (TPP1). Supraphysiological levels of TPP1 are delivered to the mouse brain by acute intravenous injection when co-administered with K16ApoE, a peptide that in trans mediates passage across the blood-brain barrier (BBB). Chronic treatment of LINCL mice with TPP1 and K16ApoE extended the lifespan from 126 to >294 days, diminished pathology, and slowed locomotor dysfunction. K16ApoE enhanced uptake of a fixable biotin tracer by brain endothelial cells in a dose-dependent manner, suggesting that its mechanism involves stimulation of endocytosis. Pharmacokinetic experiments indicated that K16ApoE functions without disrupting the BBB, with minimal effects on overall clearance or uptake by the liver and kidney. K16ApoE has a narrow therapeutic index, with toxicity manifested as lethargy and/or death in mice. To address this, we evaluated variant peptides but found that efficacy and toxicity are associated, suggesting that desired and adverse effects are mechanistically related. Toxicity currently precludes direct clinical application of peptide-mediated delivery in its present form but it remains a useful approach to proof-of-principle studies for biologic therapies to the brain in animal models.

Hematopoietic Stem Cell Gene Therapy for Storage Disease: Current and New Indications

Lysosomal storage disorders (LSDs) are a broad class of monogenic diseases with an overall incidence of 1:7,000 newborns, due to the defective activity of one or more lysosomal hydrolases or related proteins resulting in storage of un-degraded substrates in the lysosomes. The over 40 different known LSDs share a life-threatening nature, but they are present with extremely variable clinical manifestations, determined by the characteristics and tissue distribution of the material accumulating due to the lysosomal dysfunction. The majority of LSDs lack a curative treatment. This is particularly true for LSDs severely affecting the CNS. Based on current preclinical and clinical evidences, among other treatment modalities, hematopoietic stem cell gene therapy could potentially result in robust therapeutic benefit for LSD patients, with particular indication for those characterized by severe brain damage. Optimization of current approaches and technology, as well as implementation of clinical trials for novel indications, and prolonged and more extensive follow-up of the already treated patients will allow translating this promise into new medicinal products.

Chronic Enzyme Replacement to the Brain of a Late Infantile Neuronal Ceroid Lipofuscinosis Mouse Has Differential Effects on Phenotypes of Disease

Late infantile neuronal ceroid lipofuscinosis (LINCL) is a fatal inherited neurodegenerative disease caused by loss of lysosomal protease tripeptidyl peptidase 1 (TPP1). We have investigated the effects of chronic intrathecal (IT) administration using enzyme replacement therapy (ERT) to the brain of an LINCL mouse model, in which locomotor function declines dramatically prior to early death. Median lifespan was significantly extended from 126 days to >259 days when chronic IT treatment was initiated before the onset of disease. While treated animals lived longer and showed little sign of locomotor dysfunction as measured by stride length, some or all (depending on regimen) still died prematurely. One explanation is that cerebrospinal fluid (CSF)-mediated delivery may not deliver TPP1 to all brain regions. Morphological studies support this, showing delivery of TPP1 to ventral, but not deeper and dorsal regions. When IT treatment is initiated in severely affected LINCL mice, lifespan was extended modestly in most but dramatically extended in approximately one-third of the cohort. Treatment improved locomotor function in these severely compromised animals after it had declined to the point at which animals normally die. This indicates that some pathology in LINCL is reversible and does not simply reflect neuronal death.

Drug delivery in overcoming the blood-brain barrier: role of nasal mucosal grafting

The blood-brain barrier (BBB) plays a fundamental role in protecting and maintaining the homeostasis of the brain. For this reason, drug delivery to the brain is much more difficult than that to other compartments of the body. In order to bypass or cross the BBB, many strategies have been developed: invasive techniques, such as temporary disruption of the BBB or direct intraventricular and intracerebral administration of the drug, as well as noninvasive techniques. Preliminary results, reported in the large number of studies on the potential strategies for brain delivery, are encouraging, but it is far too early to draw any conclusion about the actual use of these therapeutic approaches. Among the most recent, but still pioneering, approaches related to the nasal mucosa properties, the permeabilization of the BBB via nasal mucosal engrafting can offer new potential opportunities. It should be emphasized that this surgical procedure is quite invasive, but the implication for patient outcome needs to be compared to the gold standard of direct intracranial injection, and evaluated whilst keeping in mind that central nervous system diseases and lysosomal storage diseases are chronic and severely debilitating and that up to now no therapy seems to be completely successful.

Ten plus one challenges in diseases of the lysosomal system

The advent of the first effective specific therapy for a lysosomal storage disease (LSDs), Gaucher disease type 1, by Roscoe O. Brady was foundational for development of additional treatments for this group of rare diseases. The past 26years, since the approval of enzyme therapy for Gaucher disease type 1, have witnessed a burgeoning understanding of LSDs at genetic, molecular, biochemical, cell biologic, and clinical levels. Simultaneously, this expansion of knowledge has exposed our incomplete understanding of the individual pathophysiologies of LSDs as well as difficult challenges for improvement in therapy and therapeutic outcomes for afflicted individuals. Here, 10 such challenges/problems representing major impediments, which need to be overcome, to move forward toward the goals of more effective and complete therapies for these devastating diseases.

Catalase-Laden Microdevices for Cell-Mediated Enzyme Delivery

Enzymes have been used to treat various human diseases and traumas. However, the therapeutic utility of free enzymes is impeded by their short circulation time, lack of targeting ability, immunogenicity, and inability to cross biological barriers. Cell-mediated drug delivery approach offers the unique capability to overcome these limitations, but the traditional cell-mediated enzyme delivery techniques suffer from drawbacks such as risk of intracellular degradation of and low loading capacity for the payload enzyme. This article presents the development of a novel cell-mediated enzyme delivery technique featuring the use of micrometer-sized disk-shaped particles termed microdevices. The microdevices are fabricated by layer-by-layer assembly and soft lithography with catalase being used as a model therapeutic enzyme. The amount of catalase in the microdevices can be controlled with the number of catalase layers. Catalase in the microdevices is catalytically active, and active catalase is slowly released from the microdevices. Moreover, cell-microdevice complexes are produced by attaching the catalase-laden microdevices to the external surface of both K562 cells and mouse embryonic stem cells. This technique is potentially applicable to other enzymes and cells and promises to be clinically useful.

Quantum dots and potential therapy for Krabbe's disease

Enzyme replacement therapy and substrate reduction therapy have proved useful in reversing many pathological consequences of many nonneural lysosomal storage diseases but have not yet reversed pathology or influenced disease outcome in Krabbe's disease (KD). This Review discusses the relative merits of stem cell therapy, molecular chaperone therapy, gene therapy, substrate reduction therapy, enzyme replacement therapy, and combination therapy. Given the limitations of these approaches, this Review introduces the idea of using tiny, 6-nm, intensely fluorescent quantum dots (QDs) to deliver a cell-penetrating peptide and 6 histidine residue-tagged β-D-galactocerebrosidase across the blood-brain barrier. We can therefore follow the fate of injected material and ensure that all targets are reached and that accumulated material is degraded. Uptake of lysosomal hydrolases is a complex process, and the cell-penetrating peptide JB577 is uniquely able to promote endosomal egress of the QD cargo. This Review further shows that uptake may depend on the charge of the coating of the QD, specifically, that negative charge directs the cargo to neurons. Because KD involves primarily glia, specifically oligodendroglia, we experiment with many coatings and discover a coating (polyethylene glycol 600 amino) that has a positive charge and targets oligodendrocytes. A similar effect is achieved by treating with chondroitinase ABC to degrade the extracellular matrix, indicating that enzyme replacement has several hurdles to overcome before it can become a routine CNS therapy. © 2016 Wiley Periodicals, Inc.

MYBPC1, an Emerging Myopathic Gene: What We Know and What We Need to Learn

Myosin Binding Protein-C (MyBP-C) comprises a family of accessory proteins that includes the cardiac, slow skeletal, and fast skeletal isoforms. The three isoforms share structural and sequence homology, and localize at the C-zone of the sarcomeric A-band where they interact with thick and thin filaments to regulate the cycling of actomyosin crossbridges. The cardiac isoform, encoded by MYBPC3, has been extensively studied over the last several decades due to its high mutational rate in congenital hypertrophic and dilated cardiomyopathy. It is only recently, however, that the MYBPC1 gene encoding the slow skeletal isoform (sMyBP-C) has gained attention. Accordingly, during the last 5 years it has been shown that MYBPC1 undergoes extensive exon shuffling resulting in the generation of multiple slow variants, which are co-expressed in different combinations and amounts in both slow and fast skeletal muscles. The sMyBP-C variants are subjected to PKA- and PKC-mediated phosphorylation in constitutive and alternatively spliced sites. More importantly, missense, and nonsense mutations in MYBPC1 have been directly linked with the development of severe and lethal forms of distal arthrogryposis myopathy and muscle tremors. Currently, there is no mammalian animal model of sMyBP-C, but new technologies including CRISPR/Cas9 and xenografting of human biopsies into immunodeficient mice could provide unique ways to study the regulation and roles of sMyBP-C in health and disease.

Moving towards effective therapeutic strategies for Neuronal Ceroid Lipofuscinosis

The Neuronal Ceroid Lipofuscinoses (NCLs) are a family of autosomal recessive neurodegenerative disorders that annually affect 1:100,000 live births worldwide. This family of diseases results from mutations in one of 14 different genes that share common clinical and pathological etiologies. Clinically, the diseases are subcategorized into infantile, late-infantile, juvenile and adult forms based on their age of onset. Though the disease phenotypes may vary in their age and order of presentation, all typically include progressive visual deterioration and blindness, cognitive impairment, motor deficits and seizures. Pathological hallmarks of NCLs include the accumulation of storage material or ceroid in the lysosome, progressive neuronal degeneration and massive glial activation. Advances have been made in genetic diagnosis and counseling for families. However, comprehensive treatment programs that delay or halt disease progression have been elusive. Current disease management is primarily targeted at controlling the symptoms rather than "curing" the disease. Recognizing the growing need for transparency and synergistic efforts to move the field forward, this review will provide an overview of the therapeutic approaches currently being pursued in preclinical and clinical trials to treat different forms of NCL as well as provide insight to novel therapeutic approaches in development for the NCLs.

Protease-resistant modified human β-hexosaminidase B ameliorates symptoms in GM2 gangliosidosis model

GM2 gangliosidoses, including Tay-Sachs and Sandhoff diseases, are neurodegenerative lysosomal storage diseases that are caused by deficiency of β-hexosaminidase A, which comprises an αβ heterodimer. There are no effective treatments for these diseases; however, various strategies aimed at restoring β-hexosaminidase A have been explored. Here, we produced a modified human hexosaminidase subunit β (HexB), which we have termed mod2B, composed of homodimeric β subunits that contain amino acid sequences from the α subunit that confer GM2 ganglioside-degrading activity and protease resistance. We also developed fluorescent probes that allow visualization of endocytosis of mod2B via mannose 6-phosphate receptors and delivery of mod2B to lysosomes in GM2 gangliosidosis models. In addition, we applied imaging mass spectrometry to monitor efficacy of this approach in Sandhoff disease model mice. Following i.c.v. administration, mod2B was widely distributed and reduced accumulation of GM2, asialo-GM2, and bis(monoacylglycero)phosphate in brain regions including the hypothalamus, hippocampus, and cerebellum. Moreover, mod2B administration markedly improved motor dysfunction and a prolonged lifespan in Sandhoff disease mice. Together, the results of our study indicate that mod2B has potential for intracerebrospinal fluid enzyme replacement therapy and should be further explored as a gene therapy for GM2 gangliosidoses.

From blood-brain barrier to blood-brain interface: new opportunities for CNS drug delivery

One of the biggest challenges in the development of therapeutics for central nervous system (CNS) disorders is achieving sufficient blood-brain barrier (BBB) penetration. Research in the past few decades has revealed that the BBB is not only a substantial barrier for drug delivery to the CNS but also a complex, dynamic interface that adapts to the needs of the CNS, responds to physiological changes, and is affected by and can even promote disease. This complexity confounds simple strategies for drug delivery to the CNS, but provides a wealth of opportunities and approaches for drug development. Here, I review some of the most important areas that have recently redefined the BBB and discuss how they can be applied to the development of CNS therapeutics.

Lysosomal storage diseases: from pathophysiology to therapy

Lysosomal storage diseases are a group of rare, inborn, metabolic errors characterized by deficiencies in normal lysosomal function and by intralysosomal accumulation of undegraded substrates. The past 25 years have been characterized by remarkable progress in the treatment of these diseases and by the development of multiple therapeutic approaches. These approaches include strategies aimed at increasing the residual activity of a missing enzyme (enzyme replacement therapy, hematopoietic stem cell transplantation, pharmacological chaperone therapy and gene therapy) and approaches based on reducing the flux of substrates to lysosomes. As knowledge has improved about the pathophysiology of lysosomal storage diseases, novel targets for therapy have been identified, and innovative treatment approaches are being developed.

Towards a new understanding of NCL pathogenesis

The Neuronal Ceroid Lipofuscinoses (NCLs, Batten disease) are a group of inherited neurodegenerative disorders that have been traditionally grouped together on the basis of certain shared clinical and pathological features. However, as the number of genes that appear to cause new forms of NCL continues to grow, it is timely to reassess our understanding of the pathogenesis of these disorders and what groups them together. The various NCL subtypes do indeed share features of a build-up of autofluorescent storage material, progressive neuron loss and activation of the innate immune system. The characterisation of animal models has highlighted the selective nature of neuron loss and its intimate relationship with glial activation, rather than the generalised build-up of storage material. More recent data provide evidence for the pathway-dependent nature of pathology, the contribution of glial dysfunction, and the involvement of new brain regions previously thought to be unaffected, and it is becoming apparent that pathology extends beyond the brain. These data have important implications, not just for therapy, but also for our understanding of these disorders. However, looking beneath these broadly similar pathological themes evidence emerges for marked differences in the nature and extent of these events in different forms of NCL. Indeed, given the widely different nature of the mutated gene products it is perhaps more surprising that these disorders resemble each other as much as they do. Such data raise the question whether we should rethink the collective grouping of these gene deficiencies together, or whether it would be better to consider them as separate entities. This article is part of a Special Issue entitled: Current Research on the Neuronal Ceroid Lipofuscinoses (Batten Disease).

The progressive myoclonic epilepsies

Progressive myoclonic epilepsies are a group of disorders characterised by a relentlessly progressive disease course until death; treatment-resistant epilepsy is just a part of the phenotype. This umbrella term encompasses many diverse conditions, ranging from Lafora body disease to Gaucher's disease. These diseases as a group are important because of a generally poor response to antiepileptic medication, an overall poor prognosis and inheritance risks to siblings or offspring (where there is a proven genetic cause). A correct diagnosis also helps patients and their families to accept and understand the nature of their disease, even if incurable. Here, we discuss the phenotypes of these disorders and summarise the relevant specific investigations to identify the underlying cause.

Lysosomal storage disease: gene therapy on both sides of the blood-brain barrier

Most lysosomal storage disorders affect the nervous system as well as other tissues and organs of the body. Previously, the complexities of these diseases, particularly in treating neurologic abnormalities, were too great to surmount. However, based on recent developments there are realistic expectations that effective therapies are coming soon. Gene therapy offers the possibility of affordable, comprehensive treatment associated with these diseases currently not provided by standards of care. With a focus on correction of neurologic disease by systemic gene therapy of mucopolysaccharidoses types I and IIIA, we review some of the major recent advances in viral and non-viral vectors, methods of their delivery and strategies leading to correction of both the nervous and somatic tissues as well as evaluation of functional correction of neurologic manifestations in animal models. We discuss two questions: what systemic gene therapy strategies work best for correction of both somatic and neurologic abnormalities in a lysosomal storage disorder and is there evidence that targeting peripheral tissues (e.g., in the liver) has a future for ameliorating neurologic disease in patients?

Bacterial proteins and peptides in cancer therapy: today and tomorrow

Cancer is one of the most deadly diseases worldwide. In the last three decades many efforts have been made focused on understanding how cancer grows and responds to drugs. The dominant drug-development paradigm has been the "one drug, one target." Based on that, the two main targeted therapies developed to combat cancer include the use of tyrosine kinase inhibitors and monoclonal antibodies. Development of drug resistance and side effects represent the major limiting factors for their use in cancer treatment. Nowadays, a new paradigm for cancer drug discovery is emerging wherein multi-targeted approaches gain ground in cancer therapy. Therefore, to overcome resistance to therapy, it is clear that a new generation of drugs is urgently needed. Here, regarding the concept of multi-targeted therapy, we discuss the challenges of using bacterial proteins and peptides as a new generation of effective anti-cancer drugs.

Peptide carrier-mediated non-covalent delivery of unmodified cisplatin, methotrexate and other agents via intravenous route to the brain

BACKGROUND

Rapid pre-clinical evaluation of chemotherapeutic agents against brain cancers and other neurological disorders remains largely unattained due to the presence of the blood-brain barrier (BBB), which limits transport of most therapeutic compounds to the brain. A synthetic peptide carrier, K16ApoE, was previously developed that enabled transport of target proteins to the brain by mimicking a ligand-receptor system. The peptide carrier was found to generate transient BBB permeability, which was utilized for non-covalent delivery of cisplatin, methotrexate and other compounds to the brain.

APPROACH

Brain delivery of the chemotherapeutics and other agents was achieved either by injecting the carrier peptide and the drugs separately or as a mixture, to the femoral vein. A modification of the method comprised injection of K16ApoE pre-mixed with cetuximab, followed by injection of a 'small-molecule' drug.

PRINCIPAL FINDINGS

Seven-of-seven different small molecules were successfully delivered to the brain via K16ApoE. Depending on the method, brain uptake with K16ApoE was 0.72-1.1% for cisplatin and 0.58-0.92% for methotrexate (34-50-fold and 54-92 fold greater for cisplatin and methotrexate, respectively, with K16ApoE than without). Visually intense brain-uptake of Evans Blue, Light Green SF and Crocein scarlet was also achieved. Direct intracranial injection of EB show locally restricted distribution of the dye in the brain, whereas K16ApoE-mediated intravenous injection of EB resulted in the distribution of the dye throughout the brain. Experiments with insulin suggest that ligand-receptor signaling intrinsic to the BBB provides a natural means for passive transport of some molecules across the BBB.

SIGNIFICANCE

The results suggest that the carrier peptide can non-covalently transport various chemotherapeutic agents to the brain. Thus, the method offers an avenue for pre-clinical evaluation of various small and large therapeutic molecules against brain tumors and other neurological disorders.