Safety and tolerability of putaminal AADC gene therapy for Parkinson disease

Cell reprogramming therapy for Parkinson's disease

Parkinson's disease is typically characterized by the progressive loss of dopaminergic neurons in the substantia nigra pars compacta. Many studies have been performed based on the supplementation of lost dopaminergic neurons to treat Parkinson's disease. The initial strategy for cell replacement therapy used human fetal ventral midbrain and human embryonic stem cells to treat Parkinson's disease, which could substantially alleviate the symptoms of Parkinson's disease in clinical practice. However, ethical issues and tumor formation were limitations of its clinical application. Induced pluripotent stem cells can be acquired without sacrificing human embryos, which eliminates the huge ethical barriers of human stem cell therapy. Another widely considered neuronal regeneration strategy is to directly reprogram fibroblasts and astrocytes into neurons, without the need for intermediate proliferation states, thus avoiding issues of immune rejection and tumor formation. Both induced pluripotent stem cells and direct reprogramming of lineage cells have shown promising results in the treatment of Parkinson's disease. However, there are also ethical concerns and the risk of tumor formation that need to be addressed. This review highlights the current application status of cell reprogramming in the treatment of Parkinson's disease, focusing on the use of induced pluripotent stem cells in cell replacement therapy, including preclinical animal models and progress in clinical research. The review also discusses the advancements in direct reprogramming of lineage cells in the treatment of Parkinson's disease, as well as the controversy surrounding in vivo reprogramming. These findings suggest that cell reprogramming may hold great promise as a potential strategy for treating Parkinson's disease.

From lab bench to hope: a review of gene therapies in clinical trials for Parkinson's disease and challenges

Parkinson's disease (PD) is a chronic neurological disorder that is identified by a characteristic combination of symptoms such as bradykinesia, resting tremor, rigidity, and postural instability. It is the second most common neurodegenerative disease after Alzheimer's disease and is characterized by the progressive loss of dopamine-producing neurons in the brain. Currently, available treatments for PD are symptomatic and do not prevent the disease pathology. There is growing interest in developing disease-modifying therapy that can reduce disease progression and improve patients' quality of life. One of the promising therapeutic approaches under evaluation is gene therapy utilizing a viral vector, adeno-associated virus (AAV), to deliver transgene of interest into the central nervous system (CNS). Preclinical studies in small animals and nonhuman primates model of PD have shown promising results utilizing the gene therapy that express glial cell line-derived neurotrophic factor (GDNF), cerebral dopamine neurotrophic factor (CDNF), aromatic L-amino acid decarboxylase (AADC), and glutamic acid decarboxylase (GAD). This study provides a comprehensive review of the current state of the above-mentioned gene therapies in various phases of clinical trials for PD treatment. We have highlighted the rationale for the gene-therapy approach and the findings from the preclinical and nonhuman primates studies, evaluating the therapeutic effect, dose safety, and tolerability. The challenges associated with gene therapy for heterogeneous neurodegenerative diseases, such as PD, have also been described. In conclusion, the review identifies the ongoing promising gene therapy approaches in clinical trials and provides hope for patients with PD.

Neuroimaging Applications for the Delivery and Monitoring of Gene Therapy for Central Nervous System Diseases

Neurological disease due to single gene defects represents a targetable entity for adeno-associated virus (AAV) mediated gene therapy. The delivery of AAV-mediated gene therapy to the brain is challenging, owing to the presence of the blood-brain barrier. Techniques in gene transfer, such as convection-enhanced intraparenchymal delivery and image-guided delivery to the cerebrospinal fluid (CSF) spaces of the brain has led the field into highly accurate delivery techniques, which provide correction of genetic defects in specific brain regions or more broadly. These techniques commonly use magnetic resonance imaging (MRI), computed tomography (CT), and fluoroscopic guidance. Even more, the neuroimaging changes evaluated by MRI, MR spectroscopy (MRS), diffusion tensor imaging (DTI), and functional MRI (fMRI) can serve as important biomarkers of therapy effect and overall disease progression. Here, we discuss the role of neuroimaging in delivering AAV vectors and monitoring the effect of gene therapy.

Intraparenchymal delivery of adeno-associated virus vectors for the gene therapy of neurological diseases

INTRODUCTION

In gene therapy with adeno-associated virus (AAV) vectors for diseases of the central nervous system, the vectors can be administered into blood vessels, cerebrospinal fluid space, or the brain parenchyma. When gene transfer to a large area of the brain is required, the first two methods are used, but for diseases in which local gene transfer is expected to be effective, vectors are administered directly into the brain parenchyma.

AREAS COVERED

Strategies for intraparenchymal vector delivery in gene therapy for Parkinson's disease, aromatic l-amino acid decarboxylase (AADC) deficiency, and epilepsy are reviewed.

EXPERT OPINION

Stereotactic intraparenchymal injection of AAV vectors allows precise gene delivery to the target site. Although more surgically invasive than intravascular or intrathecal administration, intraparenchymal vector delivery has the advantage of a lower vector dose, and preexisting neutralizing antibodies have little effect on the transduction efficacy. This approach improves motor function in AADC deficiency and led to regulatory approval of an AAV vector for the disease in the EU. Although further validation through clinical studies is needed, direct infusion of viral vectors into the brain parenchyma is expected to be a novel treatment for Parkinson's disease and drug-resistant epilepsy.

Emerging Gene Therapies for Alzheimer's and Parkinson's Diseases: An Overview of Clinical Trials and Promising Candidates

Gene therapy as a disease-modifying therapeutic approach for neurodegenerative diseases, such as Alzheimer's disease (AD) and Parkinson's disease (PD), is a promising avenue. Promising results in the preclinical studies involving rodents and nonhuman primates utilizing gene therapy have led to multiple clinical trials evaluating various genes of interest for AD and PD. In AD, clinical trials are assessing gene therapy involving brain-derived neurotrophic factor (BDNF) and other targets such as apolipoprotein E2 (APOE2) and human telomerase reverse transcriptase (hTERT). In PD, clinical trials are evaluating gene therapy delivering neurotrophic factors, such as glial cell line-derived neurotrophic factor (GDNF). Additionally, gene therapy delivering enzymes aromatic L-amino acid decarboxylase (AADC) and glutamic acid decarboxylase (GAD) are also being evaluated for PD. All these trials primarily utilized adeno-associated virus (AAV) to deliver the above transgene of interest. This review summarizes the current clinical trials involving gene therapy for AD and PD. It also discusses the challenges and opportunities associated with the gene therapy approach in AD and PD and ongoing developments related to increasing the safety and efficacy of the gene therapy for long-term outcomes, which include evaluation of various serotypes and administration routes. This comprehensive review emphasizes translating preclinical findings into clinical trials, further directions, and the potential for this promising therapeutic approach to alleviate neurodegenerative disease.

Adeno-associated virus vector delivery to the brain: Technology advancements and clinical applications

Adeno-associated virus (AAV) vectors have emerged as a promising tool in the development of gene therapies for various neurological diseases, including Alzheimer's disease and Parkinson's disease. However, the blood-brain barrier (BBB) poses a significant challenge to successfully delivering AAV vectors to the brain. Strategies that can overcome the BBB to improve the AAV delivery efficiency to the brain are essential to successful brain-targeted gene therapy. This review provides an overview of existing strategies employed for AAV delivery to the brain, including direct intraparenchymal injection, intra-cerebral spinal fluid injection, intranasal delivery, and intravenous injection of BBB-permeable AAVs. Focused ultrasound has emerged as a promising technology for the noninvasive and spatially targeted delivery of AAV administered by intravenous injection. This review also summarizes each strategy's current preclinical and clinical applications in treating neurological diseases. Moreover, this review includes a detailed discussion of the recent advances in the emerging focused ultrasound-mediated AAV delivery. Understanding the state-of-the-art of these gene delivery approaches is critical for future technology development to fulfill the great promise of AAV in neurological disease treatment.

Immune responses to central nervous system directed adeno-associated virus gene therapy: Does direct CNS delivery make a difference?

Adeno-associated virus (AAV) mediated gene therapy is a leading gene delivery platform with potential to transform the landscape of treatment for neurological disorders. While AAV is deemed non-immunogenic compared to other viral vectors, adverse immune reactions have been observed in the clinic, raising concerns. As the central nervous system (CNS) has a tightly regulated immune system, characterized by a degree of tolerance, it has been considered a unique target for AAV gene therapy. AAV vectors have shown promising results for the treatment of several CNS disorders including Spinal Muscular Atrophy, Giant Axonal Neuropathy, Amyotrophic Lateral Sclerosis, Tay Sachs Disease, Parkinson's Disease, and others, demonstrating safety and success. The Food and Drug Administration (FDA) approval of Zolgensma and European Medicines Agency (EMA) approval of Upstaza, for Spinal Muscular Atrophy (SMA) and Aromatic l-amino acid decarboxylase deficiency (AADC) respectively, represent this success, all while highlighting significant differences in immune responses to AAV, particularly with regards to therapeutic administration route. AAV therapies like Upstaza that are injected directly into the immune-specialized brain have been characterized by mild immune response profiles and minor adverse events, whereas therapies like Zolgensma that are injected systemically demonstrate more robust immune stimulation and off-target toxicities. Despite these contrasting parallels, these therapeutics and others in the clinic have demonstrated clinical benefit for patients, warranting further exploration of immune responses to CNS-directed AAV clinical trials. Thus, in this review, we discuss effects of different routes of AAV administration on eliciting local and peripheral immune responses specifically observed in CNS-targeted trials.

Neurosurgical gene therapy for central nervous system diseases

Viral vector mediated gene therapies for neurodegenerative and neurodevelopmental conditions that require neurosurgical administration continue to expand. We systematically reviewed the National Institutes of Health (NIH) ClinicalTrials.gov database to identify all clinical trials studying in-vivo viral vector mediated gene therapies targeted to the CNS for neurodegenerative and neurodevelopmental diseases. We isolated studies which delivered therapies using neurosurgical approaches: intracisternal, intraventricular, and/or intraparenchymal. Clinical trials primarily registered in international countries were included if they were referenced by an NIH registered clinical trial. We performed a scoping review to identify the preclinical studies that supported each human clinical trial. Key preclinical and clinical data were aggregated to characterize vector capsid design, delivery methods, gene expression profile, and clinical benefit. A total of 64 clinical trials were identified in active, completed, terminated, and long-term follow-up stages. A range of CNS conditions across pediatric and adult populations are being studied with CNS targeted viral vector gene therapy, including Alzheimer's disease, Parkinson's disease, AADC deficiency, sphingolipidoses, mucopolysaccharidoses, neuronal ceroid lipofuscinoses, spinal muscular atrophy, adrenoleukodystrophy, Canavan disease, frontotemporal dementia, Huntington's disease, Rett syndrome, Dravet syndrome, mesial temporal lobe epilepsy, and glutaric acidemia. Adeno-associated viral vectors (AAVs) were utilized by the majority of tested therapies, with vector serotypes, regulatory elements, delivery methods, and vector monitoring varying based on the disease being studied. Intraparenchymal delivery has evolved significantly, with MRI-guided convection-enhanced delivery established as a gold standard method for pioneering novel gene targets.

Stem cell therapeutics and gene therapy for neurologic disorders

Rapid advances in biological knowledge and technological innovation have greatly advanced the fields of stem cell and gene therapies to combat a broad spectrum of neurologic disorders. Researchers are currently exploring a variety of stem cell types (e.g., embryonic, progenitor, induced pluripotent) and various transplantation strategies, each with its own advantages and drawbacks. Similarly, various gene modification techniques (zinc finger, TALENs, CRISPR-Cas9) are employed with various delivery vectors to modify underlying genetic contributors to neurologic disorders. While these two individual fields continue to blaze new trails, it is the combination of these technologies which enables genetically engineered stem cells and vastly increases investigational and therapeutic opportunities. The capability to culture and expand stem cells outside the body, along with their potential to correct genetic abnormalities in patient-derived cells or enhance cells with extra gene products, unleashes the full biological potential for innovative, multifaceted approaches to treat complex neurological disorders. In this review, we provide an overview of stem cell and gene therapies in the context of neurologic disorders, highlighting recent advances and current shortcomings, and discuss prospects for future therapies in clinical settings.

Viral-mediated gene therapy in pediatric neurological disorders

BACKGROUND

Due to the broad application of next-generation sequencing, the molecular diagnosis of genetic disorders in pediatric neurology is no longer an unachievable goal. However, treatments for neurological genetic disorders in children remain primarily symptomatic. On the other hand, with the continuous evolution of therapeutic viral vectors, gene therapy is becoming a clinical reality. From this perspective, we wrote this review to illustrate the current state regarding viral-mediated gene therapy in childhood neurological disorders.

DATA SOURCES

We searched databases, including PubMed and Google Scholar, using the keywords "adenovirus vector," "lentivirus vector," and "AAV" for gene therapy, and "immunoreaction induced by gene therapy vectors," "administration routes of gene therapy vectors," and "gene therapy" with "NCL," "SMA," "DMD," "congenital myopathy," "MPS" "leukodystrophy," or "pediatric metabolic disorders". We also screened the database of ClinicalTrials.gov using the keywords "gene therapy for children" and then filtered the results with the ones aimed at neurological disorders. The time range of the search procedure was from the inception of the databases to the present.

RESULTS

We presented the characteristics of commonly used viral vectors for gene therapy for pediatric neurological disorders and summarized their merits and drawbacks, the administration routes of each vector, the research progress, and the clinical application status of viral-mediated gene therapy on pediatric neurological disorders.

CONCLUSIONS

Viral-mediated gene therapy is on the brink of broad clinical application. Viral-mediated gene therapy will dramatically change the treatment pattern of childhood neurological disorders, and many children with incurable diseases will meet the dawn of a cure. Nevertheless, the vectors must be optimized for better safety and efficacy.

Emerging Pro-neurogenic Therapeutic Strategies for Neurodegenerative Diseases: A Review of Pre-clinical and Clinical Research

The neuroscience community has largely accepted the notion that functional neurons can be generated from neural stem cells in the adult brain, especially in two brain regions: the subventricular zone of the lateral ventricles and the subgranular zone in the dentate gyrus of the hippocampus. However, impaired neurogenesis has been observed in some neurodegenerative diseases, particularly in Alzheimer's, Parkinson's, and Huntington's diseases, and also in Lewy Body dementia. Therefore, restoration of neurogenic function in neurodegenerative diseases emerges as a potential therapeutic strategy to counteract, or at least delay, disease progression. Considering this, the present study summarizes the different neuronal niches, provides a collection of the therapeutic potential of different pro-neurogenic strategies in pre-clinical and clinical research, providing details about their possible modes of action, to guide future research and clinical practice.

Development of AAV-Mediated Gene Therapy Approaches to Treat Skeletal Diseases

Adeno-associated viral (AAV) vectors have emerged as crucial tools in advancing gene therapy for skeletal diseases, offering the potential for sustained expression with low postinfection immunogenicity and pathogenicity. Preclinical studies support both the therapeutic efficacy and safety of these vectors, illustrating the promise of AAV-mediated gene therapy. Emerging technologies and innovations in AAV-mediated gene therapy strategies, such as gene addition, gene replacement, gene silencing, and gene editing, offer new approaches to clinical application. Recently, the increasing preclinical applications of AAV to rare skeletal diseases, such as fibrodysplasia ossificans progressiva (FOP) and osteogenesis imperfecta (OI), and prevalent bone diseases, such as osteoporosis, bone fracture, critical-sized bone defects, and osteoarthritis, have been reported. Despite existing limitations in clinical use, such as high cost and safety, the AAV-mediated gene transfer platform is a promising approach to deliver therapeutic gene(s) to the skeleton to treat skeletal disorders, including those otherwise intractable by other therapeutic approaches. This review provides a comprehensive overview of the therapeutic advancements, challenges, limitations, and solutions within AAV-based gene therapy for prevalent and rare skeletal diseases.

Gene therapy for aromatic L-amino acid decarboxylase deficiency: Requirements for safe application and knowledge-generating follow-up

The autosomal recessive defect of aromatic L-amino acid decarboxylase (AADC) leads to a severe neurological disorder with manifestation in infancy due to a pronounced, combined deficiency of dopamine, serotonin and catecholamines. The success of conventional drug treatment is very limited, especially in patients with a severe phenotype. The development of an intracerebral AAV2-based gene delivery targeting the putamen or substantia nigra started more than 10 years ago. Recently, the putaminally-delivered construct, Eladocagene exuparvovec has been approved by the European Medicines Agency and by the British Medicines and Healthcare products Regulatory Agency. This now available gene therapy provides for the first time also for AADC deficiency (AADCD) a causal therapy, leading this disorder into a new therapeutic era. By using a standardized Delphi approach members of the International Working Group on Neurotransmitter related Disorders (iNTD) developed structural requirements and recommendations for the preparation, management and follow-up of AADC deficiency patients who undergo gene therapy. This statement underlines the necessity of a framework for a quality-assured application of AADCD gene therapy including Eladocagene exuparvovec. Treatment requires prehospital, inpatient and posthospital care by a multidisciplinary team in a specialized and qualified therapy center. Due to lack of data on long-term outcomes and the comparative efficacy of alternative stereotactic procedures and brain target sites, a structured follow-up plan and systematic documentation of outcomes in a suitable, industry-independent registry study are necessary.

Neurodegenerative Etiology of Aromatic L-Amino Acid Decarboxylase Deficiency: a Novel Concept for Expanding Treatment Strategies

Aromatic l-amino acid decarboxylase deficiency (AADC-DY) is caused by one or more mutations in the DDC gene, resulting in the deficit in catecholamines and serotonin neurotransmitters. The disease has limited therapeutic options with relatively poor clinical outcomes. Accumulated evidence suggests the involvement of neurodegenerative mechanisms in the etiology of AADC-DY. In the absence of neurotransmitters' neuroprotective effects, the accumulation and the chronic presence of several neurotoxic metabolites including 4-dihydroxy-L-phenylalanine, 3-methyldopa, and homocysteine, in the brain of subjects with AADC-DY, promote oxidative stress and reduce the cellular antioxidant and methylation capacities, leading to glial activation and mitochondrial dysfunction, culminating to neuronal injury and death. These pathophysiological processes have the potential to hinder the clinical efficacy of treatments aimed at increasing neurotransmitters' synthesis and or function. This review describes in detail the mechanisms involved in AADC-DY neurodegenerative etiology, highlighting the close similarities with those involved in other neurodegenerative diseases. We then offer novel strategies for the treatment of the disease with the objective to either reduce the level of the metabolites or counteract their prooxidant and neurotoxic effects. These treatment modalities used singly or in combination, early in the course of the disease, will minimize neuronal injury, preserving the functional integrity of neurons, hence improving the clinical outcomes of both conventional and unconventional interventions in AADC-DY. These modalities may not be limited to AADC-DY but also to other metabolic disorders where a specific mutation leads to the accumulation of prooxidant and neurotoxic metabolites.

Adeno-associated virus as a delivery vector for gene therapy of human diseases

Adeno-associated virus (AAV) has emerged as a pivotal delivery tool in clinical gene therapy owing to its minimal pathogenicity and ability to establish long-term gene expression in different tissues. Recombinant AAV (rAAV) has been engineered for enhanced specificity and developed as a tool for treating various diseases. However, as rAAV is being more widely used as a therapy, the increased demand has created challenges for the existing manufacturing methods. Seven rAAV-based gene therapy products have received regulatory approval, but there continue to be concerns about safely using high-dose viral therapies in humans, including immune responses and adverse effects such as genotoxicity, hepatotoxicity, thrombotic microangiopathy, and neurotoxicity. In this review, we explore AAV biology with an emphasis on current vector engineering strategies and manufacturing technologies. We discuss how rAAVs are being employed in ongoing clinical trials for ocular, neurological, metabolic, hematological, neuromuscular, and cardiovascular diseases as well as cancers. We outline immune responses triggered by rAAV, address associated side effects, and discuss strategies to mitigate these reactions. We hope that discussing recent advancements and current challenges in the field will be a helpful guide for researchers and clinicians navigating the ever-evolving landscape of rAAV-based gene therapy.

Natural Adeno-Associated Virus Serotypes and Engineered Adeno-Associated Virus Capsid Variants: Tropism Differences and Mechanistic Insights

Today, adeno-associated virus (AAV)-based vectors are arguably the most promising in vivo gene delivery vehicles for durable therapeutic gene expression. Advances in molecular engineering, high-throughput screening platforms, and computational techniques have resulted in a toolbox of capsid variants with enhanced performance over parental serotypes. Despite their considerable promise and emerging clinical success, there are still obstacles hindering their broader use, including limited transduction capabilities, tissue/cell type-specific tropism and penetration into tissues through anatomical barriers, off-target tissue biodistribution, intracellular degradation, immune recognition, and a lack of translatability from preclinical models to clinical settings. Here, we first describe the transduction mechanisms of natural AAV serotypes and explore the current understanding of the systemic and cellular hurdles to efficient transduction. We then outline progress in developing designer AAV capsid variants, highlighting the seminal discoveries of variants which can transduce the central nervous system upon systemic administration, and, to a lesser extent, discuss the targeting of the peripheral nervous system, eye, ear, lung, liver, heart, and skeletal muscle, emphasizing their tissue and cell specificity and translational promise. In particular, we dive deeper into the molecular mechanisms behind their enhanced properties, with a focus on their engagement with host cell receptors previously inaccessible to natural AAV serotypes. Finally, we summarize the main findings of our review and discuss future directions.

Delivery of Adeno-Associated Virus Vectors to the Central Nervous System for Correction of Single Gene Disorders

Genetic disorders of the central nervous system (CNS) comprise a significant portion of disability in both children and adults. Several preclinical animal models have shown effective adeno-associated virus (AAV) mediated gene transfer for either treatment or prevention of autosomal recessive genetic disorders. Owing to the intricacy of the human CNS and the blood-brain barrier, it is difficult to deliver genes, particularly since the expression of any given gene may be required in a particular CNS structure or cell type at a specific time during development. In this review, we analyzed delivery methods for AAV-mediated gene therapy in past and current clinical trials. The delivery routes analyzed were direct intraparenchymal (IP), intracerebroventricular (ICV), intra-cisterna magna (CM), lumbar intrathecal (IT), and intravenous (IV). The results demonstrated that the dose used in these routes varies dramatically. The average total doses used were calculated and were 1.03 × 1013 for IP, 5.00 × 1013 for ICV, 1.26 × 1014 for CM, and 3.14 × 1014 for IT delivery. The dose for IV delivery varies by patient weight and is 1.13 × 1015 IV for a 10 kg infant. Ultimately, the choice of intervention must weigh the risk of an invasive surgical procedure to the toxicity and immune response associated with a high dose vector.

Brain-targeted delivery of neuroprotective survival gene minimizing hematopoietic cell contamination: implications for Parkinson's disease treatment

BACKGROUND

Neurodegenerative diseases, including Parkinson's disease, Amyotropic Lateral Sclerosis (ALS) and Alzheimer's disease, present significant challenges for therapeutic development due to drug delivery restrictions and toxicity concerns. Prevailing strategies often employ adeno-associated viral (AAV) vectors to deliver neuroprotective survival genes directly into the central nervous system (CNS). However, these methods have been limited by triggering immunogenic responses and risk of tumorigenicity, resulting from overexpression of survival genes in peripheral blood mononuclear cells (PBMC), thereby increasing the risk of tumorigenicity in specific immune cells. Thus, by coding selectively suppressive microRNA (miRNA) target sequences in AAV genome, we designed CNS-targeted neuroprotective gene expression vector system without leakage to blood cells.

METHODS

To minimize the potential for transgene contamination in the blood, we designed a CNS-specific AAV system. Our system utilized a self-complementary AAV (scAAV), encoding a quadruple repeated target sequence of the hematopoietic cell-specific miR142-3p at the 3' untranslated region (UTR). As a representative therapeutic survival gene for Parkinson's disease treatment, we integrated DX2, an antagonistic splice variant of the apoptotic gene AIMP2, known to be implicated in Parkinson's disease, into the vector.

RESULTS

This configuration ensured that transgene expression was stringently localized to the CNS, even if the vector found its way into the blood cells. A single injection of scAAV-DX2 demonstrated marked improvement in behavior and motor activity in animal models of Parkinson's disease induced by either Rotenone or 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP). Importantly, comprehensive preclinical data adhering to Good Laboratory Practice (GLP) standards revealed no adverse effects in the treated animals.

CONCLUSIONS

Our CNS-specific vector system, which encodes a survival transgene DX2, signifies a promising avenue for safe gene therapy, avoiding unintended expression of survival gene in blood cells, applicable to various neurodegenerative diseases.

Bi-directional regulation of AIMP2 and its splice variant on PARP-1-dependent neuronal cell death; Therapeutic implication for Parkinson's disease

BACKGROUND

Parthanatos represents a critical molecular aspect of Parkinson's disease, wherein AIMP2 aberrantly activates PARP-1 through direct physical interaction. Although AIMP2 ought to be a therapeutic target for the disease, regrettably, it is deemed undruggable due to its non-enzymatic nature and predominant localization within the tRNA synthetase multi-complex. Instead, AIMP2 possesses an antagonistic splice variant, designated DX2, which counteracts AIMP2-induced apoptosis in the p53 or inflammatory pathway. Consequently, we examined whether DX2 competes with AIMP2 for PARP-1 activation and is therapeutically effective in Parkinson's disease.

METHODS

The binding affinity of AIMP2 and DX2 to PARP-1 was contrasted through immunoprecipitation. The efficacy of DX2 in neuronal cell death was assessed under 6-OHDA and H2O2 in vitro conditions. Additionally, endosomal and exosomal activity of synaptic vesicles was gauged in AIMP2 or DX2 overexpressed hippocampal primary neurons utilizing optical live imaging with VAMP-vGlut1 probes. To ascertain the role of DX2 in vivo, rotenone-induced behavioral alterations were compared between wild-type and DX2 transgenic animals. A DX2-encoding self-complementary adeno-associated virus (scAAV) was intracranially injected into 6-OHDA induced in vivo animal models, and their mobility was examined. Subsequently, the isolated brain tissues were analyzed.

RESULTS

DX2 translocates into the nucleus upon ROS stress more rapidly than AIMP2. The binding affinity of DX2 to PARP-1 appeared to be more robust compared to that of AIMP2, resulting in the inhibition of PARP-1 induced neuronal cell death. DX2 transgenic animals exhibited neuroprotective behavior in rotenone-induced neuronal damage conditions. Following a single intracranial injection of AAV-DX2, both behavior and mobility were consistently ameliorated in neurodegenerative animal models induced by 6-OHDA.

CONCLUSION

AIMP2 and DX2 are proposed to engage in bidirectional regulation of parthanatos. They physically interact with PARP-1. Notably, DX2's cell survival properties manifest exclusively in the context of abnormal AIMP2 accumulation, devoid of any tumorigenic effects. This suggests that DX2 could represent a distinctive therapeutic target for addressing Parkinson's disease in patients.

Viral vectors for gene delivery to the central nervous system

Brain diseases with a known or suspected genetic basis represent an important frontier for advanced therapeutics. The central nervous system (CNS) is an intricate network in which diverse cell types with multiple functions communicate via complex signaling pathways, making therapeutic intervention in brain-related diseases challenging. Nevertheless, as more information on the molecular genetics of brain-related diseases becomes available, genetic intervention using gene therapeutic strategies should become more feasible. There remain, however, several significant hurdles to overcome that relate to (i) the development of appropriate gene vectors and (ii) methods to achieve local or broad vector delivery. Clearly, gene delivery tools must be engineered for distribution to the correct cell type in a specific brain region and to accomplish therapeutic transgene expression at an appropriate level and duration. They also must avoid all toxicity, including the induction of inflammatory responses. Over the last 40 years, various types of viral vectors have been developed as tools to introduce therapeutic genes into the brain, primarily targeting neurons. This review describes the most prominent vector systems currently approaching clinical application for CNS disorders and highlights both remaining challenges as well as improvements in vector designs that achieve greater safety, defined tropism, and therapeutic gene expression.

Gene therapy for neurotransmitter-related disorders

Inborn errors of neurotransmitter (NT) metabolism are a group of rare, heterogenous diseases with predominant neurological features, such as movement disorders, autonomic dysfunction, and developmental delay. Clinical overlap with other disorders has led to delayed diagnosis and treatment, and some conditions are refractory to oral pharmacotherapies. Gene therapies have been developed and translated to clinics for paediatric inborn errors of metabolism, with 38 interventional clinical trials ongoing to date. Furthermore, efforts in restoring dopamine synthesis and neurotransmission through viral gene therapy have been developed for Parkinson's disease. Along with the recent European Medicines Agency (EMA) and Medicines and Healthcare Products Regulatory Agency (MHRA) approval of an AAV2 gene supplementation therapy for AADC deficiency, promising efficacy and safety profiles can be achieved in this group of diseases. In this review, we present preclinical and clinical advances to address NT-related diseases, and summarise potential challenges that require careful considerations for NT gene therapy studies.

Disease-specific interventions: The use of cell and gene therapies for Parkinson disease

Approaches to repair the brain around the loss of the nigrostriatal dopaminergic pathways in Parkinson disease (PD) are not new and have been attempted over many years. However, of late, the situation has moved forward in two main ways. In the case of cell therapies, the ability to make large numbers of authentic midbrain dopaminergic neuroblasts from human pluripotent stem cell sources has turned what was an interesting avenue of research into a major area of investment and trialing, by academics in conjunction with Pharma. In the case of gene therapies, their use around dopamine replacement has waned, as the interest in using them for disease modification targeting PD-specific pathways has grown. In this chapter, we discuss all these developments and the current status of cell and gene therapies for PD.

Vector-Mediated Delivery of Transgenes and RNA Interference-Based Gene Silencing Sequences to Astrocytes for Disease Management: Advances and Prospectives

Astrocytes are a type of important glial cell in the brain that serve crucial functions in regulating neuronal activity, facilitating communication between neurons, and keeping everything in balance. In this abstract, we explore current methods and future approaches for using vectors to precisely target astrocytes in the fight against various illnesses. In order to deliver therapeutic cargo selectively to astrocytes, researchers have made tremendous progress by using viral vectors such as adeno-associated viruses (AAVs) and lentiviruses. It has been established that engineered viral vectors are capable of either crossing the blood-brain barrier (BBB) or being delivered intranasally, which facilitates their entrance into the brain parenchyma. These vectors are able to contain transgenes that code for neuroprotective factors, synaptic modulators, or anti-inflammatory medicines, which pave the way for multiple approaches to disease intervention. Strategies based on RNA interference (RNAi) make vector-mediated astrocyte targeting much more likely to work. Small interfering RNAs (siRNAs) and short hairpin RNAs (shRNAs) are two types of RNA that can be made to silence disease-related genes in astrocytes. Vector-mediated delivery in conjunction with RNAi techniques provides a powerful toolkit for investigating the complex biological pathways that contribute to disease development. However, there are still a number of obstacles to overcome in order to perfect the specificity, safety, and duration of vector-mediated astrocyte targeting. In order to successfully translate research findings into clinical practise, it is essential to minimise off-target effects and the risk of immunogenicity. To demonstrate the therapeutic effectiveness of these strategies, rigorous preclinical investigation and validation are required.

Experimental pharmacology: Targeting metabolic pathways

Since the discovery of the treatment for Wilson disease a growing number of treatable inherited dystonias have been identified and their search and treatment have progressively been implemented in the clinics of patients with dystonia. While waiting for gene therapy to be more widely and adequately translated into the clinical setting, the efforts to divert the natural course of dystonia reside in unveiling its pathogenesis. Specific metabolic treatments can rewrite the natural history of the disease by preventing neurotoxic metabolite accumulation or interfering with the cell accumulation of damaging metabolites, restoring energetic cell fuel, supplementing defective metabolites, and supplementing the defective enzyme. A metabolic derangement of cell homeostasis is part of the progression of many non-metabolic genetic lesions and could be the target for possible metabolic approaches. In this chapter, we provided an update on treatment strategies for treatable inherited dystonias and an overview of genetic dystonias with new experimental therapeutic approaches available or close to clinical translation.

Gene Therapy for Dopamine Dyshomeostasis: From Parkinson's to Primary Neurotransmitter Diseases

Neurological disorders encompass a broad range of neurodegenerative and neurodevelopmental diseases that are complex and almost universally without disease modifying treatments. There is, therefore, significant unmet clinical need to develop novel therapeutic strategies for these patients. Viral gene therapies are a promising approach, where gene delivery is achieved through viral vectors such as adeno-associated virus and lentivirus. The clinical efficacy of such gene therapies has already been observed in two neurological disorders of pediatric onset; for spinal muscular atrophy and aromatic L-amino acid decarboxylase (AADC) deficiency, gene therapy has significantly modified the natural history of disease in these life-limiting neurological disorders. Here, we review recent advances in gene therapy, focused on the targeted delivery of dopaminergic genes for Parkinson's disease and the primary neurotransmitter disorders, AADC deficiency and dopamine transporter deficiency syndrome (DTDS). Although recent European Medicines Agency and Medicines and Healthcare products Regulatory Agency approval of Upstaza (eladocagene exuparvovec) signifies an important landmark, numerous challenges remain. Future research will need to focus on defining the optimal therapeutic window for clinical intervention, better understanding of the duration of therapeutic efficacy, and improved brain targeting. © 2023 The Authors. Movement Disorders published by Wiley Periodicals LLC on behalf of International Parkinson and Movement Disorder Society.

Advances in AAV technology for delivering genetically encoded cargo to the nonhuman primate nervous system

Modern neuroscience approaches including optogenetics, calcium imaging, and other genetic manipulations have facilitated our ability to dissect specific circuits in rodent models to study their role in neurological disease. These approaches regularly use viral vectors to deliver genetic cargo (e.g., opsins) to specific tissues and genetically-engineered rodents to achieve cell-type specificity. However, the translatability of these rodent models, cross-species validation of identified targets, and translational efficacy of potential therapeutics in larger animal models like nonhuman primates remains difficult due to the lack of efficient primate viral vectors. A refined understanding of the nonhuman primate nervous system promises to deliver insights that can guide the development of treatments for neurological and neurodegenerative diseases. Here, we outline recent advances in the development of adeno-associated viral vectors for optimized use in nonhuman primates. These tools promise to help open new avenues for study in translational neuroscience and further our understanding of the primate brain.

Neurotrophin mimetics and tropomyosin kinase receptors: a futuristic pharmacological tool for Parkinson's

Parkinson's disease is a complex age-related progressive dopaminergic neurodegenerative disease consistently viewed as a disorder of movement and is characterized by its cardinal motor symptoms. While the motor symptoms and its clinical manifestations are attributed to the nigral dopaminergic neuronal death and basal ganglia dysfunction, studies have subsequently proven that the non-dopaminergic neurons in various brain regions are also additionally involved with the disease progression. Thus, it is now well accepted that the involvement of various neurotransmitters and other ligands accounts for the non-motor symptoms (NMS) associated with the Parkinson's disease. Consequently, this has demonstrated to possess remarkable clinical concerns to the patients in terms of various disability, such impaired to compromised quality of life and increased risk of morbidity and mortality. Currently, available pharmacological, non-pharmacological, and surgical therapeutic strategies neither prevent, arrest, nor reverse the nigral dopaminergic neurodegeneration. Thus, there is an imminent medical necessity to increase patient's quality of life and survival, which in turn decreases the incidence and prevalence of the NMS. The current research article reviews the potential direct involvement of neurotrophin and its mimetics to target and modulate neurotrophin-mediated signal transduction pathways to enlighten a new and novel therapeutic strategy along with the pre-existing treatments for Parkinson's disease and other neurological/neurodegenerative disorders which are associated with the downregulation of neurotrophins.

Molecular Neurosurgery: Introduction to Gene Therapy and Clinical Applications

To date, more than 100 clinical trials have used sequence-based therapies to address diseases of the pediatric central nervous system. The first targeted pathologies share common features: the diseases are severe; they are due (mostly) to single variants; the variants are well characterized within the genome; and the interventions are technically feasible. Interventions range from intramuscular and intravenous injection to intrathecal and intraparenchymal infusions. Whether the therapeutic sequence consists of RNA or DNA, and whether the sequence is delivered via simple oligonucleotide, nanoparticle, or viral vector depends on the disease and the involved cell type(s) of the nervous system. While only one active trial targets an epilepsy disorder—Dravet syndrome—experiences with aromatic L-amino acid decarboxylase deficiency, spinal muscular atrophy, and others have taught us several lessons that will undoubtedly apply to the future of gene therapy for epilepsies. Epilepsies, with their diverse underlying mechanisms, will have unique aspects that may influence gene therapy strategies, such as targeting the epileptic zone or nodes in affected circuits, or alternatively finding ways to target nearly every neuron in the brain. This article focuses on the current state of gene therapy and includes its history and premise, the strategy and delivery vehicles most commonly used, and details viral vectors, current trials, and considerations for the future of pediatric intracranial gene therapy.

Various AAV Serotypes and Their Applications in Gene Therapy: An Overview

Despite scientific discoveries in the field of gene and cell therapy, some diseases still have no effective treatment. Advances in genetic engineering methods have enabled the development of effective gene therapy methods for various diseases based on adeno-associated viruses (AAVs). Today, many AAV-based gene therapy medications are being investigated in preclinical and clinical trials, and new ones are appearing on the market. In this article, we present a review of AAV discovery, properties, different serotypes, and tropism, and a following detailed explanation of their uses in gene therapy for disease of different organs and systems.

AAV vectors applied to the treatment of CNS disorders: Clinical status and challenges

In recent years, adeno-associated virus (AAV) has become the most important vector for central nervous system (CNS) gene therapy. AAV has already shown promising results in the clinic, for several CNS diseases that cannot be treated with drugs, including neurodegenerative diseases, neuromuscular diseases, and lysosomal storage disorders. Currently, three of the four commercially available AAV-based drugs focus on neurological disorders, including Upstaza for aromatic l-amino acid decarboxylase deficiency, Luxturna for hereditary retinal dystrophy, and Zolgensma for spinal muscular atrophy. All these studies have provided paradigms for AAV-based therapeutic intervention platforms. AAV gene therapy, with its dual promise of targeting disease etiology and enabling 'long-term correction' of disease processes, has the advantages of immune privilege, high delivery efficiency, tissue specificity, and cell tropism in the CNS. Although AAV-based gene therapy has been shown to be effective in most CNS clinical trials, limitations have been observed in its clinical applications, which are often associated with side effects. In this review, we summarized the therapeutic progress, challenges, limitations, and solutions for AAV-based gene therapy in 14 types of CNS diseases. We focused on viral vector technologies, delivery routes, immunosuppression, and other relevant clinical factors. We also attempted to integrate several hurdles faced in clinical and preclinical studies with their solutions, to seek the best path forward for the application of AAV-based gene therapy in the context of CNS diseases. We hope that these thoughtful recommendations will contribute to the efficient translation of preclinical studies and wide application of clinical trials.

Restorative cell and gene therapies for Parkinson's disease

One of the core pathological features of Parkinson's disease (PD) is the loss of the dopaminergic nigrostriatal pathway which lies at the heart of many of the motor features of this condition as well as some of the cognitive problems. The importance of this pathological event is evident through the clinical benefits that are seen when patients with PD are treated with dopaminergic agents, at least in early-stage disease. However, these agents create problems of their own through stimulation of more intact dopaminergic networks within the central nervous system causing major neuropsychiatric problems including dopamine dysregulation. In addition, over time the nonphysiological stimulation of striatal dopamine receptors by l-dopa containing drugs leads to the genesis of l-dopa-induced dyskinesias that can become very disabling in many cases. As such, there has been much interest in trying to better reconstitute the dopaminergic nigrostriatal pathway using either factors to regrow it, cells to replace it, or gene therapies to restore dopamine transmission in the striatum. In this chapter, we lay out the rationale, history and current status of these different therapies as well as highlighting where the field is heading and what new interventions might come to clinic in the coming years.

Modulating the activity of human nociceptors with a SCN10A promoter-specific viral vector tool

Despite the high prevalence of chronic pain as a disease in our society, there is a lack of effective treatment options for patients living with this condition. Gene therapies using recombinant AAVs are a direct method to selectively express genes of interest in target cells with the potential of, in the case of nociceptors, reducing neuronal firing in pain conditions. We designed a recombinant AAV vector expressing cargos whose expression was driven by a portion of the SCN10A (Na_V1.8) promoter, which is predominantly active in nociceptors. We validated its specificity for nociceptors in mouse and human dorsal root ganglia and showed that it can drive the expression of functional proteins. Our viral vector and promoter package drove the expression of both excitatory or inhibitory DREADDs in primary human DRG cultures and in whole cell electrophysiology experiments, increased or decreased neuronal firing, respectively. Taken together, we present a novel viral tool that drives expression of cargo specifically in human nociceptors. This will allow for future specific studies of human nociceptor properties as well as pave the way for potential future gene therapies for chronic pain.

A systematic review of adeno-associated virus gene therapies in neurology: the need for consistent safety monitoring of a promising treatment

Adeno-associated virus (AAV) gene therapies are generating much excitement in the rare disease field, particularly for previously untreatable neurological conditions. Efficacy has been claimed for several gene therapy products and the number of trials is rapidly increasing. However, reports of severe treatment-related adverse reactions are emerging, including death. There is still insufficient knowledge about their aetiology, prevention and treatment. We therefore undertook to systematically review publicly available data on AAV gene therapies in order to collate existing information on both safety and efficacy. Here, we review emerging efficacy reports of these novel therapies, many of which show promise. We also collate an increasing number of adverse reactions. Overwhelmingly, these results make a case for unified reporting of adverse events. This is likely to be critical for improving the safety of these promising treatments.

Stem Cell-based and Advanced Therapeutic Modalities for Parkinson's Disease: A Risk-effectiveness Patient-centered Analysis

Treatment of Parkinson's disease (PD), the second most prevalent neurodegenerative disorder, is currently considered a challenging issue since it causes substantial disability, poor quality of life, and mortality. Despite remarkable progress in advanced conventional therapeutic interventions, the global burden of the disease has nearly doubled, prompting us to assess the riskeffectiveness of different treatment modalities. Each protocol could be considered as the best alternative treatment depending on the patient's situation. Prescription of levodopa, the most effective available medicine for this disorder, has been associated with many complications, i.e., multiple episodes of "off-time" and treatment resistance. Other medications, which are typically used in combination with levodopa, may have several adverse effects as well. As a result, the therapies that are more in line with human physiology and make the least interference with other pathways are worth investigating. On the other hand, remaining and persistent symptoms after therapy and the lack of effective response to the conventional approaches have raised expectations towards innovative alternative approaches, such as stem cell-based therapy. It is critical to not overlook the unexplored side effects of innovative approaches due to the limited number of research. In this review, we aimed to compare the efficacy and risk of advanced therapies with innovative cell-based and stemcell- based modalities in PD patients. This paper recapitulated the underlying factors/conditions, which could lead us to more practical and established therapeutic outcomes with more advantages and few complications. It could be an initial step to reconsider the therapeutic blueprint for patients with Parkinson's disease.

Routes of administration for adeno-associated viruses carrying gene therapies for brain diseases

Gene therapy is a powerful tool to treat various central nervous system (CNS) diseases ranging from monogenetic diseases to neurodegenerative disorders. Adeno-associated viruses (AAVs) have been widely used as the delivery vehicles for CNS gene therapies due to their safety, CNS tropism, and long-term therapeutic effect. However, several factors, including their ability to cross the blood-brain barrier, the efficiency of transduction, their immunotoxicity, loading capacity, the choice of serotype, and peripheral off-target effects should be carefully considered when designing an optimal AAV delivery strategy for a specific disease. In addition, distinct routes of administration may affect the efficiency and safety of AAV-delivered gene therapies. In this review, we summarize different administration routes of gene therapies delivered by AAVs to the brain in mice and rats. Updated knowledge regarding AAV-delivered gene therapies may facilitate the selection from various administration routes for specific disease models in future research.

An update on advanced therapies for Parkinson's disease: From gene therapy to neuromodulation

Advanced Parkinson's disease (PD) is characterized by increasingly debilitating impaired movements that include motor fluctuations and dyskinesias. At this stage of the disease, pharmacological management can result in unsatisfactory clinical benefits and increase the occurrence of adverse effects, leading to the consideration of advanced therapies. The scope of this review is to provide an overview of currently available therapies for advanced PD, specifically levodopa–carbidopa intestinal gel, continuous subcutaneous apomorphine infusion, radiofrequency ablation, stereotactic radiosurgery, MRI-guided focused ultrasound, and deep brain stimulation. Therapies in clinical trials are also discussed, including novel formulations of subcutaneous carbidopa/levodopa, gene-implantation therapies, and cell-based therapies. This review focuses on the clinical outcomes and adverse effects of the various therapies and also considers patient-specific characteristics that may influence treatment choice. This review can equip providers with updated information on advanced therapies in PD to better counsel patients on the available options.

CNS gene therapy: present developments and emerging trends accelerating industry-academia pathways

The recent success of first central nervous system gene therapies has reinvigorated the growing community of gene therapy researchers and strengthened the field's market position. We are witnessing an increase of clinical trials with long-term efficiency mainly for neurometabolic, neurodegenerative and neurodevelopmental diseases caused by loss-of-function mutations. The ever-expanding knowledge and accessibility to the most advanced tools allow enrichment of applications to more complex diseases. This gradually contributes towards sealing the gap between top diseases impacting current global health and those towards which gene therapy development is currently aimed. Here, we highlight innovative therapeutic approaches that have reached the clinics and outline the latest improvements of vector design and targeting. Finally, we address the pressing challenges faced by clinical trials and the direction they are heading.

Gene-Based Therapeutics for Parkinson’s Disease

Parkinson’s disease (PD) is a complex multifactorial disorder that is not yet fully surmised, and it is only when such a disease is tackled on multiple levels simultaneously that we should expect to see fruitful results. Gene therapy is a modern medical practice that theoretically and, so far, practically, has demonstrated its capability in joining the battle against PD and other complex disorders on most if not all fronts. This review discusses how gene therapy can efficiently replace current forms of therapy such as drugs, personalized medicine or invasive surgery. Furthermore, we discuss the importance of enhancing delivery techniques to increase the level of transduction and control of gene expression or tissue specificity. Importantly, the results of current trials establish the safety, efficacy and applicability of gene therapy for PD. Gene therapy’s variety of potential in interfering with PD’s pathology by improving basal ganglial circuitry, enhancing dopamine synthesis, delivering neuroprotection or preventing neurodegeneration may one day achieve symptomatic benefit, disease modification and eradication.

Transduction of Brain Neurons in Juvenile Chum Salmon (Oncorhynchus keta) with Recombinant Adeno-Associated Hippocampal Virus Injected into the Cerebellum during Long-Term Monitoring

Corpus cerebelli in juvenile chum salmon is a multiprojective region of the brain connected via afferent and efferent projections with the higher regions of the brainstem and synencephalon, as well as with multiprojection regions of the medulla oblongata and spinal cord. During the postembryonic development of the cerebellum in chum salmon, Oncorhynchus keta, the lateral part of the juvenile cerebellum gives rise to the caudomedial part of the definitive cerebellum, which is consistent with the data reported for zebrafish and mouse cerebellum. Thus, the topographic organization of the cerebellum and its efferents are similar between fish (chum salmon and zebrafish) and mammals, including mice and humans. The distributions of recombinant adeno-associated viral vectors (rAAVs) after an injection of the base vector into the cerebellum have shown highly specific patterns of transgene expression in bipolar neurons in the latero-caudal lobe of the juvenile chum tectum opticum. The distribution of rAAVs in the dorsal thalamus, epithalamus, nucleus rotundus, and pretectal complex indicates the targeted distribution of the transgene via the thalamo-cerebellar projections. The detection of GFP expression in the cells of the epiphysis and posterior tubercle of juvenile chum salmon is associated with the transgene’s distribution and with the cerebrospinal fluid flow, the brain ventricles and its outer surface. The direct delivery of the rAAV into the central nervous system by intracerebroventricular administration allows it to spread widely in the brain. Thus, the presence of special projection areas in the juvenile chum salmon cerebellum, as well as outside it, and the identification of the transgene’s expression in them confirm the potential ability of rAAVs to distribute in both intracerebellar and afferent and efferent extracerebellar projections of the cerebellum.

Stereotaxic-assisted gene therapy in Alzheimer's and Parkinson's diseases: therapeutic potentials and clinical frontiers

INTRODUCTION

Alzheimer's disease (AD) and Parkinson's disease (PD) are neurodegenerative disorders causing cognitive deficits and motor difficulties in the elderly. Conventional treatments are mainly symptomatic with little ability to halt disease progression. Gene therapies to correct or silence genetic mutations predisposing to AD or PD are currently being developed in preclinical studies and clinical trials, relying mostly on systemic delivery, which reduces their effectiveness. Imaging-guided stereotaxic procedures are used to locally deliver therapeutic cargos to well-defined brain sites, hence raising the question whether stereotaxic-assisted gene therapy has therapeutic potentials.

AREAS COVERED

The authors summarize the studies that investigated the use of gene therapy in PD and AD in animal and clinical studies over the past five years, with a special emphasis on the combinatorial potential with stereotaxic delivery. The advantages, limitations and futuristic challenges of this technique are discussed.

EXPERT OPINION

Robotic stereotaxis combined with intraoperative imaging has revolutionized brain surgeries. While gene therapies are bringing huge innovations to the medical field and new hope to AD and PD patients and medical professionals, the efficient and targeted delivery of such therapies is a bottleneck. We propose that careful application of stereotaxic delivery of gene therapies can improve PD and AD management. [Figure: see text].

Gene therapy of yeast NDI1 on mitochondrial complex I dysfunction in rotenone-induced Parkinson’s disease models in vitro and vivo

Purpose

Parkinson's disease (PD) is the second most common neurodegenerative disease without cure or effective treatment. This study explores whether the yeast internal NADH-quinone oxidoreductase (NDI1) can functionally replace the defective mammalian mitochondrial complex I, which may provide a gene therapy strategy for treating sporadic PD caused by mitochondrial complex I dysfunction.

Method

Recombinant lentivirus expressing NDI1 was transduced into SH-SY5Y cells, or recombinant adeno-associated virus type 5 expressing NDI1 was transduced into the right substantia nigra pars compacta (SNpc) of mouse. PD cell and mouse models were established by rotenone treatment. The therapeutic effects of NDI1 on rotenone-induced PD models in vitro and vivo were assessed in neurobehavior, neuropathology, and mitochondrial functions, by using the apomorphine-induced rotation test, immunohistochemistry, immunofluorescence, western blot, complex I enzyme activity determination, oxygen consumption detection, ATP content determination and ROS measurement.

Results

NDI1 was expressed and localized in mitochondria in SH-SY5Y cells. NDI1 resisted rotenone-induced changes in cell morphology, loss of cell viability, accumulation of α-synuclein and pS129 α-synuclein, mitochondrial ROS production and mitochondria-mediated apoptosis. The basal and maximal oxygen consumption, mitochondrial coupling efficiency, basal and oligomycin-sensitive ATP and complex I activity in cell model were significantly increased in rotenone + NDI1 group compared to rotenone + vector group. NDI1 was efficiently expressed in dopaminergic neurons in the right SNpc without obvious adverse effects. The rotation number to the right side (NDI1-treated side) was significantly increased compared to that to the left side (untreated side) in mouse model. The number of viable dopaminergic neurons, the expression of tyrosine hydroxylase, total and maximal oxygen consumption, mitochondrial coupling efficiency and complex I enzyme activity in right substantia nigra, and the content of dopamine in right striatum were significantly increased in rotenone + NDI1 group compared to rotenone + vector group.

Conclusion

Yeast NDI1 can rescue the defect of oxidative phosphorylation in rotenone-induced PD cell and mouse models, and ameliorate neurobehavioral and neuropathological damages. The results may provide a basis for the yeast NDI1 gene therapy of sporadic PD caused by mitochondrial complex I dysfunction.

Nanotherapeutics and the Brain

Brain disease remains a significant health, social, and economic burden with a high failure rate of translation of therapeutics to the clinic. Nanotherapeutics have represented a promising area of technology investment to improve drug bioavailability and delivery to the brain, with several successes for nanotherapeutic use for central nervous system disease that are currently in the clinic. However, renewed and continued research on the treatment of neurological disorders is critically needed. We explore the challenges of drug delivery to the brain and the ways in which nanotherapeutics can overcome these challenges. We provide a summary and overview of general design principles that can be applied to nanotherapeutics for uptake and penetration in the brain. We next highlight remaining questions that limit the translational potential of nanotherapeutics for application in the clinic. Lastly, we provide recommendations for ongoing preclinical research to improve the overall success of nanotherapeutics against neurological disease. Expected final online publication date for the Annual Review of Chemical and Biomolecular Engineering, Volume 13 is October 2022. Please see http://www.annualreviews.org/page/journal/pubdates for revised estimates.

Therapy development for spinal muscular atrophy: perspectives for muscular dystrophies and neurodegenerative disorders

BACKGROUND

Major efforts have been made in the last decade to develop and improve therapies for proximal spinal muscular atrophy (SMA). The introduction of Nusinersen/Spinraza™ as an antisense oligonucleotide therapy, Onasemnogene abeparvovec/Zolgensma™ as an AAV9-based gene therapy and Risdiplam/Evrysdi™ as a small molecule modifier of pre-mRNA splicing have set new standards for interference with neurodegeneration.

MAIN BODY

Therapies for SMA are designed to interfere with the cellular basis of the disease by modifying pre-mRNA splicing and enhancing expression of the Survival Motor Neuron (SMN) protein, which is only expressed at low levels in this disorder. The corresponding strategies also can be applied to other disease mechanisms caused by loss of function or toxic gain of function mutations. The development of therapies for SMA was based on the use of cell culture systems and mouse models, as well as innovative clinical trials that included readouts that had originally been introduced and optimized in preclinical studies. This is summarized in the first part of this review. The second part discusses current developments and perspectives for amyotrophic lateral sclerosis, muscular dystrophies, Parkinson's and Alzheimer's disease, as well as the obstacles that need to be overcome to introduce RNA-based therapies and gene therapies for these disorders.

CONCLUSION

RNA-based therapies offer chances for therapy development of complex neurodegenerative disorders such as amyotrophic lateral sclerosis, muscular dystrophies, Parkinson's and Alzheimer's disease. The experiences made with these new drugs for SMA, and also the experiences in AAV gene therapies could help to broaden the spectrum of current approaches to interfere with pathophysiological mechanisms in neurodegeneration.

Considerations for clinical trial design and conduct in the evaluation of novel advanced therapeutics in neurodegenerative disease

The recent advances in the development of potentially disease modifying cell and gene therapies for neurodegenerative disease has resulted in the production of a number of promising novel therapies which are now moving forward to clinical evaluation. The robust evaluation of these therapies pose a significant number of challenges when compared to more traditional evaluations of pharmacotherapy, which is the current mainstay of neurodegenerative disease symptom management. Indeed, there is an inherent complexity in the design and conduct of these trials at multiple levels. Here we discuss specific aspects requiring consideration in the context of investigating novel cell and gene therapies for neurodegenerative disease. This extends to overarching trial designs that could be employed and the factors that underpin design choices such outcome assessments, participant selection and methods for delivery of cell and gene therapies. We explore methods of data collection that may improve efficiency in trials of cell and gene therapy to maximize data sharing and collaboration. Lastly, we explore some of the additional context beyond efficacy evaluations that should be considered to ensure implementation across relevant healthcare settings.

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.

Safety of AADC Gene Therapy for Moderately Advanced Parkinson Disease: Three-Year Outcomes From the PD-1101 Trial

Background and Objectives

To report final, 36-month safety and clinical outcomes from the PD-1101 trial of NBIb-1817 (VY-AADC01) in participants with moderately advanced Parkinson disease (PD) and motor fluctuations.

Methods

PD-1101 was a phase 1b, open-label, dose escalation trial of VY-AADC01, an experimental AAV2 gene therapy encoding the human aromatic l-amino acid decarboxylase (AADC) enzyme. VY-AADC01 was delivered via bilateral, intraoperative MRI-guided putaminal infusions to 3 cohorts (n = 5 participants per cohort): cohort 1, ≤7.5 × 10¹¹ vector genomes (vg); cohort 2, ≤1.5 × 10¹² vg; cohort 3, ≤4.7 × 10¹² vg.

Results

No serious adverse events (SAEs) attributed to VY-AADC01 were reported. All 4 non-vector–related SAEs (atrial fibrillation and pulmonary embolism in 1 participant and 2 events of small bowel obstruction in another participant) resolved. Requirements for PD medications were reduced by 21%–30% in the 2 highest dose cohorts at 36 months. Standard measures of motor function (PD diary, Unified Parkinson's Disease Rating Scale III “off”-medication and “on”-medication scores), global impressions of improvement (Clinical Global Impression of Improvement, Patient Global Impression of Improvement), and quality of life (39-item Parkinson's Disease Questionnaire) were stable or improved compared with baseline at 12, 24, and 36 months following VY-AADC01 administration across cohorts.

Discussions

VY-AADC01 and the surgical administration procedure were well-tolerated and resulted in stable or improved motor function and quality of life across cohorts, as well as reduced PD medication requirements in cohorts 2 and 3 over 3 years.

Trial Registration Information

NCT01973543.

Classification of Evidence

This study provides Class IV evidence that, in patients with moderately advanced PD and motor fluctuations, putaminal infusion of VY-AADC01 is well tolerated and may improve motor function.

Reduced Immunogenicity of Intraparenchymal Delivery of Adeno-Associated Virus Serotype 2 Vectors: Brief Overview

Pre existing immunity to adeno-associated virus (AAV) poses a concern in AAV vector–mediated gene therapy. Localized administration of low doses of carefully chosen AAV serotypes can mitigate the risk of an immune response. This article will illustrate the low risk of immune response to AAV serotype 2 vector–mediated gene therapy to the brain with support from clinical trial data in aromatic L-amino acid decarboxylase deficiency and Parkinson disease.

Gene therapy in the putamen for curing AADC deficiency and Parkinson's disease

This commentary provides an overview of the putamen as an established target site for gene therapy in treating aromatic l-amino acid decarboxylase (AADC) deficiency and Parkinson's disease, two debilitating neurological disorders that involve motor dysfunction caused by dopamine deficiencies. The neuroanatomy and the function of the putamen in motor control provide good rationales for targeting this brain structure. Additionally, the efficacy and safety of intraputaminal gene therapy demonstrate that restoration of dopamine synthesis in the putamen by using low doses of adeno-associated viral vector serotype 2 to deliver the hAADC gene is well tolerated. This restoration leads to sustained improvements in motor and nonmotor symptoms of AADC deficiency and improved uptake and conversion of exogenous l-DOPA into dopamine in Parkinson's patients.