Gene therapy for neurological disorders: progress and prospects

Targeting α-Synuclein in Parkinson's Disease: Progress Towards the Development of Disease-Modifying Therapeutics

Parkinson's disease (PD), the second most common neurodegenerative movement disorder, is characterized by progressive motor and non-motor symptoms [1]. Despite treatment with pharmacologic and surgical therapies, the disease will continue to relentlessly advance. Hence, there is a great deal of interest in potential disease-modifying therapies with the hope that the neurodegenerative process can be slowed or halted. The purpose of this review is to highlight the role toxic α-synuclein (α-syn) plays in PD pathogenesis and critically review the relevant literature about therapeutic modalities targeting α-syn. Toxic α-syn plays a key role in PD pathogenesis, disrupting important cellular functions, and, thus, targeting α-syn is a reasonable disease-modifying strategy. Current approaches under investigation include decreasing α-syn production with RNA interference (RNAi), inhibiting α-syn aggregation, promoting intracellular degradation of α-syn aggregates (via enhancing autophagy and enhancing lysosomal degradation), and promoting extracellular degradation of α-syn via active and passive immunization.

Multifunctional cationic nanosystems for nucleic acid therapy of thoracic aortic dissection

Thoracic aortic dissection (TAD) is an aggressive vascular disease that requires early diagnosis and effective treatment. However, due to the particular vascular structure and narrowness of lesion location, there are no effective drug delivery systems for the therapy of TAD. Here, we report a multifunctional delivery nanosystem (TP-Gd/miRNA-ColIV) composed of gadolinium-chelated tannic acid (TA), low-toxic cationic PGEA (ethanolamine-aminated poly(glycidyl methacrylate)) and type IV collagen targeted peptide (ColIV) for targeted nucleic acid therapy, early diagnosis and noninvasive monitoring of TAD. Such targeted therapy with miR-145 exhibits impressive performances in stabilizing the vascular structures and preventing the deterioration of TAD. After the treatment with TP-Gd/miR-145-ColIV, nearly no dissection occurs in the thoracic aortic arches of the mice with TAD model. Moreover, TP-Gd/miRNA-ColIV also demonstrates good magnetic resonance imaging (MRI) ability and can be used to noninvasively monitor the development conditions of TAD.

Clinical translation of gene medicine

Gene therapy has recently witnessed accelerated progress as a new therapeutic strategy with the potential to treat a range of inherited and acquired diseases. Billions of dollars have been invested in basic and clinical research on gene medicine, with ongoing clinical trials focused on cancer, monogenic diseases, cardiovascular diseases and other refractory diseases. Advances addressing the inherent challenges of gene therapy, particularly those related to retaining the delivery efficacy and minimizing unwanted immune responses, provide the basis for the widespread clinical application of gene medicine. Several types of genes delivered by viral or non-viral delivery vectors have demonstrated encouraging results in both animals and humans. As augmented by clinical indications, gene medicine techniques have rapidly become a promising alternative to conventional therapeutic strategies because of their better clinical benefit and lower toxicities. Their application in the clinic has been extensive as a result of the approval of many gene therapy drugs in recent years. In this review, we provide a comprehensive overview of the clinical translation of gene medicine, focusing on the key events and latest progress made regarding clinical gene therapy products. We also discuss the gene types and non-viral materials with respect to developing gene therapeutics in clinical trials.

MicroRNAs in Alzheimer's Disease: Diagnostic Markers or Therapeutic Agents?

MicroRNAs (miRNAs) are small non-coding nucleic acids able to post-transcriptionally regulate gene expression by binding to complementary sequences of target messenger RNA (mRNA). It has been estimated that at least 1% of the human genome encodes miRNA and every miRNA can regulate up to 200 mRNAs. These findings suggest that dysregulation of miRNA expression could be associated with several human pathological conditions including central neurological disorders. Alzheimer’s disease (AD) is a neurodegenerative disorder and the most common cause of dementia in the elderly. The characteristic symptoms are a progressive loss of memory and other cognitive functions due to the impairment of particular types of neurons and synapses, leading to neuronal death. At present, the available symptomatic treatments can only slow down disease progression without stopping it. miRNAs are widely found within the nervous system where they are key regulators of functions such as neurite outgrowth, dendritic spine morphology, neuronal differentiation, and synaptic plasticity. This has been the clue for considering miRNAs crucial molecules to be studied in AD, and nowadays, dysfunction of miRNAs in AD is increasingly recognized. In this review, we summarized existing evidence about miRNAs as biomarkers or therapeutic agents. The field of miRNAs as biomarkers is more advanced in terms of human data, and it is likely that miRNAs will be used successfully in the near future. Given the huge number of miRNAs potentially involved in diagnostics, miRNA panels will be used for specific tasks such as the stage of the disease, the risk prediction, and disease progression. The field of miRNAs as therapeutics is rapidly developing, and it offers a huge variety of solutions. These include positive effects related to beta-amyloid or tau reduction, increased number of neurons, inhibition of apoptosis, protection of synapses, transformation of other cellular elements into missing/deficient neurons in AD, and so on. It is predictable that both areas of research will be carried forward. However, given the absence of an AD therapy able to stop or reverse the disease, it is desirable to accelerate research on miRNAs as therapeutic agents.

Editing the Central Nervous System Through CRISPR/Cas9 Systems

The translational gap to treatments based on gene therapy has been reduced in recent years because of improvements in gene editing tools, such as the CRISPR/Cas9 system and its variations. This has allowed the development of more precise therapies for neurodegenerative diseases, where access is privileged. As a result, engineering of complexes that can access the central nervous system (CNS) with the least potential inconvenience is fundamental. In this review article, we describe current alternatives to generate systems based on CRISPR/Cas9 that can cross the blood-brain barrier (BBB) and may be used further clinically to improve treatment for neurodegeneration in Parkinson's and Alzheimer's disease (AD).

Feasibility of using NF1-GRD and AAV for gene replacement therapy in NF1-associated tumors

Neurofibromatosis type 1, including the highly aggressive malignant peripheral nerve sheath tumors (MPNSTs), is featured by the loss of functional neurofibromin 1 (NF1) protein resulting from genetic alterations. A major function of NF1 is suppressing Ras activities, which is conveyed by an intrinsic GTPase-activating protein-related domain (GRD). In this study, we explored the feasibility of restoring Ras GTPase via exogenous expression of various GRD constructs, via gene delivery using a panel of adeno-associated virus (AAV) vectors in MPNST and human Schwann cells (HSCs). We demonstrated that several AAV serotypes achieved favorable transduction efficacies in those cells and a membrane-targeting GRD fused with an H-Ras C-terminal motif (C10) dramatically inhibited the Ras pathway and MPNST cells in a NF1-specific manner. Our results opened up a venue of gene replacement therapy in NF1-related tumors.

Adeno-associated virus vector as a platform for gene therapy delivery

Adeno-associated virus (AAV) vectors are the leading platform for gene delivery for the treatment of a variety of human diseases. Recent advances in developing clinically desirable AAV capsids, optimizing genome designs and harnessing revolutionary biotechnologies have contributed substantially to the growth of the gene therapy field. Preclinical and clinical successes in AAV-mediated gene replacement, gene silencing and gene editing have helped AAV gain popularity as the ideal therapeutic vector, with two AAV-based therapeutics gaining regulatory approval in Europe or the United States. Continued study of AAV biology and increased understanding of the associated therapeutic challenges and limitations will build the foundation for future clinical success.

Therapeutic Prospects for Friedreich's Ataxia

Friedreich's ataxia (FRDA) is a progressive disease affecting multiple organs that is caused by systemic insufficiency of the mitochondrial protein frataxin. Current therapeutic strategies aim to elevate frataxin levels and/or alleviate the consequences of frataxin deficiency. Recent significant advances in the FRDA therapeutic pipeline are bringing patients closer to a cure.

Therapeutic AAV Gene Transfer to the Nervous System: A Clinical Reality

Gene transfer has long been a compelling yet elusive therapeutic modality. First mainly considered for rare inherited disorders, gene therapy may open treatment opportunities for more challenging and complex diseases such as Alzheimer's or Parkinson's disease. Today, examples of striking clinical proof of concept, the first gene therapy drugs coming onto the market, and the emergence of powerful new molecular tools have broadened the number of avenues to target neurological disorders but have also highlighted safety concerns and technology gaps. The vector of choice for many nervous system targets currently is the adeno-associated viral (AAV) vector due to its desirable safety profile and strong neuronal tropism. In aggregate, the clinical success, the preclinical potential, and the technological innovation have made therapeutic AAV drug development a reality, particularly for nervous system disorders. Here, we discuss the rationale, opportunities, limitations, and progress in clinical AAV gene therapy.

The GPI-Linked Protein LY6A Drives AAV-PHP.B Transport across the Blood-Brain Barrier

Efficient delivery of gene therapy vectors across the blood-brain barrier (BBB) is the holy grail of neurological disease therapies. A variant of the neurotropic vector adeno-associated virus (AAV) serotype 9, called AAV-PHP.B, was shown to very efficiently deliver transgenes across the BBB in C57BL/6J mice. Based on our recent observation that this phenotype is mouse strain dependent, we used whole-exome sequencing-based genetics to map this phenotype to a specific haplotype of lymphocyte antigen 6 complex, locus A (Ly6a) (stem cell antigen-1 [Sca-1]), which encodes a glycosylphosphatidylinositol (GPI)-anchored protein whose function had been thought to be limited to the biology of hematopoiesis. Additional biochemical and genetic studies definitively linked high BBB transport to the binding of AAV-PHP.B with LY6A (SCA-1). These studies identify, for the first time, a ligand for this GPI-anchored protein and suggest a role for it in BBB transport that could be hijacked by viruses in natural infections or by gene therapy vectors to treat neurological diseases.

Gene therapy for neurological disorders: progress and prospects

This corrects the article DOI: 10.1038/nrd.2018.110.