Gene Therapy for Huntington's Disease: The Final Strategy for a Cure?

Emerging Perspectives on Prime Editor Delivery to the Brain

Prime editing shows potential as a precision genome editing technology, as well as the potential to advance the development of next-generation nanomedicine for addressing neurological disorders. However, turning in prime editors (PEs), which are macromolecular complexes composed of CRISPR/Cas9 nickase fused with a reverse transcriptase and a prime editing guide RNA (pegRNA), to the brain remains a considerable challenge due to physiological obstacles, including the blood-brain barrier (BBB). This review article offers an up-to-date overview and perspective on the latest technologies and strategies for the precision delivery of PEs to the brain and passage through blood barriers. Furthermore, it delves into the scientific significance and possible therapeutic applications of prime editing in conditions related to neurological diseases. It is targeted at clinicians and clinical researchers working on advancing precision nanomedicine for neuropathologies.

Exosomes for neurodegenerative diseases: diagnosis and targeted therapy

PURPOSE OF REVIEW

Neurodegenerative diseases are still challenging clinical issues, with no curative interventions available and early, accurate diagnosis remaining difficult. Finding solutions to them is of great importance. In this review, we discuss possible exosomal diagnostic biomarkers and explore current explorations in exosome-targeted therapy for some common neurodegenerative diseases, offering insights into the clinical transformation of exosomes in this field.

RECENT FINDINGS

The burgeoning research on exosomes has shed light on their potential applications in disease diagnosis and treatment. As a type of extracellular vesicles, exosomes are capable of crossing the blood - brain barrier and exist in various body fluids, whose components can reflect pathophysiological changes in the brain. In addition, they can deliver specific drugs to brain tissue, and even possess certain therapeutic effects themselves. And the recent advancements in engineering modification technology have further enabled exosomes to selectively target specific sites, facilitating the possibility of targeted therapy for neurodegenerative diseases. The unique properties of exosomes give them great potential in the diagnosis and treatment of neurodegenerative diseases, and provide novel ideas for dealing with such diseases.

Exploring molecular mechanisms, therapeutic strategies, and clinical manifestations of Huntington's disease

Huntington's disease (HD) is a paradigm of a genetic neurodegenerative disorder characterized by the expansion of CAG repeats in the HTT gene. This extensive review investigates the molecular complexities of HD by highlighting the pathogenic mechanisms initiated by the mutant huntingtin protein. Adverse outcomes of HD include mitochondrial dysfunction, compromised protein clearance, and disruption of intracellular signaling, consequently contributing to the gradual deterioration of neurons. Numerous therapeutic strategies, particularly precision medicine, are currently used for HD management. Antisense oligonucleotides, such as Tominersen, play a leading role in targeting and modulating the expression of mutant huntingtin. Despite the promise of these therapies, challenges persist, particularly in improving delivery systems and the necessity for long-term safety assessments. Considering the future landscape, the review delineates promising directions for HD research and treatment. Innovations such as Clustered regularly interspaced short palindromic repeats associated system therapies (CRISPR)-based genome editing and emerging neuroprotective approaches present unprecedented opportunities for intervention. Collaborative interdisciplinary endeavors and a more insightful understanding of HD pathogenesis are on the verge of reshaping the therapeutic landscape. As we navigate the intricate landscape of HD, this review serves as a guide for unraveling the intricacies of this disease and progressing toward transformative treatments.

Optimizing Screening for Intrastriatal Interventions in Huntington's Disease Using Predictive Models

BACKGROUND

Intrastriatal delivery of potential therapeutics in Huntington's disease (HD) requires sufficient caudate and putamen volumes. Currently, volumetric magnetic resonance imaging is rarely done in clinical practice, and these data are not available in large research cohorts such as Enroll-HD.

OBJECTIVE

The objective of this study was to investigate whether predictive models can accurately classify HD patients who exceed caudate and putamen volume thresholds required for intrastriatal therapeutic interventions.

METHODS

We obtained and merged data for 1374 individuals across three HD cohorts: IMAGE-HD, PREDICT-HD, and TRACK-HD/TRACK-ON. We imputed missing data for clinical variables with >72% non-missing values and used the model-building algorithm BORUTA to identify the 10 most important variables. A random forest algorithm was applied to build a predictive model for putamen volume >2500 mm3 and caudate volume >2000 mm3 bilaterally. Using the same 10 predictors, we constructed a logistic regression model with predictors significant at P < 0.05.

RESULTS

The random forest model with 1000 trees and minimal terminal node size of 5 resulted in 83% area under the curve (AUC). The logistic regression model retaining age, CAG repeat size, and symbol digit modalities test-correct had 85.1% AUC. A probability cutoff of 0.8 resulted in 5.4% false positive and 66.7% false negative rates.

CONCLUSIONS

Using easily obtainable clinical data and machine learning-identified initial predictor variables, random forest, and logistic regression models can successfully identify people with sufficient striatal volumes for inclusion cutoffs. Adopting these models in prescreening could accelerate clinical trial enrollment in HD and other neurodegenerative disorders when volume cutoffs are necessary enrollment criteria. © 2024 The Authors. Movement Disorders published by Wiley Periodicals LLC on behalf of International Parkinson and Movement Disorder Society.

The Huntington's Disease Gene Discovery

The gene for Huntington's disease (HD) was discovered in 1993, after an international collaborative initiative that led researchers to remote regions of South America. It was the most remarkable milestone, since George Huntington's initial description. Through the phenomenological discussions led by Jean-Martin Charcot and Willian Osler, and finally Americo Negrette's reports, which served as the inspiration for the Venezuela Project led by Nancy Wexler, the journey toward discovering the Huntington's disease (HD) gene was marked by substantial efforts. This monumental achievement involved the analysis of more than 18,000 blood samples and gathered dozens of researchers in an integrated effort, enabling the mapping of the gene on chromosome 4 in 1983 and leading, a decade later, to the precise localization and identification of the HTT gene. The discovery of the HD mutation represented a pivotal moment in the field of genetics and neurology, significantly enhancing our understanding of the disease and creating opportunities for future treatments. The progress made and the knowledge gained during this journey catalyzed the development of many innovative molecular techniques that have advanced research in other medical conditions. In this article, the authors celebrate three decades of this memorable event, revisiting the historical aspects, providing insights into the techniques developed, and delving into the paths that ultimately led to the discovery of the HD gene. © 2024 International Parkinson and Movement Disorder Society.

Bioinspired Approaches for Central Nervous System Targeted Gene Delivery

Disorders of the central nervous system (CNS) which include a wide range of neurodegenerative and neurological conditions have become a serious global issue. The presence of CNS barriers poses a significant challenge to the progress of designing effective therapeutic delivery systems, limiting the effectiveness of drugs, genes, and other therapeutic agents. Natural nanocarriers present in biological systems have inspired researchers to design unique delivery systems through biomimicry. As natural resource derived delivery systems are more biocompatible, current research has been focused on the development of delivery systems inspired by bacteria, viruses, fungi, and mammalian cells. Despite their structural potential and extensive physiological function, making them an excellent choice for biomaterial engineering, the delivery of nucleic acids remains challenging due to their instability in biological systems. Similarly, the efficient delivery of genetic material within the tissues of interest remains a hurdle due to a lack of selectivity and targeting ability. Considering that gene therapies are the holy grail for intervention in diseases, including neurodegenerative disorders such as Alzheimer's disease, Parkinson's Disease, and Huntington's disease, this review centers around recent advances in bioinspired approaches to gene delivery for the prevention of CNS disorders.

Positron Emission Tomography Quantitative Assessment of Off-Target Whole-Body Biodistribution of I-124-Labeled Adeno-Associated Virus Capsids Administered to Cerebral Spinal Fluid

Based on studies in experimental animals demonstrating that administration of adeno-associated virus (AAV) vectors to the cerebrospinal fluid (CSF) is an effective route to transfer genes to the nervous system, there are increasing number of clinical trials using the CSF route to treat nervous system disorders. With the knowledge that the CSF turns over four to five times daily, and evidence in experimental animals that at least some of CSF administered AAV vectors are distributed to systemic organs, we asked: with AAV administration to the CSF, what fraction of the total dose remains in the nervous system and what fraction goes off target and is delivered systemically? To quantify the biodistribution of AAV capsids immediately after administration, we covalently labeled AAV capsids with iodine 124 (I-124), a cyclotron generated positron emitter, enabling quantitative positron emission tomography scanning of capsid distribution for up to 96 h after AAV vector administration. We assessed the biodistribution to nonhuman primates of I-124-labeled capsids from different AAV clades, including 9 (clade F), rh.10 (E), PHP.eB (F), hu68 (F), and rh91(A). The analysis demonstrated that 60-90% of AAV vectors administered to the CSF through either the intracisternal or intrathecal (lumbar) routes distributed systemically to major organs. These observations have potentially significant clinical implications regarding accuracy of AAV vector dosing to the nervous system, evoking systemic immunity at levels similar to that with systemic administration, and potential toxicity of genes designed to treat nervous system disorders being expressed in non-nervous system organs. Based on these data, individuals in clinical trials using AAV vectors administered to the CSF should be monitored for systemic as well as nervous system adverse events and CNS dosing considerations should account for a significant AAV systemic distribution.

Huntington's Disease Drug Development: A Phase 3 Pipeline Analysis

Huntington's Disease (HD) is a severely debilitating neurodegenerative disorder in which sufferers exhibit different combinations of movement disorders, dementia, and behavioral or psychiatric abnormalities. The disorder is a result of a trinucleotide repeat expansion mutation that is inherited in an autosomal dominant manner. While there is currently no treatment to alter the course of HD, there are medications that lessen abnormal movement and psychiatric symptoms. ClinicalTrials.gov was searched to identify drugs that are currently in or have completed phase III drug trials for the treatment of HD. The described phase III trials were further limited to interventional studies that were recruiting, active not recruiting, or completed. In addition, all studies must have posted an update within the past year. PubMed was used to gather further information on these interventional studies. Of the nine clinical trials that met these criteria, eight involved the following drugs: metformin, dextromethorphan/quinidine, deutetrabenazine, valbenazine, Cellavita HD, pridopidine, SAGE-718, and RO7234292 (RG6042). Of these drug treatments, four are already FDA approved. This systematic review provides a resource that summarizes the present therapies for treating this devastating condition that are currently in phase III clinical trials in the United States.

CRISPR: a tool with potential for genomic reprogramming in neurological disorders

The intricate neural circuitry of the brain necessitates precise and synchronized transcriptional programs. Any disturbance during embryonic or adult development, whether caused by genetic or environmental factors, may result in refractory and recurrent neurological disorders. Inadequate knowledge of the pathogenic mechanisms underlying neurological disorders is the primary obstacle to the development of effective treatments, necessitating the development of alternative therapeutic approaches to identify rational molecular targets. Recently, with the evolution of CRISPR-Cas9 technology, an engineered RNA system provides precise and highly effective correction or silencing of disease-causing mutations by modulating expression and thereby avoiding the limitations of the RNA interference strategy. This article discusses the CRISPR-Cas9 technology, its mechanisms, and the limitations of the new technology. We provide a glimpse of how the far-reaching implications of CRISPR can open new avenues for the development of tools to combat neurological disorders, as well as a review of recent attempts by neuroscientists to launch therapeutic correction.

Gene therapy for selected neuromuscular and trinucleotide repeat disorders - An insight to subsume South Asia for multicenter clinical trials

Background

In this article, the authors discuss how they utilized the genetic mutation data in Sri Lankan Duchenne muscular dystrophy (DMD), Spinal muscular atrophy (SMA), Spinocerebellar ataxia (SCA) and Huntington's disease (HD) patients and compare the available literature from South Asian countries to identifying potential candidates for available gene therapy for DMD, SMA, SCA and HD patients.

Methods

Rare disease patients (n = 623) with the characteristic clinical findings suspected of HD, SCA, SMA and Muscular Dystrophy were genetically confirmed using Multiplex Ligation Dependent Probe Amplification (MLPA), and single plex PCR. A survey was conducted in the "Wiley database on Gene Therapy Trials Worldwide" to identify DMD, SMA, SCA, and HD gene therapy clinical trials performed worldwide up to April 2021. In order to identify candidates for gene therapy in other neighboring countries we compared our findings with available literature from India and Pakistan which has utilized the same molecular diagnostic protocol to our study.

Results

From the overall cohort of 623 rare disease patients with the characteristic clinical findings suspected of HD, SCA, SMA and Muscular Dystrophy, n = 343 (55%) [Muscular Dystrophy- 65%; (DMD-139, Becker Muscular Dystrophy -BMD-11), SCA type 1-3-53% (SCA1-61,SCA2- 23, SCA3- 39), HD- 52% (45) and SMA- 34% (22)] patients were positive for molecular diagnostics by MLPA and single plex PCR. A total of 147 patients in Sri Lanka amenable to available gene therapy; [DMD-83, SMA-15 and HD-49] were identified. A comparison of Sri Lankan finding with available literature from India and Pakistan identified a total of 1257 patients [DMD-1076, SMA- 57, and HD-124] from these three South Asian Countries as amenable for existing gene therapy trials. DMD, SMA, and HD gene therapy clinical trials (113 studies) performed worldwide up to April 2021 were concentrated mostly (99%) in High Income Countries (HIC) and Upper Middle-Income Countries (UMIC). However, studies on the potential use of anti-sense oligonucleotides (ASO) for treatment of SCAs have yet to reach clinical trials.

Conclusion

Most genetic therapies for neurodegenerative and neuromuscular disorders have been evaluated for efficacy primarily in Western populations. No multicenter gene therapy clinical trial sites for DMD, SMA and HD in the South Asian region, leading to lack of knowledge on the safety and efficacy of such personalized therapies in other populations, including South Asians. By fostering collaboration between researchers, clinicians, patient advocacy groups, government and industry in gene therapy initiatives for the inherited-diseases community in the developing world would link the Global North and Global South and breathe life into the motto "Together we can make a difference".

Pathogenesis of Huntington's Disease: An Emphasis on Molecular Pathways and Prevention by Natural Remedies

BACKGROUND

Huntington's disease is an inherited autosomal dominant trait neuro-degenerative disorder caused by changes (mutations) of a gene called huntingtin (htt) that is located on the short arm (p) of chromosome 4, CAG expansion mutation. It is characterized by unusual movements, cognitive and psychiatric disorders.

OBJECTIVE

This review was undertaken to apprehend biological pathways of Huntington's disease (HD) pathogenesis and its management by nature-derived products. Natural products can be lucrative for the management of HD as it shows protection against HD in pre-clinical trials. Advanced research is still required to assess the therapeutic effectiveness of the known organic products and their isolated compounds in HD experimental models.

SUMMARY

Degeneration of neurons in Huntington's disease is distinguished by progressive loss of motor coordination and muscle function. This is due to the expansion of CAG trinucleotide in the first exon of the htt gene responsible for neuronal death and neuronal network degeneration in the brain. It is believed that the factors such as molecular genetics, oxidative stress, excitotoxicity, mitochondrial dysfunction, neuroglia dysfunction, protein aggregation, and altered UPS leads to HD. The defensive effect of the natural product provides therapeutic efficacy against HD. Recent reports on natural drugs have enlightened the protective role against HD via antioxidant, anti-inflammatory, antiapoptotic, and neurofunctional regulation.

Mitochondrial organization and structure are compromised in fibroblasts from patients with Huntington's disease

Huntington´s disease (HD) is a progressive neurodegenerative disease with onset in adulthood that leads to a complete disability and death in approximately 20 years after onset of symptoms. HD is caused by an expansion of a CAG triplet in the gene for huntingtin. Although the disease causes most damage to striatal neurons, other parts of the nervous system and many peripheral tissues are also markedly affected. Besides huntingtin malfunction, mitochondrial impairment has been previously described as an important player in HD. This study focuses on mitochondrial structure and function in cultivated skin fibroblasts from 10 HD patients to demonstrate mitochondrial impairment in extra-neuronal tissue. Mitochondrial structure, mitochondrial fission, and cristae organization were significantly disrupted and signs of elevated apoptosis were found. In accordance with structural changes, we also found indicators of functional alteration of mitochondria. Mitochondrial disturbances presented in fibroblasts from HD patients confirm that the energy metabolism damage in HD is not localized only to the central nervous system, but also may play role in the pathogenesis of HD in peripheral tissues. Skin fibroblasts can thus serve as a suitable cellular model to make insight into HD pathobiochemical processes and for the identification of possible targets for new therapies.