Identification of a novel muscle targeting peptide in mdx mice

Systematic Review of Genetic Substrate Reduction Therapy in Lysosomal Storage Diseases: Opportunities, Challenges and Delivery Systems

BACKGROUND

Genetic substrate reduction therapy (gSRT), which involves the use of nucleic acids to downregulate the genes involved in the biosynthesis of storage substances, has been investigated in the treatment of lysosomal storage diseases (LSDs).

OBJECTIVE

To analyze the application of gSRT to the treatment of LSDs, identifying the silencing tools and delivery systems used, and the main challenges for its development and clinical translation, highlighting the contribution of nanotechnology to overcome them.

METHODS

A systematic review following the Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA) reporting guidelines was performed. PubMed, Scopus, and Web of Science databases were used for searching terms related to LSDs and gene-silencing strategies and tools.

RESULTS

Fabry, Gaucher, and Pompe diseases and mucopolysaccharidoses I and III are the only LSDs for which gSRT has been studied, siRNA and lipid nanoparticles being the silencing strategy and the delivery system most frequently employed, respectively. Only in one recently published study was CRISPR/Cas9 applied to treat Fabry disease. Specific tissue targeting, availability of relevant cell and animal LSD models, and the rare disease condition are the main challenges with gSRT for the treatment of these diseases. Out of the 11 studies identified, only two gSRT studies were evaluated in animal models.

CONCLUSIONS

Nucleic acid therapies are expanding the clinical tools and therapies currently available for LSDs. Recent advances in CRISPR/Cas9 technology and the growing impact of nanotechnology are expected to boost the clinical translation of gSRT in the near future, and not only for LSDs.

CRISPR-Cas9 delivery strategies with engineered extracellular vesicles

Therapeutic genome editing has the potential to cure diseases by directly correcting genetic mutations in tissues and cells. Recent progress in the CRISPR-Cas9 systems has led to breakthroughs in gene editing tools because of its high orthogonality, versatility, and efficiency. However, its safe and effective administration to target organs in patients is a major hurdle. Extracellular vesicles (EVs) are endogenous membranous particles secreted spontaneously by all cells. They are key actors in cell-to-cell communication, allowing the exchange of select molecules such as proteins, lipids, and RNAs to induce functional changes in the recipient cells. Recently, EVs have displayed their potential for trafficking the CRISPR-Cas9 system during or after their formation. In this review, we highlight recent developments in EV loading, surface functionalization, and strategies for increasing the efficiency of delivering CRISPR-Cas9 to tissues, organs, and cells for eventual use in gene therapies.

Anti-inflammatory nanoparticles significantly improve muscle function in a murine model of advanced muscular dystrophy

Chronic inflammation contributes to the pathogenesis of all muscular dystrophies. Inflammatory T cells damage muscle, while regulatory T cells (T_regs) promote regeneration. We hypothesized that providing anti-inflammatory cytokines in dystrophic muscle would promote proregenerative immune phenotypes and improve function. Primary T cells from dystrophic (mdx) mice responded appropriately to inflammatory or suppressive cytokines. Subsequently, interleukin-4 (IL-4)- or IL-10-conjugated gold nanoparticles (PA4, PA10) were injected into chronically injured, aged, mdx muscle. PA4 and PA10 increased T cell recruitment, with PA4 doubling CD4⁺/CD8^- T cells versus controls. Further, 50% of CD4⁺/CD8^- T cells were immunosuppressive T_regs following PA4, versus 20% in controls. Concomitant with T_reg recruitment, muscles exhibited increased fiber area and fourfold increases in contraction force and velocity versus controls. The ability of PA4 to shift immune responses, and improve dystrophic muscle function, suggests that immunomodulatory treatment may benefit many genetically diverse muscular dystrophies, all of which share inflammatory pathology.

Nanomedicine for Gene Delivery and Drug Repurposing in the Treatment of Muscular Dystrophies

Muscular Dystrophies (MDs) are a group of rare inherited genetic muscular pathologies encompassing a variety of clinical phenotypes, gene mutations and mechanisms of disease. MDs undergo progressive skeletal muscle degeneration causing severe health problems that lead to poor life quality, disability and premature death. There are no available therapies to counteract the causes of these diseases and conventional treatments are administered only to mitigate symptoms. Recent understanding on the pathogenetic mechanisms allowed the development of novel therapeutic strategies based on gene therapy, genome editing CRISPR/Cas9 and drug repurposing approaches. Despite the therapeutic potential of these treatments, once the actives are administered, their instability, susceptibility to degradation and toxicity limit their applications. In this frame, the design of delivery strategies based on nanomedicines holds great promise for MD treatments. This review focuses on nanomedicine approaches able to encapsulate therapeutic agents such as small chemical molecules and oligonucleotides to target the most common MDs such as Duchenne Muscular Dystrophy and the Myotonic Dystrophies. The challenge related to in vitro and in vivo testing of nanosystems in appropriate animal models is also addressed. Finally, the most promising nanomedicine-based strategies are highlighted and a critical view in future developments of nanomedicine for neuromuscular diseases is provided.

Polymeric nanoparticles functionalized with muscle-homing peptides for targeted delivery of phosphatase and tensin homolog inhibitor to skeletal muscle

Phosphatase and tensin homolog (PTEN) antagonizes muscle growth and repair, and inhibition of PTEN has been shown to improve the pathophysiology and dystrophic muscle function in a mouse model of Duchenne muscular dystrophy (DMD). However, conventional pharmacological delivery of PTEN inhibitors carries a high risk of off-target side effects in other non-muscle organs due to broad targeting spectrums. Here we report a muscle-targeted nanoparticulate platform for cell-specific delivery of a PTEN inhibitor. Poly(lactide-co-glycolide)-b-poly(ethylene glycol) nanoparticles (NPs) are functionalized with a muscle-homing peptide M12 to promote the selective uptake by muscle cells/tissue in vitro and in vivo. Moreover, the NPs are formulated to slowly release the PTEN inhibitor, preventing cytotoxicity associated with direct exposure to the drug and facilitating sustained inhibition of PTEN. This advanced delivery approach taking advantages of polymeric nanomaterials and muscle-homing peptides opens a new avenue for the development of long-term therapeutic strategies in DMD treatment.

Developments in reading frame restoring therapy approaches for Duchenne muscular dystrophy

INTRODUCTION

Exon skipping compounds restoring the dystrophin transcript reading frame have received regulatory approval for Duchenne muscular dystrophy (DMD). Recently, focus shifted to developing compounds to skip additional exons, improving delivery to skeletal muscle, and to genome editing, to restore the reading frame on DNA level.

AREAS COVERED

We outline developments for reading frame restoring approaches, challenges of mutation specificity, and optimizing delivery. Also, we highlight ongoing efforts to better detect exon skipping therapeutic effects in clinical trials. Searches on relevant terms were performed, focusing on recent publications (<3 years).

EXPERT OPINION

Currently, 3 AONS are approved. Whether dystrophin levels are sufficient to slowdown disease progression needs to be confirmed. Enhancing AON uptake by muscles is currently under investigation. Gene editing is an alternative, but one that involves practical and ethical concerns. Given the field's momentum, we believe the efficiency of frame-restoring approaches will improve.

PTEN Inhibition Ameliorates Muscle Degeneration and Improves Muscle Function in a Mouse Model of Duchenne Muscular Dystrophy

Duchenne muscular dystrophy (DMD) is caused by a mutation of the muscle membrane protein dystrophin and characterized by severe degeneration of myofibers, progressive muscle wasting, loss of mobility, and, ultimately, cardiorespiratory failure and premature death. Currently there is no cure for DMD. Herein, we report that skeletal muscle-specific knockout (KO) of the phosphatase and tensin homolog (Pten) gene in an animal model of DMD (mdx mice) alleviates myofiber degeneration and restores muscle function without increasing tumor incidence. Specifically, Pten KO normalizes myofiber size and prevents muscular atrophy, and it improves grip strength and exercise performance in mdx mice. Pten KO also reduces fibrosis and inflammation, and it ameliorates muscle pathology in mdx mice. Unbiased RNA sequencing reveals that Pten KO upregulates extracellular matrix and basement membrane components positively correlated with wound healing and suppresses negative regulators of wound healing and lipid biosynthesis, thus improving the integrity of muscle basement membrane at the ultrastructural level. Importantly, pharmacological inhibition of PTEN similarly ameliorates muscle pathology and improves muscle integrity and function in mdx mice. Our findings provide evidence that PTEN inhibition may represent a potential therapeutic strategy to restore muscle function in DMD.

Advance in Drug Delivery for Ageing Skeletal Muscle

The age-related loss of skeletal muscle, sarcopenia, is characterized by progressive loss of muscle mass, reduction in muscle strength, and dysfunction of physical performance. It has become a global health problem leading to several adverse outcomes in the ageing population. Research on skeletal muscle loss prevention and treatment is developing quickly. However, the current clinical approaches to sarcopenia are limited. Recently, novel drug delivery systems offer new possibilities for treating aged muscle loss. Herein, we briefly recapitulate the potential therapeutic targets of aged skeletal muscle and provide a concise advance in the drug delivery systems, mainly focus on the use of nano-carriers. Furthermore, we elaborately discuss the prospect of aged skeletal muscle treatment by nanotechnology approaches.

miR-26a Limits Muscle Wasting and Cardiac Fibrosis through Exosome-Mediated microRNA Transfer in Chronic Kidney Disease

Uremic cardiomyopathy and muscle atrophy are associated with insulin resistance and contribute to chronic kidney disease (CKD)-induced morbidity and mortality. We hypothesized that restoration of miR-26a levels would enhance exosome-mediated microRNA transfer to improve muscle wasting and cardiomyopathy that occur in CKD.

Methods: Using next generation sequencing and qPCR, we found that CKD mice had a decreased level of miR-26a in heart and skeletal muscle. We engineered an exosome vector that contained Lamp2b, an exosomal membrane protein gene fused with a muscle-specific surface peptide that targets muscle delivery. We transfected this vector into muscle satellite cells and then transduced these cells with adenovirus that expresses miR-26a to produce exosomes encapsulated miR-26a (Exo/miR-26a). Exo/miR-26a was injected once per week for 8 weeks into the tibialis anterior (TA) muscle of 5/6 nephrectomized CKD mice.

Results: Treatment with Exo/miR-26a resulted in increased expression of miR-26a in skeletal muscle and heart. Overexpression of miR-26a increased the skeletal muscle cross-sectional area, decreased the upregulation of FBXO32/atrogin-1 and TRIM63/MuRF1 and depressed cardiac fibrosis lesions. In the hearts of CKD mice, FoxO1 was activated, and connective tissue growth factor, fibronectin and collagen type I alpha 1 were increased. These responses were blunted by injection of Exo/miR-26a. Echocardiograms showed that cardiac function was improved in CKD mice treated with Exo/miR-26a.

Conclusion: Overexpression of miR-26a in muscle prevented CKD-induced muscle wasting and attenuated cardiomyopathy via exosome-mediated miR-26a transfer. These results suggest possible therapeutic strategies for using exosome delivery of miR-26a to treat complications of CKD.

Long Noncoding RNA lncMUMA Reverses Established Skeletal Muscle Atrophy following Mechanical Unloading

Reversing established muscle atrophy following mechanical unloading is of great clinical challenge. Long noncoding RNAs (lncRNAs) have been demonstrated to play important roles in myogenesis. Here we identified a lncRNA (mechanical unloading-induced muscle atrophy-related lncRNA [lncMUMA]) enriched in muscle, which was the most downregulated lncRNA during muscle atrophy development in hindlimb suspension (HLS) mice. The in vitro and in vivo data demonstrated that the decreased expression levels of lncMUMA closely associated with a reduction of myogenesis during mechanical unloading. Mechanistically, lncMUMA promoted myogenic differentiation by functioning as a miR-762 sponge to regulate the core myogenic regulator MyoD in vitro. The enforced expression of lncMUMA relieved the decreases in MyoD protein and muscle mass in miR-762 knockin mice. Therapeutically, the enforced expression of lncMUMA improved the in vitro myogenic differentiation of myoblasts under microgravity simulation, prevented the muscle atrophy development, and reversed the established muscle atrophy in HLS mice. These findings identify lncMUMA as an anabolic regulator to reverse established muscle atrophy following mechanical unloading.

Characterization of In Vivo Selected Bacteriophage for the Development of Novel Tumor-Targeting Agents with Specific Pharmacokinetics and Imaging Applications

Bacteriophage (phage) display technology is a powerful strategy for the identification of peptide-based tumor targeting agents for drug discovery. Phage selections performed in vitro often result in many phage clones/peptides with similar properties and often similar sequence. However, these phage and corresponding peptides are selected, validated, and characterized outside the complicated milieu of a living animal. Thus, there is no guarantee that peptides from in vitro selections will successfully meet the requirements of an in vivo targeting compound. In comparison, in vivo phage display selections have the distinct advantage of identifying phage clones with robust pharmacokinetics and tumor/tissue targeting ability. This capacity has allowed for the identification of peptides with specific in vivo localization and/or clearance profiles. However, in vivo phage display selections also have the potential to result in an array of phage clones with various and unknown targets and little to no sequence similarity. Given these shortcomings, we have developed methods to select phage peptide display libraries in living mice to identify phage (and corresponding synthesized peptides) with specific clearance and/or tumor-targeting propensity. Additionally, we describe the use of labeled phage clones for the efficient screening of selected phage/peptides to aid in the identification and characterization of a phage clone with an optimal and specific pharmacokinetic profile.

Evaluation of Amphiphilic Peptide Modified Antisense Morpholino Oligonucleotides In Vitro and in Dystrophic mdx Mice

A series of amphiphilic peptides modified PMO (Pt-PMO) were prepared, and their antisense effect and toxicity were evaluated both in vitro and in mdx mice. The results showed that the exon-skipping performance of Pt-PMO are relative to the structure of the conjugated peptide: the Pt3/Pt4 composed of six/seven arginines and one myristoylation modified PMO showed more efficacy and with less toxicity as compared to others, confirming that appropriate hydrophilic-lipophilic balance (HLB) and cationic sequence numbers play a crucial role in improving cell uptake and corresponding exon-skipping efficiency. This was observed particularly in enhanced delivery efficiency of PMO comparable to B-PMO in vitro, while 6-fold improved exon-skipping was achieved against naked PMO in vivo. The multi-PMO modified Pt8-PMO also showed improved exon-skipping both in vitro and in vivo, though there is lower efficiency in systemic delivery as compared to Pt4-PMO. These data suggest that with optimization of peptide in component, charge density has clear potential for exploration towards achieving higher efficiency of antisense oligonucleotide systemic delivery, and thus is more applicable for clinical application.

Translational development of splice-modifying antisense oligomers

INTRODUCTION

Antisense nucleic acid analogues can interact with pre-mRNA motifs and influence exon or splice site selection and thereby alter gene expression. Design of antisense molecules to target specific motifs can result in either exon exclusion or exon inclusion during splicing. Novel drugs exploiting the antisense concept are targeting rare, life-limiting diseases; however, the potential exists to treat a wide range of conditions by antisense-mediated splice intervention. Areas covered: In this review, the authors discuss the clinical translation of novel molecular therapeutics to address the fatal neuromuscular disorders Duchenne muscular dystrophy and spinal muscular atrophy. The review also highlights difficulties posed by issues pertaining to restricted participant numbers, variable phenotype and disease progression, and the identification and validation of study endpoints. Expert opinion: Translation of novel therapeutics for Duchenne muscular dystrophy and spinal muscular atrophy has been greatly advanced by multidisciplinary research, academic-industry partnerships and in particular, the engagement and support of the patient community. Sponsors, supporters and regulators are cooperating to deliver new drugs and identify and define meaningful outcome measures. Non-conventional and adaptive trial design could be particularly suited to clinical evaluation of novel therapeutics and strategies to treat serious, rare diseases that may be problematic to study using more conventional clinical trial structures.

Perspective on Adeno-Associated Virus Capsid Modification for Duchenne Muscular Dystrophy Gene Therapy

Duchenne muscular dystrophy (DMD) is a X-linked, progressive childhood myopathy caused by mutations in the dystrophin gene, one of the largest genes in the genome. It is characterized by skeletal and cardiac muscle degeneration and dysfunction leading to cardiac and/or respiratory failure. Adeno-associated virus (AAV) is a highly promising gene therapy vector. AAV gene therapy has resulted in unprecedented clinical success for treating several inherited diseases. However, AAV gene therapy for DMD remains a significant challenge. Hurdles for AAV-mediated DMD gene therapy include the difficulty to package the full-length dystrophin coding sequence in an AAV vector, the necessity for whole-body gene delivery, the immune response to dystrophin and AAV capsid, and the species-specific barriers to translate from animal models to human patients. Capsid engineering aims at improving viral vector properties by rational design and/or forced evolution. In this review, we discuss how to use the state-of-the-art AAV capsid engineering technologies to overcome hurdles in AAV-based DMD gene therapy.

Current understanding of molecular pathology and treatment of cardiomyopathy in duchenne muscular dystrophy

Duchenne muscular dystrophy (DMD) is a genetic muscle disorder caused by mutations in the Dmd gene resulting in the loss of the protein dystrophin. Patients do not only experience skeletal muscle degeneration, but also develop severe cardiomyopathy by their second decade, one of the main causes of death. The absence of dystrophin in the heart renders cardiomyocytes more sensitive to stretch-induced damage. Moreover, it pathologically alters intracellular calcium (Ca²⁺) concentration, neuronal nitric oxide synthase (nNOS) localization and mitochondrial function and leads to inflammation and necrosis, all contributing to the development of cardiomyopathy. Current therapies only treat symptoms and therefore the need for targeting the genetic defect is immense. Several preclinical therapies are undergoing development, including utrophin up-regulation, stop codon read-through therapy, viral gene therapy, cell-based therapy and exon skipping. Some of these therapies are undergoing clinical trials, but these have predominantly focused on skeletal muscle correction. However, improving skeletal muscle function without addressing cardiac aspects of the disease may aggravate cardiomyopathy and therefore it is essential that preclinical and clinical focus include improving heart function. This review consolidates what is known regarding molecular pathology of the DMD heart, specifically focusing on intracellular Ca²⁺, nNOS and mitochondrial dysregulation. It briefly discusses the current treatment options and then elaborates on the preclinical therapeutic approaches currently under development to restore dystrophin thereby improving pathology, with a focus on the heart.

Effective dystrophin restoration by a novel muscle-homing peptide-morpholino conjugate in dystrophin-deficient mdx mice

Antisense oligonucleotide (AO)-mediated splice correction therapy for Duchenne muscular dystrophy has shown huge promise from recent phase 2b clinical trials, however high doses and costs are required and targeted delivery can lower both of these. We have previously demonstrated the feasibility of targeted delivery of AOs by conjugating a chimeric peptide, consisting of a muscle-specific peptide and a cell-penetrating peptide, to AOs in mdx mice. Although increased uptake in muscle was observed, the majority of peptide-AO conjugate was found in the liver. To search for more effective muscle-homing peptides, we carried out in vitro biopanning in myoblasts and identified a novel 12-mer peptide (M12) showing preferential binding to skeletal muscle compared to the liver. When conjugated to phosphorodiamidate morpholino oligomers, ~25% of normal level of dystrophin expression was achieved in body-wide skeletal muscles in mdx mice with significant recovery in grip strength, whereas <2% in corresponding tissues treated with either muscle-specific peptide-phosphorodiamidate morpholino oligomer or unmodified phosphorodiamidate morpholino oligomer under identical conditions. Our data provide evidences for the first time that a muscle-homing peptide alone can enhance AO delivery to muscle without appreciable toxicity at 75 mg/kg, suggesting M12-phosphorodiamidate morpholino oligomer can be an alternative option to current AOs.

Peptide conjugation of 2'-O-methyl phosphorothioate antisense oligonucleotides enhances cardiac uptake and exon skipping in mdx mice

Antisense oligonucleotide (AON)-mediated exon skipping is a promising therapeutic approach for Duchenne muscular dystrophy that is currently being tested in various clinical trials. This approach is based on restoring the open reading frame of dystrophin transcripts resulting in shorter but partially functional dystrophin proteins as found in patients with Becker muscular dystrophy. After systemic administration, a large proportion of AONs ends up in the liver and kidneys. Therefore, enhancing AON uptake by skeletal and cardiac muscle would improve the AONs' therapeutic effect. For phosphorodiamidate morpholino oligomer, AONs use nonspecific positively charged cell penetrating peptides to enhance efficacy. However, this is challenging for negatively charged 2'-O-methyl phosphorothioate oligomer. Therefore, we screened a 7-mer phage display peptide library to identify muscle and heart homing peptides in vivo in the mdx mouse model and found a promising candidate peptide capable of binding muscle cells in vitro and in vivo. Upon systemic administration in dystrophic mdx mice, conjugation of a 2'-O-methyl phosphorothioate AON to this peptide indeed improved uptake in skeletal and cardiac muscle, and resulted in higher exon skipping levels with a significant difference in heart and diaphragm. Based on these results, peptide conjugation represents an interesting strategy to enhance the therapeutic effect of exon skipping with 2'-O-methyl phosphorothioate AONs for Duchenne muscular dystrophy.

Context Dependent Effects of Chimeric Peptide Morpholino Conjugates Contribute to Dystrophin Exon-skipping Efficiency

We have recently reported that cell-penetrating peptides (CPPs) and novel chimeric peptides containing CPP (referred as B peptide) and muscle-targeting peptide (referred as MSP) motifs significantly improve the systemic exon-skipping activity of morpholino phosphorodiamidate oligomers (PMOs) in dystrophin-deficient mdx mice. In the present study, the general mechanistic significance of the chimeric peptide configuration on the activity and tissue uptake of peptide conjugated PMOs in vivo was investigated. Four additional chimeric peptide-PMO conjugates including newly identified peptide 9 (B-9-PMO and 9-B-PMO) and control peptide 3 (B-3-PMO and 3-B-PMO) were tested in mdx mice. Immunohistochemical staining, RT-PCR and western blot results indicated that B-9-PMO induced significantly higher level of exon skipping and dystrophin restoration than its counterpart (9-B-PMO), further corroborating the notion that the activity of chimeric peptide-PMO conjugates is dependent on relative position of the tissue-targeting peptide motif within the chimeric peptide with respect to PMOs. Subsequent mechanistic studies showed that enhanced cellular uptake of B-MSP-PMO into muscle cells leads to increased exon-skipping activity in comparison with MSP-B-PMO. Surprisingly, further evidence showed that the uptake of chimeric peptide-PMO conjugates of both orientations (B-MSP-PMO and MSP-B-PMO) was ATP- and temperature-dependent and also partially mediated by heparan sulfate proteoglycans (HSPG), indicating that endocytosis is likely the main uptake pathway for both chimeric peptide-PMO conjugates. Collectively, our data demonstrate that peptide orientation in chimeric peptides is an important parameter that determines cellular uptake and activity when conjugated directly to oligonucleotides. These observations provide insight into the design of improved cell targeting compounds for future therapeutics studies.

In vivo phage display--a discovery tool in molecular biomedicine

In vivo phage display is a high-throughput method for identifying target ligands specific for different vascular beds. Targeting is possible due to the heterogeneous expression of receptors and other antigens in a particular vascular bed. Such expression is additionally influenced by the physiological or pathological status of the vasculature. In vivo phage display represents a technique that is usable in both, vascular mapping and targeted drug development. In this review, several important methodological aspects of in vivo phage display experiments are discussed. These include choosing an appropriate phage library, an appropriate animal model and the route of phage library administration. In addition, peptides or antibodies identified by in vivo phage display homing to specific types of vascular beds, including the altered vasculature present in several types of diseases are summarized. Still, confirmation in independent experiments and reproduction of identified sequences are needed for enhancing the clinical applicability of in vivo phage display research.

Optimizing tissue-specific antisense oligonucleotide-peptide conjugates

Cell-targeting peptides which improve tissue-specific delivery of antisense oligonucleotides (AONs) are a new exciting "next-generation" potential AON therapy. New peptides are regularly developed which increase targeting and cell penetration for the AON treatment of mRNA misregulated diseases. Optimization of these peptide conjugate AONs requires systematic treatment and methods of analysis. This chapter describes methods for analyzing cell-targeting peptide conjugated AONs in primary cultured cell lines and for local and systemic delivery to the mouse for the treatment of Duchenne muscular dystrophy (DMD). Chimeric and novel cell-penetrating peptides have already been described to induce high levels of exon skipping and dystrophin protein expression in tissues body-wide at very low doses of AON. Screening of future novel peptides may be achieved by preliminary in vitro screening followed by in vivo administration of the most promising peptide-conjugated AONs. Physiological and functional correction of dystrophin protein may be confirmed by a number of techniques as described and allows for the fast-tracking of candidate peptides to drug trial for DMD.

Novel compounds for the treatment of Duchenne muscular dystrophy: emerging therapeutic agents

The identification of dystrophin and the causative role of mutations in this gene in Duchenne and Becker muscular dystrophies (D/BMD) was expected to lead to timely development of effective therapies. Despite over 20 years of research, corticosteroids remain the only available pharmacological treatment for DMD, although significant benefits and extended life have resulted from advances in the clinical care and management of DMD individuals. Effective treatment of DMD will require dystrophin restitution in skeletal, cardiac, and smooth muscles and nonmuscle tissues; however, modulation of muscle loss and regeneration has the potential to play an important role in altering the natural history of DMD, particularly in combination with other treatments. Emerging biological, molecular, and small molecule therapeutics are showing promise in ameliorating this devastating disease, and it is anticipated that regulatory environments will need to display some flexibility in order to accommodate the new treatment paradigms.