Generalizable anchor aptamer strategy for loading nucleic acid therapeutics on exosomes

Clinical deployment of oligonucleotides requires delivery technologies that improve stability, target tissue accumulation and cellular internalization. Exosomes show potential as ideal delivery vehicles. However, an affordable generalizable system for efficient loading of oligonucleotides on exosomes remain lacking. Here, we identified an Exosomal Anchor DNA Aptamer (EAA) via SELEX against exosomes immobilized with our proprietary CP05 peptides. EAA shows high binding affinity to different exosomes and enables efficient loading of nucleic acid drugs on exosomes. Serum stability of thrombin inhibitor NU172 was prolonged by exosome-loading, resulting in increased blood flow after injury in vivo. Importantly, Duchenne Muscular Dystrophy PMO can be readily loaded on exosomes via EAA (EXOEAA-PMO). EXOEAA-PMO elicited significantly greater muscle cell uptake, tissue accumulation and dystrophin expression than PMO in vitro and in vivo. Systemic administration of EXOEAA-PMO elicited therapeutic levels of dystrophin restoration and functional improvements in mdx mice. Altogether, our study demonstrates that EAA enables efficient loading of different nucleic acid drugs on exosomes, thus providing an easy and generalizable strategy for loading nucleic acid therapeutics on exosomes.

Electrical impedance myography detects dystrophin-related muscle changes in mdx mice

BACKGROUND

The lack of functional dystrophin protein in Duchenne muscular dystrophy (DMD) causes chronic skeletal muscle inflammation and degeneration. Therefore, the restoration of functional dystrophin levels is a fundamental approach for DMD therapy. Electrical impedance myography (EIM) is an emerging tool that provides noninvasive monitoring of muscle conditions and has been suggested as a treatment response biomarker in diverse indications. Although magnetic resonance imaging (MRI) of skeletal muscles has become a standard measurement in clinical trials for DMD, EIM offers distinct advantages, such as portability, user-friendliness, and reduced cost, allowing for remote monitoring of disease progression or response to therapy. To investigate the potential of EIM as a biomarker for DMD, we compared longitudinal EIM data with MRI/histopathological data from an X-linked muscular dystrophy (mdx) mouse model of DMD. In addition, we investigated whether EIM could detect dystrophin-related changes in muscles using antisense-mediated exon skipping in mdx mice.

METHODS

The MRI data for muscle T2, the magnetic resonance spectroscopy (MRS) data for fat fraction, and three EIM parameters with histopathology were longitudinally obtained from the hindlimb muscles of wild-type (WT) and mdx mice. In the EIM study, a cell-penetrating peptide (Pip9b2) conjugated antisense phosphorodiamidate morpholino oligomer (PPMO), designed to induce exon-skipping and restore functional dystrophin production, was administered intravenously to mdx mice.

RESULTS

MRI imaging in mdx mice showed higher T2 intensity at 6 weeks of age in hindlimb muscles compared to WT mice, which decreased at ≥ 9 weeks of age. In contrast, EIM reactance began to decline at 12 weeks of age, with peak reduction at 18 weeks of age in mdx mice. This decline was associated with myofiber atrophy and connective tissue infiltration in the skeletal muscles. Repeated dosing of PPMO (10 mg/kg, 4 times every 2 weeks) in mdx mice led to an increase in muscular dystrophin protein and reversed the decrease in EIM reactance.

CONCLUSIONS

These findings suggest that muscle T2 MRI is sensitive to the early inflammatory response associated with dystrophin deficiency, whereas EIM provides a valuable biomarker for the noninvasive monitoring of subsequent changes in skeletal muscle composition. Furthermore, EIM reactance has the potential to monitor dystrophin-deficient muscle abnormalities and their recovery in response to antisense-mediated exon skipping.

Enhancing Antisense Oligonucleotide-Based Therapeutic Delivery with DG9, a Versatile Cell-Penetrating Peptide

Antisense oligonucleotide-based (ASO) therapeutics have emerged as a promising strategy for the treatment of human disorders. Charge-neutral PMOs have promising biological and pharmacological properties for antisense applications. Despite their great potential, the efficient delivery of these therapeutic agents to target cells remains a major obstacle to their widespread use. Cellular uptake of naked PMO is poor. Cell-penetrating peptides (CPPs) appear as a possibility to increase the cellular uptake and intracellular delivery of oligonucleotide-based drugs. Among these, the DG9 peptide has been identified as a versatile CPP with remarkable potential for enhancing the delivery of ASO-based therapeutics due to its unique structural features. Notably, in the context of phosphorodiamidate morpholino oligomers (PMOs), DG9 has shown promise in enhancing delivery while maintaining a favorable toxicity profile. A few studies have highlighted the potential of DG9-conjugated PMOs in DMD (Duchenne Muscular Dystrophy) and SMA (Spinal Muscular Atrophy), displaying significant exon skipping/inclusion and functional improvements in animal models. The article provides an overview of a detailed understanding of the challenges that ASOs face prior to reaching their targets and continued advances in methods to improve their delivery to target sites and cellular uptake, focusing on DG9, which aims to harness ASOs' full potential in precision medicine.

Loss of apical sodium bile acid transporter alters bile acid circulation and reduces biliary damage in cholangitis

Primary sclerosing cholangitis (PSC) is characterized by increased ductular reaction (DR), liver fibrosis, hepatic total bile acid (TBA) levels, and mast cell (MC) infiltration. Apical sodium BA transporter (ASBT) expression increases in cholestasis, and ileal inhibition reduces PSC phenotypes. FVB/NJ and multidrug-resistant 2 knockout (Mdr2-/-) mice were treated with control or ASBT Vivo-Morpholino (VM). We measured 1) ASBT expression and MC presence in liver/ileum; 2) liver damage/DR; 3) hepatic fibrosis/inflammation; 4) biliary inflammation/histamine serum content; and 5) gut barrier integrity/hepatic bacterial translocation. TBA/BA composition was measured in cholangiocyte/hepatocyte supernatants, intestine, liver, serum, and feces. Shotgun analysis was performed to ascertain microbiome changes. In vitro, cholangiocytes were treated with BAs ± ASBT VM, and histamine content and farnesoid X receptor (FXR) signaling were determined. Treated cholangiocytes were cocultured with MCs, and FXR signaling, inflammation, and MC activation were measured. Human patients were evaluated for ASBT/MC expression and histamine/TBA content in bile. Control patient- and PSC patient-derived three-dimensional (3-D) organoids were generated; ASBT, chymase, histamine, and fibroblast growth factor-19 (FGF19) were evaluated. ASBT VM in Mdr2-/- mice decreased 1) biliary ASBT expression, 2) PSC phenotypes, 3) hepatic TBA, and 4) gut barrier integrity compared with control. We found alterations between wild-type (WT) and Mdr2-/- mouse microbiome, and ASBT/MC and bile histamine content increased in cholestatic patients. BA-stimulated cholangiocytes increased MC activation/FXR signaling via ASBT, and human PSC-derived 3-D organoids secrete histamine/FGF19. Inhibition of hepatic ASBT ameliorates cholestatic phenotypes by reducing cholehepatic BA signaling, biliary inflammation, and histamine levels. ASBT regulation of hepatic BA signaling offers a therapeutic avenue for PSC.NEW & NOTEWORTHY We evaluated knockdown of the apical sodium bile acid transporter (ASBT) using Vivo-Morpholino in Mdr2KO mice. ASBT inhibition decreases primary sclerosing cholangitis (PSC) pathogenesis by reducing hepatic mast cell infiltration, altering bile acid species/cholehepatic shunt, and regulating gut inflammation/dysbiosis. Since a large cohort of PSC patients present with IBD, this study is clinically important. We validated findings in human PSC and PSC-IBD along with studies in novel human 3-D organoids formed from human PSC livers.

Morpholino oligonucleotide-mediated exon skipping for DMD treatment: Past insights, present challenges and future perspectives

Duchenne muscular dystrophy (DMD) is an X-linked genetic disease primarily affecting boys causing loss of the dystrophin protein, ultimately leading to muscle wastage and death by cardiac or respiratory failure. The genetic mutation involved can be overcome with antisense oligonucleotides which bind to a pre-mRNA and results in reading frame restoration by exon skipping. Phosphorodiamidate morpholino oligonucleotides (PMOs) are a class of antisense agents with a neutral backbone derived from RNA which can induce effective exon skipping. In this review, the evolution of PMOs in exon skipping therapy for the last two decades has been detailed with the gradual structural and functional advancements. Even though the success rate of PMObased therapy has been high with four FDA approved drugs, several key challenges are yet to overcome, one being the dystrophin restoration in cardiac muscle. The current scenario in further improvement of PMOs has been discussed along with the future perspectives that have the potential to revolutionize the therapeutic benefits in DMD.

Restoring Dystrophin Expression with Exon 44 and 53 Skipping in the DMD Gene in Immortalized Myotubes

Phosphorodiamidate morpholino oligomer (PMO)-mediated exon skipping is a therapeutic approach that applies to many Duchenne muscular dystrophy (DMD) patients harboring out-of-frame deletion mutations in the DMD gene. In particular, PMOs for skipping exon 44 have been developing in clinical trials, such as the drug NS-089/NCNP-02. Two exon 53 skipping PMOs, golodirsen and viltolarsen, have received conditional approval for treating patients due to their ability to restore dystrophin protein expression. Although promising, further development of exon-skipping technology is needed for patients to have more therapeutic benefit. This chapter describes evaluation methods of exon 44 and 53 skipping PMOs in immortalized DMD patient-derived skeletal muscle cells. We introduce how to quantify exon-skipping efficiencies and dystrophin rescue levels represented by RT-PCR and western blotting, respectively. The screening methods using immortalized patient myotubes can serve to find exon-skipping PMO drug candidates.

Viltolarsen: From Preclinical Studies to FDA Approval

Viltolarsen is a phosphorodiamidate morpholino antisense oligonucleotide (PMO) designed to skip exon 53 of the DMD gene for the treatment of Duchenne muscular dystrophy (DMD), one of the most common lethal genetic disorders characterized by progressive degeneration of skeletal muscles and cardiomyopathy. It was developed by Nippon Shinyaku in collaboration with the National Center of Neurology and Psychiatry (NCNP) in Japan based on the preclinical studies conducted in the DMD dog model at the NCNP. After showing hopeful results in pre-clinical trials and several clinical trials across North America and Japan, it received US Food and Drug Administration (FDA) approval for DMD in 2020. Viltolarsen restores the reading frame of the DMD gene by skipping  exon 53 and produces a truncated but functional form of dystrophin. It can treat approximately 8-10% of the DMD patient population. This paper aims to summarize the development of viltolarsen from preclinical trials to clinical trials to, finally, FDA approval, and discusses the challenges that come with fighting DMD using antisense therapy.

Inhibition of Epidermal Growth Factor Receptor Signaling by Antisense Oligonucleotides as a Novel Approach to Epidermal Growth Factor Receptor Inhibition

We report a novel method to inhibit epidermal growth factor receptor (EGFR) signaling using custom morpholino antisense oligonucleotides (ASOs) to drive expression of dominant negative mRNA isoforms of EGFR by ASO-induced exon skipping within the transmembrane (16) or tyrosine kinase domains (18 and 21). In vivo ASO formulations induced >95% exon skipping in several models of nonsmall cell lung cancer (NSCLC) and were comparable in efficacy to erlotinib in reducing colony formation, cell viability, and migration in EGFR mutant NSCLC (PC9). However, unlike erlotinib, ASOs maintained their efficacy in both erlotinib-resistant subclones (PC9-GR) and wild-type overexpressing EGFR models (H292), in which erlotinib had no significant effect. The most dramatic ASO-induced phenotype resulted from targeting the EGFR kinase domain directly, which resulted in maximal inhibition of phosphorylation of EGFR, Akt, and Erk in both PC9 and PC9GR cells. Phosphoproteomic mass spectrometry confirmed highly congruent impacts of exon 16-, 18-, and 21-directed ASOs compared with erlotinib on PC9 genome-wide cell signaling. Furthermore, EGFR-directed ASOs had no impact in EGFR-independent NSCLC models, confirming an EGFR-specific therapeutic mechanism. Further exploration of synergy of ASOs with existing tyrosine kinase inhibitors may offer novel clinical models to improve EGFR-targeted therapies for both mutant and wild-type NSCLC patients.

Cardio-respiratory and phenotypic rescue of dystrophin/utrophin-deficient mice by combination therapy

Duchenne muscular dystrophy (DMD) is a systemic progressive muscular disease caused by frame-disrupting mutations in the DMD gene. Although exon-skipping antisense oligonucleotides (AOs) are clinically approved and can correct DMD, insufficient muscle delivery limits efficacy. If AO activity can be enhanced by safe dietary supplements, clinical trials for efficacy can be undertaken rapidly to benefit patients. We showed previously that intravenous glycine enhanced phosphorodiamidate morpholino oligomer (PMO) delivery to peripheral muscles in mdx mice. Here, we demonstrate that the combination of oral glycine and metformin with intravenous PMO enhances PMO activity, dystrophin restoration, extends lifespan, and improves body-wide function and phenotypic rescue of dystrophin /utrophin double knock-out (DKO) mice without any overt adverse effects. The DKO mice treated with the combination without altering the approved administration protocol of PMO show improved cardio-respiratory and behavioral functions. Metformin and glycine individually are ineffective in DMD patients, but the combination of PMO with clinically-approved oral glycine and metformin might improve the efficacy of the treatment also in DMD patients. Our data suggest that this combination therapy might be an attractive therapy for DMD and potentially other muscle diseases requiring systemic treatment with AOs.

In Vitro Delivery of PMOs in Myoblasts by Electroporation

Antisense oligonucleotides (AONs) are small synthetic molecules of therapeutic interest for a variety of human disease. Their ability to bind mRNA and affect its splicing gives AONs potential use for exon skipping therapies aimed at restoring the dystrophin transcript reading frame for Duchenne muscular dystrophy (DMD) patients. The neutrally charged phosphorodiamidate morpholino oligomers (PMOs) are a stable and relatively nontoxic AON modification. To assess exon skipping efficiency in vitro, it is important to deliver them to target cells. Here, we describe a method for the delivery of PMOs to myoblasts by electroporation. The described protocol for the Amaxa 4D X unit nucleofector system allows efficient processing of 16 samples in one nucleocuvette strip, aiding in high-throughput PMO efficacy screens.

Fully automated fast-flow synthesis of antisense phosphorodiamidate morpholino oligomers

Rapid development of antisense therapies can enable on-demand responses to new viral pathogens and make personalized medicine for genetic diseases practical. Antisense phosphorodiamidate morpholino oligomers (PMOs) are promising candidates to fill such a role, but their challenging synthesis limits their widespread application. To rapidly prototype potential PMO drug candidates, we report a fully automated flow-based oligonucleotide synthesizer. Our optimized synthesis platform reduces coupling times by up to 22-fold compared to previously reported methods. We demonstrate the power of our automated technology with the synthesis of milligram quantities of three candidate therapeutic PMO sequences for an unserved class of Duchenne muscular dystrophy (DMD). To further test our platform, we synthesize a PMO that targets the genomic mRNA of SARS-CoV-2 and demonstrate its antiviral effects. This platform could find broad application not only in designing new SARS-CoV-2 and DMD antisense therapeutics, but also for rapid development of PMO candidates to treat new and emerging diseases.

Co-Operativity between MYC and BCL-2 Pro-Survival Proteins in Cancer

B-Cell Lymphoma 2 (BCL-2), c-MYC and related proteins are arguably amongst the most widely studied in all of biology. Every year there are thousands of papers reporting on different aspects of their biochemistry, cellular and physiological mechanisms and functions. This plethora of literature can be attributed to both proteins playing essential roles in the normal functioning of a cell, and by extension a whole organism, but also due to their central role in disease, most notably, cancer. Many cancers arise due to genetic lesions resulting in deregulation of both proteins, and indeed the development and survival of tumours is often dependent on co-operativity between these protein families. In this review we will discuss the individual roles of both proteins in cancer, describe cancers where co-operativity between them has been well-characterised and finally, some strategies to target these proteins therapeutically.

Medical management of muscle weakness in Duchenne muscular dystrophy

Introduction

Duchenne muscular dystrophy (DMD) is a childhood onset muscular dystrophy leading to shortened life expectancy. There are gaps in published DMD care guidelines regarding recently approved DMD medications and alternative steroid dosing regimens.

Methods

A list of statements about use of currently available therapies for DMD in the United States was developed based on a systematic literature review and expert panel feedback. Panelists’ responses were collected using a modified Delphi approach.

Results

Among corticosteroid regimens, either deflazacort or prednisone weekend dosing was preferred when payer requirements do not dictate choice. Most patients with exon 51 skip-amenable mutations should be offered eteplirsen, before or with a corticosteroid.

Discussion

The options available for medical management of the motor symptoms of DMD are expanding rapidly. The choice of medical therapies should balance expected benefit with side effects.

The Dystrophinopathies

PURPOSE OF REVIEW

The dystrophinopathies are among the most common neuromuscular conditions, and they include Duchenne and Becker muscular dystrophies. This article reviews the epidemiology, clinical manifestations, genetic cause, management, and new and emerging therapies for this condition.

RECENT FINDINGS

New studies have highlighted how oral corticosteroids have changed the natural history of the disease, prolonging ambulation in boys with Duchenne muscular dystrophy and reducing the risk of developing scoliosis and subsequent surgical correction, improving cardiac health, and increasing long-term survival. Additionally, recent publications have provided insights into how newer and emerging treatment options are becoming more common for this condition. With gene therapy being approved in the United States for the severe form, the dystrophinopathies represent model diseases to understand the personalization of genetic treatment.

SUMMARY

Improvement in the standardization of care and the use of oral corticosteroids have increased the life expectancy of patients with dystrophinopathy and changed the natural history of the disease. This article presents a summary of clinical features, diagnostic testing, and new and emerging treatment strategies for the dystrophinopathies.

Antisense Oligonucleotides: A Unique Treatment Approach

Synthetic Antisense oligonucleotides (ASOs) are novel and efficient laboratory tools to regulate the expression of specific genes, and have only recently come into clinical use. These are synthetic single-stranded DNA analogs, whose sequence is complementary to a target nucleotide and alter protein synthesis by several mechanisms. We herein provide a primer on the topic for pediatricians, as this group of drugs is likely to see many more drugs for previously incurable diseases.

Downregulation of hepatic stem cell factor by Vivo-Morpholino treatment inhibits mast cell migration and decreases biliary damage/senescence and liver fibrosis in Mdr2-/- mice

Primary sclerosing cholangitis (PSC) is characterized by increased mast cell (MC) infiltration, biliary damage and hepatic fibrosis. Cholangiocytes secrete stem cell factor (SCF), which is a chemoattractant for c-kit expressed on MCs. We aimed to determine if blocking SCF inhibits MC migration, biliary damage and hepatic fibrosis.

METHODS

FVB/NJ and Mdr2-/- mice were treated with Mismatch or SCF Vivo-Morpholinos. We measured (i) SCF expression and secretion; (ii) hepatic damage; (iii) MC migration/activation and histamine signaling; (iv) ductular reaction and biliary senescence; and (v) hepatic fibrosis. In human PSC patients, SCF expression and secretion were measured. In vitro, cholangiocytes were evaluated for SCF expression and secretion. Biliary proliferation/senescence was measured in cholangiocytes pretreated with 0.1% BSA or the SCF inhibitor, ISK03. Cultured HSCs were stimulated with cholangiocyte supernatant and activation measured. MC migration was determined with cholangiocytes pretreated with BSA or ISK03 loaded into the bottom of Boyden chambers and MCs into top chamber.

RESULTS

Biliary SCF expression and SCF serum levels increase in human PSC. Cholangiocytes, but not hepatocytes, from SCF Mismatch Mdr2-/- mice have increased SCF expression and secretion. Inhibition of SCF in Mdr2-/- mice reduced (i) hepatic damage; (ii) MC migration; (iii) histamine and SCF serum levels; and (iv) ductular reaction/biliary senescence/hepatic fibrosis. In vitro, cholangiocytes express and secrete SCF. Blocking biliary SCF decreased MC migration, biliary proliferation/senescence, and HSC activation.

CONCLUSION

Cholangiocytes secrete increased levels of SCF inducing MC migration, contributing to biliary damage/hepatic fibrosis. Targeting MC infiltration may be an option to ameliorate PSC progression.

The potential of utrophin and dystrophin combination therapies for Duchenne muscular dystrophy

Duchenne muscular dystrophy (DMD) is a lethal neuromuscular disorder caused by loss of dystrophin. Several therapeutic modalities are currently in clinical trials but none will achieve maximum functional rescue and full disease correction. Therefore, we explored the potential of combining the benefits of dystrophin with increases of utrophin, an autosomal paralogue of dystrophin. Utrophin and dystrophin can be co-expressed and co-localized at the same muscle membrane. Wild-type (wt) levels of dystrophin are not significantly affected by a moderate increase of utrophin whereas higher levels of utrophin reduce wt dystrophin, suggesting a finite number of actin binding sites at the sarcolemma. Thus, utrophin upregulation strategies may be applied to the more mildly affected Becker patients with lower dystrophin levels. Whereas increased dystrophin in wt animals does not offer functional improvement, overexpression of utrophin in wt mice results in a significant supra-functional benefit over wt. These findings highlight an additive benefit of the combined therapy and potential new unique roles of utrophin. Finally, we show a 30% restoration of wt dystrophin levels, using exon-skipping, together with increased utrophin levels restores dystrophic muscle function to wt levels offering greater therapeutic benefit than either single approach alone. Thus, this combination therapy results in additive functional benefit and paves the way for potential future combinations of dystrophin- and utrophin-based strategies.

Long-term treatment with eteplirsen in nonambulatory patients with Duchenne muscular dystrophy

This analysis aims to describe the outcomes of two nonambulatory patients with Duchenne muscular dystrophy (DMD) who participated in two clinical studies. The two consecutive trials of eteplirsen (studies 201 and 202) were conducted in patients with DMD (N = 12) and confirmed genetic mutations amenable to exon 51 skipping.In study 201, 12 patients were randomized to receive once-weekly, double-blind intravenous infusions of eteplirsen 30 or 50 mg/kg or placebo for 24 weeks; patients then received open-label eteplirsen during weeks 25 through 28. All 12 patients continued onto open-label extension study 202 and received long-term treatment with eteplirsen. We compared cardiac, pulmonary, and upper limb function and dystrophin production in the nonambulatory twin patients versus the 10 ambulatory patients through 240 combined treatment weeks.Ten study patients remained ambulatory through both studies, while the identical twin patients both experienced early, rapid loss of ambulation. The twin patients had greater disease severity at baseline (6-minute walk test [6MWT], 330 and 256 m) versus the other patients (n = 10; 6MWT range, 341-418 m). They maintained cardiac and upper limb function through combined week 240, with outcomes similar to those of the patients who remained ambulatory. Dystrophin production was confirmed following eteplirsen treatment.Despite the loss of ambulation, other markers of disease progression remained relatively stable in the eteplirsen-treated twin patients and were similar to those of the ambulatory patients.

Cell-Penetrating Peptide Conjugates of Steric Blocking Oligonucleotides as Therapeutics for Neuromuscular Diseases from a Historical Perspective to Current Prospects of Treatment

The review starts with a historical perspective of the achievements of the Gait group in synthesis of oligonucleotides (ONs) and their peptide conjugates toward the award of the 2017 Oligonucleotide Therapeutic Society Lifetime Achievement Award. This acts as a prelude to the rewarding collaborative studies in the Gait and Wood research groups aimed toward the enhanced delivery of charge neutral ON drugs and the development of a series of Arg-rich cell-penetrating peptides called Pip (peptide nucleic acid/phosphorodiamidate morpholino oligonucleotide [PNA/PMO] internalization peptides) as conjugates of such ONs. In this review we concentrate on these developments toward the treatment of the neuromuscular diseases Duchenne muscular dystrophy and spinal muscular atrophy toward a platform technology for the enhancement of cellular and in vivo delivery suitable for widespread use as neuromuscular and neurodegenerative ON drugs.

Peptide-conjugated phosphodiamidate oligomer-mediated exon skipping has benefits for cardiac function in mdx and Cmah-/-mdx mouse models of Duchenne muscular dystrophy

Cardiac failure is a major cause of mortality in patients with Duchenne muscular dystrophy (DMD). Antisense-mediated exon skipping has the ability to correct out-of-frame mutations in DMD to produce truncated but functional dystrophin. Traditional antisense approaches have however been limited by their poor uptake into cardiac muscle. The addition of cell-penetrating peptides to antisense molecules has increased their potency and improved their uptake into all muscles, including the heart. We have investigated the efficacy of the Peptide-conjugated phosphodiamidate morpholino oligomer (P-PMO) Pip6a-PMO, for restoration of cardiac dystrophin and functional rescue in DMD mice- the mdx mouse and the less well characterised Cmah-/-mdx mouse (which carry a human-like mutation in the mouse Cmah gene as well as a mutation in DMD). In our first study male mdx mice were administered Pip6a-PMO, i.v, fortnightly from 12 to 30 weeks of age alongside mock-injected age-matched mdx and C57BL10 controls. Mice received 4 doses of 18 mg/kg followed by 8 doses of 12.5 mg/kg. The cardiac function of the mice was analysed 2 weeks after their final injection by MRI followed by conductance catheter and their muscles were harvested for dystrophin quantification. In the second study, male Cmah-/-mdx mice, received 12.5 mg/kg Pip6a-PMO, i.v fortnightly from 8 to 26 weeks and assessed by MRI at 3 time points (12, 18 and 28 weeks) alongside mock-injected age-matched mdx, C57BL10 and Cmah-/-mdx controls. The mice also underwent MEMRI and conductance catheter at 28 weeks. This allowed us to characterise the cardiac phenotype of Cmah-/-mdx mice as well as assess the effects of P-PMO on cardiac function. Pip6a-PMO treatment resulted in significant restoration of dystrophin in mdx and Cmah-/-mdx mice (37.5% and 51.6%, respectively), which was sufficient to significantly improve cardiac function, ameliorating both right and left ventricular dysfunction. Cmah-/-mdx mice showed an abnormal response to dobutamine stress test and this was completely ameliorated by PIP6a-PMO treatment. These encouraging data suggest that total restoration of dystrophin may not be required to significantly improve cardiac outcome in DMD patients and that it may be realistic to expect functional improvements with modest levels of dystrophin restoration which may be very achievable in future clinical trials.

[Patients organizations and new drug approval in the US. Eteplirsen and Duchenne muscular dystrophy case]

INTRODUCTION

In 2016 the US Food and Drug Administration (FDA) granted the marketing authorization for eteplirsen for Duchenne muscular dystrophy. This has been a very controversial decision since it happened after a negative assessment from both the Advisory Committee and the technical FDA evaluation team. The FDA's Center for Drug Evaluation and Research (CDER) director was who ultimately approved the product, while the FDA Commissioner did not overrule that decision.

AIM

To report about the most relevant events regarding the approval of eteplirsen by the US FDA.

DEVELOPMENT

All relevant facts that occurred during the clinical development and evaluation phase following 'accelerated approval' procedure of eteplirsen are discussed in detail. The technical FDA evaluation team reasons supporting that the drug has not proven clinical benefit, the attitude of patient advocacy groups and the post-approval FDA requirements to the marketing authorization holder are discussed. Finally, we reflect on what is the situation Spanish patients face once eteplirsen is on the US market.

CONCLUSIONS

This is a unique case in the history of drug authorizations in western countries, that shows the difficulties that current regulations on accelerated approval of new medicines could have when interpreting scarce and low quality clinical development data, when dealing with rare diseases with no available therapies.

Experience-dependent reduction of soluble β-amyloid oligomers and rescue of cognitive abilities in middle-age Ts65Dn mice, a model of Down syndrome

Down syndrome (DS) is the most diffused genetic cause of intellectual disability and, after the age of forty, is invariantly associated with Alzheimer's disease (AD). In the last years, the prolongation of life expectancy in people with DS renders the need for intervention paradigms aimed at improving mental disability and counteracting AD pathology particularly urgent. At present, however, there are no effective therapeutic strategies for DS and concomitant AD in mid-life people. The most intensively studied mouse model of DS is the Ts65Dn line, which summarizes the main hallmarks of the DS phenotype, included severe learning and memory deficits and age-dependent AD-like pathology. Here we report for the first time that middle-age Ts65Dn mice display a marked increase in soluble Aβ oligomer levels in their hippocampus. Moreover, we found that long-term exposure to environmental enrichment (EE), a widely used paradigm that increases sensory-motor stimulation, reduces Aβ oligomers and rescues spatial memory abilities in trisomic mice. Our findings underscore the potential of EE procedures as a non-invasive paradigm for counteracting brain aging processes in DS subjects.

Selective Neuromuscular Denervation in Taiwanese Severe SMA Mouse Can Be Reversed by Morpholino Antisense Oligonucleotides

Spinal muscular atrophy (SMA) is an autosomal recessive motor neuron disease caused by deficiency of the survival of motor neuron (SMN) protein, which leads to synaptic defects and spinal motor neuron death. Neuromuscular junction (NMJ) abnormalities have been found to be involved in SMA pathogenesis in the SMNΔ7 SMA mouse model. However, whether similar NMJ pathological findings present in another commonly used mouse model, the Taiwanese SMA mouse, has not been fully investigated. To examine the NMJs of the Taiwanese severe SMA mouse model (Smn^-/-; SMN2^tg/0), which is characterized by severe phenotype and death before postnatal day (P) 9, we investigated 25 axial and appendicular muscles from P1 to P9. We labelled the muscles with anti-neurofilament and anti-synaptophysin antibodies for nerve terminals and α-bungarotoxin for acetylcholine receptors (AChRs). We found that severe NMJ denervation (<50% fully innervated endplates) selectively occurred in the flexor digitorum brevis 2 and 3 (FDB-2/3) muscles from P5, and an increased percentage of fully denervated endplates correlated with SMA progression. Furthermore, synaptophysin signals were absent at the endplate compared to control littermate mice, suggesting that vesicle transport might only be affected at the end stage. Subsequently, we treated the Taiwanese severe SMA mice with morpholino (MO) antisense oligonucleotides (80 μg/g) via subcutaneous injection at P0. We found that MO significantly reversed the NMJ denervation in FDB-2/3 muscles and extended the survival of Taiwanese severe SMA mice. We conclude that early NMJ denervation in the FDB-2/3 muscles of Taiwanese severe SMA mice can be reversed by MO treatment. The FDB-2/3 muscles of Taiwanese severe SMA mice provide a very sensitive platform for assessing the effectiveness of drug treatments in SMA preclinical studies.

Molecular, genetic and stem cell-mediated therapeutic strategies for spinal muscular atrophy (SMA)

Spinal muscular atrophy (SMA) is an autosomal recessive motor neuron disease. It is the first genetic cause of infant mortality. It is caused by mutations in the survival motor neuron 1 (SMN1) gene, leading to the reduction of SMN protein. The most striking component is the loss of alpha motor neurons in the ventral horn of the spinal cord, resulting in progressive paralysis and eventually premature death. There is no current treatment other than supportive care, although the past decade has seen a striking advancement in understanding of both SMA genetics and molecular mechanisms. A variety of disease modifying interventions are rapidly bridging the translational gap from the laboratory to clinical trials. In this review, we would like to outline the most interesting therapeutic strategies that are currently developing, which are represented by molecular, gene and stem cell-mediated approaches for the treatment of SMA.

[Treatment with antisense oligonucleotides in Duchenne's disease]

In this paper I review the results of the treatments directed to modify the mRNA of dystrophin with the goal of converting the severe Duchenne type to the milder Becker muscular dystrophy. Antisense oligomers potential to modify Duchenne muscular dystrophy (DMD) gene expression and therapeutic strategies to induce ribosomal read-through of nonsense mutations (PTC124) are described. They are an important advance in the treatment of DMD, so far unspecific. Significant expression of new dystrophin is observed in biopsies of peripheral muscle, although the functional improvement is not so encouraging. New modification of chemistries are expected to improve the liberation, broad distribution in muscles, as well as their efficacy and safety enough to allow a positive chronic treatment of DMD.

Morpholino-mediated increase in soluble Flt-1 expression results in decreased ocular and tumor neovascularization

Background

Angiogenesis is a key process in several ocular disorders and cancers. Soluble Flt-1 is an alternatively spliced form of the Flt-1 gene that retains the ligand-binding domain, but lacks the membrane-spanning and intracellular kinase domains of the full-length membrane bound Flt-1 (mbFlt-1) protein. Thus, sFlt-1 is an endogenous inhibitor of VEGF-A mediated angiogenesis. Synthetic mopholino oligomers directed against splice site targets can modulate splice variant expression. We hypothesize that morpholino-induced upregulation of sFlt-1 will suppress angiogenesis in clinically relevant models of macular degeneration and breast cancer.

Methods and Findings

In vivo morpholino constructs were designed to target murine exon/intron 13 junction of the Flt-1 transcript denoted VEGFR1_MOe13; standard nonspecific morpholino was used as control. After nucleofection of endothelial and breast adenocarcinoma cell lines, total RNA was extracted and real-time RT-PCR performed for sFlt-1 and mbFlt-1. Intravitreal injections of VEGFR1_MOe13 or control were done in a model of laser-induced choroidal neovascularization and intratumoral injections were performed in MBA-MD-231 xenografts in nude mice. VEGFR1_MOe13 elevated sFlt-1 mRNA expression and suppressed mbFlt-1 mRNA expression in vitro in multiple cellular backgrounds (p<0.001). VEGFR1_MOe13 also elevated sFlt/mbFlt-1 ratio in vivo after laser choroidal injury 5.5 fold (p<0.001) and suppressed laser-induced CNV by 50% (p = 0.0179). This latter effect was reversed by RNAi of sFlt-1, confirming specificity of morpholino activity through up-regulation of sFlt-1. In the xenograft model, VEGFR1_MOe13 regressed tumor volume by 88.9%, increased sFlt-1 mRNA expression, and reduced vascular density by 50% relative to control morpholino treatment (p<0.05).

Conclusions

Morpholino oligomers targeting the VEGFR1 mRNA exon/intron 13 junction promote production of soluble FLT-1 over membrane bound FLT-1, resulting in suppression of lesional volume in laser induced CNV and breast adenocarcinoma. Thus, morpholino manipulation of alternative splicing offers translational potential for therapy of angiogenic disorders.