A Randomized Phase 1 Safety, Pharmacokinetic and Pharmacodynamic Study of the Novel Myostatin Inhibitor Apitegromab (SRK-015): A Potential Treatment for Spinal Muscular Atrophy

Neuromuscular Disorders in Pediatric Respiratory Disease

Respiratory sequelae are a frequent cause of morbidity and mortality in children with NMD. Impaired cough strength and resulting airway clearance as well as sleep disordered breathing are the two main categories of respiratory sequelae. Routine clinical evaluation and diagnostic testing by pulmonologists is an important pillar of the multidisciplinary care required for children with NMD. Regular surveillance for respiratory disease and timely implementation of treatment including pulmonary clearance techniques as well as ventilation can prevent respiratory related morbidity including hospital admissions and improve survival. Additionally, novel disease modifying therapies for some NMDs are now available which has significantly improved the clinical trajectories of patients resulting in a paradigm shift in clinical care. Pulmonologists are 'learning' the new natural history for these diseases and adjusting clinical management accordingly.

Ubiquitination Insight from Spinal Muscular Atrophy-From Pathogenesis to Therapy: A Muscle Perspective

Spinal muscular atrophy (SMA) is one of the most frequent causes of death in childhood. The disease's molecular basis is deletion or mutations in the SMN1 gene, which produces reduced survival motor neuron protein (SMN) levels. As a result, there is spinal motor neuron degeneration and a large increase in muscle atrophy, in which the ubiquitin-proteasome system (UPS) plays a significant role. In humans, a paralogue of SMN1, SMN2 encodes the truncated protein SMNΔ7. Structural differences between SMN and SMNΔ7 affect the interaction of the proteins with UPS and decrease the stability of the truncated protein. SMN loss affects the general ubiquitination process by lowering the levels of UBA1, one of the main enzymes in the ubiquitination process. We discuss how SMN loss affects both SMN stability and the general ubiquitination process, and how the proteins involved in ubiquitination could be used as future targets for SMA treatment.

Pathogenesis of Sarcopenia in Chronic Kidney Disease-The Role of Inflammation, Metabolic Dysregulation, Gut Dysbiosis, and microRNA

Chronic kidney disease (CKD) is a progressive disorder associated with a decline in kidney function. Consequently, patients with advanced stages of CKD require renal replacement therapies, such as dialysis and kidney transplantation. Various conditions lead to the development of CKD, including diabetes mellitus, hypertension, and glomerulonephritis, among others. The disease is associated with metabolic and hormonal dysregulation, including uraemia and hyperparathyroidism, as well as with low-grade systemic inflammation. Altered homeostasis increases the risk of developing severe comorbidities, such as cardiovascular diseases or sarcopenia, which increase mortality. Sarcopenia is defined as a progressive decline in muscle mass and function. However, the precise mechanisms that link CKD and the development of sarcopenia are poorly understood. Knowledge about these linking mechanisms might lead to the introduction of precise treatment strategies that could prevent muscle wasting. This review discusses inflammatory mediators, metabolic and hormonal dysregulation, gut microbiota dysbiosis, and non-coding RNA alterations that could link CKD and sarcopenia.

Synergistically Acting on Myostatin and Agrin Pathways Increases Neuromuscular Junction Stability and Endurance in Old Mice

Sarcopenia is the primary cause of impaired motor performance in the elderly. The current prevailing approach to counteract such condition is increasing the muscle mass through inhibition of the myostatin system: however, this strategy only moderately improves muscular strength, not being able to sustain the innervation of the hypertrophic muscle per se, leading to a progressive worsening of motor performances. Thus, we proposed the administration of ActR-Fc-nLG3, a protein that combines the soluble activin receptor, a strong myostatin inhibitor, with the C-terminal agrin nLG3 domain. This compound has the potential of reinforcing neuro-muscular stability to the hypertrophic muscle. We previously demonstrated an enhancement of motor endurance and ACh receptor aggregation in young mice after ActR-Fc-nLG3 administration. Now we extended these observations by demonstrating that also in aged (2 years-old) mice, long-term administration of ActR-Fc-nLG3 increases in a sustained way both motor endurance and muscle strength, compared with ActR-Fc, a myostatin inhibitor, alone. Histological data demonstrate that the administration of this biological improves neuromuscular stability and fiber innervation maintenance, preventing muscle fiber atrophy and inducing only moderate hypertrophy. Moreover, at the postsynaptic site we observe an increased folding in the soleplate, a likely anatomical substrate for improved neurotransmission efficiency in the NMJ, that may lead to enhanced motor endurance. We suggest that ActR-Fc-nLG3 may become a valid option for treating sarcopenia and possibly other disorders of striatal muscles.

Safety and Efficacy of Apitegromab in Patients With Spinal Muscular Atrophy Types 2 and 3: The Phase 2 TOPAZ Study

BACKGROUND AND OBJECTIVES

Currently approved therapies for spinal muscular atrophy (SMA) reverse the degenerative course, leading to better functional outcome, but they do not address the impairment arising from preexisting neurodegeneration. Apitegromab, an investigational, fully human monoclonal antibody, inhibits activation of myostatin (a negative regulator of skeletal muscle growth), thereby preserving muscle mass. The phase 2 TOPAZ trial assessed the safety and efficacy of apitegromab in individuals with later-onset type 2 and type 3 SMA.

METHODS

In this study, designed to investigate potential meaningful combinations of eligibility and treatment regimen for future studies, participants aged 2-21 years received IV apitegromab infusions every 4 weeks for 12 months in 1 of 3 cohorts. Cohort 1 stratified ambulatory participants aged 5-21 years into 2 arms (apitegromab 20 mg/kg alone or in combination with nusinersen); cohort 2 evaluated apitegromab 20 mg/kg combined with nusinersen in nonambulatory participants aged 5-21 years; and cohort 3 blindly evaluated 2 randomized apitegromab doses (2 and 20 mg/kg) combined with nusinersen in younger participants ≥2 years of age. The primary efficacy measure was mean change from baseline using the Hammersmith Functional Motor Scale version appropriate for each cohort. Data were analyzed using a paired t test with 2-sided 5% type 1 error for the mean change from baseline for predefined cohort-specific primary efficacy end points.

RESULTS

Fifty-eight participants (mean age 9.4 years) were enrolled at 16 trial sites in the United States and Europe. Participants had been treated with nusinersen for a mean of 25.9 months before enrollment in any of the 3 trial cohorts. At month 12, the mean change from baseline in Hammersmith scale score was -0.3 points (95% CI -2.1 to 1.4) in cohort 1 (n = 23), 0.6 points (-1.4 to 2.7) in cohort 2 (n = 15), and in cohort 3 (n = 20), the mean scores were 5.3 (-1.5 to 12.2) and 7.1 (1.8 to 12.5) for the 2-mg/kg (n = 8) and 20-mg/kg (n = 9) arms, respectively. The 5 most frequently reported treatment-emergent adverse events were headache (24.1%), pyrexia (22.4%), upper respiratory tract infection (22.4%), cough (22.4%), and nasopharyngitis (20.7%). No deaths or serious adverse reactions were reported.

DISCUSSION

Apitegromab led to improved motor function in participants with later-onset types 2 and 3 SMA. These results support a randomized, placebo-controlled phase 3 trial of apitegromab in participants with SMA.

TRIAL REGISTRATION INFORMATION

This trial is registered with ClinicalTrials.gov (NCT03921528).

CLASSIFICATION OF EVIDENCE

This study provides Class III evidence that apitegromab improves motor function in later-onset types 2 and 3 spinal muscular atrophy.

Autophagy in spinal muscular atrophy: from pathogenic mechanisms to therapeutic approaches

Spinal muscular atrophy (SMA) is a devastating neuromuscular disorder caused by the depletion of the ubiquitously expressed survival motor neuron (SMN) protein. While the genetic cause of SMA has been well documented, the exact mechanism(s) by which SMN depletion results in disease progression remain elusive. A wide body of evidence has highlighted the involvement and dysregulation of autophagy in SMA. Autophagy is a highly conserved lysosomal degradation process which is necessary for cellular homeostasis; defects in the autophagic machinery have been linked with a wide range of neurodegenerative disorders, including amyotrophic lateral sclerosis, Alzheimer's disease and Parkinson's disease. The pathway is particularly known to prevent neurodegeneration and has been suggested to act as a neuroprotective factor, thus presenting an attractive target for novel therapies for SMA patients. In this review, (a) we provide for the first time a comprehensive summary of the perturbations in the autophagic networks that characterize SMA development, (b) highlight the autophagic regulators which may play a key role in SMA pathogenesis and (c) propose decreased autophagic flux as the causative agent underlying the autophagic dysregulation observed in these patients.

Sarcopenia and Diabetes: A Detrimental Liaison of Advancing Age

Sarcopenia is an age-related clinical complaint characterized by the progressive deterioration of skeletal muscle mass and strength over time. Type 2 diabetes (T2D) is associated with faster and more relevant skeletal muscle impairment. Both conditions influence each other, leading to negative consequences on glycemic control, cardiovascular risk, general health status, risk of falls, frailty, overall quality of life, and mortality. PubMed/Medline, Scopus, Web of Science, and Google Scholar were searched for research articles, scientific reports, observational studies, clinical trials, narrative and systematic reviews, and meta-analyses to review the evidence on the pathophysiology of di-abetes-induced sarcopenia, its relevance in terms of glucose control and diabetes-related outcomes, and diagnostic and therapeutic challenges. The review comprehensively addresses key elements for the clinical definition and diagnostic criteria of sarcopenia, the pathophysiological correlation be-tween T2D, sarcopenia, and related outcomes, a critical review of the role of antihyperglycemic treatment on skeletal muscle health, and perspectives on the role of specific treatment targeting myokine signaling pathways involved in glucose control and the regulation of skeletal muscle metabolism and trophism. Prompt diagnosis and adequate management, including lifestyle inter-vention, health diet programs, micronutrient supplementation, physical exercise, and pharmaco-logical treatment, are needed to prevent or delay skeletal muscle deterioration in T2D.

Spinal Muscular Atrophy: A (Now) Treatable Neurodegenerative Disease

Spinal muscular atrophy (SMA) is a progressive disease of the lower motor neurons associated with recessive loss of the SMN1 gene, and which leads to worsening weakness and disability, and is fatal in its most severe forms. Over the past six years, three treatments have emerged, two drugs that modify exon splicing and one gene therapy, which have transformed the management of this disease. When treated pre-symptomatically, many children show normal early motor development, and the benefits extend from the newborn period to adulthood. Similar treatment approaches are now under investigation for rare types of SMA associated with genes beyond SMN1.

Muscle: an independent contributor to the neuromuscular spinal muscular atrophy disease phenotype

Spinal muscular atrophy (SMA) is a pediatric-onset neuromuscular disorder caused by insufficient survival motor neuron (SMN) protein. SMN restorative therapies are now approved for the treatment of SMA; however, they are not curative, likely due to a combination of imperfect treatment timing, inadequate SMN augmentation, and failure to optimally target relevant organs. Here, we consider the implications of imperfect treatment administration, focusing specifically on outcomes for skeletal muscle. We examine the evidence that muscle plays a contributing role in driving neuromuscular dysfunction in SMA. Next, we discuss how SMN might regulate the health of myofibers and their progenitors. Finally, we speculate on therapeutic outcomes of failing to raise muscle SMN to healthful levels and present strategies to restore function to this tissue to ensure better treatment results.

Current and emerging targeted therapies for spinal muscular atrophy

INTRODUCTION

Spinal muscular atrophy (SMA) is a progressive neurodegenerative disorder caused by insufficiency or total absence of the survival motor neuron protein due to a mutation in the SMN1 gene. The copy number of its paralog, SMN2, influences disease onset and phenotype severity. Current therapeutic approaches include viral and non-viral modalities affecting gene expression. Regulatory-approved drugs Spinraza (Nusinersen), Zolgensma (Onasemnogene abeparvovec), and Evrysdi (Risdiplam) are still being investigated during clinical trials and show benefits in the long-term for symptomatic and pre-symptomatic patients. However, some ongoing interventions require repeated drug administration.

AREAS COVERED

In this review, the authors describe the existing therapy based on point of application, focusing on recent clinical trials of antisense oligonucleotides, viral gene therapy, and splice modulators and thepotential routes for correcting the mutation to provide therapeutic levels of SMN protein.

EXPERT OPINION

In the opinion of the authors, multiple treatment options for patients with SMA shifted the treatment paradigm from palliative supportive care to improvedmotor function, increased survival, and greater quality of life for such patients. They further believe that the future in SMA treatment development lies incombining existing treatment options, targeting aspects of the disease refractory to these treatments, and using gene editing technologies.

Evaluation of the orally bioavailable 4-phenylbutyrate-tethered trichostatin A analogue AR42 in models of spinal muscular atrophy

Proximal spinal muscular atrophy (SMA) is a leading genetic cause for infant death in the world and results from the selective loss of motor neurons in the spinal cord. SMA is a consequence of low levels of SMN protein and small molecules that can increase SMN expression are of considerable interest as potential therapeutics. Previous studies have shown that both 4-phenylbutyrate (4PBA) and trichostatin A (TSA) increase SMN expression in dermal fibroblasts derived from SMA patients. AR42 is a 4PBA-tethered TSA derivative that is a very potent histone deacetylase inhibitor. SMA patient fibroblasts were treated with either AR42, AR19 (a related analogue), 4PBA, TSA or vehicle for 5 days and then immunostained for SMN localization. AR42 as well as 4PBA and TSA increased the number of SMN-positive nuclear gems in a dose-dependent manner while AR19 did not show marked changes in gem numbers. While gem number was increased in AR42-treated SMA fibroblasts, there were no significant changes in FL-SMN mRNA or SMN protein. The neuroprotective effect of this compound was then assessed in SMNΔ7 SMA (SMN2+/+;SMNΔ7+/+;mSmn-/-) mice. Oral administration of AR42 prior to disease onset increased the average lifespan of SMNΔ7 SMA mice by ~ 27% (20.1 ± 1.6 days for AR42-treated mice vs. 15.8 ± 0.4 days for vehicle-treated mice). AR42 treatment also improved motor function in these mice. AR42 treatment inhibited histone deacetylase (HDAC) activity in treated spinal cord although it did not affect SMN protein expression in these mice. AKT and GSK3β phosphorylation were both significantly increased in SMNΔ7 SMA mouse spinal cords. In conclusion, presymptomatic administration of the HDAC inhibitor AR42 ameliorates the disease phenotype in SMNΔ7 SMA mice in a SMN-independent manner possibly by increasing AKT neuroprotective signaling.

Myostatin: a potential therapeutic target for metabolic syndrome

Metabolic syndrome is a complex metabolic disorder, its main clinical manifestations are obesity, hyperglycemia, hypertension and hyperlipidemia. Although metabolic syndrome has been the focus of research in recent decades, it has been proposed that the occurrence and development of metabolic syndrome is related to pathophysiological processes such as insulin resistance, adipose tissue dysfunction and chronic inflammation, but there is still a lack of favorable clinical prevention and treatment measures for metabolic syndrome. Multiple studies have shown that myostatin (MSTN), a member of the TGF-β family, is involved in the development and development of obesity, hyperlipidemia, diabetes, and hypertension (clinical manifestations of metabolic syndrome), and thus may be a potential therapeutic target for metabolic syndrome. In this review, we describe the transcriptional regulation and receptor binding pathway of MSTN, then introduce the role of MSTN in regulating mitochondrial function and autophagy, review the research progress of MSTN in metabolic syndrome. Finally summarize some MSTN inhibitors under clinical trial and proposed the use of MSTN inhibitor as a potential target for the treatment of metabolic syndrome.

New therapies for spinal muscular atrophy: where we stand and what is next

The natural history of spinal muscular atrophy has been radically changed by the advent of improved standards of care and the availability of disease-modifying therapies. The aim of this paper is to provide the current therapeutic scenario including new perspectives and to report the challenges related to new phenotypes a few years after the therapies have become available. The paper also includes a review of real-world data that provides information on safety and efficacy in individuals that were not included in clinical trials. Special attention is paid to future perspectives both in terms of new drugs that are currently investigated in clinical trials or providing details on current developments in the use of the available drugs, including combination therapies or new modalities of dose or administration.  Conclusion: Clinical trials and real world data support the efficacy and safety profiles of the available drugs. At the moment there is not enough published evidence about the superiority of one product compared to the others. What is Known: • Safety and efficacy results of clinical trials have led in the last 6 years to the marketing of three drugs for spinal muscular atrophy, with different mechanisms of action. What is New: • Since the drug's approval, real-world data allow us to have data on bigger and heterogeneous groups of patients in contrast with those included in clinical trials. • In addition to the new molecules, combinations of therapies are currently being evaluated.

Direct bioanalysis or indirect calculation of target engagement and free drug exposure: do we apply double standards?

Analysis of "free" drug/target concentrations is important to set up appropriate pharmacokinetic-pharmacodynamic models, to evaluate active-drug exposure and target engagement. Such "free-analyte" determination could be done by direct bioanalysis using an appropriate "free-analyte" assay. Development of "free" assays is often considered challenging from a technological and regulatory perspective. The application of a "total-total" approach, where the "free-analyte" concentration is determined mathematically, is considered a more convenient option. In this perspective, we examine and discuss the challenges of this "total-total" approach, from the affinity data, the importance of applying an appropriate "total" assay, the impact of additional binding partners and the variability of the total drug/target assays and their impact on the quality and variability of the final "free-analyte" dataset.

Curing SMA: Are we there yet?

Loss or deletion of survival motor neuron 1 gene (SMN1) is causative for a severe and devastating neuromuscular disease, Spinal Muscular Atrophy (SMA). SMN1 produces SMN, a ubiquitously expressed protein, that is essential for the development and survival of motor neurons. Major advances and developments in SMA therapeutics are shifting the natural history of the disease. With three relatively new available therapies, nusinersen (Spinraza), onasemnogene abeparvovec (Zolgensma), and risdiplam (Evrysdi), patients survive longer and have improved outcomes. However, patients and families continue to face many challenges associated with use of these therapies, including poor treatment response and a variability in the benefits to those that do respond, suggesting that the quest for the SMA cure is not over. In this review, we discuss the current therapies, their limitations, and highlight necessary gaps that need to be addressed to guarantee the best outcomes for SMA patients.

Preclinical in vitro evaluation of immune suppression induced by GYM329, Fc-engineered sweeping antibody

Fc-engineering is commonly used to improve the therapeutic potency of antibody (Ab) treatments. Because FcγRIIb is the only inhibitory FcγR that contains an immunoreceptor tyrosine-based inhibition motif (ITIM), Fc-engineered Abs with enhanced binding affinity to FcγRIIb might provide immune suppression in clinical contexts. GYM329 is an anti-latent myostatin Fc-engineered Ab with increased affinity to FcγRIIb which is expected to improve muscle strength in patients with muscular disorders. Cross-linking of FcγRIIb by immune complex (IC) results in phosphorylation of ITIM to inhibit immune activation and apoptosis in B cells. We examined whether the IC of Fc-engineered Abs with enhanced binding affinity to FcγRIIb causes phosphorylation of ITIM or B cell apoptosis using GYM329 and its Fc variant Abs in human and cynomolgus-monkey (cyno) immune cells in vitro. IC of GYM329 with enhanced binding affinity to human FcγRIIb (×5) induced neither ITIM phosphorylation nor B cell apoptosis. As for GYM329, FcγRIIb should work as an endocytic receptor of small IC to sweep latent myostatin, so it is preferable that GYM329 induces neither ITIM phosphorylation nor B cell apoptosis to prevent immune suppression. In contrast, IC of myo-HuCy2b, the Ab with enhanced binding affinity to human FcγRIIb (×4), induced ITIM phosphorylation and B cell apoptosis. The result of the present study demonstrated that Fc-engineered Abs with similar binding affinity to FcγRIIb had different effects. Thus, it is important to also investigate FcγR-mediated immune functions other than binding to fully understand the biological effects of Fc-engineered Abs.

Advances and limitations for the treatment of spinal muscular atrophy

Spinal muscular atrophy (5q-SMA; SMA), a genetic neuromuscular condition affecting spinal motor neurons, is caused by defects in both copies of the SMN1 gene that produces survival motor neuron (SMN) protein. The highly homologous SMN2 gene primarily expresses a rapidly degraded isoform of SMN protein that causes anterior horn cell degeneration, progressive motor neuron loss, skeletal muscle atrophy and weakness. Severe cases result in limited mobility and ventilatory insufficiency. Untreated SMA is the leading genetic cause of death in young children. Recently, three therapeutics that increase SMN protein levels in patients with SMA have provided incremental improvements in motor function and developmental milestones and prevented the worsening of SMA symptoms. While the therapeutic approaches with Spinraza^®, Zolgensma^®, and Evrysdi^® have a clinically significant impact, they are not curative. For many patients, there remains a significant disease burden. A potential combination therapy under development for SMA targets myostatin, a negative regulator of muscle mass and strength. Myostatin inhibition in animal models increases muscle mass and function. Apitegromab is an investigational, fully human, monoclonal antibody that specifically binds to proforms of myostatin, promyostatin and latent myostatin, thereby inhibiting myostatin activation. A recently completed phase 2 trial demonstrated the potential clinical benefit of apitegromab by improving or stabilizing motor function in patients with Type 2 and Type 3 SMA and providing positive proof-of-concept for myostatin inhibition as a target for managing SMA. The primary goal of this manuscript is to orient physicians to the evolving landscape of SMA treatment.    

Spinal muscular atrophy

Spinal muscular atrophy (SMA) is a neurodegenerative disorder caused by mutations in SMN1 (encoding survival motor neuron protein (SMN)). Reduced expression of SMN leads to loss of α-motor neurons, severe muscle weakness and often early death. Standard-of-care recommendations for multidisciplinary supportive care of SMA were established in the past few decades. However, improved understanding of the pathogenetic mechanisms of SMA has led to the development of different therapeutic approaches. Three treatments that increase SMN expression by distinct molecular mechanisms, administration routes and tissue biodistributions have received regulatory approval with others in clinical development. The advent of the new therapies is redefining standards of care as in many countries most patients are treated with one of the new therapies, leading to the identification of emerging new phenotypes of SMA and a renewed characterization of demographics owing to improved patient survival.

Inhibition of myostatin and related signaling pathways for the treatment of muscle atrophy in motor neuron diseases

Myostatin is a negative regulator of skeletal muscle growth secreted by skeletal myocytes. In the past years, myostatin inhibition sparked interest among the scientific community for its potential to enhance muscle growth and to reduce, or even prevent, muscle atrophy. These characteristics make it a promising target for the treatment of muscle atrophy in motor neuron diseases, namely, amyotrophic lateral sclerosis (ALS) and spinal muscular atrophy (SMA), which are rare neurological diseases, whereby the degeneration of motor neurons leads to progressive muscle loss and paralysis. These diseases carry a huge burden of morbidity and mortality but, despite this unfavorable scenario, several therapeutic advancements have been made in the past years. Indeed, a number of different curative therapies for SMA have been approved, leading to a revolution in the life expectancy and outcomes of SMA patients. Similarly, tofersen, an antisense oligonucleotide, is now undergoing clinical trial phase for use in ALS patients carrying the SOD1 mutation. However, these therapies are not able to completely halt or reverse progression of muscle damage. Recently, a trial evaluating apitegromab, a myostatin inhibitor, in SMA patients was started, following positive results from preclinical studies. In this context, myostatin inhibition could represent a useful strategy to tackle motor symptoms in these patients. The aim of this review is to describe the myostatin pathway and its role in motor neuron diseases, and to summarize and critically discuss preclinical and clinical studies of myostatin inhibitors in SMA and ALS. Then, we will highlight promises and pitfalls related to the use of myostatin inhibitors in the human setting, to aid the scientific community in the development of future clinical trials.

Molecular Pathogenesis and New Therapeutic Dimensions for Spinal Muscular Atrophy

The condition known as 5q spinal muscular atrophy (SMA) is a devastating autosomal recessive neuromuscular disease caused by a deficiency of the ubiquitous protein survival of motor neuron (SMN), which is encoded by the SMN1 and SMN2 genes. It is one of the most common pediatric recessive genetic diseases, and it represents the most common cause of hereditary infant mortality. After decades of intensive basic and clinical research efforts, and improvements in the standard of care, successful therapeutic milestones have been developed, delaying the progression of 5q SMA and increasing patient survival. At the same time, promising data from early-stage clinical trials have indicated that additional therapeutic options are likely to emerge in the near future. Here, we provide updated information on the molecular underpinnings of SMA; we also provide an overview of the rapidly evolving therapeutic landscape for SMA, including SMN-targeted therapies, SMN-independent therapies, and combinational therapies that are likely to be key for the development of treatments that are effective across a patient’s lifespan.

Recent research on the treatment of spinal muscular atrophy

Spinal muscular atrophy (SMA) is an autosomal recessive neuromuscular disease characterized by progressive muscular weakness and atrophy. SMA, as an inherited disease, is the leading cause of death in infants and young children. Rapid progress has been made in the research field of SMA in recent years, and some related treatment drugs have been successfully approved for marketing. This article reviews the recent research advances in the treatment of SMA.

Preclinical Safety Assessment and Toxicokinetics of Apitegromab, an Antibody Targeting Proforms of Myostatin for the Treatment of Muscle-Atrophying Disease

Myostatin is a negative regulator of skeletal muscle and has become a therapeutic target for muscle atrophying disorders. Although previous inhibitors of myostatin offered promising preclinical data, these therapies demonstrated a lack of specificity toward myostatin signaling and have shown limited success in the clinic. Apitegromab is a fully human, monoclonal antibody that binds to human promyostatin and latent myostatin with a high degree of specificity, without binding mature myostatin and other closely related growth factors. To support the clinical development of apitegromab, we present data from a comprehensive preclinical assessment of its pharmacology, pharmacokinetics, and safety across multiple species. In vitro studies confirmed the ability of apitegromab to inhibit the activation of promyostatin. Toxicology studies in monkeys for 4 weeks and in adult rats for up to 26 weeks showed that weekly intravenous administration of apitegromab achieved sustained serum exposure and target engagement and was well-tolerated, with no treatment-related adverse findings at the highest doses tested of up to 100 mg/kg and 300 mg/kg in monkeys and rats, respectively. Additionally, results from an 8-week juvenile rat study showed no adverse effects on any endpoint, including neurodevelopmental, motor, and reproductive outcomes at 300 mg/kg administered weekly IV. In summary, the nonclinical pharmacology, pharmacokinetic, and toxicology data demonstrate that apitegromab is a selective inhibitor of proforms of myostatin that does not exhibit toxicities observed with other myostatin pathway inhibitors. These data support the conduct of ongoing clinical studies of apitegromab in adult and pediatric patients with spinal muscular atrophy (SMA).