Pharmacological Therapies of Spinal Muscular Atrophy: A Narrative Review of Preclinical, Clinical-Experimental, and Real-World Evidence

Oligonucleotide-based therapeutics for neurodegenerative disorders: Focus on antisense oligonucleotides

Antisense oligonucleotides (ASOs) specifically bind to target RNA sequences and regulate protein expression through various mechanisms. ASOs are a promising therapeutic approach for treating neurodegenerative diseases. The ASO field is a growing area of drug development that focuses on targeting the root cause of diseases at the RNA level, providing a promising alternative to therapies that target downstream processes. Addressing challenges related to off-target effects and inadequate biological activity is essential to successfully develop ASO-based therapies. Researchers have investigated various chemical modifications and delivery strategies to overcome these challenges. This review discusses oligonucleotide-based therapies, particularly ASOs. We discuss the chemical modifications and mechanisms of action of ASOs. Additionally, we recap the results of preclinical and clinical studies testing different ASOs in various neurodegenerative disorders, including spinal muscular atrophy, Huntington's disease, amyotrophic lateral sclerosis, Alzheimer's disease, and Parkinson's disease. In conclusion, ASO drugs show promise as a therapeutic option for treating neurodegenerative diseases.

Postmarketing adverse events associated with onasemnogene abeparvovec: a real-world pharmacovigilance study

BACKGROUND

Onasemnogene abeparvovec (OA) is an adeno-associated virus vector-based gene therapy indicated for the treatment of paediatric patients with spinal muscular atrophy(SMA) with biallelic mutations in the survival motor neuron 1 (SMN1) gene. This study focused on analysis of the postmarketing adverse events(AEs) of onasemnogene abeparvovec (OA) reported in the US Food and Drug Administration public data open project (openFDA) database to assess the safety of OA in the real world and to provide a reference for the rational use of this drug in the clinic.

RESULTS

In total, 1,959 AEs were reported with "onasemnogene abeparvovec" as the primary suspected drug. The top 5 most frequent AEs were pyrexia (461 cases), vomiting (434 cases), aspartate aminotransferase increase (284 cases), alanine aminotransferase increase (260 cases), and hepatic enzyme increase (237 cases). A total of 77 alert signals were generated, 60 of which were not included in the drug label. The top 5 signals included troponin I increase ( ROR of 895.21, 95% CI: 734.43-1091.18), troponin T increase ( ROR of 313.30, 95% CI:220.85-444.44), rhinovirus infection ( ROR of 175.80, 95% CI:130.86-236.17), troponin increase ( ROR of 143.49, 95% CI:114.96-179.10), and increased bronchial secretion ( ROR of 142.71, 95% CI:96.63-210.77). Further analysis of AEs associated with gender and age differences identified 14 high-risk signals related to gender and 10 high-risk signals related to age. Female patients should be vigilant for vomiting, thrombotic microangiopathy, increased troponin T, proteinuria, haematuria, haemolytic anaemia, urinary tract infection, generalised oedema, and atypical haemolytic uraemic syndrome. Male patients should be alert to increased hepatic enzyme, increased bronchial secretion, respiratory tract infection, pallor, and increased blood creatine phosphokinase MB. Patients under 2 years of age should be vigilant for lethargy, increased monocyte count, decreased blood creatinine, and decreased neutrophil count. Patients over 2 years of age should be alert to hypertension, haematuria, rhinovirus infection, increased blood creatine phosphokinase, headache, and malaise.

CONCLUSIONS

Mining of OA alert signals using the openFDA database provides supplementary information on AEs not included in the drug label. Clinical attention should be focused on common, strong-signal, and label-unmentioned AEs to optimise medication regimens and control risks in clinical use.

Early Treatment in Preterm Twins With Spinal Muscular Atrophy

Early treatment in spinal muscular atrophy is widely recognized as critical for improving neurologic and respiratory outcomes, especially in presymptomatic infants. With the expansion of newborn screening, more infants are now diagnosed presymptomatically. Currently, there are no established treatment guidelines for preterm infants with spinal muscular atrophy, with only anecdotal reports available. Additionally, there is limited knowledge regarding the safety and efficacy of the different treatments in preterm infants. In Israel, although a newborn screening program for spinal muscular atrophy is not yet implemented, a significant portion of the population participates in genetic carrier screening. Here, we present a case of presymptomatic preterm twins, born at gestational age of 32 + 2 weeks, birth weights of 1855 and 1740 g, respectively. They were treated with risdiplam followed by onasemnogene abeparvovec at a gestational age of 35 and 43 weeks, respectively. This case adds to the limited data on treatment options for preterm infants.

Pilocytic astrocytoma in a child with spinal muscular atrophy treated with onasemnogene abeparvovec

Spinal muscular atrophy (SMA) is a severe neuromuscular disease, leading to progressive muscle weakness and potentially early mortality if untreated. Onasemnogene abeparvovec is a recombinant adeno-associated virus serotype 9 (rAAV9)-based gene therapy that has demonstrated improvements in survival and motor function for SMA patients. Here, we present a case of a patient diagnosed with a grade 1 pilocytic astrocytoma at the age of 2 years, approximately 8 months after onasemnogene abeparvovec treatment. Although vector genomes delivered by rAAVs persist primarily as episomes, rare integration events have been linked to tumor formation in neonate murine models. Therefore, we investigated the presence and possible integration of onasemnogene abeparvovec in formalin-fixed paraffin embedded (FFPE) and frozen tumor samples. In situ hybridization demonstrated variable transduction levels in individual tumor cells, while droplet digital PCR measured an average vector copy number ranging from 0.7 to 4.9 vector genomes/diploid genome. Integration site analysis identified a low number of integration sites that were not conserved between technical replicates, nor between FFPE and frozen samples, indicating that cells hosting integrating vector genomes represented a minority in the overall cell population. Thus, molecular analysis of the tumor tissue suggests that tumorigenesis was causally independent of the administration of onasemnogene abeparvovec.

Efficacy and safety of Nusinersen among children with spinal muscular atrophy from North India: A prospective cohort study (NICE-SMA study)

BACKGROUND

Intra-thecal Nusinersen has been approved for the treatment of Spinal muscular atrophy (SMA). Limited data is available regarding the efficacy and safety of Nusinersen in children with SMA type 2 and 3 from North India.

OBJECTIVE

To study the efficacy and safety of Nusinersen among children with SMA type 2 and 3 from North India compared to standard of care (SOC) over 12 months.

METHODS

Children with a genetically confirmed diagnosis of SMA and ≥2 copies of the SMN2 gene were screened for enrolment in prospective study design. Revised Hammersmith score (RHS) and revised upper limb module (RULM) were assessed every three months. Compound muscle action potentials (CMAPs) at median and ulnar nerves and quality of life (QOL) were performed at baseline and 12 months. Intra-thecal procedure-related and treatment-emergent side effects in children receiving Nusinersen therapy were recorded. Outcome measures at 6 and 12 months were compared between the Nusinersen and SOC groups.

RESULTS

Forty-two children with SMA, mean age of 85 ± 6 months, including 16 in the Nusinersen group and 26 in the SOC group, were enrolled. The mean RHS score in the Nusinersen group increased from the baseline of 35 ± 18 to 38.9 ± 19, and 39.9 ± 17 at 6 and 12 months (p value-0.001), in the SOC group increased from the baseline of 28.8 ± 15, to 29.6 ± 16, and 29.9 ± 17 at 6 and 12 months respectively (p value-0.35). The mean gain in the RHS score over 12 months in the Nusinersen group was significantly higher compared to the SOC group (p-value 0.02). RULM showed significant gain in the Nusinersen group compared to the SOC group over 12 months (p value 0.03). The median and ulnar nerve CMAPs, and QOL were similar in both the groups. A total of 119 intrathecal injections of Nusinersen were given. Most adverse events were mild and related to the intra-thecal procedure.

CONCLUSION

Intra-thecal Nusinersen therapy among children with late-onset SMA from North India over 12-month duration was associated with improvement in motor abilities as measured by RHS compared to SOC. Intra-thecal Nusinersen was safe and tolerated well.

Antisense Oligonucleotides (ASOs) in Motor Neuron Diseases: A Road to Cure in Light and Shade

Antisense oligonucleotides (ASOs) are short oligodeoxynucleotides designed to bind to specific regions of target mRNA. ASOs can modulate pre-mRNA splicing, increase levels of functional proteins, and decrease levels of toxic proteins. ASOs are being developed for the treatment of motor neuron diseases (MNDs), including spinal muscular atrophy (SMA), amyotrophic lateral sclerosis (ALS) and spinal and bulbar muscular atrophy (SBMA). The biggest success has been the ASO known as nusinersen, the first effective therapy for SMA, able to improve symptoms and slow disease progression. Another success is tofersen, an ASO designed to treat ALS patients with SOD1 gene mutations. Both ASOs have been approved by the FDA and EMA. On the other hand, ASO treatment in ALS patients with the C9orf72 gene mutation did not show any improvement in disease progression. The aim of this review is to provide an up-to-date overview of ASO research in MNDs, from preclinical studies to clinical trials and, where available, regulatory approval. We highlight the successes and failures, underline the strengths and limitations of the current ASO research, and suggest possible approaches that could lead to more effective treatments.

Modeling Spinal Muscular Atrophy in Zebrafish: Current Advances and Future Perspectives

Spinal muscular atrophy (SMA) is an autosomal recessive neurodegenerative disease characterized by degeneration of lower motor neurons (LMNs), causing muscle weakness, atrophy, and paralysis. SMA is caused by mutations in the Survival Motor Neuron 1 (SMN1) gene and can be classified into four subgroups, depending on its severity. Even though the genetic component of SMA is well known, the precise mechanisms underlying its pathophysiology remain elusive. Thus far, there are three FDA-approved drugs for treating SMA. While these treatments have shown promising results, their costs are extremely high and unaffordable for most patients. Thus, more efforts are needed in order to identify novel therapeutic targets. In this context, zebrafish (Danio rerio) stands out as an ideal animal model for investigating neurodegenerative diseases like SMA. Its well-defined motor neuron circuits and straightforward neuromuscular structure offer distinct advantages. The zebrafish's suitability arises from its low-cost genetic manipulation and optical transparency exhibited during larval stages, which facilitates in vivo microscopy. This review explores advancements in SMA research over the past two decades, beginning with the creation of the first zebrafish model. Our review focuses on the findings using different SMA zebrafish models generated to date, including potential therapeutic targets such as U snRNPs, Etv5b, PLS3, CORO1C, Pgrn, Cpg15, Uba1, Necdin, and Pgk1, among others. Lastly, we conclude our review by emphasizing the future perspectives in the field, namely exploiting zebrafish capacity for high-throughput screening. Zebrafish, with its unique attributes, proves to be an ideal model for studying motor neuron diseases and unraveling the complexity of neuromuscular defects.