Elsevier

The Lancet

Volume 388, Issue 10063, 17 December 2016–6 January 2017, Pages 3017-3026
The Lancet

Articles
Treatment of infantile-onset spinal muscular atrophy with nusinersen: a phase 2, open-label, dose-escalation study

https://doi.org/10.1016/S0140-6736(16)31408-8Get rights and content

Summary

Background

Nusinersen is a 2′-O-methoxyethyl phosphorothioate-modified antisense drug being developed to treat spinal muscular atrophy. Nusinersen is specifically designed to alter splicing of SMN2 pre-mRNA and thus increase the amount of functional survival motor neuron (SMN) protein that is deficient in patients with spinal muscular atrophy.

Methods

This open-label, phase 2, escalating dose clinical study assessed the safety and tolerability, pharmacokinetics, and clinical efficacy of multiple intrathecal doses of nusinersen (6 mg and 12 mg dose equivalents) in patients with infantile-onset spinal muscular atrophy. Eligible participants were of either gender aged between 3 weeks and 7 months old with onset of spinal muscular atrophy symptoms between 3 weeks and 6 months, who had SMN1 homozygous gene deletion or mutation. Safety assessments included adverse events, physical and neurological examinations, vital signs, clinical laboratory tests, cerebrospinal fluid laboratory tests, and electrocardiographs. Clinical efficacy assessments included event free survival, and change from baseline of two assessments of motor function: the motor milestones portion of the Hammersmith Infant Neurological Exam—Part 2 (HINE-2) and the Children's Hospital of Philadelphia Infant Test of Neuromuscular Disorders (CHOP-INTEND) motor function test, and compound motor action potentials. Autopsy tissue was analysed for target engagement, drug concentrations, and pharmacological activity. HINE-2, CHOP-INTEND, and compound motor action potential were compared between baseline and last visit using the Wilcoxon signed-rank test. Age at death or permanent ventilation was compared with natural history using the log-rank test. The study is registered at ClinicalTrials.gov, number NCT01839656.

Findings

20 participants were enrolled between May 3, 2013, and July 9, 2014, and assessed through to an interim analysis done on Jan 26, 2016. All participants experienced adverse events, with 77 serious adverse events reported in 16 participants, all considered by study investigators not related or unlikely related to the study drug. In the 12 mg dose group, incremental achievements of motor milestones (p<0·0001), improvements in CHOP-INTEND motor function scores (p=0·0013), and increased compound muscle action potential amplitude of the ulnar nerve (p=0·0103) and peroneal nerve (p<0·0001), compared with baseline, were observed. Median age at death or permanent ventilation was not reached and the Kaplan-Meier survival curve diverged from a published natural history case series (p=0·0014). Analysis of autopsy tissue from patients exposed to nusinersen showed drug uptake into motor neurons throughout the spinal cord and neurons and other cell types in the brainstem and other brain regions, exposure at therapeutic concentrations, and increased SMN2 mRNA exon 7 inclusion and SMN protein concentrations in the spinal cord.

Interpretation

Administration of multiple intrathecal doses of nusinersen showed acceptable safety and tolerability, pharmacology consistent with its intended mechanism of action, and encouraging clinical efficacy. Results informed the design of an ongoing, sham-controlled, phase 3 clinical study of nusinersen in infantile-onset spinal muscular atrophy.

Funding

Ionis Pharmaceuticals, Inc and Biogen.

Introduction

Classic proximal 5q spinal muscular atrophy (OMIM 253300), a progressive motor neuron disorder, is the most common genetic cause of childhood mortality,1, 2 having an incidence of about one in 11 000 livebirths.3 About 60% of patients with spinal muscular atrophy are born with the severe form, infantile-onset type I, developing profound limb and trunk weakness before 6 months of age, and failing to rollover or achieve independent sitting. There is a high disease burden with substantial morbidity and mortality4, 5 from dysphagia, failure to thrive, hypoventilation, poor airway clearance due to weak cough, and lower respiratory tract infections.

Deletions or mutations in the Survival Motor Neuron 1 (SMN1) gene cause spinal muscular atrophy.6 Absence of the SMN1 gene results in reliance on a nearly identical gene, SMN2, which differs from SMN1 by 11 nucleotides. SMN2 has a c.840C→T substitution at an exon splice enhancer site that regulates exon 7 inclusion,7 so that only 10–25% of SMN2 transcripts contain exon 7 and generate full-length functional SMN protein.8 Although the role of SMN protein in motor neurons is incompletely understood and the concentration required for optimum functioning unknown, the phenotype of spinal muscular atrophy (type I, II, III, or IV)9 is largely related to the number of SMN2 gene copies present.10

Research in context

Evidence before this study

Spinal muscular atrophy is caused by deletions or mutations in the Survival Motor Neuron 1 (SMN1) gene and is the most common genetic cause of childhood mortality. Infantile-onset spinal muscular atrophy presents clinically as a severe, progressive motor neuron disease, resulting in generalised weakness and impaired feeding and breathing. Survival is dependent upon a small amount of normal SMN protein translated by the backup SMN2 gene, which, due to a splice site variant, usually excludes exon 7. Less than a quarter of these infants survive beyond 2 years of age without dependence upon ventilation support. There are no approved drug treatments for spinal muscular atrophy. Antisense oligonucleotides provide a targeted strategy for spinal muscular atrophy treatment by specifically binding to repressive sites within SMN2 exon 7 or the flanking introns, thus promoting exon 7 inclusion and increased production of functional SMN protein. Nusinersen (also known as ISIS 396443 and ISIS-SMNRx) is a uniformly modified 2'-O-methoxyethyl phosphorothioate antisense oligonucleotide being developed for the treatment of spinal muscular atrophy. We searched PubMed using the keywords “nusinersen”, “ISIS 396443”, “ISIS-SMNRx “, and “ASO 10-27” with no date restrictions. Of the six publications identified, two reported the results of the phase 1 study described below, three described preclinical results using nusinersen, and one was a review article on SMA therapeutics. A phase 1, short-term, single-dose clinical study of intrathecally delivered nusinersen was previously done in children with spinal muscular atrophy.

Added value of this study

We report interim results of an ongoing open-label, phase 2, multiple-dose study of intrathecal nusinersen in patients with severe infantile-onset spinal muscular atrophy. We provide evidence that nusinersen has acceptable safety and tolerability when delivered by multiple intrathecal injections and shows promising clinical efficacy as evidenced by improvements in motor function, achievement of motor milestones, and permanent ventilation-free survival as compared with published natural history. Additionally, autopsies collected during the study indicate proof of target engagement and mechanism, as nusinersen altered SMN2 splicing, with an increase in full-length transcript that includes exon 7, and an increase in SMN protein in spinal cord motor neurons as compared with untreated infants with spinal muscular atrophy as control.

Implications of all the available evidence

Our study shows favourable safety and tolerability, pharmacokinetics, proof-of-concept pharmacodynamics, and a promising clinical response of intrathecal nusinersen. Results informed the design of an ongoing large phase 3, randomised, sham-controlled study of nusinersen in infantile-onset spinal muscular atrophy. More broadly, the mechanistic effects of nusinersen at the mRNA and protein level in participants of this study provides proof of principle for the use of antisense therapeutics in the treatment of neurological disorders. Finally, results from this study suggest treatments that increased SMN protein might provide clinical benefit to patients with spinal muscular atrophy.

Antisense oligonucleotides provide a targeted strategy for treatment of spinal muscular atrophy by specifically binding to repressive sites within SMN2 exon 7 or the flanking introns, thus promoting exon 7 inclusion, increased production of functional SMN protein, and rescuing the motor neuron pathology and improving survival in mouse models of spinal muscular atrophy.11, 12, 13, 14 Nusinersen (ISIS 396443 or ISIS-SMNRx) is a uniformly modified 2′-O-methoxyethyl phosphorothioate antisense oligonucleotide being developed for the treatment of spinal muscular atrophy (appendix).11, 12, 13, 14 A phase 1 study of nusinersen in children with type II and type III spinal muscular atrophy was previously done.15 We present here the first study of nusinersen treatment for the more severe infantile-onset spinal muscular atrophy, reporting results from an ongoing phase 2 study.

Section snippets

Study design and participants

This open-label, escalating dose phase 2 study was designed to assess the safety and tolerability, pharmacokinetics, and clinical efficacy of nusinersen in infants with spinal muscular atrophy. Eligible participants were of either gender between 3 weeks and 7 months old with onset of spinal muscular atrophy symptoms between 3 weeks and 6 months, who had SMN1 homozygous gene deletion or mutation, and who met additional eligibility criteria (appendix). The first four participants received loading

Results

20 infants with spinal muscular atrophy were enrolled between May 3, 2013, and July 9, 2014. Demographic and baseline characteristics are summarised in table 1. SMN2 copy number and gene sequencing was done on 19 infants: 17 of 19 patients had two copies of the SMN2 gene and two patients three copies (both in the 12 mg dose group). No sequence variants in the SMN2 gene were reported. One infant died before the day 85 assessment when samples for SMN2 gene copy analysis were collected. Two screen

Discussion

In this study, multiple intrathecal doses of the antisense drug nusinersen were well tolerated in infants with spinal muscular atrophy, with no safety concerns identified for up to nine doses given over 32 months of treatment. Adverse events were generally consistent with those observed in fragile infants with type I spinal muscular atrophy. Similarly, nusinersen was well tolerated in older children aged 2–15 years with type II or type III spinal muscular atrophy.15 Additionally, the

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