Biogen's Salanersen Receives FDA Breakthrough Therapy Designation for Spinal Muscular Atrophy
On June 4, 2026, Biogen announced that the U.S. Food and Drug Administration (FDA) granted Breakthrough Therapy Designation to salanersen (BIIB115), an investigational novel antisense oligonucleotide (ASO) developed for the treatment of spinal muscular atrophy (SMA). Salanersen is designed to correct the splicing of the SMN2 pre-mRNA, thereby increasing the production of functional survival motor neuron (SMN) protein. Utilizing an advanced chemistry discovered by Ionis Pharmaceuticals, salanersen is engineered for enhanced potency, stability, and durability, offering the potential for high efficacy with a convenient once-yearly intrathecal dosing regimen.
Phase 1b Clinical Evidence
The FDA's designation is supported by encouraging results from an ongoing Phase 1b study involving 24 pediatric patients (aged 0.5 to 12 years) who received doses of either 40 mg or 80 mg of salanersen:
- Neurodegeneration Slowdown: Patients with elevated baseline concentrations of neurofilament light chain (NfL)—a key biomarker of active neuronal injury—experienced a 75% reduction in NfL levels at six months, a decrease that was sustained throughout the follow-up period.
- Motor Function Improvement: All 24 participants achieved improvements from baseline on one or more motor endpoints. Remarkably, 12 of the 24 children achieved at least one new WHO motor milestone (such as sitting or walking), and none of the participants lost any motor milestones documented at baseline.
- Post-Gene Therapy Benefits: Key exploratory analyses demonstrated that children who had previously received gene therapy but continued to experience suboptimal clinical status showed significant functional gains and slowing of neurodegeneration after initiating salanersen.
Ongoing Phase 3 Global Program
Salanersen is currently being evaluated in three active Phase 3 registrational trials to establish its long-term safety and efficacy:
- STELLAR-1: Evaluating salanersen in treatment-naïve, presymptomatic infants under 6 weeks old with a genetic diagnosis of SMA.
- SOLAR: Evaluating salanersen in teenagers and adults (aged 15–60 years) who are either treatment-naïve or transitioning from risdiplam.
- STELLAR-2: Scheduled to begin enrollment in June 2026, evaluating salanersen initiated approximately 6 months after gene therapy (onasemnogene abeparvovec-xioi) in infants treated presymptomatically.
Salanersen has been generally well-tolerated, with most adverse events categorized as mild to moderate (e.g., pyrexia, vomiting, and upper respiratory tract infections). The breakthrough designation marks a critical step forward in addressing the persistent unmet needs of the SMA community, particularly for patients seeking highly durable, once-yearly alternatives to existing therapies.