Oligonucleotide-siRNA conjugate for SOD1 amyotrophic lateral sclerosis: a phase 1 trial

Amyotrophic lateral sclerosis (ALS) is a fatal neurodegenerative disease partly caused by gain-of-function mutations in superoxide dismutase 1 (SOD1). Here we developed RAG-17, an siRNA-targeting SOD1, using an accessory oligonucleotide conjugate platform for enhanced central nervous system (CNS) delivery. Preclinically, RAG-17 rescued motor neuron degeneration, delayed disease progression, preserved motor function and extended survival in SOD1^G93A ALS rodents, even with advanced-stage treatment. In cynomolgus monkeys, intrathecal RAG-17 led to dose-dependent, durable reductions in SOD1 mRNA (CNS) and protein (cerebrospinal fluid (CSF)). In a first-in-human trial in patients with SOD1-ALS (n = 6), participants were assigned to two cohorts-cohort 1 (n = 3) received an initial 60 mg dose (seven doses total) and cohort 2 (n = 3) received an initial 90 mg dose (six doses total). The dose was escalated in 30 mg steps to maintenance doses of 150 mg (n = 5) or 180 mg (n = 1). Thus, the primary safety endpoint was met, showing acceptable safety and tolerability. Treatment-emergent adverse events (TEAEs) occurred in 33% of participants (two of six). All TEAEs were mild to moderate, including muscle tremor (two patients) and elevated alanine aminotransferase (one patient), all of which resolved. No serious adverse events were reported. Furthermore, no other clinically meaningful changes were observed in laboratory parameters, vital signs, the ALS Functional Rating Scale-Revised score, physical or neurological examinations or ECG. The key secondary endpoints showed CSF SOD1 reductions of 69% (cohort 1, day 240) and 56% (cohort 2, day 210), and plasma neurofilament light chain reductions of 62% (cohort 1) and 52% (cohort 2), from baseline; no patient required invasive mechanical ventilation or died by the end of the study. These results demonstrate a favorable safety outcome, supporting the continued clinical evaluation of RAG-17 for SOD1-ALS. ClinicalTrials.gov registration: NCT05903690 .