Safety, tolerability, and efficacy of alixorexton, a selective orexin 2 receptor agonist for narcolepsy type 1 (Vibrance-1): a randomised, double-blind, placebo-controlled, phase 2 trial.
BACKGROUND: The clinical potential of orexin 2 receptor (OX2R) agonism for improving measures of wakefulness and cataplexy in patients with narcolepsy type 1 has been described in a phase 2 study. Here, we aimed to evaluate the safety, tolerability, and efficacy of alixorexton, another oral OX2R agonist, in narcolepsy type 1. METHODS: In this randomised, double-blind, placebo-controlled, phase 2 trial, adult participants (aged 18-70 years) with narcolepsy type 1 were recruited from 46 hospitals and private research centres across the USA, Europe, and Australia. Participants were centrally randomly assigned (1:1:1:1) in blocks of four via an interactive response technology system stratified by region and baseline weekly cataplexy rate (WCR) to receive 4 mg, 6 mg, or 8 mg tablets of alixorexton or placebo once daily for 6 weeks, followed by an optional 7-week open-label extension. Participants had narcolepsy type 1, diagnosed per the International Classification of Sleep Disorders, Third Edition, and confirmed by overnight polysomnography and the Multiple Sleep Latency Test or cerebrospinal hypocretin-1 concentrations. The sponsor, assessors, investigators, and participants were masked during the randomised double-blind treatment period. Efficacy and safety assessments were conducted in participants who received at least one dose of study drug. The primary endpoint was change from baseline to week 6 in mean sleep latency (MSL) on the Maintenance of Wakefulness Test (MWT). Safety endpoints included treatment-emergent adverse events. This trial was registered with ClinicalTrials.gov (NCT06358950) and is completed. FINDINGS: Between May 24, 2024, and May 5, 2025, 153 individuals were screened and 92 participants were randomly assigned to receive alixorexton 4 mg (n=23), 6 mg (n=22), 8 mg (n=24), or placebo (n=23). Mean age was 33·5 years (SD 12·1), 57 (62%) were women, and 35 (38%) were men. At week 6, the observed MSL on the MWT was 2·3 min (SD 2·7) for placebo, 24·0 min (8·7) for alixorexton 4 mg, 25·9 min (9·4) for 6 mg, and 28·2 min (11·4) for 8 mg. Alixorexton improved MSL on the MWT, with a least-squares mean placebo-corrected change from baseline of 22·2 min (95% CI 17·2-27·2) for alixorexton 4 mg, 24·1 min (19·0-29·1) for 6 mg, and 26·0 min (21·0-31·0) for 8 mg (adjusted p=0·0099 for 4 mg, adjusted p<0·0001 for 6 mg and 8 mg). Treatment-emergent adverse events occurring in at least 5% of participants given alixorexton and more frequently than those given placebo up to week 6 were pollakiuria (38 [55%]), insomnia (19 [28%]), salivary hypersecretion (17 [25%]), micturition urgency (ten [14%]), blurred vision (ten [14%]), and hyperhidrosis (five [7%]). INTERPRETATION: In this phase 2 trial, once-daily oral alixorexton provided clinically meaningful improvements at 6 weeks for participants with narcolepsy type 1, including in wakefulness, excessive daytime sleepiness, and cataplexy. The treatment was generally well tolerated, with adverse events consistent with the known on-target effects of OX2R agonists. Together, these findings support the further phase 3 evaluation of alixorexton as a potential therapeutic option for people with narcolepsy type 1. FUNDING: Alkermes.