Results of a phase II open-label, multiple-dose study of vamorolone (VBP15-006) in 7- to < 18-year-old boys with duchenne muscular dystrophy

BACKGROUND: Vamorolone is a dissociative glucocorticoid receptor agonist for treating Duchenne muscular dystrophy (DMD). The VBP15-006 study assessed vamorolone safety, tolerability, and pharmacokinetics in 2- to < 4 and 7- to < 18-year-old boys with DMD. Results for 7- to < 18-year-old boys, either corticosteroid (CS)-untreated or switching from prior CS treatment, are reported here. Exploratory objectives included efficacy and pharmacodynamic biomarkers related to safety. METHODS: In this phase II, open-label, multiple-dose study, participants received 2 or 6 mg/kg/day vamorolone for 12 weeks, followed by treatment in an expanded access protocol (EAP Canada). RESULTS: 34 participants (12 CS-untreated, 22 CS-treated) aged 7- to < 18 years were enrolled. Most treatment-emergent adverse events were mild. All 34 participants completed VBP15-006 and entered EAP Canada. During EAP Canada, CS-untreated participants maintained stable linear growth, while CS-treated participants exhibited catch-up growth consistent with serum bone biomarkers (median total vamorolone exposure 1.3 and 1.7 years, respectively). Some weight gain occurred, especially in CS-untreated participants receiving 6 mg/kg/day. Dose-dependent adrenal suppression occurred in CS-untreated and CS-treated participants; 2 individuals who switched from deflazacort to vamorolone 2 mg/kg/day had generalized weakness consistent with adrenal insufficiency. Vamorolone showed dose-dependent pharmacokinetics, rapid clearance, and no accumulation. There were no relevant efficacy changes in CS-treated and CS-untreated groups at either dose. CONCLUSIONS: Vamorolone demonstrated a consistent safety profile in 7- to < 18-year-old boys with DMD. Switching to 6 mg/kg/day vamorolone appeared to mitigate adrenal insufficiency risk. There was no negative effect on growth, and catch-up growth occurred in previously CS-treated individuals switching to vamorolone. TRIAL REGISTRATION: ClinicalTrials.gov: NCT05185622, NCT03863119. First submitted 09-11-2021.