Systemic administration of the antisense oligonucleotide NS-089/NCNP-02 for skipping of exon 44 in patients with Duchenne muscular dystrophy: study protocol for a phase I/II clinical trial

Aim: The purpose of this study is to evaluate the safety and pharmacokinetics of the novel morpholino oligomer NS-089/NCNP-02 which can induce exon 44 skipping, in patients with DMD. Additionally, we aimed to identify markers predictive of therapeutic efficacy and determine the optimal dosing for future studies. Methods: This is an open-label, dose-escalation, two-center phase I/II trial in ambulant patients with DMD, presence of an out-of-frame deletion, and a mutation amenable to exon 44 skipping. Part 1 is a stepwise dose-finding stage (4 weeks) during which NS-089/NCNP-02 will be administered intravenously at four dose levels once weekly (1.62, 10, 40, and 80 mg/kg); Part 2 is a 24-week evaluation period based on the dosages determined during Part 1. The primary (safety) endpoints are the results of physical examinations, vital signs, 12-lead electrocardiogram and echocardiography tests, and adverse event reporting. Secondary endpoints include expression of dystrophin protein, motor function assessment, exon 44 skipping efficiency, plasma and urinary NS-089/NCNP-02 concentrations, and changes in blood creatine kinase levels. Discussion: Exon-skipping therapy using ASOs shows promise in selected patients, and this first-in-human study is expected to provide critical information for subsequent clinical development of NS-089/NCNP-02.