-MEDIPAL HOLDINGS CORPORATION (TSE 7459, MEDIPAL) and JCR Pharmaceuticals Co., Ltd. (TSE 4552, JCR) announced  that the first participant has been dosed in the global Phase I/II trial of JR-446 for mucopolysaccharidosis type IIIB (Sanfilippo syndrome type B; “MPS IIIB”). JR-446 is a blood-brain barrier-penetrating α-N-acetylglucosaminidase developed by JCR using its proprietary J-Brain Cargo^® technology. MEDIPAL holds commercialization rights for JR-446 outside Japan.

MPS IIIB is a lysosomal storage disorder that causes severe central nervous system impairment. This ultra-rare disease is estimated to affect approximately 500 to 1,000 people worldwide,¹ and there is currently no approved treatment.

“Dosing the first patient in this Phase I/II clinical trial is an important milestone for the MPS IIIB community, as there is no approved treatment for this devastating and life-limiting lysosomal storage disorder that impacts patients’ neurocognitive development, independence, and quality of life,” said Dr. Irene Chang, Principal Investigator, Associate Professor of Pediatrics, Section of Biochemical Genetics, Division of Medical Genetics, at the University of California, San Francisco (UCSF). “Patients and families affected by this condition continue to face significant unmet medical needs, and we are encouraged to take this next step in evaluating the potential of this investigational therapy. We are grateful to the patients, caregivers, and study teams whose commitment made this milestone possible, and we are hopeful it may bring meaningful improvements in the quality of life for individuals living with MPS IIIB and their families.”

In September 2023, MEDIPAL and JCR entered into a licensing agreement for the commercialization of JR-446 for MPS IIIB outside Japan and a co-development and commercialization agreement in Japan.² Under this agreement, MEDIPAL holds exclusive worldwide commercialization rights, excluding Japan, with the right to sublicense. On behalf of MEDIPAL, JCR is leading the global Phase I/II trial and development activities as the sponsor.

The global, multicenter, open-label trial is being conducted in patients with MPS IIIB under six years of age. Further information is available at ClinicalTrials.gov under identifier NCT07640984.

Nonclinical studies of JR-446 have demonstrated effects on symptoms associated with MPS IIIB. A separate Phase I/II trial, JR-446-101, is ongoing in Japan under the companies’ co-development agreement. In 2025, JR-446 received orphan drug designation in the United States, the European Union, and Japan.

MEDIPAL and JCR remain committed to advancing JR-446 with the goal of bringing a new treatment option to people with MPS IIIB as quickly as possible.