San Diego-based Arcturus Therapeutics (Nasdaq: ARCT) reported encouraging interim Phase II data for ARCT-810, its investigational mRNA therapeutic for ornithine transcarbamylase (OTC) deficiency, and unveiled LUNAR 2.0, a next-generation lipid nanoparticle delivery platform being used to develop a follow-on candidate with substantially greater preclinical potency.
ARCT-810 is designed to restore functional OTC enzyme expression in the liver of patients with OTC deficiency, an X-linked urea cycle disorder that causes toxic ammonia accumulation. In the ongoing Phase II study, treatment was generally safe and well tolerated and reduced or maintained fasting ammonia within the normal range, including during periods of increased protein intake. Participants receiving 0.5 mg/kg also achieved mean glutamine levels within the normal range during treatment. Arcturus did not disclose detailed numerical efficacy results in the announcement.
The company also introduced ARCT-2601, a next-generation OTC deficiency candidate based on LUNAR 2.0 that it plans to add to the ongoing Phase II protocol by the end of 2026. In non-human primates, the new platform produced 38-fold greater human OTC protein expression than ATX-95, the key lipid used in ARCT-810, while ARCT-2601 showed a similar preclinical safety profile. Following a June 2026 Type C meeting, Arcturus said it received FDA feedback supporting the planned protocol amendment and expects ARCT-2601 to enable lower or less frequent dosing than ARCT-810.
Earlier interim data reported in June 2025 showed statistically significant reductions in glutamine and evidence of improved urea cycle function measured using 15N-ureagenesis. ARCT-810 has received FDA Orphan Drug, Fast Track, and Rare Pediatric Disease designations.