8-K: Arcturus Therapeutics Reports Positive Interim Phase 2 Results for ARCT-810 in OTC Deficiency

Arcturus Therapeutics Holdings Inc. announced positive interim Phase 2 results for its mRNA therapeutic candidate ARCT-810, showing significant reduction in glutamine levels and increased ureagenesis in patients with Ornithine Transcarbamylase (OTC) deficiency.

Summary

• ARCT-810, an mRNA therapeutic candidate, demonstrated positive Phase 2 interim results in individuals with Ornithine Transcarbamylase (OTC) deficiency.
• The treatment significantly and consistently reduced glutamine levels, a key biomarker for urea cycle function, to within the normal range (p-value = 0.0055 in combined studies).
• 15N-ureagenesis data provided the first evidence of an mRNA therapeutic improving urea cycle function, with Relative Ureagenesis Function (RUF) increasing from a baseline of 29.0% (SD; 9.1%) to 43.7% (SD; 21.7%) at 28 days post-fifth dose (p-value = 0.026).
• Ammonia levels remained stable and within the normal range in patients receiving ARCT-810 across both Phase 2 studies.
• ARCT-810 was generally safe and well tolerated in single-dose Phase 1/1b and multi-dose Phase 2 studies, involving 40 participants to date, including 20 OTC deficient participants.
• An improved 3-hour intravenous regimen has not resulted in any serious infusion-related reactions (N=8; up to 6 infusions) in the Phase 2 protocols.

Sentiment

Score: 9

Explanation: The document reports highly positive interim Phase 2 clinical trial results for a significant unmet medical need, showing strong efficacy biomarkers and a good safety profile. Management comments indicate an 'unprecedented' outcome and a 'potentially accelerated path forward' for a pivotal study, suggesting strong confidence in the drug's potential.

Positives

• Significant and consistent reduction of glutamine levels to within the normal range in both Phase 2 studies (p-value = 0.0055 combined), indicating robust biological effects.
• First evidence of an mRNA therapeutic improving urea cycle function, with a statistically significant increase in 15N-ureagenesis (RUF) from 29.0% to 43.7% (p-value = 0.026).
• Ammonia levels remained stable and within the normal range in patients receiving ARCT-810, further supporting favorable glutamine and ureagenesis data.
• ARCT-810 continues to be safe and well tolerated across all tested dose levels, with no serious infusion-related reactions observed using the improved 3-hour IV regimen.
• The combined biomarker data (glutamine and ureagenesis) is described as unprecedented for an mRNA rare disease therapeutic, suggesting a potentially accelerated path to a multi-biomarker driven pivotal study.
• Two of the three participants in the U.S. study achieved RUF > 50%, indicating a clinically meaningful improvement in urea cycle flux.

Negatives

• One participant in the European Phase 2 randomized study (receiving ARCT-810) reported a hyperammonemia event, though it was considered related to corticosteroid treatment received four weeks after the last dose.
• Glutamine levels returned to baseline over a period of several weeks after treatment completion.

Risks

• Actual results may differ materially from forward-looking statements due to known and unknown risks, uncertainties, and other factors.
• Clinical results may not be predictive of future clinical results or of potential therapeutic benefit.
• Uncertainty regarding the likelihood of continuation of the OTC program.
• Uncertainty regarding the likelihood of further enrollment in the ongoing ARCT-810 Phase 2 study.
• Uncertainty regarding the likelihood of a path toward and initiation of a multi-biomarker driven pivotal study.
• Uncertainty that continued ARCT-810 administrations will result in a progressive increase of functional OTC enzyme.
• Uncertainty regarding any regulatory agency recognizing any biomarker (including glutamine levels or 15N assay results) in determinations of regulatory approval.
• Impact of general business and economic conditions.

Future Outlook

The positive interim Phase 2 results for ARCT-810 suggest a potentially accelerated path forward to a multi-biomarker driven pivotal study. Continued administrations are anticipated to result in a progressive increase of functional OTC enzyme in the liver.

Management Comments

• "We are very pleased with these new ARCT-810 clinical results, where we have achieved strong biological effects in both Phase 2 studies, including significant and consistent reduction and normalization of abnormally elevated glutamine, an important biomarker to monitor urea cycle function." Dr. Juergen Froehlich, Chief Medical Officer of Arcturus.
• "Furthermore, in our ongoing U.S. Phase 2 study, we are excited to report the first significant relative ureagenesis function (RUF) improvements using a new and optimized 15N-ureagenesis assay. Along with the observation of stable ammonia levels in all patients during treatment, these data add a level of robustness to this new interim dataset." Dr. Juergen Froehlich.
• "I am also very pleased to see that our LUNAR delivery technology continues to be generally safe and well tolerated. The combined biomarker data is unprecedented for an mRNA rare disease therapeutic and, importantly, provides a potentially accelerated path forward to a multi-biomarker driven pivotal study." Dr. Juergen Froehlich.
• "It is extremely rewarding to see the first mRNA therapeutic produce such solid clinical results in an area of important unmet medical need. This is a very positive step for the OTC deficient community as there are currently limited options for symptomatic patients suffering from this devastating disease." Dr. Marshall Summar, CEO of Uncommon Cures.

Industry Context

This announcement positions Arcturus as a significant player in the development of mRNA therapeutics for rare diseases, specifically addressing Ornithine Transcarbamylase (OTC) deficiency, a condition with a high unmet medical need and limited treatment options beyond liver transplant. The positive results for ARCT-810 demonstrate the potential of mRNA technology to extend beyond infectious disease vaccines into genetic disorders, potentially offering a non-surgical, disease-modifying alternative to current palliative care or invasive procedures.

Comparison to Industry Standards

• Current standard of care for OTC deficiency involves a challenging low-protein diet and nitrogen scavenging medications, which do not address the underlying cause and may not prevent chronic neurotoxic effects; ARCT-810 aims to restore the OTC enzyme, addressing the root cause.
• Liver transplantation is the only cure for OTC deficiency but carries significant risks of surgical and postsurgical complications, such as organ rejection, and requires lifelong immunosuppressant drugs; ARCT-810 offers a non-surgical therapeutic approach.
• The combined biomarker data (glutamine and ureagenesis) is explicitly stated as "unprecedented for an mRNA rare disease therapeutic," suggesting a strong performance relative to other mRNA therapies in this specific therapeutic area.
• The new and optimized 15N-ureagenesis assay (Allegri et al., 2025) used in the U.S. Phase 2 study is highlighted for its ability to distinguish between symptomatic and asymptomatic OTC deficient patients, its low intraindividual variability, and its independence from ammonia scavengers, indicating an advanced and reliable diagnostic approach.
• Glutamine assessments are noted to have significantly lower intra-subject variability (15%) compared to ammonia (56%), making glutamine a more reliable biomarker for monitoring metabolic control in stable conditions, as supported by Lichter-Konecki et al., 2016.

Stakeholder Impact

• Shareholders: The positive clinical results are highly likely to increase investor confidence and potentially lead to a positive impact on the company's share price.
• Patients (OTC deficient community): Offers a promising new therapeutic option that addresses the underlying cause of the disease, potentially improving quality of life, reducing the risk of metabolic crises, and providing an alternative to liver transplant.
• Healthcare Providers: Provides a new potential treatment modality for OTC deficiency, expanding therapeutic options beyond the current standard of care.

Next Steps

• Further enrollment in the ongoing ARCT-810 Phase 2 study.
• Potential initiation of a multi-biomarker driven pivotal study for ARCT-810.

Key Dates

Recommendation

Keywords

Arcturus Therapeutics, ARCT-810, OTC deficiency, Ornithine Transcarbamylase, mRNA therapeutic, Phase 2 clinical trial, glutamine, ureagenesis, hyperammonemia, rare disease, LUNAR delivery platform, biotechnology, pharmaceuticals, clinical results, urea cycle disorder