Evaluation of Safety and Efficacy of ECUR-506A and ECUR-506D in Male Infants with Neonatal Onset Ornithine Transcarbamylase Deficiency

The primary objective of this study is to assess the **safety** and tolerability of up to two dose levels of ECUR-506 following intravenous administration of a single dose in male infants less than 9 months of age with genetically confirmed neonatal onset **Ornithine Transcarbamylase Deficiency (OTC)**. This objective is clinically relevant as it aims to determine the potential risks and adverse effects associated with the treatment, which is crucial for ensuring patient safety and guiding future therapeutic use.

Secondary objectives include:

• Assessing the pharmacokinetics and efficacy of up to two dose levels of ECUR-506 following IV administration of a single dose. This evaluation is important for understanding the drug's absorption, distribution, metabolism, and excretion, as well as its therapeutic effectiveness in the target population.

The clinical trial involves a total of **11 male participants** diagnosed with **Ornithine Transcarbamylase Deficiency (OTC)**. The study population consists of infants with a gestational or adjusted gestational age of at least 37 weeks, and an age range from 24 hours to 7 months at the time of screening. Participants were selected based on a genetically confirmed diagnosis of severe neonatal OTC deficiency, characterized by a documented hyperammonemic crisis within the first week of life, and are currently receiving treatment with dietary protein restriction and nitrogen scavenger therapy. The trial population is further defined by specific inclusion criteria, such as a weight between 3.5 kg and 10.0 kg at screening and having received all age-appropriate vaccinations. The study does not include female subjects, focusing solely on male infants, and involves a vulnerable population due to the young age and health condition of the participants. Lifestyle considerations include adherence to a restricted protein diet and ongoing medical therapy to manage the condition. The selection process ensures that participants have a family history and genetic confirmation of the disease, with prenatal or post-birth genetic testing confirming the diagnosis.

The clinical trial is designed as a **Phase I/II**, open-label, dose-escalation study to evaluate the safety and efficacy of a single intravenous administration of ECUR-506 in male infants under 9 months of age with genetically confirmed neonatal onset **Ornithine Transcarbamylase Deficiency (OTC)**. The trial aims to assess the safety and tolerability of up to two dose levels of ECUR-506. The study will involve a series of visits, starting with a screening visit to confirm eligibility based on specific inclusion criteria, such as age, genetic confirmation of OTC deficiency, and current treatment status. Participants will be monitored for treatment-emergent adverse events, changes in physical exam parameters, vital signs, and other safety assessments throughout the study duration.

The trial will commence with an inclusion visit, where participants will undergo a comprehensive screening process to ensure they meet all eligibility criteria. Following successful screening, participants will receive a single dose of the investigational product via **intravenous infusion**. Subsequent follow-up visits will be scheduled at pre-specified intervals to monitor safety and efficacy endpoints, including the incidence and severity of hyperammonemic crises, liver transduction levels, and vector pharmacokinetics. The study will conclude with an end-of-study visit, where final assessments will be conducted to evaluate the overall impact of the treatment.

The expected duration of participant involvement in the trial is approximately 24 weeks, with an immediate roll-over into a long-term follow-up protocol lasting up to 14.5 years. Conditions that may lead to early termination from the study include the occurrence of severe adverse events or non-compliance with study procedures. The trial is anticipated to start recruitment in September 2024 and is estimated to conclude by May 2026. The study is not categorized as low intervention and involves pediatric subjects, reflecting its first-in-human nature. The investigational products, ECUR-506D and ECUR-506A, are administered as infusions and are not formulated specifically for pediatric use.

The clinical trial involves the administration of two experimental medications, **ECUR-506D** and **ECUR-506A**, both developed by IECURE, INC. **ECUR-506D** is an **adeno-associated virus serotype rh79** containing the human **OTC gene**. This investigational product is formulated as an **infusion** and is administered via **intravenous infusion**. The study is designed to evaluate the safety and efficacy of a single dose of this gene therapy in male participants under 9 months of age with genetically confirmed neonatal onset **ornithine transcarbamylase deficiency**. The dosing schedule involves a single administration, and participant compliance will be monitored through clinical assessments and laboratory evaluations.

**ECUR-506A** is another investigational product used in the trial, also developed by IECURE, INC. This product is an **adeno-associated virus serotype rh79** encoding a meganuclease for targeted editing of the human **PCSK9 gene**. Similar to ECUR-506D, ECUR-506A is formulated as an **infusion** and administered via **intravenous infusion**. The trial aims to assess the safety and tolerability of this gene-editing therapy, with a focus on its potential to modify the **PCSK9 gene**. The administration involves a single dose, and compliance will be monitored through regular follow-ups and laboratory tests.

No non-experimental treatments, such as standard-of-care therapy, placebo, or comparator treatments, are specified in the study protocol. The trial is focused on the evaluation of the investigational products ECUR-506D and ECUR-506A, with no additional medications or interventions involved. The study protocol includes detailed monitoring of participant compliance and response to the treatment, ensuring the collection of comprehensive safety and efficacy data.

The efficacy of the clinical trial will be assessed through a series of primary and secondary endpoints. Primary endpoints include the evaluation of treatment-emergent adverse events, which will be measured in terms of incidence, severity, seriousness, and relatedness. Additionally, changes from baseline in physical exam parameters, vital signs, pediatric neurologist exam parameters, blood safety tests (including hematology, serum chemistry, liver function tests, and coagulation tests), urinalysis evaluations, and 12-lead ECG parameters will be assessed at pre-specified timepoints throughout the study.

Secondary endpoints focus on more specific measures related to the treatment's impact. These include the percent liver transduction via in-situ hybridization/immunofluorescence (ISH/IF), the number of **hyperammonemic crises** (HAC) defined by ammonia levels greater than 100 µmol/L with associated neurological status changes, and the severity of these crises categorized as mild, moderate, or severe. Additional secondary endpoints include vector pharmacokinetics (PK) in blood and shedding in urine and feces, scavenger drug dose per body surface area (BSA), protein allowance in grams per kilogram, and blood urea nitrogen measurements. These parameters will be collected and analyzed according to the schedule of events outlined in the study protocol.