Neoleukin Therapeutics : Neurogene Doses First Patients in Phase 1/2 Trial of NGN-401 for the Treatment of Female Pediatric Patients with Rett Syndrome - Form 8-K

Neurogene Doses First Patients in Phase 1/2 Trial of NGN-401 for the Treatment of Female Pediatric Patients with Rett Syndrome

Two pediatric patients with Rett syndrome dosed in the United States with NGN-401, Neurogene's lead gene therapy product candidate leveraging its proprietary EXACT gene regulation technology

NGN-401 has been well-tolerated to date with no treatment-emergent or procedure-related serious adverse events (SAEs) or transgene-related overexpression toxicity

Third patient dosing anticipated in 1Q24, and interim efficacy data from multiple patients in the first cohort remains on track for 4Q24

NGN-401 design and delivery approach optimized to maximize efficacy and safety profile

New York, NY - November 30, 2023 - Neurogene Inc., a clinical-stage company founded to bring life-changing genetic medicines to patients and families affected by rare neurological diseases, announced today the dosing of the first two female pediatric patients with Rett syndrome in its ongoing Phase 1/2 trial of NGN-401. Rett syndrome is a debilitating, X-linked, neurodevelopmental disorder with significant unmet medical need. To date, NGN-401 has been well-tolerated with no treatment-emergent or procedure-related SAEs, and no signs of transgene-related overexpression toxicity.

NGN-401 is an investigational adeno-associated virus (AAV) gene therapy candidate for Rett syndrome purposefully designed and administered to maximize the therapeutic activity while averting transgene overexpression toxicities. NGN-401 delivers the full-length human methyl cytosine binding protein 2 (MECP2) gene, providing an optimal gene replacement approach. Moreover, NGN-401 leverages Neurogene's novel and proprietary Expression Attenuation via Construct Tuning (EXACT) gene regulation technology, which provides highly controlled and consistent MeCP2 expression on a cell-by-cell basis, thus avoiding the overexpression related toxicities associated with conventional gene therapy. In non-clinical studies with NGN-401 at clinically relevant doses, cardinal features of Rett syndrome were ameliorated, and no overexpression toxicity was observed. These data were part of the robust non-clinical package that supported the U.S. Food and Drug Administration's (FDA) decision to allow Neurogene to proceed directly into a pediatric population for its first-in-human study. NGN-401 has also been granted Orphan Drug Designation, Rare Pediatric Disease Designation, and Fast Track Designation by the FDA.

"While gene therapy has proven to be a powerful tool in the treatment armamentarium for a number of devastating genetic conditions, the highly variable transgene expression associated with conventional gene therapies has limited its application in many complex neurological disorders, especially in Rett syndrome, in which MECP2 transgene overexpression is toxic," said Bernhard Suter, M.D., Principal Investigator of the Phase 1/2 clinical trial, and Associate Professor of Pediatrics and Neurology at Baylor College of Medicine and Texas Children's Hospital. "NGN-401 has been well tolerated to date in the first two patients dosed, consistent with the wide safety margins established in non-clinical studies conducted in disease models and in normal non-human primates."

Ongoing Phase 1/2 Trial Update

The first-in-human, open-label, single-arm, multi-center Phase 1/2 clinical trial (NCT05898620) is evaluating NGN-401 at a dose of 1×10¹⁵ total vector genomes to assess the safety and tolerability of NGN-401 in female pediatric patients ages 4-10 with Rett syndrome. NGN-401 is administered as a one-time treatment using intracerebroventricular (ICV) administration, which has been shown to maximize the delivery of the therapeutic MECP2 gene to key areas of the brain underlying Rett syndrome pathobiology. Clinical-grade NGN-401 for this trial was manufactured at Neurogene's Good Manufacturing Practices (GMP) facility.

The first two patients were dosed sequentially in the third and fourth quarter of 2023 at Texas Children's Hospital, an internationally recognized pediatric research center affiliated with Baylor College of Medicine, and the first clinical trial site to be opened in the U.S. for this study. Dr. Daniel Curry, M.D., director, Functional Neurosurgery and Epilepsy Surgery at Texas Children's Hospital and professor, Neurosurgery and Surgery at Baylor College of Medicine, performed the procedure to administer the gene therapy.

NGN-401 has been well-tolerated to date, with no treatment-emergent or procedure-related SAEs, and no observations of transgene-related overexpression. Pending successful completion of the trial's upcoming pre-planned independent Data and Safety Monitoring Board review, Neurogene expects to dose a third patient in the first quarter of 2024. The first cohort is expected to enroll a total of five female pediatric patients, with a planned expansion pending additional data and subject to review by health authorities.

"NGN-401 was purposefully designed to deliver a therapeutic benefit with the full length MECP2 gene, avoid toxicity associated with overexpression, and leverage the ICV route of delivery to maximize the biodistribution of the transgene to key areas of the brain underlying Rett syndrome. Based on published peer-reviewed non-clinical research, we know that Rett syndrome is caused by loss of function of MECP2 in the brain and spinal cord, and therefore we believe delivering robust transgene expression in these areas is essential for enabling a clinically meaningful benefit," said Rachel McMinn, Ph.D., Founder and Chief Executive Officer of Neurogene. "We are encouraged by the tolerability profile observed in our first two pediatric patients, and look forward to collecting sufficient follow up data on a larger number of patients to inform the therapeutic potential of NGN-401, which we believe could serve as a best-in-class therapy. We remain on track to report preliminary clinical data from the first cohort of patients in this trial in the fourth quarter of 2024, with additional data from an expanded number of patients expected in the second half of 2025."

Dr. McMinn added, "On behalf of the entire Neurogene team, we extend our gratitude to all those making this study possible, with special appreciation for the patients and their families. Your resilience, courage, and support not only contribute to the progress of this research, but also inspire hope within the entire Rett syndrome community. Together, we have the potential to make a meaningful impact on improving the many lives affected by this devastating disease."

About EXACT

Neurogene's novel and proprietary EXACT gene regulation platform technology is a self-contained transgene regulation platform that can be tuned to deliver a desired level of transgene expression within a narrow and therapeutically relevant range, with the goal of avoiding transgene-related toxicities associated with conventional gene therapy. EXACT is compatible with viral and non-viral delivery platforms.

About NGN-401

NGN-401 is an investigational AAV9 gene therapy being developed as a one-time treatment for Rett syndrome. It is the first clinical candidate to deliver the full-length human MECP2 gene under the control of Neurogene's EXACT technology. The EXACT technology utilized in NGN-401 is an important advancement in gene therapy for Rett syndrome, specifically because the disorder requires a treatment approach that enables targeted levels of MECP2 transgene expression without causing overexpression-related toxic effects associated with conventional gene therapy. The robust non-clinical data package for NGN-401 provides evidence of a potentially compelling efficacy and safety profile in Rett syndrome.

About Rett Syndrome

Rett syndrome is a rare genetic disorder that occurs almost exclusively in females, and leads to severe impairments that affect nearly every aspect of their lives. This includes their ability to speak, walk, eat, and breathe. The impact on patients and families is profound. Most females are nonverbal, lack motor skills, and require 24-hour care for all activities of daily living. Many females with Rett syndrome appear to understand the world around them, leaving many caregivers feeling that their daughters are intellectually and emotionally intact.

Rett syndrome is an X-linked, progressive, neurodevelopmental disorder. It has an estimated worldwide incidence of 1 out of every 10,000-15,000 live female births.

The incidence in males is currently unknown. Advances in genetic testing and phenotypic identification have revealed that MECP2 mutations in males are responsible for a wide spectrum of neurological disorders, including Rett syndrome.

Rett syndrome is caused by mutations in the MECP2 gene that lead to deficiency of the methyl cytosine binding protein 2, an important protein responsible for normal function in the brain and other parts of the nervous system.

Females with Rett syndrome typically have normal development until 6-18 months of age, followed by a progressive deterioration of acquired skills such as gross and fine motor skills, purposeful hand function and communication. They subsequently develop stereotypic hand movements such as hand-wringing.

Over time females may develop muscle contractures, rigidity, and debilitating scoliosis, along with periods of recurrent seizures, and burdensome gastrointestinal and breathing abnormalities.

Although there are treatments available for Rett syndrome, there is no treatment option that addresses the root cause of disease and a significant unmet need still exists for new treatment options.

About Neurogene

The mission of Neurogene is to treat devastating neurological diseases to improve the lives of patients and families impacted by these rare diseases. Neurogene is developing novel approaches and treatments to address the limitations of conventional gene therapy in central nervous system disorders. This includes selecting a delivery approach to maximize distribution to target tissues and designing products to maximize potency and purity for an optimized efficacy and safety profile. The Company's novel and proprietary EXACT gene regulation platform technology allows for the delivery of therapeutic levels while limiting transgene toxicity associated with conventional gene therapy. Neurogene has constructed a state-of-the-art gene therapy manufacturing facility in Houston, Texas. GMP production of NGN-401 was conducted in this facility and will support pivotal clinical development activities. For more information, visit www.neurogene.com.

Neurogene Contacts:

Investor Relations:

Melissa Forst

Argot Partners

Neurogene@argotpartners.com

Media:

David Rosen

Argot Partners

david.rosen@argotpartners.com

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