Neurogene : IRSF Clinical Safety Poster

Preliminary Safety Results from the Ph1/2 Study of NGN-401, a Novel Regulated Gene Therapy for Rett Syndrome

Suter B1, Lieberman D2, Benke T3, Neul J4 ,Jaggumantri S5, Feng C5, Albanis E5, Cobb S5, Jordan J5

1Department of Pediatrics & Neurology, Texas Children's Hospital, Baylor College of Medicine, Houston TX, 2Department of Neurology, Boston Children's Hospital, Harvard Medical School, Boston, MA, 3Department of Pediatrics-Neurology, University of Colorado School of Medicine, Children's Hospital Colorado, Anschutz Medical Campus, Aurora, CO, 4Department of Pediatrics-Neurology, Monroe Carell Jr. Children's Hospital at Vanderbilt, Vanderbilt University Medical Center, Nashville, TN, 5Neurogene Inc., New York, NY

RETT SYNDROME

NON-CLINICAL DATA

PHASE 1/2 NGN-401 PEDIATRIC TRIAL DESIGN AND BASELINE DEMOGRAPHICS

• Rett syndrome (RTT) is a severe X-linked neurodevelopmental disorder, occurring predominately in females.
• Most cases of RTT are caused by loss-of-function variants in the MECP2 gene that lead to deficiency of methyl CpG binding protein 2 (MeCP2), a ubiquitously expressed nuclear protein critical for brain function1,2.
• The cardinal clinical features of the disease phenotype include impairments in language/communication (i.e., verbal and non-verbal), ambulation, hand function, as well as autonomic dysfunction (e.g., severe daytime apnea episodes, hyperventilation).

RATIONALE FOR GENE THERAPY IN RETT SYNDROME

Gene therapy has potential to address the root cause of RTT by delivering functional copies of the MECP2 gene to the brain, thereby potentially restoring MeCP2 protein.

Fig. 1. RTT requires tight transgene regulation

NGN-401 designed to provide

therapeutic and tolerable levels of

MeCP2 within this window

MeCP2 levels

Too low	Therapeutic and tolerable	Too high
Rett Syndrome	MeCP2 Overexpression
	treatment window	Toxicity

Efficacious doses of NGN-401 established in male murine knock-out (KO) model of RTT were well-tolerated in female heterozygous murine model of RTT, which has mosaic MeCP2 expression.

Fig. 5. NGN-401 led to dose-dependent increase in survival in male murine KO model (Mecp2-/y); unregulated gene therapy led to rapid overexpression toxicity in female murine model (Mecp2+/-), while NGN-401 was well-tolerated through 26 weeks

A

Survival in Male KO Model (Mecp2-/y) B

Survival and Toxicity Score in Female Model (Mecp2+/-)

WT + Vehicle

Mecp2 male or female + Vehicle

NGN-401 1E11 vg

NGN-401 3E11 vg

Unregulated 1E11 vg

Unregulated 3E11 vg

n = 10-27 males/group n = 9-20 females/group

$ Animals culled due to toxicity in high-dose unregulated vector group.

• In Mecp2+/- heterozygous female mice with mosaic MeCP2 expression, NGN-401 exhibited no signs of toxicity at clinically relevant doses. In contrast, unregulated gene therapy was not tolerated with mice showing severe toxicity, requiring euthanasia by 3 weeks of age (Fig. 5B). The timing of toxicity onset was consistent with timing of peak transgene expression.

Intracerebroventricular (ICV) dosing resulted in significantly better distribution than intrathecal-lumbar(IT-L) to key areas of the nervous system underlying RTT pathophysiology.

Objectives

• Safety, tolerability, and preliminary efficacy of NGN-401
• Evaluate two dose levels

Key Eligibility Criteria

• Female, age ≥4 to ≤10 years with
  Classic Rett syndrome
• Clinical diagnosis and genetic confirmation of pathogenic MECP2 mutations
• Clinical Global Impression-Severity(CGI-S) score of 4-6

Key Efficacy Assessments

• Clinician Global Impression of Severity with RTT-specific anchors (CGI-S)
• Clinician Global Impression of Improvement (CGI-I)
• Rett Syndrome Behavior Questionnaire (RSBQ)

Fig. 9. RTT-200 Phase 1/2 pediatric study overview

The Phase 1/2 clinical trial of NGN-401 is concurrently enrolling low-dose and high-dose cohorts

The trial is utilizing a prophylactic
immunosuppression regimen:	Cohort 2
• Cohort 1: Corticosteroids	3E15 vg
N=8

• Cohort 2: Targeted regimen

of rituximab, sirolimus, and	Cohort 1
shorter course of	1E15 vg
N=8
corticosteroids

Table 1: Baseline characteristics of the first three participants dosed

		Low Dose: 1E15 vg (n = 3)
	Participant 1		Participant 2		Participant 3
Age at Dosing	7 years old		4 years old		6 years old
Race	Asian		White		White
MECP2 mutation	Mild		Severe		Severe
Time post- NGN-401	~11 months		~8 months		~5 months
administration

High Dose Cohort 2: First participant recently dosed

and thus far, NGN-401 has been well-tolerated

Fig. 6. NHP data support ICV as route of administration chosen for NGN-401 clinical trial4

NGN-401 SAFETY PROFILE IS FAVORABLE TO DATE

• RTT disease severity is correlated with the amount of functional MeCP2 protein.
• MECP2 duplication disorder is a distinct disease resulting from expression of two or more copies of the MECP2 gene.
• Gene therapy for RTT requires tightly controlled MeCP2 protein expression to deliver therapeutic levels of MeCP2 (in the green range) without overshooting into levels that would be toxic3.

NGN-401 GENE THERAPY INVESTIGATIONAL PRODUCT FOR RTT

NGN-401 is designed to be a best-in-class therapy for RTT.

Fig 2. NGN-401 construct design

AAV9	Promoter	EXACT	Full-length	EXACT
capsid	miRNA	human MECP2	recognition sites

• ICV is a common neurosurgical procedure, performed approximately 30,000 times annually in the U.S. alone.

EXACT provided consistent levels of MECP2 mRNA in wild-type NHPs.

Table 2:

• All treatment-emergent adverse events (TEAEs) related to NGN-401 have been mild/Grade 1 and transient or resolving, and most AEs are known potential risks of AAV
• There have been no treatment-emergent or ICV procedure-related serious AEs (SAEs)

	Number of Events
	[Number of Participants]
TEAEs related to NGN-401	13 [3]
(all mild/Grade 1)
Elevated ALT	5 [3]
Elevated AST	3 [2]
Elevated GGT	1 [1]
Decreased C3	1 [1]
Decreased C4	2 [2]
Vomiting	1 [1]

Table 3:

• No signs or symptoms indicative of MeCP2 overexpression toxicity have been reported in any participant

Clinical Sign or Symptom that May Indicate MeCP2 Protein Overexpression (derived from symptoms observed in MECP2 duplication syndrome5)

Immunopathology (e.g., lymphadenopathy,	None
recurrent respiratory infection)	reported
New onset or worsening of	None
persistent seizures	reported
Worsening of constipation	None
	reported
New onset cardiovascular events	None
	reported

NGN-401:

• Includes EXACT™ transgene regulation technology, designed to tightly control MeCP2 protein expression on a cell-by-cell basis. (Fig.3-4)
• Contains full-length human MECP2 gene, which provides potential to maximize efficacy by creating a fully functional MeCP2 protein.
• Delivered by intracerebroventricular (ICV) administration, which has been shown to have the broadest targeting of brain regions underlying RTT pathophysiology compared to other routes of administration4.

EXACT technology is designed to self-regulate transgene expression to maximize therapeutic potential while minimizing the risk of MeCP2 overexpression toxicity associated with conventional gene therapy.

Fig. 7. Expression of transgene mRNA 30 days post-dosing of NGN-401 in NHPs was below the level of endogenous MECP2 mRNA, avoiding overexpression concerns

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• Endogenous MECP2 mRNA
• NGN-4013.7E13 vg
• NGN-4011.1E14 vg

n = 3/group

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An extensive panel of studies are performed two to three times weekly for the first month post dosing, then on a weekly basis through five months, followed by decreasing frequency thereafter.

Data cut-off date for first three low-dose participants: May 31, 2024

CONCLUSIONS

•	NGN-401 gene therapy candidate is designed to be a best-in-class treatment for RTT.
•	ICV administration in NHPs resulted in significantly better distribution than IT-L to key areas of
	the nervous system underlying RTT pathophysiology, supporting route of administration in

Fig. 3. Self-regulation of transgene expression using EXACT construct

Fig. 4. Self-regulation of transgene expression using EXACT in highly transduced cells

Both NGN-401 clinical trial doses are expected to be safe and efficacious based on non-clinical data.

NGN-401 trial.

• NGN-401 safety profile is favorable to date in the first three participants who have been dosed in

Promoter	EXACT	Full-length	EXACT
miRNA	human MECP2	recognition sites

EXACT technology embeds a non-mammalian miRNA element and recognition sites to self-regulate transgene expression in each cell, designed to maintain the desired level and prevent overexpression toxicity.

Overdose

Therapeutic

Low

EXACT designed to provide therapeutic and tolerable levels of transgene expression on a cell-by-cell basis, even as dose increases AAV levels in highly transduced cells.

Fig. 8.

Cohort 1 dose is bracketed by efficacious doses in male murine knockout model, with a 4.1X safety margin to the NHP GLP toxicology study; Cohort 2 dose exceeds top efficacious dose studied in male murine knockout model and is still within the safety margins of the NHP GLP toxicology study

	Cohort 2
	Dose
	(3E15 vg)
Cohort 1
Dose
(1E15 vg)	1.4X

4.1X

Mecp2-/y	Mecp2-/y	NHP GLP
Efficacy	Efficacy	High Dose
	Mecp2+/-
	Tolerability

	the low-dose cohort, at ~11, ~8 and ~5 months post-dosing.
	•	There have been no signs or symptoms indicative of MeCP2 overexpression
		toxicity reported, including the participant with a mild variant (~11 months post-dosing),
		predicted to result in residual MeCP2 expression.
	•	Mild, asymptomatic changes in laboratory assessments that are known risks of AAV
		administration were observed. There have been no treatment-emergent or ICV procedure-
		related serious AEs.
•	Enrollment in the low-dose and high-dose cohorts is ongoing; first high-dose participant
	recently dosed. High-doseNGN-401 has been well-tolerated thus far with an early favorable
	safety profile.
•	Interim efficacy data are expected fourth quarter 2024.

References: (1) www.orpha.net. (2) Neul JL, et al. Ann Neurol 2010;68:944-50. (3) Anderson A, et al. Orphanet J Rare Dis 2014;9:87. (4) American Society of Gene & Cell Therapy 24th Annual Meeting. May 2021. (5) Ta D, et al. Orphanet J Rare Dis 2022;7:131.

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