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 SAFETY 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 gene 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 Toxicity

treatment window

• RTT disease severity is correlated with the amount of functional MeCP2 protein.

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.

NGN-401 was well-tolerated while unregulated gene therapy drove early toxicity in wild-typenon-human primates (NHPs).

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. 8. 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

Cohort 2

immunosuppression regimen:

3E15 vg

N=8

• Cohort 1: Corticosteroids

• Cohort 2: Targeted regimen of

Cohort 1

rituximab, sirolimus and shorter

1E15 vg

course of corticosteroids

N=8

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

~9 months

~6 months

~3 months

administration

•

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.

Fig. 6. NHP data confirm EXACT regulation technology and support encouraging tolerability profile for human testing

A

Unregulated and NGN-401MECP2 mRNA

B

Regulated*

Unregulated

C MECP2 mRNA

NGN-401 HAS BEEN GENERALLY WELL-TOLERATED

Table 2:

Table 3:

• All treatment-emergent adverse events (TEAEs) related to NGN-401 have

• No signs or symptoms indicative of MeCP2 overexpression toxicity

been mild/Grade 1 and transient or resolving, and most AEs are known

have been reported in any participant

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

NGN-401:

401-NGN RNA)

150

n = 3/group

100

changeFold over

(copiesper ug

50

0

5

4

3

2

1

Cortex Cortex

Cortex

Striatum

Midbrain

Pons

Cord Liver

Frontal

Motor Sensory

Hippocampus

CerebellumSpinal

Thalamus

  • NGN-4013.7E13 vg
  • NGN-4011.1E14 vg
  • Unregulated 3.7E13 vg
  • Unregulated 1.1E14 vg

2 2

3

131

Sural NCV unaltered Sural NCV reduced >3m/s

Complete loss of sural NCV response

  • Regulated includes NGN-401 and another EXACT vector at Day 30 or 92

10

8

n = 3/group

107

RNAg

10

5

copies/μ

10

6

10

3

10

4

102

101

Motor

Frontal

Sensory

Hippocampus

Midbrain Thalamus

Pons

Cord

Cortex

Cortex

Cortex

Cerebellum

Cervical

Spinal

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

potential risks of AAV

• There have been no treatment-emergent or ICV procedure-related serious

AEs (SAEs)

Number of Events

Clinical Sign or Symptom that May Indicate MeCP2 Protein

[Number of Participants]

Overexpression (derived from symptoms observed in MECP2

TEAEs related to NGN-401

13 [3]

duplication syndrome5)

Immunopathology (e.g., lymphadenopathy,

None

(all mild/Grade 1)

Elevated ALT

5 [3]

recurrent respiratory infection)

reported

New onset or worsening of

None

Elevated AST

3 [2]

Elevated GGT

1 [1]

persistent seizures

reported

Worsening of constipation

None

Decreased C3

1 [1]

reported

  • Includes EXACT gene 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.

  • In juvenile NHP ICV biodistribution study, an unregulated vector produced higher and more variable MECP2 mRNA expression compared to NGN-401 30 days post-dosing, demonstrating EXACT regulation in NHPs. (Fig. 6A)
  • EXACT regulated vectors were well-tolerated whereas unregulated vector demonstrated a loss of sural nerve conduction (NCV) in NHPs by Day 30. (Fig. 6B)
  • Expression of transgene mRNA 30 days post-dosing of NGN-401 in NHPs was below the level of endogenous MECP2 mRNA, avoiding overexpression concerns. (Fig. 6C)

Decreased C4

2 [2]

New onset cardiovascular events

None

Vomiting

1 [1]

reported

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: April 19, 2024

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.

CONCLUSIONS

Promoter

EXACT

Full-length

EXACT

miRNA

human MECP2

recognition sites

EXACT technology embeds a non-mammalian miRNA element and recognition sites to self-regulate gene 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. 7.

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

Cohort 1

(3E15 vg)

Dose

1.4X

(1E15 vg)

4.1X

Mecp2-/y

Mecp2-/y

NHP GLP

Efficacy

Efficacy

High Dose

Mecp2+/-

Tolerability

  • NGN-401gene therapy candidate is designed to be a best-in-class treatment for RTT.
  • NGN-401has been generally well-tolerated in all three participants who have been dosed in the low-dose cohort, at ~9, ~6 and ~3 months post-dosing.
  • There have been no signs or symptoms indicative of MeCP2 overexpression toxicity reported in any of the three participants, including the participant with a mild variant (~9 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 SAEs.
  • Enrollment in the low-dose and high-dose cohorts is ongoing and interim clinical data, including efficacy data, is 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) Daily JL, et al. Molecular Therapy, Vol. 29, No. 4, pp. 171-172. (5) Ta D, et al. Orphanet J Rare Dis 2022;7:131.

© 2024 Neurogene Inc. All rights reserved.

American Society of Gene and Cell Therapy 2024 | May 7-11, 2024 | Baltimore, MD I Abstract # 1408

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