AMPAKINE Compounds for the Treatment of Rett Syndrome

Mark A VarneyChief Scientific Officer

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Hypothesis

• Depressed Levels of BNDF Contribute to the Phenotype of Rett Syndrome – Lifespan

– Motor Activity

– Cortical Layer V Firing

– Breathing Abnormalities

• Increase Brain BDNF to Attenuate Rett Symptoms

Chang et al, 2006. Neuron 49, 341–348Wang et al, 2006. J Neurosci 26:10911–5

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BDNF – A Major Regulator of SynapticPlasticity

• Synthesized and stored in glutamatergic neurons and is released in an activity-dependent manner

• Critical for neuronal survival and differentiation

• Plays a role in fast excitatory synaptic transmission and synaptic plasticity, including LTP and LTD

• Critical for synaptic plasticity and memory processing in the adult brain

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Strategy

• Treat with AMPAKINE Molecules to Increase Endogenous BDNF Levels in Specific Brain Regions– AMPAKINEs are small molecules that

positively modulate the AMPA receptor

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AMPA Receptors Play a Key Role in Glutamatergic Transmission

• Glutamate is the major excitatory neurotransmitter in the CNS

• Virtually all neurons express glutamate receptors

• Fast excitatory transmission is mediated by AMPA receptors

Swanson et al. (2005)Nat Rev Drug Dis 41: 131-144

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AMPAKINE Molecules

• AMPA receptors deactivate and/or desensitize extremely rapidly (~2-10 ms)

• AMPAKINEs are allosteric positive modulators of the AMPA receptor

– Attenuate deactivation and/or desensitization of AMPA receptors

– Strengthen synaptic transmission and facilitate long term potentiation (LTP), widely regarded as the substrate for memory

– Stimulate BDNF production

Deactivation Desensitization1 ms Pulse 500 ms Pulse

Baseline + AMPAKINE Superimposed Baseline + AMPAKINE Superimposed

Deactivation Desensitization1 ms Pulse 500 ms Pulse

Baseline + AMPAKINE Superimposed Baseline + AMPAKINE Superimposed

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AMPAKINE Treatment

Acute Effects

(Lasts with the t½ of the drug)

•Memory •Cognition•Psychiatric disorders

Chronic Effects

(Trophic induction lasting

≥ one day)

•Memory •Cognition•Psychiatric disorders•Degenerative diseases

AMPAKINEs Have Acute and Chronic Effects In Vivo

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1. Brief treatment with

AMPAKINE causes long

lasting increases in BDNF

2. Use daily injections of short half-life AMPAKINEs to

chronically increase BDNF levels.

3. BDNF then promotes plasticity and neuronal viability

Chronic Effects of AMPAKINEs

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Chronic Effects of AMPAKINEs on BDNF

Rat Cortical Cultures Cultured Hippocampal Slices In Vivo

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25uM

CX92

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X929

mRNA

3 hr AMPAKINE pulse, mRNA at 18 hrs

Protein

1 injection/day for 7 days, Hippocampus collected 24

hrs after last treatment

Protein

6 hr AMPAKINE pulse, protein at 24 hrs

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Huntington’s Disease (HD)

• Progressive, hereditary brain disease that causes changes in movement, thinking and behavior

• Onset commonly between ages 30-50• 30,000 people in US (~1/10,000)• Caused by excessive CAG repeats in the

huntingtin gene • Disturbances in executive function are

probably earliest manifestation• Neuropathology, particularly in striatum, in

later phases• BDNF levels are reduced in HD postmortem

brain and transgenic mouse models

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Reduced BDNF and Defective LTP in Asymptomatic HD Knock-in Mice

Lynch et al., J. Neurosci 2007

TBS: 10 bursts of 4 pulses 100 Hz; separated by 200 msec

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AMPAKINE Treatment Paradigm

HD Knock-in Mice

Injected with Vehicle or CX929 at 5 mg/kg/day i.p. for

between 4 to 30 days

18-24 hours after the last dose, measure•Hippocampal LTP•Actin Polymerization•Locomotor Effects•BDNF Measurements•Cognition

CX929 selected because of its short t½ of 15min and robust effects on BDNF

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CX929 Up-regulates Mature BDNF in HD Knock-in Mice and Restores LTP

Mature hippocampal BDNF and LTP assayed 18 hrs after the last of 30 daily treatments with CX929

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Normal HD HD+CX929

Mature HippocampalBDNF Protein

Hippocampal LTP

•Cognitive deficits restored and motor deficits prevented by CX929

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Current Studies

• Evaluate if AMPAKINE treatment corrects Rett phenotypes in Mecp2-/y mice– Respiration

– BDNF levels

– Other behaviors

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Summary

• AMPAKINE molecules increase brain BDNF levels

• Transgenic HD mice have deficits in BDNF levels and deficits in hippocampal LTP– The short acting AMPAKINE, CX929 can restore

depressed BDNF levels and hippocampal LTP deficits

• Rett Mice have deficits in BDNF

• Currently testing AMPAKINEs in Rett mice to see if it restores normal phenotype