Lecture 8: Gene Therapy For Neurological Disease Flashcards

1
Q

Gene Therapy For

Neurological Disease

A

Kevin Foust

Sepember 23

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2
Q

When should you use gene therapy?

Gene Therapy is not a solve-all solution, as previously believed.

A

Single-gene problems, such as Hemophilia, are much more likely to be cures using gene therapies; but multi-gene issues, like diabetes, are not issues that gene therapy can really solve, at this point.

Single gene vs. complex disorder

Define the targets—gene, cell, patient

What gene(s)? What cells must be affected to bring about cure?
Are the patients young, old; do they have weak immune systems?
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3
Q

Blood Brain Barrier System

A

Keeps the environment of the brain constant.

Ensures the homeostasis of the CNS.

The BBB is formed primarily of Epithelial Cells that form tight junctions that keep things out, including disease and medications. Due to factors of size and charge, many molecules cannot get past the BBC

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4
Q

Cerebral Spinal Fluid

A

CSF is pressurized, so you have to be really careful with the volume of the injections; you don’t want to throw off the balance or cause hemorrhages.

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5
Q

ASGCT

A

The American Society of Gene & Cell Therapy

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6
Q

What is Gene Therapy?

A

Gene therapy is defined as a set of strategies that modify the expression of an individual’s genes or that correct abnormal genes.

Each strategy involves the administration of a specific DNA (or RNA).

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7
Q

Obstacles to CNS Gene Therapy

A
  • Bones (skull, vertebral column)
    Only certain patient populations can tolerate a procedure that drills through bone.

Blood Brain Barrier (BBB)

Complex anatomy

Widespread pathology

Multiple targets

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8
Q

Upper motor neurons

A

Upper motor neurons are motor neurons that originate in the motor region of the cerebral cortex or the brain stem and carry motor information down to the lower motor neurons.

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9
Q

Obstacles to CNS Gene Therapy:

Astrocytes

A

Once you have gotten beyond the BBB, astrocytes present another defense.

Astrocytes can also modulate the rate at which the brain’s vasculature lets things in and out.

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10
Q

Lower Motor Neurons

A

The final pathway in voluntary movement.

Lower motor neurons are motor neurons located in either the ventral horn of the spinal cord and anterior nerve roots (spinal lower motor neurons) or the cranial nerve nuclei of the brainstem and cranial nerves with motor function (cranial nerve lower motor neurons).

Lower motor neuron: A nerve cell that goes from the spinal cord to a muscle. The cell body of a lower motor neuron is in the spinal cord and its termination is in a skeletal muscle. The loss of lower motor neurons leads to weakness, twitching of muscle (fasciculation), and loss of muscle mass (muscle atrophy).

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11
Q

Which type of motor neurons die in diseases like ALS?

A

Lower Motor Neurons and upper…

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12
Q

Obstacles to CNS Gene Therapy:

Widespread pathology

A

Example of a disease with widespread pathology: Alzheimer’s

Can one possibly design a treatment that would go after literally everything in the brain and fix it?

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13
Q

Parkinson’s is different from Alzheimer’s.

It is very localized (Substantia Nigra), and sometimes it is treated with direct injections to the brain.

A

This is why Parkinson’s would be easier to treat with gene therapy methods than Alzheimer’s would.

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14
Q

How to Deliver a Gene Therapy to the CNS

A

Direct Injection

Cerebrospinal Fluid (CSF)

Retrograde Transport

Systemic Injection

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15
Q

Why Use Vectors?

A

Vectors can protect DNA from degradation and from causing an immune response, and vectors can enhance transfer into the target cell.

Low efficiency from naked
DNA/RNA transfer… basically meaning that if you throw just DNA at a cell, it will bounce right off. Cells don’t generally pick up nucleic acids.

In fact, the “rogue/unfamiliar” DNA of gene therapy can promote an immune response as though it was a disease.

Non-viral

Viral

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16
Q

Non-Viral Vectors

A

Scaleable, ease of manufacture:
“You can make a bucket of this stuff.” Viral vectors are more complicated.

Transient Expression: It’s active for a short time and then it goes away. This can be good or bad.

High payload capacity

Customizable

Liposomes

Polymers

Molecular Trojan Horses

Nuclear Entry –> RNAi

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17
Q

Molecular Trojan Horse

A

Antibody against human Insulin receptor

Attach protein, drug or DNA

Transient gene expression

All components FDA approved

18
Q

Viral Vectors

Types

A

Adenovirus

Lentivirus

Adeno-Associated Virus

19
Q

Adenovirus

A

The first virus to be used as a vector.

DNA Virus

3 stage replication cycle.

Based on the human Adenovirus 5, which causes Respiratory infections (like colds)

Payload size: Generations

Immunogenicity: Transient expression

Jessie Gelsinger died because of this therapy in early stages.

20
Q

Lentivirus

A

RNA virus:
Complex biology
Based on many platforms, including HIV

Integrating

Payload ~9kb

Enveloped

Life-long expression, but harder to manufacture

Stable Expression

Low Titer

21
Q

Why doesn’t DNA get through membranes?

A

Phosphates carry a negative charge. Both DNA and cell membranes have of these negative components. Negative and negative don’t go together, so they repel each other.

Thus a vector is needed to get DNA in the cell.

22
Q

Adenovirus & Cancer

A

Cancer—
Adenovirus
HSV-TK + ganciclovir

Glioblastoma multiforme

Adenovirus vectors seem to always attract immune response, which is good when dealing with cancer

23
Q

Adeno-Associated Virus (AAV)

A

VERY Small, non-pathogenic (unlike lenti. and ad. viruses) parvovirus

Gene therapy vector

Long-term transgene expression

Post-mitotic cells

Easy to convert to vector

Two types of recombinant genomes:
Single stranded—4.7kb
Self Complementary—2.5kb

Safe

Episomal

Long-term, stable expression

Efficacious

AAVs require helper viruses

24
Q

Leber’s Congenital Amaurosis

A

genetic form of blindness

Three independent groups

Unilateral subretinal injections

AAV2-RPE65

AAV injections Treat bad Eye

25
Q

What’s Next?

A

Global CNS
transduction

AAV9 crosses the BBB, soon it will be used

26
Q

Efficient Postnatal Gene Expression in MN

A

??

27
Q

Spinal Muscular Atrophy

A

1:6,000 live births

Autosomal recessive

Multiple clinical presentations

Type 1 is most common

Present by 6 months—
death by 2-3 years

Only palliative care

28
Q

Survival Motor Neuron

A

defects in the Survival Motor Neurons cause Spinal Muscular Atrophy

THE DISEASE OCCURS WHEN ONLY SMN 2s ARE PRESENT

Two copies of SMN—
SMN1 and SMN2

Identical aa sequence

SMN1 ~100% full length protein

SMN2 ~10-20% full length protein

SMN2 Is A Disease Modifier

29
Q

SMA Animal Models

A

SMA Animal Models

Mice have one copy of Smn

Smn-/- embryonic lethal

Genomic SMN2 on null mouse

Avg survival 5d

Further addition of SMN 7 cDNA

Avg survival 14-15d

30
Q

SMA Therapeutics

A

Target SMN2:
Transcriptional activation
Modify SMN2 splicing

Gene Replacement

31
Q

Postnatal SMN Expression Rescues SMA Mice

A

Survival

NMJ analysis

Intermediate body weight

Postnatal SMN Expression Normalizes Ambulation

32
Q

How Predictive is a Mouse?

A

Mouse suggests a narrow window for MN targeting

Limited data in primates

Potential problem for clinical development

33
Q

IV AAV9 Targets MNs in Young NHP

A

Male Cynomolgus Macaques

Injected at 1, 30 and 90d old

Sac’d 14-25d post injection

34
Q

IV AAV9 Targets MNs in 3yo NHP

A

Interventional radiology

2.5e13 vg/kg

Sac’d 25d post injection

35
Q

Systemic AAV9 Delivery is Well Tolerated

A

AAV9-SMN

GLP-like P1 mice (high dose)—Safe

P90 monkeys (targeted clinical dose)

P1 monkey (high dose)

Control Values

36
Q

AAV9 SMN Gene Therapy

A

Received FDA approval

First in human
 Spinal Muscular Atrophy
 AAV9
 Infants (0-6 months)

Nationwide Children’s Hospital

37
Q

MeCP2 Disorders

A

Methyl CpG binding protein

Highly abundant in neurons

Also expressed in
astrocytes and microglia

X-linked protein—XCI

Deficiency leads to Rett syndrome— primarily affects girls

Duplication causes ASD in boys
(duplication syndrome)

38
Q

AAV9 MECP2 Rescues Rett Mice

A

??

39
Q

Prosavin

A

Long-term safety and tolerability of ProSavin, a lentiviral vector-based gene therapy for Parkinson’s disease

Improves motor symptoms in
lesioned NHP

No dyskinesias

In Phase I/II in Britain

40
Q

What is Gene Therapy?

A

Gene therapy is defined as a set of strategies that
modify the expression of an individual’s genes or
that correct abnormal genes.

Each strategy involves the administration of a specific DNA
or RNA.