L6 Gene Therapy for Neurological Disorders Flashcards
What does gene replacement allow for?
Correction of loss-of-function (e.g. SMN in SMA) and gain-of-function mutations (e.g. silencing SOD1 in ALS)
What will most CNS gene-based therapies require?
A sustained delivery of the exogenous transgene throughout life, which can be achieved with AAV
AAV expression can endure for decades in __ cells, like __
post-mitotic cells like neurons
What do gene-based therapies offer?
- Ability to directly target disease pathogenesis
- Capacity to achieve a ‘permanent correction’
- A single long-lasting intervention that provides sustainable pharmacology and efficacy
Why are AAV vectors the current major players in gene-based therapies?
- demonstrate strong neuronal tropism
- widespread distribution
- have mostly shown positive safety profiles in early stage clinical trials
Essential components of gene therapy
- vector
- promoter
- transgene
AAV genome contains genes for __ and __ , which are flanked by __
Rep and Cap
inverted terminal repeats (ITRs)
How many proteins does Rep gene encode?
4, which are required for viral genome replication & packaging
Cap gene encodes…
3 overlapping structural viral capsid proteins - form the outer capsid shell that protects viral genome (also involved in cell binding & internalisation)
Importance of AAV capsid
Important in determining several key features of effective AAV gene therapy:
- Tissue tropism
- Distribution
- Susceptibility to targeting by nAbs
Administration of AAV vectors to CNS via __ route demonstrates sustained transduction of neurons
intraparenchymal
Which viral vector is most frequently used in clinical trials?
AAV2
Greatest challenges with AAV delivery for NDDs
Biodistribution and homogeneity of cellular transduction
Primary cell surface receptor used by AAVs
heparin sulfate proteoglycans
Secondary receptors for AAVs
FGF receptor, laminin receptor, αVβ5 integrin (for AAV2)
Advantages of IPa delivery
- bypasses BBB and delivery genes directly
- one and done feature
- well-tolerated
- minimal biodistribution to peripheral organs
- reduced immunogenicity
- significantly lower vector doses required
Additional routes of administration
- Intrathecal
- Intracerebroventricular
- Intracisternal
- Intravenous
Disadvantages of IV administration
- Exposes the virus to potential Ab neutralisation in subjects who have been pre-exposed to natural AAV infections
- Typically requires higher total doses to achieve efficient transduction
- Broad distribution to multiple peripheral tissues
What is spinal muscular atrophy?
A progressive monogenic lower motor neuron disease
SMA is primarily caused by…
the homozygous deletion of the SMN1 gene that encodes the survival motor neuron protein
As patients with SMA lack a functional SMN1 gene, severity of symptoms and age of disease onset is determined by…
copy numbers of the SMN2 gene
Most common form of SMA
SMA type 1: patients tend to have 2 copies of SMN2 gene
What happened in the landmark gene therapy clinical trial in 15 infants with SMA type 1?
They received a single IV injection (high or low dose) of AAV9 vector carrying SMN1 gene (AVXS-101). All patients were alive & event-free at 20 months with a historic survival rate of 8%.
When was AVXS-101 FDA approved?
2019
AAV-based gene therapies have been used to … in PD
upregulate DA signalling
3 rate-limiting enzymes that regulate DA synthesis pathway
GCH1, TH, AADC
Clinical trials with IPa administration of AAV2 encoding __ in PD patients
AADC (aromatic L-amino acid DOPA decarboxylase)
What is the benefit of administering AAVs encoding rate-limiting enzymes involved in DA synthesis pathway to PD patients?
- Patients can regulate the amount of L-DOPA they take to control the amount of dopamine produced by this new depot
- Bypasses degenerating dopaminergic neuronal projections from SN
Lentivirus-based gene therapy that delivers all 3 rate-limiting enzymes
ProSavin - well tolerated in Phase I/II
2 promising candidates involved in promoting survival of DA midbrain neurons
GDNF and Neurturin
Phase I trials to determine the safety of bilateral … injections into the putamen are ongoing
AAV2-GDNF IPa injections
A possible reason for the limited success of GDNF and NTRN in PD
Some patients show reduced expression of Ret, the receptor of both NTRN and GDNF, so these trophic factors cannot confer protection through Ret
Strategies to target genes in PD
- Attenuate LRRK2 expression
- Augment GCase activity
Where does the most common PD risk variant, G2019S, lie?
in the catalytic site of LRRK2, enhancing its kinase activity
Why is gene therapy useful for targeting LRRK2?
Because LRRK2 is also expressed in lungs, kidneys and spleen. Gene therapy can specifically inhibit LRRK2 in the brain, while avoiding pathological changes in other tissues.
LRRK2 ASO in Phase I trial
BIIB094
Why is increasing GCase activity a promising therapeutic approach in PD?
Because decreased GCase levels are seen in cases of PD with GBA1 mutations (cause GCase deficiency), as well as sporadic PD (without GBA1 mutations)
What did direct IPa injections of AAV-GBA1 in the brain of preclinical models lead to?
Decreased α-synuclein levels and pathology
Phase I/II clinical trial was recently launched to treat patients with PD by intracisternal injection of…
AAV9-GBA1 into the CSF
Preclinical models showed that injection of AAV-HTT miRNA into striatum…
significantly reduced HTT expression, which led to improved motor and behavioural deficits without over neurotoxicity
What is AMT-130?
Consists of an AAV5 vector carrying an artificial miRNA specifically tailored to silence the HTT gene (currently in Phase I/II trial)
Result of gene-based therapy for ALS in transgenic SOD1 mouse model
IV delivery of AAV9-SOD1 shRNA reduced SOD1 levels, slowed disease progression and prolonged lifespan
