Section 241: Advanced Gene Therapy and CRISPR Approaches in CBS/PSP

Section 241: Advanced Gene Therapy and CRISPR Approaches in CBS/PSP[@hudry2022]

Overview

<table class="infobox infobox-therapeutic">
<tr>
<th class="infobox-header" colspan="2">Section 241: Advanced Gene Therapy and CRISPR Approaches in CBS/PSP</th>
</tr>
<tr>
<td class="label">Serotype</td>
<td>Tropism</td>
</tr>
<tr>
<td class="label">AAV9</td>
<td>Neurons, astrocytes</td>
</tr>
<tr>
<td class="label">AAVrh.10</td>
<td>Neurons, microglia</td>
</tr>
<tr>
<td class="label">AAV2</td>
<td>Neurons (traditionally)</td>
</tr>
<tr>
<td class="label">AAV1</td>
<td>Motor neurons</td>
</tr>
<tr>
<td class="label">AAV-PHP.B</td>
<td>Enhanced CNS</td>
</tr>
<tr>
<td class="label">Promoter</td>
<td>Expression Pattern</td>
</tr>
<tr>
<td class="label">Synapsin</td>
<td>Neuron-specific</td>
</tr>
<tr>
<td class="label">GFAP</td>
<td>Astrocyte-specific</td>
</tr>
<tr>
<td class="label">CMV</td>
<td>Broad (ubiquitous)</td>
</tr>
<tr>
<td class="label">Mecp2</td>
<td>Neuron-specific</td>
</tr>
<tr>
<td class="label">hSyn</td>
<td>Strong neuronal</td>
</tr>
<tr>
<td class="label">Primary target</td>
<td>ER, multi-pathway</td>
</tr>
<tr>
<td class="label">Distribution</td>
<td>Better brain distribution</td>
</tr>
<tr>
<td class="label">Safety profile</td>
<td>Favorable</td>
</tr>
<tr>
<td class="label">ER stress reduction</td>
<td>Yes</td>
</tr>
<tr>
<td class="label">Clinical stage</

Section 241: Advanced Gene Therapy and CRISPR Approaches in CBS/PSP[@hudry2022]

Overview

<table class="infobox infobox-therapeutic">
<tr>
<th class="infobox-header" colspan="2">Section 241: Advanced Gene Therapy and CRISPR Approaches in CBS/PSP</th>
</tr>
<tr>
<td class="label">Serotype</td>
<td>Tropism</td>
</tr>
<tr>
<td class="label">AAV9</td>
<td>Neurons, astrocytes</td>
</tr>
<tr>
<td class="label">AAVrh.10</td>
<td>Neurons, microglia</td>
</tr>
<tr>
<td class="label">AAV2</td>
<td>Neurons (traditionally)</td>
</tr>
<tr>
<td class="label">AAV1</td>
<td>Motor neurons</td>
</tr>
<tr>
<td class="label">AAV-PHP.B</td>
<td>Enhanced CNS</td>
</tr>
<tr>
<td class="label">Promoter</td>
<td>Expression Pattern</td>
</tr>
<tr>
<td class="label">Synapsin</td>
<td>Neuron-specific</td>
</tr>
<tr>
<td class="label">GFAP</td>
<td>Astrocyte-specific</td>
</tr>
<tr>
<td class="label">CMV</td>
<td>Broad (ubiquitous)</td>
</tr>
<tr>
<td class="label">Mecp2</td>
<td>Neuron-specific</td>
</tr>
<tr>
<td class="label">hSyn</td>
<td>Strong neuronal</td>
</tr>
<tr>
<td class="label">Primary target</td>
<td>ER, multi-pathway</td>
</tr>
<tr>
<td class="label">Distribution</td>
<td>Better brain distribution</td>
</tr>
<tr>
<td class="label">Safety profile</td>
<td>Favorable</td>
</tr>
<tr>
<td class="label">ER stress reduction</td>
<td>Yes</td>
</tr>
<tr>
<td class="label">Clinical stage</td>
<td>Phase 1-2 completed</td>
</tr>
<tr>
<td class="label">Delivery</td>
<td>Intraparenchymal</td>
</tr>
<tr>
<td class="label">Program</td>
<td>Company</td>
</tr>
<tr>
<td class="label">BIIB080 (MAPTRx)[@mummadi2022]</td>
<td>Biogen/Ionis</td>
</tr>
<tr>
<td class="label">NIO752</td>
<td>Novartis/Ionis</td>
</tr>
<tr>
<td class="label">ARO-MAPT</td>
<td>Arrakis</td>
</tr>
<tr>
<td class="label">Factor</td>
<td>Score</td>
</tr>
<tr>
<td class="label">Mechanism</td>
<td>9/10</td>
</tr>
<tr>
<td class="label">Clinical readiness</td>
<td>6/10</td>
</tr>
<tr>
<td class="label">Delivery feasibility</td>
<td>5/10</td>
</tr>
<tr>
<td class="label">Safety profile</td>
<td>7/10</td>
</tr>
<tr>
<td class="label">CBS/PSP specificity</td>
<td>8/10</td>
</tr>
<tr>
<td class="label">Combination potential</td>
<td>8/10</td>
</tr>
<tr>
<td class="label">Total</td>
<td>43/60</td>
</tr>
</table>

Gene therapy represents one of the most promising therapeutic frontiers for corticobasal syndrome (CBS) and progressive supranuclear palsy (PSP). These approaches target the root causes of neurodegeneration at the genetic level, offering the potential for disease modification rather than merely symptomatic relief. This section covers the major gene therapy modalities—AAV-mediated gene delivery, CRISPR-based gene editing, antisense oligonucleotides (ASOs), and the critical delivery challenges that determine clinical success.

241.1 AAV Delivery Platforms

241.1.1 AAV Serotypes for CNS Delivery

Adeno-associated viruses (AAVs) are the dominant delivery platform for CNS gene therapy due to their favorable safety profile and ability to transduce neurons with long-term expression. Key serotypes for brain delivery include:

BBB Crossing Strategies: Natural AAV serotypes have limited ability to cross the blood-brain barrier (BBB). Current approaches include:

• Intraparenchymal injection: Direct brain delivery bypassing BBB
• Intrathecal delivery: Injection into cerebrospinal fluid for broader distribution
• Engineered serotypes: AAV-PHP.B and variants with enhanced CNS tropism
• Receptor-mediated transcytosis: Engineering AAV capsids with brain-targeting ligands

241.1.2 Promoter Selection

The choice of promoter determines which cell types express the therapeutic gene:

Synapsin promoters are preferred for neuronal gene therapy in CBS/PSP because they provide neuron-specific, long-term expression with minimal off-target effects.

241.1.3 Clinical-Stage AAV Programs

Parkinson's Disease (relevant to CBS/PSP):

• VY-AADC (Voyager Therapeutics): AAV-delivered AADC (aromatic L-amino acid decarboxylase) gene to convert levodopa to dopamine directly in the brain. Phase 1b showed sustained motor improvements.
• AAV-GDNF (various): AAV-delivered GDNF to provide trophic support to dopaminergic neurons. Multiple trials completed with mixed results.
• AAV-NTN (Cere-120): AAV-neurturin for trophic support.

• AAV-GRN (Biogen): AAV-delivered progranulin for FTD-GRN mutations. Relevant to CBS cases with GRN mutations.

• AAV-anti-tau: Various programs delivering anti-tau shRNA or scFv constructs.

241.2 CDNF Gene Therapy

241.2.1 Mechanism of Action

Cerebral Dopamine Neurotrophic Factor (CDNF) is a secreted protein that provides powerful neuroprotection to dopaminergic neurons through multiple mechanisms:

241.2.2 CDNF vs. GDNF Comparison

241.2.3 Clinical Trial Status

NCT01362994 (Herantis Pharma):

• First-in-human study of CDNF in Parkinson's disease
• Results: CDNF was generally well-tolerated with preliminary efficacy signals in motor function
• Status: Phase 1-2 completed; Phase 2b planned
• Relevance to CBS/PSP: CDNF's ER stress reduction mechanism is particularly relevant to 4R-tauopathies like CBS/PSP, where tau pathology induces significant ER stress

241.2.4 CBS/PSP Considerations

CDNF gene therapy for CBS/PSP patients:

• Rationale: Tau pathology causes ER stress in neurons; CDNF directly addresses this mechanism
• Delivery: Requires convection-enhanced delivery (CED) for optimal brain distribution
• Combination potential: Could be combined with anti-tau immunotherapies for multi-target approach
• Patient selection: Alpha-synuclein negative patients (like this patient) may respond better to tau-targeted approaches

241.3 Antisense Oligonucleotide (ASO) Approaches

241.3.1 ASO Mechanism

ASOs are single-stranded DNA sequences (12-24 nucleotides) that bind complementary mRNA via Watson-Crick base pairing. Upon binding, they recruit RNase H to cleave the hybridized mRNA, leading to reduced protein translation.

For tau reduction in CBS/PSP:

• Target: MAPT gene mRNA
• Outcome: Reduced tau protein production
• Delivery: Intrathecal (lumbar puncture) every 3-6 months

241.3.2 Clinical-Stage ASO Programs

BIIB080 (IONIS-MAPT):

• Most advanced tau-targeting ASO
• Phase 1/2 demonstrated dose-dependent CSF tau biomarker reductions
• Administered via intrathecal injection every 3-6 months
• Currently in Phase 2 trials for PSP and AD

• Second-generation MAPT ASO with improved CNS penetration
• Phase 1 trial completed in 2024 showing target engagement in PSP patients

241.3.3 CBS/PSP Application

ASO therapy is particularly relevant for CBS/PSP because:

• 4R-tau: ASOs can be designed to specifically reduce 4R tau isoforms
• Genetic forms: Patients with MAPT mutations could benefit from allele-specific ASOs
• Disease modification: Reduces tau at the source rather than clearing after it's produced

• Requires intrathecal delivery (lumbar puncture)
• Effects are reversible (requires repeated dosing)
• Distribution limited to spinal cord and cortex

241.4 CRISPR-Based Gene Editing

241.4.1 CRISPR-Cas9 Approaches

CRISPR-Cas9 enables precise genome editing with potential for permanent therapeutic benefit:

Applications in CBS/PSP:

241.4.2 Base Editing

Base editing allows precise single-nucleotide changes without double-strand breaks:

• Cytosine base editors (CBE): Convert C→T or G→A
• Adenine base editors (ABE): Convert A→G or T→C
• Prime editing: More versatile, allows all 12 possible base changes plus insertions/deletions

• No double-strand breaks (fewer off-target effects)
• Higher precision for point mutations
• Lower immunogenicity

241.4.3 Current Status

CRISPR-based approaches for neurodegeneration remain primarily in preclinical development:

• Delivery to the brain remains the major challenge
• AAV-delivered CRISPR components showing promise in animal models
• Clinical trials for other diseases (SCA1, Huntington's) will inform CNS CRISPR delivery

• MAPT mutations: Some familial CBS/PSP cases have MAPT mutations that could be corrected
• GRN mutations: Progranulin deficiency in some CBS cases
• GBA mutations: Associated with CBS/PSP risk

241.5 Delivery Methods

241.5.1 Intraparenchymal Injection

Direct injection into brain tissue:

• Advantages: Precise targeting, bypasses BBB
• Disadvantages: Invasive, limited distribution
• Use: GDNF, CDNF, AAV vectors

241.5.2 Convection-Enhanced Delivery (CED)

Bulk flow-mediated delivery:

• Advantages: Improved distribution vs. bolus injection
• Disadvantages: Requires specialized equipment
• Use: CDNF, GDNF, large molecules

241.5.3 Intrathecal Delivery

Injection into cerebrospinal fluid:

• Advantages: Broader CNS distribution than intraparenchymal
• Disadvantages: Limited penetration to deep brain structures
• Use: ASOs, some AAV serotypes

241.5.4 Intranasal Delivery

Non-invasive nasal administration:

• Advantages: Non-invasive, potential for repeat dosing
• Disadvantages: Limited CNS penetration
• Use: Proteins, peptides, some viral vectors (research stage)

241.5.5 BBB Modulation

Techniques to enhance BBB permeability:

• Focused ultrasound (FUS): Temporary BBB opening with microbubbles
• Chemical enhancers: Mannitol, bradykinin analogs
• Receptor-mediated transcytosis: Engineering vectors with transferrin or insulin receptor ligands

241.6 NET Assessment

241.7 Drug Interactions with Current Regimen

Levodopa/Carbidopa:

• No direct interaction with gene therapy mechanisms
• Gene therapy does not affect dopaminergic medication metabolism
• Continue standard levodopa regimen during treatment

• No direct interaction with gene therapy mechanisms
• Important: Some ASO trials use lithium as a tau phosphorylation inhibitor—lithium is CONTRAINDICATED with MAO-B inhibitors due to serotonin syndrome risk
• Verify ASO trial protocols avoid lithium if considering combination

241.8 Clinical Recommendations

For This Patient (CBS/PSP, alpha-synuclein negative)

Patient Action Items

• [ ] Discuss with neurologist about gene therapy trial eligibility
• [ ] Consider WGS to identify potentially targetable genetic variants
• [ ] Monitor BIIB080 (ASO) Phase 2 results for PSP indication
• [ ] Research CDNF Phase 2b trial availability
• [ ] Evaluate combination approach (gene therapy + anti-tau immunotherapy) once available

241.9 Cross-Links

• [Gene Therapy Overview](/therapeutics/gene-therapy) — General gene therapy principles
• [CDNF Therapy](/therapeutics/cdnf-therapy-parkinsons) — Detailed CDNF information
• [CRISPR Therapies CBS/PSP](/therapeutics/section-107-crispr-therapies-cbs-psp) — CRISPR-specific content
• [ASO Brain Delivery](/therapeutics/aso-brain-delivery) — Delivery mechanisms
• [Tau Therapeutics](/therapeutics/tau-targeted-therapeutics) — Anti-tau approaches
• [Neurotrophic Factor Therapies](/therapeutics/neurotrophic-factor-therapies) — GDNF, BDNF, CDNF comparison
• [iPSC Drug Screening](/therapeutics/ipsc-neurons-drug-screening-cbs-psp) — Patient-specific testing

References

Related Hypotheses

From the [SciDEX Exchange](/exchange) — scored by multi-agent debate

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• [Vocal Cord Neuroplasticity Stimulation](/hypothesis/h-e0183502) — <span style="color:#ffd54f;font-weight:600">0.48</span> · Target: CHR2/BDNF
• [Bacterial Enzyme-Mediated Dopamine Precursor Synthesis](/hypothesis/h-7bb47d7a) — <span style="color:#ffd54f;font-weight:600">0.44</span> · Target: TH, AADC
• [CYP46A1 Overexpression Gene Therapy](/hypothesis/h-2600483e) — <span style="color:#81c784;font-weight:600">0.79</span> · Target: CYP46A1

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