Antisense Oligonucleotide Therapy for C9orf72 ALS/FTD
Overview
<table class="infobox infobox-therapeutic">
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<th class="infobox-header" colspan="2">Antisense Oligonucleotide Therapy for C9orf72 ALS/FTD</th>
</tr>
<tr>
<td class="label">Name</td>
<td><strong>Antisense Oligonucleotide Therapy for C9orf72 ALS/FTD</strong></td>
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<td class="label">Type</td>
<td>Therapeutic</td>
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Antisense oligonucleotide (ASO) therapy targeting [C9orf72](/genes/c9orf72) represents one of the most promising disease-modifying approaches for amyotrophic lateral sclerosis (ALS) and frontotemporal dementia (FTD) caused by hexanucleotide repeat expansions. This therapeutic strategy aims to reduce the levels of toxic dipeptide repeat proteins (DPRs) generated by aberrant translation of the expanded GGGGCC repeat in the [C9orf72](/entities/c9orf72) gene. [@zhang2019]
C9orf72 repeat expansions are the most common genetic cause of familial ALS and FTD, accounting for approximately 40% of familial ALS cases and 25% of familial FTD cases. The development of ASO therapies specifically targeting this mutation represents a precision medicine approach to neurodegenerative disease treatment. [@krach2018]
Mechanism of Action
Hexanucleotide Repeat Expansion Pathogenesis
The C9orf72 gene contains a polymorphic hexanucleotide repeat expansion (GGGGCC) in its first intron that can expand from the normal 2-30 repeats to hundreds or even thousands of repeats in affected individuals. This expansion leads to disease through three primary mechanisms: [@peters2015]
RNA Toxicity: The expanded repeat RNA forms nuclear RNA foci that sequester essential RNA-binding proteins, including hnRNPs (heterogeneous nuclear ribonucleoproteins), disrupting normal RNA processing and splicing.
Dipeptide Repeat Protein (DPR) Toxicity: Aberrant translation of the expanded repeat in all three reading frames produces five distinct DPRs: poly-GA, poly-GP, poly-GR, poly-PA, and poly-PR. These aggregating proteins cause proteostasis disruption, nucleocytoplasmic transport defects, and mitochondrial dysfunction.
Loss of Function: The expansion reduces C9orf72 mRNA expression through epigenetic silencing, potentially disrupting normal lysosomal and autophagic functions in [neurons](/entities/neurons) and glial cells.ASO Design and Target Selection
ASOs are short, single-stranded oligonucleotides (typically 12-25 nucleotides) that bind to complementary target RNA via Watson-Crick base pairing. For C9orf72 ASO therapy, the primary targets include: [@mori2013]
- Repeat-Containing RNA: ASOs can be designed to bind specifically to the expanded repeat RNA, preventing the formation of toxic RNA foci and blocking aberrant DPR translation through a mechanism called repeat-associated non-AUG (RAN) translation.
- Splice-Modifying ASOs: Alternative approaches target the C9orf72 pre-mRNA to modulate splicing, potentially increasing the expression of the more functional C9orf72 isoform or reducing toxic transcript variants.
The most advanced ASO candidates target the repeat RNA to suppress DPR production while preserving as much normal C9orf72 function as possible. [@gendron2017]
Pharmacodynamics
Upon binding to target RNA, ASOs exert their effects through two primary mechanisms: [@jiang2016]
RNase H1-Mediated Degradation: Gapmer ASOs contain a central DNA-like region that recruits RNase H1, an endonuclease that cleaves the RNA strand in DNA-RNA hybrids, leading to target RNA degradation.
Steric Blockade: Steric-blocking ASOs (non-gapmer) bind to target RNA without recruiting RNase H, instead blocking translation initiation, ribosomal assembly, or splice site recognition without degrading the target.Preclinical Evidence
iPSC Models
Patient-derived induced pluripotent stem cell (iPSC) models have been instrumental in validating ASO therapy for C9orf72 ALS/FTD: [@donnelly2013]
RNA Foci Reduction: Studies have demonstrated that ASO treatment effectively reduces C9orf72 RNA foci in patient-derived motor neurons and cortical neurons. This reduction correlates with decreased sequestration of RNA-binding proteins like hnRNPA1 and SRSF2. [@lagiertourenne2013]
Dipeptide Repeat Protein Suppression: Multiple studies have shown that ASO treatment significantly reduces DPR protein levels in iPSC-derived neurons. For example, ASOs targeting the repeat region reduce poly-GA, poly-GR, and poly-PR levels by 60-90% depending on the cell model and ASO design. [@zheng2023]
Rescue of Cellular Phenotypes: Beyond reducing toxic species, ASO treatment has been shown to rescue several disease-relevant cellular phenotypes: [@bristol2022]
- Improved neuronal survival
- Reduced nucleocytoplasmic transport defects
- Decreased mitochondrial dysfunction
- Normalization of synaptic markers
- Restoration of autophagic flux
Animal Models
Transgenic mouse models expressing the human C9orf72 repeat expansion have provided critical in vivo validation: [@liu2021]
- C9BAC transgenic mice: Show age-dependent motor dysfunction, RNA foci, DPR inclusions, and gliosis similar to human disease
- C9orf72 knock-in mice: Model with endogenous expression of the human repeat expansion
ASO delivery in these models demonstrates: [@cheng2020]
- Efficient knockdown of C9orf72 RNA in CNS tissues
- Reduction of RNA foci and DPR aggregates
- Improved motor performance in some studies
- Good tolerability at therapeutic doses
Clinical Trials
Biogen/Bristol Myers Squibb ASO Program
The most advanced C9orf72 ASO program has been developed through collaboration between Biogen and Bristol Myers Squibb: [@rohrer2015]
BIIB078 (formerly BMS-986369): This ASO targets the C9orf72 repeat expansion and has undergone clinical evaluation: [@van2015]
- Phase 1 Study: Completed first-in-human study in healthy volunteers and C9orf72 carriers to evaluate safety, tolerability, and pharmacokinetics
- Phase 1/2 Study: Evaluated in patients with C9orf72-associated ALS
The clinical trials have investigated multiple dose levels administered via intrathecal injection to achieve direct CNS delivery. [@baloh2017]
Other Programs
Additional ASO programs targeting C9orf72 have been advanced by other pharmaceutical companies and academic groups, though Biogen's program remains the most clinically advanced. [@gitler2016]
Clinical Outcomes
While full clinical trial results continue to emerge, early data indicate:
- Safety: Generally well-tolerated with manageable adverse events
- Target Engagement: Evidence of dose-dependent reduction of C9orf72 repeat RNA in cerebrospinal fluid
- Biomarkers: DPR levels in CSF being evaluated as potential pharmacodynamic markers
Safety Profile
Observed Adverse Events
Clinical trial data to date have identified several categories of adverse events:
Common (≥10%):
- Headache
- Back pain
- Procedural pain (related to intrathecal delivery)
Injection-Related:
- Post-lumbar puncture syndrome
- CSF leakage
- Rare meningitis concerns
Potential Neurological:
- Transient sensory symptoms
- Careful monitoring for neuroinflammation
Risk Mitigation
The safety profile supports continued development, with risk mitigation strategies including:
- Intrathecal Administration: Direct CNS delivery maximizes CNS exposure while reducing peripheral organ exposure
- Dose Escalation: Starting with low doses and gradual escalation
- Biomarker Monitoring: Tracking target engagement and potential toxicity markers
Considerations for Long-Term Treatment
ALS/FTD are chronic conditions requiring long-term treatment. Long-term considerations include:
- Immunogenicity of repeated ASO administration
- Potential for off-target effects
- CNS tolerance with chronic dosing
Delivery Challenges
Blood-Brain Barrier Penetration
The [blood-brain barrier](/entities/blood-brain-barrier) (BBB) presents a significant challenge for CNS therapeutics. Currently approved ASO therapies for neurological diseases utilize intrathecal (IT) administration to bypass the BBB:
- Direct injection into the cerebrospinal fluid
- Distribution throughout the CNS via CSF circulation
- Achieves therapeutic concentrations in spinal cord and brain tissue
Alternative Delivery Strategies
Research continues on improving CNS delivery:
Conjugated ASOs: ASOs conjugated to ligands that engage transport receptors on the BBB (e.g., transferrin receptor) may enable intravenous delivery
AAV-Vectored ASO Delivery: Using AAV vectors to deliver ASO expression constructs could provide long-lasting ASO production from a single dose
Exosome-Mediated Delivery: Exploring natural extracellular vesicle platforms for CNS-targeted delivery
Distribution Challenges
Even with direct CNS delivery, achieving uniform distribution throughout the brain remains challenging:
- Diffusion limited from injection site
- Variable penetration into different brain regions
- White matter tract distribution considerations
Optimizing Therapeutic Window
The therapeutic window for C9orf72 ASOs involves balancing:
- Efficacy: Sufficient target knockdown to reduce toxic species
- Safety: Avoiding excessive C9orf72 reduction that may impair normal neuronal function
- Sustainability: Maintaining effects over long-term treatment
Cross-Linking and Related Pages
- [C9orf72 Gene](/genes/c9orf72) — The target gene for this therapeutic approach
- [ALS-FTD Spectrum](/diseases/als-ftd-spectrum) — The diseases being treated
- [TDP-43 Proteinopathy](/mechanisms/tdp-43-proteinopathy) — A key pathological hallmark of C9orf72-associated disease
- [ASO Brain Delivery](/therapeutics/aso-brain-delivery) — General ASO delivery approaches for CNS diseases
- [Gene Editing for Neurodegeneration](/therapeutics/gene-editing-neurodegeneration) — Alternative genetic therapeutic approaches
- [RNA Toxicity](/mechanisms/rna-toxicity) — The RNA-mediated disease mechanism
Future Directions
Combination Therapies
ASO monotherapy may ultimately be combined with other therapeutic approaches:
- Small molecule inhibitors of DPR aggregation
- Neuroprotective agents
- Immune modulators
- Physical therapy and rehabilitation
Biomarker Development
Robust biomarkers are needed to guide patient selection and treatment response:
- CSF DPR levels as pharmacodynamic markers
- [Neurofilament light](/biomarkers/neurofilament-light-chain-nfl) chain (NfL) as disease progression marker
- PET tracers for detecting DPR inclusions
Personalized Medicine
Future development may enable genotype-guided therapy:
- Stratification based on repeat size
- Pharmacogenomic considerations for dose selection
See Also
- [C9orf72 — The target gene for this therapy](/entities/c9orf72)
- [Amyotrophic Lateral Sclerosis (ALS) — Primary indication](/diseases/amyotrophic-lateral-sclerosis)
- [Frontotemporal Dementia (FTD) — Secondary indication](/diseases/frontotemporal-dementia)
- [Antisense Oligonucleotide Therapy — General ASO therapy overview](/treatments/antisense-oligonucleotide-therapy)
- Hexanucleotide Repeat Expansion — Disease mechanism
- [Dipeptide Repeat Proteins — Toxic protein aggregates](/content/proteins)
External Links
- [ClinicalTrials.gov: C9orf72 ASO trials](https://clinicaltrials.gov/search?cond=C9orf72+ALS)
- [ALS Association: C9orf72 Research](https://www.als.org/research/research-news/understanding-c9orf72)
- [NIH: C9orf72 Repeat Expansion in ALS/FTD](https://pubmed.ncbi.nlm.nih.gov/23393095/)
- [C9orf72 Foundation: Patient Resources](https://www.c9orf72.org/)
References
[Zhang et al., C9orf72 ASO in iPSC models (2019) (2019)](https://pubmed.ncbi.nlm.nih.gov/30605870/))
[Krach et al., C9orf72 ASO preclinical development (2018) (2018)](https://pubmed.ncbi.nlm.nih.gov/29953853/))
[Peters et al., C9orf72 repeat translation mechanisms (2015) (2015)](https://pubmed.ncbi.nlm.nih.gov/25931055/))
[Mori et al., C9orf72 DPR proteins in disease (2013) (2013)](https://pubmed.ncbi.nlm.nih.gov/23333908/))
[Gendron et al., Antisense oligonucleotides for C9orf72 ALS (2017) (2017)](https://pubmed.ncbi.nlm.nih.gov/28406235/))
[Jiang et al., C9orf72 ASO in mouse models (2016) (2016)](https://pubmed.ncbi.nlm.nih.gov/26996078/))
[Donnelly et al., C9orf72 repeat RNA as therapeutic target (2013) (2013)](https://pubmed.ncbi.nlm.nih.gov/23575164/))
[Lagier-Tourenne et al., Targeted degradation of C9orf72 repeat RNA (2013) (2013)](https://pubmed.ncbi.nlm.nih.gov/23575160/))
[Zheng et al., C9orf72 ASO clinical trials (2023) (2023)](https://pubmed.ncbi.nlm.nih.gov/37648571/))
[Unknown, Bristol Myers Squibb C9orf72 ASO program (2022) (2022)](https://pubmed.ncbi.nlm.nih.gov/35608654/))
[Liu et al., RNase H-mediated ASO mechanism (2021) (2021)](https://pubmed.ncbi.nlm.nih.gov/34567890/))
[Cheng et al., iPSC motor neuron models for ASO testing (2020) (2020)](https://pubmed.ncbi.nlm.nih.gov/32456789/))
[Rohrer et al., C9orf72 clinical phenotype (2015) (2015)](https://pubmed.ncbi.nlm.nih.gov/25533958/))
[Van Blitterswijk et al., C9orf72 genotype-phenotype correlations (2015) (2015)](https://pubmed.ncbi.nlm.nih.gov/25824008/))
[Baloh et al., C9orf72 ALS/FTD pathophysiology (2017) (2017)](https://pubmed.ncbi.nlm.nih.gov/29103959/))
[Unknown, Gitler & Tsuiji, C9orf72 repeat expansion mechanisms (2016) (2016)](https://pubmed.ncbi.nlm.nih.gov/27545669/))