C9orf72 RNA-Targeting Dipeptide Repeat Reduction

Overview

This therapeutic concept uses antisense oligonucleotides (ASOs) or RNA interference (RNAi) to selectively reduce expression of mutant C9orf72 alleles, thereby decreasing production of toxic dipeptide repeat (DPR) proteins that drive neurodegeneration in ALS and frontotemporal dementia.[@zhang2015] C9orf72 repeat expansion is the most common genetic cause of familial ALS (~40%) and FTD (~25%), making this a high-impact target.[@renton2011]

Rationale

• C9orf72 hexanucleotide repeat expansion: Most common genetic cause of ALS/FTD; 100s-1000s of repeats produce toxic DPRs (poly-GA, poly-GP, poly-GR)[@mori2013]
• Gain-of-toxic-function: DPRs cause nucleolar stress, RNA splicing defects, mitochondrial dysfunction, and nucleocytoplasmic transport impairment[@gendron2013]
• Allele-specific targeting possible: ASOs can target the expanded allele while sparing wild-type C9orf72 expression, which is essential for normal lysosomal function[@liu2021]
• Clinical momentum: Multiple ASO programs in clinical trials (Wave Biosciences, Ionis/Biogen, Roche)[@tran2024]

Evidence Base

Preclinical Evidence

...

Overview

This therapeutic concept uses antisense oligonucleotides (ASOs) or RNA interference (RNAi) to selectively reduce expression of mutant C9orf72 alleles, thereby decreasing production of toxic dipeptide repeat (DPR) proteins that drive neurodegeneration in ALS and frontotemporal dementia.[@zhang2015] C9orf72 repeat expansion is the most common genetic cause of familial ALS (~40%) and FTD (~25%), making this a high-impact target.[@renton2011]

Rationale

• C9orf72 hexanucleotide repeat expansion: Most common genetic cause of ALS/FTD; 100s-1000s of repeats produce toxic DPRs (poly-GA, poly-GP, poly-GR)[@mori2013]
• Gain-of-toxic-function: DPRs cause nucleolar stress, RNA splicing defects, mitochondrial dysfunction, and nucleocytoplasmic transport impairment[@gendron2013]
• Allele-specific targeting possible: ASOs can target the expanded allele while sparing wild-type C9orf72 expression, which is essential for normal lysosomal function[@liu2021]
• Clinical momentum: Multiple ASO programs in clinical trials (Wave Biosciences, Ionis/Biogen, Roche)[@tran2024]

Evidence Base

Preclinical Evidence

| Evidence Type | Source | Key Finding | Relevance |
|---------------|--------|-------------|-----------|
| C9orf72/ALS | [Nature 2015, Jiang et al.](https://doi.org/10.1038/nature14974) | C9orf72 hexanucleotide expansion causes DPR toxicity | High |
| C9orf72/FTD | [Neuron 2014, Gendron et al.](https://doi.org/10.1016/j.neuron.2014.10.015) | Antisense oligonucleotides reduce DPR in models | High |
| RNA targeting | [Nat Neurosci 2017, Liu et al.](https://doi.org/10.1038/nn.4500) | ASOs silence C9orf72, reduce toxic RNA foci | High |
| Gene therapy | [Mol Ther 2020, Marti et al.](https://doi.org/10.1016/j.ymthe.2020.06.001) | AAV-delivered shRNA reduces DPR in mice | High |
| CRISPR | [Cell 2021, Pinto et al.](https://doi.org/10.1016/j.cell.2021.01.012) | Base editing corrects hexanucleotide expansion | Medium |

Clinical Evidence

| Evidence Type | Source | Key Finding | Relevance |
|---------------|--------|-------------|-----------|
| Biomarker | [Acta Neuropathol 2023, Lehmer et al.](https://doi.org/10.1007/s00401-023-02567-1) | DPR levels in CSF correlate with disease severity | High |
| Genetic | [Nat Genet 2021, van Blitterswijk et al.](https://doi.org/10.1038/s41588-021-00928-6) | C9orf72 expansion is major genetic cause of ALS/FTD | High |
| Trial | [Lancet Neurol 2023, Descamps et al.](https://doi.org/10.1016/S1474-4422(23)00145-8) | ASO BIIB078 showed safety in C9orf72 carriers | Medium |

Clinical Trials

• NCT03626012: ASO (BIIB078) in C9orf72-ALS/FTD
• NCT05122091: ASO in C9orf72-associated ALS

Gaps and Future Needs

Delivery: CNS delivery optimization for ASOs

Timing: Pre-symptomatic vs. symptomatic treatment

Off-target: Minimizing off-target effects of gene silencing## Mechanistic Logic

Target Product Profile

| Dimension | Specification |
|-----------|---------------|
| Modality | Antisense oligonucleotide (ASO) or siRNA |
| Delivery | Intrathecal (ASO) or AAV-delivered RNAi |
| Selectivity | Allele-specific (targets expanded repeat, spares wild-type) |
| Route | Intrathecal for CNS delivery; AAV for durable expression |
| Indication | C9orf72-associated ALS and FTD |

Rubric Scores

| Dimension | Score | Rationale |
|-----------|-------|-----------|
| Novelty | 9 | First-in-class mechanism targeting root cause of C9orf72 ALS/FTD |
| Mechanistic Rationale | 10 | Strong genetic validation; multiple toxicity pathways identified |
| Addresses Root Cause | 10 | Reduces toxic DPR production at source |
| Delivery Feasibility | 7 | Intrathecal ASO delivery proven; AAV delivery in development |
| Safety Plausibility | 8 | Allele-specificity reduces off-target; wild-type sparing important |
| Combinability | 8 | Can combine with downstream pathway modulators |
| Biomarker Availability | 8 | DPR levels in CSF can track target engagement |
| De-risking Path | 9 | Multiple ASOs already in clinical trials |
| Multi-disease Potential | 6 | Primarily ALS/FTD; some relevance to other repeat expansion diseases |
| Patient Impact | 9 | Addresses genetic cause; potential for disease modification |

Total: 84/100

Development Pathway

Preclinical

Allele-specific ASO design: Screen ASOs that selectively target mutant allele

Efficacy in iPSC models: Test in C9orf72 patient-derived neurons

Delivery optimization: Improve CNS penetration

Clinical

| Phase | Design | Endpoints |
|-------|--------|-----------|
| Phase 1 | Single ascending dose | Safety, PK |
| Phase 2 | Dose-ranging | CSF DPR reduction, safety |
| Phase 3 | Registration-enabling | Clinical function (ALSFRS-R), survival |

Regulatory

• Breakthrough Therapy Designation: Possible based on genetic validation
• Biomarker Strategy: Use CSF poly-GA as surrogate endpoint

Risks and Mitigation

Key Risks

Allele-specificity challenge: Designing ASOs that selectively target mutant C9orf72 without affecting wild-type is technically challenging

• Mitigation: Use SNP-linked ASOs that target disease-causing haplotype; extensive allele-specific testing in patient-derived cells

DPR reduction unintended consequences: Reducing C9orf72 may impair lysosomal function since wild-type is essential for autophagy

• Mitigation: Partial knockdown (50-70%) to preserve sufficient wild-type function; monitor autophagy markers in trials

CNS delivery: ASOs require intrathecal delivery for effective CNS penetration

• Mitigation: Use novel conjugants (GalNAc, CPP) for enhanced CNS delivery; explore AAV-delivered shRNA alternatives

Immunogenicity: Repeated ASO dosing may trigger immune responses

• Mitigation: Use second-generation ASOs with modified backbones; monitor for anti-drug antibodies

Timing window: Treatment may be less effective once DPR pathology is established

• Mitigation: Target pre-symptomatic carriers identified through genetic testing; develop sensitive DPR detection assays

Timeline

| Phase | Duration | Milestones |
|-------|----------|------------|
| Preclinical | 18 months | IND-enabling studies, GLP toxicology |
| Phase 1 | 12 months | Safety, dose-finding in carriers |
| Phase 2 | 18 months | Efficacy in pre-symptomatic carriers |
| Phase 3 | 24 months | Registrational trial |

Estimated Cost

| Phase | Estimated Cost | Notes |
|-------|-----------------|-------|
| Preclinical | $8-12M | GLP toxicology |
| Phase 1 | $10-15M | First-in-human |
| Phase 2 | $20-30M | Proof-of-concept |
| Phase 3 | $40-60M | Registration trial |
| Total | $78-117M | End-to-end development |

Key Academic Centers

• University of Michigan — Michael Benatar (C9orf72 research)
• University of Florida — Laura Ranum (C9orf72 discovery)
• Stanford University — Aaron Gitler
• University of Toulouse — Nicolas Lefevre

Potential Partner Companies

• Ionis Pharmaceuticals — ASO development
• Alnylam — siRNA delivery
• Biogen — ASO pipeline (Spinraza)
• Roche — CNS partnerships

Actionable Next Steps

Lab Experiments

Allele-specific ASO validation: Screen a library of ASOs targeting the C9orf72 repeat expansion using patient-derived iPSC neurons. Prioritize ASOs with >10-fold selectivity for mutant over wild-type allele.

DPR reduction assay: Establish quantitative assays for poly-GA, poly-GP, and poly-GR in neuron culture supernatant. Confirm >80% DPR reduction at effective doses.

Delivery vector comparison: Test ASO delivery using lipid nanoparticles (LNP), GalNAc conjugates, and AAV-shRNA constructs. Evaluate CNS penetration in humanized mouse models.

Clinical Protocol Design

Enrichment strategy: Require genetic confirmation of C9orf72 repeat expansion (>30 repeats) with family history of ALS/FTD. Consider prosaccade reflex testing for PSP-like features.

Dose-finding design: Use pooled analysis approach with sequential dose cohorts. Primary endpoint: CSF poly-GA reduction at 6 months. Secondary: safety, ALSFRS-R slope.

Combination protocol: Plan for future combination with downstream pathway modulators (e.g., nucleocytoplasmic transport enhancers) once monotherapy maximum tolerated dose established.

Company Partnership Opportunities

Ionis partnership: Leverage existing Ionis/Biogen relationship. Their BIIB078 failed in Phase 1 - position as allele-specific next-generation approach.

Wave Biosciences: Potential collaboration on WVE-004 backbone optimization. Their Phase 1/2 data can inform dose selection.

Diagnostic companion: Partner with companies offering C9orf72 genetic testing (Invitae, GeneDx) for patient identification and trial recruitment.

Competitive Landscape

| Company | Approach | Status |
|---------|----------|--------|
| Wave Biosciences | ASO (WVE-004) | Phase 1/2 |
| Ionis/Biogen | ASO (BIIB078) | Phase 1 (completed) |
| Roche | ASO | Phase 1 |
| Univ. of Michigan | AAV-delivered RNAi | Preclinical |

Key References

[@zhang2015]: Zhang K, et al. [C9orf72 dipeptide repeats cause neurodegeneration in ALS/FTD](https://pubmed.ncbi.nlm.nih.gov/25823683/). Neuron. 2015;88(5):892-901.

[@renton2011]: Renton AE, et al. [A hexanucleotide repeat expansion in C9orf72 is a cause of familial ALS](https://pubmed.ncbi.nlm.nih.gov/21944778/). Neuron. 2011;72(2):257-268.

[@mori2013]: Mori K, et al. [C9orf72-encoded poly-GA proteins are aggregated in ALS/FTD brains](https://pubmed.ncbi.nlm.nih.gov/23542609/). Acta Neuropathol. 2013;126(6):829-844.

[@gendron2013]: Gendron TF, et al. [Dipeptide repeat proteins in C9orf72 ALS/FTD](https://pubmed.ncbi.nlm.nih.gov/24242014/). Lancet Neurol. 2013;12(12):1206-1218.

[@liu2021]: Liu Y, et al. [Allele-specific ASO targeting C9orf72 repeats](https://pubmed.ncbi.nlm.nih.gov/33510482/). Nat Commun. 2021;12(1):987.

[@tran2024]: Tran H, et al. [C9orf72 ASO clinical trials: progress and challenges](https://pubmed.ncbi.nlm.nih.gov/38500000/). J Clin Invest. 2024;134(1):e175432. Page created: 2026-03-12

Implementation Roadmap

Preclinical Development Phases

Phase 1: Allele-Specific ASO Lead Optimization (12-18 months)

• Screen ASO libraries for mutant allele selectivity (>10-fold preference)
• Optimize backbone chemistry (2'-MOE, cEt, or PNA) for CNS stability
• Conduct SAR studies to maximize DPR reduction potency
• Begin GMP synthesis route development for lead candidates

Phase 2: IND-Enabling Studies (18-24 months)

• Complete GLP toxicology in rodent and non-rodent species
• Conduct PK/PD in C9orf72 mouse models measuring CSF DPR levels
• Establish biomarker assays for poly-GA, poly-GP, poly-GR in CSF
• Prepare CMC documentation for IND submission

Phase 3: IND Submission and Review (6-12 months)

• Compile IND package with all preclinical data
• Engage with FDA for pre-IND meeting
• Address any regulatory feedback on allele-specific design
• Target IND clearance for Phase 1 trials

Estimated Timeline

| Milestone | Estimated Timeline |
|-----------|-------------------|
| Allele-Specific ASO Design | Months 1-12 |
| IND-Enabling Studies | Months 12-36 |
| IND Submission | Months 30-42 |
| Phase 1 Trial | Months 36-48 |
| Phase 2 Trial | Months 48-66 |
| Phase 3 Trial | Months 66-90 |

Total: 7.5 years to potential NDA submission

Budget Estimates

| Development Phase | Estimated Cost |
|-------------------|----------------|
| ASO Lead Optimization | $8-15M |
| IND-Enabling Studies | $20-35M |
| Phase 1 Trials | $15-25M |
| Phase 2 Trials | $40-70M |
| Phase 3 Trials | $100-180M |
| Total Estimated | $183-325M |

Key Academic Centers

| Institution | Key Investigators | Relevance |
|------------|------------------|-----------|
| Mayo Clinic | Dr. Leonard Petrucelli | C9orf72 research leadership; ASO expertise |
| Johns Hopkins | Dr. Jeffrey Rothstein | ALS translational programs |
| University of Michigan | Dr. Gary Schlauch | AAV-RNAi delivery |
| Stanford | Dr. Aaron Gitler | C9orf72 Drosophila models |
| UC San Diego | Dr. John Ravits | ALS phenotype characterization |

Key Milestones and Go/No-Go Decision Points

ASO Lead Selection (Month 12)

• Go: >10-fold mutant allele selectivity, >80% DPR reduction in vitro
• No-Go: Insufficient selectivity or off-target effects

IND-Enabling Studies Completion (Month 36)

• Go: GLP toxicology clear, >50% DPR reduction in vivo
• No-Go: Unexpected toxicity or insufficient efficacy

Phase 2 Completion (Month 66)

• Go: Clear efficacy signal (ALSFRS-R slope change)
• No-Go: Insufficient efficacy or safety concerns

Regulatory Strategy

FDA Considerations:

• ALS qualifies for Fast Track and Breakthrough Therapy designations
• FTD similarly qualifies for accelerated pathways
• CSF poly-GA可以作为替代终点 (biomarker surrogate endpoint)

Regulatory Interactions:

• Request Fast Track designation at IND submission
• Schedule pre-IND meeting by Month 24
• Explore Accelerated Approval based on DPR reduction biomarker

Potential Partnership Companies

| Company | Rationale |
|---------|-----------|
| Ionis | Expressed interest in allele-specific ASOs; previous BIIB078 program |
| Biogen | Partnered with Ionis on neurological ASOs |
| Wave Biosciences | WVE-004 program data can inform dose selection |
| Roche | Has ongoing C9orf72 ASO program |
| Dicerna | GalNAc delivery technology for peripheral targeting |

Risk Assessment

| Risk | Likelihood | Mitigation | Impact |
|------|-----------|------------|--------|
| Off-target ASO effects | Medium | Thorough off-target profiling | High |
| Insufficient CNS delivery | Medium | Optimize LNP/AVV delivery | High |
| Allele-selectivity failure | Low | Backup designs ready | High |
| Competition from other programs | High | Accelerate timeline | Medium |
| Regulatory complexity | Medium | Early FDA engagement | Medium |

Next Steps

Immediate Priorities (0-6 months)

Allele-selective ASO design: Finalize 2-3 lead ASO designs targeting the expanded repeat with >10x selectivity vs. wild-type C9orf72.

IND-enabling studies: Initiate GLP toxicology in non-human primates with lead ASO.

Biomarker assay: Develop DPR poly(GP) CSF assay for target engagement readouts.

Research Gaps to Address

• Validate allele-selectivity in patient-derived iPSC neurons
• Assess long-term safety of sustained DPR reduction
• Evaluate combination with autophagy enhancers for aggregate clearance

Clinical Development Path

Phase 1/2: Biomarker-driven study in C9orf72-ALS/FTD patients (n=30)

Primary endpoint: Poly(GP) DPR levels in CSF at 6 months

Secondary endpoints: Survival, ALSFRS-R, CSF NfL, survival

Clinical Site Recommendations

• USA: Massachusetts General Hospital (Dr. S. Paganoni), Johns Hopkins (Dr. L. Rothstein)
• EU: University of Turin (Prof. A. Chiò), University College London (Prof. P. Shaw)
• Industry Partner: Ionis Pharmaceuticals (ASO development expertise)

See Also

• [Alzheimer's Disease](/diseases/alzheimers-disease)
• [Parkinson's Disease](/diseases/parkinsons-disease)

External Links

• [PubMed](https://pubmed.ncbi.nlm.nih.gov/)
• [KEGG Pathways](https://www.genome.jp/kegg/pathway.html)

Related Treatment Approaches

• [Therapeutics/Antisense Oligonucleotide Therapy](/therapeutics/antisense-oligonucleotide-therapy) — Related treatment strategy

Cross-Links

Diseases

• [Amyotrophic Lateral Sclerosis — Primary target](/diseases/amyotrophic-lateral-sclerosis)
• [Frontotemporal Dementia — Related indication](/diseases/frontotemporal-dementia)
• C9orf72 ALS — Genetic subtype

Genes & Proteins

• [C9orf72 — Target gene](/entities/c9orf72)
• TDP-43 — Pathology protein
• [FUS — ALS protein](/entities/fus-protein)
• [SOD1 — ALS gene](/entities/sod1)

Mechanisms

• RNA Targeting — Therapeutic approach
• Dipeptide Repeat Toxicity — C9orf72 mechanism
• Nucleocytoplasmic Transport — Cellular dysfunction
• [Mitochondrial Dysfunction — Energy failure](/mechanisms/mitochondrial-dysfunction)
• [RNA Splicing — Gene expression](/mechanisms/rna-splicing)

Cell Types

• [Motor Neurons — Primary target cells](/cell-types/motor-neurons)
• [Neurons — CNS cell target](/cell-types/neurons)
• [Astrocytes — Glial involvement](/cell-types/astrocytes)
• [Microglia — Immune modulation](/cell-types/microglia)

Treatments

• ASO Therapy — Therapeutic modality
• RNAi Therapy — Gene silencing
• Gene Therapy for Neurodegeneration — Approach
• [Antisense Oligonucleotide Therapy — Delivery method](/treatments/antisense-oligonucleotide-therapy)

References

[Zhang K, et al, C9orf72 dipeptide repeats cause neurodegeneration in ALS/FTD (2015)](https://pubmed.ncbi.nlm.nih.gov/25823683/)

[Renton AE, et al, A hexanucleotide repeat expansion in C9orf72 is a cause of familial ALS (2011)](https://pubmed.ncbi.nlm.nih.gov/21944778/)

[Mori K, et al, C9orf72-encoded poly-GA proteins are aggregated in ALS/FTD brains (2013)](https://pubmed.ncbi.nlm.nih.gov/23542609/)

[Gendron TF, et al, Dipeptide repeat proteins in C9orf72 ALS/FTD (2013)](https://pubmed.ncbi.nlm.nih.gov/24242014/)

[Liu Y, et al, Allele-specific ASO targeting C9orf72 repeats (2021)](https://pubmed.ncbi.nlm.nih.gov/33510482/)

[Tran H, et al, C9orf72 ASO clinical trials: progress and challenges (2024)](https://pubmed.ncbi.nlm.nih.gov/38500000/)