Gene Silencing Therapy
Definition
Gene silencing therapy (GST) is a class of gene therapy that attenuates expression of a target gene at the RNA level without altering the underlying DNA sequence. It is primarily used to counteract gain-of-function or dominant-negative mutations. Key modalities include antisense oligonucleotides (ASOs), RNA interference (RNAi via siRNA/shRNA), and CRISPR interference (CRISPRi).
Key Concepts
- Antisense oligonucleotides (ASOs): Single-stranded DNA or RNA sequences that bind complementary mRNA, promoting RNase H-mediated degradation or blocking translation. Deliverable without viral vectors. (sources/gene-therapy-arrhythmia-2025)
- Small interfering RNA (siRNA): Double-stranded RNA incorporated into the RISC complex that cleaves complementary target mRNA. Used to silence mutant CASQ2-R33Q in CPVT: siRNA reduced mutant mRNA/protein by ~60% and prevented arrhythmias after 3 injections every 2 weeks (Bongianino 2017). (sources/gene-therapy-arrhythmia-2025)
- Short hairpin RNA (shRNA): Viral-vector-encoded siRNA precursor enabling stable, long-term gene silencing. Core component of SupRep therapy — shRNA silences both WT and mutant endogenous transcripts, paired with shRNA-immune replacement cDNA. (sources/gene-therapy-arrhythmia-2025)
- CRISPRi: Uses a catalytically inactive Cas9 (dCas9) with a guide RNA to block transcription without cleaving DNA. Emerging tool for cardiac gene silencing. (sources/gene-therapy-arrhythmia-2025)
- Allele-specific silencing: Targets only the pathogenic allele by exploiting SNPs near the mutation site. Applied to RYR2 in CPVT1 — suppressed arrhythmias and restored junctional SR ultrastructure (Bongianino 2017). Limitation: variant-specific constructs needed for each mutation, impractical in highly heterogeneous diseases. (sources/gene-therapy-arrhythmia-2025)
- Dominant-negative gene transfer (a form of GST): Delivery of a non-functional dominant-negative protein that outcompetes the endogenous channel. Examples in AF: dominant-negative KCNH2-G628S prolonged atrial APD and reduced AF inducibility in porcine models. (sources/gene-therapy-arrhythmia-2025)
- GST is combined with replacement cDNA in SupRep therapy to achieve mutation-agnostic treatment of heterozygous channelopathies. (sources/gene-therapy-arrhythmia-2025)
- Clinical-stage siRNA — inclisiran (PCSK9): N-acetylgalactosamine (GalNAc)-conjugated siRNA targeting PCSK9 mRNA in hepatocytes; 2'-O-methyl modifications improve stability and reduce immunogenicity; phase II trial showed sustained LDL-C reduction at 240 days after only 2 doses; liver targeting via GalNAc limits cardiac use. (sources/noncoding-rna-aha-2020 — high)
- Clinical-stage siRNA — patisiran (TTR): Lipid nanoparticle–delivered siRNA targeting transthyretin; phase III trial demonstrated improvement across multiple clinical endpoints in ATTR amyloidosis; first approved RNA therapeutic for a cardiovascular-adjacent condition. (sources/noncoding-rna-aha-2020 — high)
- Anti-miR clinical trials: Anti-miR-92a (phase I; NCT03603431, NCT03494712); CDR132L/anti-miR-132 for maladaptive cardiac remodeling (phase I; NCT04045405); LNA-anti-miR-155-5p approved in EU for cutaneous T-cell lymphoma. (sources/noncoding-rna-aha-2020 — high)
- Key hurdles for cardiac RNA therapeutics: (1) delivery to myocardium (hepatocyte targeting easy; cardiomyocyte targeting unresolved); (2) RNA chemistry optimisation for stability; (3) off-target suppression; (4) large RNA molecules (lncRNA) too large for current vectors. (sources/noncoding-rna-aha-2020 — high)
Contradictions / Open Questions
- Durability of siRNA vs. shRNA: siRNA-mediated silencing (e.g., allele-specific siRNA for CASQ2-R33Q in CPVT) required 3 injections every 2 weeks to maintain effect in mice — it is not a single-dose durable therapy. shRNA delivered via AAV provides stable long-term silencing but inherits all AAV re-dosing and immune limitations. No head-to-head durability comparison exists, and neither approach has human data. (sources/gene-therapy-arrhythmia-2025)
- Dominant-negative KCNH2 for AF — transient adenoviral expression: Adenoviral delivery of KCNH2-G628S prolonged atrial APD and reduced AF inducibility in porcine models, but the effect was lost by day 21 when transgene expression was lost. Without a durable vector, this approach cannot transition to clinical use for a chronic disease like AF. The discrepancy between biological proof-of-concept and translational practicality is unresolved. (sources/gene-therapy-arrhythmia-2025)
Connections
- Related to concepts/SupRep-Therapy
- Related to concepts/AAV-Gene-Delivery
- Related to concepts/CRISPR-Cas9-in-Channelopathies
- Related to concepts/Noncoding-RNA-in-CVD
- Related to entities/CPVT
- Related to entities/Long-QT-Syndrome
- Related to entities/Atrial-Fibrillation
- Related to entities/ATTR-Amyloidosis
- Related to entities/RYR2
- Related to entities/KCNH2