BioTech IP Review

1. siRNA (small interfering RNA)

Core mechanism

• Double-stranded RNA (~21–23 nt)
• Loaded into RISC (RNA-induced silencing complex)
• Guide strand directs sequence-specific cleavage of target mRNA

Net effect:
mRNA degradation → protein knockdown

Key features

• Catalytic (one siRNA can destroy many mRNAs)
• Very potent
• Requires cytoplasmic delivery

Clinical sweet spot

• Liver-expressed targets (LNPs, GalNAc)
• Chronic diseases requiring sustained knockdown

Limitations

• Delivery beyond liver is hard
• Immune activation risk
• Off-target silencing

IP focus

• Chemical modifications (2′-O-Me, phosphorothioate)
• Delivery conjugates (GalNAc)
• Target sequence selection

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2. Antisense Oligonucleotides (ASOs)

Core mechanism

• Single-stranded DNA or RNA (~15–25 nt)
• Binds target RNA via Watson–Crick base pairing
• Acts through multiple mechanisms

Major ASO mechanisms

1. RNase H–mediated cleavage (classic knockdown)
2. Splice modulation (exon skipping/inclusion)
3. Translation blocking
4. miRNA inhibition

Net effect:
Modulation of RNA processing or stability

Key features

• More flexible than siRNA
• Can act in nucleus and cytoplasm
• Not dependent on RISC

Clinical sweet spot

• Neurological diseases (intrathecal delivery)
• Splicing disorders (e.g., SMA, DMD)

Limitations

• Typically lower potency than siRNA
• Requires repeat dosing
• Toxicity from backbone chemistry

IP focus

• Backbone chemistry
• Sequence and splice-site targeting
• Dosing regimens

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3. Circular RNA (circRNA)

Core mechanism

• Covalently closed RNA loop
• Lacks 5′ cap and 3′ poly(A) tail
• Extremely resistant to exonuclease degradation

Functional roles

• Protein expression (like mRNA, but longer-lasting)
• miRNA sponges
• RNA scaffolds
• Potential regulatory functions

Net effect:
Sustained protein expression or RNA-level modulation

Key features

• Much longer half-life than linear mRNA
• Lower innate immune activation (potentially)
• Still early-stage clinically

Clinical sweet spot (emerging)

• Long-duration protein expression
• Vaccines with extended antigen display
• Gene therapy alternatives without DNA

Limitations

• Manufacturing complexity
• Translation efficiency challenges
• Immature regulatory pathway

IP focus

• Circularization methods
• Translation initiation strategies (IRES, m6A)
• Manufacturing processes

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Summary

Feature	siRNA	ASO	circRNA
Structure	dsRNA	ssDNA/RNA	Circular RNA
Primary action	mRNA cleavage	RNA modulation	Protein expression / regulation
Location	Cytoplasm	Nucleus + cytoplasm	Cytoplasm
Duration	Days–weeks	Days–weeks	Weeks–months (potential)
Delivery	LNP, GalNAc	Direct, intrathecal	LNP (emerging)
Maturity	Clinically established	Clinically established	Early / emerging
Editing DNA?	No	No	No

• siRNA → Turn genes OFF (cleanly and potently)
• ASOs → Tune RNA behavior (splicing, translation, stability)
• circRNA → Turn protein production ON for longer

siRNA destroys messages, antisense oligonucleotides rewrite them, and circular RNA turns cells into longer-lasting protein factories—each solving a different therapeutic problem at the RNA layer.