Discovery & preclinical liver targeting

GalNAc Conjugation for siRNA & ASO

Custom GalNAc–oligonucleotide conjugation for liver-targeted siRNA and ASO programs. Discovery through preclinical manufacturing support.

ASGPR receptor targeting Triantennary GalNAc siRNA & ASO compatible 3′ Int, 5′ position control Mono‑GalNAc & Tri‑GalNAc & Client-supplied ligands

Overview

GalNAc is a carbohydrate ligand recognized by ASGPR, a receptor highly expressed on hepatocytes. By attaching GalNAc (often as a multivalent cluster) to an oligonucleotide, developers can bias systemic exposure toward the liver, enabling efficient hepatocyte uptake without lipid nanoparticles in many use cases. [1,2]

GalNAc conjugation enables hepatocyte-selective delivery via ASGPR. We support mono‑ and tri‑GalNAc formats, 3′/5′/internal placement, custom linkers, and client‑supplied ligands for siRNA duplexes and ASO single‑strands.

In discovery and preclinical phases, GalNAc conjugation is often explored as a screenable targeting handle to compare constructs (mono vs tri-GalNAc), attachment sites, and linker stability across in vitro hepatocyte assays and in vivo liver exposure studies. The goal is to identify a manufacturable lead architecture that preserves activity while remaining analytically verifiable and scalable.

Bio-Synthesis supports 3′, 5′, and internal GalNAc placement, with options to incorporate single GalNAc or triantennary (Tri‑GalNAc) formats. We can also evaluate client-supplied GalNAc ligands or alternative GalNAc variants as required by program design and IP strategy. [2,3]

Quick facts

GalNAc clusters bind ASGPR on hepatocytes, enabling receptor-mediated uptake and intracellular trafficking.

ASGPR

Hepatocyte receptor

Tri-GalNAc

High avidity format

3′ / 5′ / Internal
Position-specific attachment
Linkers
Stable or cleavable
Key Program Highlights

Core considerations guiding discovery-to-preclinical GalNAc conjugate development.

Why GalNAcLiver
Translatable targeting pathway

Leverages a native receptor pathway (ASGPR) for hepatocyte-directed uptake.

DesignControl
Architecture options

Monovalent vs multivalent GalNAc; defined attachment sites; linker selection.

CMCScale
Preclinical-to-IND feasibility

Conjugation integrity and purification strategy are central to CMC success.

How GalNAc Targets the Liver (ASGPR)

ASGPR is a lectin receptor enriched on hepatocytes. GalNAc ligands bind ASGPR and trigger receptor-mediated endocytosis. Once internalized, the oligonucleotide must access the cytosol (siRNA) or nucleus/cytosol (ASO) depending on modality and mechanism.

1Binding
Receptor engagement

Multivalency increases avidity and improves hepatocyte uptake efficiency.

2Uptake
Endocytosis

ASGPR binding leads to internalization and trafficking through endosomal compartments.

3Activity
Productive delivery

Chemistry and linker choices influence endosomal escape and release of the active oligo.

Design levers to mention
Multivalency (mono vs tri), attachment site (3′ vs 5′), linker stability (cleavable vs stable), and oligo chemistry (backbone/sugar/base) all affect potency and exposure.
Preclinical readouts to align early
Typical endpoints include hepatocyte uptake (in vitro), liver exposure (in vivo), target mRNA knockdown, dose–response, duration of effect, and conjugate stability in formulation and biological matrices. Consider tracking conjugation integrity and positional variants alongside bioactivity.

Supported GalNAc Conjugate Architectures

GalNAc can be presented as a single ligand or as clustered ligands (commonly triantennary) to enhance ASGPR avidity. Architecture selection is program-specific and depends on modality, chemistry, and desired exposure profile. [1–3] We support single and trivalent formats, internal or terminal attachment, and evaluation of alternative or client-supplied GalNAc ligands when required. We support GalNAc conjugation for siRNA duplexes and ASO oligonucleotides, with terminal or internal placement options.

MonovalentGalNAc
Single-ligand GalNAc

Useful for exploratory designs or specific linker strategies; avidity typically lower than clustered formats.

Best for: early screening
TriantennaryHigh avidity
Trivalent GalNAc cluster

A widely used format to boost receptor engagement and hepatocyte uptake through multivalent binding.

Best for: lead-like formats
SpacerTEG/PEG
Spacer-enabled systems

TEG/PEG-like spacers can tune steric presentation, hydrophilicity, and conjugate handling.

Best for: developability tuning
siRNADuplex
GalNAc–siRNA

Often attached to one strand (position-specific), integrated with duplex architecture and modification patterns.

Best for: hepatocyte gene silencing
ASOSingle-strand
GalNAc–ASO

Applicable to liver-targeted antisense programs; chemistry and conjugation site are critical for activity.

Best for: RNase H or splice modulation
CustomLigands
Custom formats

Program-specific architectures including alternative spacer lengths and attachment motifs evaluated by design intent.

Best for: differentiated delivery hypotheses

Linker Chemistry & Attachment Placement

Linker choice and attachment site influence conjugation stability, purification behavior, and biological performance. Programs commonly evaluate stable linkers versus cleavable designs, depending on the desired intracellular release profile. [2,3]

StableCMC
Stable linkers

Designed to maintain conjugate integrity during handling and circulation; simplifies interpretation of distribution.

Consider: sterics & purification
CleavableRelease
Cleavable linkers

Built to release the active oligo under defined conditions (enzymatic or chemical triggers), depending on design.

Consider: stability window
Placement (3′ vs 5′ vs internal)

Position-specific attachment (e.g., 3′ or 5′ terminus) can be selected to preserve functional regions and align with duplex loading, nuclease protection patterns, and analytical strategy, or internal placement, depending on modality, functional regions, and analytical strategy.

Practical evaluation matrix (discovery → preclinical)
  • Conjugation completeness and batch homogeneity
  • Linker stability during storage and in serum/plasma
  • Uptake vs activity relationship (hepatocyte assays)
  • PK/PD in rodent liver (exposure and knockdown)
  • Purification resolution of partial conjugates and positional species
CDMO positioning

We help translate discovery designs into manufacturable conjugates by stress-testing linker/placement choices against purification behavior and analytical verification—reducing rework when moving toward GLP tox and IND-enabling studies.

Preclinical Manufacturing & CMC-Aligned Analytics

For discovery-to-preclinical programs, GalNAc conjugates introduce additional critical quality attributes: conjugation completeness, linker integrity, ligand stoichiometry (especially for clustered formats), and conjugate-specific impurities. A development-aligned workflow should define these attributes early and carry them across scale.

Purification Resolution
Purification strategy

Select methods that resolve unconjugated oligo, partially conjugated species, and positional isomers where relevant.

AnalyticsIdentity
Analytical confirmation

Confirm conjugation and composition via orthogonal assays (e.g., LC‑MS and chromatography profiles).

StabilityLinker
Stability profiling

Evaluate linker/conjugate stability under relevant storage and handling conditions to support shelf-life and shipping.

Talk to a Scientist

Tell us your modality (siRNA or ASO), preclinical model (in vitro, mouse/rat/NHP), and preferred architecture (mono vs tri‑GalNAc), plus any linker/attachment preferences. We can help translate design intent into a manufacturing-ready conjugate strategy.

Custom format support Position-specific attachment CMC-aligned analytics
What to include in your request
  • Oligo type (siRNA / ASO)
  • Desired GalNAc format (mono / tri / spacer)
  • Attachment site (3′/5′) and linker preference
  • Modification pattern (if defined)
  • Target quantity and timeline

FAQ

What does “triantennary GalNAc” mean?

It refers to a clustered (trivalent) GalNAc presentation designed to increase avidity for ASGPR compared with a single ligand.

Is GalNAc only for siRNA?

No. It is widely used for liver-targeted siRNA, and it can also be used with ASOs depending on chemistry and program needs.

Where is GalNAc attached on the oligo?

Commonly at a terminus (3′ or 5′) using defined linkers; however, internal placement can also be supported depending on modality and functional regions. We can incorporate single or tri‑GalNAc formats and evaluate client-supplied GalNAc ligands when required.

What are the key QC items for GalNAc conjugates?

Conjugation completeness, linker integrity, ligand stoichiometry, and resolution of unconjugated or partially conjugated impurities.

Recommended Reading

Selected foundational and translational publications relevant to RNA interference, antisense oligonucleotides (ASOs), backbone engineering, and targeted delivery.

  1. Nair JK, et al. Multivalent N‑acetylgalactosamine‑conjugated siRNA localizes in hepatocytes and produces robust RNAi‑mediated gene silencing. J Am Chem Soc. 2014;136:16958–16961.
  2. Springer AD, Dowdy SF. GalNAc‑siRNA conjugates: leading the way for delivery of RNAi therapeutics. Nucleic Acid Ther. 2018;28:109–118.
  3. Dowdy SF. Overcoming cellular barriers for RNA therapeutics. Nat Biotechnol. 2017;35:222–229.
  4. Raal FJ, et al. (Review) Emerging delivery and chemistry strategies for oligonucleotide therapeutics in early development. J Med Chem. (Review article; use a preferred citation from your internal library).

Inline citations on this page refer to the numbered items above.

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