73 Oligonucleotide (ASO / siRNA) CRO and CDMO vendors

What does it take to develop and manufacture a Oligonucleotide (ASO / siRNA) drug?

Oligonucleotides look deceptively simple on paper, a short string of nucleotides, but the chemistry that makes them work as drugs is where the difficulty lives. An antisense oligo (ASO) and a small interfering RNA (siRNA) are made the same way at the bench, by solid-phase phosphoramidite synthesis, yet almost everything else differs: ASOs are single strands that recruit RNase H or block splicing, siRNAs are duplexes that load into RISC. Both depend on backbone and sugar modifications (phosphorothioate linkages, 2'-MOE, 2'-O-methyl, 2'-fluoro, LNA, and the morpholino variant) to survive nucleases and stay in the body long enough to act. Get the modification pattern wrong and you have a sequence that is potent in a dish and useless in an animal.

On the discovery and preclinical side, the work that gets outsourced is sequence design and screening, chemical modification scans, in vitro potency and knockdown assays, off-target and hybridization-dependent toxicity screening, and the delivery decision. Delivery is the whole game for this modality. GalNAc conjugation gets siRNA and some ASOs into hepatocytes cleanly, which is why so many approved oligos are liver-targeted; everything outside the liver (CNS via intrathecal dosing, muscle, tumor) is harder and often leans on lipid nanoparticles or newer conjugates. A CRO that understands which delivery approach fits your target tissue saves you a year of dead ends.

On the CMC and manufacturing side, this is where specialist oligo CDMOs separate themselves from generalists. Solid-phase oligo synthesis at scale is its own discipline: it needs the right synthesizer column chemistry, controlled-pore-glass or polystyrene supports, amidite supply and quality, and a real handle on process-related impurities (n-1 and n+1 shortmers, depurination products, P=O versus P=S diastereomers). The analytical burden is heavier than most small molecules: identity and purity by ion-pair reversed-phase LC-MS, anion-exchange HPLC, capillary gel electrophoresis, and impurity characterization down the chain. A generalist API shop can run an HPLC, but it usually does not have validated oligo-specific methods, the purification trains (large-scale ion-exchange and reversed-phase), or the regulatory history of filing oligo CMC sections. For GalNAc or LNP work you also need conjugation and formulation capability under GMP, which narrows the field further.

How do you choose a CRO or CDMO for Oligonucleotide (ASO / siRNA)?

The fastest way to waste budget on this modality is to hire a competent generalist who has never actually shipped an oligo. Use a checklist built around the things that are specific to ASO and siRNA work, and ask for evidence on each, not assurances.

• Relevant platform and track record: confirmed solid-phase synthesis experience with your chemistry (phosphorothioate, 2'-MOE/2'-OMe/2'-F, LNA, or morpholino), and named programs they have actually delivered, ideally with at least one that reached the clinic. Ask which modality they do most, ASO single strands or siRNA duplexes, because annealing and duplex QC are a separate skill.
• Delivery and conjugation fit: real GalNAc conjugation capability if you are targeting liver, or LNP / lipid-conjugate formulation if you are going elsewhere. Match this to your target tissue before anything else.
• GxP and analytical capability for this modality: validated oligo-specific methods (ion-pair LC-MS, anion-exchange HPLC, CGE), impurity profiling for shortmers and process-related species, and GMP status appropriate to your stage (non-GLP for discovery screens, GLP for the tox package, GMP for clinical supply).
• Capacity and scale: can they take you from milligram research batches through GLP tox material to GMP clinical (and eventually commercial) supply without a disruptive tech transfer? Oligo demand can jump fast once a program reads out; confirm purification train size and suite availability.
• Regulatory experience: have they written oligonucleotide CMC sections that survived FDA or EMA review? Oligo impurity specs and the genotoxicity questions around them are an area where regulator-tested experience genuinely de-risks your filing.
• IP, supply chain, and quality: clear ownership of sequences and process know-how, transparent amidite and starting-material sourcing (single-source amidite risk is real), and a quality system with audit history you can review. Confirm stability-program capability, since oligo stability data drives shelf life.