Could oligonucleotide manufacturing advances redefine therapy? 

Oligonucleotides have the potential to address some of the most devastating diseases that remain stubbornly resistant to treatment. These include neurodegenerative, vascular, respiratory, and oncological illnesses. As exciting as this branch of science is, the oligo industry is still in its commercial infancy. Large-scale oligonucleotide manufacturing is not straightforward, and various challenges need addressing.

To understand these, Alejandra and Carla, two Consultant biomedical engineers at Cambridge Design Partnership (CDP), were invited to take part in the Innovation in Oligonucleotide Manufacturing Symposium hosted by CPI at their new facilities in Glasgow. After an intensive day of discussion between key stakeholders from industry, academia, government, and the regulatory sector, we present the main takeaways. For this to make sense, let’s start from the beginning.

How do oligonucleotides work?

Oligonucleotides are short DNA or RNA molecules, typically around 20  nucleotides (basic building blocks of nucleic acids) in length. They can modulate gene expression, the process by which information included in a gene informs the assembly of a protein molecule. They do this by binding to pre-mRNA and mRNA, the carriers of genetic information before the mature mRNA is translated into proteins. Because mRNAs carry code for all cellular proteins, oligonucleotides could be effective for targets and diseases not treatable by current drugs1.

What is their importance as therapeutic agents? 

Oligonucleotide therapeutics prevent or modulate the expression of almost any gene as part of highly targeted treatment. They aim to target the genetic basis of the disease rather than the symptoms. Compared to conventional therapies, oligonucleotides have a higher specificity with reduced side effects. They can target specific molecules that are currently difficult to target, such as RNA. Several oligonucleotide therapeutics are already on the market, with Novartis Pharmaceutical’s Vitravene, for treating cytomegalovirus retinitis in immunocompromised patients, being the first to be approved by the FDA in 1998. 

The list of diseases that oligonucleotides can target is ever-growing, with the market valued at USD 5.19 billion in 2020 and expected to rise to USD 26.09 billion by 20302

How are oligonucleotides manufactured? 

Oligonucleotides are synthesized chemically, where nucleotides are added stepwise, resulting in a growing chain. Each nucleotide is subjected to a series of chemical reactions to create a stable component allowing the chain to grow. 

The two different types of oligonucleotide manufacturing are solid-phase and liquid-phase synthesis. Solid-phase oligonucleotide synthesis is carried out on a solid insoluble object, such as polystyrene beads, placed in columns that enable all reagents and solvents to pass through freely.  

In liquid-phase synthesis, the oligonucleotides are grown on soluble polymeric support within a homogeneous media; the polymer-bound product is commonly recovered from the reaction mixture by precipitation, thus allowing the rapid elimination of excess reagent and soluble by-products.  

Solid phase allows high throughput synthesis and purification, with liquid phase taking longer to synthesize the oligonucleotides. However, liquid-phase has the advantage of being performed on a larger scale and typically being less expensive than solid-phase synthesis. Once the desired oligonucleotide has been synthesized, the material can be passed to the next processing steps, including purification, concentration and, commonly, lyophilization. 

What are the main challenges in the process? 

Oligonucleotide manufacturing is a complex process with many limitations, especially in scalability. The major problems researchers face are currently due to high expenses regarding the raw materials for oligonucleotide synthesis, a lack of funding for oligonucleotide therapies, and a shortage of skilled resources in the oligonucleotide synthesis field. These problems create substantial bottlenecks in the research required for therapeutic oligonucleotides and, ultimately, the clinical use of these therapies. 

Key takeaways on the manufacturing of oligonucleotides  

  • Moving towards liquid-phase oligonucleotide synthesis. Solid-phase oligonucleotide synthesis is a great tool for rapidly making lots of oligos in the lab. However, it has drawbacks when manufacturing hundreds of kg or even multi-ton quantities per year, which might be the case for emergent nucleotide products targeting more common diseases3.

    The major problems include:
    • As the oligo grows, the space for the fresh nucleotides to diffuse and react gets tight, leading to incomplete couplings. This results in an altered sequence of monomers and incorrect genetic information in the final product, which must be removed by extensive and expensive processes.  
    • It is hard to scale up the solid beds (insoluble particles to which the oligonucleotide is bound during synthesis).
    • The synthesis and purification steps generate large amounts of organic and aqueous waste.

  • Liquid-phase synthesis stands as a promising approach to increase the yield of the overall process while allowing the production of large amounts of oligonucleotides in, potentially, a more sustainable manner4.

  • New alternatives to current purification methods are under investigation. Promising approaches to simplifying the purification steps show good results in the investigational phase5. Examples are membrane-sieving technology and biocatalytic processes used for phase separation. In the biocatalytic process, oligonucleotides are synthesized in a single operation, with fewer impurities and by-product production, and in aqueous media. All these are promising features that target the current limitations of existing synthesis methods3.

  • New approaches come with new challenges: The development of novel and alternative technologies offers opportunities to address some of the limitations of solid-phase synthesis while also creating new challenges. For instance, using nanofiltration membranes to support the synthesis of oligonucleotides in liquid phase can present issues such as membrane stability and fouling. Another concern regarding the enzymatic approach is the availability of raw material with the right purity.  
    If we consider the bigger picture, another novel approach in the pharmaceutical industry is the adoption of digital manufacturing technologies. However, this up-and-coming tool may come with its own challenges due to lack of pharmaceutical manufacturing expertise and the high cost of initial funds. 

  • Raw materials suppliers are already working towards reducing the gap. Strategies to reduce the prices of chemicals and deliver sustainable solutions are already underway. For instance, Honeywell US, a major supplier of the raw material required for oligonucleotide production, recycles solvents and assigns dedicated chemical drums to individual businesses to avoid cross-contamination.

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Big wins for early pioneers 

At CDP, we see every challenge as an opportunity, and we are pleased to know that governments and large industries have already recognized these problems.  Major efforts to accelerate research in the UK have been launched, not only as funding from governmental innovation agencies but also from pharmaceutical companies. In addition, the 18 oligonucleotide therapies already approved by the US Food and Drug Administration (FDA) for clinical use are leading the way6.  

There is a need for rapid adoption of next-generation processes that reduce risk, cut costs and save time while enabling on-demand therapies for every patient. However, regulatory-wise, standards in this industry are yet to be established. The risk around safety and efficacy remains a significant concern: How do we ensure we have the right sequence in each molecule? How do these molecules behave for a specific treatment? And what is the risk for the patient? These are just a few questions that still need to be addressed. 

The event at CPI highlighted the importance of bringing experts together to shape the path and accelerate innovation. Understanding the challenges in the oligonucleotide space and planning around them will allow us to drive successful manufacturing at scale. The moment to build the future is now!

  1. Kole R, Krainer AR, Altman S. Nat Rev Drug Discov. 2012 Jan 20;11(2):125-40. doi: 10.1038/nrd3625. 
  2. Allied Market Research, Oligonucleotide Synthesis Market report, Code A08356, July 2021  
  3. Sarah Lovelock, “Biocatalytic approaches to therapeutic oligonucleotide manufacture” in “Enzyme Engineering XXVI”, Andy Bommarius, Georgia Institute of Technology, USA; Vesna Mitchell, Codexis, USA; Doug Fuerst, GSK, USA Eds, ECI Symposium Series, (2022). Abstract:  
  4. J. Org. Chem. 2021, 86, 1, 49–61 Publication Date: November 30, 2020 
  5. Dousis A, Ravichandran K, Hobert EM, Moore MJ, Rabideau AE. Nat Biotechnol. 2023 Apr;41(4):560-568. doi: 10.1038/s41587-022-01525-6. 
  6. Martin Egli, Muthiah Manoharan, Nucleic Acids Research, Volume 51, Issue 6, 11 April 2023, Pages 2529–2573.  
Find the authors on LinkedIn:

Alejandra Sanchez

Consultant Biomedical Engineer

Carla Greig

Consultant Biomedical Scientist