Green Manufacturing Breakthrough: Enzymatic Technology Solves Scalability Challenge in RNA Therapeutics Production

The past decade has witnessed a renaissance in nucleic acid-based medicine, with RNA therapeutics emerging as a transformative class of drugs. From the rapid deployment of mRNA vaccines against SARS-CoV-2 to the clinical success of antisense oligonucleotides (ASOs) like Nusinersen for spinal muscular atrophy and Inotersen for hereditary transthyretin amyloidosis, and the approval of siRNA drugs such as Patisiran, RNA-based interventions are no longer futuristic concepts—they are saving lives today. Yet behind these medical breakthroughs lies a persistent and often overlooked bottleneck: the scalable, sustainable, and cost-effective production of chemically modified nucleoside triphosphates (NTPs), the fundamental molecular building blocks required for both chemical and enzymatic synthesis of therapeutic oligonucleotides.

Traditional chemical routes to NTPs—such as the Yoshikawa or Ludwig-Eckstein methods—rely heavily on trivalent phosphorus (P(III)) chemistry. These approaches demand stringent anhydrous and anaerobic conditions, extensive use of protecting groups to prevent side reactions on reactive sites of the nucleobase and ribose, and multi-step purifications that often involve silica chromatography or ion-exchange resins. Yields are frequently low (typically below 30%), and the processes generate significant waste. Critically, the introduction of pharmacologically beneficial modifications—especially bulky 2′-O-alkyl groups like 2′-O-methoxyethyl (2′-MOE) or electronegative 2′-fluoro substituents—further complicates synthesis by reducing solubility and reactivity, driving up costs to prohibitive levels for large-scale manufacturing.

To overcome these limitations, a collaborative team from the Manchester Institute of Biotechnology (MIB) at the University of Manchester, the Centre for Glycoscience at Keele University, and Prozomix Ltd has developed a revolutionary ATP-free, three-enzyme biocatalytic cascade that leverages simple, inexpensive inorganic phosphate donors to convert commercially available modified nucleosides directly into high-value NTPs. Published in Nature Communications, this work represents a paradigm shift toward greener, more efficient, and industrially viable manufacturing of RNA therapeutics.

At the heart of the innovation is the deliberate elimination of adenosine triphosphate (ATP)—a molecule that, despite its biological ubiquity, poses significant challenges in synthetic contexts. Conventional enzymatic NTP synthesis relies on a trio of kinases that sequentially transfer phosphate groups from ATP to nucleoside → NMP → NDP → NTP. While conceptually elegant, this approach suffers from multiple drawbacks: ATP is expensive; cofactor recycling systems add complexity; and most critically, the co-produced ADP and AMP are structurally nearly identical to many target NTP analogues (e.g., 2′-F-ATP). This similarity makes purification extremely difficult, and even trace ATP contamination can hijack downstream enzymatic oligonucleotide synthesis platforms—such as terminal deoxynucleotidyl transferases (TdT) or engineered polymerases—leading to heterogeneous, impure products that fail regulatory standards.

The research team circumvented these issues by designing a completely ATP-independent phosphorylation cascade composed of three orthogonal enzymatic steps:

1. Step 1: An engineered acid phosphatase (PhoC) uses inorganic pyrophosphate (PPi) as a phosphate donor to install a 5′-monophosphate onto modified nucleosides, yielding NMPs.
2. Step 2: A polyphosphate kinase (PPK) utilizes inexpensive sodium hexametaphosphate (a form of polyphosphate, PolyP) to drive the thermodynamically controlled conversion of NMPs into mixtures of NDPs and NTPs.
3. Step 3: An acetate kinase (AcK) employs lithium potassium acetyl phosphate to quantitatively phosphorylate any residual NDPs to NTPs, maximizing overall yield.

The linchpin of this platform is the first step, which demands high activity and selectivity toward sterically hindered substrates. The wild-type PhoC from Morganella morganii showed poor activity on 2′-MOE-modified nucleosides—a key motif in blockbuster drugs like Mipomersen—and suffered from product hydrolysis. To address this, the team performed directed evolution using 2′-MOE-adenosine as a model substrate. Through two rounds of saturation mutagenesis targeting 20 active-site and flexible-loop residues per round, they screened over 3,500 variants using a high-throughput UPLC assay.

The resulting variant, PhoC_4 (carrying A90E, N151A, and D154L mutations), exhibited a dramatic 8-fold increase in conversion (from 12% to 96%) under standard conditions. Kinetic analysis revealed a 9-fold improvement in catalytic efficiency (kcat/KM), driven by both a 3.5-fold lower KM and a 3-fold higher kcat. X-ray crystallography (2.0 Å resolution) confirmed that all three mutations reside in dynamic loop regions adjacent to the active site, likely modulating conformational flexibility to accommodate bulky 2′-substituents. Site-directed mutagenesis further validated the critical roles of Arg201 and His168 in phosphate binding.

Remarkably, PhoC_4 demonstrated exceptional substrate promiscuity. It efficiently phosphorylated a diverse panel of 32 nucleosides, including:

• All four canonical bases (A, U, C, G) bearing 2′-MOE, 2′-fluoro, or 2′-methoxy modifications;
• Challenging locked nucleic acids (LNAs);
• 3′-protected nucleosides (e.g., 3′-allyl, 3′-azido)—essential for non-templated enzymatic oligonucleotide synthesis platforms.
• Under process-relevant conditions (25–100 mM substrate, 20 µM enzyme, 2-fold PPi excess), PhoC_4 maintained high conversions and tolerated up to 10% DMSO, achieving turnover numbers exceeding 5,000—clearly demonstrating industrial feasibility.

When integrated into the full three-enzyme cascade, the system successfully produced nine distinct modified NTPs with overall conversions ranging from 40% to 82%. In preparative-scale demonstrations:

• 163 mg of 2′-MOE-adenosine was converted to 2′-MOE-ATP in 76% yield (crude); after DEAE Sepharose purification, >99% pure product was obtained in 65% isolated yield.
• 713 mg of 2′-fluoro-adenosine yielded 2′-F-ATP in 77% conversion.

Most significantly, the crude NTP mixtures were used directly in enzymatic oligonucleotide synthesis without any purification. Using an engineered DNA polymerase (Tgo2M) and endonuclease V (EndoV) cascade system recently developed by the same group, the enzymatically produced 2′-F-ATP was incorporated into an 8-mer poly-2′-F-A oligonucleotide with 70% conversion. Control experiments confirmed that adding just 1–10 mol% ATP to 2′-F-ATP resulted in complex, heterogeneous products due to competitive incorporation—highlighting the unique advantage of an ATP-free synthesis route.

This work transcends mere methodology development. It embodies the principles of green chemistry and sustainable pharmaceutical manufacturing: reactions occur in aqueous buffer at mild temperatures, use earth-abundant phosphate donors, avoid toxic solvents (e.g., trimethyl phosphate), and eliminate energy-intensive purification steps. By enabling telescoped, one-pot processes with minimal enzyme loading (<0.06 mol%), the platform drastically reduces cost, waste, and environmental footprint.

Looking forward, the researchers envision several avenues for optimization: engineering PPKs and AcKs for enhanced activity on specific substrates, aligning pH optima across all three enzymes to enable true one-pot operation, and developing crystallization-based isolation methods to replace chromatography. Moreover, the modular nature of the system allows easy adaptation to new modifications as RNA drug design evolves.

In conclusion, this biocatalytic platform not only solves a decades-old synthetic challenge but also establishes a new standard for the sustainable production of next-generation therapeutics. As the RNA drug pipeline continues to expand—with over 50 candidates in late-stage clinical trials—the ability to manufacture their building blocks efficiently, cleanly, and affordably will be critical. This technology, born from interdisciplinary collaboration between academia and industry, is poised to become an indispensable tool in the global effort to deliver life-changing RNA medicines to patients worldwide.