Enzymatic STEreospecific RNA phosphorothioate modification for next-generation therapeutics

RNA therapeutics have emerged as a powerful medical modality, from COVID-19 vaccines to treatments for rare genetic diseases and cancer. However, a fundamental bottleneck limits their potential: RNA instability. Most approved RNA drugs rely on phosphorothioate (PS) modifications for stability and delivery, but current chemical synthesis produces stereochemical mixtures reducing efficacy, increasing toxicity, and complicating regulatory approval. Moreover, chemical PS synthesis is restricted to short RNAs, completely excluding therapeutic mRNAs from site-specific backbone optimization despite evidence that strategic PS placement can dramatically enhance translation efficiency. This represents a fundamental technological gap constraining millions of patients with rare genetic diseases and cancer needing personalized immunotherapies from accessing safer and more effective RNA medicines. Our ERC-funded discovery revealed the first naturally occurring stereospecific RNA PS modifications and the enzyme family responsible for their installation. This breakthrough provides a biological route to manufacturing next-generation RNA therapeutics, simultaneously eliminating stereochemical heterogeneity, enabling cost-effective stereopure synthesis (≥10x cheaper), and uniquely installing site-specific PS modifications in full-length mRNAs. This PoC will advance our technology from TRL 3 to TRL 4 through three objectives targeting industrial readiness: 1) we will demonstrate scalable enzymatic PS installation to produce stereopure modified RNA, 2) we will engineer programmable substrate specificity to create variants targeting therapeutic ASOs and mRNAs and 3) we will demonstrate commercial feasibility through techno-economic analysis and engagement with RNA therapeutics companies. Our success will address the unmet patient needs while unlocking market opportunities in the $6.5B ASO therapeutics and $11.4B mRNA therapeutics markets currently constrained by manufacturing limitations