Discovery of a Peptoid-Based Nanoparticle Platform for Therapeutic mRNA Delivery via Diverse Library Clustering and Structural Parametrization

Researchers first generated a large library of over 500 N-substituted glycine oligomers (peptoids) with diverse chemical structures and physical properties. They then used hierarchical clustering to group the peptoids into 12 distinct structural classes based on properties like molecular weight, lipophilicity, and charge.

A subset of peptoids from each cluster was then formulated into mRNA-encapsulating nanoparticles and evaluated for their ability to express a reporter gene (firefly luciferase) in vivo in mice. The researchers found significant differences in the total expression levels and tissue distribution of the reporter between the different peptoid structural classes. Some peptoids showed high selectivity for expression in the liver, while others primarily targeted the lung or spleen.

The researchers then focused on optimizing the lead peptoid motif from the liver-selective cluster. They systematically explored variations in the cationic headgroup and the lipophilic tail region of the peptoids using design of experiments methodology. This allowed them to identify key structural features that impacted nanoparticle properties such as size, charge, and membrane fusogenicity.

Ultimately, the researchers were able to identify an optimized peptoid, termed Nutshell 236, that demonstrated very high reporter gene expression selectively in the liver of mice. They further showed that Nutshell 236 could effectively deliver mRNA encoding a therapeutic anti-respiratory syncytial virus antibody, achieving serum antibody levels several fold higher than a benchmark ionizable lipid formulation.

The researchers demonstrated that the peptoid-based Nutshell platform provides a highly tunable system for optimizing mRNA delivery, with the ability to direct expression to desired tissues. The systematic optimization of the peptoid structure allowed them to identify a lead candidate with favorable properties in terms of expression, stability, and tolerability. This work highlights the potential of peptoid-based nanoparticles as a versatile platform for the development of a wide range of mRNA therapeutics.