Peptide Substitutes of PEG: Biological Outcomes on Prospective Lipid Nanoparticle Shielding Materials.

Polyethylene glycol (PEG) is a proven component in lipid nanoparticles (LNPs). PEGylated nanoparticles are known to improve LNP circulation half-life and opsonization profiles. However, the drawbacks of PEG are hypersensitivity reactions due to pre-existing PEG antibodies and poor biodegradability. These factors warrant a search for alternatives. Some large peptides have shown potent stealth properties in protein delivery. Here, we demonstrate that repeating units of serine-threonine-glutamic acid-proline (STEP) peptide conjugated to dimyristoylglycerol (DMG-STEP) and incorporated into lipid nanoparticles can perform as functional equivalents of DMG-PEG. LNPs with DMG-STEPs displayed similar physicochemical attributes and comparable Factor VII (FVII) silencing and human erythropoietin (hEPO) expression in both mouse and nonhuman primate animal models, with comparable biodistribution profile in mice. Additionally, DMG-STEP LNPs encapsulating mRNA encoding for SARS-CoV-2 Spike protein (Wuhan variant) demonstrated superior humoral immune response in a mouse study. In addition, the preliminary safety of STEP LNPs was demonstrated by quantifying liver enzymes, cytokine induction, complement activation, and anti-STEP antibody production. Results demonstrated comparable or even reduced cytokine induction responses with STEP LNPs compared to control PEG LNPs. The data presented supports translational potential of STEP LNPs.