DAPEG, a Modular Peptidomimetic Concept for Intracellular Delivery: Architecture, Trajectory, and Outlook in the Context of Peptidomimetic Transfection Reagents

Abstract

Abstract Cell-penetrating peptides (CPPs) remain a leading nonviral strategy for the intracellular delivery of polynucleotides and folded proteins, but native α-peptide CPPs are constrained by proteolysis, dose-dependent cytotoxicity, and endosomal entrapment. Peptidomimetic redesign addresses these limitations by replacing the α-amino-acid backbone, repositioning side chains, or embedding polyethylene glycol structurally. In this Topical Review, we present DAPEG, sequence-defined oligomers of 2,3-diaminopropionic acid bearing pendant polyethylene glycol arms developed at the University of Gdańsk, as a case study of how a single modular building block can migrate across functional categories within one decade, from fluorogenic protease substrates (2016, 2020) through plasmid DNA transfection with nonlipidated guanidinylated oligomers (2021) and delivery of active enzymes in breast-derived cell lines (2024) to lipidated plasmid DNA transfection in HEK-293T spheroid cultures (2025). To contextualize the chemistry, we survey eight peptidomimetic architecture classes now used as transfection reagents (peptoids and lipitoids, stearylated arginine-rich CPPs, PepFects, charge-altering releasable transporters, α-peptide/β-peptoid hybrids, PEGtides, modular peptide-PEG-oligocation constructs, peptidomimetic-functionalized lipids). We then examine DAPEG architecture and chronology; propose a mechanistic model for how N-terminal acyl-chain length tunes the balance between nucleic-acid condensation, particle size, and uptake (nonmonotonic and dependent on stoichiometry: the palmitoylated C16 variant gave the highest observed activity at a charge ratio of 1.5:1 and the acetylated C2 variant at 3:1 and 9:1, with C6 and C10 reaching the leading group only at 9:1); and acknowledge the six principal evidence gaps in the current DAPEG record as priority directions: the absence of in vivo data, unmapped cellular entry and endosomal escape, uncharacterized behavior in serum, unprofiled immunogenicity, a narrow cargo scope, and the absence of independent replication.