Cell-Penetrating Peptides in Intracellular Delivery Systems

Cell-penetrating peptides (CPPs) represent a versatile class of short polypeptides, typically rich in basic amino acids, that traverse cellular membranes to deliver diverse molecular cargos, including proteins, nucleic acids and small-molecule therapeutics. Their capacity for direct penetration or endocytic uptake enables access to intracellular targets that are otherwise impermeable, addressing a central challenge in drug and gene delivery. Key physicochemical attributes—such as cationic charge density, amphipathicity and structural disorder—mediate initial binding to anionic cell-surface components, notably glycosaminoglycans, and subsequent membrane translocation. Uptake mechanisms range from energy-dependent endocytosis to direct translocation across lipid bilayers, with the balance influenced by peptide sequence, cargo size and cell type. Major obstacles include entrapment within endosomal compartments and off-target interactions. Recent advances have focused on enhancing endosomal escape, tuning peptide–lipid interactions and introducing responsive motifs that exploit intracellular triggers, thereby improving cytosolic bioavailability. The global significance of CPP-mediated delivery spans fundamental research, diagnostic imaging and therapeutic applications, from precision oncology to gene therapy, underscoring their promise for the next generation of intracellular delivery platforms.

Research from Nature Portfolio

Recent studies have elucidated how intrinsically disordered cationic motifs govern CPP internalisation. A 2023 investigation demonstrated that a basic sequence upstream of a homeodomain selectively binds highly sulphated heparan sulfate glycosaminoglycans, finely tuning cellular uptake of a transcription factor fragment. Structural and biophysical analyses revealed that this high-affinity interaction serves as an entry gate, enhancing peptide translocation without reliance on conventional endocytic pathways. Complementing this, a foundational report utilised a split-GFP fluorescence complementation assay to quantify and optimise synthetic endosomal escape domains. By conjugating aromatic indole or phenyl moieties at defined linkers from a TAT-derived CPP, researchers achieved significant cytosolic delivery of macromolecular cargos with minimal toxicity, directly addressing the rate-limiting step of endosomal release. Together, these contributions underscore the transition from empirical design towards rational engineering of CPPs with both high membrane affinity and efficient intracellular trafficking.

Cell-Penetrating Peptides in Intracellular Delivery Systems publication trend

The graph below shows the total number of articles in cell-penetrating peptides in intracellular delivery systems across all publications each year (not limited to Nature Index journals).

Technical terms

Cell-penetrating peptide (CPP): Short peptide sequences capable of crossing cellular membranes to deliver molecular cargos into the cell interior.

Endocytosis: Energy-dependent process whereby cells internalise extracellular material within membrane-bound vesicles.

Endosomal escape: Release of internalised cargos from endosomal compartments into the cytosol, critical for functional delivery.

Glycosaminoglycans (GAGs): Negatively charged polysaccharides on the cell surface that mediate initial peptide–membrane interactions.

Membrane microdomains: Distinct regions of the lipid bilayer characterised by specific lipid packing, such as liquid-ordered and liquid-disordered states.

References

1. A cationic motif upstream Engrailed2 homeodomain controls cell internalization through selective interaction with heparan sulfates. Nature Communications (2023).
2. Arginine‐Rich Cell‐Penetrating Peptides Induce Lipid Rearrangements for Their Active Translocation across Laterally Heterogeneous Membranes. Advanced Science (2024).
3. Peptide-Based Vectors: A Biomolecular Engineering Strategy for Gene Delivery. Annual Review of Chemical and Biomolecular Engineering (2023).