Recent Advances of Cell-Penetrating Peptides and Their Application as Vectors for Delivery of Peptide and Protein-Based Cargo Molecules

Abstract

Peptides and proteins, two important classes of biomacromolecules, play important roles in the biopharmaceuticals field. As compared with traditional drugs based on small molecules, peptide- and protein-based drugs offer several advantages, although most cannot traverse the cell membrane, a natural barrier that prevents biomacromolecules from directly entering cells. However, drug delivery via cell-penetrating peptides (CPPs) is increasingly replacing traditional approaches that mediate biomacromolecular cellular uptake, due to CPPs' superior safety and efficiency as drug delivery vehicles. In this review, we describe the discovery of CPPs, recent developments in CPP design, and recent advances in CPP applications for enhanced cellular delivery of peptide- and protein-based drugs. First, we discuss the discovery of natural CPPs in snake, bee, and spider venom. Second, we describe several synthetic types of CPPs, such as cyclic CPPs, glycosylated CPPs, and D-form CPPs. Finally, we summarize and discuss cell membrane permeability characteristics and therapeutic applications of different CPPs when used as vehicles to deliver peptides and proteins to cells, as assessed using various preclinical disease models. Ultimately, this review provides an overview of recent advances in CPP development with relevance to applications related to the therapeutic delivery of biomacromolecular drugs to alleviate diverse diseases.

Keywords: CPPs; cargo delivery; discovery of CPPs; new generation of CPPs; peptides; proteins.

Figure 4

Peptide structure and membrane transport. (A) The peptide segregated domains along an alpha-helical scaffold. (B) Linear peptide primary sequence and heptad-based wheel diagram for the helical conformation of the peptide. (C) Membrane translocation and cellular internalization are modulated by the glycan residue. Reproduced with permission from reference [70].

Figure 1

Cyclic CPPs mentioned in this article.

Figure 2

Structures of the bicyclic peptide library, peptide 2 (hit #4), and peptide 7. Amino acid residues in peptide 7 are numbered from the N- to C-terminus. The CPP sequence is shown in red, while residues modified during optimization are shown in blue. B, β -alanine; CPP, cell-penetrating peptide; Hmb, hydroxylmethylbenzoyl; Pra, propargylglycine; Δ, L-2,3-diaminopropionic acid (Dap). Reprinted with permission from [60]. Copyright 2018 American Chemical Society.

Figure 3

Synthesis of trimer Tat constructs. Synthesis of tri-Tat A and tri-cTat A (A) and synthesis of tri-Tat B and tri-cTat B (D). In silico-generated ball-and-stick model of linear Tat A trimer (B). In silico-generated ball-and-stick model of cyclic Tat A trimer (C). In silico-generated ball-and-stick model of linear Tat B trimer (E). In silico-generated ball-and-stick model of cylicTat B trimer (F). Reproduced with permission from reference [63].

Figure 5

Applications of cell-penetrating peptides related to delivery of peptides and proteins into cells and across the epithelial barrier and blood–brain barrier (generated using Figdraw).