Applications and Challenges for Use of Cell-Penetrating Peptides as Delivery Vectors for Peptide and Protein Cargos

Abstract

The hydrophilic nature of peptides and proteins renders them impermeable to cell membranes. Thus, in order to successfully deliver peptide and protein-based therapeutics across the plasma membrane or epithelial and endothelial barriers, a permeation enhancing strategy must be employed. Cell-penetrating peptides (CPPs) constitute a promising tool and have shown applications for peptide and protein delivery into cells as well as across various epithelia and the blood-brain barrier (BBB). CPP-mediated delivery of peptides and proteins may be pursued via covalent conjugation of the CPP to the cargo peptide or protein or via physical complexation obtained by simple bulk-mixing of the CPP with its cargo. Both approaches have their pros and cons, and which is the better choice likely relates to the physicochemical properties of the CPP and its cargo as well as the route of administration, the specific barrier and the target cell. Besides the physical barrier, a metabolic barrier must be taken into consideration when applying peptide-based delivery vectors, such as the CPPs, and stability-enhancing strategies are commonly employed to prolong the CPP half-life. The mechanisms by which CPPs translocate cell membranes are believed to involve both endocytosis and direct translocation, but are still widely investigated and discussed. The fact that multiple factors influence the mechanisms responsible for cellular CPP internalization and the lack of sensitive methods for detection of the CPP, and in some cases the cargo, further complicates the design and conduction of conclusive mechanistic studies.

Protease-Resistant and Cell-Permeable Double-Stapled Peptides Targeting the Rab8a GTPase

“…22,23 To meet these drawbacks, numerous peptide modifications have been explored. In analogy to cell penetrating peptides (CPP), 24,25 cellular uptake can be improved by incorporation of positively charged amino acids. 17,26 Proteolytic stability can be increased by incorporation of non-natural building blocks including N-methylated, 27,28 β- [29][30][31] or D-amino acids 32,33 .…”

Expression of Cell-Penetrating Peptides Fused to Protein Cargo

“…We selected SynB, Hst5, and MPG as our CPPs, because they were each previously shown to translocate cargo into cells [Alhakamy et al, 2013;Copolovici et al, 2014;Du et al, 2017;Ilsen and Onsan, 1998;Kristensen et al, 2016;Morris et al, 2008;Shin et al, 2014;Temsamani and Laruelle, 2010;Yu et al, 2015] and use varied mechanisms for translocation [Drin et al, 2003;Gong et al, 2018;Gong and Karlsson, 2017;Rajarao et al, 2002Rajarao et al, , 2003Tan et al, 1996;Temsamani and Laruelle, 2010]. SynB (RGGRLSYSRRRFSTSTGR) is from the antimicrobial peptide protegrin 1, an 18-amino acid peptide initially isolated from porcine leukocytes [Temsamani and Laruelle, 2010].…”

The molecular mechanism of induction of unfolded protein response by Chlamydia

“…Tarp is usually translocated into the host cell cytoplasm via the T3SS but the initial in silico structural analysis indicated that it was not cell permeable (41). To facilitate the translocation of the peptide into host cells, the peptide was conjugated to the C-terminus of HIV’s trans-activator of transcription (TAT) peptide known to translocate conjugated cargos into mammalian cells (42). A non-functional TAT-fused peptide was also designed using a randomly scrambled peptide generated from the proline-rich amino acid 618–654 using PepControls web server tool (43).…”