Development of protein mimics for intracellular delivery

Abstract

Designing delivery agents for therapeutics is an ongoing challenge. As treatments and desired cargoes become more complex, the need for improved delivery vehicles becomes critical. Excellent delivery vehicles must ensure the stability of the cargo, maintain the cargo’s solubility, and promote efficient delivery and release. In order to address these issues, many research groups have looked to nature for design inspiration. Proteins, such as HIV-1 TAT and Antennapedia homeodomain protein, are capable of crossing cellular membranes. However, due to the complexities of their structures, they are synthetically challenging to reproduce in the laboratory setting. Being able to incorporate the key features of these proteins that enable cell entry into simpler scaffolds opens up a wide range of opportunities for the development of new delivery reagents with improved performance. This review charts the development of protein mimics based on cell-penetrating peptides and how structure-activity relationships with these molecules and their protein counterparts ultimately led to the use of polymeric scaffolds. These scaffolds deviate from the normal peptide backbone, allowing for simpler, synthetic procedures to make carriers and tune chemical compositions for application specific needs. Successful design of polymeric protein mimics would allow researchers to further understand the key features in proteins and peptides necessary for efficient delivery and to design the next generation of more efficient delivery reagents.

Relating structure and internalization for ROMP-based protein mimics

“…26,27 Polymers allow for the use of different, easily tailored chemistries and architectures for investigating structure activity relationships, while tuning for efficient cargo delivery. Using ring-opening metathesis polymerization (ROMP), which is functional group tolerant, well-controlled, and versatile, a highly efficient set of synthetic PTDMs has been developed.…”

“…Using ring-opening metathesis polymerization (ROMP), which is functional group tolerant, well-controlled, and versatile, a highly efficient set of synthetic PTDMs has been developed. 26,28–35 These designs, based on polyarginine, are guanidinium-rich and allow for non-covalent internalization of various biological cargos. 31–33 The ability to easily include diverse functional groups allows us to probe architecture, molecular composition, and molecular weight in a controlled manner, mimicking peptide synthesis.…”

Development of Guanidinium-Rich Protein Mimics for Efficient siRNA Delivery into Human T Cells

“…13,15,17 Although designing successful carriers for T cells has been a challenge, highly modular protein transduction domain mimics (PTDMs), sometimes referred to as cell-penetrating peptide mimics (CPPMs), have been used successfully in other more easily transfected cell types and can provide insight for the design of more efficient delivery vehicles. 18–20 …”

“…21–23 PTDMs incorporate important features of PTDs and CPPs critical for intracellular delivery 24–29 , including cationic charge content provided by guanidinium groups, and partial hydrophobicity contributed by the backbone architecture and/or the incorporation of hydrophobic monomers. 18,19 Although some PTDs and CPPs, such as CADY and MPG, possess these key features and have already been designed and commercialized for siRNA delivery, PTDMs offer many distinct advantages over their peptide counterparts. 30,31 Moving away from a peptide-based architecture provides protection from proteolysis and avoids solid phase peptide synthesis.…”

“…18,19,32 Consequently, different chemistries can be used to design molecules, and chemical compositions can be tuned more widely to improve delivery of specific cargo. 18,19,32 This design rationale has proven successful in creating more potent antimicrobial peptide mimics, where the key features, including their facially amphiphilic architecture, 33–35 were incorporated into synthetic scaffolds to yield new antimicrobial agents. 19,35–37 …”