Interactions of amphipathic carrier peptides with membrane components in relation with their ability to deliver therapeutics

Bioengineering a non-genotoxic vector for genetic modification of mesenchymal stem cells

Vectors used for stem cell transfection must be non-genotoxic, in addition to possessing high efficiency, because they could potentially transform normal stem cells into cancer-initiating cells. The objective of this research was to bioengineer an efficient vector that can be used for genetic modification of stem cells without any negative somatic or genetic impact. Two types of multifunctional vectors, namely targeted and non-targeted were genetically engineered and purified from E. coli. The targeted vectors were designed to enter stem cells via overexpressed receptors. The non-targeted vectors were equipped with MPG and Pep1 cell penetrating peptides. A series of commercial synthetic non-viral vectors and an adenoviral vector were used as controls. All vectors were evaluated for their efficiency and impact on metabolic activity, cell membrane integrity, chromosomal aberrations (micronuclei formation), gene dysregulation, and differentiation ability of stem cells. The results of this study showed that the bioengineered vector utilizing VEGFR-1 receptors for cellular entry could transfect mesenchymal stem cells with high efficiency without inducing genotoxicity, negative impact on gene function, or ability to differentiate. Overall, the vectors that utilized receptors as ports for cellular entry (viral and non-viral) showed considerably better somato- and genosafety profiles in comparison to those that entered through electrostatic interaction with cellular membrane. The genetically engineered vector in this study demonstrated that it can be safely and efficiently used to genetically modify stem cells with potential applications in tissue engineering and cancer therapy.

Increased Hydrophobic Block Length of PTDMs Promotes Protein Internalization

The plasma membrane is a major obstacle in the development and use of biomacromolecules for intracellular therapeutic applications. Protein transduction domains (PTDs) have been used to overcome this barrier, but often require covalent conjugation to their cargo and can be time consuming to synthesize. Synthetic monomers can be designed to mimic the amino acid moieties in PTDs, and their resulting polymers provide a well-controlled platform to vary molecular composition for structure-activity relationship studies. In this paper, a series of polyoxanorbornene-based synthetic mimics, inspired by PTDs, with varying cationic and hydrophobic densities, and the nature of the hydrophobic chain and degree of polymerizations were investigated in vitro to determine their ability to non-covalently transport enhanced green fluorescent protein into HeLa cells, Jurkat T cells, and hTERT mesenchymal stem cells. Polymers with high charge density lead to efficient protein delivery. Similarly, the polymers with the highest hydrophobic content and density proved to be the most efficient at internalization. The observed improvements with increased hydrophobic length and content were consistent across all three cell types, suggesting that these architectural relationships are not cell type specific. However, Jurkat T cells showed distinct variation in uptake between polymers than with the other two cell types. These results provide important design parameters for more effective delivery of biomacromolecules for intracellular delivery applications.

Peptide-mediated delivery: an overview of pathways for efficient internalization

Poor cellular delivery and low bioavailability of novel potent therapeutic molecules continue to remain the bottleneck of modern cancer and gene therapy. Cell-penetrating peptides have provided immense opportunities for the intracellular delivery of bioactive cargos and have led to the first exciting successes in experimental therapy of muscular dystrophies. This review focuses on the mechanisms by which cell-penetrating peptides gain access to the cell interior and deliver cargos. Recent advances in augmenting delivery efficacy and facilitation of endosomal escape of cargo are presented, and the cell-penetrating peptide-mediated delivery of two of the most popular classes of cargo molecules, oligonucleotides and proteins, is analyzed. The arsenal of tools for oligonucleotide delivery has dramatically expanded in the last decade enabling harnessing of cell-surface receptors for targeted delivery.

Amphiphilic cationic β(3R3)-peptides: membrane active peptidomimetics and their potential as antimicrobial agents

We introduce a novel class of membrane active peptidomimetics, the amphiphilic cationic β(3R3)-peptides, and evaluate their potential as antimicrobial agents. The design criteria, the building block and oligomer synthesis as well as a detailed structure-activity relationship (SAR) study are reported. Specifically, infrared reflection absorption spectroscopy (IRRAS) was employed to investigate structural features of amphiphilic cationic β(3R3)-peptide sequences at the hydrophobic/hydrophilic air/liquid interface. Furthermore, Langmuir monolayers of anionic and zwitterionic phospholipids have been used to model the interactions of amphiphilic cationic β(3R3)-peptides with prokaryotic and eukaryotic cellular membranes in order to predict their membrane selectivity and elucidate their mechanism of action. Lastly, antimicrobial activity was tested against Gram-positive M. luteus and S. aureus as well as against Gram-negative E. coli and P. aeruginosa bacteria along with testing hemolytic activity and cytotoxicity. We found that amphiphilic cationic β(3R3)-peptide sequences combine high and selective antimicrobial activity with exceptionally low cytotoxicity in comparison to values reported in the literature. Overall, this study provides further insights into the SAR of antimicrobial peptides and peptidomimetics and indicates that amphiphilic cationic β(3R3)-peptides are strong candidates for further development as antimicrobial agents with high therapeutic index.

A β-sheet structure interacting peptide for intracellular protein delivery into human pluripotent stem cells and their derivatives

The advance in stem cell research relies largely on the efficiency and biocompatibility of technologies used to manipulate stem cells. In our previous study, we had designed an amphipathic peptide RV24 that can deliver proteins into cancer cell lines efficiently without significant side effects. Encouraged by this observation, we moved forward to test whether RV24 could be used to deliver proteins into human embryonic stem cells and human induced pluripotent stem cells. RV24 successfully mediated protein delivery into these pluripotent stem cells, as well as their derivatives including neural stem cells and dendritic cells. Based on NMR studies and particle surface charge measurements, we proposed that hydrophobic domain of RV24 interacts with β-sheet structures of the proteins, followed by formation of "peptide cage" to facilitate delivery across cellular membrane. These findings suggest the feasibility of using amphipathic peptide to deliver functional proteins intracellularly for stem cell research.

Evaluation of the use of amphipathic peptide-based protein carrier for in vitro cancer research

Intracellular delivery of proteins offers an alternative to genetic modification or siRNA transfection for functional studies of proteins in live cells, especially for studies in cancer cells for therapeutics development. However, lack of efficient and biocompatible delivery system has limited the use of protein for in vitro cancer research. In this study, we design and evaluate an amphipathic peptide RV24, composing of a hydrophobic domain for protein binding, a flexible linker, and a hydrophilic domain to facilitate cell penetration. When using β-galactosidase as a cargo protein for comparison with commercially available peptide- and lipid-based carriers, RV24 peptide provides up to 5-fold increase in quantity delivered into 3 different cancer cell lines. Green fluorescent protein could also be delivered rapidly within 4h and transduced up to 83% of tested cancer cell lines. Although having a cell penetrating domain, RV24 peptide did not compromise cell viability, morphology and granularity significantly. These findings suggest the feasibility of using biocompatible amphipathic peptide to efficiently deliver protein-based molecules intracellularly for in vitro cancer research.

Biophysical interactions with model lipid membranes: applications in drug discovery and drug delivery

The transport of drugs or drug delivery systems across the cell membrane is a complex biological process, often difficult to understand because of its dynamic nature. In this regard, model lipid membranes, which mimic many aspects of cell-membrane lipids, have been very useful in helping investigators to discern the roles of lipids in cellular interactions. One can use drug-lipid interactions to predict pharmacokinetic properties of drugs, such as their transport, biodistribution, accumulation, and hence efficacy. These interactions can also be used to study the mechanisms of transport, based on the structure and hydrophilicity/hydrophobicity of drug molecules. In recent years, model lipid membranes have also been explored to understand their mechanisms of interactions with peptides, polymers, and nanocarriers. These interaction studies can be used to design and develop efficient drug delivery systems. Changes in the lipid composition of cells and tissue in certain disease conditions may alter biophysical interactions, which could be explored to develop target-specific drugs and drug delivery systems. In this review, we discuss different model membranes, drug-lipid interactions and their significance, studies of model membrane interactions with nanocarriers, and how biophysical interaction studies with lipid model membranes could play an important role in drug discovery and drug delivery.

A stearylated CPP for delivery of splice correcting oligonucleotides using a non-covalent co-incubation strategy

Aberrations in splicing patterns play a significant role in several diseases, and splice correction, together with other forms of gene regulation, is consequently an emerging therapeutic target. In order to achieve successful oligonucleotide transfection, efficient delivery vectors are generally necessary. In this study we present one such vector, the chemically modified cell-penetrating peptide (CPP) TP10, for efficient delivery of a splice-correcting 2'-OMe RNA oligonucleotide. Utilizing a functional splice correction assay, we assessed the transfection efficiency of non-covalent complexes of oligonucleotides and stearylated or cysteamidated CPPs. Stearylation of the CPPs Arg9 and penetratin, as well as cysteamidation of MPG and TP10, did not improve transfection, whereas the presence of an N-terminal stearyl group on TP10 improved delivery efficiency remarkably compared to the unmodified peptide. The splice correction levels observed with stearyl-TP10 are in fact in parity with the effects seen with the commercially available transfection agent Lipofectamine 2000. However, the inherent toxicity associated with cationic lipid-based transfections can be completely eliminated when using the stearylated TP10, making this vector highly promising for non-covalent delivery of negatively charged oligonucleotides.

Cell-penetrating and cell-targeting peptides in drug delivery

During the last decade, the potential of peptides for drug delivery into cells has been highlighted by the discovery of several cell-penetrating peptides (CPPs). CPPs are very efficient in delivering various molecules into cells. However, except in some specific cases, their lack of cell specificity remains the major drawback for their clinical development. At the same time, various peptides with specific binding activity for a given cell line (cell-targeting peptides) have also been reported in the literature. One of the goals of the next years will be to optimize the tissue and cell delivery of therapeutic molecules by means of peptides which combine both targeting and internalization advantages. In this review, we describe the main strategies that are currently in use or likely to be employed in the near future to associate both targeting and delivery properties.

Thermodynamic studies and binding mechanisms of cell-penetrating peptides with lipids and glycosaminoglycans

Cell-penetrating peptides (CPPs) traverse the membrane of biological cells at low micromolar concentrations and are able to take various cargo molecules along with. Despite large differences in their chemical structure, CPPs share the structural similarity of a high cationic charge density. This property confers to them the ability to bind electrostatically membrane constituents such as anionic lipids and glycosaminoglycans (GAGs). Controversies exist, however, about the biological response after the interaction of CPPs with such membrane constituents. Present review compares thermodynamic binding studies with conditions of the biological CPP uptake. It becomes evident that CPPs enter biological cells by different and probably competing mechanisms. For example, some amphipathic CPPs traverse pure lipid model membranes at low micromolar concentrations--at least in the absence of cargos. In contrast, no direct translocation at these conditions is observed for non-amphipathic CPPs. Finally, CPPs bind GAGs at low micromolar concentrations with potential consequences for endocytotic pathways.