Insight into the role of physicochemical parameters in a novel series of amphipathic peptides for efficient DNA delivery

Enhancing the Effectiveness of Oligonucleotide Therapeutics Using Cell-Penetrating Peptide Conjugation, Chemical Modification, and Carrier-Based Delivery Strategies

Oligonucleotide-based therapies are a promising approach for treating a wide range of hard-to-treat diseases, particularly genetic and rare diseases. These therapies involve the use of short synthetic sequences of DNA or RNA that can modulate gene expression or inhibit proteins through various mechanisms. Despite the potential of these therapies, a significant barrier to their widespread use is the difficulty in ensuring their uptake by target cells/tissues. Strategies to overcome this challenge include cell-penetrating peptide conjugation, chemical modification, nanoparticle formulation, and the use of endogenous vesicles, spherical nucleic acids, and smart material-based delivery vehicles. This article provides an overview of these strategies and their potential for the efficient delivery of oligonucleotide drugs, as well as the safety and toxicity considerations, regulatory requirements, and challenges in translating these therapies from the laboratory to the clinic.

Peptide-Based Nanoparticles for Therapeutic Nucleic Acid Delivery

Gene therapy offers the possibility to skip, repair, or silence faulty genes or to stimulate the immune system to fight against disease by delivering therapeutic nucleic acids (NAs) to a patient. Compared to other drugs or protein treatments, NA-based therapies have the advantage of being a more universal approach to designing therapies because of the versatility of NA design. NAs (siRNA, pDNA, or mRNA) have great potential for therapeutic applications for an immense number of indications. However, the delivery of these exogenous NAs is still challenging and requires a specific delivery system. In this context, beside other non-viral vectors, cell-penetrating peptides (CPPs) gain more and more interest as delivery systems by forming a variety of nanocomplexes depending on the formulation conditions and the properties of the used CPPs/NAs. In this review, we attempt to cover the most important biophysical and biological aspects of non-viral peptide-based nanoparticles (PBNs) for therapeutic nucleic acid formulations as a delivery system. The most relevant peptides or peptide families forming PBNs in the presence of NAs described since 2015 will be presented. All these PBNs able to deliver NAs in vitro and in vivo have common features, which are characterized by defined formulation conditions in order to obtain PBNs from 60 nm to 150 nm with a homogeneous dispersity (PdI lower than 0.3) and a positive charge between +10 mV and +40 mV.

NickFect type of cell-penetrating peptides present enhanced efficiency for microRNA-146a delivery into dendritic cells and during skin inflammation

MicroRNAs (miRNAs) are post-transcriptional gene expression regulators with potential therapeutic applications. miR-146a is a negative regulator of inflammatory processes in both tissue-resident and specialized immune cells and may therefore have therapeutic effect in inflammatory skin diseases. PepFect (PF) and NickFect (NF) type of cell-penetrating peptides (CPPs) have previously been shown to deliver miRNA mimics and/or siRNAs into cell cultures and in vivo. Here, we first demonstrate that selected PF- and NF-type of CPPs support delivery of fluorescent labelled miRNA mimics into keratinocytes (KCs) and dendritic cells (DCs). Second, we show that both PF- and NF-miR-146a nanocomplexes were equally effective in KCs, while NFs were more efficient in DCs as assessed by downregulation of miR-146a-influenced genes. None of miRNA nanocomplexes with the tested CPPs influenced the viability of KCs and DCs nor caused activation of DCs according to CD86 and CD83 markers. Transmission electron microscopy analysis with Nanogold-labelled miR-146a mimics and assessment of endocytic trafficking pathways revealed endocytosis as an active route of delivery in both KCs and DCs for all tested CPPs. However, consistent with the higher efficiency, NF-delivered miR-146a was detected more often outside endosomes in DCs. Finally, pre-injection of NF71:miR-146a nanocomplexes was confirmed to suppress inflammatory responses in a mouse model of irritant contact dermatitis as shown by reduced ear swelling response and downregulation of pro-inflammatory cytokines, including IL-6, IL-1β, IL-33 and TNF-α. In conclusion, NF71 efficiently delivers miRNA mimics into KCs as well as DCs, and therefore may have advantage in therapeutic delivery of miRNAs in case of inflammatory skin diseases.

Acylation of the antimicrobial peptide CAMEL for cancer gene therapy

Obtaining ideal gene delivery vectors is still a major goal in cancer gene therapy. CAMEL, a short hybrid antimicrobial peptide, can kill cancer cells by membrane lysis. In this study, we constructed a series of non-viral vectors by attaching fatty acids with different chain lengths to the N-terminus of CAMEL. Our results showed that the cellular uptake and transfection efficiency of acyl-CAMEL started to significantly increase from a chain length of 12 carbons. C18-CAMEL was screened for gene delivery because it had the highest transfection efficiency. Surprisingly, C18-CAMEL/plasmid complexes displayed strong endosomal escape activity after entering cells via endocytosis. Importantly, C18-CAMEL could deliver p53 plasmids to cancer cells and significantly inhibited cell proliferation by the expression of p53. In addition, the C18-CAMEL/p53 plasmid complexes and the MDM2 inhibitor nutlin-3a showed significantly synergistic anticancer activity against MCF-7 cells expressing wild-type p53. Conclusively, our study demonstrated that conjugation of stearic acid to antimicrobial peptides is a simple and successful approach for constructing efficient and economical non-viral vectors for cancer gene therapy.

Role of Cellular Retention and Intracellular State in Controlling Gene Delivery Efficiency of Multiple Nonviral Carriers

Nonviral gene delivery has seen major progress in the last two decades owing to facile synthesis, low toxicity, and ease of modification of nanocarriers that take nucleic acids to cells and tissues. Gene delivery nanocomplexes need to reach the target locations in significant amounts by overcoming multiple barriers. While the importance of nanocomplex stability, cellular uptake, intracellular trafficking, and nuclear localization has been studied extensively, the role of cellular retention and recycling of these nanocomplexes is less understood in the context of gene delivery. In this study, we used different DNA carriers and made efforts to understand the role played by cellular retention in determining their gene delivery efficiency across multiple cell lines. In addition, we also analyzed whether state of complexation and localization of the nanocomplexes play a role in conjunction with cellular retention. We observed higher transfection efficiencies for nanocomplexes showing better retention, lower unpackaging, and low recycling. Our data also suggests that nanocomplexes made of peptides with terminal cysteine modification show enhanced retention and transfection efficiency compared to their counterparts with no terminal cysteine. Overall, the work highlights myriad of factors to be considered for improving gene delivery efficiency of nanocomplexes.

Nucleic acid delivery to differentiated retinal pigment epithelial cells using cell-penetrating peptide as a carrier

Nucleic acid delivery to the eye is a promising treatment strategy for many retinal disorders. In this manuscript, retinal gene delivery with non-coated and chondroitin sulphate (CS) coated amphipathic and cationic peptides was tested. The transfection and gene knockdown efficiencies were evaluated in different retinal pigment epithelial (RPE) cell models including both dividing and differentiated cells. In addition, the mobility of peptide-based gene delivery systems was examined in porcine vitreous by particle tracking analysis. The results indicate that amphipathic and cationic peptides are safe in vitro and are capable of high transgene expression and gene knockdown in dividing cells. We further demonstrate that incorporation of CS improves the efficiency of gene delivery of peptide-based systems. Most importantly, the transgene expression mediated by both non-coated and CS coated peptides was high in differentiated as well as in human primary RPE cells which are typically difficult to transfect. Coating of peptide-based gene delivery systems with CS improved diffusion in the vitreous and enhanced the stability of the polyplexes. The results indicate that a peptide-based system can be fine-tuned as a promising approach for retinal gene delivery.

Deciphering the Role of Chondroitin Sulfate in Increasing the Transfection Efficiency of Amphipathic Peptide-Based Nanocomplexes

Glycosaminoglycans, both cell-surface and exogenous, can interfere with DNA delivery efficiency of nonviral carrier systems. In this work, we report an extensive comparative study to explore the effect of exogenously added chondroitin sulfate on biophysical characteristics, cellular uptake, transfection efficiency, and intracellular trafficking of nanocomplexes formed using primary and secondary amphipathic peptides developed in our laboratory. Our results indicate that the presence of exogenous chondroitin sulfate exhibits differential enhancement in transfection efficiency of the amphipathic peptides depending upon their chemical nature. The enhancement was more pronounced in primary amphipathic peptide-based nanocomplexes as compared to the secondary counterpart. This difference can be attributed to possible alteration of the intracellular entry pathway in addition to increased extracellular stability, less cellular toxicity, and assistance in nuclear accumulation. These results imply potential use of glycosaminoglycans such as chondroitin sulfate to improve the transfection efficiency of primary amphipathic peptides for possible in vivo applications.

Peptide nucleic acid-ionic self-complementary peptide conjugates: highly efficient DNA condensers with specific condensing mechanism

Peptide nucleic acid-ionic self-complementary peptide conjugates can induce efficient DNA condensation via base-pairing interaction and peptide association.

Peptides, polypeptides and peptide–polymer hybrids as nucleic acid carriers

Peptide, polypeptide and polymer–peptide hybrid based nucleic acid therapeutics (NAT).

Optimization of in vivo DNA delivery with NickFect peptide vectors

As the field of gene therapy progresses, an increasingly urgent need has arisen for efficient and non-toxic vectors for the in vivo delivery of nucleic acids. Cell-penetrating peptides (CPP) are very efficient transfection reagents in vitro, however, their application in vivo needs improvement. To enhance in vivo transfection we designed various CPPs based on previous knowledge of internalization studies and physiochemical properties of NickFect (NF) nanoparticles. We show that increment of the helicity of these Transportan10 analogues improves the transfection efficiency. We rationally design by modifying the net charge and the helicity of the CPP a novel amphipathic α-helical peptide NF55 for in vivo application. NF55 condenses DNA into stable nanoparticles that are resistant to protease degradation, promotes endosomal escape, and transfects the majority of cells in a large cell population. We demonstrate that NF55 mediates DNA delivery in vivo with gene induction efficiency that is comparable to commercial transfection reagents. In addition to gene induction in healthy mice, NF55/DNA nanoparticles showed promising tumor transfection in various mouse tumor models, including an intracranial glioblastoma model. The efficiency of NF55 to convey DNA specifically into tumor tissue increased even further after coupling a PEG2000 to the peptide via a disulphide-bond. Furthermore, a solid formulation of NF55/DNA displayed an excellent stability profile without additives or special storage conditions. Together, its high transfection efficacy and stability profile make NF55 an excellent vector for the delivery of DNA in vivo.

The Relation Between Thermodynamic and Structural Properties and Cellular Uptake of Peptides Containing Tryptophan and Arginine

PURPOSE

Cell-penetrating peptides (CPPs) are used for delivering drugs and other macromolecular cargo into living cells. In this paper, we investigated the relationship between the structural/physicochemical properties of four new synthetic peptides containing arginine-tryptophan in terms of their cell membrane penetration efficiency.

METHODS

The peptides were prepared using solid phase synthesis procedure using FMOC protected amino acids. Fluorescence-activated cell sorting and fluorescence imaging were used to evaluate uptake efficiency. Prediction of the peptide secondary structure and estimation of physicochemical properties was performed using the GOR V method and MPEx 3.2 software (Wimley-White scale, helical wheel projection and total hydrophobic moment).

RESULTS

Our data showed that the uptake efficiency of peptides with two tryptophans at the C- and N-terminus were significantly higher (about 4-fold) than that of peptides containing three tryptophans at both ends. The distribution of arginine at both ends also increased the uptake efficiency 2.52- and 7.18-fold, compared with arginine distribution at the middle of peptides.

CONCLUSION

According to the obtained results the value of transfer free energies of peptides from the aqueous phase to membrane bilayer could be a good predictor for the cellular uptake efficiency of CPPs.

Perspectives and Challenges of Cell-Penetrating Peptides in Effective siRNA Delivery

Over the last two decades, hundreds of cell penetrating peptides (CPPs) have been intensively developed as drug and nucleic acid delivery vectors. In many cases, however, the efficient delivery of exogenous bioactive molecules through the plasma membrane to their targets remains a tremendous challenging issue. CPPs have attracted tremendous research interest as efficient cellular delivery vehicles due to their intrinsic ability to enter cells and mediate uptake of a wide range of macromolecular cargos, such as proteins, peptides, nucleic acids, drugs and nanoparticle carriers. This review presents and discusses the current perspectives of CPP-mediated siRNA delivery system. We focus on the CPP-mediated siRNA delivery approaches, and particular emphasis is placed on the strategies for the advantages and disadvantages for each delivery approach. Lastly, the cellular uptake mechanisms of CPPs and the specific challenges associated with each delivery system of siRNAs are discussed.

Contrasting effects of cysteine modification on the transfection efficiency of amphipathic peptides

Delivery of DNA to cells remains a key challenge towards development of gene therapy. A better understanding of the properties involved in stability and transfection efficiency of the vector could critically contribute to the improvement of delivery vehicles. In the present work we have chosen two peptides differing only in amphipathicity and explored how presence of cysteine affects DNA uptake and transfection efficiency. We report an unusual observation that addition of cysteine selectively increases transfection efficiency of secondary amphipathic peptide (Mgpe-9) and causes a drop in the primary amphipathic peptide (Mgpe-10). Our results point the effect of cysteine is dictated by the importance of physicochemical properties of the carrier peptide. We also report a DNA delivery agent Mgpe-9 exhibiting high transfection efficiency in multiple cell lines (including hard-to-transfect cell lines) with minimal cytotoxicity which can be further explored for in vivo applications.