Knockdown of a G protein-coupled receptor through efficient peptide-mediated siRNA delivery

Functional small peptides for enhanced protein delivery, solubility, and secretion in microbial biotechnology

In microbial biotechnology, there is a constant demand for functional peptides to give new functionality to engineered proteins to address problems such as direct delivery of functional proteins into bacterial cells, enhanced protein solubility during the expression of recombinant proteins, and efficient protein secretion from bacteria. To tackle these critical issues, we selected three types of functional small peptides: cell-penetrating peptides (CPPs) enable the delivery of diverse cargoes into bacterial cytoplasm for a variety of purposes, protein-solubilizing peptide tags demonstrate remarkable efficiency in solubilizing recombinant proteins without folding interference, and signal peptides play a key role in enabling the secretion of recombinant proteins from bacterial cells. In this review, we introduced these three functional small peptides that offer effective solutions to address emerging problems in microbial biotechnology. Additionally, we summarized various engineering efforts aimed at enhancing the activity and performance of these peptides, thereby providing valuable insights into their potential for further applications.

SPA: a peptide antagonist that acts as a cell-penetrating peptide for drug delivery

Although cell-penetrating peptides (CPPs) has been proven to be efficient transporter for drug delivery, ideal peptide vectors for tumor therapy are still being urgently sought. Peptide antagonists have attracted substantial attention as targeting molecules because of their high tumor accumulation and antitumor activity compared with agonists. SPA, a derivative of substance P, is a potent antagonist that exhibits antitumor activity. Based on the amino acid composition of SPA, we speculate that it can translocate across cell membranes as CPPs do. In this study, our results demonstrated that SPA could enter cells similarly to a CPP. As a vector, SPA could efficiently deliver camptothecin and plasmids into cells. In addition, our results showed that SPA exhibited low toxicity to normal cells and high enzymatic stability. Taken together, our results validated the ability of SPA for efficient drug delivery. More importantly, our study opens a new avenue for designing ideal CPPs based on peptide antagonists.

Amphiphilic Peptides for Efficient siRNA Delivery

A number of amphiphilic cyclic peptides—[FR]₄, [WR]₅, and [WK]₅—containing hydrophobic and positively-charged amino acids were synthesized by Fmoc/tBu solid-phase peptide methods and evaluated for their efficiency in intracellular delivery of siRNA to triple-negative breast cancer cell lines, MDA-MB-231 and MDA-MB-468, in the presence and absence of 1,2-dioleoyl-sn-glycero-3-phosphoethanolamine (DOPE). Among the peptides, [WR]₅, which contains alternate tryptophan (W) and arginine (R) residues, was found to be the most efficient in the delivery of siRNA by improving the delivery by more than 3-fold when compared to other synthesized cyclic peptides that were not efficient. The data also showed that co-formulation of [WR]₅ with lipid DOPE significantly enhanced the efficiency of siRNA delivery by up to ~2-fold compared to peptide alone. Based on the data indicating the efficiency of [WR]₅ in siRNA delivery, peptides containing arginine residues on the ring and tryptophan residues on the side chain, [R₆K]W₆ and [R₅K]W₅, were also evaluated, and demonstrated improved delivery of siRNA. The presence of DOPE again enhanced the siRNA delivery in most cases. [WR]₅, [R₅K]W₅, and [R₆K]W₆ did not show any significant toxicity in MDA-MB-231, MDA-MB-468, and AU565 WT cells at N/P ratios of 20:1 or less, in the presence and absence of DOPE. Silencing of kinesin spindle protein (KSP) and Janus kinase 2 (JAK2) was evaluated in MDA-MB-231 cells in the presence of the peptides. The addition of DOPE significantly enhanced the silencing efficiency for all selected peptides. In conclusion, peptides containing tryptophan and arginine residues were found to enhance siRNA delivery and to generate silencing of targeted proteins in the presence of DOPE.

Peptide-Based Nanoparticles to Rapidly and Efficiently "Wrap 'n Roll" siRNA into Cells

Delivery of small interfering RNA (siRNA) as a therapeutic tool is limited due to critical obstacles such as the cellular barrier, the negative charges of the siRNA molecule, and its instability in serum. Several siRNA delivery systems have been constructed using cell-penetrating peptides (CPPs) since the CPPs have shown a high potential for oligonucleotide delivery into the cells, especially by forming nanoparticles. In this study, we have developed a new family of short (15mer or 16mer) tryptophan-(W) and arginine-(R) rich Amphipathic Peptides (WRAP) able to form stable nanoparticles and to enroll siRNA molecules into cells. The lead peptides, WRAP1 and WRAP5, form defined nanoparticles smaller than 100 nm as characterized by biophysical methods. Furthermore, they have several benefits as oligonucleotide delivery tools such as the rapid encapsulation of the siRNA, the efficient siRNA delivery in several cell types, and the high gene silencing activity, even in the presence of serum. In conclusion, we have designed a new family of CPPs specifically dedicated for siRNA delivery through nanoparticle formation. Our results indicate that the WRAP family has significant potential for the safe, efficient, and rapid delivery of siRNA for diverse applications.

PEGylation rate influences peptide-based nanoparticles mediated siRNA delivery in vitro and in vivo

Small interfering RNAs (siRNAs) present a strong therapeutic potential because of their ability to inhibit the expression of any desired protein. Recently, we developed the retro-inverso amphipathic RICK peptide as novel non-covalent siRNA carrier. This peptide is able to form nanoparticles (NPs) by self-assembling with the siRNA resulting in the fully siRNA protection based on its protease resistant peptide sequence. With regard to an in vivo application, we investigated here the influence of the polyethylene glycol (PEG) grafting to RICK NPs on their in vitro and in vivo siRNA delivery properties. A detailed structural study shows that PEGylation did not alter the NP formation (only decrease in zeta potential) regardless of the used PEGylation rates. Compared to the native RICK:siRNA NPs, low PEGylation rates (≤20%) of the NPs did not influence their cellular internalization capacity as well as their knock-down specificity (over-expressed or endogenous system) in vitro. Because the behavior of PEGylated NPs could differ in their in vivo application, we analyzed the repartition of fluorescent labeled NPs injected at the one-cell stage in zebrafish embryos as well as their pharmacokinetic (PK) profile after administration to mice. After an intra-cardiac injection of the PEGylated NPs, we could clearly determine that 20% PEG-RICK NPs reduce significantly liver and kidney accumulation. NPs with 20% PEGylation constitutes a modular, easy-to-handle drug delivery system which could be adapted to other types of functional moieties to develop safe and biocompatible delivery systems for the clinical application of RNAi-based cancer therapeutics.

Polymers for siRNA Delivery: A Critical Assessment of Current Technology Prospects for Clinical Application

The number of polymer-based vectors for siRNA delivery in clinical trials lags behind other delivery strategies; however, the molecular architectures and chemical compositions available to polymers make them attractive candidates for further exploration. Polymer vectors are extensively investigated in academic laboratories worldwide with fundamental progress having recently been made in the areas of high-throughput screening, synthetic methods, cellular internalization, endosomal escape and computational prediction and analysis. This review assesses recent advances within the field and highlights relevant developments from within the complementary fields of nanotechnology and protein chemistry with the intent to propose future work that addresses key gaps within the current body of knowledge, potentially advancing the development of the next generation of polymeric vectors.

Cyclization of a cell-penetrating peptide via click-chemistry increases proteolytic resistance and improves drug delivery

In this work we report synthesis and biological evaluation of a cell-penetrating peptide (CPP), that is partly cyclized via a triazole bridge. Recently, beneficious properties have been reported for cyclized peptides concerning their metabolic stability and intracellular uptake. A CPP based on human calcitonin was used in this study, and side chain cyclization was achieved via copper catalyzed alkyne-azide click reaction. Cell viability studies in several cell-lines revealed no cytotoxic effects. Furthermore, efficient uptake in breast cancer MCF-7 cells could be determined. Moreover, preliminary studies using this novel peptide as drug transporter for daunorubicin were performed. Copyright © 2016 European Peptide Society and John Wiley & Sons, Ltd.

Optimisation of vectorisation property: A comparative study for a secondary amphipathic peptide

RNA interference provides a powerful technology for specific gene silencing. Therapeutic applications of small interfering RNA (siRNA) however require efficient vehicles for stable complexation and intracellular delivery. In order to enhance their cell delivery, short amphipathic peptides called cell-penetrating peptides (CPPs) have been intensively developed for the last two decades. In this context, the secondary amphipathic peptide CADY has shown to form stable siRNA complexes and to improve their cellular uptake independent of the endosomal pathway. In the present work, we have described the parameters influencing CADY nanoparticle formation (buffers, excipients, presence of serum, etc.), and have followed in details the CPP:siRNA self-assembly. Once optimal conditions were determined, we have compared the ability of seven different CADY analogues to form siRNA-loaded nanoparticles compared to CADY:siRNA. First of all, we were able to show by biophysical methods that structural polymorphism (α-helix) is an important prerequisite for stable nanoparticle formation independently of occurring sequence mutations. Luciferase assays revealed that siRNA complexed to CADY-K (shorter version) shows better knock-down efficiency on Neuro2a-Luc(+) and B16-F10-Luc(+) cells compared to CADY:siRNA. Altogether, CADY-K is an ideal candidate for further application especially with regards to ex vivo or in vivo applications.

A role for peptides in overcoming endosomal entrapment in siRNA delivery - A focus on melittin

siRNA has the possibility to revolutionize medicine by enabling highly specific and efficient silencing of proteins involved in disease pathogenesis. Despite nearly 20 years of research dedicated to translating siRNA from a research tool into a clinically relevant therapeutic, minimal success has been had to date. Access to RNA interference machinery located in the cytoplasm is often overlooked, but must be considered when designing the next generation of siRNA delivery strategies. Peptide transduction domains (PTDs) have demonstrated moderate siRNA transfection, which is primarily limited by endosomal entrapment. Strategies aimed at overcoming endosomal entrapment associated with peptide vectors are reviewed here, including osmotic methods, lipid conjugation, and fusogenic peptides. As an alternative to traditional PTD, the hemolytic peptide melittin exhibits the native capacity for endosomal disruption but causes cytotoxicity. However, appropriate packaging and protection of melittin with activation and release in the endosomal compartment has allowed melittin-based strategies to demonstrate both in vitro and in vivo safety and efficacy. These data suggest that melittin's membrane disruptive properties can enable safe and effective endosomolysis, building a case for melittin as a key component in a new generation of siRNA therapeutics.

Fusogenic-oligoarginine peptide-mediated silencing of the CIP2A oncogene suppresses oral cancer tumor growth in vivo

Intracellular delivery and endosomal escape of functional small interfering RNAs (siRNAs) remain major barriers limiting the clinical translation of RNA interference (RNAi)-based therapeutics. Recently, we demonstrated that a cell-penetrating endosome-disruptive peptide we synthesized, termed 599, enhanced the intracellular delivery and bioavailability of siRNAs designed to target the CIP2A oncoprotein (siCIP2A) into oral cancer cells and consequently inhibited oral cancer cell invasiveness and anchorage-independent growth in vitro. Thus, to further assess the therapeutic potential of the 599 peptide in mediating RNAi-based therapeutics for oral cancer and its prospective applicability in clinical settings, the objective of the current study was to determine whether intratumoral dosing of the 599 peptide-siCIP2A complex could induce silencing of CIP2A and consequently impair tumor growth using a xenograft oral cancer mouse model. Our results demonstrate that the 599 peptide is able to protect siRNAs from degradation by serum and ribonucleases in vitro and upon intratumoral injection in vivo, confirming the stability of the 599 peptide-siRNA complex and its potential for therapeutic utility. Moreover, 599 peptide-mediated delivery of siCIP2A to tumor tissue induces CIP2A silencing without any associated toxicity, consequently resulting in reduction of the mitotic index and significant inhibition of tumor growth. Together, these data suggest that the 599 peptide carrier is a clinically effective mediator of RNAi-based cancer therapeutics.

[Application of target peptide in siRNA delivery for the research of lung cancer therapy]

肺癌被认为是全球发病率最高的一种恶性肿瘤，其对化疗药物不敏感且易产生耐药性，因此增强肺癌药物治疗效果是近年来研究的热点。siRNA是一种小RNA分子，可以沉默与之互补的目标mRNA，是一种基因治疗手段。靶向肽是一类小分子多肽，它可以与siRNA联合使用，利用其与肿瘤表面物质特异性结合发挥靶向作用。联合靶向肽的特异性和siRNA的治疗作用，增加siRNA在靶点位置的聚集，增强沉默效果，可以提高肺癌对药物的敏感性并降低耐药作用，进而增强肺癌治疗效果，为肺癌的靶向治疗提供新的方向和策略。本文将对靶向肽在递送siRNA进行肺癌治疗研究中的应用作一简要综述。

Cell penetrating peptides: efficient vectors for delivery of nanoparticles, nanocarriers, therapeutic and diagnostic molecules

Efficient delivery of therapeutic and diagnostic molecules to the cells and tissues is a difficult challenge. The cellular membrane is very effective in its role as a selectively permeable barrier. While it is essential for cell survival and function, also presents a major barrier for intracellular delivery of cargo such as therapeutic and diagnostic agents. In recent years, cell-penetrating peptides (CPPs), that are relatively short cationic and/or amphipathic peptides, received great attention as efficient cellular delivery vectors due to their intrinsic ability to enter cells and mediate uptake of a wide range of macromolecular cargo such as plasmid DNA (pDNA), small interfering RNA (siRNAs), drugs, and nanoparticulate pharmaceutical carriers. This review discusses the various uptake mechanisms of these peptides. Furthermore, we discuss recent advances in the use of CPP for the efficient delivery of nanoparticles, nanocarriers, DNA, siRNA, and anticancer drugs to the cells. In addition, we have been highlighting new results for improving endosomal escape of CPP-cargo molecules. Finally, pH-responsive and activable CPPs for tumor-targeting therapy have been described.

Cell-penetrating peptides: design, synthesis, and applications

The intrinsic property of cell-penetrating peptides (CPPs) to deliver therapeutic molecules (nucleic acids, drugs, imaging agents) to cells and tissues in a nontoxic manner has indicated that they may be potential components of future drugs and disease diagnostic agents. These versatile peptides are simple to synthesize, functionalize, and characterize yet are able to deliver covalently or noncovalently conjugated bioactive cargos (from small chemical drugs to large plasmid DNA) inside cells, primarily via endocytosis, in order to obtain high levels of gene expression, gene silencing, or tumor targeting. Typically, CPPs are often passive and nonselective yet must be functionalized or chemically modified to create effective delivery vectors that succeed in targeting specific cells or tissues. Furthermore, the design of clinically effective systemic delivery systems requires the same amount of attention to detail in both design of the delivered cargo and the cell-penetrating peptide used to deliver it.