Design of a multicomponent peptide-woven nanocomplex for delivery of siRNA

Recent Advances in Mesoporous Silica Nanoparticles Delivering siRNA for Cancer Treatment

Silencing genes using small interfering (si) RNA is a promising strategy for treating cancer. However, the curative effect of siRNA is severely constrained by low serum stability and cell membrane permeability. Therefore, improving the delivery efficiency of siRNA for cancer treatment is a research hotspot. Recently, mesoporous silica nanoparticles (MSNs) have emerged as bright delivery vehicles for nucleic acid drugs. A comprehensive understanding of the design of MSN-based vectors is crucial for the application of siRNA in cancer therapy. We discuss several surface-functionalized MSNs' advancements as effective siRNA delivery vehicles in this paper. The advantages of using MSNs for siRNA loading regarding considerations of different shapes, various options for surface functionalization, and customizable pore sizes are highlighted. We discuss the recent investigations into strategies that efficiently improve cellular uptake, facilitate endosomal escape, and promote cargo dissociation from the MSNs for enhanced intracellular siRNA delivery. Also, particular attention was paid to the exciting progress made by combining RNAi with other therapies to improve cancer therapeutic outcomes.

Advancing peptide siRNA-carrier designs through L/D-amino acid stereochemical modifications to enhance gene silencing

The 599 peptide has been previously shown to effectively deliver small interfering RNAs (siRNAs) to cancer cells, inducing targeted-oncogene silencing, with a consequent inhibition of tumor growth. Although effective, this study was undertaken to advance the 599 peptide siRNA-carrier design through L/D-amino acid stereochemical modifications. Consequently, 599 was modified to generate eight different peptide variants, incorporating either different stereochemical patterns of L/D-amino acids or a specific D-amino acid substitution. Upon analysis of the variants, it was observed that these modifications could, in some instances, increase/decrease the binding, nuclease/serum stability, and complex release of siRNAs, as well as influence the gene-silencing efficiencies of the complex. These modifications were also found to affect cellular uptake and intracellular localization patterns of siRNA cargo, with one particular variant capable of mediating binding of siRNAs to specific cellular projections, identified as filopodia. Interestingly, this variant also exhibited the most enhanced gene silencing in comparison to the parent 599 peptide, thus suggesting a possible connection between filopodia binding and enhanced gene silencing. Together, these data demonstrate the utility of peptide stereochemistry, as well as the importance of a key D-amino acid modification, in advancing the 599 carrier design for the enhancement of gene silencing in cancer cells.

Cell-Penetrating Peptides Delivering siRNAs: An Overview

Cell-Penetrating Peptides (CPP) are valuable tools capable of crossing the plasma membrane to deliver therapeutic cargo inside cells. Small interfering RNAs (siRNA) are double-stranded RNA molecules capable of silencing the expression of a specific protein triggering the RNA interference (RNAi) pathway, but they are unable to cross the plasma membrane and have a short half-life in the bloodstream. In this overview, we assessed the many different approaches used and developed in the last two decades to deliver siRNA through the plasma membrane through different CPPs sorted according to three different loading strategies: covalent conjugation, complex formation, and CPP-decorated (functionalized) nanocomplexes. Each of these strategies has pros and cons, but it appears the latter two are the most commonly reported and emerging as the most promising strategies due to their simplicity of synthesis, use, and versatility. Recent progress with siRNA delivered by CPPs seems to focus on targeted delivery to reduce side effects and amount of drugs used, and it appears to be among the most promising use for CPPs in future clinical applications.

Development of elastin-like polypeptide for targeted specific gene delivery in vivo

Background

The successful deliveries of siRNA depend on their stabilities under physiological conditions because greater in vivo stability enhances cellular uptake and enables endosomal escape. Viral-based systems appears as most efficient approaches for gene delivery but often compromised in terms of biocompatibility, patient safety and high cost scale up process. Here we describe a novel platform of gene delivery by elastin-like polypeptide (ELP) based targeting biopolymers.

Results

For better tumor targeting and membrane penetrating characteristics, we designed various chimeric ELP-based carriers containing a cell penetrating peptide (Tat), single or multiple copies of AP1 an IL-4 receptor targeting peptide along with coding sequence of ELP and referred as Tat-A₁E₂₈ or Tat-A₄V₄₈. These targeted polypeptides were further analyzed for its ability to deliver siRNA (Luciferase gene) in tumor cells in comparison with non-targeted controls (Tat-E₂₈ or E₂₈). The positively charged amino acids of these polypeptides enabled them to readily complex with negatively charged nucleic acids. The complexation of nucleic acid with respective polypeptides facilitated its transfection efficiency as well as stability. The targeted polypeptides (Tat-A₁E₂₈ or Tat-A₄V₄₈) selectively delivered siRNA into tumor cells in a receptor-specific fashion, achieved endosomal and lysosomal escape, and released gene into cytosol. The target specific delivery of siRNA by Tat-A₁E₂₈ or Tat-A₄V₄₈ was further validated in murine breast carcinoma 4T1 allograft mice model.

Conclusion

The designed delivery systems efficiently delivered siRNA to the target site of action thereby inducing significant gene silencing activity. The study shows Tat and AP1 functionalized ELPs constitute a novel gene delivery system with potential therapeutic applications.

Peptide carriers to the rescue: overcoming the barriers to siRNA delivery for cancer treatment

Cancer is a significant health concern worldwide and its clinical treatment presents many challenges. Consequently, much research effort has focused on the development of new anticancer drugs to combat this disease. One area of exploration, in particular, has been in the therapeutic application of RNA interference (RNAi). Although RNAi appears to be an attractive therapeutic tool for the treatment of cancer, one of the primary obstacles towards its pervasive use in the clinic has been cell/tissue type-specific cytosolic delivery of therapeutic small interfering RNA (siRNA) molecules. Consequently, varied drug delivery platforms have been developed and widely explored for siRNA delivery. Among these candidate drug delivery systems, peptides have shown great promise as siRNA carriers due to their varied physiochemical properties and functions, simple formulations, and flexibility in design. In this review, we will focus on distinguishing between the different classes of peptide carriers based on their functions, as well as summarize and discuss the various design strategies and advancements that have been made in circumventing the barriers to siRNA delivery for cancer treatment. Resolution of these challenges by peptide carriers will accelerate the translation of RNAi-based therapies to the clinic.

Dual peptide-mediated targeted delivery of bioactive siRNAs to oral cancer cells in vivo

OBJECTIVES

Despite significant advances in cancer treatment, the prognosis for oral cancer remains poor in comparison to other cancer types, including breast, skin, and prostate. As a result, more effective therapeutic modalities are needed for the treatment of oral cancer. Consequently, in the present study, we examined the feasibility of using a dual peptide carrier approach, combining an epidermal growth factor receptor (EGFR)-targeting peptide with an endosome-disruptive peptide, to mediate targeted delivery of small interfering RNAs (siRNAs) into EGFR-overexpressing oral cancer cells and induce silencing of the targeted oncogene, cancerous inhibitor of protein phosphatase 2A (CIP2A).

MATERIALS AND METHODS

Fluorescence microscopy, real-time PCR, Western blot analysis, and in vivo bioimaging of mice containing orthotopic xenograft tumors were used to examine the ability of the dual peptide carrier to mediate specific delivery of bioactive siRNAs into EGFR-overexpressing oral cancer cells/tissues.

RESULTS

Co-complexation of the EGFR-targeting peptide, GE11R9, with the endosome-disruptive 599 peptide facilitated the specific uptake of siRNAs into oral cancer cells overexpressing EGFR in vitro with optimal gene silencing observed at a 60:30:1 (GE11R9:599:siRNA) molar ratio. Furthermore, when administered systemically to mice bearing xenograft oral tumors, this dual peptide complex mediated increased targeted delivery of siRNAs into tumor tissues in comparison to the 599 peptide alone and significantly enhanced CIP2A silencing.

CONCLUSION

Herein we provide the first report demonstrating the clinical potential of a dual peptide strategy for siRNA-based therapeutics by synergistically mediating the effective targeting and delivery of bioactive siRNAs into EGFR-overexpressing oral cancer cells.

Noninvasive imaging of c(RGD)2 -9R as a potential delivery carrier for transfection of siRNA in malignant tumors

The purpose of our study was to develop and evaluate a novel integrin α_v β₃ -specific delivery carrier for transfection of siRNA in malignant tumors. We adopted arginine-glycine-aspartate (RGD) motif as a tissue target for specific recognition of integrin α_ν β₃ . A chimaeric peptide was synthesized by adding nonamer arginine residues (9-arginine [9R]) at the carboxy terminus of cyclic-RGD dimer, designated as c(RGD)₂ -9R, to enable small interfering RNA (siRNA) binding. To test the applicability of the delivery carrier in vivo, c(RGD)₂ -9R was labeled with radionuclide of technetium-99m. Biodistribution and γ-camera imaging studies were performed in HepG2 xenograft-bearing nude mice. As results, an optimal 10:1 molar ratio of ^99m Tc-c(RGD)₂ -9R to siRNA was indicated by the electrophoresis on agarose gels. ^99m Tc-c(RGD)₂ -9R/siRNA remained stable under a set of conditions in vitro. For in vivo study, tumor radioactivity uptake of ^99m Tc-c(RGD)₂ -9R/siRNA in nude mice bearing HepG2 xenografts was significantly higher than that of control probe (P < .05). The xenografts were clearly visualized at 4 hours till 6 hours noninvasively after intravenous injection of ^99m Tc-c(RGD)₂ -9R/siRNA, while the xenografts were not visualized at any time after injection of control probe. It was concluded that c(RGD)₂ -9R could be an effective siRNA delivery carrier. Technetium-99m radiolabeled-delivery carrier represents a potential imaging strategy for RNAi-based therapy.