While small interfering RNAs (siRNAs) have been rapidly appreciated to silence genes, efficient and non-toxic vectors for primary cells and for systemic in vivo delivery are lacking. Several siRNA-delivery vehicles, including cell-penetrating peptides (CPPs), have been developed but their utility is often restricted by entrapment following endocytosis. Hence, developing CPPs that promote endosomal escape is a prerequisite for successful siRNA implementation. We here present a novel CPP, PepFect 6 (PF6), comprising the previously reported stearyl-TP10 peptide, having pH titratable trifluoromethylquinoline moieties covalently incorporated to facilitate endosomal release. Stable PF6/siRNA nanoparticles enter entire cell populations and rapidly promote endosomal escape, resulting in robust RNAi responses in various cell types (including primary cells), with minimal associated transcriptomic or proteomic changes. Furthermore, PF6-mediated delivery is independent of cell confluence and, in most cases, not significantly hampered by serum proteins. Finally, these nanoparticles promote strong RNAi responses in different organs following systemic delivery in mice without any associated toxicity. Strikingly, similar knockdown in liver is achieved by PF6/siRNA nanoparticles and siRNA injected by hydrodynamic infusion, a golden standard technique for liver transfection. These results imply that the peptide, in addition to having utility for RNAi screens in vitro, displays therapeutic potential.

Introduction: Different gene therapy approaches have gained extensive interest lately and, after many initial hurdles, several promising approaches have reached to the clinics. Successful implementation of gene therapy is heavily relying on finding efficient measures to deliver genetic material to cells. Recently, non-viral delivery of nucleic acids and their analogs has gained significant interest. Among non-viral vectors, cell-penetrating peptides (CPPs) have been extensively used for the delivery of nucleic acids both in vitro and in vivo. Areas covered: In this review we will discuss recent advances of CPP-mediated delivery of nucleic acid-based cargo, concentrating on the delivery of plasmid DNA, splice-correcting ONs, and small-interfering RNAs. Expert opinion: CPPs have proved their potential as carriers for nucleic acids. However, similarly to other non-viral vectors, CPPs require further development, as efficient systemic delivery is still seldom achieved. To achieve this, CPPs should be modified with entities that would allow better endosomal escape, targeting of specific tissues and cells, and shielding agents that increase the half-life of the vehicles. Finally, to understand the clinical potential of CPPs, they require more thorough investigations in clinically relevant disease models and in pre-clinical and clinical studies.

Introduction: Delivery of macromolecular drugs is an important field in medical research. However, macromolecules are usually unable to cross the cell membrane without the assistance of a delivery system. Cell penetrating peptides (CPPs) are unique tools to gain access to the cell interior and deliver a bioactive cargo into the cytosol or nucleus. In addition to macromolecular delivery, CPPs have been used to deliver smaller bioactive molecules. Therefore CPPs have become an intensive field of research for medical treatment.Areas covered: In this review, we highlight studies that include CPP in vivo disease models. We review different strategies and approaches that have been used with specific attention on recent publications. The approaches that have been used include CPP–cargo covalent conjugation strategies and nanoparticle strategies. Various additional strategies have been used to achieve disease targeting, including active targeting, passive targeting, and combined active/passive strategies....

Gene therapy has great potential to treat a range of different diseases, such as cancer. For that therapeutic gene can be inserted into a plasmid vector and delivered specifically to tumor cells. The most frequently used applications utilize lipoplex and polyplex approaches where DNA is non-covalently condensed into nanoparticles. However, lack of in vivo efficacy is the major concern that hinders translation of such gene therapeutic applications into clinics. In this work we introduce a novel method for in vivo delivery of plasmid DNA (pDNA) and efficient tumor-specific gene induction using intravenous (i.v) administration route. To achieve this, we utilize a cell penetrating peptide (CPP), PepFect14 (PF14), double functionalized with polyethylene glycol (PEG) and a matrix metalloprotease (MMP) substrate. We show that this delivery vector effectively forms nanoparticles, where the condensed CPP and pDNA are shielded by the PEG, in an MMP-reversible manner. Administration of the complexes results in efficient induction of gene expression specifically in tumors, avoiding normal tissues. This strategy is a potent gene delivery platform that can be used for tumor-specific induction of a therapeutic gene.