An update on cell-penetrating peptides with intracellular organelle targeting.

INTRODUCTION: Cell-penetrating peptide (CPP) technologies represent an important strategy to address drug delivery to specific intracellular compartments by covalent conjugation to targeting sequences, potentially enabling strategies to combat most diseases. AREAS COVERED: This updated review article provides an overview of current intracellular organelle targeting by CPP. The targeting strategies of CPP and CPP/cargo complexes to specific cells or intracellular organelles are summarized, and the review provides an update on the current data for their pharmacological and therapeutical applications. EXPERT OPINION: Targeted drug delivery is moving from the level of tissue or specific pathogenic cell to the level of specific organelle that is the target of the drug, an important aspect in drug design and development. Organelle-targeted drug delivery results in improved efficacy, ability to control mode of action, reduction of undesired toxicities and side effects, and the possibility to overcome drug resistance mechanisms.

Mitochondrial Targeting Probes, Drug Conjugates, and Gene Therapeutics.

Mitochondria represent an important drug target for many phatology, including neurodegeneration, metabolic disease, heart failure, ischemia-reperfusion injury, and cancer. Mitochondrial dysfunctions are caused by mutation in mitochondrial DNA or in nuclear genes encoding mitochondrial proteins. Cell-penetrating peptides (CPPs) have been employed to overcome biological barriers, target this organelle, and therapeuticaly restore mitochondrial functions. Here, we describe recent methods used to deliver oligonucleotides targeting mitochondrial protein by using mitochondrial penetrating peptides. In particular, we highlight recent advances of formulated peptides/oligonucleotides nanocomplexes as a proof-of-principle for pharmaceutical form of peptide-based therapeutics.

Intracellular delivery of therapeutic antisense oligonucleotides targeting mRNA coding mitochondrial proteins by cell-penetrating peptides.

Cell-penetrating peptides are a promising therapeutic strategy for a wide variety of degenerative diseases, ageing, and cancer. Among the multitude of cell-penetrating peptides, PepFect14 has been preferentially used in our laboratory for oligonucleotide delivery into cells and in vivo mouse models. However, this activity has mainly been reported towards cytoplasm and nuclei, while the mentioned disorders have been linked to mitochondrial defects. Here, we report a library generated from a combinatorial covalent fusion of a mitochondrial-penetrating peptide, mtCPP1, and PepFect14 in order to deliver therapeutic biomolecules to influence mitochondrial protein expression. The non-covalent complexation of these peptides with oligonucleotides resulted in nano-complexes affecting biological functions in the cytoplasm and on mitochondria. This delivery system proved to efficiently target mitochondrial genes, providing a framework for the development of mitochondrial peptide-based oligonucleotide technologies with the potential to be used as a treatment for patients with mitochondrial disorders.

Magnetic fields modulate metabolism and gut microbiome in correlation with Pgc-1α expression: Follow-up to an in vitro magnetic mitohormetic study.

Exercise modulates metabolism and the gut microbiome. Brief exposure to low mT-range pulsing electromagnetic fields (PEMFs) was previously shown to accentuate in vitro myogenesis and mitochondriogenesis by activating a calcium-mitochondrial axis upstream of PGC-1α transcriptional upregulation, recapitulating a genetic response implicated in exercise-induced metabolic adaptations. We compared the effects of analogous PEMF exposure (1.5 mT, 10 min/week), with and without exercise, on systemic metabolism and gut microbiome in four groups of mice: (a) no intervention; (b) PEMF treatment; (c) exercise; (d) exercise and PEMF treatment. The combination of PEMFs and exercise for 6 weeks enhanced running performance and upregulated muscular and adipose Pgc-1α transcript levels, whereas exercise alone was incapable of elevating Pgc-1α levels. The gut microbiome Firmicutes/Bacteroidetes ratio decreased with exercise and PEMF exposure, alone or in combination, which has been associated in published studies with an increase in lean body mass. After 2 months, brief PEMF treatment alone increased Pgc-1α and mitohormetic gene expression and after >4 months PEMF treatment alone enhanced oxidative muscle expression, fatty acid oxidation, and reduced insulin levels. Hence, short-term PEMF treatment was sufficient to instigate PGC-1α-associated transcriptional cascades governing systemic mitohormetic adaptations, whereas longer-term PEMF treatment was capable of inducing related metabolic adaptations independently of exercise.

Role of autophagy in cell-penetrating peptide transfection model.

Cell-penetrating peptides (CPPs) uptake mechanism is still in need of more clarification to have a better understanding of their action in the mediation of oligonucleotide transfection. In this study, the effect on early events (1 h treatment) in transfection by PepFect14 (PF14), with or without oligonucleotide cargo on gene expression, in HeLa cells, have been investigated. The RNA expression profile was characterized by RNA sequencing and confirmed by qPCR analysis. The gene regulations were then related to the biological processes by the study of signaling pathways that showed the induction of autophagy-related genes in early transfection. A ligand library interfering with the detected intracellular pathways showed concentration-dependent effects on the transfection efficiency of splice correction oligonucleotide complexed with PepFect14, proving that the autophagy process is induced upon the uptake of complexes. Finally, the autophagy induction and colocalization with autophagosomes have been confirmed by confocal microscopy and transmission electron microscopy. We conclude that autophagy, an inherent cellular response process, is triggered by the cellular uptake of CPP-based transfection system. This finding opens novel possibilities to use autophagy modifiers in future gene therapy.

Effect of a Fusion Peptide by Covalent Conjugation of a Mitochondrial Cell-Penetrating Peptide and a Glutathione Analog Peptide.

Previously, we designed and synthesized a library of mitochondrial antioxidative cell-penetrating peptides (mtCPPs) superior to the parent peptide, SS31, to protect mitochondria from oxidative damage. A library of antioxidative glutathione analogs called glutathione peptides (UPFs), exceptional in hydroxyl radical elimination compared with glutathione, were also designed and synthesized. Here, a follow-up study is described, investigating the effects of the most promising members from both libraries on reactive oxidative species scavenging ability. None of the peptides influenced cell viability at the concentrations used. Fluorescence microscopy studies showed that the fluorescein-mtCPP1-UPF25 (mtgCPP) internalized into cells, and spectrofluorometric analysis determined the presence and extent of peptide into different cell compartments. mtgCPP has superior antioxidative activity compared with mtCPP1 and UPF25 against H2O2 insult, preventing ROS formation by 2- and 3-fold, respectively. Moreover, we neither observed effects on mitochondrial membrane potential nor production of ATP. These data indicate that mtgCPP is targeting mitochondria, protecting them from oxidative damage, while also being present in the cytosol. Our hypothesis is based on a synergistic effect resulting from the fused peptide. The mitochondrial peptide segment is targeting mitochondria, whereas the glutathione analog peptide segment is active in the cytosol, resulting in increased scavenging ability.

Cell-penetrating peptides with intracellular organelle targeting.

INTRODUCTION: One of the major limiting steps in order to have an effective drug is the passage through one or more cell membranes to reach its site of action. To reach the action-site, the specific macromolecules are required to be delivered specifically to the cell compartment/organelle in their (pre)active form. Areas covered: In this review, we will discuss cell-penetrating peptides (CPPs) developed in the last decade to transport small RNA/DNA, plasmids, antibodies, and nanoparticles into specific sites of the cell. The article describes CPPs in complex with cargo molecules that target specific intracellular organelles and their potential for pharmacological or clinical use. Expert opinion: Organelle targeting is the ultimate goal to ensure selective delivery to the site of action in the cells. CPP technologies represent an important strategy to address drug delivery to specific intracellular compartments by covalent conjugation to targeting sequences, potentially enabling strategies to combat genomic diseases as well as infections, cancer, neurodegenerative and hereditary diseases. They have proven to be successful in delivering various therapeutic agents into cells however, further in vivo experiments and clinical trials are required to demonstrate the efficacy of this technology.

Novel cell-penetrating peptide targeting mitochondria.

Cell-penetrating peptides (CPPs) are short, nontoxic peptides with cationic and/or amphipathic properties able to cross the cellular membrane. CPPs are used for the delivery of a wide variety of cargoes, such as proteins, oligonucleotides, and therapeutic molecules. The aim of the present study was to synthesize unusually small novel CPPs targeting mitochondria based on the Szeto-Schiller peptide (SS-31) to influence intramitochondrial processes and to improve the biologic effects. All the peptides used were synthesized manually using 9-fluorenylmethyloxycarbonyl chemistry. In the first part of the study, HeLa 705, U87, and bEnd.3 cells were used as in vitro delivery model. Cells were incubated for 24 h at 37°C and 5% CO2 with different concentrations of our peptides. Cell proliferation assay was performed to evaluate cell viability. Biologic effects such as mitochondrial membrane potential and antioxidant activity were evaluated. H2O2 was used as positive control. Uptake studies were performed using peptides conjugated with 5(6)-carboxyfluorescein (FAM). Fluorescent microscopy was used to determine presence and localization of peptides into the cells. Isolated mitochondria from pretreated cells and mitochondria treated after isolation were used to confirm the targeting ability of the peptide. Uptake of FAM alone was used as negative control. Microscopy studies confirmed the ability of peptides to penetrate cell. Localization analysis showed increase in uptake by 35% compared with SS-31. Mitochondrial CPP 1 (mtCPP-1) had no effect on mitochondrial membrane potential and prevented reactive oxygen species formation in bEnd.3 cells by 2-fold compared with SS-31. No cytotoxicity was observed even at high concentration (100 µM). These data suggest that mtCPP-1 is a mitochondrial CPP and protect mitochondria from oxidative damage due to its own antioxidant activities.

Peptide-based vectors: recent developments.

Peptides and peptide-cargo complexes have been used for drug delivery and gene therapy. One of the most used delivery vectors are cell-penetrating peptides, due to their ability to be taken up by a variety of cell types and deliver a large variety of cargoes through the cell membrane with low cytotoxicity. In vitro and in vivo studies have shown their possibility and full effectiveness to deliver oligonucleotides, plasmid DNA, small interfering RNAs, antibodies, and drugs. We report in this review some of the latest strategies for peptide-mediated delivery of nucleic acids. It focuses on peptide-based vectors for therapeutic molecules and on nucleic acid delivery. In addition, we discuss recent applications and clinical trials.