Mitochondrial targeting of a cationic amphiphilic polyproline helix

Unlocking the Mitochondria for Nanomedicine-based Treatments: Overcoming Biological Barriers, Improving Designs, and Selecting Verification Techniques

Enhanced targeting approaches will support the treatment of diseases associated with dysfunctional mitochondria, which play critical roles in energy generation and cell survival. Obstacles to mitochondria-specific targeting include the presence of distinct biological barriers and the need to pass through (or avoid) various cell internalization mechanisms. A range of studies have reported the design of mitochondrially-targeted nanomedicines that navigate the complex routes required to influence mitochondrial function; nonetheless, a significant journey lies ahead before mitochondrially-targeted nanomedicines become suitable for clinical use. Moving swiftly forward will require safety studies, in vivo assays confirming effectiveness, and methodologies to validate mitochondria-targeted nanomedicines' subcellular location/activity. From a nanomedicine standpoint, we describe the biological routes involved (from administration to arrival within the mitochondria), the features influencing rational design, and the techniques used to identify/validate successful targeting. Overall, rationally-designed mitochondria-targeted-based nanomedicines hold great promise for precise subcellular therapeutic delivery.

Cell-Penetrating Peptides: A Powerful Tool for Targeted Drug Delivery

The cellular membrane hinders the effective delivery of therapeutics to targeted sites. Cellpenetrating peptide (CPP) is one of the best options for rapidly internalizing across the cellular membrane. CPPs have recently attracted lots of attention because of their excellent transduction efficiency and low cytotoxicity. The CPP-cargo complex is an effective and efficient method of delivering several chemotherapeutic agents used to treat various diseases. Additionally, CPP has become another strategy to overcome some of the current therapeutic agents' limitations. However, no CPP complex is approved by the US FDA because of its limitations and issues. In this review, we mainly discuss the cellpenetrating peptide as the delivery vehicle, the cellular uptake mechanism of CPPs, their design, and some strategies to synthesize the CPP complex via some linkers such as disulfide bond, oxime, etc. Here, we also discuss the recent status of CPPs in the market.

Antibiotic-cell-penetrating peptide conjugates targeting challenging drug-resistant and intracellular pathogenic bacteria

The failure to treat everyday bacterial infections is a current threat as pathogens are finding new ways to thwart antibiotics through mechanisms of resistance and intracellular refuge, thus rendering current antibiotic strategies ineffective. Cell-penetrating peptides (CPPs) are providing a means to improve antibiotics that are already approved for use. Through coadministration and conjugation of antibiotics with CPPs, improved accumulation and selectivity with alternative and/or additional modes of action against infections have been observed. Herein, we review the recent progress of this antibiotic-cell-penetrating peptide strategy in combatting sensitive and drug-resistant pathogens. We take a closer look into the specific antibiotics that have been enhanced, and in some cases repurposed as broad-spectrum drugs. Through the addition and conjugation of cell-penetrating peptides to antibiotics, increased permeation across mammalian and/or bacterial membranes and a broader range in bacterial selectivity have been achieved.

Targeting Intracellular Pathogenic Bacteria Through N-Terminal Modification of Cationic Amphiphilic Polyproline Helices

Intracellular pathogens can thrive within mammalian cells and are inaccessible to many antimicrobial agents. Herein, we present a facile method of enhancing the cell penetrating and antibacterial properties of cationic amphiphilic polyproline helices (CAPHs) with modifications to the hydrophobic moiety at the N-terminus. These altered CAPHs display superior cell penetration within macrophage cells, and in some cases, minimal cytotoxicity. Furthermore, one CAPH, Pentyl-P14 exhibited excellent antibacterial activity against multiple strains of pathogenic bacteria and promoted the clearance of intracellular Shigella within macrophages.

Mitochondrion-Targeting Peptides and Peptidomimetics: Recent Progress and Design Principles

Mitochondria are multifunctional subcellular organelles whose operations encompass energy production, signal transduction, and metabolic regulation. Given their wide range of roles, they have been studied extensively as a potential therapeutic target for the treatment of various diseases, including cancer, diabetes, and neurodegenerative diseases. Mitochondrion-mediated pathways have been identified as promising targets in the context of these diseases. However, the delivery of specific probes and drugs to the mitochondria is one of the major problems that remains to be solved. Over the past decade, much effort has been devoted to developing mitochondrion-targeted delivery methods based on the membrane characteristics and the protein import machinery of mitochondria. While various methods utilizing small molecules to polymeric particles have been introduced, it is notable that many of these compounds share common structural elements and physicochemical properties for optimal selectivity and efficiency. In this Perspective, we will review the most recently developed mitochondrion-targeting peptides and peptidomimetics to outline the key aspects of structural requirements and design principles. We will also discuss successful and potential applications of mitochondrial delivery to assess opportunities and challenges in the targeting of mitochondria.

Ultrashort cationic lipopeptides and lipopeptoids: Evaluation and mechanistic insights against epithelial cancer cells

Peptides present an attractive scaffold for the development of new anticancer lead agents due to their accessibility and ease of modification. Synthetic ultrashort cationic lipopeptides, with four amino acids or less conjugated to a fatty acid, were developed to retain the biological activity of longer peptides in a smaller molecular size. Herein, we report the activity of amphiphilic lipotripeptides, lipotripeptoids and lipotetrapeptides against breast (MDA-MB-231, JIMT-1), prostate (DU145) and pancreas (MiaPaCa2) epithelial cancer cell lines. The lipotripeptide C16-KKK-NH2 and lipotetrapeptide C16-PCatPHexPHexPCat-NH2 were identified to possess anticancer activity. The latter lipotetrapeptide possess a short polyproline scaffold consisting of only two L-4R-aminoproline (PCat) and two L-4R-hexyloxyproline (PHex). However, all the prepared lipotripeptoids lack anticancer activity. The amphiphilic C16-PCatPHexPHexPCat-NH2 exhibited similar anticancer potency to the surfactant benzethonium chloride while superior activity was observed in comparison to myristylamine. Mechanistic studies revealed that the peptides do not lyse ovine erythrocytes nor epithelial cancer cells, thus ruling out necrosis as the mechanism of cell death. Surprisingly, the two lipopeptides exhibit different mechanisms of action that result in cancer cell death. The lipotripeptide C16-KKK-NH2 was found to induce caspase-mediated apoptosis while C16-PCatPHexPHexPCat-NH2 kills tumor cells independent of caspases.

Mitochondrion: A Promising Target for Nanoparticle-Based Vaccine Delivery Systems

Vaccination is one of the most popular technologies in disease prevention and eradication. It is promising to improve immunization efficiency by using vectors and/or adjuvant delivery systems. Nanoparticle (NP)-based delivery systems have attracted increasing interest due to enhancement of antigen uptake via prevention of vaccine degradation in the biological environment and the intrinsic immune-stimulatory properties of the materials. Mitochondria play paramount roles in cell life and death and are promising targets for vaccine delivery systems to effectively induce immune responses. In this review, we focus on NPs-based delivery systems with surfaces that can be manipulated by using mitochondria targeting moieties for intervention in health and disease.

Mitochondrial Targeting of Doxorubicin Eliminates Nuclear Effects Associated with Cardiotoxicity

The highly effective anticancer agent doxorubicin (Dox) is a frontline drug used to treat a number of cancers. While Dox has a high level of activity against cancer cells, its clinical use is often complicated by dose-limiting cardiotoxicity. While this side effect has been linked to the drug's direct activity in the mitochondria of cardiac cells, recent studies have shown that these result primarily from downstream effects of nuclear DNA damage. Our lab has developed a mitochondrially targeted derivative of Dox that enables the selective study of toxicity generated by the presence of Dox in the mitochondria of human cells. We demonstrate that mitochondria-targeted doxorubicin (mtDox) lacks any direct nuclear effects in H9c2 rat cardiomyocytes, and that these cells are able to undergo mitochondrial biogenesis. This recovery response compensates for the mitotoxic effects of Dox and prevents cell death in cardiomyocytes. Furthermore, cardiac toxicity was only observed in Dox but not mtDox treated mice. This study supports the hypothesis that mitochondrial damage is not the main source of the cardiotoxic effects of Dox.

Molecular vehicles for mitochondrial chemical biology and drug delivery

The mitochondria within human cells play a major role in a variety of critical processes involved in cell survival and death. An understanding of mitochondrial involvement in various human diseases has generated an appreciable amount of interest in exploring this organelle as a potential drug target. As a result, a number of strategies to probe and combat mitochondria-associated diseases have emerged. Access to mitochondria-specific delivery vectors has allowed the study of biological processes within this intracellular compartment with a heightened level of specificity. In this review, we summarize the features of existing delivery vectors developed for targeting probes and therapeutics to this highly impermeable organelle. We also discuss the major applications of mitochondrial targeting of bioactive molecules, which include the detection and treatment of oxidative damage, combating bacterial infections, and the development of new therapeutic approaches for cancer. Future directions include the assessment of the therapeutic benefit achieved by mitochondrial targeting for treatment of disease in vivo. In addition, the availability of mitochondria-specific chemical probes will allow the elucidation of the details of biological processes that occur within this cellular compartment.

Chemical-functional diversity in cell-penetrating peptides

Cell-penetrating peptides (CPPs) are a promising tool to overcome cell membrane barriers. They have already been successfully applied as carriers for several problematic cargoes, like e.g. plasmid DNA and (si)RNA, opening doors for new therapeutics. Although several hundreds of CPPs are already described in the literature, only a few commercial applications of CPPs are currently available. Cellular uptake studies of these peptides suffer from inconsistencies in used techniques and other experimental conditions, leading to uncertainties about their uptake mechanisms and structural properties. To clarify the structural characteristics influencing the cell-penetrating properties of peptides, the chemical-functional space of peptides, already investigated for cellular uptake, was explored. For 186 peptides, a new cell-penetrating (CP)-response was proposed, based upon the scattered quantitative results for cellular influx available in the literature. Principal component analysis (PCA) and a quantitative structure-property relationship study (QSPR), using chemo-molecular descriptors and our newly defined CP-response, learned that besides typical well-known properties of CPPs, i.e. positive charge and amphipathicity, the shape, structure complexity and the 3D-pattern of constituting atoms influence the cellular uptake capacity of peptides.

3-Substituted prolines: from synthesis to structural applications, from peptides to foldamers

Among the twenty natural proteinogenic amino acids, proline is unique as its secondary amine forms a tertiary amide when incorporated into biopolymers, thus preventing hydrogen bond formation. Despite the lack of hydrogen bonds and thanks to conformational restriction of flexibility linked to the pyrrolidine ring, proline is able to stabilize peptide secondary structures such as β-turns or polyproline helices. These unique conformational properties have aroused a great interest in the development of proline analogues. Among them, proline chimeras are tools combining the proline restriction of flexibility together with the information brought by natural amino acids side chains. This review will focus on the chemical syntheses of 3-substituted proline chimeras of potential use for peptide syntheses and as potential use as tools for SAR studies of biologically active peptides and the development of secondary structure mimetics. Their influence on peptide structure will be briefly described.

The potential role of cell penetrating peptides in the intracellular delivery of proteins for therapy of erythroid related disorders

The erythroid related disorders (ERDs) represent a large group of hematological diseases, which in most cases are attributed either to the deficiency or malfunction of biosynthetic enzymes or oxygen transport proteins. Current treatments for these disorders include histo-compatible erythrocyte transfusions or allogeneic hematopoietic stem cell (HSC) transplantation. Gene therapy delivered via suitable viral vectors or genetically modified HSCs have been under way. Protein Transduction Domain (PTD) technology has allowed the production and intracellular delivery of recombinant therapeutic proteins, bearing Cell Penetrating Peptides (CPPs), into a variety of mammalian cells. Remarkable progress in the field of protein transduction leads to the development of novel protein therapeutics (CPP-mediated PTs) for the treatment of monogenetic and/or metabolic disorders. The “concept” developed in this paper is the intracellular protein delivery made possible via the PTD technology as a novel therapeutic intervention for treatment of ERDs. This can be achieved via four stages including: (i) the production of genetically engineered human CPP-mediated PT of interest, since the corresponding native protein either is missing or is mutated in the erythroid progenitor cell (ErPCs) or mature erythrocytes of patients; (ii) isolation of target cells from the peripheral blood of the selected patients; (iii) ex vivo transduction of cells with the CPP-mediated PT of interest; and (iv) re-administration of the successfully transduced cells back into the same patients.