The current role of cell-penetrating peptides (CPPs) in cancer therapy

Cell-penetrating peptides (CPPs) are an inhomogenic class of peptides with the ability to translocate in cells and to carry attached cargos with them inside. Owing to this striking ability the further development and application of CPP-based delivery strategies have steadily emerged during the past years. The following review aims to summarize some of these recent concepts and to higlight the current role of CPPs in cancer therapy

Kiss and Run: Promoting Effective and Targeted Cellular Uptake of a Drug Delivery Vehicle Composed of an Integrin-Targeting Diketopiperazine Peptidomimetic and a Cell-Penetrating Peptide

Cell-penetrating peptides (CPPs) have emerged as powerful tools in terms of drug delivery. Those short, often cationic peptides are characterized by their usually low toxicity and their ability to transport diverse cargos inside almost any kinds of cells. Still, one major drawback is their nonselective uptake making their application in targeted cancer therapies questionable. In this work, we aimed to combine the power of a CPP (sC18) with an integrin-targeting unit (c[DKP-f3-RGD]). The latter is composed of the Arg-Gly-Asp peptide sequence cyclized via a diketopiperazine scaffold and is characterized by its high selectivity toward integrin \u3b1v\u3b23. The two parts were linked via copper-catalyzed alkyne-azide click reaction (CuAAC), while the CPP was additionally functionalized with either a fluorescent dye or the anticancer drug daunorubicin. Both functionalities allowed a careful biological evaluation of these novel peptide-conjugates regarding their cellular uptake mechanism, as well as cytotoxicity in \u3b1v\u3b23 integrin receptor expressing cells versus cells that do not express \u3b1v\u3b23. Our results show that the uptake follows a "kiss-and-run"-like model, in which the conjugates first target and recognize the receptor, but translocate mainly by CPP mediation. Thereby, we observed significantly more pronounced toxic effects in \u3b1v\u3b23 expressing U87 cells compared to HT-29 and MCF-7 cells, when the cells were exposed to the substances with only very short contact times (15 min). All in all, we present new concepts for the design of cancer selective peptide-drug conjugates

Synthetic α-Helical Peptides as Potential Inhibitors of the ACE2 SARS-CoV-2 Interaction

During viral cell entry, the spike protein of SARS-CoV-2 binds to the α1-helix motif of human angiotensin-converting enzyme 2 (ACE2). Thus, alpha-helical peptides mimicking this motif may serve as inhibitors of viral cell entry. For this purpose, we employed the rigidified diproline-derived module ProM-5 to induce α-helicity in short peptide sequences inspired by the ACE2 α1-helix. Starting with Ac-QAKTFLDKFNHEAEDLFYQ-NH2 as a relevant section of α1, a series of peptides, N-capped with either Ac-βHAsp-[ProM-5] or Ac-βHAsp-PP, were prepared and their α-helicities were investigated. While ProM-5 clearly showed a pronounced effect, an even increased degree of helicity (up to 63 %) was observed in sequences in which non-binding amino acids were replaced by alanine. The binding affinities of the peptides towards the spike protein, as determined by means of microscale thermophoresis (MST), revealed only a subtle influence of the α-helical content and, noteworthy, led to the identification of an Ac-βHAsp-PP-capped peptide displaying a very strong binding affinity (KD=62 nM)

Metal Complex-Peptide Conjugates: How to Modulate Bioactivity of Metal-Containing Compounds by the Attachment to Peptides

During the last years, the interest in combining the features of metal-containing molecules with biomolecules, particularly peptides, has been increased. Large series of new innovative organometallic compounds, as well as potent coordination complexes have been designed and, especially in medicinal chemistry, the library of bioactive compounds was excessively expanded by the introduction of metal complexes. The research foci are divers and not limited to e.g. the development of therapeutics with anti-proliferative or antibacterial activity, or the design of novel biosensors useful for pharmaceutical applications. By introduction of a metal centre, new attributes might be added that could help to overcome the problems of difficult to treat diseases, as well as to combat issues with arising drug resistances. However, the application of a number of very potent metal complexes is restricted owing to their poor water-solubility, air-stability and only poor uptake when in contact with cells. In this context, one possibility to optimize promising lead structures is to couple them to bioactive peptides. Within this review, an overview on metal complex-peptide conjugates used for drug design and future pharmaceutical application is presented

Design of a novel cell-permeable chimeric peptide to promote wound healing

Abstract Biological membranes are impermeable to almost all compounds having a molecular weight greater than 500 Da. Recently, cell penetrating peptides (CPPs) as delivery vehicles have attracted great interest in the medical sector for the development of novel therapeutic agents or cosmetic products. Herein, a wound healing promoting sequence, namely Tylotoin, was covalently coupled with a cell penetrating peptide to improve the delivery of Tylotoin across cellular membranes. Indeed, internalization studies indicated that the cellular uptake of these novel peptide conjugates into keratinocytes was significantly improved accompanied by good tolerability. In a scratch wound closure assay used to investigate the wound healing capability, the most promising novel peptide chimera (Tylotoin-sC18*) was found to promote the migration of keratinocytes indicating that the fusion to Tylotoin did not cause any loss in its activity. Even more, proliferative effects on keratinocytes were observed, an important step during the wound healing process. Still more encouraging is the capability of Tylotoin-sC18* to exhibit strong antimicrobial activities since the process of wound healing is often affected by bacterial infections. Owing to their multiple functions, the novel peptide chimera may have potential as future agents for the treatment of infected wounds

Nanoparticles Modified with Cell-Penetrating Peptides: Conjugation Mechanisms, Physicochemical Properties, and Application in Cancer Diagnosis and Therapy

Based on their tunable physicochemical properties and the possibility of producing cell-specific platforms through surface modification with functional biomolecules, nanoparticles (NPs) represent highly promising tools for biomedical applications. To improve their potential under physiological conditions and to enhance their cellular uptake, combinations with cell-penetrating peptides (CPPs) represent a valuable strategy. CPPs are often cationic peptide sequences that are able to translocate across biological membranes and to carry attached cargos inside cells and have thus been recognized as versatile tools for drug delivery. Nevertheless, the conjugation of CPP to NP surfaces is dependent on many properties from both individual components, and further insight into this complex interplay is needed to allow for the fabrication of highly stable but functional vectors. Since CPPs per se are nonselective and enter nearly all cells likewise, additional decoration of NPs with homing devices, such as tumor-homing peptides, enables the design of multifunctional platforms for the targeted delivery of chemotherapeutic drugs. In this review, we have updated the recent advances in the field of CPP-NPs, focusing on synthesis strategies, elucidating the influence of different physicochemical properties, as well as their application in cancer research

Bifunctional peptide hybrids targeting the matrix of mitochondria

The mitochondrial organelle is associated with many diseases, including diabetes, age-related neuro-degenerative diseases and cancer. Therefore, the effective delivery of drug molecules to mitochondria became increasingly important during the past years. Within this work, we designed and analyzed bifunctional hybrid peptides comprised of a mitochondrial targeting sequence (MTS) attached to a cell-penetrating peptide (CPP). Our results demonstrate that choice of the MTS must be carefully undertaken, since not every MTS that was selected was comparably capable to target mitochondria. In addition, we highlight the use of the CPP sC18 as necessary part of the hybrid construct, inducing not only cellular uptake, but likewise supporting sub-organelle uptake into the mitochondrial matrix. The herein designed cell-permeable mitochondrial targeting peptide was furthermore proven to enhance the intracellular uptake of the cytostatic drug chlorambucil, making it a powerful candidate for further studies in this important field

Design and Application of Antimicrobial Peptide Conjugates

Antimicrobial peptides (AMPs) are an interesting class of antibiotics characterized by their unique antibiotic activity and lower propensity for developing resistance compared to common antibiotics. They belong to the class of membrane-active peptides and usually act selectively against bacteria, fungi and protozoans. AMPs, but also peptide conjugates containing AMPs, have come more and more into the focus of research during the last few years. Within this article, recent work on AMP conjugates is reviewed. Different aspects will be highlighted as a combination of AMPs with antibiotics or organometallic compounds aiming to increase antibacterial activity or target selectivity, conjugation with photosensitizers for improving photodynamic therapy (PDT) or the attachment to particles, to name only a few. Owing to the enormous resonance of antimicrobial conjugates in the literature so far, this research topic seems to be very attractive to different scientific fields, like medicine, biology, biochemistry or chemistry

Application of Antimicrobial Peptides on Biomedical Implants: Three Ways to Pursue Peptide Coatings

Biofilm formation and inflammations are number one reasons of implant failure and cause a severe number of postoperative complications every year. To functionalize implant surfaces with antibiotic agents provides perspectives to minimize and/or prevent bacterial adhesion and proliferation. In recent years, antimicrobial peptides (AMP) have been evolved as promising alternatives to commonly used antibiotics, and have been seen as potent candidates for antimicrobial surface coatings. This review aims to summarize recent developments in this field and to highlight examples of the most common techniques used for preparing such AMP-based medical devices. We will report on three different ways to pursue peptide coatings, using either binding sequences (primary approach), linker layers (secondary approach), or loading in matrixes which offer a defined release (tertiary approach). All of them will be discussed in the light of current research in this area

Direct carborane-peptide conjugates: Synthesis and evaluation as non natural lipopeptide mimetics

Herein, we report the synthesis and characterization of direct carborane-peptide conjugates. Carboranes are non natural and extremely hydrophobic compounds and turned out to be suitable pharmacophores for diverse biological applications. In this work, we established an efficient procedure for the coupling of carboranes to peptides on solid support. We identified the coupling of carborane-l-carboxylic acids to amino groups to be superior to those with hydroxy-or sulfhydryl-groups. The carborane-peptide conjugates showed remarkably prolonged, and carborane isomer dependent chromatographic retention times. This effect can be used to generate non-natural lipopeptides with fine-tuned properties