Cell-Penetrating Peptides: a Useful Tool for the Delivery of Various Cargoes Into Cells

Site-Selective Functionalization of Methionine Residues via Photoredox Catalysis

Bioconjugation technologies have revolutionized the practice of biology and medicine by allowing access to novel biomolecular scaffolds. New methods for residue-selective bioconjugation are highly sought to expand the toolbox for a variety of bioconjugation applications. Herein we report a site-selective methionine bioconjugation protocol that uses photoexcited lumiflavin to generate open-shell intermediates. This reduction-potential-gated strategy enables access to residues unavailable with traditional nucleophilicity-based conjugation methods. To demonstrate the versatility and robustness of this new protocol, we have modified various proteins and further utilized this functional handle to append diverse biological payloads.

Mitochondria-Targeted Antioxidants: A Step towards Disease Treatment

Mitochondria are the main organelles that produce adenosine 5′-triphosphate (ATP) and reactive oxygen species (ROS) in eukaryotic cells and meanwhile susceptible to oxidative damage. The irreversible oxidative damage in mitochondria has been implicated in various human diseases. Increasing evidence indicates the therapeutic potential of mitochondria-targeted antioxidants (MTAs) for oxidative damage-associated diseases. In this article, we introduce the advantageous properties of MTAs compared with the conventional (nontargeted) ones, review different mitochondria-targeted delivery systems and antioxidants, and summarize their experimental results for various disease treatments in different animal models and clinical trials. The combined evidence demonstrates that mitochondrial redox homeostasis is a potential target for disease treatment. Meanwhile, the limitations and prospects for exploiting MTAs are discussed, which might pave ways for further trial design and drug development.

Transcriptional Profiling Reveals Ribosome Biogenesis, Microtubule Dynamics and Expression of Specific lncRNAs to be Part of a Common Response to Cell-Penetrating Peptides

Cell-penetrating peptides (CPPs) are short peptides that are able to efficiently penetrate cellular lipid bilayers. Although CPPs have been used as carriers in conjugation with certain cargos to target specific genes and pathways, how rationally designed CPPs per se affect global gene expression has not been investigated. Therefore, following time course treatments with 4 CPPs-penetratin, PepFect14, mtCPP1 and TP10, HeLa cells were transcriptionally profiled by RNA sequencing. Results from these analyses showed a time-dependent response to different CPPs, with specific sets of genes related to ribosome biogenesis, microtubule dynamics and long-noncoding RNAs being differentially expressed compared to untreated controls. By using an image-based high content phenotypic profiling platform we confirmed that differential gene expression in CPP-treated HeLa cells strongly correlates with changes in cellular phenotypes such as increased nucleolar size and dispersed microtubules, compatible with altered ribosome biogenesis and cell growth. Altogether these results suggest that cells respond to different cell penetrating peptides by alteration of specific sets of genes, which are possibly part of the common response to such stimulus.

The world of cell penetrating: the future of medical applications

Cell-penetrating peptides present huge biomedical applications in a variety of pathologies, thanks to their ability to penetrate membranes and carry a variety of cargoes inside cells. Progress in peptide synthesis has produced a greater availability of virtually any synthetic peptide, increasing their attractiveness. Most molecules when associated to a cell-penetrating peptides can be delivered into a cell, however, understanding of the critical factors influencing the uptake mechanism is of paramount importance to construct nanoplatforms for effective delivery in vitro and in vivo in medical applications. Focus is now on the state-of-art of the mechanisms enabling therapeutics/diagnostics to reach the site target of their activities, and in support of scientists developing platforms for drug delivery and personalized therapies.

Immune cells as tumor drug delivery vehicles

This review article describes the use of immune cells as potential candidates to deliver anti-cancer drugs deep within the tumor microenvironment. First, the rationale of using drug carriers to target tumors and potentially decrease drug-related side effects is discussed. We further explain some of the current limitations when using nanoparticles for this purpose. Next, a comprehensive step-by-step description of the migration cascade of immune cells is provided as well as arguments on why immune cells can be used to address some of the limitations associated with nanoparticle-mediated drug delivery. We then describe the benefits and drawbacks of using red blood cells, platelets, granulocytes, monocytes, macrophages, myeloid-derived suppressor cells, T cells and NK cells for tumor-targeted drug delivery. An additional section discusses the versatility of nanoparticles to load anti-cancer drugs into immune cells. Lastly, we propose increasing the circulatory half-life and development of conditional release strategies as the two main future pillars to improve the efficacy of immune cell-mediated drug delivery to tumors.

Anticancer peptide: Physicochemical property, functional aspect and trend in clinical application (Review)

Cancer is currently ineffectively treated using therapeutic drugs, and is also able to resist drug action, resulting in increased side effects following drug treatment. A novel therapeutic strategy against cancer cells is the use of anticancer peptides (ACPs). The physicochemical properties, amino acid composition and the addition of chemical groups on the ACP sequence influences their conformation, net charge and orientation of the secondary structure, leading to an effect on targeting specificity and ACP-cell interaction, as well as peptide penetrating capability, stability and efficacy. ACPs have been developed from both naturally occurring and modified peptides by substituting neutral or anionic amino acid residues with cationic amino acid residues, or by adding a chemical group. The modified peptides lead to an increase in the effectiveness of cancer therapy. Due to this effectiveness, ACPs have recently been improved to form drugs and vaccines, which have sequentially been evaluated in various phases of clinical trials. The development of the ACPs remains focused on generating newly modified ACPs for clinical application in order to decrease the incidence of new cancer cases and decrease the mortality rate. The present review could further facilitate the design of ACPs and increase efficacious ACP therapy in the near future.

Efficient Delivery of Antisense Oligonucleotides by an Amphipathic Cell-Penetrating Peptide in Acinetobacter baumannii

BACKGROUND

Carbapenem-resistant Acinetobacter baumannii (A. baumannii) was on the top of the list of the most threatening bacteria published by the WHO in 2017. Antisense oligonucleotides (ASOs) based therapy is a promising strategy for combating Multi-Drug Resistant (MDR) bacteria because of its high specificity, easy design and lower induction of resistance, but poor cellular uptake by bacteria has restricted the further utilization of this therapy.

METHODS

Here, we used CADY, a secondary amphipathic peptide of 20 residues that could successfully carry siRNA into mammalian cells, to prepare CADY/ASOs nanoparticles (CADY-NPs) targeting acpP (encoding acyl carrier protein), and evaluated the uptake features, the inhibitory effects of CADY-NPs on gene expression and the growth of MDR-A. baumannii.

RESULTS

We found that CADY-NPs could be quickly internalized by drug-sensitive and MDR-A. baumannii in an energy independent manner, which could be restrained by chlorpromazine (an inhibitor of clathrin mediated endocytosis) significantly. In addition, CADY-NPs targeting acpP concentrationdependently retarded the growth of MDR-A. baumannii, which was associated with the decreased expression of targeted genes in A. baumannii.

CONCLUSION

In conclusion, our research is the first to demonstrate that CADY can deliver ASOs into bacteria and provide a novel strategy for the treatment of MDR-A. baumannii.

Effect of TAT-DOX-PEG irradiated gold nanoparticles conjugates on human osteosarcoma cells

The paper aims to investigate the cytotoxic effect on tumor cells of irradiated AuNPs in green light and subsequently functionalized with HS-PEG-NH2. The toxicity level of gold conjugates after their functionalization with DOX and TAT peptide was also evaluated. The AuNPs were prepared using the modified Turkevich method and exposed to visible light at a wavelength of 520 nm prior their PEGylation. The optical properties were analyzed by UV-vis spectroscopy, the surface modification was investigated using FTIR and XPS spectroscopies and their sizes and morphologies were evaluated by TEM and DLS techniques. DOX and TAT peptide were linked to the surface of PEGylated AuNPs by reacting their amino groups with glycidyloxypropyl of PEGylated DOX or TAT conjugates under mild conditions at room temperature and in the presence of ethanol as catalyst. The conjugates containing DOX or DOX and TAT have been characterized by fluorescence and FTIR techniques. The changes of electrochemical features were observed using cyclic voltammetry, suggesting a better stability of irradiated nanoparticles. By mass spectrometry it was confirmed that the compounds of interest were obtained. The cell viability test showed that irradiated and non-irradiated nanoparticles coated with PEG are not toxic in normal cells. Tumor cell viability analysis showed that the PEGylated nanoparticles modified with DOX and TAT peptide were more effective than pristine DOX, indicating cytotoxicity up to 10% higher than non-irradiated ones.

Cell Penetrating Peptide: Sequence-Based Computational Prediction for Intercellular Delivery of Arginine Deiminase

Background:

Cell-Penetrating Peptides (CPPs), a family of short peptides, are broadly used as the carrier in the delivery of drugs and different therapeutic agents. Thanks to the existence of valuable databases, computational screening of the experimentally validated CPPs can help the researchers to select more effective CPPs for the intercellular delivery of therapeutic proteins. Arginine deiminase of Mycoplasma hominis, an arginine-degrading enzyme, is currently in the clinical trial for treating several arginine auxotrophic cancers. However, some tumor cells have developed resistance to ADI treatment. The ADI resistance arises from the over-expression of argininosuccinate synthetase 1 enzyme, which is involved in arginine synthesis. Intracellular delivery of ADI into tumor cells is suggested as an efficient approach to overcome the aforesaid drawback.

Objective:

In this study, in-silico tools were used for evaluating the experimentally validated CPPs to select the best CPP candidates for the intracellular delivery of ADI.

Results:

In this regard, 150 CPPs of protein cargo available at CPPsite were retrieved and evaluated by the CellPPD server. The best CPP candidates for the intracellular delivery of ADI were selected based on stability and antigenicity of the ADI-CPP fusion form. The conjugated forms of ADI with each of the three CPPs including EGFP-hcT (9-32), EGFP-ppTG20, and F(SG)4TP10 were stable and nonantigenic; thus, these sequences were introduced as the best CPP candidates for the intracellular delivery of ADI. In addition, the proposed CPPs had appropriate positive charge and lengths for an efficient cellular uptake.

Conclusion:

These three introduced CPPs not only are appropriate for the intracellular delivery of ADI, but also can overcome the limitation of its therapeutic application, including short half-life and antigenicity.

Coupling the Antimalarial Cell Penetrating Peptide TP10 to Classical Antimalarial Drugs Primaquine and Chloroquine Produces Strongly Hemolytic Conjugates

Recently, we disclosed primaquine cell penetrating peptide conjugates that were more potent than parent primaquine against liver stage Plasmodium parasites and non-toxic to hepatocytes. The same strategy was now applied to the blood-stage antimalarial chloroquine, using a wide set of peptides, including TP10, a cell penetrating peptide with intrinsic antiplasmodial activity. Chloroquine-TP10 conjugates displaying higher antiplasmodial activity than the parent TP10 peptide were identified, at the cost of an increased hemolytic activity, which was further confirmed for their primaquine analogues. Fluorescence microscopy and flow cytometry suggest that these drug-peptide conjugates strongly bind, and likely destroy, erythrocyte membranes. Taken together, the results herein reported put forward that coupling antimalarial aminoquinolines to cell penetrating peptides delivers hemolytic conjugates. Hence, despite their widely reported advantages as carriers for many different types of cargo, from small drugs to biomacromolecules, cell penetrating peptides seem unsuitable for safe intracellular delivery of antimalarial aminoquinolines due to hemolysis issues. This highlights the relevance of paying attention to hemolytic effects of cell penetrating peptide-drug conjugates.