Amphiphilic Cell-Penetrating Peptides Containing Natural and Unnatural Amino Acids as Drug Delivery Agents

Cancer-Targeting Applications of Cell-Penetrating Peptides

Cell-penetrating peptides (CPPs) offer a unique and efficient mechanism for delivering therapeutic agents directly into cancer cells. These peptides can traverse cellular membranes, overcoming one of the critical barriers in drug delivery systems. In this review, we explore recent advancements in the application of CPPs for cancer treatment, focusing on mechanisms, delivery strategies, and clinical potential. The review highlights the use of CPP-drug conjugates, CPP-based vaccines, and their role in targeting and inhibiting tumor growth.

Beyond chloroquine: Cationic amphiphilic drugs as endosomal escape enhancers for nucleic acid therapeutics

Nucleic acid (NA) therapeutics have the potential to treat or prevent a myriad of diseases but generally require cytosolic delivery to be functional. NA drugs are therefore often encapsulated into delivery systems that mediate effective endocytic uptake by target cells, but unfortunately often display limited endosomal escape efficiency. This review will focus on the potential of repurposing cationic amphiphilic drugs (CADs) to enhance endosomal escape. In general terms, CADs are small molecules with one or more hydrophobic groups and a polar domain containing a basic amine. CADs have been reported to accumulate in acidified intracellular compartments (e.g., endosomes and lysosomes), integrate in cellular membranes and alter endosomal trafficking pathways, ultimately resulting in improved cytosolic release of the endocytosed cargo. As many CADs are widely used drugs, their repurposing offers opportunities for combination therapies with NAs.

Novel Angiotensin-Converting Enzyme-Inhibitory Peptides Obtained from Trichiurus lepturus: Preparation, Identification and Potential Antihypertensive Mechanism

Peptides possessing antihypertensive attributes via inhibiting the angiotensin-converting enzyme (ACE) were derived through the enzymatic degradation of Trichiurus lepturus (ribbonfish) using alkaline protease. The resulting mixture underwent filtration using centrifugation, ultrafiltration tubes, and Sephadex G-25 gels. Peptides exhibiting ACE-inhibitory properties and DPPH free-radical-scavenging abilities were isolated and subsequently purified via LC/MS-MS, leading to the identification of over 100 peptide components. In silico screening yielded five ACE inhibitory peptides: FAGDDAPR, QGPIGPR, IFPRNPP, AGFAGDDAPR, and GPTGPAGPR. Among these, IFPRNPP and AGFAGDDAPR were found to be allergenic, while FAGDDAPRR, QGPIGPR, and GPTGPAGP showed good ACE-inhibitory effects. IC50 values for the latter peptides were obtained from HUVEC cells: FAGDDAPRR (IC50 = 262.98 μM), QGPIGPR (IC50 = 81.09 μM), and GPTGPAGP (IC50 = 168.11 μM). Peptide constituents derived from ribbonfish proteins effectively modulated ACE activity, thus underscoring their therapeutic potential. Molecular docking and modeling corroborated these findings, emphasizing the utility of functional foods as a promising avenue for the treatment and prevention of hypertension, with potential ancillary health benefits and applications as substitutes for synthetic drugs.

Hydrophobicity: The door to drug delivery

The engineering of intracellular delivery systems with the goal of achieving personalized medicine has been encouraged by advances in nanomaterial science as well as a greater understanding of diseases and of the biochemical pathways implicated in many disorders. The development of vectors able to transport the drug to a target location and release it only on demand is undoubtedly the primary issue. From a molecular perspective, the topography of drug carrier surfaces is directly related to the design of an effective drug carrier because it provides a physical hint to modifying its interactions with biological systems. For instance, the initial ratio of hydrophilic to hydrophobic surfaces and the changes brought about by external factors enable the release or encapsulation of a therapeutic molecule and the ability of the nanosystem to cross biological barriers and reach its target without causing systemic toxicity. The first step in creating new materials with enhanced functionality is to comprehend and characterize the interplay between hydrophilic and hydrophobic molecules at the molecular level. Therefore, the focus of this review is on the function of hydrophobicity, which is essential for matching the complexity of biological environments with the intended functionality.

Peptide nanostructures-based delivery of DNA nanomaterial therapeutics for regulating gene expression

Self-assembled branched DNA (bDNA) nanomaterials have exhibited their functionality in various biomedical and diagnostic applications. However, the anionic cellular membrane has restricted the movement of bDNA nanostructures. Recently, amphiphilic peptides have been investigated as cationic delivery agents for nucleic acids. Herein, we demonstrate a strategy for delivering functional bDNA nanomaterials into mammalian cells using self-assembled linear peptides. In this study, antisense oligonucleotides of vascular endothelial growth factor (VEGF) were inserted in the overhangs of bDNAs. Novel linear peptides have been synthesized and the peptide-bound bDNA complex formation was examined using various biophysical experiments. Interestingly, the W4R4-bound bDNAs were found to be exceptionally stable against DNase I compared to other complexes. The delivery of fluorescent-labeled bDNAs into the mammalian cells confirmed the potential of peptide transporters. Furthermore, the functional efficacy of the peptide-bound bDNAs has been examined through RT-PCR and western blot analysis. The observed results revealed that W4R4 peptides exhibited excellent internalization of antisense bDNAs and significantly suppressed (3- to 4-fold) the transcripts and translated product of VEGF compared to the control. In summary, the results highlight the potential use of peptide-based nanocarrier for delivering bDNA nanostructures to regulate the gene expression in cell lines.

Amphiphilic Cell-Penetrating Peptides Containing Arginine and Hydrophobic Residues as Protein Delivery Agents

The entry of proteins through the cell membrane is challenging, thus limiting their use as potential therapeutics. Seven cell-penetrating peptides, designed in our laboratory, were evaluated for the delivery of proteins. Fmoc solid-phase peptide synthesis was utilized for the synthesis of seven cyclic or hybrid cyclic-linear amphiphilic peptides composed of hydrophobic (tryptophan (W) or 3,3-diphenylalanine (Dip) and positively-charged arginine (R) residues, such as [WR]₄, [WR]₉, [WWRR]₄, [WWRR]₅, [(RW)₅K](RW)₅, [R₅K]W₇, and [DipR]₅. Confocal microscopy was used to screen the peptides as a protein delivery system of model cargo proteins, green and red fluorescein proteins (GFP and RFP). Based on the confocal microscopy results, [WR]₉ and [DipR]₅ were found to be more efficient among all the peptides and were selected for further studies. [WR]₉ (1-10 µM) + protein (GFP and RFP) physical mixture did not show high cytotoxicity (>90% viability) in triple-negative breast cancer cells (MDA-MB-231) after 24 h, while [DipR]₅ (1-10 µM) physical mixture with GFP exhibited more than 81% cell viability. Confocal microscopy images revealed internalization of GFP and RFP in MDA-MB-231 cells using [WR]₉ (2-10 μM) and [DipR]₅ (1-10 µM). Fluorescence-activated cell sorting (FACS) analysis indicated that the cellular uptake of GFP was concentration-dependent in the presence of [WR]₉ in MDA-MB-231 cells after 3 h of incubation at 37 °C. The concentration-dependent uptake of GFP and RFP was also observed in the presence of [DipR₅] in SK-OV-3 and MDA-MB-231 cells after 3 h of incubation at 37 °C. FACS analysis indicated that the cellular uptake of GFP in the presence of [WR]₉ was partially decreased by methyl-β-cyclodextrin and nystatin as endocytosis inhibitors after 3 h of incubation in MDA-MB-231 cells, whereas nystatin and chlorpromazine as endocytosis inhibitors slightly reduced the uptake of GFP in the presence of [DipR]₅ after 3 h of incubation in MDA-MB-231. [WR]₉ was able to deliver therapeutically relevant proteins (Histone H2A) at different concentrations. These results provide insight into the use of amphiphilic cyclic peptides in the delivery of protein-related therapeutics.

Cyclic and Linear Peptides Containing Alternate WW and RR Residues as Molecular Cargo Delivery Tools

Cell-impermeable and negatively charged compounds' cellular uptake across the cell membranes remains challenging. Herein, the synthesis of four linear [(WWRR)₂, (WWRR)₃, (WWRR)₄, and (WWRR)₅] and four cyclic ([WWRR]₂, [WWRR]₃, [WWRR]₄, and [WWRR]₅) peptides containing alternate two tryptophan (WW) and two arginine (RR) residues and their biological evaluation as molecular transporters are reported. The peptides did not show any significant cytotoxicity in different cell lines (MDA-MB-23, SK-OV-3, and HEK 293) at a concentration of 5 μM and after 3 h of incubation time. The uptake of fluorescence-labeled cargo molecules (F'-GpYEEI, F'-siRNA, and F'-3TC) in the presence of the peptides was monitored in different cell lines (SK-OV-3 and MDA-MB-231) with fluorescence-activated cell sorting. Among all the peptides, [WWRR]₅ (C4) showed the highest cellular uptake of cargo molecules, indicating it can act as effective molecular transporter. Confocal microscopy in MDA-MB-231 cells showed the cellular uptake of F'-GpYEEI in the presence of C4 and the intracellular localization of fluorescence-labeled C4 (F'-C4) in the cytosol. The F'-C4 cellular uptake was found to be concentration- and time-dependent, as shown by flow cytometry in MDA-MB-231 cells. Confocal microscopy and flow cytometry of F'-C4 in MDA-MB-231 cells were examined alone and in the presence of different endocytosis inhibitors (chlorpromazine, methyl-β-cyclodextrin, chloroquine, and nystatin). The data showed that the cellular uptake of F'-C4 in the presence of chlorpromazine, chloroquine, and methyl-β-cyclodextrin was reduced but not completely eliminated, indicating that both energy-independent and energy-dependent pathways contributed to the cellular uptake of F'-C4. Similar results were obtained using the confocal microscopy of C4 and F'-GpYEEI in the presence of endocytosis inhibitors (chlorpromazine, methyl-β-cyclodextrin, chloroquine, and nystatin). These data indicate that C4 has the potential to be used as a cell-penetrating peptide and cargo transporter.

A new amino acid, hybrid peptides and BODIPY analogs: synthesis and evaluation of 2-aminotroponyl-L-alanine (ATA) derivatives

Natural aromatic α-amino acid residues play critical roles in the structural and functional organization of proteins owing to π-interactions. Their aromatic residues are derived from benzenoid scaffolds. Non-benzenoid aromatic scaffolds such as tropone and tropolone are also constituents of troponoid natural products. Tropolone has also the ability to exhibit π-interactions along with additional hydrogen bonding. Thus, amino acids comprising troponyl could be potential building blocks of novel peptidomimetics. This report describes the synthesis of the L-aminotroponylalanine amino acid (ATA) and its unusual activity with the peptide coupling agent EDC. Importantly, its di-peptides form β-sheet/-turn type secondary structures in organic solvents owing to the troponyl residue. This amino acid is an excellent scaffold for the synthesis of fluorescent amino acids such as BODIPY amino acid analogs. Nevertheless, this amino acid and its BODIPY derivatives can enter HeLa cells without exhibiting significant cytotoxicity at low concentrations (∼50 μM). Hence, ATA and its BODIPY derivatives are promising aromatic amino acids for the construction of potential peptidomimetics and fluorescent labelling of target peptides.