Donghoon Oh

Enhanced Cellular Uptake of Short Polyarginine Peptides through Fatty Acylation and Cyclization

Many of the reported arginine-rich cell-penetrating peptides (CPPs) for the enhanced delivery of drugs are linear peptides composed of more than seven arginine residues to retain the cell penetration properties. Herein, we synthesized a class of nine polyarginine peptides containing 5 and 6 arginines, namely, R5 and R6. We further explored the effect of acylation with long chain fatty acids (i.e., octanoic acid, dodecanoic acid, and hexadecanoic acid) and cyclization on the cell penetrating properties of the peptides. The fluorescence-labeled acylated cyclic peptide dodecanoyl-[R5] and linear peptide dodecanoyl-(R5) showed approximately 13.7- and 10.2-fold higher cellular uptake than that of control 5,6-carboxyfluorescein, respectively. The mechanism of the peptide internalization into cells was found to be energy-dependent endocytosis. Dodecanoyl-[R5] and dodecanoyl-[R6] enhanced the intracellular uptake of a fluorescence-labeled cell-impermeable negatively charged phosphopeptide (F′-GpYEEI) in human ovarian cancer cells (SK-OV-3) by 3.4-fold and 5.5-fold, respectively, as shown by flow cytometry. The cellular uptake of F′-GpYEEI in the presence of hexadecanoyl-[R5] was 9.3- and 6.0-fold higher than that in the presence of octanoyl-[R5] and dodecanoyl-[R5], respectively. Dodecanoyl-[R5] enhanced the cellular uptake of the phosphopeptide by 1.4–2.5-fold higher than the corresponding linear peptide dodecanoyl-(R5) and those of representative CPPs, such as hepta-arginine (CR7) and TAT peptide. These results showed that a combination of acylation by long chain fatty acids and cyclization on short arginine-containing peptides can improve their cell-penetrating property, possibly through efficient interaction of rigid positively charged R and hydrophobic dodecanoyl moiety with the corresponding residues in the cell membrane phospholipids.

Cyclic peptide-selenium nanoparticles as drug transporters.

A cyclic peptide composed of five tryptophan, four arginine, and one cysteine [W5R4C] was synthesized. The peptide was evaluated for generating cyclic peptide-capped selenium nanoparticles (CP–SeNPs) in situ. A physical mixing of the cyclic peptide with SeO3–2 solution in water generated [W5R4C]–SeNPs via the combination of reducing and capping properties of amino acids in the peptide structure. Transmission electron microscopy (TEM) images showed that [W5R4C]–SeNPs were in the size range of 110–150 nm. Flow cytometry data revealed that a fluorescence-labeled phosphopeptide (F′-PEpYLGLD, where F′ = fluorescein) and an anticancer drug (F′-dasatinib) exhibited approximately 25- and 9-times higher cellular uptake in the presence of [W5R4C]–SeNPs than those of F′-PEpYLGLD and dasatinib alone in human leukemia (CCRF-CEM) cells after 2 h of incubation, respectively. Confocal microscopy also exhibited higher cellular delivery of F′-PEpYLGLD and F′-dasatinib in the presence of [W5R4C]–SeNPs compared to the parent fluorescence-labeled drug alone in human ovarian adenocarcinoma (SK-OV-3) cells after 2 h of incubation at 37 °C. The antiproliferative activities of several anticancer drugs doxorubicin, gemcitabine, clofarabine, etoposide, camptothecin, irinotecan, epirubicin, fludarabine, dasatinib, and paclitaxel were improved in the presence of [W5R4C]–SeNPs (50 μM) by 38%, 49%, 36%, 36%, 31%, 30%, 30%, 28%, 24%, and 17%, respectively, after 48 h incubation in SK-OV-3 cells. The results indicate that CP–SeNPs can be potentially used as nanosized delivery tools for negatively charged biomolecules and anticancer drugs.

Antibacterial activities of amphiphilic cyclic cell-penetrating peptides against multidrug-resistant pathogens.

Multidrug-resistant pathogens have become a major public health concern. There is a great need for the development of novel antibiotics with alternative mechanisms of action for the treatment of life-threatening bacterial infections. Antimicrobial peptides, a major class of antibacterial agents, share amphiphilicity and cationic structural properties with cell-penetrating peptides (CPPs). Herein, several amphiphilic cyclic CPPs and their analogues were synthesized and exhibited potent antibacterial activities against multidrug-resistant pathogens. Among all the peptides, cyclic peptide [R4W4] (1) showed the most potent antibacterial activity against methicillin-resistant Staphylococcus aureus [MRSA, exhibiting a minimal inhibitory concentration (MIC) of 2.67 μg/mL]. Cyclic [R4W4] and the linear counterpart R4W4 exhibited MIC values of 42.8 and 21.7 μg/mL, respectively, against Pseudomonas aeruginosa. In eukaryotic cells, peptide 1 exhibited the expected cell penetrating properties and showed >84% cell viability at a concentration of 15 μM (20.5 μg/mL) in three different human cell lines. Twenty-four hour time-kill studies evaluating [R4W4] with 2 times the MIC in combination with tetracycline demonstrated bactericidal activity at 4 and 8 times the MIC of tetracycline against MRSA (MIC = 0.5 μg/mL) and 2–8 times the MIC against Escherichia coli (MIC = 2 μg/mL). This study suggests that when amphiphilic cyclic CPPs are used in combination with an antibiotic such as tetracycline, they provide significant benefit against multidrug-resistant pathogens when compared with the antibiotic alone.

Self-Assembled Surfactant Cyclic Peptide Nanostructures as Stabilizing Agents

A number of cyclic peptides including [FR]4, [FK]4, [WR]4, [CR]4, [AK]4, and [WK]n (n = 3-5) containing L-amino acids were produced using solid-phase peptide synthesis. We hypothesized that an optimal balance of hydrophobicity and charge could generate self-assembled nanostructures in aqueous solution by intramolecular and/or intermolecular interactions. Among all the designed peptides, [WR]n (n = 3-5) generated self-assembled vesicle-like nanostructures at room temperature as shown by transmission electron microscopy (TEM), scanning electron microscopy (SEM), and/or dynamic light scattering (DLS). This class of peptides represents the first report of surfactant-like cyclic peptides that self-assemble into nanostructures. A plausible mechanistic insight into the self-assembly of [WR]5 was obtained by molecular modeling studies. Modified [WR]5 analogues, such as [WMeR]5, [WR(Me)2]5, [WMeR(Me)2]5, and [WdR]5, exhibited different morphologies to [WR]5 as shown by TEM observations. [WR]5 exhibited a significant stabilizing effect for generated silver nanoparticles and glyceraldehyde-3-phosphate dehydrogenase activity. These studies established a new class of surfactant-like cyclic peptides that self-assembled into nanostructures and could have potential applications for the stabilization of silver nanoparticles and protein biomolecules.

Amphiphilic bicyclic peptides as cellular delivery agents.

Two bicyclic peptides composed of tryptophan and arginine residues were synthesized from monocyclic peptide building blocks and evaluated as cellular delivery agents. [W5G]‐(triazole)‐[KR5] and [W5E]‐(β‐Ala)‐[KR5] containing triazole and β‐alanine linkers improved the cellular delivery of fluorescein (F′)‐labeled phosphopeptide F′‐GpYEEI (F′‐PP) by 7.6‐ and 19.3‐fold, respectively, in human ovarian adenocarcinoma cells. However, parent monocyclic peptide [R5] and monocyclic peptide [WR]4 only enhanced the cellular uptake of the phosphopeptide by only 1.3‐ and 3.7‐fold, respectively. Confocal microscopy showed that the corresponding fluorescein‐labeled bicyclic peptide F′‐[KW4E]‐(β‐Ala)‐[KR5] was localized in the cytosol and nucleus. Studying the cellular uptake of F′‐[KW4E]‐(β‐Ala)‐[KR5] in the presence of endocytosis inhibitors indicated that the clathrin‐ and caveolin‐dependent endocytosis are the main pathways for cellular uptake. The bicyclic peptide was able to improve antiproliferative activity of doxorubicin by 20 %. These data suggest that this bicyclic peptide can be utilized as a new class of cell‐penetrating peptides and cellular delivery tools.

Cationic Cell-Penetrating Peptides Are Potent Furin Inhibitors

Cationic cell-penetrating peptides have been widely used to enhance the intracellular delivery of various types of cargoes, such as drugs and proteins. These reagents are chemically similar to the multi-basic peptides that are known to be potent proprotein convertase inhibitors. Here, we report that both HIV-1 TAT47-57 peptide and the Chariot reagent are micromolar inhibitors of furin activity in vitro. In agreement, HIV-1 TAT47-57 reduced HT1080 cell migration, thought to be mediated by proprotein convertases, by 25%. In addition, cyclic polyarginine peptides containing hydrophobic moieties which have been previously used as transfection reagents also exhibited potent furin inhibition in vitro and also inhibited intracellular convertases. Our finding that cationic cell-penetrating peptides exert potent effects on cellular convertase activity should be taken into account when biological effects are assessed.

Design, Synthesis, Antiviral Activity, and Pre-Formulation Development of Poly-L-Arginine-Fatty Acyl Derivatives of Nucleoside Reverse Transcriptase Inhibitors

GRAPHICAL ABSTRACT The objective of this work was to design conjugates of anti-HIV nucleosides conjugated with fatty acids and cell-penetrating poly-L-arginine (polyArg) peptides. Three conjugates of polyArg cell-penetrating peptides with fatty acyl derivatives of alovudine (FLT), lamivudine (3TC), and emtricitabine (FTC) were synthesized. In general, the compounds exhibited anti-HIV activity against X4 and R5 cell-free virus with EC50 values of 1.5–16.6 μM. FLT-CO-(CH2)12-CO-(Arg)7 exhibited EC50 values of 2.9 μM and 3.1 μM against X4 and R5 cell-free virus, respectively. The FLT conjugate was selected for further preformulation studies by determination of solution state degradation and lipid solubility. The compound was found to be stable in neutral and oxidative conditions and moderately stable in heated conditions.

Amphiphilic Triazolyl Peptides: Synthesis and Evaluation as Nanostructures

A new class of amphiphilic triazolyl peptides was designed and synthesized from peptide-based building blocks containing alkyne and azide functional groups namely linear (W(pG))3, cyclic[W(pG)]3, and Ac-K(N3)R-NH2, where W, R, K, and pG represent tryptophan, arginine, lysine, and propargylglycine residues, respectively. The linear (W(pG))3 and cyclic [W(pG)]3 peptides containing alkyne residues were conjugated with Ac-K(N3)R-NH2 functionalized with azide group through click chemistry in the presence of CuSO4.5H2O, Cu (powder), sodium ascorbate, and N,N-disopropylethylamine in methanol:water to afford amphiphilic triazolyl linear-linear (WG(triazole-KR-NH2))3 and cyclic-linear [WG(triazole-KR-NH2)]3 peptides, respectively. The secondary structures of both peptides were similar to a distorted α-helix as shown by CD spectroscopy. TEM imaging showed that linear-linear (WG(triazole-KR-NH2))3 and cyclic-linear [WG(triazole-KR-NH2)]3 peptides formed nano-sized structures in the size range of 50-100 nm and 50-80 nm, respectively.

Corrigendum: Amphiphilic Bicyclic Peptides as Cellular Delivery Agents

The authors wish to make it known that co-author Dr. Shaban Anwar Darwish was also affiliated with the Organometallic and Organometalloid Chemistry Department, National Research Centre (El Bohouth St. , Dokki, Giza, Egypt). Dr. Darwish was a visiting researcher at the University of Rhode Island but was still affiliated with the National Research Centre in Egypt at that time. D. Oh, S. A. Darwish, A. N. Shirazi, R. K. Tiwari, K. Parang* Amphiphilic Bicyclic Peptides as Cellular Delivery Agents