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

Abstract

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.

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

“…The combination of [DipR] 5 ( Figure 4 and Figure S3, Tables S3 and S5, Supporting Information ) with GFP (50 nM to 500 nM) after 3 h in MDA-MB-231 cells showed cell viability of more than 81%. Based on these findings and previous data about the cytotoxicity of other peptides [ 38 , 39 , 45 , 46 , 47 , 48 , 49 ] used in this study, cellular uptake experiments were conducted with peptides and protein models (GFP and RFP) concentrations not higher than 10 µM and 50 nM, respectively, and 3 h of incubation.…”

“…Cytotoxicity of the peptides has been previously reported by us [ 38 , 39 , 45 , 46 , 47 , 48 , 49 ]. For example, [(RW) 5 K](RW) 5 did not exhibit any significant cytotoxicity in different cell lines, such as human epithelial mammary gland adenocarcinoma cells (MDA-MB-231), human leukemia carcinoma cell line (CCRF-CEM), human ovarian adenocarcinoma cells (SK-OV-3), and human epithelial embryonic kidney healthy (HEK-293) at the concentration of 10 μM after 3 h of incubation [ 46 ].…”

“…Peptides were synthesized as described previously by us [ 38 , 39 , 45 , 46 , 47 , 48 , 49 ]. Fmoc solid-phase peptide synthesis followed by solution-phase cyclization was utilized to synthesize cyclic peptides [ 39 ].…”

“…Similar studies were conducted with GFP (50 nM) and other peptides, [WR] 4 , [WWRR] 4 , [WWRR] 5 , [(RW) 5 K](RW) 5 , [R 5 K]W 7 , and [DipR] 5 in MD-MB-231 and/or SK-OV-3 cells. Peptide concentrations ranged from 1 to 10 µM, depending on the previous cytotoxicity studies of the peptides [ 34 , 35 , 41 , 42 , 43 , 44 , 45 ] and the results described above.…”

“…In fact, many studies have reported multiple efficient CPPs for macromolecule delivery, sharing the feature of the presence of arginine in the sequence [ 40 , 41 , 42 , 43 , 44 ]. In addition to [WR] 4 [ 37 ], [WR] 5 [ 38 ], and [WR] 9 [ 39 ], we have also reported a number of cyclic peptides and hybrid cyclic–linear peptides, [WWRR] 4 and [WWRR] 5 [ 45 ], [(RW) 5 K](RW) 5 [ 46 ], [R 5 K]W 7 [ 47 , 48 ], and [DipR] 5 [ 49 ] ( Figure 1 ) as molecular transporters of phosphopeptides, nucleic acids, or small molecules.…”