Click-Free Synthesis of a Multivalent Tricyclic Peptide as a Molecular Transporter.

Sumit Kumar,Dindyal Mandal,Saghar Mozaffari,Shaima Ahmed El-Mowafi,Keykavous Parang,Rakesh Kumar Tiwari

doi:10.3390/pharmaceutics12090842

Abstract

The cellular delivery of cell-impermeable and water-insoluble molecules remains an ongoing challenge to overcome. Previously, we reported amphipathic cyclic peptides c[WR]4 and c[WR]5 consisting of alternate arginine and tryptophan residues as nuclear-targeting molecular transporters. These peptides contain an optimal balance of positive charge and hydrophobicity, which is required for interactions with the phospholipid bilayer to facilitate their application as a drug delivery system. To further optimize them, we synthesized and evaluated a multivalent tricyclic peptide as an efficient molecular transporter. The monomeric cyclic peptide building blocks were synthesized using Fmoc/tBu solid-phase chemistry and cyclization in the solution and conjugated with each other through an amide bond to afford the tricyclic peptide, which demonstrated modest antibacterial activity against methicillin-resistant Staphylococcus aureus (MRSA), Klebsiella pneumoniae, Pseudomonas aeruginosa, and Escherichia coli (E. coli) with a minimum inhibitory concentration (MIC) of 64–128 µg/mL. The tricyclic peptide was found to be nontoxic up to 30 µM in the breast cancer cell lines (MDA-MB-231). The presence of tricyclic peptide enhanced cellular uptakes of fluorescently-labeled phosphopeptide (F’-GpYEEI, 18-fold), anti-HIV drugs (lamivudine (F’-3TC), emtricitabine (F’-FTC), and stavudine (F’-d4T), 1.7–12-fold), and siRNA (3.3-fold) in the MDA-MB-231 cell lines.

Highlights

Multivalency is a pervasive phenomenon that has attracted attention for therapeutic development with the examples of multivalent aptamers, a multivalent effect in glycosidase inhibition, and many more [1,2,3,4]
We discovered that a block of four subsequent tryptophan and positive-charged arginine residues generated amphipathic antibacterial peptide c[R4W4], which demonstrated minimum inhibitory concentration (MIC) of 4 μg/mL against methicillin-resistant Staphylococcus aureus (MRSA) and 16 μg/mL against E. coli [23]
We have previously shown that higher cellular uptake of a phosphopeptide in the presence of bicyclic peptide containing amide linkage c[W5E]-(β-Ala)-c[KR5] than bicyclic peptide (c[W5G]-(triazole)-c[KR5] [22], presumably due to the more flexibility of the linker between two cyclic peptides containing the amide linker for generating a proper conformation for effective interaction with the cell membrane

Summary

Introduction

Multivalency is a pervasive phenomenon that has attracted attention for therapeutic development with the examples of multivalent aptamers, a multivalent effect in glycosidase inhibition, and many more [1,2,3,4]. The multivalency of carefully designed supramolecular peptide ligands was utilized in enhancing binding interaction with β-cyclodextrin (β-CD) to study host–guest relationships [7]. In another approach, multivalency was achieved using self-assembly of a coil/fiber-forming peptide to study the binding interaction with antibody and carbohydrate-binding motifs [8]. Henning et al observed tenfold enhanced binding affinity of the lead peptide by generating multivalent property using dendritic polymer containing polyethylene glycol (PEG) against one of WW binding domains of FBP21 protein, which is important for splicing of pre-mRNA in the nucleus [9]. Multivalency is an important aspect, which needs more exploitation for other applications, such as molecular transporter and drug delivery, especially using peptide-based transporters

Methods

Results

Conclusion