Cysteine and arginine-rich peptides as molecular carriers

A number of linear and cyclic peptides containing alternative arginine and cysteine residues, namely linear (CR)₃, linear (CR)₄, linear (CR)₅, cyclic [CR]₄, and cyclic [CR]₅, were synthesized. The peptides were evaluated for their ability to deliver two molecular cargos, fluorescence-labeled cell-impermeable negatively charged phosphopeptide (F′-GpYEEI) and fluorescence-labeled lamivudine (F′-3TC), intracellularly in human leukemia cancer (CCRF-CEM) cells. We investigated the role of cyclization and the number of amino acids in improving the transporting ability of the peptides. The flow cytometry studies suggested that the synthesized peptides were able to work efficiently as transporters for both cargos. Among all compounds, cyclic [CR]₄ was found to be the most efficient peptide in transporting the cargo into cells. For instance, the cellular uptake of F′-3TC (5 μM) and F′-GpYEEI (5 μM) was enhanced by 16- and 20-fold, respectively, in the presence of cyclic [CR]₄ compared to that of the parent compound alone. The mechanism of F′-GpYEEI uptake by cells was found to be energy-independent. The results showed that the number of amino acids and their cyclic nature can impact the efficiency of the peptide in transporting the molecular cargos.