Cyclic Peptide Containing Hydrophobic and Positively Charged Residues as a Drug Delivery System for Curcumin.

Due to the low water solubility and hydrophobic nature of curcumin, an efficient cellular uptake is critical for its biological activity. We have previously developed a number of homochiral L-cyclic peptides containing arginine and tryptophan as cell-penetrating peptides. Among the synthesized peptides, [WR]5 containing five arginine and five tryptophan residues was found to be the most efficient one. Here, we have compared the application of [WR]5 to improve the intracellular uptake of curcumin by using both peptide-curcumin conjugate and physical mixture (peptide + curcumin) strategies. Flow cytometry results showed that the intracellular uptake of curcumin (50 μM) was enhanced through the physical mixing with [WR]5 by 5.7 folds compared to that of curcumin alone in human leukemia (CCRFCEM) cells after 3 h. When [WR]5 was conjugated with curcumin, the intracellular uptake was enhanced by 4 fold. These data suggest that the physical mixture can work more efficiently in enhancing the cellular delivery of curcumin. Furthermore, the antiproliferative activity of curcumin was enhanced by 20% and ∼13% through the physical mixture and the conjugate, respectively, in CCRF-CEM cells after 72 h.