Hypericin Delivery System Based on P84 Copolymeric Micelles Linked with N‑(3-Aminopropyl)-2-pyrrolidone for Melanoma-Targeted Photodynamic Therapy

A hypericin (HYP) delivery system was developed on the basis of P84 copolymeric micelles linked covalently with N-(3-aminopropyl)-2-pyrrolidone (APP). The higher monomeric amounts of HYP when loaded in different proportions of P84 and P84-APP micelles were predicted by using a chemometric experimental design. Dynamic light scattering (DLS), ζ potential, loading efficiency, and transmission electron microscopy (TEM) were performed for characterizations of the copolymeric micelles. The particle size and low negative ζ potential showed that APP conjugation provides high levels of stability in the aqueous medium of P84 micelles. ¹H¹H-NOESY spectroscopy and theoretical calculations were applied to provide accurate insight on the preferential interaction sites of HYP-loaded P84 and P84-APP copolymeric micelles. The findings showed that HYP molecules were preferentially located in the core of both P84 and P84-APP micellar nanostructures. Self-assembled HYP molecules (in a more stable “head-to-tail” conformation) were observed when loaded into P84 micelles. In accordance with the chemometric experimental design the optimal ratio of P84/P84-APP (1:1) showed that the most pronounced HYP phototoxicity effect against B16-F10 melanoma cells recorded survival index that reached 18% at 10.0 μmol L^–1. The findings pointed out that the high phototoxicity observed is related to the capacity of APP molecules in enhancing the HYP uptake by melanoma cells.