Hypericin photodynamic activity in DPPC liposomes - part II: stability and application in melanoma B16-F10 cancer cells.

Hypericin (Hyp) is considered a promising photosensitizer for Photodynamic Therapy (PDT) due its high hydrophobicity, affinity for cell membranes, low toxicity and high photooxidation activity. In this study, Hyp photophysical properties and photodynamic activity against melanoma B16-F10 cells were optimized using DPPC liposome (1,2-dipalmitoyl-sn-glycero-3-phosphocholine) as a drug delivery system. This nanoparticle is used as cell membranes biomimetic model and solubilizes hydrophobic drugs. Hyp oxygen singlet lifetime (τ) in DPPC was approximately 2 fold larger than in P-123 micelles (PluronicTM surfactants), reflecting a more hydrophobic environment provided by the DPPC liposome. On the other hand, singlet oxygen quantum yield (ΦΔ1O2) in DPPC and in P-123 were similar; Hyp molecules were preserved as monomers. Hyp/DPPC liposome aqueous dispersion was stable for fluorescence emission and liposome diameter for at least 5 days at 30 oC. However, the liposomes collapsed after lyophilization/rehydration process, which was resolved by adding the lyoprotectant Trehalose to liposome the dispersion prior to lyophilization. Cell viability of the Hyp/DPPC formulation was assessed against the healthy HaCat cells and high-metastatic melanoma B16-F10 cells. Hyp incorporated in the DPPC carrier presented higher selectivity index than Hyp sample previously solubilized in ethanol under illumination effect. Moreover, the IC50 was lower for Hyp in DPPC than for Hyp pre-solubilized in ethanol. These results enable the formulation Hyp/DPPC for future biomedical applications in PDT treatment