The chemical nature of the sensitizer and its selective uptake by malignant cells are decisive to choose an appropriate biocompatible carrier, able to preserve the photosensitizing characteristics of the
dye. In this paper we demonstrate the photodynamic properties of three chlorins, derived from
chlorophyll a, and the usefulness of liposomal carriers to design
pharmaceutical formulations. The chlorins have been quantitatively incorporated into stable
liposomes obtained from a mixture of L-alpha-
palmitoyloleoylphosphatidylcholine and L-alpha-dioleoylphosphatidylserine in a 13.5:1.5 molar ratio (POPC/OOPS-
liposomes). The
chlorin uptake by skin fibroblasts increases steadily, reaching in all cases a plateau level dependent on both the
chlorin structure and the vehicle employed. The photophysical properties of the three chlorins in THF are nearly identical and fulfill the requirements for a
PDT photosensitizer. Incorporation of chlorins into
liposomes induces important changes in their photophysics, but does not impair their cellular uptake or their cell
photosensitization ability. In fact we observe in the cells the same photophysical behavior as in THF
solution. Specifically, we demonstrate, by recording the near-IR phosphorescence of 1O2, that the chlorins are able to photosensitize the production of 1O2 in the cell membrane. The cell-
photosensitization efficiency depended on the
chlorin and cell line nature, the carrier, and the length of pre-incubation and post-irradiation periods. The high photodynamic activity of
chlorin-loaded
liposomes and the possibility to design liposomal carriers to achieve a specific target site favors this approach to obtain an eventual
pharmaceutical formulation.