Delivery of the tumour photosensitizer zinc(II)-phthalocyanine to serum proteins by different liposomes: studies in vitro and in vivo.

Zn-phthalocyanine (Zn-Pc) incorporated into liposomes of different phospholipids has been incubated in vitro with human serum and administered i.v. to rabbits. In both cases, chromatographic and density gradient ultracentrifugation studies indicate that Zn-Pc is almost exclusively bound by the 3 major lipoprotein components of the plasma (VLDL, LDL and HDL). The amounts of Zn-Pc recovered from the different lipoprotein fractions reflect their relative concentration in the serum. The presence of 20% moles of cholesterol in liposomes of dipalmitoyl phosphatidylcholine (DPPC) optimizes the release of Zn-Pc to LDL. This fact is important for enhancing the selectivity of drug delivery to tumors since LDL display a preferential interaction with neoplastic cells.