Fluorescence resonance energy transfer measurements as a tool to detect fusion and drug exchange in liposomal suspensions

摘要

Zinc-(II)-phthalocyanine (ZnPc) is a drug that can potentially be used in photodynamic therapy. A promising formulation approach for the strongly hydrophobic ZnPc is to embed the molecule in liposomes. CGP 55847 is such a liposomal ZnPc formulation. From our data, we could conclude that approximately one quarter of the drug molecules were only loosely bound to the liposomes and exchanged between them with a relaxation time of about 15 min. Energy transfer measurements before and after the lyophilization process revealed that the liposomes were stable when suspended in a 10% lactose solution, i.e. no fusion of liposomes took place. In aqueous solution, however, lyophilization induced fusion of liposomes to a small extent with a concomitant increase in size.