The fluorescence study of the binding of zinc phthalocyanine to breast cancer cells solubilized in synthetic liposomes.

Steady state fluorescence spectroscopy is used to study the binding characteristics of zinc phthalocyanine (ZnPc) to MCF-7 human breast cancer cells solubilized in a liposomal vesicle prepared with L-alpha-phosphatidic acid, dipalmitoyl. The observed apparent binding constant, K', of 1.14 x 10(7) together with the free energy of binding, deltaG, of -40.38 kJ/mole suggests a very strong affinity and spontaneous binding between the breast cancer cells and ZnPc. The wavelength of excitation of ZnPc in the liposomal vesicle (611 nm) is favorable to cytotoxic reactive singlet oxygen (1O2*) production necessary for photooxygenation reaction with the cancerous cells and is within the energy threshold that has good penetration to normal tissues without undue skin necrosis.