COMPARISON OF DIRECT AND LIPOSOMAL ANTIBODY CONJUGATES OF SULFONATED ALUMINUM PHTHALOCYANINES FOR SELECTIVE PHOTOIMMUNOTHERAPY OF HUMAN BLADDER-CARCINOMA

There is a need to improve the selectivity of photodynamic therapy and for better targeting of tumor cells within specific tumor compartment s. Selective in vitro phototoxicity of a human bladder carcinoma cell line 647V has been achieved by targeting sulfonated aluminum phthalocy anines (AlSPc) with monoclonal antibodies. Aluminum tetra-3 sulfonyl c hloride phthalocyanine (PC) or rhodamine sulfonyl chloride were direct ly coupled to antibodies by a sulfonamide linkage and AlSPc or carboxy fluorescein were encapsulated in liposomes of the small unilamellar ve sicle type (SUV) bearing antibody. Antibody E7 (IgM subclass), which r ecognized an antigenic determinant expressed on 647V but was absent on T24 a control human bladder carcinoma cell line, and a control IgM an tibody were used. The effects of the two types of conjugate were compa red. Immunofluorescence studies on living cells demonstrated specific cell surface localization of conjugates at 4 degrees C and internaliza tion at 37 degrees C. Phototoxicity was measured by 3-(4,5-dimethylthi azol-2-5-diphenyltetrazolium) bromide assay after exposing AlSPc-sensi tized cells to red light. Significant AlSPc dose-dependent phototoxici ty of the order 4 degrees C < 4 degrees C plus 37 degrees C < 37 degre es C was observed with E7-SUV and E7-PC in the range 1-8 mu M AlSPc. A t equimolar AlSPc doses absolute toxicity was similar for the two conj ugate types, but at equimolar antibody doses, the liposomal conjugate was more effective by up to 13-fold. Addition of urine during illumina tion decreased toxicity, which was attributed to the presence of prote ctive elements. The results suggest that photosensitizers such as AlSP c could be used for antibody-directed therapy and in particular for se lectively damaging tumor cells of the epithelial cell compartment in b ladder carcinoma by intrabladder administration. The therapeutic ratio , which takes into account both specific and nonspecific toxicity, was greater for the liposome conjugate than for the direct conjugate indi cating their greater suitability for in vivo instillation.