Antibody-targeted photolysis: in vitro studies with Sn(IV) chlorin e6 covalently bound to monoclonal antibodies using a modified dextran carrier.

A monoclonal antibody-dextran-Sn(IV) chlorin e6 immunoconjugate was prepared by a technique involving the site-specific covalent modification of the monoclonal antibody oligosaccharide moiety. Dextran carriers were synthesized with a single chain-terminal hydrazide group, which was used as the coupling point between the carrier and the monoclonal antibody carbohydrate. Selective in vitro photolysis of SK-MEL-2 human malignant melanoma cells was accomplished using several conjugates prepared from anti-melanoma 2.1 (chromophore:antibody molar ratios, 6.8 and 11.2). Phototoxicity, as measured by clonogenic assay, was dependent on the delivered dose of 634-nm light and was observed only for conjugates that bound SK-MEL-2 cells. As judged by competitive inhibition radioimmunoassay, conjugates prepared in this fashion showed excellent retention of antigen binding activity relative to the unmodified antibody.