Abstract:
Two zinc(II) phthalocyanines (ZnPcs) were conjugated with a monoclonal antibody (MAb)
directed against carcinoembryonic antigen (CEA), using an in situ activated carboxylic acid on the
ZnPcs. The bioconjugate with the highest ZnPc/MAb ratio of 3 was investigated in vitro for its
ability to target and fluorescently label human colorectal HT-29 cells. The ZnPc-CEA MAb 2 was
observed to efficiently target HT-29 cells, about 37 times more than unconjugated ZnPc.
Furthermore, in the presence of a 4-fold excess of unlabelled anti-CEA antibody, the fluorescence
signal of 2 was reduced by ~90% showing that the targeting is CEA-mediated. These studies
further confirm the high specificity of Pc-antibody conjugates for antigens over-expressed on
tumor cells and warrant further investigations of these immunoconjugates and their derivatives for
imaging of colorectal cancer.
