Preparation, phototoxicity and biodistribution studies of anti-carcinoembryonic antigen monoclonal antibody-phthalocyanine conjugates

Immunophototherapy of cancer combines the specificity of a monoclonal antib ody (MAb) to an overexpressed tumor marker with the phototoxic properties o f a conjugated dye. Aluminum tetrasulfophthalocyanine (AlPcS4) was covalent ly coupled to a 35A7 MAb directed against carcinoembryonic antigen (CEA) vi a a five-carbon spacer chain (A(1)) to yield conjugates with a molar ratio ranging from 5 to 16 mol of AlPcS4 per mel of 35A7 MAb. Conjugates were lab eled with radioiodine for characterization. The immunoreactivity of the con jugates, determined in a direct binding assay on CEA coupled to sepharose, was net modified by the coupled AlPcS(4)A(1) molecules. In vivo, these conj ugates were evaluated in nude mice bearing human colon carcinoma xenografts (T380), 35A7 MAb-(AlPcS(4)A(1))(5), 35A7 MAb-(AlPcS(4)A(1))(12) and 35A7 M Ab-(AlPcS(4)A(1))(16) conjugates displayed a tumor uptake of 35 +/- 5.0%, 4 0 +/- 5.7% and 32 +/- 3.3% of the injected dose per gram of tumor tissue, r espectively, corresponding to an uptake of 97%, 104% and 91% as compared to that of the unconjugated 35A7 MAb. In each experimental group, the tumor-t o-normal tissue ratios obtained with the conjugates were almost identical t o those obtained with unconjugated 35A7 MAb. Average values of 1.8, 7 and a bout 30 were obtained for blood, liver and muscle, respectively. Phototoxic efficacy of the 35A7 MAb-(AlPcS(4)A(1))(12) conjugate was demonstrated in vitro on the LoVo cell line giving a 91% growth inhibition for a 2.50 mu g/ mL AlPcS4A(1), concentration. We conclude that these conjugates demonstrate clear in vivo tumor-seeking capacity and in vitro photocytotoxic propertie s. Such conjugates could thus be promising candidate drugs for clinical pho todynamic therapy of cancers expressing CEA.