Preparation, Phototoxicity and Biodistribution Studies of Anti‐Carcinoembryonic Antigen Monoclonal Antibody‐Phthalocyanine Conjugates

Abstract

Immunophototherapy of cancer combines the specificity of a monoclonal antibody (MAb) to an overexpressed tumor marker with the phototoxic properties of a conjugated dye. Aluminum tetrasulfophthalocyanine (AlPcS4) was covalently coupled to a 35A7 MAb directed against carcinoembryonic antigen (CEA) via a five-carbon spacer chain (A1) to yield conjugates with a molar ratio ranging from 5 to 16 mol of AlPcS4 per mol of 35A7 MAb. Conjugates were labeled with radioiodine for characterization. The immunoreactivity of the conjugates, determined in a direct binding assay on CEA coupled to sepharose, was not modified by the coupled AlPcS4A1 molecules. In vivo, these conjugates were evaluated in nude mice bearing human colon carcinoma xenografts (T380). 35A7 MAb-(AlPcS4A1)5, 35A7 MAb-(AlPcS4A1)12 and 35A7 MAb-(AlPcS4A1)16 conjugates displayed a tumor uptake of 35 +/- 5.0%, 40 +/- 5.7% and 32 +/- 3.3% of the injected dose per gram of tumor tissue, respectively, corresponding to an uptake of 97%, 104% and 91% as compared to that of the unconjugated 35A7 MAb. In each experimental group, the tumor-to-normal tissue ratios obtained with the conjugates were almost identical to those obtained with unconjugated 35A7 MAb. Average values of 1.8, 7 and about 30 were obtained for blood, liver and muscle, respectively. Phototoxic efficacy of the 35A7 MAb-(AlPcS4A1)12 conjugate was demonstrated in vitro on the LoVo cell line giving a 91% growth inhibition for a 2.50 micrograms/mL AlPcS4A1 concentration. We conclude that these conjugates demonstrate clear in vivo tumor-seeking capacity and in vitro photocytotoxic properties. Such conjugates could thus be promising candidate drugs for clinical photodynamic therapy of cancers expressing CEA.

Current status of phthalocyanines in the photodynamic therapy of cancer

“…However, the Pc-antibody conjugates were photoinactive, most likely due to inefficient subcellular targeting. Employing similar compounds, AlPcS 4 was covalently coupled to monoclonal antibodies directed against carcinoembryonic antigen (CEA) [76]. In vivo studies using nude mice bearing human colon carcinoma xenografts (T380) demonstrated increased uptake of the antibody-Pc conjugate as compared to the free Pc.…”

Phthalocyanines Covalently Bound to Biomolecules for a Targeted Photodynamic Therapy

“…The Ad-AlPcS 4 derivatives were tested both in vitro and in vivo. The penton base-AlPcS 4 conjugated via two linkers (compound pentonIn 1999, Carcenac et al used the same methodology to link AlPcS 4 8 to MAb 35A7 for a selective photoimmunotherapy directed against carcinoembryonic antigen (CAE) [71]. A limited immunoreactivity was observed: the 35A7 MAb-Pc conjugates showed an immunoreactivity close to that of the unconjugated antibody, independently of the number of Pcs anchored on the MAb (5, 12 or 16 mol of Pc per mol of MAb).…”

Active Targeting of Nano-Photosensitizer Delivery Systems for Photodynamic Therapy of Cancer Stem Cells

“…However, their production is resource intensive, and they often cause immune reactions. Nevertheless, conjugates of photosensitizers with mAbs directed against a variety of targets have been produced, including those that target receptors for signal transduction pathways, 87 oncofoetal antigens 88 and growth factor receptors. 89 Pereira et al studied a novel PS conjugated with bovine and human serum albumin (BSA and HSA, respectively) and a monoclonal antibody, anti-CD104.…”