Potent and specific antitumor effect of CEA‐targeted photoimmunotherapy

• Published in: International journal of cancer Vol. 135; no. 11; pp. 2697 - 2710
• Main Authors: Shirasu, Naoto, Yamada, Hiromi, Shibaguchi, Hirotomo, Kuroki, Motomu, Kuroki, Masahide
• Format: Journal Article
• Language: English
• Published: United States Wiley Subscription Services, Inc 01.12.2014
• Subjects: Animals; Antibodies, Monoclonal - immunology; Antibodies, Monoclonal - therapeutic use; Antitumor activity; Apoptosis - drug effects; Bioluminescence; bioluminescence imaging; Blotting, Western; Brain tumors; Cancer; Carcinoembryonic antigen; Carcinoembryonic Antigen - immunology; Carcinoembryonic Antigen - metabolism; Caspase; Cell death; Cell Proliferation - drug effects; Cytotoxicity; Female; Flow Cytometry; Fluorescent Dyes - therapeutic use; Gastric cancer; Humans; Hypoxia; Immunoconjugates - administration & dosage; Immunotherapy; Incubation; Inhibition; Irradiation; Lipid Peroxidation; Localization; Medical research; Mice; Mice, Inbred BALB C; Mice, Nude; Monoclonal antibodies; near‐infrared light; Neoplasms - drug therapy; Neoplasms - immunology; Neoplasms - metabolism; Peroxidation; Photochemotherapy; Photodynamic therapy; photoimmunoconjugate; photoimmunotherapy; Photosensitizing Agents - therapeutic use; Phototoxicity; Radiation; Reactive oxygen species; Rodents; Tumor cells; Tumor Cells, Cultured; Tumors; Xenograft Model Antitumor Assays; Xenografts; bioluminescence imaging; near-infrared light; carcinoembryonic antigen; photoimmunotherapy; photoimmunoconjugate; photodynamic therapy
• ISSN: 0020-7136; 1097-0215
• DOI: 10.1002/ijc.28907

Conventional photodynamic therapy (PDT) for cancer is limited by the insufficient efficacy and specificity of photosensitizers. We herein describe a highly effective and selective tumor‐targeted PDT using a near‐infrared (NIR) photosensitizer, IRDye700DX, conjugated to a human monoclonal antibody (Ab) specific for carcinoembryonic antigen (CEA). The antitumor effects of this Ab‐assisted PDT, called photoimmunotherapy (PIT), were investigated in vitro and in vivo. The Ab‐IRDye conjugate induced potent cytotoxicity against CEA‐positive tumor cells after NIR‐irradiation, whereas CEA‐negative cells were not affected at all, even in the presence of excess photoimmunoconjugate. We found an equivalent phototoxicity and a predominant plasma membrane localization of Ab‐IRDye after both one and six hours of incubation. Either no or little caspase activation and membrane peroxidation were observed in PIT‐treated cells and a panel of scavengers for reactive oxygen species showed only partial inhibition of the phototoxic effect. Strikingly, Ab‐IRDye retained significant phototoxicity even under hypoxia. We established a xenograft model, which allowed us to sensitively investigate the therapeutic efficacy of PIT by non‐invasive bioluminescence imaging. Luciferase‐expressing MKN‐45‐luc human gastric carcinoma cells were subcutaneously implanted into both flanks of nude mice. NIR‐irradiation was performed for only the tumor on one side. In vivo imaging and measurement of the tumor size revealed that a single PIT treatment, with intraperitoneal administration of Ab‐IRDye and subsequent NIR‐irradiation, caused rapid cell death and significant inhibition of tumor growth, but only on the irradiated side. Together, these data suggest that Ab‐IRDye‐mediated PIT has great potential as an anticancer therapeutics targeting CEA‐positive tumors. What's new? Photodynamic therapy (PDT) is a minimally invasive treatment modality that involves the administration of a photosensitizer followed by its excitation with low‐energy light of a specific wavelength. While PDT results in extensive cellular damage, its application for cancer is limited by the insufficient tumor selectivity of the photosensitizing agents. This study demonstrates that tumor‐targeted PDT using a near‐infrared photosensitizer conjugated to an anti‐human carcinoembryonic antigen (CEA)‐monoclonal antibody exhibits highly specific antitumor effects in vitro and in vivo. This photoimmunotherapy can kill CEA‐positive tumor cells in an immunoconjugate internalization‐independent manner, and is effective even under hypoxia, representing a promising therapeutic modality.