title: 64Cu-DOTA-anti-CTLA-4 mAb enabled PET visualization of CTLA-4 on the T-cell infiltrating tumor tissues.
abstract: Cytotoxic T lymphocyte-associated antigen-4 (CTLA-4) targeted therapy by anti-CTLA-4 monoclonal antibody (mAb) is highly effective in cancer patients. However, it is extremely expensive and potentially produces autoimmune-related adverse effects. Therefore, the development of a method to evaluate CTLA-4 expression prior to CTLA-4-targeted therapy is expected to open doors to evidence-based and cost-efficient medical care and to avoid adverse effects brought about by ineffective therapy. In this study, we aimed to develop a molecular imaging probe for CTLA-4 visualization in tumor. First, we examined CTLA-4 expression in normal colon tissues, cultured CT26 cells, and CT26 tumor tissues from tumor-bearing BALB/c mice and BALB/c nude mice by reverse transcription polymerase chain reaction (RT-PCR) analysis and confirmed whether CTLA-4 is strongly expressed in CT26 tumor tissues. Second, we newly synthesized 64Cu-1,4,7,10-tetraazacyclododecane-N,N',N″,N‴-tetraacetic acid-anti-mouse CTLA-4 mAb (64Cu-DOTA-anti-CTLA-4 mAb) and evaluated its usefulness in positron emission tomography (PET) and ex-vivo biodistribution analysis in CT26-bearing BALB/c mice. High CTLA-4 expression was confirmed in the CT26 tumor tissues of tumor-bearing BALB/c mice. However, CTLA-4 expression was extremely low in the cultured CT26 cells and the CT26 tumor tissues of tumor-bearing BALB/c nude mice. The results suggested that T cells were responsible for the high CTLA-4 expression. Furthermore, 64Cu-DOTA-anti-CTLA-4 mAb displayed significantly high accumulation in the CT26 tumor, thereby realizing non-invasive CTLA-4 visualization in the tumor. Together, the results indicate that 64Cu-DOTA-anti-CTLA-4 mAb would be useful for the evaluation of CTLA-4 expression in tumor.
authors.affiliation: Graduate School of Medicine, Dentistry, and Pharmaceutical Sciences, Okayama University, Okayama, Japan; Japan Society for the Promotion of Science, Tokyo, Japan.
authors.forename: Kei
authors.initials: K
authors.lastname: Higashikawa
authors.affiliation: Graduate School of Medicine, Dentistry, and Pharmaceutical Sciences, Okayama University, Okayama, Japan.
authors.forename: Katsuharu
authors.initials: K
authors.lastname: Yagi
authors.affiliation: Graduate School of Medicine, Dentistry, and Pharmaceutical Sciences, Okayama University, Okayama, Japan.
authors.forename: Keiko
authors.initials: K
authors.lastname: Watanabe
authors.affiliation: Next-generation Imaging Team, RIKEN Center for Life Science Technologies, Kobe, Japan.
authors.forename: Shinichiro
authors.initials: S
authors.lastname: Kamino
authors.affiliation: Graduate School of Medicine, Dentistry, and Pharmaceutical Sciences, Okayama University, Okayama, Japan.
authors.forename: Masashi
authors.initials: M
authors.lastname: Ueda
authors.affiliation: Next-generation Imaging Team, RIKEN Center for Life Science Technologies, Kobe, Japan.
authors.forename: Makoto
authors.initials: M
authors.lastname: Hiromura
authors.affiliation: Graduate School of Medicine, Dentistry, and Pharmaceutical Sciences, Okayama University, Okayama, Japan; Next-generation Imaging Team, RIKEN Center for Life Science Technologies, Kobe, Japan.
authors.forename: Shuichi
authors.initials: S
authors.lastname: Enomoto
mesh_terms: D000818:Animals; D000911:Antibodies, Monoclonal; D060908:CTLA-4 Antigen / Q000037:antagonists & inhibitors / Q000235:genetics / Q000378:metabolism*; D045744:Cell Line, Tumor; D003301:Copper Radioisotopes; D004195:Disease Models, Animal; D005260:Female; D015870:Gene Expression; D006801:Humans; D016246:Lymphocytes, Tumor-Infiltrating / Q000378:metabolism*; D051379:Mice; D009369:Neoplasms / Q000175:diagnosis* / Q000235:genetics / Q000378:metabolism*; D009942:Organometallic Compounds; D049268:Positron-Emission Tomography / Q000379:methods; D011485:Protein Binding; D019275:Radiopharmaceuticals
chemical_list: D000911:Antibodies, Monoclonal; D060908:CTLA-4 Antigen; D003301:Copper Radioisotopes; D009942:Organometallic Compounds; D019275:Radiopharmaceuticals