Abstract 2863: Preclinical evaluation of astatine-211-conjugated anti-tissue factor antibody
Authors: Takashima Hiroki , Koga Yoshikatsu , Onuki Kazunobu , Manabe Shino , Tsumura Ryo , Anzai Takahiro , Iwata Nozomi , Yasunaga Masahiro , Yang Wang , Yokokita Takuya , Komori Yukiko , Mori Daiki , Haba Hiromitsu , Fujii Hirofumi , Matsumura Yasuhiro 
Published: September 2020

Abstract
It has been well-known that tissue factor (TF), the trigger protein of the extrinsic blood coagulation cascade, is overexpressed in various cancers including gastric cancer, pancreatic cancer and malignant gliomas. So far, we produced anti-TF monoclonal antibodies for targeting overexpressed TF in tumor site. Moreover, among them, we found that the clone 1084 possessed deep penetration property leading to more homogenous distribution in tumor than others.
Currently, we are focusing on developing clone 1084 antibody armed with alpha emitters for cancer treatment, because alpha-particles are characterized by higher liner energy transfer (LET) and shorter range in tissue than other types of radiation, resulting in efficient deoxyribonucleic acid (DNA) double-strand breaks in cancer cells and minor effects on normal cells adjacent to tumor.
In this study, we synthesized astatine-211, one of the most promising alpha-particle emitters, in the 209Bi(α,2n)211At reaction using the RIKEN Azimuthally Varying Field (AVF) cyclotron and labeled humanized clone 1084 with this radionuclide. First, we chemically attached a linker containing organic tin compound to the antibody and then labeled the liker-antibody complex with astatine-211 via a halogen-exchange reaction. Thin-layer chromatography (TLC) and sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE) studies showed that we successfully labeled the antibody with astatine-211 and purified the radioactive antibody.
We evaluated binding activity and in vitro cytocidal effect of the radioactive antibody by flow cytometry and water-soluble tetrazolium salt (WST-8) assay, respectively. The radioactive antibody specifically bound to TF expressed on cell membrane of gastric cancer cells and showed potent cell killing activity depending on TF expression of the cancer cells. Single photon emission computed tomography/computed tomography (SPECT/CT) study revealed that astatine-211 alone selectively accumulated in stomach and thyroid such as radioactive iodine. On the other hand, radioactive antibody showed similar pharmacokinetics to the naked 1084 antibody. Moreover, we confirmed in vivo anti-tumor effects of the radioactive antibody in a TF-overexpressing gastric cancer xenograft model.
In conclusion, we successfully created astatine-211-conjugated anti-TF antibody and confirmed its anti-tumor effects.
Citation Format: Hiroki Takashima, Yoshikatsu Koga, Kazunobu Onuki, Shino Manabe, Ryo Tsumura, Takahiro Anzai, Nozomi Iwata, Masahiro Yasunaga, Wang Yang, Takuya Yokokita, Yukiko Komori, Daiki Mori, Hiromitsu Haba, Hirofumi Fujii, Yasuhiro Matsumura. Preclinical evaluation of astatine-211-conjugated anti-tissue factor antibody [abstract]. In: Proceedings of the Annual Meeting of the American Association for Cancer Research 2020; 2020 Apr 27-28 and Jun 22-24. Philadelphia (PA): AACR; Cancer Res 2020;80(16 Suppl):Abstract nr 2863.