Abstract 4602: The dissociation constant rate of ADC would be an important factor for antitumor activity in vivo
Authors: Tsumura Ryo , Manabe Shino , Koga Yoshikatsu , Yasunaga Masahiro , Matsumura Yasuhiro 
Published: July 2017

Abstract
Introduction: Antibody-drug conjugates (ADCs), consisting of a monoclonal antibody, a potent cytotoxic agent and a linker, are currently considered as promising potent agents for cancer therapy. However, especially in solid tumors, the tumor stroma would hinder ADCs from accessing to cancer cells, leading to decline the efficacy of ADCs in clinical study. In order to overcome these difficulties and to maximize the ADC potential, the optimization of ADC components is needed. And it’s well-known that antitumor activity of ADCs depends on PK properties, binding affinity, internalization efficiency and other functions. In present study, therefore, we focused on the characteristics of antibody for ADC design, and investigated what characteristics could affect anti-tumor effects in vivo.
Materials and Method: First, we prepared 4 types of monoclonal antibodies against tissue factor (TF) which is known as a 47-kDa transmembrane glycoprotein and an initiation factor of the extrinsic blood coagulation. And then, anti-TF antibodies were conjugated with maleimidocaproyl-valine-citrulline-p-amino-benzoyloxycarbonyl linker and monomethyl auristatin E. Both of them were well-known liker system and drug for current ADC design. After conjugation, we investigated the characteristics, including binding parameters, internalization efficiencies, drug release rates, cytotoxicity against human pancreatic cancer cell lines in vitro, half-life in vivo, anti-tumor effects using xenograft model, and distribution in tumor tissues.
Results: In SPR analysis, anti-TF ADCs showed the significant differences of binding kinetics parameters. However, in other assays, anti-TF ADCs showed almost same internalization efficiencies, drug release rates, cytotoxicity against cancer cell lines in vitro, half-life in vivo. The efficacy of anti-TF ADCs was examined in BxPC3 xenograft model when the average tumor size reached 200 mm3. Although anti-TF ADCs significantly inhibited BxPC3 tumor growth compared with control groups, there was no difference of anti-tumor effects among anti-TF ADCs. We further examined the anti-tumor effects when the average tumor size reached 600 mm3. Interestingly, the antitumor effect of ADC using the clone with high dissociation constant was superior to that with low dissociation constant against large size tumor, especially in the early phase. Furthermore, the distribution of ADC in BxPC3 tumor demonstrated that the former clone showed higher penetration ability than the latter clone.
Conclusion: We concluded that binding kinetics parameters, in particular, the dissociation constant rate contributed to the tumor penetration ability of anti-TF ADCs and the different distribution in BxPC3 tumor. The distribution changes would affect the differences of anti-tumor effects in large size BxPC3 tumor. Therefore we suggested that the dissociation constant rate would be an important factor for ADCs design.
Citation Format: Ryo Tsumura, Shino Manabe, Yoshikatsu Koga, Masahiro Yasunaga, Yasuhiro Matsumura. The dissociation constant rate of ADC would be an important factor for antitumor activity in vivo [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2017; 2017 Apr 1-5; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2017;77(13 Suppl):Abstract nr 4602. doi:10.1158/1538-7445.AM2017-4602