Abstract 2274: Development of bispecific antibodies using molecular imaging

(Background and purpose) A bispecific antibody (BsAb), as a next-generation therapeutic antibody, has two antigen binding sites in an antibody molecule. Many formats have been exploited for decades. Among them, we focused on T cell dependent BsAb (TDB), which can engage and redirect cytotoxic T cells against tumor cells and is expected to be effective in treating refractory cancer. However, although many studies revealed its potent antitumor effect in animal models, it has not been applied to solid tumors yet in clinics. In this context, we think that it is necessary to clarify pharmacokinetics (PK), pharmacodynamics (PD) and mechanism of action (MOA) of TDB, especially within tumor tissue. For this aim, we have decided to develop the molecular imaging-based systems for the evaluation of TDB in order to visualize antigen binding to two target antigens, BsAb delivery or immunological synapse formation. (Materials a& Methods) We used hEx3 which is a humanized IgG-like antibody with bivalent Fv regions against each EGFR and CD3. We applied the TDB to colorectal cancer (CRC) cells with or without KRAS or BRAF mutation. In the first part, we visualized the BsAb binding to two antigens, EGFR on CRC cells and CD3 on T cells. Next, immunological synapse formation as a cutting-edge mechanism involving T cells-killing tumor cells, which is an important MOA of TDB, was visualized in combination with Granzyme staining. In the second part, we evaluated in vitro cytotoxicity and the in vivo antitumor effect of hEx3 in NOD-SCID mice bearing CRC xenografts with KRAS or BRAF mutation following human PBMC administration. (Results) We found that CRC cells were damaged via Granzyme accumulation through immunological synapse. In the ELISA data, we also found that released gamma interferons can damage CRC cells. In vitro and In vivo studies showed that the hEx3 demonstrated a significant cytocidal effect and antitumor activity not only for KRAS wild but also mutant. (Conclusion) we established a molecular imaging-based TDB evaluation system and visualized antigen-binding and immunological synapse formation as a MOA of TDB. Present data indicated that TDB can damage CRC cells in two distinct manners, namely immunological synapse-dependent and -independent manners using cytokines including a gamma interferon. TDB may thus be a promising next generation antibody therapy against CRC regardless KRAS status. Citation Format: Daisuke Kamakura, Masahiro Yasunaga, Ryutaro Asano, Yasuhiro Matsumura. Development of bispecific antibodies using molecular imaging [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 2274.