Abstract 1892: KK2260: A fully human tetravalent bispecific antibody targeting TfR1 and EGFR for the treatment of EGFR-expressing tumors

Abstract Background: TfR1 is a transmembrane glycoprotein involved in iron uptake and regulation of cell growth. High TfR1 expression has been reported in different types of cancers, therefore recognized as a target molecule for cancer therapy. Despite the promise of potent efficacy of TfR1-targeted agents, there is a risk of side effects (i. e. , severe anemia), since TfR1 is also highly expressed in certain normal cells (e. g. , reticulocytes). KK2260 is a fully human tetravalent bispecific antibody (bsAb) based on REGULGENTTM technology targeting TfR1 and EGFR. This bsAb was designed for EGFR-expressing cell selective anti-cancer drug which could not be achieved by conventional monospecific Ab. In this study, we evaluated the mechanism of action (MOA), anti-cancer effect, and toxicity of KK2260. Methods: Binding activity of KK2260 to TfR1 and EGFR was evaluated by surface plasmon resonance method. Ligand blocking activity was evaluated by binding competition on esophageal squamous cell carcinoma (ESCC) OE21 cells. Growth inhibitory activity of KK2260 on cancer cells or hematopoietic progenitor cells was evaluated by proliferation inhibition assay. In some studies, excessive iron or anti-EGFR parent Ab was added. Effect on the cell surface target expression levels was evaluated by flow cytometry. The intracellular iron level was evaluated by cell imaging. Effect on EGF induced EGFR phosphorylation was evaluated by Western blotting. The in vivo efficacy of KK2260 was evaluated in cell line-derived and patient-derived xenograft (PDX) models of ESCC selected for high EGFR expression level. The toxicity of KK2260 was evaluated in cynomolgus monkeys. Results: KK2260 bound to TfR1 and EGFR with no ligand binding inhibition. KK2260 inhibited cell growth of moderate to high EGFR-expressing cancer cells, but not against EGFR-negative cancer cells or hematopoietic progenitor cells. KK2260 downregulated TfR1 expression on OE21 cells and the intracellular iron level decreased, but no effect was observed on EGFR phosphorylation. The growth inhibitory activity of KK2260 was abolished by adding excessive amounts of iron or reduced by inhibiting the binding to EGFR. Potent anti-tumor activity was observed in the ESCC PDX models with tumor regression. In the intermittent-dose toxicity study of cynomolgus monkeys, KK2260 was well-tolerated. Conclusions: KK2260 demonstrated potent anti-cancer effect both in vitro and in vivo. Intriguingly, KK2260 did not inhibit EGFR phosphorylation while EGFR-binding dependent TfR1 downregulation resulted in intracellular iron deficiency, which was considered as the MOA of KK2260. KK2260 was well tolerated in non-human primates. These preclinical data suggest the unique property of KK2260 is expected to provide significant benefit to patients with advanced ESCC and other EGFR-expressing tumors and Phase 1 study is currently on going in Japan (jRCT2031230372). Citation Format: Keisuke Mitamura, Hironori Otsuki, Keiko Nakahashi, Ayaka Kitagawa, Masayo Kamigaki, Yohei Kurio, Miho Inoue, Yasunori Uemura. KK2260: A fully human tetravalent bispecific antibody targeting TfR1 and EGFR for the treatment of EGFR-expressing tumors abstract. In: Proceedings of the American Association for Cancer Research Annual Meeting 2024; Part 1 (Regular Abstracts) ; 2024 Apr 5-10; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2024;84 (6Suppl): Abstract nr 1892.