Abstract 438: Antibody drug conjugate using a novel anti-CDCP1 antibody with low hematopoietic stem-cell binding and rapid internalization showed high efficacy for solid cancer

Abstract CUB domain containing protein 1 (CDCP1) is a single transmembrane protein that is highly expressed in a broad range of solid cancers, including lung, breast, colorectal, pancreas, prostate, and ovarian cancers. Although no soluble ligand for CDCP1 is known, CDCP1 transduces signals resulting in cancer cell motility, epithelial mesenchymal transition, and metastasis by activating downstream signaling via homodimerization or heterodimerization with other cell surface molecules such as EGFR, HER2, and ITGB1. Owing to its important roles in cancer, CDCP1 has been reported as a promising therapeutic target for the treatment of solid cancers. While it is overexpressed in many of the abovementioned solid cancer types, several normal tissues such as esophagus, skin, and bone marrow hematopoietic stem cells (HSCs) also express CDCP1. To minimize the risk of toxicity, we generated novel anti-CDCP1 antibodies that bind weakly to bone marrow HSCs. Three isolated anti-CDCP1 monoclonal antibodies and their humanized versions showed weak binding to HSCs compared to other anti-CDCP1 antibodies reported from other groups. Although they only showed moderate binding activity to cancer cell lines, rapid internalization and efficient lysosomal trafficking was observed following CDCP1 binding. Subsequently, we generated antibody drug conjugates (ADCs) of the 3 anti-CDCP1 antibodies using PBD, MMAE, and MMAF as a cytotoxic payload with both a cleavable and non-cleavable linker. All constructed ADCs showed strong anti-tumor activity in multiple cancer cell lines in vitro. The cytotoxic activities of these ADCs were correlated to CDCP1 surface expression levels and internalization activity. The anti-CDCP1 ADCs showed strong anti-tumor efficacy in multiple cell line xenograft models. We selected the clone h14A043 for further evaluation owing to its observed potent anti-tumor activity both in vitro and in vivo. We then constructed h14A043-ATAC (Antibody Targeted Amanitin Conjugate), which has a site-specifically conjugated amanitin derivative with DAR 2 and an Fc domain mutation that reduces the effector function of human IgG1. h14A043-ATAC showed good anti-tumor potency both in vitro and in vivo. In human prostate cancer PC3 cell line xenograft model, we observed significant tumor growth delay following treatment by h14A043-ATAC with a single administration of 0.1 mg/kg. Furthermore, we observed complete tumor remission in 3 out of 8 mice at 40 days after a single administration of 1 mg/kg. In the non-GLP single dose toxicity study using cynomolgus monkeys, h14A043-ATAC showed good serum stability and no hematological toxicity. Our results suggest that ADC using an anti-CDCP1 mAb with weak binding to bone marrow HSC and sufficient internalization activity could provide a new treatment option for refractory solid cancer patients. Citation Format: Shu-ichi Hashimoto, Shiori Miyamoyo, Aki Takaiwa, Koji Nakamura, Yukihito Tsukumo, Yoshinori Yamashita. Antibody drug conjugate using a novel anti-CDCP1 antibody with low hematopoietic stem-cell binding and rapid internalization showed high efficacy for solid cancer [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2023; Part 1 (Regular and Invited Abstracts); 2023 Apr 14-19; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2023;83(7_Suppl):Abstract nr 438.