Abstract 3147: DXC025, a novel anti-MUC1/EGFR bispecific antibody-tubulysin conjugate with a function linker, exhibits potent anti-tumor efficacy

Abstract Antibody-drug conjugates (ADCs) have become a promised drug class in cancer therapy. Armed with three main components-an antibody, a linker molecule, and a cytotoxic agent (“payload”), plus sites of the antibody conjugation and the distribution of tumor-associate antigens, nowadays ADCs have proved the unique ability of the precision of targeted therapy, a great leap forward from traditional chemotherapeutic approaches that cause widespread effects without specificity. Both epidermal growth factor receptor (EGFR) and mucin 1 (MUC1) are tumor-associated antigens (TAA) that are co-expressed in many solid tumors, such as, colon cancer, non-small cell lung cancer (NSCLC), esophageal cancer, epidermal cancer, and pancreatic cancer. In particular, MUC1, a glycoprotein essential for the formation of the epithelial mucous barrier, is hypoglycosylated and dimerizes with EGFR, a potent oncoprotein, in transformed cells. For our anti-Muc1 ADC clinical program, for treatment of colon and pancreatic cancers, it was found out that the highly glycosylated transmembrane Muc1 had much more turning over rates on the luminal surface of epithelial cells. Here, we first designed and generated bispecific Fab/scFv antibodies targeting both MUC1 and EGFR, using the knob-into-hole technology. The addition of the affinity- and internalization-optimized anti-EGFR arm to the other single Muc1 arm was aimed to broaden tumor selectivity and to reduce on-target toxicity, for the treatment of gastrointestinal tumors in comparison to individual full IgG1-ADC, either EGFR or Muc1-ADC. Indeed, many of generated anti- MUC1/EGFR bispecific antibodies (BsAbs) showed strong binding affinity in MUC1modetateEGFRmodetate cells, in addition to both MUC1 and EGFR highly expressed cells. Internalization assays demonstrated that the BsAbs were endocytosed in tumor cells co-expressing EGFR and MUC1 more efficiently than monoclonal antibodies targeting MUC1. The selected BsAbs were subsequently conjugated with tubulysin B analogs with varieties of Tubulysin B analog payloads and function peptidyl spacer/linkers to generate bispecific ADC (DXC025) candidates. DXC025 candidates exhibited very potent cytotoxicity in vitro against epidermal cancer, lung adenocarcinoma, and pancreatic cancer cell lines with IC50 of single or tens digital pM. In in vivo cell-derived xenograft (CDX) models, DXC025 candidates demonstrated much superior efficacies of tumor growth inhibition in comparison with parental (monoclonal), either Muc1- or EGFR- ADC for the treatment of gastrointestinal tumors. These results indicated that the MUC1/EGFR-ADC (DXC025) would be a promising ADC candidate for targeted treatment of either Muc1- or EGFR-expressing gastrointestinal tumors. Citation Format: Xingyan Jiang, Junxiang Jia, Huihui Guo, Xiangfei Kong, Yongfang Xu, Sishi Ye, Yong Du, Zhicang Ye, Qikuang Cen, Lingli Zhang, Yongxiang Chen, Gaituo Chen, Lu Bai, Yunxia Zheng, Wei Zheng, Jun Zheng, Juan Wang, Wenjun Li, Yuanyuan Huang, Linyao Zhao, Yifang Xu, Mengmeng Liu, Binbin Chen, Meng Dai, Miaomiao Chen, Zhixiang Guo, Qingliang Yang, Robert Y. Zhao. DXC025, a novel anti-MUC1/EGFR bispecific antibody-tubulysin conjugate with a function linker, exhibits potent anti-tumor efficacy [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(6_Suppl):Abstract nr 3147.