1164 BSA01, a bispecific antibody-drug conjugate targeting EGFR and membrane-bound MUC-1-C, exhibits anti-tumor efficacyin vivo

Background

EGFR and the surface glycoprotein MUC-1 are commonly co-expressed in several malignancies, including esophageal squamous cell carcinomas, non-small cell lung cancers (NSCLC), and triple-negative breast cancers. To overcome limitations of current EGFR- and MUC-1-targeting therapies, we generated a novel bispecific antibody-drug conjugate conjugated with monomethyl auristatin E, BSA01, which targets both antigens. EGFR and MUC-1 antibodies were identified using RenLite® fully human common light chain mice and further evaluated for efficacy and specificity in vitro and in vivo.

Methods

Parental MUC1 antibody was tested in a binding competition assay alongside a benchmark identifying cleaved MUC-1.¹ Surface plasmon resonance and flow cytometry was employed to determine the affinity and species cross-reactivity of anti-MUC1. Binding avidity was assessed by flow cytometry. Internalization and cytotoxicity were assessed by Incucyte® live cell imaging. The specificity of BSA01 was assessed by comparing the cytotoxicity of tumor cells and neonatal Human Epidermal Keratinocytes (HEKn). The efficacy of BSA01 in preventing growth of cell line-derived (CDX) and patient-derived xenograft (PDX) tumors in vivo was subsequently evaluated.

Results

Binding competition assays indicate that the parental MUC1 antibody of BSA01 binds to MUC1-C*, which remains membrane-bound after cleavage. The affinity of the anti-MUC1 antibody was similar to human and cynomolgus monkey antigens. BSA01 BsAbs bound EGFR+MUC-1+ cell lines (HCC827 and HCC70) with stronger avidity than a single-positive cell line (A431). The internalization activity of BSA01 BsAbs was superior to its monovalent parental antibodies. BSA01 was able to effectively induce cytotoxicity in vitro, while only marginally affecting human normal cells that express low levels of MUC1 and EGFR. Notably, BSA01 showed superior anti-tumor efficacy when compared with benchmark ADCs in CDX and pancreatic PDX models in vivo, In NSCLC PDX tumors, BSA01 performed similar to MUC-1 benchmark.

Conclusions

We generated a novel bispecific ADC targeting EGFR and MUC-1. The MUC-1 arm of BSA01 binds to the cleaved MUC1-C*protein, which remains membrane bound on tumor cells. BSA01 exhibits strong affinity and internalization activity in vitro, while also demonstrating a good safety profile. Moreover, BSA01 shows superior anti-tumor efficacy to benchmarks in certain in vivo PDX models evaluated.

Reference

Wu G, Kim D, Kim JN, Park S, Maharjan S, Koh H, Moon K, Lee Y, Kwon HJ. A Mucin1 C-terminal Subunit-directed Monoclonal Antibody Targets Overexpressed Mucin1 in Breast Cancer. Theranostics, 2018;8(1):78–91. https://doi.org/10.7150/thno.21278

Ethics Approval

All animal studies were reviewed and approved by the Institutional Animal Care and Use Committee (IACUC) of Biocytogen Beijing Co., Ltd.