Abstract LB216: Discovery of BCG033, a Novel Anti-Ptk7 X TROP2 Bispecific Antibody-Drug Conjugate with Promising Efficacy Against Triple-Negative Breast Cancer

Abstract Triple-negative breast cancer (TNBC) accounts for 15-20% of metastatic breast cancer incidence, and remains an area of unmet clinical need due to the low rates of overall survival. Recently, the TROP2-targeting ADC sacituzumab govitecan has received an accelerated approval from the FDA for adult patients with metastatic TNBC, as more than 85% of TNBC is marked by TROP2 overexpression. However, the clinical efficacy of ADC therapies targeting TROP2 alone is limited by its on-target toxicity. In an effort to offer therapeutic alternatives that limit this toxicity, we sought to identify other targets to combat metastatic TNBC in combination with TROP2. PTK7 is highly expressed in breast cancer; notably, PTK7 expression is higher in TNBC than non-TNBC, and is correlated with worse prognosis, tumor metastasis and TNBC progression. PTK7 has also been demonstrated to be enriched in tumor-initiating cells (TICs) in low-passage TNBC, OVCA, and NSCLC patient-derived xenografts (PDXs). We generated fully human anti-human PTK7 x TROP2 bispecific antibodies (bsAbs) from RenLite® mice, which harbor the complete human heavy chain immunoglobulin variable domain with a common human kappa light chain for subsequent bispecific antibody assembly. These bsAbs demonstrated reactivity to human, monkey, and dog antigens, and showed enhanced internalization in vitro compared with parental PTK7 antibodies. In addition, these bsAbs showed favorable tumor cell selectivity, as there was minimal internalization of the monovalent antibodies. These bsAbs were than conjugated with Monomethyl auristatin E (MMAE) to generate anti-PTK7 x TROP2 bispecific ADC (BCG033) candidates. BCG033 candidates showed potent anti-tumor activity in several cell line-derived xenografts including TNBC xenografts, indicating that BCG033 has strong therapeutic potential in TNBC and other PTK7/TROP2 co-expressing cancers. Patient-derived TNBC xenografts with co-expression of PTK7 and TROP2 have been screened for future in vivo drug efficacy screening. In summary, BCG033 has the potential to exert anti-tumor efficacy in TNBC and other solid tumors co-expressing PTK7 and TROP2. Citation Format: Sufei Yao, Chengzhang Shang, Gao An, Ellen Zhang, Qingcong Lin, Yi Yang. Discovery of BCG033, a novel anti-PTK7 x TROP2 bispecific antibody-drug conjugate with promising efficacy against triple-negative breast cancer [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2023; Part 2 (Clinical Trials and Late-Breaking Research); 2023 Apr 14-19; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2023;83(8_Suppl):Abstract nr LB216.