Abstract 2882: Development and preclinical characterization of HER2×Trop-2 bispecific antibody-drug conjugates (bsADCs) with auristatin microtubule inhibitors

Abstract Background: The emerging field of biparatopic (bpADC) and bispecific antibody-drug conjugates (bsADC) provides an innovative therapeutic category combining the merits of ADCs and bispecific/biparatopic antibodies. Promise in the field stems from the ability of bsADCs to overcome the existing clinical challenges associated with ADCs, such as poor internalization, drug resistance, and off-target toxicity. To date, more than 10 bsADCs are undergoing clinical trials, including HER2×Trop2 BsADCs. HER2 is a well-established target for ADCs such as trastuzumab emtansine and trastuzumab deruxtecan, demonstrating significant clinical benefits in HER2-positive breast cancers. The human cell-surface trophoblast protein 2 (Trop-2) is overexpressed in a wide range of solid tumors, including HER2-low expressing tumors, with minimal expression in normal tissues. Trop-2-directed ADCs such as sacituzumab govitecan and datopotamab deruxtecan have demonstrated potent antitumor efficacy in a broad range of solid tumors including patients with advanced triple-negative breast cancer, lung cancers and urothelial cancers. The dual-targeting approach offered by bsADCs has the potential to increase tumor cell binding affinity and internalization, leading to enhanced payload delivery and better tumor efficacy. Methods and Results: We developed two different HER2×Trop-2 bispecific antibodies (Saci/Tras-hIgG1 and Dato/Tras-hIgG1) leveraging a monovalent bispecific IgG1 format, which is monovalent for each antigen based on the Fab fragments of trastuzumab, sacituzumab or datopotamab. The fully human anti-HER2/Trop-2 bispecific antibodies were conjugated with monomethyl auristatin E (MMAE) via a lysosomally cleavable linker to generate uniform HER2×Trop-2 bsADCs (Saci/Tras-vc-MMAE and Dato/Tras-vc-MMAE) with an average DAR of 4.2. The binding affinity and specificity of anti-HER2/Trop-2 bsADC was evaluated by ELISA and FACS, respectively. The bsAb-vc-MMAE conjugates exhibited greater tumor killing efficiency and specificity with an IC50 in sub nM level in cell lines with high Trop-2 expression and medium/low HER2 expression. Furthermore, in vivo studies demonstrated antitumor activity with improved efficacy compared to monotherapy ADCs targeting either HER2 or Trop-2 alone, with favorable safety and pharmacokinetic profiles. Conclusion: HER2×Trop2 bsADCs represent a novel and exciting class of therapeutic agents with the potential to transform the treatment of multiple cancer types. Preclinical studies of HER2×Trop2 bsADCs have demonstrated that bsADCs can effectively inhibit tumor growth and prolong survival in xenograft animal models, with a favorable safety profile and low incidence of severe adverse events. Citation Format: Daniel He, Greg Liang, Haixia Chen, Mingqi Shao, Songyan Huang, Qiong Wang, Yinfei Yin, Qikuan Chen. Development and preclinical characterization of HER2×Trop-2 bispecific antibody-drug conjugates (bsADCs) with auristatin microtubule inhibitors [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2025; Part 1 (Regular Abstracts); 2025 Apr 25-30; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2025;85(8_Suppl_1):Abstract nr 2882.