Abstract 3449: The role of N-terminal cleavage of Trop2 in tumor progression and therapeutic resistance in triple negative breast cancer

Abstract Background: Triple negative breast cancer (TNBC) is the most aggressive subtype of breast cancer (BC), with risk factors including greater frequency of recurrence and metastasis and lower overall survival rate compared to other BC subtypes. While the drivers of TNBC are unclear, Trop2 is a transmembrane protein that has been found to be highly expressed in TNBC, whose role in tumor progression is not well understood. High expression of Trop2 has led to the development of antibody-drug conjugates (ADCs) targeting wild-type Trop2, including Sacituzumab govitecan (SG) and Datopotamab deruxtecan (Dato-dxd). However, Trop2 is an intronless gene but can be posttranslationally cleaved by ADAM10 and other proteases in malignant tissues. Cleavage of Trop2 and its effect on tumor progression and drug resistance have not been previously explored, which is becoming increasingly crucial to understand as more Trop2-targeting therapies enter clinical practice. Experimental Methods and Results: To determine the oncogenic capacity of cleaved Trop2, our lab has generated a construct of N-terminally cleaved Trop2 ∆Q31-R87 called Trop2-∆N and have stably transduced mouse TNBC MM3MG cells, a cell line that is not well transformed and grows poorly in immune competent mice. SCID-beige mice who lack T and B cells and have non-functional NK cells and immune competent BALB/c were injected with wild-type Trop2, an uncleavable form of Trop2 called Trop2-87/88, Trop2-∆N, and control to find that Trop2-∆N conferred a proliferative phenotype, which was comparable to the known oncogene HER2∆16. Additionally, MM3MG cells were stained for SG, Dato-dxd, and their parental monoclonal antibodies and analyzed for binding via flow cytometry. We found that SG and Dato-dxd had lowered binding capacity towards Trop2-∆N expressing cells. To determine if the killing capacity of these ADCs were altered, we transduced the human breast epithelial cell line MCF10AT with our constructs of uncleavable Trop2-87/88 and Trop2-∆N to find that both SG and Dato-dxd to have lowered killing against Trop2-∆N expressing cells. Conclusions: Our studies found that N-terminally cleaved Trop2 induces a proliferative phenotype in vivo, reduce binding capacity of Trop2 ADCs, and are more resistance to ADC-induced killing in vitro. These data provide insight into the potential importance of N-terminally cleaved Trop2 in tumor progression and drug resistance that have not been explored. Future experiments will elucidate the mechanisms that underlie cleavage of Trop2 and refining Trop2-targeting therapies. Citation Format: Andrea E. Wilson, Junping Wei, Gangjun Lei, Tao Wang, Xiao-Yi Yang, Melissa Gajda, Cong-Xiao Liu, Zachary C. Hartman. The role of N-terminal cleavage of Trop2 in tumor progression and therapeutic resistance in triple negative breast cancer. [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 3449.