Abstract

Abstract Background: Datopotamab deruxtecan (Dato-DXd), is a humanized anti-TROP2 IgG1 monoclonal antibody linked to a potent topoisomerase I inhibitor payload (DXd). Dato-DXd has already shown antitumor activity in breast cancer; however, the determinants of response, including the importance of TROP2 expression, remain unclear. We tested the activity of Dato-DXd in a panel of breast cancer patient-derived xenografts (BCXs) varying in TROP2 expression. Methods: The antitumor activity of Dato-DXd and isotype-control-DXd (IgG-DXd) was assessed against 11 BCXs varying in TROP2 expression, 10 representing tumors post-neoadjuvant chemotherapy. Pharmacodynamic effects were assessed at 24 and 72 hours. The effects of TROP2 expression on Dato-DXd activity was assessed in vitro and in vivo using viral overexpression in BCX-derived cell lines. Results: Models differed in their sensitivity to both Dato-DXd and IgG-DXd. Dato-DXd (10 mg/kg) led to objective response in 4 (36%) models and statistically significant prolongation of event-free survival (EFS) in 8 (73%) models while IgG-DXd (10 mg/kg) led to response in 1 (9%) and prolonged EFS in 3 (27%) models. TROP2 RNA and protein was significantly higher in Dato-DXd-sensitive models. In isogenic cell lines derived from Dato-DXd-resistant BCXs, overexpression of TROP2 conferred Dato-DXd antitumor activity in vitro and in vivo. Dato-DXd increased γH2AX and phospho-KAP1 in the 2 Dato-DXd-sensitive BCXs but not in a Dato-DXd-resistant BCX. In Dato-DXd-sensitive models, antitumor activity was enhanced in combination with PARP inhibitor, olaparib. Conclusion: Dato-DXd is active in breast cancer models. Dato-DXd has TROP2 dependent and independent mediators of activity; however, high TROP2 expression enhances Dato-DXd antitumor activity.