In Vivo and In Vitro Efficacy of Enhertu in Uterine Serous Carcinoma (047)

Abstract

Objectives: Uterine serous carcinoma (USC) is an aggressive subtype of epithelial endometrial cancer, comprising approximately 40% of endometrial cancer-related deaths. HER2 overexpression is detected in about 35% of patients with USC. Enhertu is a novel humanized monoclonal anti-HER2 antibody (trastuzumab) linked to the topoisomerase I inhibitor payload deruxtecan by a cleavable linker. Enhertu is FDA-approved for HER2-expressing metastatic breast and gastric cancers; however, its efficacy has not been tested in endometrial cancer. The objective of this study was to study the in vitro and in vivo efficacy of Enhertu in USC. Methods: HER2 expression was analyzed with flow cytometry in primary USC cell lines: ARK2, ARK4, ARK7, and ARK20. Cell lines were treated with 0.05, 0.010, 0.025, 0.05, 0.2 μg/ml of Enhertu or Control antibody-drug conjugate (Control ADC). The inhibitory concentration 50 (IC50) was assessed by counting the viable cells using a flow cytometer. Apoptosis and necrosis were assessed with Annexin V and propidium iodide (PI) staining. GFP-expressing ARK4 (ARK4-GFP) cells were co-cultured with ARK2 cells for the bystander effect assay. For in vivo experiments, eight million ARK2 cells were injected subcutaneously into SCID mice. Animals were randomized to intravenous injection of PBS (n=5), control ADC (4 mg/kg, n=6) or Enhertu (4 mg/kg, n=5) treatment. Kruskal Wallis, Friedman, and Log Rank tests were used for statistical analysis. Graphical Abstract View Large Image Figure Viewer Download Hi-res image Graphical Abstract View Large Image Figure Viewer Download Hi-res image Conclusions: Enhertu showed significant preclinical efficacy against HER2 overexpressing uterine serous carcinoma cell lines. Further clinical trials in USC are warranted. Objectives: Uterine serous carcinoma (USC) is an aggressive subtype of epithelial endometrial cancer, comprising approximately 40% of endometrial cancer-related deaths. HER2 overexpression is detected in about 35% of patients with USC. Enhertu is a novel humanized monoclonal anti-HER2 antibody (trastuzumab) linked to the topoisomerase I inhibitor payload deruxtecan by a cleavable linker. Enhertu is FDA-approved for HER2-expressing metastatic breast and gastric cancers; however, its efficacy has not been tested in endometrial cancer. The objective of this study was to study the in vitro and in vivo efficacy of Enhertu in USC. Methods: HER2 expression was analyzed with flow cytometry in primary USC cell lines: ARK2, ARK4, ARK7, and ARK20. Cell lines were treated with 0.05, 0.010, 0.025, 0.05, 0.2 μg/ml of Enhertu or Control antibody-drug conjugate (Control ADC). The inhibitory concentration 50 (IC50) was assessed by counting the viable cells using a flow cytometer. Apoptosis and necrosis were assessed with Annexin V and propidium iodide (PI) staining. GFP-expressing ARK4 (ARK4-GFP) cells were co-cultured with ARK2 cells for the bystander effect assay. For in vivo experiments, eight million ARK2 cells were injected subcutaneously into SCID mice. Animals were randomized to intravenous injection of PBS (n=5), control ADC (4 mg/kg, n=6) or Enhertu (4 mg/kg, n=5) treatment. Kruskal Wallis, Friedman, and Log Rank tests were used for statistical analysis. Conclusions: Enhertu showed significant preclinical efficacy against HER2 overexpressing uterine serous carcinoma cell lines. Further clinical trials in USC are warranted.