Overcoming HER2-directed antibody-drug conjugate resistance with disitamab vedotin in metastatic prostate cancer.

Abstract

e17078 Background: Metastatic prostate cancer (PCa) is a highly aggressive disease with limited treatment options following castration resistance. Prior studies have associated elevated Human Epidermal Growth Factor Receptor 2 (HER2) protein expression with advanced stage PCa, prompting evaluation of HER2 as a therapeutic target using HER2-directed antibody-drug conjugates (ADCs). Furthermore, clinical co-expression of HER2 with Epidermal Growth Factor Receptor (EGFR) or Human Epidermal Growth Factor Receptor 3 (HER3) has been implicated in other solid tumors for HER2 ADC resistance due to receptor heterodimerization and impaired ADC internalization. Therefore, we aimed to investigate HER2 ADC resistance using metastatic PCa models with elevated HER2 and variable EGFR and HER3 expression to support rational development of HER2-targeted therapy such as Disitamab Vedotin (DV) into clinical trials. Methods: We identified metastatic castration-resistant PCa cell line and organoid model systems representative of HER2 ADC resistance using RNAseq gene expression datasets from Human Protein Atlas and the Gene Expression Omnibus platform (GSE199596). HER2, EGFR, and HER3 protein expression was confirmed by immunofluorescence. The efficacy of HER2 ADCs was evaluated in cell lines and PDXOs using 2D and 3D CellTiter-Glo, respectively, complemented by image-based analysis. ADC internalization was assessed using pH-sensitive dye–labeled HER2 ADCs and live-cell imaging with Incucyte. Results: HER2 ADCs were screened in two metastatic PCa cell lines, DU145 and LNCaP clone FGC. Despite distinct receptor expression profiles, with DU145 characterized by high EGFR and LNCaP clone FGC by high HER3 expression, DV retained cytotoxic efficacy across both models. Patient-derived xenograft organoids (PDXOs) from the LuCaP PDX series were evaluated for gene expression of the targets with LuCaP 167 emerging as a suitable model confirming increased HER2, EGFR, and HER3 expression and membrane localization. Notably, DV induced robust cytotoxicity and significant organoid disintegration in LuCaP 167 PDXOs. Incucyte analysis further confirmed efficient ADC internalization in both cell lines and PDXOs, demonstrating that EGFR and HER3 expression did not prevent DV internalization. Conclusions: These findings demonstrate that DV retains efficacy across metastatic prostate cancer models independent of EGFR and HER3 expression and may overcome EGFR and HER3-associated resistance mechanisms reported with other HER2 ADCs. Our study also supports the further translational development of HER2-targeted ADCs for patients with metastatic prostate cancer.