Abstract 5497: Sacituzumab govitecan screening in a large organoid panel reveals the importance of functional assays for predicting ADC tumor response

Introduction: Antibody-drug conjugates (ADCs) represent an innovative approach in targeted cancer therapy, combining antibodies' specificity with therapeutic modalities such as cytotoxic or targeted chemical compounds. This study presents an ADC testing platform, leveraging patient-derived organoids (PDO) and advanced 3D high-content imaging. Methods: The efficacy of FDA-approved ADC Sacituzumab Govitecan/SN38 (SG), was evaluated in the CellTiter-Glo (CTG)-based OrganoidXplore panel, a 3D in vitro screening panel of 50 organoid models across 7 indications. The panel was characterized by NGS (WES, RNAseq) but selected without bias for TROP2/TACSTD2 expression. The OrganoidXplore screen was followed up with validating SG and payload responses using CTG and high-content imaging (HCI). ADC target engagement was assessed via immunofluorescence (IF) and ADC responses were validated in a selection of in vivo PDX models. Results: SG demonstrated a broad differential response (<0.01nM<IC50<50nM) in the OrganoidXplore panel, with 18 models showing strong responses (IC50<0.01nM). Response rates did not correlate with mRNA expression TROP2/TACSTD2. IF staining of the original PDX tumor tissues and organoids confirmed the correspondence between TROP2/TACSTD2 mRNA and protein expression levels, reaffirming that SG sensitivity did not directly correlate with gene and protein expression. Additional studies were performed with SG and SN38 in selected resistant and sensitive organoid models by HCI analysis. Similarly to the CTG assay, TROP2/TACSTD2 protein expression did not correlate with increased SG efficacy, showing that PDO sensitivity was not primarily driven by absolute target levels but rather through the mode of action of ADC uptake and payload sensitivity. Preliminary in vivo ADC efficacy results supported the in vitro findings. Conclusion: The OrganoidXplore screening platform provides insights into ADC efficacy, and responses and target engagement were validated with HCI. Combined, this demonstrates a lack of correlation between target expression (mRNA and protein) and drug efficacy, and the importance of functional testing for efficacy across a diverse patient population. The unique application of the 3D HCI platform for additional characterization, including ADC binding and uptake assays, will be an essential step to gain insight into the mode of action requirements for ADCs to be effective. These findings highlight the application of functional screening in organoid to better understand the complexity of ADC efficacy and identify responder/non-responder patient profiles to guide on resistance mechanism, in vivo modeling, and biomarker identification for patient stratification. Citation Format: Marten Hornsveld, Jinxi Wang, Jun Zhou, Xiaolong Tu, Peter van Schaik, Mariusz Madej, Hester Bange, Jessie J.J. Wang, Ludovic Bourre, Marrit Putker. Sacituzumab govitecan screening in a large organoid panel reveals the importance of functional assays for predicting ADC tumor response [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 5497.