Abstract 50: Development of paired enfortumab vedotin-resistant urothelial cancer models using organoid and PDX

Abstract Nectin-4 has emerged as a promising target for antibody-drug conjugates (ADCs) due to its high expression in bladder cancer (BC) cells. Enfortumab vedotin (EV), an anti-Nectin-4 ADC conjugated with MMAE toxin, has demonstrated potent therapeutic activity, particularly in combination with pembrolizumab. However, resistance to EV presents a significant clinical challenge. This study aims to develop EV resistant models among Urosphere's biobank of BC patient-derived xenografts (PDX) and organoids for screening anti-Nectin-4 compounds and investigating mechanisms of resistance to EV. RNA sequencing/Affymetrix and immunohistochemistry (IHC) were performed to quantify Nectin-4 expression. Sixteen PDX models were treated with EV (4 mg/kg, twice) to evaluate antitumor activity. Two PDX models (coded as B521 and F659) highly responsive to EV were selected to generate acquired-resistant models. They were treated with repeated EV treatments until tumors no longer regressed. Subsequently, tumor fragments from both PDX models were implanted into new NMRI mice and treated with EV to validate the resistance acquisition. Starting from PDX tumors no longer responding to EV, organoid model was established and treated to EV from 0.003 up to 10 µg/mL for five days, followed by cell viability assessment using the CellTiter-Glo® 3D assay to confirm their resistance. Urosphere’s PDX biobank encompasses diverse Nectin-4 expression profiles. EV efficacy in vivo was not strictly correlated with Nectin-4 expression. B521 did not acquire any resistance whereas F659 PDX model developed resistance after ∼200 days of repeated administration. We established the corresponding organoids and we showed that IC50 and Emax were significantly different between sensitive and resistant models. Nectin-4 expression remained stable in resistant models (mRNA and protein levels), indicating that resistance was unrelated to target loss. Transcriptomic analyses highlighted several potential mechanisms, including the upregulation of efflux transporters such as MDR1 and MRP3, which may contribute to resistance. Urosphere’s PDX and organoid biobank serves as a powerful platform for advancing research on Nectin-4-targeted therapies. From the F659 PDX model, we successfully developed paired in vitro and in vivo models resistant to EV. These novel models provide valuable tools for assessing innovative therapeutic approaches for resistant tumors. Additionally, the EV-resistant models underscore the potential role of ABC transporter upregulation in resistance mechanisms, offering critical insights for the development of alternative treatment strategies. Citation Format: Claire Béraud, Emilie Decaup, Anne-Sophie Bajeot, Céline Rouget, Karine Rollet, Mathieu Roumiguié, Xavier Gamé, Philippe Lluel, Nadège Bidan. Development of paired enfortumab vedotin-resistant urothelial cancer models using organoid and PDX [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 50.