Abstract B014: FGFR inhibition upregulates Nectin-4 expression in FGFR3 altered urothelial carcinoma
Authors: Clark-Garvey Sean , Zhou Mi , Sturdivant Michael , Beckabir Wolfgang , Kim Lucia , Toomer E. Drew , McCabe Ian , Hamada Akihiro , Crona Daniel , Damrauer Jeffrey S. , Kim William Y. 
Published: May 2024

Abstract
Bladder urothelial carcinoma (UC) is a common malignancy and remains a significant cause of mortality; however, in recent years there have been substantial advances in the treatment of metastatic UC (mUC). This includes the approval of the antibody drug conjugate (ADC) enfortumab vedotin, which targets Nectin-4, and the fibroblast growth factor receptor (FGFR) inhibitor erdafitinib (in FGFR2/3 altered tumors). Despite the impressive efficacy of these agents, most patients will ultimately develop progressive disease, underlining the need for further therapeutic development. Previous work has demonstrated that NECTIN4 expression and FGFR3 alterations are enriched in luminal subtypes of UC and NECTIN4 expression is higher in FGFR altered tumors. We validate these findings in scRNAseq from primary tumors as well as bulk RNAseq from murine models. Given the positive correlation between NECTIN4 and FGFR3 alterations we hypothesized that FGFR3 inhibition would downregulate Nectin-4 expression. To our surprise we found in vitro treatment with erdafitinib in cell lines with FGFR3 fusion proteins (RT112, RT4, SW780) lead to an increase in Nectin-4 protein levels. Additionally, in vitro FGFR inhibition in the UMUC-14 cell line which harbors an FGFR3S249C hotspot mutation, upregulates Nectin-4 protein levels. To further investigate this phenomenon, we engineered the FGFR3 WT cell line, 5637 to overexpress FGFR3-TACC3 or FGFR3S249C. We saw that FGFR3-TACC3 and FGFR3S249C overexpression both down regulated Nectin-4 indicating that FGFR3 activity negatively regulates Nectin-4 expression. We have also investigated the association between FGFR inhibition and Nectin-4 expression in two in vivo models: (1) in a xenograft model using the RT112 line we found an overall increase in Nectin-4 expression in tumors treated with a 5-day course of erdafitinib; (2) in a UPFL1 (a cell line derived from a genetically engineered mouse with a S249C mutation) syngeneic model we also saw an increase in Nectin-4 expression after erdafitinib treatment. We have observed that the increase in Nectin-4 expression persists in vitro even after withdrawal of erdafitinib treatment, indicating that intermittent dosing of erdafitinib maybe be sufficient to prime a tumor for Nectin-4 targeted therapy. Lastly, preliminary in vitro investigation of the combination of erdafitinib and enfortumab vedotin in RT112 cells showed synergy, particularly with lower doses of both agents, providing further support of our hypothesis that FGFR3 inhibition may act to sensitize UC to Nectin-4 ADC therapy. A potential synergistic relationship is further supported by the recent results of the phase 1 trial investigating the combination of erdafitinib plus enfortumab vedotin in which the objective response rate was 100% (9/9 patients: 8 PRs & 1CR).
Citation Format: Sean Clark-Garvey, Mi Zhou, Michael Sturdivant, Wolfgang Beckabir, Lucia Kim, E. Drew Toomer, Ian McCabe, Akihiro Hamada, Daniel Crona, Jeffrey S. Damrauer, William Y. Kim. FGFR inhibition upregulates Nectin-4 expression in FGFR3 altered urothelial carcinoma [abstract]. In: Proceedings of the AACR Special Conference on Bladder Cancer: Transforming the Field; 2024 May 17-20; Charlotte, NC. Philadelphia (PA): AACR; Clin Cancer Res 2024;30(10_Suppl):Abstract nr B014.