Abstract 4867: Effect of FGFR3 activity on Nectin-4 expression in urothelial carcinoma
Authors: Clark-Garvey Sean , Zhou Mi , Truong Andrew , Beckabir Wolfgang , Sturdivant Michael , Kim William 
Published: April 2023

Abstract
Bladder cancer is a common malignancy in the U.S. and cause of significant morbidity and mortality. Combination platinum-based chemotherapy has long been the mainstay in the treatment of metastatic urothelial carcinoma (mUC); however, over the last decade there have been significant advances in systemic therapy, which includes the FDA approval of the pan-FGFR inhibitor erdafitinib (approved for tumors with FGFR2/3 alterations) and the antibody drug conjugate (ADC) enfortumab vedotin (which targets the cell surface protein Nectin-4). Despite these advances, most patients with mUC will progress and succumb from their disease, highlighting the need for further therapeutic development. In parallel to therapeutic advances, there have been significant advances in the molecular characterization of UC, including identification of luminal and basal subsets. NECTIN4 and FGFR3 alterations are known to be enriched in luminal subtypes and we have found, via query of the TCGA data, that NECTIN4 expression was significantly higher in FGFR3 altered tumors. Given this association we sought to investigate the effect of FGFR3 activity on Nectin-4 expression. Using erdafitinib, in select luminal UC cell lines (RT112, RT4, SW780) with FGFR3 fusion proteins, we found, much to our surprise, that FGFR inhibition increased Nectin-4 expression. Western blots, probing for Nectin-4, following 24H, 48H, and 72H of treatment with erdafitinib (50 nM) showed a significant increase in protein expression in all three cell lines. Importantly, we consistently saw increased expression of what we believe corresponds to the membrane bound form of Nectin-4 and have now confirm such by flow cytometry and immunofluorescence probing for Nectin-4 in the RT112 cell line. We have also seen statistically significant increases in NECTIN4 on RT-PCR following treatment with erdafitinib; however, we believe that Nectin-4 regulation by FGFR inhibition is not merely transcriptional because the induction of Nectin-4 protein appears significantly greater than the fold increase in mRNA. Notably, in two additional UC cell lines (HT1376 - a luminal cell line with high Nectin-4 expression & UMUC3 - a basal cell line with low Nectin-4 expression), with no alterations in FGFR3, we did not see a significant change in Nectin-4 expression following treatment with erdafitinib. Based on our above results, we hypothesize that FGFR3 inhibition, in tumors harboring FGFR3 alterations, may act as a sensitize agent to Nectin-4 ADC targeted therapy; however, our results are preliminary and further investigation, particularly with in vivo models, is warranted.
Citation Format: Sean Clark-Garvey, Mi Zhou, Andrew Truong, Wolfgang Beckabir, Michael Sturdivant, William Kim. Effect of FGFR3 activity on Nectin-4 expression in urothelial carcinoma. [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2023; Part 1 (Regular and Invited Abstracts); 2023 Apr 14-19; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2023;83(7_Suppl):Abstract nr 4867.