Abstract 5774: Enhancing urothelial carcinoma treatment with nectin-4-PET: A predictor of enfortumab vedotin efficacy

Introduction: Enfortumab vedotin (EV), an antibody-drug conjugate targeting nectin-4, has shown significant promise in treating urothelial carcinoma (UC). However, optimizing its efficacy while minimizing treatment-related toxicities necessitates a deeper understanding of EV’s target engagement at tumors and its correlation with therapeutic outcomes. To address this, we developed a peptide-based nectin-4 specific positron emission tomography (PET) radiotracer, [68Ga]AJ647, to visualize and quantify EV-induced pharmacodynamics (target engagement) across different EV doses. Methods: Six UC cell lines representing luminal (HT-1376, UC-14, RT-112) and basal (UC-9, SCaBER, T24) morphologies were used to evaluate in vitro and in vivo nectin-4 specificity of [68Ga]AJ647. Effect of EV on [68Ga]AJ647 uptake was evaluated using competitive binding studies. Target engagement was defined as the percentage reduction in [68Ga]AJ647 tumor uptake, pre-therapy normalized, following EV therapy. In vivo EV target engagement was assessed via PET in HT-1376 xenografts at FDA-equivalent doses (6, 9, 15 mg/kg) on days 1, 3, and 6 post-treatment. Long-term responses to 6 and 15 mg/kg with Nectin-4-PET evaluated target engagement metrics' predictive value. Results: In vitro assays revealed a strong correlation between [68Ga]AJ647 uptake and nectin-4 expression (R2=0.85). PET and biodistribution studies confirmed nectin-4-specific uptake across xenografts at 60 minutes post-injection. EV treatment reduced [68Ga]AJ647 uptake in a dose-dependent manner, validating the tracer’s ability to measure unoccupied nectin-4. At 24 hours post-treatment, unoccupied nectin-4 levels were similar between 15, 9, and 6 mg/kg groups at approximately 23%. By day 6, these levels diverged significantly, indicating reduced target engagement over time, particularly at lower doses. Further analyses revealed that tumor volume reductions exhibited dose-dependent trends but showed high variability. While pre- and post-treatment [68Ga]AJ647 imaging measures (standard uptake values) were not strongly predictive of therapeutic outcomes, the normalized ΔSUV, reflecting EV-induced target engagement, demonstrated a stronger correlation (r=-0.7877). Mice with less than 25% target engagement showed significantly poorer therapeutic responses, regardless of injected dose. ROC analysis confirmed the predictive power of normalized ΔSUV, with an AUC of 0.87 and a 25% engagement threshold as a robust predictor of positive therapeutic outcomes. Conclusion: [68Ga]AJ647-PET provides a non-invasive quantitative approach to assessing nectin-4 expression and EV-induced pharmacodynamics. Normalized ΔSUV values, which integrate pre- and post-treatment data, serve as reliable predictors of therapeutic efficacy. These findings highlight the potential of nectin-4 PET to optimize personalized EV dosing. Citation Format: Akhilesh Mishra, Ajay K. Sharma, Kuldeep Gupta, Burles A. Johnson, Jeannie Hoffman-Censits, David J. McConkey, Sridhar Nimmagadda. Enhancing urothelial carcinoma treatment with nectin-4-PET: A predictor of enfortumab vedotin efficacy [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 5774.