Abstract 7227: <i>NECTIN4-a</i> mplified breast cancer targeted by Zelenectide Pevedotin: Amplification and expression are frequent, concordant, and stable

Abstract Background: NECTIN4 amplification (amp) can predict response to Nectin4-targeted therapy. In the Phase I/II Duravelo-1 trial (NCT04561362), NECTIN4-amp breast cancer (BC) showed higher response rates to the Bicycle® Drug Conjugate (BDC™) zelenectide pevedotin (zele, formerly BT8009) versus non-amp tumors (57.1% vs. 6.3%) (Klümper et al, SABCS 2024). These findings led to FDA Fast Track designation and the Phase II Duravelo-3 trial in NECTIN4-amp BC (NCT06840483). To further characterize NECTIN4 and its targetability, we assessed its prevalence, biology across BC datasets, and describe its structure-activity based targeting. Methods: Public, multi-omic primary BC data from METABRIC (n=2173), TCGA (n=1079), and TRANSNEO (n=166) were analyzed. Proprietary primary tissue data (Cologne cohort, n=252) linked high NECTIN4 copy number (CN; amp/polysomy via FISH) with expression and BC subtypes. Metastatic analyses were conducted on META-PRISM (n=59). High NECTIN4 CN was defined as &amp;gt;2× ploidy (amp) or ≥6 copies (polysomy). Structural and biophysical studies (crystallography, SPR) assessed zele’s binding. Results: High NECTIN4 CN was observed in 21.1% (METABRIC), 30.8% (TCGA), and 29.5% (TRANSNEO) of cases, ranking in the 97.5th percentile for amp (TCGA, all genes). By subtype, HR+, HER2+, and TNBC tumors exhibited high CN in 21%, 19%, and 20% (METABRIC) and 30%, 29%, and 36% (TCGA), respectively. CN correlated with elevated mRNA (p &amp;lt; 2 × 10-16) and protein expression (p = 2 × 10-6). No differences were observed by immune infiltrate or germline BRCA status. In the Cologne cohort, high NECTIN4 CN (19.1%) strongly correlated with membranous Nectin-4 expression (median H-score 150 vs 0, p = 8.8 × 10-28). In META-PRISM metastases, high CN prevalence was similar (29%) and correlated with RNA expression (r2 = 0.34, p &amp;lt; 0.00001). Zelenectide pevedotin binds Nectin-4 domain 1 with high affinity (Kd 2.5 ± 1.5 nM) and minimal conformational change (RMSD 0.435 Å). Its compact bicyclic scaffold (4.2 kDa, surface area 1900 Å2) provides a smaller footprint than conventional antibodies while maintaining strong target engagement, and rapid renal clearance (t½ &amp;lt;1 h), which should support rapid tumor penetration, and efficient delivery of the MMAE payload. Conclusions: NECTIN4 amplification is frequent, concordant with high RNA and protein expression, and stable in frequency between primary and metastatic BC. Nectin-4 can be effectively engaged by the BDC zelenectide pevedotin with high affinity. The frequency and stability of NECTIN4 amplification across breast cancer subtypes supports its evaluation as a biomarker for patient selection in Nectin-4-targeted trials. Citation Format: Alexander Azizi, Niklas Klümper, Emma Colliver, Alexander Quaas, Birgid Schoemig-Markiefka, Arndt Hartmann, Christoph Kuppe, Manuel Ritter, Viktor Grünwald, Michael Hölzel, Chris Bailey, Gustavo Arruda Bezerra, Nicholas Guthertz, Sergey Nikolaev, Fabrice Andre, Charles Swanton, Johannes Braegelmann, Markus Eckstein. NECTIN4-amplified breast cancer targeted by Zelenectide Pevedotin: Amplification and expression are frequent, concordant, and stable [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2026; Part 1 (Regular Abstracts); 2026 Apr 17-22; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2026;86(7 Suppl):Abstract nr 7227.