Abstract 1323: Preclinical evaluation of target-mediated clearance and alternative payloads in CDH17-directed antibody drug conjugates.

Abstract Cadherin 17 (CDH17), is an emerging target for antibody-based therapeutics in colorectal cancer (CRC), with multiple CDH17-directed chimeric antigen receptor-T/natural killer, bispecific antibodies and antibody drug conjugates (ADCs) in preclinical and early-stage clinical development. Success of these molecules depends on their ability to overcome high expression of P-glycoprotein (P-gp) pumps in CRCs and CDH17 in normal gut epithelium. Here, we investigate the therapeutic potential of CDH17-directed ADCs.High frequency expression of CDH17 in patient tumor microarrays and cell line derived xenografts (CDXs) was confirmed by IHC assay. CDH17-directed ADCs were generated through conjugation of a fully humanized CDH17 mAb to either an anti-mitotic (CDH17-MMAE) or topoisomerase 1 inhibitor (CDH17-exatecan) payload via a cleavable linker. Selective ADC binding and internalization were confirmed by flow cytometry and immunofluorescence.CDH17-MMAE treatment induced significant anti-tumor activity in 5/5 CDH17+ CRC CDXs models, with the strongest and most prolonged responses observed in xenografts that were P-gp low/negative. Head-to-head comparison of CDH17-MMAE and CDH17-exatecan payloads demonstrated improved efficacy for CDH17-exatecan over CDH17-MMAE in high P-gp expressing models. The functional role of P-gp in resistance to MMAE-based ADCs was confirmed using cell lines engineered to either overexpress P-gp through transfection or to lose P-gp expression through CRISPR knockdown. Forced overexpression of P-gp in SNUC1 CDH17+ cells conferred resistance to CDH17-MMAE, while sensitivity to CDH17-exatecan remained. Conversely, CRISPR knockdown of P-gp in CDH17+ LS513 cells reversed resistance to CDH17-MMAE. These findings were confirmed in xenograft studies.Due to lack of binding of the anti-human CDH17-ADCs with mouse or rat CDH17, a mouse model expressing human CDH17 extracellular ECD (B-hCDH17 mice) was used in pharmacokinetic (PK) studies. In wild-type mice, both ADCs exhibited PK profiles consistent with those typically observed for most ADCs. However, in humanized B-hCDH17 mice, both CDH17-MMAE and CDH17-exatecan ADCs were completely cleared from mouse serum less than 96 hours post-dosing, indicating that CDH17 expression in normal colon and ileum may act as a clearance sink for the ADCs.Data presented here support use of topoisomerase 1 inhibitor payloads in cancers where P-gp expression is high. Target-mediated clearance driven by normal gut CDH17 expression presents a pharmacokinetic challenge that may limit clinical utility and require dose optimization or alternative dosing strategies to achieve sufficient tumor exposure while managing potential on-target, off-tumor toxicity. Citation Format: Neil A. O'Brien, Jun Zhang, Martina SJ McDermott, Ke Wei Gong, Ming Lu, Benjamin Hoffstrom, Min Liang, Weiping Jia, Tong Luo, Athena M. Madrid, Raul Ayala, John A. Glaspy, Leonard Presta, Dennis J. Slamon.. Preclinical evaluation of target-mediated clearance and alternative payloads in CDH17-directed antibody drug conjugates 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 1323.