Abstract 1786: AST-203, a novel Trop2-targeting aptamer-drug conjugate, exhibits potent antitumor efficacy for the treatment of solid tumors

Abstract Background: Trophoblast cell surface antigen 2 (Trop2), a transmembrane glycoprotein overexpressed in various epithelial cancers, including pancreatic ductal adenocarcinoma (PDAC), breast, lung, and bile duct cancers, represents an attractive target for cancer therapy. Trodelvy, a Trop2-targeting antibody-drug conjugate (ADC) linked to the topoisomerase I inhibitor SN-38, has been approved for the treatment of triple-negative breast cancer. This study focuses on the development of a novel Trop2 aptamer-MMAE conjugate (AST-203) and its characterization in comparison to the ADC. Methods: AST-203 was designed by attaching a Trop2-targeting aptamer to three MMAE molecules (a microtubule inhibitor) using a proprietary branched linker (Blinker). Binding affinity (kd) to rhTrop2 was measured by BLI, with specific Trop2 targeting confirmed by FACS and ICC. The internalization rate of the aptamer was determined by FACS. In vitro cytotoxicity was evaluated in 2D and 3D cultures using CellTiter-Glo assays. The penetration capability was assessed through ICC in BxPC3 spheroid models. For in vivo studies, AST-203 was administered intravenously at doses of 2, 3, and 4 mpk, and Trodelvy (6 mpk) was used as a comparator in a PDAC xenograft model. Results: The Trop2 aptamer binds to human Trop2 with an affinity of 8.6 nM and specifically targets Trop2-positive cells (BxPC3, Capan1) but not Trop2-negative PANC1 cells. It internalizes with a half-time of 15.23 minutes (95% CI: 11.30-23.34 minutes), localizing to lysosomes as confirmed by ICC. The IC50 of AST-203 was 20 nM in BxPC3 cells and 99 nM in Capan-1, while >1 µM in PANC1 cells. Additionally, studies on the anticancer effects in various cancer cells revealed a correlation with Trop2 expression levels. Notably, the Trop2 aptamer showed 6-10 times better penetration in spheroid cultures than a Trop2 antibody. AST-203 treatment significantly reduced Ki-67 expression in spheroid interiors compared to Trodelvy, consistent with its superior penetration. In addition, conditioned media from AST-203-treated cells also elicited a bystander effect on Trop2-negative PANC1 cells. Cell cycle arrest and the activation of apoptotic signal cascade was demonstrated as the mechanism of cell death. AST-203 showed minimal cytotoxicity in PBMCs and megakaryocyte (platelets precursor cell) compared to Trodelvy. In vivo, AST-203 effectively inhibited tumor growth in a BxPC xenograft model, showing superior efficacy at doses of 3 and 4 mpk compared to Trodelvy (6mpk). Conclusion: AST-203 shows the potential of a promising next-generation therapeutic for Trop2-positive solid tumors. Its superior efficacy and safety compared to traditional antibody-drug conjugates highlight its potential to improve therapeutic outcomes for Trop2-expressing cancers. These findings underscore AST-203 as a significant advancement in aptamer-based therapeutics. Citation Format: Ju-hyung Kang, Daekyun Lee, Seo-young Kwak, Jieon Lee. AST-203, a novel Trop2-targeting aptamer-drug conjugate, exhibits potent antitumor efficacy for the treatment of solid tumors [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 1786.