Abstract 4430: WuXiTecan2: A hydrophilic exatecan linker-payload for dual-payload ADC discovery

Abstract Background: Exatecan, a camptothecin-derived topoisomerase inhibitor, demonstrates high potency along with robust bystander activity. Several exatecan-based ADCs against diverse targets have now entered into late-stage clinical trials. In parallel, the need to overcome resistance mechanisms have intensified interest in dual-payload ADC strategies, with exatecan emerging as a compelling payload option in these combination formats. However, its hydrophobic physicochemical properties can lead to ADC aggregation, non-specific uptake, reduced plasma stability, particularly at DAR8, or in dual-payload settings. Therefore, the introduction of hydrophilic moieties via linker design is essential to improve ADC hydrophilicity and physicochemical behavior. Here, we developed a super-hydrophilic linker payload, named WuXiTecan2, that overcomes exatecan’s hydrophobicity and shows strong efficacy and good tolerability in vitro and in-vivo, both as DAR8 ADC and in dual-payload ADC formats. Methods: WuXiTecan2 was conjugated to Trastuzumab at DAR8 or formulated as a trastuzumab-dual payload ADC paired with an MMAE payload using WuXiDARX Technology. The resulting ADCs were fully characterized by HIC-HPLC, SEC-HPLC, and LC-MS. The in-vitro activity was assessed across breast and gastric cancer cell lines with varied HER2 expressions. Plasma stability was evaluated in the mouse, and human plasma. In-vivo efficacy was determined in Her2 expressing CDX models, and the tolerability of trastuzumab-WuXiTecan2 ADC(DAR8) was evaluated in mice and preliminary cynomolgus monkey studies. Results: WuXitecan2 was conjugated to trastuzumab at DAR8 and incorporated into a dual-payload ADC pairing with MMAE payload. Both formats were successfully generated and demonstrated highly uniform conjugation profiles. Notably, the introduction of WuXiTecan2 showed excellent ADC hydrophilicity, which is very close to naked antibody. In-vitro, both ADC formats displayed sub-nanomolar IC50 across a panel of breast and gastric cancer cell lines spanning HER2 expression levels. Both DAR8 and dual-payload ADCs showed improved plasma stability in mouse and human plasma, consistent with the enhanced hydrophilicity of the linker and its stabilizing effect on the exatecan payload. In Her2-expressing CDX models, the dual-payload ADC achieved superior tumor growth inhibition relative to the single-payload DAR8 ADC at comparable doses. Treatment was well tolerated; the trastuzumab-WuXiTecan2 DAR8 ADC demonstrated acceptable tolerability in mouse studies at a single dose up to 250mg/kg,and tolerated well in preliminary cynomolgus monkey studies at 45mg/kg, Q3Wx3. Conclusions: WuXitecan2, enabled by the hydrophilic linker moiety design, demonstrated strong efficacy, stability and tolerability, supporting its use as a promising dual-payload ADC component. Citation Format: Hu Chen, Qirui Fan, Zili Xu, Xiaomei Li, Ding Wei, Lin Zhang, Chenghu Hu, Cindy Cheng, Marie Zhu. WuXiTecan2: A hydrophilic exatecan linker-payload for dual-payload ADC discovery 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 4430.