Abstract 1793: Pre-targeting with in vivo click chemistry enables preferential drug exposure in tumors versus normal tissues

Abstract Off-target toxicity has long been a dose-limiting factor for antibody-drug conjugates (ADCs) and targeted radiopharmaceutical therapies (TRT). This fundamental limitation primarily arises due to the catabolic elimination process of both therapeutic modalities which exposes healthy tissues to cytotoxic agents. Pre-targeting offers a transformative solution to overcome these challenges as it separates the tumor-targeting and payload-delivery steps, thereby minimizing systemic exposure and maximizing on-target effects. Leveraging this concept, we present Click Activated Protodrugs Against Cancer (CAPAC®) technology as the ideal pre-targeting reunion platform. CAPAC uses in vivo click chemistry to selectively capture drug payloads at tumors with minimal systemic exposure, thus extending the therapeutic window of targeted therapies. CAPAC employs a two-component system: 1) a clickable binder infusion targeting a tumor antigen, and 2) a subsequent infusion of a clickable payload (“protodrug”). These two components “click” at tumors, enabling delivery of high therapeutic payload to the target while sparing normal tissues. We have generated proof-of-concept data on CAPAC using clickable binders against HER2, TROP2, and CEACAM5, which we paired with different clickable payloads, including a trans-cyclooctene (TCO)-modified biotin probe and a protodrug of monomethyl auristatin E (MMAE). We evaluated the anti-tumor efficacy, pharmacokinetics (PK), and biodistribution across CDX models or in tumor-free mice. Payload capture was antigen-dependent and markedly higher in tumors vs plasma and normal tissues, with tumor levels exceeding systemic levels by more than 10-fold at 8.5 hours post-infusion. Tumor payload exposure was proportional with receptor density, as the HER2-binder captured more biotin than the TROP2-binder. Slower antigen internalization (HER2, CEACAM5) extended the duration of payload exposure in tumor vs plasma compared to faster internalization (TROP2). These PK and biodistribution results validate the highly selective tumor targeting of CAPAC. Importantly, enhanced tumor payload exposure translated into significant anti-tumor efficacy with the MMAE protodrug, which achieved dose-dependent tumor growth inhibition across various CDX models. These findings underscore CAPAC’s potential to overcome the limitations of off-target toxicities and extend the applicability of cytotoxic agents to poorly internalizing targets. Our preclinical data confirm in vivo click chemistry as a powerful pre-targeting reunion technology, offering modularity to accommodate various antigen targets and payloads. By delivering targeted therapies with unprecedented precision, CAPAC fulfills Paul Erlich’s vision of a truly targeted delivery system. CAPAC opens new avenues for safer and more effective cancer treatments, addressing needs are yet unmet by ADCs and TRTs. Citation Format: Travis L. Biechele, Masa Aleckovic, Stefanie Wagner, George Coricor, Sangeetha Srinivasan, Tri-Hung Nguyen, Jesse M. McFarland, Nathan A. Yee, Michael Zakharian, Jose M. Oneto. Pre-targeting with in vivo click chemistry enables preferential drug exposure in tumors versus normal tissues [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 1793.