Abstract 5174: High-throughput capillary immunoassays enable precise quantitation of protein degrader potency and kinetics in oncology discovery

Abstract Protein degraders such as PROteolysis TArgeting Chimeras (PROTAC degraders) have transformed oncology drug discovery by enabling catalytic removal of disease-relevant proteins rather than occupancy-based inhibition. To effectively rank and optimize degrader candidates, discovery teams need quantitative, reproducible assays that resolve both potency (e.g., DC50, Dmax) and degradation kinetics across large panels of compounds, concentrations, and time points. Conventional Western blotting lacks the throughput and consistency required for this role early in the screening funnel. Here, we demonstrate how Simple Western capillary immunoassays with the Leo system enables precise, quantitative degrader assessment with 96-sample throughput for upstream primary and secondary screening. Using androgen receptor (AR) degraders in AR-expressing MDA-MB-453 breast cancer cells as a model system, this method delivered robust, dose- and time-dependent AR degradation profiles with single-digit coefficients of variation and highly consistent DC50, Dmax, and degradation rate (kdeg) estimates between biological and technical replicates. The open antibody platform flexibility of Leo provides endogenous protein expression measurements for orthogonal validation of model systems such as anti-HiBiT antibodies. By resolving proteins by size, Leo can distinguish true target degradation from artifacts in plate-based assays (e.g., luminescent or fluorescence reporter loss), thereby validating plate-based screening hits and revealing false readouts that lack corresponding size-resolved changes in the target or reporter. These results establish high-throughput Simple Western assays on Leo as a fit-for-purpose solution for precise degrader quantitation at scale. The combination of open, antibody-agnostic detection chemistry, size-resolved readouts, and 96-sample throughput enables richer pharmacologic insight earlier in oncology screening funnels and supports data-driven prioritization and orthogonal validation of protein degrader candidates before advancing into more complex, resource-intensive models. Citation Format: Charles Haitjema, Francisco Ramirez, Bhamini Purandare, Pallavi Joshi, Chris Heger. High-throughput capillary immunoassays enable precise quantitation of protein degrader potency and kinetics in oncology 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 5174.