Abstract 5459: Accelerating the development of biologics: PRISM high throughput screening enables rapid preclinical characterization of antibodies, ADCs and payloads

Biologic agents, such as monoclonal antibodies and antibody-drug conjugates (ADCs), have emerged as a highly promising class of the cancer therapeutics due to their ability to target specific tumor antigens with high specificity, be engineered for selective delivery of cytotoxic payloads, and work through diverse mechanisms of action. While these complex characteristics render biologics highly effective in vivo, they pose difficulty for systematically evaluating these agents in vitro. Here, we describe a multiplexed screening approach to overcome these challenges using the PRISM assay, where antibodies and ADCs are screened across 900+ cancer cell lines. We first investigated a panel of HER2-targeting ADCs conjugated to several different linkers and payloads. We assessed target selectivity and observed a clear association between cell line sensitivity and HER2 expression, with the strongest effects on viability observed in a subset of cell lines overexpressing HER2. We further compared profiles across different ADC targets and payloads to investigate predictive biomarkers of payload sensitivity and characterize bystander killing capabilities. Finally, we developed an antibody internalization reporter (AIR) assay to enable screening of unconjugated monoclonal antibodies. We optimized the AIR methodology using a secondary Fab-drug conjugate which can be used to load drug payload onto any IgG antibody to target and kill cells that are recognized by the primary antibody. To validate this approach, we screened trastuzumab in combination with a secondary Fab conjugated to MMAF via a non-cleavable linker. Comparative profiling with trastuzumab directly conjugated to the same payload revealed similar cytotoxic potency and target selectivity. These results demonstrate how the PRISM AIR method can enable screening of antibody candidates for ADC development to evaluate antigen-specific binding, internalization and cell killing potential. Overall, our study highlights the capabilities of the PRISM assay for investigating antibodies and ADCs. Citation Format: Jillian N. Eskra, Alvin Kalathungal, Aydin Golabi, Bailey Porter, Antonella Masciotti, Nashielli Diaz-Gallegos, Anup Jonchhe, Maha Naim, Lia Petronio, Maggie LeMaitre, Jacob Asiedu, Ashish Bino George, Mustafa Kocak, Melissa M. Ronan, Matthew G. Rees, Jennifer A. Roth. Accelerating the development of biologics: PRISM high throughput screening enables rapid preclinical characterization of antibodies, ADCs and payloads [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 5459.