Abstract 4363: Establishment of plasma inhibitory kinase assays (PIA) to detect functional drug levels in patient plasma

Abstract Anticipation of the in vivo activity of an investigational new drug (IND) is challenging. In the context of the living body, compounds are subjected to degradation, metabolic modification or binding to plasma proteins - mechanisms that are well described to potentially compromise the in vivo activity seen in the patient compared to its predicted potential to inhibit its target in specific in vitro assays. As such assays are performed in artificial cell-culture media, we had previously modified our proprietary cellular FLT3 kinase phosphorylation assay to measure the activity of FLT3 inhibitors directly in and from human plasma, similar as described by Levis et al. 1. We hence established a method to analyze the activity of kinase inhibitors in human or rodent plasma (plasma inhibitory activity assay, PIA) in ELISA-based cellular kinase assays. We have successfully applied this methodology to determine the pharmaco-kinetics of a newly developed inhibitor of FLT3 in the context of a clinical trial targeting FLT3. We have now expanded this methodology for the detection of further kinase targets of potential clinical relevance. We were able to compile in vitro PIA assay data for further kinases such as VEGFR2 and BCR-Abl which will allow us to better predict the in vivo effect of specific inhibitors of these kinases and to determine the amount of freely available active test substance in the blood/sera of treated cancer patients. 1: Levis et al. Blood. 2006; 108 (10):3477-3483 Citation Format: Lena Pilgermayer, Eva M. Egenter, Katharina Schaich, Daniel Feger, Jan E. Ehlert. Establishment of plasma inhibitory kinase assays (PIA) to detect functional drug levels in patient plasma [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 4363.