Abstract 1769: CSox-based sensors for continuous, homogeneous and quantitative monitoring of protein kinase and phosphatase activity
Authors: Schaefer Erik M. , Cornell-Kennon Susan , Lu Bill 
Published: August 2019

Abstract
Introduction: Protein kinases are a diverse group of 518 enzymes whose dysregulation lies at the center of many diseases. Currently, 30% of all drug development efforts are focused on protein kinases. Although 41 drugs are approved and &gt;120 in clinical trials, these are predominately ATP-competitive inhibitors. More recently, there has been an expanded focus on kinase inhibitors with different modes of action, where new tools are needed to effectively characterize inhibitor mechanism of action, predict drug potency and to drive decisions earlier in the drug development process. We developed a simple yet powerful method for the generation of peptide sensors that can be used for the continuous, quantitative and homogenous detection of kinase and phosphatase activity with recombinant enzymes and crude lysates to enable target discovery and drug development.
Experimental Procedures: We harnessed chelation-enhanced fluorescence by combining next generation sulfonamido-oxine (Sox) chromophore technology with high-throughput solid-phase peptide synthesis methods to identify optimized sequences based on physiological substrates. Enzyme activity is monitored kinetically using fluorescence intensity (Ex/Em 360/485 nm) or in endpoint mode using Europium and time-resolved fluorescence (Ex/Em 360/620 nm).
Results: We demonstrate the ability to rapidly identify novel optimized substrates, where performance measures included higher reaction rates, lower Km's, higher signal/background, increased sensitivity and specificity. We identified highly generic substrates (for robust detection of 80 Tyrosine kinases) and highly-selective substrates (for quantitative detection of targeted kinases in crude cell or tissue lysates for profiling, potency assessments and SAR). We have developed sensors to monitor activity of high-profile tyrosine kinases, including the EGFR and clinically-relevant mutants, JAK kinases, Tec-kinases, and, serine/threonine kinases, including CDK1-9, MAPK pathway (MAP4Ks, MAP3Ks, MAPKs & MAPKAPKs), PKR/EIF2AKs and PIM1. In addition, CSox-based phosphopeptide substrates are used to monitor protein phosphatases with specificity for tyrosine (PTP1B, SHP1/2) or serine/threonine (PP2A, PP2C, PHLPP).
Conclusions: The generation of robust activity-based sensors, even where peptide assays previously weren’t available, opens new areas for effective drug discovery. The Sox-based kinetic assay format is ideal for elucidating drug mechanism of action, potency, and enzyme regulation. The PhosphoSens-Red endpoint format is ideal for HTS, SAR and profiling. Together, these formats can be applied across the entire target discovery and drug development workflow, providing a quantum improvement in performance and productivity needed to address the challenges and opportunities of next generation protein kinase and phosphatase inhibitors.
Citation Format: Erik M. Schaefer, Susan Cornell-Kennon, Bill Lu. CSox-based sensors for continuous, homogeneous and quantitative monitoring of protein kinase and phosphatase activity [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2019; 2019 Mar 29-Apr 3; Atlanta, GA. Philadelphia (PA): AACR; Cancer Res 2019;79(13 Suppl):Abstract nr 1769.