Inexpensive High-Throughput Screening of Kinase Inhibitors Using One-Step Enzyme-Coupled Fluorescence Assay for ADP Detection

Protein kinases are attractive targets for both biological research and drug development. Several assay kits, especially for the detection of adenosine diphosphate (ADP), which is universally produced by kinases, are commercially available for high-throughput screening (HTS) of kinase inhibitors, but their cost is quite high for large-scale screening. Here, we report a new enzyme-coupled fluorescence assay for ADP detection, which uses just 10 inexpensive, commercially available components. The assay protocol is very simple, requiring only the mixing of test solutions with ADP detection solution and reading the fluorescence intensity of resorufin produced by coupling reaction. To validate the assay, we focused on CDC2-like kinase 1 (CLK1), a dual-specificity kinase that plays an important role in alternative splicing, and we used the optimized assay to screen an in-house chemical library of about 215,000 compounds for CLK1 inhibitors. We identified and validated 12 potent inhibitors of CLK1, including a novel inhibitory scaffold. The results demonstrate that this assay platform is not only simple and cost-effective, but also sufficiently robust, showing good reproducibility and giving similar results to those obtained with the widely used ADP-Glo bioluminescent assay.