CHEMBL5738801

Alexa Fret: The PCSK9 Alexa FRET Standard assay measured the interaction between PCSK9 and an AlexaFluor647 (AF) tagged cyclic peptide, Reagent A (KD=83 nM). A solution containing 1 nM biotinylated PCSK9+2.5 nM Lance Streptavidin Europium (Strep-Eu) was made in 50 mM HEPES pH 7.4, 0.15 M NaCl, 5 mM CaCl2), 0.01% BSA, and 0.01% Surfactant P20. A separate solution containing 40 nM of the AlexaFluor tagged cyclic peptide was made in the same buffer system. An Echo was used to transfer 0.750 ul of compound to an assay plate followed by the addition of 15 ul of PCSK9+Stept-Eu and 15 ul of AF peptide. The final assay volume was 30.750 ul containing 0.5 nM PCSK9, 1.25 nM Strep-Eu, and 20 nM AF cyclic peptide. The reaction was incubated at room temperature for at least two hours prior to fluorescence measurements using an Envision Multilabel Reader. IC50 values were determined by fitting data to a sigmoidal dose-response curve using nonlinear regression. Ki was then calculated from the IC50 and the KD of AF cyclic peptide. Counts (B-counts) of the europium-labeled PCSK9 were followed to observe if compounds were adversely PCSK9.