The present application relates to an
assay method using affinity crosslinking of
DNA-linked ligands to proteins to enable
small molecule screening and determination of apparent affinity constants of ligands to the proteins. This method has been applied to determine 96 compounds' dissociation constants to a
protein target simultaneously, and directly determine a compound's IC50 against five
protein targets concurrently in crude
cell lysates. Additionally, this approach was used to screen a
Library of Pharmacologically Active Compounds (LOPAC)
library against
dihydrofolate reductase (eDHFR), enabling the discovery of a novel eDHFR inhibitor (IC50=7.9 μM). An
assay kit and the method of uses are within the scope of this disclosure.