Screening of a one bead–one compound combinatorial library for β-actin identifies molecules active toward Ramos B-lymphoma cells

The search for small molecules that specifically recognize protein targets is a laborious process if conducted in a one protein–one compound manner. A high-throughput antibody-based screening of one bead–one compound (OBOC) combinatorial small molecule libraries is described here, whereby libraries containing thousands of different small molecule ligands are synthesized on individual TentaGel beads and simultaneously screened for protein binding to individual beads, each with a different compound. The use of OBOC libraries greatly facilitates this simultaneous screening of thousands of compounds. Now, through the use of monoclonal or affinity-purified antibodies, small molecules that bind a particular protein contained in a complex mixture of biological molecules have been identified. This method identified small molecule ligands that bound β-actin present in cytoplasmic cell extracts of Ramos B-lymphoma cells. These small molecule ligands were resynthesized in immobilized and soluble forms and tested for binding of β-actin present in Ramos B-cell extracts and for activity against Ramos lymphoma cells. This high-throughput screening immunoassay method has great promise for improving our ability to find relevant, bioactive small molecules that target a specific native protein in a complex protein mixture without purification of the protein.