Development of a Screening Assay to Measure the Loss of Antibacterial Activity in the Presence of Proteins: Its Use in Optimizing Compound Structure

Abstract

An assay quantifying the loss of antibacterial potency of compounds, originally identified via target-based screening, in the presence of increasing albumin concentration was developed and used as a technique to measure potential association of com-pounds with proteins unrelated to their molecular target. Minimum inhibitory concentrations (MICs) of test compounds were measured against Staphylococcus aureus strain ATCC 6538 in the presence of 0-12 [.proportional]M bovine serum albumin (BSA). The linear regression coefficient r2for the correlation between MIC and BSA concentration was ≥ 0.9 for 49 and > 0.5 for 62 out of a total of 69 compounds tested. The slope of these correlations varied widely from < 1 to 99, suggesting that the loss of potency due to a given concentration of BSA could vary from compound to compound due to wide variation in the apparent stoichiometry for protein-ligand association. Follow-up experiments using additional proteins and a fatty acid, oleic acid, showed that this compound:BSA association was not protein specific, but was likely driven by hydrophobicity. The method described in this report can be used to optimize compound design and minimize this undesirable effect. ( Journal of Biomolecular Screening 2003:555-558)