Biological Characterization of Neurokinin Antagonists Discovered Through Screening of a Combinatorial Library

Recent advances in combinatorial chemistry have resulted in the rapid screening of libraries against biological targets. Another advance in biological screening is the ability to design and utilize novel, automated, nonradioactive assays for targets of pharmaceutical interest. Using encoding technology and europium time-resolved fluorescence, we have designed primary receptor binding assays to define active compounds against the neurokinin-1 and neurokinin-2 receptor subtypes. In addition, a secondary, cell-based, functional assay measuring intracellular calcium flux with calcium sensitive fluorophores was used to determine receptor agonist or antagonist activities. We adapted a cuvette based assay to a CCD camera and digital imaging system that allowed us to demonstrate functional receptor antagonist activity in all 96 wells of a microtiter plate simultaneously. The screening of a 20,000 member library using europium labeled neurokinin ligands resulted in the identification of 43 active compounds for neurokinin-1 and 27 for neurokinin-2. Through medicinal chemistry and structure-activity relationships, a compound was synthesized with balanced dual antagonist activity at both neurokinin receptors with greater than 100-fold less activity against the neurokinin-3 receptor subtype. The structure-activity relationships generated from this initial library can now be used to design a new focused library to improve on neurokinin-1/neurokinin-2 receptor potency and selectivity.