Schizophrenia affects almost 1% of the world population. While therapeutic benefit has been established with current antipsychotics to treat positive syndromes of schizophrenia, efficacy has not been established in treatment of negative syndromes and cognitive dysfunction of the illness. All current antipsychotic drugs act promiscuously on a family of biogenic amine G protein-coupled receptors (GPCRs). The relationships remain obscure between the psychotic syndromes and specific therapeutic targets, which forms a major obstacle in developing novel antipsychotics. In order to better evaluate the actions of current antipsychotics at receptor level, we propose to establish a multiplexed high throughput functional assay platform applying a novel realtime cAMP assay in combination with a well-establsihed calcium assay. In contrast to the traditional competitive immunoassay of cAMP, the novel assay uses a cyclic nucleotide-gated channel to monitor free [cAMP] in living cells, providing kinetic measurement of activity of both Gs- and Gi-coupled receptors with excellent signal-to-noise ratio and sensitivity. The assay can be scaled up applying FLIPR or potentially the cell-array platform. In this feasibility study, we will apply the novel cAMP assay to measure intrinsic efficacy of several partial agonists against the dopamine D2 receptor, and to determine relative potency and efficacy of the most common antipsychotic drugs, olanzapine, quetiapine, clozapine, and aripiprazole against several potential GPCR targets. The long-term goal of the project is to characterize currently important antipsychotics against all biogenic amine receptors and other potential receptor targets to provide a solid receptor profile of antipsychotics. The link between receptor activity profile and clinical pharmacology of antipsychotics established through this project should facilitate future drug development programs by enabling early prediction of safe and effective new antipsychotics.
