Unique effect of clozapine on adenosine A-dopamine D receptor heteromerization.

The striatal dopamine D receptor (DR) is generally accepted to be involved in positive symptoms of schizophrenia and is a main target for clinically used antipsychotics. DR are highly expressed in the striatum, where they form heteromers with the adenosine A receptor (AR). Changes in the density of AR-DR heteromers have been reported in postmortem tissue from patients with schizophrenia, but the degree to which AR are involved in schizophrenia and the effect of antipsychotic drugs is unknown. Here, we examine the effect of exposure to three prototypical antipsychotic drugs on AR-DR heteromerization in mammalian cells using a NanoBiT assay. After 16 h of exposure, a significant increase in the density of AR-DR heteromers was found with haloperidol and aripiprazole, but not with clozapine. On the other hand, clozapine, but not haloperidol or aripiprazole, was associated with a significant decrease in AR-DR heteromerization after 2 h of treatment. Computational binding models of these compounds revealed distinctive molecular signatures that explain their different influence on heteromerization. The bulky tricyclic moiety of clozapine displaces TM 5 of DR, inducing a clash with AR, while the extended binding mode of haloperidol and aripiprazole stabilizes a specific conformation of the second extracellular loop of DR that enhances the interaction with AR. It is proposed that an increase in AR-DR heteromerization is involved in the extrapyramidal side effects (EPS) of antipsychotics and that the specific clozapine-mediated destabilization of AR-DR heteromerization can explain its low EPS liability.