CLOZAPINE'S ANTAGONISM IS ROBUST AGAINST KNOWN DRD2 MUTATIONS

Schizophrenia is among the top 15 causes of disability worldwide, affecting approximately 3.7 million adults in the United States alone and creating over $300 billion in economic costs. Despite advancements in treatment, schizophrenia remains challenging to manage, with a recovery rate as low as 13%. Clozapine remains the gold standard pharmacological therapy for treatment-resistant schizophrenia (TRS). While research suggests that up to 40% of patients with TRS respond to clozapine, its use is limited. Given its rare but life-threatening side effects, clozapine is often not used as a first-line agent. Current clinical practice continues to rely heavily on a trial-and-error approach in antipsychotic selection in treating schizophrenia, and the responsiveness varies greatly in individuals. In our study, we combine both in silico and in vitro techniques to examine 14 frequently observed mutations of the human DRD2 receptor and their effects on antipsychotic-DRD2 receptor dynamics. We compared the effects of these genetic variants on clozapine-induced DRD2 antagonism with other frequently used antipsychotics. Using Bioluminence Resonance Energy Transfer (BRET), we quantitatively measured the functional activation of these DRD2 mutants to dopamine in HEK293T cells. Among the 14 DRD2 SNPs and 10 antipsychotics we screened, 11 out of the 14 SNPs significantly changed promazine’s DRD2 antagonism; 9 out of the 14 SNPs significantly changed pimozide’s DRD2 antagonism; 6 out of the 14 SNPs significantly changed fluphenazine’s DRD2 antagonism; and 4 out of the 14 SNPs significantly changed perphenazine’s DRD2 antagonism. Critically, none of the 14 SNPs significantly altered clozapine’s DRD2 antagonism. Here we provide the first functional cellular evidence of clozapine’s molecular resilience to DRD2 genetic variation, potentially explaining its robust clinical efficacy in treating patients with TRS.