Combination of Haloperidol with UNC9994, β-arrestin-biased analog of Aripiprazole, ameliorates schizophrenia-related phenotypes induced by NMDAR deficit in mice

Background Glutamatergic system dysfunction, particularly involving the N-methyl-D-aspartate receptor (NMDAR), contributes to a full spectrum of schizophrenia-like symptoms, including the cognitive and negative symptoms that are resistant to treatment with antipsychotic drugs (APDs). Aripiprazole, an atypical antipsychotic drug (APD), acts as a dopamine partial agonist and its combination with haloperidol (a typical APD) has been suggested as a potential strategy to improve schizophrenia symptoms. Recently, an analog of aripiprazole - UNC9994 was developed. UNC9994 does not affect D2R-mediated Gi/o protein signaling but acts as a partial agonist for D2R/β-arrestin interactions. Hence, our objective was to probe the effects of co-administrating haloperidol with UNC9994 in NMDAR mouse models of schizophrenia. Methods NMDAR hypofunction was induced pharmacologically by acute injection of MK-801 (NMDAR pore blocker; 0.15 mg/kg) and genetically by knockdown of Grin1 gene expression in mice, which have a 90% reduction in NMDAR levels (Grin1-KD). After intraperitoneal injections of vehicle, haloperidol (0.15 mg/kg), UNC9994 (0.25 mg/kg) or their combination mice were tested in open field, Pre-Pulse inhibition (PPI), Y-maze and Puzzle box. Results Our findings indicate that low dose co-administration of UNC9994 and haloperidol reduces hyperactivity in MK-801-treated animals and in Grin1-KD mice. Furthermore, this dual administration effectively reverses PPI deficits, repetitive/rigid behavior in the Y-maze, and deficient executive function in the Puzzle box in both animal models. Conclusions The dual administration of haloperidol with UNC9994 at low doses represents a promising approach to ameliorate positive, negative, and cognitive symptoms of schizophrenia. Significance statement Schizophrenia is a devastating mental disorder and characterized by positive, negative, and cognitive symptoms. Cognitive and negative symptoms remain a focus of research dedicated to development of effective antipsychotic drugs (APDs). Aripiprazole, an atypical APD, acts as a dopamine partial agonist and its combination with haloperidol (a typical APD) has been suggested as a potential strategy to improve schizophrenia symptoms. An analog of aripiprazole - UNC9994 was recently developed, which does not affect D2R-mediated Gi/o protein signaling but acts as a partial agonist for D2R/β-arrestin interactions. Our pre-clinical findings on pharmacological (MK-801, 0.15 mg/kg) and genetic (Grin1-KD) mouse models of NMDAR deficiency showed that the dual administration of UNC9994 (0.25 mg/kg) with haloperidol (0.15 mg/kg) at low doses reduces hyperactivity, corrects prepulse inhibition (PPI) deficits, rigid behavior in the Y-maze, and deficient executive function in the Puzzle box. Further studies of the polypharmacy of UNC9994 with APDs is essential to facilitate translational studies in clinics. ### Competing Interest Statement The authors have declared no competing interest.