Evaluation of the acute oral toxicity and antipsychotic activity of a dual inhibitor of PDE1B and PDE10A in rat model of schizophrenia

Phosphodiesterase 1B (PDE1B) and PDE10A are dual-specificity PDEs that hydrolyse both cyclic adenosine monophosphate and cyclic guanosine monophosphate, and are highly expressed in the striatum. Several reports have suggested that PDE10A inhibitors may present a promising approach for the treatment of positive symptoms of schizophrenia, whereas PDE1B inhibitors may present a novel mechanism to modulate cognitive deficits. Previously, we have reported a novel dual inhibitor of PDE1B and PDE10A, compound 2 [(3-fluorophenyl)(2-methyl-2,3-dihydro-4H-benzo[b][1,4]oxazin-4-yl)methanone] which has shown inhibitory activity for human recombinant PDE1B and PDE10A in vitro. In the present study, the safety profile of compound 2 has been evaluated in rats in the acute oral toxicity study, as well as; the antipsychotic-like effects in the rat model of schizophrenia. Compound 2 was tolerated up to 1 g/kg when administered at a single oral dose. Additionally, compound 2 has strongly suppressed ketamine-induced hyperlocomotion, which presented a model for the positive symptoms of schizophrenia. It has also shown an ability to attenuate social isolation induced by chronic administration of ketamine and enhanced recognition memory of rats ​in the novel object recognition test. Altogether, our results suggest that compound 2 represents a promising therapy for the treatment of the three symptomatic domains of schizophrenia.