The Novel Phosphodiesterase 9A Inhibitor BI 409306 Increases Cyclic Guanosine Monophosphate Levels in the Brain, Promotes Synaptic Plasticity, and Enhances Memory Function in Rodents.

Holger Rosenbrock,Cornelia Dorner-Ciossek,Anelise Marti,Klaus G Reymann,Ulrich H Schröder,Eliza Koros,Gerhard Schänzle,Riccardo Giovannini,Holger Fuchs,Frank Runge,Ernesto Fedele

doi:10.1124/jpet.119.260059

Abstract

N-methyl-d-aspartate (NMDA) receptor-dependent long-term potentiation (LTP) is an established cellular model underlying learning and memory, and involves intracellular signaling mediated by the second messenger cyclic guanosine monophosphate (cGMP). As phosphodiesterase (PDE)9A selectively hydrolyses cGMP in areas of the brain related to cognition, PDE9A inhibitors may improve cognitive function by enhancing NMDA receptor-dependent LTP. This study aimed to pharmacologically characterize BI 409306, a novel PDE9A inhibitor, using in vitro assays and in vivo determination of cGMP levels in the brain. Further, the effects of BI 409306 on synaptic plasticity evaluated by LTP in ex vivo hippocampal slices and on cognitive performance in rodents were also investigated. In vitro assays demonstrated that BI 409306 is a potent and selective inhibitor of human and rat PDE9A with mean concentrations at half-maximal inhibition (IC50) of 65 and 168 nM. BI 409306 increased cGMP levels in rat prefrontal cortex and cerebrospinal fluid and attenuated a reduction in mouse striatum cGMP induced by the NMDA-receptor antagonist MK-801. In ex vivo rat brain slices, BI 409306 enhanced LTP induced by both weak and strong tetanic stimulation. Treatment of mice with BI 409306 reversed MK-801-induced working memory deficits in a T-maze spontaneous-alternation task and improved long-term memory in an object recognition task. These findings suggest that BI 409306 is a potent and selective inhibitor of PDE9A. BI 409306 shows target engagement by increasing cGMP levels in brain, facilitates synaptic plasticity as demonstrated by enhancement of hippocampal LTP, and improves episodic and working memory function in rodents. SIGNIFICANCE STATEMENT: This preclinical study demonstrates that BI 409306 is a potent and selective PDE9A inhibitor in rodents. Treatment with BI 409306 increased brain cGMP levels, promoted long-term potentiation, and improved episodic and working memory performance in rodents. These findings support a role for PDE9A in synaptic plasticity and cognition. The potential benefits of BI 409306 are currently being investigated in clinical trials.

Highlights

concentration at half-maximal inhibition (IC50) values of 1.45 and 1.17 mM were calculated for PDE1A and PDE1C, respectively, and no inhibitory activity was observed for PDE2A, 3A, 4B, 5A, 6AB, 7A, and 10A with BI 409306 up to a concentration of 10 mM (Table 1)
Enzymatic and receptor binding assays demonstrated that BI 409306 is a potent and selective inhibitor of human PDE9A (IC50 5 65 nM), with weak affinity for PDE1 and .100fold selectivity for PDE9A over other PDE enzymes as well as a range of non-PDE targets
Systemic administration of BI 409306 led to an increase in cyclic guanosine monophosphate (cGMP) levels in the rat prefrontal cortex and cerebrospinal fluid (CSF), and to a reversal of cGMP reduction induced by the NMDA receptor antagonist MK-801 in mouse striatal tissue

Summary

Introduction

Memory, and learning are closely associated with glutamatergic neurotransmission, with the postsynaptic N-methyl-D-aspartate (NMDA) receptor playing an. Primary laboratory of origin: Boehringer Ingelheim International GmbH, Biberach an der Riss, Germany. Giovannini was the inventor of BI 409306. Parts of this work have been published previously in abstract form: DornerCiossek C, Giovannini R, and Rosenbrock H (2015) BI 409306, a novel phosphodiesterase 9A inhibitor, part I: potency, selectivity and in-vitro functional characterization on synaptic plasticity. Schizophr Bull 41(Suppl 1):S31; Rosenbrock H, Marti A, Koros E, Runge F, Fuchs H, Giovannini R, and Dorner-Ciossek C (2015) BI 409306, a novel phosphodiesterase 9A inhibitor, part II: in-vivo characterization regarding target engagement and cognition tasks in rodents.

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