Phosphodiesterase 2A Inhibitor TAK-915 Ameliorates Cognitive Impairments and Social Withdrawal in N-Methyl-d-Aspartate Receptor Antagonist-Induced Rat Models of Schizophrenia.

The pathophysiology of schizophrenia has been associated with glutamatergic dysfunction. Modulation of the glutamatergic signaling pathway, including N-methyl-d-aspartate (NMDA) receptors, can provide a new therapeutic target for schizophrenia. Phosphodiesterase 2A (PDE2A) is highly expressed in the forebrain, and is a dual substrate enzyme that hydrolyzes both cAMP and cGMP, which play pivotal roles as intracellular second messengers downstream of NMDA receptors. Here we characterize the in vivo pharmacological profile of a selective and brain-penetrant PDE2A inhibitor, (N-{(1S)-1-[3-fluoro-4-(trifluoromethoxy)phenyl]-2-methoxyethyl}-7-methoxy-2-oxo-2,3-dihydropyrido[2,3-b]pyrazine-4(1H)-carboxamide) (TAK-915) as a novel treatment of schizophrenia. Oral administration of TAK-915 at 3 and 10 mg/kg significantly increased cGMP levels in the frontal cortex, hippocampus, and striatum of rats. TAK-915 at 10 mg/kg significantly upregulated the phosphorylation of α-amino-3-hydroxy-5-methylisoxazole-4-proprionic acid receptor subunit GluR1 in the rat hippocampus. TAK-915 at 3 and 10 mg/kg significantly attenuated episodic memory deficits induced by the NMDA receptor antagonist (+)-MK-801 hydrogen maleate (MK-801) in the rat passive avoidance test. TAK-915 at 10 mg/kg significantly attenuated working memory deficits induced by MK-801 in the rat radial arm maze test. Additionally, TAK-915 at 10 mg/kg prevented subchronic phencyclidine-induced social withdrawal in social interaction in rats. In contrast, TAK-915 did not produce antipsychotic-like activity; TAK-915 had little effect on MK-801- or methamphetamine-induced hyperlocomotion in rats. These results suggest that TAK-915 has a potential to ameliorate cognitive impairments and social withdrawal in schizophrenia.

Induction of c-fos transcription in the medaka brain (Oryzias latipes) in response to mating stimuli.

Immediate-early genes (IEGs) are useful for mapping active brain regions in various vertebrates. Here we identified a c-fos homologue gene in medaka and demonstrated that the amounts of c-fos transcripts and proteins in the medaka brain increased in relation to an artificially evoked seizure, suggesting that the homologue gene has the characteristics of IEGs, which are used as markers of neural activity. Next, quantitative reverse-transcription-polymerase chain reaction revealed that female mating behaviors upregulated c-fos transcription in some brain regions including the telencephalon, optic tectum, and cerebellum. In addition, we performed in situ hybridization with a c-fos intron probe to detect the de novo synthesis of c-fos transcripts and confirmed induction of c-fos transcription in these brain regions after mating. This is the first report of IEG induction in response to mating stimuli in teleost fish. Our results indicated that c-fos expression was induced in response to behavioral stimuli in the medaka brain and that medaka c-fos could be a useful marker of neural activity.

Mass spectrometric map of neuropeptide expression and analysis of the gamma-prepro-tachykinin gene expression in the medaka (Oryzias latipes) brain.

Neuropeptides have important roles in modulating behavioral patterns such as social interaction. With the aim to determine the presence of neuropeptides known to be involved in social interaction as well as novel peptides, we used MALDI-TOF/MS to analyze neuropeptide profiles in some medaka brain regions. In the telencephalon, hypothalamus, and pituitary gland, 3, 6, and 10 peaks, respectively, were identified as neuropeptides (Arg-vasotocin [AVT], growth hormone-releasing hormone [GHRH], neuropeptide FF, substance P [SP], somatostatin-1 and -2, melanin-concentrating hormone [MCH], MCH gene-related peptide [Mgrp], melanocyte-stimulating hormone [MSH], corticotropin-like intermediate lobe peptide [CLIP], and beta-endorphin). The neuropeptide profile of telencephalon similar to that of the hypothalamus, but completely different from that of pituitary gland. For the future genetic analysis, we identified cDNAs encoding precursor proteins for the identified peptides. We also detect its expression of gamma-prepro-tachykinin gene encoding a SP precursor protein in both the telencephalon and hypothalamus. Our results indicated that the medaka brain contains some neuropeptides (AVT, SP, and somatostatins) that may be involved in modulating medaka behaviors such as social interaction.

Discovery of an Orally Bioavailable, Brain-Penetrating, in Vivo Active Phosphodiesterase 2A Inhibitor Lead Series for the Treatment of Cognitive Disorders.

Herein, we describe the discovery of a potent, selective, brain-penetrating, in vivo active phosphodiesterase (PDE) 2A inhibitor lead series. To identify high-quality leads suitable for optimization and enable validation of the physiological function of PDE2A in vivo, structural modifications of the high-throughput screening hit 18 were performed. Our lead generation efforts revealed three key potency-enhancing functionalities with minimal increases in molecular weight (MW) and no change in topological polar surface area (TPSA). Combining these structural elements led to the identification of 6-methyl-N-((1R)-1-(4-(trifluoromethoxy)phenyl)propyl)pyrazolo[1,5-a]pyrimidine-3-carboxamide (38a), a molecule with the desired balance of preclinical properties. Further characterization by cocrystal structure analysis of 38a bound to PDE2A uncovered a unique binding mode and provided insights into its observed potency and PDE selectivity. Compound 38a significantly elevated 3',5'-cyclic guanosine monophosphate (cGMP) levels in mouse brain following oral administration, thus validating this compound as a useful pharmacological tool and an attractive lead for future optimization.

Discovery of Clinical Candidate N-((1S)-1-(3-Fluoro-4-(trifluoromethoxy)phenyl)-2-methoxyethyl)-7-methoxy-2-oxo-2,3-dihydropyrido[2,3-b]pyrazine-4(1H)-carboxamide (TAK-915): A Highly Potent, Selective, and Brain-Penetrating Phosphodiesterase 2A Inhibitor for the Treatment of Cognitive Disorders.

Phosphodiesterase (PDE) 2A inhibitors have emerged as a novel mechanism with potential therapeutic option to ameliorate cognitive dysfunction in schizophrenia or Alzheimer's disease through upregulation of cyclic nucleotides in the brain and thereby achieve potentiation of cyclic nucleotide signaling pathways. This article details the expedited optimization of our recently disclosed pyrazolo[1,5-a]pyrimidine lead compound 4b, leading to the discovery of clinical candidate 36 (TAK-915), which demonstrates an appropriate combination of potency, PDE selectivity, and favorable pharmacokinetic (PK) properties, including brain penetration. Successful identification of 36 was realized through application of structure-based drug design (SBDD) to further improve potency and PDE selectivity, coupled with prospective design focused on physicochemical properties to deliver brain penetration. Oral administration of 36 demonstrated significant elevation of 3',5'-cyclic guanosine monophosphate (cGMP) levels in mouse brains and improved cognitive performance in a novel object recognition task in rats. Consequently, compound 36 was advanced into human clinical trials.

A neural mechanism underlying mating preferences for familiar individuals in medaka fish.

Social familiarity affects mating preference among various vertebrates. Here, we show that visual contact of a potential mating partner before mating (visual familiarization) enhances female preference for the familiarized male, but not for an unfamiliarized male, in medaka fish. Terminal-nerve gonadotropin-releasing hormone 3 (TN-GnRH3) neurons, an extrahypothalamic neuromodulatory system, function as a gate for activating mating preferences based on familiarity. Basal levels of TN-GnRH3 neuronal activity suppress female receptivity for any male (default mode). Visual familiarization facilitates TN-GnRH3 neuron activity (preference mode), which correlates with female preference for the familiarized male. GnRH3 peptides, which are synthesized specifically in TN-GnRH3 neurons, are required for the mode-switching via self-facilitation. Our study demonstrates the central neural mechanisms underlying the regulation of medaka female mating preference based on visual social familiarity.

Proliferation zones in adult medaka (Oryzias latipes) brain.

Cell proliferation in the adult mammalian brain is maintained at a low rate, but cell proliferation in the adult fish brain is prominent. To compare the distribution of proliferating cells among fish species, mutants, and under different growing environments, we mapped the zones of cell proliferation in the adult medaka (Oryzias latipes) brain and identified 17 proliferation zones in both male and female brains. These zones were distributed in the telencephalon (4 zones), preoptic area (2 zones), pineal body (1 zone), hypophysis (1 zone), habenular nucleus (1 zone), optic tectum (2 zones), third ventricular zone (1 zone), ventromedial nucleus (1 zone), hypothalamus (1 zone), and cerebellum (3 zones). Of the 17 zones, 16 corresponded to brain regions where cells proliferate in the zebrafish brain, suggesting that the persistence of the generation of new cells, at least in these zones, might be conserved among some fish species. We then compared the distribution of proliferation zones using two body-color mutant medaka, the T5 and Quintet, the latter of which is an albino mutant that completely lacks pigmentation. There was no apparent difference in the distribution pattern among these mutant strains. Finally, we compared these proliferation zones in the brains of isolated- and group-reared fish and detected no significant difference between the two groups. These findings demonstrate that there is persistent cell proliferation in at least these 16 zones of the adult medaka brain, irrespective of sex, body-color, and growth environment, suggesting that proliferation capacity in the 16 zones is maintained robustly in the adult medaka brain.

Coordinated and cohesive movement of two small conspecific fish induced by eliciting a simultaneous optomotor response.

BACKGROUND: In animal groups such as herds, schools, and flocks, a certain distance is maintained between adjacent individuals, allowing them to move as a cohesive unit. Proximate causations of the cohesive and coordinated movement under dynamic conditions, however, have been poorly understood. METHODOLOGY/PRINCIPAL FINDINGS: We established a novel and simple behavioral assay using pairs of small fish (medaka and dwarf pufferfish) by eliciting a simultaneous optomotor response (OMR). We demonstrated that two homospecific fish began to move cohesively and maintained a distance of 2 to 4 cm between them when an OMR was elicited simultaneously in the fish. The coordinated and cohesive movement was not exhibited under a static condition. During the cohesive movement, the relative position of the two fish was not stable. Furthermore, adult medaka exhibited the cohesive movement but larvae did not, despite the fact that an OMR could be elicited in larvae, indicating that this ability to coordinate movement develops during maturation. The cohesive movement was detected in homospecific pairs irrespective of body-color, sex, or albino mutation, but was not detected between heterospecific pairs, suggesting that coordinated movement is based on a conspecific interaction. CONCLUSIONS/SIGNIFICANCE: Our findings demonstrate that coordinated behavior between a pair of animals was elicited by a simultaneous OMR in two small fish. This is the first report to demonstrate induction of a schooling-like movement in a pair of fish by an OMR and to investigate the effect of age, sex, body color, and species on coordination between animals under a dynamic condition.