<i>In vitro</i> autoradiography (ARG) using [³H]TAK-063 in sagittal rat brain sections.

<p>The chemical structure of [³H]TAK-063 (A). Sections adjacent to those used for <i>in vitro</i> ARG of [³H]TAK-063, were stained with hematoxylin and eosin (B). The autoradiogram shows the high accumulation of [³H]TAK-063 in the caudate putamen (CPu; white arrow), nucleus accumbens (NAc; black arrow), globus pallidus (GP; white arrow head), substantia nigra (SN; black arrow head), and striatonigral projection (gray arrow; C). <i>In vitro</i> ARGs in the presence of an excess amount of MP-10 (D) or TAK-063 (E) were performed with adjacent sections. Radioactivity levels in several brain regions were represented as photostimulated luminescence (PSL) values in the presence or absence of an excess amount of MP-10 or TAK-063 (F). Statistical analyses were performed using Dunnett's test (*<i>P</i> ≤ 0.05, **<i>P</i> ≤ 0.01 vs total binding, n = 3). Fcx, frontal cortex; Thal, thalamus; Bs, brainstem; Hipp, hippocampus; Cb, cerebellum.</p

Percent inhibition of enzymes by TAK-063 at 10 μM.

<p>EGF, epidermal growth factor; HMG CoA, 3-hydroxy-3-methyl-glutaryl coenzyme A. Negative value of percent inhibition indicates activation of enzyme activity.</p><p>Percent inhibition of enzymes by TAK-063 at 10 μM.</p

<i>In vitro</i> autoradiography (ARG) using [³H]TAK-063 in mouse brain sections.

<p>[³H]TAK-063 selectively accumulated in the caudate putamen (CPu; black arrow) and nucleus accumbens (NAc; white arrow) of wild-type (WT) mouse brain sections (A). The selective accumulation of [³H]TAK-063 in these areas did not occur in <i>Pde10a</i>-KO mouse brain sections (B). Radioactivity levels in the CPu of brain sections in the presence and absence of an excess amount of MP-10 are represented as a percent of total binding of WT mice (C). Data are represented as mean ± SEM.</p

Concentration of T-773 in the rat brain and displacement by TAK-063.

<p>The data (ng/g tissue) are represented as mean (n = 2 at 0.3 mg/kg) or mean ± SEM (n = 3).</p><p>Concentration of T-773 in the rat brain and displacement by TAK-063.</p

<i>In vivo</i> ARG of [¹⁴C]TAK-063 in rats.

<p>The chemical structure of [¹⁴C]TAK-063 (A). The asterisk denotes the labeled position. Autoradiograms of head sections were obtained from male rats 6 h after single oral administration of [¹⁴C]TAK-063. The autoradiograms of 40 μm sagittal sections between 2.1 to 2.4 mm lateral to midline were taken (B). The locations for each coronal section relative to the bregma were 1.7 to 1.2 mm (C), 0.48 to −0.26 mm (D), −0.4 to −0.8 mm (E), −2.8 to −3.1 mm (F), −6.0 to −6.3 mm (G), and −12.7 to −12.8 mm (H). Acc, nucleus accumbens; Cb, cerebellum; Cpu, caudate putamen; Ctx, cortex; Fcx, frontal cortex; GP, globus pallidus; Hipp, hippocampus; MO, medulla oblongata; OT, olfactory tubercle; SN, substantia nigra; Thal, thalamus; VP, ventral pallidum.</p

Percent inhibition of receptors by TAK-063 at 10 μM.

<p>AMPA, α-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid; NMDA, N-methyl-D-aspartic acid. Negative value of percent inhibition indicates stimulation of receptor activity.</p><p>Percent inhibition of receptors by TAK-063 at 10 μM.</p

Saturation binding analysis using [³H]TAK-063 in rat brain coronal sections.

<p>A saturation binding assay was performed with a range of concentrations of [³H]TAK-063. Regions of interest (ROIs) were the bilateral caudate putamen (CPu; arrows) and nucleus accumbens (NAc) shell (arrowheads) in the autoradiograms (A). Total and non-specific binding in each ROI was represented as PSL values (/mm²), and saturation binding curves from the CPu (B) and NAc shell (C) were analyzed by nonlinear regression. K_d values in the CPu and NAc shell were estimated at 7.2 ± 1.2 nM and 2.6 ± 0.5 nM, respectively. All data were represented as mean ± SEM.</p

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 <b>18</b> 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-<i>N</i>-((1<i>R</i>)-1-(4-(trifluoromethoxy)­phenyl)­propyl)­pyrazolo­[1,5-<i>a</i>]­pyrimidine-3-carboxamide (<b>38a</b>), a molecule with the desired balance of preclinical properties. Further characterization by cocrystal structure analysis of <b>38a</b> bound to PDE2A uncovered a unique binding mode and provided insights into its observed potency and PDE selectivity. Compound <b>38a</b> 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 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 <b>18</b> 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-<i>N</i>-((1<i>R</i>)-1-(4-(trifluoromethoxy)­phenyl)­propyl)­pyrazolo­[1,5-<i>a</i>]­pyrimidine-3-carboxamide (<b>38a</b>), a molecule with the desired balance of preclinical properties. Further characterization by cocrystal structure analysis of <b>38a</b> bound to PDE2A uncovered a unique binding mode and provided insights into its observed potency and PDE selectivity. Compound <b>38a</b> 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 <i>N</i>‑((1<i>S</i>)‑1-(3-Fluoro-4-(trifluoromethoxy)phenyl)-2-methoxyethyl)-7-methoxy-2-oxo-2,3-dihydropyrido[2,3‑<i>b</i>]pyrazine-4(1<i>H</i>)‑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-<i>a</i>]­pyrimidine lead compound <b>4b</b>, leading to the discovery of clinical candidate <b>36</b> (TAK-915), which demonstrates an appropriate combination of potency, PDE selectivity, and favorable pharmacokinetic (PK) properties, including brain penetration. Successful identification of <b>36</b> 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 <b>36</b> 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 <b>36</b> was advanced into human clinical trials