Shizuo Kasai

A new class of potent nonpeptide luteinizing hormone-releasing hormone (LHRH) antagonists: design and synthesis of 2-phenylimidazo[1,2-a]pyrimidin-5-ones.

The design and synthesis of a new class of nonpeptide luteinizing hormone-releasing hormone (LHRH) receptor antagonists, the 2-phenylimidazo[1,2-a]pyrimidin-5-ones, is reported. Among compounds described in this study, we identified the potent antagonist 15b with nanomolar in vitro functional antagonism. The result might suggest that the heterocyclic 5-6-ring system possessing a pendant phenyl group attached to the five-membered ring is the important structural feature for a scaffold of small molecule LHRH antagonists.

Melanin-concentrating hormone receptor 1 antagonists. Synthesis and structure-activity relationships of novel 3-(aminomethyl)quinolines.

It was found that 3-(aminomethyl)quinoline derivatives showed high binding affinities for melanin-concentrating hormone receptor 1 (MCHR1) with reduced affinity for serotonin receptor 2c (5-HT2c) when the dihydronaphthalene nucleus of compound 1 (human MCHR1, IC(50) = 1.9 nM; human 5-HT2c receptor, IC(50) = 0.53 nM) was replaced by other bicyclic core scaffolds. Among the synthesized compounds, 8-methylquinoline derivative 5v especially showed high binding affinity (IC(50) = 0.54 nM), potent in vitro antagonistic activity (IC(50) = 2.8 nM) for MCHR1, and negligible affinity for 5-HT2c receptor (IC(50) > 1000 nM). Oral administration of 5v significantly and dose-dependently suppressed nocturnal food intake in diet-induced obese rats and did not affect food intake in MCHR1-deficient mice. These results and rat pharmacokinetic study findings suggested that compound 5v is a highly potent, orally bioavailable, and centrally acting nonpeptide MCHR1 antagonist.

Synthesis, Structure–Activity Relationship, and Pharmacological Studies of Novel Melanin-Concentrating Hormone Receptor 1 Antagonists 3-Aminomethylquinolines: Reducing Human Ether-a-go-go-Related Gene (hERG) Associated Liabilities

Recently, we discovered 3-aminomethylquinoline derivative 1, a selective, highly potent, centrally acting, and orally bioavailable human MCH receptor 1 (hMCHR1) antagonist, that inhibited food intake in F344 rats with diet-induced obesity (DIO). Subsequent investigation of 1 was discontinued because 1 showed potent hERG K(+) channel inhibition in a patch-clamp study. To decrease hERG K(+) channel inhibition, experiments with ligand-based drug designs based on 1 and a docking study were conducted. Replacement of the terminal p-fluorophenyl group with a cyclopropylmethoxy group, methyl group introduction on the benzylic carbon at the 3-position of the quinoline core, and employment of a [2-(acetylamino)ethyl]amino group as the amine portion eliminated hERG K(+) channel inhibitory activity in a patch-clamp study, leading to the discovery of N-{3-[(1R)-1-{[2-(acetylamino)ethyl]amino}ethyl]-8-methylquinolin-7-yl}-4-(cyclopropylmethoxy)benzamide (R)-10h. The compound (R)-10h showed potent inhibitory activity against hMCHR1 and dose-dependently suppressed food intake in a 2-day study on DIO-F344 rats. Furthermore, practical chiral synthesis of (R)-10h was performed to determine the molecules absolute configuration.

Melanin-concentrating hormone receptor 1 antagonists: synthesis, structure-activity relationship, docking studies, and biological evaluation of 2,3,4,5-tetrahydro-1H-3-benzazepine derivatives.

Melanin-concentrating hormone receptor 1 (MCHR1) antagonists have been studied as potential agents for the treatment of obesity. Initial structure-activity relationship studies of in-house hit compound 1a and subsequent optimization studies resulted in the identification of tetrahydroisoquinoline derivative 23, 1-(2-acetyl-1,2,3,4-tetrahydroisoquinolin-7-yl)-4-[4-(4-chlorophenyl)piperidin-1-yl]butan-1-one, as a potent hMCHR1 antagonist. A homology model of hMCHR1 suggests that these compounds interact with Asn 294 and Asp 123 in the binding site of hMCHR1 to enhance binding affinity. Oral administration of compound 23 dose-dependently reduced food intake in diet-induced obesity (DIO)-F344 rats.

A Selective Bombesin Receptor Subtype 3 Agonist Promotes Weight Loss in Male Diet-Induced–Obese Rats With Circadian Rhythm Change

Bombesin receptor subtype 3 (BRS-3) is an orphan G protein-coupled receptor. Based on the obese phenotype of male BRS-3-deficient mice, BRS-3 has been considered an attractive target for obesity treatment. Here, we developed a selective BRS-3 agonist (compound-A) and evaluated its antiobesity effects. Compound-A showed anorectic effects and enhanced energy expenditure in diet-induced-obese (DIO)-F344 rats. Moreover, repeated oral administration of compound-A for 7 days resulted in a significant body weight reduction in DIO-F344 rats. We also evaluated compound-A for cardiovascular side effects using telemeterized Sprague-Dawley (SD) rats. Oral administration of compound-A resulted in transient blood pressure increases in SD rats. To investigate the underlying mechanisms of BRS-3 agonist effects, we focused on the suprachiasmatic nucleus (SCN), the main control center of circadian rhythms in the hypothalamus, also regulating sympathetic nervous system. Compound-A significantly increased the messenger RNA expression of Brs-3, c-fos, and circadian rhythm genes in SCN of DIO-F344 rats. Because SCN also controls the hypothalamic-pituitary-adrenal (HPA) axis, we evaluated the relationship between BRS-3 and the HPA axis. Oral administration of compound-A caused a significant increase of plasma corticosterone levels in DIO-F344 rats. On this basis, energy expenditure enhancement by compound-A may be due to a circadian rhythm change in central and peripheral tissues, enhancement of peripheral lipid metabolism, and stimulation of the sympathetic nervous system. Furthermore, the blood pressure increase by compound-A could be associated with sympathetic nervous system stimulation via SCN and elevation of plasma corticosterone levels through activation of the HPA axis.

Amine-free melanin-concentrating hormone receptor 1 antagonists: Novel 1-(1H-benzimidazol-6-yl)pyridin-2(1H)-one derivatives and design to avoid CYP3A4 time-dependent inhibition

Melanin-concentrating hormone (MCH) is an attractive target for antiobesity agents, and numerous drug discovery programs are dedicated to finding small-molecule MCH receptor 1 (MCHR1) antagonists. We recently reported novel pyridine-2(1H)-ones as aliphatic amine-free MCHR1 antagonists that structurally featured an imidazo[1,2-a]pyridine-based bicyclic motif. To investigate imidazopyridine variants with lower basicity and less potential to inhibit cytochrome P450 3A4 (CYP3A4), we designed pyridine-2(1H)-ones bearing various less basic bicyclic motifs. Among these, a lead compound 6a bearing a 1H-benzimidazole motif showed comparable binding affinity to MCHR1 to the corresponding imidazopyridine derivative 1. Optimization of 6a afforded a series of potent thiophene derivatives (6q-u); however, most of these were found to cause time-dependent inhibition (TDI) of CYP3A4. As bioactivation of thiophenes to form sulfoxide or epoxide species was considered to be a major cause of CYP3A4 TDI, we introduced electron withdrawing groups on the thiophene and found that a CF3 group on the ring or a Cl adjacent to the sulfur atom helped prevent CYP3A4 TDI. Consequently, 4-[(5-chlorothiophen-2-yl)methoxy]-1-(2-cyclopropyl-1-methyl-1H-benzimidazol-6-yl)pyridin-2(1H)-one (6s) was identified as a potent MCHR1 antagonist without the risk of CYP3A4 TDI, which exhibited a promising safety profile including low CYP3A4 inhibition and exerted significant antiobesity effects in diet-induced obese F344 rats.

A novel and selective melanin-concentrating hormone receptor 1 antagonist ameliorates obesity and hepatic steatosis in diet-induced obese rodent models.

ABSTRACT Melanin‐concentrating hormone (MCH), a cyclic neuropeptide expressed predominantly in the lateral hypothalamus, plays an important role in the control of feeding behavior and energy homeostasis. Mice lacking MCH or MCH1 receptor are resistant to diet‐induced obesity (DIO) and MCH1 receptor antagonists show potent anti‐obesity effects in preclinical studies, indicating that MCH1 receptor is a promising target for anti‐obesity drugs. Moreover, recent studies have suggested the potential of MCH1 receptor antagonists for treatment of non‐alcoholic fatty liver disease (NAFLD). In the present study, we show the anti‐obesity and anti‐hepatosteatosis effect of our novel MCH1 receptor antagonist, Compound A. Repeated oral administration of Compound A resulted in dose‐dependent body weight reduction and had an anorectic effect in DIO mice. The body weight lowering effect of Compound A was more potent than that of pair‐feeding. Compound A also reduced lipid content and the expression level of lipogenesis‐, inflammation‐, and fibrosis‐related genes in the liver of DIO mice. Conversely, intracerebroventricular infusion of MCH caused induction of hepatic steatosis as well as increase in body weight in high‐fat diet‐fed wild type mice, but not MCH1 receptor knockout mice. The pair‐feeding study revealed the MCH‐MCH1 receptor system affects hepatic steatosis through a mechanism that is independent of body weight change. Metabolome analysis demonstrated that Compound A upregulated lipid metabolism‐related molecules, such as acylcarnitines and cardiolipins, in the liver. These findings suggest that our novel MCH1 receptor antagonist, Compound A, exerts its beneficial therapeutic effect on NAFLD and obesity through a central MCH‐MCH1 receptor pathway.

A pyridone derivative activates SERCA2a by attenuating the inhibitory effect of phospholamban

ABSTRACT The cardiac sarco/endoplasmic reticulum Ca2+‐dependent ATPase 2a (SERCA2a) plays a central role in Ca2+ handling within cardiomyocytes and is negatively regulated by phospholamban (PLN), a sarcoplasmic reticulum (SR) membrane protein. The activation of SERCA2a, which has been reported to improve cardiac dysfunction in heart failure, is a potential therapeutic approach for heart failure. Therefore, we developed a novel small molecule, compound A and characterized it both in vitro and in vivo. Compound A activated the Ca2+‐dependent ATPase activity of cardiac SR vesicles but not that of skeletal muscle SR vesicles that lack PLN. The surface plasmon resonance assay revealed a direct interaction between compound A and PLN, suggesting that the binding of compound A to PLN attenuates its inhibition of SERCA2a, resulting in SERCA2a activation. This was substantiated by inhibition of the compound A‐mediated increase in Ca2+ levels within the SR of HL‐1 cells by thapsigargin, a SERCA inhibitor. Compound A also increased the Ca2+ transients and contraction and relaxation of isolated adult rat cardiomyocytes. In isolated perfused rat hearts, the compound A enhanced systolic and diastolic functions. Further, an infusion of compound A (30 mg/kg, i.v. bolus followed by 2 mg/kg/min, i.v. infusion) significantly enhanced the diastolic function in anesthetized normal rats. These results indicate that compound A is a novel SERCA2a activator, which attenuates PLN inhibition and enhances the systolic and diastolic functions of the heart in vitro and in vivo. Therefore, compound A might be a novel therapeutic lead for heart failure.

Discovery of novel somatostatin receptor subtype 5 (SSTR5) antagonists: Pharmacological studies and design to improve pharmacokinetic profiles and human Ether-a-go-go-related gene (hERG) inhibition

Somatostatin (SST) is a peptide hormone comprising 14 or 28 amino acids that inhibits endocrine and exocrine secretion via five distinct G-protein-coupled receptors (SSTR1-5). SSTR5 has an important role in inhibiting the secretion of pancreatic and gastrointestinal hormones (e.g., insulin, GLP-1, PYY) through the binding of SSTs; hence, SSTR5 antagonists are expected to be novel anti-diabetic drugs. In the course of our lead generation program of SSTR5 antagonists, we have discovered a novel spiroazetidine derivative 3a. However, pharmacological evaluation of 3a revealed that it had to be administered at a high dose (100mg/kg) to show a persistent glucose-lowering effect in an oral glucose tolerance test (OGTT). We therefore initiated an optimization study based on 3a aimed at improving the antagonistic activity and mean residence time (MRT), resulting in the identification of 2-cyclopropyl-5-methoxybiphenyl derivative 3k. However, 3k did not show a sufficient persistent glucose-lowering effect in an OGTT; moreover, hERG inhibition was observed. Hence, further optimization study of the biphenyl moiety of compound 3k, focused on improving the pharmacokinetic (PK) profile and hERG inhibition, was conducted. Consequently, the introduction of a chlorine atom at the 6-position on the biphenyl moiety addressed a putative metabolic soft spot and increased the dihedral angle of the biphenyl moiety, leading to the discovery of 3p with an improved PK profile and hERG inhibition. Furthermore, 3p successfully exhibited a persistent glucose-lowering effect in an OGTT at a dose of 3mg/kg.

Amine-free melanin-concentrating hormone receptor 1 antagonists: Novel non-basic 1-(2H-indazole-5-yl)pyridin-2(1H)-one derivatives and mitigation of mutagenicity in Ames test.

To develop non-basic melanin-concentrating hormone receptor 1 (MCHR1) antagonists with a high probability of target selectivity and therapeutic window, we explored neutral bicyclic motifs that could replace the previously reported imidazo[1,2-a]pyridine or 1H-benzimidazole motif. The results indicated that the binding affinity of a chemically neutral 2H-indazole derivative 8a with MCHR1 (hMCHR1: IC50=35nM) was comparable to that of the imidazopyridine and benzimidazole derivatives (1 and 2, respectively) reported so far. However, 8a was positive in the Ames test using TA1537 in S9- condition. Based on a putative intercalation of 8a with DNA, we introduced a sterically-hindering cyclopropyl group on the indazole ring to decrease planarity, which led to the discovery of 1-(2-cyclopropyl-3-methyl-2H-indazol-5-yl)-4-{[5-(trifluoromethyl)thiophen-3-yl]methoxy}pyridin-2(1H)-one 8l without mutagenicity in TA1537. Compound 8l exerted significant antiobesity effects in diet-induced obese F344 rats and exhibited promising safety profile.