Design, synthesis and biological evaluation of a novel series of potent, orally active adenosine A1 receptor antagonists with high blood-brain barrier permeability.

A novel series of 3-(2-substituted-3-oxo-2,3-dihydropyridazin-6-yl)-2-phenylpyrazolo[1,5-a]pyridines (5-38) were synthesized and evaluated for their in vitro adenosine A1 and A(2A) receptor binding activities, and in vitro metabolism by rat liver in order to search for orally active compounds. Most of the test compounds were potent adenosine A1 receptor antagonists with high A1 selectivity and the A1 affinity and A1 selectivity of carbonyl derivatives (5-11) was particularly high. In particular, compound 7 was an extremely potent and selective adenosine A1 antagonist with high A1 selectivity (Ki=0.026 nM, A(2A)/A1=5400). In terms of metabolic stability, 2-oxopropyl (5), 2-hydroxypropyl (12), N-methylacetamide (16), 2-(piperidin-1-yl)ethyl (28) and 1-methylpiperidin-4-yl (32, FR194921) were the most stable compounds in this series of analogues. Further in vivo evaluation indicated that compounds 5, 13, 17, 28 and 32 were detected in both plasma and brain after oral administration in rats. In particular, 32 displayed good plasma and brain concentrations (dose: 32 mg/kg (n=3); after 30 min, plasma conc.=3390+/-651nM, brain conc.=3670+/-496nM; after 60min, plasma conc.=1580+/-348nM, brain conc.=2143+/-434nM), and a good brain/plasma ratio (1.11+/-0.060 (30min), 1.39+/-0.172 (60min)). As a result, we could show that 32 is a good candidate for an orally active adenosine A1 receptor antagonist with high blood-brain barrier permeability and good bioavailability (Ki=6.6nM, A(2A)/A1=820, BA=60.6+/-4.9% (32 mg/kg)).

Exon/intron boundaries, novel polymorphisms, and association analysis with schizophrenia of the human synaptic vesicle monoamine transporter (SVMT) gene.

The synaptic vesicular monoamine transporter (SVMT), alternatively vesicular monoamine transporter 2 (VMAT2), pumps cytosolic monoamines including dopamine, norepinephrine, serotonin, and histamine into synaptic vesicles. Altered functions of SVMT have been implicated in the pathogensis of several neuropsychiatric diseases. We determined exon/intron boundaries of the human SVMT gene and performed mutational analysis for the exonic and neighboring intronic regions of the gene. Detected polymorphisms were subject to association analysis with schizophrenia in a family-based design. The human SVMT gene consists, of 16 exons and 15 introns, which is consistent with the murine SVMT gene. When mutational analysis was performed by the single strand conformational polymorphism (SSCP) analysis, we found two and four single nucleotide polymorphisms (SNPs) in exons and neighboring introns, respectively. Neither exonic SNP results in an amino acid change. In family-based association analyses in a sample of 50 Japanese schizophrenics and their parents, no significant association was found for the intronic polymorphisms. Our data suggest that there is no common polymorphism in the SVMT gene affecting the primary structure of the human SVMT protein. Furthermore, we obtained no evidence for the major effect of the novel polymorphisms on susceptibility to schizophrenia.

No evidence for an association between the Glu298Asp polymorphism of the NOS3 gene and Alzheimer's disease.

Recently a significant association of a missense mutation (Glu298Asp) of the endothelial nitric oxide synthase (NOS3) gene with late-onset Alzheimer's disease (LOAD) was reported. We tried to replicate this finding in a Japanese sample of 121 patients with LOAD, 51 with early-onset AD (EOAD), and 165 medical controls. However, the genotype and allelic distributions for the Glu298Asp polymorphism were similar for these three groups, suggesting that the Glu298Asp polymorphism of the NOS3 gene has no relevance to the development of AD in Japanese.

Novel adenosine A1 receptor antagonists. Synthesis and structure-activity relationships of a novel series of 3-(2-cyclohexenyl-3-oxo-2,3-dihydropyridazin-6-yl)-2-phenylpyrazolo[1,5 -a]pyridines.

A novel series of 3-(2-cyclohexenyl-3-oxo-2,3-dihydropyridazin-6-yl)-2-phenylpyrazol o[1,5-a]pyridines was synthesized and evaluated for in vitro adenosine A1 and A2A receptor binding activities. Most of the cyclohexenyl derivatives (7a-e, 8a-s) were found to be potent adenosine A1 receptor antagonists. In a series of analogues of FR166124 (3a), alcohol 7c, nitrile 7e and amide derivatives (7d, 8c, 8r) were found to be more potent A1 antagonists with higher A2A/A1 selectivity than FR166124. Amongst them, 8r showed considerable water solubility (33.3 mg/mL), but lower than that of the sodium salt of FR166124 (> 200 mg/mL). Additionally, FR166124 had strong diuretic activity by both p.o. and iv administration in rats (minimum effective dose=0.1 and 0.032 mg/kg, respectively).

Discovery of FR166124, a novel water-soluble pyrazolo-[1,5-a]pyridine adenosine A1 receptor antagonist.

Novel 3-(2-cycloalkyl and cycloalkenyl-3-oxo-2,3-dihydropyridazin-6-yl)-2-phenylpyrazo lo [1,5-a]-pyridines were synthesized and evaluated for their adenosine A1 receptor binding activities. In this series, FR166124 (3) was found to be the most potent and selective adenosine A1 receptor antagonist, and the double bond of the cyclohexenyl acetic acid group was essential for selectivity of A1 receptor binding. Furthermore, the solubility in water of the sodium salt of FR 166124 was high.

Pyrazolopyridine derivatives act as competitive antagonists of brain adenosine A1 receptors: [35S]GTPgammaS binding studies.

The effects of adenosine receptor ligands and three novel pyrazolopyridine derivatives on guanosine-5'-O-(3-[35S]thio)triphosphate ([35S]GTPgammaS) binding to rat cerebral cortical membranes were examined. [35S]GTPgammaS binding was stimulated in a concentration dependent manner by several adenosine receptor agonists. The adenosine A2a receptor selective agonist, 2-p-(2-carboxyethyl)phenethylamino-5'-N-ethylcarboxamidoadenosine (CGS 21680), was ineffective confirming specificity for adenosine A1 receptor activation. 2-Chloro-N6-cyclopentyladenosine (CCPA; 10(-7) M)-stimulated [35S]GTPgammaS binding was inhibited by xanthine and pyrazolopyridine based adenosine receptor antagonists. The concentration-response curve for CCPA-stimulated [35S]GTPgammaS binding was shifted to the right with increasing concentrations of antagonist without significant changes in maximal response. Schild analyses determined pK(B) values of 8.97, 8.88, 8.21, 8.16, 7.79 and 7.65 for 8-cyclopentyl-1,3-dipropylxanthine (DPCPX), (R)-1-[(E)-3-(2-phenylpyrazolo[1,5a]pyridin-3-yl) acryloyl]-2-piperidine ethanol (FK453), 6-oxo-3-(2-phenylpyrazolo[1,5a]pyridin-3-yl)-1(6H)-pyridazinebutyric+ ++ acid (FK838), 9-chloro-2-(2-furyl)[1,2,4]triazolo-[1,5c]quinazolin-5-amine (CGS 15943), 8-cyclopentyl-1,3-methylxanthine (CPT) and (R)-1-[(E)-3-(2-phenylpyrazolo[1,5a]pyridin-3-yl) acryloyl]-piperidin-2-yl acetic acid (FK352), respectively. Schild slopes were close to unity, confirming that these novel pyrazolopyridine derivatives act as competitive antagonists at rat brain adenosine A1 receptors.

Pharmacological characterization of a simple behavioral response mediated selectively by central adenosine A1 receptors, using in vivo and in vitro techniques.

The behavioral profile of a range of adenosine receptor ligands was examined in rats using a locomotor activity model. Adenosine receptor agonists, including the selective A1 receptor agonist, N6-cyclopentyladenosine (CPA) and the A2A agonist, 2-[(2-aminoethylamino)carbonylethyl-phenylethylamino]- 5'-ethylcarboxa midoadenosine (APEC), reduced spontaneous motor activity in a dose-dependent manner. CPA-induced locomotor depression was attenuated by adenosine A1 receptor selective antagonists, such as 8-cyclopentyl-1,3-dipropylxanthine (DPCPX), (R)-1-[(E)-3-(2-phenylpyrazolo[1, 5-a]pyridin-3-yl)-acryloyl]-2-piperidine ethanol (FK453), and (R)-1-[(E)-3-(2-phenylpyrazolo[1, 5-a]pyridin-3-yl)-acryloyl]-piperidin-2-yl acetic acid (FK352), but not by the A2A receptor antagonist, (E)-1,3-dipropyl-8-(3, 4-dimethoxystyryl)-7-methylxanthine (KF17837). By contrast, APEC-induced hypolocomotion was attenuated by KF17837 but not by DPCPX, confirming that adenosine A1 and A2A receptor activation mediates locomotor output independently. It was found that two peripheral adenosine receptor antagonists, 8-(p-sulphophenyl)-1, 3-dipropylxanthine (DPSPX) and 8-(p-sulphophenyl)-1, 3-dimethylxanthine (8-PST), did not alter CPA-induced hypolocomotion. This confirmed that pharmacological reversal of the adenosine A1 receptor-mediated response involved a central site of drug action. The relationship between occupancy of central adenosine A1 receptors and behavioral effect was therefore assessed. Regression analysis on log transformed data confirmed associations between antagonist affinity for brain [3H]DPCPX binding sites and, in order of increasing significance, the equivalent behavioral dose (EBD) for reversal of CPA-induced hypolocomotion (r2 = 0.32), the serum concentration of drug (r2 = 0.65), and most significantly with the brain concentration of drug detected 20 min after administration of the (EBD) (r2 = 0.95). These data suggest that competition between agonists and antagonists, for occupancy of central adenosine A1 receptors, is intrinsic to the pharmacological reversal of CPA-induced hypolocomotion. The validity of the model as a simple predictive screen for the blood/brain barrier permeability of adenosine A1 receptor antagonists was thereby confirmed.

Species differences in brain adenosine A1 receptor pharmacology revealed by use of xanthine and pyrazolopyridine based antagonists.

1. The pharmacological profile of adenosine A1 receptors in human, guinea-pig, rat and mouse brain membranes was characterized in a radioligand binding assay by use of the receptor selective antagonist, [3H]-8-cyclopentyl-1,3-dipropylxanthine ([3H]-DPCPX). 2. The affinity of [3H]-DPCPX binding sites in rat cortical and hippocampal membranes was similar. Binding site affinity was higher in rat cortical membranes than in membranes prepared from guinea-pig cortex and hippocampus, mouse cortex and human cortex. pKD values (M) were 9.55, 9.44, 8.85, 8.94, 8.67, 9.39 and 8.67, respectively. The binding site density (Bmax) was lower in rat cortical membranes than in guinea-pig or human cortical membranes. 3. The rank order of potency of seven adenosine receptor agonists was identical in each species. With the exception of 5'-N-ethylcarboxamidoadenosine (NECA), agonist affinity was 3.5-26.2 fold higher in rat cortical membranes than in human and guinea-pig brain membranes; affinity in rat and mouse brain membranes was similar. While NECA exhibited 9.3 fold higher affinity in rat compared to human cortical membranes, affinity in other species was comparable. The stable GTP analogue, Gpp(NH)p (100 microM) reduced 2-chloro-N6-cyclopentyladenosine (CCPA) affinity 7-13.9 fold, whereas the affinity of DPCPX was unaffected. 4. The affinity of six xanthine-based adenosine receptor antagonists was 2.2-15.9 fold higher in rat cortical membranes compared with human or guinea-pig membranes. The rank order of potency was species-independent. In contrast, three pyrazolopyridine derivatives, (R)-1-[(E)-3-(2-phenylpyrazolo[1,5-a]pyridin-3-yl) acryloyl]-2-piperidine ethanol (FK453), (R)-1-[(E)-3-(2-phenylpyrazolo[1,5-a]pyridin-3-yl) acryloyl]-piperidin-2-yl acetic acid (FK352) and 6-oxo-3-(2-phenylpyrazolo[1,5-a]pyridin-3-yl)-1(6H)-pyridazinebutyric acid (FK838) exhibited similar affinity in human, guinea-pig, rat and mouse brain membranes. pKi values (M) for [3H]-DPCPX binding sites in human cortical membranes were 9.31, 7.52 and 7.92, respectively. 5. Drug affinity for adenosine A2A receptors was determined in a [3H]-2-[4-(2-carboxyethyl)phenethylamino]-5'-N-ethylcarboxamido ade nosine ([3H]-CGS 21680) binding assay in rat striatal membranes. The pyrazolopyridine derivatives, FK453, FK838 and FK352 exhibited pKi values (M) of 5.90, 5.92 and 4.31, respectively, compared with pKi values of 9.31, 8.18 and 7.57 determined in the [3H]-DPCPX binding assay in rat cortical membranes. These novel pyrazolopyridine derivatives therefore represent high affinity, adenosine A1 receptor selective drugs that, in contrast to xanthine based antagonists, exhibit similar affinity for [3H]-DPCPX binding sites in human, rat, mouse and guinea-pig brain membranes.

General pharmacology of the new non-xanthine adenosine A1 receptor antagonist (+)-(R)-[(E)-3-(2-phenylpyrazolo[1,5-a]pyridin-3-yl)acryloyl]-2- piperidine ethanol.

FK 453 ((+)-(R)-[(E)-3-(2-phenylpyrazolo[1,5-a]pyridin-3-yl) acryloyl]-2-piperidine ethanol, CAS 121524-18-3) is a potent non-xanthine adenosine A1 receptor antagonist with diuretic and renal vasodilatory activity. The general pharmacology of FK 453 was investigated in mice, rats, guinea-pigs and dogs. In in vivo tests, FK 453 had little effect on the central nervous system (general behaviour, spontaneous motor activity, potentiation of barbiturate anesthesia, anticonvulsant activity, analgesic activity and body temperature), hematological system (bleeding time, coagulation time and recalcification time) and intestinal charcoal transit. FK 453 also did not show any cardiovascular (blood pressure, heart rate and femoral blood flow) or respiratory effects. In in vitro tests, although FK 453 had little effect on noradrenaline-induced contraction in rat vas deferens and histamine-induced contraction in guinea-pig trachea, FK 453 inhibited the acetylcholine-, histamine- and barium-induced contraction in isolated guinea-pig ileum and serotonin-induced contraction in isolated rat stomach. FK 453 also exerted significant inhibitory activity on collagen- and U 46619-induced platelet aggregation. However these effects of FK 453 on isolated tissue and platelet were observed only at high concentrations. These results suggest that FK 453 possesses a selective pharmacological profile, and one promising therapeutic site for this drug is in the kidney.

A novel non-xanthine adenosine A1 receptor antagonist.

FK453, (+)-(R)-[(E)-3-(2-phenylpyrazolo[1,5-alpha]pyridin-3-yl) acryloyl]-2-piperidine ethanol, was examined for adenosine receptor antagonistic activity using isolated guinea-pig atria and aorta and for affinity for adenosine receptors in the rat cerebral cortex and striatum in comparison with FR113452 (S enantiomer of FK453), PD116948 (1,3-dipropyl-8-cyclopentylxanthine), theophylline (1,3-dimethylxanthine) and CGS15943 ([1,2,4]triazolo[1,5-c]quinazolone). FK453 showed potent inhibition of the negative inotropic activity elicited by 10 microM adenosine with an IC50 of 560 pM in guinea-pig atria. However, FK453 was less potent in inhibiting the relaxation induced by 3.2 microM adenosine and had an IC50 of 1.18 microM in guinea-pig aorta. The IC50 values for FR113452, PD116948, theophylline and CGS15943 were 1.18 microM, 1.31 nM, 20.2 microM and 74.2 nM in atria and > 100 microM, 656 nM, 239 microM, 127 nM in aorta respectively. In the binding study, FK453 antagonized [3H]N6-cyclohexyladenosine binding to the rat cortical adenosine A1 receptor with an IC50 of 17.2 nM. The IC50 values for FR113452, PD116948, theophylline and CGS15943 were 10.1 microM, 4.7 nM, 67.7 microM and 241 nM respectively. FK453 inhibited [3H]5'-N-ethylcarboxamideadenosine binding to rat striatum adenosine A2 receptor with an IC50 of 11.3 microM. FK453 had no adenosine A1 receptor agonistic activity, since it had no negative inotropic activity up to 100 microM in isolated guinea-pig atria. These results demonstrate that FK453 is a novel non-xanthine adenosine receptor antagonist and is potent and selective for the adenosine A1 receptor subtype.

Synthesis and anticholinergic activity of the four stereoisomers of 4-(dimethylamino)-2-phenyl-2-(2-pyridyl)pentanamide.

The four stereoisomers of 4-(dimethylamino)-2-phenyl-(2-pyridyl)pentanamide were synthesized, and the absolute configurations were determined by X-ray crystallography. Pharmacological testing for anticholinergic activity revealed great differences in potency among 10 (2R,4R,IC50 = 0.40 microM), 11 (2S,4S,31 microM), 12 (2R,4S,170 microM), and 13 (2S,4R,0.13 microM). A new drug application for the racemate 8 (FK176, vamicamide) has been filed in Japan for the treatment of overactive detrusor syndrome.