Tricyclic imidazoline derivatives as potent and selective adenosine A1 receptor antagonists

Novel tricyclic imidazoline antagonists of the adenosine A1 receptor are described. For key compounds, the selectivity level over other adenosine receptor subtypes is examined along with their in vivo effects in a rat diuresis model. Compound 14, the (R)-isomer of 7,8-dihydro-8-ethyl-2-(4-bicyclo[2.2.2]octan-1-ol)-4-propyl-1H-imidazo[2,1-i]purin-5(4H)-one, is a particularly potent adenosine A1 receptor antagonist with good selectivity over the other three adenosine receptor subtypes: A1 (human) Ki=22 nM; A2A (human) Ki=4400 nM; A2B (human) Ki=580 nM; A3 (human) Ki>or=10,000 nM. Imidazoline 14 is a competitive adenosine A1 receptor antagonist with a pA2 value of 8.88 and is highly soluble in water (>100 mg/mL). In addition, it has an oral bioavailability of 84% and an oral half-life of 3.8 h in rats. When orally administered in a rat diuresis model, compound 14 promoted sodium excretion (ED50=0.01 mg/kg). This level of efficacy is comparable to that of BG9928, a selective adenosine A1 receptor antagonist that is currently in clinical trials as a treatment for congestive heart failure. Additional modifications to 14 also showed that the bridgehead hydroxyl group could be replaced with a propionic acid (compound 36) without a significant loss in binding affinity or in vivo activity.     

Piperazine derivatives of [1,2,4]triazolo[1,5-a][1,3,5]triazine as potent and selective adenosine A2a receptor antagonists

The [1,2,4]triazolo[1,5-a]triazine derivative 3, more commonly known in the field of adenosine research as ZM-241385, has previously been demonstrated to be a potent and selective adenosine A2a receptor antagonist, although with limited oral bioavailability. This [1,2,4]triazolo[1,5-a]triazine core structure has now been improved by incorporating various piperazine derivatives. With some preliminary optimization, the A2a binding affinity of some of the best piperazine derivatives is almost as good as that of compound 3. The selectivity level over the adenosine A1 receptor subtype for some of the more active analogues is also fairly high, > 400-fold in some cases. Many compounds within this piperazine series of [1,2,4]triazolo[1,5-a]triazine have now been shown to have good oral bioavailability in the rat, with some as high as 89% (compound 35). More significantly, some piperazines derivatives of [1,2,4]triazolo[1,5-a]triazine also possessed good oral efficacy in rodent models of Parkinson's disease. For instance, compound 34 was orally active in the rat catalepsy model at 3 mg/kg. In the 6-hydroxydopamine-lesioned rat model, this compound was also quite effective, with a minimum effective dose of 3 mg/kg po.     

H2-receptor antagonist and gastric acid antisecretory properties of Wy-45,662

Investigations were carried out to delineate the biological activity of Wy-45,662, a new H2-receptor antagonist. In the pylorus-ligated rat after intraduodenal administration, total acid output (TAO) over 4 hours was inhibited by Wy-45,662 with an ED50 of 0.3 mg/kg as compared to ranitidine (ED50 = 7 mg/kg) and cimetidine (ED50 = 12 mg/kg); i.v. or i.m. administration increased Wy-45,662's potency 10-fold. In dogs with innervated gastric pouches Wy-45,662 inhibited food-stimulated TAO with ED50's of 0.35 mg/kg (p.o.), 0.045 mg/kg (i.v.) and 0.065 mg/kg (i.m.); cimetidine (ED50 = 6 mg/kg p.o.) and ranitidine (ED50 = 1 mg/kg p.o.) were less potent. Wy-45,662 also inhibited pentagastrin- or histamine-stimulated acid secretion in the conscious fistula rat. In vitro, Wy-45,662 antagonized the histamine-stimulated a) positive chronotropism in guinea pig atria and b) [14C]aminopyrine uptake by rat gastric mucosal cells, confirming its H2-receptor antagonist properties.     

1,8-disubstituted xanthine derivatives: synthesis of potent A2B-selective adenosine receptor antagonists

3-Unsubstituted xanthine derivatives bearing a cyclopentyl or a phenyl residue in the 8-position were synthesized and developed as A2B adenosine receptor antagonists. Compounds bearing polar substituents were prepared to obtain water-soluble derivatives. 1-Alkyl-8-phenylxanthine derivatives were found to exhibit high affinity for A2B adenosine receptors (ARs). 1,8-disubstituted xanthine derivatives were equipotent to or more potent than 1,3,8-trisubstituted xanthines at A2B ARs, but generally less potent at A1 and A2A, and much less potent at A3 ARs. Thus, the new compounds exhibited increased A2B selectivity versus all other AR subtypes. 9-Deazaxanthines (pyrrolo[2,3-d]pyrimidindiones) appeared to be less potent at A2B ARs than the corresponding xanthine derivatives. 1-Propyl-8-p-sulfophenylxanthine (17) was the most selective compound of the present series, exhibiting a K(i) value of 53 nM at human A2B ARs and showing greater than 180-fold selectivity versus human A1 ARs. Compound 17 was also highly selective versus rat A1 ARs (41-fold) and versus the other human AR subtypes (A2A > 400-fold and A3 > 180-fold). The compound is highly water-soluble due to its sulfonate function. 1-Butyl-8-p-carboxyphenylxanthine (10), another polar analogue bearing a carboxylate function, exhibited a K(i) value of 24 nM for A2B ARs, 49-fold selectivity versus human and 20-fold selectivity versus rat A1 ARs, and greater than 150-fold selectivity versus human A2A and A3 ARs. 8-[4-(2-Hydroxyethylamino)-2-oxoethoxy)phenyl]-1-propylxanthine (29) and 1-butyl-8-[4-(4-benzyl)piperazino-2-oxoethoxy)phenyl]xanthine (35) were among the most potent A2B antagonists showing K(i) values at A2B ARs of 1 nM, 57-fold (29) and 94-fold (35) selectivity versus human A1, ca. 30-fold selectivity versus rat A1, and greater than 400-fold selectivity versus human A2A and A3 ARs. The new potent, selective, water-soluble A2B antagonists may be useful research tools for investigating A2B receptor function.     

Nonsteroidal selective glucocorticoid modulators: the effect of C-10 substitution on receptor selectivity and functional potency of 5-allyl-2,5-dihydro-2,2,4-trimethyl-1H-[1]benzopyrano[3,4-f]quinolines

The preparation and characterization of a series of C-10 substituted 5-allyl-2,5-dihydro-2,2,4-trimethyl-1H-[1]benzopyrano[3,4-f]quinolines as a novel class of selective ligands for the glucocorticoid receptor is described. Substitution at the C-10 position of the tetracyclic core with linear, two-atom appendages (OCH(3), OCF(2)H, NHMe, SMe, CH=CH(2), Ctbd1;CH, CH(2)OH) provided molecules of high affinity (K(i) = 2-8 nM) for the human glucocorticoid receptor (hGR) with limited cross-reactivity with other steroid receptors (PR, MR, AR, ER). Optimal analogues showed slightly less potent but highly efficacious E-selectin repression with reduced levels of GRE activation efficacy in reporter gene assays relative to prednisolone. Preliminary SAR of analogues containing substitution at the C-9 and C-10 positions identified the 9-OH, 10-OMe analogue 50 and the 9-OH, 10-Cl analogue 58 as compounds that demonstrated potent, GR-mediated inhibition in a conconavalin A stimulated T-cell proliferation assay in both rodent and human whole blood monocytes. When evaluated for their in vivo effects in carrageenan-induced paw edema in rats, 50, 58, and 10-OCF(2)H analogue 35 showed dose-dependent anti-inflammatory effects (50, ED(50) = 16 mg/kg; 58, ED(50) = 15 mg/kg; 35, ED(50) = 21 mg/kg vs ED(50) = 15 mg/kg for 18 and ED(50) = 4 mg/kg for prednisolone).     

(3)H]MRE 3008F20: a novel antagonist radioligand for the pharmacological and biochemical characterization of human A(3) adenosine receptors

The lack of a radiolabeled selective A(3) adenosine receptor antagonist is a major drawback for an adequate characterization of this receptor subtype. This paper describes the pharmacological and biochemical characterization of the tritiated form of a new potent A(3) adenosine receptor antagonist, the pyrazolo triazolo pyrimidine derivative [(3)H]5N-(4-methoxyphenylcarbamoyl)amino-8-propyl-2-(2-furyl )pyrazolo [4,3-e] -1,2,4- triazolo[1,5-c]pyrimidine ([(3)H]MRE 3008F20). [(3)H]MRE 3008F20 bound specifically to the human adenosine A(3) receptor expressed in CHO cells (hA(3)CHO), and saturation analysis revealed a single high affinity binding site, K(D) = 0.80 +/- 0.06 nM, with a B(max) = 300 +/- 33 fmol/mg protein. This new ligand displayed high selectivity (1294-, 165-, and 2471-fold) in binding assay to human A(3) versus A(1), A(2A), and A(2B) receptors, respectively, and binds to the rat A(3) receptors with a K(i) > 10 microM. The pharmacological profile of [(3)H]MRE 3008F20 binding to hA(3)CHO cells was evaluated using known adenosine receptor agonists and antagonists with a rank order of potency consistent with that typically found for interactions with the A(3) adenosine receptors. In the adenylyl cyclase assay the same compounds exhibited a rank order of potency identical with that observed in binding experiments. Thermodynamic data indicated that [(3)H]MRE 3008F20 binding to hA(3)CHO is entropy- and enthalpy-driven in agreement with the typical behavior of other adenosine antagonists to A(1) and A(2A) receptors. These results show that [(3)H]MRE 3008F20 is the first antagonist radioligand with high affinity and selectivity for the human A(3) adenosine receptor and may be used to investigate the physiopathological role of A(3) adenosine receptors.     

Discriminative stimulus properties of eltoprazine in the pigeon.

Twelve pigeons were successfully (ED50 = 2.4 mg/kg p.o.) trained to discriminate the 5-HT(1A/B) receptor agonist eltoprazine (5.0 mg/kg p.o.) from its vehicle in a fixed-ratio (FR)30 two-key operant drug discrimination procedure. Tests for generalization and antagonism showed that 5-HT1A receptor agonists, such as 8-OH-DPAT (8-hydroxy-2-(di-n-propylamino)tetralin) (66.7%), flesinoxan (72.7%), buspirone (58.3%), and ipsapirone (36.4%) only partially substituted for the eltoprazine cue. Compounds with mixed agonistic action at 5-HT1 receptors, completely (> or = 80%) [(eltoprazine; TFMPP (1-(3-trifluoromethylphenyl) piperazine (ED50 = 7.68 mg/kg) and RU 24969 (5-methoxy-3-(1,2,3,6-tetrahydropyridin-4-yl-1H-indole) (ED50 = 15.8 mg/kg)] substituted for eltoprazine; whereas m-CPP (1-(3-chlorophenyl)piperazine) did not. The selective 5-HT reuptake inhibitor fluvoxamine partially (44%) substituted for the eltoprazine cue. The 5-HT1A receptor antagonist NAN-190 (1-(2-methoxyphenyl)-4-[4-(2-phtalimido)butyl]piperazine) fully blocked the eltoprazine cue. Both (+/-)-pindolol and (+/-)-propranolol showed partial antagonism of the eltoprazine cue (66.7 and 50.0%, respectively). (+/-)-Pindolol also showed partial substitution (50%) for the eltoprazine cue, but NAN-190 and (+/-)propranolol did not. It is concluded that the discriminatory stimulus properties of eltoprazine in the pigeon are mediated by 5-HT1A and 5-HT1B receptors.     

In vivo pharmacologic profile of YM158, a new dual antagonist for leukotriene D4 and thromboxane A2 receptors

The antagonistic activity of oral YM158 (3-[(4-tert-butylthiazol-2-yl)methoxy]-5'-[3-(4-chlorobenzenesu lfonyl)propyl]-2'-(1H-tetrazol-5-ylmethoxy)benzanilide monosodium salt monohydrate), a new dual antagonist for leukotriene (LT) D4 and thromboxane (TX) A2 receptors, was investigated. Oral YM158 caused dose-dependent inhibition of LTD4-induced increases in plasma leakage and LTD4- or U46619-induced increases in airway resistance, with ED50 values of 6.6, 8.6 and 14 mg/kg, respectively. The dose-range of YM158's inhibitions was almost the same for both LTD4 and TXA2 receptors, and repeated oral doses did not affect its efficacy. Furthermore, oral YM158 inhibited antigen-induced bronchoconstriction. Although the potency of pranlukast for LTD4 receptor antagonism (ED50 = 0.34 mg/kg) is greater than that of YM158 (ED50 = 8.6 mg/kg), the doses of both pranlukast and YM158 for significant inhibition of the antigen-evoked airway response were the same, indicating that the TXA2 receptor antagonism of YM158 plays an important role in its anti-asthmatic effects. In conclusion, YM158 promises to be a novel agent for treating bronchial asthma.     

MEN15596, a novel nonpeptide tachykinin NK2 receptor antagonist

The pharmacological profile of MEN15596 or (6-methyl-benzo[b]thiophene-2-carboxylic acid [1-(2-phenyl-1R-{[1-(tetrahydropyran-4-ylmethyl)-piperidin-4-ylmethyl]-carbamoyl}-ethylcarbamoyl)-cyclopentyl]-amide), a novel potent and selective tachykinin NK2 receptor antagonist endowed with oral activity, is described. At the human recombinant tachykinin NK2 receptor, MEN15596 showed subnanomolar affinity (pKi 10.1) and potently antagonized (pKB 9.1) the neurokinin A-induced intracellular calcium release. MEN15596 selectivity for the tachykinin NK2 receptor was assessed by binding studies at the recombinant tachykinin NK1 (pKi 6.1) and NK3 (pKi 6.4) receptors, and at a number of 34 molecular targets including receptors, transporters and ion channels. In isolated smooth muscle preparations MEN15596 showed a marked species selectivity at the tachykinin NK2 receptor with the highest antagonist potency in guinea-pig colon, human and pig bladder (pKB 9.3, 9.2 and 8.8, respectively) whereas it was three orders of magnitude less potent in the rat and mouse urinary bladder (pKB 6.3 and 5.8, respectively). In agreement with binding experiments, MEN15596 showed low potency in blocking selective NK1 or NK3 receptor agonist-induced contractions of guinea-pig ileum preparations (pA2相似文献   

Hypotensive effects of intravenously administered uridine and cytidine in conscious rats: involvement of adenosine receptors

In the present study, we investigated the cardiovascular effects of intravenously injected uridine or cytidine, and the role of adenosine receptors in mediating these effects, in conscious normotensive rats. Intravenous (i.v.) administration of uridine (124, 250, 500 mg/kg) dose-dependently decreased arterial pressure and heart rate. Cytidine (124, 250, 500 mg/kg; i.v.) produced slight dose-related hypotension without changing heart rate. Plasma uridine and cytidine concentrations increased time- and dose-dependently while plasma adenosine levels did not change after injection of the respective nucleosides. Pretreatment with intravenous caffeine (20 mg/kg), 8-phenyltheophylline (8-PT) (1 mg/kg), nonselective adenosine receptor antagonists, or 8-p-sulfophenyltheophylline (8-SPT) (20 mg/kg), a nonselective adenosine receptor antagonist which does not cross the blood-brain barrier, abolished the cardiovascular effects of uridine (250 mg/kg; i.v.) or cytidine (250 mg/kg; i.v.). Intracerebroventricular (i.c.v.) caffeine (200 microg) or 8-SPT (50 microg) pretreatment did not change the magnitude of the cardiovascular responses induced by nucleosides. Intravenous 8-cyclopenthyl-1,3-dipropylxanthine (DPCPX) (5 mg/kg), a selective adenosine A(1) receptor antagonist, greatly attenuated the cardiovascular responses to uridine and cytidine. Pretreatment with 3,7,-dimethyl-1-propargylxanthine (DMPX) (2 mg/kg), an adenosine A(1)/A(2) receptor antagonist, attenuated hypotension induced by uridine and blocked the arterial pressure decrease in response to cytidine. Uridine-induced bradycardia was blocked by DMPX. 4-(2-[7-amino-2-(2-furyl[1,2,4]-triazolo[2,3-a[1,3,5]triazin-5-yl-aminoethyl)phenol (ZM241385) (1 mg/kg; i.v.), a selective adenosine A(2A) receptor antagonist, pretreatment produced an only very small blockade in the first minute of the hypotensive effects of uridine without affecting the bradycardia. ZM241385 pretreatment completely blocked cytidine's hypotensive effect. In Langendorff-perfused rat heart preparation, uridine (10(-3) M), but not cytidine, decreased the heart rate. Our results show that intravenously injected uridine or cytidine is able to decrease arterial pressure by activating peripheral adenosine receptors. The data also implicates that the mainly adenosine A(1) receptor activation is involved in the uridine-induced cardiovascular effects, while both adenosine A(1) and A(2A) receptor activations mediate the cytidine's effects.     

Nitric oxide generation, tachyphylaxis and cross-tachyphylaxis from nitrovasodilators in vivo

We have studied the effects of selective and non-selective adenosine receptor agonists and antagonists in audiogenic-seizure-sensitive DBA/2 mice, an animal model of generalized reflex epilepsy. With the exception of the adenosine A3 receptor agonist, N6-(3-iodobenzyl)-5'-N-methylcarboxamidoadenosine (IB-MECA), all the agonists studied prevented the development of audiogenic seizures in a dose-dependent manner. The ED50 values against the clonic phase of the audiogenic seizures were low, that is: 0.06 mg/kg, i.p., for the adenosine A1 receptor agonist, 2-chloro-N6-cyclopentyladenosine (CCPA), 0.02 and 0.03 mg/kg, i.p., for the adenosine A2A receptor agonists, 2-(4-(2-carboxyethyl)-phenylamino)-5'-N-ethylcarboxamidoadenosine (CGS 21680) and 2-hexynyl-5'-N-ethyl-carboxamidoadenosine (2-HE-NECA), and 0.7 mg/kg, i.p., for the adenosine A1/A3 receptor agonist, N6-2-(4-aminophenyl)ethyladenosine (APNEA). Conversely, the non-selective agonist, N-ethyl-carboxamidoadenosine (NECA), was highly potent, the ED50 being 0.0005 mg/kg, i.p. In the absence of auditory stimulation, the adenosine receptor antagonists increased the incidence of both clonic and tonic seizures in DBA/2 mice. The ED50 values were: for caffeine, 207.5 mg/kg, i.p., for the adenosine A1 receptor antagonist, 8-cyclopentyl-1,3-dipropylxanthine (DPCPX), 327.8 mg/kg i.p., for the adenosine A2A receptor antagonists, 3,7-dimethyl-1-propylxanthine (DPMX), 86.7 mg/kg i.p., for the (E,18%-Z,82%)7-methyl-8-(3,4-dimethoxystyryl)-1,3-dipropylxanthine (KF 17837), 69.1 mg/kg i.p., and 5-amino-7-(2-phenylethyl)-2-(2-furyl)-pyrazolo-(4,3-c)1,2,4-triazolo(1,5 -c)-pyrimidine (SCH 58261), 321.8 mg/kg i.p. The rank order of convulsant potency in our epileptic model, following intracerebroventricular administration, was DPCPX > DMPX > 1,3,7-trimethyl-8-(3-chlorostyryl)xanthine (CSC) > KF 17837 > Caffeine > SCH 58261 > 5-amino-9-chloro-2-(2-furyl)-1,2,4-triazolo(1,5-c)quinazoline (CGS 15943). Following a subconvulsant audiogenic stimulus of 83 dB, all adenosine receptor antagonists induced both tonic and clonic seizures. The ED50 values for such proconvulsant effects were: for caffeine 0.04 mg/kg, i.p., for the adenosine A receptor antagonist, DPCPX, 5.84 mg/kg, i.p., for the adenosine A2A receptor antagonists, DMPX, 0.02 mg/kg, i.p., CGS 15943, 0.29 mg/kg i.p., KF 17837, 0.57 mg/kg, i.p., CSC 0.12 mg/kg, i.p. and SCH 58261 0.07 mg/kg, i.p., respectively. These data suggest that stimulation of adenosine A1 and A2A receptors is involved in the suppression of seizures.     

Effect of chronic Albizzia julibrissin treatment on 5-hydroxytryptamine1A receptors in rat brain

Quantitative receptor autoradiography and behavioral studies were employed to investigate whether the aqueous extract of Albizzia julibrissin (AEAJ) specifically targets serotonergic systems in rat brain. AEAJ was orally administered at 50 and 200 mg/kg to adult male SD rats for 7 days. Treatment with AEAJ (200 mg/kg) significantly increased time-spent in open arms and the number of open arm entries in an elevated plus-maze (EPM) versus saline controls (P<0.05). Moreover, those effects of AEAJ were blocked by WAY 100635, a 5-HT1A receptor antagonist. Following behavioral evaluation, the binding of [3H]8-hyroxy-2-(di-n-propylamino) tertalin ([3H]8-OH-DPAT) to 5-HT1A receptors in rat brain was investigated. [3H]8-OH-DPAT binding after AEAJ (200 mg/kg) treatment showed a marked increase in the frontal cortex, hippocampus (CA2 and CA3 regions) and in the lateral septum versus vehicle-treated controls. No changes of [3H]8-OH-DPAT binding were observed in the caudate putamen, dentate gyrus and CA1 areas of the hippocampus or in the hypothalamus. In the dorsal raphe region, [3H]8-OH-DPAT binding was significantly reduced by AEAJ (50 mg/kg) treatment but was unchanged by AEAJ (200 mg/kg). These results suggest that the anxiolytic-like effect of A. julibrissin is mediated by the changes of serotonergic nervous system, especially 5-HT1A receptors.     

The in vivo and in vitro activity of AHR-13268D, a new antiallergic/antihistaminic agent

AHR-13268D (4-[3-[4-[Bis(4-fluorophenyl)hydroxymethyl]-1- piperidinyl]propoxy]benzoic acid, sodium salt) is a potent, long-acting water soluble, antiallergic and antihistaminic agent. AHR-13268D protects sensitive guinea pigs from collapse induced by aerosolized antigen; 1, 5, and 24 h ED50s in the test were 0.27, 0.25, 0.93 mg/kg, PO, respectively. AHR-13268D was also active when given as an aerosol, the 1 h ED50 = 0.29%. In the rat passivefoot anaphylaxis test. AHR-13268D was slightly more active (1.55 times) than AHR-5333B when given orally 1 h prior to challenge and equipotent to cromolyn when given intravenously immediately prior to challenge. AHR-13268D displayed potent, long-acting antihistaminic activity in naive guinea pigs; the 1, 5, and 24 h oral ED50s being in the range of 0.3 mg/kg. AHR-13268D (10 to 20 mg/kg, PO) attenuated the skin responses to ascaris antigen in sensitive dogs and did not alter the EEG pattern or sleep/wake patterns of cats at doses in vast excess of its antihistaminic activity. In vitro, AHR-13268D was a potent inhibitor of histamine release from rat peritoneal mast cells (IC50 = 0.51 nM) and was as potent as the reference 5-LO inhibitor phenidone in inhibiting antigen-induced contractions of guinea pig ileum in the presence of pyrilamine, atropine, and imidazole (IC50 approximately 300 microM). AHR-13268B was bioavailable (approximately 88%) from capsules or from oral solutions.     

Effects of the A 2A adenosine receptor antagonist KW6002 in the nucleus accumbens in vitro and in vivo

In this study, we have used the selective A 2A adenosine receptor antagonist KW6002 to investigate the function of A 2A receptors in the Lister hooded rat nucleus accumbens in vitro and in vivo. Radioligand binding studies confirmed a greater than 50-fold selectivity of KW6002 for A 2A receptors compared to A1 receptors. Release of [3H]-dopamine from nucleus accumbens slices in vitro was almost doubled in the presence of 300 nM KW6002, while GABA release was inhibited by approximately one third. In vivo, intraperitoneal administration of KW6002 (4 mg kg(-1)) increased dopamine overflow almost 4-fold in the nucleus accumbens. In behavioural testing, KW6002 elicited place preference and increased locomotor activity at 1, 2 and 4 mg kg(-1). Taken together, these results suggest a role for tonic activation of A 2A adenosine receptors in reward-related phenomena.     

Adenosine kinase inhibitors. 6. Synthesis, water solubility, and antinociceptive activity of 5-phenyl-7-(5-deoxy-beta-D-ribofuranosyl)pyrrolo[2,3-d]pyrimidines substituted at C4 with glycinamides and related compounds

4-(Phenylamino)-5-phenyl-7-(5-deoxy-beta-D-ribofuranosyl)pyrrolo[2,3-d]pyrimidine 1 and related compounds known as "diaryltubercidin" analogues are potent inhibitors of adenosine kinase (AK) and are orally active in animal models of pain such as the rat formalin paw model (GP3269 ED50= 6.4 mg/kg). However, the utility of this compound class is limited by poor water solubility that can be attributed to the high energy of crystallization caused by stacking of the parallel C4 and C5 aryl rings in the solid state (compound 1 and GP3269 each with pH 7.4 solubility <0.05 microg/mL). To increase water solubility, the hydrophobic C4-phenylamino substituent was replaced with a more hydrophilic group, glycinamide. This modification resulted in improved water solubility while retaining AK inhibition potency. Analogues were studied where changes in the glycinamide moiety were combined with changes to the base and sugar. A lead compound, 4-N-(N-cyclopropylcarbamoylmethyl)amino-5-phenyl-7-(5-deoxy-beta-D-ribofuranosyl)pyrrolo[2,3-d]pyrimidine (16c) (IC50= 3 nM and water solubility = 32 +/- 9 microg/mL at pH 7.4), was further characterized in biological assays. Compound 16c exhibited strong oral efficacy in the rat formalin paw model (ED50 of 2.5 mg/kg). In the most advanced assay, 16c was found to inhibit bradykinin-induced licking in marmoset monkeys with an ED50 estimated at 0.9 mg/kg without producing evidence of side effects such as ataxia, sedation, and emesis at this dose. However, lethal toxicity in the rat formalin paw model occurred with high doses of 16c, and further work on this series was discontinued.     

Modulation of paracetamol antinociception by caffeine and by selective adenosine A2 receptor antagonists in mice

This study investigated the involvement of adenosine receptors in the interaction between paracetamol and caffeine in mice, using the adenosine A2A receptor antagonist 5-amino-7-(2-phenylethyl)-2-(2-furyl)pyrazolo[4,3-e]-1,2,4-triazolo[1,5-c]pyrimidine (SCH58261) and the adenosine A2B receptor antagonist 1-propyl-8-p-sulfophenylxanthine (PSB1115), in the tail immersion and hot-plate tests. Paracetamol (10-200 mg/kg) was antinociceptive in both tests, but, in contrast to previous studies, caffeine (10 mg/kg) was pronociceptive in the tail immersion test, and reduced the effects of paracetamol in both tests. SCH58261 (3 mg/kg) was antinociceptive in both tests and in its presence paracetamol (50 mg/kg) had no further effect. PSB1115 (10 mg/kg) had little effect alone but potentiated the effect of paracetamol (50 mg/kg) in the hot-plate test and abolished it in the tail immersion test. These results suggest that adenosine A2B receptors may be involved in the action of paracetamol in a pathway-dependent manner, and also support the existence of pronociceptive adenosine A2A receptors.     

Novel 1-phenylcycloalkanecarboxylic acid derivatives as potential anticonvulsant agents

A series of analogues based on the anticonvulsant carbetapentane (1, 2-[2-(diethylamino)ethoxy]ethyl 1-phenyl-1-cyclopentylcarboxylate) was prepared as potential novel anticonvulsant drugs. Structure-activity relationships of analogues in which the ester function and cyclopentane moieties were modified have been investigated by evaluating their ability to prevent seizures in the rat maximal electroshock test. These compounds (11, ED50 = 16 mumol/kg; 12, ED50 = 86 mumol/kg, and 23, ED50 = 173 mumol/kg) were effective anticonvulsants. Compound 11, an alkyl ether derivative of 1, was more potent than the parent compound (ED50 = 48 mumol/kg) and also showed a 2-fold increase in potency compared to that of the prototypic anticonvulsant drug diphenylhydantoin.     

Pharmacologic actions of the second generation leukotriene B4 receptor antagonist LY293111: in vivo pulmonary studies

We examined the in vivo actions of LY293111 sodium (2-[2-propyl-3-[3-[2-ethyl-4-(4-fluorophenyl)-5-hydroxyphenoxy]pro poxy]phenoxy] benzoic acid sodium salt). Guinea pigs were used to evaluate the effect of this agent on (1) acute airway obstruction produced by intravenous leukotriene B4, (2) pulmonary granulocyte infiltration and delayed onset airway obstruction resulting from a 4-h leukotriene B4 inhalation and (3) lung inflammation after aerosol challenge with the divalent cationic ionophore A23187 (6S-[6alpha(2S*,3S*),8beta(R*),9beta,11alpha]-5- (methylamino)-2-[[3,9,11-trimethyl-8-[1-methyl-2-oxo-2-(1H-pyrrol-2-yl)e thyl]-1,7-dioxaspiro[5.5]undec-2-yl]methyl]-4-benzoxazole carboxylic acid). Airway obstruction was quantitated using pulmonary gas trapping measurements and lung inflammation was evaluated by bronchoalveolar lavage (BAL) and histology. LY293111 sodium produced a dose-related inhibition of acute leukotriene B4-induced airway obstruction when administered i.v. (ED50=14 microg/kg) or p.o. (ED50=0.4 mg/kg). In contrast, LY293111 sodium did not inhibit the pulmonary gas trapping caused by aerosols of histamine, leukotriene D4, or the thromboxane mimetic U46619 (15 [(S)-hydroxy11a,9a-(epoxymethano)prosta-5Z,13E-dienoic acid]). Oral LY293111 sodium inhibited leukotriene B4-induced bronchoalveolar lavage granulocyte infiltration and delayed onset airway obstruction at doses as low as 0.3 mg/kg. In A23187-challenged animals, pulmonary inflammation was markedly inhibited at 1 h, but not 2 h and 4 h post-exposure. We conclude that LY293 11 sodium is a selective leukotriene B4 receptor antagonist with potent pulmonary anti-inflammatory activity.     

Metabotropic glutamate 1 receptor distribution and occupancy in the rat brain: a quantitative autoradiographic study using [3H]R214127

We used the selective metabotropic glutamate (mGlu) 1 receptor antagonist [3H]1-(3,4-dihydro-2H-pyrano[2,3-b]quinolin-7-yl)-2-phenyl-1-ethanone ([3H]R214127) to investigate the distribution of mGlu1 receptor binding sites in rat brain. We found high mGlu1 receptor binding in the cerebellum, thalamus, dentate gyrus and medial central gray, moderate binding within the CA3 of the hippocampus and hypothalamus, and low mGlu1 receptor binding in the basal ganglia and cortex. The mGlu1 receptor is also present in variable degree in the dorsal lateral septal nucleus, amygdala, interpeduncular nucleus and median raphe nucleus. Additionally, we employed [3H]R214127 autoradiography as a means of investigating the occupancy of central mGlu1 receptors following in vivo administration of mGlu1 receptor antagonists that prevent binding of this radioligand. We found that the mGlu1 receptor antagonist (3aS,6aS)-6a-naphtalan-2-ylmethyl-5-methyliden-hexahydro-cyclopenta[c]furan-1-on (BAY 36-7620), administered subcutaneously (s.c.) at 10 mg/kg, only occupied about 30% of cerebellar and thalamic mGlu1 receptors. The mGlu1/5 receptor antagonist 2-quinoxaline-carboxamide-N-adamantan-1-yl (NPS 2390) exhibited a relatively high potency in occupying mGlu1 receptors in rat cerebellum (ED50 = 0.75 mg/kg, s.c.) and thalamus (ED50 = 0.63 mg/kg, s.c). In the future, this method can be employed to gain more insight into the in vivo profile and central activity of potential therapeutic agents that act upon the mGlu1 receptor.     

WAY100635 prevents the changes induced by fluoxetine upon the 5-HT1A receptor functionality

5-HT1A receptor-mediated signalling in rat brain was evaluated after chronic administration (14 days; s.c.) of the selective serotonin reuptake inhibitor (SRRI) fluoxetine (10 mg/kg/day) alone, or in combination with the 5-HT1A receptor antagonist WAY100635 (0.1 mg/kg/day). The density of 5-HT1A binding sites was unchanged following fluoxetine, WAY100635, or the combination of fluoxetine and WAY100635. However, the net stimulation of [35S]GTPgammaS binding induced by the 5-HT1A agonist 8-OH-DPAT was significantly attenuated in dorsal raphe nucleus (DRN), but not in hippocampus, after chronic fluoxetine. Moreover, depending of the area analysed, the basal binding of [35S]GTPgammaS was differentially affected by this treatment: increased in DRN and decreased in hippocampal dentate gyrus. Interestingly, the changes in [35S]GTPgammaS basal binding and on 5-HT1A receptors functionality were prevented by the concomitant administration of WAY100635. The inhibition of dorsal raphe firing by 8-OH-DPAT was also attenuated in fluoxetine-treated rats (ED50 = 2.12 +/- 0.32 microg/kg and 4.34 +/- 0.09 microg/kg, for vehicle and fluoxetine respectively), an effect which was also prevented by the concomitant administration of WAY100635 (ED50 = 2.10 +/- 0.58 microg/kg). Chronic administration of WAY100635 alone did not affect the 5-HT1A receptor-induced stimulation of [35S]GTPgammaS binding, nor the 8-OH-DPAT-induced inhibition of 5-HT neuron firing. These results demonstrate that the concomitant blockade of 5-HT1A receptors when administering fluoxetine prevents those adaptive changes of 5-HT1A receptor function associated with the chronic administration of this antidepressant. These findings could be relevant from the therapeutic point of view, and further support the potential benefit of treatments with a SSRI/5-HT1A receptor antagonist combination.