Feeding increases dopamine metabolism in the rat brain.

Feeding induced by food deprivation is accompanied by an increased production of the dopamine metabolite 3,4-dihydroxyphenylacetic acid in the brains of rats. This neurochemical change occurs in the nucleus accumbens, the posterior hypothalamus, and the amygdala but not in other dopaminergic nerve terminal fields such as the corpus striatum. These results indicate that the release of dopamine from particular groups of central neurons is increased during feeding and suggest that anatomically distinct subgroups of central dopaminergic neurons serve different roles in the regulation of food intake.

Pharmacologic/pharmacokinetic evaluation of emesis induced by analogs of RSU 1069 and its control by antiemetic agents.

RB 6145, the ring-opened analog of RSU 1069, and PD 130908, the desoxy ring-opened analog of RSU 1069, were compared to RSU 1069 for their emetic potential in dogs. When RB 6145 and PD 130908 were administered intravenously at doses ranging from 20% to 50% of the mouse equivalent maximum tolerated dose (MTD), both analogs were less emetic than RSU 1069 on a molar basis. Furthermore, the 5HT3 antagonist ondansetron prevented emesis at doses as high as 75% of the MTD. The reactivity, and hence the emetic liability of these compounds, is thought to be mediated by formation of the corresponding aziridine intermediate. In mouse plasma, both analogs rapidly converted to two products, the reactive aziridine and a stable oxiazolidinone species formed upon reaction with bicarbonate in the blood. A positive correlation exists between the amounts of aziridine formed by these analogs and their emetic potential.

Lack of involvement of haloperidol-sensitive sigma binding sites in modulation of dopamine neuronal activity and induction of dystonias by antipsychotic drugs.

The present studies evaluated previous suggestions that haloperidol-sensitive sigma binding sites are involved in the modulation of dopamine (DA) neuronal activity and in the induction of the dystonic effects of antipsychotic drugs. These issues were addressed by evaluating the effects of compounds that have differing affinities for sigma binding sites, on the firing activity of DA neurons in the substantia nigra in chloral hydrate-anesthetized rats and on the ability to induce extrapyramidal motor dysfunction in squirrel monkeys sensitized to the dystonic effects of haloperidol. The agents studied included haloperidol, DTG (1,3-di-o-tolylguanidine), (+)-pentazocine, (+)-SKF 10,047, BMY 14802, 8-OH-DPAT and sulpiride. There was no relationship between affinity for sigma binding sites and the ability to either alter DA neuronal activity or to induce extrapyramidal motor dysfunction.

The pharmacology of the novel and selective sigma ligand, PD 144418.

The pharmacology of PD 144418 (1-propyl-5-(3-p-tolyl-isoxazol-5-yl)-1,2,3,6-tetrahydropyridine) was characterized using neurochemical, biochemical and behavioral techniques. For sigma (sigma 1 and sigma 2 respectively) sites, PD 144418 affinities were determined using whole guinea pig brain membranes with [3H](+)-pentazocine and neuroblastoma x glioma cell membranes using [3H]1,3,di-O-tolylguanidine (DTG) in the presence of 200 nM (+)-pentazocine. PD 144418 exhibited an affinity for sigma 1 of 0.08 nM (Ki) versus a K1 of 1377 nM for sigma 2 site. Additional receptor binding studies indicated that PD 144418 lacked affinity for dopaminergic, adrenergic, muscarinic and a variety of other receptors. In vitro studies indicated that PD 144418 reversed the N-methyl-D-aspartate (NMDA)-induced increase in cyclic GMP (cGMP) in rat cerebellar slices without affecting the basal levels, suggesting that sigma 1 sites may be important in the regulation of glutamine-induced actions. PD 144418 potentiated the decrease in 5-hydroxytryptophan caused by haloperidol in the mesolimbic region, but by itself had no effect in 5-hydroxytrypamine (5-HT) and dopamine (DA) synthesis. Behaviorally, similar to other sigma ligands, PD 144418 antagonized mescaline-induced scratching at doses that did not alter spontaneous motor activity. This action is suggestive of potential antipsychotic property. It exhibited no anxiolytic and antidepressant properties in the models used. These results show that PD 144418 is a very selective sigma 1 agent, devoid of any significant affinity for other receptors and that sigma 1 site may modulate actions in the CNS.

PD 158771, a potential antipsychotic agent with D2/D3 partial agonist and 5-HT(1A) agonist actions. II. Preclinical behavioral effects.

PD 158771 has been described in receptor binding and biochemical tests as a partial agonist at dopamine (DA) D2 and D3 receptors as well as an agonist at serotonin (5-HT)(1A) receptors. The present studies describe the profile of PD 158771 in rodent and primate behavioral tests. PD 158771 reduced spontaneous locomotor activity in mice (ED(50)=0.38 mg/kg, i.p.) and rats (ED(50) = 1.2 mg/kg, i.p. and 0.16 mg/kg, s.c.), and reduced amphetamine-stimulated locomotion in mice (ED(50) = 0.13 mg/kg, i.p.). At relatively higher doses up to 3 mg/kg, s.c. in rats, PD 158771 did not produce locomotor stimulation or induce stereotypy, indicating a lack of postsynaptic DA agonist activity. PD 158771 reduced apomorphine stimulated locomotion in rats at a dose 4.6-fold greater than those that reduced spontaneous locomotor activity, indicating weak postsynaptic DA antagonist actions; results consistent with a partial agonist profile. PD 158771 produced anxiolytic-like effects in the water-lick (Vogel) conflict test, effects possibly due to the 5-HT(1A) activity. However, PD 158771 was inactive in the water wheel behavioral despair model in rats, indicating lack of antidepressant properties. Similar to known antipsychotics, PD 158771 produced a potent and long-lasting inhibition of conditioned avoidance responding in squirrel monkeys. In contrast to standard antipsychotics, and similar to clozapine, PD 158771 did not cause catalepsy in rats at a dose 20-fold higher than the ED(50) dose for locomotor inhibition. PD 158771 also had a somewhat lower liability than haloperidol to produce extrapyramidal dysfunction in squirrel and cebus monkeys sensitized to the dystonic effects of haloperidol. The data indicate that PD 158771 is a DA partial agonist with weak intrinsic activity that selectively activates brain DA autoreceptors. PD 158771 produced behavioral effects consistent with potential antipsychotic and anxiolytic efficacy, and has an improved profile in the extrapyramidal side effect model when compared to certain currently available antipsychotic agents.

PD 158771, a potential antipsychotic agent with D(2)/D(3) partial agonist and 5-HT(1A) agonist actions. I. Neurochemical effects.

The neurochemical effects of a novel dopamine (DA) D(2)-like and serotonin (5-HT) 5-HT(1A) agonist, PD 158771, are described. PD 158771 exhibited affinities for human D(2L), D(3) and D(4.2) receptors expressed in Chinese hamster ovary (CHO)-K1 cells with K(i) (nM) values of 5.2, 13.7 and 34.8 respectively. PD 158771 showed high affinity for cloned human 5-HT(1A) (K(i) = 2.6 nM) and rat hippocampal 5-HT(1A) receptors (K(i) = 3.5 nM). Weaker affinities were observed at alpha 1-adrenergic (K(i) = 43 nM), histamine H(1) (IC(50) = 30 nM), 5-HT(2A) (K(i) = 24.5 nM) and sigma (sigma) -1 binding sites (K(i) = 24.5 nM). In measures of in vitro functional activity, PD 158771 stimulated [(3)H]thymidine uptake in CHO p-5 cells transfected with hD(3) receptors with a maximal effect of 23% relative to quinpirole. In hD(2)L, the corresponding value was 60% with an EC(50) of 29 nM, again indicating partial DA agonist action of PD 158771. In vivo, PD 158771 produced a dose-related decrease in DA synthesis in the striatum and mesolimbic regions of rat brain treated with gamma-butyrolactone (GBL), indicating a DA autoreceptor agonist action. In animals not treated with GBL, PD 158771 produced a dose-related decrease in DA synthesis and extracellular DA. A decrease in 5-HT synthesis in several brain areas was observed consistent with an agonist response. Further support for DA autoreceptor agonist action is that PD 158771 produced a partial inhibition of the firing of substantia nigra zona compacta DA neurons, an effect reversed by haloperidol. In conclusion, PD 158771 exhibited affinities for DA and 5-HT receptors, appears to possess DA and 5-HT agonist actions; and it could provide improved antipsychotic profile with minimal side effects.

Dopamine autoreceptor agonists as potential antipsychotics. 2. (Aminoalkoxy)-4H-1-benzopyran-4-ones.

The synthesis and pharmacological properties of a novel type of [(arylpiperazinyl)alkoxy]-4H-1-benzopyran-4-ones with dopaminergic activity are described. The nature of the arylpiperazine (AP) moiety determines the dopamine (DA) agonist/antagonist character of this series of compounds; when the aryl portion of the AP is unsubstituted the compounds appear to be DA autoreceptor agonists while substituted aryl groups seem to impart DA antagonist activity. A heterocyclic piperazine, 7-[3-[4-(2-pyridinyl)-1-piperazinyl]propoxy]-4H-1-benzopyran-4-one (31, PD 119819) has been identified as an extremely selective DA autoreceptor agonist in tests that include [3H]haloperidol binding, inhibition of spontaneous locomotor activity, inhibition of brain DA synthesis, inhibition of brain DA neuronal firing, stereotypy assessment, and reversal of 6-hydroxydopamine (6-OHDA) induced akinesia in rats. In addition, 31 possesses good oral activity in the Sidman avoidance test in squirrel monkeys, a predictor of clinical antipsychotic efficacy. In another primate model, 31 has been found to lack the liability for extrapyramidal side effects observed with currently available antipsychotic drugs.

Synthesis and dopaminergic activity of pyridine analogs of 5-hydroxy-2-(di-n-propylamino)tetralin.

The pyridine analogs of 5-hydroxy-2-(di-n-propylamino)tetralin (5-OH-DPAT), 4-6, were synthesized, and their biological activity was compared to that of 5-OH-DPAT. Compounds 4 and 6 exhibited activity similar to 5-OH-DPAT in dopamine (DA) D2 and D3 receptor binding and in autoreceptor activation as measured by their ability to reverse the gamma-butyrolactone-induced increase in rat DA synthesis. Behaviorally, 4 and 6 decreased locomotor activity (LMA) in rats (sc) at low doses but did not increase LMA to the same extent as 5-OH-DPAT at higher doses, indicating that 4 and 6 may be more selective for the DA autoreceptor. While 4 was less active orally in rats, 6 appeared to retain most of its behavioral potency. Analog 5 showed little activity in vivo or in vitro.

Dopamine autoreceptor agonists as potential antipsychotics. 1. (Aminoalkoxy)anilines.

The synthesis and pharmacological properties of a novel type of [(arylpiperazinyl)alkoxy]anilines with dopaminergic properties are described. One of these compounds, 3-[3-(4-phenyl-1-piperazinyl)propoxy]benzenamine (4c), has been identified as a selective dopamine (DA) autoreceptor agonist in tests that include [3H]haloperidol binding, inhibition of striatal DA synthesis, inhibition of DA neuronal firing, inhibition of spontaneous locomotor activity, and reversal of reserpine-induced depression in rats. In addition, 4c possesses good oral activity in the Sidman conditioned avoidance test in squirrel monkeys, which is indicative of antipsychotic activity. In a primate model, 4c was found to lack the liability for extrapyramidal side effects usually associated with antipsychotic drugs.

(5-Amino-1,3-dimethyl-1H-pyrazol-4-yl)(2-fluorophenyl)methanones . A series of novel potential antipsychotic agents.

(5-Amino-1,3-dimethyl-1H-pyrazol-4-yl)(2-fluorophenyl)methanone (1) was found to have an antipsychotic-like profile in behavioral tests predictive of antipsychotic efficacy but, unlike available antipsychotic agents, did not bind in vitro to dopamine receptors. Upon further evaluation, 1 was found to cause clonic seizures in aged rodents. An examination of related structures revealed that 5-(substituted aminoacetamide) analogues of 1 shared this novel pharmacology and did not cause seizures. The synthesis and pharmacological evaluation of this series of compounds are described. Two compounds, 2-(diethylamino)acetamide (25) and 2-[[3-(2-methyl-1-piperidinyl)propyl]-amino]acetamide (38), were selected for examination in secondary tests. Like known antipsychotics both compounds reduced spontaneous locomotion in mice at doses that did not cause ataxia and inhibited conditioned avoidance selectively in both rats and monkeys. Unlike known antipsychotics neither 25 nor 38 elicited dystonic movements in haloperidol-sensitized cebus monkeys, a primate model of antipsychotic-induced extrapyramidal side effects. Biochemical studies indicated that these compounds act via a nondopaminergic mechanism. Neither 25 nor 38 bound to dopamine receptors in vitro or caused changes in striatal dopamine metabolism in vivo. In addition, they did not raise serum prolactin levels as do known antipsychotics. Although adverse animal toxicological findings have precluded clinical evaluation of these agents, the present results indicate that it is possible to identify at the preclinical level nondopaminergic compounds with antipsychotic-like properties.

4-(1,2,5,6-Tetrahydro-1-alkyl-3-pyridinyl)-2-thiazolamines: a novel class of compounds with central dopamine agonist properties.

The design, synthesis, and pharmacological properties of a novel type of 4-(1,2,5,6-tetrahydro-1-alkyl-3-pyridinyl)-2-thiazolamine with dopaminergic properties are described. In particular, 4-(1,2,5,6-tetrahydro-1-propyl-3-pyridinyl)-2-thiazolamine (4c, PD 118440) and its allyl analogue (4i, PD 120697) have been identified as orally active dopamine (DA) agonists with pronounced central nervous system effects in tests that include [3H]-haloperidol and [3H]-N-propylnorapomorphine binding, inhibition of striatal DA synthesis, inhibition of DA neuronal firing, inhibition of spontaneous locomotor activity, and reversal of reserpine-induced depression in rats. The DA autoreceptor selectivity of these heterocyclic analogues of 3-(1-propyl-3-piperidinyl)phenol (3-PPP) was also evaluated. In this series, DA agonist activity was found to be highly dependent on the size of the N-alkyl substituent, the saturation level of the six-membered ring, and the mode of attachment of the 2-aminothiazole ring.

Synthesis and dopamine agonist properties of (+-)-trans-3,4,4a,10b-tetrahydro-4-propyl-2H,5H-[1]benzopyrano [4,3-b]-1,4-oxazin-9-ol and its enantiomers.

The dopamine agonist profile of (+-)-trans-3,4,4a,10b-tetrahydro-4-propyl-2H,5H-[1]benzopyrano [4,3-b]-1,4-oxazin-9-ol (16a) and its enantiomers (16b-c) was examined. Racemic 16a exhibited moderate affinity for the dopamine (DA) D2 receptor labeled with the DA antagonist ligand [3H]haloperidol and moderate in vivo activity; it attenuated gamma-butyrolactone-stimulated DA synthesis, decreased DA neuronal firing of substantia nigra DA neurons, and inhibited exploratory locomotor activity in rats, a profile consistent with a DA autoreceptor agonist mechanism of action. The (+)-enantiomer 16b possessed greater DA receptor affinity with the agonist ligand [3H]-N-propylnorapomorphine than with the antagonist ligand. In rats it potently inhibited DA synthesis and neuronal firing and also inhibited exploratory locomotion. The (-)-enantiomer, on the other hand, did not have significant activity in any of these tests. This profile indicates that like many other rigid DA agonists, the dopaminergic activity resides in one enantiomer, in this case the (+)-enantiomer 16b. On the basis of single-crystal X-ray analysis of a key intermediate, the absolute configuration of 16b was found to be 4aR, 10bR.

Synthesis and potential antipsychotic activity of 1H-imidazo[1,2-c]pyrazolo[3,4-e]pyrimidines.

The synthesis of a series of 1H-imidazo[1,2-c]pyrazolo[3,4-e]pyrimidines is reported along with the effects of these compounds in preclinical tests for antipsychotic activity. Certain of these compounds displayed antipsychotic-like effects in conditioned avoidance tests, but unlike currently used antipsychotic drugs, they did not have affinity for brain dopamine receptors. These compounds also did not cause dystonias predictive of extrapyramidal side effects in monkeys at doses that produced behavioral effects. On the basis of this unique biological profile, a member of this series 7,8-dihydro-8-ethyl-1,3,5-trimethyl-1H-imidao[1,2-c]pyrazol[3,4-e] pyrimidine (19, CI-943), has been selected for clinical evaluation as an antipsychotic agent.

6- and 8-hydroxy-3,4-dihydro-3-(dipropylamino)-2H-1-benzopyrans. Dopamine agonists with autoreceptor selectivity.

The dopamine agonist profiles of 3,4-dihydro-3-(3-dipropylamino)-2H-1-benzopyran-6- and -8-ol (4 and 5, respectively) were examined. Both 4 and 5 exhibited greater relative affinity for receptors labeled with the dopamine agonist ligand [3H]propylnorapomorphine than for those labeled with the dopamine antagonist ligand [3H]haloperidol. Both compounds attenuated the stimulation of brain dopamine synthesis caused by gamma-butyrolactone (GBL) and decreased the firing rate of substantia nigra dopamine neurons in rats. This profile of activity, together with the ability of the dopamine antagonist haloperidol to reverse the inhibition of dopamine neuronal firing, indicate that both compounds are brain dopamine agonists.

Chromeno[3,4-c]pyridin-5-ones: selective human dopamine D4 receptor antagonists as potential antipsychotic agents.

The discovery of a series of chromeno[3,4-c]pyridin-5-ones with selective affinity for the dopamine D4 receptor is described. Target compounds were tested for binding to cloned human dopamine D2, D3, and D4 receptor subtypes expressed in Chinese hamster ovary (CHO) K-1 cells. Several compounds demonstrated single digit nanomolar Ki values for binding to the D4 receptor with several hundred-fold selectivities toward the D2 and D3 receptors. A limited SAR study of this series is discussed. In a mitogenesis assay measuring [3H]thymidine uptake, the target compounds showed antagonist to weak partial agonist activity at the D4 receptor, with intrinsic activities ranging from 0 to 35%. Compound 6, 3-benzyl-8-methyl-1,2,3,4-tetrahydrochromeno[3,4-c]pyridin-5-one, increased DOPA (L-3,4-dihydroxyphenylalanine) synthesis 84% in the hippocampus and 10% in the striatum of rat brain when dosed orally at 10 mg/kg.

Dopamine autoreceptor agonists as potential antipsychotics. 3.6-Propyl-4,5,5a,6,7,8-hexahydrothiazolo[4,5-f]quinolin-2-amine.

A series of rigid tricyclic analogues of the dopamine (DA) agonist PD 118440 [4-(1,2,5,6-tetrahydro-1-propyl-3-pyridinyl)-2-thiazolamine] was synthesized and evaluated for dopaminergic activity and DA autoreceptor selectivity. (R)-(+)-6-Propyl-4,5,5a,6,7,8-hexahydrothiazolo[4,5-f]quinolin+ ++-2-amine [+)-6) was identified as the most selective DA autoreceptor agonist from this group of compounds. It inhibited spontaneous locomotor activity (LMA) in rodents, reversed the gamma-butyrolactone (GBL) induced accumulation of rat striatal DOPA and inhibited brain DA neuronal firing, all suggestive of direct DA autoreceptor agonist activity. However, (+)-6 is not completely free of postsynaptic DA activity, as evidenced by its stimulation of LMA in rats at high doses and its ability to produce stereotypy. On the other hand, (-)-6 appears to be a weak partial DA agonist with some effects on brain DA synthesis only at high doses. Like other DA autoreceptor agonists and DA antagonists, (+)-6 inhibited Sidman conditioned avoidance in squirrel monkeys, a test predictive of clinical antipsychotic activity. However, unlike classical antipsychotics, (+)-6 did not induce dystonias in haloperidol-sensitized squirrel monkeys, suggesting a minimal propensity toward extrapyramidal side effects (EPS).

(Aryloxy)alkylamines as selective human dopamine D4 receptor antagonists: potential antipsychotic agents.

The discovery of a series of novel (aryloxy)alkylamines with selective affinity for the dopamine D4 receptor is described. Target compounds were tested for binding to cloned human dopamine D2, D3, and D4 receptor subtypes expressed in Chinese hamster ovary (CHO) K-1 cells. A number of compounds demonstrated subnanomolar Ki values for binding to the D4 receptor, with several 100-fold selectivities toward the D2 and D3 receptors. Several compounds with combined D3/D4 receptor binding selectivity were also identified. A limited structure-activity relationship study of this chemical series is discussed. In a mitogenesis functional assay, the effect of the test compounds on cellular uptake of [3H]thymidine in D4-transfected CHO 10,001 cells was measured and compared to the response of the full dopamine agonist quinpirole. The activity of the compounds varied from full antagonist to weak partial agonist activity (intrinsic activity of 0-19% in comparison to quinpirole).

Studies of the active conformation of a novel series of benzamide dopamine D2 agonists.

Analogs of dopamine D2 agonist 11 were prepared in which a rigid trans decalin ring system was used to mimic various conformations of 11. The four rigid analogs where compared for their ability to bind to the DA D2 receptor and to inhibit forskolin-stimulated cAMP formation, a measure of DA agonist activity. Of the four rigid analogs of compound 11, only compound 12b had significant activity in both assays. Molecular modeling studies of 12a-d showed each had a single conformation with regard to the distance between the benzamide aryl-centroid and the 4-nitrogen atom of the pyridylpiperazine. Compound 12b was shown to have a greater distance between these functionalities (11.8 A) as compared to the other isomers (9.8-10.4 A). The distance between these two functionalities in 12b was similar to that of a conformer of 11 which has an extended conformation. This suggest that 11 is likely in an extended conformation when bound to the DA D2 receptor.

Design, synthesis, and evaluation of chromen-2-ones as potent and selective human dopamine D4 antagonists.

The discovery of a series of chromen-2-ones with selective affinity for the dopamine (DA) D4 receptor is described. Target compounds were tested for binding to cloned human DA D2L, D3, and D4.2 receptor subtypes expressed in Chinese hamster ovary K1 cells. Several compounds demonstrated high affinity (<20 nM, K(i)) and greater than 100-fold selectivity for DA D4.2 versus DA D2L receptors. The results of a SAR study are discussed within. In a DA D4 functional assay measuring [(3)H]thymidine uptake, target compounds showed antagonist activity at the D4.2 receptor. Compound 22, 7-[(2-phenylaminoethylamino)methyl]chromen-2-one, increased DOPA (L-3,4-dihydroxyphenylalanine) accumulation 51% in the hippocampus and 23% in the striatum of rat brains when dosed orally at 20 mg/kg.

Ribose-modified adenosine analogues as adenosine receptor agonists.

Analogues of the potent adenosine receptor agonist (R)-N-(1-methyl-2-phenylethyl)adenosine (R-PIA), modified at N9, were prepared and evaluated for adenosine A1 and A2 receptor binding and in vivo central nervous system and cardiovascular effects. The modifications at N9 include deoxy sugars, 5'-substituted-5'-deoxyriboses, non-ribose sugars, sugar ring homologues, and acyclic sugar analogues. Most of the derivatives have poor affinity for adenosine receptors. Only minor modifications at C5' and C3' maintain potent binding. In general, those derivatives exhibiting in vivo behavioral or cardiovascular effects also have the highest affinity for adenosine receptors.