3-arylimino-2-indolones are potent and selective galanin GAL3 receptor antagonists

A series of 3-imino-2-indolones are the first published, high-affinity antagonists of the galanin GAL3 receptor. One example, 1,3-dihydro-1-phenyl-3-[[3-(trifluoromethyl)phenyl]imino]-2H-indol-2-one (9), was shown to have high affinity for the human GAL3 receptor (Ki=17 nM) and to be highly selective for GAL3 over a broad panel of targets, including GAL1 and GAL2. Compound 9 was also shown to be an antagonist in a human GAL3 receptor functional assay (Kb=29 nM).

Structure-activity relationships of pregabalin and analogues that target the alpha(2)-delta protein

Pregabalin exhibits robust activity in preclinical assays indicative of potential antiepileptic, anxiolytic, and antihyperalgesic clinical efficacy. It binds with high affinity to the alpha(2)-delta subunit of voltage-gated calcium channels and is a substrate of the system L neutral amino acid transporter. A series of pregabalin analogues were prepared and evaluated for their alpha(2)-delta binding affinity as demonstrated by their ability to inhibit binding of [(3)H]gabapentin to pig brain membranes and for their potency to inhibit the uptake of [(3)H]leucine into CHO cells, a measure of their ability to compete with the endogenous substrate at the system L transporter. Compounds were also assessed in vivo for their ability to promote anxiolytic, analgesic, and anticonvulsant actions. These studies suggest that distinct structure activity relationships exist for alpha(2)-delta binding and system L transport inhibition. However, both interactions appear to play an important role in the in vivo profile of these compounds.

Orally active oxime derivatives of the dopaminergic prodrug 6-(N,N-di-n-propylamino)-3,4,5,6,7,8-hexahydro-2H-naphthalen-1-one. Synthesis and pharmacological activity

A series of racemic and enantiomerically pure oxime derivatives of the potential anti-Parkinson prodrug 6-(N,N-di-n-propylamino)-3,4,5,6,7,8-hexahydro-2H-naphthalen-1-one (1) were synthesized and pharmacologically evaluated. The oximes induced rotational behavior in the Ungerstedt rat rotation model for Parkinson's disease after oral administration. Especially the unsubstituted oxime ((-)-3) and the acetyl-oxime ((-)-10) induced a pronounced and long lasting effect. In this model, large individual differences were observed in responsiveness to treatment between rats. Though less potent than the parent prodrug, the oxime derivatives of (+/-)-1 and (-)-1 can be orally active, acting as cascade prodrugs.

Orally active analogues of the dopaminergic prodrug 6-(N,N-di-n-propylamino)-3,4,5,6,7,8-hexahydro-2H-naphthalen-1-one: synthesis and pharmacological activity

A series of analogues of 6-(N,N-di-n-propylamino)-3,4,5,6,7,8-hexahydro-2H-naphthalen-1-one (6), an enone prodrug of the mixed DA D(1)/D(2) agonist 5,6-diOH-DPAT (2), was synthesized. The pharmacological profiles of these new enones and their in vivo pharmacological activities were investigated in the Ungerstedt rat rotation model for Parkinson's disease. At 0.1 mg kg(-1) po, the N-methyl-N-n-propyl (12) and the N-ethyl-N-propyl (13) analogues induced pronounced and long lasting pharmacological effects. The pharmacological profile of enone 12 was found to be similar to that of 6, while enone 13 was significantly more potent than 6 (p < 0.01). Analyses of rat brains after the administration of (-)-6 and 13 indicated the presence of hydroxylated metabolites of the parent enones. It is speculated that such metabolites are alpha'-hydroxylated enones that may constitute the first step in the formation of the corresponding catechols.

Further characterization of structural requirements for ligands at the dopamine D(2) and D(3) receptor: exploring the thiophene moiety

The present study describes the synthesis and in vitro pharmacology of a novel series of dopaminergic agents in which the classical phenylethylamine pharmacophore is replaced by a thienylethylamine moiety. In general, the novel compounds showed a moderate affinity for the dopamine (DA) D(2) and D(3) receptors. When the thienylethylamine moiety is fixed in a rigid system, the affinity for the DA receptor is significantly increased. However, in the tricyclic hexahydrothianaphthoxazine structure, the affinity for the DA receptors is diminished.

A new type of prodrug of catecholamines: an opportunity to improve the treatment of Parkinson's disease

After decades of research around dopamine agonists, we have found a promising compound in S-PD148903 that represents a new type of prodrug, which in the rat is bioactivated to the catecholamine S-5,6-diOH-DPAT, known to display mixed dopamine D(1)/D(2) receptor agonist properties just like apomorphine. This prodrug has an enone structure which by an oxidative bioactivation mechanism is converted to the corresponding catechol and is delivered enantioselectively into the CNS. This novel concept has the potential to revolutionize the treatment of Parkinson's disease by competing with L-DOPA, the current treatment of choice.

The discovery of PD 89211 and related compounds: selective dopamine D4 receptor antagonists

The dopamine (DA) D2 family of receptors consists of the D2, D3, and D4 receptors. The DA D4 receptor is of interest as a target for drugs to treat schizophrenia based upon its high affinity for the atypical antipsychotic clozapine and its localization to the limbic and cortical regions of the brain. As part of a program to identify novel DA D4 receptor antagonists, a high-volume screen using the Parke-Davis compound library was initiated. This led to the discovery of PD 89211 (benzenemethanol, 2-chloro-4-[4-[(1H-benzimidazol-2-yl)methyl]-1-piperzinyl]) that displaced [3H]spiperone binding to hD4.2 with an affinity (Ki) of 3.7 nM. PD 89211 exhibited high selectivity for the DA D4.2 receptor (> 800-fold) as compared to other hDA receptor subtypes, rat brain serotonin, and adrenergic receptors. In vitro, PD 89211 had D4 receptor antagonist activity reversing quinpirole-induced [3H]thymidine uptake in CHOpro5 cells (IC50 = 2.1 nM). Limited structure-activity relationship (SAR) studies indicated that compounds with a 4-chloro-, 4-methyl-, and 3-chloro- substituents on the phenyl ring retained high affinity for D4 receptors, while those with a 4-methoxy- and no substituent had less affinity. While all clinically effective antipsychotics increase DA synthesis (DOPA accumulation) in rodents, PD 89211 did not increase DA synthesis in the DA-enriched striatum, indicating no effect on DA turnover and low propensity for exhibiting motor side effects. However, it did increase catecholamine synthesis in rat hippocampus, as did clozapine. Moreover, PD 89211 selectivity increased catecholamine synthesis in the hippocampus of wild type but not in mice lacking D4 receptors, suggesting that one function of D4 receptors may be to modulate DA/norepinephrine (NE) turnover in this brain area known to possess D4 receptors. The discovery of compounds like PD 89211 provides a tool to help in understanding the function of DA D4 receptors in the CNS.

Thiazoloindans and thiazolobenzopyrans: a novel class of orally active central dopamine (partial) agonists

The 2-aminothiazole moiety has proven its value in medicinal chemistry as a stable and lipophilic bioisosteric replacement of a phenol group. This approach has provided dopamine (DA) agonists with good oral availability. To further explore its use in the development of DA agonists, we have combined the 2-aminothiazole moiety with 2-aminoindans and 3-aminobenzopyrans, which are known templates for DA agonists. In this study we have synthesized 6-amino-3-(N,N-di-n-propylamino)-3,4-dihydro-2H-thiazolo[5, 4-f]-[1]benzopyran (12) and 6-amino-2-(N, N-di-n-propylamino)thiazolo[4,5-f]indan (20) and several analogues (13, 17, and 21). The affinity of the thiazolobenzopyrans and thiazoloindans for DA receptors was evaluated, which revealed compound 20 to have high affinity for DA D(3) receptors. In addition, the compounds were screened for their potential to inhibit lipid peroxidation, to determine their radical scavenging properties. Compounds 12, 20, and 21 were subjected to further pharmacological evaluation in a functional assay to determine intrinsic activity. Compound 20 was also studied with microdialysis (to determine effects on DA turnover in striatum) and in unilaterally 6-OH-DA lesioned rats (to determine their potential as DA agonists). These studies selected compound 20 (GMC 1111) as particularly interesting. Compound 20 caused a rotation activation in unilaterally 6-OH-DA lesioned rats and an increase in DA turnover in rat striatum. This dual agonist/antagonist action is best accounted for by its partial agonism at striatal DA D(2) receptors. Interestingly, 20 displayed long-lasting activity and excellent oral availability in 6-OH-DA lesioned rats, making this compound potentially useful for the treatment of Parkinson's disease.

Subtype-selective N-methyl-D-aspartate receptor antagonists: synthesis and biological evaluation of 1-(heteroarylalkynyl)-4-benzylpiperidines

4-[4-(4-Benzylpiperidin-1-yl)but-1-ynyl]phenol (8) and 4-[3-(4-benzylpiperidin-1-yl)prop-1-ynyl]phenol (9) are potent NR1A/2B receptor antagonists (IC(50) values 0.17 and 0.10 microM, respectively). Administered intraperitoneally, they both potentiated the activity of L-DOPA in the unilaterally 6-hydroxydopamine-lesioned (6-OHDA) rat, a model of Parkinson's disease. However, compound 9 was not active orally, likely due to rapid first-pass metabolism of the phenol moiety. The phenol was replaced by several bicyclic heterocyclic systems containing an NH group to function as a H-bond donor in the hope that these would be less likely to undergo rapid metabolism. In general, indoles, indazoles, benzotriazoles, indolones, and isatins gave analogues with weaker NR1A/2B activity than the parent phenols, while benzimidazolones and benzimidazolinones gave equipotent or more potent analogues. The preference for a para arrangement between the H-bond donor and the linking acetylene moiety was confirmed, and a propyne link was preferred over a butyne link. Substitution on the benzyl group or a 4-hydroxyl group on the piperidine had little effect on NR1A/2B potency; however, 4-hydroxypiperidines demonstrated slightly improved selectivity for NR1A/2B receptors versus alpha-1 adrenergic and dopamine D2 receptor affinity. From this study, 5-[3-(4-benzylpiperidin-1-yl)prop-1-ynyl]-1, 3-dihydrobenzoimidazol-2-one (46b) was identified as a very potent, selective NR1A/2B receptor antagonist (IC(50) value 0.0053 microM). After oral administration at 10 and 30 mg/kg, 46b potentiated the effects of L-DOPA in the 6-OHDA-lesioned rat and seemed to have improved oral bioavailability but lower brain penetration compared to phenol 9.

Synthesis and pharmacological evaluation of thiopyran analogues of the dopamine D3 receptor-selective agonist (4aR,10bR)-(+)-trans-3,4,4a,10b-tetrahydro-4-n-propyl-2H,5H [1]b enzopyrano[4,3-b]-1,4-oxazin-9-ol (PD 128907)

Benzopyranoxazine (+)-7 (PD 128907) is the most dopamine (DA) D3 receptor-selective agonist presently known. The only structural feature which distinguishes 7 from the analogous nonselective naphthoxazines is an oxygen atom in the 6-position. To extend this series of tricyclic DA agonists we used a classic bioisoster approach and synthesized thiopyran analogues of 7, which have a sulfur atom in the 6-position. We prepared trans-4-n-propyl-3,4,4a,10b-tetrahydro-2H,5H-[1]benzothiopyrano[4, 3-b]-1,4-oxazin-9-ol (9, trans-9-OH-PTBTO), its enantiomers ((+)-9 and (-)-9), the racemic cis-analogue (10), and the racemic trans-sulfoxide (11) and studied the potency and selectivity for DA receptors of these compounds. As with other rigid DA agonists, the highest affinity for DA receptors resided in one of the enantiomers, in this case the (-)-enantiomer of 9. On the basis of a single-crystal X-ray analysis of a key intermediate, the absolute configuration of (-)-9 was found to be 4aS,10bR, which is homochiral with (+)-(4aR,10bR)-7. In contrast to (+)-7 however, (-)-9 displayed no selectivity for any of the DA receptors. In addition, it has affinity for 5HT1A receptors. (+/-)-cis-4-n-Propyl-3,4,4a,10b-tetrahydro-2H,5H-[1]benzothiopyrano++ +[4,3-b]-1,4-oxazin-9-ol (10), which was expected to be inactive, displayed affinity and selectivity for the DA D3 receptor, whereas the sulfoxide 11 displayed some DA D3 selectivity, but with a lower affinity. Further pharmacological evaluation revealed that (-)-9 is a very potent full agonist at DA D2 receptors and a partial agonist at DA D3 receptors. The cis-analogue (+/-)-10 displayed the same profile, but with lower potency. These findings were confirmed in vivo: in reserpinized rats (-)-9 displayed short-acting activation of locomotor activity (DA D2 agonism) and also lower lip retraction and flat body posture, (5HT1A agonism). Compound (+/-)-10 had no effect on locomotor activity. In unilaterally 6-OH-DA lesioned rats, (-)-9 gave short-acting locomotor activation. Furthermore, in microdialysis studies in rat striatum, (-)-9 potently decreased DA release, confirming its activation of presynaptic DA D2 receptors.

Subtype-selective N-methyl-D-aspartate receptor antagonists: benzimidazalone and hydantoin as phenol replacements

Previous work in our laboratories investigating compounds with structural similarity to ifenprodil (5) and 6 (CP101,606) resulted in compound 7 as a potent and selective antagonist of the NR1/2B subtype of the NMDA receptors. Replacement of the phenol group of 7 with a benzimidazalone group tethered by a three-carbon chain to 4-benzylpiperidine resulted in a slightly less active, but selective, compound. Lengthening the carbon tether resulted in a decrease in NR1/2B potency. Replacement of the phenol ring with a hydantoin resulted in weak antagonists. Compound 11a was one of the most potent NR1/2B antagonists from this study. Compound 11a also potentiated the effects of L-DOPA in a rat model of Parkinson's disease (the 6-hydroxydopamine-lesioned rat), dosed at 30 mg/kg orally.

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.

Parallel synthesis of a series of subtype-selective NMDA receptor antagonists

A series of 1-(heteroarylthioalkyl)-4-benzylpiperidines was rapidly synthesized through the use of parallel synthesis to investigate the binding affinity for the NR1A/2B receptor subtype.

A series of 6- and 7-piperazinyl- and -piperidinylmethylbenzoxazinones with dopamine D4 antagonist activity: discovery of a potential atypical antipsychotic agent

As part of a program to develop dopamine D4 antagonists for the treatment of schizophrenia, we discovered a series of 6- and 7-(phenylpiperazinyl)- and -(phenylpiperidinyl)methylbenzoxazinones through mass screening of our compound library. A structure-activity relationship SAR study was carried out involving substituents on the phenyl ring, and several selective D4 antagonists were identified. The 7-substituted benzoxazinones showed more activity in neurochemical and behavioral tests than the 6-substituted series. One of the most potent and selective compounds (26) was found to have potent activity in animal tests predictive of antipsychotic activity in humans after oral administration. This paper describes the SAR of the benzoxazinone series and the preclinical characterization of 26.

Discovery of subtype-selective NMDA receptor ligands: 4-benzyl-1-piperidinylalkynylpyrroles, pyrazoles and imidazoles as NR1A/2B antagonists

4-Benzyl-1-[4-(1H-imidazol-4-yl)but-3-ynyl]piperidine (8) has been identified as a potent antagonist of the NR1A/2B subtype of the NMDA receptor. When dosed orally, this compound potentiates the effects of L-DOPA in the 6-hydroxydopamine-lesioned rat, a model of Parkinson's disease.

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.

4-Hydroxy-1-[2-(4-hydroxyphenoxy)ethyl]-4-(4-methylbenzyl)piperidine: a novel, potent, and selective NR1/2B NMDA receptor antagonist

A structure-based search and screen of our compound library identified N-(2-phenoxyethyl)-4-benzylpiperidine (8) as a novel N-methyl-D-aspartate (NMDA) receptor antagonist that has high selectivity for the NR1/2B subunit combination (IC(50) = 0.63 microM). We report on the optimization of this lead compound in terms of potency, side effect liability, and in vivo activity. Potency was assayed by electrical recordings in Xenopus oocytes expressing cloned rat NMDA receptors. Side effect liability was assessed by measuring affinity for alpha(1)-adrenergic receptors and inhibition of neuronal K(+) channels. Central bioavailability was gauged indirectly by determining anticonvulsant activity in a mouse maximal electroshock (MES) assay. Making progressive modifications to 8, a hydroxyl substituent on the phenyl ring para to the oxyethyl tether (10a) resulted in a approximately 25-fold increase in NR1A/2B potency (IC(50) = 0.025 microM). p-Methyl substitution on the benzyl ring (10b) produced a approximately 3-fold increase in MES activity (ED(50) = 0.7 mg/kg iv). Introduction of a second hydroxyl group into the C-4 position on the piperidine ring (10e) resulted in a substantial decrease in affinity for alpha(1) receptors and reduction in inhibition of K(+) channels with only a modest decrease in NR1A/2B and MES potencies. Among the compounds described, 10e (4-hydroxy-N-[2-(4-hydroxyphenoxy)ethyl]-4-(4-methylbenzyl)piperid ine, Co 101244/PD 174494) had the optimum pharmacological profile and was selected for further biological evaluation.

Subtype-selective N-methyl-D-aspartate receptor antagonists: synthesis and biological evaluation of 1-(arylalkynyl)-4-benzylpiperidines

A search of our compound library for compounds with structural similarity to ifenprodil (5) and haloperidol (7) followed by in vitro screening revealed that 4-benzyl-1-(4-phenyl-3-butynyl)piperidine (8) was a moderately potent and selective antagonist of the NR1A/2B subtype of NMDA receptors. Substitution on the benzyl group of 8 did not significantly affect NR1A/2B potency, while addition of hydrogen bond donors in the para position of the phenyl group enhanced NR1A/2B potency. Addition of a hydroxyl moiety to the 4-position of the piperidine group slightly reduced NR1A/2B potency while reducing alpha-1 adrenergic and dopamine D2 receptor binding affinities substantially, resulting in improved overall selectivity for NR1A/2B receptors. Finally, the butynyl linker was replaced with propynyl or pentynyl. When the phenyl was para substituted with amine or acetamide groups, the NR1A/2B potency order was butynyl > pentynyl >> propynyl. For the para methanesulfonamide or hydroxyl groups, the order was butynyl approximately propynyl > pentynyl. The hydroxyl propyne (48) and butyne (23) were among the most potent NR1A/2B antagonists from this study. They both potentiated the effects of L-DOPA in the 6-hydroxydopamine-lesioned rat, a model of Parkinson's disease, dosed at 10 mg/kg ip, but 48 was not active at 30 mg/kg po.

Pyrazolo[1,5-a]pyrimidine CRF-1 receptor antagonists

A series of 3-phenylpyrazolo[1,5-a]pyrimidines was prepared and found to have affinity for the human CRF-1 receptor. The 3-dimensional structure of one of the most potent analogs in this series, 10d, was determined by X-ray crystallography and suggests the spatial requirements for potent CRF-1 receptor binding affinity in this series.

Placental P-glycoprotein deficiency enhances susceptibility to chemically induced birth defects in mice

A subpopulation of the CF-1 mouse strain contains a spontaneous mutation in the P-glycoprotein (Pgp) mdr1a gene, which leads to a lack of mdr1a expression in the placenta as well as brain and intestine. Individual CF-1 mice can be identified according to their Pgp status by a restriction fragment length polymorphism. Male and female mice selected on the basis of Pgp genotype were mated and the pregnant dams exposed during gestation to the known Pgp substrate, L-652,280, the 8,9 Z photoisomer of the naturally occurring avermectin Bla, which is known to produce cleft palate in mice. Fetal examination demonstrated that within individual litters, fetuses deficient in Pgp (-/-) were 100% susceptible to cleft palate, whereas their +/- heterozygote littermates were less sensitive. The homozygous +/+ fetuses with abundant Pgp were totally insensitive at the doses tested. The degree of chemical exposure of fetuses within each litter was inversely related to expression of placental Pgp, which was determined by the fetal genotype. These results demonstrate the importance of placental Pgp in protecting the fetus from potential teratogens and suggest that Pgp inhibitors should be carefully evaluated for their potential to increase susceptibility to chemical-induced teratogenesis.

Isoindolinone enantiomers having affinity for the dopamine D4 receptor

PD 108635 (1) was identified as a potent dopamine D4 ligand and we wanted to replace the benzylic alcohol with a metabolically more stable moiety. Investigations led to the discovery of a series of isoindolinones having D4 affinity.

Comparison of motility and membrane integrity to assess rat sperm viability

Rat sperm motility and membrane integrity were compared as endpoints for viability. Sperm motility was measured by computer-assisted semen analysis (CASA), whereas membrane integrity was assessed by flow cytometric analysis of sperm stained with two nucleic acid stains, SYBR-14 and propidium iodide. The two techniques were compared in experiments that examined sperm viability over time and by analysis of known mixtures of control and freeze/thaw-killed sperm. Results from the two approaches were quantitatively very similar. Sperm from rats treated with dibromoacetic acid (600 or 1200 mg/kg) or alpha-chlorhyrin (100 mg/kg) were also analyzed. Neither technique detected a treatment-related effect with dibromoacetic acid. CASA identified a significant decrease in sperm motility in alpha-chlorhyrin-treated rats, whereas flow cytometric analysis did not find a measureable change in sperm membrane integrity. Because decreases in sperm motility would be expected to directly affect fertility, CASA may be a more robust endpoint for risk assessment in reproductive toxicology studies than flow cytometric analysis of membrane integrity.

Pharmacological characterization of PD 152255, a novel dimeric benzimidazole dopamine D3 antagonist

152255 (E-1,1'-(2-butene-1,4-diyl)bis[2-[4-[3-(1-piperidinyl)propoxy]-phe nyl]-1H-benzimidazole]) exhibited high affinity (Ki = 12.7 nM) for human dopamine (DA) D3 receptors expressed in CHO K1 cells but not for DA D2L receptors (Ki = 565 nM), DA D42 or DA D1 receptors (Ki > 3 microM) and a number of other neurotransmitter receptors. Affinity for human muscarinic receptors was seen in vitro but no functional muscarinic agonist and/or antagonist action was observed in vivo. Antagonist activity at DA D3 receptors was demonstrated by blockade of quinpirole-stimulated [3H]-thymidine uptake in D3 transfected cells, an effect that was 28-fold more potent than in D2-transfected cells. Unlike classical DA D2 antagonists, PD 152255 did not increase rat brain DA synthesis and it increased locomotion in habituated rats. However, like antipsychotics, PD 152255 reduced locomotor activity in mice and reduced spontaneous and amphetamine-stimulated locomotion in nonhabituated rats. These results demonstrate that PD 152255 is a DA D3 antagonist that may have antipsychotic activity.

(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).

Identification of a P-glycoprotein-deficient subpopulation in the CF-1 mouse strain using a restriction fragment length polymorphism

There is a subpopulation of the CF-1 mouse strain that is very sensitive to the neurotoxicity induced by the avermectins, a class of natural products widely used in veterinary and human medicine as anti-parasitic agents. This sensitivity results from a lack of P-glycoprotein in the intestine and brain of sensitive animals, allowing increased penetration of these compounds in the blood and brain, respectively. We describe a restriction fragment length polymorphism that is able to predict which animals will be deficient in this protein, confirming at the genetic level a heterogeneous population of this mouse strain. Breeding studies demonstrated that the inheritance of the markers follows a normal Mendelian autosomal pattern. Sensitive "-/-" animals are deficient in P-glycoprotein in those tissues known to express primarily mdr1a, but have normal P-glycoprotein levels in tissues known to express primarily mdr1b or mdr2, suggesting that the defect in the sensitive animals is limited to the mdr1a gene. The P-glycoprotein expression in the brain is dependent on the genotype, which also determines the susceptibility to the avermectin-induced neurotoxicity, with the "-/-" animals being most sensitive, and the "+/-" animals having less P-glycoprotein and therefore increased CNS sensitivity compared to the "+/+" animals. The ability to segregate this strain into -/- and +/+ animals may prove useful for examining the physiological role of P-glycoprotein in drug absorption and distribution and related toxicity. These data also provide a warning that experiments carried out with P-glycoprotein substrates in the heterogeneous population of the CF-1 mouse must be interpreted with caution.

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.

Developmental neurotoxicity evaluation of the avermectin pesticide, emamectin benzoate, in Sprague-Dawley rats

The potential of emamectin benzoate (EB) to cause developmental neurotoxicity in Sprague-Dawley rats was assessed using a study design by the US EPA. Dosages of 0 (deionized water), 0.1, 0.6, or 3.6 mg/kg/day were administered at 5 ml/kg by oral gavage from gestational day (GD) 6 to lactational day (LD) 20 to groups of 25 mated females each. Between GD 17 and 20 the high dose was reduced to 2.5 mg/kg/day because of pup tremors observed at this dose level in a concurrent two-generation study. Females were allowed to deliver and the young were evaluated for survival, growth, development, behavior, and histological changes to brain, spinal cord, peripheral nerve, and skeletal muscle. Behavioral assessment of the offspring consisted of open field motor activity, auditory startle habituation, and passive avoidance tests; each was conducted on weanling and adult animals (one animal/sex/litter). Histopathological examination of the CNS and PNS was conducted on one animal/sex/litter on postnatal days (PND) 11 and 60. There were significant increases in average F0 maternal body weight gains during gestation in the 0.6 and 3.6/2.5 mg/kg/day groups, but no other effects were observed in pregnant females of these or the low-dose groups during the study. Beginning on PND 6, tremors were observed in high-dose pups, and this was followed by hindlimb splay in all high-dose pups by PND 15-26. Both of these physical signs disappeared by PND 34 (i.e., 10-11 days after weaning). There were no compound-related deaths in F1 offspring. Beginning on PND 11, progressive decreases in preweaning average weights were observed in the high-dose group (to 42% below control in females on PND 21). Average weight gain during the postweaning period was significantly decreased in the 3.6/2.5 mg/kg/day group. There were EB-related effects in behavioral tests only in the high-dose group. A significant increase in PND 13 average horizontal motor activity was due to stereotypical movements. Average horizontal activity was decreased on PND 17 and in adult females, but there was no effects on PND 21. Average peak auditory startle response amplitude was decreased on PND 22 and in adults. There were no EB-related effects in the passive avoidance test, relative brain weights, or in the histological examination (including morphometry) of the nervous system. These results demonstrate that the high-dose EB exposure during gestation and lactation to rats produced evidence of neurotoxicity in the F1 offspring, and a clear No Observed Adverse Effect Level (NOAEL) for developmental neurotoxicity of EB was determined to be 0.6 mg/kg/day.

Characterization of the effect of dopamine D3 receptor stimulation on locomotion and striatal dopamine levels

By examining the effect of dopamine (DA) D3 receptor stimulation on locomotor activity and extracellular levels of DA in striatum we show that inhibition of locomotor activity induced by DA D3 receptor-selective agonists is mediated by two interacting mechanisms: (1) directly via the stimulation of DA D3 receptors that inhibit locomotor activity, and (2) indirectly via a decrease in extracellular levels of DA. Thus, the moderately DA D3 receptor-selective agonist R-(+)-7-OH- DPAT (R-(+)-7-hydroxy-2-(N,N-di-n-propylamino)tetralin) decreased locomotor activity after administration of 10 nmol/kg and extracellular DA levels in accumbens and striatum after administration of 30 nmol/kg. A decrease in locomotor activity that coincided with a decrease in extracellular DA levels in striatum was observed after administration of 100 nmol/kg of the DA D3 receptor-selective agonist PD128907 ((+)-trans-3,4,4a,10b-tetrahydro-4-propyl-2H,5H-[1]benzopyrano[4,3 b]-1,4-oxasin-9-ol. In combination with the partial, DA D3 receptor-selective agonist PD151328 (2-[4[3-(4-phenyl)-1- piperazinyl)propoxy]phenyl]-benzamidazole), a reversal of the attenuating effect of PD128907 on locomotor activity was observed, without an effect on extracellular levels of DA. In combination with a low--10 nmol/kg--dose of haloperidol, a reversal of the inhibitory effect of PD128907 on locomotor activity was observed that coincided with an increase in extracellular levels of DA. In the presence of 0.5 mg/kg amphetamine, PD128907 decreased amphetamine-induced locomotor activity. This effect could be reversed by PD151328.

Terminology of developmental abnormalities in common laboratory mammals (version 1)

This paper presents the first version of an internationally-developed glossary of terms for structural developmental abnormalities in common laboratory animals. The glossary is put forward by the International Federation of Teratology Societies (IFTS) Committee on International Harmonization of Nomenclature in Developmental Toxicology, and represents considerable progress toward harmonization of terminology in this area. The purpose of this effort is to provide a common vocabulary that will reduce confusion and ambiguity in the description of developmental effects, particularly in submissions to regulatory agencies worldwide. The glossary contains a primary term or phrase, a definition of the abnormality, and notes, where appropriate. Selected synonyms or related terms, which reflect a similar or closely related concept, are noted. Nonpreferred terms are indicated where their usage may be incorrect. Modifying terms used repeatedly in the glossary (e.g., absent, branched) are listed and defined separately, instead of repeating their definitions for each observation. Syndrome names are generally excluded from the glossary, but are listed separately in an appendix. The glossary is organized into broad sections for external, visceral, and skeletal observations, then subdivided into regions, structures, or organs in a general overall head to tail sequence. Numbering is sequential, and not in any regional or hierarchical order. Uses and misuses of the glossary are discussed. Comments, questions, suggestions, and additions from practitioners in the field of developmental toxicology are welcomed on the organization of the glossary as well as on the specific terms and definitions. Updates of the glossary are planned based on the comments received.

3-[[(4-Aryl-1-piperazinyl)alkyl]cyclohexyl]-1H-indoles as dopamine D2 partial agonists and autoreceptor agonists

A series of arylpiperazines and tetrahydropyridines joined to indoles by semirigid cycloalkyl spacers were prepared. Target compounds were studied for their ability to bind to the DA D2 receptor in vitro and to inhibit dopamine synthesis and spontaneous locomotor activity in rats. Effects of tether length and relative stereochemistry were assessed for a series of 2-pyridylpiperazines. The cyclohexylethyl spacer was found to be the most active in the series. Further studies explored effects of changes in the arylpiperazine and indole portions of the molecule. From these studies trans-2-[[4-(1H-3-indolyl)cyclohexyl]ethyl]-4- (2-pyridinyl)piperazine (30a) was selected for further evaluation. It was characterized as a partial agonist of DA D2 receptors in vitro and caused decreases in dopamine synthesis and release as well as dopamine neuronal firing. Compound 30a was shown to be devoid of behavioral effects associated with postsynaptic DA D2 receptor activation. Furthermore, compound 30a was shown both to decrease DA synthesis and to inhibit Sidman avoidance responding in squirrel monkeys. These findings suggest that DA D2 partial agonists with the appropriate level of intrinsic activity can act to decrease dopamine synthesis and release and may have potential utility as antipsychotic agents.

Autoradiographic localisation of D3-dopamine receptors in the human brain using the selective D3-dopamine receptor agonist (+)-[3H]PD 128907

The selective D3-dopamine receptor agonist 4aR, 10bR-(+)-trans-3,4,4a, 10b-tetrahydro-4-[N-propyl-2,3-3H]-2H,5H-[1] benzopyrano[4,3-b]-1,4-oxazin-9-ol ([3H]PD 128907) was used to visualise D3-dopamine receptors in whole hemisphere cryosections from post-mortem human brain. [3H]PD 128907 has an 18- to 40-fold selectivity for D3- over D2-dopamine receptors as compared to a 7- to 24-fold selectivity of the more commonly used ligand [3H]7-OH-DPAT. [3H]PD 128907 accumulated markedly in the nucleus accumbens and in the ventral parts of caudate nucleus and putamen, with a slightly heterogeneous (patch-matrix like) distribution. The binding in the lateral parts of caudate nucleus and putamen was much less dense. No binding was obtained in any other regions. A very high proportion of [3H]PD 128907 was specifically bound, as judged from the low binding remaining in the presence of the D2/D3-dopamine receptor antagonist raclopride. This gives the ligand a potential for the detection of low density D3-dopamine receptors in the human brain. The binding obtained with [3H]PD 128907 was qualitatively similar to that using [3H]7-OH-DPAT in the presence of GTP. However, [3H]7-OH-DPAT labelled, in contrast to [3H]PD 128907, also D3-dopamine receptors in neocortex. The new compound [3H]PD 128907 appears to be a suitable radioligand for autoradiographic examination of the D3-dopamine receptor localisation in the human brain, and should also be useful for pharmacological studies of this receptor subtype.

Affinity for dopamine D2, D3, and D4 receptors of 2-aminotetralins. Relevance of D2 agonist binding for determination of receptor subtype selectivity

A series of 2-aminotetralins, substituted with a methoxy or a hydroxy group on the 5- or 7-position, and with varying N-alkyl or N-arylalkyl substituents, were prepared and evaluated in binding assays for human dopamine (DA) D2, D3, and D4 receptors. Some members of this series were prepared in former studies, but were never tested in vitro with single receptor subtypes, and these were examined again. None of the tested 2-aminotetralins showed high affinity for the dopamine D4 receptor. However, a number of the 2-aminotetralins showed high affinity for both the D2 and the D3 DA receptors, as exemplified by compounds 11-15 and 21-26, while some had a reasonable selectivity for the DA D3 receptors. The affinities of the 2-aminotetralins for the D21, receptor depended on the type of radioligand (agonist or antagonist) used. The agonist affinity data, obtained by using the agonist ligand [3H]N-0437, are thought to be more relevant for calculating DA receptor subtype selectivity.

Aryl 1-but-3-ynyl-4-phenyl-1,2,3,6-tetrahydropyridines as potential antipsychotic agents: synthesis and structure-activity relationships

A novel series of aryl 1-but-3-ynyl-4-phenyl-1,2,3,6-tetrahydropyridines with dopaminergic activity is described. The structure-activity relationships of this series were studied by synthesis of analogs and evaluation of their affinities for the dopamine (DA) D2 receptor and inhibition of locomotor activity (LMA) in rodents. The basic amine, alkyne chain length, and aryl groups were varied. Compounds having a 4-phenyl-1,2,3,6-tetrahydropyridine and an aryl group with hydrogen-bonding substituents separated by a butynyl chain were found to have the most potent dopaminergic activity. Several compounds that were found to have exceptional in vivo activity in LMA inhibition in rodents were evaluated for additional pharmacological activity including binding affinities for other DA receptor subtypes as well as effects on brain DA synthesis, DA neuronal firing, and conditioned avoidance responding in squirrel monkeys.

Methods for assessing sperm motility, morphology, and counts in the rat, rabbit, and dog: a consensus report. ILSI Risk Science Institute Expert Working Group on Sperm Evaluation

Reproductive toxicity studies are increasingly including assessments of sperm parameters including motility, morphology, and counts. While these assessments can provide valuable information for the determination of potential reproductive toxicity, the methods for conducting the assessments have not been well developed in all laboratories and are continually evolving. The use of different methods in different laboratories makes comparison of data among laboratories difficult. To address the differences in methods, a working group was convened to discuss methods currently in use, share data, and try to reach consensus about optimal methods for assessing sperm parameters in rats, rabbits, and dogs. This article presents the consensus report, as well as future research needs, with the hope that optimized common methods will aid in the detection of reproductive effects and enhance interlaboratory comparisons.

Identification, characterization and pharmacological profile of three metabolites of (R)-(+)-1,2,3,6-tetrahydro-4-phenyl-1-[(3-phenylcyclohexen-1- yl)methyl]pyridine (CI-1007), a dopamine autoreceptor agonist and potential antipsychotic agent

Liquid chromatographic-mass spectrometric (LC-MS) analysis of plasma taken from cynomolgus monkeys dosed orally with (R)-(+)-1,2,3,6-tetrahydro-4-phenyl-1-[(3-phenylcyclohexen-1- yl)methyl]pyridine (1), a dopamine (DA) autoreceptor agonist and potential antipsychotic agent, revealed several metabolites. The molecular masses of three major metabolites suggested that they were mono- and dihydroxylated derivatives of 1. We synthesized compounds 2 and 3, the two possible mono-p-hydroxyphenyl derivatives of 1, along with the bis-p-hydroxyphenyl derivative 4. These compounds coeluted by HPLC with the three hydroxylated metabolites of 1. Compounds 2-4 all had high affinities for DA D2 and D3 receptors and moderate affinities for D4 receptors. Like 1, compound 2 decreased DA synthesis and neuronal firing in rat brain, indicative of DA autoreceptor activation. Compound 2 inhibited exploratory locomotor activity in rodents and was active in the Sidman avoidance test in squirrel monkeys, predictive of antipsychotic activity in humans. Compounds 3 and 4 showed weak activity in all these tests. After squirrel monkeys were dosed with 1 orally at the ED100 dose of the Sidman avoidance test, the plasma concentration of 2 was below the limit of quantitation. Therefore, these metabolites are unlikely to contribute greatly to the potent activity seen with 1 in the Sidman avoidance test.

Characterization of binding of [3H]PD 128907, a selective dopamine D3 receptor agonist ligand, to CHO-K1 cells

PD 128907 [4a R, 10 b R-(+)-trans-3, 4, 4a, 10 b - tetrahydro - 4- n -propyl2 H,5H-[1]benzop-yrano[4,3-b]1,4-oxazin-9-ol.], a selective dopamine (DA) D3 receptor agonist ligand exhibits about a 1000-fold selectivity for human D3 receptors (Ki, 1 nM) versus human D2 receptors (Ki, 1183 nM) and a 10000-fold selectivity versus human D4 receptors (Ki, 7000 nM) using [3H]spiperone as the radioligand in CHO-K1-cells. Studies with [3H]PD 128907, showed saturable, high affinity binding to human D3 receptors expressed in CHO-K1 cells (CHO-K1-D3) with an equilibrium dissociation constant (Kd) of 0.99 nM and a binding density (Bmax) of 475 fmol/mg protein. Under the same conditions, there was no significant specific binding in CHO-K1-cells expressing human D2 receptors (CHO-K1-D2). The rank order of potency for inhibition of [3H]PD 128907 binding with reference DA agents was consistent with reported values for D3 receptors. These results indicate that [3H]PD 128907 is a new, highly selective D3 receptor ligand with high specific activity, high specific binding and low non-specific binding and therefore should be useful for further characterizing the DA D3 receptors.

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.

CI-1007, a dopamine partial agonist and potential antipsychotic agent. II. Neurophysiological and behavioral effects

CI-1007 has been described in receptor binding and biochemical tests as a dopamine (DA) partial agonist that exhibits DA autoreceptor agonist effects. The present studies describe the profile of CI-1007 in electrophysiological and behavioral tests. CI-1007 inhibited the firing of substantia nigra DA neurons with intrinsic DA agonist activity that was less than that of the full agonists apomorphine and talipexole but greater than that of the weak partial agonist SDZ 208-912. CI-1007 was more potent after intracerebroventricular versus intraperitoneal injection in inhibiting spontaneous locomotor activity in mice, indicating a central site of action. In rats, CI-1007 inhibited locomotor activity after i.v. and p.o. injection, but did not produce locomotor stimulation or induce stereotypy, indicating a lack of postsynaptic DA agonist activity. The relative potencies of CI-1007 for inhibiting apomorphine-stimulated behaviors versus spontaneous locomotor activity in rodents indicated weak postsynaptic DA antagonist actions, consistent with a partial agonist profile. Similar to known antipsychotics, CI-1007 potently inhibited Sidman avoidance responding in squirrel monkeys, but, in contrast to most available antipsychotics, CI-1007 caused only mild extrapyramidal dysfunction in squirrel and cebus monkeys sensitized to the dystonic effects of haloperidol. These data indicate that CI-1007 is a DA partial agonist of moderate intrinsic activity that activates brain DA autoreceptors, produces behavioral effects predictive of antipsychotic efficacy and has a low liability for induction of extrapyramidal side effects.

Development and submission of a nonclinical (pharmacology/toxicology) CANDA

The experience with the submission of a nonclinical (pharmacology and toxicology) computer-assisted New Drug Application (CANDA) is reviewed. This system consisted of a stand-alone personal computer running several commercial programs in Microsoft Windows to access both text and data. WordPerfect was used as the word processor that contained all the documents and data tables (in read-only format) that were submitted in hard copy, and Andyne GQL was used as a tool to query the data in an Oracle relational database. Microsoft Excel was provided as a spreadsheet for graphics and analysis of data. Documents appeared virtually identical to those in the hard copy NDA submission. Searching the text was facilitated by the use of buttons on the screen, which allowed the NDA to be searched for a particular term. Data could be located either in WordPerfect documents, or in an Oracle database (using Andyne GQL) by querying the data. The data queries could be performed ad hoc, in which the reviewer selected all the parameters for a search, or with predefined query buttons, which retrieved data for principal treatment-related changes. This type of system also could serve as a useful model for both in-house nonclinical review and the submission of INDs and IND amendments.