AZD0284, a Potent, Selective, and Orally Bioavailable Inverse Agonist of Retinoic Acid Receptor-Related Orphan Receptor C2

Inverse agonists of the nuclear receptor RORC2 have been widely pursued as a potential treatment for a variety of autoimmune diseases. We have discovered a novel series of isoindoline-based inverse agonists of the nuclear receptor RORC2, derived from our recently disclosed RORC2 inverse agonist 2. Extensive structure-activity relationship (SAR) studies resulted in AZD0284 (20), which combined potent inhibition of IL-17A secretion from primary human TH17 cells with excellent metabolic stability and good PK in preclinical species. In two preclinical in vivo studies, compound 20 reduced thymocyte numbers in mice and showed dose-dependent reduction of IL-17A containing γδ-T cells and of IL-17A and IL-22 RNA in the imiquimod induced inflammation model. Based on these data and a favorable safety profile, 20 was progressed to phase 1 clinical studies.

Discovery of the Oral Leukotriene C4 Synthase Inhibitor (1S,2S)-2-({5-[(5-Chloro-2,4-difluorophenyl)(2-fluoro-2-methylpropyl)amino]-3-methoxypyrazin-2-yl}carbonyl)cyclopropanecarboxylic Acid (AZD9898) as a New Treatment for Asthma

While bronchodilators and inhaled corticosteroids are the mainstay of asthma treatment, up to 50% of asthmatics remain uncontrolled. Many studies show that the cysteinyl leukotriene cascade remains highly activated in some asthmatics, even those on high-dose inhaled or oral corticosteroids. Hence, inhibition of the leukotriene C4 synthase (LTC4S) enzyme could provide a new and differentiated core treatment for patients with a highly activated cysteinyl leukotriene cascade. Starting from a screening hit (3), a program to discover oral inhibitors of LTC4S led to (1S,2S)-2-({5-[(5-chloro-2,4-difluorophenyl)(2-fluoro-2-methylpropyl)amino]-3-methoxypyrazin-2-yl}carbonyl)cyclopropanecarboxylic acid (AZD9898) (36), a picomolar LTC4S inhibitor (IC₅₀ = 0.28 nM) with high lipophilic ligand efficiency (LLE = 8.5), which displays nanomolar potency in cells (peripheral blood mononuclear cell, IC_50,free = 6.2 nM) and good in vivo pharmacodynamics in a calcium ionophore-stimulated rat model after oral dosing (in vivo, IC_50,free = 34 nM). Compound 36 mitigates the GABA binding, hepatic toxicity signal, and in vivo toxicology findings of an early lead compound 7 with a human dose predicted to be 30 mg once daily.

Phenylketonuria screening registry as a resource for population genetic studies

BACKGROUND

Neonatal screening for metabolic diseases, involving samples stored on filter paper (Guthrie spots), provides a potential resource for genetic epidemiological studies.

OBJECTIVE

To develop a method to make these dried blood spots available for large scale genetic epidemiology.

METHODS

DNA from untraceable Guthrie spots was extracted using a saponin and chelex-100 based method and preamplified by improved primer preamplification. Analyses were done on 38 samples each of fresh, 10, and 25 year old Guthrie spots and the success rate determined for PCR amplification for five amplicon lengths.

RESULTS

The method was applicable even on 25 year old samples. The success rate was 100% for 100 bp amplicons and 80% for 396 bp amplicons. Ninety four Guthrie samples were genotyped, including carriers of two different PKU mutations; all carriers were found (six R158Q, four R252W), with no false positives. Finally, 2132 anonymous samples from the Swedish PKU registry were extracted and preamplified and the allele frequencies of APOepsilon4, PPARgamma Pro12Ala, and the CCR5 32 bp deletion determined. Local variations in allele frequencies suggested subpopulation structuring. There was a significant difference (p<0.01) in regional allele frequencies for the CCR5 32 bp deletion in the Swedish population.

CONCLUSION

Whole genome amplification makes it feasible to conduct large genetic epidemiological studies using PKU screening registries.

Non-psychotic psychiatric disorder and subsequent risk of schizophrenia. Cohort study

BACKGROUND

Those with schizophrenia often give a history of premorbid non-psychotic psychiatric disorder.

AIMS

To investigate the association between non-psychotic psychiatric disorders and the later development of schizophrenia.

METHOD

Men aged 18 or 19 years, conscripted to the Swedish army in 1970 (n=50 054) were linked to the Swedish National Psychiatric Case Register.

RESULTS

There was an increased risk of schizophrenia in those with ICD-8 diagnoses of neurosis (OR=4.6,95% Cl 3.2-6.9), personality disorder (OR=8.2, 95% Cl 5.4-12.3), alcohol abuse (OR=5.5, 95% Cl 1.7-17.5) or substance abuse (OR=14.0, 95% Cl 7.8-25.0) at age 18. Of those who developed schizophrenia, 38% (95% Cl 32-45) received a diagnosis of non-psychotic psychiatric disorder at age 18. Only those with personality disorder had a significantly increased risk of schizophrenia (OR=2.4, 95% Cl 1.1-5.2) with onset after age 23.

CONCLUSIONS

Personality factors could represent an underlying vulnerability to schizophrenia. Other diagnoses occurring before schizophrenia may reflect a prodromal phase of the illness.

Site-directed mutations in the third intracellular loop of the serotonin 5-HT(1A) receptor alter G protein coupling from G(i) to G(s) in a ligand-dependent manner

The effect of mutations (V344E and T343A/V344E) in the third intracellular loop of the serotonin 5-HT(1A) receptor expressed transiently in human embryonic kidney 293 cells have been examined in terms of receptor/G protein interaction and signaling. Serotonin, (R)-8-hydroxy-2-dipropylaminotetralin [(R)-8-OH-DPAT], and buspirone inhibited cyclic AMP production in cells expressing native and mutant 5-HT(1A) receptors. Serotonin, however, produced inverse bell-shaped cyclic AMP concentration-response curves at native and mutant 5-HT(1A) receptors, indicating coupling not only to G(i)/G(o), but also to G(s). (R)-8-OH-DPAT, however, induced stimulation of cyclic AMP production only after inactivation of G(i)/G(o) proteins by pertussis toxin and only at the mutant receptors. The partial agonist buspirone was unable to induce coupling to G(s) at any of the receptors, even after pertussis toxin treatment. The basal activities of native and mutant 5-HT(1A) receptors in suppressing cyclic AMP levels were not found to be significantly different. The receptor binding characteristics of the native and mutant receptors were investigated using the novel 5-HT(1A) receptor antagonist [(3)H]NAD-299. For other receptors, analogous mutations have produced constitutive activation. This does not occur for the 5-HT(1A) receptor, and for this receptor the mutations seem to alter receptor/G protein coupling, allowing ligand-dependent coupling of receptor to G(s) in addition to G(i)/G(o) proteins.

Doctors who kill themselves: a study of the methods used for suicide

Medical practitioners have a relatively high rate of suicide. Death entry data for doctors who died by suicide or undetermined cause between 1979 and 1995 in England and Wales were used to compare methods used for suicide by doctors with those used by the general population. Methods used were analysed according to gender, occupational status and speciality, to assess the extent to which access to dangerous means influences the pattern of suicide. Self-poisoning with drugs was more common in the doctors than in general population suicides (57% vs. 26.6%; OR=3.65, 95% CI 2.85-4. 68), including in retired doctors. Barbiturates were the most frequent drugs used. Half of the anaesthetists who died used anaesthetic agents. Self-cutting was also more frequently used as a method of suicide. The finding that the greater proportion of suicide deaths in doctors were by self-poisoning may reflect the fact that doctors have ready access to drugs, and have knowledge of which drugs and doses are likely to cause death. The specific finding that a large proportion of suicides in anaesthetists involved anaesthetic agents supports this explanation. Availability of method may be a factor contributing to the relatively high suicide rate of doctors. This fact might influence clinical management of doctors who are known to be depressed or suicidal.

Derivatives of (R)-2-amino-5-methoxytetralin: antagonists and inverse agonists at the dopamine D2A receptor

A series of N-arylmethyl substituted (R)-5-methoxy-2-(propylamino)tetralins has been prepared and evaluated for affinity and efficacy at dopamine (DA) D2A receptors. The novel compounds appeared to be antagonists or inverse agonists. (R)-2-[(Benzyl)propylamino]-5-methoxytetralin (7) was characterized as a potent inverse agonists at DA D2A receptors in a [35S]GTPgammaS binding assay.

The geographical distribution of suicides in farmers in England and Wales

Farmers in England and Wales have an elevated risk of suicide. The aim of this study was to investigate the geographical distribution of suicides in farmers. Rates of suicide (including suicide and open verdicts) of farmers in England and Wales between 1981 and 1993 were calculated on a county basis. Trends in rates and differences in rates between counties, regions and England and Wales were then analysed. There were 719 suicides (634 suicide verdicts and 85 open verdicts). There was evidence of a decline in annual rates of suicide in farmers during the study period in England but not Wales. There was no evidence of geographical heterogeneity of farming suicides according to counties, but a relatively high rate for Devon (N = 62 suicides). County farming suicide rates did not appear to be related to local general population suicide rates, density of farmers or type of farm holding. While identification of counties with relatively large numbers of farming suicides should assist targeting of local preventive programmes, it is clear that any significant prevention strategies should be implemented on a national basis.

An introductory hospice experience for third-year medical students

BACKGROUND

An organized and distinct curriculum in hospice and palliative care education is lacking in most United States medical school programs. Because of this knowledge deficit, physicians are often not able to meet the needs of their terminally ill patients and their families.

METHODS

A five-day combined didactic and clinical rotation in hospice and palliative care for third-year medical students was developed and is presented. The program is run through a home-based hospice in conjunction with the state's medical school.

RESULTS

The pilot program has been well accepted by the participating students as a valuable learning experience. Although brief, it has also been successful in changing some of their attitudes about death and the care of the dying.

CONCLUSIONS

This one-week program is an effective means to provide an intense course in hospice education. It should be easily transportable to other health care curricula.

Stress in farmers: a survey of farmers in England and Wales

OBJECTIVES

To investigate potential sources of stress for farmers in England and Wales

METHOD

A postal questionnaire was sent to a randomly selected group of 800 members of the National Farmers' Union and 200 members of the Farmers' Union of Wales.

RESULTS

500 questionnaires (51%) were returned completed between October 1995 and March 1996. Farmers had problems with record keeping and paperwork (62%), difficulty understanding forms (56%), and problems arising from the effects of new legislation and regulations (49%). Nearly a quarter (23%) reported financial problems and most worried about money (79%). Very few were socially isolated, with over 90% having at least one confidant. 70% worked > 10 hours a day, and 31% had health problems which interfered with their work, including more than a quarter of those < 50. 16% of the sheep farmers reported symptoms which they attributed to organophosphate poisoning. The farmers most vulnerable to financial and other problems were those with small farms and mixed farming operations. Farmers in Wales also seemed more vulnerable than those in England, but a lower response rate from members of the Farmers' Union of Wales means this difference should be interpreted cautiously.

CONCLUSION

The survey confirms findings from several regional studies that many farmers are experiencing considerable stress from various causes. Local and national initiatives to assist farmers, including outreach programmes, should be encouraged. Policy makers should be aware of the potential impact of legislation, particularly on the more vulnerable groups.

Methods used for suicide by farmers in England and Wales. The contribution of availability and its relevance to prevention

BACKGROUND

Farmers in the UK have an elevated risk of suicide. It has been suggested that this may be related to their ease of access to dangerous means for suicidal behaviour. The extent to which farmers use these means and changes in their use may be relevant to suicide prevention.

METHOD

Data on 719 deaths in farmers of both genders in England and Wales between 1981 and 1993 in which a verdict of suicide or undetermined cause (open verdict) was recorded were analysed.

RESULTS

Of 702 deaths in male farmers, firearms were involved in 40.0%, hanging in 29.6%, carbon monoxide in 16.4%, poisoning in 8.0% (over half of which involved agricultural or horticultural poisons) and other methods in 6.1%. There was a considerable excess of deaths due to firearms compared with the distribution of methods of suicide and open verdict deaths in males in the general population. Hanging was also somewhat more frequent. During the study period there was a reduction in firearm death rates, particularly after 1989 when there was national legislation on firearm ownership, registration and storage. There were also fewer farming suicides after this date. By the end of the study period hanging was more frequent than deaths involving firearms.

CONCLUSIONS

Farmers who commit suicide tend to use methods to which they have easy access. Restriction of the ready availability of such methods, particularly in farmers known to be depressed or otherwise at risk, might prevent some suicides.

The psychological autopsy approach to studying suicide: a review of methodological issues

The psychological autopsy approach to studying suicide is becoming an increasingly used research method. It presents considerable methodological problems. In order to assist future researchers in this field and to help readers assess reports of psychological autopsy studies the authors have reviewed these issues on the basis of their own experience and those of other workers. The areas covered include research design, identification of subjects, sources of information and the particular issues concerned with approaching relatives and other informants, choice and recruitment of controls, the difficulties of conducting psychological autopsy interviews with relatives, problems for interviewers, the selection of appropriate measures to obtain information, and achieving valid and reasonably reliable conclusions from diverse information sources.

Interactions of ligands with active and inactive conformations of the dopamine D2 receptor

The affinities of 19 pharmacologically diverse dopamine D2 receptor ligands were determined for the active and inactive conformations of cloned human dopamine D2 receptors expressed in Ltk cells. The agonist [3H]quinpirole was used to selectively label the guanine nucleotide-binding protein-coupled, active receptor conformation. The antagonist [3H]raclopride, in the presence of the non-hydrolysable GTP-analogue Gpp(NH)p and sodium ions and in the absence of magnesium ions, was used to label the free inactive receptor conformation. The intrinsic activities of the ligands were determined in a forskolin-stimulated cyclic AMP assay using the same cells. An excellent correlation was shown between the affinity ratios (KR/KRG) of the ligands for the two receptor conformations and their intrinsic activity (r=0.96). The ligands included eight structurally related and enantiopure 2-aminotetralin derivatives; the enantiomers of 5-hydroxy-2-(dipropylamino)tetralin, 5-methoxy-2-(dipropylamino)tetralin, 5-fluoro-2-(dipropylamino)tetralin and 2-(dipropylamino)tetralin. The (S)-enantiomers behaved as full agonists in the cyclic AMP assay and displayed a large KR/KRG ratio. The (R)-enantiomers were classified as partial agonists and had lower ratios. The structure-affinity relationships of these compounds at the active and the inactive receptor conformations were analysed separately, and used in conjunction with a homology based receptor model of the dopamine D2 receptor. This led to proposed binding modes for agonists, antagonists and partial agonists in the 2-aminotetralin series. The concepts used in this study should be of value in the design of ligands with predetermined affinity and intrinsic activity.

Premorbid adjustment and personality in people with schizophrenia

BACKGROUND

Schizoid personality and poor social adjustment have been thought of as common antecedents of schizophrenia but the existing literature is inconclusive. We have carried out a large cohort study with improved methodology.

METHOD

The premorbid personality and adjustment of 50,054 Swedish men were assessed on entry into the army at the age of 18. Individuals who developed schizophrenia or another psychosis after 15-year follow-up were identified. Odds ratios for variables independently associated with the later development of schizophrenia were calculated, adjusting for potential confounders.

RESULTS

Four variables reflecting early problems with interpersonal relationships were strongly associated with later schizophrenia and, to a lesser extent, non-schizophrenic psychoses, but also occurred commonly in the cohort as a whole. These associations with schizophrenia persisted after early-onset cases were excluded, though their predictive value was low (3.0%, 95% CI 1.5-4.5).

CONCLUSIONS

Some aspects of premorbid personality and adjustment may act as risk factors for schizophrenia. The results appear to be most consistent with a multi-factorial aetiology for schizophrenia and offer tentative support for a psychological disturbance mediating genetic and environmental effects on the causal pathway to the illness.

IQ and risk for schizophrenia: a population-based cohort study

BACKGROUND

This study aimed to quantify the association between low IQ and the later development of psychosis in a population-based cohort study of 18-year-old conscripts.

METHODS

Fifty thousand males conscripted into the Swedish army in 1969-1970 were followed by means of the Swedish National Register of Psychiatric Care up to 1983. Tests of verbal and visuospatial abilities, general and mechanical knowledge and several psychosocial variables were recorded at conscription.

RESULTS

One hundred and ninety-five subjects were admitted to hospital with schizophrenia and 192 with a non-schizophrenic psychosis on ICD-8 criteria. The distribution of scores in those later diagnosed as suffering from schizophrenia was shifted in a downward direction, with a linear relationship between low IQ and risk. This remained after adjustment for potential confounders. The risk for non-schizophrenic disorders was also higher in those with lower IQ but the effect was less marked and non-linear. Only poorer performance on the verbal tasks and mechanical knowledge test conferred a significantly increased risk for schizophrenia after taking into account general intellectual ability. Low IQ at conscription was not related to age of onset.

CONCLUSIONS

The results confirm the importance of low intellectual ability as a risk factor for schizophrenia and other psychoses. This is unlikely to be due to prodromal decline or known confounders. The association could be directly causal with cognitive impairment leading to false beliefs and perceptions, or could be indirect with any factors causing lower IQ, such as abnormal brain development increasing the risk for schizophrenia.

A study of suicide in farmers in England and Wales

The proportional mortality ratio for suicide is higher in farmers than in the general population. The reasons for this are likely to be complex, but may include easy availability of firearms, stress related to work, financial difficulties, and family problems. A psychological autopsy study of suicide in 84 farmers who died between 1991-1994 is presented and some preliminary findings are discussed.

Novel (R)-2-amino-5-fluorotetralins: dopaminergic antagonists and inverse agonists

A series of secondary and tertiary N-alkyl derivatives of (R)-2-amino-5-fluorotetralin have been prepared. The affinities of the compounds for [3H]raclopride-labeled cloned human dopamine (DA) D2 and D3 receptors as well as [3H]-8-OH-DPAT-labeled rat hippocampal 5-HT1A receptors were determined. In order to selectively determine affinities for the high-affinity agonist binding site at DA D2 receptors, the agonist [3H]quinpirole was used. The intrinsic activities of the compounds at DA D2 and D3 receptors were evaluated in a [35S]GTP gamma S binding assay. The novel compounds were characterized as dopaminergic antagonists or inverse agonists. The antagonist (R)-2-(butylpropylamino)-5-fluorotetralin (16) bound with high affinity (Ki = 4.4 nM) to the DA D3 receptor and was the most D3-selective compound (10-fold). (R)-2-[[4-(8-Aza-7, 9-dioxospiro[4.5]decan-8-yl)butyl]propylamino]-5-fluorote tralin (18) bound with very high affinity to both DA D3 and 5-HT1A receptors (Ki = 0.2 nM) and was also characterized as a dopaminergic antagonist. (R)-2-(Benzylpropylamino)-5-fluorotetralin (10) behaved as an inverse agonist at both DA D2 and D3 receptors. It decreased the basal [35S]GTP gamma S binding and potently inhibited the DA-stimulated [35S]GTP gamma S binding. It is apparent that the intrinsic activity of a 2-aminotetralin derivative may be modified by varying the N-alkyl substituents.

Differential serotoninergic and dopaminergic activities of the (R)- and the (S)-enantiomers of 2-(di-n-propylamino)tetralin

Racemic 2-(di-n-propylamino)tetralin ((R,S)-DPAT), which lacks phenolic or other aromatic substituents, induces both dopaminergic (sniffing, licking and gnawing) and serotoninergic (forepaw treading and flat body posture) behavioural responses. The present study shows that s.c. administration of (R)-DPAT induces typical 5-HT1A receptor agonist behaviours. These effects are blocked by the 5-HT1A receptor antagonist (S)-5-fluoro-8-hydroxy-2-(di-n-propylamino)tetralin ((S)-UH-301). Administration of (S)-DPAT induces dopaminergic behaviours, which are fully antagonised by raclopride, a dopamine D2 receptor antagonist. Both enantiomers induce hypothermia, (R)-DPAT being antagonised by (S)-UH-301, whereas (S)-DPAT is antagonised by raclopride. The accumulation of 5-hydroxytryptophan and DOPA (3,4-dihydroxyphenylalanine) after decarboxylase inhibition that reflects presynaptic actions on 5-HT (5-hydroxytryptamine, serotonin) and dopamine neurons, respectively, are inhibited by both enantiomers of DPAT. (R)-DPAT is more potent than (S)-DPAT as an inhibitor of 5-hydroxytryptophan accumulation whereas (S)-DPAT is more potent than (R)-DPAT as an inhibitor of DOPA accumulation. Thus, in functional tests of postsynaptic actions (R)-DPAT behaves as a 5-HT1A receptor agonist and (S)-DPAT as a dopamine D2 receptor agonist. Presynaptically, (R)-DPAT shows selectivity for 5-HT1A receptors and (S)-DPAT for dopamine D2 receptors. Receptor binding studies, utilizing [3H]8-hydroxy-2-(di-n-propylamino)tetralin and [3H]quinpirole as radioligands for 5-HT1A and dopamine D2 receptors, respectively, showed (R)-DPAT to have a 3-fold higher affinity than (S)-DPAT for 5-HT1A receptors, whereas (S)-DPAT had a 6-fold higher affinity than (R)-DPAT for dopamine D2 receptors. Thus, the results from receptor binding studies support the conclusion that (R)- and (S)-DPAT are agonists showing selectivity for 5-HT1A and dopamine D2 receptors, respectively. Taken together, these findings may explain previous controversies with regard to the pharmacology of racemic DPAT and re-emphasise the necessity to study pure enantiomers of chiral compounds.

Critical reevaluation of spiperone and benzamide binding to dopamine D2 receptors: evidence for identical binding sites

There are several inconsistencies in the literature as regards the characteristics of benzamide and butyrophenone binding to dopamine D2-like receptors. The variations observed in Bmax, Kd and Ki values have led to hypotheses, such as the existence of a specific "benzamide binding site' and that dopamine D2 receptors exist in a monomer-dimer equilibrium, where benzamides are supposed to bind receptor monomers and butyrophenones receptor dimers. We have previously suggested that the discrepant results may instead be related to methodological difficulties associated with the use of very high-affinity radioligands (e.g. ligand depletion and failure to achieve equilibrium). The present study was designed to reinvestigate and critically reevaluate the binding characteristics of [3H]spiperone, [3H]nemonapride, [125I](S)-3-iodo-N-[(1-ethyl-2-pyrrolidinyl)methyl]-5,6- dimethylsalicylamide ([125I]NCQ-298) and [3H]raclopride to cloned human dopamine D2A and rat striatal dopamine D2 receptors in order to establish whether they label the same receptor population. We found that the Kd values of [3H]spiperone, [125I]NCQ-298 and [3H]nemonapride were about 20 pM and that of [3H]raclopride about 1 nM. We did not find any significant differences between the Bmax values determined with the various radioligands. Furthermore, the Ki values of spiperone and NCQ-298 (derived from cross-competition studies) for dopamine D2 receptors labelled with either [3H]spiperone or [125I]NCQ-298 were in good agreement with the corresponding Kd values. In conclusion, our results clearly demonstrate that when studied under correct experimental conditions, all four radioligands label an identical receptor population.

Why does clozapine stimulate the motor activity of reserpine-pretreated rats when combined with a dopamine D1 receptor agonist?

The aim of the present experiments was to investigate the locomotor stimulant effects of the atypical antipsychotic agent, clozapine, in rats depleted of their dopamine by reserpine and alpha-methyl-p-tyrosine pretreatment. Clozapine itself induced a slight but never significant stimulation of locomotor activity which was enhanced by the addition of the selective dopamine D1 receptor agonist, SKF38393 (2,3,4,5-tetrahydro-7,8-dihydroxy-1-phenyl-1H-3- benzazepine), but not by the selective dopamine D2 receptor agonist, quinpirole. The stimulation produced by clozapine plus SKF38393 was blocked by the selective dopamine D1 receptor antagonist, SCH23390 (7-chloro-8-hydroxy-3-methyl-1-phenyl-2,3,4,5- tetrahydro-1H-3-benzapine hydrochloride), while the selective dopamine D2 receptor antagonist, haloperidol, was ineffective. A combination of SCH23390 and haloperidol blocked the clozapine plus SKF38393-induced locomotion. Unlike clozapine, neither the selective 5-HT2 receptor antagonist, ritanserin, nor the dopamine D2 receptor antagonists, haloperidol and remoxipride, caused locomotor activation when given alone or in combination with SKF38393. The indirectly acting sympathomimetic amine, d-amphetamine, was inactive in the monoamine-depleted rats, indicating that no dopamine was available for release by d-amphetamine. The muscarinic receptor antagonist, scopolamine, alone did not alter locomotion, but produced marked stimulation when combined with SKF38393 but not with quinpirole. This stimulation was not affected by haloperidol. However, the scopolamine plus SKF38393-induced stimulation was partially blocked by SCH23390 or by a combination of haloperidol and SCH23390. The data indicate that clozapine, in rats depleted of their dopamine stores, exhibits properties consistent with those of a dopamine receptor agonist.(ABSTRACT TRUNCATED AT 250 WORDS)

Characterization of [3H]quinpirole binding to human dopamine D2A and D3 receptors: effects of ions and guanine nucleotides

The in vitro receptor binding characteristics of [3H]quinpirole to cloned human dopamine D2A (long isoform) and D3 receptors were investigated and compared with those of rat striatal dopamine receptors. [3H]Quinpirole selectively labeled the high-affinity state of cloned dopamine D2A and striatal D2 receptors with an affinity of about 4 nM. In the striatum, [3H]quinpirole bound to 70% of the receptors labeled by the antagonist [3H]raclopride, whereas the corresponding value for cloned dopamine D2A receptors was 26%. [3H]Quinpirole labeled both the high- and "low-"affinity states of the dopamine D3 receptor with the affinities of 0.6 nM (36% of the receptors) and 7.3 nM, respectively. At all three receptors, sodium decreased the proportion of receptors labeled by [3H]quinpirole, whereas its affinity for the remaining high-affinity sites was not changed. Further addition of guanine nucleotides completely converted the high-affinity binding into low. Thus, even the dopamine D3 receptor was regulated by sodium and guanine nucleotides. Competition studies for [3H]quinpirole and [3H]raclopride binding revealed that the agonists (+)-(R)-7-hydroxy-2-dipropylaminotetralin and quinpirole, previously claimed to be highly dopamine D3-selective (approximately 100-fold), displayed high affinity for the high-affinity agonist states of both dopamine D2 and D3 receptors. When these values were compared, instead of the apparent affinities from the one-site analysis, the dopamine D3-selectivities were 20-fold for (+)-(R)-7-hydroxy-2-dipropylaminotetralin and 8-fold for quinpirole. Thus, it is of importance to consider both high- and low-affinity agonist states when receptor selectivities are evaluated.

Are there neurological and sensory risk factors for schizophrenia?

The association between left-handedness, epilepsy, and hearing impairment with schizophrenia was investigated using data from a cohort of 50,000 male Swedish conscripts linked to the Swedish National Register of Psychiatric Care. Though epilepsy was rare in this cohort, no association with schizophrenia was found. Left-handedness was associated with neither schizophrenia nor other psychoses. The study shows that, when studied from a population base, the apparent increase in neurodevelopmental anomalies in schizophrenia may be an artefact of bias. However, schizophrenia was 1.81 (95% CI 1.2-2.7) times higher amongst those with severe hearing loss, which may be preventable.

In vitro receptor binding characteristics of the new dopamine D2 antagonist [125I]NCQ-298: methodological considerations of high affinity binding

The substituted benzamide [125I]NCQ-298 is a recently developed radioligand that has been shown to bind with high affinity and selectivity to dopamine D2 receptors. The present studies were designed to optimize the in vitro receptor binding method of [125I]NCQ-298 and to determine whether it labels the same receptor population as the widely used benzamide [3H]raclopride. Rat striatal D2 receptors and cloned human D2 and D3 receptors were used. We found that due to the high affinity of [125I]NCQ-298 (Kd approximately 20 pmol/l), long incubation time (4 hrs at 30 degrees C) and low receptor concentration (approximately 2 pmol/l) were necessary in order to reach equilibrium and avoid ligand depletion. The optimal composition of the incubation buffer for rat striatal [125I]NCQ-298 binding assays was (in mM): 50 Tris-HCI, 120 NaCl, 5 KCl, 1 MgCl2, 0.01 pargyline, 0.1 EDTA, 0.05 protease inhibitors (PMSF and bacitracin) and 0.01% ascorbic acid. It is concluded that, when studied under correct experimental conditions, [125I]NCQ-298 is an excellent high-affinity D2 receptor radioligand which labels the same receptor population as [3H]raclopride (Bmax values; 32 +/- 3 and 36 +/- 1 pmol/g w.w., respectively).

Molecular basis for the binding of 2-aminotetralins to human dopamine D2A and D3 receptors

The affinities of a series of stereochemically well defined 2-aminotetralin derivatives for cloned human dopamine D2A (443 amino acids) and D3 receptors expressed in mammalian cell lines have been determined using [3H]raclopride as radioligand. Several of the compounds tested showed high selectivity for the D3 receptor. Notably, (R)-7-hydroxy-2-dipropylaminotetralin displayed 70-fold selectivity for the D3 receptor and its cis-C1-methyl analog, (1S,2R)-AJ-148, displayed 38-fold selectivity. Large differences in receptor binding affinities between the compounds were obtained, despite the close structural relationship of the compounds. To better understand the receptor interactions of these compounds, we have constructed homology-based receptor models of the human D2A and D3 receptors by using bacteriorhodopsin as a template. The resulting model was used in conjunction with an indirect model. The indirect model describes a proposed active agonist conformation for dopaminergic 2-aminotetralins and related compounds and consists of a receptor excluded volume that was used to define the agonist binding site. We docked a number of ligands into the D2A and D3 binding sites by optimizing attractive interactions and minimizing repulsive interactions. In the binding site model of the D2A receptor, the protonated nitrogen of the ligands interacts with Asp-114 in transmembrane region (TM) 3 through a reinforced ionic bond. The aspartic acid is surrounded by aromatic residues that may stabilize the ion pair formed with the protonated ligands. In addition, a hydrogen bond is formed from the phenolic hydrogen of the agonist ligands to Ser-193 (TM 5). Aromatic edge-to-face interactions occur between Phe-390 (TM 6) and the aromatic ring of the agonists. 2-Aminotetralin-based dopaminergic antagonists [e.g., (1S,2R)-UH-232] structurally related to agonists have a different but partly overlapping mode of binding, with the aromatic ring located more extracellularly, compared with agonists. The structure-activity relationships that are apparent from this and previous studies are qualitatively rationalized by the binding site models.

Binding characteristics of remoxipride and its metabolites to dopamine D2 and D3 receptors

The substituted benzamide, remoxipride, is a new atypical antipsychotic agent with good clinical efficacy and low extrapyramidal side-effect potential. In the present study, the in vitro receptor binding properties of remoxipride and several of its metabolites to rat striatal dopamine D2 and cloned human dopamine D2A and D3 receptors were investigated. Remoxipride bound to [3H]raclopride-labelled dopamine D2 receptors in rat striatum with an affinity (Ki) of 113 nM. The significantly lower affinities of remoxipride reported when [3H]spiperone was used as a radioligand are suggested to be due to methodological problems associated with the use of very high-affinity radioligands. Some of the phenolic metabolites of remoxipride found mainly in rat exhibited considerably higher affinities to dopamine D2 and D3 receptors than remoxipride itself. The pyrrolidone metabolites found mainly in the human had very low dopamine D2 and D3 affinities. The present in vitro results suggest that the behavioural effects of remoxipride in rats may reflect the effect of remoxipride and some of its high-affinity metabolites.

Unique binding characteristics of antipsychotic agents interacting with human dopamine D2A, D2B, and D3 receptors

In the present study we have compared the pharmacological properties of human dopamine (DA) D2A, D2B, and D3 receptors expressed in mammalian cell lines, using [3H]raclopride as a radioligand. Most of the compounds tested had about equal affinity for D2A and D3 receptors, with the exception of remoxipride, which displayed a 10-fold D2 selectivity, and the aminotetralin (+)-UH 232, which displayed a 5-fold D3 selectivity. Several antipsychotic agents, including clozapine and substituted benzamides, bound with 2-3-fold higher to the D2B (short) than to the D2A (long) isoform, whereas others failed to differentiate between the two isoforms. The atypical antipsychotic agent clozapine bound in a biphasic manner and with unexpectedly high affinity (35 nM) to the D2B receptor, suggesting that clozapine may not be as D4 selective as reported previously. In addition, remoxipride, a new antipsychotic agent with low potential to produce extrapyramidal side effects, displayed 2-3-fold higher affinity for the D2B receptor than for the D2A receptor. Furthermore, sodium differently regulated clozapine and benzamide binding to the various DA receptor subtypes. Thus, sodium decreased the affinity of clozapine for D2A and D2B receptors about 3-fold, whereas the affinity for D3 receptors was unaltered. In contrast, the affinity of raclopride for the three DA receptor subtypes was increased by sodium. Whether the unique characteristics of the binding of clozapine and benzamides to cloned DA receptors demonstrated in the present study are related to the favorable clinical properties of these compounds remains to be elucidated.