Quetiapine and its metabolite norquetiapine: translation from in vitro pharmacology to in vivo efficacy in rodent models.

BACKGROUND AND PURPOSE: Quetiapine has a range of clinical activity distinct from other atypical antipsychotic drugs, demonstrating efficacy as monotherapy in bipolar depression, major depressive disorder and generalized anxiety disorder. The neuropharmacological mechanisms underlying this clinical profile are not completely understood; however, the major active metabolite, norquetiapine, has been shown to have a distinct in vitro pharmacological profile consistent with a broad therapeutic range and may contribute to the clinical profile of quetiapine. EXPERIMENTAL APPROACH: We evaluated quetiapine and norquetiapine, using in vitro binding and functional assays of targets known to be associated with antidepressant and anxiolytic drug actions and compared these activities with a representative range of established antipsychotics and antidepressants. To determine how the in vitro pharmacological properties translate into in vivo activity, we used preclinical animal models with translational relevance to established antidepressant-like and anxiolytic-like drug action. KEY RESULTS: Norquetiapine had equivalent activity to established antidepressants at the noradrenaline transporter (NET), while quetiapine was inactive. Norquetiapine was active in the mouse forced swimming and rat learned helplessness tests. In in vivo receptor occupancy studies, norquetiapine had significant occupancy at NET at behaviourally relevant doses. Both quetiapine and norquetiapine were agonists at 5-HT1A receptors, and the anxiolytic-like activity of norquetiapine in rat punished responding was blocked by the 5-HT1A antagonist, WAY100635. CONCLUSIONS AND IMPLICATIONS: Quetiapine and norquetiapine have multiple in vitro pharmacological actions, and results from preclinical studies suggest that activity at NET and 5-HT1A receptors contributes to the antidepressant and anxiolytic effects in patients treated with quetiapine.

Preclinical pharmacology of AZD2327: a highly selective agonist of the δ-opioid receptor.

In the present article, we summarize the preclinical pharmacology of 4-{(R)-(3-aminophenyl)[4-(4-fluorobenzyl)-piperazin-1-yl]methyl}-N,N-diethylbenzamide (AZD2327), a highly potent and selective agonist of the δ-opioid receptor. AZD2327 binds with sub-nanomolar affinity to the human opioid receptor (K(i) = 0.49 and 0.75 nM at the C27 and F27 isoforms, respectively) and is highly selective (>1000-fold) over the human µ- and κ-opioid receptor subtypes as well as >130 other receptors and channels. In functional assays, AZD2327 shows full agonism at human δ-opioid receptors ([(35)S]GTPγ EC(50) = 24 and 9.2 nM at C27 and F27 isoforms, respectively) and also at the rat and mouse δ-opioid receptors. AZD2327 is active in a wide range of models predictive of anxiolytic activity, including a modified Geller-Seifter conflict test and social interaction test, as well as in antidepressant models, including learned helplessness. In animals implanted with microdialysis probes and then given an acute stressor by pairing electric shock delivery with a flashing light, there is an increase in norepinephrine release into the prefrontal cortex associated with this acute anxiety state. Both the benzodiazepine anxiolytic standard diazepam and AZD2327 blocked this norepinephrine release equally well, and there was no evidence of tolerance to these effects of AZD2327. Overall, these data support the role of the δ-opioid receptor in the regulation of mood, and data suggest that AZD2327 may possess unique antidepressant and anxiolytic activities that could make a novel contribution to the pharmacotherapy of psychiatric disorders.

Attenuation of fear conditioning by antisense inhibition of brain corticotropin releasing factor-2 receptor.

Corticotropin releasing factor (CRF) is an important regulator of the endocrine, behavioral, autonomic and immune responses to stress. Two high affinity CRF receptors have been identified, which are distributed in distinct anatomical regions. CRF(1) receptors have been relatively well characterized and antagonists to this receptor effectively block stress-induced behaviors in rodents. The function of CRF(2) receptors, which are highly expressed in limbic brain regions, is less well understood. Therefore, an antisense oligonucleotide approach was used to study the role of CRF(2) receptors in the lateral septum in rats. An antisense oligonucleotide directed against the CRF(2) receptor mRNA reduced expression of CRF(2) receptors by 60--80%. In shock-induced freezing tests, animals administered the antisense oligonucleotide exhibited a significant reduction in freezing duration. However, pain sensitivity and locomotor activity were unaltered. A four-base mismatch of the antisense sequence had no significant effects on CRF(2) receptor density and on freezing behavior. These data support the involvement of CRF(2) receptors in fear conditioning. CRF(1) receptor antagonists also reduce freezing in this test. Additional studies to determine the effects of simultaneous inhibition of both receptor subtypes show that rats receiving both CRF(2) receptor antisense oligonucleotide and CRF(1) receptor antagonist froze significantly less than animals treated with either agent alone. These results provide additional evidence for the role of CRF(2) receptors in mediating the stress-induced actions of endogenous CRF.

2-Fluoro-4-pyridinylmethyl analogues of linopirdine as orally active acetylcholine release-enhancing agents with good efficacy and duration of action.

In an effort to improve the pharmacokinetic and pharmacodynamic properties of the cognition-enhancer linopirdine (DuP 996), a number of core structure analogues were prepared in which the 4-pyridyl pendant group was systematically replaced with 2-fluoro-4-pyridyl. This strategy resulted in the discovery of several compounds with improved activity in acetylcholine (ACh) release-enhancing assays, in vitro and in vivo. The most effective compound resulting from these studies, 10, 10-bis[(2-fluoro-4-pyridinyl)methyl]-9(10H)-anthracenone (9), is between 10 and 20 times more potent than linopirdine in increasing extracellular hippocampal ACh levels in the rat with a minimum effective dose of 1 mg/kg. In addition to superior potency, 9 possesses an improved pharmacokinetic profile compared to that of linopirdine. The half-life of 9 (2 h) in rats is 4-fold greater than that of linopirdine (0.5 h), and it showed a 6-fold improvement in brain-plasma distribution over linopirdine. On the basis of its pharmacologic, pharmacokinetic, absorption, and distribution properties, 9 (DMP543) has been advanced for clinical evaluation as a potential palliative therapeutic for treatment of Alzheimer's disease.

Two new potent neurotransmitter release enhancers, 10,10-bis(4-pyridinylmethyl)-9(10H)-anthracenone and 10,10-bis(2-fluoro-4-pyridinylmethyl)-9(10H)-anthracenone: comparison to linopirdine.

Linopirdine (3,3-bis(4-pyridinylmethyl)-1-phenylindolin-2-one, DUP996) is an extensively studied representative of a class of cognition enhancing compounds that increase the evoked release of neurotransmitters. Recent studies suggest that these agents act through the blockade of specific K+ channels. We have recently identified more potent anthracenone analogs of linopirdine: 10,10-bis(4-pyridinylmethyl)-9(10H)-anthracenone (XE991) and 10,10-bis(2-fluoro-4-pyridinylmethyl)-9(10H)-anthracenone (DMP 543). Although linopirdine possesses an EC50 of 4.2 microM for enhancement of [3H]ACh release from rat brain slices, XE991 and DMP 543 have EC50S of 490 and 700 nM, respectively. In addition to greater in vitro potency relative to linopirdine, both compounds show greater in vivo potency and duration of action. Although 5 mg/kg (p.o.) linopirdine does not lead to statistically significant increases in hippocampal extracellular acetylcholine levels, 5 mg/kg (p.o.) XE991 leads to increases (maximal effect > 90% over baseline) which are sustained for 60 min. Moreover, DMP 543 at 1 mg/kg causes more than a 100% increase in acetylcholine levels with the effect lasting more than 3 hr. At doses relevant to their release-enhancing properties, the only overt symptom consistently observed was tremor, possible via a cholinergic mechanism. These results suggest that XE991 and DMP 543 may prove to be superior to linopirdine as Alzheimer's disease therapeutics. In addition, these agents should be useful pharmacological tools for probing the importance of particular ion channels in the control of neurotransmitter release.

Stability of isoproturon, bentazone, terbuthylazine and alachlor in natural groundwater, surface water and soil water samples stored under laboratory conditions.

The stability of isoproturon, bentazone, terbuthylazine and alachlor was investigated in groundwater (GrW), surface water (SuW) and soil water from the unsaturated zone (SoW). Samples fortified with a low spiking level (LSL) of about 0.3-0.5 microgram/L and a high spiking level (HSL) of about 0.9-1.3 micrograms/L were stored for 1, 2, 14 (GrW) and 30 days (SuW and SoW) at 4 degrees C in amber glass bottles without biological inhibition. The initial pesticide concentration played a significant role, the lowest concentrations being the least stable for all pesticides. Nevertheless, after 14 days of storage, no concentration had decreased significantly compared to day 0 values, except for bentazone LSL in the GrW and SuW. Significant losses of alachlor were observed only after 30 days. Terbuthylazine and isoproturon were stable for 30 days, except for a slight loss of terbuthylazine HSL in the SoW. The very poor recovery of bentazone from the SoW gave poor results for interpretation. Overall, the stability of the molecules was highest in the GrW and lowest in the SoW. For SoW, the variability of triplicate determinations at a given storage time was, in some cases, as great as the changes in mean concentrations observed over the total 30 day storage period.

Studies on the role of K+, Cl- and Na+ ion permeabilities in the acetylcholine release enhancing effects of linopirdine (DuP 996) in rat cortical slices.

Linopirdine is a compound being assessed for value in reversing the dementia associated with Alzheimer's disease. The drug improves learning and memory performance in several rodent behavioral paradigms. Its proposed mechanism of action is the enhancement of neurotransmitter release, but the molecular site which mediates this action is unknown. The present study examines the possible involvement of channels which mediate the movement of K+, Cl- and Na+, which are important to the polarization state of excitable membranes, in the release-enhancing effects of linopirdine. Linopirdine causes a shift in the K+ dose response for the release of tritium from cerebral cortical slices preloaded with [3H]choline ([3H]acetylcholine (ACh) released) to the left, consistent with the blockade of a site, such as a K+ channel, involved in dampening the response of neuronal terminals to depolarizing stimuli. Linopirdine does not appear to act at aminopyridine-sensitive K+ channels, inasmuch as the aminopyridines and linopirdine have different patterns of effects regarding [3H]ACh release. Tetraethylamonium (TEA), on the other hand, does share common effects with linopirdine. TEA enhances K(+)-evoked [3H]ACh release to as much as 620% of control without affecting basal efflux of the neurotransmitter. Experiments using the muscarinic agonist carbachol indicate that linopirdine does not affect the cholinergic autoreceptor influence on [3H]ACh release. Linopirdine also does not appear to act at tetrodotoxin-sensitive Na+ channels. The anion channel blocker 4-acetamido-4'-isothiocyanatostilbene-2,2'-disulfonic acid and Cl(-)-deficient media do not affect the level of linopirdine release enhancement.