The dopamine D1 receptor positive allosteric modulator, DETQ, improves cognition and social interaction in aged mice and enhances cortical and hippocampal acetylcholine efflux

Dopamine (DA) D1 and D2 receptors (Rs) are critical for cognitive functioning. D1 positive allosteric modulators (D1PAMs) activate D1Rs without desensitization or an inverted U-shaped dose response curve. DETQ, [2-(2,6-dichlorophenyl)-1-((1S,3R)-3-(hydroxymethyl)-5-(2-hydroxypropan-2-yl)-1-methyl-3,4-dihydroisoquinolin-2(1H)-yl)ethan-1-one] is highly selective for the human D1Rs as shown in humanized D1R knock-in (hD1Ki) mice. Here, we have ascertained the efficacy of DETQ in aged [13-23-month-old (mo)] hD1Ki mice and their corresponding age-matched wild-type (WT; C57BL/6NTac) controls. We found that in aged mice, DETQ, given acutely, subchronically, and chronically, rescued both novel object recognition memory and social behaviors, using novel object recognition (NOR) and social interaction (SI) tasks, respectively without any adverse effect on body weight or mortality. We have also shown, using in vivo microdialysis, a significant decrease in basal DA and norepinephrine, increase in glutamate (Glu) and gamma-amino butyric acid (GABA) efflux with no significant changes in acetylcholine (ACh) levels in aged vs young mice. In young and aged hD1Ki mice, DETQ, acutely and subchronically increased ACh in the medial prefrontal cortex and hippocampal regions in aged hD1Ki mice without affecting Glu. These results suggest that the D1PAM mechanism is of interest as potential treatment for cognitive and social behavioral deficits in neuropsychiatric disorders including but not restricted to neurodegenerative disorders, such as Parkinson's disease.

Effects of DPTQ, a novel positive allosteric modulator of the dopamine D1 receptor, on spontaneous eye blink rate and spatial working memory in the nonhuman primate

RATIONALE

Dopamine (DA) signaling through the D1 receptor has been shown to be integral to multiple aspects of cognition, including the core process of working memory. The discovery of positive allosteric modulators (PAMs) of the D1 receptor has enabled treatment modalities that may have alternative benefits to orthosteric D1 agonists arising from a synergism of action with functional D1 receptor signaling.

OBJECTIVES

To investigate this potential, we have studied the effects of the novel D1 PAM DPTQ on a spatial delayed response working memory task in the rhesus monkey. Initial studies indicated that DPTQ binds to primate D1R with high affinity and selectivity and elevates spontaneous eye blink rate in rhesus monkeys in a dose-dependent manner consistent with plasma ligand exposures and central D1activation.

RESULTS

Based on those results, DPTQ was tested at 2.5 mg/kg IM in the working memory task. No acute effect was observed 1 h after dosing, but performance was impaired 48 h later. Remarkably, this deficit was immediately followed by a significant enhancement in cognition over the next 3 days. In a second experiment in which DPTQ was administered on days 1 and 5, the early impairment was smaller and did not reach statistical significance, but statistically significant enhancement of performance was observed over the following week. Lower doses of 0.1 and 1.0 mg/kg were also capable of producing this protracted enhancement without inducing any transient impairment.

CONCLUSIONS

DPTQ exemplifies a class of D1PAMs that may be capable of providing long-term improvements in working memory.

Mutual Cooperativity of Three Allosteric Sites on the Dopamine D1 Receptor

An amine-containing molecule called Compound A has been reported by a group from Bristol-Myers Squibb to act as a positive allosteric modulator (PAM) at the dopamine D1 receptor. We synthesized the more active enantiomer of Compound A (BMS-A1) and compared it with the D1 PAMs DETQ and MLS6585, which are known to bind to intracellular loop 2 and the extracellular portion of transmembrane helix 7, respectively. Results from D1/D5 chimeras indicated that PAM activity of BMS-A1 tracked with the presence of D1 sequence in the N-terminal/extracellular region of the D1 receptor, a unique location compared with either of the other PAMs. In pairwise combinations, BMS-A1 potentiated the small allo-agonist activity of each of the other PAMs, while the triple PAM combination (in the absence of dopamine) produced a cAMP response about 64% of the maximum produced by dopamine. Each of the pairwise PAM combinations produced a much larger leftward shift of the dopamine EC₅₀ than either single PAM alone. All three PAMs in combination produced a 1000-fold leftward shift of the dopamine curve. These results demonstrate the presence of three non-overlapping allosteric sites that cooperatively stabilize the same activated state of the human D1 receptor. SIGNIFICANCE STATEMENT: Deficiencies in dopamine D1 receptor activation are seen in Parkinson disease and other neuropsychiatric disorders. In this study, three positive allosteric modulators of the dopamine D1 receptor were found to bind to distinct and separate sites, interacting synergistically with each other and dopamine, with the triple combination causing a 1000-fold leftward shift of the response to dopamine. These results showcase multiple opportunities to modulate D1 tone and highlight new pharmacological approaches for allosteric modulation of G-protein-coupled receptors.

Ensemble Docking Approach to Mitigate Pregnane X Receptor-Mediated CYP3A4 Induction Risk

Three structurally closely related dopamine D1 receptor positive allosteric modulators (D1 PAMs) based on a tetrahydroisoquinoline (THIQ) scaffold were profiled for their CYP3A4 induction potentials. It was found that the length of the linker at the C5 position greatly affected the potentials of these D1 PAMs as CYP3A4 inducers, and the level of induction correlated well with the activation of the pregnane X receptor (PXR). Based on the published PXR X-ray crystal structures, we built a binding model specifically for these THIQ-scaffold-based D1 PAMs in the PXR ligand-binding pocket via an ensemble docking approach and found the model could explain the observed CYP induction disparity. Combined with our previously reported D1 receptor homology model, which identified the C5 position as pointing toward the solvent-exposed space, our PXR-binding model coincidentally suggested that structural modifications at the C5 position could productively modulate the CYP induction potential while maintaining the D1 PAM potency of these THIQ-based PAMs.

Synthesis and Preclinical Characterization of LY3154885, a Human Dopamine D1 Receptor Positive Allosteric Modulator with an Improved Nonclinical Drug-Drug Interaction Risk Profile

Results from recently completed clinical studies suggest the dopamine D1 receptor positive allosteric modulator (PAM) mevidalen (1) could offer unique value for lewy body dementia (LBD) patients. In nonclinical assessments, 1 was mainly eliminated by CYP3A4-mediated metabolism, therefore at the risk of being a victim of drug-drug interactions (DDI) with CYP3A4 inhibitors and inducers. An effort was initiated to identify a new D1 PAM with an improved DDI risk profile. While attempts to introduce additional metabolic pathways mediated by other CYP isoforms failed to provide molecules with an acceptable profile, we discovered that the relative contribution of CYP-mediated oxidation and UGT-mediated conjugation could be tuned to reduce the CYP3A4-mediated victim DDI risk. We have identified LY3154885 (5), a D1 PAM that possesses similar in vitro and in vivo pharmacologic properties as 1, but is metabolized mainly by UGT, predicting it could potentially offer lower victim DDI risk in clinic.

Safety and Efficacy of Mevidalen in Lewy Body Dementia: A Phase 2, Randomized, Placebo-Controlled Trial

BACKGROUND

Mevidalen is a selective positive allosteric modulator (PAM) of the dopamine D1 receptor subtype.

OBJECTIVE

To assess the safety and efficacy of mevidalen for treatment of cognition in patients with Lewy body dementia (LBD).

METHODS

PRESENCE was a phase 2, 12-week study in participants with LBD (N = 344) randomly assigned (1:1:1:1) to daily doses of mevidalen (10, 30, or 75 mg) or placebo. The primary outcome measure was change from baseline on Cognitive Drug Research Continuity of Attention (CoA) composite score. Secondary outcomes included Alzheimer's Disease Assessment Scale-Cognitive Subscale 13 (ADAS-cog₁₃ ), Movement Disorder Society-Unified Parkinson's Disease Rating Scale (MDS-UPDRS), and Alzheimer's Disease Cooperative Study-Clinical Global Impression of Change (ADCS-CGIC). Numerous safety measures were collected.

RESULTS

Mevidalen failed to meet primary or secondary cognition endpoints. Mevidalen resulted in significant, dose-dependent improvements of MDS-UPDRS total score (sum of Parts I-III, 10 mg P < 0.05, 30 mg P < 0.05, 75 mg P < 0.01, compared to placebo). The 30 mg and 75 mg mevidalen doses significantly improved ADCS-CGIC scores compared to placebo (minimal or better improvement: 30 mg P < 0.01, 75 mg P < 0.01; moderate or better improvement: 30 mg P < 0.05, 75 mg P < 0.001). Increases in blood pressure, adverse events, and cardiovascular serious adverse events were most pronounced at the 75 mg dose.

CONCLUSIONS

Mevidalen harnesses a novel mechanism of action that improves motor symptoms associated with LBD on top of standard of care while improving or not worsening non-motor symptoms associated with traditional dopaminergic therapy. © 2021 The Authors. Movement Disorders published by Wiley Periodicals LLC on behalf of International Parkinson and Movement Disorder Society.

Safety, Tolerability, and Pharmacokinetics of Mevidalen (LY3154207), a Centrally Acting Dopamine D1 Receptor-Positive Allosteric Modulator, in Patients With Parkinson Disease

Mevidalen (LY3154207) is a positive allosteric modulator of the dopamine D1 receptor that enhances the affinity of dopamine for the D1 receptor. The safety, tolerability, motor effects, and pharmacokinetics of mevidalen were studied in patients with Parkinson disease. Mevidalen or placebo was given once daily for 14 days to 2 cohorts of patients (cohort 1, 75 mg; cohort 2, titration from 15 to 75 mg). For both cohorts, the median time to maximum concentration for mevidalen plasma concentration was about 2 hours, the apparent steady-state clearance was 20-25 L/h, and mevidalen plasma concentrations were similar between the 1st and 14th administration in cohort 1, indicating minimal accumulation upon repeated dosing. Mevidalen was well tolerated, and most treatment-emergent adverse events were mild. Blood pressure and pulse rate increased when taking mevidalen, but there was considerable overlap with patients taking placebo, and vital signs normalized with repeated dosing. In the Movement Disorder Society-United Parkinson's Disease Rating Scale, all patients taking mevidalen showed a better motor examination sub-score on day 6 compared to only some patients in the placebo group. These data support examining mevidalen for symptomatic treatment of patients with Parkinson disease and Lewy body dementia.

Safety, Tolerability, and Pharmacokinetics of Mevidalen (LY3154207), a Centrally Acting Dopamine D1 Receptor-Positive Allosteric Modulator (D1PAM), in Healthy Subjects

Activation of the brain dopamine D1 receptor has attracted attention because of its promising role in neuropsychiatric diseases. Although efforts to develop D1 agonists have been challenging, a positive allosteric modulator (PAM), represents an attractive approach with potential better drug-like properties. Phase 1 single-ascending-dose (SAD; NCT03616795) and multiple-ascending-dose (MAD; NCT02562768) studies with the D1PAM mevidalen (LY3154207) were conducted with healthy subjects. There were no treatment-related serious adverse events (AEs) in these studies. In the SAD study, 25-200 mg administered orally showed dose-proportional pharmacokinetics (PK) and acute dose-related increases in systolic blood pressure (SBP) and diastolic blood pressure DBP) and pulse rate at doses ≥ 75 mg. AE related to central activation were seen at doses ≥ 75 mg. At 25 and 75 mg, central penetration of mevidalen was confirmed by measurement of mevidalen in cerebrospinal fluid. In the MAD study, once-daily doses of mevidalen at 15-150 mg for 14 days showed dose-proportional PK. Acute dose-dependent increases in SBP, DBP, and PR were observed on initial administration, but with repeated dosing the effects diminished and returned toward baseline levels. Overall, these findings support further investigation of mevidalen as a potential treatment for a range of neuropsychiatric disorders.

Synthesis and Pharmacological Characterization of 2-(2,6-Dichlorophenyl)-1-((1S,3R)-5-(3-hydroxy-3-methylbutyl)-3-(hydroxymethyl)-1-methyl-3,4-dihydroisoquinolin-2(1H)-yl)ethan-1-one (LY3154207), a Potent, Subtype Selective, and Orally Available Positive Allosteric Modulator of the Human Dopamine D1 Receptor

Clinical development of catechol-based orthosteric agonists of the dopamine D1 receptor has thus far been unsuccessful due to multiple challenges. To address these issues, we identified LY3154207 (3) as a novel, potent, and subtype selective human D1 positive allosteric modulator (PAM) with minimal allosteric agonist activity. Conformational studies showed LY3154207 adopts an unusual boat conformation, and a binding pose with the human D1 receptor was proposed based on this observation. In contrast to orthosteric agonists, LY3154207 showed a distinct pharmacological profile without a bell-shaped dose-response relationship or tachyphylaxis in preclinical models. Identification of a crystalline form of free LY3154207 from the discovery lots was not successful. Instead, a novel cocrystal form with superior solubility was discovered and determined to be suitable for development. This cocrystal form was advanced to clinical development as a potential first-in-class D1 PAM and is now in phase 2 studies for Lewy body dementia.

Positive allosteric modulators of the dopamine D1 receptor: A new mechanism for the treatment of neuropsychiatric disorders

The dopamine D1 receptor plays an important role in motor activity, reward, and cognition. Efforts to develop D1 agonists have been mixed due to poor drug-like properties, tachyphylaxis, and inverted U-shaped dose-response curves. Recently, positive allosteric modulators (PAMs) for the dopamine D1 receptor were discovered and initial pharmacological profiling has suggested that several of the above issues could be addressed with this mechanism. This paper presents an overview of key findings for DETQ (2-(2,6-dichlorophenyl)-1-((1S,3R)-3-(hydroxymethyl)-5-(2-hydroxypropan-2-yl)-1-methyl-3,4-dihydroisoquinolin-2(1H)-yl)ethan-1-one), which is currently the only D1 PAM for which published in vivo data is available. In vitro studies showed selective potentiation of the human D1 receptor without significant allosteric agonist effects. Due to a species difference in affinity for DETQ, transgenic mice expressing the human D1 receptor (hD1 mice) were used in vivo. In contrast to D1 agonists, DETQ increased locomotor activity over a wide dose-range without inverted U-shaped dose response or tachyphylaxis. DETQ also reversed hypo-activity in mice with dopamine depletion due to reserpine pretreatment, suggesting potential for treatment of motor symptoms in Parkinson's disease. Potential pro-cognitive effects were supported by improved performance in the novel object recognition task, enhanced release of cortical acetylcholine and histamine, and increased phosphorylation of the AMPA receptor (GluR1) and the transcription factor CREB. In addition, DETQ enhanced wakefulness in EEG studies and decreased immobility in the forced-swim test. Together, these results provide support for potential utility of D1 PAMs in the treatment of several neuropsychiatric disorders. LY3154207, a close analog of DETQ, is currently in phase 2 clinical trials.

Preclinical profile of a dopamine D1 potentiator suggests therapeutic utility in neurological and psychiatric disorders

DETQ, an allosteric potentiator of the dopamine D1 receptor, was tested in therapeutic models that were known to respond to D1 agonists. Because of a species difference in affinity for DETQ, all rodent experiments used transgenic mice expressing the human D1 receptor (hD1 mice). When given alone, DETQ reversed the locomotor depression caused by a low dose of reserpine. DETQ also acted synergistically with L-DOPA to reverse the strong hypokinesia seen with a higher dose of reserpine. These results indicate potential as both monotherapy and adjunct treatment in Parkinson's disease. DETQ markedly increased release of both acetylcholine and histamine in the prefrontal cortex, and increased levels of histamine metabolites in the striatum. In the hippocampus, the combination of DETQ and the cholinesterase inhibitor rivastigmine increased ACh to a greater degree than either agent alone. DETQ also increased phosphorylation of the AMPA receptor (GluR1) and the transcription factor CREB in the striatum, consistent with enhanced synaptic plasticity. In the Y-maze, DETQ increased arm entries but (unlike a D1 agonist) did not reduce spontaneous alternation between arms at high doses. DETQ enhanced wakefulness in EEG studies in hD1 mice and decreased immobility in the forced-swim test, a model for antidepressant-like activity. In rhesus monkeys, DETQ increased spontaneous eye-blink rate, a measure that is known to be depressed in Parkinson's disease. Together, these results provide support for potential utility of D1 potentiators in the treatment of several neuropsychiatric disorders, including Parkinson's disease, Alzheimer's disease, cognitive impairment in schizophrenia, and major depressive disorder.

Preclinical findings predicting efficacy and side-effect profile of LY2940094, an antagonist of nociceptin receptors

Nociceptin/Orphanin FQ (N/OFQ) is a 17 amino acid peptide whose receptor is designated ORL1 or nociceptin receptor (NOP). We utilized a potent, selective, and orally bioavailable antagonist with documented engagement with NOP receptors in vivo to assess antidepressant‐ and anxiolytic‐related pharmacological effects of NOP receptor blockade along with measures of cognitive and motor impingement. LY2940094 ([2‐[4‐[(2‐chloro‐4,4‐difluoro‐spiro[5H‐thieno[2,3‐c]pyran‐7,4′‐piperidine]‐1′‐yl)methyl]‐3‐methyl‐pyrazol‐1‐yl]‐3‐pyridyl]methanol) displayed antidepressant‐like behavioral effects in the forced‐swim test in mice, an effect absent in NOP^−/− mice. LY2940094 also augmented the behavioral effect of fluoxetine without changing target occupancies (NOP and serotonin reuptake transporter [SERT]). LY2940094 did not have effects under a differential‐reinforcement of low rate schedule. Although anxiolytic‐like effects were not observed in some animal models (conditioned suppression, 4‐plate test, novelty‐suppressed feeding), LY2940094 had effects like that of anxiolytic drugs in three assays: fear‐conditioned freezing in mice, stress‐induced increases in cerebellar cGMP in mice, and stress‐induced hyperthermia in rats. These are the first reports of anxiolytic‐like activity with a systemically viable NOP receptor antagonist. LY2940094 did not disrupt performance in either a 5‐choice serial reaction time or delayed matching‐to‐position assay. LY2940094 was also not an activator or suppressor of locomotion in rodents nor did it induce failures of rotarod performance. These data suggest that LY2940094 has unique antidepressant‐ and anxiolytic‐related pharmacological effects in rodents. Clinical proof of concept data on this molecule in depressed patients have been reported elsewhere.

An Allosteric Potentiator of the Dopamine D1 Receptor Increases Locomotor Activity in Human D1 Knock-In Mice without Causing Stereotypy or Tachyphylaxis

Allosteric potentiators amplify the sensitivity of physiologic control circuits, a mode of action that could provide therapeutic advantages. This hypothesis was tested with the dopamine D1 receptor potentiator DETQ [2-(2,6-dichlorophenyl)-1-((1S,3R)-3-(hydroxymethyl)-5-(2-hydroxypropan-2-yl)-1-methyl-3,4-dihydroisoquinolin-2(1H)-yl)ethan-1-one]. In human embryonic kidney 293 (HEK293) cells expressing the human D1 receptor, DETQ induced a 21-fold leftward shift in the cAMP response to dopamine, with a K_b of 26 nM. The maximum response to DETQ alone was ∼12% of the maximum response to dopamine, suggesting weak allosteric agonist activity. DETQ was ∼30-fold less potent at rat and mouse D1 receptors and was inactive at the human D5 receptor. To enable studies in rodents, an hD1 knock-in mouse was generated. DETQ (3–20 mg/kg orally) caused a robust (∼10-fold) increase in locomotor activity (LMA) in habituated hD1 mice but was inactive in wild-type mice. The LMA response to DETQ was blocked by the D1 antagonist SCH39166 and was dependent on endogenous dopamine. LMA reached a plateau at higher doses (30–240 mg/kg) even though free brain levels of DETQ continued to increase over the entire dose range. In contrast, the D1 agonists SKF 82958, A-77636, and dihydrexidine showed bell-shaped dose-response curves with a profound reduction in LMA at higher doses; video-tracking confirmed that the reduction in LMA caused by SKF 82958 was due to competing stereotyped behaviors. When dosed daily for 4 days, DETQ continued to elicit an increase in LMA, whereas the D1 agonist A-77636 showed complete tachyphylaxis by day 2. These results confirm that allosteric potentiators may have advantages compared with direct-acting agonists.

Group II metabotropic glutamate receptor type 2 allosteric potentiators prevent sodium lactate-induced panic-like response in panic-vulnerable rats

Rats with chronic inhibition of GABA synthesis by infusion of l-allyglycine, a glutamic acid decarboxylase inhibitor, into their dorsomedial/perifornical hypothalamus are anxious and exhibit panic-like cardio-respiratory responses to treatment with intravenous (i.v.) sodium lactate (NaLac) infusions, in a manner similar to what occurs in patients with panic disorder. We previously showed that either NMDA receptor antagonists or metabotropic glutamate receptor type 2/3 receptor agonists can block such a NaLac response, suggesting that a glutamate mechanism is contributing to this panic-like state. Using this animal model of panic, we tested the efficacy of CBiPES and THIIC, which are selective group II metabotropic glutamate type 2 receptor allosteric potentiators (at 10-30 mg/kg i.p.), in preventing NaLac-induced panic-like behavioral and cardiovascular responses. The positive control was alprazolam (3mg/kg i.p.), a clinically effective anti-panic benzodiazepine. As predicted, panic-prone rats given a NaLac challenge displayed NaLac-induced panic-like cardiovascular (i.e. tachycardia and hypertensive) responses and "anxiety" (i.e. decreased social interaction time) and "flight" (i.e. increased locomotion) -associated behaviors; however, systemic injection of the panic-prone rats with CBiPES, THIIC or alprazolam prior to the NaLac dose blocked all NaLac-induced panic-like behaviors and cardiovascular responses. These data suggested that in a rat animal model, selective group II metabotropic glutamate type 2 receptor allosteric potentiators show an anti-panic efficacy similar to alprazolam.

Typical and atypical antipsychotic drugs increase extracellular histamine levels in the rat medial prefrontal cortex: contribution of histamine h(1) receptor blockade

Atypical antipsychotics such as clozapine and olanzapine have been shown to enhance histamine turnover and this effect has been hypothesized to contribute to their improved therapeutic profile compared to typical antipsychotics. In the present study, we examined the effects of antipsychotic drugs on histamine (HA) efflux in the mPFC of the rat by means of in vivo microdialysis and sought to differentiate the receptor mechanisms which underlie such effects. Olanzapine and clozapine increased mPFC HA efflux in a dose related manner. Increased HA efflux was also observed after quetiapine, chlorpromazine, and perphenazine treatment. We found no effect of the selective 5-HT(2A) antagonist MDL100907, 5-HT(2c) antagonist SB242084, or the 5-HT(6) antagonist Ro 04-6790 on mPFC HA efflux. HA efflux was increased following treatment with selective H(1) receptor antagonists pyrilamine, diphenhydramine, and triprolidine, the H(3) receptor antagonist ciproxifan and the mixed 5-HT(2A)/H(1) receptor antagonist ketanserin. The potential novel antipsychotic drug FMPD, which has a lower affinity at H(1) receptors than olanzapine, did not affect HA efflux. Similarly, other antipsychotics with lower H(1) receptor affinity (risperidone, aripiprazole, and haloperidol) were also without effect on HA efflux. Finally, HA efflux after antipsychotic treatment was significantly correlated with affinity at H(1) receptors whereas nine other receptors, including 5-HT(2A), were not. These results demonstrate that both typical and atypical antipsychotics increase mPFC histamine efflux and this effect may be mediated via antagonism of histamine H(1) receptors.

Modulation of neurotransmitter release in orexin/hypocretin-2 receptor knockout mice: a microdialysis study

Orexinergic neurons are discretely localized within the lateral hypothalamus and have widespread projections to the whole brain. Here, the role of orexin/hypocretin-2 receptors (OX2) in modulating extracellular concentrations of neurotransmitters was evaluated in the hypothalamus and the prefrontal cortex (PFC) of OX2 knockout (KO) mice by using a microdialysis technique. In the hypothalamus, basal concentrations of norephinephrine (NE), acetylcholine (ACh), and histamine (Hist) were significantly higher in KO mice, whereas KCl perfusion (147 mM) resulted in significantly lesser increases in NE, ACh, and Hist release in KO compared with wild-type (WT) mice. No differences in basal concentrations or evoked release of serotonin (5-HT) or dopamine (DA) were found in the hypothalamus between genotypes. In the PFC, no differences in the basal concentrations of the studied neurotransmitters were found between genotypes. After KCl perfusion, significantly higher increases in NE, 5-HT, and DA release were found in KO compared with WT mice. No differences in the evoked release of ACh and Hist in the PFC were found between genotypes. The present results demonstrate that genetic deletion of OX2 receptors differentially modulates extracellular concentrations of distinct neurotransmitters in the somatodendritic region vs. a nerve terminal region of the orexinergic neurons. In the hypothalamus, an inhibitory role of the OX2 receptors in modulating basal concentrations of NE, ACh, and Hist was revealed, which probably accounts for the reduced responsiveness to KCl as well. In the PFC, the evoked release of the monoamines NE, 5-HT, and DA seems to be controlled negatively by OX2 receptors.

In vitro and in vivo evidence for a lack of interaction with dopamine D2 receptors by the metabotropic glutamate 2/3 receptor agonists 1S,2S,5R,6S-2-aminobicyclo[3.1.0]hexane-2,6-bicaroxylate monohydrate (LY354740) and (-)-2-oxa-4-aminobicyclo[3.1.0] Hexane-4,6-dicarboxylic acid (LY379268)

Some recently published in vitro studies with two metabotropic glutamate 2/3 receptor (mGluR(2/3)) agonists [(-)-2-oxa-4-aminobicyclo[3.1.0] hexane-4,6-dicarboxylic acid (LY379268) and 1S,2S,5R,6S-2-aminobicyclo[3.1.0]hexane-2,6-bicaroxylate monohydrate (LY354740)] suggest that these compounds may also directly interact with dopamine (DA) D(2) receptors. The current in vitro and in vivo studies were undertaken to further explore this potential interaction with D(2) receptors. LY379268 and LY354740 failed to inhibit D(2) binding in both native striatal tissue homogenates and cloned receptors at concentrations up to 10 microM. LY379268 and LY354740 (up to 10 microM) also failed to stimulate [(35)S]GTPgammaS binding in D(2L)- and D(2S)-expressing clones in the presence of NaCl or N-methyl-d-glucamine. In an in vivo striatal D(2) receptor occupancy assay, LY379268 (3-30 mg/kg) or LY354740 (1-10 mg/kg) failed to displace raclopride (3 microg/kg i.v.), whereas aripiprazole (10-60 mg/kg) showed up to 90% striatal D(2) receptor occupancy. LY379268 (10 mg/kg) and raclopride (3 mg/kg) blocked d-amphetamine and phencyclidine (PCP)-induced hyperactivity in wild-type mice. However, the effects of LY379268 were lost in mGlu(2/3) receptor knockout mice. In DA D(2) receptor-deficient mice, LY379268 but not raclopride blocked both PCP and d-amphetamine-evoked hyperactivity. In the striatum and nucleus accumbens, LY379268 (3 and 10 mg/kg) was without effect on the DA synthesis rate in reserpinized rats and also failed to prevent S-(-)-3-(3-hydroxyphenyl)-N-propylpiperidine-induced reductions in DA synthesis rate. Taken together, the current data fail to show evidence of direct DA D(2) receptor interactions of LY379268 and LY354740 in vitro or in vivo. Instead, these results provide further evidence for a novel antipsychotic mechanism of action for mGluR(2/3) agonists.

Neurochemical and behavioral profiling of the selective GlyT1 inhibitors ALX5407 and LY2365109 indicate a preferential action in caudal vs. cortical brain areas

Selective inhibitors of the glycine transporter 1 (GlyT1) have been implicated in central nervous system disorders related to hypoglutamatergic function such as schizophrenia. The selective GlyT1 inhibitors ALX5407 (NFPS) and LY2365109 {[2-(4-benzo[1,3]dioxol-5-yl-2-tert-butylphenoxy)ethyl]-methylamino}-acetic acid increased cerebrospinal fluid levels of glycine and potentiated NMDA-induced increases in dialysate levels of neurotransmitters in the prefrontal cortex (PFC) and the striatum. However, higher doses produced both stimulatory and inhibitory effects on motor performance and impaired respiration, suggesting significant involvement of cerebellar and brain stem areas. A dual probe microdialysis study showed that ALX5407 transiently elevated extracellular levels of glycine in the PFC with more sustained increases in the cerebellum. In support of these findings, immuno-staining with pan-GlyT1 and GlyT1a antibodies showed a higher abundance of immunoreactivity in the brain stem/cerebellum as compared to the frontal cortical/hippocampal brain areas in four different species studied, including the mouse, rat, monkey and human. In addition, the inhibitory effects of ALX5407 on cerebellar levels of cGMP in the mouse could be reversed by the glycine A receptor antagonist strychnine but not the glycine B receptor antagonist L-701324. We propose that the adverse events seen with higher doses of ALX5407 and LY2365109 are the result of high GlyT1 inhibitory activity in caudal areas of the brain with sustained elevations of extracellular glycine. High levels of glycine in these brain areas may result in activation of strychnine-sensitive glycine A receptors that are inhibitory on both motor activity and critical brain stem functions such as respiration.

Evidence for the role of metabotropic glutamate (mGlu)2 not mGlu3 receptors in the preclinical antipsychotic pharmacology of the mGlu2/3 receptor agonist (-)-(1R,4S,5S,6S)-4-amino-2-sulfonylbicyclo[3.1.0]hexane-4,6-dicarboxylic acid (LY404039)

(-)-(1R,4S,5S,6S)-4-amino-2-sulfonylbicyclo[3.1.0]hexane-4,6-dicarboxylic acid (LY404039) is a potent and selective group II metabotropic glutamate [(mGlu)2 and mGlu3] receptor agonist for which its prodrug LY2140023 [(1R,4S,5S,6S)-2-thiabicyclo[3.1.0]-hexane-4,6-dicarboxylic acid,4-[(2S)-2-amino-4-(methylthio)-1-oxobutyl]amino-, 2,2-dioxide monohydrate] has recently been shown to have efficacy in the treatment of the positive and negative symptoms of schizophrenia. In this article, we use mGlu receptor-deficient mice to investigate the relative contribution of mGlu2 and mGlu3 receptors in mediating the antipsychotic profile of LY404039 in the phencyclidine (PCP) and d-amphetamine (AMP) models of psychosis. To further explore the mechanism of action of LY404039, we compared the drugs' ability to block PCP-induced hyperlocomotion to that of atypical antipsychotics in wild-type and mice lacking mGlu2/3 receptors. In wild-type animals, LY404039 (3-30 mg/kg i.p.) significantly reversed AMP (5 mg/kg, i.p.)-induced increases in ambulations, distance traveled, and reduced time spent at rest. LY404039 reversed PCP (7.5 mg/kg i.p.)-evoked behaviors at 10 mg/kg. The antipsychotic-like effects of LY404039 (10 mg/kg i.p.) on PCP and AMP-evoked behavioral activation were absent in mGlu2 and mGlu2/3 but not in mGlu3 receptor-deficient mice, indicating that the activation of mGlu2 and not mGlu3 receptors is responsible for the antipsychotic-like effects of the mGlu2/3 receptor agonist LY404039. In contrast, the atypical antipsychotic drugs clozapine and risperidone inhibited PCP-evoked behaviors in both wild-type and mGlu2/3 receptor-deficient mice. These data demonstrate that the antipsychotic-like effects of the mGlu2/3 receptor agonist LY404039 in psychostimulant models of psychosis are mechanistically distinct from those of atypical antipsychotic drugs and are dependent on functional mGlu2 and not mGlu3 receptors.

Pharmacological characterization of cGMP regulation by the biarylpropylsulfonamide class of positive, allosteric modulators of alpha-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid receptors

The biarylpropylsulfonamide class of alpha-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid (AMPA) potentiators represented by N-2-(4-(4-cyanophenol)phenol)propyl-2-propanesulfonamide (LY404187) and (R)-4'-[1-fluoro-1-methyl-2-(propane-2-sulfonylamino)-ethyl]-biphenyl-4-carboxylic acid methylamide (LY503430) are positive, allosteric AMPA receptor activators, which enhance AMPA receptor-mediated neurotransmission by reducing desensitization of the ion channel. Although these compounds have efficacy in in vivo rodent models of cognition, depression, and Parkinson's disease, little is known about biochemical pathways activated by these agents. Given the well established regulation of the nitric oxide/cGMP pathway by excitatory neurotransmission, the current study characterized AMPA receptor potentiator-mediated cGMP response in mouse cerebellum. Acute treatment by both LY404187 and LY503430 [2.0, 5.0, or 10 mg/kg subcutaneously (s.c.)] elevated basal cerebellar cGMP levels in a dose-dependent manner. Pretreatment with the noncompetitive, allosteric AMPA receptor-selective antagonist 7H-1,3-dioxolo[4,5-h][2,3]benzodiazepine-7-carboxamide, 5-(4-aminophenyl)-8,9-dihydro-N,8-dimethyl-monohydrochloride-(9CI) (GYKI 53655) [3.0 mg/kg intraperitoneally (i.p.)], completely blocked the effect of LY404187, demonstrating that activation of AMPA receptors induces cGMP levels. Interestingly, pretreatment with the N-methyl-d-aspartate (NMDA) open channel blocker dizocilpine (0.3 and 1.0 mg/kg i.p.) also abolished the AMPA receptor potentiator-mediated cGMP accumulation, indicating that activation of AMPA receptors leads to NMDA receptor-mediated transmission involved in cGMP regulation. Pharmacological augmentation of the endogenous glutamate tone via the alkaloid harmaline (20-60 mg/kg i.p.) synergized with AMPA potentiator activity and provided further direct evidence of in vivo allosteric activation of AMPA receptors by LY404187. The synergism between harmaline and LY404187 was specific, since cGMP accumulation induced by foot-shock stress was not augmented by the AMPA receptor potentiator. Taken together, these data indicate that the cGMP system may play an important role in pharmacological efficacy of the biarylpropylsulfonamide class of AMPA receptor potentiators.

Effect of the attention deficit/hyperactivity disorder drug atomoxetine on extracellular concentrations of norepinephrine and dopamine in several brain regions of the rat

Atomoxetine is a selective inhibitor of norepinephrine transporters and is currently being used in the pharmacotherapy of attention deficit/hyperactivity disorder (ADHD). We have previously shown that atomoxetine increased extracellular (EX) concentrations of norepinephrine and dopamine in prefrontal cortex, but unlike the psychostimulant methylphenidate, did not alter dopamine(EX) in nucleus accumbens or striatum. Using the in vivo microdialysis technique in rat, we investigated the effects of atomoxetine on norepinephrine(EX) and dopamine(EX) concentrations in several other brain regions and also evaluated the role of inhibitory autoreceptors on atomoxetine-induced increases of norepinephrine(EX) concentrations. Atomoxetine (3mg/kg i.p.) increased norepinephrine(EX) robustly in prefrontal cortex, occipital cortex, lateral hypothalamus, dorsal hippocampus and cerebellum, suggesting that norepinephrine(EX) is increased throughout the brain by atomoxetine. In lateral hypothalamus and occipital cortex where dopamine(EX) was quantifiable, atomoxetine did not increase dopamine(EX) concentrations, in contrast to parallel increases of norepinephrine(EX) and dopamine(EX) in prefrontal cortex, indicating a unique effect in prefrontal cortex. Administration of the alpha(2)-adrenergic antagonist idazoxan 1h after atomoxetine resulted in increases in prefrontal cortical norepinephrine efflux greater than either compound alone, indicating an attenuating effect of the adrenergic autoreceptors on norepinephrine efflux.

The Dopamine Stabilizers (S)-(-)-(3-Methanesulfonyl-phenyl)-1-propyl-piperidine [(-)-OSU6162] and 4-(3-Methanesulfonylphenyl)-1-propyl-piperidine (ACR16) Show High in Vivo D2Receptor Occupancy, Antipsychotic-Like Efficacy, and Low Potential for Motor Side Effects in the Rat

"Dopamine stabilizers" are a new class of compounds that have the ability to reverse both hypo- as well as hyperdopaminergia in vivo. This class, exemplified by the phenylpiperidines (S)-(-)-3-(3-methanesulfonyl-phenyl)-1-propyl-piperidine [(-)-OSU6162] and 4-(3-methanesulfonyl-phenyl)-1-propyl)-piperidine [ACR16] although lacking high in vitro binding affinity for dopamine D2 receptor [(-)-OSU6162, Ki = 447 nM; ACR16, Ki > 1 microM], shows functional actions, suggestive of their interaction. Hence, we evaluated in vivo D2 occupancy of these agents in rats and correlated it to observed effects in a series of behavioral, neurochemical, and endocrine models relevant to the dopamine system and antipsychotic effect. Both (-)-OSU6162 and ACR16 showed robust dose-dependent striatal D2 occupancy with ED50 values of 5.27 and 18.99 mg/kg s.c., respectively, and functional assays showed no partial agonism. Over an occupancy range of 37 to 87% (3-60 mg/kg) for (-)-OSU6162 and 35 to 74% (10-60 mg/kg) for ACR16, we observed both inhibitory (amphetamine-induced locomotor activity) and stimulatory effects (in habituated rats). Haloperidol, over a similar occupancy range (33-78%), potently inhibited psychostimulant activity and induced catalepsy, but it failed to activate habituated animals. In the conditioned avoidance response assay, ACR16 was clearly more efficacious than (-)-OSU6162. In addition, both these compounds demonstrated significant preferential Fos induction in the nucleus accumbens compared with the dorsolateral striatum, a strong predictor of atypical antipsychotic efficacy. The results suggest that dopamine stabilizers exhibit locomotor stabilizing as well as antipsychotic-like effects, with low motor side effect liability, in a dose range that corresponds to high D2 in vivo occupancy.

Dopamine agonist-induced yawning in rats: a dopamine D3 receptor-mediated behavior

A specific role for the dopamine D3 receptor in behavior has yet to be elucidated. We now report that dopamine D2/D3 agonists elicit dose-dependent yawning behavior in rats, resulting in an inverted U-shaped dose-response curve. A series of experiments was directed toward the hypothesis that the induction of yawning is a D3 receptor-mediated effect, whereas the inhibition of the yawning observed at higher doses is due to competing D2 receptor activity. We compared several dopaminergic agonists with a range of in vitro D3 selectivity, including PD-128,907 [(S)-(+)-(4aR, 10bR)-3,4,4a,10b-tetrahydro-4-propyl-2H,5H-[1]benzopyrano-[4,3-b]-1,4-oxazin-9-ol HCl], PD-128,908 [(R)-(-)-(4aS,10bS)-3,4,4a,10b-tetrahydro-4-propyl-2H,5H-[1]benzopyrano-[4,3-b]-1,4-oxazin-9-ol HCl], quinelorane [(5aR-trans)-5,5a,6,7,8, 9,9a,10-octahydro-6-propylpyrido[2,3-g]quinazolin-2-amine dihydrochloride], pramipexole (N'-propyl-4,5,6,7-tetrahydrobenzothiazole-2,6-diamine), 7-OH-DPAT [(+/-)-7-hydroxy-2-dipropylaminotetralin HBr], quinpirole [trans-(-)-(4aR)-4,4a,5,6,7,8, 8a,9-octahydro-5-propyl-1H-pyrazolo[3,4-g]quinoline HCl], bromocriptine [(+)-2-bromo-12'-hydroxy-2'-(1-methylethyl)-5'-(2-methylpropyl) ergotaman-3',6'-18-trione methanesulfonate], and apomorphine [(R)-(-)-5,6,6a,7-tetrahydro-6-methyl-4H-dibenzo-[de,g]quinoline-10,11-diol HCl] with respect to their ability to induce yawning in rats. A series of D2/D3 antagonists differing in selectivity for D3 over D2 receptors were evaluated for their ability to alter the effects of the dopamine agonists. The antagonists L-741,626 (3-[4-(4-chlorophenyl)-4-hydroxypiperidin-l-yl]methyl-1H-indole), haloperidol (4-[4-(4-chlorophenyl)-4-hydroxy-1-piperidinyl]-1-(4-fluorophenyl)-1-butanone HCl), nafadotride (N-[(1-butyl-2-pyrrolidinyl)methyl]-4-cyano-1-methoxy-2-naphtha-lenecarboxamide), U99194 (2,3-dihydro-5,6-dimethoxy-N,N-dipropyl-1H-inden-2-amine maleate), SB-277011A (trans-N-[4-[2-(6-cyano-1,2,3,4-tetrahydroisoquinolin-2-yl)ethyl]cyclohexyl]-4-quinolinecarboxamide), and PG01037 (N-{4-[4-(2,3-dichlorophenyl)-piperazin-1-yl]-trans-but-2-enyl}-4-pyridine-2-yl-benzamide HCl) were used to determine effects on dose-response curves for D2/D3 agonist-induced yawning. In addition, the potential contribution of cholinergic and/or serotonergic mechanisms to the yawning response was investigated using a series of pharmacological tools including scopolamine [(a,S)-a-(hydroxymethyl)benzeneacetic acid (1a,2b,4b,5a,7b)-9-methyl-3-oxa-9-azatricyclo[3.3.1.02,4]-non7-yl ester hydrobromide], mianserin (1,2,3,4,10,14b-hexahydro-2-methyldibenzo[c,f]pyrazino[1,2-a]azepine HCl), and the D3-preferring antagonists nafadotride, U99194, SB-277011A, and PG01037 to differentially modulate yawning induced by PD-128,907, physostigmine [(3aS)-cis-1,2,3,3a,8,8a-hexahydro-1,3a,8-trimethylpyrrolo[2,3-b]indol-5-ol methylcarbamate hemisulfate], and N-[3-(trifluoromethyl)phenyl]piperazine HCl. The results of these experiments provide convergent evidence that dopamine D2/D3 agonist-induced yawning is a D3 agonist-mediated behavior, with subsequent inhibition of yawning being driven by competing D2 agonist activity. Thus, dopamine agonist-induced yawning may represent an in vivo method for selectively identifying D3 and D2 receptor-mediated activities.

2,3,4,5-tetrahydro- and 2,3,4,5,11,11a-hexahydro-1H-[1,4]diazepino[1,7-a]indoles: new templates for 5-HT(2C) agonists

The design and synthesis of the novel 2,3,4,5-tetrahydro-1H-[1,4]diazepino[1,7-a]indole 5 is described. This azepinoindole has excellent affinity for 5-HT(2C) (K(i) 4.8 nM) and modest selectivity over 5-HT(2A) ( approximately 4-fold). Several N- and C(11)-substituted analogues of 5 were prepared, as were a number of biaryl indoline derivatives. The anxiolytic potential for the azepinoindole template 5 is demonstrated by activity in a mouse shock-aggression assay.

PNU-96391A (OSU6162) antagonizes the development of behavioral sensitization induced by dopamine agonists in a rat model for Parkinson's disease

PNU-96391A is a weak dopamine (DA) D(2) receptor antagonist with behavioral stabilizing properties. Previous experiments revealed that PNU-96391A antagonizes the expression of L-DOPA induced behavioral sensitization (dyskinesias) in lesioned primates without inducing akinesia or reducing the anti-Parkinsonian efficacy of L-DOPA. This study evaluated the ability of PNU-96391A to block the development of DA agonist-induced behavioral sensitization in rats with unilateral 6-OH-DA lesions of the median forebrain bundle. Repeated twice daily treatment with L-DOPA and the decarboxylase inhibitor benserazide (15 and 5 mg/kg, IP, respectively), or quinpirole (D(2)/D(3) agonist, 0.1 mg/kg, SC) increased the contralateral rotations measured on day 7 and 14 as compared to day 1. PNU-96391A (10-60 mg/kg, SC, bid.) antagonized the development of behavioral sensitization induced by both agonists. The basal activity of L-DOPA was not affected while a reduction of quinpirole-induced rotations was observed after 30-60 mg/kg, SC of PNU-96391A. Neurochemical analyses confirmed >99 % reductions of striatal DA levels, unilaterally. Concomitant treatment with PNU-96391A and L-DOPA did not affect plasma levels of PNU-96391A indicating that the effects observed are not related to pharmacokinetic interactions. These results suggest that PNU-96391A could be therapeutically useful to prevent the development of behavioral sensitization induced by DA agonists.

Dopamine D(3) receptor antagonists. 1. Synthesis and structure-activity relationships of 5,6-dimethoxy-N-alkyl- and N-alkylaryl-substituted 2-aminoindans

5,6-Dimethoxy-2-(N-dipropyl)-aminoindan (3, PNU-99194A) was found to be a selective dopamine D(3) receptor antagonist with potential antipsychotic properties in animal models. To investigate the effects of nitrogen substitution on structure-activity relationships, a series of 5,6-dimethoxy-N-alkyl- and N-alkylaryl-substituted 2-aminoindans were synthesized and evaluated in vitro for binding affinity and metabolic stability. The results indicate that substitution at the amine nitrogen of the 2-aminoindans is fairly limited to the di-N-propyl group in order to achieve selective D(3) antagonists. Thus, combinations of various alkyl groups were generally inactive at the D(3) receptor. Although substitution with an N-alkylaryl or N-alkylheteroaryl group yields compounds with potent D(3) binding affinity, the D(2) affinity is also enhanced, resulting in a less than 4-fold preference for the D(3) receptor site, and no improvements in metabolic stability were noted. A large-scale synthesis of the D(3) antagonist 3 has been developed that has proven to be reproducible with few purification steps. The improvements include the use of 3,4-dimethoxybenzaldehyde as a low-cost starting material to provide the desired 5,6-dimethoxy-1-indanone 5c in good overall yield (65%) and the formation of a soluble silyl oxime 17 that was reduced efficiently with BH(3).Me(2)S. The resulting amino alcohol was alkylated and then deoxygenated using a Lewis acid and Et(3)SiH to give the desired product 3 in good overall yield of ( approximately 65%) from the indanone 5c.

Common discriminative stimulus properties in rats of muscarinic antagonists, clozapine and the D3 preferring antagonist PNU-99194a: an analysis of possible mechanisms

Dopamine D3 receptors have been implicated in the aetiology of schizophrenia and the actions of antipsychotic drugs. The initial studies reported here assessed the involvement of such receptors in the in vivo actions of the atypical antipsychotic clozapine and the putative D3-preferring antagonist PNU-99194A in drug discrimination assays. Rats trained to discriminate clozapine consistently generalized to PNU-99194A in two separate studies. However, four other putative D3-preferring antagonists (PD 152255, (+)-S14297, nafadotride and (+)-AJ 76) did not induce generalization to clozapine. In rats trained to discriminate PNU-99194A, which has been suggested to induce a stimulus mediated specifically by D3 antagonism, the D3-preferring antagonist (+)-UH 232 and clozapine both induced full generalization. However, the PNU-99194A-trained animals also generalized fully to the muscarinic antagonists scopolamine and trihexyphenidyl. A possible explanation for the symmetrical generalization observed between clozapine and PNU-99194A is that these drugs have common muscarinic antagonist actions, since muscarinic antagonists have been reported to substitute for clozapine in numerous prior studies. However, in vitro receptor binding studies with M1-M5 receptors indicated that (with the possible exception of the M4 receptor), no muscarinic receptor subtype had high affinity for both clozapine, PNU-99194A and scopolamine. In addition, other binding studies indicated that whereas clozapine and PNU-99194A had high affinity for the D3 receptor, scopolamine did not. It is therefore concluded that: (1) The generalization seen between clozapine, PNU-99194A and muscarinic antagonists may be mediated by common effects 'downstream' from either muscarinic or D3 receptors; (2) D3 antagonism does not play a critical role in the clozapine stimulus (since D3-preferring antagonists did not consistently induce generalization to clozapine); (3) although D3 antagonism plays a role in the PNU-91994A stimulus (since the D3-preferring antagonist (+)-UH 232 induced full generalization, in accord with results from prior studies with other D3-preferring antagonists, the PNU-99194A stimulus also has commonalities with that induced by muscarinic antagonists and clozapine. The in vivo differences observed between PNU-99194A and other D3-preferring antagonists should be borne in mind when this agent is used as a tool to study D3 receptor functioning in vivo. The similarities between the PNU-99194A and clozapine stimuli suggest tentatively that compounds with a profile like PNU-99194A may have antipsychotic actions similar to clozapine. Some preclinical data are suggestive of such effects of PNU-99194A.

[Hereditary thyroid cancer can be cured by prophylactic surgery]

Multiple endocrine neoplasia type 2 (MEN 2) is a rare syndrome in which the consequences for the patient and family members are considerable. Mutation analysis of the RET proto-oncogene is crucial for decision-making regarding each patient. Today, carriers of MEN 2 mutations should be offered prophylactic thyroidectomy with the potential to eliminate the risk for potentially lethal medullary thyroid carcinoma (MTC). Here, we present the first Swedish experience of such operations performed mainly on the basis of genetic analysis. Twenty patients underwent total thyroidectomy at a mean age of 13.5 (6-43) years. In all cases, either manifest MTC (n = 11) or C-cell hyperplasia was found. So far, no patient has any sign of recurrence or developmental insufficiency at 1-5 years follow-up. As the medical and ethical problems in this group of patients are substantial, and as the operations are performed in otherwise healthy children, they should be treated at centers with adequate multidisciplinary expertise and competence.

BACE knockout mice are healthy despite lacking the primary beta-secretase activity in brain: implications for Alzheimer's disease therapeutics

Alzheimer's disease (AD) is a neurodegenerative disorder characterized by accumulation of amyloid plaques and neurofibrillary tangles in the brain. The major components of plaque, beta-amyloid peptides (Abetas), are produced from amyloid precursor protein (APP) by the activity of beta- and gamma-secretases. beta-secretase activity cleaves APP to define the N-terminus of the Abeta1-x peptides and, therefore, has been a long- sought therapeutic target for treatment of AD. The gene encoding a beta-secretase for beta-site APP cleaving enzyme (BACE) was identified recently. However, it was not known whether BACE was the primary beta-secretase in mammalian brain nor whether inhibition of beta-secretase might have effects in mammals that would preclude its utility as a therapeutic target. In the work described herein, we generated two lines of BACE knockout mice and characterized them for pathology, beta-secretase activity and Abeta production. These mice appeared to develop normally and showed no consistent phenotypic differences from their wild-type littermates, including overall normal tissue morphology and brain histochemistry, normal blood and urine chemistries, normal blood-cell composition, and no overt behavioral and neuromuscular effects. Brain and primary cortical cultures from BACE knockout mice showed no detectable beta-secretase activity, and primary cortical cultures from BACE knockout mice produced much less Abeta from APP. The findings that BACE is the primary beta-secretase activity in brain and that loss of beta-secretase activity produces no profound phenotypic defects with a concomitant reduction in beta-amyloid peptide clearly indicate that BACE is an excellent therapeutic target for treatment of AD.

Direct injection of human plasma samples after ultrafiltration into programmed temperature vaporiser-gas chromatography-mass spectrometry with packed liner

The direct injection of plasma samples after ultrafiltration into a gas chromatograph using a packed injector liner was investigated. Ropivacaine, a local anaesthetic of the amide type and one of its metabolites (PPX) were used as model compounds in this evaluation. Phosphoric acid was added to the plasma to minimize the protein binding. After ultrafiltration, 50 microl of the sample was directly injected into the chromatographic system. No interfering peaks or damage to the GC or MS system were observed using ultrafiltration as a sample-preparation method. The validation of the method demonstrated good linearity and selectivity. The limits of quantification were 1.1 nM (301 pg/ml) and 1.4 nM (325 pg/ml) for ropivacaine and PPX, respectively. The liner had to be changed after 20 injections.

Effects of acute and repeated treatment with a novel dopamine D2 receptor ligand on L-DOPA-induced dyskinesias in MPTP monkeys

(S)-(-)-3-(3-(methylsulfonyl)phenyl)-1-propylpiperidine ((-)-OSU6162) is a phenylpiperidine derivative which exhibits low affinity to the dopamine D2 receptor in vitro. However, in vivo, positron emission tomography scanning studies show that the compound displaces the selective dopamine D2 receptor antagonist, raclopride. We have evaluated, in this study, the effect of (-)-OSU6162, on L-3,4-dihydroxyphenylalanine (L-DOPA)-induced dyskinesias in a primate model of Parkinson's disease. Five 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP)-treated cynomolgus monkeys with a stable parkinsonian syndrome and reproducible dyskinesias to L-DOPA were used in this study. The monkeys were housed in observation cages equipped with an electronic motility monitoring system. They were injected subcutaneously (s.c.) with L-DOPA methyl ester (125 mg per animal) plus benserazide (50 mg per animal; L-DOPA/benserazide) alone or in combination with (-)-OSU6162 (1.0, 3.0, 6.0 or 10 mg/kg, s.c.). Subcutaneous injection of sterile saline was used as control. L-DOPA/benserazide increased locomotion and improved parkinsonism but also induced dyskinesias. Co-administration of (-)-OSU6162 with L-DOPA/benserazide produced a significant reduction in L-DOPA-induced dyskinesias. This improvement in L-DOPA-induced dyskinesias occurred mainly at the onset of the L-DOPA/benserazide effect as reflected by an increase in the duration of the "ON" state without dyskinesias up to 3.4 fold after (-)-OSU6162 co-administration as compared to L-DOPA/benserazide alone. The anti-dyskinetic effect of (-)-OSU6162 was maintained during 14 days and no tolerance to this effect was observed. Our data suggests that (-)-OSU6162 could be of significant clinical value to reduce L-DOPA-induced dyskinesias in fluctuating advanced Parkinson's disease patients.

Long term experience after subtotal adrenalectomy for multiple endocrine neoplasia type IIa

OBJECTIVE

To evaluate the long-term results after subtotal adrenalectomy in patients with multiple endocrine neoplasia type IIa (MEN IIa).

DESIGN

Retrospective study.

SETTING

University Hospital, Sweden.

SUBJECTS

Five patients who underwent partial adrenalectomy between 1985 and 1989.

INTERVENTIONS

Subtotal adrenalectomy with a rim of cortical tissue left in situ.

MAIN OUTCOME MEASURES

Follow up by interview, measurement of cortisol and catecholamine excretion in urine, and cortisol concentration in serum in response to stimulation with ACTH.

RESULTS

Three patients took no corticosteroids regularly, but during upper respiratory tract infections, or periods of severe stress they took 25 mg cortisone acetate daily. This is confirmed by their normal values of 24 hour urinary cortisol excretion and subnormal responses to an ACTH-stimulation test. The fourth and fifth patients had low concentrations of endogenous corticosteroids postoperatively, which is being replaced with 25 mg cortisone acetate daily. Postoperatively all five patients had low urinary adrenaline excretion.

CONCLUSION

Subtotal adrenalectomy in patients with MEN IIa resulted in basal endogenous corticosteroids within the reference range in three of five patients. There was no evidence of reduced adrenocortical function with time, nor were there any signs of recurrence of the pheochromocytoma.

The dopamine D3 receptor antagonist PNU-99194A fails to block (+)-7-OH-DPAT substitution for D-amphetamine or cocaine

The present study examined the role of dopamine D3 receptor actions in the stimulus generalization produced by (+)-7-OH-DPAT in rats trained to discriminate either D-amphetamine or cocaine from saline. Twelve male Sprague-Dawley rats were trained to discriminate D-amphetamine (1.0 mg/kg) and 12 rats were trained to discriminate cocaine (5.0 mg/kg) from saline in a two-choice, water-reinforced operant procedure. Stimulus generalization tests were administered with the D3 receptor-preferring agonist, (+)-7-hydroxy-N, N-di-n-propyl-2-aminotetralin ((+)-7-OH-DPAT, 0.01-1.0 mg/kg) as well as the D3-preferring antagonist, 5,6-di-methoxy-2-(dipropylamino)indan-hydrochloride (PNU-99194A, 5-40 mg/kg). PNU-99194A (10-40 mg/kg) was also administered in combination with the training dose of D-amphetamine or cocaine to test for antagonism of each training drug cue. Finally, to assess the role of D3 receptor actions in the stimulus generalization produced by (+)-7-OH-DPAT (0.1 mg/kg), PNU-99194A (10, 20 mg/kg) was tested in combination with this compound in each training group. The results showed complete stimulus generalization with (+)-7-OH-DPAT in rats trained to discriminate D-amphetamine, although only partial stimulus generalization was observed with this compound in rats trained to discriminate cocaine. PNU-99194A produced partial substitution for both training drugs, and failed to block the discriminative stimulus effects of either D-amphetamine or cocaine. Moreover, this compound failed to block the stimulus generalization produced by (+)-7-OH-DPAT in rats trained to discriminate D-amphetamine. These results question the importance of D3 receptor actions in the discriminative stimulus effects of psychostimulants and their similarities to (+)-7-OH-DPAT.

Discriminative stimulus properties of the dopamine D3 antagonist PNU-99194A

It was recently documented that the relatively selective dopamine D3 receptor antagonist, PNU-99194A, is capable of establishing discriminative stimulus control in rats and that the discriminative cue associated with this compound is not similar to that produced by psychostimulants. The present experiment further characterized the discriminative stimulus properties of PNU-99194A by examining several other dopaminergic agents for stimulus generalization in 23 male Sprague-Dawley rats trained to discriminate 10 mg/kg PNU-99194A (SC, 15 min) from vehicle in a two-choice discrimination procedure under an FR10 schedule of food reinforcement. Rats achieved a criterion of ten consecutive sessions with correct lever choice after a median of 35.5 sessions (range 23-78). In substitution tests, the non-selective D2 receptor antagonist, haloperidol (0.01- 0.1 mg/kg), and the mixed D2/D3 antagonists, amisulpiride (3.2-32 mg/kg) and sulpiride (32-200 mg/kg), failed to produce stimulus generalization, while the D3-preferring antagonists, (-)-DS121 (1-10 mg/kg) and (+)-AJ76 (3.2-32 mg/kg), produced complete stimulus generalization. Direct and indirect DA agonists, including apomorphine (0.01-0.32 mg/kg) and d-amphetamine (0.1-1 mg/kg), the D1 agonist SKF38393 (10-100 mg/kg), the D2 selective agonist PNU-95666E (0.32-3.2 mg/kg) and the D3-preferring agonist pramipexole (0.032-1 mg/kg), all produced non-significant amounts of drug-appropriate responding and significantly reduced response rate. It is concluded that PNU-99194A produces a distinctive subjective cue which is probably based on D3 receptor antagonism.

The role of dopamine D4 receptor in the induction of behavioral sensitization to amphetamine and accompanying biochemical and molecular adaptations

Our studies examined the role of dopamine D4 receptors in the induction of behavioral sensitization to amphetamine (Amp) and accompanying neurochemical and molecular adaptive responses using a highly selective D4 antagonist, PNU-101387G. Behavioral sensitization to an acute challenge of Amp (2 mg/kg, s.c.) was observed in rats pretreated with five daily doses of Amp (2 mg/kg/d, s.c.) followed by 7-day withdrawal. Interestingly, coadministration of PNU-101387G with Amp during pretreatment completely blocked the sensitized response to an acute Amp challenge. The behavioral sensitization and its blockade by the D4 antagonist were observed in the absence of significant differences in cerebellar Amp levels among the various pretreatment groups. Accompanying behavioral sensitization were two postsynaptic neuroadaptive responses: reduction in the ability of Amp to induce c-fos gene expression in the infralimbic/ventral prelimbic cortex and NT/N mRNA in the accumbal shell. However, concurrent blockade of D4 receptors during Amp pretreatment prevented the refractoriness in c-fos and NT/N responsiveness to acute Amp. We observed also a presynaptic neuroplastic response associated with the behavioral sensitization: a significant augmentation in the ability of Amp to increase extracellular dopamine concentrations in the nucleus accumbens shell. As with the behavioral sensitization and associated postsynaptic adaptive responses, concurrent administration of PNU-101387G with Amp during pretreatment blocked the augmentation in Amp-induced dopamine release. Taken together, these data demonstrate that dopamine D4 receptors play an important role in the induction of behavioral sensitization to Amp and accompanying adaptations in pre- and postsynaptic neural systems associated with the mesolimbocortical dopamine projections.

Assessment of the discriminative stimulus effects of the D3 dopamine antagonist PNU-99194A in rats: comparison with psychomotor stimulants

The present study examined the discriminative stimulus effects of the D3 dopamine receptor antagonist PNU-99194A [5,6-di-methoxy-2-(dipropylamino)indan-hydrochloride] in male Sprague-Dawley rats. Eight rats were trained to discriminate cocaine (10 mg/kg, i.p.) from saline in a two-choice, water-reinforced drug discrimination procedure. In tests of stimulus generalization, PNU-99194A (1.25-40.0 mg/kg, s.c. and i.p.) did not substitute for cocaine. PNU-99194A (5.0-20 mg/kg) also did not significantly block the discrimination of cocaine (10 mg/kg), nor did it potentiate a low dose (1.25 mg/kg) of cocaine. A separate group of eight rats were trained to discriminate PNU-99194A from saline. These subjects met the discrimination criterion within an average of 68 (S.E.M. = 6.5) training sessions; the ED50 for PNU-99194A was 2.6 mg/kg. In stimulus generalization tests, cocaine (1.25-10 mg/kg) did not substitute for PNU-99194A, when administered by either i.p. or by s.c. injection. In addition, neither amphetamine (0.25-1.0 mg/kg) nor caffeine (8.0-64 mg/kg) produced stimulus generalization in these rats. These results indicate that D3 receptors do not play a critical role in the discriminative stimulus effects of cocaine. Furthermore, although PNU-99194A is capable of establishing and maintaining discriminative stimulus control in rats, the effects of this D3-preferring antagonist are dissimilar from those of psychomotor stimulants. Given the unique behavioral profile of D3 receptor antagonists, the potential utility of these agents as adjunctive treatments for psychostimulant abuse is discussed.

Interactions between cocaine and (-)-DS 121: studies with 2-deoxyglucose autoradiography and microdialysis in the rat brain

(-)-DS 121 [S-(-)-3-(3-cyanophenyl)-N-n-propyl piperidine], a dopamine autoreceptor preferring antagonist, has been shown to stimulate locomotor activity and induce conditioned place preference. However, the drug fails to facilitate intracranial self-stimulation or substitute for cocaine in cueing experiments, and it blocks cocaine self-administration. In the present study using 2-deoxyglucose autoradiography, (-)-DS 121 (at 50 but not 15 mg/kg i.p.) significantly and selectively increased local cerebral glucose utilization in the olfactory cortex, medial and lateral septum, hippocampal areas, substantia nigra pars reticulata, caudate, and mammillary body. Local cerebral glucose utilization was depressed in caudal areas of the cortex. Interestingly, however, both doses of (-)-DS 121 blocked the increases in local cerebral glucose utilization produced by 5 mg/kg i.v. cocaine. The present study also evaluated the effects of (-)-DS 121 of extracellular striatal dopamine levels using microdialysis in freely moving rats. By itself, 15 mg/kg of (-)-DS 121 increased extracellular striatal dopamine levels to approximately 300% of controls. Cocaine (5 mg/kg i.v.) produced a 370% increase in striatal dopamine levels. When rats were pretreated with (-)-DS 121, a subsequent dose of cocaine augmented the increase in extracellular striatal dopamine to 870% of controls. The results support the contention that (-)-DS 121 possesses weak cocaine-mimetic effects and that its antagonism of cocaine's subjective effects are due to interactions with dopamine at postsynaptic sites. It is hypothesized that, like other preferential autoreceptor antagonists, (-)-DS 121 may be useful as a pharmacotherapy in drug addiction.

Pharmacological characterization of U-101387, a dopamine D4 receptor selective antagonist

Dopamine D2-like receptors play an important role in the pharmacotherapy of psychotic disorders. Molecular and cellular techniques have identified distinct gene products (D2-long, D2-short, D3 and D4) displaying the D2 receptor pharmacology. However, the contribution of each subtype in antipsychotic effects of or their physiological role remain unclear. Here we describe the pharmacological effects of a selective D4 antagonist, U-101387. U-101387 displayed moderately high affinity (Ki = 10 nM) and selectivity for the dopamine D4.2 receptor expressed in clonal cell lines. It lacked measurable affinity for not only other dopamine receptors but also noradrenalin, serotonin and histamine receptor families (Ki > 2000 nM). It fully and dose-dependently antagonized quinpirole-induced cAMP inhibition (without producing any effect by itself) in stably transfected cells. U-101387 also displayed excellent oral bioavailability, brain penetration and other pharmacokinetic characteristics. Unlike classical neuroleptics (e.g., haloperidol), U-101387 neither blocked acute behavioral effects of amphetamine or apomorphine nor did it alter spontaneous locomotion by itself. Additionally, U-101387 was without effect in behavioral and biochemical tests predictive of extrapyramidal and neuroendocrine side effects. Consistent with the lack of autoreceptor function of D4, acute administration of U-101387 failed to alter dopamine neuronal firing by itself or reverse the inhibition produced by dopamine agonists and to affect monoamine turnover in areas innervated by the mesencephalic or hypothalamic dopamine neurons. However, U-101387 potently induced c-fos mRNA expression in the infralimbic/ventral prelimbic cortex to a level similar to that produced by the atypical antipsychotic, clozapine. This is consistent with the predominantly cortical distribution of the D4 receptor. Taken together, these results demonstrate that the D4-selective antagonist, U-101387, produces effects that are distinct from those of the nonselective D2 antagonists as well as D3-preferring agents. U-101387 offers a unique tool to understand the role of dopamine D4 receptors in diseases involving central dopamine systems.

Characterization of U-92016A as a selective, orally active, high intrinsic activity 5-hydroxytryptamine1A agonist

The purpose of the present study was to characterize U-92016A [(+)-R)-2-cyano-N,N-dipropyl-8-amino-6,7,8,9-tetrahydro-3H-benz[e] indole] as a 5-hydroxytryptamine (5-HT)1A receptor agonist and to compare its activity with that of standard 5-HT1A receptor agonists. U-92016A binds with high affinity to human 5-HT1A receptors expressed in Chinese hamster ovary cells (Ki = 0.2 nM). Radioligand binding studies also indicate that U-92016A is selective for the 5-HT1A receptor over other biogenic amine receptors. In Chinese hamster ovary cells expressing the human 5HT1A receptor, U-92016A decreased the forskolin-induced increase in cyclic AMP synthesis and had an intrinsic activity of 0.82 relative to 5-HT. U-92016A potently decreased rectal temperature in mice. The maximum temperature decrease was significantly greater than that observed for 8-hydroxy-di-n-propyl aminotetralin, buspirone, gepirone, ipsapirone or flesinoxan. U-92016A also elicited the 5-HT-mediated syndrome in rats and resulted in a dose-related decrease in 5-hydroxytryptophan accumulation. The compound also decreased arterial blood pressure in spontaneously hypertensive rats and inhibited sympathetic nerve activity in cats. In these assays U-92016A displayed excellent potency and a long duration of action. U-92016A also inhibited the firing of dorsal raphe 5-HT neurons and was active in two social interaction assays. The p.o. bioavailability of U-92016A was calculated to be 45%. Taken together, these data indicate that U-92016A is a metabolically stable, p.o. active 5-HT1A receptor agonist with an exceptionally high degree of intrinsic activity.