Discovery of (R)-(3-fluoropyrrolidin-1-yl)(6-((5-(trifluoromethyl)pyridin-2-yl)oxy)quinolin-2-yl)methanone (ABBV-318) and analogs as small molecule Nav1.7/ Nav1.8 blockers for the treatment of pain.

The voltage-gated sodium channel Nav1.7 is an attractive target for the treatment of pain based on the high level of target validation with genetic evidence linking Nav1.7 to pain in humans. Our effort to identify selective, CNS-penetrant Nav1.7 blockers with oral activity, improved selectivity, good drug-like properties, and safety led to the discovery of 2-substituted quinolines and quinolones as potent small molecule Nav1.7 blockers. The design of these molecules focused on maintaining potency at Nav1.7, improving selectivity over the hERG channel, and overcoming phospholipidosis observed with the initial leads. The structure-activity relationship (SAR) studies leading to the discovery of (R)-(3-fluoropyrrolidin-1-yl)(6-((5-(trifluoromethyl)pyridin-2-yl)oxy)quinolin-2-yl)methanone (ABBV-318) are described herein. ABBV-318 displayed robust in vivo efficacy in both inflammatory and neuropathic rodent models of pain. ABBV-318 also inhibited Nav1.8, another sodium channel isoform that is an active target for the development of new pain treatments.

ß2 -Adrenoceptor agonist activity of higenamine.

Higenamine was included in the World Anti-Doping Agency (WADA) Prohibited Substances and Methods List as a ß2 -adrenoceptor agonist in 2017, thereby resulting in its prohibition both in and out of competition. The present mini review describes the physiology and pharmacology of adrenoceptors, summarizes the literature addressing the mechanism of action of higenamine and extends these findings with previously unpublished in silico and in vitro work. Studies conducted in isolated in vitro systems, whole-animal preparations and a small number of clinical studies suggest that higenamine acts in part as a ß2 -adrenoceptor agonist. In silico predictive tools indicated that higenamine and possibly a metabolite have a high probability of interacting with the ß2 -receptor as an agonist. Stable expression of human ß2 -receptors in Chinese hamster ovary (CHO) cells to measure agonist activity not only confirmed the activity of higenamine at ß2 but also closely agreed with the in silico prediction of potency for this compound. These data confirm and extend literature findings supporting the inclusion of higenamine in the Prohibited List.

Improving Translational Research Outcomes for Opioid Use Disorder Treatments.

Purpose of Review: Pharmacotherapies are the most effective means of reducing the harms associated with opioid use disorder (OUD). Translational research seeking to develop novel medications to treat OUD has been challenging due to the complex etiology of addiction. Preclinical outcome measures are often behavioral, and it is difficult, if not impossible, to fully mirror the various emotional and cognitive processes that motivate opioid use in humans. The goal of the current narrative review was to summarize the translational progression of three potential medications for OUD, which had varying levels of success. Recent Findings: Memantine, lorcaserin, and lofexidine all showed promise in preclinical studies; however, only lofexidine was able to consistently replicate these findings in human subjects, and receive FDA approval. It was the authors' objective to use this review to identify areas of needed improvement in translational research for OUD. Summary: Preclinical studies vary significantly in their ability to forecast effectiveness in clinical trials. Among the various preclinical models, suppression of opioid self-administration appears to have the best predictive validity. As they model a mostly physiological phenomenon, preclinical assessments of opioid withdrawal also appear to have high predictive validity. In our review of the literature, the authors noted numerous examples of clinical trials that were underpowered, lack precision, and proper outcomes. Better-validated preclinical targets and improved design of proof-of-concept human studies should allow investigators to more efficiently develop and test medications for OUD.

ß-Phenylethylamine and various monomethylated and para-halogenated analogs. Acute toxicity studies in mice.

Phenylethylamine's acute toxic effects in a population of adult (10 to 12 weeks old; ∼30 g) Swiss male albino mice are significantly increased by para-position aromatic ring halogenation. LDLO, LD50, and LD100 values (mg/kg; x ± SEM) for p-F- (116.7 ± 3.3, 136.7 ± 1.7, and 160.0 ± 2.9), p-Br- (126.7 ± 3.3, 145.0 ± 2.9, and 163.3 ± 3.3), p-Cl- (133.3 ± 3.3, 146.7 ± 1.7, and 165.0 ± 2.9), and p-I-PEA (133.3 ± 3.3, 153.3 ± 1.7, and 168.3 ± 1.7), compared to PEA 203.3 ± 3.3, 226.7 ± 4.4, and 258.3 ± 8.8). Like PEA, the difference between LDLO and LD50, and LD50 and LD100 for individual amines were similar and in the range (10 to 20%). Toxicity variation between the various p-halogenatedPEAs also fell within a relatively narrow range (as a group: LDLO 116.7 ± 3.3 to 133.3 ± 3.3, LD50 136.7 ± 1.7 to 153.3 ± 1.7, and LD100 160.0 ± 2.9 to 168.3 ± 1.7 mg/kg). PEA methylation, (exception of its α-methyl derivative), results in relatively modest changes in acute toxicity. LDLO, LD50, and LD100 values (mg/kg; x ± SEM) for N-Me- (176.6 ± 3.3, 200.0 ± 2.9, and 221.7 ± 3.3), p-Me- (183.3 ± 3.3, 206.7 ± 3.3, and 225.0 ± 2.9), o-Me- (210.0 ± 5.8, 233.3 ± 3.3, and 258.3 ± 1.7), and ß-MePEA (220.0 ± 5.8, 243.3 ± 4.4, and 278.3 ± 44). Similar to PEA, and the p-HPEAs, the difference between LDLO and LD50 and LD50 and LD100 values for individual amines fell within a relatively narrow range (10 to 20%). Variation in toxicity among the methylatedPEAs also fell within a limited range (as a group: LDLO 176 ± 3.3 to 220 ± 5.8, LD50 200.0 ± 2.9 to 243.3 ± 4.4 and LD100 221.7 ± 3.3 to 278.3 ± 4.4 mg/kg). With the exception of PEA's methyl derivative (amphetamine) all the amines studied are rapidly metabolized by monoamine oxidase. This pharmacokinetics difference would help to explain the markedly higher amphetamine toxicity [(LDLO, LD50 and LD100 (mg/kg; x ± SEM) of 21.3 ± 0.9, 25.0 ± 0.6, and 29.3 ± 0.7, respectively)].

Abuse liability assessment for biologic drugs - All molecules are not created equal.

The development of novel drug candidates involves the thorough evaluation of potential efficacy and safety. To facilitate the safety assessment in light of global increases in prescription drug misuse/abuse, health authorities have developed guidance documents which provide a framework for evaluating the abuse liability of candidate therapeutics. The guidances do not distinguish between small molecules and biologics/biotherapeutics; however, there are key differences between these classes of therapeutics which are important drivers of concern for abuse. An analysis of these properties, including ability to distribute to the central nervous system, pharmacokinetic properties (e.g., half-life and metabolism), potential for off-target binding, and the physiochemical characteristics of biologic drug products suggests that the potential for abuse of a biologic is limited. Many marketed antibodies and recombinant proteins have been associated with adverse effects such as headache and dizziness. However, biologics have not historically engendered the rapid-onset psychoactive effects typically present for drugs of abuse, thus further underscoring their low risk for abuse potential. The factors to be taken into consideration before conducting nonclinical abuse liability studies with biologics are described herein; importantly, the aggregate assessment of these factors leads to the conclusion that abuse liability studies are unlikely to be necessary for this class of therapeutics.

Preclinical abuse liability assessment of ABT-126, an agonist at the α7 nicotinic acetylcholine receptor (nAChR).

ABT-126 is a nicotinic acetylcholine receptor (nAChR) agonist that is selective for the α7 subtype of the receptor. nAChRs are thought to play a role in a variety of neurocognitive processes and have been a pharmacologic target for disorders with cognitive impairment, including schizophrenia and Alzheimer's disease. As part of the preclinical safety package for ABT-126, its potential for abuse was assessed. While the involvement of the α4ß2 subtype of the nicotinic receptor in the addictive properties of nicotine has been demonstrated, the role of the α7 receptor has been studied much less extensively. A number of preclinical assays of abuse potential including open-field, drug discrimination and self-administration were employed in male rats. ABT-126 had modest effects on locomotor activity in the open-field assay. In nicotine and d-amphetamine drug discrimination assays, ABT-126 administration failed to produce appreciable d-amphetamine-like or nicotine-like responding, suggesting that its interoceptive effects are distinct from those of these drugs of abuse. In rats trained to self-administer cocaine, substitution with ABT-126 was similar to substitution with saline, indicating that it lacks reinforcing effects. No evidence of physical dependence was noted following subchronic administration. Overall, these data suggest that ABT-126 has a low potential for abuse. Together with other literature on this drug class, it appears that drugs that selectively activate α7 nAChRs are not likely to result in abuse or dependence.

Drug Tolerance: A Known Unknown in Translational Neuroscience.

In neuropsychiatric drug development, the rate of successful translation of preclinical to clinical efficacy has been disappointingly low. Tolerance, defined as a loss of efficacy with repeated drug exposure, is rarely addressed as a potential source of clinical failures. In this review, we argue that preclinical methods of tolerance development may have predictive validity and, therefore, inclusion of studies using repeated drug exposure early during the drug discovery and development process should serve to mitigate a proportion of clinical failures. Our analysis indicates that many published preclinical efficacy studies in the neuropsychiatry arena are conducted with acute drug administration only. Furthermore, specifically in the field of schizophrenia, there are several examples where tolerance development may be suspected as a factor contributing to translational failures. These and other examples highlight the need for built-for-purpose tolerance studies to be conducted, regardless of the target interaction mode of the drugs (i.e., agonist or antagonist, allosteric or orthosteric). We suggest that, for compounds that have failed in clinical studies, preclinical efficacy data sets need to be revisited to estimate the potential impact of tolerance development, one of the most significant known unknowns in the preclinical-to-clinical translation.

A retrospective evaluation of species-specific sensitivity for neurological signs in toxicological studies: Is the dog more sensitive than the non-human primate?

Selection of the appropriate non-rodent species in preclinical programs is crucial for good translatability and human safety. There is no data available in the literature which provides exact comparison of dog and non-human primate (NHP) sensitivity regarding neurological signs in toxicological studies. We performed a retrospective analysis of 174 toxicity studies with 15 neuroscience substances. Neurological signs in dogs and NHPs were evaluated in correlation to exposure data. Overall incidence of substance induced convulsions was similar in both species and no gender differences were observed. The reported liability of beagles to spontaneous convulsions was not confirmed in our studies. The symptom tremor showed the best inter-species translatability. The current toxicological study design does not include exposure assessment at the time-point of neurological signs, therefore, we propose to include additional toxicokinetic samples. Our analysis revealed factors including housing, handling, and behavior, which prevents direct species comparison. In addition only one non-rodent species is routinely tested in development programs, therefore data for both species is rare. We however, had sufficient data which enabled comparison for one compound. In the spirit of 3Rs further examples should be evaluated.

A randomized, placebo-controlled pilot trial of the delta opioid receptor agonist AZD2327 in anxious depression.

RATIONALE: Patients with anxious major depressive disorder (AMDD) have more severe symptoms and poorer treatment response than patients with non-AMDD. Increasing evidence implicates the endogenous opioid system in the pathophysiology of depression. AZD2327 is a selective delta opioid receptor (DOR) agonist with anxiolytic and antidepressant activity in animal models. OBJECTIVE: This double-blind, parallel group design, placebo-controlled pilot study evaluated the safety and efficacy of AZD2327 in a preclinical model and in patients with AMDD. METHODS: We initially tested the effects of AZD2327 in an animal model of AMDD. Subsequently, 22 subjects with AMDD were randomized to receive AZD2327 (3 mg BID) or placebo for 4 weeks. Primary outcome measures included the Hamilton Depression Rating Scale (HAM-D) and the Hamilton Anxiety Rating Scale (HAM-A). We also evaluated neurobiological markers implicated in mood and anxiety disorders, including vascular endothelial growth factor (VEGF) and electroencephalogram (EEG). RESULTS: Seven (54 %) patients responded to active drug and three (33 %) responded to placebo. No significant main drug effect was found on either the HAM-D (p = 0.39) or the HAM-A (p = 0.15), but the HAM-A had a larger effect size. Levels of AZ12311418, a major metabolite of AZD2327, were higher in patients with an anti-anxiety response to treatment compared to nonresponders (p = 0.03). AZD2327 treatment decreased VEGF levels (p = 0.02). There was a trend (p < 0.06) for those with an anti-anxiety response to have higher EEG gamma power than nonresponders. CONCLUSION: These results suggest that AZD2327 has larger potential anxiolytic than antidepressant efficacy. Additional research with DOR agonists should be considered.

The Utility of Impulsive Bias and Altered Decision Making as Predictors of Drug Efficacy and Target Selection: Rethinking Behavioral Screening for Antidepressant Drugs.

Cognitive dysfunction may be a core feature of major depressive disorder, including affective processing bias, abnormal response to negative feedback, changes in decision making, and increased impulsivity. Accordingly, a translational medicine paradigm predicts clinical action of novel antidepressants by examining drug-induced changes in affective processing bias. With some exceptions, these concepts have not been systematically applied to preclinical models to test new chemical entities. The purpose of this review is to examine whether an empirically derived behavioral screen for antidepressant drugs may screen for compounds, at least in part, by modulating an impulsive biasing of responding and altered decision making. The differential-reinforcement-of-low-rate (DRL) 72-second schedule is an operant schedule with a documented fidelity for discriminating antidepressant drugs from nonantidepressant drugs. However, a theoretical basis for this empirical relationship has been lacking. Therefore, this review will discuss whether response bias toward impulsive behavior may be a critical screening characteristic of DRL behavior requiring long inter-response times to obtain rewards. This review will compare and contrast DRL behavior with the five-choice serial reaction time task, a test specifically designed for assessing motoric impulsivity, with respect to psychopharmacological testing and the neural basis of distributed macrocircuits underlying these tasks. This comparison suggests that the existing empirical basis for the DRL 72-second schedule as a pharmacological screen for antidepressant drugs is complemented by a novel hypothesis that altering impulsive response bias for rodents trained on this operant schedule is a previously unrecognized theoretical cornerstone for this screening paradigm.

Behavioral effects of ß-phenylethylamine and various monomethylated and monohalogenated analogs in mice are mediated by catecholaminergic mechanisms.

The effects of the administration [intraperitoneally, 15 and 75 mg/kg, except α-MePEA (amphetamine, AMPH) at 5 and 10 mg/kg] of ß-phenylethylamine (PEA), its methylated (o-Me-, p-Me-, α-Me-, ß-Me-, N-Me-, p-OMe-, N,N-di-Me-, and 3,4-diOH-N-Me-), para-halogenated (Br-, Cl-, F-, and I-), and other derivatives for example, p-OHPEA (p-tyramine), on Swiss male albino mice caged behavior fall into 3 broad categories. (1) N,N-diMe-, 3,4-diOH-N-Me-, and o-MePEA tend to reduce the behavioral activity, (2) p-OH and p-IPEA were without noticeable effects, and (3) the remaining compounds increased locomotor activity, produced hyperexcitability and fighting, jumping and vocalization, and convulsion in a graded manner (listed in increasing order p-OMe-, ß-Me-, p-Cl-, p-Br-, p-F-, p-Me-, and N-MePEA, PEA itself and α-MePEA). The latter compound (amphetamine) being the most potent among them; equieffective but with lower potency were p-MePEA, N-MePEA, and PEA itself. The effects of PEAs upon group cage behavior were increased by pretreatment with pargyline (1.5 hours; 15 mg/kg) and decreased after reserpine or haloperidol [4 hours and/or 24 hours (2.5 and/or 2.5 mg/kg) and 1 hour (1 mg/kg), respectively], reaching full suppression with the double-dose regimen of reserpine and single dose of haloperidol. As expected, none of these substances by themselves were noticeable changed group mice activity or stereotypic behavior. The effects of test amines and catecholamine-modulating agents on stereotypy were assessed by rating the sequentially occurring behaviors: increased exploratory behavior with increased sniffing; occasional side-to-side head weaving; paw-licking and other grooming; gnawing, fighting and continuous side-to-side head weaving, and periodic episodes of "popcorn" behavior, during which all mice in the cage ran, jumped, and vocalized. In general, rank efficacy in eliciting stereotype aligned with rank efficacy in affecting group cage behavior. Our results show that a number of as yet little studied monomethylated and monohalogenated PEA analogs share a similar behavioral profile with PEA and AMPH. Behavioral changes observed appear to be, at least in part, mediated by catecholaminergic mechanism as they are modulated by drugs known to influence catecholamine activity. PEA analogs provide a large number of clinically useful drugs; whether further studies on these novel amines will lead to the rational design of newer, safer, and effective PEA-class drugs remains to be seen.

Translational Biomarkers of Neurotoxicity: A Health and Environmental Sciences Institute Perspective on the Way Forward.

Neurotoxicity has been linked to a number of common drugs and chemicals, yet efficient and accurate methods to detect it are lacking. There is a need for more sensitive and specific biomarkers of neurotoxicity that can help diagnose and predict neurotoxicity that are relevant across animal models and translational from nonclinical to clinical data. Fluid-based biomarkers such as those found in serum, plasma, urine, and cerebrospinal fluid (CSF) have great potential due to the relative ease of sampling compared with tissues. Increasing evidence supports the potential utility of fluid-based biomarkers of neurotoxicity such as microRNAs, F2-isoprostanes, translocator protein, glial fibrillary acidic protein, ubiquitin C-terminal hydrolase L1, myelin basic protein, microtubule-associated protein-2, and total tau. However, some of these biomarkers such as those in CSF require invasive sampling or are specific to one disease such as Alzheimer's, while others require further validation. Additionally, neuroimaging methodologies, including magnetic resonance imaging, magnetic resonance spectroscopy, and positron emission tomography, may also serve as potential biomarkers and have several advantages including being minimally invasive. The development of biomarkers of neurotoxicity is a goal shared by scientists across academia, government, and industry and is an ideal topic to be addressed via the Health and Environmental Sciences Institute (HESI) framework which provides a forum to collaborate on key challenging scientific topics. Here we utilize the HESI framework to propose a consensus on the relative potential of currently described biomarkers of neurotoxicity to assess utility of the selected biomarkers using a nonclinical model.

Analgesic effects of ß-phenylethylamine and various methylated derivatives in mice.

Administration of ß-phenylethylamine (PEA), the simplest endogenous neuroamine, and various methylated PEA derivatives including α-methyl PEA (amphetamine, AMP) elicits analgesia in mice. Five or 20 min after intraperitoneal PEA injection of as little as 6 mg/kg resulted in an increased latency response time (from 2.4 ± 0.4 to 8.5 ± 2.3 or 7.0 ± 3.0 s, respectively) to the thermal stimulus (hot-plate test), which reached statistical significance at the 15 mg/kg (20 min; 13.1 ± 0.4 s) or 25 mg/kg dose (5 min; 15.3 ± 4.1 s). This PEA effect, was dose-dependent (albeit non-linear: 6, 12, 15, 25, 50 and 100 mg/kg), reached the cut-off time of 45 s at the upper PEA dose (5 min), and it was consistently enhanced by pretreatment with the monoamine oxidase inhibitor pargyline (P). Methylated PEA derivatives (15 and 100 mg/kg dose) produced various degrees of analgesia (in decreasing order p-Me PEA > PEA > N,N-diMe PEA > N-Me PEA) which, likewise to PEA itself, were consistently increased by P and declined over time (mice tested 5, 20 and 60 min after amine injection); small but statistically significant o- and ß-Me PEA antinociceptive effects (5 min) were observed only at the higher dose (in the presence of P for ß-Me PEA). A small analgesic effect was observed after the administration of AMP (5 or 10 mg/kg) which failed, even after P, to reach statistically significance. Independent of the amine and concentration tested, individual compound's antinociceptive properties were reliably increased by P (exception of AMP), decreased by reserpine (R) or haloperidol (H), and remained essentially unchanged after naloxone (N) administration suggesting the involvement of catecholamines, but not opioid peptides, in their observed analgesic effects. Injection of P + N produced results similar to those seen after P alone. Under the experimental conditions described neither P, R, H or N had any effects by themselves. These findings suggest additional understanding of the mechanism of action responsible for the analgesic effects of these amines would be of interest, leading further to controlled studies on their alleged usefulness as weight reducing agents and sport performance enhancers.

Assessment of the abuse liability of ABT-288, a novel histamine H3 receptor antagonist.

RATIONALE: Histamine H3 receptor antagonists, such as ABT-288, have been shown to possess cognitive-enhancing and wakefulness-promoting effects. On the surface, this might suggest that H3 antagonists possess psychomotor stimulant-like effects and, as such, may have the potential for abuse. OBJECTIVES: The aim of the present study was to further characterize whether ABT-288 possesses stimulant-like properties and whether its pharmacology gives rise to abuse liability. METHODS: The locomotor-stimulant effects of ABT-288 were measured in mice and rats, and potential development of sensitization was addressed. Drug discrimination was used to assess amphetamine-like stimulus properties, and drug self-administration was used to evaluate reinforcing effects of ABT-288. The potential development of physical dependence was also studied. RESULTS: ABT-288 lacked locomotor-stimulant effects in both rats and mice. Repeated administration of ABT-288 did not result in cross-sensitization to the stimulant effects of d-amphetamine in mice, suggesting that there is little overlap in circuitries upon which the two drugs interact for motor activity. ABT-288 did not produce amphetamine-like discriminative stimulus effects in drug discrimination studies nor was it self-administered by rats trained to self-administer cocaine. There were no signs of physical dependence upon termination of repeated administration of ABT-288 for 30 days. CONCLUSIONS: The sum of these preclinical data, the first of their kind applied to H3 antagonists, indicates that ABT-288 is unlikely to possess a high potential for abuse in the human population and suggests that H3 antagonists, as a class, are similar in this regard.

Rat brain-uptake index for phenylethylamine and various monomethylated derivatives.

Phenylethylamine and its monomethylated derivatives p-methylphenylethylamine, α-methylphenylethylamine, phenylethylamine itself, N-methylphenylethylamine, o-methylphenylethylamine, and ß-methylphenylethylamine, readily cross the blood-brain barrier showing a brain-uptake index (%) ± SD (water considered 100 %), of 108 ± 11, 98 ± 14, 83 ± 6, 78 ± 11, 62 ± 7 and 56 ± 6, respectively (injection of tritiated water and 100 µg standard amine, which was measured by gas-liquid chromatography). Similar brain-uptake index values (determined by double isotope counting) were obtained for phenylethylamine and α-methylphenylethylamine (amphetamine) after the injection of tritiated water and C(14)-labeled amine (either 3 µg or when added 100 µg standard compound), suggesting that they entered the brain via passive diffusion. Accordingly, both amines distributed rather evenly in the various rat brain areas examined: uptake index (%) ± SD (double isotope counting; non-, and diluted labeled amine) for phenylethylamine (89 ± 8 and 78 ± 7, 83 ± 9 and 86 ± 9, 96 ± 6 and 84 ± 7) and for α-methylphenylethylamine (88 ± 11 and 87 ± 9, 93 ± 14 and 87 ± 11, 97 ± 12 and 87 ± 9) for the cerebellum, frontal cortex, and striatum, respectively. These results will aid a greater understanding of the pharmacological and behavioral effects observed after the administration of phenylethylamine and methylphenylethylamine derivatives.

4-Piperidin-4-ylidenemethyl-benzamides as δ-opioid receptor agonists for CNS indications: identifying clinical candidates.

A series of 4-piperidin-4-ylidenemethyl-benzamide δ-opioid receptor agonists is described with an emphasis on balancing the potency, subtype selectivity and in vitro ADME and safety properties. The three sites impacting SAR are substitutions on the aryl group (R(1)), the piperidine nitrogen (R(2)), and the amide (R(3)). Each region contributes to the balance of properties for δ opioid activity and a desirable CNS profile, and two clinical candidates (20 and 24) were advanced.

Multiparameter exploration of piperazine derivatives as δ-opioid receptor agonists for CNS indications.

A novel series of piperazine derivatives exhibits sub-nanomolar binding and enhanced subtype selectivity as δ-opioid agonists. The synthesis and SAR are described as well as the application of computational models to improve in vitro ADME and safety properties suitable for CNS indications, specifically microsomal clearance, permeability, and hERG channel inhibition.

Acute nicotine and phencyclidine increase locomotor activity of the guinea pig with attenuated potencies relative to their effects on rat or mouse.

Behavioral assays of the responses to psychomotor stimulants can be used to model certain aspects of CNS pathologies such as psychosis and addiction. However, species-dependent differences in the effects of neuromodulators in these assays can confound the interpretation of the results. The goal of this study was to determine the utility of the guinea pig as a model for assessing the behavioral actions of nicotinic receptor agonists and NMDA receptor antagonists. In the present study, the locomotor activity of adult male guinea pigs was measured, prior to and following an acute injection of nicotine, MK-801 or phencyclidine. Each animal received a single dose of the drug. Nicotine produced a dose-dependent increase in activity with an ED(50) of 1.5mg/kg. Phencyclidine also increased activity, with an ED(50) of 3.4 mg/kg. Nicotine produced increases in locomotion in all individual subjects tested, whereas at the maximally-effective dose of phencyclidine, only a fraction of the animals had locomotor activation. There was no change in activity in response to a single dose of MK-801 (0.5mg/kg). Haloperidol had a significant inhibitory effect on locomotor activity independent of the stimulant administered. Thus, both phencyclidine and nicotine are psychomotor stimulants when given to guinea pigs, although the intensity of the response and the potencies of these drugs are lower than in mice or rats under otherwise similar conditions.

Mechanistic investigation of N,N-diethyl-4-(phenyl-piperidin-4-ylidenemethyl)-benzamide-induced insulin depletion in the rat and RINm5F cells.

These studies describe the effect of N,N-diethyl-4-(phenyl-piperidin-4-ylidenemethyl)-benzamide (AR-M100390), a delta-opioid agonist, on the pancreas and its mechanisms for pancreatic toxicity. Rats were treated with 5, 100, and 600 micromol/kg of AR-M100390 for 3 and/or 7 days; another group of rats treated with 600 micromol/kg of compound were allowed to recover for 14 days. AR-M100390 (600 micromol/kg) caused vacuolation in the beta-cell of the rat pancreas that was associated with depletion of insulin and hyperglycemia after 7 days of dosing. The loss of insulin by AR-M100390 was due to specific inhibition of rat insulin2 mRNA transcription in vivo. Insulin depletion and hyperglycemia were reversible. The effects of AR-M100390 in rats were reproduced in the rat pancreatic beta-cell line RINm5F, where it inhibited intracellular insulin content and secretion without affecting cell survival. Loss of insulin in vitro was also a result of specific inhibition of insulin2 mRNA transcription and was reversible. Pretreatment of cells with the delta-opioid antagonist naltrindole or pertussis toxin did not reverse loss of insulin in AR-M100390-treated cells suggesting that the effects were not mediated by the delta-opioid receptor. AR-M100390 inhibited KCl-mediated calcium mobilization in RINm5F cells, suggesting that L-type calcium channels found in these cells and in pancreatic beta-cells may partially play a role in the inhibition of insulin secretion by this compound. In summary, the in vitro and in vivo studies suggest that inhibition of insulin by AR-M100390 is due to a combination of inhibition of insulin synthesis and/or release.