N-[2-(m-methoxyphenyl)ethyl]-N-ethyl-2-(1-pyrrolidinyl)ethylamine (UMB 116) is a novel antagonist for cocaine-induced effects

Ultra-performance liquid chromatography tandem mass spectrometry method for the determination of AZ66, a sigma receptor ligand, in rat plasma and its application to in vivo pharmacokinetics

Methamphetamine abuse continues as a major problem in the USA owing to its powerful psychological addictive properties. AZ66, 3-[4-(4-cyclohexylpiperazine-1-yl)pentyl]-6-fluorobenzo[d]thiazole-2(3H)-one, an optimized sigma receptor ligand, is a promising therapeutic agent against methamphetamine. To study the in vivo pharmacokinetics of this novel sigma receptor ligand in rats, a sensitive ultra-performance liquid chromatography/tandem mass spectrometry (UPLC/MS/MS) method was developed in rat plasma and validated. The developed method requires a small volume of plasma (100 μL) and a simple liquid-liquid extraction. The chromatographic separations were achieved in 3.3 min using an Acquity UPLC BEH Shield RP18 column. The mass spectrophotometric detection was carried out using a Waters Micromass Quattro MicroTM triple-quadrupole system. Multiple reaction monitoring was used for the quantitation with transitions m/z 406 → m/z 181 for AZ66 and m/z 448 → m/z 285 for aripiprazole. The method was validated over a concentration range of 1-3500 ng/mL and the lower limit of quantitation was determined to be 1 ng/mL. Validation of the assay demonstrated that the developed UPLC/MS/MS method was sensitive, accurate and selective for the determination of AZ66 in rat plasma. The present method has been successfully applied to an i.v. pharmacokinetic study in Sprague-Dawley rats.

Determination of a highly selective mixed-affinity sigma receptor ligand, in rat plasma by ultra performance liquid chromatography mass spectrometry and its application to a pharmacokinetic study

A selective, rapid and sensitive ultra performance liquid chromatography mass spectrometry (UPLC/MS) method was developed and validated to quantitate a highly selective mixed-affinity sigma receptor ligand, CM156 (3-(4-(4-cyclohexylpiperazin-1-yl)butyl)benzo[d] thiazole-2(3H)-thione), in rat plasma. CM156 and the internal standard (aripiprazole) were extracted from plasma samples by a single step liquid-liquid extraction using chloroform. The analysis was carried out on an ACQUITY UPLC™ BEH HILIC column (1.7 μm, 2.1 mm×50 mm) with isocratic elution at flow rate of 0.2 mL/min using 10mM ammonium formate in 0.1% formic acid and acetonitrile (10:90) as the mobile phase. The detection of the analyte was performed on a mass spectrometer operated in selected ion recording (SIR) mode with positive electrospray ionization (ESI). The validated analytical method resulted in a run time of 4 min and the retention times observed were 2.6±0.1 and 2.1±0.1 min for CM156 and the IS, respectively. The calibration curve exhibited excellent linearity over a concentration range of 5-4000 ng/mL with the lower limit of quantification of 5 ng/mL. The intra- and inter-day precision values were below 15% and accuracy ranged from -6.5% to 5.0%. The mean recovery of CM156 from plasma was 96.8%. The validated method was applied to a pilot intravenous pharmacokinetic study in rats.

Pharmacology and therapeutic potential of sigma(1) receptor ligands

Sigma (σ) receptors, initially described as a subtype of opioid receptors, are now considered unique receptors. Pharmacological studies have distinguished two types of σ receptors, termed σ₁ and σ₂. Of these two subtypes, the σ₁ receptor has been cloned in humans and rodents, and its amino acid sequence shows no homology with other mammalian proteins. Several psychoactive drugs show high to moderate affinity for σ₁ receptors, including the antipsychotic haloperidol, the antidepressant drugs fluvoxamine and sertraline, and the psychostimulants cocaine and methamphetamine; in addition, the anticonvulsant drug phenytoin allosterically modulates σ₁ receptors. Certain neurosteroids are known to interact with σ₁ receptors, and have been proposed to be their endogenous ligands. These receptors are located in the plasma membrane and in subcellular membranes, particularly in the endoplasmic reticulum, where they play a modulatory role in intracellular Ca²⁺ signaling. Sigma₁ receptors also play a modulatory role in the activity of some ion channels and in several neurotransmitter systems, mainly in glutamatergic neurotransmission. In accordance with their widespread modulatory role, σ₁ receptor ligands have been proposed to be useful in several therapeutic fields such as amnesic and cognitive deficits, depression and anxiety, schizophrenia, analgesia, and against some effects of drugs of abuse (such as cocaine and methamphetamine). In this review we provide an overview of the present knowledge of σ₁ receptors, focussing on σ₁ ligand neuropharmacology and the role of σ₁ receptors in behavioral animal studies, which have contributed greatly to the potential therapeutic applications of σ₁ ligands.

A thermally stable form of bacterial cocaine esterase: a potential therapeutic agent for treatment of cocaine abuse

Rhodococcal cocaine esterase (CocE) is an attractive potential treatment for both cocaine overdose and cocaine addiction. CocE directly degrades cocaine into inactive products, whereas traditional small-molecule approaches require blockade of the inhibitory action of cocaine on a diverse array of monoamine transporters and ion channels. The usefulness of wild-type (wt) cocaine esterase is hampered by its inactivation at 37 degrees C. Herein, we characterize the most thermostable form of this enzyme to date, CocE-L169K/G173Q. In vitro kinetic analyses reveal that CocE-L169K/G173Q displays a half-life of 2.9 days at 37 degrees C, which represents a 340-fold improvement over wt and is 15-fold greater than previously reported mutants. Crystallographic analyses of CocE-L169K/G173Q, determined at 1.6-A resolution, suggest that stabilization involves enhanced domain-domain interactions involving van der Waals interactions and hydrogen bonding. In vivo rodent studies reveal that intravenous pretreatment with CocE-L169K/G173Q in mice provides protection from cocaine-induced lethality for longer time periods before cocaine administration than wt CocE. Furthermore, intravenous administration (pretreatment) of CocE-L169K/G173Q prevents self-administration of cocaine in a time-dependent manner. Termination of the in vivo effects of CoCE seems to be dependent on, but not proportional to, its clearance from plasma as its half-life is approximately 2.3 h and similar to that of wt CocE (2.2 h). Taken together these data suggest that CocE-L169K/G173Q possesses many of the properties of a biological therapeutic for treating cocaine abuse but requires additional development to improve its serum half-life.

Nitrile analogs of meperidine as high affinity and selective sigma-1 receptor ligands

A series of N-substituted-4-cyano-4-phenylpiperidine analogs were synthesized and evaluated for binding affinity at opioid receptors and showed no affinity. The series similarity to previously reported sigma ligands prompted analysis at sigma receptors to determine the SAR for affinity at sigma receptors. Within the N-substituent series the saturated analogs showed increased affinity at both sigma receptors. Optimal chain length in the N-arylalkyl series for sigma(1) and sigma(2) receptors proved to be N-propylphenyl; extension to a four carbon chain dramatically decreased affinity at both receptors. Substituents in the 4-position affect only sigma(1) affinity; no change in affinity at sigma(2) was shown. The N-isobutyl, N-phenylpropyl, and N-benzyl analogs are worth pursuing due to their good affinity and selectivity at the sigma(1) receptor, whereas the N-benzyl analog exhibits the greatest selectivity for sigma(1).

Novel sigma (sigma) receptor agonists produce antidepressant-like effects in mice

Many antidepressant drugs interact with sigma receptors and accumulating evidence suggests that these proteins mediate antidepressant-like effects in animals and humans. sigma Receptors are localized in brain regions affected in depression, further strengthening the hypothesis that they represent logical drug development targets. In this study, two novel sigma receptor agonists (UMB23, UMB82) were evaluated for antidepressant-like activity in mice. First, radioligand binding studies confirmed that the novel compounds had preferential affinity for sigma receptors. Second, the forced swim test, a well established animal model for screening potential antidepressant drugs, showed that both compounds dose-dependently reduced immobility time. The sigma receptor antagonist BD1047 attenuated the antidepressant-like effects of UMB23 and UMB82. Third, locomotor activity suggested that the effects of UMB23 and UMB82 in the forced swim test were not due to non-specific motor activating effects. Together, the data provide further evidence that sigma receptor agonists represent a possible new class of antidepressant medication.

Differential effects of sigma1 receptor blockade on self-administration and conditioned reinstatement motivated by cocaine vs natural reward

Growing evidence suggests a role for sigma(1) (sigma(1)) receptors in cognitive function, anxiety, depression, regulation of stress responses, and, recently, the appetitive effects of cocaine as measured by conditioned place preference. This study was designed to extend understanding of the role of sigma(1) receptors in addiction-relevant conditioned effects of cocaine by testing the effects of a potent and selective sigma(1) receptor antagonist, BD1047, on conditioned reinstatement of cocaine-seeking. To determine whether modification of conditioned reinstatement by BD1047 is selective for drug-directed behavior or reflects general suppressant effects on motivated behavior, BD1047 was tested also on reinstatement induced by stimuli conditioned to a natural reward, sweetened condensed milk (SCM). Additionally, because sigma(1) receptors have been implicated also in processes linked to the acute reinforcing actions of cocaine, tests of the effects of BD1047 on cocaine self-administration-including a comparison with the sigma(1) antagonist effects on SCM self-administration-were conducted as well. Cocaine self-administering male Wistar rats were trained to associate a discriminative stimulus (S(D)) with the availability of cocaine or SCM, and then subjected to reinstatement tests following extinction of cocaine or SCM-reinforced behavior. BD1047 (1-30 mg/kg) reversed response reinstatement induced by the cocaine S(D) at 20 and 30 mg/kg but did not modify SCM S(D)-induced responding at all but the highest 30 mg dose, at which responding was reversed to extinction levels. BD1047 did not modify responding reinforced directly by SCM or cocaine. The findings support a role for sigma(1) receptors in regulating conditioned responses to cocaine-related contextual stimuli and identify this receptor as a potential treatment target for the prevention of craving and relapse.

Cocaine esterase: interactions with cocaine and immune responses in mice

Cocaine esterase (CocE) is the most efficient protein catalyst for the hydrolysis of cocaine characterized to date. The aim of this study was to investigate the in vivo potency of CocE in blocking cocaine-induced toxicity in the mouse and to assess CocE's potential immunogenicity. Cocaine toxicity was quantified by measuring the occurrence of convulsions and lethality. Intravenous administration of CocE (0.1-1 mg) 1 min before cocaine administration produced dose-dependent rightward shifts of the dose-response curve for cocaine toxicity. More important, i.v. CocE (0.1-1 mg), given 1 min after the occurrence of cocaine-induced convulsions, shortened the recovery time after the convulsions and saved the mice from subsequent death. Effects of repeated exposures to CocE were evaluated by measuring anti-CocE antibody titers and the protective effects of i.v. CocE (0.32 mg) against toxicity elicited by i.p. cocaine (320 mg/kg) (i.e., 0-17% occurrence of convulsions and lethality). CocE retained its potency against cocaine toxicity in mice after a single prior CocE exposure (0.1-1 mg), and these mice did not show an immune response. CocE retained similar effectiveness in mice after three prior CocE exposures (0.1-1 mg/week for 3 weeks), although these mice displayed 10-fold higher antibody titers. CocE partially lost effectiveness (i.e., 33-50% occurrence of convulsions and lethality) in mice with four prior exposures to CocE (0.1-1 mg/2 week for four times), and these mice displayed approximately 100-fold higher antibody titers. These results suggest that CocE produces robust protection and reversal of cocaine toxicity, indicating CocE's therapeutic potential for acute cocaine toxicity. Repeated CocE exposures may increase its immunogenicity and partially reduce its protective ability.