Effects of Two Novel D3-Selective Compounds, NGB 2904 [N-(4-(4-(2,3-Dichlorophenyl)piperazin-1-yl)butyl)-9H-fluorene-2-carboxamide] and CJB 090 [N-(4-(4-(2,3-Dichlorophenyl)piperazin-1-yl)butyl)-4-(pyridin-2-yl)benzamide], on the Reinforcing and Discriminative Stimulus Effects of Cocaine in Rhesus Monkeys

Structure-activity relationships for a novel series of dopamine D2-like receptor ligands based on N-substituted 3-aryl-8-azabicyclo[3.2.1]octan-3-ol

Discovering dopamine D2-like receptor subtype-selective ligands has been a focus of significant investigation. The D2R-selective antagonist 3-[4-(4-chlorophenyl)-4-hydroxypiperidinyl]methylindole (1, L741,626; K(i)(D2R/D3R) = 11.2:163 nM) has previously provided a lead template for chemical modification. Herein, analogues have been synthesized where the piperidine was replaced by a tropane ring that reversed the selectivity seen in the parent compound, in human hD2(L)R- or hD3R-transfected HEK 293 cells (31, K(i)(D2R/D3R) = 33.4:15.5 nM). Further exploration of both N-substituted and aryl ring-substituted analogues resulted in the discovery of several high affinity D2R/D3R ligands with 3-benzofurylmethyl-substituents (e.g., 45, K(i)(D2R/D3R) = 1.7:0.34 nM) that induced high affinity not achieved in similarly N-substituted piperidine analogues and significantly (470-fold) improved D3R binding affinity compared to the parent ligand 1. X-ray crystallographic data revealed a distinctive spatial arrangement of pharmacophoric elements in the piperidinol vs tropine analogues, providing clues for the diversity in SAR at the D2 and D3 receptor subtypes.

Influence of thyroid hormones on 3,4-methylenedioxymethamphetamine-induced thermogenesis and reinforcing strength in monkeys

In monkeys, elevating ambient temperature has been shown to increase sensitivity to 3,4-methylenedioxymethamphetamine (MDMA) reinforcement. Earlier rodent studies have shown that elevations in thyroid levels (hyperthyroidism) parallel changes in elevating the ambient temperature on MDMA-induced thermogenesis, but the interaction has not been examined in monkeys. This study was designed to evaluate the effects of chronic levothyroxine (3.0 or 4.5 microg/kg/day, intramuscularly; Levo) treatment on MDMA-induced increases in body temperature following 1.5 mg/kg (intravenously) MDMA and self-administration when MDMA (0.03-0.3 mg/kg/injection) and food were available under a concurrent fixed-ratio 30 schedule of reinforcement in rhesus monkeys (n=4). Earlier studies had shown that 1.5 mg/kg MDMA did not affect thermoregulation at 24 degrees C. Chronic Levo treatment resulted in significant increases in MDMA-induced thermogenesis. In the self-administration experiment, MDMA choice increased with dose, such that food was preferred over saline and a low MDMA dose (0.03 mg/kg/injection), whereas 0.1 and 0.3 mg/kg/injection MDMA was preferred over food. Although elevating ambient temperature had been shown to increase MDMA potency, there was no effect of chronic Levo treatment on MDMA choice. These results suggest that changes in thyroxine levels do not parallel the changes in ambient temperature in altering the reinforcing strength of MDMA.

New treatments for cocaine dependence: a focused review

Cocaine, already a significant drug problem in North and South America, has become a more prominent part of the European drug scene. Cocaine dependence has major somatic, psychological, psychiatric, socio-economic, and legal implications. No specific effective pharmacological treatment exists for cocaine dependence. Recent advances in neurobiology have identified various neuronal mechanisms implicated in cocaine addiction and suggested several promising pharmacological approaches. Data were obtained from Medline, EMBASE, and PsycINFO searches of English-language articles published between 1985 and June 2007 using the key words: cocaine, addiction, cocaine dependence, clinical trials, pharmacotherapy(ies) singly and in combination. Large well-controlled studies with appropriate statistical methods were preferred. Pharmacological agents such as GABA agents (topiramate, tiagabine, baclofen and vigabatrin) and agonist replacement agents (modafinil, disulfiram, methylphenidate) seem to be the most promising in treatment of cocaine dependence. The results from trials of first- and second-generation neuroleptics are largely negative. Aripiprazole, a partial dopaminergic agonist that may modulate the serotonergic system, shows some promise. Preliminary results of human studies with anti-cocaine vaccine, N-acetylcysteine, and ondansetron, are promising, as are several compounds in preclinical development. While no medication has received regulatory approval for the treatment of cocaine dependence, several medications marketed for other indications have shown efficacy in clinical trials. An anti-cocaine vaccine and several compounds in preclinical development have also shown promise. Findings from early clinical trials must be confirmed in larger, less selective patient populations.

The effects of two highly selective dopamine D3 receptor antagonists (SB-277011A and NGB-2904) on food self-administration in a rodent model of obesity

In the current study, we examined the effect of the selective D(3) receptor antagonists SB-277011A and NGB 2904 on operant food self-administration (FSA) in Zucker obese and lean rats. Obese (Ob) and lean (Le) Zucker rats were maintained under a restricted feeding regimen (70% of ad-libitum rat chow) and were trained to lever press for food during daily, 2 hour fixed-ratio 4 (FR4) schedules. Once rats reached a stable baseline for FSA, they were injected with vehicle until a stable FSA criterion was achieved. Animals then received daily injections of different random doses of SB-277011A (3, 10, and 30 mg/kg i.p.), and NGB-2904 (0.3, 1 and 3 mg/kg i.p.). SB-277011A produced a significant decrease in both food intake and active lever responses in both Ob and Le rats. In contrast, NGB-2904 did not decrease food intake levels or lever presses for food in Ob and Le rats. These results suggest that along with its involvement in seeking behavior for drugs of abuse, the D(3) dopamine receptor may also be involved in seeking behavior for natural reinforcers such as food.

Effects of ambient temperature on the relative reinforcing strength of MDMA using a choice procedure in monkeys

RATIONALE

3,4-Methylenedioxymethamphetamine (MDMA, ecstasy) is frequently used in hot environments, such as rave parties. Studies in laboratory animals have shown that ambient temperature can alter the behavioral and neurochemical effects of MDMA.

OBJECTIVE

To examine the influence of ambient temperature on the relative reinforcing strength of MDMA and reinstatement of behavior previously maintained by MDMA is the objective of the study.

METHODS

The effects of cool (18 degrees C), room (24 degrees C), and warm (31 degrees C) temperatures were examined when MDMA was available under a concurrent fixed-ratio 30 schedule of MDMA (saline, 0.03-0.3 mg/kg/injection) and food choice in rhesus monkeys (n = 5). During saline substitutions, the effect of noncontingent MDMA (0.03-0.3 mg/kg) on response allocation was examined at each ambient temperature.

RESULTS

At room temperature, MDMA choice increased as a function of dose, such that food was preferred over a low MDMA dose (0.03 mg/kg/injection), whereas higher doses were preferred over food. Elevating the ambient temperature significantly increased the relative reinforcing strength of 0.03 mg/kg/injection MDMA, and lowering the ambient temperature significantly attenuated the choice of 0.1 mg/kg/injection MDMA. Noncontingent injections of MDMA administered before a session in which saline was the alternative to food dose-dependently increased injection-lever responding; this effect was not influenced by ambient temperature.

CONCLUSIONS

These results suggest that ambient temperature can affect the relative reinforcing strength of MDMA, but not MDMA-induced reinstatement. Furthermore, these results suggest environmental strategies for decreasing the reinforcing strength of MDMA.

Heterocyclic Analogues of N-(4-(4-(2,3-Dichlorophenyl)piperazin-1-yl)butyl)arylcarboxamides with Functionalized Linking Chains as Novel Dopamine D3 Receptor Ligands: Potential Substance Abuse Therapeutic Agents

Dopamine D3 receptor antagonists and partial agonists have been shown to modulate drug-seeking effects induced by cocaine and other abused substances. Compound 6 [PG01037, (N-(4-(4-(2,3-dichlorophenyl)piperazin-1-yl)-trans-but-2-enyl)-4-pyridine-2-ylbenzamide)] and related analogues are currently being evaluated in animal models of drug addiction. In these studies, a discrepancy between in vitro binding affinity, in vivo occupancy, and behavioral potency has been observed. The purpose of this study was to examine (1) modifications of the 2-pyridylphenyl moiety of 6 and (2) hydroxyl, acetyl, and cyclopropyl substitutions on the butylamide linking chain systematically coupled with 2-fluorenylamide or 2-pyridylphenylamide and 2-methoxy- or 2,3-dichloro-substituted phenylpiperazines to measure the impact on binding affinity, D2/D3 selectivity, lipophilicity, and function. In general, these modifications were well tolerated at the human dopamine D3 (hD3) receptor (Ki = 1-5 nM) as measured in competition binding assays. Several analogues showed >100-fold selectivity for dopamine D3 over D2 and D4 receptors. In addition, while all the derivatives with an olefinic linker were antagonists, in quinpirole-stimulated mitogenesis at hD3 receptors, several of the hydroxybutyl-linked analogues (16, 17, 21) showed partial agonist activity. Finally, several structural modifications reduced lipophilicities while retaining the desired binding profile.

Ambient Temperature Effects on 3,4-Methylenedioxymethamphetamine-Induced Thermodysregulation and Pharmacokinetics in Male Monkeys

Changes in ambient temperature are known to alter both the hyperthermic and the serotonergic consequences of 3,4-methylenedioxymethamphetamine (MDMA). Metabolism of MDMA has been suggested to be a requisite for these neurotoxic effects, whereas the hyperthermic response is an important contributing variable. The aim of the present study was to investigate the interaction between ambient temperature, MDMA-induced thermodysregulation, and its metabolic disposition in monkeys. MDMA (1.5 mg/kg i.v.) was administered noncontingently at cool (18 degrees C; n = 5), room (24 degrees C; n = 7), and warm (31 degrees C; n = 7) ambient temperatures. For 240 min following MDMA administration, core temperature was recorded and blood samples were collected for analysis of MDMA and its metabolites 3,4-dihydroxymethamphetamine (HHMA), 3,4-dihydroxyamphetamine, and 3,4-methylenedioxyamphetamine (MDA). A dose of 1.5 mg/kg MDMA induced a hypothermic response at 18 degrees C, a hyperthermic response at 31 degrees C, and did not significantly change core temperature at 24 degrees C. Regardless of ambient temperature, plasma MDMA concentrations reached maximum within 5 min, and HHMA was a major metabolite. Curiously, the approximate elimination half-life (t(1/2)) of MDMA at 18 degrees C (136 min) and 31 degrees C (144 min) was increased compared with 24 degrees C (90 min) and is most likely because of volume of distribution changes induced by core temperature alterations. At 18 degrees C, there was a significantly higher MDA area under the concentration-time curve (AUC) and a trend for a lower HHMA AUC compared with 24 degrees C and 31 degrees C, suggesting that MDMA disposition was altered. Overall, induction of hypothermia in a cool environment by MDMA may alter its disposition. These results could have implications for MDMA-induced serotonergic consequences.

Pharmacological actions of NGB 2904, a selective dopamine D3 receptor antagonist, in animal models of drug addiction

As a continuation of our work with SB-277011A, we have examined the effects of another highly elective dopamine (DA) D3 receptor antagonist, N-(4-[4-{2,3-dichlorophenyl}-1-piperazinyl]butyl)-2-fluorenylcarboxamide (NGB 2904), in animal models of addiction. Our results indicate that by systemic administration, NGB 2904 inhibits intravenous cocaine self-administration maintained under a progressive-ratio (PR) reinforcement schedule, cocaine- or cocaine cue-induced reinstatement of cocaine-seeking behavior, and cocaine- or other addictive drug-enhanced brain stimulation reward (BSR). The action of NGB 2904 on PR cocaine self-administration was long-lasting (1-2 days) after a single injection, supporting its potential use in treatment of cocaine addiction. The effects of NGB 2904 in the BSR paradigm were dose-dependent for both NGB 2904 and cocaine; that is, only lower doses of NGB 2904 were effective, and their putative antiaddiction effect could be overcome by increasing the doses of cocaine or other addictive drugs. A dopamine-dependent mechanism is proposed to explain the effects of NGB 2904 on cocaine's actions in these animal models of drug addiction. The data reviewed in this paper suggest that NGB 2904 or other D3-selective antagonists may have potential in controlling motivation for drug-taking behavior or relapse to drug-seeking behavior, but may have a limited role in antagonizing the acute rewarding effects produced by cocaine or other addictive drugs. In addition, NGB 2904 may also act as a useful tool to study the role of D3 receptors in drug addiction.