1-[1-(2-Benzo[b]thiopheneyl)cyclohexyl]piperidine hydrochloride (BTCP) yields two active primary metabolites in vivo: Identification and quantification of BTCP primary metabolites in mice plasma, urine, and brain and their affinity for the neuronal dopamine transporter

1-[1-(2-Benzo[b]thiopheneyl)cyclohexyl]piperidine hydrochloride (BTCP) and cocaine bind to the neuronal dopamine transporter (DAT) to strongly inhibit dopamine (DA) reuptake. Although similar to acute administration, cocaine and BTCP produce sensitization and tolerance, respectively, on chronic administration. We previously found that liver microsomes produced two primary metabolites from BTCP with a high affinity for DAT. Because such metabolites, if produced in vivo, could account for the pharmacological difference with cocaine, it was important to compare BTCP biotransformations in vitro and in vivo. Therefore, we identified and quantified BTCP and primary metabolites in mice urine, plasma, and brain after acute i.p. administration. The low recovery yield suggest that BTCP might behave like its close analogue, phencyclidine, with long-term storage of metabolites. Two active metabolites found in vitro were found in mice brain with estimated half-life values similar to that of BTCP (0.3 h). Although respective brain concentrations were 20 and 40 times lower than that of BTCP, their potency to displace in vivo [³H]BTCP bound to the DAT was 50 and 10 times higher, respectively, than that of BTCP. They could, therefore, contribute to the inhibition of DA transport and play an important role in BTCP pharmacology. They could also explain the differences between BTCP and cocaine on repeated administration.     

Modulation by dopamine of [3H]N-[1-(2-benzo(b)thiophenyl)cyclohexyl]piperidine ([3H]BTCP, a phencyclidine derivative) binding to the dopamine uptake complex.

The modulation by dopamine of the binding of [3H]BTCP to the dopamine (DA) uptake complex was investigated in vivo (in control, reserpine- and L-DOPA-treated mice) and in vitro (on membrane preparations of the striatum of the rat). In both cases increasing doses of DA exerted a non-competitive inhibition of binding of [3H]BTCP, with a Ki value close to its K0.5, determined in competition experiments. Amphetamine and cocaine were also non-competitive inhibitors of the binding of [3H]BTCP, while GBR 12783 was competitive. In the presence of DA, the amount of cocaine required to inhibit the binding of [3H]BTCP was increased both in vitro and in vivo. These results suggest that inhibitors of the uptake of DA, such as BTCP or GBR 12783, modulate allosterically the uptake of DA, by binding to a site different from the DA recognition site. Cocaine, however, seems to share the same recognition site as DA.     

N-[1-(2-benzo[b]thiophenyl)Cyclohexyl]- piperidine (BTCP) exerts cocaine-like actions on drug-maintained responding in rats.

The effects of N-[1-(2-benzo[b]thiophenyl)cyclohexyl]- piperidine (BTCP), a phencyclidine derivative that acts as a potent dopamine reuptake inhibitor, were examined on cocaine self-administration in rats. The effects of BTCP (0, 4, 8, 16, and 32 mg/kg, i.p.) on cocaine self-administration were tested against cocaine doses on both the ascending (0.0625 mg/infusion) and descending (0.25 mg/infusion) limb of the dose-response function. BTCP decreased self-administration of the 0.25-mg cocaine dose in a dose-dependent manner. A 16-mg/kg dose of BTCP that strongly suppressed self-administration of the 0.25-mg cocaine dose increased the intake at the 0.0625-mg dose of cocaine. Moreover, cocaine and BTCP pretreatments produced similar patterns of decreases in self-administration of cocaine on the descending limb of the dose-response function. The results suggest that BTCP has cocaine-like actions and produces a leftward shift of the dose-response curve for cocaine self-administration, indicating that the phencyclidine analog may substitute under certain conditions for the reinforcing effects of cocaine in self-administering rats.     

Non reciprocal cross-sensitization between cocaine and BTCP on locomotor activity in the rat

Measurement of locomotor sensitization was employed to characterize the effect of intermittent treatment with N-[1-(2-benzo[b]thiophenyl)cyclohexyl]piperidine (BTCP) and cocaine in the rat. Like cocaine, BTCP possesses high affinity for the dopamine transporter and inhibits dopamine reuptake. Although both drugs exhibit similar behavioral and neurochemical profiles with acute administration, there is tentative evidence to suggest that following chronic treatment BTCP does not induce neurochemical sensitization, and can attenuate cocaine-induced neurochemical sensitization in the striatum. Male Wistar rats were randomly divided into five groups after determining baseline locomotor activity. Three groups were treated with either saline (saline/saline), cocaine (20 mg/kg; cocaine/cocaine), or BTCP (10 mg/kg; BTCP/BTCP) for 10 days. The remaining two groups were treated with cocaine (20 mg/kg) or BTCP (10 mg/kg) for 3 days, followed by administration of BTCP (10 mg/kg; cocaine/BTCP) or cocaine (20 mg/kg; BTCP/cocaine) for 7 days. Locomotor sensitization was observed in all groups. However, although cross-sensitization on the day of substitution (day 4) was found in the BTCP/cocaine group, cross-sensitization was not observed in the cocaine/BTCP group. These results suggest that although the locomotor-activating effects of BTCP and cocaine are similar, the two drugs do not act identically, and different neural mechanisms may underlie BTCP and cocaineinduced sensitization.     

BTCP is a potent reinforcer in rats: comparison of behavior maintained on fixed- and progressive-ratio schedules

N-[1-(2-benzo[b]thiophenyl)cyclohexyl]piperidine (BTCP) is a phencyclidine (PCP) derivative that acts as a potent dopamine (DA) reuptake inhibitor. Earlier studies have shown that BTCP can substitute for the reinforcing effects of cocaine. Therefore, the aim of the study was to further characterize the reinforcing effects of BTCP. The reinforcing actions of BTCP were compared to those of cocaine at equimolar concentrations in drug-na?ve rats. Two groups of animals were implanted with jugular catheters and trained to intravenously self-administer BTCP or cocaine (0.25 mg/infusion) on a fixed-ratio five schedule (FR 5) of reinforcement. Both BTCP and cocaine produced comparable inverted U-shaped dose-effect curves on this schedule over doses of 0.03, 0.06, 0.125, and 0.25 mg/infusion. Two doses (0.125 and 0.25 mg/infusion) that produced reliable self-administration in all the animals for cocaine and BTCP were then tested on a progressive-ratio schedule. At each dose, BTCP supported higher breaking points (BPs) than cocaine. The results demonstrate that rats readily acquire responding maintained by BTCP and suggest that BTCP may have greater reinforcing effects than cocaine at equimolar concentrations.     

Evidence for mutually exclusive binding of cocaine, BTCP, GBR 12935, and dopamine to the dopamine transporter.

The present study addressed the possibility that there are distinct but allosterically interacting populations of binding sites for dopamine/cocaine and BTCP/GBR (N-[1-(2-benzo[b]thiophenyl)cyclohexyl]piperidine/1-(2-diphenylmethox y) - ethyl]-4-(3-phenylpropyl)piperazine) (selective dopamine uptake blockers) on the dopamine transporter in the rat striatum. Dopamine uptake sites were labeled in vitro with the cocaine analog [3H]CFT (2 beta-carbomethoxy-3 beta-(4-fluorophenyl)-tropane), and the inhibition of binding by CFT or cocaine was measured. A graphic method was adopted for studying shifts in inhibitory potency resulting from the addition of a second compound. Under the conditions used, the co-presence of dopamine, GBR 12935, or BTCP decreased the inhibitory potency of CFT or cocaine to the extent predicted by a model in which all compounds bind to the same site or the binding of all compounds is mutually exclusive. No evidence for negative allosteric interactions between CFT and BTCP was found in experiments comparing inhibition of [3H]CFT binding by BTCP at a low and high concentration of [3H]CFT.     

3H]N-[1-(2-benzo(b)thiophenyl)cyclohexyl]piperidine ([3H]BTCP): a new phencyclidine analog selective for the dopamine uptake complex

A benzothiophenyl group instead of a phenyl ring on phencyclidine (PCP) yields a molecule N-[1-(2-benzo(b)thiophenyl)cyclohexyl]piperidine (BTCP), which is one of the more potent known dopamine (DA) uptake inhibitors (IC50 = 7 nM). This compound also has low affinity for the PCP receptor (K0.5 = 6 microM). The sodium-dependent [3H]BTCP binding to rat striatal membranes was investigated. [3H]BTCP bound to two different sites: one with very high affinity (Kd1 = 0.9 nM, Bmax1 = 3.5 pmol/mg protein) which paralleled the distribution of dopaminergic nerve endings and a second with lower affinity (Kd2 = 20 nM, Bmax2 = 7.5 pmol/mg protein). There was a good correlation between the abilities of drugs specific for the DA uptake complex and of PCP analogs to inhibit high affinity [3H]BTCP binding and [3H]DA synaptosomal uptake. This study also demonstrated that PCP interacts with the DA uptake site since it is a competitive inhibitor of high affinity [3H]BTCP binding. This site, however, is not the PCP receptor, which has a different pharmacological selectivity.     

Structure-activity relationship studies of 4-[2-(diphenylmethoxy)ethyl]-1-benzylpiperidine derivatives and their N-analogues: evaluation of O-and N-analogues and their binding to monoamine transporters

In our effort to develop a pharmacotherapy for the treatment of cocaine addiction, we embarked on synthesizing novel molecules targeting the dopamine transporter (DAT) molecule in the brain as DAT has been implicated strongly in the reinforcing effect of cocaine. Our previously developed DAT-selective piperidine analogue, 4-[2-(diphenylmethoxy)ethyl]-1-benzylpiperidine, was the basis for our current structure-activity relationship (SAR) studies exploring the significance of the contribution of the benzhydryl O- and N-atoms in these molecules in interacting with the DAT. Thus, we replaced the benzhydryl O-atom with an N-atom, altered the location of the benzhydryl N-atom to an adjacent position, and in one other occasion converted the benzhydryl O-ether linkage into an oxime-type derivative. Furthermore, we also evaluated the important contribution of the piperidine N-atom to binding by altering its pK(a) value chemically. Novel analogues were tested for potency in inhibiting [3H]WIN 35,428, [3H]citalopram, and [3H]nisoxetine binding at the DAT, serotonin transporter (SERT), and norepinepherine transporter (NET). [3H]DA was used to measure DA reuptake inhibition. The results indicated that the benzhydryl O- and N-atoms are exchangeable for the most part. On the other hand, an enhanced interaction with the SERT was observed when the benzhydryl N-atom moved to an adjacent position (21a; DAT (IC(50)) = 19.7, SERT (IC(50)) = 137 nM, NET (IC(50)) = 1111 nM). In either cases, further alkylation of the N-atom reduced the activity for the transporter. The presence of a powerful electron-withdrawing cyano group in compound 5d expectedly produced the most potent and selective ligand for the DAT (DAT (IC(50)) = 3.7 nM, DAT/SERT = 615). Selected compounds were further analyzed in the dopamine reuptake inhibition assay. Preliminary behavioral assessment of some of the selected compounds in mice indicated that these compounds are much less stimulating when compared with cocaine at comparable doses. In drug-discrimination studies these selected compounds incompletely generalized from the cocaine stimulus in mice trained to discriminate 10 mg/kg cocaine from vehicle.     

Expansion of structure-activity studies of piperidine analogues of 1-[2-(diphenylmethoxy)ethyl]-4-(3-phenylpropyl)piperazine (GBR 12935) compounds by altering substitutions in the N-benzyl moiety and behavioral pharmacology of selected molecules.

A series of substituted N-benzyl analogues of the dopamine transporter (DAT) specific compound, 4-[2-(diphenylmethoxy)ethyl]-1-benzylpiperidine were synthesized and biologically characterized. Different 4'-alkyl, 4'-alkenyl, and 4'-alkynyl substituents were introduced in the phenyl ring of the benzyl moiety along with the replacement of the same phenyl ring by the isomeric alpha- and beta-naphthyl groups. Different polar substitutions at the 3'- and 4'-position were also introduced. Novel compounds were tested for their binding affinity at the dopamine, serotonin, and norepinephrine transporter systems in the brain by competing for [(3)H]WIN 35 428, [(3)H]citalopram, and [(3)H]nisoxetine, respectively. Selected compounds were also evaluated for their activity in inhibiting the uptake of [(3)H]dopamine. Binding results demonstrated that alkenyl and alkynyl substitutions at the 4'-position produced potent compounds in which compound 6 with a vinyl substitution was the most potent. In vivo evaluation of three selected compounds indicated that despite their high potency at the DAT, these compounds stimulated locomotor activity (LMA) less than cocaine when tested across similar dose ranges. In a drug discrimination study procedure, none of these three compounds generalized from cocaine in mice trained to discriminate 10 mg/kg cocaine from vehicle. In a 4 h time course LMA experiment, one of our previous lead piperidine derivatives (1a) showed considerable prolonged action. Thus, in this report, we describe a structure-activity relationship study of novel piperidine analogues assessed by both in vitro transporter assays and in vivo behavioral activity measurements.     

Pharmacological characterization of the discriminative stimulus properties of the phencyclidine analog, N-[1-(2-benzo(b)thiophenyl)-cyclohexyl]piperidine

Rationale: Although both cocaine and the phencyclidine analog, BTCP, have dopamine (DA) re-uptake blocking properties, under some conditions their behavioral effects can be differentiated. Therefore, we examined whether the discriminative stimulus (DS) effects of BTCP are different from those of cocaine. Objectives: To compare the effects of monoamine re-uptake blockers, varying in their in vitro potencies as inhibitors of DA, norepinephrine (NE), or serotonin re-uptake, in different groups of rats trained to discriminate either BTCP or cocaine from saline. Additionally, drugs from other pharmacological classes were tested in both groups. Methods: Rats were trained to discriminate either BTCP (5 mg/kg, i.p.) or cocaine (10 mg/kg, i.p.) from saline under a two-lever FR10 drug discrimination procedure. Results: BTCP and cocaine cross-substituted in BTCP- and cocaine-trained rats. The DA re-uptake blockers, mazindol, indatraline, methylphenidate, GBR12909, and GBR12935, occasioned dose-related drug-lever (DL) selection both in cocaine- and in BTCP-trained rats, with potencies that were significantly correlated. In contrast, the NE re-uptake blockers, nisoxetine, desipramine, and nortriptyline, produced higher levels of DL selection in BTCP-trained rats than in cocaine-trained rats, a profile like that reported in low-dose cocaine-trained rats. Drugs from other classes acted similarly in both discriminations. Further, the α₁-adrenergic antagonist prazosin dose dependently blocked the DS effects of the training dose of BTCP, but not of cocaine. Conclusions: Theresults suggest that the DS effects of BTCP are similar to cocaine, and resemble those of a low training dose of cocaine. Received: 6 October 1998 / Final version: 19 March 1999     

Development of long-acting dopamine transporter ligands as potential cocaine-abuse therapeutic agents: chiral hydroxyl-containing derivatives of 1-[2-[bis(4-fluorophenyl)methoxy]ethyl]-4-(3-phenylpropyl)piperazine and 1-[2-(diphenylmethoxy)ethyl]-4-(3-phenylpropyl)piperazine

In our search for long-acting agents for the treatment of cocaine abuse, a series of optically pure hydroxylated derivatives of 1-[2-[bis(4-fluorophenyl)methoxy]ethyl]-4-(3-phenylpropyl)piperazine (1) and 1-[2-(diphenylmethoxy)ethyl]-4-(3-phenylpropyl)piperazine (2) (GBR 12909 and GBR 12935, respectively) were synthesized and evaluated in vitro and in vivo. The enantiomers of the 2-hydroxylated analogues displayed substantial enantioselectivity. The S enantiomers displayed higher dopamine transporter (DAT) affinity and the R enantiomers were found to interact at the serotonin transporter (SERT) with higher affinity. The two-carbon spacer between the hydroxyl group and the piperazine ring was essential for enantioselectivity, and the length of the alkyl chain between the phenyl group and the piperazine ring influenced binding affinity and selectivity for the DAT and SERT. Phenylethyl analogues had a higher binding affinity for the SERT and a weaker affinity and selectivity for the DAT than the corresponding phenylpropyl analogues. Thus, (S)-(+)-1-[4-[2-[bis(4-fluorophenyl)methoxy]ethyl]piperazinyl]-3-phenylpropan-2-ol (6) displayed the highest affinity to the DAT, and (S)-(+)-1-[4-[2-(diphenylmethoxy)ethyl]piperazinyl]-3-phenylpropan-2-ol (8) had the highest selectivity. The latter (8) is one of the most DAT selective ligands known. In accord with the in vitro data, 6 showed greater potency than 7 in elevating extracellular dopamine levels in a microdialysis assay and in inhibiting cocaine-maintained responding in rhesus monkeys.     

Novel 3-aminomethyl- and 4-aminopiperidine analogues of 1-[2-(diphenylmethoxy)ethyl]-4-(3-phenylpropyl)piperazines: synthesis and evaluation as dopamine transporter ligands

We have undertaken a program to develop cocaine antagonists based on the premise that such compounds should block cocaine binding but permit reuptake of dopamine at the dopamine transporter (DAT). To evaluate the structural features of potential cocaine antagonists, 3-aminomethylpiperidine and 4-aminopiperidine moieties were incorporated at the central bridge region (piperazine ring) of GBR 12935. The compounds were assayed as inhibitors of [(125)I]RTI-55 binding at the DAT and monoamine transport. The results indicated that most of the new compounds preferentially inhibited norepinephrine reuptake by its transporter (NET) but in some cases retained binding selectivity for the DAT. In general, the binding selectivity and potency of [(3)H]NE reuptake inhibition were very sensitive to modifications of the central bridge diamine moiety (position of two basic nitrogen atoms). Compound 6 exhibited the highest ratio (14-fold) of DA reuptake inhibition to RTI-55 binding inhibition at the DAT; however, in an in vitro assay of cocaine antagonism, this compound failed to reduce inhibition of [(3)H]DA uptake by cocaine. These results demonstrated that separation of biological activities into the binding and reuptake inhibition can be achieved by alterations in the internal diamine component of GBR 12935, but additional modifications are necessary before these agents constitute lead compounds for development as cocaine antagonists.     

A comparison of the reinforcing efficacy of PCP, the PCP derivatives TCP and BTCP, and cocaine using a progressive ratio schedule in the rat

This study was designed to compare the reinforcing efficacy of PCP (phencyclidine:phenylcyclohexyl-piperidine) and the PCP-derivatives BTCP (N-[1-(2-benzo(b)thiophenyl) cyclohexyl]piperidine) and TCP (N-[1-(2-thienyl)cyclohexyl]-piperidine) to that of cocaine, using a progressive ratio schedule of reinforcement (PR). On the PR schedule the number of responses required to obtain an i.v. infusion of drug was escalated with each injection until a breaking point was reached when the animal stopped responding. Since BTCP has an affinity for the DA uptake site comparable to that of cocaine, it was hypothesized that BTCP and cocaine would show similar patterns of self-administration and comparable breaking points. In contrast, the high affinity of TCP and PCP for the NMDA-ion channel complex suggested that these two compounds would also support comparable self-administration behaviors. Rats were trained to self-administer i.v. cocaine during daily 5h sessions under a fixed-ratio-1 (FR1) schedule. Once consistent lever-pressing behavior was established, BTCP, PCP or TCP was substituted for cocaine. Under the FRI schedule, BTCP elicited a regular pattern of lever pressing, unlike PCP and TCP. However, under the PR schedule BTCP elicited breaking points comparable to those produced by equivalent doses of cocaine, whereas TCP and PCP produced considerably lower breaking points. These results suggest that BTCP has comparable rewarding properties to that of cocaine, and that like those of cocaine they are most probably mediated through a site of action at the DA transporter. In contrast, the relatively weak reinforcing efficacy of PCP and TCP would correlate better with their primary site of action on the PCP binding site within the NMDA-ion channel complex.     

Cocaine and GBR12909 produce equivalent motoric responses at different occupancy of the dopamine transporter.

The motoric-stimulating effect of dopamine (DA) reuptake blockers is thought to result from the increase in synaptic dopamine levels, which occurs as a consequence of blockade of DA reuptake. The present study tested measured occupancy of the DA transporter in vivo produced by behaviorally equivalent doses of the DA reuptake blockers GBR12909 (20 mg/kg), cocaine (20 mg/kg), WIN35-065-2 (1 mg/kg), and nomifensine (5 mg/kg). Two methods were used to measure in vivo occupancy of the DA transporter: a) an ex vivo method, in which the ability of whole brain supernatants, prepared from rats administered the test drugs, were tested for their ability to inhibit the reuptake of [3H]DA by striatal synaptosomes; and b) an in vivo binding assay using [3H]N-[1-(2-benzo(b)thiophenyl)cyclohexyl]piperidine ([3H]BTCP) to label the striatal DA transporter in vivo. Considerable data support the notion that this measurement is predictive of transporter occupancy in the nucleus accumbens. Similar results were obtained with both methods: The order of potency for apparent transporter occupancy was GBR12909 > nomifensine > WIN35-065-2 = cocaine. These data indicate that it takes greater occupancy of the DA transporter by GBR12909 to produce behavioral effects equivalent to those produced by cocaine at lower transporter occupancy. The data of the present study suggest, therefore, that studies relating the effects of DA reuptake inhibitors on DA-mediated motoric behaviors to DA transporter occupancy might facilitate the identification of novel compounds potentially useful for the pharmacotherapy of cocaine abuse.     

Synthesis and transporter binding properties of bridged piperazine analogues of 1-[2-[bis(4-fluorophenyl)methoxy]ethyl]-4-(3-phenylpropyl)piperazine (GBR 12909)

A series of analogues related to 1-[2-(diphenylmethoxy)ethyl]-4-(3-phenylpropyl)piperazine (2) and 1-?2-[bis(4-fluorophenyl)methoxy]ethyl?-4-(3-phenylpropyl)piperazine (3) (GBR 12935 and GBR 12909, respectively), in which the piperazine moiety was replaced by bridged piperazines for structural rigidity, has been designed, synthesized, and evaluated for their ability to bind to the dopamine transporter (DAT) and to inhibit the uptake of (3)H-labeled dopamine (DA). The binding data indicated that compounds 7 and 11, the N-methyl- and N-propylphenyl-3,8-diaza[3.2. 1]bicyclooctane analogues of 3, showed high affinity for the DAT (IC(50) = 8.0 and 8.2 nM, respectively), and 7 had high selectivity at the DAT relative to the serotonin transporter (SERT) (88- and 93-fold for binding and reuptake, respectively). They also displayed linear activity in DA uptake inhibition, possessing a similar binding and reuptake inhibition profile to 3. The N-indolylmethyl analogue 16 showed the highest affinity (IC(50) = 1.4 nM) of the series, with a 6-fold increase over its corresponding N-phenypropyl derivative 11. Interestingly, this compound exhibited a high ratio (29-fold) of IC(50) for the inhibition of DA reuptake versus binding to the DAT. Replacing the piperazine moiety of 2 and 3 with (1S, 4S)-2,5-diazabicyclo[2.2.1]heptane resulted in compounds 23-26, which showed moderate to poor affinity (IC(50) = 127-1170 nM) for the DAT. Substitution of the homopiperazine moiety of 4 with a more rigid 3,9-diazabicyclo[4.2.1]nonane gave compounds 28-33. However, the binding data showed that compound 32 displayed a 10-fold decrease in affinity at the DAT and a 100-fold decrease in selectivity at the DAT relative to the SERT compared to its corresponding homopiperazine compound 4.     

Priming with BTCP, a dopamine reuptake blocker, reinstates cocaine-seeking and enhances cocaine cue-induced reinstatement

N-[1-(2-benzo[b]thiophenyl)cyclohexyl]piperidine (BTCP), a potent dopamine reuptake inhibitor, substitutes for the reinforcing effects of cocaine and meets other criteria for possible agonist pharmacotherapeutic potential. The purpose of this study was to determine (1) whether BTCP modifies reinstatement of cocaine-seeking elicited by cocaine-related environmental stimuli and (2) whether this compound produces priming effects. Male Wistar rats were trained to associate discriminative stimuli (S(D)) with cocaine availability (0.25 mg/infusion) versus non-reward and then were subjected to repeated extinction sessions during which the reinforcer and S(D) were withheld. Subsequent presentation of the cocaine S(D) produced recovery of cocaine-seeking. BTCP (2.5-30 mg/kg; i.p.) did not attenuate the conditioned reinstatement induced by the cocaine S(D) but, rather, potentiated this effect at 10 mg/kg. To test whether BTCP, by itself, exerts priming effects, different groups of rats were trained to self-administer cocaine (0.25 mg/infusion) for 2 weeks. After a 2-week extinction period, BTCP (5, 10 and 20 mg/kg, i.p.) reinstated cocaine-seeking, showing that BTCP not only increases cocaine-seeking induced by cocaine-related stimuli but also produces priming effects following abstinence. The results suggest that, in cocaine abstinent rats, BTCP produces cocaine-like effects.     

Oxygenated analogues of 1-[2-(Diphenylmethoxy)ethyl]- and 1-[2-[Bis(4-fluorophenyl)methoxy]ethyl]-4-(3-phenylpropyl)piperazines (GBR 12935 and GBR 12909) as potential extended-action cocaine-abuse therapeutic agents

An investigation into the preparation of potential extended-release cocaine-abuse therapeutic agents afforded a series of compounds related to 1-[2-(diphenylmethoxy)ethyl]-4-(3-phenylpropyl)piperazine (1a) and 1-[2-[bis(4-fluorophenyl)methoxy]ethyl]-4-(3-phenylpropyl)piperazine (1b) (GBR 12935 and GBR 12909, respectively), which were designed, synthesized, and evaluated for their ability to bind to the dopamine transporter (DAT) and to inhibit the uptake of [(3)H]-labeled dopamine (DA). The addition of hydroxy and methoxy substituents to the benzene ring on the phenylpropyl moiety of 1a-1d resulted in a series of potent and selective ligands for the DAT (analogues 5-28). The hydroxyl groups were included to incorporate a medium-chain carboxylic acid ester into the molecules, to form oil-soluble prodrugs, amenable to "depot" injection techniques. The introduction of an oxygen-containing functionality to the propyl side chain provided ketones 29 and 30, which demonstrated greatly reduced affinity for the DAT and decreased potency in inhibiting the uptake of [(3)H]DA, and benzylic alcohols 31-36, which were highly potent and selective at binding to the DAT and inhibiting [(3)H]DA uptake. The enantiomers of 32 (34 and 36) were practically identical in biological testing. Compounds 1b, 32, 34, and 36 all demonstrated the ability to decrease cocaine-maintained responding in monkeys without affecting behaviors maintained by food, with 34 and 36 equipotent to each other and both more potent in behavioral tests than the parent compound 1b. Intramuscular injections of compound 41 (the decanoate ester of racemate 32) eliminated cocaine-maintained behavior for about a month following one single injection, without affecting food-maintained behavior. The identification of analogues 32, 34, and 36, thus, provides three potential candidates for esterification and formulation as extended-release cocaine-abuse therapeutic agents.     

Desipramine and the phencyclidine derivative BTCP differently inhibit [3H]TCP binding to high- and low-affinity sites.

The effects of N-[1-(2-benzo(b)thiophenyl)cyclohexyl]piperidine (BTCP) and desipramine on [3H]N-[1-(2-thienyl)cyclohexyl]piperidine ([3H]TCP) binding were investigated in vivo and in vitro. In the cerebrum, both drugs were competitive inhibitors of high-affinity [3H]TCP binding. Conversely, in the cerebellum, they were non-competitive inhibitors of low-affinity [3H]TCP binding. These results imply that the different [3H]TCP binding sites have distinct pharmacological properties, and show that, although chemically related to TCP, BTCP has an effect similar to that of desipramine.     

The effects of the phencyclidine analogs BTCP and TCP on nigrostriatal dopamine neuronal activity

Extracellular single unit recording techniques were used to evaluate the effects of two phencyclidine (PCP) derivatives. N-[1-(2-benzo(b)thiophenyl)cyclohexyl]piperidine (BTCP) and N-[1-(2-thiophenyl)cyclohexyl]piperidine (TCP) on the electrophysiological activity of antidromically identified nigrostriatal dopamine (DA) neurons in chloral hydrate-anesthetized rats. I.v. BTCP produced a dose-dependent decrease in the firing rate of identified nigrostriatal DA neurons whereas TCP elicited a dose-dependent biphasic effect which was characterized by an activation of cell firing at low doses followed by a reversal of the response with larger doses. A hemitransection of the brain anterior to the substantia nigra significantly reduced the inhibitory effect of BTCP while this surgical procedure did not affect the response to TCP. However, iontophoretic application of BTCP induced a current-dependent inhibition of the spontaneous activity of cells while local application of TCP had no effect on the firing rate of these cells. These data indicate that PCP analogs are able to interact with the nigrostriatal DAergic pathway through distinct and opposing mechanisms. The results are discussed in light of recent observations that BTCP is selective for the DA uptake site while TCP is selective for the high affinity PCP binding site.     

Effects of heterocyclic amines in food on dopamine metabolism in nigro-striatal dopaminergic neurons

We investigated the effects of 14 heterocyclic amines in food on nigro-striatal dopaminergic neurons. Among 14 compounds tested, 3-amino-1,4-dimethyl-5H-pyrido[4,3-b]indole (Trp-P-1) and 3-amino-1-methyl-5H-pyrido[4,3-b]indole (Trp-P-2) caused substantial decreases in 3,4-dihydroxy-phenylalanine (DOPA) formation in striatal tissue slice system. When Trp-P-1 or Trp-P-2 was unilaterally infused in the rat striatum by an in vivo micro-dialysis technique, both compounds produced a transient increase of dopamine (DA) and continuous decreases in the metabolites, homovanillic acid (HVA) and 3,4-dihydroxyphenylacetic acid (DOPAC) in the perfusate. This suggests that the two compounds inhibit monoamine oxidase (MAO) in vivo. Indeed they were found to be very potent inhibitors of MAO in vitro. Systemic administration of Trp-P-1 to C57 Black mice caused a marked decrease of DOPAC content and a significant increase of DA in the striatum, indicating inhibition of MAO in vivo. These results suggest that Trp-P-1 and Trp-P-2 contained in food could alter the metabolism of DA in the brain.