Discovery of Drugs to Treat Cocaine Dependence: Behavioral and Neurochemical Effects of Atypical Dopamine Transport Inhibitors (original) (raw)
Related papers
Psychopharmacology, 2001
Rationale: Previous SAR studies demonstrated that small halogen substitutions on the diphenylether system of benztropine (BZT), such as a para-Cl group, retained high affinity at the cocaine binding site on the dopamine transporter. Despite this high affinity, the compounds generally had behavioral effects different from those of cocaine. However, compounds with meta-Cl substitutions had effects more similar to those of cocaine. Objectives: A series of phenyl-ring analogs of benztropine (BZT) substituted with 3′-, 4′-, 3′,4′′- and 4′,4′′-position Cl-groups were synthesized and their pharmacology was evaluated in order to assess more fully the contributions to pharmacological activity of substituents in these positions. Methods: Compounds were synthesized and their pharmacological activity was assessed by examining radioligand binding and behavioral techniques. Results: All of the compounds displaced [3H]WIN 35,428 binding with affinities ranging from 20 to 32.5 nM. Affinities at norepinephrine ([3H]nisoxetine) and serotonin ([3H]citalopram) transporters, respectively, ranged from 259 to 5120 and 451 to 2980 nM. Each of the compounds also inhibited [3H]pirenzepine binding to muscarinic M1 receptors, with affinities ranging from 0.98 to 47.9 nM. Cocaine and the BZT analogs produced dose-related increases in locomotor activity in mice. However, maximal effects of the BZT analogs were uniformly less than those produced by cocaine, and were obtained 2–3 h after injection compared to the relatively rapid onset (within 30 min) of cocaine effects. In rats trained to discriminate IP saline from 29 µmol/kg cocaine (10 mg/kg), cocaine produced a dose-related increase in responding on the cocaine lever, reaching 100% at the training dose; however, none of the BZT analogs fully substituted for cocaine, with maximum cocaine responding from 20 to 69%. Despite their reduced efficacy compared to cocaine in cocaine discrimination, none of the analogs antagonized the effects of cocaine. As has been reported previously for 4′-Cl-BZT, the cocaine discriminative-stimulus effects were shifted leftward by co-administration of the present BZT analogs. Conclusions: The present results indicate that although the BZT analogs bind with relatively high affinity and selectivity at the dopamine transporter, their behavioral profile is distinct from that of cocaine. The present results suggest that analogs of BZT may be useful as treatments for cocaine abuse in situations in which an agonist treatment is indicated. These compounds possess features such as reduced efficacy compared to cocaine and a long duration of action that may render them particularly useful leads for the development of therapeutics for cocaine abusers.
Journal of Pharmaceutical Sciences, 2008
A second generation of N-substituted 3a-[bis(4 0 -fluorophenyl)methoxy]tropanes (GA 1-69, JHW 005 and JHW 013) binds with high affinity to the dopamine transporter (DAT) and are highly selective toward DAT compared to muscarinic receptor binding (M 1 ). The objective of this study was to characterize brain distribution, pharmacokinetics, and pharmacodynamics [extracellular brain dopamine (DA) levels] of three novel N-substituted benztropine (BZT) analogs in male Sprague-Dawley rats. The BZT analogs displayed a higher distribution (V d ¼ 8.69-34.3 vs. 0.9 L/kg) along with longer elimination (t 1/2 : 4.1-5.4 vs. 0.5 h) than previously reported for cocaine. Brain-toplasma partition coefficients were 1.3-2.5 vs. 2.1 for cocaine. The effect of the BZT analogs on extracellular brain (DA) levels ranged from minimal effects (GA 1-69) to several fold elevation ($850% of basal DA for JHW 013) at the highest dose evaluated. PK/PD analysis of exposure-response data resulted in lower IC 50 values for the BZT analogs compared to cocaine indicating their higher potency to inhibit DA reuptake (0.1-0.3 vs. 0.7 mg/L). These BZT analogs possess significantly different PK and PD profiles as compared to cocaine suggesting that further evaluation as cocaine abuse therapeutics is warranted. ß
Journal of Neurochemistry, 2008
The widely abused psychostimulant cocaine is thought to elicit its reinforcing effects primarily via inhibition of the neuronal dopamine transporter (DAT). However, not all DAT inhibitors share cocaine's behavioral profile, despite similar or greater affinity for the DAT. This may be due to differential molecular interactions with the DAT. Our previous work using transporter mutants with altered conformational equilibrium (W84L and D313N) indicated that benztropine and GBR12909 interact with the DAT in a different manner than cocaine. Here, we expand upon these previous findings, studying a number of structurally different DAT inhibitors for their ability to inhibit [ 3 H]CFT binding to wildtype, W84L and D313N transporters. We systematically tested structural intermediates between cocaine and benztropine, structural hybrids of benztropine and GBR12909 and a number of other structurally heterologous inhibitors. Derivatives of the stimulant desoxypipradrol (2-benzhydrylpiperidine) exhibited a cocaine-like binding profile with respect to mutation, whereas compounds possessing the diphenylmethoxy moiety of benztropine and GBR12909 were dissimilar to cocaine-like compounds. In tests with specific isomers of cocaine and tropane analogues, compounds with 3α stereochemistry tended to exhibit benztropine-like binding, whereas those with 3β stereochemistry were more cocaine-like. Our results point to the importance of specific molecular features-most notably the presence of a diphenylmethoxy moiety-in determining a compound's binding profile. This study furthers the concept of using DAT mutants to differentiate cocaine-like inhibitors from atypical inhibitors in vitro. Further studies of the molecular features that define inhibitor-transporter interaction could lead to the development of DAT inhibitors with differential clinical utility.
Identification of a Dopamine Transporter Ligand That Blocks the Stimulant Effects of Cocaine
Journal of Neuroscience, 2005
There is a large unmet medical need for cocaine addiction treatments. Studies have indicated that the dopamine transporter (DAT) is the primary biological target of cocaine, and most drugs that have DAT affinity have behavioral effects like those of cocaine. However, analogs of benztropine have high DAT affinity and behavioral effects that show varying degrees of similarity to cocaine. We now report the discovery that a benztropine analog, JHW007, with high affinity for the DAT does not have cocaine-like behavioral effects and antagonizes the effects of cocaine. JHW007 occupied the DAT in vivo more slowly than did cocaine and had not reached an apparent plateau up to 270 min after injection. The in vivo binding of cocaine to the DAT suggested rate of DAT occupancy as an important contributor to its behavioral effects, and the slow association with the DAT may provide an explanation for JHW007 being relatively devoid of cocaine-like behavioral effects. The antagonism of cocaine suggests that DAT ligands with reduced cocaine-like activity can function as cocaine antagonists and suggests JHW007 as a lead for discovery of cocaine-abuse pharmacotherapeutics.
Journal of Pharmacology and Experimental Therapeutics, 2005
Analogs of benztropine (BZT) bind to the dopamine (DA) transporter and inhibit DA uptake but often have behavioral effects that differ from those of cocaine and other DA-uptake inhibitors. To better understand these differences, we examined the relationship between locomotor-stimulant effects of cocaine, 1-{2-[bis-(4-fluorophenyl)methoxy]ethyl}-4-(3-phenylpropyl)piperazine (GBR 12909), and BZT analogs [(3␣-[bis(4Јfluorophenyl)methoxy]-tropane) (AHN 1-055) and (N-allyl-3␣-[bis(4Ј-fluorophenyl)methoxy]-tropane) (AHN 2-005)] and their in vivo displacement of the DA transporter ligand [ 125 I]3-(4iodophenyl)-tropan-2-carboxylic acid isopropyl ester hydrochloride (RTI-121) in striatum. Cocaine, GBR 12909, and BZT analogs each displaced [ 125 I]RTI-121 and stimulated locomotor activity in a dose-and time-dependent manner. The time course revealed a slower onset of both effects for AHN 1-055 and AHN 2-005 compared with cocaine and GBR 12909. The BZT analogs were less effective than cocaine and GBR 12909 in stimulating locomotor activity. Locomotor stimulant effects of cocaine were generally greater than predicted by the regression of displacement of [ 125 I]RTI-121 and effect at short times after injection and less than predicted at longer times after injection. This result suggests that the apparent rate of occupancy of the DA transporter, in addition to percentage of sites occupied, contributes to the behavioral effects of cocaine. The present results suggest that among drugs that act at the DA transporter, the slower apparent rates of occupancy with the DA transporter by the BZT analogs may contribute in an important way to differences in their effectiveness. Article, publication date, and citation information can be found at http://jpet.aspetjournals.org.
Journal of Pharmacology and Experimental Therapeutics, 2005
Analogs of benztropine (BZT) bind to the dopamine (DA) transporter and inhibit DA uptake but often have behavioral effects that differ from those of cocaine and other DA-uptake inhibitors. To better understand these differences, we examined the relationship between locomotor-stimulant effects of cocaine, 1-{2-[bis-(4-fluorophenyl)methoxy]ethyl}-4-(3-phenylpropyl)-piperazine (GBR 12909), and BZT analogs [(3alpha-[bis(4'-fluorophenyl)methoxy]-tropane) (AHN 1-055) and (N-allyl-3alpha-[bis(4'-fluorophenyl)methoxy]-tropane) (AHN 2-005)] and their in vivo displacement of the DA transporter ligand [125I]3beta-(4-iodophenyl)-tropan-2beta-carboxylic acid isopropyl ester hydrochloride (RTI-121) in striatum. Cocaine, GBR 12909, and BZT analogs each displaced [125I]RTI-121 and stimulated locomotor activity in a dose- and time-dependent manner. The time course revealed a slower onset of both effects for AHN 1-055 and AHN 2-005 compared with cocaine and GBR 12909. The BZT analogs were less effective than cocaine and GBR 12909 in stimulating locomotor activity. Locomotor stimulant effects of cocaine were generally greater than predicted by the regression of displacement of [125I]RTI-121 and effect at short times after injection and less than predicted at longer times after injection. This result suggests that the apparent rate of occupancy of the DA transporter, in addition to percentage of sites occupied, contributes to the behavioral effects of cocaine. The present results suggest that among drugs that act at the DA transporter, the slower apparent rates of occupancy with the DA transporter by the BZT analogs may contribute in an important way to differences in their effectiveness.
Neurochemistry International, 2019
The dopamine transporter (DAT) is a neuronal membrane protein that is responsible for reuptake of dopamine (DA) from the synapse and functions as a major determinant in control of DA neurotransmission. Cocaine and many psychostimulant drugs bind to DAT and block reuptake, inducing DA overflow that forms the neurochemical basis for euphoria and addiction. Paradoxically, however, some ligands such as benztropine (BZT) bind to DAT and inhibit reuptake but do not produce these effects, and it has been hypothesized that differential mechanisms of binding may stabilize specific transporter conformations that affect downstream neurochemical or behavioral outcomes. To investigate the binding mechanisms of BZT on DAT we used the photoaffinity BZT analog [ 125 I]N-[n-butyl-4-(4‴-azido-3‴-iodophenyl)]-4′,4″-difluoro-3α-(diphenylmethoxy)tropane ([ 125 I]GA II 34) to identify the site of cross-linking and predict the binding pose relative to that of previously-examined cocaine photoaffinity analogs. Biochemical findings show that adduction of [ 125 I]GA II 34 occurs at residues Asp79 or Leu80 in TM1, with molecular modeling supporting adduction to Leu80 and a pharmacophore pose in the central S1 site similar to that of cocaine and cocaine analogs. Substituted cysteine accessibility method protection analyses verified these findings, but identified some differences in structural stabilization relative to cocaine that may relate to BZT neurochemical outcomes.
Dopamine Transporter Dynamics of N-Substituted Benztropine Analogs with Atypical Behavioral Effects
Journal of Pharmacology and Experimental Therapeutics, 2018
Atypical dopamine transporter (DAT) inhibitors, despite high DAT affinity, do not produce the psychomotor stimulant and abuse profile of standard DAT inhibitors such as cocaine. Proposed contributing features for those differences include off-target actions, slow onsets of action, and ligand bias regarding DAT conformation. Several 3a-(49,499-difluorodiphenylmethoxy)tropanes were examined, including those with the following substitutions: N-(indole-399-ethyl)-(GA1-69), N-(R)-299-amino-399-methyl-n-butyl-(GA2-50), N-299aminoethyl-(GA2-99), and N-(cyclopropylmethyl)-(JHW013). These compounds were previously reported to have rapid onset of behavioral effects and were presently evaluated pharmacologically alone or in combination with cocaine. DAT conformational mode was assessed by substitutedcysteine accessibility and molecular dynamics (MD) simulations. As determined by substituted-cysteine alkylation, all BZT analogs except GA2-99 showed bias for a cytoplasmicfacing DAT conformation, whereas cocaine stabilized the extracellular-facing conformation. MD simulations suggested that several analog-DAT complexes formed stable R85-D476 "outer gate" bonds that close the DAT to extracellular space. GA2-99 diverged from this pattern, yet had effects similar to those of other atypical DAT inhibitors. Apparent DAT association rates of the BZT analogs in vivo were slower than that for cocaine. None of the compounds was self-administered or stimulated locomotion, and each blocked those effects of cocaine. The present findings provide more detail on ligandinduced DAT conformations and indicate that aspects of DAT conformation other than "open" versus "closed" may facilitate predictions of the actions of DAT inhibitors and may promote rational design of potential treatments for psychomotorstimulant abuse.
Journal of Pharmacology and Experimental Therapeutics, 2013
ABSTRACT An N-butyl analog of benztropine, JHW007, binds to dopamine transporters (DAT), but has reduced cocaine-like behavioral effects and antagonizes various effects of cocaine. The present studies further examined mechanisms underlying these effects. Cocaine dose-dependently increased locomotion, whereas JHW007 was minimally effective, but increased activity 24-hr after injection. JHW007 (3-10 mg/kg) dose-dependently and fully antagonized the locomotor-stimulant effects of cocaine (5-60 mg/kg), whereas N-methyl and N-allyl analogs and the dopamine (DA) uptake inhibitor, GBR12909, stimulated activity and failed to antagonize effects of cocaine. JHW007 also blocked the locomotor-stimulant effects of the DAT inhibitor, GBR12909, but not stimulation produced by the δ-opioid agonist, SNC80, which increases activity through non-dopaminergic mechanisms. JHW007 blocked locomotor-stimulant effects of cocaine in both DA D2 and CB1 receptor knock-out and wild-type mice, indicating a lack of involvement of these targets. Further, JHW007 also blocked effects of cocaine on stereotyped rearing but enhanced stereotyped sniffing; suggesting that interference with locomotion by enhanced stereotypies is not responsible for the cocaine-antagonist effects of JHW007. Time-course data indicate that administration of JHW007 antagonized the locomotor-stimulant effects of cocaine within 10-min of injection, whereas occupancy at the DAT determined in vivo did not reach a maximum until 4.5 hr after injection. The sigma1-receptor antagonist, BD1008, blocked the locomotor-stimulant effects of cocaine. Overall, these findings suggest that the JHW007 has cocaine-antagonist effects that are deviate from its DAT occupancy and that some other mechanism, possibly sigma-receptor antagonist activity, may contribute to the cocaine-antagonist effect of JHW007 and like drugs.
Life Sciences, 1990
Structure-activlty relationships for cocaine and analog binding at the depamine, norepinephrine and serotonin transporters were determined. Cocaine inhibition of llgand binding to each of these sites has a stereospecific requirement for the levorotatory isomer. Binding potencies of cocaine derivatives involving N-substltution, C2 and C3 substituent modifications, however, revealed differences in structure-activity relationships for cocaine binding at the transporters. Removal of the N-methyl groups produced little change in binding potency at the dopamlne transporter site hut produced increases in binding potency at norepinephrlne and serotonin transporter sites. Changes in structure at the C2 substituent produced changes in binding potency at the dopamlne transporter which were generally similar in direction, but not necessarily in magnitude at the noreplnephrine and serotonin transporters. Modifications to the C3 substituent, especially substitution of a hydroxyl moiety, produce changes in affinity at norepinephrine and serotonin transporters which are much larger than those observed at dopamine transporters. In general, our results indicate that unique structural requirements exist for each transporter site, but that cocaine binding at norepinephrine and dopamine transporters can be described by more similar structure-actlvity relationships than those found for the serotonin transporter. Reguirements for cocaine binding to the dopamine transporter, which we have previously shown to be associated with the reinforcing effects of cocaine, include levorotatory sterospeclficlty, the benzene ring at C3, at least some portions of the tropane ring, and the presence of the C2 methyl ester group in the ~ conformation. A variety of psychoactive drugs are known to inhibit the active neurotransmitter uptake process and as well as llgand binding to transporter sites. Cocaine, in particular, has been shown to inhibit the transport of dop~nine, norepinephrine and serotonin (i, 2, 3, 4, 5) and to interact with some receptors (6, 7, 8). Recently, Ritz et al. (9) presented evidence that the cocaine inhibition of 3H-mazindol binding to the dopamine transporter may be related to the reinforcing properties of cocaine and related drugs.