Population pharmacokinetics, brain distribution, and pharmacodynamics of 2nd generation dopamine transporter selective benztropine analogs developed as potential substitute therapeutics for treatment of cocaine abuse (original) (raw)
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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 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.
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 Medicinal Chemistry, 2003
A series of 8-substituted-3-azabicyclo[3.2.1]octanes (isotropanes) were synthesized and tested for inhibitor potency using [ 3 H]WIN 35,428 binding at the dopamine (DA) transporter, [ 3 H]citalopram binding at the serotonin (5-HT) transporter, and [ 3 H]DA uptake assays. The synthesis started with a Mannich condensation of cyclopentanone, benzylamine, and fomaldehyde to afford N-benzyl-3-azabicyclo[3.2.1]octan-8-one (6). The 8-phenyl group was introduced by Grignard addition to ketone 6 or nucleophilic displacement via a triflate of the corresponding alcohol 7a. The 8-phenyl-8R-alcohols from Grignard addition generally have low affinity for the two transporters and do not effectively inhibit the uptake of [ 3 H]DA. The 8-phenyl compound (14) without the hydroxyl group at C-8 was much more potent (22-fold) for [ 3 H]WIN 35,428 binding inhibition than the corresponding 8-phenyl-8R-hydroxy compound (7a). The 8R-phenyl compound 8a was almost as potent as cocaine in binding to the DA transporter (IC 50) 234 nM vs 159 nM for cocaine), whereas the C-8 epimer, compound 14, was somewhat less potent (IC 50) 785 nM). The lower potency of 14 (-orientation of 8-phenyl group) as compared to 8a (R-orientation) was unexpected, based on modeling studies comparing the new compounds to WIN 35,065-2, an analogue of cocaine. The benzhydryl ethers at C-8 (17), analogous to the benztropines, had better selectivity than the corresponding phenyl compounds, 8a and 14, for the DA transporter as compared to the 5-HT transporter. The isotropane and benzisotropine analogues seem to bind in a manner that is more similar to that of the benztropine compounds 5 rather than those of cocaine and WIN 35,065-2.
Psychopharmacology, 2000
RATIONALE: The reinforcing effects of many psychomotor stimulants have been related to increased dopaminergic neurotransmission. Drugs that block dopamine (DA) uptake have generally been found to function as positive reinforcers. Benztropine (BZT) and several of its halogenated analogs have previously been characterized as potent DA-uptake inhibitors with behavioral profiles that indicate diminished psychomotor stimulant effects relative to cocaine. OBJECTIVES: The present experiments were designed to examine, in rhesus monkeys, the reinforcing effects of the DA-uptake inhibitor BZT and two chloro-analogs 3'-Cl-BZT and 4'-Cl-BZT, and to compare self-administration and binding profiles. METHODS: Four rhesus monkeys self-administered cocaine i.v. under a fixed-ratio 10 (FR10) schedule until stable responding was established. Saline, and various doses of cocaine, BZT, and the BZT analogs were then made available for self-administration. Binding of these compounds to monoaminergic and cholinergic sites in monkey brain were determined using standard radioligand binding techniques. RESULTS: Self-administration was maintained by both 3'-Cl-BZT and 4'-Cl-BZT, but not by BZT. Results suggested that 3'-Cl-BZT and 4'-Cl-BZT were weak positive reinforcers. BZT and analogs bound DA transporters (DAT) with affinities higher than that of cocaine and had affinity for muscarinic binding sites. CONCLUSIONS: Surprisingly, high affinity at DATs was associated with weak or no reinforcing effects. The mechanism(s) that may underlie this dissociation between DAT actions and reinforcing effects remains to be established. These data support the proposal that a lead for the discovery of a pharmacotherapeutic agent for cocaine abuse may come from this group of compounds.
Behavioral effects of novel cocaine analogs: a comparison with in vivo receptor binding potency
The Journal of pharmacology and experimental therapeutics, 1992
Several novel cocaine analogs, previously shown to be very potent in in vitro binding studies, have been examined for their stimulatory effects on locomotor activity and for their ability to displace [3H]WIN 35,428 binding in vivo in mice. These compounds, like WIN 35,428, lack an ester link between the phenyl group and the tropane ring and have para-substitutions on the phenyl ring. They were much more potent than (-)-cocaine in producing increases in locomotor activity. In addition, they were more potent than (-)-cocaine in inhibiting [3H]WIN 35,428 binding in vivo in mouse striatum. Thus, these compounds demonstrate similar high potency in behavioral tests and in receptor binding assays, both in vivo and in vitro. Results support the hypothesis of a relationship between binding at the dopamine transporter and the behavioral effects of cocaine-like drugs. Further, assuming that maximal occupancy occurs with total displacement of [3H]WIN 35,428 binding in vivo, the data suggest tha...
Journal of Pharmacology and Experimental Therapeutics, 2009
Benztropine (BZT) analogs inhibit dopamine uptake but are less effective than cocaine in producing behavioral effects predicting abuse liability. The present study compared reinforcing effects of intravenous BZT analogs with those of standard monoamine uptake inhibitors and the effects of their oral pretreatment on cocaine self-administration. Responding of rats was maintained by cocaine [0.032-1.0 mg/kg/injection (inj)] or food reinforcement under fixed-ratio five-response schedules. Maximal rates of responding were maintained by 0.32 mg/kg/inj cocaine or substituted methylphenidate, with lower rates maintained at lower and higher doses. The N-methyl BZT analog, AHN 1-055 (3␣-[bis(4Ј-fluorophenyl)methoxy]-tropane), also maintained responding (0.1 mg/kg/inj), although maximal rates were less than those with cocaine. Responding was not maintained above vehicle levels by the N-allyl, AHN 2-005 (N-allyl-3␣-[bis(4Ј-fluorophenyl)methoxy]-tropane), and N-butyl, JHW 007 [N-(n-butyl)-3␣-[bis(4Ј-fluorophenyl)methoxy]-tropane], BZT analogs, and it was not maintained with nisoxetine or