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B K Madras

Publications and source records attributed to B K Madras.

At least 37 records · Page 2Linked to original sources
PubMed1998

Altropane, a SPECT or PET imaging probe for dopamine neurons: II. Distribution to dopamine-rich regions of primate brain.

The dopamine transporter in brain, localized almost exclusively on dopamine neurons, is an effective window on dopamine neurons. SPECT or PET imaging of the transporter in brain requires selective imaging agents that display appropriate pharmacokinetic properties. We previously reported that [125I]altropane ([125I]IACFT,2beta-carbomethoxy-3beta-(4-fluorophenyl)-n-(1- iodoprop-1-en-3-yl)nortropane) bound with high affinity (Kd: 5.33 nM) to a single site on the dopamine transporter and was selective for dopamine over the serotonin transporter in homogenates of monkey striatum. To determine whether the selective binding of [125I]altropane is reflected in its brain distribution, the in vitro and ex vivo distribution of [125I]altropane in squirrel monkey (Saimiri sciureus) brain was determined by quantitative autoradiography of coronal brain sections. In vitro, [125I]altropane (2 nM) distribution was discrete and was detectable primarily in the dopamine-rich putamen, caudate nucleus, and nucleus accumbens. The resulting putamen:cerebellum ratio exceeded 120:1 (n = 3). The selective in vitro binding of [125I]altropane to the dopamine transporter, at concentrations approaching its Kd value (Kd: 5.33 nM, a single high affinity site), highlight its suitability for investigating the density of the dopamine transporter in various brain regions in vitro. Ex vivo autoradiography was conducted in monkeys to determine whether the brain distribution of [125I]altropane in vitro was predictive of its brain distribution pattern after intravenous administration. Thirty minutes after intravenous injection, highest levels of [125I]altropane (0.3 nmol/kg) were detected in the caudate-putamen and nucleus accumbens and lowest levels in the cerebellum and cortex. The putamen or caudate:cerebellum ratio was 7. SPECT imaging of the brain within 30 min of i.v. injection confirmed the rapid and selective accumulation of [123I]altropane to the striatum. The selective binding of altropane to the dopamine-rich striatum within 30 min of i.v. administration indicates that it is uniquely suited for SPECT or PET imaging of the dopamine transporter and associated dopamine neurons.

Animals↗
PubMed1998

Altropane, a SPECT or PET imaging probe for dopamine neurons: III. Human dopamine transporter in postmortem normal and Parkinson's diseased brain.

Increasing evidence suggests that the dopamine transporter is situated almost exclusively on dopamine neurons. Accordingly, it is an valuable marker for Parkinson's disease and other pathological states of dopamine neurons. We previously demonstrated that the potent dopamine transport inhibitor [125I]altropane (IACFT:E-N-iodoallyl-2beta-carbomethoxy-3beta-(4-fluor ophenyl)tropane) is a high affinity selective probe for the dopamine transporter in monkey brain and an effective SPECT imaging agent in nonhuman primate brain. We now report the binding properties of [125I]altropane in postmortem tissue of normal human brain and compare the findings to Parkinson's diseased brain. In homogenates of human brain putamen, [125I]altropane bound with high affinity (KD: 4.96 +/- 0.38 nM, n = 4) and site density (BMAX: 212 +/- 41.1 pmol/g original wet tissue weight) well within the density range reported previously for the dopamine transporter in this brain region. Drugs inhibited [125I]altropane binding with a rank order of potency that corresponded closely to their rank order for blocking dopamine transport (r 0.98, P < 0.001). In postmortem Parkinson's diseased brain, bound [125I]altropane (1 nM) was markedly reduced (89%, 99% in putamen, depending on measures of nonspecific binding) compared with normal aged-matched controls (normal putamen: 49.2 +/- 8.1 pmol/g; Parkinson's diseased putamen: 0.48 +/- 0.33 pmol/g; n = 4). In vitro autoradiography, conducted in tissue sections at a single plane of the basal ganglia, revealed high levels of [125I]altropane binding the caudate nucleus and putamen, but lower levels (73% of the caudate-putamen) in the nucleus accumbens (n = 7). In Parkinson's diseased brains (n = 4), [125I]altropane binding was 13% of the levels detected in normal putamen, 17% of normal values in the caudate nucleus, and 25% of normal levels in nucleus accumbens. The association of [125I]altropane to the dopamine transporter in human postmortem tissue, the marked reduction of [125I]altropane binding in Parkinson's diseased brains, its rapid entry into brain and highly localized distribution in dopamine-rich brain regions, support its use as a probe for monitoring the dopamine transporter in vitro and in vivo by SPECT imaging.

Aged↗
PubMed1998

Rapid detection of Parkinson's disease by SPECT with altropane: a selective ligand for dopamine transporters.

Increasing evidence indicates that dopamine (DA) transporter density declines in Parkinson's disease (PD). 2Beta-carbomethoxy-3beta-(4-fluorophenyl)-n-(1-iodoprop-1-en -3-yl) nortropane (IACFT, Altropane) is a cocaine analog with high affinity and selectivity for dopamine transporter (DAT) sites in the striatum. In this study, single photon emission computed tomography (SPECT) with [123I]altropane was used to measure DAT density in seven healthy volunteers (five males, age 37-75, and two females, ages 26 and 39) and eight male patients with Parkinson's disease (age 14-79, Hoehn and Yahr stage: 1.5-3 (n = 5) and 4-5 (n = 3)). Dynamic SPECT images and arterial blood samples were acquired over 1.5-2 hr and plasma radioactivity was analyzed chromatographically to obtain metabolite corrected arterial input functions. Binding potential (BP, B'max/KD) for striatal (Str) DAT sites was calculated by two methods using occipital cortex (Occ) as a reference. In the first method, tissue time-activity curves (TAC) and metabolite corrected arterial input functions were analyzed by a linear graphical method developed for reversible receptor ligands. In the second method, the expression (Str(TAC) - Occ(TAC)) was fitted to a gamma variate function and the maximum divided by Occ(TAC) at the same time was used to estimate BP. In five of the PD patients, the SPECT data were compared with the results of PET with [18F] 6-fluoro DOPA (FD-PET). Plasma analysis indicated that [123I]altropane is rapidly converted to polar metabolites. SPECT images in healthy volunteers showed that [123I] altropane accumulated rapidly and selectively in the striatum and yielded excellent quality images within 1 h after injection. Both methods of analysis revealed a 7.6%/decade reduction in BP and average striatal values (corrected to age 25) were 1.83 +/- 0.22 and 2.09 +/- 0.20 by methods 1 and 2. In all the PD patients, striatal accumulation was markedly reduced and the pattern of loss was similar to that reported for DA; most profound in the posterior putamen with relative sparing of the caudate nuclei. A comparable pattern was observed with FD-PET. For total striatum, age-corrected BP was significantly (P < 0.001) reduced; 0.83 +/- 0.06 (method 1), 0.84 +/- 0.07 (method 2). BPs measured by the two methods were remarkably similar and highly correlated r2 = 0.88, (P < 0.001). These results indicate that [123I]altropane is an excellent SPECT ligand for imaging the DAT/DA neurons in human brain. The high selectivity and rapid striatal accumulation of the ligand allows for accurate quantitation of DAT sites in less than 2 hr. The results further demonstrate that [123I]altropane is an effective marker for PD.

Adolescent↗
PubMed1998

Altropane, a SPECT or PET imaging probe for dopamine neurons: I. Dopamine transporter binding in primate brain.

Increasing evidence suggests that the dopamine transporter is an important marker for physiological and pathological changes in dopamine neurons. Potent dopamine transport inhibitors of the phenyltropane series (e.g., WIN 35,428 or CFT) are particularly suitable for PET (positron emission tomography) or SPECT (single photon emission computed tomography) imaging of the dopamine transporter in living brain. We investigated whether altropane, an N-iodoallyl analog of WIN 35,428 (IACFT:E-N-iodoallyl-2 -carbomethoxy-3beta-(4-fluorophenyl)tropane), displayed in vitro properties suitable for evaluation as a SPECT imaging agent. In brain striatum of cynomolgus monkey (Macaca fascicularis), the unlabeled E-isomer (IC50: 6.62 +/- 0.78 nM) was more potent than the Z-isomer (IC50: 52.6 +/- 0.3 nM) and displayed a relatively high dopamine:serotonin transporter selectivity (28-fold). In radiolabeled form, [125I]altropane bound to sites in the striatum with a single high affinity (KD: 5.33 +/- 0.55 nM) and with a site density (BMAX: 301 pmol/g original wet tissue weight) that was within the density range reported previously for the dopamine transporter in striatum. Drugs inhibited [125I]altropane binding with a rank order of potency that corresponded closely to their potencies for inhibiting [3H]WIN 35,428 binding (r2: 0.99; P < 0.0001) to the blocking dopamine transport. The favorable binding properties of altropane, together with its rapid entry into primate brain and highly localized distribution in dopamine-rich brain regions, suggest it is a suitable iodinated probe for monitoring the dopamine transporter in vitro and in vivo by SPECT or PET imaging.

Animals↗
PubMed1998

Anti-hyperactivity medication: methylphenidate and amphetamine.

How do 'stimulants' reduce hyperactivity in children and adults? How can drugs which raise extracellular dopamine result in psychomotor slowing of hyperactive children when dopamine is known to enhance motor activity, such as in Parkinson's disease? These apparent paradoxes are the focus of this brief review on the mechanism of action of stimulant medications used in the treatment of children, and of an increasing number of adults who meet diagnostic criteria for attention deficit hyperactivity disorder.

Adult↗
PubMed1997

2-Carbomethoxy-3-aryl-8-oxabicyclo[3.2.1]octanes: potent non-nitrogen inhibitors of monoamine transporters.

Cocaine is a potent stimulant of the mammalian central nervous system. Its reinforcing and stimulant properties have been associated with its propensity to bind to monoamine transporter systems. It has generally been assumed that the amino function on monoamines is a requirement for binding to monoamine transporters. In particular, the 8-amino function on the tropane skeleton of cocaine and cocaine analogs has been assumed to provide an ionic bond to the aspartic acid residue on the dopamine transporter (DAT). We have prepared the first 8-oxa analogs of the 3-aryltropanes (WIN compounds) and have found that the 3 beta-(3,4-dichlorophenyl) (6g) and 3 alpha-(3,4-dichlorophenyl) (7g) analogs are particularly potent (IC50 = 3.27 and 2.34 nM, respectively) inhibitors of the dopamine transporter. We now describe the synthesis and biology of the family of 2-carbomethoxy-3-aryl-8-oxabicyclo[3.2.1]octanes and demonstrate that an amino nitrogen is not required for binding to the DAT.

Animals↗
PubMed1997

A technetium-99m SPECT imaging agent which targets the dopamine transporter in primate brain.

The dopamine transporter (DAT), located presynaptically on dopamine neurons, provides a marker for certain neurological diseases. In particular, the DAT is depleted in Parkinson's disease, and the extent of depletion correlates with the loss of dopamine. Herein we describe the design, synthesis, and biological evaluation of technepine, the first 99mTc-labeled SPECT imaging agent which targets the dopamine transporter in striatum. We have demonstrated that the DAT can accommodate a chelating unit attached to the 8-amine function of a tropane skeleton. Further, we have demonstrated for the first time that a molecule can be designed to carry the radionuclide 99mTc across the blood-brain barrier in sufficient quantity to obtain in vivo images of the striatum in monkeys. This advance will undoubtedly lead to the design of new receptor and transporter-mediated 99mTc agents which can label specific transporter and receptor targets in the central nervous system.

Animals↗
PubMed1997

SPECT imaging of dopamine transporter sites in normal and MPTP-Treated rhesus monkeys.

UNLABELLED: Parkinson's disease is characterized by degeneration of dopamine (DA) neurons and their terminals. Since these neurons contain dopamine transporters (DAT), radioligands that bind to these sites are promising radiopharmaceuticals for diagnosis and therapeutic monitoring of disease progression. We evaluated [123I]-2 beta-carbomethoxy- 3 beta-(4-fluorophenyl)-N-(1-iodoprop-1-en-3-yl)nortropane ([123I]IACFT) for SPECT imaging in an MPTP model of parkinsonism. METHODS: Three rhesus monkeys were imaged before and at 1 and 2 mo after treatment with MPTP. The SPECT results were correlated with motor behavior and PET imaging with [11C]-2 beta-carbomethoxy-3 beta-aryltropane ([11C]-CFT). Also, biodistribution was measured by planar imaging. RESULTS: In normal animals, striatal accumulation of radioactivity was rapid and peaked within 30 min. Striatal accumulation of [123I]IACFT was nearly completely displaceable with unlabeled CFT (1 mg/kg) but was not affected by a similar dose of the serotonin (5-HT) transport inhibitor, citalopram. The striatal to cerebellar ratio measured at 30 min, after injection of [123I]IACFT was significantly higher (p < 0.01) than with [11C]CFT; approximately 6; 1 versus approximately 2.5; 1. After MPTP treatment this ratio decreased to 1.02:1 with IACFT and 1.23:1 with [11C]CFT. Blood clearance of [123I]IACFT was rapid with a terminal t1/2 of approximately 30 min. HPLC of plasma samples demonstrated that the concentration of intact ligand decreases rapidly, approaching zero by 60 min. Low levels of accumulation were measured in extracranial tissues. CONCLUSION: These results demonstrate that [123I]IACFT is an excellent SPECT ligand for dopamine transporter sites that combines the critical characteristics of: (a) high striatal to cerebellar ratios, (b) high selectivity for dopamine versus 5-HT transporter sites, (c) convenient preparation at high-specific activity and radiochemical purity and (d) a striatal localization rate that is well matched to the physical t1/2 of 123I.

1-Methyl-4-phenyl-1,2,3,6-tetrahydropyridine↗
PubMed1996

2-Carbomethoxy-3-(diarylmethoxy)-1 alpha H, 5 alpha H-tropane analogs: synthesis and inhibition of binding at the dopamine transporter and comparison with piperazines of the GBR series.

We recently reported a new class of tropanes, based on benztropine, that bind uniquely, in the S-configuration, to the dopamine transporter. We have now extended this series to evaluate the effects of substituents on the nitrogen and the diarylmethoxy group. Herein we have described the synthesis and biological evaluation of a series of 2-carbomethoxy-3-(diaryl-methoxy)-1 alpha H, 5 alpha H-tropane (2-carbomethoxybenztropine) analogs. Examination of the binding data obtained for these compounds shows that while the 4,4'-difluoro compound is potent and selective for the dopamine transporter, introduction of larger groups such as 4,4'-dichloro, 4,4'- dibromo, 4,4'-diiodo, or 4,4'dimethyl on the 3-diphenylmethoxy moiety reduces this potency. However, although introduction of only one group (e.g., 4-chloro, 4-bromo, 4-iodo, or 4-methyl) leads to a similar reduction of binding affinity, these monosubstituted 2-carbomethoxybenztropines are significantly more potent than the related disubstituted compounds. Finally, from the data for the N-substituted 2-carbomethoxybenztropine analogs, it is evident that steric bulk can be tolerated at the nitrogen site. A comparison of structure-activity relationship data for the tropanes, GBR analogs, and these benztropines indicates that the 2-carbomethoxybenztropine analogs may be more like the GBR analogs in their mode of binding to the dopamine transporter than like the tropanes. This conclusion supports the notion that the binding site for (-)-cocaine [and the (1R)-tropanes] may differ from of the 2-carbomethoxybenztropine analogs.

Animals↗
PubMed1996

Quantification of dopamine transporter density in monkeys by dynamic PET imaging of multiple injections of 11C-CFT.

Idiopathic Parkinson's disease (PD) is characterized by loss of dopaminergic terminals in the basal ganglia. The cocaine analog, CFT (WIN 35,428), has been shown to bind selectively to the pre-synaptic dopamine transporters and thus represents an important probe for monitoring disease progression. In this study, we evaluated [11C] labeled CFT as a PET ligand for the quantitative in vivo assay of dopamine transporter density in three normal rhesus monkeys (Macaca mulatta). One of the animals was studied after treatment with the neurotoxin, MPTP. Simulation studies demonstrated that a three injection protocol is necessary for quantitation of dopamine transporter density. The protocol consists of an initial high specific activity injection, a low specific activity "displacement dose" at 30 min, and a final high specific activity injection at approximately 90 min. Dynamic PET imaging and arterial blood sampling were started immediately before the first injection and continued for 2 h. Blood data were corrected for [11C] labeled CFT metabolites. Compartmental models describing the dynamics of labeled and the unlabeled ligand explicitly were fitted to the PET and metabolite corrected blood data. Prior to MPTP treatment, modeling of the striatal data required a saturable receptor term and yielded mean estimates of: B'max = 113 pmol/g and KD = 33 nm (n = 3). These values for B'max are in reasonable agreement with published values for [3H] CFT binding in vitro. After multiple treatments with MPTP (0.6 mg/kg x 3), B'max in one of the animals was reduced from 122 to 10.2 pmol/g. KD was relatively unaffected by MPTP treatment. These data provide additional basis for the use of [11C] CFT in monitoring the progression of Parkinson's disease and other conditions that are associated with the loss of dopaminergic nerve terminals.

Animals↗
PubMed1996

Nitrogen-based drugs are not essential for blockade of monoamine transporters.

In brain, monoamine transporters are principal targets of widely used therapeutic drugs including antidepressants, methylphenidate (Ritalin), and the addictive drug cocaine. Without exception, these transport blocking agents contain an amine nitrogen. A prevalent view and untested premise is that an amine nitrogen is needed to bind to the same counterion on the transporter as does the amine nitrogen of the monoamine neurotransmitter. We report that several compounds without nitrogen (8-oxa-bicyclo-3-aryl-[3.2.1] octanes, or aryloxatropanes) are active at monoamine transporters. One of these, tropoxane (0-914), bound with high affinity to the dopamine (IC50: 3.35 +/- 0.39 nM), serotonin (IC50: 6.52 +/- 2.05 nM), and norepinephrine (IC50: 20.0 +/- 0.3 nM) transporters in monkey brain, the human striatal dopamine transporter (IC50: 5.01 +/- 1.74 nM), and blocked dopamine transport (IC50: 7.2 +/- 3.0 nM) in COS-7 cells transfected with the human dopamine transporter. These unique compounds require a revision of current concepts of the drug binding domains on monoamine transporters, open avenues for discovery of a new generation of drugs and raise the issue of whether mammalian transporters and receptors may respond to, as yet, undiscovered non-amine bearing neurotransmitters or drugs.

Animals↗
PubMed1996

Agonist efficacy and the behavioral effects of dopamine D1 receptor ligands: drug interaction studies in squirrel monkeys.

Dopamine agonists that reportedly differ in intrinsic activity at dopamine D1 receptors were compared for their behavioral effects in squirrel monkeys responding under a fixed-ration schedule of reinforcement. When administered alone, all drugs produced dose-related decreases in fixed-ratio response rates. Pretreatment with the dopamine D1 receptor blocker SCH 39166, but not the dopamine D2 receptor blocker eticlopride, produced rightward shifts in the dose-effect functions for the high-efficacy dopamine D1 agonists SKF 82958 (R,S-6-chloro-7,8-dihydroxy-3-allyl-1-phenyl-2,3,4,5-tetrahydro- 1H-3-benzazepine) SKF 81297 (R,S-6-chloro-7,8-dihydroxy-1-phenyl-2,3,4,5-tetrahydro-1H-3-benzazepine ) and dihydrexidine, indicative of surmountable antagonism at dopamine D1 receptors. Pretreatment with SCH 39166, however, did not antagonize the effects of the low-efficacy dopamine D1 agonists SKF 75670 (R,S-7,8-dihydroxy-3-methyl-1-phenyl-2,3,4,5-tetrahydro-1H-3-benzazepine ), SKF 77434 (R,S-7,8-dihydroxy-3-allyl-phenyl-2,3,4,5-tetrahydro-1H-3-benzazepine) or R-SKF 38393 (R-7,8-dihydroxy-1-phenyl-2,3,4,5-tetrahydro-1H-3-benzazepine); instead, dose-effect functions for each of these drugs were shifted downward and to the left. In additional experiments, pretreatment with SKF 75670 produced overall rightward shifts in the dose-effect functions for dihydrexidine and SKF 81297; pretreatment with R-SKF 38393 produced an overall rightward shift in the dose-effect function for dihydrexidine, but not SKF 81297; and pretreatment with SKF 81297 failed to produce a rightward shift in the dose-effect function for dihydrexidine. These findings provide further evidence that the behavioral effects of dopamine D1 agonists in monkeys are mediated primarily by their actions at dopamine D1 receptors. The differing susceptibility of dopamine D1 agonists to antagonism by SCH 39166 and their differing interactions provide functional evidence for differences in their dopamine D1 agonist efficacy.

Animals↗
PubMed1996

Cocaine congeners as PET imaging probes for dopamine terminals.

UNLABELLED: The PET imaging properties of three phenyltropane drugs with differing affinities and selectivities for the dopamine over serotonin transporter, were compared. METHODS: Carbon-11-CFT (WIN 35,428, 2 beta-carbomethoxy-3 beta-(4-fluorophenyl)tropane), 11C-CCT (RTI-131, 2 beta-carbomethoxy-3 beta-(4-monochlorophenyl)tropane), and 11C-CDCT (dichloropane, 2 beta-carbomethoxy-3 beta-(3,4-dichlorophenyl)tropane) were evaluated as imaging probes for dopamine neurons in five normal and in two MPTP-treated cynomolgus monkeys (macaca fascicularis) using a high-resolution PET imaging system (PCR-I). RESULTS: For 11C-CFT, the specific binding ratio (as defined by the ratio of radioactivity levels in striatum versus cerebellum) was 4.2 +/- 0.8 in caudate and 4.9 +/- 1.2 in putamen at 60 min and 4.9 +/- 1.2 and 5.5 +/- 1.1 at 90 min in control animals. In MPTP-treated monkeys the corresponding ratios were 1.4 +/- 0.1 in caudate and 1.5 +/- 0.1 in putamen at 60 min and 1.3 +/- 0.1 in caudate and 1.4 +/- 0.3 in putamen at 90 min. For the monochloro analog of CFT, 11C-CCT, the ratios in control caudate and putamen were 2.7 +/- 0.4 and 3.4 +/- 0.3, respectively, at 60 min and 3.7 +/- 0.5 and 4.4 +/- 0.6, respectively, at 90 min. In MPTP-treated animals, corresponding ratios were 1.4 +/- 0.4 and 1.5 +/- 0.3 at 60 min and 1.4 +/- 0.4 and 1.6 +/- 0.4 at 90 min. The dichloro analog of CFT, CDCT, which has the highest affinity for the dopamine transporter, generated the lowest ratios in control brains, 2.3 +/- 0.4 in caudate and 2.4 +/- 0.5 in putamen at 60 min. In one MPTP-treated monkey, the corresponding ratios were 1.6 +/- 0.4 and 1.8 +/- 0.3. In comparison with 11C-CFT, both 11C-CCT and 11C-CDCT were less selective and had high uptake in the thalamus. CONCLUSION: The present results clearly indicate that 11C-CFT is a useful ligand for monitoring dopamine neuronal degeneration.

1-Methyl-4-phenyl-1,2,3,6-tetrahydropyridine↗
PubMed1996

Preparation and biological evaluation of iodine-125-IACFT: a selective SPECT agent for imaging dopamine transporter sites.

UNLABELLED: Parkinson's disease is a progressive neurodegenerative disorder that is associated with the loss of nerve terminals from specific brain areas, particularly in the caudate and putamen, which contains the highest concentrations of dopamine transporter sites. Previously, we synthesized and evaluated a series of 11C-labeled 2 beta-carbomethoxy -3 beta-aryltropane (WIN 35,428; CFT) derivatives as markers for the dopamine transporter system. These ligands have high affinity and specificity for dopamine transporter sites in vitro and in vivo in laboratory animals. The goal of this study was the preparation and preliminary biological characterization of two new ligands based on the structure of WIN 35,428, the E and Z isomers of N-iodoallyl-2 beta -carbomethoxy-3 beta-(4-fluorophenyl)tropane (E and A IACFT). METHODS: E and Z IACFT were synthesized and radiolabeled with 125I. The ligands were characterized by in vitro assays of binding to dopamine and serotonin transporters and by autoradiography. RESULTS: Iodine-125-IACFT was prepared in > 60% radiochemical yield, and > 98% radiochemical purity. Specific activity was 1500 Ci/mmole. In vitro, E-IACFT showed higher affinity for dopamine transporter sites than WIN 35,428 (6.6 versus 11 nM) and better selectivity than RTI-55. The Z isomer was found to have much lower affinity. One hour after an intravenous injection of 125I IACFT in monkeys, ex vivo autoradiographs of the brain revealed high concentrations of tracer in dopamine rich regions such as the caudateputamen. The striatum-to-cerebellum, striatum-to-cortex and striatum-to-thalamus ratios were 10.8, 7.2 and 8.3. CONCLUSION: These result suggest that radiolabeled E-IACFT may be a useful radioligand for SPECT imaging of dopamine transporter sites. IACFT could prove to be extremely useful for the noninvasive evaluation of patients with early Parkinson's disease.

Animals↗
PubMed1995

[3H]WIN 35,428 ([3H]CFT) binds to multiple charge-states of the solubilized dopamine transporter in primate striatum.

Caudate-putamen membranes of rhesus monkey were solubilized (1% digitonin; w/v) and [3H]WIN 35,428 ([3H]CFT: 2 beta-carbomethoxy-3- beta-(4-fluorophenyl)-N-[3H]methyltropane) binding assayed. Saturation analysis revealed high- and low-affinity binding components (KHIGH: 7.48 +/- 2.77 nM; KLOW: 292 +/- 788 nM; mean +/- SEM). Monoamine transport inhibitors and neurotransmitters had similar affinities for soluble and membrane [3H]CFT binding sites (r, 0.998; P < .001). The rank order of potency of these compounds for inhibiting [3H]CFT binding (Lu 19-005 > mazindol > CFT > GBR 12909 > (-)-cocaine > talsupram > dopamine > norepinephrine > citalopram) was consistent with [3H]CFT labeling cocaine binding sites on the dopamine transporter. [3H]CFT binding sites were separated into three protein fractions by anion-exchange chromatography. Monoamine transport inhibitors and neurotransmitters inhibited [3H]CFT binding in each fraction with a rank order of potency consistent with binding to the dopamine transporter. Detection of multiple binding components for [3H]CFT labeled sites by these drugs varied in each fraction. Size-exclusion chromatography indicated [3H]CFT bound to a single protein in each fraction (apparent molecular weight, 170 kDa). Therefore, multiple binding components for cocaine reside solely on the dopamine transporter and exhibit different affinities for drugs depending on the charge-state of the transporter.

Animals↗
PubMed1994

The discovery of an unusually selective and novel cocaine analog: difluoropine. Synthesis and inhibition of binding at cocaine recognition sites.

Cocaine is a stimulant drug with a high abuse liability. Although it inhibits several monamine transporters in the mammalian brain, its primary mechanism of action has been ascribed to its inhibition of the dopamine transporter. The synthesis, characterization, and receptor binding properties of all eight isomers of a unique tropane analog, 2-carbomethoxy-3-[bis(4-fluorophenyl)-methoxy]tropane is described. In addition, we report that the S-enantiomer, (S)-(+)-2 beta- carbomethoxy-3 alpha-[bis(4-fluorophenyl)methoxy]tropane, Difluoropine, is a potent (IC50 10.9 nM) and selective (324 [DA/5HT]) ligand for the dopamine transporter.

Animals↗