Tacrolimus clinical studies for atopic dermatitis and other conditions

The first topical immunomodulator approved for human use, tacrolimus ointment (Protopic, Fujisawa, Healthcare, Inc, Deerfield, IL), has been shown to be effective and safe in the treatment of children (aged 2 years and older) and adults with atopic dermatitis (AD). Clinical trials conducted worldwide have involved 12,000 patients, with safety and efficacy data available for up to 3 years of treatment. In addition to its beneficial effects in the management of AD, topical tacrolimus has also been reported to be of benefit in other immunologically mediated skin diseases including: hand dermatitis, contact dermatitis, eyelid dermatitis, erosive lichen planus, steroid-induced rosacea, pyoderma gangrenosum, and graft-versus-host disease. This article reviews the clinical experience of topical tacrolimus in the treatment of AD and other skin conditions.

Psychomotor stimulant effects of beta-phenylethylamine in monkeys treated with MAO-B inhibitors

RATIONALE AND OBJECTIVE

Sufficiently high doses of beta-phenylethylamine (beta-PEA), a trace amine that is rapidly metabolized by monoamine oxidase-type B (MAO-B), can produce effects comparable to those of cocaine or methamphetamine (MA). The present experiments were conducted to study how the discriminative-stimulus (S(D)) and reinforcing-stimulus (S(R)) effects of beta-PEA in monkeys are modified by treatment with inhibitors of MAO-B [R-(-)-deprenyl and MDL 72974].

METHODS AND RESULTS

In studies of its S(D) effects, doses of beta-PEA up to 30 mg/kg engendered only sporadic responding on the drug-associated lever in squirrel monkeys that discriminated intramuscular injections of 0.3 mg/kg MA from vehicle whereas lower doses of 0.3-1.0 mg/kg beta-PEA produced full substitution when administered after either R-(-)-deprenyl or MDL 72974 (0.3 mg/kg). The MA-like S(D) effects of beta-PEA were attenuated by either dopamine D(1) or D(2) receptor blockers. In studies of its S(R) effects, high doses of beta-PEA maintained responding in two of three monkeys under a second-order fixed-interval schedule (3.0 or 10 mg/kg per injection) and two of three monkeys under a simple fixed ratio (FR) schedule (0.3-1.0 mg/kg per injection) of intravenous (i.v.) self-administration. MAO-B inhibition by R-(-)-deprenyl or MDL 72974 enhanced the S(R) effects of beta-PEA in all monkeys and, under the FR schedule, induced a 30-fold or greater leftward shift in the dose-response function for its i.v. self-administration. Based on time-course determinations, the enhanced S(R) effects of beta-PEA under the FR schedule were long-lasting and dissipated gradually over 3-7 days.

CONCLUSIONS

These results show that inhibition of MAO-B enhances S(D) and S(R) effects of beta-PEA in monkeys, presumably by delaying its inactivation. MAO-B inhibition leading to increased levels of beta-PEA may be useful, alone or in combination with other therapeutic agents, in the pharmacological management of selected aspects of drug dependence.

Personality traits and brain dopaminergic function in Parkinson's disease

A distinctive personality type, characterized by introversion, inflexibility, and low novelty seeking, has been suggested to be associated with Parkinson's disease. To test the hypothesis that Parkinson's disease is associated with a specific dopamine-related personality type, the personality structures of 61 unmedicated Parkinson's disease patients and 45 healthy controls were examined. Additionally, in 47 Parkinson's disease patients, the dopaminergic function in the brain was directly measured with 6-[(18)F]fluoro-l-dopa ((18)F-dopa) positron emission tomography (PET) with MRI coregistration. The novelty-seeking personality score, supposedly associated with the parkinsonian personality, was slightly lower in the Parkinson's disease group compared with controls, but it did not have a significant relationship with (18)F-dopa uptake in any of the brain regions studied (r = -0.12 to 0.11, P > 0.15). The harm-avoidance personality score, associated with anxiety and depression, was clearly increased in patients with Parkinson's disease and it had a paradoxical, highly significant positive correlation with the (18)F-dopa uptake in the right caudate nucleus (r = 0.53, P = 0.04, Bonferroni corrected for 220 comparisons). Although the results of this study are not in disagreement with the concept of low-novelty-seeking personality type in Parkinson's disease, the personality type does not seem to be dopamine dependent. The correlation between the personality trait of harm avoidance and (18)F-dopa may reflect a specific feedback circuitry of neurotransmitters that is associated with negative emotionality in Parkinson's disease.

Imaging of blood flow and hypoxia in head and neck cancer: initial evaluation with [(15)O]H(2)O and [(18)F]fluoroerythronitroimidazole PET

Hypoxia is a characteristic feature of malignant tumors that should be evaluated before the start of therapy. (18)F-labeled fluoroerythronitroimidazole (FETNIM) is a possible candidate for imaging tumor hypoxia with PET. Quantitative analysis of [(18)F]FETNIM uptake in vivo is necessary before proceeding to assays predicting hypoxia.

METHODS

Eight patients with untreated head and neck squamous cell carcinoma were enrolled in the study. All patients underwent dynamic PET imaging with [(18)F]FETNIM, coupled with measurements of blood flow with [(15)O]H(2)O and blood volume with [(15)O]CO. The metabolically active tumor volume was determined from [(18)F]FDG PET performed on a separate day. [(18)F]FETNIM uptake in the tumor was correlated with that in neck muscles and arterial plasma and compared with the findings of other PET studies.

RESULTS

Blood flow in tumor was 5- to 30-fold greater than in muscle, in contrast to blood volume, which did not significantly differ in the 2 tissues. With [(18)F]FETNIM PET, muscle activity remained invariably less than plasma activity, whereas activity in whole tumors was always greater than that in muscle. In 4 instances, the maximum tumor uptake of [(18)F]FETNIM was 1.2-2.0 times higher than plasma activity in the late dynamic phase. A kinetic model developed for calculation of distribution volume of reversibly trapping tracers was successfully applied in the [(18)F]FETNIM studies. Tumor distribution volume correlated strongly with the standardized uptake value of [(18)F]FETNIM between 60 and 120 min and with blood flow but not with the standardized uptake value of [(18)F]FDG. The relationship between [(18)F]FETNIM uptake and the blood flow of the tumor was less obvious on a pixel-by-pixel level.

CONCLUSION

Uptake of [(18)F]FETNIM in head and neck cancer is highly variable and seems to be governed by blood flow at least in the early phase of tissue accumulation. Maximum tumor-to-muscle tracer uptake ratios > 180 min were in the range of 1-4, comparing favorably with those reported previously for [(18)F]fluoromisonidazole. Assessment of the distribution volume of [(18)F]FETNIM after the initial blood-flow phase is feasible for subsequent evaluation of hypoxia-specific retention.

Decreased striatal dopamine transporter binding in vivo in chronic schizophrenia

We have previously reported that average striatal dopamine transporter (DAT) binding in vivo is unaltered in neuroleptic-naive first-episode schizophrenic patients [Laakso et al., Am. J. Psychiatry 157 (2000) 269]. However, as it has been suggested that some of the brain changes in schizophrenia may vary depending on the illness phase, we studied DAT density in eight stable, medicated chronic schizophrenic patients and eight matched controls using positron emission tomography and [18F]CFT, a marker of dopamine nerve terminals. [18F]CFT binding potentials were significantly lower in chronic schizophrenic patients than in controls, both in the caudate and the putamen (-9 to -16%). Together with the finding of unchanged average striatal DAT levels in first-episode patients and relative insensitivity of striatal [18F]CFT binding to endogenous dopamine and neuroleptic drugs, the result is in line with a relative loss of striatal dopaminergic nerve terminals and/or decreased expression of DAT in a subset of chronic schizophrenic patients.

Synthesis of S-([18F]fluoromethyl)-(+)-McN5652 as a potential PET radioligand for the serotonin transporter

The present study describes the synthesis of the [18F]fluoromethyl analogue of (+)-McN5652 ([18F]FMe-McN) as a new potential tracer for the serotonin transporter. In vitro binding studies have shown that FMe-McN displays only slightly lower affinity for the serotonin transporter (K(i) = 2.3 +/- 0.1 nM) than (+)-McN5652 (K(i) = 0.72 +/- 0.2 nM). The radiofluorinated tracer [18F]FMe-McN was prepared by reaction of normethyl (+)-McN5652 with the fluoromethylation agent [18F]bromofluoromethane in an overall radiochemical yield of 5 +/- 1% (decay-corrected, related to [18F]fluoride) and with high specific radioactivity (200-2,000 GBq/micromol at the end of synthesis).

Positron emission tomography shows that impaired frontal lobe functioning in Parkinson's disease is related to dopaminergic hypofunction in the caudate nucleus

We examined the relation between the dopaminergic function and the cognitive performance of patients with Parkinson's disease (PD). The subject sample consisted of ten patients in the early course of PD and with no previous antiparkinsonian medication. The dopaminergic function of the caudate nucleus and the putamen was studied with [(18)F]fluorodopa positron emission tomography, and the cognitive performance with a comprehensive battery of neuropsychological tests including tests sensitive to frontal lobe function. The decreased [(18)F]fluorodopa uptake in the right caudate nucleus was found to be related to slow processing time, measured as the difference between the incongruent and the congruent subtests of the Stroop Test (r=-0.85, P=0.002), a similar trend was seen in the left caudate (r=-0.60, P=0.07). Similar correlation was not detected in the putamen. The present findings provide evidence that the decreased dopaminergic function in the right caudate nucleus is related to the impaired performance in tests sensitive to frontal lobe function in patients at an early stage of PD and with no antiparkinsonian medication.

Pharmacokinetics of [18F]FETNIM: a potential marker for PET

18F-labeled fluoroerythronitroimidazole (FETNIM) has been suggested as a marker of tumor hypoxia for use with PET. Our goal was to evaluate the pharmacokinetic properties of [18F]FETNIM in rats and analyze metabolites in human, dog, and rat plasma and urine. Metabolites in liver and tumor homogenates from tumor-bearing rats, as well as the biodistribution of the tracer, were also studied.

METHODS

Radio-thin-layer chromatography and digital autoradiography were used to distinguish metabolites from the parent drug in urine and plasma from 8 patients, 3 dogs, and 18 rats, as well as in liver and tumor homogenates from Sprague-Dawley rats bearing 7,12-dimethylbenzanthracene-induced rat mammary carcinoma. Biodistribution of [18F]FETNIM was also studied in rats at 15, 30, 60, 120, and 240 min after tracer injection.

RESULTS

Most of the radioactivity in plasma and urine was the unchanged tracer, whereas rat liver homogenates contained almost only metabolites of [18F]FETNIM. None of the species studied showed binding of tracer to plasma proteins. A large variation-3%-70%-in the radioactivity represented by unchanged [18F]FETNIM was found in rat tumor. A negative correlation was found between the percentage of radioactivity represented by unchanged [18F]FETNIM in tumor tissue and tumor uptake (percentage injected dose per gram of tissue) at later times. The highest radioactivity was seen in urine and kidney; the lowest uptake was in fat, cerebellum, and bone matrix. In contrast to matrix, bone marrow had high uptake of 18F. The tumor-to-blood ratio reached a maximum of 1.80 +/- 0.64 at 2 h.

CONCLUSION

We conclude that [18F]FETNIM shows low peripheral metabolism, little defluorination, and possible metabolic trapping in hypoxic tumor tissue. These suggest a potential use for this tracer in PET studies on hypoxia of cancer patients.

Different types of GABA(A) receptors may mediate the anticonflict and response rate-decreasing effects of zaleplon, zolpidem, and midazolam in squirrel monkeys

RATIONALE

The role of different types of GABA(A) receptors in mediating anticonflict and response rate-decreasing effects of benzodiazepines in primate species is not known.

OBJECTIVE

To examine the behavioral effects of the benzodiazepine-site, GABA(A) agonists zolpidem, zaleplon, and midazolam in the presence of two antagonists, flumazenil and beta-carboline-3-carboxylate-t-butyl ester (beta-CCt) in squirrel monkeys.

METHODS

Two schedules of operant responding were used: (1) a multiple fixed-ratio (FR) schedule of food presentation involving punished and nonpunished behavior, and (2) an FR schedule of stimulus shock-termination.

RESULTS

Midazolam (0.03-1.0 mg/kg), zolpidem (0.1-3.0 mg/kg), and zaleplon (0.1-3.0 mg/kg) increased rates of punished responding and decreased rates of nonpunished responding under the multiple schedule. Pretreatment with flumazenil (0.3-1.0 mg/kg) antagonized the anticonflict and response rate-decreasing effects of all three agonists. Pretreatment with beta-CCt (3-10 mg/kg) antagonized the anticonflict and rate-decreasing effects of midazolam, as well as the rate-decreasing effects of zolpidem and zaleplon. However, beta-CCt did not antagonize the anticonflict effects of zolpidem and zaleplon; instead, these effects of zolpidem and zaleplon were apparently enhanced in the presence of beta-CCt. Under the schedule of stimulus shock-termination, both flumazenil and beta-CCt antagonized zolpidem and zaleplon; however, the effects of beta-CCt were less consistent than the effects of flumazenil.

CONCLUSION

In nonhuman primates, different types of GABAA receptors may mediate the anticonflict and the response rate-decreasing effects of the nonselective GABAA agonist midazolam and the selective GABAA1 agonists zolpidem and zaleplon.

Increased frontal [(18)F]fluorodopa uptake in early Parkinson's disease: sex differences in the prefrontal cortex

Previous imaging studies in Parkinson's disease have focused mainly on the striatum, a region with very high dopaminergic activity. Using modern high-sensitivity 3D [(18)F]fluorodopa (Fdopa)-PET, mesocortical monoamine projections can be studied. To study the frontal monoaminergic system in unmedicated early Parkinson's disease in vivo, we examined 20 early Parkinson's disease patients (10 women, 10 men) and 16 healthy subjects (nine women, seven men) with 3D Fdopa-PET, using standard region-of-interest-based analysis with MRI co-registration. Women with Parkinson's disease had 87% higher Fdopa uptake in the right dorsolateral prefrontal cortex (area 46) compared with men with Parkinson's disease, whereas there was no sex difference in the control group (sex x disease interaction, P = 0.03). The uptake in the right dorsolateral prefrontal cortex was 82% higher in men with Parkinson's disease and 219% higher in women with Parkinson's disease compared with control groups (effect of disease, P < 0.0001). Also in the left dorsolateral prefrontal cortex and in the medial frontal cortex, early Parkinson's disease patients had significantly (18-94%) higher Fdopa uptake compared with healthy controls. In the putamen, both men and women with Parkinson's disease had a significantly lower (27-46%) uptake compared with healthy controls. These results indicate that frontal monoaminergic activity is increased and that there is a sex difference in the prefrontal monoaminergic system in early Parkinson's disease. The reported sex difference may be linked to clinical sex differences in the symptoms and treatment response in Parkinson's disease.

Rate of progression in Parkinson's disease: a 6-[18F]fluoro-L-dopa PET study

The aim of this study was to investigate the rate of progression in Parkinson's disease (PD) with 6-[(18)F]fluoro-L-dopa (FDOPA) positron emission tomography (PET). We investigated 21 patients with PD and eight healthy controls. Ten of the patients were de novo at the time of the first PET scan and antiparkinsonian medication was started thereafter, with a favourable response. A FDOPA PET scan was carried out twice at an approximately 5-year interval. The regions of interest were drawn on individual magnetic resonance imaging (MRI) images, matched with the PET images. At the first PET scan, in PD patients the mean k(i)(occ) (x 10(-3) min(-1)) in the anterior putamen was 5.6 +/- 2.7 (mean +/- S.D.; 55% of the control mean) and in the posterior putamen 4.5 +/- 2.4 (45% of the control mean). The k(i)(occ) value for the caudate nucleus was 7.5 +/- 2.1 (x 10(-3) min(-1); 76% of the control mean). The FDOPA uptake declined by the time of the second PET scan and the annual rate of decline was 8.3 +/- 6.3% (P < 0.001) of the baseline mean in the anterior putamen and 10.3 +/- 4.8% (P < 0.001) in the posterior putamen. In the caudate nucleus, FDOPA uptake decreased by 5.9 +/- 5.1% (P < 0.001) of the baseline mean per year. The estimated preclinical period was longest for the posterior putamen being 6.5 years. For the anterior putamen the preclinical period was 4.6 years. In the caudate nucleus, the estimated FDOPA uptake was at normal level at disease onset. In healthy controls, there was no significant decline in FDOPA uptake in any striatal subregion. Our results suggest that the disease process in PD first affects posterior putamen, followed by the anterior putamen and the caudate nucleus, but once started, the absolute rate of decline is the same. In healthy controls, no significant decline in FDOPA was detected.

[(18)F]FDOPA and [(18)F]CFT are both sensitive PET markers to detect presynaptic dopaminergic hypofunction in early Parkinson's disease

The aim of this study was to compare two PET ligands, 6-[(18)F]fluoro-L-dopa ([(18)F]FDOPA) and (18)F-labeled CFT, 2beta-carbomethoxy-3beta-(4-[(18)F]-fluorophenyl)tropane ([(18)F]CFT), in detecting presynaptic dopaminergic hypofunction in early Parkinson's disease (PD). These ligands reflect different aspects of presynaptic dopaminergic function, since [(18)F]FDOPA mainly reflects 6-[(18)F]fluorodopamine (fluorodopamine) synthesis and storage whereas [(18)F]CFT uptake is related to dopamine transporter function. Eight de novo patients with PD who had never been on antiparkinsonian medication were investigated with [(18)F]FDOPA and [(18)F]CFT PET. Five healthy volunteers were studied as controls. In PD patients, both [(18)F]FDOPA and [(18)F]CFT uptakes were significantly reduced both in the contralateral and ipsilateral anterior and posterior putamen. The reduction was greatest in the contralateral posterior putamen (to 28% of control mean for [(18)F]FDOPA, P < 0.0001 and to 16% for [(18)F]CFT, P < 0.0001). Individually, all patients' [(18)F]FDOPA and [(18)F]CFT uptake values in the contralateral anterior and posterior putamen were below 3 SD of the control mean. In the caudate nucleus, the mean uptake of both tracers was significantly reduced both ipsilaterally and contralaterally, but less severely than in the putamen (to 69% of the control mean for [(18)F]FDOPA, P = 0.003 and to 60% for [(18)F]CFT, P = 0.001 contralaterally). Our results show that both [(18)F]FDOPA as well as [(18)F]CFT sensitively detect presynaptic dopaminergic hypofunction in early PD. They demonstrate a considerable reduction of tracer uptake that is greatest in the posterior putamen, followed by the anterior putamen and the caudate nucleus.

Automated synthesis and purification of [18F]bromofluoromethane at high specific radioactivity

[18F]Bromofluoromethane was synthesised from dibromomethane by substitution of bromine with [18F]fluoride. The synthesis and separation of the [18F]bromofluoromethane were automated. [18F]Bromofluoromethane was used to convert a phenolic and a thiophenolic precursor into a labelled ether and thioether, respectively. The specific radioactivity of these labelled products was determined with both high-performance liquid chromatography (with UV-absorbance detection) and liquid chromatography (with mass spectrometric detection). The median for the specific radioactivity, corrected at the end of radionuclide production, was 934GBq/micromol (range 40-9900 GBq/micromol; n = 83).

Total syntheses of the benzodiazepine alkaloids circumdatin F and circumdatin C

Total syntheses of circumdatin F and circumdatin C, which both possess a 3H-quinazolin-4-one as well as a 1,4-benzodiazepin-5-one moiety, are described. A tripeptide derivative was synthesized as a key intermediate and dehydrated to a benzoxazine by reaction with triphenylphosphine, iodine, and a tertiary amine. The natural products were attained via rearrangements to an amidine intermediate, deprotection with 45% HBr in acetic acid, and cyclization on silica gel.

Enadoline discrimination in squirrel monkeys: effects of opioid agonists and antagonists

Squirrel monkeys were trained to discriminate i.m. injections of the kappa-opioid receptor agonist enadoline (0.0017 mg/kg) from saline in a two-lever drug-discrimination procedure. Enadoline produced a reliable discriminative stimulus that was reproduced by the kappa-selective agonists PD 117302, U 50,488, GR 89686A, (-)-spiradoline, ICI 204448, and EMD 61753, and by the mixed-action kappa/mu-agonists bremazocine and ethylketocyclazocine. The discriminative stimulus effects of enadoline were not reproduced by the mu-selective agonist morphine, the delta-selective agonist BW373U86, the mixed-action opioids nalbuphine and nalorphine, or by the less active enantiomers of enadoline and spiradoline PD 129829 and (+)-spiradoline, respectively. The selective mu-opioid antagonist beta-funaltrexamine (10.0 mg/kg) did not appreciably alter the dose-effect function for enadoline in any subject. However, the nonselective and kappa-selective opioid antagonists quadazocine (0.03-3.0 mg/kg) and nor-BNI (3-10 mg/kg), and the mixed-action opioid nalbuphine (0.3-30 mg/kg) served to surmountably antagonize enadoline's discriminative stimulus effects. The antagonist effects of nor-BNI were long-lasting and did not distinguish between drugs purported to act at different kappa-receptor subtypes. The present results bolster the view that common discriminative stimulus effects of enadoline and other opioids are mediated by kappa-agonist actions that are surmountably antagonized by nor-BNI in a long-lasting manner. The enadoline-antagonist effects of nalbuphine support the idea that it acts with low efficacy at kappa-opioid receptors.

Detection of response to COMT inhibition in FDOPA PET in advanced Parkinson's disease requires prolonged imaging

The aim was to investigate whether the improved 6-[(18)F]fluoro-L-dopa (FDOPA) availability induced by catechol-O-methyltransferase (COMT) inhibition can be more clearly seen during late than during standard (early) imaging in FDOPA uptake in Parkinson's disease (PD) patients with severe dopaminergic hypofunction. Six PD patients and six healthy controls were investigated up to 3.5 h after FDOPA injection with and without a single 400-mg dose of a peripheral COMT inhibitor, entacapone. Prolonged (late) imaging showed a significantly higher increase in FDOPA uptake than standard 1.5 h (early) imaging after entacapone both in controls and in PD patients. The increase in the (putamen-occipital):occipital ratios was 37.4% during early and 70.4% during late imaging in controls. In PD patients, there was no significant change in the ratios during early imaging, but the late imaging showed a significant increase in the putamen-to-occipital ratio of 54.2% after COMT inhibition. Late imaging reveals more clearly the prolonged FDOPA availability induced by COMT inhibition leading to higher cumulated striatal activity compared with early imaging. This might be worth considering in FDOPA studies, especially if investigations are planned to do without blood sampling. Late imaging shows the storing potential of FDA better than is seen during early FDOPA PET imaging after entacapone administration. In patients with severe presynaptic dopaminergic hypofunction, its detection requires prolonged imaging.

Antagonism of cocaine self-administration by selective dopamine D(1) and D(2) antagonists

Effects of the dopamine D(1) antagonist SCH 39166 were compared with those of the D(2) antagonist eticlopride in squirrel monkeys responding under a second-order fixed-interval schedule of i.v. self-administration of cocaine. Dose-response curves were determined for a range of doses of self-administered cocaine (0.01-1.7 mg/kg/injection) alone and after pretreatment with SCH 39166 (0.01-0.1 mg/kg) or eticlopride (0.001-0.006 mg/kg). Cocaine maintained self-administration behavior in a dose-related manner; as the dose of cocaine was increased, rates of responding first increased and then either decreased or leveled off. Optimum doses (0.03-0.3 mg/kg) maintained high rates of responding (0.7-1.7 responses per second) among the different monkeys, and patterns of responding that were characteristic for second-order schedules. Pretreatment with either SCH 39166 or eticlopride altered self-administration behavior in all monkeys. In most cases, dose-response curves for cocaine were shifted to the right, indicative of surmountable antagonism, and a 3 to 6-fold increase in dose of cocaine was necessary to restore optimal performances. In some instances, dose-response curves were shifted either downward or downward and to the right, indicating that the antagonistic effects of SCH 39166 and eticlopride were not always fully surmountable. These results show that self-administration of cocaine can be comparably modified by drugs that selectively block dopamine D(1) or D(2) receptors.

Ring opening of benzo[a]pyrene in the germ-free rat is a novel pathway for formation of potentially genotoxic metabolites

The metabolism of benzo[a]pyrene (BP) is known to lead to a large number of oxygenated compounds, some of which can bind covalently to DNA. We have studied the integrated metabolism of BP in vivo in germ-free rats given (14)C-labeled BP. Urinary metabolites were separated into groups according to acidity using lipophilic ion exchangers. The groups were analyzed by mass spectrometry and were further fractionated by high-performance liquid chromatography. The fraction of urinary metabolites previously shown to contain N-acetylcysteine and glucuronic acid conjugates was found to contain derivatives of 7-oxo-benz[d]anthracene-3,4-dicarboxylic acid as major components. These compounds, which were identified by mass spectrometry and NMR, accounted for about 30% of the total metabolites in urine, demonstrating that, surprisingly, ring opening is a major pathway for metabolism of BP in the germ-free rat. The dicarboxylic acid may be excreted in urine as an ester glucuronide. By using the single cell gel electrophoresis or COMET assay, we were able to demonstrate that the anhydride of 7-oxo-benz[d]anthracene-3, 4-dicarboxylic acid was an efficient inducer of DNA damage. Taken together, these results indicate that the novel ring opening metabolic pathway may provide alternative mechanisms for the toxicity of BP.

Agonist efficacy, drug dependence, and medications development: preclinical evaluation of opioid, dopaminergic, and GABAA-ergic ligands

BACKGROUND

The general premise that receptor theory provides a useful framework for understanding the behavioral effects of psychoactive drugs has been a central tenet of behavioral pharmacology.

OBJECTIVES

The purpose of this review is to reiterate this basic theme and, in particular, the proposition that current concepts of pharmacological efficacy can be effectively used to examine behavioral effects of drugs with abuse or dependence potential in a way that contributes to the discovery of drugs to treat drug dependence.

EXPERIMENTAL DATA

The review begins by briefly introducing the concept of efficacy and follows with several illustrations of how our current understanding of efficacy can be used to address important research questions in drug discovery. In the first, the likelihood of developing novel opioid analgesics with reduced abuse potential is addressed by considering the different efficacy requirements for the discriminative-stimulus and antinociceptive effects of mu-opioids. From a pharmacologically different perspective within drug abuse research, the review continues with an exposition of efficacy-related differences in the behavioral effects of dopamine D1 agonists and how such differences might be exploited in different medications strategies for treating cocaine dependence. The principles of pharmacological efficacy also have come to guide the development of novel GABAA-related antianxiety medications, and this is illustrated in a discussion of the utility of low-efficacy agonists in the treatment of benzodiazepine dependence. The second half of the paper provides counterpoint to the several examples of how principles of efficacy can be applied in drug discovery. The counterpoint includes, first, a critical evaluation of how the concept of efficacy has been applied in the development of monoamine transport inhibitors as anti-cocaine medications and, in particular, the difficulties this may pose for data analysis. The review ends with a discussion of efficacy-based analysis in drug discrimination research and illustrates some of the obstacles that may be encountered in pharmacologically classifying drugs on this basis.

CONCLUSIONS

Ample evidence indicates that many receptor systems can be activated in a graded manner and that principles of efficacy can be judiciously applied to understand and exploit the behavioral effects of drugs that result from such graded activation. However, as cautioned in the last sections, the misapplication of pharmacological concepts in behavioral studies of drugs may obscure their behavioral pharmacology and potentially confound drug discovery.

Reproducibility and effect of levodopa on dopamine transporter function measurements: a [18F]CFT PET study

The objective of this article was to study the reproducibility and effect of levodopa on dopamine transporter function measurements using 2beta-carbomethoxy-3beta-(4-[18F]fluorophenyl)tropane ([18F]CFT) positron emission tomography (PET). Seven de novo patients with Parkinson's disease (PD) were studied twice, before and after three months of levodopa medication. Eight healthy volunteer subjects participated in the reproducibility study. The [18F]CFT PET scan was done twice with an interval of approximately 2.5 months. The regions of interest (anterior and posterior putamen, caudate nucleus, and cerebellum) were drawn on individual magnetic resonance imaging (MRI) images, matched with the PET images, and copied onto the PET images. The [18F]CFT uptake was calculated as the region-cerebellum:cerebellum ratio at 180 to 210 minutes. Three-month levodopa treatment in PD patients had no significant effect on [18F]CFT uptake in any striatal subregion between the two PET scans. In PD patients, the percent change from baseline was 4.1% in the anterior putamen, 1.9% in the posterior putamen, and 4.0% in the caudate nucleus. No significant differences in [18F]CFT uptake between the first and second PET scan in any striatal subregion occurred in healthy controls. The intraclass correlation, indicating the reproducibility of the PET scan within subjects, was 0.94 for the anterior putamen, 0.86 for the posterior putamen, and 0.91 for the caudate nucleus. The percent change from baseline was 4.0% in the anterior putamen, 1.1% in the posterior putamen, and 2.8% in the caudate nucleus. Long-term levodopa treatment in PD patients had no effect on the [18F]CFT uptake in the striatum and the test-retest reproducibility was very high. These findings confirm [18F]CFT as a suitable ligand to monitor progression of PD.

Massive baclofen overdose

A case is presented of a massive baclofen overdose with the highest blood baclofen concentrations currently reported. Interesting clinical features included profound hypotension, distributive shock and absent brainstem reflexes. Cerebral recovery was surprisingly slow but complete, and was then unexpectedly terminated by a sudden major splenic arterial haemorrhage followed by a severe haemorrhage of the aorta which proved to be due to cystic medial necrosis. This arterial anatomic abnormality and cause of death may have been coincidental, or may instead be a previously unreported complication of massive baclofen toxicity.

Effects of dopamine D1-like and D2-like agonists in rats trained to discriminate cocaine from saline: influence of experimental history

Effects of D1-like and D2-like agonists were compared in rats (Rattus norvegicus) with differing levels of experience (24 or 9 mo) in a cocaine discrimination procedure (5.6 mg/kg cocaine; fixed-ratio 20 schedule of food presentation). Cocaine, d-amphetamine, and D2-like agonists (quinelorane, 7-OH-DPAT) dose-dependently substituted for cocaine in both groups of rats. In contrast, D1-like agonists (SKF 82958, SKF 77434) substituted for cocaine only in rats with less discrimination experience. Pretreatment with D2-like agonists increased the stimulus effects of low cocaine-doses in both groups, whereas D1-like agonists produced these effects only in rats with less discrimination experience. The data suggest that the stimulus effects of cocaine overlap with those of D2-like agonists across a broader range of conditions than with those of D1-like agonists. Thus, D2-like receptors may play an especially important role in cocaine's behavioral effects.