Effects of the substituted (S)-3-phenylpiperidine (-)-OSU6162 on PET measurements in subhuman primates: evidence for tone-dependent normalization of striatal dopaminergic activity

(-)-OSU6162 in the treatment of fatigue and other sequelae after aneurysmal subarachnoid hemorrhage: a double-blind, randomized, placebo-controlled study

OBJECTIVE

Fatigue after aneurysmal subarachnoid hemorrhage (aSAH) is common and usually long-lasting, and it has a considerable negative impact on health-related quality of life (HRQOL), social functioning, and the ability to return to work (RTW). No effective treatment exists. The dopaminergic regulator (-)-OSU6162 has shown promising results regarding the mitigation of fatigue in various neurological diseases, and therefore the authors aimed to investigate the efficacy of (-)-OSU6162 in alleviating fatigue and other sequelae after aSAH.

METHODS

A double-blind, randomized, placebo-controlled, single-center trial was performed in which 96 participants with post-aSAH fatigue were administered 30-60 mg/day of (-)-OSU6162 or placebo over a period of 12 weeks. Efficacy was assessed using the Fatigue Severity Scale (FSS), the Mental Fatigue Scale (MFS), the Beck Anxiety Inventory (BAI), the Beck Depression Inventory II (BDI-II), the SF-36 questionnaire, and a neuropsychological test battery. Assessments were performed at baseline, after 1, 4, 8, and 12 weeks of treatment, and at follow-up, 8 weeks after treatment.

RESULTS

The 96 participants with post-aSAH fatigue were randomized to treatment with (-)-OSU6162 (n = 49) or placebo (n = 47). The FSS, MFS, and BDI scores improved significantly in both groups after 12 weeks of treatment, whereas the BAI scores improved in the placebo group only. HRQOL improved significantly in the SF-36 domain "Vitality" in both groups. Neuropsychological test performances were within the normal range at baseline and not affected by treatment. The FSS score was distinctly improved in patients with complete RTW upon treatment with (-)-OSU6162. Concomitant use of antidepressants improved the efficacy of (-)-OSU6162 on the FSS score at week 1 beyond the placebo response, and correspondingly the use of beta- or calcium-channel blockers improved the (-)-OSU6162 efficacy beyond the placebo response in MFS scores at week 4 of treatment. There was a significant correlation between improvement in FSS, BAI, and BDI scores and the plasma concentration of (-)-OSU6162 at the dose of 60 mg/day. No serious adverse events were attributable to the treatment, but dizziness was reported more often in the (-)-OSU6162 group.

CONCLUSIONS

Fatigue and other sequelae after aSAH were similarly alleviated by treatment with (-)-OSU6162 and placebo. (-)-OSU6162 improved fatigue, as measured with the FSS score, significantly in patients with complete RTW. There seemed to be synergetic effects of (-)-OSU6162 and medications interfering with dopaminergic pathways that should be explored further. The strong placebo response may be exploited in developing nonpharmacological treatment programs for post-aSAH fatigue.

The monoamine stabilizer OSU6162 has anxiolytic-like properties and reduces voluntary alcohol intake in a genetic rat model of depression

Alcohol use disorders (AUD) often co-occur with anxiety and depressive disorders, and anxiety often drives relapse during alcohol abstinence. Optimal AUD pharmacotherapies may thus need to target both excessive alcohol intake and elevated anxiety. (−)-OSU6162 (OSU) is a monoamine stabilizer that attenuates alcohol-mediated behaviors in both preclinical and clinical settings. However, OSU’s effect on anxiety-like behavior following long-term drinking remains unknown. To this end, we utilized a genetic rat model that exhibits increased anxiety- and depression-like behaviors (Flinders Sensitive Line; FSL) and their controls (Flinders Resistant Line; FRL). Using the novelty suppressed feeding (NSF) test, we evaluated anxiety-like behaviors (1) at baseline, (2) following long-term voluntary drinking and after 24 h of alcohol deprivation, and (3) following OSU administration in the same animals. At baseline, FSL animals displayed significantly elevated anxiety-like characteristics compared to FRL. Compared to alcohol-naïve animals, long-term drinking significantly reduced anxiety-like behaviors in FSL, without any significant effects in FRL animals. Compared to vehicle, OSU administration significantly reduced anxiety-like behaviors in alcohol-naïve FSL and long-term drinking FRL animals. While there was no significant difference in alcohol intake between FSL and FRL, OSU attenuated alcohol intake in both strains. Conclusively, in addition to the compound’s previously identified ability to suppress alcohol-mediated behaviors, OSU may also possess anxiolytic properties, warranting further clinical evaluation in both AUD and anxiety disorder settings.

Pharmaco-fMRI in Patients With Traumatic Brain Injury: A Randomized Controlled Trial With the Monoaminergic Stabilizer (-)-OSU6162

OBJECTIVE

To examine the effects of monoaminergic stabilizer (-)-OSU6162 on brain activity, as measured by blood-oxygen-level-dependent (BOLD) functional magnetic resonance imaging (fMRI), in patients in the chronic phase of traumatic brain injury suffering from fatigue.

SETTING

Neurorehabilitation clinic.

PARTICIPANTS

Patients with traumatic brain injury received either placebo (n = 24) or active treatment (n = 28). Healthy controls (n = 27) went through fMRI examination at one point and were used in sensitivity analysis on normalization of BOLD response.

DESIGN

Randomized, double-blinded, placebo-controlled design.

MAIN MEASURES

Effects on BOLD signal changes from before to after treatment during performance of a fatiguing attention task.

RESULTS

The fMRI results revealed treatment effects within the right occipitotemporal cortex and the right orbitofrontal cortex. In these regions, the BOLD response was normalized relative to healthy controls at the postintervention fMRI session. No effects were seen in regions in which we previously observed activity differences between patients and healthy controls while performing this fMRI task, such as the striatum.

CONCLUSION

(-)-OSU6162 treatment had influences on functional brain activity, although the normalized regional BOLD response was observed in regions that were not a priori hypothesized to be sensitive to this particular treatment, and was not accompanied by any effects on in-scanner test performance or on fatigue.

The Effects of the Monoamine Stabilizer (-)-OSU6162 on Binge-Like Eating and Cue-Controlled Food-Seeking Behavior in Rats

Binge-eating disorder (BED) is characterized by recurring episodes of excessive consumption of palatable food and an increased sensitivity to food cues. Patients with BED display an addiction-like symptomatology and the dopamine system might be a potential treatment target. The clinically safe monoamine stabilizer (-)-OSU6162 (OSU6162) restores dopaminergic dysfunction in long-term alcohol-drinking rats and shows promise as a novel treatment for alcohol use disorder. Here, the effects of OSU6162 on consummatory (binge-like eating) and appetitive (cue-controlled seeking) behavior motivated by chocolate-flavored sucrose pellets were evaluated in non-food-restricted male Lister Hooded rats. OSU6162 significantly reduced binge-like intake of chocolate-flavored sucrose pellets without affecting prior chow intake. Furthermore, OSU6162 significantly reduced the cue-controlled seeking of chocolate-flavored sucrose pellets under a second-order schedule of reinforcement before, but not after, the delivery and ingestion of reward, indicating a selective effect on incentive motivational processes. In contrast, the dopamine D2/D3 receptor antagonist raclopride reduced the seeking of chocolate-flavored sucrose pellets both pre- and post reward ingestion and also reduced responding under simpler schedules of seeking behavior. The D1/5 receptor antagonist SCH23390 had no effect on instrumental behavior under any reinforcement schedule tested. Finally, local administration of OSU6162 into the nucleus accumbens core, but not dorsolateral striatum, selectively reduced cue-controlled sucrose seeking. In conclusion, the present results show that OSU6162 reduces binge-like eating behavior and attenuates the impact of cues on seeking of palatable food. This indicates that OSU6162 might serve as a novel BED medication.

The effects of the monoamine stabilizer (-)-OSU6162 on craving in alcohol dependent individuals: A human laboratory study

Alcohol dependence is associated with a dysregulated dopamine system modulating reward, craving and cognition. The monoamine stabilizer (-)-OSU6162 (OSU6162) can counteract both hyper- and hypo-dopaminergic states and we recently demonstrated that it attenuates alcohol-mediated behaviors in long-term drinking rats. The present Phase II exploratory human laboratory study investigated to our knowledge for the first time the effects of OSU6162 on cue- and priming-induced craving in alcohol dependent individuals. Fifty-six alcohol dependent individuals were randomized to a 14-day-treatment period of OSU6162 or placebo after their baseline impulsivity levels had been determined using the Stop Signal Task. On Day 15, participants were subjected to a laboratory alcohol craving test comprised of craving sessions induced by: i) active - alcohol specific cues, ii) neutral stimuli and iii) priming - intake of an alcoholic beverage (0.20g ethanol/kg bodyweight). Subjective ratings of alcohol craving were assessed using the shortened version of the Desire for Alcohol Questionnaire and visual analog scales (VAS). OSU6162 treatment had no significant effect on cue-induced alcohol craving, but significantly attenuated priming-induced craving. Exploratory analysis revealed that this effect was driven by the individuals with high baseline impulsivity. In addition, OSU6162 significantly blunted the subjective liking of the consumed alcohol (VAS). Although the present 14-day-treatment period, showed that OSU6162 was safe and well tolerated, this exploratory human laboratory study was not designed to evaluate the efficacy of OSU6162 to affect alcohol consumption. Thus a larger placebo-controlled efficacyclinical trial is needed to further investigate the potential of OSU6162 as a novel medication for alcohol dependence.

Update on Huntington's disease: advances in care and emerging therapeutic options

INTRODUCTION

Huntington's disease (HD) is the most common hereditary neurodegenerative disorder. Despite the fact that both the gene and the mutation causing this monogenetic disorder were identified more than 20 years ago, disease-modifying therapies for HD have not yet been established.

REVIEW

While intense preclinical research and large cohort studies in HD have laid foundations for tangible improvements in understanding HD and caring for HD patients, identifying targets for therapeutic interventions and developing novel therapeutic modalities (new chemical entities and advanced therapies using DNA and RNA molecules as therapeutic agents) continues to be an ongoing process. The authors review recent achievements in HD research and focus on approaches towards disease-modifying therapies, ranging from huntingtin-lowering strategies to improving huntingtin clearance that may be promoted by posttranslational HTT modifications.

CONCLUSION

The nature and number of upcoming clinical studies/trials in HD is a reason for hope for HD patients and their families.

6-[18F]fluoro-L-DOPA: a well-established neurotracer with expanding application spectrum and strongly improved radiosyntheses

For many years, the main application of [(18)F]F-DOPA has been the PET imaging of neuropsychiatric diseases, movement disorders, and brain malignancies. Recent findings however point to very favorable results of this tracer for the imaging of other malignant diseases such as neuroendocrine tumors, pheochromocytoma, and pancreatic adenocarcinoma expanding its application spectrum. With the application of this tracer in neuroendocrine tumor imaging, improved radiosyntheses have been developed. Among these, the no-carrier-added nucleophilic introduction of fluorine-18, especially, has gained increasing attention as it gives [(18)F]F-DOPA in higher specific activities and shorter reaction times by less intricate synthesis protocols. The nucleophilic syntheses which were developed recently are able to provide [(18)F]F-DOPA by automated syntheses in very high specific activities, radiochemical yields, and enantiomeric purities. This review summarizes the developments in the field of [(18)F]F-DOPA syntheses using electrophilic synthesis pathways as well as recent developments of nucleophilic syntheses of [(18)F]F-DOPA and compares the different synthesis strategies regarding the accessibility and applicability of the products for human in vivo PET tumor imaging.

Third generation antipsychotic drugs: partial agonism or receptor functional selectivity?

Functional selectivity is the term that describes drugs that cause markedly different signaling through a single receptor (e.g., full agonist at one pathway and antagonist at a second). It has been widely recognized recently that this phenomenon impacts the understanding of mechanism of action of some drugs, and has relevance to drug discovery. One of the clinical areas where this mechanism has particular importance is in the treatment of schizophrenia. Antipsychotic drugs have been grouped according to both pattern of clinical action and mechanism of action. The original antipsychotic drugs such as chlorpromazine and haloperidol have been called typical or first generation. They cause both antipsychotic actions and many side effects (extrapyramidal and endocrine) that are ascribed to their high affinity dopamine D(2) receptor antagonism. Drugs such as clozapine, olanzapine, risperidone and others were then developed that avoided the neurological side effects (atypical or second generation antipsychotics). These compounds are divided mechanistically into those that are high affinity D(2) and 5-HT(2A) antagonists, and those that also bind with modest affinity to D(2), 5-HT(2A), and many other neuroreceptors. There is one approved third generation drug, aripiprazole, whose actions have been ascribed alternately to either D(2) partial agonism or D(2) functional selectivity. Although partial agonism has been the more widely accepted mechanism, the available data are inconsistent with this mechanism. Conversely, the D(2) functional selectivity hypothesis can accommodate all current data for aripiprazole, and also impacts on discovery compounds that are not pure D(2) antagonists.

The test-retest reliability of 18F-DOPA PET in assessing striatal and extrastriatal presynaptic dopaminergic function

Brain presynaptic dopaminergic function can be assessed using 18F-DOPA positron emission tomography (PET). Regional 18F-DOPA utilization may be used to index dopaminergic abnormalities over time or dopaminergic response to treatment in clinical populations. Such studies require prior knowledge of the stability of the 18F-DOPA signal in the brain regions of interest. Test-retest reliability was examined in eight healthy volunteers who each received two 18F-DOPA PET scans, approximately 2 years apart. 18F-DOPA utilization (k(i)(cer)) was determined using graphical analysis relative to a reference tissue input (Patlak and Blasberg, 1985). Reproducibility (measured as the within-subjects variation) and reliability (measured as intraclass correlation coefficients, ICCs) of 18F-DOPA k(i)(cer) were assessed in the structural and functional subdivisions of the striatum and select extrastriatal brain regions. Voxel-based median ICC maps were used to visualize the distribution of 18F-DOPA k(i)(cer) reliability across the brain. The caudate and putamen, and associative and sensorimotor, striatal subdivisions showed good reliability across the two scan sessions with bilateral ICCs ranging from 0.681 to 0.944. Reliability was generally lower in extrastriatal regions, with bilateral ICCs ranging from 0.235 in the amygdala to 0.894 in the thalamus. These data confirm the utility of 18F-DOPA PET in assessing dopaminergic function in the striatum and select extrastriatal areas but highlight the limitations in using this approach to measure dopaminergic function in low uptake extrastriatal brain areas. This information can be used to optimize the experimental design of future studies investigating changes in brain dopaminergic function with 18F-DOPA.

The dopaminergic stabilizers pridopidine (ACR16) and (-)-OSU6162 display dopamine D(2) receptor antagonism and fast receptor dissociation properties

A new pharmacological class of CNS ligands with the unique ability to stimulate or suppress motor and behavioral symptoms depending on the prevailing dopaminergic tone has been suggested as "dopaminergic stabilizers". The molecular mode-of-action of dopaminergic stabilizers is not yet fully understood, but they are assumed to act via normalization of dopaminergic signaling, through interactions with the dopamine D(2) receptor. Here we have evaluated the dopaminergic stabilizers pridopidine (ACR16) and (-)-OSU6162, as well as the new compound N-{[(2S)-5-chloro-7-(methylsulfonyl)-2,3-dihydro-1,4-benzodioxin-2-yl]methyl}ethanamine (NS30678) in a series of cellular in vitro dopamine D(2) receptor functional and binding assays. Neither ACR16, (-)-OSU6162, nor NS30678 displayed detectable dopamine D(2) receptor-mediated intrinsic activity, whereas they concentration-dependently antagonized dopamine-induced responses with IC(50) values of 12.9microM, 5.8microM, and 7.0nM, respectively. In contrast to the high-affinity typical antipsychotics haloperidol and raclopride, the dopaminergic stabilizers ACR16 and (-)-OSU6162 both displayed fast dopamine D(2) receptor dissociation properties, a feature that has previously been suggested as a contributing factor to antipsychotic atypicality and attributed mainly to low receptor affinity. However, the finding that NS30678, which is equipotent to haloperidol and raclopride, also displays fast receptor dissociation, suggests that the agonist-like structural motif of the dopaminergic stabilizers tested is a critical dissociation rate determinant. The results demonstrate that dopaminergic stabilizers exhibit fast competitive dopamine D(2) receptor antagonism, possibly allowing for temporally variable and activity-dependent dopamine D(2) receptor occupancy that may partly account for their unique stabilization of dopamine dependent behaviors in vivo.

Application of stable isotope methodology in the evaluation of the pharmacokinetics of (S,S)-3-[3-(methylsulfonyl)phenyl]-1-propylpiperidine hydrochloride in rats

The primary objective of this study was to demonstrate the use of stable isotope (SI)-labeled compound as an approach for pharmacokinetic analysis such as fraction absorbed, hepatic extraction ratio, and fraction metabolized from the parent drug to a metabolite. (S,S)-3-[3-(Methylsulfonyl)phenyl]-1-propylpiperidine hydrochloride (PNU96391) was selected as the model compound because of its simple biotransformation pathway, i.e., the predominant metabolic pathway to the N-despropyl metabolite (M1), which makes it a suitable candidate. The second objective was to fully characterize the pharmacokinetics of PNU96391 in rats using the SI coadministration approach with quantitative analysis by liquid chromatography-tandem mass spectrometry. Overall the present study showed that 1) absorption of PNU96391 from the gastrointestinal tract was near complete (>90% of the dose), 2) PNU96391 was predominantly metabolized to M1 (approximately 70% of the dose), and 3) M1 was exclusively eliminated into urine with negligible biotransformation (ratio of renal clearance to plasma clearance approximately 0.9). Therefore, the present study demonstrated the utility of the SI methodology for characterizing the pharmacokinetics of a compound within the drug discovery and development process. Furthermore, the compartmental pharmacokinetic modeling provided insights into the disposition and biotransformation rates of PNU96391 and M1, suggesting that the modeling could add further advantages to the SI coadministration approach. Despite the greater availability of SI-labeled compounds, absorption, distribution, metabolism, and excretion (ADME) scientists have yet to take full advantage of the potential use of these analogs for mechanistic ADME studies. These SI-labeled compounds can be used more widely to gain a better understanding of ADME properties in drug discovery and development.

Altered pattern of brain dopamine synthesis in male adolescents with attention deficit hyperactivity disorder

BACKGROUND

Limited data from positron emission tomography (PET) studies of subjects with attention-deficit/hyperactivity disorder (ADHD) indicate alterations in brain dopamine neurotransmission. However, these studies have used conventional univariate approaches that are less sensitive to detect complex interactions that may exist between different brain dopamine pathways and individual symptoms of ADHD. We aimed to investigate these potential interactions in adolescents with ADHD.

METHODS

We used a 3D PET scan to measure utilization of native L-[11C]-DOPA to map dopamine presynaptic function in various cortical, striatal and midbrain regions in a group of 8 male adolescents with ADHD and 6 age matched controls. To evaluate the interactions between the studied brain regions, multivariate statistical methods were used.

RESULTS

Abnormal dopaminergic function was found in multiple brain regions of patients with ADHD. A main finding was lower L-[11C]-DOPA utilization in adolescent with ADHD as compared to control subjects, especially in subcortical regions. This pattern of dopaminergic activity was correlated specifically with symptoms of inattention.

CONCLUSION

Dopamine signalling in the brain plays an important modulatory role in a variety of motor and cognitive functions. We have identified region-specific functional abnormalities in dopaminergic function, which may help better account for the symptoms of ADHD.

The Dopamine Stabilizers (S)-(-)-(3-Methanesulfonyl-phenyl)-1-propyl-piperidine [(-)-OSU6162] and 4-(3-Methanesulfonylphenyl)-1-propyl-piperidine (ACR16) Show High in Vivo D2Receptor Occupancy, Antipsychotic-Like Efficacy, and Low Potential for Motor Side Effects in the Rat

"Dopamine stabilizers" are a new class of compounds that have the ability to reverse both hypo- as well as hyperdopaminergia in vivo. This class, exemplified by the phenylpiperidines (S)-(-)-3-(3-methanesulfonyl-phenyl)-1-propyl-piperidine [(-)-OSU6162] and 4-(3-methanesulfonyl-phenyl)-1-propyl)-piperidine [ACR16] although lacking high in vitro binding affinity for dopamine D2 receptor [(-)-OSU6162, Ki = 447 nM; ACR16, Ki > 1 microM], shows functional actions, suggestive of their interaction. Hence, we evaluated in vivo D2 occupancy of these agents in rats and correlated it to observed effects in a series of behavioral, neurochemical, and endocrine models relevant to the dopamine system and antipsychotic effect. Both (-)-OSU6162 and ACR16 showed robust dose-dependent striatal D2 occupancy with ED50 values of 5.27 and 18.99 mg/kg s.c., respectively, and functional assays showed no partial agonism. Over an occupancy range of 37 to 87% (3-60 mg/kg) for (-)-OSU6162 and 35 to 74% (10-60 mg/kg) for ACR16, we observed both inhibitory (amphetamine-induced locomotor activity) and stimulatory effects (in habituated rats). Haloperidol, over a similar occupancy range (33-78%), potently inhibited psychostimulant activity and induced catalepsy, but it failed to activate habituated animals. In the conditioned avoidance response assay, ACR16 was clearly more efficacious than (-)-OSU6162. In addition, both these compounds demonstrated significant preferential Fos induction in the nucleus accumbens compared with the dorsolateral striatum, a strong predictor of atypical antipsychotic efficacy. The results suggest that dopamine stabilizers exhibit locomotor stabilizing as well as antipsychotic-like effects, with low motor side effect liability, in a dose range that corresponds to high D2 in vivo occupancy.

The substituted (S)-3-phenylpiperidine (−)-OSU6162 reduces apomorphine- and amphetamine-induced behaviour in Cebus apella monkeys

Low affinity dopamine (DA) D2 antagonists such as the substituted (S)-3-phenylpiperidine (-)-OSU6162 have been proposed to be putative antipsychotic agents not endowed with extrapyramidal side effects (EPS). In the present study we investigated the effects of (-)-OSU6162 on (-)-apomorphine and d-amphetamine-induced behaviours in EPS sensitised Cebus apella monkeys. (-)-OSU6162 was administered subcutaneously in doses of 1, 3, 6 and 9 mg/kg alone and in combination with (-)-apomorphine (0.25 mg/kg) or d-amphetamine (0.5 mg/kg). (-)-OSU6162 inhibited (-)-apomorphine-(1-9 mg/kg) as well as d-amphetamine (3-9 mg/kg)-induced arousal and stereotypy. EPS did not occur when (-)-OSU6162 was administered in combination with (-)-apomorphine or d-amphetamine. However, when (-)-OSU6162 was administered alone, dystonia was observed at high doses (6 and 9 mg/kg) in two out of six monkeys. The present study shows that (-)-OSU6162 can inhibit (-)-apomorphine-induced behaviours in non-human primates at doses that do not cause EPS. When (-)-OSU6162 was tested against d-amphetamine-induced behaviours a separation between dose levels that inhibit d-amphetamine effects and cause EPS was not observed. The data further substantiate a role for low affinity DA D2 antagonists in the pharmacological treatment of psychosis.

Single oral dose safety, tolerability, and pharmacokinetics of PNU-96391 in healthy volunteers

The safety, tolerability, and pharmacokinetics of PNU-96391, an orally active weak dopamine D2 receptor antagonist with modulatory properties of central dopaminergic function, was characterized. Fifty-three healthy normal volunteers were enrolled in this randomized, double-blinded, placebo-controlled, single-dose study. Subjects were assigned to single oral doses of placebo and 1, 3, 10, 30, 100, 150, and 200 mg PNU-96391. Safety and tolerability were assessed using telemetry, Holter monitoring, surface ECG, vital signs, safety laboratories, and adverse event reports. Pharmacokinetic parameters were determined by model-independent techniques. Adverse events were infrequent, of mild to moderate intensity, and in the dose range of 1 to 150 mg. Dose escalation was stopped at 200 mg because of severe nausea, dizziness, lightheadedness, and tachycardia. Besides the increase in heart rate, no other drug-related effects on vital signs were observed. Safety laboratory measurements were not significantly changed. Evidence of drug activity was demonstrated by a dose-dependent elevation in serum prolactin. PNU-96391 was rapidly absorbed, with maximum concentrations achieved between 0.5 and 4 hours in all subjects. The half-life of the drug was short (2 to 6 h). The main metabolite, PNU-100014, was rapidly formed, with a t(max) ranging from 1 to 6 hours. Peak levels of the metabolite are approximately half of the parent drug, and the half-life is slightly longer (4 to 10 h). Increases in dose resulted in linear increases in exposure for both PNU-96391 and PNU-100014. Hence, PNU-96391 was well tolerated at doses ranging from 1 to 150 mg.

COMPARISON OF PREDICTION METHODS FOR IN VIVO CLEARANCE OF (S,S)-3-[3-(METHYLSULFONYL)PHENYL]-1-PROPYLPIPERIDINE HYDROCHLORIDE, A DOPAMINE D2 RECEPTOR ANTAGONIST, IN HUMANS

The purpose of this study is to investigate reliable prediction methods for in vivo pharmacokinetics and the likelihood of drug interactions with several cytochrome P450 inhibitors in humans for (S,S)-3-[3-(methylsulfonyl)phenyl]-1-propylpiperidine (PNU-96391). By allometric scaling of in vivo animal data, clearance of PNU-96391 in humans was over-predicted by 4-fold, half-life was under-predicted by 3-fold, and volume of distribution was accurately predicted. High correlation coefficients (>0.99) were observed for these parameters. Neither the in vitro-in vivo correlation approach nor the modified allometric scaling with maximum life span potential or brain weight accurately provided the predicted clearance value. Using an alternative method, based on normalization of in vitro human data with the ratio of in vivo to in vitro animal data, the in vivo clearance in humans was predicted to be 0.39 l/h/kg. This value correlated well with the in vivo value (0.43 l/h/kg). Regarding the interactions of PNU-96391 with cytochrome P450 inhibitors, only quinidine, haloperidol, and ketoconazole showed significant inhibition on the metabolic clearance of PNU-96391 in human hepatocytes. By comparing in vitro K(i) values with in vivo maximum unbound concentrations of the inhibitor, the increases in systemic exposure of PNU-96391 by coadministration of the inhibitors were estimated to be less than 1.5-fold. A preliminary comparison of pharmacokinetics of PNU-96391 between CYP2D6 extensive and poor metabolizers in the clinical study showed only a slight increase in systemic exposure in poor metabolizers (approximately 1.4-fold as area under the concentration-time curve). Therefore, clinically significant drug-drug interactions of PNU-96391 would be unlikely to occur with coadministration of CYP2D6 inhibitors.

Antipsychotic treatment in schizophrenia: atypical options and NICE guidance

Following the reintroduction of clozapine, several atypical antipsychotics have become available for the treatment of schizophrenia. These drugs are at least as effective as conventional treatment. Although each has an individual pattern of affinities, new work suggests that the hallmark of atypicality is fast dissociation at the dopamine-2 receptor. Numerous novel drugs are in development, but it is not clear how these conform to this theory of therapeutic effect. Atypical antipsychotics cause less extrapyramidal side effects than conventional treatment, but other effects such as hyperprolactinaemia, weight gain, glucose dysregulation and prolonged QTc interval remain problematic for some. Current antipsychotic prescribing practice is far from ideal: the NICE guidance stresses that atypical treatments should be considered unless symptoms are well controlled and side effects are acceptable, or depot formulation is indicated. There is a welcome emphasis on drug treatment as part of an integrated package of care negotiated with patients and their carers.

Different corticostriatal patterns of L-DOPA utilization in patients with untreated schizophrenia and patients treated with classical antipsychotics or clozapine

Positron emission tomography (PET) has been shown to be of great importance in elucidating the mechanism of action of antipsychotic drugs. In psychotic patients L-[11C]DOPA PET has been used to demonstrate some differences in dopaminergic activity compared with that in healthy volunteers. Ten healthy volunteers were investigated with PET and L-[11C]DOPA. Ten drug-free patients with psychosis, nine stable schizophrenics treated with clozapine, and nine stable patients treated with classical antipsychotics were also investigated with L-[11C]DOPA. Principal-component analysis was employed for the analysis of L-[11C]DOPA Ki values across a number of corticostriatal brain regions. These data revealed a significant three-component model with clear-cut separation between healthy controls and patients with unmedicated schizophrenia. Stable optimal treatment with either classical neuroleptics or clozapine partially, albeit differentially, reversed the aberrant patterns seen in drug-free schizophrenia. It can thus be concluded that schizophrenia is associated with abnormal patterns of L-[11C]DOPA utilization in corticostriatal systems. Treatment with clozapine or classical neuroleptics induces partial, albeit differential, normalization of the abnormal patterns seen in untreated schizophrenia.

Motor effects of a dopamine stabilizer (GMC1111) in primate models of Parkinson and hemiparkinsonism

The effects on motor behavior of a new potential dopamine stabilizer: 2-amino-6-(N,N-di-n-propylamino)thiazolo[4,5-f]indan (GMC1111) were investigated in common marmosets with 6-hydroxydopamine lesions within the median forebrain bundle (12 unilateral, 6 bilateral). GMC1111 was administered orally or subcutaneously (s.c.) to unilaterally 6-hydroxydopamine lesioned monkeys, either alone or together with s.c. injections of apomorphine (0.2 mg/kg) and the effect on rotational behavior was examined. GMC1111 (0.03-3.0 mg/kg) alone, orally or s.c., did not induce rotational behavior. When apomorphine and GMC1111 were injected simultaneously, rotations were nearly abolished in three monkeys with a baseline apomorphine-induced rotation rate below 13/min, whereas GMC1111 did not modify the rotations in three high-rotating animals (>17/min). Oral administration of GMC1111 (1.0 and 3.0 mg/kg) abolished the apomorphine-induced rotations in another six unilaterally dopamine-denervated monkeys, indicating a good oral bioavailability. A low dose of GMC1111 (0.3 mg/kg) administered s.c. to marmosets with bilateral nigrostriatal lesions produced a reduction of Parkinson symptoms of approximately the same degree as with levodopa/benserazide (15/3.75 mg/kg), while higher doses of GMC1111 were less effective. When levodopa/benserazide was administered together with various doses of GMC1111 (0.3-3.0 mg/kg), the levodopa-induced peak-dose dyskinesias were reduced with the highest dose of GMC1111 (3 mg/kg). Taken together, GMC1111 modifies dopaminergic activity in a normalizing direction. Parkinson symptoms, as well as levodopa-induced dyskinesias are both reduced. This suggests the arrival of another member of the new dopamine stabilizer family.

Multiple cytochrome P450 enzymes responsible for the oxidative metabolism of the substituted (S)-3-phenylpiperidine, (S,S)-3-[3-(methylsulfonyl)phenyl]-1-propylpiperidine hydrochloride, in human liver microsomes

(S,S)-3-[3-(Methylsulfonyl)phenyl]-1-propylpiperidine hydrochloride [(-)-OSU6162] is a weak dopamine D2 receptor modulator that possesses potential for the treatment of levodopa (L-DOPA)-induced dyskinesias in patients with Parkinson's disease. In this report, incubations with human liver microsomes revealed that (-)-OSU6162 is selectively metabolized via N-dealkylation to yield N-depropyl (-)-OSU6162. Kinetics evidence is presented that the N-depropylation of (-)-OSU6162 in human hepatic microsomes is mediated by multiple cytochrome p450 (p450) enzymes, in particular CYP2D6. This hypothesis is borne out by several lines of in vitro evidence; 1). incubations of (-)-OSU6162 (5 micro M) with hepatic microsomes from a panel of human donors showed that (-)-OSU6162 N-depropylase activity correlated well with CYP2D6-catalyzed dextromethorphan O-demethylase activity but not with other p450 enzyme-specific activities; 2). quinidine, a CYP2D6-specific inhibitor, inhibited (-)-OSU6162 N-depropylation, whereas other p450 enzyme-specific substrates/inhibitors did not significantly inhibit this activity; 3). CYP2D6 possessed highest intrinsic (-)-OSU6162 N-depropylase activity when compared with a battery of recombinant heterologously expressed human p450 enzymes. In addition, the selectivity of (-)-OSU6162 to inhibit six human p450 enzymes (CYP1A2, CYP2C9, CYP2C19, CYP2E1, CYP2D6 and CYP3A4) was evaluated using an in vitro inhibition screen. Of the enzymes examined, only the activity of CYP2D6 was inhibited by coincubation with (-)-OSU6162. Thus, it is concluded that (-)-OSU6162 is metabolized by several p450 enzymes and that CYP2D6 accounts for the majority of the observed p450 N-depropylase activity in vitro.

PNU-96391A (OSU6162) antagonizes the development of behavioral sensitization induced by dopamine agonists in a rat model for Parkinson's disease

PNU-96391A is a weak dopamine (DA) D(2) receptor antagonist with behavioral stabilizing properties. Previous experiments revealed that PNU-96391A antagonizes the expression of L-DOPA induced behavioral sensitization (dyskinesias) in lesioned primates without inducing akinesia or reducing the anti-Parkinsonian efficacy of L-DOPA. This study evaluated the ability of PNU-96391A to block the development of DA agonist-induced behavioral sensitization in rats with unilateral 6-OH-DA lesions of the median forebrain bundle. Repeated twice daily treatment with L-DOPA and the decarboxylase inhibitor benserazide (15 and 5 mg/kg, IP, respectively), or quinpirole (D(2)/D(3) agonist, 0.1 mg/kg, SC) increased the contralateral rotations measured on day 7 and 14 as compared to day 1. PNU-96391A (10-60 mg/kg, SC, bid.) antagonized the development of behavioral sensitization induced by both agonists. The basal activity of L-DOPA was not affected while a reduction of quinpirole-induced rotations was observed after 30-60 mg/kg, SC of PNU-96391A. Neurochemical analyses confirmed >99 % reductions of striatal DA levels, unilaterally. Concomitant treatment with PNU-96391A and L-DOPA did not affect plasma levels of PNU-96391A indicating that the effects observed are not related to pharmacokinetic interactions. These results suggest that PNU-96391A could be therapeutically useful to prevent the development of behavioral sensitization induced by DA agonists.

Evidence for protean agonism of RX 831003 at alpha 2A-adrenoceptors by co-expression with different G alpha protein subunits

Intrinsic properties of alpha(2) AR ligands were investigated by measuring two distinct signalling pathways via the alpha(2A) AR protein in CHO-K1 cells: (i) a Ca(2+) response mediated by a promiscuous G(alpha 15) protein; and (ii) a pertussis toxin-resistant [(35)S]GTP gamma S binding response mediated by a G(alpha o)Cys(351)Ile protein. The dexefaroxan analogue RX 831003 was virtually without intrinsic activity at the wt alpha(2A) AR via a G(alpha 15) protein, but induced a partial positive Ca(2+) response [pEC(50): 7.79 (0.17), E(max): 38+/-1% vs (-)-adrenaline] at the mutant Thr(373L)ys alpha(2A) AR. RX 831003 displayed a similar potency (pIC(50): 7.68 (0.21) for both the wt (E(max): -18+/-4%) and Thr(373)Lys alpha(2A) AR (E(max): -19+/-4%) inhibition of basal [(35)S]GTP gamma S binding via a G(alpha o)Cys(351)Ile protein. These data indicate that the alpha(2) AR ligand RX 831003 behaves as a protean agonist at the alpha(2A) AR and that its activity is highly dependent on the co-expressed G(alpha) protein subunit.

A paradigm shift in brain research

As late as the 1950s, it was assumed that communication between nerve cells in the brain occurred predominantly, if not entirely, by electrical impulses. A decade later, the theory of chemical transmission, which until then had been thought to occur only in the peripheral nervous system, had gained strong entrance for the central nervous system. This paradigm shift opened up an enormous new perspective in brain research, not least by facilitating the study of brain function by means of chemical tools, which in different ways could modify the chemical signaling between nerve cells. Moreover, such tools sometimes turned out to be useful as therapeutic agents. Thus for the first time, a variety of disorders in the central nervous system could be treated effectively.

Acute neuroleptic stimulates DOPA decarboxylase in porcine brain in vivo

The activity of DOPA decarboxylase measured in homogenates from rat striatum, or calculated from the rate of tracer decarboxylation measured ex vivo, is stimulated following acute treatment with antagonists of dopamine D2-like receptors. We used compartmental kinetics to test the hypothesis that utilization of the DOPA decarboxylase substrate [(18)F]fluorodopa is potentiated in living striatum following acute treatment with a typical neuroleptic. The kinetics of the tracer uptake were determined in eight anesthetized female pigs (40 kg) and in three animals receiving an infusion of haloperidol (75 microg kg(-1) h(-1)) for 1 h prior to tracer administration and throughout the 2-h positron emission recording. The relative activity of DOPA decarboxylase in striatum was increased threefold by the treatment. This potentiation of DOPA decarboxylation after pharmacological blockade of dopamine D2-like receptors may be used to optimize the utilization of exogenous DOPA in the treatment of Parkinson's disease.

Coadministration of (-)-OSU6162 with l-DOPA normalizes preproenkephalin mRNA expression in the sensorimotor striatum of primates with unilateral 6-OHDA lesions

The substituted phenylpiperidine (-)-OSU6162 is a novel modulator of the dopaminergic systems with low affinity for dopamine D(2) receptors and potent normalizing effects on l-DOPA-induced dyskinesias. We studied the effects of coadministration of (-)-OSU6162 with l-DOPA on the regulation of striatal preproenkephalin (PPE) and prodynorphin (PDyn) mRNA expression in the primate brain by in situ hybridization histochemistry. Common marmoset monkeys sustaining unilateral 6-hydroxydopamine lesions of the nigrostriatal pathway received l-DOPA/carbidopa, l-DOPA/carbidopa plus (-)-OSU6162, or vehicle over 14 days. In vehicle-treated animals, PPE mRNA levels were markedly increased in the sensorimotor territory of the lesioned striatum. By contrast, a rather uniform lesion-induced reduction of PDyn mRNA levels was found in the vehicle group. Subchronic l-DOPA treatment induced a further increase in PPE mRNA expression in a number of sensorimotor and associative subregions of the denervated striatum. Coadministration of (-)-OSU6162 with l-DOPA partially reversed the lesion- and l-DOPA-induced elevation of PPE expression and, by affecting PPE mRNA expression differentially on the intact and lesioned striatum, markedly reduced the side-to-side difference in PPE mRNA expression. The effects on PPE mRNA expression were apparent throughout the rostrocaudal extent of the putamen and the dorsal portions of the caudate nucleus. l-DOPA treatment resulted in an enhancement in PDyn mRNA expression in all functional compartments of the striatum. Coadministration of (-)-OSU6162 had no apparent influence on these l-DOPA-induced changes in PDyn mRNA expression. The present results suggest that (-)-OSU6162 acts primarily by modifying striatal output via the indirect pathway.

Use of positron emission tomography in analysing receptor function in vivo

The non-invasive radiotracer technique positron emission tomography (PET) may provide valuable information in the toxicokinetic-toxicodynamic evaluation of endogenous or toxic environmental compounds. Assessment of mechanism of action of toxins is often difficult to validate. In this respect, PET may offer advantages since it can quantify not only the distribution and kinetics of the radiolabelled toxin in the body, but also the altered rates of physiological or biochemical processes induced by the toxin. It is even possible to validate the body distribution and tissue accumulation of the toxic compound in primates, since linear kinetics can be assumed after administration of the radiolabelled compound in minute amounts without any toxic or physiological effects. Quantitative estimates can be derived with accuracy and high precision. Using a multi-tracer protocol, it is often possible to illuminate both the kinetics and the dynamics of a toxic compound. Long-term effects of different toxins on dopamine receptor function have been evaluated with PET as well as the influence of Parkinson disease medication on pre- and postsynaptic dopaminergic receptor function over the course of the disease. In conclusion, PET may provide very informative insight into complex receptor interactions of both toxic compounds and drugs under development.

Effects of acute and repeated treatment with a novel dopamine D2 receptor ligand on L-DOPA-induced dyskinesias in MPTP monkeys

(S)-(-)-3-(3-(methylsulfonyl)phenyl)-1-propylpiperidine ((-)-OSU6162) is a phenylpiperidine derivative which exhibits low affinity to the dopamine D2 receptor in vitro. However, in vivo, positron emission tomography scanning studies show that the compound displaces the selective dopamine D2 receptor antagonist, raclopride. We have evaluated, in this study, the effect of (-)-OSU6162, on L-3,4-dihydroxyphenylalanine (L-DOPA)-induced dyskinesias in a primate model of Parkinson's disease. Five 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP)-treated cynomolgus monkeys with a stable parkinsonian syndrome and reproducible dyskinesias to L-DOPA were used in this study. The monkeys were housed in observation cages equipped with an electronic motility monitoring system. They were injected subcutaneously (s.c.) with L-DOPA methyl ester (125 mg per animal) plus benserazide (50 mg per animal; L-DOPA/benserazide) alone or in combination with (-)-OSU6162 (1.0, 3.0, 6.0 or 10 mg/kg, s.c.). Subcutaneous injection of sterile saline was used as control. L-DOPA/benserazide increased locomotion and improved parkinsonism but also induced dyskinesias. Co-administration of (-)-OSU6162 with L-DOPA/benserazide produced a significant reduction in L-DOPA-induced dyskinesias. This improvement in L-DOPA-induced dyskinesias occurred mainly at the onset of the L-DOPA/benserazide effect as reflected by an increase in the duration of the "ON" state without dyskinesias up to 3.4 fold after (-)-OSU6162 co-administration as compared to L-DOPA/benserazide alone. The anti-dyskinetic effect of (-)-OSU6162 was maintained during 14 days and no tolerance to this effect was observed. Our data suggests that (-)-OSU6162 could be of significant clinical value to reduce L-DOPA-induced dyskinesias in fluctuating advanced Parkinson's disease patients.

Motor effects of (-)-OSU6162 in primates with unilateral 6-hydroxydopamine lesions

The effects of the novel compound, (-)-OSU6162 ((S)-(-)-3-methylsulfonylphenyl-1-propylpiperidine), on rotational behavior induced by dopamine receptor agonists was investigated in common marmosets (Callithrix jacchus) with unilateral 6-hydroxydopamine lesions. (-)-OSU6162 per se displayed no effect on the animals' behavior. On the other hand, pretreatment with (-)-OSU6162 attenuated rotational behavior induced by apomorphine (apomorphini hydrochloridum), L-DOPA (3,4-dihydroxyphenylalanine), and the dopamine D2 receptor agonist, quinpirole (trans-(-)-4aR-4,4a, 5,6,7,8,8a,9-octahydro-5-propyl-1H-pyrazolol[3,4-g]quinoline hydrochloride), without inducing motor impairment such as akinesia or dystonia. In addition, treatment with (-)-OSU6162 for 5 consecutive days almost completely abolished the rotational behavior provoked by apomorphine and produced a transient subsensitization of such apomorphine-induced effects after it was discontinued. Moreover, pretreatment with (-)-OSU6162 in two monkeys augmented the rotational behavior elicited by the dopamine D1 receptor agonists, SKF-81297 (R(+)-6-chloro-7,8,dihydroxy-1-phenyl-2,3,4, 5-tetrahydro-1H-3-benzazepine hydrobromide) and A-77636 ((-)-(1R, 3S)-3-adamantyl-1-(aminomethyl)-3,4-dihydro-5, 6-dihydroxy-1H-2-benzopyran hydrochloride). The findings indicate that (-)-OSU6162 can exert indirect state-dependent effects that differentially affect dopamine D1 and dopamine D2 receptor agonist-induced behavior.

Effects of the substituted (S)-3-phenylpiperidine (-)-OSU6162 on PET measurements of [11C]SCH23390 and [11C]raclopride binding in primate brains

The substituted (S)-3-phenylpiperidine (-)-OSU6162 belongs to a novel class of functional modulators of dopaminergic systems. In vivo, (-)-OSU6162 has a unique stabilising profile on dopaminergic functions. In vitro this compound exhibits low affinity for the dopamine D2 receptor, but due to its similarity to neuroleptics on brain dopaminergic neurochemistry and different postsynaptic effects it has been characterised as a preferential dopamine autoreceptor antagonist. To further clarify the effects of (-)-OSU6162 on the postjunctional nigrostriatal dopaminergic system, dopamine receptor binding was measured in rhesus monkeys (Macaca mulatta) by positron emission tomography (PET) using the D1 and D2 dopamine receptor radioligands [11C]SCH23390 and [11C]raclopride respectively, before and during continuous intravenous infusions of(-)-OSU6162. Additionally, the test-retest variability of sequential [11C]SCH23390 scans was estimated. Following the administration of (-)-OSU6162, [11C]raclopride binding in striatum was dose-dependently decreased with a 76% reduction occurring after 3.0 mg/kg per h continuous infusion. Whereas (-)-OSU6162 in the lower doses had no effect on [11C]SCH23390 binding, the highest dose, 3.0 mg/kg per h, increased [11C]SCH23390 binding, which may indicate a potentiating effect on D1 dopamine receptor mediated functions. Thus, in contrast to the conditions in vitro, (-)-OSU6162 produces a high displacement of raclopride from D2 receptors in vivo.

Effect of apomorphine infusion on dopamine synthesis rate relates to dopaminergic tone

The effects of apomorphine on the striatal L-[11C]DOPA influx rate was examined in anaesthetized Rhesus monkeys using positron emission tomography (PET). In comparison with baseline conditions, the addition of a continuous infusion of apomorphine produced decreases in the striatal L-[11C]DOPA influx rate in all the monkeys examined. The effect of apomorphine infusion also showed a dose-dependent trend. In individual monkeys, the magnitude of the effect showed a baseline dopaminergic tone-dependency; that is, the effect of apomorphine was most pronounced in monkeys with high baseline influx rates, and in monkeys with lower baseline values apomorphine induced a weaker effect. Studies of radiolabeled tracer and radiolabeled metabolites formed in plasma confirmed that apomorphine infusion did not induce any change in the peripheral elimination or metabolite formation of L-[11C]DOPA. The decreased striatal L-[11C]DOPA influx rate induced by apomorphine was interpreted as an agonist effect on dopamine autoreceptors regulating the dopamine synthesis rate. The observation of a baseline dopaminergic tone-dependent effect is in agreement with earlier results showing this influence on the striatal influx rate as measured with the tracer L-[11C]DOPA. A priori, it can be established that L-[11C]DOPA and PET provide a method not only to study the structural integrity of the presynaptic dopaminergic system but also to study the homeostasis-regulating mechanisms of this neurotransmitter system in vivo. The ability to measure condition-dependent effects in individuals should be of great importance in determining specific pathophysiological mechanisms underlying degenerative and functional disorders affecting the dopaminergic system.