Matts Kågedal

A positron emission tomography study in healthy volunteers to estimate mGluR5 receptor occupancy of AZD2066 — Estimating occupancy in the absence of a reference region

AZD2066 is a new chemical entity pharmacologically characterized as a selective, negative allosteric modulator of the metabotropic glutamate receptor subtype 5 (mGluR5). Antagonism of mGluR5 has been implicated in relation to various diseases such as anxiety, depression, and pain disorders. To support translation from preclinical results and previous experiences with this target in man, a positron emission tomography study was performed to estimate the relationship between AZD2066 plasma concentrations and receptor occupancy in the human brain, using the mGluR5 radioligand [(11)C]-ABP688. The study involved PET scans on 4 occasions in 6 healthy volunteers. The radioligand was given as a tracer dose alone and following oral treatment with different doses of AZD2066. The analysis was based on the total volume of distribution derived from each PET-assessment. A non-linear mixed effects model was developed where ten delineated brain regions of interest from all PET scans were included in one simultaneous fit. For comparison the analysis was also performed according to a method described previously by Lassen et al. (1995). The results of the analysis showed that the total volume of distribution decreased with increasing drug concentrations in all regions with an estimated Kipl of 1170 nM. Variability between individuals and occasions in non-displaceable volume of distribution could explain most of the variability in the total volume of distribution. The Lassen approach provided a similar estimate for Kipl, but the variability was exaggerated and difficult to interpret.

Non-linear mixed effects modelling of positron emission tomography data for simultaneous estimation of radioligand kinetics and occupancy in healthy volunteers

The aim of this work was to develop a model simultaneously estimating (11)C-AZD9272 radioligand kinetics and the relationship between plasma concentration of AZD9272 and receptor occupancy in the human brain. AZD9272 is a new chemical entity pharmacologically characterised as a noncompetitive antagonist at the metabotropic glutamate receptor subtype 5 (mGluR5). Positron emission tomography (PET) was used to measure the time course of ((11)C-AZD9272) in the brain. The study included PET measurements in six healthy volunteers where the radioligand was given as a tracer dose alone as well as post oral treatment with different doses of unlabelled AZD9272. Estimation of radioligand kinetics, including saturation of receptor binding was performed by use of non-linear mixed effects modelling. Data from the regions with the highest (ventral striatum) and lowest (cerebellum) radioligand concentrations were included in the analysis. It was assumed that the extent of non-displaceable brain uptake was the same in both regions while the rate of CNS uptake and the receptor density differed. The results of the analysis showed that AZD9272 binding at the receptor is saturable with an estimated plasma concentration corresponding to 50% occupancy of approximately 200 nM. The density of the receptor binding sites was estimated to 800 nM and 200 nM in ventral striatum and cerebellum respectively. By simultaneously analysing data from several PET measurements and different brain regions in a non-linear mixed effects framework it was possible to estimate parameters of interest that would otherwise be difficult to quantify.

Modelling a spontaneously reported side effect by use of a Markov mixed-effects model.

Aims: To present a method for analyzing side-effect data where change in severity is spontaneously reported during the experiment. Methods: A clinical study in 12 healthy volunteers aimed to investigate the concentration-response characteristics of a CNS-specific side-effect was conducted. After an open session where the subjects experienced the side-effect and where the individual pharmacokinetic parameters were evaluated they were randomized to a sequence of three different infusion rates of the drug in a double-blinded crossover way. The infusion rates were individualized to achieve the same target concentration in all subjects and different drug input rates were selected to mimic absorption profiles from different formulations. The occurrence of the specific side-effect and any subsequent change in severity was self-reported by the subjects. Severity was recorded as 0 = no side-effect, 1 = mild side-effect and 2 = moderate or severe side-effect. Results: The side-effect data were analyzed using a mixed-effects model for ordered categorical data with and without Markov elements. The former model estimated the probability of having a certain side-effect score conditioned on the preceding observation and drug exposure. The observed numbers of transitions between scores were from 0 −> 1: 24, from 0− > 2: 11, from 1 − >, 2: 23, from 2− > 1: 1, from 2− > 0: 32 and from 1 − >0: 2. The side-effect model consisted of an effect-compartment model with a tolerance compartment. The predictive performance of the Markov model was investigated by a posterior predictive check (PPC), where 100 datasets were simulated from the final model. Average number of the different transitions from the PPC was from 0 − > 1: 26, from 0 − > 2: 11, from 1 − > 2: 25, from 2 − >1: 1, from 2 − >0: 35 and from 1 − > 0: 1. A similar PPC for the model without Markov elements was at considerable disparity with the data. Conclusion: This approach of incorporating Markov elements in an analysis of spontaneously reported categorical side-effect data could adequately predict the observed side-effect time course and could be considered in analyses of categorical data where dependence between observations is an issue.

Distribution of Zolmitriptan into the CNS in Healthy Volunteers

AbstractObjective: Triptans are highly effective in the treatment of migraine. Both central and peripheral mechanisms of action have been suggested. Until now, firm data about the passage of triptans into the CNS in humans have been lacking. The aim of the current study was to evaluate, using positron emission tomography (PET), the uptake and distribution of zolmitriptan into the CNS after intranasal administration. Subjects and methods: Eight healthy volunteers, five males and three females (mean ages 23 and 26 years, respectively), were included. Radioactive [carbonyl-11C]zolmitriptan was infused intravenously for 5 minutes on two occasions: once alone, and once 30–40 minutes after intranasal administration of unlabelled zolmitriptan 5mg. PET was used to measure the concentration of labelled zolmitriptan in the brain, from the start of the tracer infusion for 90 minutes. Regional cerebral blood volume was determined with [15O]carbon monoxide. In addition, an MRI scan was performed to obtain anatomical information.The PET images were analysed quantitatively for different areas of the brain, generating [11C]zolmitriptan time-activity data corrected for circulating tracer activity. The rate of uptake of intranasal zolmitriptan into the CNS was estimated by kinetic modelling using the PET data. Results: PET data from this study demonstrate a rapid dose-proportional uptake of [11C]zolmitriptan into the brain. Significant concentrations of [11C]zolmitriptan were found in all brain regions studied. Calculated CNS concentrations after intranasal zolmitriptan administration showed a gradual increase, reaching about 2nM (0.5 μg/L) 30 minutes after administration and 3.5nM (1.0 μg/L), or one-fifth of the plasma concentration, 1 hour after administration. Five minutes after zolmitriptan administration, the mean CNS concentration had already reached 0.5nM, which is higher than in vitro values for initiation of the agonistic action on 5-HT1B/1D receptors. Conclusion: This study demonstrates by direct measurements that zolmitriptan enters the brain parenchyma in humans, achieving an uptake rate and concentration compatible with a central mode of action.

Norepinephrine transporter occupancy in the human brain after oral administration of quetiapine XR

Quetiapine, originally developed as an antipsychotic, demonstrates efficacy in clinical studies of schizophrenia, bipolar mania and depression, major depressive disorder and generalized anxiety disorder. This broad spectrum of efficacy was not predicted from the preclinical pharmacology of quetiapine. Binding studies in vitro show that quetiapine and its major active human metabolite, norquetiapine, have moderate to high affinity for dopamine D2 and serotonin 5-HT2A receptors, while norquetiapine alone has high affinity for the norepinephrine transporter (NET). This positron emission tomography (PET) study measured NET occupancy in human subjects treated with extended-release quetiapine (quetiapine XR) at doses relevant in the treatment of depression. PET measurements using the specific NET radioligand (S,S)-[(18)F]FMeNER-D2 were performed before and after quetiapine XR treatment at 150 and 300 mg/d for 6-8 d in nine healthy males (aged 21-33 yr). Regions of interest were defined for the thalamus, using the caudate as reference region. NET occupancy was calculated using a target:reference region ratio method. Plasma concentrations of quetiapine and norquetiapine were monitored during PET measurements. Following quetiapine XR treatment, the mean NET occupancy in the thalamus was 19 and 35%, respectively, at quetiapine XR doses of 150 and 300 mg/d. The estimated plasma concentration of norquetiapine corresponding to 50% NET occupancy was 161 ng/ml. This is the first demonstration of NET occupancy by an antipsychotic in the human brain. NET inhibition is accepted as a mechanism of antidepressant activity. NET occupancy may therefore contribute to the broad spectrum of efficacy of quetiapine.

True nasopharyngeal absorption of zolmitriptan after administration via nasal spray in healthy male volunteers

ObjectiveThe aim of this study was to quantify the fraction of zolmitriptan that is absorbed directly through the nasal mucosa after administration of zolmitriptan nasal spray.MethodsFollowing confirmation that activated charcoal blocks gastrointestinal absorption of zolmitriptan, healthy male volunteers were given zolmitriptan nasal spray 5mg (with and without charcoal) and zolmitriptan 5mg oral tablets (with and without charcoal) in a randomized, crossover design. Blood samples for pharmacokinetic analysis were collected up to 9 hours post-dose. Twelve subjects completed all treatments.ResultsThe fraction of bioavailable dose absorbed through the nasal mucosa was calculated to be 29% (95% CI 19, 43). Intranasal absorption contributed 71% of zolmitriptan exposure during the first hour post-dose and 49% during the first 2 hours.ConclusionsThis study confirms true nasopharyngeal absorption of zolmitriptan after nasal spray administration. This route of absorption contributed approximately 30% of total zolmitriptan exposure, with much higher proportions of exposure seen during the first 2 hours post-dose when patients would expect to benefit from treatment. These results suggest that intranasal absorption plays an important role in the early onset of efficacy of zolmitriptan nasal spray seen in clinical trials.

Early phase drug development for treatment of chronic pain — Options for clinical trial and program design

Due to high prevalence and unmet medical need, chronic pain has become an important area for development of new medicines. Chronic pain disorders are heterogeneous with regard to pathophysiological mechanisms and clinical presentation. While a mechanism-based classification of pain is generally advocated, it is not yet applicable for diagnostic use. Many new analgesic drug candidates believed to act on scientifically relevant pain targets have failed to show efficacy in clinical trials. These might be true observations of inferior efficacy and/or safety. However, in part, these failures may be due to difficulties with selection of an appropriate study population and/or appropriate doses. For a new chemical entity (NCE) with a novel pharmacological mechanism, the only guidance for selection of study population and doses is often based on preclinical data. Thus, there may be considerable uncertainty in defining the population with a pain generating mechanism targeted by the NCE. Therefore, further exploration of the right population and dose may be needed in early clinical phase why alternatives to conventional trial designs may be considered. We have reviewed characteristics of three alternative design options from an early (Phase 2) drug development perspective; enriched enrolment, dose titration and adaptive dosing. The advantages and disadvantages of each type of study design were analyzed and discussed from a clinical development program perspective. It is concluded that these designs can be useful in addressing different types of issues in early development of novel analgesic drugs for chronic pain.

A Study of Organic Acid Transporter‐Mediated Pharmacokinetic Interaction Between NXY‐059 and Cefuroxime

N is a novel, free-radical-trapping neuroprotectant that, until recently, was in clinical development for the treatment of acute ischemic stroke based on effects seen in experimental animal models. NXY-059 is eliminated primarily by renal excretion, and initial studies have shown that approximately 30% is via active tubular secretion. A phase I study has demonstrated that the active tubular secretion of NXY-059 occurs through an organic acid transporter (OAT). The half-life of NXY-059 is approximately 4 hours in healthy subjects. The antibiotic cefuroxime has a half-life of approximately 66 minutes and is eliminated renally, with approximately 45% accounted for by an OAT. The relatively large fraction of cefuroxime eliminated via an OAT compared with most other drugs makes it a suitable model drug to study any effect of NXY-059 on this transporter. Furthermore, the clinical dose of cefuroxime is relatively high (1.5 g or approximately 3.5 mmol), resulting in concentrations that can potentially saturate the OAT and thereby affect the active elimination of NXY-059. The primary objectives of this study were to explore the effect of NXY-059 on the renal clearance (CLR) of the model drug cefuroxime and, vice versa, to estimate the degree of interaction to be expected with NXY-059 when coadministered with other drugs mainly eliminated by the kidney, with some contribution from active transportation by OAT.

Autoradiographic Mapping of 5-HT1B/1D Binding Sites in the Rhesus Monkey Brain Using [carbonyl-11C]zolmitriptan

Zolmitriptan is a serotonin 5-HT1B/1D receptor agonist that is an effective and well-tolerated drug for migraine treatment. In a human positron emission tomography study, [11C]zolmitriptan crossed the blood-brain barrier but no clear pattern of regional uptake was discernable. The objective of this study was to map the binding of [11C]zolmitriptan in Rhesus monkey brain using whole hemisphere in vitro autoradiography with [11C]zolmitriptan as a radioligand. In saturation studies, [11C]zolmitriptan showed specific (90%) binding to a population of high-affinity binding sites (Kd 0.95–5.06 nM). There was regional distribution of binding sites with the highest density in the ventral pallidum, followed by the external globus pallidus, substantia nigra, visual cortex, and nucleus accumbens. In competitive binding studies with 5-HT1 receptor antagonists, [11C]zolmitriptan binding was blocked by selective 5-HT1B and 5-HT1D ligands in all target areas. There was no appreciable change in binding with the addition of a 5-HT1A receptor antagonist.

Pharmacokinetic–pharmacodynamic modeling of fostamatinib efficacy on ACR20 to support dose selection in patients with rheumatoid arthritis (RA)

R788 (fostamatinib) is an oral prodrug that is rapidly converted into a relatively selective spleen tyrosine kinase (SYK) inhibitor R406, evaluated for the treatment of rheumatoid arthritis (RA). This analysis aimed at developing a pharmacodynamic model for efficacy using pooled ACR20 data from two phase II studies in patients with rheumatoid arthritis (TASKi1 and TASKi2), describing the effect of fostamatinib as a function of fostamatinib exposure (dose, R406 plasma concentration) and other explanatory variables. The exposure–response relationship of fostamatinib was implemented into a continuous time Markov model describing the time course of transition probabilities between the three possible states of ACR20 non‐responder, responder, and dropout at each visit. The probability of transition to the ACR20 response state was linearly (at the rate constant level) related to average R406 plasma concentrations and the onset of this drug effect was fast. Further, increases of fostamatinib dose resulted in increased dropout and subsequent loss of efficacy. This analysis provided an increased understanding of the exposure–response relationship, and provided support for fostamatinib 100 mg BID an appropriate dose regimen for further clinical evaluation.