Microsome Mediated in Vitro Metabolism: A Convenient Method for the Preparation of the PET Radioligand Metabolite [18F]FE-PE2I-OH for Translational Dopamine Transporter Imaging

Undesired radiometabolites can be detrimental to the development of positron emission tomography (PET) radioligands. Methods for quantifying radioligand metabolites in brain tissue include ex vivo studies in small animals or labeling and imaging of the radiometabolite(s) of interest. The latter is a time- and resource-demanding process, which often includes multistep organic synthesis. We hypothesized that this process could be replaced by making use of liver microsomes, an in vitro system that mimics metabolism. In this study, rat liver microsomes were used to prepare radiometabolites of the dopamine transporter radioligand [18F]FE-PE2I for in vitro imaging using autoradiography and in vivo imaging using PET in rats and nonhuman primates. The primary investigated hydroxy-metabolite [18F]FE-PE2I-OH ([18F]2) was obtained in a 2% radiochemical yield and >99% radiochemical purity. In vitro and in vivo imaging demonstrated that [18F]2 readily crossed the blood-brain barrier and bound specifically and reversibly to the dopamine transporter. In conclusions, the current study demonstrates the potential of liver microsomes in the production of radiometabolites for translational imaging studies and radioligand discovery.

Betula alba Bark Extract and Empetrum nigrum Fruit Juice, a Natural Alternative to Niacinamide for Skin Barrier Benefits

The Scandinavian region is home to a unique biome with endemic plant species. The aim of this study was to explore this natural diversity and identify plant extracts providing positive skin barrier effects. Six plant extracts were identified as starting material. Following biochemical screening, two candidates outperformed the rest: Betula alba (BA) and Empetrum nigrum (EN). Quantitative PCR analysis showed that BA and EN upregulated barrier genes, when used individually and in combination. Betula alba increased AQP3 and OCLN protein expression, something niacinamide was incapable of. Additionally, the skin barrier was strengthened, evidenced by inhibition of KLK5 and hyaluronidase and showed strong antioxidant and anti-inflammatory activity through DPPH and COX2 inhibition, respectively. A first split-face clinical study was conducted using the combination of extracts versus placebo. There was a significantly better skin restructuring effect and corneocyte cohesion on the side treated with combined extracts. A second split-face clinical study assessed the combined extracts versus 3% niacinamide. Significant variations in skin hydration and TEWL were observed in favor of the extract treated side. In conclusion, we identified a natural alternative to niacinamide for improving skin barrier health, in Scandinavian plant extracts, which yield strong performance, but at a lower concentration.

Target occupancy study and whole-body dosimetry with a MAGL PET ligand [11C]PF-06809247 in non-human primates

Background

Monoacylglycerol lipase (MAGL) is a key serine hydrolase which terminates endocannabinoid signaling and regulates arachidonic acid driven inflammatory responses within the central nervous system. To develop [¹¹C]PF-06809247 into a clinically usable MAGL positron emission tomography (PET) radioligand, we assessed the occupancy of MAGL by an inhibitor in the non-human primate (NHP) brain. Additionally, we measured the whole-body distribution of [¹¹C]PF-06809247 in NHP and estimated human effective radiation doses.

Methods

Seven cynomolgus monkeys were enrolled for brain PET measurements. Two PET measurements along with arterial blood sampling were performed in each NHP: one baseline and one pretreatment condition with intravenous administration of PF-06818883, a pro-drug of a selective MAGL inhibitor (total of seven doses between 0.01 and 1.27 mg/kg). Kinetic parameters K₁, k₂ and k₃ were estimated by a two tissue compartment (2TC) model using metabolite corrected plasma radioactivity as the input function. k₄ was set as 0 according to the irreversible binding of [¹¹C]PF-06809247. K_i by 2TC and Patlak analysis were calculated as the influx constant. The target occupancy was calculated using K_i at baseline and pretreatment conditions. Two cynomolgus monkeys were enrolled for whole-body PET measurements. Estimates of the absorbed radiation dose in humans were calculated with OLINDA/EXM 1.1 using the adult male reference model.

Results

Radioactivity retention was decreased in all brain regions following pretreatment with PF-06818883. Occupancy was measured as 25.4–100.5% in a dose dependent manner. Whole-body PET showed high radioactivity uptake values in the liver, small intestine, kidney, and brain. The effective dose of [¹¹C]PF-06809247 was calculated as 4.3 μSv/MBq.

Conclusions

[¹¹C]PF-06809247 is a promising PET ligand for further studies of MAGL in the human brain.

Supplementary Information

The online version contains supplementary material available at 10.1186/s13550-022-00882-2.

A novel multifunctional skin care formulation with a unique blend of antipollution, brightening and antiaging active complexes

BACKGROUND

High demand on anti-aging skin care encourage the improvement and development of more personalized formulations with additional benefits for general skin health and age associated skin signs. The skin aging physical and biological phenotypes manifest differently between diverse ethnic populations. A highly polluted environment can be viewed as an extrinsic factor accelerating the skin aging process.

AIM

To develop a unique formula with active complexes, having multifunctional effects for anti-pollution, brightening and anti-aging/barrier strengthening purposes with confirmed activities in vitro and ex vivo skin models, suitable for polluted skin.

METHODS

In vitro culture model with primary human skin cells, ex vivo studies with full-thickness human skin, melanocyte 3D coculture model, gene expression of epidermal and dermal genes, anti-glycation, proteasomal activity, melanin, and cytokine assays.

RESULTS

In vitro and ex vivo studies clearly demonstrated that diglucosyl gallic acid (active A) and the formulation complex inhibited pollution mediated MMP1 protein, CYP1A1 gene expression, and IL-6 protein secretion, while caprylic/capric triglyceride, diacetyl boldine (active B) had anti-melanogenic effect in in vitro primary melanocyte monoculture and 3D spheroid model. Another active compound, acetyl dipeptide 1 cetyl ester (active D), significantly upregulated epidermal barrier genes (Aquaporin 3 [AQP3], Filaggrin [FLG], caspase 14, and keratin 10) in human primary keratinocytes. Interestingly, both acetyl dipeptide 1 cetyl ester (active D) and niacinamide (active C) improved dermal gene expression (fibrillin-1, Collagen type 1 alpha 1, Decorin, Lysyl oxidase-like 1) and, moreover, had significant anti-glycant and proteasomal promoter activity in human primary fibroblasts.

CONCLUSION

Considering consumers need in heavily polluted areas, we developed a multipurpose formulation comprised of unique active complexes toward pollution, pollution induced inflammation, skin brightening, and antiaging concerns with beneficial results demonstrated by in vitro and ex vivo studies.

Effect of clinically relevant doses of vortioxetine and citalopram on serotonergic PET markers in the nonhuman primate brain

Vortioxetine is a multimodal antidepressant approved for treatment of major depressive disorder. Preclinical studies have demonstrated that the mechanism of action of vortioxetine might be different from selective serotonin reuptake inhibitors (SSRIs), including larger serotonin (5-HT) release and direct modulation of several 5-HT receptors. In the current positron emission tomography (PET) study, we evaluated the mechanism of action of vortioxetine by comparing its effect to the SSRI citalopram on the binding of [¹¹C]AZ10419369 to the 5-HT_1B receptor in the nonhuman primate brain. Initially, the 5-HT transporter (5-HTT) binding of vortioxetine was determined by [¹¹C]MADAM PET measurements before and after administration of vortioxetine (0.1-3.0 mg/kg) and data were used to confirm clinically relevant dosing in subsequent PET measurements with [¹¹C]AZ10419369. The 5-HT_1B receptor binding was significantly decreased after 0.3 mg/kg of citalopram in the dorsal raphe nucleus (5%), as well as after 0.3 mg/kg of vortioxetine in six brain regions (~25%) or 1.0 mg/kg of vortioxetine in all 12 examined regions (~48%). Moreover, there was no effect of 1.0 mg/kg of vortioxetine on the binding of [¹¹C]Cimbi-36 to the 5-HT_2A receptor, which has comparable sensitivity to 5-HT release as [¹¹C]AZ10419369 binding. In conclusion, at clinically relevant doses, vortioxetine induced larger reductions in [¹¹C]AZ10419369 binding than citalopram. These observations suggest that vortioxetine binds to the 5-HT_1B receptor at clinically relevant doses. Future studies are warranted to evaluate the role of the 5-HT_1B receptor in the therapeutic effects of vortioxetine and as a potential target for the development of novel antidepressant drugs.

A Nonhuman Primate PET Study: Measurement of Brain PDE4 Occupancy by Roflumilast Using (R)-[11C]Rolipram

PURPOSE

Phosphodiesterase 4 (PDE4) inhibition in the brain has been reported to improve cognitive function in animal models. Therefore, PDE4 inhibitors are one of key targets potential for drug development. Investigation of brain PDE4 occupancy would help to understand the effects of PDE4 inhibition to cognitive functions. Roflumilast is a selective phosphodiesterase type 4 (PDE4) inhibitor used clinically for severe chronic obstructive pulmonary disease, but the effects to the brain have not been well investigated. In this study, we aimed to investigate whether roflumilast entered the brain and occupied PDE4 in nonhuman primates.

PROCEDURES

Positron emission tomography (PET) measurements with (R)-[¹¹C]rolipram were performed at baseline and after intravenous (i.v.) administration of roflumilast (3.6 to 200 μg/kg) in three female rhesus monkeys. Arterial blood samples were taken to obtain the input function. Protein binding was measured to obtain the free fraction (fp) of the radioligand. Total distribution volume (V_T) and V_T/fp were calculated as outcome measures from two tissue compartment model. Lassen plot approach was taken to estimate the target occupancy.

RESULTS

The brain uptake of (R)-[¹¹C]rolipram decreased after roflumilast administration. PDE 4 occupancy by roflumilast showed dose- and plasma concentration-dependent increase, although PDE4 occupancy did not reach 50 % even after the administration of up to 200 μg/kg of roflumilast, regardless of outcome measures, V_T or V_T/fp.

CONCLUSIONS

This PET study showed that the brain PDE4 binding was blocked to a certain extent after i.v. administration of clinical relevant doses of roflumilast in nonhuman primates. Further clinical PET evaluation is needed to understand the relationship between PDE4 inhibition and potential improvement of cognitive function in human subjects.

Synthesis and evaluation of two new candidate high-affinity full agonist PET radioligands for imaging 5-HT1B receptors

INTRODUCTION

The serotonin 1B receptor subtype is of interest in the pathophysiology and treatment of depression, anxiety, and migraine. Over recent years 5-HT_1B receptor binding in human brain has been examined with PET using radioligands that are partial but not full agonists. To explore how the intrinsic activity of a PET radioligand may affect imaging performance, two high-affinity full 5-HT_1B receptor agonists (AZ11136118, 4; and AZ11895987, 5) were selected from a large compound library and radiolabeled for PET examination in non-human primates.

METHODS

[¹¹C]4 was obtained through Pd(0)-mediated insertion of [¹¹C]carbon monoxide between prepared iodoarene and homochiral amine precursors. [¹¹C]5 was obtained through N-¹¹C-methylation of N-desmethyl precursor 6 with [¹¹C]methyl triflate. [¹¹C]4 and [¹¹C]5 were studied with PET in rhesus or cynomolgus monkey. [¹¹C]4 was studied with PET in mice and rats to measure brain uptake and specific binding. Ex-vivo experiments in rats were performed to identify whether there were radiometabolites in brain. Physiochemical parameters for [¹¹C]4 (pKa, logD and conformational energetics) were evaluated.

RESULTS

Both [¹¹C]4 and [¹¹C]5 were successfully produced in high radiochemical purity and in adequate amounts for PET experiments. After intravenous injection of [¹¹C]4, brain radioactivity peaked at a low level (0.2 SUV). Pretreatment with tariquidar, an inhibitor of the brain P-gp efflux transporter, increased brain exposure four-fold whereas pretreatment with a high pharmacological dose of the 5-HT_1B antagonist, AR-A000002, had no effect on the binding. Ex-vivo experiments in rats showed no radiometabolites entering brain. [¹¹C]5 also failed to enter monkey brain under baseline conditions.

CONCLUSIONS

[¹¹C]4 and [¹¹C]5 show too low brain uptake and specific binding to be useful PET radioligands. Low brain uptake is partly ascribed to efflux transporter action as well as unfavorable conformations.

Quantitative Analysis of 18F-PF-06684511, a Novel PET Radioligand for Selective β-Secretase 1 Imaging, in Nonhuman Primate Brain

β-secretase 1 (BACE1) is a key enzyme in the generation of β-amyloid, which is accumulated in the brain of Alzheimer disease patients. PF-06684511 was identified as a candidate PET ligand for imaging BACE1 in the brain and showed high specific binding in an initial assessment in a nonhuman primate (NHP) PET study using ¹⁸F-PF-06684511. In this effort, we aimed to quantitatively evaluate the regional brain distribution of ¹⁸F-PF-06684511 in NHPs under baseline and blocking conditions and to assess the target occupancy of BACE1 inhibitors. In addition, NHP whole-body PET measurements were performed to estimate the effective radiation dose. Methods: Initial brain PET measurements were performed at baseline and after oral administration of 5 mg/kg of LY2886721, a BACE1 inhibitor, in 2 cynomolgus monkeys. Kinetic analysis was performed with the radiometabolite-corrected plasma input function. In addition, a wide dose range of another BACE1 inhibitor, PF-06663195, was examined to investigate the relationship between the brain target occupancy and plasma concentration of the drug. Finally, the effective radiation dose of ¹⁸F-PF-06684511 was estimated on the basis of the whole-body PET measurements in NHPs. Results: Radiolabeling was accomplished successfully with an incorporation radiochemical yield of 4%-12% (decay-corrected) from ¹⁸F ion. The radiochemical purity was greater than 99%. The whole-brain uptake of ¹⁸F-PF-06684511 peaked (∼220% SUV) at approximately 20 min and decreased thereafter (∼100% SUV at 180 min). A 2-tissue-compartment model described the time-activity curves well. Pretreatment with LY2886721 reduced the total distribution volume of ¹⁸F-PF-06684511 by 48%-80% depending on the brain region, confirming its in vivo specificity. BACE1 occupancy of PF-06663195, estimated using the Lassen occupancy plot, showed a dose-dependent increase. The effective dose of ¹⁸F-PF-06684511 was 0.043 mSv/MBq for humans. Conclusion: ¹⁸F-PF-06684511 is the first successful PET radioligand for BACE1 brain imaging that demonstrates favorable in vivo binding and brain kinetics in NHPs.

Development of [ Carbonyl-11C]AZ13198083, a Novel Histamine Type-3 Receptor Radioligand with Favorable Kinetics

The histamine subtype-3 receptor (H₃R) is implicated in a range of central nervous system disorders, and several radioligands have been developed for H₃R positron emission tomography imaging. However, a limitation of currently used PET radioligands for H₃R is the slow binding kinetics in high density brain regions. To address this, we herein report the development of three novel candidate H₃R radioligands, namely, [ carbonyl-¹¹C]AZ13153556 ([ carbonyl-¹¹C]4), [ carbonyl-¹¹C]AZD5213([ carbonyl-¹¹C]5), and [ carbonyl-¹¹C]AZ13198083 ([ carbonyl-¹¹C]6), and their subsequent preclinical evaluation in nonhuman primates (NHP). Radioligands [ carbonyl-¹¹C]4-6 were produced and isolated in high radioactivity (>1000 MBq), radiochemical purity (>99%), and moderate molar activity (19-28 GBq/μmol at time of injection) using a palladium-mediated ¹¹C-aminocarbonylation protocol. All three radioligands showed high brain permeability as well as a regional brain radioactivity distribution in accordance with H₃R expression (striatum > cortex > cerebellum). [ Carbonyl-¹¹C]6 displayed the most favorable in vivo kinetics and brain uptake, with an early peak in the striatal time-activity curve followed by a progressive washout from the brain. The specificity and on-target kinetics of [ carbonyl-¹¹C]6 were next investigated in pretreatment and displacement studies. After pretreatment or displacement with 5 (0.1 mg/kg), a uniformly low distribution of radioactivity across the NHP brain was observed. Collectively, this work demonstrates that [ carbonyl-¹¹C]6 is a promising candidate for H₃R imaging in human subjects.

The metabotropic glutamate receptor 5 radioligand [11C]AZD9272 identifies unique binding sites in primate brain

The metabotropic glutamate receptor 5 (mGluR5) is a target for drug development and for imaging studies of the glutamate system in neurological and psychiatric disorders. [¹¹C]AZD9272 is a selective mGluR5 PET radioligand that is structurally different from hitherto applied mGluR5 radioligands. In the present investigation we compared the binding patterns of radiolabeled AZD9272 and other mGluR5 radioligands in the non-human primate (NHP) brain. PET studies were undertaken using [¹¹C]AZD9272 and the commonly applied mGluR5 radioligand [¹¹C]ABP688. Autoradiography studies were performed in vitro using [³H]AZD9272 and the standard mGluR5 radioligands [³H]M-MTEP and [³H]ABP688 in NHP tissue. Competition binding studies were undertaken in vivo and in vitro using different mGluR5 selective compounds as inhibitors. In comparison to other mGluR5 radioligands radiolabeled AZD9272 displayed a distinct regional distribution pattern with high binding in ventral striatum, midbrain, thalamus and cerebellum. While the binding of [¹¹C]AZD9272 was almost completely inhibited by the structurally unique mGluR5 compound fenobam (2.0 mg/kg; 98% occupancy), it was only partially inhibited (46% and 20%, respectively) by the mGluR5 selective compounds ABP688 and MTEP, at a dose (2.0 mg/kg) expected to saturate the mGluR5. Autoradiography studies using [³H]AZD9272 confirmed a distinct pharmacologic profile characterized by preferential sensitivity to fenobam. The distinctive binding in ventral striato-pallido-thalamic circuits and shared pharmacologic profile with the pro-psychotic compound fenobam warrants further examination of [¹¹C]AZD9272 for potential application in psychiatric neuroimaging studies.

[11C]AZ10419096 - a full antagonist PET radioligand for imaging brain 5-HT1B receptors

INTRODUCTION

The serotonergic system is widely present in all regions of the central nervous system (CNS) and plays a key modulatory role in many of its functions. Positron emission tomography (PET) is used to study several serotonin receptors in CNS in vivo. The G-protein coupled receptor 5-HT_1B is mostly present in the occipital cortex and in midbrain and is linked to several psychiatric disorders. There is evidence that agonist PET radioligands for neuroreceptors are more sensitive to endogenous neurotransmitters than antagonists. Our previously developed 5-HT_1B receptor PET radioligand, [¹¹C]AZ10419369, is now considered a partial agonist. In this work we are aiming to develop a full antagonist PET radioligand for imaging brain 5-HT_1B receptors, and evaluate its sensitivity to increased endogenous serotonin concentration.

MATERIALS

[¹¹C]AZ10419096 was synthesized by rapid methylation of the prepared corresponding N-desmethyl precursor with [¹¹C]methyl triflate. Five PET measurements were performed in cynomolgus monkeys, consisting of two at baseline, one after treatment of a monkey with a 5-HT_1B antagonist, AR-A000002, and two in which fenfluramine was administered during scanning to induce endogenous serotonin release.

RESULTS AND DISCUSSION

[¹¹C]AZ10419096 was synthesized in high yield and purity within 30 min, including purification, formulation and sterile filtration. The baseline PET measurements demonstrated [¹¹C]AZ10419096 to have favorable radioligand characteristics, including high specific binding in brain regions that have high 5-HT_1B density, such as occipital cortex and globus pallidus, as well as subsequent rapid elimination from brain and a minor abundance of lipophilic radiometabolites in plasma. AR-A00002 completely blocked radioligand receptor-specific binding. Fenfluramine produced a distinct displacement of radioligand consistent with an expected increase of synaptic endogenous serotonin concentration.

CONCLUSIONS

[¹¹C]AZ10419096, a full 5-HT_1B antagonist PET radioligand, demonstrates high specific binding in monkey brain that is sensitive to competition from a known 5-HT_1B antagonist as well as to putatively increased endogenous serotonin levels.

Revisiting the Logan plot to account for non-negligible blood volume in brain tissue

Background

Reference tissue-based quantification of brain PET data does not typically include correction for signal originating from blood vessels, which is known to result in biased outcome measures. The bias extent depends on the amount of radioactivity in the blood vessels. In this study, we seek to revisit the well-established Logan plot and derive alternative formulations that provide estimation of distribution volume ratios (DVRs) that are corrected for the signal originating from the vasculature.

Results

New expressions for the Logan plot based on arterial input function and reference tissue were derived, which included explicit terms for whole blood radioactivity. The new methods were evaluated using PET data acquired using [¹¹C]raclopride and [¹⁸F]MNI-659. The two-tissue compartment model (2TCM), with which signal originating from blood can be explicitly modeled, was used as a gold standard.

DVR values obtained for [¹¹C]raclopride using the either blood-based or reference tissue-based Logan plot were systematically underestimated compared to 2TCM, and for [¹⁸F]MNI-659, a proportionality bias was observed, i.e., the bias varied across regions. The biases disappeared when optimal blood-signal correction was used for respective tracer, although for the case of [¹⁸F]MNI-659 a small but systematic overestimation of DVR was still observed.

Conclusions

The new method appears to remove the bias introduced due to absence of correction for blood volume in regular graphical analysis and can be considered in clinical studies. Further studies are however required to derive a generic mapping between plasma and whole-blood radioactivity levels.

Electronic supplementary material

The online version of this article (doi:10.1186/s13550-017-0314-z) contains supplementary material, which is available to authorized users.

Patterns of age related changes for phosphodiesterase type-10A in comparison with dopamine D2/3 receptors and sub-cortical volumes in the human basal ganglia: A PET study with 18F-MNI-659 and 11C-raclopride with correction for partial volume effect

Phosphodiesterase 10A enzyme (PDE10A) is an important striatal target that has been shown to be affected in patients with neurodegenerative disorders, particularly Huntington´s disease (HD). PDE10A is expressed on striatal neurones in basal ganglia where other known molecular targets are enriched such as dopamine D_2/3 receptors (D_2/3 R). The aim of this study was to examine the availability of PDE10A enzyme in relation with age and gender and to compare those changes with those related to D_2/3 R and volumes in different regions of the basal ganglia. As a secondary objective we examined the relative distribution of D_2/3 R and PDE10A enzyme in the striatum and globus pallidus. Forty control subjects (20F/20M; age: 44±11y, age range 27-69) from an ongoing positron emission tomography (PET) study in HD gene expansion carriers were included. Subjects were examined with PET using the high-resolution research tomograph (HRRT) and with 3T magnetic resonance imaging (MRI). The PDE10A radioligand ¹⁸F-MNI-659 and D_2/3 R radioligand ¹¹C-raclopride were used. The outcome measure was the binding potential (BP_ND) estimated with the two-tissue compartment model (¹⁸F-MNI-659) and the simplified reference tissue model (¹¹C-raclopride) using the cerebellum as reference region. The PET data were corrected for partial volume effects. In the striatum, PDE10A availability showed a significant age-related decline that was larger compared to the age-related decline of D_2/3 R availability and to the age-related decline of volumes measured with MRI. In the globus pallidus, a less pronounced decline of PDE10A availability was observed, whereas D_2/3 R availability and volumes seemed to be rather stable with aging. The distribution of the PDE10A enzyme was different from the distribution of D_2/3 R, with higher availability in the globus pallidus. These results indicate that aging is associated with a considerable physiological reduction of the availability of PDE10A enzyme in the striatum. Moreover as result of the analysis, in the striatum for both the molecular targets, we observed a gender effect with higher BP_ND the female group.

In vivo measurement of PDE10A enzyme occupancy by positron emission tomography (PET) following single oral dose administration of PF-02545920 in healthy male subjects

Phosphodiesterase 10A (PDE10A) is an enzyme highly enriched in the striatal medium spiny neurons. It is involved in the regulation of cytoplasmic levels of cAMP and cGMP and signaling within the basal ganglia. This study with PDE10A radioligand [¹⁸F]MNI-659 was designed to measure the enzyme occupancy of PF-02545920 in 8 healthy male volunteers (48 ± 4 years) after a single oral dose (10 mg or 20 mg) and to evaluate safety and tolerability. Arterial blood sampling was performed to obtain a metabolite-corrected plasma input function for the quantification of [¹⁸F]MNI-659 binding to PDE10A. The occupancy of PF-02545920 was calculated with two different methods: In Method 1, [¹⁸F]MNI-659 enzyme occupancy was calculated from the estimates of binding potential, using the cerebellum as a reference region; in Method 2, occupancy was estimated from the slope of the revised Lassen's plot. Serum concentrations of PF-02545920 were measured to determine the relationship between concentration and occupancy. Based on Method 1, striatal PDE10A occupancy increased with increasing PF-02545920 dose: 14-27% at 10 mg dose (N = 4) and 45-63% at 20 mg dose (N = 3). Comparable occupancies were observed using Lassen's plot Method 2: 10 mg: 14-37%; 20 mg: 46-55%. The relationship between exposure and occupancy was best described using an Emax model. The serum concentration associated with 50% occupancy was estimated to be 93.2 ng/mL. Single oral doses of 10 mg or 20 mg of PF-02545920 were safe and well tolerated in healthy male volunteers [NCT# 01918202].

Characterization of [11C]Lu AE92686 as a PET radioligand for phosphodiesterase 10A in the nonhuman primate brain

Purpose

[¹¹C]Lu AE92686 is a positron emission tomography (PET) radioligand that has recently been validated for examining phosphodiesterase 10A (PDE10A) in the human striatum. [¹¹C]Lu AE92686 has high affinity for PDE10A (IC₅₀ = 0.39 nM) and may also be suitable for examination of the substantia nigra, a region with low density of PDE10A. Here, we report characterization of regional [¹¹C]Lu AE92686 binding to PDE10A in the nonhuman primate (NHP) brain.

Methods

A total of 11 PET measurements, seven baseline and four following pretreatment with unlabeled Lu AE92686 or the structurally unrelated PDE10A inhibitor MP-10, were performed in five NHPs using a high resolution research tomograph (HRRT). [¹¹C]Lu AE92686 binding was quantified using a radiometabolite-corrected arterial input function and compartmental and graphical modeling approaches.

Results

Regional time-activity curves were best described with the two-tissue compartment model (2TCM). However, the distribution volume (V_T) values for all regions were obtained by the Logan plot analysis, as reliable cerebellar V_T values could not be derived by the 2TCM. For cerebellum, a proposed reference region, V_T values increased by ∼30 % with increasing PET measurement duration from 63 to 123 min, while V_T values in target regions remained stable. Both pretreatment drugs significantly decreased [¹¹C]Lu AE92686 binding in target regions, while no significant effect on cerebellum was observed. Binding potential (BP_ND) values, derived with the simplified reference tissue model (SRTM), were 13–17 in putamen and 3–5 in substantia nigra and correlated well to values from the Logan plot analysis.

Conclusions

The method proposed for quantification of [¹¹C]Lu AE92686 binding in applied studies in NHP is based on 63 min PET data and SRTM with cerebellum as a reference region. The study supports that [¹¹C]Lu AE92686 can be used for PET examinations of PDE10A binding also in substantia nigra.

Electronic supplementary material

The online version of this article (doi:10.1007/s00259-016-3544-9) contains supplementary material, which is available to authorized users.

Accelerated wound healing in a diabetic rat model using decellularized dermal matrix and human umbilical cord perivascular cells

There is an unmet clinical need for novel wound healing strategies to treat full thickness skin defects, especially in diabetic patients. We hypothesized that a scaffold could perform dual roles of a biomechanical support and a favorable biochemical environment for stem cells. Human umbilical cord perivascular cells (HUCPVCs) have been recently reported as a type of mesenchymal stem cell that can accelerate early wound healing in skin defects. However, there are only a limited number of studies that have incorporated these cells into natural scaffolds for dermal tissue engineering. The aim of the present study was to promote angiogenesis and accelerate wound healing by using HUCPVCs and decellularized dermal matrix (DDM) in a rat model of diabetic wounds. The DDM scaffolds were prepared from harvested human skin samples and histological, ultrastructural, molecular and mechanical assessments were carried out. In comparison with the control (without any treatment) and DDM alone group, full thickness excisional wounds treated with HUCPVCs-loaded DDM scaffolds demonstrated an accelerated wound closure rate, faster re-epithelization, more granulation tissue formation and decreased collagen deposition. Furthermore, immunofluorescence analysis showed that the VEGFR-2 expression and vascular density in the HUCPVCs-loaded DDM scaffold treated group were also significantly higher than the other groups at 7days post implantation. Since the rates of angiogenesis, re-epithelization and formation of granulation tissue are directly correlated with full thickness wound healing in patients, the proposed HUCPVCs-loaded DDM scaffolds may fulfil a role neglected by current treatment strategies. This pre-clinical proof-of-concept study warrants further clinical evaluation.

STATEMENT OF SIGNIFICANCE

The aim of the present study was to design a novel tissue-engineered system to promote angiogenesis, re-epithelization and granulation of skin tissue using human umbilical cord perivascular stem cells and decellularized dermal matrix natural scaffolds in rat diabetic wound models. The authors of this research article have been working on stem cells and tissue engineering scaffolds for years. According to our knowledge, there is a lack of an efficient system for the treatment of skin defects using tissue engineering strategy. Since the rates of angiogenesis, re-epithelization and granulation tissue are directly correlated with full thickness wound healing, the proposed HUCPVCs-loaded DDM scaffolds perfectly fills the niche neglected by current treatment strategies. This pre-clinical study demonstrates the proof-of-concept that necessitates clinical evaluations.

Efficacy of Crocus sativus L. on reduction of cadmium-induced toxicity on spermatogenesis in adult rats

Cadmium is a toxic heavy metal element, which probably cause infertility by impairment in spermatogenesis. The present work aimed (i) to study the toxic effect of cadmium on spermatogenesis in rat, as well as (ii) the protective effect of Crocus sativus L. on cadmium-intoxicated rats. Cadmium chloride was administered intraperitoneally during 16 days at intervals of 48 h between subsequent treatments. Crocus sativus L. was pre-treated in both of control and cadmium-injected rats. Animals were sacrificed on day 17 after the first treatment. The left cauda epididymis was removed and immediately immersed into Hank's balanced salt solution for the evaluation of sperm count and viability, and left testis was fixed in 10% formalin for histological evaluation. Following contamination with cadmium, a decrease was observed in the number and viability of cauda epididymis sperm, which were increased by Crocus sativus L. pre-treatment (P < 0.05). In addition, cadmium decreased both cell proliferation and Johnsen Scores in the seminiferous tubules, which were reversed by Crocus sativus pre-treatment (P < 0.05). Furthermore, cadmium-induced decrease in the amount of free serum testosterone as well as an increase in lipid peroxidation activity in the testicular tissue was reversed by Crocus sativus L. (P < 0.05). These findings may support the concept that Crocus sativus L. can improve the cadmium toxicity on spermatogenesis.

Impact of early postoperative platelet count on volumetric liver gain and perioperative outcomes after major liver resection

Background

Although perioperative platelet count has been associated with postoperative morbidity and mortality, its impact on liver regeneration has not been examined directly. This study sought to determine the impact of platelet count on liver regeneration after major liver resection using cross-sectional imaging volumetric assessment.

Methods

Patients who underwent major liver resection between 2004 and 2015 and had available data on immediate postoperative platelet count, as well as preoperative and postoperative CT images, were identified retrospectively. Resected liver volume was subtracted from total liver volume (TLV) to define postoperative remnant liver volume (RLVp). The liver regeneration index was defined as the relative increase in liver volume within 2 months ((RLV2m – RLVp)/RLVp, where RLV2m is the remnant liver volume around 2 months after surgery). The association between platelet count, liver regeneration and outcomes was assessed.

Results

A total of 99 patients met the inclusion criteria. Overall, 25 patients (25 per cent) had a low platelet count (less than 150 × 109/l), whereas 74 had a normal–high platelet count (at least 150 × 109/l). Despite having comparable clinicopathological characteristics and RLVp/TLV at surgery (P = 0·903), the relative increase in liver volume within 2 months was considerably lower in the low-platelet group (3·9 versus 16·5 per cent; P = 0·043). Patients with a low platelet count had an increased risk of postoperative complications (72 versus 38 per cent; P = 0·003), longer hospital stay (8 versus 6 days; P = 0·004) and worse median overall survival (24·5 versus 67·3 months; P = 0·005) than those with a normal or high platelet count.

Conclusion

After major liver resection, a low postoperative platelet count was associated with inhibited liver regeneration, as well as worse short- and long-term outcomes. Immediate postoperative platelet count may be an early indicator to identify patients at increased risk of worse outcomes.

Discovery and Preclinical Validation of [(11)C]AZ13153556, a Novel Probe for the Histamine Type 3 Receptor

The histamine type 3 receptor (H3) is a G protein-coupled receptor implicated in several disorders of the central nervous system. Herein, we describe the radiolabeling and preclinical evaluation of a candidate radioligand for the H3 receptor, 4-(1S,2S)-2-(4-cyclobutylpiperazine-1-carbonyl)cyclopropyl]-N-methyl-benzamide (5), and its comparison with one of the frontrunner radioligands for H3 imaging, namely, GSK189254 (1). Compounds 1 and 5 were radiolabeled with tritium and carbon-11 for in vitro and in vivo imaging experiments. The in vitro binding of [(3)H]1 and [(3)H]5 was examined by (i) saturation binding to rat and nonhuman primate brain tissue homogenate and (ii) in vitro autoradiography on tissue sections from rat, guinea pig, and human brain. The in vivo binding of [(11)C]1 and [(11)C]5 was examined by PET imaging in mice and nonhuman primates. Bmax values obtained from Scatchard analysis of [(3)H]1 and [(3)H]5 binding were in good agreement. Autoradiography with [(3)H]5 on rat, guinea pig, and human brain slices showed specific binding in regions known to be enhanced in H3 receptors, a high degree of colocalization with [(3)H]1, and virtually negligible nonspecific binding in tissue. PET measurements in mice and nonhuman primates demonstrated that [(11)C]5 binds specifically and reversibly to H3 receptors in vivo with low nonspecific binding in brain tissue. Whereas [(11)C]1 showed similar binding characteristics in vivo, the binding kinetics appeared faster for [(11)C]5 than for [(11)C]1.

CONCLUSIONS

[(11)C]5 has suitable properties for quantification of H3 receptors in nonhuman primate brain and has the potential to offer improved binding kinetics in man compared to [(11)C]1.

Cardiac screening of intact Drosophila melanogaster larvae under exposure to aqueous and gaseous toxins in a microfluidic device

We present a semi-automated microfluidic chip for orientation, immobilization, chemical exposure, and cardiac screening of 3rd instar Drosophila melanogaster larvae.

Clinical and morphometric parameters of frailty for prediction of mortality following hepatopancreaticobiliary surgery in the elderly

BACKGROUND

Although frailty is a known determinant of poor postoperative outcomes, it can be difficult to identify in patients before surgery. The authors sought to develop a preoperative frailty risk model to predict mortality among patients aged 65 years or more.

METHODS

Clinical and morphometric data including total psoas area (TPA), total psoas volume (TPV) and psoas density (Hounsfield unit average calculation, HUAC) were collected for patients undergoing hepatopancreaticobiliary (HPB) surgery between 2012 and 2014. Multivariable Cox proportional hazards regression was used to identify preoperative risk factors associated with 1-year mortality.

RESULTS

The median age of the 518 patients included in the study was 72 (i.q.r. 68-76) years; 55·6 per cent of patients were men, and half of the cohort had multiple co-morbidities (Charlson co-morbidity index (CCI) of 4 or more, 55·6 per cent). TPA cut-offs to define sarcopenia were 552·7 mm(2) /m(2) in women and 702·9 mm(2) /m(2) in men; cut-offs for TPV were 18·2 cm(3) /m(2) in women and 26·2 cm(3) /m(2) in men, whereas HUAC cut-offs were 31·1 HU in women and 33·3 HU in men. The overall 1-year mortality rate was 14·1 per cent. In multivariable analysis, risk factors associated with 1-year mortality included CCI of 4 or above (hazard ratio (HR) 2·91, 95 per cent c.i. 1·47 to 5·77; P = 0·002), malignant disease (HR 3·94, 1·17 to 13·30; P = 0·027) and sarcopenia by HUAC (HR 1·85, 1·10 to 3·10; P = 0·021). A weighted 25-point composite score was developed to stratify patients at risk of 1-year postoperative mortality. The 1-year mortality rate was noted to be 2·5 per cent among patients scoring 0-10 (low risk), 17·3 per cent among patients scoring 11-20 (intermediate risk) and 29·2 per cent among those scoring between 21 and 25 (high risk) (P < 0·001).

CONCLUSION

Clinical and morphometric measures of frailty accurately predict the risk of 1-year mortality following HPB surgery in elderly patients, and can be used to risk-stratify patients appropriately.

[11C]MADAM Used as a Model for Understanding the Radiometabolism of Diphenyl Sulfide Radioligands for Positron Emission Tomography (PET)

In quantitative PET measurements, the analysis of radiometabolites in plasma is essential for determining the exact arterial input function. Diphenyl sulfide compounds are promising PET and SPECT radioligands for in vivo quantification of the serotonin transporter (SERT) and it is therefore important to investigate their radiometabolism. We have chosen to explore the radiometabolic profile of [11C]MADAM, one of these radioligands widely used for in vivo PET-SERT studies. The metabolism of [11C]MADAM/MADAM was investigated using rat and human liver microsomes (RLM and HLM) in combination with radio-HPLC or UHPLC/Q-ToF-MS for their identification. The effect of carrier on the radiometabolic rate of the radioligand [11C]MADAM in vitro and in vivo was examined by radio-HPLC. RLM and HLM incubations were carried out at two different carrier concentrations of 1 and 10 μM. Urine samples after perfusion of [11C]MADAM/MADAM in rats were also analysed by radio-HPLC. Analysis by UHPLC/Q-ToF-MS identified the metabolites produced in vitro to be results of N-demethylation, S-oxidation and benzylic hydroxylation. The presence of carrier greatly affected the radiometabolism rate of [11C]MADAM in both RLM/HLM experiments and in vivo rat studies. The good concordance between the results predicted by RLM and HLM experiments and the in vivo data obtained in rat studies indicate that the kinetics of the radiometabolism of the radioligand [11C]MADAM is dose-dependent. This issue needs to be addressed when the diarylsulfide class of compounds are used in PET quantifications of SERT.

Test-retest reproducibility of [(11)C]PBR28 binding to TSPO in healthy control subjects

PURPOSE

The PET radioligand [(11)C]PBR28 binds to the translocator protein (TSPO), a marker of brain immune activation. We examined the reproducibility of [(11)C]PBR28 binding in healthy subjects with quantification on a regional and voxel-by-voxel basis. In addition, we performed a preliminary analysis of diurnal changes in TSPO availability.

METHODS

Twelve subjects were examined using a high-resolution research tomograph and [(11)C]PBR28, six in the morning and afternoon of the same day, and six in the morning on two separate days. Regional volumes of distribution (V T) were derived using a region-of-interest based two-tissue compartmental analysis (2TCM), as well as a parametric approach. Metabolite-corrected arterial plasma was used as input function.

RESULTS

For the whole sample, the mean absolute variability in V T in the grey matter (GM) was 18.3 ± 12.7 %. Intraclass correlation coefficients in GM regions ranged from 0.90 to 0.94. Reducing the time of analysis from 91 to 63 min yielded a variability of 16.9 ± 14.9 %. There was a strong correlation between the parametric and 2TCM-derived GM values (r = 0.99). A significant increase in GM V T was observed between the morning and afternoon examinations when using secondary methods of quantification (p = 0.028). In the subjects examined at the same time of the day, the absolute variability was 15.9 ± 12.2 % for the 91-min 2TCM data.

CONCLUSION

V T of [(11)C]PBR28 binding showed medium reproducibility and high reliability in GM regions. Our findings support the use of parametric approaches for determining [(11)C]PBR28 V T values, and indicate that the acquisition time could be shortened. Diurnal changes in TSPO binding in the brain may be a potential confounder in clinical studies and should be investigated further.

Synthesis of ([(11)C]carbonyl)raclopride and a comparison with ([(11)C]methyl)raclopride in a monkey PET study

INTRODUCTION

The selective dopamine D2 receptor antagonist raclopride is usually labeled with carbon-11 using [(11)C]methyl iodide or [(11)C]methyl triflate for use in the quantification of dopamine D2 receptors in human brain. The aim of this work was to label raclopride at the carbonyl position using [(11)C]carbon monoxide chemistry and to compare ([(11)C]carbonyl)raclopride with ([(11)C]methyl)raclopride in non-human primate (NHP) using PET with regard to quantitative outcome measurement, metabolism of the labeled tracers and protein binding.

METHODS

Palladium-mediated carbonylation using [(11)C]carbon monoxide, 4,6-dichloro-2-iodo-3-methoxyphenol and (S)-(-)-2-aminomethyl-1-ethylpyrrolidine was applied in the synthesis of ([(11)C]carbonyl)raclopride. The reaction was performed at atmospheric pressure using xantphos as supporting phosphine ligand and palladium (π-cinnamyl) chloride dimer as the palladium source. ([(11)C]Methyl)raclopride was prepared by a previously published method. In the PET study, two female cynomolgus monkeys were used under gas anesthesia of sevoflurane. A dynamic PET measurement was performed for 63 min with an HRRT PET camera after intravenous injection of ([(11)C]carbonyl)raclopride and ([(11)C]methyl)raclopride, respectively, during the same day. The order of injection of the two PET radioligands was changed between the two monkeys. The venous blood sample for measurement of protein binding was taken 3 min prior to the PET scan. Binding potential (BPND) of the putamen and caudate was calculated with SRTM using the cerebellum as a reference region.

RESULTS

The target compound ([(11)C]carbonyl)raclopride was obtained with 50 ± 5% decay corrected radiochemical yield and 95% radiochemical purity. The trapping efficiency (TE) of [(11)C]carbon monoxide was 65 ± 5% and the specific radioactivity of the final product was 34 ± 1 GBq/μmol after a 50 min of synthesis time. The radiochemical yield of ([(11)C]methyl)raclopride was in the same range as published previously i. e. 50-60% and specific radioactivity of those two batches which were used in the present PET study were 192 GBq/μmol and 638 GBq/μmol respectively after a synthesis time of 32 min. In monkey PET studies, the percentage difference of BPND in putamen was <3% and that in caudate was <9% for the two radioligands. The plasma protein binding was 86.2 ± 0.3% and 85.7 ± 0.6% for ([(11)C]carbonyl)raclopride and ([(11)C]methyl)raclopride, respectively. The radiometabolite pattern was similar for both radioligands.

CONCLUSION

Raclopride was (11)C-labeled at the carbonyl position using a palladium-mediated [(11)C]carbonylation reaction. A comparison between ([(11)C]carbonyl)raclopride and ([(11)C]methyl)raclopride with regard to quantitative PET outcome measurements, metabolism of radioligands and protein binding in monkey was performed. The monkey PET study with ([(11)C]carbonyl)raclopride showed similar results as for ([(11)C]methyl)raclopride. The PET studies were performed on 2 subjects.

Positron Emission Tomography studies with [11C]PBR28 in the Healthy Rodent Brain: Validating SUV as an Outcome Measure of Neuroinflammation

Molecular imaging of the 18 kD Translocator protein (TSPO) with positron emission tomography (PET) is of great value for studying neuroinflammation in rodents longitudinally. Quantification of the TSPO in rodents is, however, quite challenging. There is no suitable reference region and the use of plasma-derived input is not an option for longitudinal studies. The aim of this study was therefore to evaluate the use of the standardized uptake value (SUV) as an outcome measure for TSPO imaging in rodent brain PET studies, using [¹¹C]PBR28. In the first part of the study, healthy male Wistar rats (n = 4) were used to determine the correlation between the distribution volume (V_T, calculated with Logan graphical analysis) and the SUV. In the second part, healthy male Wistar rats (n = 4) and healthy male C57BL/6J mice (n = 4), were used to determine the test-retest variability of the SUV, with a 7-day interval between measurements. Dynamic PET scans of 63 minutes were acquired with a nanoScan PET/MRI and nanoScan PET/CT. An MRI scan was made for anatomical reference with each measurement. The whole brain V_T of [¹¹C]PBR28 in rats was 42.9 ± 1.7. A statistically significant correlation (r² = 0.96; p < 0.01) was found between the V_T and the SUV. The test-retest variability in 8 brain region ranged from 8 to 20% in rats and from 7 to 23% in mice. The interclass correlation coefficient (ICC) was acceptable to excellent for rats, but poor to acceptable for mice. In conclusion: The SUV of [¹¹C]PBR28 showed a high correlation with V_T as well as good test-retest variability. For future longitudinal small animal PET studies the SUV can thus be used to describe [¹¹C]PBR28 uptake in healthy brain tissue. Based on the present observations, further studies are needed to explore the applicability of this approach in small animal disease models, with special regard to neuroinflammatory models.

Evaluation of a novel PDE10A PET radioligand, [(11) C]T-773, in nonhuman primates: brain and whole body PET and brain autoradiography

Phosphodiesterase 10A (PDE10A) is considered to be a key target for the treatment of several neuropsychiatric diseases. The characteristics of [(11) C]T-773, a novel positron emission tomography (PET) radioligand with high binding affinity and selectivity for PDE10A, were evaluated in autoradiography and in nonhuman primate (NHP) PET. Brain PET measurements were performed under baseline conditions and after administration of a selective PDE10A inhibitor, MP-10. Total distribution volume (VT ) and binding potential (BPND ) were calculated using various kinetic models. Whole body PET measurements were performed to calculate the effective dose of [(11) C]T-773. Autoradiography studies in postmortem human and monkey brain sections showed high accumulation of [(11) C]T-773 in the striatum and substantia nigra which was blocked by MP-10. Brain PET showed high accumulation of [(11) C]T-773 in the striatum, and the data could be fitted using a two tissue compartment model. BPND was approximately 1.8 in the putamen when the cerebellum was used as the reference region. Approximately 70% of PDE10A binding was occupied by 1.8 mg/kg of MP-10. Whole body PET showed high accumulation of [(11) C]T-773 in the liver, kidney, heart, and brain in the initial phase. The radioligand was partly excreted via bile and the gastrointestinal tract, and partly excreted through the urinary tract. The calculated effective dose was 0.007 mSv/MBq. In conclusion, [(11) C]T-773 was demonstrated to be a promising PET radioligand for PDE10A with favorable brain kinetics. Dosimetry results support multiple PET measurements per person in human studies. Further research is required with [(11) C]T-773 in order to test the radioligand's potential clinical applications.

Development of a series of novel carbon-11 labeled PDE10A inhibitors

Phosphodiesterase 10A (PDE10A) is a member of the PDE family of enzymes that degrades cyclic adenosine monophosphate (cAMP) and cyclic guanosine monophosphate (cGMP). Our aim was to label a series of structurally related PDE10A inhibitors with carbon-11 and evaluate them as potential positron emission tomography (PET) radioligands for PDE10A using nonhuman primates. The series consisted of seven compounds based on the 3-(1H-pyrazol-5-yl)pyridazin-4(1H)-one backbone. These compounds were selected from the initial larger library based on a number of parameters such as affinity, selectivity for hPDE10A in in vitro tests, lipophilicity, and on the results of multidrug resistance protein 1 (MDR1)-LLCPK1 and the parallel artificial membrane permeability assays. Seven radioligands (KIT-1, 3, 5, 6, 7, 9, and 12) were radiolabeled with carbon-11 employing O-methylation on the hydroxyl moiety using [(11)C]methyl triflate. In vivo examination of each radioligand was performed using PET in rhesus monkeys; analysis of radiometabolites in plasma also was conducted using HPLC. All seven radioligands were labeled with high (>90%) incorporation of [(11)C]methyl triflate into their appropriate precursors and with high specific radioactivity. Carbon-11 labeled KIT-5 and KIT-6 showed high accumulation in the striatum, consistent with the known anatomical distribution of PDE10A in brain, accompanied by fast washout and high specific binding ratio. In particular [(11)C]KIT-6, named [(11)C]T-773, is a promising PET tool for further examination of PDE10A in human brain.

Large Variation in Brain Exposure of Reference CNS Drugs: a PET Study in Nonhuman Primates

BACKGROUND

Positron emission tomography microdosing of radiolabeled drugs allows for noninvasive studies of organ exposure in vivo. The aim of the present study was to examine and compare the brain exposure of 12 commercially available CNS drugs and one non-CNS drug.

METHODS

The drugs were radiolabeled with (11)C (t 1/2 = 20.4 minutes) and examined using a high resolution research tomograph. In cynomolgus monkeys, each drug was examined twice. In rhesus monkeys, a first positron emission tomography microdosing measurement was repeated after preadministration with unlabeled drug to examine potential dose-dependent effects on brain exposure. Partition coefficients between brain and plasma (KP) were calculated by dividing the AUC0-90 min for brain with that for plasma or by a compartmental analysis (VT). Unbound KP (KP u,u) was obtained by correction for the free fraction in brain and plasma.

RESULTS

After intravenous injection, the maximum radioactivity concentration (C max, %ID) in brain ranged from 0.01% to 6.2%. For 10 of the 12 CNS drugs, C max, %ID was >2%, indicating a preferential distribution to brain. A lower C max, %ID was observed for morphine, sulpiride, and verapamil. K P ranged from 0.002 (sulpiride) to 68 (sertraline) and 7 of 13 drugs had KP u,u close to unity. For morphine, sulpiride, and verapamil, K P u,u was <0.3, indicating impaired diffusion and/or active efflux. Brain exposure at microdosing agreed with pharmacological dosing conditions for the investigated drugs.

CONCLUSIONS

This study represents the largest positron emission tomography study on brain exposure of commercially available CNS drugs in nonhuman primates and may guide interpretation of positron emission tomography microdosing data for novel drug candidates.

Synthesis, radiolabeling, and in vivo pharmacokinetic evaluation of the amyloid beta radioligand [11C]AZD4694 in nonhuman primates

PURPOSE

[(18)F]AZD4694 (2-(2-(18)F-fluoro-6-(methylamino)-3-pyridyl)benzofuran-5-ol) is a radioligand suitable for imaging of amyloid beta deposits in the living human brain using positron emission tomography (PET). Here, we report the preparation and pharmacokinetic profile of its carbon-11 (t1/2 = 20.4 min) labeled isotopolog [(11)C]AZD4694 and compare [(11)C]AZD4694 with the hitherto most widely applied amyloid PET radioligand [(11)C]Pittsburgh Compound B (PiB).

PROCEDURES

The immediate unlabeled precursor to [(11)C]AZD4694 was prepared in a four-step convergent synthesis. Subsequent N-(11)C-methylation of this precursor with [(11)C]methyl iodide yielded [(11)C]AZD4694, which after isolation and formulation was injected into cynomolgus monkeys. The radioactivity in nonhuman primate brain following injection of [(11)C]AZD4694 and [(11)C]PiB was measured using PET.

RESULTS

[(11)C]AZD4694 was prepared in a 60 % incorporation yield. In a head to head comparison with [(11)C]PiB, it appeared that [(11)C]AZD4694 displayed slightly lower nonspecific binding in white matter than [(11)C]PiB as well as more rapid pharmacokinetics in the brain.

CONCLUSIONS

The advantageous pharmacokinetic profile and low nonspecific binding render [(11)C]AZD4694 a promising PET radioligand for imaging of amyloid beta in the human brain with PET.

SALDI-MS signal enhancement using oxidized graphitized carbon black nanoparticles

The signal intensity of low-molecular-weight compounds analyzed using surface-assisted laser desorption/ionization time-of-flight mass spectrometry (SALDI-TOF-MS) was significantly enhanced when oxidized graphitized carbon black (GCB) particles were used as the desorption/ionization surface. The surface of oxidized GCB contains more carboxylic acid groups than non-oxidized GCB. Carboxylic acid groups enhance the efficiency of the ionization process and the desorption of more hydrophobic compounds. A common pharmaceutical compound, propranolol, was successfully extracted from Baltic Sea blue mussels and quantified using oxidized GCB as the SALDI surface, whereas deuterated propranolol was used as the internal standard. The calibration curve showed a wide linear dynamic range of response (0.1-20 microg/mL) and good reproducibility (RSD < 10%). It was not possible to detect propranolol in Baltic Sea blue mussels when non-oxidized GCB was used as the SALDI surface.

Matrix-less laser desorption/ionisation mass spectrometry of polyphenols in red wine

Matrix-assisted laser desorption/ionisation (MALDI) of small molecules is challenging and in most cases impossible due to interferences from matrix ions precluding analysis of molecules <300-500 Da. A common matrix such as ferulic acid belongs to an important class of compounds associated with antioxidant activity. If the shared phenolic structure is related to the propensity as an active MALDI matrix then it follows that direct laser desorption/ionisation should be possible for polyphenols. Indeed matrix-less laser desorption/ionisation mass spectrometry is achieved whereby the analyte functions as a matrix and was used to monitor low molecular weight compounds in wine samples. Sensitivity ranging from 0.12-87 pmol/spot was achieved for eight phenolic acids (4-coumaric, 4-hydroxybenzoic, caffeic, ferulic, gallic, protocatechuic, syringic, vanillic) and 0.02 pmol/spot for trans-resveratrol. Additionally, 4-coumaric, 4-hydroxybenzoic, caffeic, ferulic, gallic, syringic, vanillic acids and trans-resveratrol were identified in wine samples using accurate mass measurements consistent with reported profiles based on liquid chromatography (LC)/MS. Minimal sample pre-treatment make the technique potentially appropriate for fingerprinting, screening and quality control of wine samples.