In vivo imaging of brain androgen receptors in rats: a [18F]FDHT PET study

AbstractIntroductionSteroid hormones like androgens play an important role in the development and maintenance of several brain functions. Androgens can act through androgen receptors (AR) in the brain. This study aims to demonstrate the feasibility of positron emission tomography (PET) with 16β-[18F]fluoro-5α-dihydrotestosterone ([18F]FDHT) to image AR expression in the brain.MethodsMale Wistar rats were either orchiectomized to inhibit endogenous androgen production or underwent sham-surgery. Fifteen days after surgery, rats were subjected to a 90-min dynamic [18F]FDHT PET scan with arterial blood sampling. In a subset of orchiectomized rats, 1mg/kg dihydrotestosterone was co-injected with the tracer in order to saturate the AR. Plasma samples were analyzed for the presence of radioactive metabolites by radio-TLC. Pharmacokinetic modeling was performed to quantify brain kinetics of the tracer. After the PET scan, the animals were terminated for ex-vivo biodistribution.ResultsPET imaging and ex vivo biodistribution studies showed low [18F]FDHT uptake in all brain regions, except pituitary. [18F]FDHT uptake in the surrounding cranial bones was high and increased over time. [18F]FDHT was rapidly metabolized in rats. Metabolism was significantly faster in orchiectomized rats than in sham-orchiectomized rats. Quantitative analysis of PET data indicated substantial spill-over of activity from cranial bones into peripheral brain regions, which prevented further analysis of peripheral brain regions. Logan graphical analysis and kinetic modeling using 1- and 2-tissue compartment models showed reversible and homogenously distributed tracer uptake in central brain regions. [18F]FDHT uptake in the brain could not be blocked by endogenous androgens or administration of dihydrotestosterone.ConclusionThe results of this study indicate that imaging of AR availability in rat brain with [18F]FDHT PET is not feasible. The low AR expression in the brain, the rapid metabolism of [18F]FDHT in rats and the poor brain penetration of the tracer likely contributed to the poor performance of [18F]FDHT PET in this study

A guideline for clinicians performing clinical studies with fluorescence imaging.

Fluorescence imaging is an emerging imaging technique that has shown many benefits for clinical care. Currently, the field is in rapid clinical translation, and an unprecedented number of clinical trials are performed. Clinicians are inundated with numerous opportunities and combinations of different imaging modalities. To streamline this process, a multidisciplinary approach is needed with drug discovery, software and systems engineering, and translational medicine. Here, we discuss the main constituents of a uniform fluorescence imaging protocol to match the clinical need and ensure consistent study designs and reliable data collection in clinical trials. In an era in which the potential of fluorescence imaging has become evident, consistent conduct of studies, data analysis, and data interpretation is essential for implementation into the standard of care

UPLC®-RAD the new standard in quality control of PET radiopharmaceutical

Objectives: Good Manufacturing Practice (GMP) compliant productions require validated, quality control procedures of the radiopharmaceutical. Quality control of the final product is conventionally performed by High Performance Liquid Chromatography (HPLC) with UV and radioactivity (RAD) detection. To use an ACQUITY Ultra Performance Liquid Chromatography (UPLC®) with an online UV and RAD detector we improved not only the analysis time, but also linearity, resolution, reproducibility, precision, accuracy, signal-to-noise ratio, limit of quantitation (LOQ) and limit of detection (LOD) compared to conventional HPLC quality control analysis. Materials and Methods: A Waters H-class UPLc® with a variable UV detector and an online Berthold flowstar LB 513 radioactivity detector was used to measure the (radioactive) concentrations of the radiopharmaceutical and impurities in the samples. The UPLc® columns used were from the Waters ACQUITY UPLC® line, with a 2.1 or 3.0 mm i.d. by 50 mm length and a particle size of 1.7μm Flow rates can vary from 0.4 till 1.0 ml/min dependent on the procedure. Total run time of a quality control method is 2-3 minutes. Aliquots from 1-10 μL are needed for quality control. To validated new UPLC® analysis Methods we performed a full validation (PQ). As part of the validation of the new UPLC® Methods we performed a comparison with the conventional HPLC Methods. PET radiopharmaceuticals; such as fluorine-18 labeled FLT, FAZA, FDOPA, FES and carbon-11 labeled PK11195, PIB, 5-HTP and methionine were used in this study. Results: Due to shorter conditioning-run- and rinse times, the solvents cost reduced up to 80% significantly. The higher resolution and lower LOQ gave a better and more accurate result of the concentration of compounds. Both for the UV and radioactivity signal, the measurability of impurities possible present in the production sample is considerably increased. Indeed, more impurities are detected. However, the total amounts of these impurities are far below the release criteria of 1 mg. L-1. Radioactivity concentrations > 0.3 MBq/ml could reliably be measured with the Berthold RAD detector. Conclusion: The UPLC®-RAD gave better linearity, reproducibility, sensitivity and higher resolution then conventional HPLC with UV/RAD detection. Especially for the11C radiopharmaceuticals, a reduction in the analysis time of 12 min leads to 34% more released radioactivity, ready for injection. For18F-radiopharmaceuticals the profit is still 7%. Thus, UPLc®-RAD might become the new standard in quality control of PET radiopharmaceuticals

A dual inhibitor of matrix metalloproteinases and a disintegrin and metalloproteinases, [F-18]FB-ML5, as a molecular probe for non-invasive MMP/ADAM-targeted imaging

Bio-organic Synthesi

Population pharmacokinetics of cutamesine in rats using NONMEM, 11C-SA4503, and microPET

Cutamesine (SA4503) is a selective sigma-1 receptor agonist, currently in Phase II clinical trials for depression and post stroke neurological disturbances. Cutamesine has been found to be effective in several rodent models of amnesia and depression. We used data obtained with carbon-11-labeled cutamesine (11CSA4503) in rats to develop a population pharmacokinetic (PK) model. Nonlinear mixed effects modeling (NONMEM) provides a tool for analyzing repeated measurements data in which the relationship between the explanatory and response variables can be modeled as a single function, allowing the parameters to differ between individuals. This modeling framework can be useful to scale preclinical drug kinetic information to clinical settings. METHODS: MicroPET scans of the brain region of male Wistar Hannover rats (age 1.5-32 months) were made and11C-SA4503 time-activity curves were obtained for the entire brain, A femoral artery cannula was used for blood sampling, and metabolite-corrected plasma time-activity curves were obtained. The PK model using NONMEM was constructed in two steps. In the first step, one-, two- or three-compartment PK models were explored to describe the plasma time course. In the second step, the model was extended to include brain11C-SA4503 time course data, while allowing brain distribution to influence plasma PK and vice versa. Bootstrap resampling (n=1000) technique was used as a model evaluation tool. The effects of covariates (age, weight, presence or absence of pituitary tumors) on PK parameters will be investigated for the final model. RESULTS: Plasma PK was best described by a twocompartment model. When brain PK was included, a three-compartment model performed best. The three compartments were: a central compartment (plasma) and two brain compartments (free and bound). Population PK parameters (relative standard error), not accounting for covariates are: central clearance (CL) 17.4 ml min-1(13%), central volume of distribution (VC) 25.3 ml (23%), brain volume of distribution (Vbr) 84.9 ml (23%), clearance into brain (Qin) 61.8 ml min-1(12%), clearance out of brain (Qout) 14.4 ml min-1(38%), clearance into bound compartment (Qon) 5.83 ml min-1(27%), clearance out of bound compartment (Qoff) 1.55 ml min-1(4%). Population estimates of the model are in close agreement with the median values of successful bootstrap replicates. CONCLUSION: Population PK modelling can be used successfully to analyze PET data of11C-labeled cutamesine

PET imaging of disease progression and treatment effects in the experimental autoimmune encephalomyelitis rat model

The experimental autoimmune encephalomyelitis model is a model of multiple sclerosis that closely mimics the disease characteristics in humans. The main hallmarks of multiple sclerosis are neuroinflammation (microglia activation, monocyte invasion, and T-cell infiltration) and demyelination. PET imaging may be a useful noninvasive technique for monitoring disease progression and drug treatment efficacy in vivo. Methods: Experimental autoimmune encephalomyelitis was induced by myelin-oligodendrocyte glycoprotein immunization in female Dark Agouti rats. Experimental autoimmune encephalomyelitis rats were imaged at baseline and at days 6, 11, 15, and 19 after immunization to monitor monocyte and microglia activation (11C-PK11195) and demyelination ( 11C-MeDAS) during normal disease progression and during treatment with dexamethasone. Results: 11C-PK11195 PET detected activation of microglia and monocytes in the brain stem and spinal cord during disease progression. The uptake of 11C-PK11195 was elevated in dexamethasone-treated animals that had shown mild clinical symptoms that had resolved at the time of imaging. Demyelination was not detected by 11C-MeDAS PET, probably because of the small size of the lesions (average, 0.13 mm). Conclusion: PET imaging of neuroinflammation can be used to monitor disease progression and the consequences of treatment in the experimental autoimmune encephalomyelitis rat model. PET imaging was more sensitive than clinical symptoms for detecting inflammatory changes in the central nervous system. COPYRIGHT © 2014 by the Society of Nuclear Medicine and Molecular Imaging, Inc.Chemicals/CAS: dexamethasone acetate, 1177-87-

Delay and impairment in brain development and function in rat offspring after maternal exposure to methylmercury

Maternal exposure to the neurotoxin methylmercury (MeHg) has been shown to have adverse effects on neural development of the offspring in man. Little is known about the underlying mechanisms by which MeHg affects the developing brain. To explore the neurodevelopmental defects and the underlying mechanism associated with MeHg exposure, the cerebellum and cerebrum of Wistar rat pups were analyzed by [(18)F]FDG PET functional imaging, field potential analysis, and microarray gene expression profiling. Female rat pups were exposed to MeHg via maternal diet during intrauterinal and lactational period (from gestational day 6 to postnatal day (PND)10), and their brain tissues were sampled for the analysis at weaning (PND18-21) and adulthood (PND61-70). The [(18)F]FDG PET imaging and field potential analysis suggested a delay in brain activity and impaired neural function by MeHg. Genome-wide transcriptome analysis substantiated these findings by showing (1) a delay in the onset of gene expression related to neural development, and (2) alterations in pathways related to both structural and functional aspects of nervous system development. The latter included changes in gene expression of developmental regulators, developmental phase-associated genes, small GTPase signaling molecules, and representatives of all processes required for synaptic transmission. These findings were observed at dose levels at which only marginal changes in conventional developmental toxicity endpoints were detected. Therefore, the approaches applied in this study are promising in terms of yielding increased sensitivity compared with classical developmental toxicity tests

Quantifying effects of radiotherapy-induced microvascular injury; review of established and emerging brain MRI techniques

Neuro Imaging Researc

Imaging histamine receptors using PET and SPECT

The histaminergic system contains four subtypes of G-protein-coupled receptors:

GMP compliant radiosynthesis of11C and18F-labeled PET radiopharmaceuticals with a modular disposable cassette system

Background Many nuclear medicine departments have an extensive radiopharmaceutical portfolio. Consequently, these multiple PET radiopharmaceuticals have to be produced with the same synthesis module. An important consideration in GMP-compliant PET production is to avoid potential cross-contamination. Flexible cassette-based synthesis modules with disposable components could provide an attractive solution to overcome this hurdle. Because only disposable materials are used, validation of cleaning procedures is not required and maintenance of the system can be reduced. For this purpose, we aimed to develop cassette-based synthesis methods for a variety of11C and18F labeled PET radiopharmaceuticals. Methods In our study, the production processes for the radiosynthesis of [11C]choline, [11C]methionine, [11C]PK11195, [18F]CP18, [18F]FDHT and [18F]FES were implemented on the cassette-based Eckert & Ziegler PharmTracer synthesis module. In order to achieve this goal, there is a need for each tracer to develop a dedicated design of its corresponding cassette. The radiopharmaceuticals were validated according to GMP guidelines and compliance to the required pharmaceutical criteria was tested including novel UPLC analytical QC methods. Results Radiochemical yields obtained with the cassette based system were comparable to literature; [11C]choline 28-52%; [11C]methionine 24-39%; [11C]PK11195 9-15%, [18F]CP18 7-13%, [18F]FDHT 5-10%, [18F]FES 16-28%. Synthesis time was 25 min for [11C]choline and [11C]methionine, 55 min for [11C]PK11195 and 2 h for the 18Flabeled radiopharmaceuticals. All radiopharmaceuticals meets the requirements for specific activities and were >95% pure, isotonic, and complied to the prospective specification for endotoxins, sterility and organic solvents. Discussion and conclusion Multistep synthesis procedures for PET radiopharmaceuticals, involving11C-methylation,11F-fluorination, click chemistry, distillation and solid phase extraction, are feasible with the used cassette-based synthesis module. In addition, purification with HPLC and formulation of the radiopharmaceuticals were successfully performed. The design of the cassettes and the synthesis programs of individual radiopharmaceuticals can easily be adapted for the production of other radiopharmaceuticals, which makes the system very flexible. All cassettes and other materials are disposable; therefore no cross-contamination is possible between the productions of different radiopharmaceuticals. In conclusion, our results show that a variety of11C and11F-radiopharmaceuticals can be reliably produced under GMP-compliant conditions using a common synthesis module with disposable cassettes