Role of [18F]-dopa-PET imaging in assessing movement disorders

Automatic Production of [18F]F-DOPA Using the Raytest SynChrom R&D Module

[¹⁸F]F-DOPA is widely used in PET diagnostics. Diseases diagnosed with this tracer are schizophrenia, Parkinson's disease, gliomas, neuroendocrine tumors, pheochromocytomas, and pancreatic adenocarcinoma. It should be noted that the [¹⁸F]F-DOPA tracer has been known for over 30 years. However, the methods of radiosynthesis applied in the past did not allow its clinical use due to low efficiency and purity. Currently, in the market, one encounters different types of radiosynthesis using the fluorine ¹⁸F isotope and variants of the same method. The synthesis and its modifications were carried out using a Raytest Synchrom R&D module. The synthesis consists of the following steps: (a) binding of the fluoride anion ¹⁸F^- on an anion exchange column; (b) elution with TBAHCO₃^-; (c) nucleophilic fluorination to the ABX 1336 precursor; (d) purification of the intermediate product on the C18ec column; (e) Baeyer-Villiger oxidation; (f) hydrolysis; and (gfinal purification of the crude product on a semipreparative column. The nucleophilic synthesis of [¹⁸F]F-DOPA was successfully performed in 120 min, using the ABX 1336 precursor on the Raytest SynChrom R&D module, with a radiochemical yield (RCY) of 15%, radiochemical purity (RCP) ≥ 97%, and enantiomeric purity (ee) ≥ 96%.

Comparison of 18 F-DOPA and 18 F-DTBZ for PET/CT Imaging of Idiopathic Parkinson Disease

OBJECTIVE

The aim of this study was to compare 2 imaging tracers, 18 F-DOPA and 18 F-DTBZ, for PET/CT imaging in idiopathic Parkinson disease (PD).

METHODS

We recruited 32 PD patients and 12 healthy controls in this study. All subjects underwent both 18 F-DOPA and 18 F-DTBZ PET/CT, and the results were interpreted by visual analysis and semiquantitative analysis (specific uptake ratios [SURs]). A 1-way analysis of variance was used to compare the clinical data and the SURs among the patients at different stages. Regression analysis was performed to analyze the correlation between the SURs and the clinical data.

RESULTS

Among the PD patients, there were 7 patients in Hoehn and Yahr stage I, 14 patients in stage II, and 11 patients in stage III. Linear correlation was found in striatal SURs between the 2 tracers ( P < 0.05). In patients of early stages, the striatal SUR decrease percent of 2 tracers had no statistical difference (paired t test, P > 0.05). By initial visual analysis, all the patients were interpreted as positive with 18 F-DBTZ (6 unilaterally, 26 bilaterally), and 31 cases were regarded as positive with 18 F-DOPA (8 unilaterally, 23 bilaterally). After setting the upper limit of SUR images with the putamen SURs of healthy controls (SUR T ), all patients were interpreted as positive with both tracers ( 18 F-DTBZ: 5 unilaterally, 27 bilaterally; 18 F-DOPA: 4 unilaterally, 28 bilaterally).

CONCLUSION

18 F-DTBZ and 18 F-DOPA could reflect the same level of dopaminergic neuron degeneration for PD in early stages, and they have the consistent visual analysis results.

Candidate metabolic biomarkers for schizophrenia in CNS and periphery: Do any possible associations exist?

Due to the limitations of analytical techniques and the complicity of schizophrenia, nowadays it is still a challenge to diagnose and stratify schizophrenia patients accurately. Many attempts have been made to identify and validate available biomarkers for schizophrenia from CSF and/or peripheral blood in clinical studies with consideration to disease stages, antipsychotic effects and even gender differences. However, conflicting results handicap the validation and application of biomarkers for schizophrenia. In view of availability and feasibility, peripheral biomarkers have superior advantages over biomarkers in CNS. Meanwhile, schizophrenia is considered to be a devastating neuropsychiatric disease mainly taking place in CNS featured by widespread defects in multiple metabolic pathways whose dynamic interactions, until recently, have been difficult to difficult to investigate. Evidence for these alterations has been collected piecemeal, limiting the potential to inform our understanding of the interactions among relevant biochemical pathways. Taken these points together, it will be interesting to investigate possible associations of biomarkers between CNS and periphery. Numerous studies have suggested putative correlations within peripheral and CNS systems especially for dopaminergic and glutamatergic metabolic biomarkers. In addition, it has been demonstrated that blood concentrations of BDNF protein can also reflect its changes in the nervous system. In turn, BDNF also interacts with glutamatergic, dopaminergic and serotonergic systems. Therefore, this review will summarize metabolic biomarkers identified both in the CNS (brain tissues and CSF) and peripheral blood. Further, more attentions will be paid to discussing possible physical and functional associations between CNS and periphery, especially with respect to BDNF.

Longitudinal study of striatal aromatic l-amino acid decarboxylase activity in patients with idiopathic rapid eye movement sleep behavior disorder

STUDY OBJECTIVES

To determine if nigrostriatal dopaminergic system function, evaluated by aromatic l-amino acid decarboxylase (AADC) activity using 6-[¹⁸F]fluoro-meta-tyrosine brain positron emission tomography (FMT-PET) can accurately and efficiently identify idiopathic rapid-eye-movement behavior disorder (IRBD) individuals at risk for conversion to a clinical diagnosis of Parkinson's disease (PD) or dementia with Lewy bodies (DLB).

METHODS

We assessed prospectively striatal aromatic l-amino acid decarboxylase activity using FMT brain PET imaging in IRBD patients who were followed systematically every 1-3 months for 1-10 years. IRBD patients (n = 27) were enrolled in this prospective cohort study starting in 2009. Those who underwent follow-up scans between January 2011 and September 2014 (n = 24) were analyzed in the present study.

RESULTS

Of the 24 IRBD patients with baseline and follow-up FMT-PET scans, 11 (45.8%) developed PD (n = 6) or DLB (n = 5). Compared to IRBD patients who were still disease-free, those who developed PD (n = 5) or DLB with parkinsonism (n = 1) had significantly reduced bilateral putaminal FMT uptake during the follow-up. Furthermore, the rate of FMT decline between baseline and follow-up scans was higher in all converted patients, even for those with DLB without parkinsonism, than in IRBD patients who remained disease-free.

CONCLUSIONS

FMT-PET, which represents a dynamic change in AADC activity over time, may also be a useful predictor for the risk of conversion to PD or DLB over short-term clinical follow-up periods, or when testing neuroprotective and restorative strategies in the prodromal phases of PD or DLB.

Green and efficient synthesis of the radiopharmaceutical [18F]FDOPA using a microdroplet reactor

From an efficiency standpoint, microdroplet reactors enable significant improvements in the preparation of radiopharmaceuticals due to the vastly reduced reaction volume. To demonstrate these advantages, we adapt the conventional (macroscale) synthesis of the clinically-important positron-emission tomography tracer [18F]FDOPA, following the nucleophilic diaryliodonium salt approach, to a newly-developed ultra-compact microdroplet reaction platform. In this first microfluidic implementation of [18F]FDOPA synthesis, optimized via a high-throughput multi-reaction platform, the radiochemical yield (non-decay-corrected) was found to be comparable to macroscale reports, but the synthesis consumed significantly less precursor and organic solvents, and the synthesis process was much faster. In this initial report, we demonstrate the production of [18F]FDOPA in 15 MBq [400 μCi] amounts, sufficient for imaging of multiple mice, at high molar activity.

Brain positron emission tomography with 2-18F-2-deoxi-D-glucose of patients with dystonia and essential tremor detects differences between these disorders

We studied patients with dystonia (D) and essential tremor (ET) using positron emission tomography (PET) equipped with Cortex ID software. This allowed PET brain visualisation to be compared to scans of a control group by means of the z-score. The study revealed hypo-metabolism in both D and ET groups, and additionally revealed a difference between these two groups of patients in certain areas of the brain. These two nosological forms overlap in clinical features and are difficult to differentiate. The PET picture may help to provide a differential diagnosis in addition to the biochemical difference in dopamine exchange previously revealed by us in this group of patients.

11 C-PE2I and 18 F-Dopa PET for assessing progression rate in Parkinson's: A longitudinal study

BACKGROUND

¹⁸ F-dopa PET measuring aromatic l-amino acid decarboxylase activity is regarded as the gold standard for evaluating dopaminergic function in Parkinson's disease. Radioligands for dopamine transporters are also used in clinical trials and for confirming PD diagnosis. Currently, it is not clear which imaging marker is more reliable for assessing clinical severity and rate of progression. The objective of this study was to directly compare ¹⁸ F-dopa with the highly selective dopamine transporter radioligand ¹¹ C-PE2I for the assessment of motor severity and rate of progression in PD.

METHODS

Thirty-three mild-moderate PD patients underwent ¹⁸ F-dopa and ¹¹ C-PE2I PET at baseline. Twenty-three were followed up for 18.8 ± 3.4 months.

RESULTS

Standard multiple regression at baseline indicated that ¹¹ C-PE2I BP_ND predicted UPDRS-III and bradykinesia-rigidity scores (P < 0.05), whereas ¹⁸ F-dopa K_i did not make significant unique explanatory contributions. Voxel-wise analysis showed negative correlations between ¹¹ C-PE2I BP_ND and motor severity across the whole striatum bilaterally. ¹⁸ F-Dopa K_i clusters were restricted to the most affected putamen and caudate. Longitudinally, negative correlations were found between striatal Δ¹¹ C-PE2I BP_ND , ΔUPDRS-III, and Δbradykinesia-rigidity, whereas no significant associations were found for Δ¹⁸ F-dopa K_i . One cluster in the most affected putamen was identified in the longitudinal voxel-wise analysis showing a negative relationship between Δ¹¹ C-PE2I BP_ND and Δbradykinesia-rigidity.

CONCLUSIONS

Striatal ¹¹ C-PE2I appears to show greater sensitivity for detecting differences in motor severity than ¹⁸ F-dopa. Furthermore, dopamine transporter decline is closely associated with motor progression over time, whereas no such relationship was found with aromatic l-amino acid decarboxylase. ¹¹ C-PE2I may be more effective for evaluating the efficacy of neuroprotective treatments in PD. © 2017 International Parkinson and Movement Disorder Society.

Radiosynthesis and biological evaluation of N-(2-[18F]fluoropropionyl)-3,4-dihydroxy-l-phenylalanine as a PET tracer for oncologic imaging

INTRODUCTION

Several ¹¹C and ¹⁸F labeled 3,4-dihydroxy-l-phenylalanine (l-DOPA) analogues have been used for neurologic and oncologic diseases, especially for brain tumors and neuroendocrine tumors PET imaging. However, ¹⁸F-labeled N-substituted l-DOPA analogues have not been reported so far. In the current study, radiosynthesis and biological evaluation of a new ¹⁸F-labeled l-DOPA analogue, N-(2-[¹⁸F]fluoropropionyl)-3,4-dihydroxy-l-phenylalanine ([¹⁸F]FPDOPA) for tumor PET imaging are performed.

METHODS

The synthesis of [¹⁸F]FPDOPA was via a two-step reaction sequence from 4-nitrophenyl-2-[¹⁸F]fluoropropionate ([¹⁸F]NFP). The biodistribution of [¹⁸F]FPDOPA was determined in normal Kunming mice. In vitro competitive inhibition and protein incorporation experiments were performed with SPC-A-1 lung adenocarcinoma cell lines. PET/CT studies of [¹⁸F]FPDOPA were conducted in C6 rat glioma and SPC-A-1 human lung adenocarcinoma and H460 human large cell lung cancer-bearing nude mice.

RESULTS

[¹⁸F]FPDOPA was prepared with a decay-corrected radiochemical yield of 28±5% and a specific activity of 50±15GBq/μmol (n=10) within 125min. In vitro cell experiments showed that [¹⁸F]FPDOPA uptake in SPC-A-1 cells was primarily transported through Na⁺-independent system L, with Na⁺-dependent system B^0,+ and system ASC partly involved in it. Biodistribution data in mice showed that renal-bladder route was the main excretory system of [¹⁸F]FPDOPA. PET imaging demonstrated intense accumulation of [¹⁸F]FPDOPA in several tumor xenografts, with (8.50±0.40)%ID/g in C6 glioma, (6.30±0.12)%ID/g in SPC-A-1 lung adenocarcinoma, and (6.50±0.10)%ID/g in H460 large cell lung cancer, respectively.

CONCLUSION

A novel N-substituted ¹⁸F-labeled L-DOPA analogue [¹⁸F]FPDOPA is synthesized and evaluated in vitro and in vivo. The results support that [¹⁸F]FPDOPA seems to be a potential PET tracer for tumor imaging, especially be a better potential PET tracer than [¹⁸F]fluoro-2-deoxy-d-glucose ([¹⁸F]FDG) for brain tumor imaging.

Enhanced copper-mediated (18)F-fluorination of aryl boronic esters provides eight radiotracers for PET applications

[(18)F]FMTEB, [(18)F]FPEB, [(18)F]flumazenil, [(18)F]DAA1106, [(18)F]MFBG, [(18)F]FDOPA, [(18)F]FMT and [(18)F]FDA are prepared from the corresponding arylboronic esters and [(18)F]KF/K222 in the presence of Cu(OTf)2py4. The method was successfully applied using three radiosynthetic platforms, and up to 26 GBq of non-carrier added starting activity of (18)F-fluoride.

Total Radiosynthesis: Thinking outside "the box"

The logic of total synthesis transformed a stagnant state of medicinal and synthetic organic chemistry when there was a paucity of methods and reagents to synthesize drug molecules and/or natural products. Molecular imaging by positron emission tomography (PET) is now experiencing a renaissance in the way radiopharmaceuticals for molecular imaging are synthesized, however, a paradigm shift is desperately needed in the discovery pipeline to accelerate in vivo imaging studies. A significant challenge in radiochemistry is the limited choice of labeled reagents (or building blocks) available for the synthesis of novel radiopharmaceuticals with the most commonly used short-lived radionuclides carbon-11 (11C; half-life ~20 minutes) and fluorine-18 (18F; half-life ~2 hours). In fact, most drugs cannot be labeled with 11C or 18F due to a lack of efficient and diverse radiosynthetic methods. In general, routine radiopharmaceutical production relies on the incorporation of the isotope at the last or penultimate step of synthesis, ideally within one half-life of the radionuclide, to maximize radiochemical yields and specific activities thereby reducing losses due to radioactive decay. Reliance on radiochemistry conducted within the constraints of an automated synthesis unit ("box") has stifled the exploration of multi-step reactions with short-lived radionuclides. Radiopharmaceutical synthesis can be transformed by considering logic of total synthesis to develop novel approaches for 11C- and 18F-radiolabeling complex molecules via retrosynthetic analysis and multi-step reactions. As a result of such exploration, new methods, reagents and radiopharmaceuticals for in vivo imaging studies are discovered. A new avenue to develop radiotracers that were previously unattainable due to the lack of efficient radiosynthetic methods is necessary to work towards our ultimate, albeit impossible goal - the concept we term total radiosynthesis - to radiolabel virtually any molecule. As with the vast majority of drugs, most radiotracers also fail, therefore expeditious evaluation of tracers in preclinical models prior to optimization or derivatization of the lead molecules/drugs is necessary. Furthermore the exact position of the 11C and 18F radionuclide in tracers is often critical for metabolic considerations, and flexible methodologies to introduce the radiolabel are needed. Using the principles of total synthesis our laboratory and others have shown that multi-step radiochemical reactions are indeed suitable for preclinical and even clinical use. As the goal of total synthesis is to be concise, we have also simplified the syntheses of radiopharmaceuticals. We are presently developing new strategies via [11C]CO2 fixation which has enabled library radiosynthesis as well as labeling non-activated arenes using [18F]fluoride via iodonium ylides. Both of which have proven to be suitable for human PET imaging. We concurrently utilize state-of-the-art automation technologies including microfluidic flow chemistry and rapid purification strategies for radiopharmaceutical production. In this account we highlight how total radiosynthesis has impacted our radiochemistry program, with prominent examples from others, focusing on its impact towards preclinical and clinical research studies.

Abnormal striatal dopamine transmission in schizophrenia

Despite numerous revisions and reformulations, dopamine (DA) hypothesis of schizophrenia remains a pivotal neurochemical hypothesis of this illness. The aim of this review is to expose and discuss findings from positron emission tomography (PET) or single-photon-emission computed tomography (SPECT) studies investigating DA function in the striatum of medicated, drug-naïve or drug-free patients with schizophrenia and in individuals at risk compared with healthy volunteers.

DA function was studied at several levels: i) at a presynaptic level where neuroimaging studies investigating DOPA uptake capacity clearly show an increase of DA synthesis in patients with schizophrenia; ii) at a synaptic level where neuroimaging studies investigating dopamine transporter availability (DAT) does not bring any evidence of dysfunction; iii) and finally, neuroimaging studies investigating DA receptor density show a mild increase of D2 receptor density in basic condition and, an hyperreactivity of DA system in dynamic condition.

These results are discussed regarding laterality, sub-regions of striatum and implications for the at-risk population. Striatal DA abnormalities are now clearly demonstrated in patients with schizophrenia and at risk population and could constitute an endophenotype of schizophrenia. Subtle sub-clinical striatal DA abnormalities in at risk population could be a biomarker of transition from a vulnerability state to the expression of frank psychosis.

Dual PET/CT with (18)F-DOPA and (18)F-FDG in metastatic medullary thyroid carcinoma and rapidly increasing calcitonin levels: Comparison with conventional imaging

BACKGROUND

To evaluate the role of a multi-imaging PET with (18)F-DOPA and (18)F-FDG in comparison with conventional imaging (CI) in recurrent medullary thyroid carcinoma (MTC).

METHODS

18 MTC patients who had thyroidectomy were included; they presented with elevated and rapidly increasing calcitonin levels during follow up. CI had revealed metastatic deposits in 9 patients. Patients were referred to us for a PET/CT with (18)F-DOPA and (18)F-FDG. Histologic/cytologic confirmation of recurrent MTC was obtained in at least one PET-positive lesion in all patients.

RESULTS

Foci of abnormal uptake were observed in 15 patients at (18)F-DOPA and in 11 at (18)F-FDG; 8 patients showed the same number of positive lesions with both tracers, 2 showed more lesions on (18)F-FDG, 1 was positive at (18)F-FDG alone and 5 at (18)F-DOPA alone. In 3 patients with a DOPA-positive loco-regional relapse a re-operation with curative intent was offered. SUV(max) values were higher for (18)F-FDG compared to (18)F-DOPA (mean 12.7+/-4.1 vs. 5.5+/-2.1, p<0.05). Calcitonin was higher in PET-positive patients compared to PET negative ones, while no significant differences were observed between (18)F-DOPA and (18)F-FDG positive patients.

CONCLUSIONS

In MTC patients with rapidly increasing calcitonin levels during follow up, (18)F-DOPA has a good sensitivity and a complementary role with (18)F-FDG PET/CT in detecting metastatic deposits. In our experience, the sensitivity of a multi-imaging (18)F-DOPA &(18)F-FDG PET/CT approach is greater than that obtained with CI. The higher SUV(max) values found with (18)F-FDG in some patients may reflect more aggressive tumors.

Molecular PET/CT imaging-guided radiation therapy treatment planning

The role of positron emission tomography (PET) during the past decade has evolved rapidly from that of a pure research tool to a methodology of enormous clinical potential. (18)F-fluorodeoxyglucose (FDG)-PET is currently the most widely used probe in the diagnosis, staging, assessment of tumor response to treatment, and radiation therapy planning because metabolic changes generally precede the more conventionally measured parameter of change in tumor size. Data accumulated rapidly during the last decade, thus validating the efficacy of FDG imaging and many other tracers in a wide variety of malignant tumors with sensitivities and specificities often in the high 90 percentile range. As a result, PET/computed tomography (CT) had a significant impact on the management of patients because it obviated the need for further evaluation, guided further diagnostic procedures, and assisted in planning therapy for a considerable number of patients. On the other hand, the progress in radiation therapy technology has been enormous during the last two decades, now offering the possibility to plan highly conformal radiation dose distributions through the use of sophisticated beam targeting techniques such as intensity-modulated radiation therapy (IMRT) using tomotherapy, volumetric modulated arc therapy, and many other promising technologies for sculpted three-dimensional (3D) dose distribution. The foundation of molecular imaging-guided radiation therapy lies in the use of advanced imaging technology for improved definition of tumor target volumes, thus relating the absorbed dose information to image-based patient representations. This review documents technological advancements in the field concentrating on the conceptual role of molecular PET/CT imaging in radiation therapy treatment planning and related image processing issues with special emphasis on segmentation of medical images for the purpose of defining target volumes. There is still much more work to be done and many of the techniques reviewed are themselves not yet widely implemented in clinical settings.

Non-natural amino acids for tumor imaging using positron emission tomography and single photon emission computed tomography

Amino acids are required nutrients for proliferating tumor cells, and amino acid transport is upregulated in many tumor types. Studies of radiolabeled amino acids in animals and humans demonstrate that amino acid based tracers have advantageous characteristics relative to 2-[(18)F]fluoro-2-deoxyglucose in certain tumors, particularly brain gliomas. Non-natural amino acids for tumor imaging generally have greater metabolic stability and can be labeled with longer-lived radionuclides for positron emission tomography and single photon emission computed tomography such as fluorine-18 and iodine-123. Amino acids enter cells via amino acid transport with varying selectivity based on their chemical structure. This review focuses on the rationale, biological basis, current status and future prospects of radiolabeled non-natural amino acids for tumor imaging and discusses various classes of these compounds including aromatic, alicyclic and alpha,alpha-dialkyl amino acids.

6-L-18F-fluorodihydroxyphenylalanine PET in neuroendocrine tumors: basic aspects and emerging clinical applications

In recent years, 6-l-18F-fluorodihydroxyphenylalanine (18F-DOPA) PET has emerged as a new diagnostic tool for the imaging of neuroendocrine tumors. This application is based on the unique property of neuroendocrine tumors to produce and secrete various substances, a process that requires the uptake of metabolic precursors, which leads to the uptake of 18F-DOPA. This nonsystematic review first describes basic aspects of 18F-DOPA imaging, including radiosynthesis, factors involved in tracer uptake, and various aspects of metabolism and imaging. Subsequently, this review provides an overview of current clinical applications in neuroendocrine tumors, including carcinoid tumors, pancreatic islet cell tumors, pheochromocytoma, paraganglioma, medullary thyroid cancer, hyperinsulinism, and various other clinical entities. The application of PET/CT in carcinoid tumors has unsurpassed sensitivity. In medullary thyroid cancer, pheochromocytoma, and hyperinsulinism, results are also excellent and contribute significantly to clinical management. In the remaining conditions, the initial experience with 18F-DOPA PET indicates that it seems to be less valuable, but further study is required.

Small molecule receptors as imaging targets

The aberrant expression and function of certain receptors in tumours and other diseased tissues make them preferable targets for molecular imaging. PET and SPECT radionuclides can be used to label specific ligands with high affinity for the target receptors. The functional information obtained from imaging these receptors can be used to better understand the systems under investigation and for diagnostic and therapeutic applications. This review discusses some of the aspects of receptor imaging with small molecule tracers by PET and SPECT and reviews some of the tracers for the receptor imaging of tumours and brain, heart and lung disorders.

Applications of Clinical Dopamine Imaging

Recent technologic advances make it increasingly possible to image neurotransmitter systems in living human brain, The dopamine system has been most intensively studied owing to its involvement in several brain disorders such as Parkinson's disease and Huntington's disease, as well as psychiatric disorders such as schizophrenia, depression, and compulsive behavioral disorders of multiple types. A variety of aspects of dopamine receptor density, function, and dopaminergic terminal status can now be assessed using the minimally invasive neuroimaging techniques of positron emission tomography and single-photon emission computed tomography. Although these techniques are currently used most often in the context of research, clinical applications are rapidly emerging.