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Supplementary Figure 1 shows [18F]F-AraG Structure and Schematic of AraG Uptake into T Cells Supplementary Figure 2 shows [18F]F-AraG and [3H]F-AraC Uptake and Retention Across Various Immune Cell Lines Supplementary Figure 3 shows AraG Competitive Inhibition of [18F]F-AraG Uptake Across Various Immune Cell Lines Supplementary Figure 4 shows Comparison of [18F]F-AraG and [3H]F-AraC Uptake and Retention Across Various Solid Tumor Cell Lines Supplementary Figure 5 shows Western Blot Analysis of dCK Expression in Wild-type and Mutant CCRF-CEM cells Supplementary Figure 6 shows dGK overexpression in CHO-K1 cells leads to increased [18F]F-AraG uptake and retention Supplementary Figure 7 shows [3H]F-AraC Accumulates in Cells via dCK Activity Supplementary Figure 8 shows Uptake of [18F]F-AraG in Activated Versus Resting Murine T Cells Supplementary Figure 9 shows Isolation and Activation of Primary Human T Cells Supplementary Figure 10 shows Uptake and Retention of [3H]AraG and [3H]F-AraC in Resting and Activated Human Primary T Cells Supplementary Figure 11 shows Evaluation of GFP+ Donor T cells in Spleens and Cervical Lymph Nodes (CLNs) at Day 3 and Day 10 of Acute GVHD Supplementary Figure 12 shows Evaluation of Proliferation of Donor T Cells in Cervical Lymph Nodes

A major barrier to successful use of allogeneic hematopoietic cell transplantation is acute graft-versus-host disease (aGVHD), a devastating condition that arises when donor T cells attack host tissues. With current technologies, aGVHD diagnosis is typically made after end-organ injury and often requires invasive tests and tissue biopsies. This affects patient prognosis as treatments are dramatically less effective at late disease stages. Here, we show that a novel PET radiotracer, 2′-deoxy-2′-[18F]fluoro-9-β-D-arabinofuranosylguanine ([18F]F-AraG), targeted toward two salvage kinase pathways preferentially accumulates in activated primary T cells. [18F]F-AraG PET imaging of a murine aGVHD model enabled visualization of secondary lymphoid organs harboring activated donor T cells prior to clinical symptoms. Tracer biodistribution in healthy humans showed favorable kinetics. This new PET strategy has great potential for early aGVHD diagnosis, enabling timely treatments and improved patient outcomes. [18F]F-AraG may be useful for imaging activated T cells in various biomedical applications. Cancer Res; 77(11); 2893–902. ©2017 AACR.

Compelling evidence points to immune cell infiltration as a critical component of successful immunotherapy. However, there are currently no clinically available, noninvasive methods capable of evaluating immune contexture prior to or during immunotherapy. In this study, we evaluate a T-cell–specific PET agent, [18F]F-AraG, as an imaging biomarker predictive of response to checkpoint inhibitor therapy. We determined the specificity of the tracer for activated T cells in vitro and in a virally induced model of rhabdomyosarcoma. Of all immune cells tested, activated human CD8+ effector cells showed the highest accumulation of [18F]F-AraG. Isolation of lymphocytes from the rhabdomyosarcoma tumors showed that more than 80% of the intratumoral signal came from accumulation of [18F]F-AraG in immune cells, primarily CD8+ and CD4+. Longitudinal monitoring of MC38 tumor-bearing mice undergoing anti-PD-1 treatment revealed differences in signal between PD-1 and isotype antibody–treated mice early into treatment. The differences in [18F]F-AraG signal were also apparent between responders and nonresponders to anti-PD-1 therapy. Importantly, we found that the signal in the tumor-draining lymph nodes provides key information about response to anti-PD-1 therapy. Overall, [18F]F-AraG has potential to serve as a much needed immunomonitoring clinical tool for timely evaluation of immunotherapy.Significance:These findings reveal differences in T-cell activation between responders and nonresponders early into anti-PD-1 treatment, which may impact many facets of immuno-oncology, including patient selection, management, and development of novel combinatorial approaches.

CHO Cell Transfection Tracer Uptake and Efflux Assays for Adherent Cells Western Blot Immunofluorescence Staining of Lymphoid Organs Ex Vivo Donor T Cell Proliferation Analysis Automated preparation of [18F]FAraG for human imaging using the Neptis perform PET synthesizer Imaging Studies in Humans Statistics

FACS analyses, expression of transporters and kinases in immune cells, tumor growth.

Background: Given the high frequency of liver metastases in neuroendocrine tumor patients, we aimed to determine whether hepatic intra-arterial (IA) injection of 90Y-DOTATOC Peptide Receptor Radionuclide Therapy (PRRT) would achieve higher intratumoral concentrations than intravenous (IV) injection, thus maintaining efficacy while reducing systemic toxicity. Methods: PRRT-naive adult NET patients with liver-dominant metastases involving

Currently, there exists no accurate, noninvasive clinical imaging method to detect living bacteria in vivo. Our goal is to provide a positron emission tomography (PET) method to image infection by ...

Compelling evidence points to immune cell infiltration as a critical component of successful immunotherapy. However, there are currently no clinically available, noninvasive methods capable of evaluating immune contexture prior to or during immunotherapy. In this study, we evaluate a T-cell–specific PET agent, [18F]F-AraG, as an imaging biomarker predictive of response to checkpoint inhibitor therapy. We determined the specificity of the tracer for activated T cells in vitro and in a virally induced model of rhabdomyosarcoma. Of all immune cells tested, activated human CD8+ effector cells showed the highest accumulation of [18F]F-AraG. Isolation of lymphocytes from the rhabdomyosarcoma tumors showed that more than 80% of the intratumoral signal came from accumulation of [18F]F-AraG in immune cells, primarily CD8+ and CD4+. Longitudinal monitoring of MC38 tumor-bearing mice undergoing anti-PD-1 treatment revealed differences in signal between PD-1 and isotype antibody–treated mice early into treatment. The differences in [18F]F-AraG signal were also apparent between responders and nonresponders to anti-PD-1 therapy. Importantly, we found that the signal in the tumor-draining lymph nodes provides key information about response to anti-PD-1 therapy. Overall, [18F]F-AraG has potential to serve as a much needed immunomonitoring clinical tool for timely evaluation of immunotherapy. Significance: These findings reveal differences in T-cell activation between responders and nonresponders early into anti-PD-1 treatment, which may impact many facets of immuno-oncology, including patient selection, management, and development of novel combinatorial approaches.

PurposeThere are several important positron emission tomography (PET) imaging scenarios that require imaging with very low photon statistics, for which both quantitative accuracy and visual quality should not be neglected. For example, PET imaging with the low photon statistics is closely related to active efforts to significantly reduce radiation exposure from radiopharmaceuticals. We investigated two examples of low-count PET imaging: (a) imaging [90Y]microsphere radioembolization that suffers the very small positron emission fraction of Y-90's decay processes, and (b) cancer imaging with [68Ga]citrate with uptake time of 3-4 half-lives, necessary for visualizing tumors. In particular, we investigated a type of penalized likelihood reconstruction algorithm, block sequential regularized expectation maximization (BSREM), for improving both image quality and quantitative accuracy of these low-count PET imaging cases.ProceduresThe NEMA/IEC Body phantom filled with aqueous solution of Y-90 or Ga-68 was scanned to mimic the low-count scenarios of corresponding patient data acquisitions on a time-of-flight (TOF) PET/magnetic resonance imaging system. Contrast recovery, background variation, and signal-to-noise ratio were evaluated in different sets of count densities using both conventional TOF ordered subset expectation (TOF-OSEM) and TOF-BSREM algorithms. The regularization parameter, beta, in BSREM that controls the tradeoff between image noise and resolution was evaluated to find a value for improved confidence in image interpretation. Visual quality assessment of the images obtained from patients administered with [68Ga]citrate (n = 6) was performed. We also made preliminary visual image quality assessment for one patient with [90Y]microspheres. In Y-90 imaging, the effect of 511-keV energy window selection for minimizing the number of random events was also evaluated.ResultsQuantitatively, phantom images reconstructed with TOF-BSREM showed improved contrast recovery, background variation, and signal-to-noise ratio values over images reconstructed with TOF-OSEM. Both phantom and patient studies of delayed imaging of [68Ga]citrate show that TOF-BSREM with beta = 500 gives the best tradeoff between image noise and image resolution based on visual assessment by the readers. The NEMA-IQ phantom study with [90Y]microspheres shows that the narrow energy window (460-562keV) recovers activity concentrations in small spheres better than the regular energy window (425-650keV) with the beta value of 2000 using the TOF-BSREM algorithm. For the images obtained from patients with [68Ga]citrate using TOF-BSREM with beta = 500, the visual analogue scale (VAS) was improved by 17% and the Likert score was increased by 1 point on average, both in comparison to corresponding scores for images reconstructed using TOF-OSEM.ConclusionOur investigation shows that the TOF-BSREM algorithm improves the image quality and quantitative accuracy in low-count PET imaging scenarios. However, the beta value in this algorithm needed to be adjusted for each radiopharmaceutical and counting statistics at the time of scans.

Agents targeting prostate-specific membrane antigen (PSMA) comprise a rapidly emerging class of radiopharmaceuticals for diagnostic imaging of prostate cancer. Unlike most other PSMA agents with a urea backbone, CTT1057 is based on a phosphoramidate scaffold that irreversibly binds to PSMA. We conducted a first-in-humans phase I study of CTT1057 in patients with localized and metastatic prostate cancer. Methods: Two patient cohorts were recruited. Cohort A patients had biopsy-proven localized prostate cancer preceding radical prostatectomy, and cohort B patients had metastatic castration-resistant prostate cancer. Cohort A patients were imaged at multiple time points after intravenous injection with 362 ± 8 MBq of CTT1057 to evaluate the kinetics of CTT1057 and estimate radiation dose profiles. Mean organ-absorbed doses and effective doses were calculated. CTT1057 uptake in the prostate gland and regional lymph nodes was correlated with pathology, PSMA staining, and the results of conventional imaging. In cohort B, patients were imaged 60–120 min after injection of CTT1057. PET images were assessed for overall image quality, and areas of abnormal uptake were contrasted with conventional imaging. Results: In cohort A (n = 5), the average total effective dose was 0.023 mSv/MBq. The kidneys exhibited the highest absorbed dose, 0.067 mGy/MBq. The absorbed dose of the salivary glands was 0.015 mGy/MBq. For cohort B (n = 15), CTT1057 PET detected 97 metastatic lesions, and 44 of 56 bone metastases detected on CTT1057 PET (78.5%) were also detectable on bone scanning. Eight of 32 lymph nodes positive on CTT1057 PET (25%) were enlarged by size criteria on CT. Conclusion: CTT1057 is a promising novel phosphoramidate PSMA-targeting (18)F-labeled PET radiopharmaceutical that demonstrates similar biodistribution to urea-based PSMA-targeted agents, with lower exposure to the kidneys and salivary glands. Metastatic lesions are detected with higher sensitivity on CTT1057 imaging than on conventional imaging. Further prospective studies with CTT1057 are warranted to elucidate its role in cancer imaging.

A major barrier to successful use of allogeneic hematopoietic cell transplantation is acute graft-versus-host disease (aGVHD), a devastating condition that arises when donor T cells attack host tissues. With current technologies, aGVHD diagnosis is typically made after end-organ injury and often requires invasive tests and tissue biopsies. This affects patient prognosis as treatments are dramatically less effective at late disease stages. Here, we show that a novel PET radiotracer, 2′-deoxy-2′-[18F]fluoro-9-β-D-arabinofuranosylguanine ([18F]F-AraG), targeted toward two salvage kinase pathways preferentially accumulates in activated primary T cells. [18F]F-AraG PET imaging of a murine aGVHD model enabled visualization of secondary lymphoid organs harboring activated donor T cells prior to clinical symptoms. Tracer biodistribution in healthy humans showed favorable kinetics. This new PET strategy has great potential for early aGVHD diagnosis, enabling timely treatments and improved patient outcomes. [18F]F-AraG may be useful for imaging activated T cells in various biomedical applications. Cancer Res; 77(11); 2893–902. ©2017 AACR.

Given the high frequency of liver metastases in neuroendocrine tumor patients, we aimed to determine whether hepatic intraarterial administration of

A series of phosphoramidate-based prostate specific membrane antigen (PSMA) inhibitors of increasing lipophilicity were synthesized (4, 5, and 6), and their fluorine-18 analogs were evaluated for use as positron emission tomography (PET) imaging agents for prostate cancer. To gain insight into their modes of binding, they were also cocrystallized with the extracellular domain of PSMA. All analogs exhibited irreversible binding to PSMA with IC50 values ranging from 0.4 to 1.3 nM. In vitro assays showed binding and rapid internalization (80-95%, 2 h) of the radiolabeled ligands in PSMA(+) cells. In vivo distribution demonstrated significant uptake in CWR22Rv1 (PSMA(+)) tumor, with tumor to blood ratios of 25.6:1, 63.6:1, and 69.6:1 for [(18)F]4, [(18)F]5, and [(18)F]6, respectively, at 2 h postinjection. Installation of aminohexanoic acid (AH) linkers in the phosphoramidate scaffold improved their PSMA binding and inhibition and was critical for achieving suitable in vivo imaging properties, positioning [(18)F]5 and [(18)F]6 as favorable candidates for future prostate cancer imaging clinical trials.

Introduction In this study, a structurally modified phosphoramidate scaffold, with improved prostate-specific membrane antigen (PSMA) avidity, stability and in vivo characteristics, as a PET imaging agent for prostate cancer (PCa), was prepared and evaluated. Methods p-Fluorobenzoyl-aminohexanoate and 2-(3-hydroxypropyl)glycine were introduced into the PSMA-targeting scaffold yielding phosphoramidate 5. X-ray crystallography was performed on the PSMA/5 complex. [ 18 F]5 was synthesized, and cell uptake and internalization studies were conducted in PSMA(+) LNCaP and CWR22Rv1 cells and PSMA(−) PC-3 cells. In vivo PET imaging and biodistribution studies were performed at 1 and 4h post injection in mice bearing CWR22Rv1 tumor, with or without blocking agent. Results The crystallographic data showed interaction of the p -fluorobenzoyl group with an arene-binding cleft on the PSMA surface. In vitro studies revealed elevated uptake of [ 18 F]5 in PSMA(+) cells (2.2% in CWR22Rv1 and 12.1% in LNCaP) compared to PSMA(−) cells (0.08%) at 4h. In vivo tumor uptake of 2.33% ID/g and tumor-to-blood ratio of 265:1 was observed at 4h. Conclusions We have successfully synthesized, radiolabeled and evaluated a new PSMA-targeted PET agent. The crystal structure of the PSMA/5 complex highlighted the interactions within the arene-binding cleft contributing to the overall complex stability. The high target uptake and rapid non-target clearance exhibited by [ 18 F]5 in PSMA(+) xenografts substantiates its potential use for PET imaging of PCa. Advances in Knowledge The only FDA-approved imaging agent for PCa, Prostascint®, targets PSMA but suffers from inherent shortcomings. The data acquired in this manuscript confirmed that our new generation of [ 18 F]-labeled PSMA inhibitor exhibited promising in vivo performance as a PET imaging agent for PCa and is well-positioned for subsequent clinical trials. Implications for Patient Care Our preliminary data demonstrate that this tracer possesses the required imaging characteristics to be sensitive and specific for PCa imaging in patients at all stages of the disease.

To evaluate a simultaneous PET/MRI approach to imaging patients with neuroendocrine tumor using a combination of (68)Ga-DOTA-TOC as a PET contrast agent and gadoxetate disodium as a hepatobiliary MRI contrast agent.Ten patients with neuroendocrine tumor with known or suspected hepatic disease were imaged using a (68)Ga-DOTA-TOC PET/CT immediately followed by a 3.0T time-of-flight PET/MRI, using a combined whole body and liver specific imaging. The presence of lesions and DOTA-TOC avidity were assessed on CT, PET from PET/CT, diffusion weighted imaging, hepatobiliary phase imaging (HBP), and PET from PET/MRI. Maximum standardized uptake values (SUVmax) in hepatic lesions and nodal metastases were compared between PET/CT and PET/MRI, as were detection rates using each imaging approach.A total of 101 hepatic lesions were identified, 47 of which were DOTA-TOC avid and able to be individually measured on both PET/CT and PET/MRI. HBP imaging had a higher sensitivity for detection of hepatic lesions compared to CT or PET (99% vs. 46% and 64%, respectively; p values0.001). There was a strong correlation between SUVmax of liver lesions obtained with PET/CT compared to PET/MR imaging (Pearson's correlation = 0.91). For nodal disease, CT had a higher sensitivity compared to whole body MRI (p = 0.015), although PET acquired from PET/MRI detected slightly more lesions compared to PET from PET/CT.A simultaneous PET/MRI using both (68)Ga-DOTA-TOC and gadoxetate disodium was successful in whole body staging of patients with neuroendocrine tumor. HBP imaging had an increased detection rate for hepatic metastases.

Dopamine transporter (DAT) function is altered by many neurodegenerative diseases. For instance, in Parkinson disease DAT density has been shown to decrease in early disease and to play a role in the occurrence of motor complications. DAT is thus an important imaging target with potential therapeutic relevance in humans and animal models of disease. The PET DAT marker 11C-methylphenidate is commonly used to quantify DAT function. Here we investigate the characteristics of the 11C-methylphenidate–derived quantification of DAT in rodents using the 6-hydroxydopamine Parkinson disease rat model. Methods: Seven unilaterally 6-hydroxydopamine–lesioned rats (dopaminergic denervation [DD] range, 36%–94%) were injected with 3.7 MBq/100 g of body weight and tracer masses ranging from 93.8 to 0.0041 μg/100 g of body weight. We evaluated the maximum available transporter density and the in vivo (apparent) ligand-transporter dissociation constant (Bmax and K d app , respectively) with an in vivo Scatchard method using several modeling approaches and estimated the transporter occupancy as a function of the amount of tracer injected and tracer specific activity (SA). Results: Strong evidence of different nonspecific binding in the striatal region, compared with the reference region, leading to bias in the estimate of DD severity was found. One percent transporter occupancy was reached with 0.14 μg of tracer/100 g of body weight, corresponding to an SA of 5.7 kBq/pmol for the given radioactivity dose, and 10% occupancy was reached at 1.5 μg of tracer/100 g of body weight, corresponding to an SA of 0.57 kBq/pmol. The 6-hydroxydopamine lesion affected Bmax (control, 402 ± 94 pmol/mL; lesioned, 117 ± 120 pmol/mL; P = 0.003) but not K d app (control, 331 ± 63 pmol/mL; lesioned, 362 ± 119 pmol/mL; P = 0.63). Conclusion: Although DAT imaging can be performed at a relatively high mass of 11C-methylphenidate (low SA), the additional nonspecific binding found in the striatum can introduce a DD severity–dependent bias in the estimate of tissue-derived binding potential and care must be taken in comparing 11C-methylphenidate–derived assessment of DD with that obtained using other dopaminergic tracers.

An improved method to remove the 2-nitrophenylsulfenyl protecting group in the conventional radiosynthesis of the PET radiotracer [C-11]d-threo-methylphenidate was developed. The method uses the nonvolatile reagents sulfuric acid and L-cysteine. In addition it was demonstrated that solid phase extraction (SPE, C18 and ion exchange) can be used to purify the final product instead of semi-preparative HPLC. Copyright © 2006 John Wiley & Sons, Ltd.

The motion of 18F radioactively labeled papermaking fibers settling in the midst of a suspension of nonradioactive fibers has been studied using positron emission tomography (PET). Various fractions were separated from the whole-pulp suspension, radioactively labeled, and reintroduced into the original suspension. Tracer concentration profiles were measured dynamically throughout the sedimenting structure over the first 2 h of settling. These profiles were then used in conjunction with the Eulerian volume-averaged two-phase flow equations to estimate the permeability and solid-phase stress functions for this suspension. Good agreement was found between the experimental data and the numerical model using particular functional forms for permeability and solid stress. The general approach outlined here can be used to examine the networking characteristics of different mixed suspensions of fibers. © 2006 American Institute of Chemical Engineers AIChE J, 2006

The synthesis of the precursor for [11C]carfentanil and the precursor labelling with 11C have both been improved. The problem ‘bottleneck’ step in the carfentanil precursor synthesis, due to low chemical yield (14%) of intermediates nitrile into amide conversion, has been solved. Application of a H2O2/K2CO3/DMSO reaction method significantly increased the yield of this chemical transformation (up to 84%). A simple and straight-forward synthesis of [11C]carfentanil was achieved by combining in-loop methylation of the ammonia salt of the precursor by [11C]CH3I, using tetrabutylammonium hydroxide as a base, with a previously developed product purification procedure using a C2 extraction disc. A decay corrected yield with respect to [11C]CH3I of [11C]carfentanil was 64±12% (n=6) with the synthesis time of 21 min. The radiochemical purity was >98%. Comparatively high specific radioactivity of [11C]carfentanil [11.2±4.8 Ci/μmol (EOS, n=5)] was partially attributed to the use of [11C]methane target gas for production of carbon-11 methyl iodide. Copyright © 2003 John Wiley & Sons, Ltd.

A new thin window support system for the accelerator production of positron emitters (e.g. 17 F, 18 F 11 C, 15 O) has been developed. The integrated support grid and cooling design has been optimized for 6–13 MeV protons or deuterons. The water-cooled support grid regularly operated at >100 μA of 6 MeV deuterons and protons. The grid performed without failure at ⩾50 μA of 13 MeV protons on a 3.1 MPa gas target using 25.4 μm aluminum target foil. Transmission for the smallest hole grid of 72% based on uniform parallel beam agreed with the measured yield of 71±1% compared to the theoretical maximum yield.

The clinically oriented NEMA NU-2 2000+ performance standards have been performed on an ADAC molecular coincidence detection dual-head camera. At 1 cm radius, the transverse resolution full-width at half-maximum was measured to be 5.2 (10.0) mm and the axial was 5.0 (10.6) mm. At 10 cm radius, the transverse radial resolution was 4.7 (7.4) mm and the transverse tangential was 8.5 (20.9) mm. The axial resolution was 14.0 (41.1) mm. The peak true count rate was 4370 counts/s at a concentration of 4.3 kBq/ml. The peak noise equivalent count rate (NECR) was 1620 counts/s at 2.9 kBq/ml. The system scatter fraction was 48%, The maximum relative count rate error observed at the NECR peak was -42%. The sensitivity was 1010 counts/sm/rSq in the center and 870 counts/s/MBq at an offset of 10 cm. The contrast for the hot spheres ranged from 18.5 (11.6)% to 11.6 (7.9)% for a contrast ratio of 8:1 (4:1). For the cold spheres, it ranged from 41% to 25% with an overall background variability of 7%. The residual error in scatter and attenuation correction was approximately 50%. All measurements were performed at the maximum allowed crystal-to-crystal distance of 810 mm.

Studies of dopamine (DA) receptor binding in early parkinsonian patients, or in models of Parkinson's disease, have revealed a supersensitivity of the D2-like receptor subtype as compared to age-matched controls. The lack of upregulation in advanced patients is often attributed to the effects of prolonged antiparkinsonian therapy, but the impact of therapy vs. intrinsic mechanisms in untreated patients or animals with long-term lesions of the DA nigrostriatal pathway has been difficult to address. We studied, in vivo, by PET using the DA D2 receptor ligand raclopride, the status of the DA receptors in normal rhesus monkeys and those with acute (3 months) or long-term (10 years) MPTP-induced nigrostri- atal lesions. Compared to age-matched controls, there was no change in raclopride binding in MPTP-treated animals without parkinsonian symptoms. There was a significant increase in raclopride binding in the putamen (but not caudate nucleus) of all the animals displaying rigidity, hypo- and bradykinesia. This increase was greater in the animals with acute lesions (32%) than with established, long-term lesions (18%). There was no correlation between the postmortem striatal DA concentrations and in vivo raclopride binding but there was a correlation between PET raclopride binding and ( 3 H)raclopride binding in vitro. Complex changes in D2 receptor binding occur in various stages of parkinsonism. Antiparkinsonian therapy is unlikely to be solely responsible for the lack of upregulation found in advanced parkinsonian patients but may be a contributing factor. Synapse 38:105-113, 2000. © 2000 Wiley-Liss, Inc.

The synthesis of [18F]FDG using tetrabutylammonium bicarbonate has been successfully modified to accommodate automation using the Optomux® control system. Noteworthy changes to the methods previously reported are the addition of a small ion exchange column which serves to quantitatively trap [18F]fluoride from the target water and the extensive use of thermocouple and radiation detector feedback for process control. The radiochemical yields observed over 30 runs are: 50.3 ± 9% decay corrected and 34.6 ± 6% decay uncorrected.

3-O-Methyl-6-[18F]fluorodopa was synthesized in 20% radiochemical yield in 60 min, with a specific activity of 500 mCi/mmol, by the fluorination of a stannylated dopa precursor with [18F]-acetyl hypofluorite.

Background: Electroconvulsive therapy (ECT), an effective treatment for depression, also improves motor symptomatology in Parkinson’s disease (PD). We have previously demonstrated that ECT stimulates dopamine (DA) function in the striatum of healthy non-human primates, suggesting that DA may contribute to antidepressant effects. Objective: We investigated the potential role of DA mechanisms in the amelioration of PD symptoms following a clinical course of ECT. Methods: We treated non-human primates rendered mildly bilaterally or unilaterally parkinsonian with 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP), with a course of 6 ECT treatments. Using positron emission tomography, animals were scanned at baseline and at various time points after ECT with tracers of the DA system. Data were analyzed using the Logan reference tissue model and statistics were performed using orthogonal polynomial contrasts. Results: There was no change in binding of the DA transporter tracer in the lesioned striata after ECT as opposed to what we measured in the striatum of healthy animals. Raclopride binding to the D2/3 receptors was unaffected in all groups. However, there were increases in vesicular monoamine transporter type 2 and D1 receptor binding in the MPTP-lesioned striata after ECT, returning towards baseline by 6 weeks. Conclusion: We suggest that the effects of ECT in PD may proceed from a mechanism similar to that in healthy animals but with a blunted dopaminergic response, likely due to the significant loss of striatal DA terminals. The safety of ECT, its mild side effects and its stimulatory effects of the DA system may thus make it an attractive adjunct to antiparkinsonian treatment.

There is a real need to develop a superior high yield target system for the production of large quantities of 18F-fluoride with the increasing numbers of clinical PET centers worldwide. Therefore we have investigated a route to higher yield target system for 18F-fluoride production which relies on gas target designs. (1)

3-O-Methyl-2- and 6-[18F]-fluorodopa were synthesized in 8% radiochemical yield by the direct fluorination of a protected L-dopa derivative with [18F]-acetyl hypofluorite. The 2- and 6-fluoro isomers were separated and purified by reverse phase HPLC.

The in situ production of [11C]CH4 using a niobium metal target chamber is described. Improved yields are observed in comparison to the previously reported aluminum conical target under similar conditions of beam energy and current. An empirical expression is proposed that quantifies the loss of yield as a function of irradiation time.

A convenient three-step synthesis of the title compound from commercially available 3,4-dimethoxyphenethylamine is described. The title compound is a stable, crystalline, organic-soluble solid which reacts with carrier-added [18F]acetyl hypofluorite to yield 6-[18F]fluorodopamine (20 ± 7% radiochemical yield EOS, n = 3) following deprotection with hydriodic acid.

Traditionally, autoradiography of neuroreceptors is performed in vitro using tritiated ligands and low sensitivity X-ray film, requiring long exposure times. In vivo imaging of neuroreceptors using positron emission tomography (PET) suffers poor spatial resolution, but in vitro PET autoradiography is difficult with film due to the short half-life of the isotopes. Storage phosphor screens provide an extremely sensitive alternative to film. To demonstrate and validate quantitative in vitro phosphor imaging with PET and tritiated ligands, we treated rats chronically with the antidepressant desipramine, which results in decreased binding to serotonin 5-HT 2 receptors. Serotonin 5-HT 2 binding decreased significantly in all cortical regions examined as measured by both [ 3 H]ketanserin and [ 18 F]setoperone. The data from the two radioligands were not significantly different, and the distribution of the receptors was in agreement with previous reports. We also present data on the reusability of tritium-sensitive phosphor screens, and show that the use of simple corrections allows receptor binding data with PET ligands to be compared across different days. The results indicate that phosphor imaging is a valid, fast, and quantifiable technique for measuring neuroreceptor regulation, and that it provides an excellent tool to corroborate in vivo PET data in vitro at higher resolution.

A series of experiments were performed to better understand the mechanism of the In-loop [11C]CH3I-methylation. The timing of [11C]CH3I delivery is critical for the high yield of radiolabeling since in-loop radioactivity trapping is reversible. Trapped radioactivity escapes faster from a Tefzel loop compared to a PEEK- or stainless steel loop. Up to 50% of delivered radioactivity may be concentrated at the loop origin (representing 8.1% of the total loop volume). A five-fold reduction of the reaction solvent volume and/or precursor amount may lead to a decrease of the product radiochemical yield either by lowering the in-loop radioactivity trapping or by diminishing conversion of [11C]CH3I into the product.

The ligand-receptor binding potential determined by in vivo PET studies at high ligand-specific radioactivity reflects both the receptor density and ligand-receptor affinity. This ambiguity has been resolved by various methods based on the administration of multiple unlabeled ligand concentrations. The authors aimed to implement and refine an approach to multiple ligand concentration receptor assay that combined maximum simplicity and a minimum of assumptions and model dependence that would nonetheless reliably distinguish density from affinity effects. The approach uses administration by bolus followed by infusion to obtain a true equilibrium between bound ligand and the other components of the ligand concentration, and does not require measurements of ligand in blood plasma. Four approaches to the optimization of the desired density and affinity parameters from the measured equilibrium data were implemented and compared in the analysis of raclopride studies performed in both normal control and MPTP-lesioned nonhuman primates. The authors conclude that the method is simple enough for routine use and yet reliable enough to apply in ongoing studies of both chronic and acute drug effects in the dopamine system.

The status of the dopamine (DA) D1 receptors after degeneration of the DA-nigrostriatal neurons, either in Parkinson’s disease (PD) or experimental parkinsonism induced by neurotoxins such as 1-methyl-4-phenyl1,2,3,6-tetrahydropyridine (MPTP) and 6-hydroxydopamine (6-OH-DA), is unclear. While an abundant literature of postmortem and in vivo data exists, the reports are often contradictory. In humans, monkeys, and rodents with parkinsonism, the striatal DA D1 receptors have been reported increased (Gnanalingham et al., 1993; Iwata et al., 1996; Rioux et al., 2001), unchanged (Alexander et al., 1991; Graham et al., 1990; Laihinen et al., 1994; Rinne et al., 1990; Shinotoh et al., 1993), and decreased (Marshall et al., 1989; Turjanski et al., 1997). Studies of D1 receptor mRNA are as confusing as those of receptor binding, with both decreases (Goulet et al., 1997) and no changes (Hurley et al., 2001) reported and correlate poorly with D1 binding in the same subject. Part of the confusion may rest with differences in the severity of the disease/ lesion, its duration, the tracer used, and/or the different methodological approaches used. In addition, in PD patients the influence of previous antiparkinsonian therapy before measurement or assay has also been shown to affect the results (Raisman et al., 1985). In this study, we measured the binding potential of [C]-SCH23390, a tracer widely used to study DA D1 receptors both in vivo and in vitro, in rhesus monkeys, normal and with MPTP-induced lesions of the DA nigrostriatal pathway. The normal controls were housed with the MPTP-lesioned animals and were exposed to the same living conditions and anesthetic regimens. Thus, the main differences between the animals resided in the degree of MPTP-lesion, which was assessed by in vivo measurements of 6-[F]fluoro-L-dopa (FDOPA) uptake in an earlier study (Doudet et al., 1998). This population was an ideal means to resolve the controversy over DA D1 binding in vivo. MATERIALS AND METHODS

The effectiveness of 6-[18F]fluoro-L- m-tyrosine (6FMT) to evaluate dopamine presynaptic integrity was compared to that of 6-[18F]fluoro-L-dopa (6FDOPA) in vivo by positron emission tomography (PET). Six normal and six 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) -lesioned monkeys received 6FDOPA and 6FMT PET scans on separate occasions with identical scanning protocols. Four measures, the rate of uptake of tracer into striatum using either the arterial input function ( Ki) or the activity in the occipital cortex as the input function ( Kc), the rate of loss of striatal radioactivity ( kloss), and an index of “effective turnover” of dopamine ( kloss/ Ki), were obtained for both tracers during extended PET studies. 6-[18F]Fluoro-L- m-tyrosine was as effective as 6FDOPA in separating normals from MPTP-lesioned subjects on the basis of the uptake rate constants Ki and Kc. However, in contrast to 6FDOPA, it was not possible to differentiate the normal from the lesioned animal using kloss or kloss/ Ki for 6FMT. Thus, FMT appears to be a reasonable, highly specific tracer for studying the activity of aromatic dopa decarboxylase enzyme as an index of presynaptic integrity. However, if one is interested in investigating further the metabolic pathway and obtaining an in vivo estimate of the effective turnover of dopamine (after pharmacologic manipulation, for example), 6FDOPA remains the tracer of choice.

The respective advantages and disadvantages of 6-fluoro-L-DOPA (6FD0PA) and 6-fluoro-L-m-tyrosine (6FMT) labeled with 18F to image the dopamine (DA) presynaptic system in vivo were investigated by positron emission tomography (PET) in normal monkeys and in monkeys with l-methyl-4-phenyl-1,2,3,6-tetrahydropyridine-induced lesions of the DA nigrostriatal neurons. Peripheral metabolism of the radiotracers was analyzed throughout the course of the PET studies. Using a modification of the extended graphical method of analysis, three measures of central DA function were examined: the rate of uptake of the tracer, the rate of loss of striatal radioactivity, and the effective turnover of DA. 6FMT presented a simpler metabolic profile compared to 6FDOPA, having no peripheral metabolites able to cross the blood-brain barrier. The uptake rates of 6FMT and 6FDOPA (decreased in lesioned animals) were found to be equally sensitive to abnormalities in the DA system. 6FDOPA, but not 6FMT, was able to separate normals from lesioned animals based on their increased striatal radioactivity loss rate and effective DA turnover. 6FMT was found to be an excellent tracer for brief clinical studies. However, 6FDOPA remains a promising tracer for the study of the storage processes of exogenous L-DOPA and of drug therapies aimed at DA preservation.

This chapter demonstrates the graphical analysis of 6-fluorodopa (6-FD) with the time course in cortex as the input function to discriminate strongly between those with Parkinson's disease and normal subjects. However, this uptake measure is biased downward by the accumulation of the metabolite 6-fluoro-3-O-methyldopa (3-O-MFD) in the cortical input function. Methods to correct for this and other effects of the metabolite are limited by the large intersubject variability of 3-O-MFD kinetics and the large uncertainties of 3-O-MFD kinetics determined directly from 6-FD studies by compartmental analysis. Data from paired 6-FD and 3-O-MFD studies performed in 10 subjects are used to demonstrate that the required 3-O-MFD kinetic parameters may be derivable from the graphical analysis of the 6-FD data. The same data are used to perform preliminary tests of particular correction schemes. Although the corrections yielded only marginal improvement in the discrimination of five Parkinsonian subjects from five normal controls, results clearly indicated that the rank order of apparent disease severity can be influenced by extremes of metabolite distribution volume in brain.

There are two general approaches to regulating the production of radiopharmaceuticals. One is based on performance standards and the other is through prescriptive regulations. With performance standards, the general requirements are defined that describe the production and quality control of a radiopharmaceutical. This approach allows for the institution to arrive at a suitable protocol as long as it meets the specified goal of applicability for human use. Thus, a system based on performance standards must have highly trained personnel.

There are essentially two reasons why a synthetic procedure for producing a radiopharmaceutical is automated. The first is to reduce radiation exposure and the second is to increase reliability.