PET imaging of prostate cancer xenografts with a highly specific antibody against the prostate-specific membrane antigen.

UNLABELLED: Prostate-specific membrane antigen (PSMA), a transmembrane glycoprotein, is highly expressed by virtually all prostate cancers and is currently the focus of several diagnostic and therapeutic strategies. We have previously reported on the generation of several monoclonal antibodies (mAb) and antibody fragments that recognize and bind with high affinity to the extracellular domain of cell-adherent PSMA. This article reports the in vivo behavior and tumor uptake of the radiolabeled anti-PSMA mAb 3/A12 and its potential as a tracer for PET. METHODS: The mAb 3/A12 was conjugated with the chelating agent 1,4,7,10-tetraazacyclododecane-N,N',N'',N'''-tetraacetic acid (DOTA) and radiolabeled with (64)Cu. Severe combined immunodeficient mice bearing PSMA-positive C4-2 prostate carcinoma xenografts were used for small-animal PET imaging. Mice with PSMA-negative DU 145 tumors served as controls. For PET studies, each animal received 20-30 microg of radiolabeled mAb corresponding to an activity of 7.6-11.5 MBq. Imaging was performed 3, 24, and 48 h after injection. After the last scan, the mice were sacrificed and tracer in vivo biodistribution was measured by gamma-counting. RESULTS: Binding of the mAb 3/A12 on PSMA-expressing C4-2 cells was only minimally influenced by DOTA conjugation. The labeling efficiency using (64)Cu and DOTA-3/A12 was 95.3% +/- 0.3%. The specific activity after (64)Cu labeling was between 327 and 567 MBq/mg. After tracer injection, static small-animal PET images of mice with PSMA-positive tumors revealed a tumor-to-background ratio of 3.3 +/- 1.3 at 3 h, 7.8 +/- 1.4 at 24 h, and 9.6 +/- 2.7 at 48 h. In contrast, no significant tracer uptake occurred in the PSMA-negative DU 145 tumors. These results were confirmed by direct counting of tissues after the final imaging. CONCLUSION: Because of the high and specific uptake of (64)Cu-labeled mAb 3/A12 in PSMA-positive tumors, this ligand represents an excellent candidate for prostate cancer imaging and potentially for radioimmunotherapy.

The specificity and sensitivity of transcranial ultrasound in the differential diagnosis of Parkinson's disease: a prospective blinded study.

BACKGROUND: Increased echogenicity of the substantia nigra (SN), as determined by transcranial sonography (TCS), is characteristic of idiopathic Parkinson's disease (iPD). The results of initial retrospective studies indicate that this ultrasound sign is specific for iPD and can help to differentiate it from atypical parkinsonian syndromes (aPS); however, these early studies were done in patients with later disease stages and known clinical diagnosis. We aimed to determine the diagnostic value of TCS in the early stages of parkinsonian syndromes, when the clinical symptoms often do not enable a definite diagnosis to be made. METHODS: 60 patients who presented with the first, but still unclear, clinical symptoms of parkinsonism had TCS in this prospective blinded study. Investigators were blinded to the results of the clinical investigations, the ultrasound findings, and the diagnosis at time of investigation. The patients were followed-up every 3 months for 1 year to assess and re-evaluate the clinical symptoms. The patients in whom a clinical diagnosis could not be made with certainty were investigated with raclopride PET or dopamine transporter single-photon emission computed tomography (SPECT), or both. FINDINGS: A clinical diagnosis of parkinsonism could not be established at baseline in 38 patients. At 12 months, 39 patients were clinically categorised as having iPD. Compared with endpoint diagnosis, the sensitivity of TCS at baseline was 90%7% and the specificity was 82.4%; the positive predictive value of TCS for iPD was 92.9% and the classification accuracy was 88.3%. INTERPRETATION: TCS is an easy to implement, non-invasive, and inexpensive technique that could help in the early differential diagnosis of parkinsonian syndromes. The routine use of TCS in the clinic could enable disease-specific therapy to be started earlier. FUNDING: Michael J Fox Foundation for Parkinson's Research.

Intratumoral spatial distribution of hypoxia and angiogenesis assessed by 18F-FAZA and 125I-Gluco-RGD autoradiography.

UNLABELLED: The hypoxia-inducible factor-1 alpha (HIF-1 alpha) activates angiogenesis in response to cellular hypoxia, suggesting a spatial correlation between angiogenesis and tissue hypoxia. METHODS: Using digital autoradiography of coinjected 18F-labeled azomycin arabinoside (8F-FAZA) (assessing regional hypoxia) and a glycosylated RGD-containing peptide (125I-3-iodo-dTyr(4)-cyclo(-Arg-Gly-Asp-dTyr-Lys(SAA)-), or 125I-Gluco-RGD) (assessing angiogenesis via binding to alpha v beta 3 integrin receptors on endothelial cells) performed on 22 EMT6 tumor xenografts, we investigated the intratumoral spatial distribution of these tracers. We applied a Bayesian bivariate image analysis using the mean tumor-to-muscle ratio as a discriminator, resulting in 4 groups: FAZA high/RGD high (Q1), FAZA low/RGD high (Q2), FAZA low/RGD low (Q3), and FAZA high/RGD low (Q4). In an additional 18 xenografts, the immunohistochemically derived HIF-1 alpha protein distribution was compared with 18F-FAZA autoradiography. Animals were divided into groups breathing either room air or carbogen (95% oxygen, 5% CO2) for 4 h until sacrifice. RESULTS: Under room air conditions, roughly 60% of the tumor surface displayed a spatial coupling of 18F-FAZA and 125I-Gluco-RGD uptake: either high (Q1) or low (Q3) uptake for both tracers, with Q1 indicating spatial association of hypoxia and angiogenesis and Q3 indicating adequate oxygenation without active angiogenesis. However, the remaining approximately 40% of the tumor surface showed discordant 18F-FAZA and 125I-Gluco-RGD uptake, indicating that hypoxia and angiogenesis are not necessarily spatially linked to each other and highlighting substantial intratumoral heterogeneity of the 18F-FAZA and 125I-Gluco-RGD uptake. Although carbogen breathing conditions significantly decreased the mean 18F-FAZA tumor-to-muscle ratio, no significant changes were observed for 125I-Gluco-RGD, indicating that an acute increase in tumor oxygenation did not influence alpha v beta 3 integrin receptor expression. The HIF-1 alpha-positive (HIFpos) tumor cell fraction was not significantly influenced by breathing conditions and covered between 0% and 35% of the total tumor section surface. However, the HIFpos tumor section surface was much smaller than the tumor section surface of increased 18F-FAZA uptake, suggesting that both markers are identifying distinctly different biologic processes associated with hypoxia. CONCLUSION: The study revealed a substantial spatial discordance of the 18F-FAZA and 125I-Gluco-RGD tumor distribution suggesting that hypoxia and angiogenesis are not necessarily spatially linked in malignancies. These results may prove essential in developing advanced targeted systemic chemotherapeutic approaches (such as combinations of hypoxia-activated cytotoxins and antiangiogenic drugs) for hypoxic tumors.

Radioiodination of 1-(2-deoxy-beta-D-ribofuranosyl)-2,4-difluoro-5-iodobenzene (dRFIB), a putative thymidine mimic nucleoside for cell proliferation studies.

Iodine-124 was produced via the (124)Te(p,n)(124)I reaction by 15 MeV proton irradiation of an in-house solid mass tellurium dioxide target, using the Tübingen PETtrace (General Electric Medical Systems) cyclotron. 1-(2-Deoxy-beta-D-ribofuranosyl)-2,4-difluoro-5-iodobenzene (dRFIB), a stable, non-polar thymidine mimic nucleoside, was synthesized in 5 steps following a literature method, for radioiodination with [(124)I] iodide via isotope exchange in the presence of copper sulphate and ammonium sulphate in methanol-water. The radiolabelling procedure was optimized with respect to temperature, amount of dRFIB, amount of sodium hydroxide and reaction time, to produce radiochemical yields of up to 85% with a 1-h reaction at 140 degrees C. With routine I-124 production of 30 MBq/run, relatively high specific activities, approaching 100 MBq/mmol, can be expected. The activation energy for dRFIB radioiodination was calculated from temperature-time RCY data to be approximately 100 kJ/mol using no-carrier-added [(124)I]iodide.

Pretreatment 18F-FAZA PET predicts success of hypoxia-directed radiochemotherapy using tirapazamine.

UNLABELLED: We evaluated the predictive value of PET using the hypoxia tracer (18)F-fluoroazomycin arabinoside ((18)F-FAZA) for success of radiotherapy in combination with tirapazamine, a specific cytotoxin for hypoxic cells. METHODS: Imaging was performed on EMT6 tumor-bearing nude mice before allocating mice into 4 groups: radiochemotherapy (RCT: 8 fractions of 4.5 Gy within 4 d combined with tirapazamine, 14 mg/kg), radiotherapy alone (RT), chemotherapy alone (tirapazamine) (CHT), or control. Treatment success was assessed by several tumor growth assays, including tumor growth time from 70 to 500 microL and absolute growth delay (aGD). The median pretreatment (18)F-FAZA tumor-to-background ratio served as a discriminator between "hypoxic" and "normoxic" tumors. RESULTS: The mean tumor growth was significantly accelerated in hypoxic control tumors (growth time from 70 to 500 microL, 11.0 d) compared with normoxic control tumors (growth time from 70 to 500 microL, 15.6 d). Whereas RT delayed tumor growth regardless of the level of hypoxia, an additive beneficial therapeutic effect of tirapazamine to RT was observed only in hypoxic tumors (aGD, 12.9 d) but not in normoxic tumors (aGD, 6.0 d). CONCLUSION: This study provides compelling evidence that hypoxia imaging using (18)F-FAZA PET is able to predict the success of RCT of tumor-bearing mice using the hypoxia-activated chemotherapeutic agent tirapazamine. Pretreatment (18)F-FAZA PET, therefore, offers a way for the individualization of tumor treatment involving radiation. The data suggest that by reserving hypoxia-directed therapy to tumors with high (18)F-FAZA uptake, improvement of the therapeutic ratio is possible, as the therapeutic effect of tirapazamine seems to be restricted to hypoxic tumors.

Hypoxia-imaging with (18)F-Misonidazole and PET: changes of kinetics during radiotherapy of head-and-neck cancer.

BACKGROUND AND PURPOSE: PET with (18)F-Misonidazole (FMISO-PET) is a non-invasive method for measuring tumor hypoxia. We analysed changes of FMISO-uptake during radiotherapy and their impact on patient outcome. MATERIALS AND METHODS: Fourteen patients with HNC underwent repeated FMISO-PET prior to radiotherapy and after 30Gy. Dynamic and static PET-scans (2+4h p.i.) were acquired. FMISO-uptake was quantified by calculating standard uptake values (SUV) and tumor-muscle-ratios (TMR). Kinetic curve types representing tissue hypoxia were defined. Change of curve type was correlated with patient outcome. RESULTS: The mean SUV 4h p.i. and the TMR decreased significantly during radiotherapy. SUV decreased clearly in 12/14 patients, and increased in 2 patients. TMR decreased in 11 patients, and increased in 3 patients. Prior to radiotherapy, three different shapes of kinetic curve types indicative for the degree of hypoxia could be defined in 12/14 patients: (1) accumulation type (severe hypoxia (n=8)), (2) intermediate type (intermediate degree of hypoxia (n=3)), and (3) wash-out type (low degree of hypoxia (n=1)). Curve type changed towards a lower degree of hypoxia at 30Gy in all but 3 patients. In three patients curve type remained unchanged. CONCLUSIONS: The changes in tumor FMISO-uptake during radiotherapy indicate radio-induced reoxygenation.

Synthetic approaches and bio-distribution studies of [11C]methyl-phenidate.

PURPOSE: The purpose of this study was a) to present a facilitated method for the preparation and workup of [11C]d-threo-methylphenidate ([11C]d-threo-MP) (a ligand that was shown to bind selectively to the presynaptic dopaminergic transporters) from [11C]methyliodide ([11C]CH3I), b) to demonstrate that the ligand can as well be produced by an alternative labeling method employing [11C]diazomethane as the labeling agent and c) to present biodistribution data for this tracer obtained in rats. METHODS: 11C-labeling with [11C]CH3I was performed using either [d-threo-1-(2-nitrophenylsulfanyl)piperidin-2-yl]phenyl-acetic acid (d-threo-N-NPS-ritalinic acid) under addition of sodium hydroxide as base or the previously prepared sodium salt of d-threo-N-NPS-ritalinic acid. The two approaches were compared with regard to radiochemical yield and purification procedures needed in order to obtain a sufficiently pure tracer solution for human use. For the alternative reaction pathway using [11C]diazo-methane as the labeling agent the reaction was performed with d-threo-N-NPS-ritalinic acid. The biodistribution of [11C]d-threo-MP was determined in rats at 5, 10 and 30 min post injection of the tracer. RESULTS: The application of the sodium salt of d-threo-N-NPS-ritalinic acid as precursor resulted in higher radiochemical yields than the use of the free acid under basic conditions, the yields were 20 +/- 8% and 6 +/- 3%, respectively for the final isolated product (based on [11C]CH3I starting activity). The alternative labeling approach by means of [11C]diazomethane as the labeling agent was demonstrated to give radiochemical yields of 76 +/- 8% (based on [11C]diazomethane starting activity, determined by HPLC analysis of the crude reaction mixture before final work-up) within shorter process times. Based on [11C]methane starting activity both approaches result in similar yields (17% and 15%, respectively) Biodistribution studies in rats revealed a low blood activity (0.09% injected dose/g (% ID/g)) at 5 min post injection (p.i.), as well as a relatively high liver uptake (15.9% ID at 30 min) compared to a lower kidney uptake (3.2% ID at 30 min). Brain uptake was 0.9% ID/g already 5 and 10 min p.i.. CONCLUSIONS: The application of the sodium salt of d-threo-N-NPS-ritalinic acid as precursor for the radiosynthesis of [11C]d-threo-MP reduces the amount of [11C]methanol formed from the reaction of [11C]CH3I with sodium hydroxide, that is added to generate the carboxylic anion of d-threo-N-NPS-ritalinic acid needed for labeling with [11C]CH3I. The purification process could be simplified (omission of one solid phase extraction step), resulting in an easily automated process for the production of the tracer. The preparation of [11C]d-threo-MP by means of [11C]diazomethane as the labeling agent appears to be an interesting alternative to the [11C]CH3I methods because of shorter overall process times and high labeling yields. Biodistribution data show a rapid extraction of the tracer from the blood pool. Tracer excretion seems to take place predominantly via the hepatic pathway since liver uptake at 30 min was considerably higher than kidney uptake. [11C]d-threo-MP exhibits a rapid and sufficiently high brain uptake in rats.

Decarbonylation of multi-substituted [18F]benzaldehydes for modelling syntheses of 18F-labelled aromatic amino acids.

For 18F-labelling of aromatic amino acids such as tyrosine and DOPA simple and efficient procedures have been under development for quite a while. The direct introduction of 18F using [18F]fluoride can principally be realized by nucleophilic aromatic substitution (SNAr). However, this requires the presence of an appropriate leaving group and an auxiliary substituent, which is able to reduce the electron density of the benzene ring. Furthermore, this auxiliary substituent should be removable easily after the introduction of 18F. The electron-withdrawing formyl substituent meets both requirements. It facilitates nucleophilic attack in the ortho and/or para position and is easily removed in a decarbonylation reaction mediated by Wilkinson's catalyst (RhCl(PPh3)3). In order to evaluate the reaction conditions for a possible synthesis of 2-[18F]fluoro-5-hydroxyphenylalanine ([18F]-m-tyrosine), 2-[18F]fluoro-4-hydroxyphenylalanine ([18F]-p-tyrosine) or 2-[18F]fluoro-4,5-hydroxyphenylalanine ([18F]FDOPA), the dependence of the decarbonylation reaction on solvent, temperature, reaction time and catalyst concentration was studied using appropriate model compounds. Optimum yields of 81%, 89% and 88% could be achieved using benzonitrile as solvent and 2M equivalents of RhCl(PPh3)3 (based on labelling precursor) at 150 degrees C reaction temperature within 20 min reaction time for compounds modelling [18F]-m-tyrosine, [18F]-p-tyrosine and [18F]FDOPA, respectively.

Correlation of stable elevations in striatal mu-opioid receptor availability in detoxified alcoholic patients with alcohol craving: a positron emission tomography study using carbon 11-labeled carfentanil.

BACKGROUND: The pleasant effects of food and alcohol intake are partially mediated by mu-opiate receptors in the ventral striatum, a central area of the brain reward system. Blockade of mu-opiate receptors with naltrexone reduces the relapse risk among some but not all alcoholic individuals. OBJECTIVE: To test the hypothesis that alcohol craving is pronounced among alcoholic individuals with a high availability of mu-opiate receptors in the brain reward system. DESIGN: Patients and comparison sample. The availability of central mu-opiate receptors was measured in vivo with positron emission tomography (PET) and the radioligand carbon 11-labeled carfentanil in the ventral striatum and compared with the severity of alcohol craving as assessed by the Obsessive Compulsive Drinking Scale (OCDS). SETTING: Hospitalized care. PARTICIPANTS: Volunteer sample of 25 male alcohol-dependent inpatients assessed after detoxification of whom 12 underwent PET again 5 weeks later. Control group of 10 healthy men. MAIN OUTCOME MEASURES: After 1 to 3 weeks of abstinence, the availability of mu-opiate receptors in the ventral striatum, including the nucleus accumbens, was significantly elevated in alcoholic patients compared with healthy controls and remained elevated when 12 alcoholic patients had these levels measured 5 weeks later (P<.05 corrected for multiple testing). Higher availability of mu-opiate receptors in this brain area correlated significantly with the intensity of alcohol craving as assessed by the OCDS. CONCLUSIONS: Abstinent alcoholic patients displayed an increase in mu-opiate receptors in the ventral striatum, including the nucleus accumbens, which correlated with the severity of alcohol craving. These findings point to a neuronal correlate of alcohol urges.

Hypoxia-specific tumor imaging with 18F-fluoroazomycin arabinoside.

UNLABELLED: The study was performed to compare the (18)F-labeled nitroimidazole compound fluoroazomycin arabinoside ((18)F-FAZA) with the standard hypoxia tracer fluoromisonidazole ((18)F-FMISO) in detection of tumor tissue hypoxia and to verify the oxygenation dependency of (18)F-FAZA uptake. METHODS: Biodistribution of (18)F-FAZA was studied at various time points in EMT6 tumor-bearing BALB/c mice and in AR42J and A431 tumor-bearing nude mice and compared with that of (18)F-FMISO. The presence of tumor tissue hypoxia was verified in 5 EMT6 and 5 AR42J tumors using an oxygen-sensing needle electrode system. To evaluate the oxygenation dependency of (18)F-FAZA uptake, using the Munich prototype animal PET scanner, 2 serial PET scans were performed in 13 A431 tumor-bearing nude mice breathing pure oxygen or room air on 1 d and then selecting the other oxygen breathing condition on the following day. In addition, digital autoradiography was performed with EMT6 tumor-bearing (18)F-FAZA-dosed, nude mice breathing either room air (n = 8) or carbogen (n = 9). RESULTS: Tissue partial pressure of oxygen (Po(2)) electrode measurements revealed that tumor hypoxia was present under room air breathing in EMT6 (tissue Po(2) = 2.9 +/- 2.6) and AR42J tumors (tissue Po(2) = 0.4 +/- 0.2), which was significantly lower compared with that of reference tissue (tissue Po(2) = 25.8 +/- 6.7 and tissue Po(2) = 29.0 +/- 3.0 [mean +/- SD], respectively; P < 0.01). In all tumor models, (18)F-FAZA displayed significantly higher tumor-to-muscle and tumor-to-blood ratios compared with (18)F-FMISO, indicating a faster clearance of (18)F-FAZA from normal tissues. In AR42J tumors, (18)F-FAZA tumor-to-normal ratios were found to increase over time. Serial animal (18)F-FAZA PET studies showed that the tumor-to-background ratio was significantly higher in animals breathing room air compared with that of animals breathing pure oxygen (7.3 +/- 2.3 vs. 4.2 +/- 1.2, respectively; P < 0.001). Similarly, autoradiography showed significantly higher tumor-to-muscle ratios in mice breathing room air compared with those of animals breathing carbogen (5.3 +/- 0.8 vs. 2.2 +/- 0.8; respectively; P < 0.02). CONCLUSION: (18)F-FAZA shows superior biokinetics and is, thus, a promising PET tracer for the visualization of tumor hypoxia. This study also verified a hypoxia-specific uptake mechanism for (18)F-FAZA in murine tumor models.

A priori identifiability of a one-compartment model with two input functions for liver blood flow measurements.

An extended dual-input Kety-Schmidt model can be applied to positron emission tomography data for the quantification of local arterial (f(a)) and local portal-venous blood flow (f(p)) in the liver by freely diffusible tracers (e.g., [15O]H2O). We investigated the a priori identifiability of the three-parameter model (f(a), f(p) and distribution volume (Vd)) under ideal (noise-free) conditions. The results indicate that the full identifiability of the model depends on the form of the portal-venous input function (c(p)(t)), which is assumed to be a sum of m exponentials convolved with the arterial input function (c(a)(t)). When m>or=2, all three-model parameters are uniquely identifiable. For m=1 identifiability of f(p) fails if c(p)(t) coincides with tissue concentration (q(t)/Vd), which occurs if c(p)(t) is generated from an intestinal compartment with transit time Vd/f(a). Any portal input, f(p) c(p)(t), is balanced by the portal contribution, f(p) q(t)/Vd, to the liver efflux, leaving q(t) unchanged by f(p) and only f(a) and Vd are a priori uniquely identifiable. An extension to this condition of unidentifiability is obtained if we leave the assumption of a generating intestinal compartment system and allow for an arbitrary proportionality constant between c(p)(t) and q(t). In this case, only f(a) remains a priori uniquely identifiable. These findings provide important insights into the behaviour and identifiability of the model applied to the unique liver environment.

Increased sensitivity in detection of a porcine high-turnover osteopenia after total gastrectomy by dynamic 18F-fluoride ion PET and quantitative CT.

UNLABELLED: High-resolution (18)F-fluoride ion PET in combination with quantitative CT (QCT) allows the assessment of bone metabolism in relation to bone mass. This combined imaging approach was used to elucidate porcine bone metabolic changes after gastrectomy, which are frequently associated with osteopenia or osteomalacia. METHODS: Six months after total gastrectomy (n = 7) or sham operation (n = 6), bone blood flow and bone metabolic activity (K(i), K(flux)) were calculated from dynamic PET measurements from vertebral bodies and compared with corresponding QCT bone mineral density (BMD) measurements. RESULTS: Total gastrectomy resulted in a significant reduction of the BMD (-21%; P < 0.005), whereas 1,25-(OH)(2)-vitamin D, serum phosphate, and parathyroid hormone were significantly increased compared with that of sham-operated animals. Because of the significant increase of the rate constant k(3) (+325%; P < 0.05), describing chemisorption and incorporation of (18)F-fluoride onto or into the bone matrix, K(i) (+36%) and K(flux) (+37%) were significantly elevated after total gastrectomy compared with that of control animals (P < 0.01), whereas bone blood flow was not significantly different between groups. The normalization of K(i) and K(flux) values by the specific bone mass (K(i/BMD); K(flux/BMD)) largely increased the differences between groups (K(i/BMD), +74%; K(flux), +76%; P < 0.001). CONCLUSION: Dynamic (18)F-fluoride ion PET revealed that porcine bone loss after total gastrectomy is related to a high-turnover bone disease without significant changes in bone blood flow. In mini pigs, the increased bone metabolism is probably related to an elevated parathyroid hormone secretion, thus maintaining serum calcium homeostasis at the expense of the bone mineral content. Normalizing bone metabolic activity by the specific bone mass increases the sensitivity in the detection of osteopenic high-turnover bone diseases. Therefore, the combination of QCT and (18)F-fluoride ion PET seems to be the method of choice for the classification of metabolic bone diseases and for monitoring treatment effects quantitatively.

Molecular modeling of potential new and selective PET radiotracers for the serotonin transporter. Positron Emission Tomography.

PURPOSE: Imaging the serotonin transporter (SERT) with Positron Emission Tomography (PET) provides a useful tool for understanding alterations of the serotonergic system. However, no optimal PET radiotracer for the SERT yet exists. The main purpose of this study was to design potential new and selective PET radiotracers for the SERT and to predict their binding affinity at both the SERT and the norepinephrine transporter. METHODS: Molecular Modeling was used for ligand design. Predictions of binding affinity were based on models generated by Comparative Molecular Field Analysis (CoMFA) and Comparative Molecular Similarity Indices Analysis (CoMSIA). RESULTS: A series of 100 compounds were suggested. As diphenyl sulfide derivatives like [(11)C] DASB have recently proven to be promising PET ligands, rational modification of the diphenyl sulfide scaffold has been performed. The novel compounds were predicted to be selective high affinity SERT ligands. Important new ideas are the introduction of a fluoroethyl-oxycarbonyl group (ester) and a fluorethyl-carbonyl group (ketone), as well as a formyl group (aldehyde), and its corresponding oxime and imine. Another innovative suggestion is the replacement of the sulfur bridge with a cyanamide group and a fluoroethylamino group. CONCLUSIONS: The suggested compounds possess features providing new possibilities for carbon-11 or fluorine-18 labeling. Synthesis, biological testing, and screening for PET suitability are reasonable further steps.

Synthesis, Radiolabelling and In Vitro Characterization of the Gallium-68-, Yttrium-90- and Lutetium-177-Labelled PSMA Ligand, CHX-A''-DTPA-DUPA-Pep.

Since prostate-specific membrane antigen (PSMA) has been identified as a diagnostic target for prostate cancer, many urea-based small PSMA-targeting molecules were developed. First, the clinical application of these Ga-68 labelled compounds in positron emission tomography (PET) showed their diagnostic potential. Besides, the therapy of prostate cancer is a demanding field, and the use of radiometals with PSMA bearing ligands is a valid approach. In this work, we describe the synthesis of a new PSMA ligand, CHX-A''-DTPA-DUPA-Pep, the subsequent labelling with Ga-68, Lu-177 and Y-90 and the first in vitro characterization. In cell investigations with PSMA-positive LNCaP C4-2 cells, KD values of ≤14.67 ± 1.95 nM were determined, indicating high biological activities towards PSMA. Radiosyntheses with Ga-68, Lu-177 and Y-90 were developed under mild reaction conditions (room temperature, moderate pH of 5.5 and 7.4, respectively) and resulted in nearly quantitative radiochemical yields within 5 min.

PET and MRI reveal early evidence of neurodegeneration in spinocerebellar ataxia type 17.

UNLABELLED: Spinocerebellar ataxia type 17 (SCA17) is a rare autosomal dominantly inherited neurodegenerative disorder presenting with a variable phenotype including ataxia, dystonia, chorea, and parkinsonism, as well as cognitive impairment. We evaluated morphologic and functional imaging characteristics to elucidate evidence of neurodegeneration in SCA17, even in the presymptomatic stage of the disease. METHODS: Nine individuals of 3 large SCA17 pedigrees, including 4 presymptomatic mutation carriers, underwent cranial 3-dimensional MRI volumetry, as well as multitracer PET with (18)F-FDG, (11)C-d-threo-methylphenidate, and (11)C-raclopride. Healthy subjects showing no signs of a neurologic or psychiatric disease served as controls. RESULTS: MRI volumetry revealed atrophy of the cerebellum and caudate nucleus in manifesting patients (P = 0.04 and 0.05, respectively) and in presymptomatic mutation carriers (P = 0.04 and 0.01, respectively). PET demonstrated decreased glucose metabolism in the striatum, as well as in the cuneus, cingulum, and parietal lobe, in all SCA17 patients and presymptomatic mutation carriers. In addition, PET was closely correlated with motor performance as assessed by the Scale for the Assessment and Rating of Ataxia (P = 0.037) and Unified Parkinson Disease Rating Scale (P = 0.05) and with cognitive function as assessed by the Mini-Mental Status Examination (P = 0.037). Furthermore, (11)C-raclopride PET showed impairment of the postsynaptic dopaminergic compartment of the putamen and caudate nucleus not only in manifest SCA17 patients (P = 0.04 and 0.008, respectively) but also in yet-unaffected mutation carriers (P = 0.05 and 0.05, respectively). The degree of postsynaptic dopaminergic dysfunction was associated with impairment of motor performance. In contrast, significant presynaptic dopaminergic deficits assessed with (11)C-d-threo-methylphenidate PET were not detected. CONCLUSION: MRI volumetry, as well as (11)C-raclopride and (18)F-FDG PET, reveal neuronal dysfunction and neurodegeneration even in the presymptomatic stage and may serve as markers for disease activity in upcoming interventional trials on SCA17.

Radiosynthesis of a new PSMA targeting ligand ([18F]FPy-DUPA-Pep).

Due to the specificity of expression of PSMA (prostate specific membrane antigen) particularly in prostate cancer cells (e.g. LNCaP), numerous PSMA ligands have been synthesized until now. In the current study, we synthesized DUPA-Pep having 2-[3-(1,3-dicarboxypropyl)ureido]pentanedioic acid (DUPA) linked via 8-aminooctanoic acid to two phenylalanine residues and chose 6-[(18)F]fluoronicotinic acid 2,3,5,6-tetrafluorophenyl ester [(18)F]FPy-TFP as a prosthetic group for coupling. [(18)F]FPy-DUPA-Pep was obtained in a radiochemical yield of 48±0.9% (decay uncorrected) within 50 min with a chemical purity of >98%.

Significant impact of different oxygen breathing conditions on noninvasive in vivo tumor-hypoxia imaging using [¹8F]-fluoro-azomycinarabino-furanoside ([¹8F]FAZA).

BACKGROUND: [18F]FAZA is a PET biomarker with great potential for imaging tumor hypoxia. Aim of our study was to compare [18F]FAZA uptake in mice with subcutaneous exogenous CT26 colon carcinomas and endogenous polyoma middle-T (PyV-mT) mammary carcinomas and to analyze the influence of different breathing protocols in CT26 colon carcinomas as well as the reversibility or irreversibility of [18F]FAZA uptake. METHODS: We injected subcutaneous CT26 colon carcinoma or polyomavirus middle-T (PyV-mT) mammary carcinoma-bearing mice intravenously with18F-FAZA and performed PET scans 1-3 h post injection (p.i.). To analyze the impact of oxygen supply in CT26 carcinomas we used three different breathing protocols: (P0) air; (P1) 100% oxygen 1 h prior injection until 3 h p.i.; (P2) 100% oxygen breathing starting 2 min prior tracer injection until 1 h p.i. and during the PET scans; mice were breathing air between the 2 h and 3 h 10 min static scans. Normalized PET images were analyzed by using defined regions of interest. Finally, some mice were dissected for pimonidazole immunohistochemistry. RESULTS: There was no difference in18F-FAZA uptake 1-3 h p.i. between the two carcinoma types (CT26: 1.58 ± 0.45%ID/cc; PyV-mT: 1.47 ± 0.89%ID/cc, 1 h p.i., tumor size < 0.5 cm3). We measured a significant tracer clearance, which was more pronounced in muscle tissue (P0). The [18F]FAZA tumor-to-muscle-ratios in CT26 colon carcinoma-bearing mice 2 h and 3 h, but not 1 h p.i. were significantly higher when the mice breathed air (P0: 3.56 ± 0.55, 3 h) compared to the oxygen breathing protocols (P1: 2.45 ± 0.58; P2: 2.77 ± 0.42, 3 h). Surprisingly, the breathing protocols P1 and P2 showed no significant differences in T/M ratios, thus indicating that the crucial [18F]FAZA uptake phase is during the first hour after [18F]FAZA injection. Importantly, the muscle clearance was not affected by the different oxygen breathing conditions while the tumor clearance was lower when mice were breathing air. CONCLUSION: Exogenous CT26 colon carcinomas and endogenous polyoma middle-T (PyV-mT) mammary carcinomas showed no differences in [18F]FAZA uptake 1-3 h p.i. Our analysis using various breathing protocols with air (P0) and with pure oxygen (P1, P2) clearly indicate that [18F]FAZA is an appropriate PET biomarker for in vivo analysis of hypoxia revealing an enhanced tracer uptake in tumors with reduced oxygen supply. [18F]FAZA uptake was independent of tumor-type.

Assessment of PET tracer uptake in hormone-independent and hormone-dependent xenograft prostate cancer mouse models.

UNLABELLED: The pharmacokinetics of (18)F-fluorodeoxythymidine (FLT), (18)F-FDG, (11)C-choline, and (18)F-fluoroethylcholine (FEC) in 2 hormone-independent (PC-3, DU145) and 2 hormone-dependent (CWR22, PAC120) prostate cancer xenograft mouse models were evaluated by PET and compared by immunohistochemistry. Further investigation was performed to determine whether PET can detect early changes in tumor metabolism after androgen ablation therapy through surgical castration. METHODS: PET was performed on 4 consecutive days. In addition, the CWR22 and PAC120 tumor models were surgically castrated after the baseline measurement and imaged again after castration. The tracer uptake was analyzed using time-activity curves, percentage injected dose per volume (%ID/cm(3)), and tumor-to-muscle ratio (T/M). RESULTS: Regarding the hormone-independent prostate tumor models, (18)F-FLT showed the best T/M and highest %ID/cm(3) in PC-3 (2.97 ± 0.63 %ID/cm(3)) and DU145 (2.06 ± 0.75 %ID/cm(3)) tumors. (18)F-FDG seemed to be the tracer of choice for delineation of the PC-3 tumors but not for the DU145 tumors. Using (11)C-choline (PC-3: 1.33 ± 0.29 %ID/cm(3), DU145: 1.60 ± 0.27 %ID/cm(3)) and (18)F-FEC, we did not find any significant uptake in the tumors, compared with muscle tissue. Regarding the hormone-dependent prostate tumor models, the CWR22 model showed a highly significant (P < 0.01) decrease in tumor (18)F-FDG uptake from 4.11 ± 1.29 %ID/cm(3) to 2.19 ± 1.45 %ID/cm(3) after androgen ablation therapy. However, the (18)F-FLT, (11)C-choline, or (18)F-FEC tracers did not provide sufficient uptake or reliable information about therapy response in CWR22 tumors. The PAC120 model showed a significant increase in (18)F-FLT tumor uptake (P = 0.015) after androgen ablation therapy. The accumulation of (18)F-FEC (before: 2.32 ± 1.01 %ID/cm(3), after: 1.36 ± 0.39 %ID/cm(3)) was found to be the next highest after (18)F-FDG (before: 2.45 ± 0.93 %ID/cm(3), after: 2.18 ± 0.65 %ID/cm(3)) in PAC120 tumors before castration and is better suited for monitoring therapy response. CONCLUSION: This comprehensive study in 2 hormone-dependent and 2 hormone-independent prostate tumor mouse models shows that (18)F-FLT and (18)F-FDG are the most appropriate tracers for delineation of PC-3, DU145 (except (18)F-FDG), and CWR22 tumors, but not for PAC120 tumors. (18)F-FEC and (11)C-choline, in particular, revealed insufficient T/M ratio in the prostate tumor models. The results may indicate that radiolabeled choline and choline derivatives compete with a high concentration of the precursor dimethylaminoethanol, resulting in reduced uptake in small-rodent tumor models, a hypothesis that is currently under investigation in our laboratory.