Imaging proliferation in vivo with [F-18]FLT and positron emission tomography.

Positron emission tomography (PET) is now regularly used in the diagnosis and staging of cancer. These uses and its ability to monitor treatment response would be aided by the development of imaging agents that can be used to measure tissue and tumor proliferation. We have developed and tested [F-18]FLT (3'-deoxy-3'-fluorothymidine); it is resistant to degradation, is retained in proliferating tissues by the action of thymidine kinase 1 (TK), and produces high-contrast images of normal marrow and tumors in canine and human subjects.

Anxiety is associated with reduced central serotonin transporter availability in unmedicated patients with unipolar major depression: a [11C]DASB PET study.

Serotonergic dysfunction may contribute to negative mood states in affective disorders. Some in vivo imaging studies showed reduced availability of serotonin transporters (5-HTT) in the brainstem and thalamus of patients with major depression. We tested the hypothesis that 5-HTT availability is reduced in unmedicated unipolar patients with major depression compared to healthy control subjects matched for gender, age, genotype and smoking status. Availability of 5-HTT was measured in vivo with positron emission tomography and [(11)C]-3-amino-4-(2-dimethylaminomethyl-phenylsulfanyl)-benzonitrile (DASB) in the midbrain, thalamus and amygdala. DASB binding was correlated with the severity of depression (Beck's Depression Inventory), anxiety (Spielberger's State-Trait Anxiety Inventory) and personality traits (Temperament and Character Inventory). Patients with major depression displayed reduced 5-HTT availability in the thalamus (P=0.005). In patients, low serotonin transporter availability correlated with high anxiety (thalamus: r=-0.78, P=0.004; midbrain: r=-0.78, P=0.004; amygdala: r=-0.80, P=0.003). Correlations with severity of depression were weaker and did not survive correction for multiple testing. These results support the hypothesis that central serotonergic dysfunction is associated with negative mood states in affective disorders. In the thalamus, a low serotonin reuptake capacity may interfere with thalamic control of cortical excitability and contribute to anxiety rather than depression per se in major depression.

Occupancy of dopamine D(1), D (2) and serotonin (2A) receptors in schizophrenic patients treated with flupentixol in comparison with risperidone and haloperidol.

RATIONALE: Flupentixol (FLX) has been used as a neuroleptic for nearly 4 decades. In vitro data show comparable affinity to dopamine D(2), D(1) and 5-HT(2A) receptors and recently, FLX showed to be not inferior to risperidone in schizophrenic patients with predominant negative symptomatology, which was implicated with flupentixol's interaction with 5-HT(2A) and/or D(1) receptors. OBJECTIVES: To assess in vivo receptor occupancy (RO) in patients clinically treated with FLX (n = 13, 5.7 +/- 1.4 mg/day) in comparison with risperidone (RIS, n = 11, 3.6 +/- 1.3 mg/day) and haloperidol (HAL, n = 11, 8.5 +/- 5.5 mg/day). MATERIALS AND METHODS: Each patient underwent two PET scans with 3-N-[(11)C]methylspiperone (target: frontal 5-HT(2A)), [(11)C]SCH23390 (striatal D(1)) or [(11)C]raclopride (striatal D(2)). RO was calculated as the percentage reduction of specific binding in comparison with healthy controls. RESULTS: D(2)-RO under FLX was between 50% and 70%, indicating an ED(50) of about 0.7 ng/ml serum. 5-HT(2A) and D(1)-RO was 20 +/- 10% and 20 +/- 5% (mean, SEM). Under HAL, D(1)-RO was 14 +/- 6% and under RIS not significantly different from zero. CONCLUSIONS: We were able to demonstrate a moderate 5-HT(2A) and D(1) occupancy under clinically relevant doses of flupentixol, albeit lower than expected from in vitro data and clearly below saturation. Therefore, if flupentixol's efficacy on negative symptoms is based on its interaction with 5-HT(2A) and/or D(1) receptors, it should be highly dependent on serum concentration and thus on dosage and metabolism. However, these data suggest that mechanisms other than D(1) or 5-HT(2A) antagonism may contribute to flupentixol's efficacy on negative symptoms.

Production of [11C]chloroform by direct chlorination of [11C]methane without catalyst support for the synthesis of [11C]diazomethane.

The preparation of [11C]chloroform by direct chlorination of [11C]methane using gaseous chlorine by variation of temperature and reaction time (inert gas flow) without catalyst support for the online production of [11C]diazomethane in a flow-through synthesis apparatus is described in this work. At an oven temperature of 400 degrees C and a He flow of 50 mL/min, [11C]chloroform was synthesized inside a quartz glass column in a radiochemical yield of 31+/-2% with respect to [11C]methane. The online preparation of [11C]diazomethane by reaction of [11C]chloroform with hydrazine in an ethanolic KOH solution with small amounts of 18-crown-6-crownether succeeded with a radiochemical yield of 20+/-3% with respect to [11C]methane. The product [11C]diazomethane was measured indirectly in the form of 4-nitrobenzoic acid[11C]methylester using the esterification of 4-nitrobenzoic acid as a monitor reaction.

Synthesis, physicochemical characterization and preliminary pharmacological in vitro evaluation of two novel cytotoxic benzophenone-linked 3,3-dimethyltriazenes.

The synthesis, physicochemical characterization and preliminary pharmacological evaluation of the cytotoxic effects of two novel substances, 1-(4-benzoylphenyl)-3,3-dimethyltriazene and 1-(2-benzoylphenyl)-3,3-dimethyltriazene is presented. The cytotoxicity of the novel benzophenone-linked triazenes and of ten other 1-phenyl-3,3-dimethyl triazene derivatives as well as of the referent alkylating drug melphalan was assessed using the MTT-dye reduction assay. A panel of human tumor cell lines was used: the chronic lymphoid leukemia SKW-3, the acute promyelocyte leukemia HL-60 and its multi-drug-resistant subline HL-60/Dox. Both novel compounds showed strong cytotoxic activity, comparable to that of the referent alkylating agent melphalan, whereas the ten ring-substituted 1-phenyl-3,3-dimethyl triazenes proved to be far less active in vitro. DNA-fragmentation analysis indicated that after 24 h treatment the novel benzophenone-linked triazenes induced programmed cell death in HL-60 cells.

Efficient radiosynthesis of carbon-11 labelled uncharged Thioflavin T derivatives using [11C]methyl triflate for beta-amyloid imaging in Alzheimer's Disease with PET.

The synthesis of carbon-11 amino function labelled uncharged Thioflavin T derivatives is known to be performed by reaction of the demethyl-precursors with [11C]methyl iodide but the labelling yields are only mediocre. The use of [11C]methyl triflate improved the radiochemical yield of three potential beta-amyloid imaging PET-radiotracers significantly. Performance of the labelling reaction by reacting the corresponding precursor molecules with [11C]methyl triflate for 1 min at 80 degrees C led to radiochemical yields of 44+/-10% (n=5) for [11C]6-Me-BTA-1, 68+/-4% (n=10) for [11C]BTA-1 and 58+/-2% (n=5) for [11C]6-OH-BTA-1 with respect to [11C]methyl triflate. In production runs (60 min, 50 microA) up to 6500 MBq (mean: 4000+/-1900 MBq) of [11C]6-Me-BTA-1, 7900 MBq (mean: 6000+/-1000 MBq) of [11C]BTA-1 and 7100 MBq (mean: 6300+/-600 MBq) of [11C]6-OH-BTA-1 could be obtained ready for intravenous injection. The radiochemical purity was >95% with specific activities in the range of 80-120 GBq/micromol (EOS) within a total synthesis time of less than 40 min after EOB.

Preparation of the hypoxia imaging PET tracer [18F]FAZA: reaction parameters and automation.

18F-labeling of the nitroimidazole nucleoside analogue 1-(5-fluoro-5-deoxy-alpha-D-arabinofuranosyl)-2-nitroimidazole (FAZA) was developed to use this tracer in PET for detection of hypoxia. Parameters for labeling and hydrolysis were optimized with regard to amount of precursor, temperature and time. Labeling yields reached a maximum of 62+/-4% at 100 degrees C within 5 min using 5 mg of precursor. Hydrolysis was best performed with 1 mL of 0.1 N NaOH at 20 degrees C for 2 min. Transfer of these conditions to an automated synthesizer resulted in an overall radiochemical yield of 20.7+/-3.5%. Absolute yields at EOS were 9.8+/-2.3 GBq of [18F]FAZA ready for injection (n=21; 50 min after EOB; irradiation parameters: 35 microA, 60 min). Thus, a convenient approach suitable for large-scale production of [18F]FAZA was developed by an automated process.

Blood flow measurements with [(15)O]H2O and [18F]fluoride ion PET in porcine vertebrae.

A dual positron emission tomography (PET) tracer study with [18F]fluoride and the freely diffusible tracer [(15)O]H2O was performed to measure the capillary transport of [18F]fluoride and to evaluate the potential of [18F]fluoride ion PET to quantitate bone blood flow. Under the condition of a high predictable single-pass extraction fraction (E(F)) for [18F]fluoride, the [18F]fluoride ion influx transport constant (K1F), derived from kinetic [18F]fluoride ion PET measurements, can be used to estimate bone blood flow. Bone blood flow was measured in vertebral bodies by dynamic [(15)O]H2O PET during continuous ventilation with N2O, O2, and Isoflurane (FiO2 = 0.3) in seven adult mini pigs, followed by dynamic [18F]fluoride ion PET. The mean blood flow measured by [(15)O]H2O (FlowH2O) was 0.145 +/- 0.047 ml x minute(-1) x ml(-1) and the mean K1F was 0.118 +/- 0.031 ml x minute(-1) x ml(-1), respectively (mean +/- SD). Regional analysis showed excellent agreement between FlowH2O and K1F at low flow and a significant underestimation of flow by K1F relative to FlowH2O in regions of normal and elevated flow. The observed relationship between parameters followed the Renkin-Crone distribution. The permeability-surface product was determined as 0.25 minute(-1) for vertebral bodies consisting of a mixture of trabecular and cortical bone. We conclude that [18F]fluoride ion PET can be used to estimate bone blood flow in low and normal flow regions, as long as the flow dependency of the E(F) is taken into consideration. Above blood flow values of 0.2 to 0.35 ml x minute(-1) x ml(-1), the magnitude of K1F is increasingly independent on blood flow because diffusion limits tracer transport.

15(p-[123I]Iodophenyl)pentadecanoic acid as tracer of lipid metabolism: comparison with [1-14C]palmitic acid in murine tissues.

Uptake and turnover of 15-(p-[123I]iodophenyl)pentadecanoic acid (I-PPA), a radioiodinated free-fatty-acid analog, was examined in heart, lung, liver, kidneys, and spleen and compared with that of [1-14C]palmitic acid (PA). High cardiac uptake of both I-PPA (4.4% dose/g) and PA (2.8% dose/g) was followed by a two-component tracer clearance. Kinetics of I-PPA were linked to those of PA in tissues with primary oxidation of free fatty acids or their preferential storage. Tissue lipids of all organs investigated were labeled concordantly by both tracers. Fractional distributions of PA and I-PPA incorporation in tissue lipids were significantly correlated. Thus general pathways of FFA tissue metabolism are traced by this radioiodinated free-fatty-acid analog. High-quality metabolic imaging of the heart is possible by means of I-PPA with conventional scintigraphic equipment or cross-sectional imaging with single photon emission computerized tomography facilities.

Comparative evaluation of fatty acids labeled with C-11, Cl-34m, Br-77, and I-123 for metabolic studies of the myocardium: concise communication.

Various long-chain fatty acids have been labeled with C-11, Cl-34m, Br-77, and I-123 and evaluated for their potential application in measuring myocardial metabolism in vivo. Comparative studies of the kinetics of accumulation and clearance from the heart muscle of mice indicate that the extraction of omega-halofatty acids is more efficient than that of alpha-halofatty acids. Among the omega-halofatty acids, the highest uptake is observed for the 17-iodoheptadecanoic acid, which shows an extraction behavior almost identical to that of [1-11C] palmitic acid, although with a higher radioactivity level in blood due to the release of free iodide.

Myocardial imaging and metabolic studies with [17-123I]iodoheptadecanoic acid.

After intravenous administration of the stearic acid analogue [17-123I]iodoheptadecanoic acid (I-123 HA), myocardial metabolism was studied in ten normal individuals, eight patients with coronary artery disease and three patients with congestive heart failure. High-quality images were obtained in sequential scintigraphy of I-123 metabolically bound in myocardial tissue. Infarcted zones as well as ischemic regions are indicated by reduced tracer uptake. Iodine-123 in the blood pool and interstitial space consists mainly of radioiodide that is liberated by fatty-acid metabolism and was corrected for. Using the proposed correction not only are the images improved but the uptake and elimination of the I-123 in the myocardial cells can be followed. The average disappearance half-time of I-123 HA from the myocardium of normal persons was 24 +/- 4.7 min. In patients with coronary artery disease significant differences between myocardial regions were observed.

Tracer kinetics of 15-(ortho-123/131I-phenyl)-pentadecanoic acid (oPPA) and 15-(para-123/131I-phenyl)-pentadecanoic acid (pPPA) in animals and man.

The human myocardium retains oPPA as opposed to pPPA. Therefore turnover of oPPA was compared with that of pPPA in rat hearts and in man, the latter by using substrates double-labeled with 123/131I and 14C. Moreover, substrate binding to coenzyme-A was tested in vitro. In rats, oPPA remained mainly in the pool of free fatty acids, as opposed to pPPA, which was metabolized by mitochondrial beta-oxidation. Binding to coenzyme-A at maximum was 62% for oPPA, 81% for pPPA and 90% for palmitic acid. In man, after i.v. and intracoronary injection of double-labeled oPPA, the two radionuclides reappeared together in venous blood and in coronary sinus respectively, in an unchanged ratio but at a significantly lower rate than with pPPA. It can be concluded that oPPA is bound to coenzyme-A and is retained in the cytosolic lipid pool, while pPPA is metabolized by mitochondrial beta-oxidation. A dual-tracer application of oPPA and pPPA has the potential of being a specific probe for the function of the carnitine shuttle.

Assessment of porcine bone metabolism by dynamic.

UNLABELLED: The aim of this study was to quantify regional bone blood flow and [(18)F]fluoride ion influx with [(18)F]fluoride ion PET and correlate the results with specific static and dynamic indices of bone metabolism in healthy pigs. METHODS: During continuous ventilation (fractional concentration of oxygen in inspired gas = 0.3), dynamic PET scans 120 min in duration were obtained for 9 mini pigs after intravenous injection of 10.0 +/- 1.2 MBq (mean +/- SD) of [(18)F]fluoride ion per kilogram of body weight. Iliac crest bone biopsies were performed immediately before the PET scan to determine static and dynamic indices of bone metabolism (i.e., the mineral apposition rate) by bone histomorphometry. Kinetic rate constants describing influx (K(1)) and efflux (k(2)) of [(18)F]fluoride as well as chemisorption and incorporation of [(18)F]fluoride (k(3)) and reverse transport (k(4)) were determined for 6 vertebral bodies in each animal. Blood flow estimates (f) were derived from K(1) values corrected for the permeability-surface area product using a previously derived correction algorithm. A rate constant describing the net forward transport rate of fluoride (K(i)) and the fluoride volume flux (K(flux)) derived from a 2-tissue-compartment model was calculated and compared with the results of Patlak graphic analysis (K(pat)). RESULTS: A significant correlation was found between mineral apposition rate and K(i) (P < 0.005), K(flux) (P < 0.01), K(pat), K(1), and f (P < 0.05). The values of f, K(i), K(flux), and K(pat) did not correlate significantly with other static or dynamic histomorphometric indices or with age, serum alkaline phosphatase, or parathyroid hormone levels. The values of f and K(i) correlated linearly (y = 0.023 + 0.32x; r(2) = 0.74; P < 0.001). CONCLUSION: PET bone studies using [(18)F]fluoride ion provide quantitative estimates of bone blood flow and metabolic activity that correlate with histomorphometric indices of bone formation in the normal bone tissue of the mini pig. Therefore, it seem reasonable to assume that [(18)F]fluoride ion PET can reduce the number of invasive bone biopsies, thus facilitating follow-up of patients with metabolic bone diseases.

Dependency of the [18F]fluoromisonidazole uptake on oxygen delivery and tissue oxygenation in the porcine liver.

We have previously shown that the accumulation of fluorine-18-labeled fluoromisonidazole ([(18)F]FMISO) is inversely correlated to tissue oxygenation, allowing the quantification of porcine liver tissue hypoxia in vivo. We determined the activity from administered [(18)F]FMISO in relation to the hepatic oxygen availability and the partial pressure of oxygen in tissue (tPO(2)) to define a critical oxygen delivery on a regional basis. [(18)F]FMISO was injected 2 h after onset of regional liver hypoxia due to arterial occlusion of branches of the hepatic artery in 10 domestic pigs. During the experimental procedure the fractional concentration of inspired oxygen (FiO(2)) was set to 0.67 in group A ( N=5) and to 0.21 in group B ( N=5) animals. Immediately before sacrifice, the tPO(2) was determined in normal flow and flow-impaired liver segments. The standardized uptake values (SUV) for [(18)F]FMISO was calculated from 659 single tissue samples obtained 3 h after injection of approximately 10 MBq/kg body weight [(18)F]FMISO and was compared with the regional total hepatic oxygen delivery (DO(2)) calculated from the regional arterial and portal venous flow (based on (141)Ce- and (99m)Tc-microspheres measurements) and the oxygen content of the arterial and portal venous blood. In 121 tPO(2)-measured liver tissue samples, the mean DO(2) was significantly decreased in occluded liver tissue samples [group A: 0.063 (0.044-0.089); group B: 0.046 (0.032-0.066)] compared to normal flow segments [group A: 0.177 (0.124-0.252); group B: 0.179 (0.128-0.25) mL x min(-1) x g(-1); geometric mean (95% confidence limits); p < 0.01 in group A and p < 0.001 in group B]. The tPO(2) of occluded segments [group A: 5.1 (3.2-8.1); group B: 3.9 (2.4-6.2) mm Hg] was significantly decreased compared to normal flow segments [group A: 20.2 (12.6-32.5); group B: 22.4 (14.3-35.2) mm Hg; p < 0.01 in group A and p < 0.001 in group B]. Three hours after [(18)F]FMISO administration, the mean [(18)F]FMISO SUV determined in tPO(2)-measured occluded segments was significantly higher [group A: 4.08 (3.12-5.34), group B: 5.43 (4.14-7.13)] compared to normal liver tissue [group A: 1.57 (1.2-2.06), group B: 1.5 (1.16-1.93); p < 0.001 for both groups]. The [(18)F]FMISO SUV allowed prediction of the tPO(2) with satisfying accuracy in hypoxic regions using the exponential regression curve [[(18)F]FMISO=1.05+6.7((-0.117 tPO(2))); r(2)=0.75; p < 0.001]. In addition, regardless of ventilation conditions, a significant exponential relationship between the DO(2) and the [(18)F]FMISO SUV was found ( r(2)=0.39, p < 0.001). Our results suggest that the reduction of the oxygen delivery below the critical range of 0.1-0.11 mL x min(-1) x g(-1) regularly causes liver tissue hypoxia. The severity of hypoxia is reflected by the [(18)F]FMISO accumulation and allows the in vivo estimation of the tPO(2) in hypoxic regions.

Use of 3-fluoro-deoxyglucose for the assessment of cerebral perfusion and glucose transport. I. Theory.

A new model is described applying dynamic positron emission tomography (dPET) and 3-fluoro-deoxyglucose (3FDG) to the measurement of local cerebral perfusion and glucose transport across the blood-brain-barrier (BBB). The model takes advantage of 3FDG being practically not metabolized in brain and being transported back from tissue into the circulation. Simultaneous registration of tracer concentration in blood and tissue by dPET permits the in vivo determination of the Michaelis-Menten constant (K) and maximal velocity (V) for 3FDG and glucose transport across the BBB as well as the determination of local perfusion rate. Values obtained in normal cortex using this method were K = 6.3 mumol/g and V = 2.46 mumol/g min. Local perfusion rate ranged between 0.8 and 0.98 ml/min g.

Use of 3-fluoro-deoxyglucose for the assessment of cerebral perfusion and glucose transport. II. Evaluation of patients undergoing EC-IC bypass surgery.

Dynamic positron emission tomography (dPET) and 3-fluoro-deoxy-glucose (3FDG) have been applied to the followup of selected patients undergoing extracranial-intracranial (EC-IC) bypass surgery. To determine glucose transport across the blood-brain-barrier and local perfusion rate a new mathematical model has been used. Immediately following EC-IC surgery, dPET shows an increase in perfusion of approx. 7 ml/min 100g over both the operated and the contralateral hemispheres indicative of reversal of interhemispheric steal. Followup studies show reduction of local perfusion rate combined with an improvement of glucose transport rates. This finding suggests improvement of cerebral metabolic capacity following improvement of perfusion suggestive of longterm beneficial effects of EC-IC bypass.

On biologically conformal boost dose optimization.

A method is described that allows the inclusion of biological imaging data in the optimization of intensity-modulated radiotherapy to produce dose boosts that conform with target subvolumes of potentially reduced radiosensitivity. The biological image (e.g. PET, fMRI, etc) is transformed into a dose efficiency distribution using a piecewise linear calibration function with a prescribed maximum boost factor. Instead of dose alone, the cost function of the optimization algorithm depends on the product of the physical dose times dose efficiency. An example case of a base-of-tongue tumour which was imaged with the hypoxia tracer fluoro-misonidazole is presented, showing the excellent capability of IMRT to produce dose distributions that conform to spatially variable dose prescriptions.

Cardiac metabolism of 15 (p-I-123 phenyl-) pentadecanoic acid after intracoronary tracer application.

Myocardial turnover of omega-(p123I-Phenyl-) pentadecanoic acid and release of its metabolites into the coronary sinus and peripheral blood has been studied in patients with coronary artery and valvular heart disease. After intracoronary tracer injection myocardial extraction fractions of 45-53% in control subjects were observed. In patients with coronary artery disease (CAD) normal to reduced values (34-61%) were established. Hydrophilic catabolites of I-PPA, probably p123I-benzoic and -hippuric acid as well as small amounts of the non-metabolized tracer were found in coronary sinus and peripheral blood. Myocardial tracer uptake and clearance patterns were clearly different in normal myocardium when compared to that obtained in patients with CAD. Thus, evaluation of myocardial I-PPA metabolism might provide a new diagnostic tool for assessment of integrity of the heart's muscular metabolic function.

Recent developments in the field of 123I-radiopharmaceuticals.

Due to its advantageous nuclear physical properties iodine-123 is an excellent label for radiopharmaceuticals very well suited for measurements by gamma-cameras and single-photon emission tomography. The development of 123I-radiopharmaceuticals should be based on a clear biochemical concept, reliable labelling procedures and careful pharmacokinetic studies in order to evaluate the physiological behaviour of the radioiodinated compounds being analogues of metabolic substrates. The development of 123I-labelled fatty acids and biogenic amines clearly proved the successful use of 123I for labelling compounds applied in medical diagnosis.

Synthesis of, and animal experiments with, N-isopropyl-p-123I-iodo-amphetamine (IMP) and 18F-3-deoxy-3-fluoro-D-glucose (3-FDG) as tracers in brain and heart diagnostic studies.

For the investigation of brain functions 18F-3-deoxy-3-fluoro-D-glucose (3-FDG) and N-isopropyl-p-123I-iodo-amphetamine (IMP) were synthesized and the course of radioactivity measured in several organs of mice. The results can be summarized as follows: IMP is rapidly extracted from the blood and reaches a value of less than 1% g within the first 15 min; 123I-radioactivity in the lungs shows a maximum of 76%/g as soon as half a minute after injection and decreases with a concomitant increase in the liver and brain; The maximum 123I-uptake in the brain of 11%/g is reached after 30 min and levels off at a constant value of 10%/g; 30 min after injection the brain/blood ratio for IMP is about 14; The time course of 3-FDG in the brain has a maximum of 4.8%/g as soon as 5 min after injection and decreases to a constant value of 3%/g within 1 hr; and Accumulation of 18F- radioactivity in the heart reaches a maximum of 14%/g after 1 hr and is eliminated with a half-life of 300 min. Comparative clinical studies with 3-FDG and 3-0-11C-methyl-D-glucose (CMG) have shown that 3-FDG can be considered as a CMG-analogue and thus can be used for the in-vivo determination of local glucose perfusion and transport rates.