Imaging amyloid deposition in Lewy body diseases.

BACKGROUND: Extrapyramidal motor symptoms precede dementia in Parkinson disease (PDD) by many years, whereas dementia occurs early in dementia with Lewy bodies (DLB). Despite this clinical distinction, the neuropsychological and neuropathologic features of these conditions overlap. In addition to widespread distribution of Lewy bodies, both diseases have variable burdens of neuritic plaques and neurofibrillary tangles characteristic of Alzheimer disease (AD). OBJECTIVES: To determine whether amyloid deposition, as assessed by PET imaging with the beta-amyloid-binding compound Pittsburgh Compound B (PiB), can distinguish DLB from PDD, and to assess whether regional patterns of amyloid deposition correlate with specific motor or cognitive features. METHODS: Eight DLB, 7 PDD, 11 Parkinson disease (PD), 15 AD, and 37 normal control (NC) subjects underwent PiB-PET imaging and neuropsychological assessment. Amyloid burden was quantified using the PiB distribution volume ratio. RESULTS: Cortical amyloid burden was higher in the DLB group than in the PDD group, comparable to the AD group. Amyloid deposition in the PDD group was low, comparable to the PD and NC groups. Relative to global cortical retention, occipital PiB retention was lower in the AD group than in the other groups. For the DLB, PDD, and PD groups, amyloid deposition in the parietal (lateral and precuneus)/posterior cingulate region was related to visuospatial impairment. Striatal PiB retention in the DLB and PDD groups was associated with less impaired motor function. CONCLUSIONS: Global cortical amyloid burden is high in dementia with Lewy bodies (DLB) but low in Parkinson disease dementia. These data suggest that beta-amyloid may contribute selectively to the cognitive impairment of DLB and may contribute to the timing of dementia relative to the motor signs of parkinsonism.

Detection of inflamed atherosclerotic lesions with diadenosine-5',5'''-P1,P4-tetraphosphate (Ap4A) and positron-emission tomography.

Diadenosine-5',5'''-P(1),P(4)-tetraphosphate (Ap(4)A) and its analog P(2),P(3)-monochloromethylene diadenosine-5',5'''-P(1),P(4)-tetraphosphate (AppCHClppA) are competitive inhibitors of adenosine diphosphate-induced platelet aggregation, which plays a central role in arterial thrombosis and plaque formation. In this study, we evaluate the imaging capabilities of positron-emission tomography (PET) with P(2),P(3)-[(18)F]monofluoromethylene diadenosine-5',5'''-P(1),P(4)-tetraphosphate ([(18)F]AppCHFppA) to detect atherosclerotic lesions in male New Zealand White rabbits. Three to six months after balloon injury to the aorta, the rabbits were injected with [(18)F]AppCHFppA, and microPET imaging showed rapid accumulation of this radiopharmaceutical in the atherosclerotic abdominal aorta, with lesions clearly visible 30 min after injection. Computed tomographic images were coregistered with PET images to improve delineation of aortoiliac tracer activity. Plaque macrophage density, quantified by immunostaining with RAM11 against rabbit macrophages, correlated with PET measurements of [(18)F]AppCHFppA uptake (r = 0.87, P < 0.0001), whereas smooth-muscle cell density, quantified by immunostaining with 1A4 against smooth muscle actin, did not. Biodistribution studies of [(18)F]AppCHFppA in normal rats indicated typical adenosine dinucleotide behavior with insignificant myocardial uptake and fast kidney clearance. The accumulation of [(18)F]AppCHFppA in macrophage-rich atherosclerotic plaques can be quantified noninvasively with PET. Hence, [(18)F]AppCHFppA holds promise for the noninvasive characterization of vascular inflammation.

Novel monoamine transporter ligands reduce cocaine-induced enhancement of brain stimulation reward.

Six novel monoamine reuptake inhibitors were screened for their intrinsic effects on brain stimulation reward (BSR), as well as for their potential to reduce cocaine-induced reward-enhancement in that paradigm. Two of the compounds, nocaine-3B and 5-ara-74A (disubstituted piperidines) significantly reduced locus of rise (LOR), threshold measure of reward, at some doses. One compound, 1-RV-96A (a hybrid of the GBR and WIN-like agents) significantly reduced reward (increased LOR), but only at the highest dose tested. No effect of dose was found for MC9-20 (a GBR-like acyclic analogue of the N-bisarylmethoxyethyl-N'-phenylpropyl piperazine), nocaine-250B or 4-ara-42C (disubstituted piperidines). When cocaine (10 mg/kg, ip) and selected, hedonically neutral doses of novel compounds were combined, the following findings were obtained: MC9-20 (2.5 mg/kg, ip) showed a significant increase in cocaine-induced reward enhancement (0.2 log units or 53%). In contrast, nocaine-250B and 1-RV-96A (both at 10 mg/kg, ip) demonstrated a significant reduction (0.13 log units or 41%) in cocaine-induced reward enhancement (P<.01 and P<.05, respectively), as measured by changes in LOR. There were no differences in the maximum behavioral output (MAX) at either dose of each of the six drugs, or when selected doses were combined with cocaine. These results indicate that nocaine-250B and 1-RV-96A constitute two potential anticocaine compounds worthy of further behavioral and biochemical evaluation.

Novel 3-aminomethyl- and 4-aminopiperidine analogues of 1-[2-(diphenylmethoxy)ethyl]-4-(3-phenylpropyl)piperazines: synthesis and evaluation as dopamine transporter ligands.

We have undertaken a program to develop cocaine antagonists based on the premise that such compounds should block cocaine binding but permit reuptake of dopamine at the dopamine transporter (DAT). To evaluate the structural features of potential cocaine antagonists, 3-aminomethylpiperidine and 4-aminopiperidine moieties were incorporated at the central bridge region (piperazine ring) of GBR 12935. The compounds were assayed as inhibitors of [(125)I]RTI-55 binding at the DAT and monoamine transport. The results indicated that most of the new compounds preferentially inhibited norepinephrine reuptake by its transporter (NET) but in some cases retained binding selectivity for the DAT. In general, the binding selectivity and potency of [(3)H]NE reuptake inhibition were very sensitive to modifications of the central bridge diamine moiety (position of two basic nitrogen atoms). Compound 6 exhibited the highest ratio (14-fold) of DA reuptake inhibition to RTI-55 binding inhibition at the DAT; however, in an in vitro assay of cocaine antagonism, this compound failed to reduce inhibition of [(3)H]DA uptake by cocaine. These results demonstrated that separation of biological activities into the binding and reuptake inhibition can be achieved by alterations in the internal diamine component of GBR 12935, but additional modifications are necessary before these agents constitute lead compounds for development as cocaine antagonists.

Design, synthesis, and biological evaluation of novel non-piperazine analogues of 1-[2-(diphenylmethoxy)ethyl]- and 1-[2-[bis(4-fluorophenyl)methoxy]ethyl]-4-(3-phenylpropyl)piperazines as dopamine transporter inhibitors.

A series of novel diamine, amine-amide, and piperazinone analogues of N-[2-(bisarylmethoxy)ethyl]-N'-(phenylpropyl)piperazines, GBR 12909 and 12935, were synthesized and evaluated as inhibitors of presynaptic monoamine neurotransmitter transporters. The primary objective of the study was to determine the structural requirements for selectivity of ligand binding and potency for neurotransmitter reuptake inhibition. In general, the target compounds retained transporter affinity; however, structural variations produced significant effects on reuptake inhibition and transporter selectivity. For example, analogues prepared by replacing the piperazine ring in the GBR structure with an N, N'-dimethylpropyldiamine moiety displayed enhanced selectivity for binding and reuptake inhibition at the norepinephrine (NE) transporter site (e.g. 4 and 5). Congeners in which the amide nitrogen atom was attached to the aralkyl moiety of the GBR molecule showed moderate affinity (K(i) = 51-61 nM) and selectivity for the dopamine transporter (DAT) site. In contrast, introduction of a carbonyl group adjacent to either nitrogen atom of the piperazine ring (e.g. 25 and 27) was not well tolerated. From the compounds prepared, analogue 16 was selected for further evaluation. With this congener, locomotor activity induced by cocaine at a dose of 20 mg/kg was attenuated with an AD(50) (dose attenuating cocaine-induced stimulation by 50%) of 60.0 +/- 3.6 mg/kg.

Combined PET/MRS brain studies show dynamic and long-term physiological changes in a primate model of Parkinson disease.

We used brain imaging to study long-term neurodegenerative and bioadaptive neurochemical changes in a primate model of Parkinson disease. We gradually induced a selective loss of nigrostriatal dopamine neurons, similar to that of Parkinson disease, by creating oxidative stress through infusion of the mitochondrial complex 1 inhibitor MPTP for 14+/-5 months. Repeated evaluations over 3 years by positron emission tomography (PET) demonstrated progressive and persistent loss of neuronal dopamine pre-synaptic re-uptake sites; repeated magnetic resonance spectroscopy (MRS) studies indicated a 23-fold increase in lactate and macromolecules in the striatum region of the brain for up to 10 months after the last administration of MPTP. By 2 years after the MPTP infusions, these MRS striatal lactate and macromolecule values had returned to normal levels. In contrast, there were persistent increases in striatal choline and decreases in N-acetylaspartate. Thus, these combined PET/MRS studies demonstrate patterns of neurochemical changes that are both dynamic and persistent long after selective dopaminergic degeneration.

Altropane, a SPECT or PET imaging probe for dopamine neurons: I. Dopamine transporter binding in primate brain.

Increasing evidence suggests that the dopamine transporter is an important marker for physiological and pathological changes in dopamine neurons. Potent dopamine transport inhibitors of the phenyltropane series (e.g., WIN 35,428 or CFT) are particularly suitable for PET (positron emission tomography) or SPECT (single photon emission computed tomography) imaging of the dopamine transporter in living brain. We investigated whether altropane, an N-iodoallyl analog of WIN 35,428 (IACFT:E-N-iodoallyl-2 -carbomethoxy-3beta-(4-fluorophenyl)tropane), displayed in vitro properties suitable for evaluation as a SPECT imaging agent. In brain striatum of cynomolgus monkey (Macaca fascicularis), the unlabeled E-isomer (IC50: 6.62 +/- 0.78 nM) was more potent than the Z-isomer (IC50: 52.6 +/- 0.3 nM) and displayed a relatively high dopamine:serotonin transporter selectivity (28-fold). In radiolabeled form, [125I]altropane bound to sites in the striatum with a single high affinity (KD: 5.33 +/- 0.55 nM) and with a site density (BMAX: 301 pmol/g original wet tissue weight) that was within the density range reported previously for the dopamine transporter in striatum. Drugs inhibited [125I]altropane binding with a rank order of potency that corresponded closely to their potencies for inhibiting [3H]WIN 35,428 binding (r2: 0.99; P < 0.0001) to the blocking dopamine transport. The favorable binding properties of altropane, together with its rapid entry into primate brain and highly localized distribution in dopamine-rich brain regions, suggest it is a suitable iodinated probe for monitoring the dopamine transporter in vitro and in vivo by SPECT or PET imaging.

Altropane, a SPECT or PET imaging probe for dopamine neurons: II. Distribution to dopamine-rich regions of primate brain.

The dopamine transporter in brain, localized almost exclusively on dopamine neurons, is an effective window on dopamine neurons. SPECT or PET imaging of the transporter in brain requires selective imaging agents that display appropriate pharmacokinetic properties. We previously reported that [125I]altropane ([125I]IACFT,2beta-carbomethoxy-3beta-(4-fluorophenyl)-n-(1- iodoprop-1-en-3-yl)nortropane) bound with high affinity (Kd: 5.33 nM) to a single site on the dopamine transporter and was selective for dopamine over the serotonin transporter in homogenates of monkey striatum. To determine whether the selective binding of [125I]altropane is reflected in its brain distribution, the in vitro and ex vivo distribution of [125I]altropane in squirrel monkey (Saimiri sciureus) brain was determined by quantitative autoradiography of coronal brain sections. In vitro, [125I]altropane (2 nM) distribution was discrete and was detectable primarily in the dopamine-rich putamen, caudate nucleus, and nucleus accumbens. The resulting putamen:cerebellum ratio exceeded 120:1 (n = 3). The selective in vitro binding of [125I]altropane to the dopamine transporter, at concentrations approaching its Kd value (Kd: 5.33 nM, a single high affinity site), highlight its suitability for investigating the density of the dopamine transporter in various brain regions in vitro. Ex vivo autoradiography was conducted in monkeys to determine whether the brain distribution of [125I]altropane in vitro was predictive of its brain distribution pattern after intravenous administration. Thirty minutes after intravenous injection, highest levels of [125I]altropane (0.3 nmol/kg) were detected in the caudate-putamen and nucleus accumbens and lowest levels in the cerebellum and cortex. The putamen or caudate:cerebellum ratio was 7. SPECT imaging of the brain within 30 min of i.v. injection confirmed the rapid and selective accumulation of [123I]altropane to the striatum. The selective binding of altropane to the dopamine-rich striatum within 30 min of i.v. administration indicates that it is uniquely suited for SPECT or PET imaging of the dopamine transporter and associated dopamine neurons.

Rapid detection of Parkinson's disease by SPECT with altropane: a selective ligand for dopamine transporters.

Increasing evidence indicates that dopamine (DA) transporter density declines in Parkinson's disease (PD). 2Beta-carbomethoxy-3beta-(4-fluorophenyl)-n-(1-iodoprop-1-en -3-yl) nortropane (IACFT, Altropane) is a cocaine analog with high affinity and selectivity for dopamine transporter (DAT) sites in the striatum. In this study, single photon emission computed tomography (SPECT) with [123I]altropane was used to measure DAT density in seven healthy volunteers (five males, age 37-75, and two females, ages 26 and 39) and eight male patients with Parkinson's disease (age 14-79, Hoehn and Yahr stage: 1.5-3 (n = 5) and 4-5 (n = 3)). Dynamic SPECT images and arterial blood samples were acquired over 1.5-2 hr and plasma radioactivity was analyzed chromatographically to obtain metabolite corrected arterial input functions. Binding potential (BP, B'max/KD) for striatal (Str) DAT sites was calculated by two methods using occipital cortex (Occ) as a reference. In the first method, tissue time-activity curves (TAC) and metabolite corrected arterial input functions were analyzed by a linear graphical method developed for reversible receptor ligands. In the second method, the expression (Str(TAC) - Occ(TAC)) was fitted to a gamma variate function and the maximum divided by Occ(TAC) at the same time was used to estimate BP. In five of the PD patients, the SPECT data were compared with the results of PET with [18F] 6-fluoro DOPA (FD-PET). Plasma analysis indicated that [123I]altropane is rapidly converted to polar metabolites. SPECT images in healthy volunteers showed that [123I] altropane accumulated rapidly and selectively in the striatum and yielded excellent quality images within 1 h after injection. Both methods of analysis revealed a 7.6%/decade reduction in BP and average striatal values (corrected to age 25) were 1.83 +/- 0.22 and 2.09 +/- 0.20 by methods 1 and 2. In all the PD patients, striatal accumulation was markedly reduced and the pattern of loss was similar to that reported for DA; most profound in the posterior putamen with relative sparing of the caudate nuclei. A comparable pattern was observed with FD-PET. For total striatum, age-corrected BP was significantly (P < 0.001) reduced; 0.83 +/- 0.06 (method 1), 0.84 +/- 0.07 (method 2). BPs measured by the two methods were remarkably similar and highly correlated r2 = 0.88, (P < 0.001). These results indicate that [123I]altropane is an excellent SPECT ligand for imaging the DAT/DA neurons in human brain. The high selectivity and rapid striatal accumulation of the ligand allows for accurate quantitation of DAT sites in less than 2 hr. The results further demonstrate that [123I]altropane is an effective marker for PD.

Rapid noninvasive detection of experimental atherosclerotic lesions with novel 99mTc-labeled diadenosine tetraphosphates.

The development of a noninvasive imaging procedure for identifying atherosclerotic lesions is extremely important for the clinical management of patients with coronary artery and peripheral vascular disease. Although numerous radiopharmaceuticals have been proposed for this purpose, none has demonstrated the diagnostic accuracy required to replace invasive angiography. In this report, we used the radiolabeled purine analog, 99mTc diadenosine tetraphosphate (Ap4A; AppppA, P1,P4-di(adenosine-5')-tetraphosphate) and its analogue 99mTc AppCHClppA for imaging experimental atherosclerotic lesions in New Zealand White rabbits. Serial gamma camera images were obtained after intravenous injection of the radiolabeled dinucleotides. After acquiring the final images, the animals were sacrificed, ex vivo images of the aortas were recorded, and biodistribution was measured. 99mTc-Ap4A and 99mTc AppCHClppA accumulated rapidly in atherosclerotic abdominal aorta, and lesions were clearly visible within 30 min after injection in all animals that were studied. Both radiopharmaceuticals were retained in the lesions for 3 hr, and the peak lesion to normal vessel ratio was 7.4 to 1. Neither of the purine analogs showed significant accumulation in the abdominal aorta of normal (control) rabbits. The excised aortas showed lesion patterns that were highly correlated with the in vivo and ex vivo imaging results. The present study demonstrates that purine receptors are up-regulated in experimental atherosclerotic lesions and 99mTc-labeled purine analogs have potential for rapid noninvasive detection of plaque formation.

SPECT imaging of dopamine transporter sites in normal and MPTP-Treated rhesus monkeys.

UNLABELLED: Parkinson's disease is characterized by degeneration of dopamine (DA) neurons and their terminals. Since these neurons contain dopamine transporters (DAT), radioligands that bind to these sites are promising radiopharmaceuticals for diagnosis and therapeutic monitoring of disease progression. We evaluated [123I]-2 beta-carbomethoxy- 3 beta-(4-fluorophenyl)-N-(1-iodoprop-1-en-3-yl)nortropane ([123I]IACFT) for SPECT imaging in an MPTP model of parkinsonism. METHODS: Three rhesus monkeys were imaged before and at 1 and 2 mo after treatment with MPTP. The SPECT results were correlated with motor behavior and PET imaging with [11C]-2 beta-carbomethoxy-3 beta-aryltropane ([11C]-CFT). Also, biodistribution was measured by planar imaging. RESULTS: In normal animals, striatal accumulation of radioactivity was rapid and peaked within 30 min. Striatal accumulation of [123I]IACFT was nearly completely displaceable with unlabeled CFT (1 mg/kg) but was not affected by a similar dose of the serotonin (5-HT) transport inhibitor, citalopram. The striatal to cerebellar ratio measured at 30 min, after injection of [123I]IACFT was significantly higher (p < 0.01) than with [11C]CFT; approximately 6; 1 versus approximately 2.5; 1. After MPTP treatment this ratio decreased to 1.02:1 with IACFT and 1.23:1 with [11C]CFT. Blood clearance of [123I]IACFT was rapid with a terminal t1/2 of approximately 30 min. HPLC of plasma samples demonstrated that the concentration of intact ligand decreases rapidly, approaching zero by 60 min. Low levels of accumulation were measured in extracranial tissues. CONCLUSION: These results demonstrate that [123I]IACFT is an excellent SPECT ligand for dopamine transporter sites that combines the critical characteristics of: (a) high striatal to cerebellar ratios, (b) high selectivity for dopamine versus 5-HT transporter sites, (c) convenient preparation at high-specific activity and radiochemical purity and (d) a striatal localization rate that is well matched to the physical t1/2 of 123I.

Positron emission tomographic analysis of central 5-hydroxytryptamine2 receptor occupancy in healthy volunteers treated with the novel antipsychotic agent, ziprasidone.

Ziprasidone is a novel antipsychotic agent, with high affinity for dopamine D2 and serotonin (5-HT2) receptors in vitro and in animal models. The goal of this study was to determine the time course of 5-HT2 receptor occupancy (%RO) in healthy humans after a single p.o. dose. Positron emission tomography with the 5-HT2 ligand, [18F]setoperone, was performed in eight male volunteers, in the drug-naive, base-line (BL) state and 4 to 18 hr after ziprasidone (40 mg). Cerebral cortical binding potential [BP, maximum number of available receptors/KD or association rate for specific binding (k3)/dissociation rate for specific binding (k4)] was estimated using the cerebellum as reference. Transport rate from plasma to brain (K1), transport rate from brain to plasma (k2), association rate of nonspecific binding (k5) and dissociation rate of nonspecific binding (k6) were derived by fitting cerebellar time-activity curves to a three-compartment model. Fitting of cortical data to a 4-compartment model with K1/k2, k5 and k6, fixed at cerebellar values, was used to determine k3 and k4. %RO was calculated using the relation: %RO = [(BPBL-BPDRUG)/BPBL] x 100%. At BL, cortical parameter (mean +/- S.E.M) were: K1 = 0.121 +/- 0.0072 ml.min-1.g-1; k2 = 0.0581 +/- 0.004 min-1; k3 = 0.321 +/- 0.0026 min-1; k4 = 0.0957 +/- 0.0059 min-1; k5 = 0.0147 +/- 0.00066 min-1; and k6 = 0.0059 +/- 0.00042 min-1. Ziprasidone did not effect K1, k2, k5 or k6; however, k3 was reduced and k4 was elevated (P < .01). RO was nearly complete at 4 hr after dosing (98%) and remained elevated at 18 hr (46%). Plasma concentrations were well described by a biexponential function and decreased much more rapidly than RO. These results establish that ziprasidone has high potency for blocking 5-HT2 receptors in healthy humans; a potentially important characteristic of atypical antipsychotic agents.

Cocaine congeners as PET imaging probes for dopamine terminals.

UNLABELLED: The PET imaging properties of three phenyltropane drugs with differing affinities and selectivities for the dopamine over serotonin transporter, were compared. METHODS: Carbon-11-CFT (WIN 35,428, 2 beta-carbomethoxy-3 beta-(4-fluorophenyl)tropane), 11C-CCT (RTI-131, 2 beta-carbomethoxy-3 beta-(4-monochlorophenyl)tropane), and 11C-CDCT (dichloropane, 2 beta-carbomethoxy-3 beta-(3,4-dichlorophenyl)tropane) were evaluated as imaging probes for dopamine neurons in five normal and in two MPTP-treated cynomolgus monkeys (macaca fascicularis) using a high-resolution PET imaging system (PCR-I). RESULTS: For 11C-CFT, the specific binding ratio (as defined by the ratio of radioactivity levels in striatum versus cerebellum) was 4.2 +/- 0.8 in caudate and 4.9 +/- 1.2 in putamen at 60 min and 4.9 +/- 1.2 and 5.5 +/- 1.1 at 90 min in control animals. In MPTP-treated monkeys the corresponding ratios were 1.4 +/- 0.1 in caudate and 1.5 +/- 0.1 in putamen at 60 min and 1.3 +/- 0.1 in caudate and 1.4 +/- 0.3 in putamen at 90 min. For the monochloro analog of CFT, 11C-CCT, the ratios in control caudate and putamen were 2.7 +/- 0.4 and 3.4 +/- 0.3, respectively, at 60 min and 3.7 +/- 0.5 and 4.4 +/- 0.6, respectively, at 90 min. In MPTP-treated animals, corresponding ratios were 1.4 +/- 0.4 and 1.5 +/- 0.3 at 60 min and 1.4 +/- 0.4 and 1.6 +/- 0.4 at 90 min. The dichloro analog of CFT, CDCT, which has the highest affinity for the dopamine transporter, generated the lowest ratios in control brains, 2.3 +/- 0.4 in caudate and 2.4 +/- 0.5 in putamen at 60 min. In one MPTP-treated monkey, the corresponding ratios were 1.6 +/- 0.4 and 1.8 +/- 0.3. In comparison with 11C-CFT, both 11C-CCT and 11C-CDCT were less selective and had high uptake in the thalamus. CONCLUSION: The present results clearly indicate that 11C-CFT is a useful ligand for monitoring dopamine neuronal degeneration.

Preparation and biological evaluation of iodine-125-IACFT: a selective SPECT agent for imaging dopamine transporter sites.

UNLABELLED: Parkinson's disease is a progressive neurodegenerative disorder that is associated with the loss of nerve terminals from specific brain areas, particularly in the caudate and putamen, which contains the highest concentrations of dopamine transporter sites. Previously, we synthesized and evaluated a series of 11C-labeled 2 beta-carbomethoxy -3 beta-aryltropane (WIN 35,428; CFT) derivatives as markers for the dopamine transporter system. These ligands have high affinity and specificity for dopamine transporter sites in vitro and in vivo in laboratory animals. The goal of this study was the preparation and preliminary biological characterization of two new ligands based on the structure of WIN 35,428, the E and Z isomers of N-iodoallyl-2 beta -carbomethoxy-3 beta-(4-fluorophenyl)tropane (E and A IACFT). METHODS: E and Z IACFT were synthesized and radiolabeled with 125I. The ligands were characterized by in vitro assays of binding to dopamine and serotonin transporters and by autoradiography. RESULTS: Iodine-125-IACFT was prepared in > 60% radiochemical yield, and > 98% radiochemical purity. Specific activity was 1500 Ci/mmole. In vitro, E-IACFT showed higher affinity for dopamine transporter sites than WIN 35,428 (6.6 versus 11 nM) and better selectivity than RTI-55. The Z isomer was found to have much lower affinity. One hour after an intravenous injection of 125I IACFT in monkeys, ex vivo autoradiographs of the brain revealed high concentrations of tracer in dopamine rich regions such as the caudateputamen. The striatum-to-cerebellum, striatum-to-cortex and striatum-to-thalamus ratios were 10.8, 7.2 and 8.3. CONCLUSION: These result suggest that radiolabeled E-IACFT may be a useful radioligand for SPECT imaging of dopamine transporter sites. IACFT could prove to be extremely useful for the noninvasive evaluation of patients with early Parkinson's disease.

Effect of monounsaturation of a branched fatty acid on organ selectivity.

UNLABELLED: 1-[11C]-3-R,S-methylheptadecanoic acid (BMHA) is a branched chain fatty acid analog that is transported into the myocardium. Due to incomplete metabolism, however, radiolabeled products are trapped within myocytes. Recently, we demonstrated that this compound is an excellent tracer to monitor fatty acid metabolism. METHOD: To evaluate the effect of mono-unsaturation on myocardial substrate utilization, we prepared 1-[11C]-3-R,S-methyl-trans--heptadec-7-enoic acid (t-7-BMHA) and measured its biodistribution in rats. In addition, preliminary PET studies were performed on dogs. RESULTS: Biodistribution studies demonstrated that myocardial-to-lung and myocardial-to-blood ratios for t-7-BMHA are higher than those for BMHA. Fifteen minutes after injection, heart-to-lung ratios were 5.23 compared to 2.92 and heart-to-liver ratios were 3.07 compared to 1.41 for t-7-BMHA and BMHA. By 30 min postinjection heart-to-lung ratios were 7.03 compared to 5.88 and heart-to-liver ratios were 4.43 compared to 1.09. The heart-to-blood ratio of t-7-BMHA was greater than 11:1. PET imaging with 1-[11C]-t-7-BMHA demonstrated high myocardial extraction, prolonged retention of radioactivity and excellent image quality. Accumulation of radioactivity in the myocardium reached a plateau within 10 min postinjection, with heart-to-blood ratios exceeding 20:1 and heart-to-lung ratios exceeding 10:1. Blood clearance of radioactivity was biphasic with half-times of 1.46 and 14.7 min, respectively. CONCLUSION: These data suggest that introduction of a trans-double bond in BMHA improves myocardial selectivity and results in a potentially superior imaging agent.

The use of pentafluorophenyl derivatives for the 18F labelling of proteins.

A simple, one-step method for the radiolabelling of proteins with 18F is described. A series of pentafluorophenyl derivatives were synthesized and tested for 18F exchange using tetrabutylammonium-[18F]fluoride in DMSO, with microwave heating. A number of the compounds examined incorporated 18F quickly and in high yield. Two compounds, pentafluorobenzaldehyde and 2,3,5,6-tetrafluorophenylpentafluorobenzoate, were used to label HSA in good yield. The methods produce low specific activity labelled proteins, but are fast. The yields are reasonable and the reagents do not require a separate modification or activation step for protein labelling.

Synthesis of fluorine-18-labeled biotin derivatives: biodistribution and infection localization.

UNLABELLED: Recently there has been much interest in the exploitation of the high binding affinity of avidin/biotin as a means of targeting drugs and radionuclides for in vivo applications. We are interested in broadening the application of the avidin/biotin complex to PET. To this end we set out to prepare 18F-labeled biotin analogs. METHODS: Two 18F biotin derivatives, [3aS-(3a alpha,4 beta,6a alpha)]-hexahydro-2-oxo-1H-thieno[3,4- d]imidazole-4-(N-3-(1-[18F]fluoropropyl))pentanamide (1) and [3aS-(3a alpha,4 beta,6a alpha)]-tetrahydro-4-(5-(1-[18F]fluoropentyl)- 1H-thieno[3,4-d]imidazol-2(3H)-(2) were prepared with high specific activity (NCA) and evaluated for their potential in infection localization. RESULTS: Compound 1 binds to avidin and the biodistribution of these derivatives were studied in Escherichia coli infected rats. Half of the infected rats were treated with avidin 24 hr prior to intravenous injection of the 18F-labeled biotin analogs. Biotin 1, without avidin pretreatment, showed a selectivity of 6.08 +/- 1.12 for infection compared to normal muscle. With avidin pretreatment, selectivity increased slightly, giving an infection to normal muscle ratio of 6.39 +/- 0.96. In contrast, the biodistribution of biotin 2 indicated more binding to normal muscle with an infection to normal muscle ratio of 0.58 +/- 0.07. This lack of selectivity illustrates the importance of the side-chain amide group in infection localization. There was some defluorination of 1 and 2, as evidenced by increased 18F bone uptake after 60 min: 2.94 +/- 0.37 and 1.17 +/- 0.21 %IG/g +/- s.d., respectively. CONCLUSIONS: Biotin derivatives could be radiofluorinated with high specific activity. Biotin 1, is a potential positron tomography tracer for infection imaging.

Synthesis of 2-[18F]fluoro-2-deoxy-L-glucose and positron emission tomography studies in monkeys.

2-[18F]Fluoro-2-deoxy-L-glucose was synthesized from its trifluoromethanesulfonyl precursor. The precursor was prepared by selective acetylation and triflation of L-mannose. L-Mannose was first treated with acetic anhydride in the presence of a catalytic amount of perchloric acid and then reacted with phosphorus tribromide followed by aqueous sodium acetate to produce pure 1,3,4,6-tetra-O-acetyl-a-L-mannopyranose in 32% yield. This compound was treated with trifluoromethanesulfonic anhydride and pyridine in methylene chloride to form 1,3,4,6-tetra-O-acetyl-O-tritrifluoromethanesulfonyl-a-L-mannopyra nose in 77% yield. Nucleophilic substitution of the triflate with 18F-in the presence of Kryptofix 2,2,2 followed by acid hydrolysis produced 2-[18F]fluoro-2-deoxy-L-glucose with a radiochemical yield of 20-30% (EOS) within 90 min. Biodistribution studies in rats and PET imaging in Rhesus monkeys demonstrated that this sugar analog distributes in the extracellular space of most organs but is excluded from the CNS.

Myocardial extraction of 1-[11C] betamethylheptadecanoic acid.

UNLABELLED: Betamethylheptadecanoic acid (BMHA) is a branched chain fatty acid analog that is transported into myocardial cells by the same long chain fatty acid carrier protein mechanism as natural fatty acids, but cannot be completely catabolized and accumulates in the tissue. Thus, 11C-labeled BMHA is a useful tracer for the noninvasive evaluation of myocardial fatty acid utilization by positron emission tomography (PET). METHODS: As a prelude to PET studies, the metabolism of BMHA was studied by classical techniques. We measured the net extraction fraction (En) of 1-[11C]-beta-R,S-methylheptadecanoic acid (1-[11C]BMHA) and compared it to that of natural fatty acids in dogs, using arterial/venous measurements and a mathematical model. Two groups of conditioned dogs were studied. In the first group, measurements were made under fasting (normal control) conditions and in the second group, measurements were made during glucose and insulin infusion. Myocardial blood flow, and the extraction/utilization of other substrates (glucose, oxygen and lactate) were also measured. RESULTS: For natural fatty acids in the basal state, En(FA) was 0.335. After glucose/insulin infusion, this value decreased to 0.195. The 1-[11C]BMHA showed a similar decrease in En(BMHA) from 0.220 in the control group to 0.100 in the group treated with glucose/insulin infusion. Preliminary PET studies with 1-[11C]BMHA verified the validity of performing these measurements noninvasively. CONCLUSION: The results of these studies indicate that rates of fatty acid metabolism in the myocardium can be determined from steady-state concentrations of 1-[11C]BMHA.

Synthesis and biodistribution of a new 99mtechnetium fatty acid.

The synthesis and biodistribution is described for a new 99mTc-labeled fatty acid. The requisite diaminodithiol (N2S2) ligand, 9,10-bis[N-(2'-methyl-2'-mercapto)propyl] aminooctadecanoic acid, was prepared in nine steps from ethyl oleate and characterized by fast atom bombardment mass spectrometry and elemental analysis of its nickell(II) complex. The radiolabeling procedure provided a liposoluble 99mTc-labeled complex (99mTc-11) which was administered intravenously to rats concomitantly with 15-(p-[125I]-iodophenyl) pentadecanoic acid (IPPA). The myocardial profile of 99mTc-11 was inferior to that of IPPA.