Preclinical in vivo and in vitro comparison of the translocator protein PET ligands [18F]PBR102 and [18F]PBR111.

PURPOSE: To determine the metabolic profiles of the translocator protein ligands PBR102 and PBR111 in rat and human microsomes and compare their in vivo binding and metabolite uptake in the brain of non-human primates (Papio hamadryas) using PET-CT. METHODS: In vitro metabolic profiles of PBR102 and PBR111 in rat and human liver microsomes were assessed by liquid chromatography-tandem mass spectrometry. [18F]PBR102 and [18F]PBR111 were prepared by nucleophilic substitution of their corresponding p-toluenesulfonyl precursors with [18F]fluoride. List mode PET-CT brain imaging with arterial blood sampling was performed in non-human primates. Blood plasma measurements and metabolite analysis, using solid-phase extraction, provided the metabolite profile and metabolite-corrected input functions for kinetic model fitting. Blocking and displacement PET-CT scans, using PK11195, were performed. RESULTS: Microsomal analyses identified the O-de-alkylated, hydroxylated and N-de-ethyl derivatives of PBR102 and PBR111 as the main metabolites. The O-de-alkylated compounds were the major metabolites in both species; human liver microsomes were less active than those from rat. Metabolic profiles in vivo in non-human primates and previously published rat experiments were consistent with the microsomal results. PET-CT studies showed that K1 was similar for baseline and blocking studies for both radiotracers; VT was reduced during the blocking study, suggesting low non-specific binding and lack of appreciable metabolite uptake in the brain. CONCLUSIONS: [18F]PBR102 and [18F]PBR111 have distinct metabolic profiles in rat and non-human primates. Radiometabolites contributed to non-specific binding and confounded in vivo brain analysis of [18F]PBR102 in rodents; the impact in primates was less pronounced. Both [18F]PBR102 and [18F]PBR111 are suitable for PET imaging of TSPO in vivo. In vitro metabolite studies can be used to predict in vivo radioligand metabolism and can assist in the design and development of better radioligands.

Tumour necrosis factor (TNF) inhibitor therapy in Susac's syndrome.

Susac's syndrome is the clinical triad of encephalopathy, branch retinal artery occlusions and sensorineural hearing loss (Susac 1994) [1]. It occurs predominantly in young females and is believed to be an immune-mediated endotheliopathy of small vessels of the brain, retina and cochlea (Neumayer et al. 2009) [2]. Early, aggressive, and sustained immunosuppressive therapy has been recommended for Susac's syndrome and anecdotal evidence has suggested a therapeutic role for monoclonal antibodies (Rennebohm et al. 2008, Lee and Amezcua 2009) [3,4]. We report a case of Susac's syndrome in which the patient improved immediately after tumour necrosis factor (TNF) inhibition with the monoclonal antibody, infliximab.

The impact of PET-CT in suspected recurrent ovarian cancer: A prospective multi-centre study as part of the Australian PET Data Collection Project.

OBJECTIVE: To assess the impact of FDG PET-CT on the management of patients with suspected recurrent ovarian cancer and to determine the incremental information provided by PET-CT. METHODS: This was a prospective, multi-centre, cohort study. Ninety women (mean age 59.9 years; age range 35-85 years) with a previous history of treated epithelial ovarian carcinoma and suspected recurrence based on elevated CA-125, anatomical imaging or clinical symptoms were studied with FDG PET-CT across two States. Referring doctors were asked to specify a management plan pre-PET, if management was altered after PET-CT and, the impact (rated - none, low, medium, high) of PET-CT on patient management. The pre-PET management plan could include radiotherapy, chemotherapy, surgery, and 'other' including observation. Patients were followed at 6 and 12 months and clinical status, evidence of recurrence and progression were recorded. RESULTS: Patients were referred by 34 individual specialists. At least 168 additional sites of disease in 61 patients (68%), not identified by conventional imaging were identified by PET-CT. In 77% the additional lesions were located below the diaphragm and most were nodal or peritoneal. PET-CT affected management in 60% (49% high, 11% medium impact). Patients where more disease was detected with PET-CT were more likely to progress in the following 12 months. CONCLUSIONS: For women with previously treated ovarian carcinoma with recurrent disease, PET-CT can: a) alter management in close to 60% of patients, b) detect more sites of disease than abdominal and pelvic CT, c) is superior in the detection of nodal, peritoneal and subcapsular liver disease and d) offers the opportunity for technology replacement in this setting.

Positron emission tomography-computerized tomography findings in a urinary bladder paraganglioma.

We present the staging fluorodeoxyglucose (FDG) positron emission tomography (PET-CT) findings in a patient with a functional urinary bladder paraganglioma. The PET-CT scan showed markedly increased FDG uptake into bilateral pelvic nodes that was consistent with regional nodal involvement. These findings were confirmed on histopathology. At present, there are no reports of PET-CT findings in urinary bladder paragangliomas.

Sarcomatoid renal cell carcinoma: rapid dissemination detected on FDG PET-CT.

We present the FDG PET-CT findings in a patient with persistent pain 7 weeks after a nephrectomy and lymph node dissection for a sarcomatoid renal cell carcinoma. Although conventional imaging was unable to detect evidence of metastatic spread outside the para-aortic nodes, a PET-CT scan showed unexpected extensive dissemination. Currently, there are no reports in the literature of the PET-CT findings in sarcomatoid renal cell carcinomas.

Detection of metastatic disease in patients with uveal melanoma using positron emission tomography.

OBJECTIVE: Positron emission tomography with [(18)F]fluorodeoxyglucose (FDG-PET) is of proven value in the detection of metastases in patients with cutaneous melanoma. However, little is known about its value in uveal melanoma (UM). In this study the results of FDG-PET in patients with UM were evaluated. METHODS: Patients with UM recorded in the Sydney Melanoma Unit database who had been assessed with FDG-PET were selected. Comparative data (imaging or histopathology) providing information about metastatic disease were obtained within 14 weeks of the FDG-PET study and compared with the FDG-PET result. Sensitivity, specificity, accuracy, and positive and negative predictive values for the detection of liver metastases (LMs) by FDG-PET were calculated. RESULTS: FDG-PET was performed in 22 patients with UM between April 1993 and March 2003. The presence of at least one focus of metastatic melanoma was confirmed in 14 of 18 patients with positive FDG-PET, and three of four negative FDG-PET studies were confirmed. LMs were demonstrated by FDG-PET in 17 patients. In 15 of these patients this finding was confirmed with anatomical imaging. In two patients LMs indicated by FDG-PET initially appeared to be false positive, but in one of them the diagnosis was confirmed after longer follow-up. Seven of the confirmed lesions were isolated LMs. For LMs FDG-PET showed sensitivity, specificity and accuracy of 100%, 67% and 90% respectively, a positive predictive value of 88% and a negative predictive value of 100%. CONCLUSION: FDG-PET is a valuable investigation for the detection of LMs in UM patients. It appears to be particularly useful in the detection of isolated LMs that are potentially resectable.

Detection of unsuspected spinal cord compression in melanoma patients by 18F-fluorodeoxyglucose-positron emission tomography.

AIM: Positron emission tomography (PET) using (18)F-fluorodeoxyglucose can detect early or small metastatic deposits of melanoma and guide subsequent correlative anatomical imaging and treatment. The aim of this study was to assess the value of PET in demonstrating spinal cord compression by otherwise unsuspected metastatic disease. METHODS: Reports of 1365 PET studies performed on patients with melanoma were reviewed. Fifty patients considered to be at risk of spinal cord compression on the basis of PET were identified and 35 patients were analysed. Magnetic resonance imaging and computed tomography were used to confirm or refute the diagnosis. The symptoms and signs at the time of PET and follow-up status were compared between patients with and without confirmed spinal cord compression. RESULTS: In nine patients (26%) compression of the spinal cord or adjacent neurological structures was confirmed and eight of these patients had immediate treatment. Survival was poor in both patient groups, but three patients with confirmed compression maintained good neurological functional status following treatment. CONCLUSION: PET can detect imminent, unsuspected spinal cord compression in patients with metastatic melanoma. Immediate anatomical imaging of the spine is recommended in patients who have evidence of spinal cord compression on PET.

3-Pyridyl ethers as SPECT radioligands for imaging nicotinic acetylcholine receptors.

To develop a suitable single photon emission computed tomography (SPECT) radioligand for neuronal nicotinic acetylcholine receptors (nAChRs) that displays faster in vivo kinetics than 5-[123I]iodo-A-85380, we synthesised the radioiodinated analogue of A-84543. 5-[123I]Iodo-A-84543 was prepared by electrophilic iododestannylation in a modest yield of 23%. In the baboon brain, 5-[123I]iodo-A-85380 displayed a profile consistent with the known distribution of nAChRs, however, 5-[123I]iodo-A-84543 displayed a homogenous uptake with no preferential localisation in regions known to contain nAChRs. To examine the effect of halogen substitution on the 3-pyridyl ether, A-84543, the 5-chloro, 5-bromo and 5-iodo analogues were synthesised and evaluated with respect to nAChR binding. In vitro binding data revealed that halogen substitution at the 5-position of A-84543 was not well tolerated with an increase in halogen size resulting in lower binding towards nAChRs. The 5-chloro analogue 4 displayed highest affinity, Ki =1.3 nM, compared to the 5-bromo and 5-iodo compounds, 5 Ki =3.3 nM and 3 Ki =40.8 nM, respectively. Taken together, these results clearly indicate that 5-[123I]iodo-A-84543 is not suitable for the study of nAChRs in vivo using SPECT.

The effects of mesial temporal and cerebellar hypometabolism on learning and memory.

The effects of mesial temporal (MT) and cerebellar hypometabolism were studied using measures of verbal, visual and motor skill learning. Twelve patients with refractory temporal lobe epilepsy who showed asymmetrical mesial temporal lobe hypometabolism on [18F] fluoro-2-deoxy-glucose positron emission tomography (FDG-PET) were given tests involving 4 consecutive learning trials and a 30-min delayed recall trial. Delayed recognition was also assessed for the words and designs, and skill transfer was evaluated for mirror drawing. Compared to 9 normal control participants, patients with more marked MT hypometabolism on the left had impaired delayed recall of words and patients with more marked MT hypometabolism on the right showed impaired learning of novel designs, but normal retention over delay. Patients were not impaired in their mirror-drawing performance. The findings for MT hypometabolism correspond well to those obtained in other studies where patients have been classified on the basis of side of hippocampal atrophy or temporal lobe excision.

Simultaneous estimation of physiological parameters and the input function--in vivo PET data.

Dynamic imaging with positron emission tomography (PET) is widely used for the in vivo measurement of regional cerebral metabolic rate for glucose (rCMRGlc) with [18F]fluorodeoxy-D-glucose (FDG) and is used for the clinical evaluation of neurological disease. However, in addition to the acquisition of dynamic images, continuous arterial blood sampling is the conventional method to obtain the tracer time-activity curve in blood (or plasma) for the numeric estimation of rCMRGlc in mg glucose/100-g tissue/min. The insertion of arterial lines and the subsequent collection and processing of multiple blood samples are impractical for clinical PET studies because it is invasive, has the remote, but real potential for producing limb ischemia, and it exposes personnel to additional radiation and risks associated with handling blood. In this paper, based on our previously proposed method for extracting kinetic parameters from dynamic PET images, we developed a modified version (post-estimation method) to improve the numerical identifiability of the parameter estimates when we deal with data obtained from clinical studies. We applied both methods to dynamic neurologic FDG PET studies in three adults. We found that the input function and parameter estimates obtained with our noninvasive methods agreed well with those estimated from the gold standard method of arterial blood sampling and that rCMRGlc estimates were highly correlated (r = 0.973). More importantly, no significant difference was found between rCMRGlc estimated by our methods and the gold standard method (P > 0.16). We suggest that our proposed noninvasive methods may offer an advance over existing methods.

In vivo imaging of nicotinic receptor upregulation following chronic (-)-nicotine treatment in baboon using SPECT.

To quantify changes in neuronal nAChR binding in vivo, quantitative dynamic SPECT studies were performed with 5-[(123)I]-iodo-A-85380 in baboons pre and post chronic treatment with (-)-nicotine or saline control. Infusion of (-)-nicotine at a dose of 2.0 mg/kg/24h for 14 days resulted in plasma (-)-nicotine levels of 27.3 ng/mL. This is equivalent to that found in an average human smoker (20 cigarettes a day). In the baboon brain the regional distribution of 5-[(123)I]-iodo-A-85380 was consistent with the known densities of nAChRs (thalamus > frontal cortex > cerebellum). Changes in nAChR binding were estimated from the volume of distribution (V(d) ) and binding potential (BP) derived from 3-compartment model fits. In the (-)-nicotine treated animal V(d) was significantly increased in the thalamus (52%) and cerebellum (50%) seven days post cessation of (-)-nicotine treatment, suggesting upregulation of nAChRs. The observed 33% increase in the frontal cortex failed to reach significance. A significant increase in BP was seen in the thalamus. In the saline control animal no changes were observed in V(d) or BP under any experimental conditions. In this preliminary study, we have demonstrated for the first time in vivo upregulation of neuronal nAChR binding following chronic (-)-nicotine treatment.

The influence of tomograph sensitivity on kinetic parameter estimation in positron emission tomography imaging studies of the rat brain.

We investigated the influence of tomograph sensitivity on reliability of parameter estimation in positron emission tomography studies of the rat brain. The kinetics of two tracers in rat striatum and cerebellum were simulated. A typical injected dose of 10 MBq and a reduced dose of 1 MBq were assumed. Kinetic parameters were estimated using a region of interest (ROI) analysis and two pixel-by-pixel analyses. Striatal binding potential was estimated as a function of effective tomograph sensitivity (S(eff)) using a simplified reference tissue model. A S(eff) value of > or =1% was required to ensure reliable parameter estimation for ROI analysis and a S(eff) of 3-6% was required for pixel-by-pixel analysis. We conclude that effective tomograph sensitivity of 3% may be an appropriate design goal for rat brain imaging.

Progressive supranuclear palsy pathology caused by a novel silent mutation in exon 10 of the tau gene: expansion of the disease phenotype caused by tau gene mutations.

Genetic mutations in the tau gene on chromosome 17 are known to cause frontotemporal dementias. We have identified a novel silent mutation (S305S) in the tau gene in a subject without significant atrophy or cellular degeneration of the frontal and temporal cortices. Rather the cellular pathology was characteristic of progressive supranuclear palsy, with neurofibrillary tangles concentrating within the subcortical regions of the basal ganglia. Two affected family members presented with symptoms of dementia and later developed neurological deficits including abnormality of vertical gaze and extrapyramidal signs. The third presented with dystonia of the left arm and dysarthria, and later developed a supranuclear gaze palsy and falls. The mutation is located in exon 10 of the tau gene and forms part of a stem-loop structure at the 5' splice donor site. Although the mutation does not give rise to an amino acid change in the tau protein, functional exon-trapping experiments show that it results in a significant 4.8-fold increase in the splicing of exon 10, resulting in the presence of tau containing four microtubule-binding repeats. This study provides direct molecular evidence for a functional mutation that causes progressive supranuclear palsy pathology and demonstrates that mutations in the tau gene are pleiotropic.

Decreased brain glucose utilization in patients with Cushing's disease.

UNLABELLED: Glucocorticoid hormones affect glucose use in different tissues, and the results of several experimental studies have suggested that glucocorticoids have a central action on cerebral metabolism. PET, using the radiotracer 18F-fluorodeoxyglucose (FDG), permits the measurement of cerebral glucose metabolism. METHODS: To investigate whether cerebral glucose metabolism would be altered in patients with increased plasma glucocorticoid levels, we analyzed the FDG PET studies that were done on 13 patients with Cushing's disease and compared the results with those obtained in 13 age-matched normal control subjects. A second FDG PET scan was performed on 4 patients after surgical removal of the pituitary adenoma. RESULTS: Patients with Cushing's disease had a significant reduction in cerebral glucose metabolism compared with normal controls. In the patients on whom a second PET scan was performed, there was a trend toward increased glucose metabolism on the second scan when comparing pre- and postsurgery values for each patient. CONCLUSION: We suggest that the decreased cerebral glucose metabolism we observed in Cushing's disease is attributable to increased glucocorticoid levels, and we speculate that abnormal cerebral glucose metabolism might contribute to the cognitive and psychiatric abnormalities that are frequently observed in patients with Cushing's disease.

Pretreatment and posttreatment positron emission tomographic scan imaging in a 20-year-old patient with Wilson's disease.

Wilson's disease is an autosomal-recessive inherited disorder that results in predominantly hepatic and neurologic manifestations. Neurologic abnormalities include tremor, ataxia, bradykinesia, rigidity, chorea, and dystonia. We report the clinical, radiologic, and serial FDG PET findings in a 20-year-old woman who presented with an asymmetric upper limb tremor caused by Wilson's disease. Reduced striatal and cerebral cortical glucose metabolism was demonstrated on a FDG PET study performed before the commencement of D-penicillamine therapy. After 6 months of treatment, the patient had shown only minimal clinical improvement, despite an increase in striatal and cerebral cortical glucose metabolism on a repeat FDG PET study. After 14 months of treatment, however, a moderate clinical improvement was noted and there was further increase in glucose metabolism on FDG PET.

Simultaneous emission and transmission (SET) scanning in neurological PET studies.

PURPOSE: We evaluated the impact of simultaneous emission and transmission (SET) measurements of quantification and noise in neurological PET studies. METHOD: Bias in SET was measured as a function of emission count rate and used to predict distortion in simulated FDG tissue curves and its effect on model parameter estimates. Studies were performed on a brain phantom and a patient to verify predicted bias and examine the effect of SET on noise. RESULTS: In static imaging, SET underestimated tracer concentration by approximately 2%. In kinetic studies, tracer concentration was overestimated initially and underestimated during the mid to late part of the study, but bias in measurement of glucose metabolic rate was < 5% by simulation and < 10% in the patient study. SET imaging takes 10% longer than the emission part of a conventional scan to achieve comparable statistics. CONCLUSION: Accurate neurological PET studies can be performed with SET. The relatively small bias can be predicted and potentially corrected.

Two novel (M233T and R278T) presenilin-1 mutations in early-onset Alzheimer's disease pedigrees and preliminary evidence for association of presenilin-1 mutations with a novel phenotype.

Eleven early-onset dementia families, all with affected individuals who have either presented clinical symptoms of early onset familial Alzheimer's disease (EOFAD) or have been confirmed to have EOFAD by autopsy, and two early onset cases with biopsy-confirmed AD pathology, were screened for missense mutations in the entire coding region of presenilin-1 (PS-1) and -2 (PS-2) genes. Missense mutations were detected by direct sequence analysis of PCR products amplified from genomic DNA templates of affected individuals. Three pedigrees were attributable to known mutations in the PS-1 gene: P264L, E280A and the splice acceptor site (G to T) mutation, which results in the deletion of residues 290-319 of PS-1 (PS-1 delta 290-319). In a fourth pedigree, a novel PS-1 mutation was identified in exon 7 (M233T), which is homologous to a pathogenic PS-2 mutation (M239V), and is characterized by a very early average age of onset (before the age of 35). In one early onset case, another novel PS-1 mutation was identified in exon 8 (R278T). Of the five remaining families and the other early onset case, none have missense mutations in the PS-1 or PS-2 genes, or in exon 16 and 17 of the APP gene. Moreover, two of the PS-1 mutations, PS-1 delta 290-319 and R278T, are associated with the co-presentation of familial spastic paraparesis (FSP) in some of the affected family members. Our data raise the possibility that the phenotypic spectrum associated with PS-1 mutations may extend beyond typical FAD to include FSP, a disease heretofore unsuspected to bear any relationship to FAD. In addition, our data suggest that other novel EOFAD loci, in addition to APP and the presenilin genes, are involved in the aetiology of up to 50% of EOFAD cases.