A dual-time-window protocol to reduce acquisition time of dynamic tau PET imaging using [F-18]MK-6240

Background [F-18]MK-6240 is a PET tracer with sub-nanomolar affinity for neurofibrillary tangles. Therefore, tau quantification is possible with [F-18]MK-6240 PET/CT scans, and it can be used for assessment of Alzheimer's disease. However, long acquisition scans are required to provide fully quantitative estimates of pharmacokinetic parameters. Therefore, on the present study, dual-time-window (DTW) acquisitions was simulated to reduce PET/CT acquisition time, while taking into consideration perfusion changes and possible scanning protocol non-compliance. To that end, time activity curves (TACs) representing a 120-min acquisition (TAC(120)) were simulated using a two-tissue compartment model with metabolite corrected arterial input function from 90-min dynamic [F-18]MK-6240 PET scans of three healthy control subjects and five subjects with mild cognitive impairment or Alzheimer's disease. Therefore, TACs corresponding to different levels of specific binding were generated and then various perfusion changes were simulated. Next, DTW acquisitions were simulated consisting of an acquisition starting at tracer injection, a break and a second acquisition starting at 90 min post-injection. Finally, non-compliance with the PET/CT scanning protocol were simulated to assess its impact on quantification. All TACs were quantified using reference Logan's distribution volume ratio (DVR) and standardized uptake value ratio (SUVR90) using the cerebellar cortex as reference region. Results It was found that DVR from a DTW protocol with a 60-min break between two 30-min dynamic scans closely approximates the DVR from the uninterrupted TAC(120), with a regional bias smaller than 2.5%. Moreover, SUVR90 estimates were more susceptible (regional bias</p

Evaluation of New Adenoviral Mediated In Vivo FES-Herl PET Tracer-Reporter Gene System for Gene Therapy Monitoring.

The Fifth Annual Meeting The Society for Molecular Imagin

In vivo Evaluation of Adenoviral Mediated FES-hERL PET Tracer-Reporter Gene System for Gene Therapy Monitoring

A key step in advancing gene therapy protocols is to establish an efficient monitoring system following target gene delivery. Earlier, we reported our new adenoviral mediated PET reporter gene system utilizing [18F]16alpha-fluoroestradiol (FES) as PET probe and human estrogen receptor alpha ligand binding domain (hERL) as PET reporter gene and evaluated basic cell culture and initial in vivo autoradiographic studies in mice [1]. Now, we report further cell model studies and in vivo PET imaging in rats.An in vitro FES binding study was performed on MRC-5 (human lung fibroblasts) and Cos-7 (African green monkey kidney) cells infected with varying titers of test and control viruses or transfected with varying amounts of test plasmid. After 10 min uptake and 30 min intermittent wash, the FES accumulation was higher in both the cell lines infected with test virus than those transfected by test plasmid. The uptake also increased with rise in viral titer in contrast to decreasing uptake with increased plasmid amounts. The co-expression of hERL and a model therapeutic gene by the correspondingly infected cells confirmed the results of binding study.The rats were injected with test and control adenoviruses into opposite hind limb adductor muscles. In vivo PET imaging in 6-days post-infected rat yielded positive accumulation of FES on the side injected with test virus. Furthermore, the correspondingly resected muscle samples were subjected to immunohistochemical staining and the expression of reporter and therapeutic genes were confirmed. Thus, we could successfully image the expression of our reporter gene hERL in vivo in a localized area of muscle tissue in rats. We hope confirmation of reporter gene expression following infection in other target areas will enable our system to be a significant addition to the existing repertoires of reporter gene system.Joint Molecular Imaging Conferenc

In vivo evalustaion of adenoviral mediated FES-hERL PET tracer-reporter gene system for gene therapy monitoring

第２回日本分子イメージング学会総会・学術集

Basic evaluation of FES-hERL PET tracer-reporter gene system for in vivo monitoring of adenoviral-mediated gene therapy

PURPOSE: The purpose of the study is to evaluate the feasibility of human estrogen receptor alpha ligand binding domain (hERL) as a reporter gene in combination with positron emission tomography (PET) probe, 16alpha-[18F]fluoro-17beta-estradiol (FES), in an adenovirus gene delivery system. METHODS: An adenoviral vector (test), carrying hERL gene and a model angiogenesis therapeutic gene (human thymidine phosphorylase, hTP) was constructed along with a control vector. In vitro radioligand binding and expression studies were performed on various cell lines. The control and test viruses were injected into contralateral adductor muscles of a rat followed by FES-PET imaging and immunohistochemical staining of resected muscle samples. RESULTS: A high FES uptake accompanied by hERL and hTP expression was obtained both in vitro and in vivo by the test adenovirus infection. CONCLUSION: Considering the versatile tissue permeability of the probe, highly efficient gene expression, and safeness for human use, we expect our reporter gene system to have favorable characteristics for clinical application

Is metabotropic glutamate receptor 5 upregulated in prefrontal cortex in fragile X syndrome?

Abstract Background: Fragile X syndrome (FXS) is a common inherited form of intellectual disability caused by loss of function of the fragile X mental retardation protein. Recent animal studies suggest that upregulated downstream signaling by metabotropic glutamate receptor 5 (mGluR5) might be an important mechanism for cognitive and behavioral abnormalities associated with FXS. However, mGluR5 density in human FXS remains unknown. Methods: Receptor binding and protein expression were measured in the postmortem prefrontal cortex of 14 FXS patients or carriers and 17 age- and sex-matched control subjects without neurological disorders. In-vitro binding assays were performed using [[superscript 3]H]-labeled 3-methoxy-5-pyridin-2-ylethynylpyridine (MPEPy), a selective and high-affinity negative allosteric modulator of mGluR5, to measure receptor density and the radioligand&#8217;s dissociation constant, which is inversely proportional to affinity. Immunoblotting was also performed, to measure mGluR5 protein expression. Results: The mGluR5 density increased with marginal significance (+16%; P = 0.058) in the prefrontal cortex of FXS patients or carriers compared with matched healthy controls. No significant change in dissociation constant (-4%; P = 0.293) was observed. Immunoblotting found a significant elevation (+32%; P = 0.048) in mGluR5 protein expression. Conclusions: Both mGluR5 binding density and protein expression were increased in the brains of FXS patients or carriers, but only expression was significantly different, which could be because of the small sample size and moderate variability. Another important caveat is that the effects of psychotropic medications on mGluR5 expression are largely unknown. Future in-vivo measurement of mGluR5 with positron emission tomography might characterize the role of this receptor in the pathophysiology of FXS and facilitate trials of mGluR5-oriented treatments for this disorder.National Institute of Mental Health (U.S.)National Institutes of Health (U.S.) (IRP-NIMHNIH

Comparison of two PET radioligands, [11C]FPEB and [11C]SP203, for quantification of metabotropic glutamate receptor 5 in human brain

Of the two (18)F-labeled PET ligands currently available to image metabotropic glutamate receptor 5 (mGluR5), [(18)F]FPEB is reportedly superior because [(18)F]SP203 undergoes glutathionlyation, generating [(18)F]-fluoride ion that accumulates in brain and skull. To allow multiple PET studies on the same day with lower radiation exposure, we prepared [(11)C]FPEB and [(11)C]SP203 from [(11)C]hydrogen cyanide and compared their abilities to accurately quantify mGluR5 in human brain, especially as regards radiometabolite accumulation. Genomic plot was used to estimate the ratio of specific-to-nondisplaceable uptake (BPND) without using a receptor blocking drug. Both tracers quantified mGluR5; however [(11)C]SP203, like [(18)F]SP203, had radiometabolite accumulation in brain, as evidenced by increased distribution volume (VT) over the scan period. Absolute VT values were ∼30% lower for (11)C-labeled compared with (18)F-labeled radioligands, likely caused by the lower specific activities (and high receptor occupancies) of the (11)C radioligands. The genomic plot indicated ∼60% specific binding in cerebellum, which makes it inappropriate as a reference region. Whole-body scans performed in healthy subjects demonstrated a low radiation burden typical for (11)C-ligands. Thus, the evidence suggests that [(11)C]FPEB is superior to [(11)C]SP203. If prepared in higher specific activity, [(11)C]FPEB would presumably be as effective as [(18)F]FPEB for quantifying mGluR5 in human brain