Yuriko Saito

What Can Be Seen by 18F-FDG PET in Atherosclerosis Imaging? The Effect of Foam Cell Formation on 18F-FDG Uptake to Macrophages In Vitro

18F-FDG PET is a promising tool for detecting vulnerable plaques, depending on the extent of macrophage infiltration; however, it is still not clear which stage of the lesion can be detected by 18F-FDG PET. Methods: In this study, we investigated the effect of foam cell formation on 18F-FDG uptake using cultured mouse peritoneal macrophages. Results: 18F-FDG accumulation was increased by foam cell formation, but the uptake was decreased to the control level after complete differentiation to foam cells. Changes in hexokinase activity tended to accompany changes in 18F-FDG uptake. In contrast, changes in glucose-6-phosphatase activity and glucose transporter 1 expression did not parallel 18F-FDG uptake. Conclusion: Our results suggest that 18F-FDG PET detects the early stage of foam cell formation in atherosclerosis.

Alterations in α4β2 nicotinic receptors in cognitive decline in Alzheimer’s aetiopathology

Nicotinic acetylcholine receptor subtype α4β2 is considered important in the regulation of attention and memory, and cholinergic degeneration is known as one pathophysiology of Alzheimers disease. Brain amyloid-β protein deposition is also a key pathological marker of Alzheimers disease. Recent amyloid-β imaging has shown many cognitively normal subjects with amyloid-β deposits, indicating a missing link between amyloid-β deposition and cognitive decline. To date, the relationship between the α4β2 nicotinic acetylcholine receptor and amyloid-β burden has not been elucidated in vivo. In this study we investigated the relation between α4β2 nicotinic acetylcholine receptor availability in the brain, cognitive functions and amyloid-β burden in 20 non-smoking patients with Alzheimers disease at an early stage and 25 age-matched non-smoking healthy elderly adults by measuring levels of α4β2 nicotinic acetylcholine receptor binding estimated from a simplified ratio method (BPRI) and Logan plot-based amyloid-β accumulation (BPND) using positron emission tomography with α4β2 nicotinic acetylcholine receptor tracer (18)F-2FA-85380 and (11)C-Pittsburgh compound B. The levels of tracer binding were compared with clinical measures for various brain functions (general cognition, episodic and spatial memory, execution, judgement, emotion) using regions of interest and statistical parametric mapping analyses. Between-group statistical parametric mapping analysis showed a significant reduction in (18)F-2FA-85380 BPRI in the cholinergic projection region in patients with Alzheimers disease with a variety of (11)C-Pittsburgh compound B accumulation. Spearman rank correlation analyses showed positive correlations of (18)F-2FA-85380 BPRI values in the medial frontal cortex and nucleus basalis magnocellularis region with scores of the Frontal Assessment Battery (a test battery for executive functions and judgement) in the Alzheimers disease group (P < 0.05 corrected for multiple comparison), and also positive correlations of the prefrontal and superior parietal (18)F-2FA-85380 BPRI values with the Frontal Assessment Battery score in the normal group (P < 0.05 corrected for multiple comparison). These positive correlations indicated an in vivo α4β2 nicotinic acetylcholine receptor role in those specific functions that may be different from memory. Both region of interest-based and voxelwise regression analyses showed a negative correlation between frontal (11)C-Pittsburgh compound B BPND and (18)F-2FA-85380 BPRI values in the medial frontal cortex and nucleus basalis magnocellularis region in patients with Alzheimers disease (P < 0.05 corrected for multiple comparison). These findings suggest that an impairment of the cholinergic α4β2 nicotinic acetylcholine receptor system with the greater amount of amyloid deposition in the system plays an important role in the pathophysiology of Alzheimers disease.

Comparison of semiquantitative fluorescence imaging and PET tracer uptake in mesothelioma models as a monitoring system for growth and therapeutic effects

INTRODUCTIONnVarious techniques are available for in vivo imaging, and precise understanding of their characteristics is essential for effective use of the imaging results. We established human mesothelioma cell lines expressing red fluorescent protein (RFP) and examined their fluorescence intensity and uptake of positron emission tomography (PET) tracer analogs to compare their characteristics and assess their usefulness in the evaluation of therapeutics.nnnMETHODnA human mesothelioma cell line was stably transfected to express RFP. Fluorescence, cell number and protein amount were measured during cell growth and treatment with cytotoxic reagents. In in vivo experiments, RFP-expressing cells were injected subcutaneously or into the pleural cavity of nude mice, and fluorescence images were taken with or without pemetrexed treatment. The uptake of [(3)H]3-deoxy-3-fluorothymidine ([(3)H]FLT) and [(14)C]2-fluoro-2-deoxy-d-glucose ([(14)C]FDG) under treatment with the above reagents in vitro and in vivo were examined.nnnRESULTSnStrong correlation was observed between fluorescence intensity and total cell number with or without cytotoxic treatment. The uptake of [(3)H]FLT and [(14)C]FDG decreased rapidly after the initiation of treatment with actinomycin D or cycloheximide. When treated with pemetrexed, the uptake of [(3)H]FLT temporarily increased. The cells formed subcutaneous and orthotopic tumors, with fluorescence intensity correlating with tumor volume. The correlation was sustained under pemetrexed treatment. The uptake of [(3)H]FLT in vivo increased significantly early after pemetrexed treatment.nnnCONCLUSIONnFluorescence imaging could be used to semiquantitatively monitor tumor size, whereas PET could be used to monitor tumor response to therapeutic treatments, and especially, FLT might be a good marker of the response to anti-folate chemotherapeutics.

Basic Studies on Radioimmunotargeting of CD133-Positive HCT116 Cancer Stem Cells

As cancer stem cells (CSCs) are postulated to play critical roles in cancer development, including metastasis and recurrence, CSC imaging would provide valuable information for cancer treatment and lead to CSC-targeted therapy. To assess the possibility of in vivo CSC targeting, we conducted basic studies on radioimmunotargeting of cancer cells positive for CD133, a CSC marker recognized in various cancers. Antibodies against CD133 were labeled with 125I, and their in vitro cell binding properties were tested. Using the same isotype IgG as a control, in vivo biodistribution of the labeled antibody retaining immunoreactivity was examined in mice bearing an HCT116 xenograft in which a population of the cancer cells expressed CD133. Intratumoral distribution of the labeled antibody was examined and compared to the CD133 expression pattern. The 125I-labeled anti-CD133 antibody showed a modest but significantly higher accumulation in the HCT116 xenograft compared to the control IgG. The intratumoral distribution of the labeled antibody mostly overlapped with the CD133 expression, whereas the control IgG was found in the area close to the necrotic tumor center. Our results indicate that noninvasive in vivo targeting of CSCs could be possible with radiolabeled antibodies against cell membrane markers.

Fusion protein based on Grb2-SH2 domain for cancer therapy

Epidermal growth factor receptor (EGFR) is one of the very attractive targets for cancer therapy. In this study, we generated fusion proteins containing one or two Src-homology 2 (SH2) domains of growth factor receptor bound protein 2 (Grb2), which bind to phosphorylated EGFR, added with HIV-1 transactivating transcription for cell membrane penetration (termed TSF and TSSF, respectively). We examined if they can interfere Grb2-mediated signaling pathway and suppress tumor growth as expected from the lack of SH3 domain, which is necessary to intermediate EGFR-Grb2 cell signaling, in the fusion proteins. The transduction efficiency of TSSF was similar to that of TSF, but the binding activity of TSSF to EGFR was higher than that of TSF. Treatment of EGFR-overexpressing cells showed that TSSF decreased p42-ERK phosphorylation, while TSF did not. Both the proteins delayed cell growth but did not induce cell death in culture. TSSF also significantly suppressed tumor growth in vivo under consecutive administration. In conclusion, TSSF showed an ability to inhibit EGFR-Grb2 signaling and could have a potential to treat EGFR-activated cancer.

Development of radioiodinated lipophilic cationic compounds for myocardial imaging

INTRODUCTIONnTc-99m compounds are mainly used in myocardial blood flow studies. These compounds, however, are produced by a generator and alternate single photon emission computed tomography (SPECT) radiopharmaceuticals are therefore required to avoid the risks posed by generator failure. Three radiolabeled compounds, including [(125)I]p-iodobenzyl triphenylphosphonium ([(125)I]ITPP), [(125)I]p-Iodobenzyl dipropylphenylphosphonium ([(125)I]IDPP) and [(125)I]p-iodobenzyl methyldiphenylphosphonium ([(125)I]IMPP), have been synthesized in the current study. All three of these compounds contain a lipophilic cation, which enhances their cell permeability properties and allows them to accumulate in the myocardium as SPECT probes.nnnMETHODSn4-(2-Tributylstannyl) benzyl alcohol was mixed with [(125)I]NaI in the presence of aqueous hydrogen peroxide and hydrochloric acid to allow for the synthesis of 4-[(125)I]iodobenzyl alcohol. Bromination of the alcohol under standard conditions gave 4-[(125)I]iodo benzyl bromide, which was treated with triphenylphosphine, dipropylphenylphosphine or methyldiphenylphosphine to give [(125)I]ITPP, [(125)I]IDPP and [(125)I]IMPP, respectively. These compounds were evaluated in biodistribution and SPECT studies in normal ddY mice.nnnRESULTSnAll three of the radiolabeled compounds were synthesized in approximately 60% yield with radiochemical purities greater than 99%. The specific activity of each compound was 74 GBq/μmol. The results of the biodistribution and SPECT studies showed that all compounds accumulated preferentially in the heart in vivo, especially [(125)I]IDPP.nnnCONCLUSIONn[(123)I] IDPP could be used in clinical practice as a novel myocardial imaging agent.