Current Perspectives on 89Zr-PET Imaging.

89Zr is an emerging radionuclide that plays an essential role in immuno-positron emission tomography (PET) imaging. The long half-life of 89Zr (t1/2 = 3.3 days) is favorable for evaluating the in vivo distribution of monoclonal antibodies. Thus, the use of 89Zr is promising for monitoring antibody-based cancer therapies. Immuno-PET combines the sensitivity of PET with the specificity of antibodies. A number of studies have been conducted to investigate the feasibility of 89Zr immuno-PET imaging for predicting the efficacy of radioimmunotherapy and antibody therapies, imaging target expression, detecting target-expressing tumors, and the monitoring of anti-cancer chemotherapies. In this review, we summarize the current status of PET imaging using 89Zr in both preclinical and clinical studies by highlighting the use of immuno-PET for the targets of high clinical relevance. We also present 89Zr-PET applications other than immuno-PET, such as nanoparticle imaging and cell tracking. Finally, we discuss the limitations and the ongoing research being performed to overcome the remaining hurdles.

Therapeutic effect of mesenchymal stem cells in an animal model of Alzheimer's disease evaluated by ß-amyloid positron emission tomography imaging.

OBJECTIVE: We evaluated the effects of bone marrow-derived mesenchymal stem cells in a model of Alzheimer's disease using serial [18F]Florbetaben positron emission tomography. METHODS: 3xTg Alzheimer's disease mice were treated with intravenously injected bone marrow-derived mesenchymal stem cells, and animals without stem cell therapy were used as controls. Serial [18F]Florbetaben positron emission tomography was performed after therapy. The standardized uptake value ratio was measured as the cortex standardized uptake value divided by the cerebellum standardized uptake value. Memory function and histological changes were observed using the Barnes maze test and ß-amyloid-reactive cells. RESULTS: Standardized uptake value ratio decreased significantly from day 14 after stem cell administration in the bone marrow-derived mesenchymal stem cells-treated group (n = 28). In contrast, there was no change in the ratio in control mice (n = 25) at any time point. In addition, mice that received bone marrow-derived mesenchymal stem cell therapy also exhibited significantly better memory function and less ß-amyloid-immunopositive plaques compared to controls. CONCLUSION: The therapeutic effect of intravenously injected bone marrow-derived mesenchymal stem cells in a mouse model of Alzheimer's disease was confirmed by ß-amyloid positron emission tomography imaging, memory functional studies and histopathological evaluation.

Expression of Cellular Receptors in the Ischemic Hemisphere of Mice with Increased Glucose Uptake.

Many previous studies have shown reduced glucose uptake in the ischemic brain. In contrast, in a permanent unilateral common carotid artery occlusion (UCCAO) mouse model, our pilot experiments using 18F-fluorodeoxyglucose positron emission tomography (FDG PET) revealed that a subset of mice exhibited conspicuously high uptake of glucose in the ipsilateral hemisphere at 1 week post-occlusion (asymmetric group), whereas other mice showed symmetric uptake in both hemispheres (symmetric group). Thus, we aimed to understand the discrepancy between the two groups. Cerebral blood flow and histological/metabolic changes were analyzed using laser Doppler flowmetry and immunohistochemistry/Western blotting, respectively. Contrary to the increased glucose uptake observed in the ischemic cerebral hemisphere on FDG PET (p<0.001), cerebral blood flow tended to be lower in the asymmetric group than in the symmetric group (right to left ratio [%], 36.4±21.8 vs. 58.0±24.8, p=0.059). Neuronal death was observed only in the ischemic hemisphere of the asymmetric group. In contrast, astrocytes were more activated in the asymmetric group than in the symmetric group (p<0.05). Glucose transporter-1, and monocarboxylate transporter-1 were also upregulated in the asymmetric group, compared with the symmetric group (p<0.05, respectively). These results suggest that the increased FDG uptake was associated with relatively severe ischemia, and glucose transporter-1 upregulation and astrocyte activation. Glucose metabolism may thus be a compensatory mechanism in the moderately severe ischemic brain.

Cell cycle synchronisation using thiazolidinediones affects cellular glucose metabolism and enhances the therapeutic effect of 2-deoxyglucose in colon cancer.

The effect of cell cycle synchronisation on glucose metabolism in cancer cells is not known. We assessed how cell cycle synchronisation by thiazolidinediones (TZDs) can affect glucose uptake by cancer cells and investigated the anti-cancer effect of combination therapy with TZDs and 2-deoxy-glucose (2-DG) in colon cancer cells and in mouse xenograft models. Troglitazone (58.1 ± 2.0 vs 48.6 ± 1.3%, p = 0.002) or pioglitazone (82.9 ± 1.9 vs 61.6 ± 3.4%, p < 0.001) induced cell cycle arrest in SW480 cells at G1 phase. Western blot analysis showed the degradation of cyclin D1 and CDK4, and an increase in the expression levels of p21 and p27 after TZDs treatment. Withdrawal of troglitazone treatment induced significant increase in cellular 3H-DG uptake (141.5% ± 12.9% of controls) and membrane GLUT1 expression levels (146.3% of controls) by 24 h; 1 mM 2-DG treatment alone decreased cell survival by 5.8% as compared with the controls.; however, combination therapy enhanced the anti-tumour effects to 34.6% or 20.3% as compared with control cells. In vivo, each combination treatment group showed significant anti-tumour effects unlike the 2-DG alone group. Cell cycle synchronisation using TZDs induced cellular glucose uptake, which significantly enhanced the therapeutic effect of 2-DG in colon cancer.

Zr-89 Immuno-PET Targeting Ectopic ATP Synthase Enables In-Vivo Imaging of Tumor Angiogenesis.

In this study, we synthesized a Zr-89-labeled anti-adenosine triphosphate synthase monoclonal antibody (ATPS mAb) for applications in immuno-positron emission tomography (PET) and evaluated its feasibility for angiogenesis imaging. The cellular uptake of Zr-89 ATPS mAb was measured after treatment of cancer cell lines in vitro, and its biodistribution was evaluated at 4, 24 and 48 h in vivo in mice bearing xenografts. PET images were acquired at 4, 24, 48, and 96 h after Zr-89 ATPS mAb administration. Tumor angiogenesis was analyzed using anti-CD31 immunofluorescence staining. The cellular uptake of Zr-89 ATPS mAb increased over time in MDA-MB-231 breast cancer cells but did not increase in PC3 prostate cancer cells. The tumor uptake of Zr-89 ATPS mAb at 24 h was 9.4 ± 0.9% ID/g for MDA-Mb-231 cells and was 3.8 ± 0.6% ID/g for PC3 cells (p = 0.004). Zr-89 ATPS mAb uptake in MDA-MB-231 xenografts was inhibited by the administration of cold ATPS mAb (4.4 ± 0.5% ID/g, p = 0.011). Zr-89 ATPS mAb uptake could be visualized by PET for up to 96 h in MDA-MB-231 tumors. In contrast, there was no distinct tumor uptake detected by PET in the PC3 xenograft model. CD31-positive tumor vessels were abundant in MDA-MB-231 tumors, whereas they were scarcely detected in PC3 tumors. In conclusion, ATPS mAb was successfully labeled with Zr-89, which could be used for immuno-PET imaging targeting tumor angiogenesis.

In vivo tracking of intravenously injected mesenchymal stem cells in an Alzheimer's animal model.

PURPOSE: The purpose of this study was to investigate how intravenously injected bone marrow-derived mesenchymal stem cells (BMSCs) are distributed in the body of an Alzheimer's disease (AD) animal model. METHODS: Stem cells were collected from bone marrow of mice and labeled with Indium-111 (111In). The 111In-labeled BMSCs were infused intravenously into 3×Tg-AD mice in the AD group and non-transgenic mice (B6129SF2/J) as controls. Biodistribution was evaluated with a gamma counter and gamma camera 24 and 48 h after injecting the stem cells. RESULTS: A gamma count of the brain showed a higher distribution of labeled cells in the AD model than in the control group at 24 (p = .0004) and 48 h (p = .0016) after injection of the BMSCs. Similar results were observed by gamma camera imaging (i.e., brain uptake in the AD model was significantly higher than that in the control group). Among the other organs, uptake by the spleen was the highest in both groups. More BMSCs were found in the lungs of the control group than in those of the AD group. CONCLUSIONS: These results suggest that more intravenously infused BMSCs reached the brain in the AD model than in the control group, but the numbers of stem cells reaching the brain was very small.

Radiolabeled Anti-Adenosine Triphosphate Synthase Monoclonal Antibody as a Theragnostic Agent Targeting Angiogenesis.

INTRODUCTION: The potential of a radioiodine-labeled, anti-adenosine triphosphate synthase monoclonal antibody (ATPS mAb) as a theragnostic agent for simultaneous cancer imaging and treatment was evaluated. METHODS: Adenosine triphosphate synthase monoclonal antibody was labeled with radioiodine, then radiotracer uptake was measured in 6 different cancer cell lines. In vivo biodistribution was evaluated 24 and 48 hours after intravenous injection of 125I-ATPS mAb into MKN-45 tumor-bearing mice (n = 3). For radioimmunotherapy, 18.5 MBq 131I-ATPS mAb (n = 7), isotype immunoglobulin G (IgG) (n = 6), and vehicle (n = 6) were injected into MKN-45 tumor-bearing mice for 4 weeks, and tumor volume and percentage of tumor growth inhibition (TGI) were compared each week. RESULTS: MKN-45 cells showed the highest in vitro cellular binding after 4 hours (0.00324 ± 0.00013%/µg), which was significantly inhibited by unlabeled ATPS mAb at concentrations of greater than 0.4 µM. The in vitro retention rate of 125I-ATPS mAb in MKN-45 cells was 64.1% ± 1.0% at 60 minutes. The highest tumor uptake of 125I-ATPS mAb in MKN-45 tumor-bearing mice was achieved 24 hours after injection (6.26% ± 0.47% injected dose [ID]/g), whereas tumor to muscle and tumor to blood ratios peaked at 48 hours. The 24-hour tumor uptake decreased to 3.43% ± 0.85% ID/g by blocking with unlabeled ATPS mAb. After 4 weeks of treatment, mice receiving 131I-ATPS mAb had significantly smaller tumors (679.4 ± 232.3 mm3) compared with control (1687.6 ± 420.4 mm3, P = .0431) and IgG-treated mice (2870.2 ± 484.1 mm3, P = .0010). The percentage of TGI of 131I-ATPS mAb was greater than 50% during the entire study period (range: 53.7%-75.9%). CONCLUSION: The specific binding and antitumor effects of radioiodinated ATPS mAb were confirmed in in vitro and in vivo models of stomach cancer.

Enhancing the Therapeutic Efficacy of 2-Deoxyglucose in Breast Cancer Cells Using Cell-cycle Synchronization.

AIM: We assessed the effect of cell-cycle synchronization using the T-type calcium channel inhibitor mibefradil on the anticancer effects of 2-deoxy-D-glucose (2-DG) and glucose metabolism in breast cancer cells. MATERIALS AND METHODS: MDA-MB-231 cells were treated with mibefradil, followed by 2-DG with/without paclitaxel, then cells were assessed for viability. Glucose metabolism was evaluated by 3H-2-DG uptake, lactate concentration, and membrane glucose transporter 1 expression after mibefradil treatment. RESULTS: Viability was significantly lower in cells receiving the combination therapy of mibefradil and 2-DG relative to 2-DG treatment alone; addition of paclitaxel to the combination therapy further reduced the viability of breast cancer cells. Withdrawal of mibefradil resulted in a significant increase in cellular 3H-2-DG uptake uptake, a slight accumulation of lactate, and increased membrane glucose transporter 1 expression. CONCLUSION: Mibefradil-induced cell-cycle synchronization enhanced the anticancer activity of 2-DG in breast cancer cells due to an increase in cellular glucose metabolism.

Improved dopamine transporter binding activity after bone marrow mesenchymal stem cell transplantation in a rat model of Parkinson's disease: small animal positron emission tomography study with F-18 FP-CIT.

OBJECTIVES: We evaluated the effects of bone marrow-derived mesenchymal stem cells (BMSCs) in a model of Parkinson's disease (PD) using serial F-18 fluoropropylcarbomethoxyiodophenylnortropane (FP-CIT) PET. METHODS: Hemiparkinsonian rats were treated with intravenously injected BMSCs, and animals without stem cell therapy were used as the controls. Serial FP-CIT PET was performed after therapy. The ratio of FP-CIT uptake in the lesion side to uptake in the normal side was measured. The changes in FP-CIT uptake were also analyzed using SPM. Behavioural and histological changes were observed using the rotational test and tyrosine hydroxylase (TH)-reactive cells. RESULTS: FP-CIT uptake ratio was significantly different in the BMSCs treated group (n = 28) at each time point. In contrast, there was no difference in the ratio in control rats (n = 25) at any time point. SPM analysis also revealed that dopamine transporter binding activity was enhanced in the right basal ganglia area in only the BMSC therapy group. In addition, rats that received BMSC therapy also exhibited significantly improved rotational behaviour and preservation of TH-positive neurons compared to controls. CONCLUSIONS: The therapeutic effect of intravenously injected BMSCs in a rat model of PD was confirmed by dopamine transporter PET imaging, rotational functional studies, and histopathological evaluation. KEY POINTS: • Mesenchymal stem cells were intravenously injected to treat the PD rats • Dopamine transporter binding activity was improved after stem cell therapy • Stem cell therapy induced functional recovery and preservation of dopaminergic neurons • The effect of stem cells was confirmed by FP-CIT PET.

High-dose (111)in induces g1 cell cycle arrest and cell death in rat bone marrow mesenchymal stem cells.

PURPOSE: This study was performed to evaluate the effect of (111)In-labeling on the cell growth, cycle and viability of bone marrow mesenchymal stem cells (BMSCs). METHODS: Rat BMSCs were labeled with various doses of (111)In (0.4-11.1 Bq/cell). The growth curve of (111)In-BMSCs was obtained up to 14th day of labeling. The cell cycle was evaluated by 5-bromo-2-deoxyuridine (BrdU) labeling or propidium iodide (PI) staining. Senescent cells were counted under a light microscope after staining with 5-bromo-4-chloro-3-indolyl-D-galactopyranoside. Flow cytometry was performed to measure apoptotic and necrotic fractions after staining with annexin V-FITC and PI. RESULTS: The growth of BMSCs labeled with higher doses of (111)In (4.4 or 11.1 Bq/cell) was significantly inhibited from the 3rd day of labeling. Flow cytometry revealed less BrdU-positive BMSCs at 11.1 Bq (111)In/cell during all measurement days and G1 arrest at 4.4 and 11.1 Bq (111)In/cell. Significant increases in apoptosis and necrosis were also observed at 4.4 (3.04%/1.35%) and 11.1 Bq (111)In/cell (9.07%/3.18%) on the 14th day (control = 1.60%/0.39%). However, no cellular senescence was visualized up to the 14th day. CONCLUSION: A high dose of (111)In-labeling induced cell cycle arrest and death in BMSCs; therefore, it should be used with a careful dosimetry in case of applying it to humans.

Early distribution of intravenously injected mesenchymal stem cells in rats with acute brain trauma evaluated by (99m)Tc-HMPAO labeling.

INTRODUCTION: Stem cell tracking is essential for evaluation of its migration, transplantation and therapeutic response. The aim of this study was to evaluate early distribution of intravenously transplanted rat bone marrow mesenchymal stem cells (BMSCs) in rats with acute cerebral trauma by labeling with (99m)Tc-hexamethylpropyleneamine oxime ((99m)Tc-HMPAO). METHODS: (99m)Tc-HMPAO-labeled BMSCs were injected intravenously to trauma rats (n=14) and sham-operated controls (n=13). Gamma camera images were acquired at 4 h after injection, and then organs were removed for gamma counting. Confocal microscope was used to confirm the migration of (99m)Tc-BMSCs by co-labeling with PKH26. Cytometric analysis was performed to evaluate apoptotic or necrotic change until the seventh day after labeling. RESULTS: (99m)Tc-BMSCs were distributed mostly to lungs, liver and spleen at 4 h, and uptake of these organs was not significantly different between traumatic rats and controls. Meanwhile, the cerebral uptake of (99m)Tc-BMSCs was significantly higher in the traumatic rats than in controls (0.40% vs. 0.20%; P=.0002). Additionally, (99m)Tc-BMSCs' uptake of traumatic hemisphere was significantly higher than that of contralateral ones (0.27% vs. 0.13%; P=.0001) in traumatic rats. Regardless of radiolabeling, BMSCs migrated to traumatic regions, but not to nontraumatic hemispheres. However, gamma camera failed to demonstrate (99m)Tc-BMSCs in traumatic hemispheres. No significant apoptotic or necrotic change was observed until 7 days after radiolabeling. CONCLUSIONS: Early distribution of BMSCs in traumatic brain disease could be monitored by (99m)Tc-labeling, which does not induce cellular death. However, our data showed that the amount of migrated (99m)Tc-BMSCs was not enough to be demonstrated by clinical gamma camera.

In vivo tracking of 111In-labeled bone marrow mesenchymal stem cells in acute brain trauma model.

INTRODUCTION: This study was to evaluate the in vivo distribution of intravenously transplanted bone marrow-derived mesenchymal stem cells (BMSCs) in an acute brain trauma model by (111)In-tropolone labeling. METHODS: Rat BMSCs were labeled with 37 MBq (111)In-tropolone. Their labeling efficiency and in vitro retention rate were measured. The viability and proliferation of labeled BMSCs were evaluated for 14 days after labeling. The biodistribution of (111)In-labeled BMSCs in trauma models was compared with those of sham-operated rats and normal rats on gamma camera images. The migration of (111)In-BMSCs to the traumatic brain was evaluated using confocal microscope. RESULTS: The labeling efficiency of (111)In-BMSCs was 66+/-5%, and their retention rate was 85.3% at 1 h after labeling. There was no difference in the number of viable cells between (111)In-BMSCs and controls at 48 h after labeling. However, the proliferation of (111)In-BMSCs was inhibited after the third day of labeling, and it did not reach confluency. On gamma camera images, most of the (111)In-BMSCs uptake was observed in the liver and spleen at the second day of injection. The brain uptake of (111)In-BMSCs was detected prominently in trauma models (1.4%) than in sham-operated (0.5%) or normal rats (0.3%). Radiolabeled BMSCs were observed at the traumatic brain on the confocal microscope as they have a homing capacity, although its proliferation capacity was suppressed. CONCLUSION: Although growth inhibition by (111)In-labeling need to be evaluated further prior to use in humans, (111)In-labeled BMSCs are useful for the tracking of intravenously transplanted mesenchymal stem cells in brain disease models.

Effects of theophylline on radioiodide uptake in MCF-7 breast cancer and NIS gene-transduced SNU-C5 colon cancer cells.

BACKGROUND: We investigated whether theophylline has the potential to increase radioiodide uptake in nonthyroidal cancer cells. MATERIALS AND METHODS: MCF-7 cells that express endogenous sodium/iodide symporter (NIS) and SNU-C5 cells adenovirally transduced with the human NIS gene (SNU-C5/NIS) were treated with 10(-7)-2x10(-4) mol/L theophylline for 24 hours before incubation with (125)I, and then, radioiodide uptake and retention were measured. NIS expression was assessed by immunohistochemistry and Western blot analysis, using an antihuman NIS monoclonal antibody. RESULTS: Theophylline at 10(-6)-2x10(-4) mol/L significantly and dose dependently augmented radioiodide uptake in MCF-7 cells and at 10(-6)-10(-5) mol/L in SNU-C5/NIS cells, without affecting radioiodide efflux. Abrogation by KClO(4)(-) demonstrated that the effect of theophylline occurred through specific iodide transport. Immunohistochemistry revealed dose-dependent increases of NIS staining in MCF-7 and SNU-C5/NIS cells by 10(-6)-10(-4) and 10(-6)-10(-5) mol/L theophylline, respectively. Western blot analysis demonstrated similar findings, showing increased expression of NIS on the membrane of SNU-C5/NIS and MCF-7 cells by theophylline treatment. CONCLUSIONS: Theophylline can augment radioiodide uptake in breast cancer cells and NIS gene-transduced cancer cells through the upregulation of NIS expression. Therefore, further investigations are warranted to explore the potential utility of this phenomenon for enhancing radioiodide-based imaging and therapies of NIS gene-transduced cancer cells.