The objective of this study is to determine the reproducibility of static 2-deoxy-2-[18F] fluoro-D-glucose (18F-FDG), 3′-deoxy-3′-[18F]fluorothymidine (18F-FLT), and [18F]-fluoromisonidazole (18F-FMISO) microPET measurements, as well as kinetic parameters returned from analyses of dynamic 18F-FLT and 18F-FMISO data.
HER2+ xenografts were established in nude mice. Dynamic data were acquired for 60 min, followed by a repeat injection and second scan 6 h later. Reproducibility was assessed for the percent-injected dose per gram (%ID/g) for each radiotracer, and with kinetic parameters (K1–k4, Ki) for 18F-FLT and 18F-FMISO.
The value needed to reflect a change in tumor physiology is given by the 95 % confidence interval (CI), which is ±14, ±5, and ±6 % for 18F-FDG (n=12), 18F-FLT (n=11), and 18F-FMISO (n=11) %ID/g, respectively. Vd (=K1/k2), k3, and KFLT are the most reproducible 18F-FLT (n=9) kinetic parameters, with 95 % CIs of ±18, ±10, and ±18 %, respectively. Vd and KFMISO are the most reproducible 18F-FMISO kinetic parameters (n=7) with 95 % CIs of ±16 and ±14 %, respectively.
Percent-injected dose per gram measurements are reproducible and appropriate for detecting treatment-induced changes. Kinetic parameters have larger threshold values, but are potentially sufficiently reproducible to detect treatment response.
Reproducibility; 18F-FDG; 18F-FLT; 18F-FMISO; Kinetic modeling
Near-infrared fluorescence (NIRF) imaging is an attractive technique for studying diseases at the molecular level in vivo. Glucose transporters are often used as targets for in vivo imaging of tumors. The efficiency of a tumor-seeking fluorescent probe can be enhanced by attaching one or more glucosamine (GlcN) moieties. This study was designed to evaluate the use of previously developed GlcN-linked NIRF probes for in vitro and in vivo optical imaging of cancer.
Cellular uptake of the probes (1 μM) was investigated in monolayer cultures of luciferase-expressing PC3 (PC3-luc) cells. The prostate tumors were established as subcutaneous xenografts using PC3-luc cells in nude mice. The biodistributions and tumor-targeting specificities of cypate (cyp), cypate-d-(+)-glucosamine (cyp-GlcN), and d-(+)-gluosamine-cypate-d-(+)-gluosamine (cyp-2GlcN) were studied. The tumor, muscle, and major organs were collected for ex vivo optical imaging.
The tumor cell uptake of the probe containing two glucosamine residues, cyp-2GlcN, was significantly higher than the uptake of both the probe with one glucosamine residue, cyp-GlcN, and the probe without glucosamine, cyp only. Similarly, in in vivo experiments, cyp-2GlcN demonstrated higher maximum fluorescence intensity and longer residence lifetime in tumors than cyp-GlcN or cyp. The ex vivo biodistribution analysis revealed that tumor uptake of cyp-2GlcN and cyp-GlcN was four- and twofold higher than that of cyp at 24 h post-injection, respectively.
Both cyp-GlcN and cyp-2GlcN NIRF probes exhibited good tumor-targeting properties in prostate cancer cell cultures and live mice. The cyp-2GlcN probe showed the highest uptake with good retention characteristics in vivo. The uptake of cyp-2GlcN and cyp-GlcN is likely mediated by glucosamine-recognizing transporters. The uptake mechanism is being explored further for developing cypate-glucosamine-based probes for in vivo imaging.
Optical imaging; Near-infrared fluorescence; Tumor; Prostate cancer; Glucosamine; Cypate
Patients with locally-advanced rectal cancer typically undergo neoadjuvant chemoradiotherapy to decrease the postsurgical recurrence rate. However, neoadjuvant therapy is associated with significant morbidity and not all patients benefit equally. The purpose of this pilot study was to evaluate whether tumor uptake of 18F-labeled 3′-deoxy-3′fluorothymidine (FLT), a proliferative radiotracer, at baseline and early during therapy, is predictive of outcome in locally-advanced rectal cancer.
Methods and Materials
Fourteen patients with rectal cancer underwent positron emission tomography (PET) with FLT before and approximately 2 weeks after initiation of neoadjuvant chemoradiotherapy. All patients underwent PET/CT with 18F-fluorodeoxyglucose (FDG) as part of clinical staging prior to institution of therapy. FLT and FDG uptake were evaluated qualitatively and semiquantitatively by determining the maximum standardized uptake value (SUVmax). Tumor FLT and FDG uptake were correlated with disease-free survival (DFS). Patients were followed for a median of 20 months (range 8 to 37 months).
Thirteen patients underwent surgery following neoadjuvant therapy and one patient died prior to surgery with progressive disease. Overall, pretherapy FDG uptake in the primary tumor was significantly greater than that of pretherapy FLT uptake (p=0.003). FDG-PET/CT was positive for regional lymph node metastases in 5 and FLT-PET detected metastatic disease in only one of these patients. After initiation of therapy, tumor FLT uptake decreased significantly from baseline (p<0.0001). High pretherapy FDG uptake (SUVmax≥14.3), low during-therapy FLT uptake (SUVmax<2.2) and high percentage change in FLT uptake (≥60%) were predictive of improved DFS (p<0.05 for all three values). Pretherapy FLT uptake was not a significant predictor of outcome and did not correlate with DFS (p=NS).
In this pilot study, pretherapy FDG uptake, during-therapy FLT uptake and percentage change in FLT uptake were equally predictive of DFS. In addition, FDG-PET/CT was superior to FLT-PET in detection of metastasis, and thus, in staging rectal cancer.
Positron emission tomography; rectal cancer; proliferation; FLT; PET
The purpose is to address the problem in magnetic resonance imaging (MRI) of contrast agent dilution.
In situ magnetic labeling of cells and MRI were used to assess distribution and growth of human hepatic stem cells (hHpSCs) transplanted into SCID/nod mice. It was done with commercially available magnetic microbeads coupled to an antibody to a surface antigen, Epithelial Cell Adhesion Molecule (EpCAM), uniquely expressed in the liver by hepatic progenitors.
We validated the microbead connection to cells and related MRI data to optical microscopy observations in order to develop a means to quantitatively estimate cell numbers in the aggregates detected. Cell counts of hHpSCs at different times post-transplantation revealed quantifiable evidence of cell engraftment and expansion.
This magnetic labeling methodology can be used with any antibody coupled to a magnetic particle to target any surface antigen that distinguishes transplanted cells from host cells, thus facilitating studies that define methods and strategies for clinical cell therapy programs.
Magnetic resonance imaging (MRI); Cell labeling and tracking; Human hepatic stem cells; Cell therapies; EpCAM
The aim of this study is to compare the utility of two PET imaging ligands ((+)-[11C]dihydrotetrabenazine ([11C]DTBZ) and the fluoropropyl analogue ([18F]FP-(+)-DTBZ)) that target islet β-cell vesicular monoamine transporter type II (VMAT2) to measure pancreatic β-cell mass (BCM).
[11C]DTBZ, or [18F]FP-(+)-DTBZ was injected, and serial PET images were acquired in rat models of diabetes (streptozotocin-treated and Zucker Diabetic Fatty) and β-cell compensation (Zucker Fatty). Radiotracer standardized uptake values (SUV) were correlated to pancreas insulin content measured biochemically and histomorphometrically.
On a group level, a positive correlation of [11C]DTBZ pancreatic SUV with pancreas insulin content and BCM was observed. In the STZ-diabetic model, both [18F]FP-(+)-DTBZ and [11C]DTBZ correlated positively with BCM, although only ~25% of uptake could be attributed to β-cell uptake. [18F]FP-(+)-DTBZ displacement studies indicate that there is a substantial fraction of specific binding that is not to pancreatic islet β-cells.
PET imaging with [18F]FP-(+)-DTBZ provides a non-invasive means to quantify insulin-positive BCM, and may prove valuable as a diagnostic tool in assessing treatments to maintain or restore BCM.
The sigma-2 (σ2) receptor is a potential biomarker of proliferative status of solid tumors. Specific synthetic probes using N-substituted-9-azabicyclo[3.3.1]nonan-3α-yl carbamate analogs have been designed and implemented for experimental cancer diagnosis and therapy.
We employed the fluorescently-labeled σ2 receptor probe, SW120, to evaluate σ2 receptor expression in human stem cells (SC), including: bone marrow stromal (BMSC), neural progenitor (NPC), amniotic fluid (AFSC), hematopoetic (HSC) and embryonic stem cells (ESC). We concurrently evaluated the intensity of SW120 and 5-ethynyl-2′-deoxyuridine (EdU) relative to passage number and multipotency.
We substantiated significantly higher σ2 receptor density among proliferating SC relative to lineage-restricted cell types. Additionally, cellular internalization of the σ2 receptor in SC was consistent with receptor-mediated endocytosis and confocal microscopy indicated SW120 specific co-localization with a fluorescent marker of lysosomes in all SC imaged.
These results suggest that σ2 receptors may serve to monitor stem cell differentiation in future experimental studies.
sigma 2 receptor; embryonic stem cell; amniotic fluid stem cell; bone marrow stromal cells; hematopoietic stem cell; differentiation; proliferation; EdU; Ki 67
Blood flow is an important factor in bone production and repair, but its role in osteogenesis induced by mechanical loading is unknown. Here, we present techniques for evaluating blood flow and fluoride metabolism in a pre-clinical stress fracture model of osteogenesis in rats.
Bone formation was induced by forelimb compression in adult rats. 15O water and 18F fluoride PET imaging were used to evaluate blood flow and fluoride kinetics 7 days after loading. 15O water was modeled using a one-compartment, two-parameter model, while a two-compartment, three-parameter model was used to model 18F fluoride. Input functions were created from the heart, and a stochastic search algorithm was implemented to provide initial parameter values in conjunction with a Levenberg–Marquardt optimization algorithm.
Loaded limbs are shown to have a 26% increase in blood flow rate, 113% increase in fluoride flow rate, 133% increase in fluoride flux, and 13% increase in fluoride incorporation into bone as compared to non-loaded limbs (p < 0.05 for all results).
The results shown here are consistent with previous studies, confirming this technique is suitable for evaluating the vascular response and mineral kinetics of osteogenic mechanical loading.
18F fluoride; 15O water; bone blood flow; mechanical loading
123I-labeled human serum amyloid P component (SAP) is used clinically only in the UK for imaging visceral amyloidosis to assist with diagnosis, disease staging and monitoring response to therapy. We compare a new amyloid-reactive probe, peptide p5, with SAP for imaging amyloidosis.
Dual-energy SPECT/CT images were acquired of 125I-labeled SAP and 99mTc-labeled p5 in mice with systemic AA amyloidosis (n = 3). Twelve organs and tissues were harvested for radiotracer biodistribution assessment and for micro-autoradiographic analysis.
125I-SAP and 99mTc-p5 localized equivalently in amyloid deposits in liver (~10 %ID/g) whereas, 125I-SAP was 2 fold higher in the spleen (~20 %ID/g; 99mTc-p5, ~10 %ID/g). In contrast, 99mTc-p5 was bound to pancreatic and intestinal amyloid ~5-fold more efficiently as evidenced in biodistribution data.
Radiolabeled p5 is an effective amyloid-imaging radiotracer as compared to SAP in the murine model of amyloidosis and may be rapidly translated for imaging patients with visceral amyloidosis in the USA.
Visceral amyloidosis; peptide imaging; dual isotope SPECT; serum amyloid P component; AA amyloid
Amide proton transfer (APT) imaging is able to extend the achievable MRI contrast to the protein level. In this study, we demonstrate the feasibility of applying a turbo spin echo (TSE)-based, three-dimensional (3D) APT sequence into routine clinical practice for patients with brain tumors.
Experiments were performed on a Philips 3T MRI scanner using an eight-channel phased-array coil for reception. A fast 3D APT sequence with a TSE acquisition was proposed (saturation power, 2 μT; saturation time, 500 ms; 8 slices). The gradient echo (GRE)-based field-mapping technique or water-saturation-shift-referencing (WASSR) technique was used to acquire B0 maps to correct for B0-induced artifacts in APT images. The test was performed on a box of homogenous protein solution, four healthy volunteers, and eight patients with high-grade gliomas.
The experimental data from a homogenous, protein-containing phantom and healthy volunteers show that the sequence produced a uniform contrast across all slices. The average MTRasym(3.5ppm) values with GRE B0-corrected 3D APT imaging and WASSR-corrected 3D APT imaging were both comparable to the values obtained using the undemanding single-slice acquisition. The average APT image intensity was consistently higher in the tumor core than in the peripheral edema and in the contralateral normal-appearing white matter (both P < 0.001).
3D APT imaging of brain tumors can be performed in about five minutes at 3T using a routine, commercial eight-channel SENSE coil.
APT imaging; CEST imaging; 3D; Brain tumor; Protein; MRI
Molecular imaging using positron emission tomography (PET) radiotracers targeted to tumor vasculature offers a noninvasive method for early detection of tumor angiogenesis and efficient monitoring of response to anti-tumor vasculature therapy. The previous in vitro results demonstrated that the GX1 peptide, identified by phage display technology, is a tumor vasculature endothelium-specific ligand. In this study, we evaluated a 64Cu-labeled GX1 peptide as a potential radiotracer for microPET imaging of tumor vasculature in a U87MG tumor xenografted mouse model.
Macrocyclic chelating agent 1,4,7,10-tetraazacyclododecane-N, N′, N″, N‴-tetraacetic acid (DOTA)-conjugated GX1 peptide was synthesized and radiolabeled with 64Cu (t1/2=12.7 h) in ammonium acetate buffer. The 64Cu-labeled GX1 peptide was then subjected to in vitro tumor cell uptake study, small animal PET and direct tissue sampling biodistribution studies in a U87MG tumor xenografted mouse model.
The in vitro experiment demonstrated that 64Cu-DOTA-GX1 is stable in PBS with more than 91% of 64Cu-DOTA-GX1 peptide remaining intact after 24 h of incubation. Cellular uptake and retention studies revealed 64Cu-DOTA-GX1 binds to U87MG glioma cells and has good tumor cell retention. For small animal PET imaging studies, the U87MG tumors were all clearly visible with high contrast to contralateral background at all measured time points after injection of 64Cu-DOTA-GX1 while high accumulation in liver and kidneys were also observed at early time points. The U87MG tumor uptake was determined to be the highest (7.97±0.75%ID/g) at 24 h pi. The blocking experiment was achieved by co-injection of 64Cu-DOTA-GX1 with non-radiolabeled GX1 peptide (20 mg/kg) at 24 h pi, suggesting 64Cu-DOTA-GX1 is a target-specific tracer. Furthermore, the biodistribution results were consistent with the quantification of microPET imaging, demonstrating the highest ratio (16.09±1.21) of tumor/muscle uptake of 64Cu-DOTA-GX1 at 24 h pi for non-blocking group and significant decreased ratio (6.57±0.58) for blocking group. Finally, metabolic studies suggested that 64Cu-DOTA-GX1 is stable in mouse blood and urine in vivo at early time point while the metal transchelation may also occur in mouse liver and kidneys.
Our studies demonstrate that 64Cu-DOTA-GX1 is a promising radiotracer for imaging tumor vasculature.
64Cu-Labeled GX1 peptide; PET imaging; Tumor vasculature; Phage display
Metabolism, and especially glucose uptake, is a key quantitative cell trait that is closely linked to cancer initiation and progression. Therefore, developing high-throughput assays for measuring glucose uptake in cancer cells would be enviable for simultaneous comparisons of multiple cell lines and microenvironmental conditions. This study was designed with two specific aims in mind: the first was to develop and validate a high-throughput screening method for quantitative assessment of glucose uptake in “normal” and tumor cells using the fluorescent 2-deoxyglucose analog 2-[N-(7-nitrobenz-2-oxa-1,3-diazol-4-yl)amino]-2-deoxyglucose (2-NBDG), and the second was to develop an image-based, quantitative, single-cell assay for measuring glucose uptake using the same probe to dissect the full spectrum of metabolic variability within populations of tumor cells in vitro in higher resolution.
The kinetics of population-based glucose uptake was evaluated for MCF10A mammary epithelial and CA1d breast cancer cell lines, using 2-NBDG and a fluorometric microplate reader. Glucose uptake for the same cell lines was also examined at the single-cell level using high-content automated microscopy coupled with semi-automated cell-cytometric image analysis approaches. Statistical treatments were also implemented to analyze intra-population variability.
Our results demonstrate that the high-throughput fluorometric assay using 2-NBDG is a reliable method to assess population-level kinetics of glucose uptake in cell lines in vitro. Similarly, single-cell image-based assays and analyses of 2-NBDG fluorescence proved an effective and accurate means for assessing glucose uptake, which revealed that breast tumor cell lines display intra-population variability that is modulated by growth conditions.
These studies indicate that 2-NBDG can be used to aid in the high-throughput analysis of the influence of chemotherapeutics on glucose uptake in cancer cells.
2-NBDG; Metabolism; High-throughput; Single-cell; Glycolysis
A reliable and routine process to introduce a new 18F-labeled dimeric RGD-peptide tracer ([18F]FPP(RGD)2) for noninvasive imaging of αvβ3 expression in tumors needed to be developed so the tracer could be evaluated for the first time in man. Clinical-grade [18F]FPP (RGD)2 was screened in mouse prior to our first pilot study in human.
[18F]FPP(RGD)2 was synthesized by coupling 4-nitrophenyl-2-[18F]fluoropropionate ([18F]NPE) with the dimeric RGD-peptide (PEG3-c(RGDyK)2). Imaging studies with [18F]FPP (RGD)2 in normal mice and a healthy human volunteer were carried out using small animal and clinical PET scanners, respectively.
Through optimization of each radiosynthetic step, [18F]FPP(RGD)2 was obtained with RCYs of 16.9±2.7% (n=8, EOB) and specific radioactivity of 114±72 GBq/μmol (3.08±1.95 Ci/μmol; n=8, EOB) after 170 min of radiosynthesis. In our mouse studies, high radioactivity uptake was only observed in the kidneys and bladder with the clinical-grade tracer. Favorable [18F]FPP (RGD)2 biodistribution in human studies, with low background signal in the head, neck, and thorax, showed the potential applications of this RGD-peptide tracer for detecting and monitoring tumor growth and metastasis.
A reliable, routine, and automated radiosynthesis of clinical-grade [18F]FPP(RGD)2 was established. PET imaging in a healthy human volunteer illustrates that [18F]FPP(RGD)2 possesses desirable pharmacokinetic properties for clinical noninvasive imaging of αvβ3 expression. Further imaging studies using [18F]FPP(RGD)2 in patient volunteers are now under active investigation.
Oncology; Peptides; Radiopharmaceuticals; [18F]FPP(RGD)2; Automated radiosynthesis; Clinical PET; Tumor angiogenesis; Integrins
Radioscintigraphic imaging during sentinel lymph node (SLN) mapping could potentially improve localization; however, parallel-hole collimators have certain limitations. In this study, we explored the use of coded aperture (CA) collimators.
Equations were derived for the six major dependent variables of CA collimators (i.e., masks) as a function of the ten major independent variables, and an optimized mask was fabricated. After validation, dual-modality CA and near-infrared (NIR) fluorescence SLN mapping was performed in pigs.
Mask optimization required the judicious balance of competing dependent variables, resulting in sensitivity of 0.35%, XY resolution of 2.0 mm, and Z resolution of 4.2 mm at an 11.5 cm FOV. Findings in pigs suggested that NIR fluorescence imaging and CA radioscintigraphy could be complementary, but present difficult technical challenges.
This study lays the foundation for using CA collimation for SLN mapping, and also exposes several problems that require further investigation.
Coded apertures; coded-aperture collimation; radioscintigraphy; sentinel lymph node mapping; image-guided surgery; near-infrared fluorescence imaging
We report from the First International Workshop on positron emission tomography/magnetic resonance imaging (PET/MRI) that was organized by the University of Tübingen in March 2012. Approximately 100 imaging experts in MRI, PET and PET/computed tomography (CT), among them early adopters of pre-clinical and clinical PET/MRI technology, gathered from March 19 to 24, 2012 in Tübingen, Germany. The objective of the workshop was to provide a forum for sharing first-hand methodological and clinical know-how and to assess the potential of combined PET/MRI in various applications from pre-clinical research to scientific as well as clinical applications in humans. The workshop was comprised of pro-active sessions including tutorials, specific discussion panels and grand rounds. Pre-selected experts moderated the sessions, and feedback from the subsequent discussions is presented here to a greater readership. Naturally, the summaries provided herein are subjective descriptions of the hopes and challenges of PET/MR imaging as seen by the workshop attendees at a very early point in time of adopting PET/MRI technology and, as such, represent only a snapshot of current approaches.
Combined imaging; Molecular imaging; PET/CT; PET/MRI; Quantification; Artifacts; MR-based attenuation correction; Workflow; Standardization
To evaluate by sequential 18F-FDG PET/CT imaging the therapeutic response to a novel monoclonal antibody targeting human EMMPRIN (extracellular matrix metalloproteinase inducer) in combination with gemcitabine in a pancreatic-tumor xenograft murine model.
Four groups of SCID mice bearing orthotopic pancreatic tumor xenografts were injected with PBS, gemcitabine (120mg/kg BW), anti-EMMPRIN antibody (0.2mg), or combination, respectively twice weekly for 2 weeks, while 18F-FDG PET/CT imaging was performed weekly for 3 weeks. Changes in mean standardized uptake value (SUVmean) of 18F-FDG and volume of tumors were determined.
The tumor SUVmean change in the group receiving combination therapy was significantly lower than those of the other groups. Tumor-volume changes of groups treated with anti-EMMPRIN monotherapy or combined therapy were significantly lower than that of the control group.
These data provide support for clinical studies of anti-EMMPRIN therapy with gemcitabine for pancreatic cancer treatment.
FDG-PET; CT; EMMPRIN; Gemcitabine; Pancreatic cancer
Visualization of the cell cycle in living subjects has long been a big challenge. The present study aimed to noninvasively visualize mitotic arrest of the cell cycle with an optical reporter in living subjects.
An N-terminal cyclin B1–luciferase fusion construct (cyclin B-Luc) controlled by the cyclin B promoter, as a mitosis reporter, was generated. HeLa or HCT116 cells stably expressing cyclin B-Luc reporter were used to evaluate its cell cycle-dependent regulation and ubiquitination-mediated degradation. We also evaluated its feasibility to monitor the mitotic arrest caused by Taxotere both in vitro and in vivo.
We showed that the cyclin B-Luc fusion protein was regulated in a cell cycle-dependent manner and accumulated in the mitotic phase (M phase) in cellular assays. The regulation of cyclin B-Luc reporter was mediated by proteasome ubiquitination. In the present study, in vitro imaging showed that antimitotic reagents like Taxotere upregulated the reporter through cell cycle arrest in the M phase. Noninvasive longitudinal bioluminescence imaging further demonstrated an upregulation of the reporter consistent with mitotic arrest induced in tumor xenograft models. Induction of this reporter was also observed with a kinesin spindle protein inhibitor, which causes cell cycle blockage in the M phase.
Our results demonstrate that the cyclin B-Luc reporter can be used to image whether compounds are capable, in vivo, of causing an M phase arrest and/or altering cyclin B turnover. This reporter can also be potentially used in high-throughput screening efforts aimed at discovering novel molecules that will cause cell cycle arrest at the M phase in cultivated cell lines and animal models.
Optical imaging; Mitotic arrest; Cell cycle; Cyclin B1; Bioluminescence
To obtain estimates of human normal-organ radiation doses of 18F-SKI-249380, as a prerequisite step towards first-in-human trial. 18F-SKI-249380 is a first-of-its-kind PET tracer for imaging the in vivo pharmacokinetics of dasatinib, an investigational targeted therapy for solid malignancies.
Isoflurane-anesthetized mice received tracer dose via tail vein. Organ time-integrated activity coefficients, fractional urinary and hepatobiliary excretion, and total-body clearance kinetics were derived from PET data, with allometric extrapolation to the Standard Man anatomic model and normal-organ-absorbed dose calculations using OLINDA/EXM software.
The human effective dose was 0.031 mSv/MBq. The critical organ was the upper large intestine, with a dose equivalent of 0.25 mSv/MBq. A 190-MBq administered activity of 18F-SKI-249380 is thus predicted to expose an adult human to radiation doses generally comparable to those of routinely used diagnostic radiopharmaceuticals.
Animal-based human dose estimates support first-in-human testing of 18F-SKI-249380.
Positron emission tomography; Dasatinib (substance name); Protein-tyrosine kinases [Mesh]; Molecular imaging; SKI-249380
This study aims to determine feasibility and utility of copper-64(II) chloride (64CuCl2) as a tracer for positron emission tomography (PET) of copper metabolism imbalance in human Wilson’s disease (WD).
Atp7b−/− mice, a mouse model of human WD, were injected with 64CuCl2 intravenously and subjected to PET scanning using a hybrid PET-CT (computerized tomography) scanner, with the wild-type C57BL mice as a normal control. Quantitative PET analysis was performed to determine biodistribution of 64Cu radioactivity and radiation dosimetry estimates of 64Cu were calculated for PET of copper metabolism in humans.
Dynamic PET analysis revealed increased accumulation and markedly reduced clearance of 64Cu from the liver of the Atp7b−/− mice, compared to hepatic uptake and clearance of 64Cu in the wild-type C57BL mice. Kinetics of copper clearance and retention was also altered for kidneys, heart, and lungs in the Atp7b−/− mice. Based on biodistribution of 64Cu in wild-type C57BL mice, radiation dosimetry estimates of 64Cu in normal human subjects were obtained, showing an effective dose (ED) of 32.2 μ (micro)Sv/MBq (weighted dose over 22 organs) and the small intestine as the critical organ for radiation dose (61 μGy/MBq for males and 69 μGy/MBq for females). Radiation dosimetry estimates for the patients with WD, based on biodistribution of 64Cu in the Atp7b−/− mice, showed a similar ED of 32.8 μ (micro)Sv/MBq (p= 0.53), with the liver as the critical organ for radiation dose (120 μSv/MBq for male and 161 μSv/MBq for female).
Quantitative PET analysis demonstrates abnormal copper metabolism in the mouse model of WD with improved time–resolution. Human radiation dosimetry estimates obtained in this preclinical study encourage direct radiation dosimetry of 64CuCl2 in human subjects. The results suggest feasibility of utilizing 64CuCl2 as a tracer for noninvasive assessment of copper metabolism in WD with PET.
Copper metabolism; Wilson’s disease; ATP7B copper transporter; Positron emission tomography; Copper-64 (II) chloride; Radiation dosimetry
The purpose of writing this review is to showcase the Molecular Imaging and Contrast Agent Database (MICAD; www.micad.nlm.nih.gov) to students, researchers and clinical investigators interested in the different aspects of molecular imaging. This database provides freely accessible, current, online scientific information regarding molecular imaging (MI) probes and contrast agents (CA) used for positron emission tomography, single-photon emission computed tomography, magnetic resonance imaging, x-ray/computed tomography, optical imaging and ultrasound imaging. Detailed information on >1000 agents in MICAD is provided in a chapter format and can be accessed through PubMed. Lists containing >4250 unique MI probes and CAs published in peer-reviewed journals and agents approved by the United States Food and Drug Administration (FDA) as well as a CSV file summarizing all chapters in the database can be downloaded from the MICAD homepage. Users can search for agents in MICAD on the basis of imaging modality, source of signal/contrast, agent or target category, preclinical or clinical studies, and text words. Chapters in MICAD describe the chemical characteristics (structures linked to PubChem), the in vitro and in vivo activities and other relevant information regarding an imaging agent. All references in the chapters have links to PubMed. A Supplemental Information Section in each chapter is available to share unpublished information regarding an agent. A Guest Author Program is available to facilitate rapid expansion of the database. Members of the imaging community registered with MICAD periodically receive an e-mail announcement (eAnnouncement) that lists new chapters uploaded to the database. Users of MICAD are encouraged to provide feedback, comments or suggestions for further improvement of the database by writing to the editors at: firstname.lastname@example.org
Molecular imaging probes; Contrast agents; Database; positron emission tomography (PET); single-photon emission computed tomography (SPECT); magnetic resonance imaging (MRI); x-ray/computed tomography (x-ray/CT); optical imaging (OI); ultrasound imaging
In this study, protein-shell microspheres filled with a suspension of iron oxide nanoparticles in oil are demonstrated as multimodal contrast agents in magnetic resonance imaging (MRI), magnetomotive optical coherence tomography (MM-OCT), and ultrasound imaging. The development, characterization, and use of multifunctional multimodal microspheres are described for targeted contrast and therapeutic applications.
A preclinical rat model was used to demonstrate the feasibility of the multimodal multifunctional microspheres as contrast agents in ultrasound, MM-OCT and MRI. Microspheres were functionalized with the RGD peptide ligand, which is targeted to αvβ3 integrin receptors that are over-expressed in tumors and atherosclerotic lesions.
These microspheres, which contain iron oxide nanoparticles in their cores, can be modulated externally using a magnetic field to create dynamic contrast in MM-OCT. With the presence of iron oxide nanoparticles, these agents also show significant negative T2 contrast in MRI. Using ultrasound B-mode imaging at a frequency of 30 MHz, a marked enhancement of scatter intensity from in vivo rat mammary tumor tissue was observed for these targeted protein microspheres.
Preliminary results demonstrate multimodal contrast-enhanced imaging of these functionalized microsphere agents with MRI, MM-OCT, ultrasound imaging, and fluorescence microscopy, including in vivo tracking of the dynamics of these microspheres in real-time using a high-frequency ultrasound imaging system. These targeted oil-filled protein microspheres with the capacity for high drug-delivery loads offer the potential for local delivery of lipophilic drugs under image guidance.
Magnetomotive optical coherence tomography; Ultrasound imaging; Magnetic resonance imaging; Contrast agents; Protein microspheres; Iron oxide; RGD peptide; Alpha(v) beta(3) targeting
This study investigates methodologies for the estimation of small animal anatomy from non-tomographic modalities, such as planar X-ray projections, optical cameras, and surface scanners. The key goal is to register a digital mouse atlas to a combination of non-tomographic modalities, in order to provide organ-level anatomical references of small animals in 3D.
A 2D/3D registration method was developed to register the 3D atlas to the combination of non-tomographic imaging modalities. Eleven combinations of three non-tomographic imaging modalities were simulated, and the registration accuracy of each combination was evaluated.
Comparing the 11 combinations, the top-view X-ray projection combined with the side-view optical camera yielded the best overall registration accuracy of all organs. The use of a surface scanner improved the registration accuracy of skin, spleen, and kidneys.
The methodologies and evaluation presented in this study should provide helpful information for designing preclinical atlas-based anatomical data acquisition systems.
Small animal imaging; Mouse atlas registration; 2D/3D registration; Planar X-ray projection; 3D surface scanner
Cellular receptor targeted imaging agents present the potential to target extracellular molecular expression in cancerous lesions; however, the image contrast in vivo does not reflect the magnitude of overexpression expected from in vitro data. Here, the in vivo delivery and binding kinetics of epidermal growth factor receptor (EGFR) was determined for normal pancreas and AsPC-1 orthotopic pancreatic tumors known to overexpress EGFR.
EGFR in orthotopic xenograft AsPC-1 tumors was targeted with epidermal growth factor (EGF) conjugated with IRDye800CW. The transfer rate constants (ke,K12, k21, k23, and k32) associated with a three-compartment model describing the vascular delivery, leakage rate and binding of targeted agents were determined experimentally. The plasma excretion rate, ke, was determined from extracted blood plasma samples. K12, k21, and k32 were determined from ex vivo tissue washing studies at time points ≥24 h. The measured in vivo uptake of IRDye800CW-EGF and a non-targeted tracer dye, IRDye700DX-carboxylate, injected simultaneously was used to determined k23.
The vascular exchange of IRDye800CW-EGF in the orthotopic tumor (K12 and k21) was higher than in the AsPC-1 tumor as compared to normal pancreas, suggesting that more targeted agent can be taken up in tumor tissue. However, the cellular associated (binding) rate constant (k23) was slightly lower for AsPC-1 pancreatic tumor (4.1×10−4 s−1) than the normal pancreas (5.5×10−4s−1), implying that less binding is occurring.
Higher vascular delivery but low cellular association in the AsPC-1 tumor compared to the normal pancreas may be indicative of low receptor density due to low cellular content. This attribute of the AsPC-1 tumor may indicate one contributing cause of the difficulty in treating pancreatic tumors with cellular targeted agents.
Three-compartment model; Epidermal growth factor receptor; Pancreatic tumor; Fluorescence imaging; Cellular associated rate constant
Receptor availability represents a key component of current cancer management. However, no approaches have been adopted to do this clinically, and the current standard of care is invasive tissue biopsy. A dual-reporter methodology capable of quantifying available receptor binding potential of tumors in vivo within a clinically relevant time scale is presented.
To test the methodology, a fluorescence imaging-based adaptation was validated against ex vivo and in vitro measures of epidermal growth factor receptor (EGFR) binding potential in four tumor lines in mice, each line expected to express a different level of EGFR.
A strong correlation was observed between in vivo and ex vivo measures of binding potential for all tumor lines (r=0.99, p<0.01, slope=1.80±0.48, and intercept=−0.58±0.84) and between in vivo and in vitro for the three lines expressing the least amount of EGFR (r=0.99, p<0.01, slope=0.64±0.32, and intercept=0.47±0.51).
By providing a fast and robust measure of receptor density in tumors, the presented methodology has powerful implications for improving choices in cancer intervention, evaluation, and monitoring, and can be scaled to the clinic with an imaging modality like SPECT.
Molecular imaging; Fluorescence; Targeted reporter; Epidermal growth factor receptor; Mouse model