Detection of Pancreatic Carcinomas by Imaging Lactose-Binding Protein Expression in Peritumoral Pancreas Using [18F]Fluoroethyl-Deoxylactose PET/CT

BACKGROUND: Early diagnosis of pancreatic carcinoma with highly sensitive diagnostic imaging methods could save lives of many thousands of patients, because early detection increases resectability and survival rates. Current non-invasive diagnostic imaging techniques have inadequate resolution and sensitivity for detection of small size ( approximately 2-3 mm) early pancreatic carcinoma lesions. Therefore, we have assessed the efficacy of positron emission tomography and computer tomography (PET/CT) imaging with beta-O-D-galactopyranosyl-(1,4')-2'-deoxy-2'-[(18)F]fluoroethyl-D-glucopyranose ([(18)F]FEDL) for detection of less than 3 mm orthotopic xenografts of L3.6pl pancreatic carcinomas in mice. [(18)F]FEDL is a novel radioligand of hepatocarcinoma-intestine-pancreas/pancreatitis-associated protein (HIP/PAP), which is overexpressed in peritumoral pancreatic acinar cells. METHODOLOGY/PRINCIPAL FINDINGS: Dynamic PET/CT imaging demonstrated rapid accumulation of [(18)F]FEDL in peritumoral pancreatic tissue (4.04+/-2.06%ID/g), bi-exponential blood clearance with half-lives of 1.65+/-0.50 min and 14.14+/-3.60 min, and rapid elimination from other organs and tissues, predominantly by renal clearance. Using model-independent graphical analysis of dynamic PET data, the average distribution volume ratio (DVR) for [(18)F]FEDL in peritumoral pancreatic tissue was estimated as 3.57+/-0.60 and 0.94+/-0.72 in sham-operated control pancreas. Comparative analysis of quantitative autoradiographic images and densitometry of immunohistochemically stained and co-registered adjacent tissue sections demonstrated a strong linear correlation between the magnitude of [(18)F]FEDL binding and HIP/PAP expression in corresponding regions (r = 0.88). The in situ analysis demonstrated that at least a 2-4 fold apparent lesion size amplification was achieved for submillimeter tumors and to nearly half a murine pancreas for tumors larger than 3 mm. CONCLUSION/SIGNIFICANCE: We have demonstrated the feasibility of detection of early pancreatic tumors by non-invasive imaging with [(18)F]FEDL PET/CT of tumor biomarker HIP/PAP over-expressed in peritumoral pancreatic tissue. Non-invasive non-invasive detection of early pancreatic carcinomas with [(18)F]FEDL PET/CT imaging should aid the guidance of biopsies and additional imaging procedures, facilitate the resectability and improve the overall prognosis

Imaging Long-Term Fate of Intramyocardially Implanted Mesenchymal Stem Cells in a Porcine Myocardial Infarction Model

The long-term fate of stem cells after intramyocardial delivery is unknown. We used noninvasive, repetitive PET/CT imaging with [18F]FEAU to monitor the long-term (up to 5 months) spatial-temporal dynamics of MSCs retrovirally transduced with the sr39HSV1-tk gene (sr39HSV1-tk-MSC) and implanted intramyocardially in pigs with induced acute myocardial infarction. Repetitive [18F]FEAU PET/CT revealed a biphasic pattern of sr39HSV1-tk-MSC dynamics; cell proliferation peaked at 33–35 days after injection, in periinfarct regions and the major cardiac lymphatic vessels and lymph nodes. The sr39HSV1-tk-MSC–associated [18F]FEAU signals gradually decreased thereafter. Cardiac lymphography studies using PG-Gd-NIRF813 contrast for MRI and near-infrared fluorescence imaging showed rapid clearance of the contrast from the site of intramyocardial injection through the subepicardial lymphatic network into the lymphatic vessels and periaortic lymph nodes. Immunohistochemical analysis of cardiac tissue obtained at 35 and 150 days demonstrated several types of sr39HSV1-tk expressing cells, including fibro-myoblasts, lymphovascular cells, and microvascular and arterial endothelium. In summary, this study demonstrated the feasibility and sensitivity of [18F]FEAU PET/CT imaging for long-term, in-vivo monitoring (up to 5 months) of the fate of intramyocardially injected sr39HSV1-tk-MSC cells. Intramyocardially transplanted MSCs appear to integrate into the lymphatic endothelium and may help improve myocardial lymphatic system function after MI

Optimizing Imaging of Three-Dimensional Multicellular Tumor Spheroids with Fluorescent Reporter Proteins Using Confocal Microscopy

Tumor spheroids more faithfully mimic tumor biology than monolayer cultures and require three-dimensional microscopy. Our goal in this study was to overcome the limitations of signal to noise ratio that have traditionally limited three-dimensional imaging to depths of 100 μm or less. We studied the expression of hypoxia-inducible factor 1α (HIF-1α), the main regulator of cellular hypoxic response in C6 glioma spheroids. In our spheroids, red fluorescent protein is expressed constitutively and green fluorescent protein is expressed conditionally under control of a HIF-1α promoter. In this article, we show a series of optimizations that allowed us to obtain excellent quality confocal microscopy images at imaging depths of up to 320 μm. The combined use of special objectives, glass-bottomed culture dishes, and depth-dependent laser output modulation extended our depth range beyond previously accepted limits. This allowed us to image up to the equator of spheroids of 650 μm diameter, allowing interrogation of HIF-1α expression from the spheroid periphery to its hypoxic center

Optimizing Imaging of Three-Dimensional Multicellular Tumor Spheroids with Fluorescent Reporter Proteins Using Confocal Microscopy

Tumor spheroids more faithfully mimic tumor biology than monolayer cultures and require three-dimensional microscopy. Our goal in this study was to overcome the limitations of signal to noise ratio that have traditionally limited three-dimensional imaging to depths of 100 μm or less. We studied the expression of hypoxia-inducible factor 1α (HIF-1α), the main regulator of cellular hypoxic response in C6 glioma spheroids. In our spheroids, red fluorescent protein is expressed constitutively and green fluorescent protein is expressed conditionally under control of a HIF-1α promoter. In this article, we show a series of optimizations that allowed us to obtain excellent quality confocal microscopy images at imaging depths of up to 320 μm. The combined use of special objectives, glass-bottomed culture dishes, and depth-dependent laser output modulation extended our depth range beyond previously accepted limits. This allowed us to image up to the equator of spheroids of 650 μm diameter, allowing interrogation of HIF-1α expression from the spheroid periphery to its hypoxic center

Synthesis and preliminary evaluation of [ 18F]-labeled 2-oxoquinoline derivatives for PET imaging of cannabinoid CB 2 receptor

INTRODUCTION: The cannabinoid receptor type 2 (CB2) is an important target for development of drugs and imaging agents for diseases, such as neuroinflammation, neurodegeneration, and cancer. Recently we reported synthesis and results of in vitro receptor binding of a focused library of fluorinated 2-oxoquinoline derivatives as CB2 receptor ligands. Some of the compounds demonstrated as good CB2-specific ligands with Ki values in the nanomolar to sub-nanomolar concentrations; therefore, we pursued the development of their (18)F-labeled analogues that should be useful for PET imaging of CB2 receptor expression. Here, we report the radiosynthesis of two (18)F-labeled 2-oxoquinoline derivatives, and preliminary in vitro and ex-vivo evaluation of one compound as a CB2-specific radioligand. METHODS: 4-[(18)F]Fluorobenzyl amine [(18)F]-3 was prepared by radiofluorination of 4-cyano-N,N,N-trimethylanilinium triflate salt followed by reduction with LiAlH(4) and then coupled with acid chlorides 11 and 12 to afford [(18)F]-13 and [(18)F]-14. In vitro CB2 receptor binding assay was performed using U87 cells transduced with CB2- and CB1-receptor. Ex-vivo autoradiography was performed with [(18)F]-14 on spleen, CB2- and CB1-expressing and wild type U87 subcutaneous tumors grown in mice. RESULTS: The radiochemical yields of [(18)F]-13 and [(18)F]-14 were 10%-15.0% with an average of 12% (n=10); radiochemical purity was > 99% with specific activity 1200 mCi/μmole. The dissociation constant Kd for [(18)F]-14 was 3.4 nM. Ex-vivo autoradiography showed accumulation of [(18)F]-14 in the CB2-expressing tumor. CONCLUSION: Two new [(18)F]-labeled CB2 ligands have been synthesized. Compound [(18)F]-14 appears to be a potential PET imaging agent for the assessment of CB2 receptor expression in vivo