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

Targeted molecular-genetic imaging and ligand-directed therapy in aggressive variant prostate cancer

Aggressive variant prostate cancers (AVPC) are a clinically defined group of tumors of heterogeneous morphologies, characterized by poor patient survival and for which limited diagnostic and treatment options are currently available. We show that the cell surface 78-kDa glucose-regulated protein (GRP78), a receptor that binds to phage-display-selected ligands, such as the SNTRVAP motif, is a candidate target in AVPC. We report the presence and accessibility of this receptor in clinical specimens from index patients. We also demonstrate that human AVPC cells displaying GRP78 on their surface could be effectively targeted both in vitro and in vivo by SNTRVAP, which also enabled specific delivery of siRNA species to tumor xenografts in mice. Finally, we evaluated ligand-directed strategies based on SNTRVAP-displaying adeno-associated virus/phage (AAVP) particles in mice bearing MDA-PCa-118b, a patient-derived xenograft (PDX) of castration-resistant prostate cancer bone metastasis that we exploited as a model of AVPC. For theranostic (a merging of the terms therapeutic and diagnostic) studies, GRP78-targeting AAVP particles served to deliver the human Herpes simplex virus thymidine kinase type-1 (HSVtk) gene, which has a dual function as a molecular-genetic sensor/reporter and a cell suicide-inducing transgene. We observed specific and simultaneous PET imaging and treatment of tumors in this preclinical model of AVPC. Our findings demonstrate the feasibility of GPR78-targeting, ligand-directed theranostics for translational applications in AVPC

MLH1-rheMac hereditary nonpolyposis colorectal cancer syndrome in rhesus macaques

Over the past two decades, 33 cases of colonic adenocarcinomas have been diagnosed in rhesus macaques (Macaca mulatta) at the nonhuman primate colony of the Keeling Center for Comparative Medicine and Research at The University of Texas MD Anderson Cancer Center. The distinctive feature in these cases, based on PET/computed tomography (CT) imaging, was the presence of two or three tumor lesions in different locations, including proximal to the ileocecal juncture, proximal to the hepatic flexure, and/or in the sigmoid colon. These colon carcinoma lesions selectively accumulated [18F]fluorodeoxyglucose ([18F]FDG) and [18F]fluoroacetate ([18F]FACE) at high levels, reflecting elevated carbohydrate and fatty acid metabolism in these tumors. In contrast, the accumulation of [18F]fluorothymidine ([18F]FLT) was less significant, reflecting slow proliferative activity in these tumors. The diagnoses of colon carcinomas were confirmed by endoscopy. The expression of MLH1, MSH2, and MSH6 proteins and the degree of microsatellite instability (MSI) was assessed in colon carcinomas. The loss of MLH1 protein expression was observed in all tumors and was associated with a deletion mutation in the MLH1 promoter region and/or multiple single-nucleotide polymorphism (SNP) mutations in the MLH1 gene. All tumors exhibited various degrees of MSI. The pedigree analysis of this rhesus macaque population revealed several clusters of affected animals related to each other over several generations, suggesting an autosomal dominant transmission of susceptibility for colon cancer. The newly discovered hereditary nonpolyposis colorectal cancer syndrome in rhesus macaques, termed MLH1-rheMac, may serve as a model for development of novel approaches to diagnosis and therapy of Lynch syndrome in humans

Systemic combinatorial peptide selection yields a non-canonical iron-mimicry mechanism for targeting tumors in a mouse model of human glioblastoma

The management of CNS tumors is limited by the blood-brain barrier (BBB), a vascular interface that restricts the passage of most molecules from the blood into the brain. Here we show that phage particles targeted with certain ligand motifs selected in vivo from a combinatorial peptide library can cross the BBB under normal and pathological conditions. Specifically, we demonstrated that phage clones displaying an ironmimic peptide were able to target a protein complex of transferrin and transferrin receptor (TfR) through a non-canonical allosteric binding mechanism and that this functional protein complex mediated transport of the corresponding viral particles into the normal mouse brain. We also showed that, in an orthotopic mouse model of human glioblastoma, a combination of TfR overexpression plus extended vascular permeability and ligand retention resulted in remarkable brain tumor targeting of chimeric adeno-associated virus/ phage particles displaying the iron-mimic peptide and carrying a gene of interest. As a proof of concept, we delivered the HSV thymidine kinase gene for molecular-genetic imaging and targeted therapy of intracranial xenografted tumors. Finally, we established that these experimental findings might be clinically relevant by determining through human tissue microarrays that many primary astrocytic tumors strongly express TfR. Together, our combinatorial selection system and results may provide a translational avenue for the targeted detection and treatment of brain tumors

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

Direct Comparison of Radiolabeled Probes FMAU, FHBG, and FHPG as PET Imaging Agents for HSV1-tk Expression in a Human Breast Cancer Model

2′-Deoxy-2′-fluoro-5-methyl-1-β-d-arabinofuranosyluracil (FMAU), 9-(4-fluoro-3-hydroxy-methyl-butyl)guanine (FHBG) and 9-[(3-fluoro-1-hydroxy-2-propoxy)methyl]-guanine (FHPG) have been evaluated in a human breast cancer model as potential radiotracers for PET imaging of HSV1-tk gene expression. In vitro accumulation of [14C]FMAU, [18F]FHBG, and [18F]FHPG in HSV1-tk-expressing cells was 14- to 16-fold (p < .001), 9- to 13-fold (p < .001), and 2- to 3-fold (p < .05) higher than tk-negative control cells, respectively, between 30 and 240 min. Accumulation of FMAU and FHBG in vector-transduced cells was 10- to 14-fold and 6- to 10-fold higher than wild-type cells, respectively. At 2 hr, uptake of [14C]FMAU in tk-positive cells was 6.3-fold and 60-fold higher than [18F]FHBG and [18F]FHPG, respectively. In vivo, tumor uptake of [14C]FMAU in HSV1-tk-expressing cells was 3.7-fold and 5.5-fold (p < .001) higher than tk-negative control cells at 1 and 2 hr, respectively. Tumor uptake of [18F]FHBG was 4.2-fold and 12.6-fold higher (p < .001) than tk-negative cells at the same time points. Incorporation of [14C]FMAU in tk-positive tumor was 18-fold and 24-fold higher (p < .001) than [18F]FHBG at 1 and 2 hr, respectively. Micro-PET images support the biodistribution results and indicate that both [18F]FMAU and [18F]FHBG are useful for imaging HSV1-tk expression in breast cancer. Although FMAU demonstrates higher total incorporation (%dose/g) in tumor tissue compared with the other tracers, FHBG is superior in terms of specific accumulation in transfected cells at later time points

Improved detection and measurement of low levels of [ 18F]fluoride metabolized from [ 18F]-labeled pyrimidine nucleoside analogues in biological samples

INTRODUCTION: It is important to identify all circulating metabolites, including free fluoride, for accurate pharmacokinetic modeling of [(18)F]-labeled radiotracers. We sought to determine the most efficient method to detect and quantify low levels of free [(18)F]fluoride in biological samples. METHODS: Low levels of [(18)F]fluoride were analyzed using two methods: A) an ion-exchange cartridge and gamma counting; and B) radio-HPLC, to compare the detection limits of these two analytical methods. Twenty microliters of [(18)F]fluoride solution was loaded onto an ion-exchange cartridge then eluted with 20% MeCN/water (5 mL) and radioactivity trapped in the cartridge counted on a gamma counter. [(18)F]-Fluoride was also determined in plasma and urine from mice injected with [(18)F]-labeled thymidine analogues using method A. RESULTS: The detection sensitivity of method A was 9.4-fold higher than that of method B (0.075±0.004 nCi vs. 0.71±0.02 nCi). Using method A, [(18)F]fluoride was determined in plasma for [(18)F]FLT, [(18)F]FMAU, [(18)F]FEAU and N(3)-[(18)F]FPrT as 1.4±0.31% (n=4), 0.17±0.49% (n=3), 4.88±1.62% (n=3) and 12.94±0.48% (n=4), respectively. The amount of [(18)F]fluoride determined in the urine was 11.49±1.60% (n=4) from [(18)F]FLT, 5.36±2.34% (n=3) from [(18)F]FMAU, 13.57±1.96% (n=3) from [(18)F]FEAU, and 11.19±1.98% (n=4) from N(3)-[(18)F]FPrT. CONCLUSION: Low levels of [(18)F]fluoride in biological samples can be detected and quantified using an ion-exchange cartridge and gamma counting. This methodology is simple, accurate and superior to the standard use of radio-HPLC on a C(18) column for metabolite analysis; and it should be useful in pharmacokinetic modeling for animal imaging studies using an [(18)F]-labeled radiotracer and PET