PET imaging of inflammation and adenocarcinoma xenografts using vascular adhesion protein 1 targeting peptide 68Ga-DOTAVAP-P1: comparison with 18F-FDG.

PURPOSE: The aim of this study was to evaluate inflammation and tumour imaging with a vascular adhesion protein 1 (VAP-1) targeting peptide (68)Ga-DOTAVAP-P1 in comparison with (18)F-FDG. METHODS: Rats with both subcutaneous human pancreatic adenocarcinoma xenografts and turpentine oil-induced acute sterile inflammation were evaluated by dynamic positron emission tomography (PET) and by digital autoradiography of tissue cryosections. Subsequently, the autoradiographs were combined with histological and immunohistological analysis of the sections. RESULTS: (68)Ga-DOTAVAP-P1 delineated acute, sterile inflammation comparable with (18)F-FDG. However, the tumour uptake of (68)Ga-DOTAVAP-P1 was low in contrast to prominent (18)F-FDG uptake. The standardised uptake values of inflammation and tumours by PET were 1.1 +/- 0.4 (mean +/- SEM) and 0.4 +/- 0.1 for (68)Ga-DOTAVAP-P1 and 2.0 +/- 0.5 and 1.6 +/- 0.8 for (18)F-FDG, respectively. In addition, PET studies showed inflammation to muscle and tumour to muscle ratios of 5.1 +/- 3.1 and 1.7 +/- 0.3 for (68)Ga-DOTAVAP-P1 and 6.2 +/- 0.7 and 4.6 +/- 2.2 for (18)F-FDG, respectively. Immunohistochemistry revealed increased expression of luminal VAP-1 on the endothelium at the site of inflammation and low expression in the tumour CONCLUSION: The (68)Ga-DOTAVAP-P1 PET was able to visualise inflammation better than tumour, which was in accordance with the luminal expression of VAP-1 on vasculature in these experimental models.

68Ga-chloride PET reveals human pancreatic adenocarcinoma xenografts in rats--comparison with FDG.

PURPOSE: The aim of the study was to compare (68)Ga-chloride with 2-[(18)F]fluoro-2-deoxy-D: -glucose (FDG) for the imaging of pancreatic xenografts. PROCEDURES: Rats with subcutaneous human pancreatic adenocarcinoma xenografts were evaluated in vivo by dynamic positron emission tomography (PET) and ex vivo by measuring radioactivity of excised tissues and by digital autoradiography of tumor cryosections. RESULTS: Both tracers were capable of delineating all subcutaneous tumors from surrounding tissues by PET. The standardized uptake values of tumors by PET were 0.9 +/- 0.3 (mean +/- SD) for (68)Ga-chloride (n = 13) and 1.8 +/- 1.2 for FDG (n = 11). Ex vivo studies showed tumor-to-muscle ratio of 4.0 +/- 0.3 for (68)Ga-chloride (n = 4) and 7.9 +/- 3.2 for FDG (n = 4). CONCLUSIONS: (68)Ga-chloride delineated subcutaneously implanted pancreatic adenocarcinoma xenografts by PET, but the uptake was lower than FDG. Further studies to clarify the value of (68)Ga-chloride for PET imaging of tumors are warranted.

Synthesis, 68Ga labeling and preliminary evaluation of DOTA peptide binding vascular adhesion protein-1: a potential PET imaging agent for diagnosing osteomyelitis.

INTRODUCTION: Vascular adhesion protein-1 (VAP-1) is an infection/inflammation-inducible endothelial glycoprotein. Based on our previous studies, the most VAP-1-selective peptide (VAP-P1) was 1,4,7,10-tetraazacyclododecane-N',N'',N''',N-tetraacetic acid (DOTA)-conjugated, 68gallium (68Ga)-labeled (named [68Ga]DOTAVAP-P1) and evaluated preliminarily. METHODS: Targeting was evaluated by using VAP-1-transfected cells. Biodistribution of [68Ga]DOTAVAP-P1 was studied by positron emission tomography imaging of healthy rats and rats with bone inflammation caused by Staphylococcus aureus infection. Uptake of [(68)Ga]DOTAVAP-P1 in osteomyelitis was compared with negative control peptide and competition with an excess of unlabeled DOTAVAP-P1. RESULTS: [68Ga]DOTAVAP-P1 bound more efficiently to VAP-1-transfected cells than to controls. In rats, [68Ga]DOTAVAP-P1 cleared rapidly from blood circulation, excreted quickly in urine and showed an in vivo half-life of 26+/-2.3 min. Imaging of osteomyelitis demonstrated modest target-to-background ratio. Studies with the negative control peptide and competitors revealed a significantly lower uptake at the infection site compared to [68Ga]DOTAVAP-P1. CONCLUSIONS: The results represent a proof-of-concept that infection-induced VAP-1 can be targeted by [68Ga]DOTA peptide. [68Ga]DOTAVAP-P1 is just the first candidate peptide and an essential opening for developing VAP-1-specific imaging agents.

(68)Ga-DOTAVAP-P1 PET imaging capable of demonstrating the phase of inflammation in healing bones and the progress of infection in osteomyelitic bones.

PURPOSE: Differentiation between bacterial infection and nonbacterial inflammation remains a diagnostic challenge. Vascular adhesion protein 1 (VAP-1) is a human endothelial protein whose cell surface expression is induced under inflammatory conditions, thus making it a highly promising target molecule for studying inflammatory processes in vivo. We hypothesized that positron emission tomography (PET) with gallium-68-labeled 1,4,7,10-tetraazacyclododecane-N',N'',N''',N''''-tetraacetic acid-peptide targeted to VAP-1 ((68)Ga-DOTAVAP-P1) could be feasible for imaging the early inflammatory and infectious processes in healing bones. MATERIALS AND METHODS: Thirty-four Sprague-Dawley rats with diffuse Staphylococcus aureus tibial osteomyelitis and 34 rats with healing cortical bone defects (representing the inflammation stage of healing) were PET imaged using (68)Ga-DOTAVAP-P1 as a tracer. In addition, peripheral quantitative computed tomography and conventional radiography were performed. Bone samples for quantitative bacteriology and specimens were also processed for histomorphometry of inflammatory and infectious reactions. RESULTS: PET imaging showed an uptake of (68)Ga-DOTAVAP-P1 in both the osteomyelitic bones and the healing cortical bone defects during the first 36 h after surgery. Thereafter, only the osteomyelitic tibias were delineated by PET. The osteomyelitic and control animals showed a similar uptake of the (68)Ga-DOTAVAP-P1 at 24 h, whereas a significant difference was observed at 7 days (p < 0.0001). CONCLUSIONS: The current study showed that PET imaging with the new (68)Ga-DOTAVAP-P1 is capable of accurately demonstrating the phase of inflammation in healing bones and the progress of bacterial infection in osteomyelitic bones. Consequently, this novel imaging agent allowed for the differentiation of bone infection due to S. aureus and normal bone healing as soon as 7 days after onset.

Biodistribution of 68Ga-labelled phosphodiester, phosphorothioate, and 2'-O-methyl phosphodiester oligonucleotides in normal rats.

Antisense oligonucleotides may hybridise with high selectivity to mRNA sequences allowing monitoring of gene expression or inhibition of the manifestation of altered genes inducing diseases. As part of the development of positron emission tomography methods, 17-mer antisense phosphodiester (PO), phosphorothioate (PS) and 2'-O-methyl phosphodiester (OMe) oligonucleotides specific for point mutationally activated human K-ras oncogene were labelled with 68Ga radionuclide via a chelator coupled to the probe. Hybridisation in solution and non-denaturing polyacrylamide gel electrophoresis (PAGE) with a subsequent exposure of the gels was performed to verify the hybridisation ability after labelling. The biodistribution was studied in male Sprague-Dawley rats by injecting 2MBq of 68Ga-oligonucleotides via the tail vein and measuring the organ radioactivity concentration after 20, 60 and 120 min or using whole-body autoradiography with 10 MBq 68Ga-oligonucleotide and 20 min incubation time. Control experiments were performed with 68GaCl3 and 68Ga-chelator complex. The results revealed that 68Ga-labelling did not change the hybridisation abilities of the oligonucleotides. The biodistribution pattern depended on the nature of the oligonucleotide backbone. Bone marrow, kidney, liver, spleen and urinary bladder were the five organs of highest uptake with each oligonucleotide. The PO accumulated highly in the liver, whereas high kidney uptake dominated the PS and OMe patterns. Intact PS and OMe were detected in plasma samples taken 20 and 60 min after injection. This study supplies a base for the further development of 68Ga-labelled oligonucleotides as pharmacokinetic tools and a potential future use for in vivo imaging of gene expression.

Biodistribution and blood metabolism of 1-11C-methyl-4-piperidinyl n-butyrate in humans: an imaging agent for in vivo assessment of butyrylcholinesterase activity with PET.

UNLABELLED: 1-(11)C-Methyl-4-piperidinyl n-butyrate ((11)C-MP4B) is a new radiopharmaceutical for the in vivo assessment of butyrylcholinesterase (BuChE) activity using PET. To quantify in vivo activity of BuChE with a kinetic model, investigators must determine the time course of radioactivity associated with unchanged (11)C-MP4B. We aimed at clarifying the metabolic fate and whole-body distribution of intravenously administered (11)C-MP4B in man. METHODS: High-performance liquid chromatography and thin-layer chromatography assays were performed to determine the amounts of intact (11)C-MP4B and its radioactive hydrolysis product in blood withdrawn during PET. In addition, we evaluated the distribution and kinetics of (11)C-MP4B uptake in human brain and main organs. RESULTS: The analysis of plasma samples of 28 human subjects (10 patients with Alzheimer's disease [AD] and 18 healthy controls) showed that the level of unmetabolized (11)C-MP4B decreases rapidly from 28% +/- 14% (mean +/- SD) at 0.5 min to 7% +/- 6% at 15 min after injection. Large individual variation was observed in the rate of plasma (11)C-MP4B hydrolysis, but no significant differences were found in the degradation of (11)C-MP4B either between male and female or between healthy subjects and patients. The whole-body distribution of (11)C-MP4B showed the highest activities in the urinary bladder, renal pelvis, stomach, salivary glands, liver, kidneys, spleen, vertebral column, and brain. In patients with AD, (11)C-MP4B activity in the brain was highest in cerebellum, followed by striatum, pons, and thalamus. Lower (11)C-MP4B activity was seen in cortical areas. CONCLUSION: Our results indicate that (11)C-MP4B is excreted rapidly through the renal system. Careful analysis of plasma metabolites is required to determine the accurate arterial input function for quantitative PET measurement. Biodistribution of (11)C-MP4B in the brains of patients with AD appears to be in accordance with the distribution of BuChE seen in postmortem studies of human brain, except for the observed higher activity in striatum than in cortex. Further studies of the cerebral distribution and regional kinetic analysis of (11)C-MP4B are in progress.

68Ga-labeled oligonucleotides for in vivo imaging with PET.

UNLABELLED: The biologic evaluation in living rats of (68)Ga-labeled oligonucleotides as imaging agents for PET is reported. METHODS: (68)Ga, a positron-emitting radionuclide (half-life, 68 min), along with a macrocyclic chelating agent, 1,4,7,10-tetraazacyclododecane-N,N',N",N"'-tetraacetic acid (DOTA), was used for labeling of antisense oligonucleotides targeting activated human K-ras oncogene. The biologic properties of 3 different forms of the oligonucleotides-that is, 2'-deoxyphosphodiester (PO), 2'-deoxyphosphorothioate (PS), and 2'-O-methyl phosphodiester (OMe)-were studied first. The biodistribution and biokinetics were evaluated in vivo in athymic rats, each bearing a tumor of A549 cells, containing K-ras point mutation in codon 12, and a tumor of BxPC-3 cells, containing wild-type K-ras. Dynamic PET imaging lasting up to 2 h was performed immediately after intravenous injection of (68)Ga-oligonucleotide. Blank studies were performed using (68)GaCl(3) or (68)Ga-DOTA alone without oligonucleotide. The (68)Ga-antisense oligonucleotide uptake in tumors was also compared with the (18)F-FDG and (68)Ga-sense oligonucleotide uptakes. In addition, oligonucleotide binding to human plasma proteins and to human albumin was examined by means of ultrafiltration. RESULTS: The oligonucleotides can be stably labeled with (68)Ga and DOTA chelate. Intravenously injected (68)Ga-oligonucleotides of 17-mer length revealed high-quality PET images, allowing quantification of the biokinetics in major organs and in tumors. The biodistribution and biokinetics of intravenously administered (68)Ga-oligonucleotide varied considerably with the nature of the oligonucleotide backbone. CONCLUSION: We conclude that (68)Ga labeling of oligonucleotides is a convenient approach for in vivo imaging and quantification of oligonucleotide biokinetics in living animals with PET.