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[en] Introduction: The 11C/18F–choline is a PET/CT radiopharmaceutical useful in detecting tumors with high lipogenesis. 11C/18F–choline uptake can occur in physiological conditions or tumors. The knowledge of its bio-distribution is essential to recognize physiologic variants or diagnostic pitfalls. Moreover, few information are available on the bio-distribution of this tracer in female patients. Our aim was to discuss some documented 18F–choline PET/CT pitfalls in prostate cancer patients. Our secondary aim was to describe the 18F–choline bio-distribution in the female body. Methods: We collected diagnostic pitfalls in three PET centers examining 1000 prostate cancer by 18F–choline PET/CT. All pitfalls were ensured by follow-up, imaging and/or histology. We also performed whole body 18F–choline PET/CT in 5 female patients. Results: 169/1000 (16.9%) patients showed pitfalls not owing to prostate cancer. These findings were due to inflammation, benign tumors while, in 1% of examined patients, a concomitant neoplasm was found. In the female body, the breast showed low physiological uptake. Conclusions: The accurate knowledge of 18F–choline PET/CT bio-distribution and diagnostic pitfalls is essential. Correlative imaging and histological exam are often necessary to depict pitfalls. In women, the uptake in the breast is due to the physiological gradient of 18F–choline uptake in the exocrine glands. Advances in knowledge: Our results confirm the possibility of 18F–choline uptake in several diseases other than prostate cancer. However, our experience was acquired on a large population and shows that a conspicuous amount of 18F–choline diagnostic pitfalls are easily recognizable and attributable to inflammation. A new advance in knowledge is the minimal difference in terms of physiological tracer bio-distribution between male and female patients. Implications for patient care: The knowledge of the physiological bio-distribution and of the potential pitfalls linked of a tracer could help physicians to choose the best diagnostic and therapeutic approaches for a better patient quality of life.
[en] Introduction: Previously, our laboratory has shown that 64Cu-TP3805 can specifically target VPAC1 receptors and be used for positron emission tomography (PET) imaging of breast (BC) and prostate cancer (PC) in humans. Present work is aimed at the formulation of a freeze-dried diaminedithiol-peptide (N2S2-TP3805) kit and it's evaluation for the preparation of 64Cu labeled TP3805. Parameters such as pH, temperature and incubation time were examined that influenced the radiolabeling efficiency and stability of the product. Methods: Kits were prepared under different conditions and radiolabeling efficiency of TP3805 kit was evaluated for a range of pH 3.5–8.5, after addition of 64Cu in 30 μl, 0.1 M HCl. Incubation temperature (37-90 °C) and time (30-120 min.) were also investigated. Kits were stored at −10 °C and their long term stability was determined as a function of their radiolabeling efficiency. Further, stability of 64Cu-TP3805 complex was evaluated in presence of fetal bovine serum and bovine serum albumin by using SDS polyacrylamide gel electrophoresis. Kits were then used for PET imaging of BC and PC following eIND (101550) and institutional approvals. Specificity of 64Cu-TP3805 for VPAC1 was examined with digital autoradiography (DAR) of prostate tissues obtained after prostatectomy, benign prostatic hyperplasia (BPH) tissue, and benign and malignant lymph nodes. Results were compared with corresponding tissue histology. Results: Radiolabeling efficiency was ≥95% at final pH ~7.2 when incubated at 50 °C for 90 min. Kits were stable up to 18 months when stored at −10 °C, and 64Cu-TP3805 complex exhibited excellent stability for up to 4 h at room temperature. 64Cu-TP3805 complex did not show any transchelation even after 2 h incubation at 37 °C in 10% FBS as well as in BSA as determined by SDS PAGE analysis. DAR identified ≥95% of malignant lesions 11 new PC lesions, 20 high grade prostatic intraepithelial neoplasia, 2/2 ejaculatory ducts and 5/5 urethra verumontanum not previously identified The malignant lymph nodes were correctly identified by DAR and for 3/3 BPH patients, and 5/5 cysts, DAR was negative. In human BC (n = 19) and PC (n = 26) were imaged with 100% sensitivity. Conclusion: Availability of ready to use N2S2-peptide kits for 64Cu labeling is convenient and eliminates possible day to day variation during its routine preparation for clinical use.
[en] The bombesin receptor family, in particular the gastrin-releasing peptide receptor (GRPr), is an attractive target in the field of nuclear oncology due to the high density of these receptors on the cell surface of several human tumors. The successful clinical implementation of 64Cu-CB-TE2A-AR06, 68Ga-RM2 and 68Ga-NODAGA-MJ9, prompted us to continue the development of GRPr-antagonists. The aim of the present study was to assess if N-terminal modulations of the statine-based GRPr-antagonist influence the binding affinity, the pharmacokinetic performance and the in vivo metabolic stability. Methods: The GRPr-antagonist (D-Phe-Gln-Trp-Ala-Val-Gly-His-Sta-Leu-NH2) was functionalized with the chelator 1,4,7,10-tetraazacyclododecane-1,4,7,10-tetraacetic acid (DOTA) via the spacer 4-amino-1-carboxymethyl-piperidine (Pip) and the amino acid N-Methyl-β-Ala, to obtain NMe-RM2 and labeled with 68Ga and 177Lu. The GRPr affinity of the corresponding metalloconjugates determined using [125I–Tyr4]-BN as radioligand. In vitro evaluation included internalization studies using PC3 cells. The 68Ga-conjugate was evaluated in PC3 xenografts by biodistribution and PET studies, while investigations on the metabolic stability and plasma protein binding were performed. Results: The half maximum inhibitory concentrations (IC50) of the metalloconjugates, using [125I–Tyr4]-BN, are in the low nanomolar range. PC3-cell culture binding studies of both metallated NMe-RM2 and RM2 show high GRPr-bound activity and low internalization. Metabolic studies showed that 68Ga-NMe-RM2 and 68Ga-RM2 are being cleaved in a similar fashion into three metabolites, with a good proportion of about 50% of the remaining blood activity at 15 min post injection (p.i.) being represented by the intact radiotracer. 68Ga-NMe-RM2 was shown to target specifically PC3 xenografts, with high and sustained tumor uptake of about 13% IA/g within a time frame of 3 h. The PET images clearly visualized the tumor. Conclusions: The relatively high percentage of the remaining intact radiotracer in blood 15 min post injection sufficiently enables in vivo targeting of GRPr positive tumors, finding which has been also shown in clinical trials.
[en] Oxytocin plays a major role in the regulation of social interactions in mammals by interacting with the oxytocin receptor (OTR) expressed in the brain. Furthermore, the oxytocin system appears as a possible therapeutic target in autism spectrum disorders and other psychiatric troubles, justifying current pharmacological researches. Since no specific PET radioligand is currently available to image OTR in the brain, the aim of this study was to radiolabel the specific OTR antagonist PF-3274167 and to evaluate [11C]PF-3274167 as a potential PET tracer for OTR in rat brains.
[en] 111In-DTPA-d-Phe1-octreotide scintigraphy is an important method of detecting neuroendocrine tumors. We previously reported that a new derivative of 111In-DTPA-d-Phe1-octreotide, 111In-DTPA-d-Phe−1-Asp0-d-Phe1-octreotide, accomplished the reduction of prolonged renal accumulation of radioactivity. The aim of this study was to evaluate the tumor accumulation of 111In-DTPA-d-Phe−1-Asp0-d-Phe1-octreotide in vitro and in vivo by comparing it with 111In-DTPA-d-Phe1-octreotide.
[en] Herein we have evaluated the uptake of O-(2-18F-fluoroethyl)-l-tyrosine (18F-FET) in insulinoma in comparison with those of 6-18F-fluoro-3,4-dihydroxy-l-phenylalanine (18F-FDOPA) providing first data from both murine xenograft model and one patient with proved endogenous hyperinsulinemic hypoglycemia.
[en] The endocannabinoid system participates in many processes in the body, including memory, reward, pain, motor activity, food intake, energy metabolism, and gastrointestinal functions. [18F]MK-9470 is a positron emission tomography (PET) ligand that binds with high affinity and selectivity to the cannabinoid type 1 receptor. In order to fully characterize ligand behavior, tracer uptake measured using in vivo microPET was compared with results from ex vivo tissue dissection. Twelve male Sprague–Dawley rats were divided into three subgroups and scanned over time periods of 10 min, 30 min and 90 min using PET. Afterwards, a number of the animals' organs were dissected. Uptake of radioactivity was expressed in terms of %ID/ml and %ID/(g tissue). For comparison of in vivo and ex vivo methods, Bland–Altman plots were computed. The highest uptake of [18F]MK-9470 was found in the liver and small intestine; the brain showed less uptake, while low and unspecific binding was observed in tissue of the heart, lung, kidney and bone. In the brain, normalized uptake of [18F]MK-9470 was on average 0.25%ID/ml (range: 0.16 to 0.28%ID/ml). Bland–Altman plots revealed the best agreement between methods for the 90 min acquisition protocols. High hepatic accumulation and metabolism of [18F]MK-9470 occur with mainly enteral excretion, which may vary considerably over time — a finding which may be of relevance in metabolite determination in quantitative brain studies. Comparisons between in vivo and ex vivo methods showed that whole-body distribution of [18F]MK-9470 using positron emission tomography is a preferable alternative to ex vivo biodistribution, and requires a significantly smaller number of animals.
[en] Endothelial cells and their metabolic state regulate glucose transport into underlying tissues. Here, we show that low oxygen tension stimulates human umbilical vein endothelial cell 18F–fluorodeoxyglucose (18F–FDG) uptake and lactate production. This was accompanied by augmented hexokinase activity and membrane Glut-1, and increased accumulation of hypoxia-inducible factor-1α (HIF1α). Restoration of oxygen reversed the metabolic effect, but this was blocked by HIF1α stabilization. Hypoxia-stimulated 18F–FDG uptake was completely abrogated by silencing of HIF1α expression or by a specific inhibitor. There was a rapid and marked increase of reactive oxygen species (ROS) by hypoxia, and ROS scavenging or NADPH oxidase inhibition completely abolished hypoxia-stimulated HIF1α and 18F–FDG accumulation, placing ROS production upstream of HIF1α signaling. Hypoxia-stimulated HIF1α and 18F–FDG accumulation was blocked by the protein kinase C (PKC) inhibitor, staurosporine. The phosphatidylinositol 3-kinase (PI3K) inhibitor, wortmannin, blocked hypoxia-stimulated 18F–FDG uptake and attenuated hypoxia-responsive element binding of HIF1α without influencing its accumulation. Thus, ROS-driven HIF1α accumulation, along with PKC and PI3K signaling, play a key role in triggering accelerated glycolysis in endothelial cells under hypoxia, thereby contributing to 18F–FDG transport.
[en] Introduction: Erlotinib is a tyrosine kinase inhibitor prescribed for non-small cell lung cancer (NSCLC) patients bearing epidermal growth factor receptor mutations in the kinase domain. The objectives of this study were to (1) establish a human dosimetry profile of [11C]erlotinib and (2) assess the consistency of calculated equivalent dose across species using the same dosimetry model. Methods: Subjects examined in this multi-species study included: a stage IIIa NSCLC patient, 3 rhesus macaque monkeys, a landrace pig, and 4 athymic nude-Fox1nu mice. [11C]erlotinib PET data of the whole body were acquired dynamically for up to 120 min. Regions of interest (ROIs) were manually drawn to extract PET time activity curves (TACs) from identifiable organs. TACs were used to calculate time-integrated activity coefficients (residence times) in each ROI, which were then used to calculate the equivalent dose in OLINDA. Subject data were used to predict the equivalent dose to the organs of a 73.7 kg human male. Results: In three of four species, the liver was identified as the organ receiving the highest equivalent dose (critical organ). The mean equivalent doses per unit of injected activity to the liver based on human, monkey, and mouse data were 29.4 μSv/MBq, 17.4 ± 6.0 μSv/MBq, and 5.27 ± 0.25 μSv/MBq, respectively. The critical organ based on the pig data was the gallbladder wall (20.4 μSv/MBq) but the liver received a nearly identical equivalent dose (19.5 μSv/MBq). Conclusions: (1) When designing PET studies using [11C]erlotinib, the liver should be considered the critical organ. (2) In organs receiving the greatest equivalent dose, mouse data underestimated the dose in comparison to larger species. However, the effective dose of [11C]erlotinib to the whole body of a 73.7 kg man was predicted with good consistency based on mice (3.14 ± 0.05 μSv/MBq) or the larger species (3.46 ± 0.25 μSv/MBq).
[en] Rationale: Ataxia telangiectasia and Rad3-related (ATR) threonine serine kinase is one of the key elements in orchestrating the DNA damage response (DDR). As such, inhibition of ATR can amplify the effects of chemo- and radiation-therapy, and several ATR inhibitors (ATRi) have already undergone clinical testing in cancer. For more accurate patient selection, monitoring and staging, real-time in vivo imaging of ATR could be invaluable; the development of appropriate imaging agents has remained a major challenge. Methods: 3-amino-N-(4-[18F]phenyl)-6-(4-(methylsulfonyl)phenyl) pyrazine-2-carboxamide ([18F]-ATRi), a close analogue of Ve-821, (a clinical ATRi candidate), was readily accomplished similarly to already established synthetic procedures. Structurally, 18F was introduced at the 4-position of the aromatic ring of Ve-821 for generating a labeled ATR inhibitor. In vitro experiments were conducted in U251 MG glioblastoma cell lines and ex vivo biodistribution were performed in subcutaneous U251 MG xenograft bearing athymic nude mice following microPET imaging. Results: [18F]-ATRi has a similar pharmacokinetic profile to that of Ve-821. Using an U251 MG glioblastoma mouse model, we evaluated the in vivo binding efficiency of [18F]-ATRi. Blood and tumor showed a statistically significant difference between mice injected with only the probe or following blocking experiment with Ve-821 (1.48 ± 0.40%ID/g vs. 0.46 ± 0.12%ID/g in tumor and 1.85 ± 0.47%ID/g vs. 0.84 ± 0.3%ID/g in blood respectively). Conclusions: [18F]-ATRi represents the first 18F positron emission tomography (PET) ATR imaging agent, and is designed on a low nanomolar and clinically relevant ATR inhibitor.