Positron emission tomography with [18F]fluorodeoxyglucose to evaluate neutrophil kinetics during acute lung injury

We measured neutrophil glucose uptake with positron emission tomographic imaging and [18F]fluorodeoxyglucose ([18F]FDG-PET) in anesthetized dogs after intravenous oleic acid-induced acute lung injury (ALI; OA group, n = 6) or after low-dose intravenous endotoxin (known to activate neutrophils without causing lung injury) followed by OA (Etx + OA group, n = 7). The following two other groups were studied as controls: one that received no intervention (n = 5) and a group treated with Etx only (n = 6). PET imaging was performed 1.5 h after initiating experimental interventions. The rate of [3H]deoxyglucose ([3H]DG) uptake was also measured in vitro in cells recovered from bronchoalveolar lavage (BAL) performed after PET imaging. Circulating neutrophil counts fell significantly in animals treated with Etx but not in the other two groups. The rate of [18F]FDG uptake, measured by the influx constant Ki, was significantly elevated (P < 0.05) in both Etx-treated groups (7.9 +/- 2.6 x 10(-3) ml blood x ml lung(-1) x min(-1) in the Etx group, 9.3 +/- 4.8 x 10(-3) ml blood x ml lung(-1) x min(-1) in the Etx + OA group) but not in the group treated only with OA (3.4 +/- 0.8 x 10-3 ml blood x ml lung(-1) x min(-1)) when compared with the normal control (1.6 +/- 0.4 x 10(-3) ml blood x ml lung(-1) x min(-1)). [3H]DG uptake was increased (73 +/- 7%) in BAL neutrophils recovered from the Etx + OA group (P < 0.05) but not in the OA group. Ki and [3H]DG uptake rates were linearly correlated (R2 = 0.65). We conclude that the rate of [18F]FDG uptake in the lungs during ALI reflects the state of neutrophil activation. [18F]FDG-PET imaging can detect pulmonary sequestration of activated neutrophils, despite the absence of alveolar neutrophilia. Thus [18F]FDG-PET imaging may be a useful tool to study neutrophil kinetics during ALI.     

Lumped constant for [(18)F]fluorodeoxyglucose in skeletal muscles of obese and nonobese humans

Quantitative 2-[(18)F]fluoro-2-deoxy-D-glucose ([(18)F]FDG) positron emission tomography (PET) has been widely used to calculate glucose utilization in skeletal muscle. FDG-PET results depend partly on the lumped constant (LC), which accounts for the differences in the transport and phosphorylation between [(18)F]FDG and glucose. In this study, we estimated the LC for [(18)F]FDG directly in normal and in insulin-resistant obese subjects by combining FDG PET with the microdialysis technique. Eight obese [age 29.4 +/- 1.0 yr, body mass index (BMI) 33.6 +/- 1.0 kg/m(2)] and eight nonobese (age 25.0 +/- 1.0 yr, BMI 23.1 +/- 1.0 kg/m(2)) males were studied during euglycemic hyperinsulinemia (1 mU. kg(-1).min(-1) for 150 min). Muscle blood flow was measured using (15)O-labeled water and PET. Muscle [(18)F]FDG uptake (rGU(FDG)) was calculated with Patlak graphic analysis. Interstitial glucose concentration of the quadriceps femoris muscle was measured simultaneously with [(18)F]FDG scanning using microdialysis. Muscle glucose uptake (by microdialysis, rGU(MD)) was calculated by multiplying glucose extraction by regional muscle blood flow. A significant correlation was found between rGU(MD) and rGU(FDG) (r = 0.78, P < 0.01). The LC was determined as the ratio of the rGU(FDG) to the rGU(MD). The LC averaged 1.16 +/- 0.16 and was similar in the obese and nonobese subjects (1.15 +/- 0.11 vs. 1.16 +/- 0.07, respectively, not significant). In conclusion, the microdialysis technique can be reliably combined with FDG PET to measure glucose uptake in skeletal muscle. Direct measurements with these two independent techniques suggest an LC value of 1.2 for [(18)F]FDG in human skeletal muscle during insulin stimulation, and the LC appears not to be sensitive to insulin resistance.     

Molecular imaging of lung glucose uptake after endotoxin in mice

Positron emission tomographic imaging after administration of the glucose analog fluorine-18 fluorodeoxyglucose ([18F]FDG) may be useful to study neutrophilic inflammation of the lungs. In this study, we sought to determine the specificity of the increase in lung [18F]FDG uptake after intraperitoneal endotoxin (Etx) for neutrophil influx into mouse lungs and to determine the regulation of glucose uptake after Etx by Toll-like receptors (TLRs) and TNF-alpha. Lung tissue radioactivity measurements by imaging were validated against counts in a gamma well counter. Glucose uptake was quantified as the [18F]FDG tissue-to-blood radioactivity ratio (TBR) after validating this measure against the "gold standard" measure of glucose uptake, the "net influx rate constant." TBR measurements were made in a control group (no intervention), a group administered Etx, and a group administered Etx plus an additional agent (e.g., vinblastine) or Etx administered to a mutant mouse strain. The glucose uptake measurements were compared with measurements of myeloperoxidase. Increases in TBR after Etx were significantly but not completely eliminated by neutrophil depletion with vinblastine. Increases in TBR after Etx were consistent with signaling via either TLR-4 or TLR-2 (the latter probably secondary to peptidoglycan contaminants in Etx preparation) and were decreased by drug inhibition of TLR-4 but not by inhibition of TNF-alpha. Thus molecular imaging can be used to noninvasively monitor biological effects of Etx on lungs in mice, and changes in lung glucose uptake can be used to monitor effects of anti-inflammatory agents. Such imaging capacity provides a powerful new paradigm for translational "mouse-to-human" pulmonary research.     

Neutrophil defensins mediate acute inflammatory response and lung dysfunction in dose-related fashion

High concentrations of neutrophil defensins from airway and blood have been reported in patients with inflammatory lung diseases, but their exact role is unclear. We investigated the direct effect of defensins on the lungs of mice. Intratracheal instillation of purified defensins (5-30 mg/kg) induced a progressive reduction in peripheral arterial O(2) saturation, increased lung permeability, and enhanced the lung cytochrome c content. These indexes of acute lung dysfunction were associated with an increased total cell number and a significant neutrophil influx into the lung [5.1 +/- 0.04% in control vs. 48.6 +/- 12.7% in the defensin (30 mg/kg) group, P < 0.05]. Elastase concentrations in the bronchoalveolar lavage (BAL) fluids increased from 38 +/- 11 ng/ml (control) to 80 +/- 4 ng/ml (defensins, P < 0.05). Five hours after defensin instillation, concentrations of tumor necrosis factor-alpha and macrophage inflammatory protein-2 in BAL fluid were significantly increased. High levels of monocyte chemoattractant protein-1 in BAL fluid and plasma were also found after defensin stimulation. We conclude that intratracheal instillation of defensins causes acute lung inflammation and dysfunction, suggesting that high concentrations of defensins in the airways may play an important role in the pathogenesis of inflammatory lung diseases.     

Near-infrared fluorescent deoxyglucose analogue for tumor optical imaging in cell culture and living mice

2-deoxy-2-[18F]fluoro-D-glucose ([18F]FDG) has extensively been used for clinical diagnosis, staging, and therapy monitoring of cancer and other diseases. Nonradioactive glucose analogues enabling the screening of the glucose metabolic rate of tumors are of particular interest for anticancer drug development. A nonradioactive fluorescent deoxyglucose analogue may have many applications for both imaging of tumors and monitoring therapeutic efficacy of drugs in living animals and may eventually translate to clinical applications. We found that a fluorescent 2-deoxyglucose analogue, 2-[N-(7-nitrobenz-2-oxa-1,3-diazol-4-yl)amino]-2-deoxy-D-glucose (2-NBDG), can be delivered in several tumor cells via the glucose transporters (GLUTs). We therefore conjugated D-glucosamine with a near-infrared (NIR) fluorphor Cy5.5 and tested the feasibility of the Cy5.5-D-glucosamine (Cy5.5-2DG) conjugate for NIR fluorescence imaging of tumors in a preclinical xenograft animal model. Cy5.5-2DG was prepared by conjugating Cy5.5 monofunctional N-hydroxysuccinimide ester (Cy5.5-NHS) and D-glucosamine followed by high-performance liquid chromatography purification. The accumulation of Cy5.5-2DG and Cy5.5-NHS in different tumor cell lines at 37 and 4 degrees C were imaged using a fluorescence microscope. Tumor targeting and retention of Cy5.5-2DG and Cy5.5-NHS in a subcutaneous U87MG glioma and A375M melanoma tumor model were evaluated and quantified by a Xenogen IVIS 200 optical cooled charged-coupled device system. Fluorescence microscopy imaging shows that Cy5.5-2DG and Cy5.5-NHS are taken up and trapped by a variety of tumor cell lines at 37 degrees C incubation, while they exhibit marginal uptake at 4 degrees C. The tumor cell uptake of Cy5.5-2DG cannot be blocked by the 50 mM D-glucose, suggesting that Cy5.5-2DG may not be delivered in tumor cells by GLUTs. U87MG and A375M tumor localization was clearly visualized in living mice with both NIR fluorescent probes. Tumor/muscle contrast was clearly visible as early as 30 min postinjection (pi), and the highest U87MG tumor/muscle ratios of 2.81 +/- 0.10 and 3.34 +/- 0.23 were achieved 24 h pi for Cy5.5-2DG and Cy5.5-NHS, respectively. While as a comparison, the micropositron emission tomography imaging study shows that [18F]FDG preferentially localizes to the U87MG tumor, with resulting tumor/muscle ratios ranging from 3.89 to 4.08 after 30 min to 2 h postadministration of the probe. In conclusion, the NIR fluorescent glucose analogues, Cy5.5-2DG and Cy5.5-NHS, both demonstrate tumor-targeting abilities in cell culture and living mice. More studies are warranted to further explore their application for optical tumor imaging. To develop NIR glucose analogues with the ability to target GLUTs/hexokinase, it is highly important to select NIR dyes with a reasonable molecular size.     

[18F]FDG Accumulation in Early Coronary Atherosclerotic Lesions in Pigs

Objective

Inflammation is an important contributor to atherosclerosis progression. A glucose analogue ¹⁸F-fluorodeoxyglucose ([¹⁸F]FDG) has been used to detect atherosclerotic inflammation. However, it is not known to what extent [¹⁸F]FDG is taken up in different stages of atherosclerosis. We aimed to study the uptake of [¹⁸F]FDG to various stages of coronary plaques in a pig model.

Methods

First, diabetes was caused by streptozotocin injections (50 mg/kg for 3 days) in farm pigs (n = 10). After 6 months on high-fat diet, pigs underwent dual-gated cardiac PET/CT to measure [¹⁸F]FDG uptake in coronary arteries. Coronary segments (n = 33) were harvested for ex vivo measurement of radioactivity and autoradiography (ARG).

Results

Intimal thickening was observed in 16 segments and atheroma type plaques in 10 segments. Compared with the normal vessel wall, ARG showed 1.7±0.7 times higher [¹⁸F]FDG accumulation in the intimal thickening and 4.1±2.3 times higher in the atheromas (P = 0.004 and P = 0.003, respectively). Ex vivo mean vessel-to-blood ratio was higher in segments with atheroma than those without atherosclerosis (2.6±1.2 vs. 1.3±0.7, P = 0.04). In vivo PET imaging showed the highest target-to-background ratio (TBR) of 2.7. However, maximum TBR was not significantly different in segments without atherosclerosis (1.1±0.5) and either intimal thickening (1.2±0.4, P = 1.0) or atheroma (1.6±0.6, P = 0.4).

Conclusions

We found increased uptake of [¹⁸F]FDG in coronary atherosclerotic lesions in a pig model. However, uptake in these early stage lesions was not detectable with in vivo PET imaging. Further studies are needed to clarify whether visible [¹⁸F]FDG uptake in coronary arteries represents more advanced, highly inflamed plaques.     

Role of acetyl-L-carnitine in the brain: revealed by Bioradiography

To elucidate the role of acetyl-l-carnitine in the brain, we used a novel method, ‘Bioradiography,’ in which the dynamic process could be followed in living slices by use of positron-emitter labeled compounds and imaging plates. We studied the incorporation of 2-[¹⁸F]fluoro-2-deoxy-d-glucose ([¹⁸F]FDG) into rat brain slices incubated in oxygenated Krebs-Ringer solution. Under the glucose-free condition, [¹⁸F]FDG uptake rate decreased with time and plateaued within 350 min in the cerebral cortex and cerebellum, and the addition of 1 or 5 mM acetyl-l-carnitine did not alter the [¹⁸F]FDG uptake rate. When a glutaminase inhibitor, 0.5 mM 6-diazo-5-oxo-l-norleucine (DON), was added under the normal glucose condition, [¹⁸F]FDG uptake rate decreased. Acetyl-l-carnitine (1 mM), which decreased [¹⁸F]FDG uptake rate, reversed this DON-induced decrease in [¹⁸F]FDG uptake rate in the cerebral cortex. These results suggest that acetyl-l-carnitine can be used for the production of releasable glutamate rather than as an energy source in the brain.     

[18F]FLT and [18F]FDG PET for Non-invasive Treatment Monitoring of the Nicotinamide Phosphoribosyltransferase Inhibitor APO866 in Human Xenografts

Introduction

APO866 is a new anti-tumor compound inhibiting nicotinamide phosphoribosyltransferase (NAMPT). APO866 has an anti-tumor effect in several pre-clinical tumor models and is currently in several clinical phase II studies. 3′-deoxy-3′-[18F]fluorothymidine ([18F]FLT) is a tracer used to assess cell proliferation in vivo. The aim of this study was non-invasively to study effect of APO866 treatment on [18F]FLT and 2-deoxy-2-[18F]fluoro-D-glucose ([18F]FDG) uptake.

Methods

In vivo uptake of [18F]FLT and [18F]FDG in human ovary cancer xenografts in mice (A2780) was studied at various time points after APO866 treatment. Baseline [18F]FLT or [18F]FDG scans were made before treatment and repeated after 24 hours, 48 hours and 7 days. Tumor volume was followed with computed tomography (CT). Tracer uptake was quantified using small animal PET/CT. One hour after iv injection of tracer, static PET scans were performed. Imaging results were compared with Ki67 immunohistochemistry.

Results

Tumors treated with APO866 had volumes that were 114% (24 h), 128% (48 h) and 130% (Day 7) relative to baseline volumes at Day 0. In the control group tumor volumes were 118% (24 h), 145% (48 h) and 339% (Day 7) relative to baseline volumes Day 0. Tumor volume between the treatment and control group was significantly different at Day 7 (P = 0.001). Compared to baseline, [18F]FLT SUVmax was significantly different at 24 h (P<0.001), 48 h (P<0.001) and Day 7 (P<0.001) in the APO866 group. Compared to baseline, [18F]FDG SUVmax was significantly different at Day 7 (P = 0.005) in the APO866 group.

Conclusions

APO866 treatment caused a significant decrease in [18F]FLT uptake 24 and 48 hours after treatment initiation. The early reductions in tumor cell proliferation preceded decrease in tumor volume. The results show the possibility to use [18F]FLT and [18F]FDG to image treatment effect early following treatment with APO866 in future clinical studies.     

Imaging of rats with mammary cancer with two 2-deoxy-2-[18F]fluoro-d-hexoses

Rats with mammary cancer were imaged by scintigraphy: 10 rats with 2-deoxy-2-[¹⁸F]fluoro-d-glucose ([¹⁸F]FDG) and 10 rats with [¹⁸F]F-d-galactose. The uptake of both tracers was similar in the tumors—the tumor-to-normal tissue ratio was 2.7 ± 1.1 for [¹⁸F]FDG and 2.3 ± 0.9 for [¹⁸F]FDGal at 120 min after injection. In addition to the tumors [¹⁸F]FDG accumulated in the brain, bladder and heart, [¹⁸F]FDGal in the brain, bladder and liver. [¹⁸F]FDGal may be useful for tumor imaging in man; further studies should be addressed to elucidate the mechanism of [¹⁸F]FDGal uptake into tumors.     

Early Detection of Erlotinib Treatment Response in NSCLC by 3′-Deoxy-3′-[18F]-Fluoro-L-Thymidine ([18F]FLT) Positron Emission Tomography (PET)

Background

Inhibition of the epidermal growth factor receptor (EGFR) has shown clinical success in patients with advanced non-small cell lung cancer (NSCLC). Somatic mutations of EGFR were found in lung adenocarcinoma that lead to exquisite dependency on EGFR signaling; thus patients with EGFR-mutant tumors are at high chance of response to EGFR inhibitors. However, imaging approaches affording early identification of tumor response in EGFR-dependent carcinomas have so far been lacking.

Methodology/Principal Findings

We performed a systematic comparison of 3′-Deoxy-3′-[¹⁸F]-fluoro-L-thymidine ([¹⁸F]FLT) and 2-[¹⁸F]-fluoro-2-deoxy-D-glucose ([¹⁸F]FDG) positron emission tomography (PET) for their potential to identify response to EGFR inhibitors in a model of EGFR-dependent lung cancer early after treatment initiation. While erlotinib-sensitive tumors exhibited a striking and reproducible decrease in [¹⁸F]FLT uptake after only two days of treatment, [¹⁸F]FDG PET based imaging revealed no consistent reduction in tumor glucose uptake. In sensitive tumors, a decrease in [¹⁸F]FLT PET but not [¹⁸F]FDG PET uptake correlated with cell cycle arrest and induction of apoptosis. The reduction in [¹⁸F]FLT PET signal at day 2 translated into dramatic tumor shrinkage four days later. Furthermore, the specificity of our results is confirmed by the complete lack of [¹⁸F]FLT PET response of tumors expressing the T790M erlotinib resistance mutation of EGFR.

Conclusions

[¹⁸F]FLT PET enables robust identification of erlotinib response in EGFR-dependent tumors at a very early stage. [¹⁸F]FLT PET imaging may represent an appropriate method for early prediction of response to EGFR TKI treatment in patients with NSCLC.     

Place de la tomographie par émission de positons (TEP) au [18F]FDG dans l’exploration des vascularites

[¹⁸F]fluorodeoxyglucose (¹⁸FDG) positron emission tomography (PET) is a noninvasive metabolic imaging modality that is well suited to the assessment of activity and extent of large vessel vasculitis, such as giant cell arteritis and Takayasu arteritis. PET could be more effective than magnetic resonance imaging in detecting the earliest stages of vascular wall inflammation. The visual grading of vascular [¹⁸F]FDG uptake makes it possible to discriminate arteritis from atherosclerosis, providing therefore high specificity. High sensitivity can be achieved provided scanning is performed during active inflammatory phase, preferably before starting corticosteroid treatment. Large scale prospective studies are needed to determine the exact value of PET imaging in assessing the large vessel vasculitis outcome and response to immunosuppressive treatment.     

Tumor diagnosis by pet: potential of seven tracers examined in five experimental tumors including an artificial metastasis model

The potential of seven tracers for the metabolic imaging of tumors by positron emission tomography was studied using five experimental tumor models. The tracers examined were 2-deoxy-2-[¹⁸F]fluoro-d-glucose ([¹⁸F]FDG), 2-deoxy-2-[¹⁸F]fluoro-d-galactose (2-[¹⁸F]FdGal) and 2-deoxy-2-[¹⁸F]fluoro-l-fucose (2-[¹⁸F]FdFuc) for investigating energy metabolism. l-[methyl-¹¹C]Methionine ([¹¹C]Met) and 6-[¹⁸F]fluoro-l-fucose (6-[¹⁸F]FFuc) were used for assessing protein and glycoprotein synthesis, while [³H]thymidine ([³ H]Thd) and 2-deoxy-5′-[¹⁸F]fluorouridine ([¹⁸F]FdUrd) were used to investigate nucleic acid metabolism. The highest mean uptake by the five different tumors was found for [³H]Thd, followed in order by [¹⁸F]FDG, [¹¹C]Met, 2-[¹⁸F]FdGal, [¹⁸F]FdUrd, 2-[¹⁸F]FdFuc and 6-[¹⁸F]FFuc. The tumor-to-tissue uptake ratios indicated that the nucleosides, [¹¹C]Met and 6-[¹⁸F]FFuc were better tracers in the brain region. All the tracers except for the fucose analogs were suitable for the thoracic region, while [¹¹C]Thd and [¹⁸ F]FDG were superior in the abdominal region. In comparison with the primary tumor model of Lewis lung carcinoma (3LL), [³H]Thd uptake in the artificial metastatic 3LL model showed the maximum enhancement, followed by [¹⁸F]FDG, [¹¹C]Met and the other tracers. The [¹⁸F]FDG uptake correlated with the [³H]Thd uptake. [¹⁸F]FdUrd, 6-[¹⁸F]FFuc and 2-[¹⁸F]FdGal could be used for distinguishing different types of tumors. The combined use of these radiotracers can possibly allow the assessment of tumor metabolism, and this indicates the viability of tumors.     

Bone formation rather than inflammation reflects Ankylosing Spondylitis activity on PET-CT: a pilot study

Introduction

Positron Emission Tomography - Computer Tomography (PET-CT) is an interesting imaging technique to visualize Ankylosing Spondylitis (AS) activity using specific PET tracers. Previous studies have shown that the PET tracers [¹⁸F]FDG and [¹¹C](R)PK11195 can target inflammation (synovitis) in rheumatoid arthritis (RA) and may therefore be useful in AS. Another interesting tracer for AS is [¹⁸F]Fluoride, which targets bone formation. In a pilot setting, the potential of PET-CT in imaging AS activity was tested using different tracers, with Magnetic Resonance Imaging (MRI) and conventional radiographs as reference.

Methods

In a stepwise approach different PET tracers were investigated. First, whole body [¹⁸F]FDG and [¹¹C](R)PK11195 PET-CT scans were obtained of ten AS patients fulfilling the modified New York criteria. According to the BASDAI five of these patients had low and five had high disease activity. Secondly, an extra PET-CT scan using [¹⁸F]Fluoride was made of two additional AS patients with high disease activity. MRI scans of the total spine and sacroiliac joints were performed, and conventional radiographs of the total spine and sacroiliac joints were available for all patients. Scans and radiographs were visually scored by two observers blinded for clinical data.

Results

No increased [¹⁸F]FDG and [¹¹C](R)PK11195 uptake was noticed on PET-CT scans of the first 10 patients. In contrast, MRI demonstrated a total of five bone edema lesions in three out of 10 patients. In the two additional AS patients scanned with [¹⁸F]Fluoride PET-CT, [¹⁸F]Fluoride depicted 17 regions with increased uptake in both vertebral column and sacroiliac joints. In contrast, [¹⁸F]FDG depicted only three lesions, with an uptake of five times lower compared to [¹⁸F]Fluoride, and again no [¹¹C](R)PK11195 positive lesions were found. In these two patients, MRI detected nine lesions and six out of nine matched with the anatomical position of [¹⁸F]Fluoride uptake. Conventional radiographs showed structural bony changes in 11 out of 17 [¹⁸F]Fluoride PET positive lesions.

Conclusions

Our PET-CT data suggest that AS activity is reflected by bone activity (formation) rather than inflammation. The results also show the potential value of PET-CT for imaging AS activity using the bone tracer [¹⁸F]Fluoride. In contrast to active RA, inflammation tracers [¹⁸F]FDG and [¹¹C](R)PK11195 appeared to be less useful for AS imaging.     

[18F]FLT PET for Non-Invasive Assessment of Tumor Sensitivity to Chemotherapy: Studies with Experimental Chemotherapy TP202377 in Human Cancer Xenografts in Mice

Aim

3′-deoxy-3′-[¹⁸F]fluorothymidine ([18F]FLT) is a tracer used to assess cell proliferation in vivo. The aim of the study was to use [18F]FLT positron emission tomography (PET) to study non-invasively early anti-proliferative effects of the experimental chemotherapeutic agent TP202377 in both sensitive and resistant tumors.

Methods

Xenografts in mice from 3 human cancer cell lines were used: the TP202377 sensitive A2780 ovary cancer cell line (n = 8–16 tumors/group), the induced resistant A2780/Top216 cell line (n = 8–12 tumors/group) and the natural resistant SW620 colon cancer cell line (n = 10 tumors/group). In vivo uptake of [18F]FLT was studied at baseline and repeated 6 hours, Day 1, and Day 6 after TP202377 treatment (40 mg/kg i.v.) was initiated. Tracer uptake was quantified using small animal PET/CT.

Results

TP202377 (40 mg/kg at 0 hours) caused growth inhibition at Day 6 in the sensitive A2780 tumor model compared to the control group (P<0.001). In the A2780 tumor model TP202377 treatment caused significant decrease in uptake of [18F]FLT at 6 hours (-46%; P<0.001) and Day 1 (-44%; P<0.001) after treatment start compared to baseline uptake. At Day 6 uptake was comparable to baseline. Treatment with TP202377 did not influence tumor growth or [18F]FLT uptake in the resistant A2780/Top216 and SW620 tumor models. In all control groups uptake of [18F]FLT did not change. Ki67 gene expression paralleled [18F]FLT uptake.

Conclusion

Treatment of A2780 xenografts in mice with TP202377 (single dose i.v.) caused a significant decrease in cell proliferation assessed by [18F]FLT PET after 6 hours. Inhibition persisted at Day 1; however, cell proliferation had returned to baseline at Day 6. In the resistant A2780/Top216 and SW620 tumor models uptake of [18F]FLT did not change after treatment. With [18F]FLT PET it was possible to distinguish non-invasively between sensitive and resistant tumors already 6 hours after treatment initiation.     

Synthesis and biological evaluation of novel F-18 labeled pyrazolo[1,5-a]pyrimidine derivatives: potential PET imaging agents for tumor detection

Two novel pyrazolo[1,5-a]pyrimidine derivatives, 7-(2-[¹⁸F]fluoroethylamino)-5-methylpyrazolo[1,5-a]pyrimidine-3-carbonitrile ([¹⁸F]FEMPPC, [¹⁸F]1) and N-(2-(3-cyano-5-methylpyrazolo[1,5-a]pyrimidin-7-ylamino)ethyl)-2-[¹⁸F]fluoro-4-nitrobenzamide ([¹⁸F]FCMPPN, [¹⁸F]2), have been designed and successively labeled with ¹⁸F by the nucleophilic substitution employing tosylate and nitryl as leaving groups, respectively. The radiochemical synthesis of both compounds was completed within 60 min with final high-performance liquid chromatography purification included. The corresponding radiochemical yields (without decay correction) were approximately 35% and 30%, respectively. Meanwhile, we compared the uptake characteristics of [¹⁸F]1 and [¹⁸F]2 with those of [¹⁸F]FDG and L-[¹⁸F]FET in S180 tumor cells. Furthermore, the tumor uptake of [¹⁸F]1 and [¹⁸F]2 was assessed in mice bearing S180 tumor and compared with [¹⁸F]FDG and L-[¹⁸F]FET in the same animal model. In vitro cell uptake studies showed [¹⁸F]1 had higher uptake than [¹⁸F]FDG, [¹⁸F]2 and L-[¹⁸F]FET over the 2 h period. In ex vivo biodistribution showed tumor/brain uptake ratios of [¹⁸F]2 were 12.35, 10.44, 8.69 and 5.13 at 15 min, 30 min, 60 min and 120 min post-injection, much higher than those of L-[¹⁸F]FET (2.43, 2.54, 2.93 and 2.95) and [¹⁸F]FDG (0.59, 0.61, 1.02 and 1.33) at the same time point. What’s more, the uptake of [¹⁸F]1 in tumor was 1.88, 4.37, 5.51, 2.95 and 2.88 at 5 min, 15 min, 30 min, 60 min and 120 min post-injection, respectively. There was a remarkable increasing trend before 30 min. The same trend was present for L-[¹⁸F]FET before 30 min and [¹⁸F]FDG before 60 min. Additionally, the tumor/brain uptake ratios of [¹⁸F]1 were superior to those of [¹⁸F]FDG at all the selected time points, the tumor/muscle and tumor/blood uptake ratios of [¹⁸F]1 at 30 min were higher than those of L-[¹⁸F]FET at the same time point. MicroPET image of [¹⁸F]1 administered into S180 tumor-bearing mouse acquired at 30 min post-injection illustrated that the uptake in S180 tumor was obvious. These results suggest that compound [¹⁸F]1 could be a new probe for PET tumor imaging.     

The use of 2-[18F]fluoro-2-deoxy-d-glucose as a potential in vitro agent for labelling human granulocytes for clinical studies by positron emission tomography

In this study, 2-[¹⁸F]fluoro-2-deoxy-d-glucose, ([¹⁸F]FDG) was used to radiolabel human granulocytes in vitro for possible clinical use by positron emission tomography (PET). Uptake of [¹⁸F]FDG was dependent on the amount of glucose in the labelling medium, e.g. when 1 × 10⁷ granulocytes were incubated with [¹⁸F]FDG containing 15μg/mL glucose 80% of [¹⁸F]FDG was incorporated within 30 min, but in the presence of 1 mg/mL of glucose it was reduced to 2%. Increasing the cell concentration and activating the granulocytes with Streptococcus pneumoniae, opsonized zymosan or phorbol myristate acetate all increased the uptake of [¹⁸F]FDG. Retention of the [¹⁸F]FDG by the cells as [¹⁸F]FDG-6-phosphate was also dependent on the extracellular glucose concentration, 9% was released within 60 min in the absence of glucose, but 27% in the presence of 1 mg/mL glucose.     

The effect of dynamic knee-extension exercise on patellar tendon and quadriceps femoris muscle glucose uptake in humans studied by positron emission tomography.

Both tendon and peritendinous tissue show evidence of metabolic activity, but the effect of acute exercise on substrate turnover is unknown. We therefore examined the influence of acute exercise on glucose uptake in the patellar and quadriceps tendons during dynamic exercise in humans. Glucose uptake was measured in five healthy men in the patellar and quadriceps tendons and the quadriceps femoris muscle at rest and during dynamic knee-extension exercise (25 W) using positron emission tomography and [18F]-2-fluoro-2-deoxy-D-glucose ([18F]FDG). Glucose uptake index was calculated by dividing the tissue activity with blood activity of [18F]FDG. Exercise increased glucose uptake index by 77% in the patellar tendon (from 0.30 +/- 0.09 to 0.51 +/- 0.16, P = 0.03), by 106% in the quadriceps tendon (from 0.37 +/- 0.15 to 0.75 +/- 0.36, P = 0.02), and by 15-fold in the quadriceps femoris muscle (from 0.31 +/- 0.11 to 4.5 +/- 1.7, P = 0.005). The exercise-induced increase in the glucose uptake in neither tendon correlated with the increase in glucose uptake in the quadriceps muscle (r = -0.10, P = 0.87 for the patellar tendon and r = -0.30, P = 0.62 for the quadriceps tendon). These results show that tendon glucose uptake is increased during exercise. However, the increase in tendon glucose uptake is less pronounced than in muscle and the increases are uncorrelated. Thus tendon glucose uptake is likely to be regulated by mechanisms independently of those regulating skeletal muscle glucose uptake.     

Imaging of Treatment Response to the Combination of Carboplatin and Paclitaxel in Human Ovarian Cancer Xenograft Tumors in Mice Using FDG and FLT PET

Introduction

A combination of carboplatin and paclitaxel is often used as first line chemotherapy for treatment of ovarian cancer. Therefore the use of imaging biomarkers early after initiation of treatment to determine treatment sensitivity would be valuable in order to identify responders from non-responders. In this study we describe the non-invasive PET imaging of glucose uptake and cell proliferation using 2-deoxy-2-[¹⁸F]fluoro-D-glucose (FDG) and 3’-deoxy-3’-[¹⁸F]fluorothymidine (FLT) for early assessment of treatment response in a pre-clinical mouse model of human ovarian cancer treated with carboplatin and paclitaxel.

Methods

In vivo uptake of FLT and FDG in human ovarian cancer xenografts in mice (A2780) was determined before treatment with carboplatin and paclitaxel (CaP) and repeatedday 1, 4 and 8 after treatment start. Tracer uptake was quantified using small animal PET/CT. Tracer uptake was compared with gene expression of Ki67, TK1, GLUT1, HK1 and HK2.

Results

Tumors in the CaP group was significantly smaller than in the control group (p=0.03) on day 8. On day 4 FDG SUVmax ratio was significantly lower in the CaP group compared to the control group (105±4% vs 138±9%; p=0.002) and on day 8 the FDG SUVmax ratio was lower in the CaP compared to the control group (125±13% vs 167±13%; p=0.05). On day 1 the uptake of FLT SUVmax ratio was 89±9% in the CaP group and 109±6% in the control group; however the difference was not statistically significant (p=0.08).

Conclusions

Our data suggest that both FDG and FLT PET may be used for the assessment of anti-tumor effects of a combination of carboplatin and paclitaxel in the treatment of ovarian cancer. FLT provides an early and transient signal and FDG a later and more prolonged response. This underscores the importance of optimal timing between treatment and FLT or FDG imaging since treatment response may otherwise be overlooked.     

The Elusive Link Between Cancer FDG Uptake and Glycolytic Flux Explains the Preserved Diagnostic Accuracy of PET/CT in Diabetes

This study aims to verify in experimental models of hyperglycemia induced by streptozotocin (STZ-DM) to what degree the high competition between unlabeled glucose and metformin (MET) treatment might affect the accuracy of cancer FDG imaging. The study included 36 “control” and 36 “STZ-DM” Balb/c mice, undergoing intraperitoneal injection of saline or streptozotocin, respectively. Two-weeks later, mice were subcutaneously implanted with breast (4 T1) or colon (CT26) cancer cells and subdivided in three subgroups for treatment with water or with MET at 10 or 750 mg/Kg/day. Two weeks after, mice were submitted to micro-PET imaging. Enzymatic pathways and response to oxidative stress were evaluated in harvested tumors. Finally, competition by glucose, 2-deoxyglucose (2DG) and the fluorescent analog 2-[N-(7-nitrobenz-2-oxa-1,3-diazol-4-yl)amino]-2-deoxyglucose (2-NBDG) on FDG uptake was studied in 4 T1 and CT26 cultured cells. STZ-DM slightly decreased cancer volume and FDG uptake rate (MRF). More importantly, it also abolished MET capability to decelerate lesion growth and MRF. This metabolic reprogramming closely agreed with the activity of hexose-6-phosphate dehydrogenase within the endoplasmic reticulum. Finally, co-incubation with 2DG virtually abolished FDG and 2-NBDG uptake within the endoplasmic reticulum in cultured cells. These data challenge the current dogma linking FDG uptake to glycolytic flux and introduce a new model to explain the relation between glucose analogue uptake and hexoses reticular metabolism. This selective fate of FDG contributes to the preserved sensitivity of PET imaging in oncology even in chronic moderate hyperglycemic conditions.     

Construction and Evaluation of Quantitative Small-Animal PET Probabilistic Atlases for [18F]FDG and [18F]FECT Functional Mapping of the Mouse Brain

Automated voxel-based or pre-defined volume-of-interest (VOI) analysis of small-animal PET data in mice is necessary for optimal information usage as the number of available resolution elements is limited. We have mapped metabolic ([¹⁸F]FDG) and dopamine transporter ([¹⁸F]FECT) small-animal PET data onto a 3D Magnetic Resonance Microscopy (MRM) mouse brain template and aligned them in space to the Paxinos co-ordinate system. In this way, ligand-specific templates for sensitive analysis and accurate anatomical localization were created. Next, using a pre-defined VOI approach, test-retest and intersubject variability of various quantification methods were evaluated. Also, the feasibility of mouse brain statistical parametric mapping (SPM) was explored for [¹⁸F]FDG and [¹⁸F]FECT imaging of 6-hydroxydopamine-lesioned (6-OHDA) mice.

Methods

Twenty-three adult C57BL6 mice were scanned with [¹⁸F]FDG and [¹⁸F]FECT. Registrations and affine spatial normalizations were performed using SPM8. [¹⁸F]FDG data were quantified using (1) an image-derived-input function obtained from the liver (cMR_glc), using (2) standardized uptake values (SUV_glc) corrected for blood glucose levels and by (3) normalizing counts to the whole-brain uptake. Parametric [¹⁸F]FECT binding images were constructed by reference to the cerebellum. Registration accuracy was determined using random simulated misalignments and vectorial mismatch determination.

Results

Registration accuracy was between 0.21–1.11 mm. Regional intersubject variabilities of cMR_glc ranged from 15.4% to 19.2%, while test-retest values were between 5.0% and 13.0%. For [¹⁸F]FECT uptake in the caudate-putamen, these values were 13.0% and 10.3%, respectively. Regional values of cMR_glc positively correlated to SUV_glc measured within the 45–60 min time frame (spearman r = 0.71). Next, SPM analysis of 6-OHDA-lesioned mice showed hypometabolism in the bilateral caudate-putamen and cerebellum, and an unilateral striatal decrease in DAT availability.

Conclusion

MRM-based small-animal PET templates facilitate accurate assessment and spatial localization of mouse brain function using VOI or voxel-based analysis. Regional intersubject- and test-retest variations indicate that for these targets accuracy comparable to humans can be achieved.