Tumor Tracer Research Articles

18F-glutathione conjugate as a PET tracer for imaging tumors that overexpress L-PGDS enzyme.

Lipocalin-type prostaglandin D synthase (L-PGDS) has been correlated with the progression of neurological disorders. The present study aimed at evaluating the imaging potency of a glutathione conjugate of fluorine-18-labeled fluorobutyl ethacrynic amide ([18F]FBuEA-GS) for brain tumors. Preparation of [18F]FBuEA-GS has been modified from the -4-tosylate derivative via radiofluorination in 5% radiochemical yield. The mixture of nonradioactive FBuEA-GS derived from a parallel preparation has be resolved to two isomers in a ratio of 9∶1 using analytic chiral reversed phase high performance liquid chromatography (RP-HPLC). The two fluorine-18-labeled isomers purified through nonchiral semipreparative RP-HPLC as a mixture were studied by assessing the binding affinity toward L-PGDS through a gel filtration HPLC, by analyzing radiotracer accumulation in C6 glioma cells, and by evaluating the imaging of radiotracer in a C6 glioma rat with positron emission tomography. The inhibition percentage of the production of PGD2 from PGH2 at the presence of 200 µM of FBuEA-GS and 4-Dibenzo[a,d]cyclohepten-5-ylidene-1-[4-(2H-tetrazol-5-yl)butyl]piperidine (AT-56) were 74.1±4.8% and 97.6±16.0%, respectively. [18F]FBuEA-GS bound L-PGDS (16.3–21.7%) but not the isoform, microsomal prostaglandin E synthase 1. No binding to GST-alpha and GST-pi was observed. The binding strength between [18F]FBuEA-GS and L-PGDS has been evaluated using analytic gel filtration HPLC at the presence of various concentrations of the cold competitor FBuEA-GS. The contrasted images indicated that the radiotracer accumulation in tumor lesions is probably related to the overexpression of L-PGDS.

Pilot study of (89)Zr-bevacizumab positron emission tomography in patients with advanced non-small cell lung cancer.

BackgroundThe aim of this pilot study was to evaluate whether the uptake of 89Zr-bevacizumab in non-small cell lung cancer (NSCLC) tumors could be visualized and quantified. The correlation between tumor 89Zr-bevacizumab uptake and tumor response to antitumor therapy with a bevacizumab-based regimen was explored.MethodsSeven NSCLC patients underwent static PET scans at days 4 and 7 after injection of 36.4 ± 0.9 MBq (mean ± SD) 89Zr-bevacizumab, prior to commencing carboplatin-paclitaxel-bevacizumab chemotherapy (CPB). Overall survival (OS) and progression-free survival (PFS) to CPB followed by bevacizumab maintenance therapy was correlated to tumor tracer uptake, quantified using peak standardized uptake values (SUVpeak).ResultsZr-bevacizumab uptake (SUVpeak) was approximately four times higher in tumor tissues (primary tumor and metastases) than in non-tumor tissues (healthy muscle, lung, and fat) on days 4 and 7. A positive trend but no significant correlation could be found between SUVpeak and OS or PFS.ConclusionsThis pilot study shows that 89Zr-bevacizumab PET imaging in NSCLC is feasible. Further investigation to validate this technique as a predictive biomarker for selecting patients for bevacizumab treatment is warranted.Electronic supplementary materialThe online version of this article (doi:10.1186/s13550-014-0035-5) contains supplementary material, which is available to authorized users.

Diesterified derivatives of 5-iodo-2'-deoxyuridine as cerebral tumor tracers.

With the aim to develop beneficial tracers for cerebral tumors, we tested two novel 5-iodo-2′-deoxyuridine (IUdR) derivatives, diesterified at the deoxyribose residue. The substances were designed to enhance the uptake into brain tumor tissue and to prolong the availability in the organism. We synthesized carrier added 5-[125I]iodo-3′,5′-di-O-acetyl-2′-deoxyuridine (Ac2[125I]IUdR), 5-[125I]iodo-3′,5′-di-O-pivaloyl-2′-deoxyuridine (Piv2[125I]IUdR) and their respective precursor molecules for the first time. HPLC was used for purification and to determine the specific activities. The iodonucleoside tracer were tested for their stability against human thymidine phosphorylase. DNA integration of each tracer was determined in 2 glioma cell lines (Gl261, CRL2397) and in PC12 cells in vitro. In mice, we measured the relative biodistribution and the tracer uptake in grafted brain tumors. Ac2[125I]IUdR, Piv2[125I]IUdR and [125I]IUdR (control) were prepared with labeling yields of 31–47% and radiochemical purities of >99% (HPLC). Both diesterified iodonucleoside tracers showed a nearly 100% resistance against degradation by thymidine phosphorylase. Ac2[125I]IUdR and Piv2[125I]IUdR were specifically integrated into the DNA of all tested tumor cell lines but to a less extend than the control [125I]IUdR. In mice, 24 h after i.p. injection, brain radioactivity uptakes were in the following order Piv2[125I]IUdR>Ac2[125I]IUdR>[125I]IUdR. For Ac2[125I]IUdR we detected lower amounts of radioactivities in the thyroid and stomach, suggesting a higher stability toward deiodination. In mice bearing unilateral graft-induced brain tumors, the uptake ratios of tumor-bearing to healthy hemisphere were 51, 68 and 6 for [125I]IUdR, Ac2[125I]IUdR and Piv2[125I]IUdR, respectively. Esterifications of both deoxyribosyl hydroxyl groups of the tumor tracer IUdR lead to advantageous properties regarding uptake into brain tumor tissue and metabolic stability.

Development of [18F]afatinib as new TKI-PET tracer for EGFR positive tumors.

Afatinib is an irreversible ErbB family blocker that was approved for the treatment of EGFR mutated non-small cell lung cancer in 2013. Positron emission tomography (PET) with fluorine-18 labeled afatinib provides a means to obtain improved understanding of afatinib tumor disposition in vivo. PET imaging with [(18)F]afatinib may also provide a method to select treatment responsive patients. The aim of this study was to label afatinib with fluorine-18 and evaluate its potential as TKI-PET tracer in tumor bearing mice. A radiochemically novel coupling, using peptide coupling reagent BOP, was explored and optimized to synthesize [(18)F]afatinib, followed by a metabolite analysis and biodistribution studies in two clinically relevant lung cancer cell lines, xenografted in nude mice. A reliable [(18)F]afatinib radiosynthesis was developed and the tracer could be produced in yields of 17.0 ± 2.5% calculated from [(18)F]F(-) and >98% purity. The identity of the product was confirmed by co-injection on HPLC with non-labeled afatinib. Metabolite analysis revealed a moderate rate of metabolism, with >80% intact tracer in plasma at 45 min p.i. Biodistribution studies revealed rapid tumor accumulation and good retention for a period of at least 2 hours, while background tissues showed rapid clearance of the tracer. We have developed a method to synthesize [(18)F]afatinib and related fluorine-18 labeled 4-anilinoquinazolines. [(18)F]Afatinib showed good stability in vivo, justifying further evaluation as a TKI-PET tracer.

18F-FLT PET/CT imaging in a Wister rabbit inflammation model

The aim of the present study was to determine the tumour specificity of the newly developed nucleoside metabolic positron emission tomography (PET) tracer, 3′-deoxy-3′-18F-fluorothymidine (18F-FLT). Using 18F-FLT PET imaging, DNA synthesis and cell proliferation were detected in Staphylococcus aureus (S. aureus) abscess and calcium sulphate models in Wister rabbits. A total of eight rabbits were implanted with S. aureus in the left tibia to induce an inflammatory process. Calcium sulphate + gentamicin was implanted in the right tibia to induce a physical stimulus without bacterial multiplication. After four weeks, the animals underwent 18F-FLT PET imaging, bacterial culturing and tissue pathology. The uptake of 18F-FLT was significantly higher in the abscess site compared with that in the granuloma, with maximum standardised uptake values of 5.76±0.25 and 1.15±0.32, respectively (P<0.01). This indicates that 18F-FLT is not a specific tumour tracer since active inflammation also results in the uptake of this compound. However, the tumour specificity of this tracer is higher compared with that of 18F-fluorodeoxyglucose. Therefore, 18F-FLT may be useful in the differential diagnosis of benign and malignant tumours.

Imaging of Epidermal Growth Factor Receptor Expression in Head and Neck Cancer with SPECT/CT and 111In-Labeled Cetuximab-F(ab′)2

Combined treatment of advanced head and neck squamous cell carcinomas (HNSCC) with radiotherapy and the epidermal growth factor receptor (EGFR) inhibitor cetuximab improves clinical outcome in comparison to radiotherapy alone but is effective only in a few cases. To select those patients most likely to benefit from EGFR inhibition, it can be advantageous to quantify the tumor EGFR status before and possibly during therapy. The aim of this study was to develop and characterize the (111)In-cetuximab-F(ab')2 tracer to image EGFR targeting in vivo. The affinity and internalization kinetics of (111)In-cetuximab-F(ab')2 were determined in vitro. The optimal protein-fragment dose for imaging was determined in nude mice with a subcutaneous head and neck carcinoma model (FaDu). Mice with FaDu tumors were imaged using ultra-high-resolution SPECT with (111)In-cetuximab-F(ab')2 or (111)In-cetuximab IgG at 4, 24, 48, and 168 h after injection. Tumor tracer uptake was determined on micro-SPECT and autoradiography images of tumor sections. Immunohistochemical staining was used to analyze EGFR expression in the tumor. In vitro, more than 50% of (111)In-cetuximab-F(ab')2 was internalized into FaDu cells within 24 h. The half maximal inhibitory concentration (IC50) of (111)In-cetuximab-F(ab')2 and (111)In-cetuximab was similar: 0.42 ± 0.16 nM versus 0.28 ± 0.14 nM, respectively. The protein dose-escalation study showed that the highest uptake of (111)In-cetuximab-F(ab')2 in tumors was obtained at doses of 10 μg/mouse or less (13.5 ± 5.2 percentage injected dose per gram [%ID/g]). Tumor uptake of (111)In-cetuximab was significantly higher (26.9 ± 3.3 %ID/g, P < 0.01). However, because of rapid blood clearance, tumor-to-blood ratios at 24 h after injection were significantly higher for (111)In-cetuximab-F(ab')2 (31.4 ± 3.8 vs. 1.7 ± 0.2, respectively; P < 0.001). The intratumoral distribution of (111)In-cetuximab-F(ab')2 correlated well with the immunohistochemical distribution of EGFR (r = 0.64 ± 0.06, P < 0.0001). micro-SPECT images of (111)In-cetuximab-F(ab')2 clearly showed preferential uptake in the tumor from 4 h onward, with superior tumor-to-background contrast at 24 h, compared with (111)In-cetuximab (107.0 ± 17.0 vs. 69.7 ± 3.9, respectively; P < 0.05). (111)In-cetuximab-F(ab')2 displays higher tumor-to-blood ratios early after injection than (111)In-cetuximab in an HNSCC model, making it more suitable for EGFR visualization and potentially for selecting patients for treatment with EGFR inhibitors.

68Ga-DOTA0-Tyr3-octreotide positron emission tomography in head and neck squamous cell carcinoma

⁶⁸Ga-labelled DOTA⁰-Tyr³-octreotide positron emission tomography (PET)/CT (⁶⁸Ga-DOTATOC PET/CT) is a routinely used imaging modality for neuroendocrine tumours expressing somatostatin receptors (SSTRs). Recent studies have shown that SSTRs are also expressed in head and neck squamous cell carcinoma (HNSCC). This is the first prospective clinical trial investigating SSTR expression in patients with HNSCC using ⁶⁸Ga-DOTATOC. Patients with previously untreated HNSCC underwent ⁶⁸Ga-DOTATOC PET/CT (120 MBq, range 81-150 MBq). Tumour tracer uptake was scored, the maximum standardized uptake value (SUVmax) was measured and the tumour to background uptake ratio was calculated. For each patient, PET/CT findings were correlated with immunohistochemical SSTR expression in tumour specimens. Fifteen HNSCC patients were included in the study from May 2011 to May 2012. Tumour-specific ⁶⁸Ga-DOTATOC uptake was detected in all patients with an median SUVmax of 4.0 (range 2.2-6.5). Uptake was weak in seven (47%), moderate in five (33%) and strong in three (20%) patients. All tumour specimens were SSTR positive on immunohistochemistry. Of the 15 patients, 14 were positive for SSTR subtype 2, characterized by the highest affinity to octreotide. SSTR expression in HNSCC can be visualized clinically using ⁶⁸Ga-DOTATOC PET/CT. SSTR expression in HNSCC could provide a potential target for SSTR-based therapy in patients not amenable to standard treatment modalities, but this cannot be predicted by SSTR immunohistochemistry.

123I]Iodooctyl fenbufen amide as a SPECT tracer for imaging tumors that over-express COX enzymes

This study is concerned with the development of an agent for single photon emission computer tomography (SPECT) for imaging inflammation and tumor progression. [123I]Iodooctyl fenbufen amide ([123I]IOFA) was prepared from the precursor N-octyl-4-oxo-4-(4′-(trimethylstannyl)biphenyl-4-yl)butanamide with a radiochemical yield of 15%, specific activity of 37 GBq/μmol, and radiochemical purity of 95%. Analysis of the binding of [123I]IOFA to COX-1 and COX-2 enzymes by using HPLC and a gel filtration column showed a selectivity ratio of 1:1.3. An assay for the competitive inhibition of substrate transfer showed that IOFA exhibited a comparable IC50 value compared to fenbufen. In the normal rat liver, a lower level and homogeneous pattern of [123I]IOFA radioactivity was observed by SPECT. In contrast, in the rat liver with thioacetamide-induced cholangiocarcinoma, a higher uptake and heterogeneous pattern of [123I]IOFA radioactivity was seen as hot spots in tumor lesions by SPECT imaging. Importantly, elevated COX-1 and COX-2 expressions from immunostaining were found in the bile ducts of tumor rats but not of normal rats. Therefore, [123I]IOFA was found to exhibit the potential for imaging tumors that over-express COX.

Biological evaluation of 3-[18F]fluoro-α-methyl-d-tyrosine (d-[18F]FAMT) as a novel amino acid tracer for positron emission tomography

3-[(18)F]Fluoro-α-methyl-L-tyrosine (L-[(18)F]FAMT) is a useful amino acid tracer for positron emission tomography (PET) imaging of malignant tumors. Because D-amino acids are not well distributed in non-target organs and are rapidly excreted in urine, the D-isomer of [(18)F]FAMT could allow clear PET imaging of tumors early after administration. In this study, we prepared 3-[(18)F]fluoro-α-methyl-D-tyrosine (D-[(18)F]FAMT) and evaluated its usefulness. D-[(18)F]FAMT was synthesized according to the method for preparation of L-[(18)F]FAMT. The in vitro and in vivo stability of [(18)F]FAMT were evaluated by high-performance liquid chromatography. Cellular uptake of [(18)F]FAMT was evaluated using LS180 colon adenocarcinoma cells. Biodistribution studies were performed in LS180 tumor-bearing mice, and the tumors were imaged using a small-animal PET scanner. The radiolabeling yield of D-[(18)F]FAMT was approximately 10 %, similar to that of L-[(18)F]FAMT. Over 95 % of D-[(18)F]FAMT remained intact in mice until 60 min after administration. D-[(18)F]FAMT was gradually taken up by the LS180 cells. Tumor uptake of D-[(18)F]FAMT was competitively inhibited by pretreatment with α-methyl-L-tyrosine, a selective substrate for the system L-amino acid transporter 1 (LAT1), suggesting the involvement of LAT1 in tumor uptake of D-[(18)F]FAMT. In biodistribution studies, D-[(18)F]FAMT showed rapid clearance from the blood, marked accumulation and retention in the tumor, and lower accumulation in non-target organs, especially kidney and pancreas, compared to L-[(18)F]FAMT. The amount of D-[(18)F]FAMT in the tumor was also reduced, and tumor-to-blood ratio and tumor-to-muscle ratio of D-[(18)F]FAMT were similar to those of L-[(18)F]FAMT at every time point. PET imaging with D-[(18)F]FAMT did not provide a clear image of the tumor early after administration. However, D-[(18)F]FAMT provided higher tumor-to-background contrast than L-[(18)F]FAMT. D-[(18)F]FAMT showed rapid blood clearance, low accumulation in non-target organs, and tumor-selective imaging compared with L-[(18)F]FAMT. Thus, D-[(18)F]FAMT could potentially serve as a novel PET tracer for imaging malignant tumors.

PET hypoxia imaging with FAZA: reproducibility at baseline and during fractionated radiotherapy in tumour-bearing mice

Tumour hypoxia is linked to treatment resistance. Positron emission tomography (PET) using hypoxia tracers such as fluoroazomycin arabinoside (FAZA) may allow identification of patients with hypoxic tumours and the monitoring of the efficacy of hypoxia-targeting treatment. Since hypoxia PET is characterized by poor image contrast, and tumour hypoxia undergoes spontaneous changes and is affected by therapy, it remains unclear to what extent PET scans are reproducible. Tumour-bearing mice are valuable in the validation of hypoxia PET, but identification of a reliable reference tissue value (blood sample or image-derived muscle value) for repeated scans may be difficult due to the small size of the animal or absence of anatomical information (pure PET). Here tumour hypoxia was monitored over time using repeated PET scans in individual tumour-bearing mice before and during fractionated radiotherapy. Mice bearing human SiHa cervix tumour xenografts underwent a PET scan 3 h following injection of FAZA on two consecutive days before initiation of treatment (baseline) and again following irradiation with four and ten fractions of 2.5 Gy. On the last scan day, mice were given an intraperitoneal injection of pimonidazole (hypoxia marker), tumours were collected and the intratumoral distribution of FAZA (autoradiography) and hypoxia (pimonidazole immunohistology) were determined in cryosections. Tissue section analysis revealed that the intratumoral distribution of FAZA was strongly correlated with the regional density of hypoxic (pimonidazole-positive) cells, even when necrosis was present, suggesting that FAZA PET provides a reliable measure of tumour hypoxia at the time of the scan. PET-based quantification of tumour tracer uptake relative to injected dose showed excellent reproducibility at baseline, whereas normalization using an image-derived nonhypoxic reference tissue (muscle) proved highly unreliable since a valid and reliable reference value could not be determined. The intratumoral distribution of tracer was stable at baseline as shown by a voxel-by-voxel comparison of the two scans (R = 0.82, range 0.72-0.90). During treatment, overall tracer retention changed in individual mice, but there was no evidence of general reoxygenation. Hypoxia PET scans are quantitatively correct and highly reproducible in tumour-bearing mice. Preclinical hypoxia PET is therefore a valuable and reliable tool for the development of strategies that target or modify hypoxia.

PET of EGFR Expression with an 18F-Labeled Affibody Molecule

Epidermal growth factor receptor (EGFR) is often overexpressed in a variety of human cancers, and its expression is associated with poor prognosis for many cancer types. However, an accurate technique to noninvasively image EGFR expression in vivo is not available in the clinical setting. In this research, an Affibody analog, anti-EGFR Ac-Cys-Z(EGFR:1907), was successfully site-specifically (18)F-labeled for PET of EGFR expression. The prosthetic group N-[2-(4-(18)F-fluorobenzamido) ethyl] maleimide ((18)F-FBEM) was conjugated to Ac-Cys-Z(EGFR:1907) under mild conditions (pH 7) to produce the probe (18)F-FBEM-Cys-Z(EGFR:1907). The binding affinity and specificity tests of (18)F-FBEM-Cys-Z(EGFR:1907) to EGFR were conducted using A431 cancer cells. Small-animal PET and biodistribution studies were conducted on various mice tumor xenograft models with EGFR overexpression (6 types) after injection of approximately 2.0 MBq of (18)F-FBEM-Cys-Z(EGFR:1907) with or without coinjection of unlabeled Ac-Cys-Z(EGFR:1907) for up to 3 h after injection. A correlation study between (18)F-FBEM-Cys-Z(EGFR:1907) small- animal PET quantification and ex vivo Western blot analysis of tumor EGFR expression was conducted in those 6 types of tumor models. (18)F-FBEM-Cys-Z(EGFR:1907) binds to EGFR with low nanomolar affinity (37 nM) in A431 cells. (18)F-FBEM-Cys-Z(EGFR:1907) rapidly accumulated in the tumor and cleared from most of the normal organs except the liver and kidneys at 3 h after injection, allowing excellent tumor-to-normal tissue contrast to be obtained. In the A431 tumor xenograft model, coinjection of the PET probe with 45 μg of Ac-Cys-Z(EGFR:1907) was able to improve the tumor uptake (3.9 vs. 8.1 percentage of the injected radioactive dose per gram of tissue, at 3 h after injection) and tumor imaging contrast, whereas coinjection with 500 μg of Ac-Cys-Z(EGFR:1907) successfully blocked the tumor uptake significantly (8.1 vs. 1.0 percentage of the injected radioactive dose per gram of tissue, at 3 h after injection, 88% inhibition, P < 0.05). Moderate correlation was found between the tumor tracer uptake at 3 h after injection quantified by PET and EGFR expression levels measured by Western blot assay (P = 0.007, R = 0.59). (18)F-FBEM-Cys-Z(EGFR:1907) is a novel protein scaffold-based PET probe for imaging EGFR overexpression of tumors, and its ability to differentiate tumors with high and low EGFR expression in vivo holds promise for future clinical translation.

SU-D-217A-04: Evaluation of the Spatial Concordance Between the Intratumoral Patterns of 18F-FLT and 18F-FDG Uptake in a Small Animal Tumor Model.

PET imaging allows for the visualization of tumor microenvironment and identification of aggressive or radioresistant tumor subvolumes that can be targeted with an escalated radiation dose. Multiple PET tracers have been developed for visualization of different aspects of tumor microenvironment; however, the spatial distribution of tracers in tumors is equally affected by tumor tissue viability and tracer delivery limitations. Given these issues and the low resolution associated with PET imaging, two different PET tracers can produce very similar images. Therefore, it is important to demonstrate that a novel PET tracer does provide additional useful information to that obtained with other tracers. This study investigates the added value of performing 18F-FLT PET imaging as well as 18F-FDG imaging. Head and neck tumor xenografts grown in nude mice were used to study intratumoral tracerdistributions. 18F-FDG and 18F-FLT PET images were obtained on subsequent days using a small animal PET/CT. Pinnacle 9 was used to deformably register the CT image from the FLT PET/CT to the FDG PET/CT image set. The generated deformation was applied to the FLT PET image to achieve an unbiased FLT to FDG PET image registration. The Pearson correlation coefficient between FDG and FLT was calculated voxel- by-voxel within a tumor contour. Overlap analysis of thresholded tracer distributions was carried out by comparing Dice similarity coefficients. Both SQ20B and FaDu tumors showed a moderate voxel-by-voxel correlation between FDG and FLT intratumoral patterns of uptake with an average rho value of .56 and .63 respectively (range .37-.76) despite significant differences in tumor morphology. The average volumes under thedice coefficient surface for SQ20B and FaDu tumors were not significantly different. Despite being equally affected by the issues of tracer delivery, necrosis and PET resolution, FDG and FLT PET images displayed an observable difference at clinically relevant thresholds.

Molecular imaging of brain tumors with 18F-DOPA PET and PET/CT

The objective of this study was to give an overview of the potential clinical utility of [18F]-L-dihydroxyphenylalanine (18F-DOPA) PET and PET/CT for imaging of brain tumors. Review articles and reference lists were used to supplement the search findings. 18F-DOPA has been investigated as a PET tracer for primary brain tumors, metastases of somatic cancer, and evaluation of relapse of pathology in patients with brain tumor after surgery and/or radiotherapy on the basis of enhanced cell proliferation. Available studies have provided encouraging preliminary results for diagnosis of brain tumors and relapse after surgery/radiotherapy. In the brain, excellent discrimination between tumor and normal tissue can be achieved because of the low physiological uptake of 18F-DOPA and the high ratio between tumor and normal hemispheric tissue. Information on evaluation of brain metastases is limited but encouraging. PET and PET/CT with 18F-DOPA are useful in diagnosing primary brain tumors and should be recommended in the diagnosis of relapse of disease after surgical treatment and/or radiotherapy. Semiquantitative analysis could improve diagnosis while correlative imaging with MRI is essential. Limits are due to low knowledge of potential pitfalls.

89 Zr-bevacizumab PET imaging in metastatic renal cell carcinoma patients before and during antiangiogenic treatment.

10581 Background: Renal cell cancer (RCC) is characterized by high VEGF production leading to excessive angiogenesis. To visualize VEGF, we performed serial 89Zr-bevacizumab-PET scans before and during antiangiogenic treatment in RCC patients. Methods: Metastatic (m) RCC patients who received sunitinib (50 mg once daily, 4 out of 6 weeks) or bevacizumab (10 mg/kg every 2 weeks) plus interferon (IFN 3-9 MU 3x/week), underwent 89Zr-bevacizumab-PET scans at baseline and after 2 and 6 weeks, and CT scans at baseline and every 3 months. Tracer uptake in tumor lesions was quantified with maximum Standardized Uptake Value (SUVmax). Relationship between baseline and Δ SUVmax and time to progression (TTP) was analyzed. Wilcoxon test was used to compare scans, Kaplan-Meier method for survival analysis. Results: 22 out of 26 patients were evaluable, 11 per treatment. On 89Zr-bevacizumab-PET, 131 out of 231 lesions ≥ 10 mm (detection limit) were visible and 125 quantifiable. Mean SUVmax at baseline was 10.1 (SD 8.4; range 2.3 - 46.9). During bevacizumab/IFN treatment, SUVmax consistently decreased (mean decrease 47.0% 95% CI 39.1-54.9, P&lt;0.0001) at 2 weeks with a further decrease of 9.7% (95% CI 0.86-18.5, P=0.016) at 6 weeks. After 2 weeks sunitinib, there was only a modest decrease in mean SUVmax (14.6%, 95% CI 1.57-27.63, P=0.0064) with a wide range (-80.4% to +269.9%) and an overshoot of 84.4% (95% CI 47.8-120.9, P=0.0001) after 2 drug free weeks. TTP was longer in (n=15) patients with baseline SUVmax &gt; 11.1 (highest normal tissue uptake) in the 3 most intense lesions than in those with a lower value (median 89.7 vs 22.8 weeks, HR 0.16, 95% CI 0.04 - 0.70). TTP was longer in patients (n=11) with an absolute Δ SUVmax &gt;6.00 in the most intense lesion at 2 weeks (HR 0.25, 95% CI 0.06-0.98). Conclusions: 89Zr-bevacizumab-PET visualizes tumor lesions in mRCC patients. Different changes in tumor tracer uptake after start of bevacizumab/IFN versus sunitinib indicate that these drugs induce different angiogenic responses. High baseline SUVmax and large change in SUVmax corresponded with longer TTP, suggesting that 89Zr-bevacizumab-PET may help to identify patients who benefit the most from antiangiogenic treatment.

PET Imaging of Glutaminolysis in Tumors by 18F-(2S,4R)4-Fluoroglutamine

Changes in gene expression, metabolism, and energy requirements are hallmarks of cancer growth and self-sufficiency. Upregulation of the PI3K/Akt/mTor pathway in tumor cells has been shown to stimulate aerobic glycolysis, which has enabled (18)F-FDG PET tumor imaging. However, of the millions of (18)F-FDG PET scans conducted per year, a significant number of malignant tumors are (18)F-FDG PET-negative. Recent studies suggest that several tumors may use glutamine as the key nutrient for survival. As an alternative metabolic tracer for tumors, (18)F-(2S,4R)4-fluoroglutamine was developed as a PET tracer for mapping glutaminolytic tumors. A series of in vitro cell uptake and in vivo animal studies were performed to demonstrate tumor cell addiction to glutamine. Cell uptake studies of this tracer were performed in SF188 and 9L glioblastoma tumor cells. Dynamic small-animal PET studies of (18)F-(2S,4R)4-fluoroglutamine were conducted in 2 animal models: xenografts produced in F344 rats by subcutaneous injection of 9L tumor cells and transgenic mice with M/tomND spontaneous mammary gland tumors. In vitro studies showed that both transformed 9L and SF188 tumor cells displayed a high rate of glutamine uptake (maximum uptake, ≈ 16% dose/100 μg of protein). The cell uptake of (18)F-(2S,4R)4-fluoroglutamine by SF188 cells is comparable to that of (3)H-L-glutamine but higher than that of (18)F-FDG. The tumor cell uptake can be selectively blocked. Biodistribution and PET studies showed that (18)F-(2S,4R)4-fluoroglutamine localized in tumors with a higher uptake than in surrounding muscle and liver tissues. Data suggest that certain tumor cells may use glutamine for energy production. The results support that (18)F-(2S,4R)4-fluoroglutamine is selectively taken up and trapped by tumor cells. It may be useful as a novel metabolic tracer for tumor imaging.

A methodical 68Ga‐labelling study of DO2A‐(butyl‐ l‐tyrosine)2 with cation‐exchanger post‐processed 68Ga: practical aspects of radiolabelling

Positron emission tomography (PET) with (68)Ga is a fast-growing field in molecular imaging, both in research and in clinical routine. The availability of (68)Ga via the (68)Ge/(68)Ga radionuclide generator facilitates the development and production of radiopharmaceuticals independent of a cyclotron. The presented work shows a complete (68) Ga labelling study exemplified on [(68)Ga]DO2A-(butyl-L-tyrosine)(2), a potential tumour tracer for PET. A methodical sequence is followed to optimize the (68)Ga-labelling reaction. Practical aspects are described and the different parameters contributing to the labelling yield are demonstrated. The influence of temperature, time, amount of labelling precursor and pH value on the radiochemical yields is demonstrated. A conventional heating method is compared with microwave irradiation as an alternative labelling method. Finally, purification of (68)Ga-labelled compounds via solid-phase extraction and quality control is shown. The procedure described in this manuscript may serve as a guideline for optimizing (68)Ga labelling reactions.

Sensitivity Analysis of an Image-Based Solid Tumor Computational Model with Heterogeneous Vasculature and Porosity

An MR image-based computational model of a murine KHT sarcoma is presented that allows the calculation of plasma fluid and solute transport within tissue. Such image-based models of solid tumors may be used to optimize patient-specific therapies. This model incorporates heterogeneous vasculature and tissue porosity to account for nonuniform perfusion of an MR-visible tracer, gadolinium-diethylenetriamine pentaacetic acid (Gd-DTPA). Dynamic contrast-enhanced magnetic resonance imaging (DCE-MRI) was conducted following intravenous infusion of Gd-DTPA to provide 1 h of tracer-concentration distribution data within tissue. Early time points (19 min) were used to construct 3D K(trans) and porosity maps using a two-compartment model; tracer transport was predicted at later time points using a 3D porous media model. Model development involved selecting an arterial input function (AIF) and conducting a sensitivity analysis of model parameters (tissue, vascular, and initial estimation of solute concentration in plasma) to investigate the effects on transport for a specific tumor. The developed model was then used to predict transport in two additional tumors. The sensitivity analysis suggests that plasma fluid transport is more sensitive to parameter changes than solute transport due to the dominance of transvascular exchange. Gd-DTPA distribution was similar to experimental patterns, but differences in Gd-DTPA magnitude at later time points may result from inaccurate selection of AIF. Thus, accurate AIF estimation is important for later time point prediction of low molecular weight tracer or drug transport in smaller tumors.

68Ga-DOTA-affibody molecule for in vivo assessment of HER2/neu expression with PET.

Overexpression of HER2/neu in breast cancer is correlated with a poor prognosis. It may vary between primary tumors and metastatic lesions and change during the treatment. Therefore, there is a need for a new means to assess HER2/neu expression in vivo. In this work, we used (68)Ga-labeled DOTA-Z(HER2:2891)-Affibody to monitor HER2/neu expression in a panel of breast cancer xenografts. DOTA-Z(HER2:2891)-Affibody molecules were labeled with (68)Ga. In vitro binding was characterized by a receptor saturation assay. Biodistribution and PET imaging studies were conducted in athymic nude mice bearing subcutaneous human breast cancer tumors with three different levels of HER2/neu expression. Nonspecific uptake was analyzed using non-HER2-specific Affibody molecules. Signal detected by PET was compared with ex vivo assessment of the tracer uptake and HER2/neu expression. The (68)Ga-DOTA-Z(HER2:2891)-Affibody probe showed high binding affinity to MDA-MB-361 cells (K (D) = 1.4 ± 0.19 nM). In vivo biodistribution and PET imaging studies demonstrated high radioactivity uptake in HER2/neu-positive tumors. Tracer was eliminated quickly from the blood and normal tissues, resulting in high tumor-to-blood ratios. The highest concentration of radioactivity in normal tissue was seen in the kidneys (227 ± 14%ID/g). High-contrast PET images of HER2/neu-overexpressing tumors were recorded as soon as 1 h after tracer injection. A good correlation was observed between PET imaging, biodistribution estimates of tumor tracer concentration, and the receptor expression. These results suggest that PET imaging using (68)Ga-DOTA-Z(HER2:2891)-Affibody is sensitive enough to detect different levels of HER2/neu expression in vivo.

Synthesis of O-(2-[18F]fluoroethyl)-l-tyrosine based on a cartridge purification method

O-(2-[(18)F]fluoroethyl)-L-tyrosine (FET) is widely used as a positron emission tomography tracer for brain tumors. Usually, a high-performance liquid chromatography (HPLC) purification at the end of the two-step synthesis is applied. In this work, we report an automatic radiosynthesis of FET with a purification procedure based on standard cartridges. O-(2-[(18)F]fluoroethyl)-L-tyrosine was prepared by [(18)F]fluoroethylation of L-tyrosine by a two-step synthesis using a modified [(11)C]methionine module (Nuclear Interface). In the first reaction step, we synthesized [(18)F]fluoroethyltosylate starting from [(18)F]fluoride. After a purification step, L-tyrosine was [(18)F]fluoroethylated with [(18)F]fluoroethyltosylate. The final reaction mixture was purified by means of solid phase extraction. The FET was trapped on an SCX cartridge, eluted with saline solution and trapped again on an HRX cartridge. For a second purification step, the FET was eluted from the HRX cartridge with ammonium acetate buffer and collected on two SCX cartridges followed by a washing step with water. The final product was eluted with saline solution and neutralised with 450 μl NaHCO(3) solution (8.4%). The synthesis was finished after 50 min and delivered the FET in a range of 3-16 GBq. The synthesis typically yielded 41% (21 experiments) of FET (d.c.) without an HPLC purification step. The radiochemical purity ranged between 97% and 100%. We present a radiosynthesis of FET where the usually used HPLC purification procedure has been substituted by a purification step based on standard cartridges. This method is useful for automatic modules without an expensive HPLC purification unit and for the routine production of FET.

A comparative study of dynamic contrast‐enhanced MRI parameters as biomarkers for anti‐angiogenic drug therapy

The aim of the present study was to compare three tracer kinetics methods for the analysis of dynamic contrast-enhanced (DCE) MRI data, namely the generalized kinetics model, the distributed-parameter model and the initial area under the tumor tracer curve (IAUC) method, in a Phase I study of an anti-angiogenic drug ABT -869; and to explore their utility as biomarkers. Twenty-eight patients with a range of tumors formed the study population. DCE MRI performed at baseline and 2 weeks post-treatment was analyzed using all three methods, yielding percentage changes for various tracer kinetics parameters. Correlation analyzes were performed between these parameters and in relation to drug exposure. The association of these parameters with time-to-progression was examined using receiver-operating characteristic and Kaplan-Meier curves. Significant correlation with drug exposure was found for the following parameters: normalized IAUC (IAUC(norm)), fractional interstitial volume v(e), fractional intravascular volume v(1) and permeability PS. However, only v(e) and PS were effective in predicting late progression. A decrease in v(e) of more than 1.7% and a decrease in PS of more than 25.1% observed at 2 weeks post-treatment could be associated with late progression. All three tracer kinetics methods have biomarker potential for assessing the effects of anti-angiogenic therapy.