Localization, mechanism and reduction of renal retention of technetium-99m labeled epidermal growth factor receptor-specific nanobody in mice.

BACKGROUND: Nanobodies are single-domain antigen binding fragments derived from functional heavy-chain antibodies elicited in Camelidae. They are powerful probes for radioimmunoimaging, but their renal uptake is relatively high. In this study we have evaluated the role of megalin on the renal uptake of anti-EGFR (99m)Tc-7C12 nanobody and the potency of gelofusine and/or lysine to reduce renal uptake of (99m)Tc-7C12. METHODS: First we compared the renal uptake of (99m)Tc-7C12 in megalin-deficient and megalin-wild-type mice using pinhole SPECT/microCT and ex vivo analysis. The effect of gelofusine and lysine administration on renal accumulation of (99m)Tc-7C12 was analyzed in CD-1 mice divided into lysine preload at 30 min before tracer injection (LysPreload), LysPreload + gelofusine coadministration (LysPreload + GeloCoad), lysine coadministration (LysCoad), gelofusine coadministration (GeloCoad) and LysCoad + GeloCoad. The combined effect of gelofusine and lysine on tumor uptake was tested in mice xenografts. RESULTS: Renal uptake of (99m)Tc-7C12 was 44.22 ± 3.46% lower in megalin-deficient compared with megalin-wild-type mice. In CD-1 mice, lysine preload had no effect on the renal retention whereas coinjection of lysine or gelofusine with the tracer resulted in 25.12 ± 2.99 and 36.22 ± 3.07% reduction, respectively. The combined effect of gelofusine and lysine was the most effective, namely a reduction of renal retention of 45.24 ± 2.09%. Gelofusine and lysine coadministration improved tumor uptake. CONCLUSION: Megalin contributes to the renal accumulation of (99m)Tc-7C12. Gelofusine and lysine coinjection with the tracer reduces the renal uptake while tumor uptake is improved. Although this methodology allows for optimization of imaging protocol using nanobodies, further improvements are needed before using these molecules for radionuclide therapy.

Evaluation of the radiation dose in micro-CT with optimization of the scan protocol.

INTRODUCTION: Micro-CT provides non-invasive anatomic evaluation of small animals. Serial micro-CT measurements are, however, hampered by the severity of ionizing radiation doses cumulating over the total period of follow-up. The dose levels may be sufficient to influence experimental outcomes such as animal survival or tumor growth. AIM: This study was designed to evaluate the radiation dose of micro-CT and to optimize the scanning protocol for longitudinal micro-CT scans. METHODS AND MATERIALS: Normal C57Bl/6 mice were euthanized. Radiation exposure was measured using individually calibrated lithium fluoride thermoluminescent dosimeters (TLDs). Thirteen TLDs were placed in the mice at the thyroid, lungs, liver, stomach, colon, bladder and near the spleen. Micro-CT (SkyScan 1178) was performed using two digital X-ray cameras which scanned over 180 degrees at a resolution of 83 microm, a rotation step of 1.08 degrees , 50 kV, 615 microA and 121 s image acquisition time. The TLDs were removed after each scan. CTDI(100) was measured with a 100 mm ionization chamber, centrally positioned in a 2.7 cm diameter water phantom, and rotation steps were increased to reduce both scan time and radiation dose. RESULTS: Internal TLD analysis demonstrated median organ dose of 5.5 +/- 0.6 mGy per mA s, confirmed by CTDI(100) with result of 6.6 mGy per mA s. A rotation step of 2.16 resulted in qualitatively accurate images. At a resolution of 83 microm the scan time is reduced to 63 s with an estimated dose of 2.9 mGy per mA s. At 166 microm resolution, the scan time is limited to 27 s, with a concordant dose of 1.2 mGy per mA s. CONCLUSIONS: The radiation dose of a standard micro-CT scan is relatively high and could influence the experimental outcome. We believe that the presented adaptation of the scan protocol allows for accurate imaging without the risk of interfering with the experimental outcome of the study.

In vitro analysis and in vivo tumor targeting of a humanized, grafted nanobody in mice using pinhole SPECT/micro-CT.

UNLABELLED: Nanobodies are a novel type of immunoglobulinlike, antigen-binding protein with beneficial pharmacologic and pharmacokinetic properties that are ideally suited to targeting cellular antigens for molecular imaging or therapeutic purposes. However, because of their camelid, nonhuman origin, the possible immunogenicity of Nanobodies when used in the clinic is a concern. Here we present a new strategy to quickly generate humanized Nanobodies for molecular imaging purposes. METHODS: We genetically grafted the antigen-binding loops of NbCEA5, a Nanobody with specificity for the colon carcinoma marker carcinoembryonic antigen (CEA), onto the framework of a humanized Nanobody scaffold. This scaffold has been previously characterized in our laboratory as a stable Nanobody that can serve as a universal loop acceptor for antigen-binding loops from donor Nanobodies and has been additionally mutated at about 10 crucial surface-exposed sites to resemble the sequence of human variable immunoglobulin domains. The 3 recombinant Nanobodies (NbCEA5, humanized scaffold, and humanized CEA5 graft) were produced in bacteria and purified. Unlabeled and (99m)Tc-labeled Nanobodies were biochemically characterized in vitro and tested as probes for SPECT/CT of xenografted tumors. RESULTS: The success of loop-grafting was confirmed by comparing these Nanobodies for their capacity to recognize soluble CEA protein in enzyme-linked immunosorbent assay and by surface plasmon resonance and to bind to CEA-positive LS174T colon carcinoma cells and CEA-transfected but not untransfected Chinese hamster ovary cells in flow cytometry. Specificity of binding was confirmed by competition studies. All Nanobodies were heat-stable, could be efficiently labeled with (99m)Tc, and recognized both soluble and membrane-bound CEA protein in binding studies. Finally, biodistribution experiments were performed with intravenously injected (99m)Tc-labeled Nanobodies in LS174T tumor-bearing mice using pinhole SPECT/micro-CT. These in vivo experiments revealed specificity of tumor targeting and rapid renal clearance for all Nanobodies, with low signals in all organs besides the kidneys. CONCLUSION: This study shows the potency of antigen-binding loop-grafting to efficiently generate humanized Nanobodies that retain their targeting capacities for noninvasive in vivo imaging of tumors.

Preliminary in vivo evaluation of [131I]-2-iodo-D-phenylalanine as a potential radionuclide therapeutic agent in R1M-fluc rhabdomyosarcoma tumor-bearing NuNu mice using bioluminescent imaging.

BACKGROUND: Carrier-added [(123)I]-2-iodo-D-phenylalanine (CA [(123)I]-2-I-D-Phe) was previously found to have a preferential retention in tumors with a high tumor background contrast in animal models. A previous human dosimetry study demonstrated a favorable biodistribution and radiation burden in human subjects. AIM: The aim of this study was to investigate the potential of CA [(131)I]-2-I-D-Phe as an agent for radionuclide therapy. METHODS: Sixty (60) nude athymic mice were inoculated subcutaneously with firefly luciferase-transduced R1M rhabdomyosarcoma cells. The mice in the therapy group were injected intravenously (i.v.) with 148 MBq [(131)I]-2-I-D-Phe (432 GBq/mmol) in kit solution. Controls were injected with kit solution without radioactivity, with physiological saline, or with 148 MBq [(131)I](-) in physiological saline. Tumor growth was quantified using bioluminescent imaging and caliper measurements. RESULTS: [(131)I]-2-I-D-Phe clearly reduced tumor growth in the treated mice compared with the control groups. A tumor growth-rate reduction of at least 33% was found for mice receiving a therapeutic dose. There were no serious adverse side-effects of the therapy. CONCLUSIONS: In conclusion, i.v. injection of CA 148 MBq [(131)I]-2-I-D-Phe specifically reduces tumor growth in athymic nude mice without relevant side-effects on the animals' health.

Tracheobronchomalacia incidentally detected on Tc-99m ventilation/perfusion SPECT.

A Tc-99m Technegas MAA-SPECT was performed on an 81-year-old woman to exclude pulmonary embolism. It showed hypoperfusion and practically absent ventilation of the entire left lung, suggesting a left-sided centrally localized airway obstruction or compression with secondary hypoxic vasoconstriction. Subsequent bronchoscopy and CT scan detected tracheobronchomalacia with significant narrowing of the left bronchus.Tracheobronchomalacia is a rare, benign condition, referring to the deficiency in cartilage of the tracheobronchial tree, caused by a variety of factors.

Imaging characteristics of heterotopic mesenteric ossification on FDG PET and Tc-99m bone SPECT.

A CT scan of a 69-year-old male patient, performed for staging of suspected lung carcinoma, incidentally showed an irregular lesion of 10 cm in the upper abdomen. Further investigation using FDG-PET showed only moderately increased glucose metabolism, whereas Tc-99m MDP SPECT revealed intense osteoblastic activity inside the lesion. A CT-guided biopsy was performed and histologic analysis established the diagnosis of heterotopic mesenteric ossification. This pathology is rare and mostly diagnosed when it is complicated by small bowel obstruction.

SPECT imaging with 99mTc-labeled EGFR-specific nanobody for in vivo monitoring of EGFR expression.

PURPOSE: Overexpression of the epidermal growth factor receptor (EGFR) occurs with high incidence in various carcinomas. The oncogenic expression of the receptor has been exploited for immunoglobulin-based diagnostics and therapeutics. We describe the use of a llama single-domain antibody fragment, termed Nanobody, for the in vivo radioimmunodetection of EGFR overexpressing tumors using single photon emission computed tomography (SPECT) in mice. METHODS: Fluorescence-activated cell sorting (FACS) analysis was performed to evaluate the specificity and selectivity of 8B6 Nanobody to bind EGFR on EGFR overexpressing cells. The Nanobody was then labeled with (99m)Tc via its C-terminal histidine tail. Uptake in normal organs and tissues was assessed by ex vivo analysis. In vivo tumor targeting of (99m)Tc-8B6 Nanobody was evaluated via pinhole SPECT in mice bearing xenografts of tumor cells with either high (A431) or moderate (DU145) overexpression of EGFR. RESULTS: FACS analysis indicated that the 8B6 Nanobody only recognizes cells overexpressing EGFR. In vivo blood clearance of (99m)Tc-8B6 Nanobody is relatively fast (half-life, 1.5 h) and mainly via the kidneys. At 3 h postinjection, total kidney accumulation is high (46.6+/-0.9%IA) compared to total liver uptake (18.9+/-0.6%IA). Pinhole SPECT imaging of mice bearing A431 xenografts showed higher average tumor uptake (5.2+/-0.5%IA/cm(3)) of (99m)Tc-8B6 Nanobody compared to DU145 xenografts (1.8+/-0.3%IA/cm(3), p<0.001). CONCLUSION: The EGFR-binding Nanobody investigated in this study shows high specificity and selectivity towards EGFR overexpressing cells. Pinhole SPECT analysis with (99m)Tc-8B6 Nanobody enabled in vivo discrimination between tumors with high and moderate EGFR overexpression. The favorable biodistribution further corroborates the suitability of Nanobodies for in vivo tumor imaging.

Dynamic bioluminescence imaging for quantitative tumour burden assessment using IV or IP administration of D: -luciferin: effect on intensity, time kinetics and repeatability of photon emission.

INTRODUCTION: In vivo bioluminescence imaging (BLI) is a promising technique for non-invasive tumour imaging. D: -luciferin can be administrated intraperitonealy or intravenously. This will influence its availability and, therefore, the bioluminescent signal. The aim of this study is to compare the repeatability of BLI measurement after IV versus IP administration of D: -luciferin and assess the correlation between photon emission and histological cell count both in vitro and in vivo. MATERIALS AND METHODS: Fluc-positive R1M cells were subcutaneously inoculated in nu/nu mice. Dynamic BLI was performed after IV or IP administration of D: -luciferin. Maximal photon emission (PE(max)) was calculated. For repeatability assessment, every acquisition was repeated after 4 h and analysed using Bland-Altman method. A second group of animals was serially imaged, alternating IV and IP administration up to 21 days. When mice were killed, PE(max) after IV administration was correlated with histological cell number. RESULTS: The coefficients of repeatability were 80.2% (IV) versus 95.0% (IP). Time-to-peak is shorter, and its variance lower for IV (p < 0.0001). PE(max) was 5.6 times higher for IV. A trend was observed towards lower photon emission per cell in larger tumours. CONCLUSION: IV administration offers better repeatability and better sensitivity when compared to IP. In larger tumours, multiple factors may contribute to underestimation of tumour burden. It might, therefore, be beneficial to test novel therapeutics on small tumours to enable an accurate evaluation of tumour burden.

D- and L-[123I]-2-I-phenylalanine show a long tumour retention compared with D- and L-[123I]-2-I-tyrosine in R1M rhabdomyosarcoma tumour-bearing Wag/Rij rats.

The aim of this study was the comparison of the tumour uptake and the long-term retention of [(123)I]-2-I-L-phenylalanine and [(123)I]-2-I-D-phenylalanine with those of [(123)I]-2-I-L-tyrosine and [(123)I]-2-I-D-tyrosine in R1M rhabdomyosarcoma tumour-bearing rats. The biodistribution of the radioactivity as a function of time in R1M tumour-bearing rats was measured by planar gamma camera imaging (dynamic and static). If dissection was applied, the activity in the tumours and tissues of interest was measured by gamma counting. [(123)I]-2-iodo-L-phenylalanine, [(123)I]-2-iodo-D-phenylalaine, [(123)I]-2-I-L-tyrosine showed a considerable tumour uptake reaching a maximum between 10 and 30 min. At 30 min p.i. the differential uptake ratio values of this uptake were, respectively, 2.1, 2.3, 2.5 and 1.7. The activity in the tumour was shown to be related to a tumour cell uptake and not to an increased blood pool activity. All the tracers showed a clearance from the blood to the bladder without renal retention. At longer times both L- and D- [(123)I]-2-I-tyrosine were cleared for a large part from the tumours and the body. [(123)I]-2-I-L-Phe and [(123)I]-2-I-D-Phe showed a considerable and equal retention in the tumours: as compared with 0.5 h, 91% at 24 h and 80% at 48 h. This was related to the longer retention of activity in the blood pool noticed for these compounds (81% at 24 h and 65% at 48 h). The tumour-to-background ratio increased with 25% at those longer times. At short times all the tracers were taken up to a considerable extent in the tumours. In the R1M-bearing Wag/Rij rat model only [(123)I]-2-I-L-phenylalanine and [(123)I]-2-I-D-phenylalanine showed an especially high retention at long times without any significant difference between the enantiomers.

Intra-individual comparison of the human biodistribution and dosimetry of the D and L isomers of 2-[123I]iodo-phenylalanine.

PURPOSE: Several authors have shown in animal studies that D-enantiomeric amino acid analogues can have better tumour imaging properties compared to their L-analogues. In our group, the D and L isomers of 2-[I]iodo-phenylalanine were identified as tumour-specific tracers in rat and mouse tumour models, with an advantage for the D-isomer. Here we compare, intra-individually, the normal biodistribution and dosimetry of both tracers in healthy human subjects. METHODS: Five male volunteers received both the L- and D-enantiomers, ranging from 84 to 114 MBq, with a 1 week interval between the tracers, allowing intra-individual comparison. Whole-body scans were performed and blood and urine samples were collected and analysed up to 24 h. Dosimetry was calculated using OLINDA 1.0 software. RESULTS: The biodistributions of the tracers are comparable as both show a moderate uptake in heart and the liver, a marked uptake in muscle tissue and clearance via the renal system. However, due to faster clearance, from 2.5 h, the uptake of the D-enantiomer was significantly lower compared to the L-isomer in all organs. The radiation dose estimations showed an effective dose of, respectively, 0.0120+/-0.0020 mSv x Bq(-1) and 0.0106+/-0.0038 mSv x Bq(-1) for 2-123I-L-Phe and 2-123I-D-Phe (P=0.18). In both cases the organ receiving the highest dose was the bladder wall. CONCLUSION: Both 2-123I-L-Phe and 2-123I-D-Phe show comparable moderate uptake in all organs. 2-123I-D-Phe is the more promising tracer, as it shows a faster clearance resulting in a lower dose and a lower background, favouring tumour imaging with respect to the tumour/background ratio.

In vivo model of drug-induced valvular heart disease in rats: pergolide-induced valvular heart disease demonstrated with echocardiography and correlation with pathology.

AIMS: Valvular heart disease (VHD), inducing valvular regurgitation, has been described in carcinoid heart disease and recently in Parkinson's patients treated with pergolide. The aim of this study was to develop an in vivo model of drug-induced valvulopathy with pergolide in rats. METHODS AND RESULTS: Thirty male Wistar rats were given daily injections of either pergolide (0.5 mg/kg intraperitoneally) (n = 8), serotonin (20 mg/kg subcutaneously) (n = 8), or the vehicle only (n = 14) for 5 months. At 20 weeks, echocardiography demonstrated the presence of aortic regurgitation (AR) and/or mitral regurgitation (MR) in serotonin (86% AR, P = 0.0001; 57% MR, P = 0.006) and in pergolide animals (67% AR, P = 0.003; 67% MR, P = 0.003) compared with none in placebo. Pulmonary regurgitation (PR) and tricuspid regurgitation (TR) were found in the serotonin (71% PR, P = 0.19; 100% TR, P = 0.06 vs. placebo), pergolide (100% PR, P = 0.014; 83% TR, P = 0.35 vs. placebo), and placebo groups (36% PR; 57% TR). Tricuspid regurgitant area ratio (jet/atrium), however, was more severe in the serotonin [median 26.5 (range 17-42)%; P = 0.02] and pergolide animals [32 (17-39) %; P = 0.03] compared with placebo [12.5 (5-33)%]. We found a good correlation between valvular regurgitation and histologically assessed valvular thickness. Histological examination revealed the presence of diffusely thickened and myxoid aortic, mitral, and tricuspid valves in serotonin and pergolide animals as seen in VHD. CONCLUSION: We demonstrated, for the first time, that long-term pergolide administration led to VHD in rats. This small animal model will permit further in vivo investigation of drug-induced valvulopathies.

123I-2-iodo-tyrosine, a new tumour imaging agent: human biodistribution, dosimetry and initial clinical evaluation in glioma patients.

PURPOSE: 123I-2-iodo-tyrosine (123I-2IT) has been identified as a promising new amino acid tracer in animals. Uptake is mediated by LAT1 transport, which is increased in tumour cells. In this study we present the human biodistribution and first clinical results in glioma patients. METHODS: For the biodistribution study, six male volunteers received 60-95 MBq 123I-2IT. Whole-body scans and blood and urine samples were obtained up to 24 h after injection; dosimetry was calculated using OLINDA 1.0 software. Initial clinical evaluation of 123I-2IT SPECT was performed in 35 patients with suspected or known glioma, either as primary diagnosis or for detection of recurrence. Tumour-to-background (T/B) ratios were calculated for semi-quantitative analysis. The results were correlated with clinical and MRI follow-up data or histology. RESULTS: 123I-2IT showed both renal and intestinal clearance. Bladder (0.12 mGy/MBq) and small intestine (0.03 mGy/MBq) received the highest absorbed doses. The effective dose equivalent and effective dose were estimated at 0.020 and 0.016 mSv/MBq, respectively. In patients, 123I-2IT SPECT did not differentiate between neoplastic and non-neoplastic lesions after an indeterminate MRI. In follow-up of known glioma, 13/15 patients with disease recurrence had increased T/B values (range 1.39-3.91). Out of seven recurrence-negative patients, two showed an important increase in T/B, in one case due to radionecrosis (T/B 1.59) and in the other probably due to residual but stable disease (T/B 2.07). CONCLUSION: 123I-2IT has a favourable biodistribution for a tumour imaging agent. It shows increased uptake in central nervous system glioma and is potentially useful in the follow-up of glioma patients.

Comparison of the uptake of [123/125I]-2-iodo-D-tyrosine and [123/125I]-2-iodo-L-tyrosine in R1M rhabdomyosarcoma cells in vitro and in R1M tumor-bearing Wag/Rij rats in vivo.

INTRODUCTION: Recently, promising results concerning uptake in vivo in tumors of D-amino acids have been published. Therefore, we decided to evaluate the tumor uptake of the D-analogue of [(123)I]-2-iodo-L-tyrosine, a tracer recently introduced by our group into clinical trials. The uptake of 2-amino-3-(4-hydroxy-2-[(123/125)I]iodophenyl)-D-propanoic acid (2-iodo-D-tyrosine) was studied in vitro in LAT1-expressing R1M rat rhabdomyosarcoma cells and in vivo in R1M tumor-bearing Wag/Rij rats. METHODS: The uptake of [(125)I]-2-iodo-L-tyrosine and [(125)I]-2-iodo-D-tyrosine into R1M cells was determined in appropriate buffers, allowing the study of the involved transport systems. In vivo, the biodistribution in R1M-bearing rats of [(123)I]-2-iodo-L-tyrosine and [(123)I]-2-iodo-D-tyrosine was performed by both dynamic and static planar imaging with a gamma camera. RESULTS: In in vitro conditions, the uptake of both [(125)I]-2-iodo-L-tyrosine and [(125)I]-2-iodo-D-tyrosine in the HEPES buffer was 25% higher in the presence of Na(+) ions. In the absence of Na(+) ions, [(125)I]-2-iodo-D-tyrosine was taken up reversibly in the R1M cells, with an apparent accumulation, probably for the larger part by the LAT1 system. Dynamic planar imaging showed that the uptake in the tumors of [(123)I]-2-iodo-D-tyrosine was somewhat lower than that of [(123)I]-2-iodo-L-tyrosine. At 30 min postinjection, the mean differential uptake ratio values of the L- and D-enantiomers are 2.5+/-0.7 and 1.7+/-0.6, respectively. Although the uptake of the D-isomer is lower, probably due to a faster clearance from the blood, the tumor-background ratio is the same as that of the l-analogue. CONCLUSION: A large part (75%) of [(125)I]-2-iodo-D-tyrosine in vitro and [(123)I]-2-iodo-D-tyrosine in vivo is reversibly highly taken up in R1M tumor cells by Na(+)-independent LAT transport systems, more likely by the LAT1. The clearance from the blood of [(123)I]-2-iodo-D-tyrosine in the rats is faster than that of the L-analogue, resulting in a slightly lower tumor uptake but with the same tumor-background ratio.

Percutaneous placement of marking coils before stereotactic radiation therapy of malignant lung lesions.

PURPOSE: To evaluate a technique for implantation of radiopaque markers in lung nodules as an aid in extracranial stereotactic radiation therapy. MATERIALS AND METHODS: An implantation technique was developed for marking intrapulmonary lung lesions by introducing a vascular coil through a coaxial needle in or near the target tumor. The markers were placed percutaneously through 15- or 20-gauge coaxial needles in 41 lesions (25 patients) under computed tomographic fluoroscopic guidance. Two different types of vascular helical coils where used. RESULTS: All lesions were accessible for puncture and coils could be placed in all lesions. Four types of complications were observed, some as a result of the learning curve in the technique: (i) coil misplacement subcutaneously (5%); (ii) small needle trajectory bleeding in the lung (10%); (iii) pneumothorax, for which one patient (10%) in whom the coil was placed through a 15-gauge coaxial needle needed chest tube drainage and required hospitalization; and (iv) one subcutaneous metastasis probably unrelated to the puncture (2.5%). CONCLUSION: With this technique, lung nodules can be marked with radiopaque implants in a safe and accurate way.

SPECT and PET amino acid tracer influx via system L (h4F2hc-hLAT1) and its transstimulation.

UNLABELLED: System L amino acid transport is increased in various types of cancer. The tracer 123I-2-iodotyrosine (2IT), which is accumulated via system L, could thus serve to allow visualization of cancer in vivo. Here, we studied the transport of 125I-2IT by h4F2hc-hLAT1, the major transporter subserving system L in growing cells, using the Xenopus laevis oocyte expression system. We compared the apparent affinity of 125I-2IT with that of tyrosine, tested the influence of intracellular methionine availability on the influx rate of this substrate, and then compared the transport of 2IT with that of the other tracers-iodo-alpha-methyltyrosine (IMT), fluoroethyltyrosine (FET), and 2-fluorotyrosine (2FT)-by measuring their transstimulating effect on phenylalanine efflux. METHODS: Transport experiments were performed with Xenopus laevis oocytes expressing h4F2hc-hLAT1 (the functional transporter) and oocytes expressing only h4F2hc (negative control). The values obtained for the functional transporter were corrected for endogenous background transport by subtracting the values for the negative controls. RESULTS: The apparent affinity for 125I-2IT and 3H-tyrosine was 29.3 +/- 9.3 micromol/L and 21.2 +/- 4.2 micromol/L, respectively. The influx rate of 125I-2IT was, similarly to that of 3H-phenylalanine, transstimulated by a factor of > or =3 when the oocytes were preinjected with methionine or phenylalanine. The proportion of preinjected 3H-phenylalanine that effluxed within 90 s in the presence of an extracellular 2IT concentration of 0.1 mmol/L was 4.1% +/- 0.5%, compared with 3.3% +/- 0.4% for extracellular IMT, 1.3% +/- 0.3% for FET, 9.3% +/- 0.8% for 2FT, and 9.1% +/- 0.5% for phenylalanine. CONCLUSION: 2IT has a high affinity for h4F2hc-hLAT1, comparable to that of natural tyrosine, and its influx rate is transstimulated by intracellular amino acids. The 2IT influx rate is comparable to that of IMT but lower than that of phenylalanine. In contrast to FET, which is only poorly transported, 2FT displays a high influx rate equal to that of phenylalanine.

Comparative biodistribution of iodinated amino acids in rats: selection of the optimal analog for oncologic imaging outside the brain.

UNLABELLED: 3-(123)I-Iodo-alpha-methyltyrosine ((123)I-3-IMT) is used for the detection of residual and recurrent brain tumors. The application of (123)I-3-IMT for the study of extracerebral malignancies is limited by its marked and rapid renal uptake. In this study, we compared the tumor uptake, biodistribution, and specificity of 5 structurally related iodinated amino acids with those of (123)I-3-IMT. The aim was to select the optimal analog for oncologic imaging outside the brain. METHODS: We studied 3-(123)I-iodotyrosine ((123)I-3-IT), 2-(123)I-iodotyrosine ((123)I-2-IT), (123)I-iodo-azatyrosine ((123)I-IAzaT), 2-(123)I-iodophenylalanine ((123)I-2-IPhe), and 4-(123)I-iodophenylalanine ((123)I-4-IPhe). Tumor uptake and renal uptake in sarcoma-bearing rats were measured by use of in vivo dynamic imaging. The differential uptake ratio (average counts per pixel of the region of interest divided by the average counts per pixel inside the total body) and rates of tracer accumulation (K(1) values) were calculated. Results were compared with the values obtained for (123)I-3-IMT in the same rat. Tracers that demonstrated high tumor uptake were labeled with (125)I and coinjected with (18)F-FDG in rats with turpentine-induced acute inflammation. After 30 min, the rats were sacrificed and dissected. Amino acid tracer uptake in organs and tissues was measured, and the increase in uptake in the inflamed muscle was expressed relative to the increase in (18)F-FDG uptake. RESULTS: Tumor uptake and K(1) values for (123)I-2-IT and (123)I-2-IPhe were comparable to those for (123)I-3-IMT. (123)I-4-IPhe showed high tumor uptake but a reduced K(1) value because of high blood-pool activity. (123)I-3-IT and (123)I-IAzaT did not accumulate markedly in tumor tissue. Renal accumulation of (123)I-2-IT, (123)I-2-IPhe, and (123)I-4-IPhe was at least 6 times lower than that of (123)I-3-IMT. (18)F-FDG uptake was markedly increased in areas of acute inflammation (215%). The increases for (125)I-3-IMT and (125)I-4-IPhe were 35.5% and 22.2%, respectively, of the increase for (18)F-FDG. Almost no increase was found for (125)I-2-IT (3.3%) and (125)I-2-IPhe (2.8%). CONCLUSION: (123)I-2-IT and (123)I-2-IPhe are promising tracers for oncologic imaging outside the brain. (123)I-2-IT has the advantage of an established kit for radiosynthesis.

Optimal dose of 18F-FDG required for whole-body PET using an LSO PET camera.

Reducing the acquisition time of whole-body fluorine-18 fluorodeoxyglucose positron emission tomography (18F-FDG PET) (corrected for attenuation) is of major importance in clinical practice. With the introduction of lutetium oxyorthosilicate (LSO), the acquisition time can be dramatically reduced, provided that patients are injected with larger amounts of tracer and/or the system is operated in 3D mode. The aim of this study was to determine the optimal dose of 18F-FDG required in order to achieve good-to-excellent image quality when a "3-min emission, 2-min transmission/bed position" protocol is used for an LSO PET camera. A total of 218 consecutive whole-body 18F-FDG PET studies were evaluated retrospectively. After excluding patients with liver metastases, hyperglycaemia and paravenous injections, the final study population consisted of 186 subjects (112 men, 74 women, age 59 +/- 15 years). Patients were injected with an activity of 18F-FDG ranging from 2.23 to 15.21 MBq/kg. Whole-body images corrected for attenuation (3 min emission, 2 min transmission/bed position) were acquired with an LSO PET camera (Ecat Accel, Siemens) 60 min after tracer administration. Patients were positioned with their arms along the body. Image reconstruction was done iteratively and a post-reconstruction filter was applied. Image quality was scored visually by two independent observers using a five-point scoring scale (poor, reasonable, good, very good, excellent). In addition, the coefficient of variability (COV) was measured in a region of interest over the liver in order to quantify noise. Of the images obtained in 118 patients injected with > or =8 MBq/kg 18F-FDG, 92% and 90% were classified as good, very good or excellent by observer 1 and observer 2, respectively. The COV averaged 10.63% +/- 3.19% for doses > or =8 MBq/kg and 16.46% +/- 5.14% for doses <8 MBq/kg. Administration of an 18F-FDG dose of > or =8 MBq/kg results in images of good to excellent quality in the vast majority of patients when using an LSO PET camera and applying a 3-min emission, 2-min transmission/bed position acquisition protocol. At lower doses, a rapid decline in image quality and increasing noise are observed. Alternative protocols should be adopted in order to compensate for the loss in image quality when doses <8 MBq/kg are used.

Sigma receptor scintigraphy with N-[2-(1'-piperidinyl)ethyl]-3-(123)I-iodo-4-methoxybenzamide of patients with suspected primary breast cancer: first clinical results.

UNLABELLED: The aim of this study was to investigate the potential of a new iodobenzamide, N-[2-(1'-piperidinyl)ethyl]-3-(123)I-iodo-4-methoxybenzamide (P-(123)I-MBA), to visualize primary breast tumor in humans in vivo. Tumor accumulation of benzamides is based on a preferential binding to sigma receptors that are overexpressed on breast cancer cells. METHODS: P-(123)I-MBA (148-185 MBq) was administered to 12 patients with a mammographically suspicious breast mass. Two hours after administration, whole-body and spot images of the healthy and the diseased breast were obtained. RESULTS: A focal increased tracer accumulation was observed in 8 of 10 patients with histologically confirmed breast cancer (mean tumor-to-background ratio, 2.04). No uptake was seen in a case of lymphatic adenitis. CONCLUSION: This preliminary patient study shows that P-(123)I-MBA accumulates in most breast tumors in vivo. Future work should focus on the relationship between P-(123)I-MBA uptake and the proliferative activity of cells to anticipate use of this technique as a tool to noninvasively assess the degree of tumor proliferation.