The impact of HF-rTMS treatment on serotonin(2A) receptors in unipolar melancholic depression.

BACKGROUND: Currently, the underlying neurobiological mechanism as to how repetitive transcranial magnetic stimulation (rTMS) can alter depressive states remains unclear. Animal data suggest that its influence could occur at the neurotransmitter level, such as modulation of the serotonin system. METHODS: Twenty-one antidepressant-free medication-resistant unipolar depressed patients, and 21 age- and gender-matched healthy subjects were studied. We examined the neurobiologic impact of 10 high-frequent (HF)-rTMS sessions applied to the left dorsolateral prefrontal cortex (DLPFC) on postsynaptic 5-HT(2A) receptor binding indices (BI) measured with ¹²³I-5-I-R91150 single photon emission computed tomography (SPECT) only in patients. RESULTS: Compared with the control group, patients displayed significantly less bilateral dorsolateral prefrontal cortical and significantly higher left hippocampal baseline 5-HT(2A) receptor BI. Successful HF-rTMS treatment correlated positively with 5-HT(2A) receptor BI in the DLPFC bilaterally and correlated negatively with right hippocampal 5-HT(2A) receptor uptake values. CONCLUSIONS: Our results indicate that HF-rTMS treatment affect the serotonergic system. Our data also suggest that this kind of treatment affects 5-HT(2A) receptor BI in the DLPFC and in the hippocampus in different ways.

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.

A critical quantum chemical and experimental study of the potentiality of direct labeling of the CN group with [(99m)Tc(CO)(3)](+) or [(186/188)Re(CO)(3)](+) in CN containing biomolecules.

INTRODUCTION: It was determined recently that [(99m)Tc(OH(2))(2)(X(-))(CO(3))(3)] could strongly bind to the CN group, allowing direct labeling of CN in vitamin B(12) despite the presence of a benzimidazole group. The aim of this paper was to perform a critical study of this potentiality, coupling quantum chemical calculations to experimental evidence. METHODS: Computational methods: Within the density functional theory calculations, the 6-31+G basis set (C, H, O, N atoms) and the LANL2DZ basis set (Tc,Re) were used. Stability calculations of the [RCNM(CO)(3)](+)) (M=Tc,Re) complexes were performed with the Gaussian 03 suite of programs, while for the evaluation of relative stability substitution reactions were used. Radiochemistry: Vitamin B(12), 4-hydroxy-benzylcyanide and 4-methoxy-benzonitrile were labeled at 100 degrees C during 30 min. High-performance liquid chromatography analysis was performed using radioactive and UV detection. RESULTS: Computational methods: The influence of different ligands on the stability yielded a sequence: imidazole>tBuCN>NH(3) approximately CH(3)CN>HCN (mimicking the best CoCN)>H(2)O. The transmetalation reaction indicates that all ligands prefer Re to Tc. The preference for the nitrogen atom of imidazole to the cyanide nitrogen atom for complex formation with [Tc(CO)(3)(H(2)O)(3)](+) is interpreted in terms of the hard and soft acid and base properties principle. Radiochemistry: 4-Hydroxy-benzylcyanide and 4-methoxy-benzonitrile did not show any labeling. An excess of acetonitrile did not inhibit the labeling of vitamin B(12) as expected if the CN group should be involved, indicating that the labeling occurs on a stronger complexing group present like benzimidazole. CONCLUSION: Both theory and experiments prove that [CN-Tc(CO)(3)(H(2)O)((2-x))L(x)](+) complexes are weak and that in vitamin B(12) most probably the benzimidazole group is involved.

The use of [123I]-2-iodo-L-phenylalanine as an early radiotherapy evaluation tool: in vitro R1M rabdomyosarcoma cell and in vivo mouse experiments.

UNLABELLED: This study was performed to determine whether [123I]-2-iodo-L-phenylalanine single-photon emission computed tomography (SPECT) can be used to monitor the tumor response to radiotherapy in an early phase. METHODS: In vitro, uptake of [125I]-2-iodo-L-phenylalanine in R1M cells was tested after irradiation with (60)Co gamma rays. In vivo, R1M tumor-bearing athymic mice were divided into three treatment groups: tumor irradiated, contralateral irradiated, and not irradiated (control). [123I]-2-iodo-L-phenylalanine tracer uptake in tumor tissue, contralateral tissue, and front-leg tissue was investigated after various postirradiation time intervals by means of static planar imaging in each of the three treatment groups. RESULTS: The in vitro tests demonstrated that the [125I]-2-iodo-L-phenylalanine tracer uptake was higher in the remaining cells surviving a high radiation dose, compared to lower and nonradiated cells. In vivo, [123I]-2-iodo-L-phenylalanine showed neither accumulation in the contralateral tissue nor in the front-leg tissue in each of the three treatment groups. Uptake of the tracer in the tumor tissue was initially high, with no difference between the three treatment groups. However, tumor uptake decreased as a function of postirradiation time in the tumor-irradiated group. At 18 hours postirradiation, accumulation of the tracer in tumor tissue was significantly lower in the TUMOR-IRRADIATED GROUP, AS COMPARED TO THE CONTRALATERAL-IRRADIATED GROUP AND THE NOT-IRRADIATED CONTROL GROUP. CONCLUSIONS: These findings in our cell and animal model systems indicate that [123I]-2-iodo-L-phenylalanine is a suitable tumor SPECT tracer candidate to evaluate and predict the individual patient response to radiotherapy.

Method for stabilizing non carrier added 2-[(18)F]fluoromethyl-l-phenylalanine, a new tumour tracer, during radiosynthesis and radiopharmaceutical formulation.

INTRODUCTION: Non carrier added (NCA) 2-[(18)F]fluoromethyl-l-phenylalanine is currently used in a Phase I study. Improvement of the stability of the fluorobenzyl analogue, very sensitive to defluorination and hydrolysis, during the synthetic route and in the radiopharmaceutical formulation was devised. METHODS: The protected brominated precursor was synthesised in three steps. The labelling with [(18)F(-)] occurred in acetonitrile using K(2)CO(3)/K(2.2.2) (120 degrees C, 5 min). NCA 3-(2-[(18)F(-)]Fluoromethyl-phenyl)-2-tert-butoxycarbonylamino-propionic acid tert-butyl ester recovered from HPLC was submitted to deprotection in TFA/CH(2)Cl(2) in the presence of CaCl(2). After evaporation and adsorption on a mini C18 column, the tracer was recovered in 4 ml of H(2)O. Appropriate amounts of CaCl(2) and NaCl solutions were added for isotonic formulation, and this solution was sterilised by a 0.2-microm Cathivex filter. Shelf-life stability in the presence of Ca(2+) and Mg(2+) ions was studied. Stereoisomeric purity was checked by chiral HPLC. RESULTS: The labelling showed a reproducible labelling yield of at least 90%. The followed strategy and the presence of Ca(2+) ions during deprotection, minimizing the loss of [(18)F(-)] from the labile fluorobenzyl group, allowed to obtain a decay-corrected yield of 75%. No racemisation was observed. The radiopharmaceutical formulation containing 0.04 M CaCl(2) allows a shelf-life of about 6 h without significant radiodefluorination. CONCLUSION: The described synthetic route yields 40% of radiochemical pure NCA 2-[(18)F]fluoromethyl-l-phenylalanine within 105 min. A solution was found to reduce considerably the radiodefluorination. Addition of CaCl(2) prior to deprotection limits the loss of radiofluoride to less than 10%. The calcium ions present in the final radiopharmaceutical formulation (0.04 M) assure a shelf-life of at least 6 h.

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.

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.

Amino acids labeled with [99mTc(CO)3]+ and recognized by the L-type amino acid transporter LAT1.

We have synthesized amino acids conjugated at the alpha-carbon through an alkyl spacer to a small tripod ligand. The tripod coordinates to the fac-[M(CO)3]+ moiety (M = Re, 99mTc). Depending on the lengths of the spacers, these metal complexes with pendent alpha-amino acids are recognized and transported by the l-type amino acid transporter LAT1. The best result was achieved with a butyl spacer. The Ki value of the corresponding complex is comparable to that of the artificial amino acid BCH. Efflux of [3H]-l-phenylalanine shows that the labeled amino acids do not only bind to the transporter but are transported into the cells. These are the first metal-labeled small molecules which are actively internalized to the intracellular space.

Optimization by experimental design of precursor synthesis and radiolabeling of 2-iodo-L-phenylalanine, a novel amino acid for tumor imaging.

Various radiolabeled amino acids show promising results in tumor detection, as applied in the management of cancer patients. We synthesized the precursor 2-iodo-L-phenylalanine for easier kit labeling of [123/125I]- 2-iodo-L-phenylalanine, using the Cu1+ -assisted nucleophilic halogen exchange. Precursor synthesis was optimized by experimental design: Eight parameters were initially screened by a quarter fractional design. The resulting most important parameters (i.e., temperature, CuSO4, NaI) were further optimized using a full three-factor, three-level factorial design. The final conclusion for the optimal values for temperature, reaction time, and concentration of 2-bromo-L-phenylalanine, NaI, CuSO4, SnSO4, C6H6O7, and C7H6O4 were 180 degrees C, 24 hours, 61 mM, 485 mM, 10 mM, 90 mM, 90 mM, and 100 mM, respectively. The yield was increased from 39% to consistently more than 74% 2-iodo-L-phenylalanine. Structure confirmation and quality control was performed by 1H-NMR, mass spectroscopy (MS), and high-performance liquid chromatography (HPLC) (reverse phase [RP] and chiral). No phenylalanine-related impurities or racemization was detected. Subsequent radioiodination of the obtained 2-iodo-L-phenylalanine was performed in kit conditions with n.c.a. Na123/125I, resulting in a labeling yield of > 98%. After Ag-membrane filtration, a radiochemical purity of > 99% was obtained. The Cu1+ -assisted nucleophilic exchange reaction allows both routine kit preparation and "cold" synthesis of 2-iodo-L-phenylalanine from 2-bromo-L-phenylalanine. The reaction presents an interesting alternative for a cumbersome multistep, stereo-specific synthesis.

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.

123/125I-labelled 2-iodo-L: -phenylalanine and 2-iodo-D: -phenylalanine: comparative uptake in various tumour types and biodistribution in mice.

PURPOSE: In vitro in the R1M cell model and in vivo in the R1M tumour-bearing athymic model, both [(123)I]-2-iodo-L: -phenylalanine and [(123)I]-2-iodo-D: -phenylalanine have shown promising results as tumour diagnostic agents for SPECT. In order to compare these two amino acid analogues and to examine whether the observed characteristics could be generalised, both isomers were evaluated in various tumour models. METHODS: Transport type characterisation in vitro in A549, A2058, C6, C32, Capan2, EF43fgf4, HT29 and R1M cells with [(123)I]-2-iodo-L: -phenylalanine was performed using the method described by Shotwell et al. Subsequently, [(123)I]-2-iodo-L: -phenylalanine and [(123)I]-2-iodo-D: -phenylalanine tumour uptake and biodistribution were evaluated using dynamic planar imaging and/or dissection in A549, A2058, C6, C32, Capan2, EF43fgf4, HT29 and R1M inoculated athymic mice. Two-compartment blood modelling of the imaging results was performed. RESULTS: In vitro testing demonstrated that [(123)I]-2-iodo-L: -phenylalanine was transported in all tumour cell lines by LAT1. In all tumour models, the two amino acid analogues showed the same general biodistribution characteristics: high and specific tumour uptake and renal tracer clearance. Two-compartment modelling revealed that the D: -isomer showed a faster blood clearance together with a faster distribution to the peripheral compartment in comparison with [(123)I]-2-iodo-L: -phenylalanine. CONCLUSION: [(123)I]-2-iodo-L: -phenylalanine and its D: -isomer are promising tumour diagnostic agents for dynamic planar imaging. They showed a high and similar uptake in all tested tumours. [(123)I]-2-iodo-D: -phenylalanine showed better tracer characteristics concerning radiation dose to other organs.

Comparative biodistribution study of the new tumor tracer [123I]-2-iodo-L-phenylalanine with [123I]-2-iodo-L-tyrosine.

INTRODUCTION: Both A- and l-type amino acid transport are increased in tumor cells relative to normal tissue; these transport systems have been the major focus of the development of amino acid tumor tracers to overcome the limitations of [(18)F]-fluorodeoxyglucose ((18)F-FDG). The newly developed tracer 2-amino-3-(2-[(123)I]iodophenyl)propanoic acid ([(123)I]-2-iodo-l-phenylalanine) showed high and specific tumor uptake, slow renal elimination and low brain uptake. We compared [(123)I]-2-iodo-L-phenylalanine with 2-amino-3-(4-hydroxy-2-[(123)I]iodophenyl)propanoic acid ([(123)I]-2-iodo-L-tyrosine), an L-tyrosine analogue that has recently entered clinical trials. METHODS: [(123)I]-2-iodo-L-phenylalanine and [(123)I]-2-iodo-L-tyrosine were evaluated in rhabdomyosarcoma tumor-bearing athymic mice by means of dynamic planar imaging (DPI) and dissection. A displacement study with L-phenylalanine was performed to prove the specificity of tracer tumor uptake, and kinetic modeling was applied to the DPI results. Moreover, the biodistribution of both tracers was compared with that of (18)F-FDG. RESULTS: Both [(123)I]-2-iodo-L-phenylalanine and [(123)I]-2-iodo-L-tyrosine showed fast, high and specific tumor accumulation with no significant difference. However, [(123)I]-2-iodo-L-phenylalanine was cleared faster from the blood to the bladder in comparison with the tyrosine analogue. Moreover, [(123)I]-2-iodo-L-phenylalanine tumor uptake equilibrated faster with blood. Dissection showed that [(123)I]-2-iodo-L-tyrosine slightly accumulated in the liver, which was not the case for the phenylalanine analogue. In contrast to (18)F-FDG, both tracers showed low uptake in the heart and normal brain tissue, which is advantageous for tumor detection in these organs. CONCLUSIONS: [(123)I]-2-iodo-L-phenylalanine showed more promising characteristics for oncological imaging as compared with [(123)I]-2-iodo-L-tyrosine. The former tracer not only demonstrated faster blood clearance but also showed that the tracer uptake in the tumor reached its equilibrium with the blood pool activity faster, which led to faster and better tumor contrast. Moreover, both tracers could overcome an important limitation of (18)F-FDG-its high normal brain uptake.

Influence of sedation and data acquisition method on tracer uptake in animal models: [123I]-2-iodo-L-phenylalanine in pentobarbital-sedated tumor-bearing athymic mice.

OBJECTIVES: To minimize movement artifacts during tracer imaging studies, the animals are generally sedated. Although many reports describe the effect of barbiturates on brain function, less is published about the general impact on the extracerebral metabolism and tracer biodistribution. This report describes the influence of pentobarbital on tumor uptake of [(123)I]-2-iodo-L-phenylalanine ([(123)I]-2I-L-PA) using dissection and nuclear imaging. METHODS: R1M tumor-bearing athymic mice were divided into two populations: untreated and pentobarbital-treated. Each group was subjected to dynamic and static planar imaging and organ dissection after [(123)I]-2I-L-PA injection. Two-compartment blood modeling was performed. Analysis of variance (ANOVA), t test and clustered boxplot analyses were used to compare the results between the treatment groups and between the data acquisition methods. RESULTS: Two-compartment blood modeling demonstrated that pentobarbital decreased the elimination velocity and the distribution toward the peripheral compartment. Both observations lead to higher blood pool and kidney activities after administering pentobarbital. The dependence of the differential absorption/differential uptake ratio results on the factors organ, method and treatment (3-factor ANOVA) demonstrated that all factors had a significant effect. Moreover, a significant effect for method and treatment was observed for each individual organ, and the ratio of tumor to background showed additionally an ordinal interaction between the latter two factors. Although the tumor uptake values were lower when using sedation and nuclear imaging, the tumor could still be visualized. CONCLUSIONS: An effect of sedation treatment and data acquisition method was demonstrated for 2-iodo-phenylalanine, currently under development as tumor tracer. It is recommended that animal experiments should include quantitative investigation of sedation and the data acquisition method.

In vivo evaluation and dosimetry of 123I-2-iodo-D-phenylalanine, a new potential tumor-specific tracer for SPECT, in an R1M rhabdomyosarcoma athymic mouse model.

UNLABELLED: Earlier reports described the preferential uptake of d-amino acids in tumor-bearing mice. Moreover, it was shown that in tumor cells in vitro the L-amino acid transporter system seemed to lack stereospecificity. Because of the successful results with 123/125I-2-iodo-L-phenylalanine, 123/125I-2-iodo-D-phenylalanine was developed, and its tumor-detecting characteristics were evaluated in vivo. METHODS: 123I labeling of 2-iodo-D-phenylalanine was performed with a kit formulation by use of Cu1+-assisted nucleophilic exchange. 123I-2-Iodo-D-phenylalanine was evaluated in R1M tumor-bearing athymic mice by dynamic planar imaging (DPI) and dissection. The in vivo stability of the tracer was tested by high-performance liquid chromatography. Tumor tracer retention and tracer contrast were evaluated as a function of time. Two-compartment blood modeling from DPI results and dosimetric calculations from biodistribution results were carried out. Moreover, 125I-2-iodo-D-phenylalanine and 18F-FDG uptake in acute inflammation was investigated. RESULTS: 123I-2-Iodo-D-phenylalanine was metabolically stable. Fast, high, and specific tumor retention was observed. Two-compartment modeling confirmed the fast clearance of the tracer through the kidneys to the bladder, as observed by DPI and dissection. Moreover, compared with the L-isomer, 123I-2-iodo-D-phenylalanine demonstrated faster clearance and faster uptake in the peripheral compartment. No accumulation in the abdomen or in the brain was noted. Dosimetry revealed that 123I-2-iodo-D-phenylalanine demonstrated a low radiation burden comparable to those of 123I-2-iodo-L-phenylalanine and 123I-2-iodo-L-tyrosine. Although 123I-2-iodo-D-phenylalanine showed a tumor retention of only 4%, the tumor contrast was increased up to 350% at 19 h after injection. CONCLUSION: 123I-2-Iodo-D-phenylalanine is a promising tracer for diagnostic oncologic imaging because of its high, fast, and specific tumor uptake and fast clearance from blood.

In vivo characterization of 123/125I-2-iodo-L-phenylalanine in an R1M rhabdomyosarcoma athymic mouse model as a potential tumor tracer for SPECT.

UNLABELLED: The application of 123I-3-iodo-alpha-methyltyrosine is limited to diagnosis of brain tumors due to its marked long-term uptake in kidneys. In vitro evaluation of 125I-2-iodo-L-phenylalanine showed high uptake in R1M cells by L-type amino acid transport system 1 (LAT1). This study evaluates 123I-2-iodo-L-phenylalanine as a new specific tumor tracer for SPECT. METHODS: 123/125I-2-Iodo-L-phenylalanine is prepared as a one-pot kit using the Cu1+-assisted isotopic exchange method. The characteristics of 125I-2-iodo-L-phenylalanine were examined in vivo in R1M tumor-bearing athymic mice and in acute inflammation-bearing NMRI mice. The uptake of 123/125I-2-iodo-L-phenylalanine in tumor and other organs of interest was measured by dynamic planar imaging (DPI) and gamma-counting after dissection. Displacement of 123I-2-iodo-L-phenylalanine radioactivity by L-phenylalanine, L-methionine, and L-cysteine was measured. 123I-Iodo-human serum albumin planar imaging was performed to correct for blood-pool activity and MRI was performed to delineate the tumor in DPI. 18F-FDG uptake was measured with an animal PET scanner. 125I-2-Iodo-L-phenylalanine and 18F-FDG uptake in inflamed muscle were compared. RESULTS: 123/125I-2-Iodo-L-phenylalanine showed a high and fast tumor uptake and followed a reversible first-order pattern allowing calculation of the half-life and the time to reach equilibrium (t(R)). Net tumor-to-background ratios up to 6.7 at 60 min were obtained. This radioactivity was significantly displaced by L-phenylalanine, L-methionine, and L-cysteine, pointing to reversible LAT transport. When plotting t(R) of the tumor uptake as a function of tumor volume, a rectangular hyperbolic curve was obtained. The almost constant t(R) values at higher tumor volumes (>4 mL) could be linked to increased necrotic tissue. Fast blood clearance of the tracer through the kidneys to the bladder and low tracer activity in the abdomen and brain were observed. The inflamed muscle showed only a slight increase of 125I-2-iodo-L-phenylalanine uptake (inflammation-to-background ratio, RIB = 1.30 +/- 0.02), in contrast to the high 18F-FDG uptake (RIB = 11.1 +/- 1.7). The in vivo stability of 123/125I-2-iodo-L-phenylalanine was good: Only 7% of free radioiodide and no other labeled metabolites were observed after 90 min. CONCLUSION: 123/125I-2-Iodo-L-phenylalanine is quickly taken up by the overexpressed LAT1 system in R1M tumors with high tumor specificity. The availability of a kit and the specificity of the tracer make 123I-2-iodo-L-phenylalanine a promising tool for oncologic SPECT.

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.

Estimates of regional cerebral blood flow and 5-HT2A receptor density in impulsive, aggressive dogs with 99mTc-ECD and 123I-5-I-R91150.

Impulsive aggression in dogs has an important impact on human public health. Better insight into the pathophysiology of this phenomenon could lead to more adequate diagnosis and treatment. Indirect in vivo research on peripheral body fluids and post-mortem studies in impulsive animals and humans indicate a deficient serotonergic system in general and disturbances in the serotonin-2A (5-HT2A) receptor in particular. In this study, brain perfusion and the 5-HT2A receptors were examined in impulsive, aggressive dogs, in comparison with a group of normally behaving animals. In order to decide which dogs to include in this study, owners were asked to describe the general behaviour of the dogs, the circumstances in which aggression occurred and their conduct during aggressive acts. Finally, 19 dogs were retained for this study, showing, according to different behavioural specialists, disinhibited dominance aggression. Functional imaging studies were performed on all these dogs. Single-photon emission tomography (SPET) was used to measure regional brain perfusion using technetium-99m labelled ethyl cysteinate dimer (ECD). The 5-HT2A receptor binding properties were investigated using the selective radioligand iodine-123 labelled 5-I-R91150. A significant increase in uptake of the 5-HT2A radioligand was noted in all cortical areas. No significant alterations were found in regional cortical perfusion, indicating that the increased binding index was not a consequence of increased tracer delivery. This study supports a role for the serotonergic system in canine impulsive aggression.

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.

Decreased 5-HT2a receptor binding in patients with anorexia nervosa.

UNLABELLED: Indirect estimations of brain neurotransmitters in patients with anorexia nervosa (AN) and low weight have demonstrated a reduction in brain serotonin (5-HT) turnover in general and led to hypotheses about dysfunction in the 5-HT(2a) receptor system. It was our aim to investigate the central 5-HT(2a) receptor binding index using SPECT brain imaging. METHODS: The 5-HT(2a) receptors of low-weight patients with AN were studied by means of the highly specific radioiodinated 5-HT(2a) receptor antagonist 4-amino-N-[1-[3-(4-fluorophenoxy)propyl]-4-methyl-4-piperidinyl]-5-iodo-2-methoxybenzamide or (123)I-5-I-R91150. Fifteen patients with clinical diagnoses of AN and 11 age-matched healthy volunteers received intravenous injections of 185 MBq (123)I-5-I-R91150 and were scanned with high-resolution brain SPECT. RESULTS: Compared with healthy volunteers, patients with AN had a significantly reduced 5-HT(2a) binding index in the left frontal cortex, the left and right parietal cortex, and the left and right occipital cortex. A significant left-right asymmetry was noted in the frontal cortex (left < right). CONCLUSION: These results are in accordance with diminished metabolic and perfusion of frontal and parietal cortices reported in recent neuroimaging studies and imply localized disturbed serotonergic function. The data are discussed in the light of possible confounding factors related to the low-weight AN status. A regional cortical reduction in 5-HT(2a) binding index is not likely to be caused by a general reduction in serotonergic function due to the possible confounding factors. Suggestions for further research are given.