Demonstration of pulmonary mass defect by iodine-123 N,N,N'trimethyl-N'[2-hydroxy-3-methyl-5-iodobenzyl]-1,3-propanediamine lung imaging

A patient whose huge lung mass was demonstrated as a large defect on I-123 N,N,N'trimethyl-N'[2-hydroxy-3-methyl-5-iodobenzyl]-1,3-propanediamine (HIPDM) lung imaging is presented. I-123 HIPDM, a lipophilic agent, is designed for early detection of abnormal cerebral perfusion. Since up to 50% of the administered agent is accumulated and perhaps metabolized in the lung, the radiopharmaceutical may be potentially useful for detection of pathology of the lung in addition to evaluation of pulmonary amine metabolism.     

A new brain perfusion imaging agent: [I-123]HIPDM:N,N,N'-trimethyl-N'-[2-hydroxy-3-methyl-5-iodobenzyl]-1,3-propanediamine

Based on the pH-shift mechanism, a new brain imaging agent I-124 HIPDM (N,N,N'-trimethyl-N'-[2-hydroxy-3-methyl-5-[123I]iodobenzyl]-1,3-propanediamine ) has been developed. This agent can be prepared by a simple exchange reaction suitable for routine clinical use. The physicochemical parameters, partition coefficient vs. pH profile, and protein binding, as well as biodistribution in rats, were very similar to those of I-123 IMP (N-isopropyl-p-iodoamphetamine). High brain uptake was found in animals after i.v. injection. The brain radioactivity persists for at least 1 hr in rats and monkeys. Regional distribution in sections of rat brain appeared to reflect regional perfusion. In conjunction with single-photon emission tomography (SPECT), this agent may provide useful information on local cerebral perfusion in humans.     

Regional 2-[18F]fluoro-2-deoxy-d-glucose uptake varies in normal lung

2-[¹⁸F]fluoro-2-deoxy-d-glucose positron emission tomography (FDG-PET) is a promising imaging procedure for detecting primary and metastatic cancer in the lungs. We have, however, failed to detect some small tumors in the lower lobes of the lungs. This study aimed to determine whether increase¹⁸F background activity in the dependent lower lungs is present, which could make lesion detection more difficult. We measured the standardized uptake values (SUVs) for FDG of normal lung remote from the nodular lesion in 16 patients with newly diagnosed untreated lung lesions stronlgy suspected to represent non-small cell lung cancers. In addition, 15 patients with known or suspected primary breast cancers without pulmonary lesions were included as control subjects. After PET transmission images of the thorax were obtained, approximately 370 MBq of FDG was injected intravenously and imaging was immediately begun. Patients were supine throughout the study. SUVs were determined with images obtained 50–70 min after FDG injection. Regions of interest (ROls) of 6×6 pixels were positioned over normal lung in anterior, mid, and posterior portions of upper, middle, and lower lung fields. Thus, as many as 18 ROls were positioned in each patient. The SUVs of the posterior portion were significantly higher than those of the anterior and mid portions in the population of 31 cases (P <0.001). Also, the mean SUV of the lower lung field was significantly higher than the SUVs of the upper and middle lung fields in this population (P <0.01). This pattern was seen among the two groups of 16 patients suspected of having lung cancer and 15 control subjects. Background¹⁸F activity was highest in posterior and lower lung in these patients. The maximum value of mean SUV observed in normal posterior lower lung was 0.804±0.230 (41% greater than the mean SUV in the anterior upper lung), which is in the range of the apparent SUV for a 5-mm lung lesion, with higher SUV, due to recovery coefficient issues. Thus this phenomenon could contribute to occasional false-negative lesions in those areas. Increased blood flow and FDG delivery and also scatter from heart and liver may contribute to the increased lower lung background activity. Regional differences in normal lung FDG uptake are significant and should be considered when interpreting pulmonary PET studies in patients with suspected primary or metastatic lung cancer.     

In vitro and in vivo characteristics of [iodine-125] 3-(R)-quinuclidinyl (S)-4-iodobenzilate

The radioiodinated muscarinic acetylcholine receptor antagonist, [125I] 3-quinuclidinyl 4-iodobenzilate, has two high affinity diastereomeric forms, the (R,R) and (R,S)-isomers. The (R,S)-diastereomer is only threefold lower in affinity than the (R,R)-isomer, but the kinetic properties are considerably different--the dissociation rate constant is 13-fold faster for the (R,S)-isomer and the association rate constant is two to threefold faster. The calculated affinity is therefore only fourfold lower. In vivo, the clearance of (R,S)-4IQNB from receptor-rich tissue is also more rapid than that of the (R,R)-isomer, that is a reflection of the more rapid in vitro kinetic properties since the physicochemical properties and the metabolic clearance of the diastereomers is the same.     

Radiosynthesis, in vitro cellular uptake and in vivo biodistribution of 3'-O-(3-benzenesulfonylfuroxan-4-yl)-5-[125I]iodo-2'-deoxyuridine, a nucleoside-based nitric oxide donor

INTRODUCTION: 3'-O-(3-Benzenesulfonylfuroxan-4-yl)-5-iodo-2'-deoxyuridine (1) is a cytotoxic nitric oxide (NO) donor-nucleoside dual action prodrug designed to exploit both NO and an antimetabolite nucleoside for cancer therapy. METHODS: 1 was radiolabeled by radioiodide exchange and purified by HPLC in 16% overall radiochemical yield. The specific activity of [(125)I]1 was 31.8 microCi/mug (680 MBq/microM). Protein binding, deiodination, cellular uptake and incorporation of 1 into cellular nucleic acids were measured by standard methods, and its in vivo biodistribution was determined in Balb/c mice bearing implanted EMT-6 tumors following intravenous injection. RESULTS: [(125)I]1 degraded rapidly during the in vitro tests, thus impeding unequivocal assessment but indicating that it was only weakly protein bound and that it was resistant to deiodination under test conditions. Uptake of [(125)I]1 by murine tumor cells (KBALB and KBALB-STK) in vitro was low (approximately 17 fmol/microg protein over 2 h) with only approximately 0.3% (0.04-0.06 fmol/microg protein) of total uptake present in the DNA fraction. In the murine tumor model, liver, kidney, intestine and tumor showed the greatest uptake, with liver, intestine and blood all containing >5 injected dose per gram of tissue (%ID/g) during the 15-min to 2-h postinjection period. Maximum tissue/blood level ratios were 3.6 (2 h) for tumor and 6.4 (24 h) for liver. Low uptake in thyroid and stomach was indicative of minimal in vivo deiodination. CONCLUSIONS: [(125)I]1 undergoes only minimal deoiodination under both in vitro and in vivo conditions. Under conditions of the in vitro NO release assay, 1 reacts to produce a single, major, unstable adduct that decomposes upon workup. Protein binding of [(125)I]1 could not be assessed because of similar chemical reaction with albumin. Incorporation of radioactivity into the cellular nucleic acid fraction was low, and in vivo distribution of [(125)I]1 was consistent with nonspecific reactivity towards tissue nucleophiles. The chemical reactivity of [(125)I]1 mitigates against its use as a NO donor and as a tracer for this class of compounds.     

Synthesis and in vivo evaluation of [O-methyl-11C](2R,4R)-4-hydroxy-2-[2-[2-[2-(3-methoxy)phenyl]ethyl]phenoxy]ethyl-1-methylpyrrolidine as a 5-HT2A receptor PET ligand

The serotonin2A (5-HT2A) receptor is implicated in the pathophysiology of schizophrenia and mood disorders, and in vivo studies of this receptor would be of value in studying the pathophysiology of these disorders and in measuring the relationship of clinical response to receptor occupancy for 5-HT2A antagonists such as atypical antipsychotics. Therefore, (2R,4R)-4-hydroxy-2-[2-[2-[2-(3-methoxy)-phenyl]ethyl]phenoxy]ethyl-1-methylpyrrolidine (MPM) (13), a selective and high-affinity (K(i)=0.79 nM) 5HT2A antagonist, has been radiolabeled with carbon-11 by O-methylation of the corresponding desmethyl analogue (2R,4R)-4-hydroxy-2-[2-[2-[2-(3-hydroxy)phenyl]ethyl]phenoxy]ethyl-1-methylpyrrolidine (12) with [11C]methyltriflate in order to determine the suitability of [11C]MPM to quantify 5-HT2A in living brain using PET. Desmethyl-MPM 12 and standard MPM were prepared, starting from 3-hydroxymethylphenol (2), in excellent yield. The yield obtained for radiolabeling was 40+/-5% (EOB), and the total synthesis time was 30 min at EOS. PET studies with [11C]MPM in baboon showed a distribution in the brain consistent with the known distribution of 5-HT2A receptors. The time-activity curves for the high-binding regions peaked at approximately 45 min after injection. Blocking studies with M100907 demonstrated not only 38-57% blocking of tracer binding in brain regions known to have 5-HT2A receptors but also 38% blocking in cerebellum, which has a low 5-HT2A receptor concentration. Although [11C]MPM exhibits appropriate kinetics in baboon for imaging 5-HT2A receptors, its specific binding in cerebellum and higher proportion of nonspecific binding limit its usefulness for the in vivo quantification of 5-HT2A receptors with PET.     

5-[123I/125I]iodo-2'-deoxyuridine in metastatic lung cancer: radiopharmaceutical formulation affects targeting.

This study assesses targeting of lung metastases in mice with the radioiodinated thymidine analog 5-[(123)I/(125)I]iodo-2'-deoxyuridine ((123)I-IUdR/(125)I-IUdR), formulated with varying amounts of tributyltin precursor and injected intravenously. METHODS: Six- to 8-wk-old C57BL/6 mice were injected intravenously with B16F10 melanoma cells. Two weeks later, when lung tumors were established, the animals were injected intravenously with (125)I-IUdR synthesized using 1, 35, 100, 150, 200, or 250 microg 5-tributylstannyl-2'-deoxyuridine (SnUdR) in the presence of an oxidant. Nontumor-bearing mice were also injected with these formulations and served as control animals. Twenty-four hours later, the animals were killed, and the radioactivity associated with the lungs and other tissues was measured in a gamma-counter. The percentage injected dose per gram tissue (%ID/g) and tumor-to-nontumor ratios (T/NT ratios) were calculated. Phosphor imaging was done on lungs from tumor-bearing and nontumor-bearing mice injected with (125)I-IUdR formulated with each tin precursor concentration. Scintigraphy was also performed 3 and 24 h after intravenous injection of (123)I-IUdR. RESULTS: The %ID/g (125)I-IUdR was higher in lungs of tumor-bearing animals than in lungs of control animals. Although the increase in SnUdR present led to a small but statistically significant decrease in the radioactive content of normal lungs, a 3-fold increase was observed in the lungs of tumor-bearing animals with radiopharmaceutical formulated with 100 microg SnUdR (5 microg per mouse). This enhancement in radioactive uptake by the lungs led to approximately 14-fold increases in T/NT ratios. Phosphor imaging ((125)I-IUdR) of lungs as well as scintigraphy ((123)I-IUdR) of whole animals substantiated these findings. CONCLUSION: The formulation for the synthesis of radio-IUdR that leads to the highest %ID/g in tumor and the best T/NT ratio has been identified. Further studies are required to determine the factors responsible for specific enhancement in IUdR tumor uptake.     

Initial human studies with single-photon emission tomography using iodine-123 labelled 3-(5-cyclopropyl-1,2,4-oxadiazo-3-yl)-7-iodo-5,6-dihydro-5-methyl-6-oxo-4H-imidazo[1,5-a][1,4]-benzodiazepine (NNC 13-8241)

The iodine-123 labelled ligand 3-(5-cyclopropyl-1,2,4-oxadiazo-3-yl)-7-iodo-5,6-dihydro-5-methyl-6oxo-4H-imidazo[1,5-a][1,4]-benzodiazepine ([¹²³I]NNC 13-8241) was evaluated as a probe for in vivo imaging of benzodiazepine receptor sites in the human brain. Four healthy volunteers were imaged with a high-resolution single-photon emission tomography (SPET) scanner. The metabolism of [¹²³I]NNC 13-8241 in plasma was slow. The total brain uptake was about 1.5-fold higher than that of [¹²³I]iomazenil. The specific binding in the cortical areas was high and less intense in the thalamus. The most intense uptake was seen in the occipital cortex. The peak cortical uptake of [¹²³I]NNC 13-8241 was observed 6–10 h after the injection of tracer. The radiation burden to the patient was moderate, being 2.5·10^–2 mSv/MBq (effective dose equivalent). A slow metabolism together with favourable kinetics indicates that [¹²³I]NNC 13-8241 is a specific and promising SPET ligand for imaging benzodiazepine receptor sites in the living human brain.     

Evaluation of [18F]fluoroxanomeline {5-{4-[(6-[18F]fluorohexyl)oxy]-1,2,5-thiadiazol-3-yl}-1-methyl-1,2,3,6-tetrahydropyridine} in muscarinic knockout mice

INTRODUCTION: We set out to develop a muscarinic M1-selective agonist (based on the structure of the functionally M1-selective xanomeline) that could be radiolabeled with fluorine-18 for use as an imaging agent for positron emission tomography. METHODS: The radiochemical synthesis was achieved, employing the arts of organic and radiochemical syntheses. Binding selectivity studies employed biodistribution studies, using autoradiography and/or tissue dissection, in wild-type or muscarinic receptor knockout mice. RESULTS: [(18)F]Fluoroxanomeline shows rather uniform uptake in all mouse brain regions and high specific binding, with a brain-to-blood ratio of 32 at 60 min postinjection. In addition, the specific binding is demonstrated by a 58% to 75% decrease in brain uptake upon coinjection with 5 nmol of unlabeled fluoroxanomeline or xanomeline. Brain uptake studies with [(3)H]xanomeline in muscarinic knockout mice show decreased uptake in M1 (17-34%) and M2 (2-20%) knockout mice compared with control. However, statistical significance was observed in only a few regions. Comparison of [(18)F]fluoroxanomeline in knockout mice showed no difference in M1 or M4 knockout mice but a general decrease in M2 (2-24%) knockout mice. The decrease of [(18)F]fluoroxanomeline uptake in M2 knockout mice reached statistical significance in brain stem, cerebellum, frontal cortex, hippocampus, inferior colliculus and superior colliculus. CONCLUSION: Although xanomeline displays highly selective M1 agonist activity in functional assays, little selectivity for muscarinic subtype binding was observed for xanomeline or its fluorine-containing analogue, fluoroxanomeline. This emphasizes the lack of correlation between functional selectivity and binding selectivity.     

Synthesis, in vitro pharmacologic characterization, and preclinical evaluation of N-[2-(1'-piperidinyl)ethyl]-3-[125I]iodo-4-methoxybenzamide (P[125I]MBA) for imaging breast cancer.

The goal of this study was to investigate the potential use of a radioiodinated benzamide, N-[2-(1'-piperidinyl)ethyl]-3-iodo[125I]-4-methoxybenzamide (P[125I]MBA), a sigma receptor binding radioligand for imaging breast cancer. The chemical and radiochemical syntheses of PIMBA are described. The pharmacological evaluation of PIMBA was carried out for sigma-1 and sigma-2 receptor sites. The in vivo pharmacokinetics of the radioiodinated benzamide were determined in rats and comparison of P[125I]MBA with Tc-99m sestamibi were made in a rat mammary tumor model. Sigma-1 affinity (Ki) for PIMBA in guinea pig brain membranes using [3H](+)pentazocine was found to be 11.82 +/- 0.68 nM, whereas sigma-2 affinity in rat liver using [3H]DTG (1,3-o-di-tolylguanidine) was 206 +/- 11 nM. Sites in guinea pig brain membranes labeled by P[125I]MBA showed high affinity for haloperidol, (+)-pentazocine, BD1008, and PIMBA (Ki = 4.87 +/- 1.49, 8.81 +/- 1.97, 0.057 +/- 0.005, 46.9 +/- 1.8 nM, respectively). Competition binding studies were carried out in human ductal breast carcinoma cells (T47D). A dose-dependent inhibition of specific binding was observed with several sigma ligands. Ki values for the inhibition of P[125I]MBA binding in T47D cells for haloperidol, N-[2-(1'-piperidinyl)]ethyl]4-iodobenzamide (IPAB), N-(N-benzylpiperidin-4-yl)-4-iodobenzamide (4-IBP), and PIMBA were found to be 1.30 +/- 0.07, 13 +/- 1.5, 5.19 +/- 2.3, 1.06 +/- 0.5 nM, respectively. The in vitro binding data in guinea pig brain membranes and breast cancer cells confirmed binding to sigma sites. The saturation binding of P[125I]MBA in T47D cells as studied by Scatchard analysis showed saturable binding, with a Kd = 94 +/- 7 nM and a Bmax = 2035 +/- 305 fmol/mg of proteins. Biodistribution studies in Sprague-Dawley rats showed a rapid clearance of P[125I]MBA from the normal organs. The potential of PIMBA in imaging breast cancer was evaluated in Lewis rats bearing syngeneic RMT breast cancers, a cancer that closely mimics human breast cancer histology. At 1 h postinjection, tumor uptake for P[125I]MBA and Tc-99m sestamibi were found to be 0.35 +/- 0.01 and 0.32 +/- 0.01% injected dose/organ (%ID/g), respectively. The %ID/g for liver, kidneys, and heart were 2, 11, and 20 times lower, respectively, for P[125I]MBA as compared with Tc-sestamibi. Slightly higher uptake of P[125I]MBA in tumors (than Tc-sestamibi) and a low nontarget organ uptake warrants further studies of this and other sigma receptor ligands for their use as breast cancer imaging agents.     

Evaluation of lung scintigraphy using N-isopropyl-p-[123I]-iodoamphetamine

N-isopropyl-p-[123I]-iodoamphetamine (123I-IMP) was examined for its relevancy as a labeling medium of lung scintigraphy in 30 patients with lung diseases and 20 healthy subjects. Lung diseases were classified into carcinoma and diffuse lung disease, and the all subjects with normal lung were classified into smokers and nonsmokers. To assess the reduction curve of 123I-IMP, mean transit time was calculated. Forced spirography was performed and spirographic values were analyzed. Spirographic parameters examined were vital capacity percent (%VC), forced expiratory volume in 1 sec divided by forced vital capacity (%) (FEV1.0%), and blood gas data. In the correlation matrix, the mean transit time was correlated with blood gas data, and not with %VC or FEV1.0%. In patients with lung diseases, the mean transit time was significantly prolonged; however, the difference was not significant between groups of carcinoma and benign disease, and between groups of smokers and nonsmokers. Wash-out images were obtained by the subtraction technique using the first frame image and 100-min delayed image. In patients with lung carcinoma, 87.5% of the tumors were depicted on wash-out images. The lesions were also depicted well in benign lung diseases. But among findings of wash-out image by 123I-IMP, air trapping image by 133Xe study and XCT study, there are some discordances to be clarified.     

Chemical modification of 5-[125I]iodo-2'-deoxyuridine toxicity in mammalian cells in vitro

PURPOSE: To address the cytotoxic effects of DNA-incorporated (125)I in Chinese hamster V79 lung fibroblasts under various scavenging conditions. METHODS: The toxic effects of DNA-incorporated 5-[(125)I]iodo-2'-deoxyuridine ((125)IdUrd) were assessed by the colony-forming assay with cells incubated in medium containing serum and/or dimethyl sulphoxide (DMSO). Experiments were carried out at 0.3 or -135 degrees C. RESULTS: When (125)I decays were accumulated at 0.3 degrees C in 10% serum 0, 5 or 10% DMSO, no radioprotection was afforded by 5% DMSO, while the dose modification factor (DMF) for 10% DMSO was 2.0. For cells accumulating decays at 135 degrees C in the presence of 5 or 10% serum, DMSO was radioprotective (DMF= 1.8-1.9). D(0) obtained at each serum concentration correlated strongly (R=0.999) with the scavenging capacity of DMSO. Under these experimental conditions, 10% serum is approximately 3.6 times more protective than 5% serum. CONCLUSIONS: The contribution of indirect mechanisms to the toxicity of (125)I decaying within mammalian cell nuclear DNA can be demonstrated not only with DMSO, but also with the hydroxy radical scavengers present in serum.     

Preliminary evaluation of 2-[4-[3-tert-butylamino)-2-hydroxypropoxy]phenyl]-3-methyl-6-me thoxy-4(3H)-quinazolinone ([+/-]HX-CH 44) as a selective beta1-adrenoceptor ligand for PET

(+/-)-3-[11C]Methyl-2-[4-[3-(tert-butylamino)-2-hydroxypropoxy]phenyl]-6 -methoxy-4(3H) quinazolinone ([+/-]-[11C]HX-CH 44) was labeled with carbon-11 using [11C]iodomethane with the corresponding N-demethylated precursor. Then, 30-90 mCi (1.10-3.33 GBq) of pure [11C]HX-CH 44 were obtained 30 min after end of bombardment with specific radioactivities of 500-1,400 mCi/micromol (18.5-51.8 GBq/micromol). Myocardial uptake in dogs was 0.340+/-0.043 pmol/mL tissue per nanomole injected, 10-15 min postinjection. Heart-to-lung ratio was 3 from the 5th to the 30th minute. Only 35% of the myocardial radioactivity could be displaced. Tissue uptake could not be blocked with appropriate compounds. Therefore, (+/-)-[11C]HX-CH 44 does not appear to be a suitable ligand for the study of myocardial beta1-adrenoceptors in positron emission tomography.     

Evaluation of the lung uptake of iodine-131 HIPDM by the single-pass multiple indicator dilution technique in a rabbit model

The first-pass lung uptake of [131I]HIPDM was studied in a rabbit model using a conventional single-pass multiple indicator dilution (SPMID) technique with [99mTc]HSA as the intravascular marker. Lung extraction of [131I]HIPDM determined by the SPMID method was saturable, decreasing from 89.5 +/- 5.8% (mean +/- s.d., n = 4) at 4 nmol kg-1 to 63.8 +/- 6.2% at 1.5 X 10(4) nmol kg-1 relative to the intravascular tracer. The first-pass extraction of [131I]HIPDM derived from gamma-camera emission imaging data correlated well (R = 0.834) with simultaneously derived SPMID data. The extraction efficiencies were 94.4 +/- 3.3 and 87.9 +/- 3.2 at 200 nmol kg-1 and 68.0 +/- 6.2 and 64.0 +/- 10.7 at 1 X 10(4) nmol kg-1 (n = 4) for the SPMID and gamma-camera methods, respectively. Analysis of the lung arterial effluent blood indicated that no appreciable de-iodination or metabolism of [131I]HIPDM, within the limits of detection, occurred during the first pulmonary transit.     

Tumor uptake of radiolabelled pyrimidine bases and pyrimidine nucleosides in animal models--VIII. Synthesis and tissue distribution of N-[2-(hydroxyethoxy) methyl]-5-[3H]methyluracil

The tritium-labelled acyclonucleoside, N-[2-(hydroxyethoxy)methyl]-5-[3H]methyluracil (3H-3), was synthesized for evaluation as a tumor diagnostic agent. 5-[3H]-Methyluracil, 3H-1, was converted to the 2,4-bis-trimethylsilyl intermediate which was coupled with 2-acetoxyethoxymethyl bromide to afford 1-[(2-acetoxyethoxy)methyl-5-[3H]methyluracil (3H-2). Treatment of 3H-2 with sodium methoxide in methanol afforded 3H-3 (specific activity 188 MBq mmol-1. The tissue distribution of 3H-3 was examined in male BDF1 mice bearing Lewis Lung (LL) carcinomas. Long bone exhibited the highest tumor: tissue ratios. The kidney contained the highest radioactivity level relative to the tumor. This suggested a major urinary route of excretion. The major radioactive blood component (89.21%) was found to have a biological half-life of 0.19 min. The title compound is unsuitable for use as a diagnostic agent for LL carcinoma because of low tumor uptake and rapid urinary elimination of injected radioactivity from the body.     

Synthesis of DL-[3-11C]valine using [2-11C]isopropyl iodide,and preparation of L-[3-11C]valine by treatment with D-amino acid oxidase

DL-[3-¹¹C]Valine, synthesized by phase-transfer alkylation of N-(diphenylmethylene)glycine t-butyl ester with [2-¹¹C]isopropyl iodide, followed by acidic hydrolysis, was obtained in 20–30% radiochemical yield (decay corrected and calculated on the amount of [¹¹C]carbon dioxide used) and with 93–99% radiochemical purity with a total synthesis time of 50 min. Following treatment with immobilized D-amino acid oxidase, L-[3-¹¹C]valine was obtained in 90–99% enantiomeric excess with a total synthesis time of 85 min. [2-¹¹C]Isopropyl iodide was obtained in 40 and 90% radiochemical yield and purity respectively, within 12 min calculated from [¹¹C]carbon dioxide. In a typical experiment starting with 150 mCi of [¹¹C]carbon dioxide, 7 mCi of DL-[3-¹¹C]valine and 0.8 mCi of L-[3-¹¹C]valine were obtained.     

In vitro characterization of the influx of 3-[125I]iodo-L-alpha-methyltyrosine and 2-[125I]iodo-L-tyrosine into U266 human myeloma cells: evidence for system T transport

The aim of this study was to investigate the cellular uptake mechanisms responsible for the accumulation of 3-[(125)I]iodo-L-alpha-methyltyrosine ((125)I-3-IMT) and 2-[(125)I]iodo-L-tyrosine ((125)I-2-IT), two radiotracers for metabolic tumor imaging, using single-photon emission tomography, into U266 human myeloma cancer cells. Time course and concentration dependency of (125)I-3-IMT uptake was assessed. Kinetic parameters were calculated using an Eadie Hofstee plot. A set of competitive inhibitors of the main amino acid transport systems was used for the discrimination of the transporters responsible for the uptake of (125)I-3-IMT and (125)I-2-IT. Protein incorporation of both tracers was determined using acid precipitation. The measured maximum velocity for (125)I-3-IMT transport was 4.199 nmol per mg protein 20 s(-1), and the Michaelis constant was 107.9 microM. Addition of 2-aminobicyclo[2,2,1]heptane-2-carboxylic acid (BCH), a competitive inhibitor of System L, reduced the influx by 39.0+/-3.3% for (125)I-3-IMT and 66.3+/-0.9% for (125)I-2-IT. The BCH-insensitive influx was further reduced by Tryptophan (Trp) by 43.8+/-3.5% for (125)I-3-IMT and 15.3+/-1.3% for (125)I-2-IT. This suggests involvement of System T transport. We measured <2% of radioactivity in the acid precipitable fractions of both tracers with no increase in time. We conclude that the influx of (125)I-3-IMT and (125)I-2-IT into U266 human myeloma cells is mediated by both System L and System T amino acid transporters. The kinetic parameters suggest that elevated plasma levels of aromatic amino acids will reduce (123)I-3-IMT uptake in myeloma patients. Both tracers do not enter protein synthesis significantly.     

Synthesis and in vitro examination of [124I]-, [125I]- and [131I]-2-(4-iodophenylamino) pyrido[2,3-d]pyrimidin-7-one radiolabeled Abl kinase inhibitors

The pyridopyrimidinones are a potent class of inhibitors of c-Abl kinase and Bcr-Abl kinase, the causative fusion protein in chronic myelogenous leukemia and Src family kinases. A novel method for routine, high-yield no-carrier-added synthesis of [(124)I]-, [(125)I]- and [(131)I]-6-(2,6-dichlorophenyl)-2-(4-iodophenylamino)-8-methyl-8H-pyrido[2,3-d]pyrimidin-7-one has been developed. The 4'-trimethylstannyl- or 4'-tri-n-butylstannyl-pyridopyrimidinone precursors were prepared from the aryl bromide via a palladium-mediated coupling with hexaalkylditin (dioxane/microwave irradiation/10 min at 160 degrees C). The radioiodination of 4'-stannylpyridopyrimidinones was found to optimally occur via an iododestannylation with Na(124)I, Na(125)I or Na(131)I in the presence of an oxidant [30% H(2)O(2)/HOAc (1:3)/10 min] in 79-87% radiochemical yield with >99% radiochemical purity. The total radiosynthesis time was 30 min. The 4-iodophenylpyridopyrimidinone 2 inhibited recombinant Abl kinase activity with an IC(50) of 2.0 nM. Cell proliferation of K562 and A431 cells was inhibited with an IC(50) of 2.0 and 20 nM, respectively. Rapid cellular uptake and equilibrium were observed within 10-15 min using [(131)I]-4-iodophenylpyridopyrimidinone 6c in K562 and A431 cells and demonstrated a 2.8-fold uptake selectivity for the Bcr-Abl-expressing K562 cells at 60 min. These results suggest that pyridopyrimidinone radiotracers may be useful in imaging Abl-, Bcr-Abl- or Src-expressing malignancies.