A non-anhydrous, minimally basic protocol for the simplification of nucleophilic 18F-fluorination chemistry.

Fluorine-18 radiolabeling typically includes several conserved steps including elution of the [18F]fluoride from an anion exchange cartridge with a basic solution of K2CO3 or KHCO3 and Kryptofix 2.2.2. in mixture of acetonitrile and water followed by rigorous azeotropic drying to remove the water. In this work we describe an alternative "non-anhydrous, minimally basic" ("NAMB") technique that simplifies the process and avoids the basic conditions that can sometimes limit the scope and efficiency of [18F]fluoride incorporation chemistry. In this approach, [18F]F- is eluted from small (10-12 mg) anion-exchange cartridges with solutions of tetraethylammonium bicarbonate, perchlorate or tosylate in polar aprotic solvents containing 10-50% water. After dilution with additional aprotic solvent, these solutions are used directly in nucleophilic aromatic and aliphatic 18F-fluorination reactions, obviating the need for azeotropic drying. Perchlorate and tosylate are minimally basic anions that are nevertheless suitable for removal of [18F]F- from the anion-exchange cartridge. As proof-of-principle, "NAMB" chemistry was utilized for the synthesis of the dopamine D2/D3 antagonist [18F]fallypride.

New chemical and radiochemical routes to [18F]Rho6G-DEG-F, a delocalized lipophilic cation for myocardial perfusion imaging with PET.

New chemical and radiochemical syntheses are described for the preparation of [18F]Rho6G-DEG-F, an 18F-labeled analogue of the fluoresecent dye rhodamine 6G, which has shown promise as myocardidal perfusion imaging agent. Tosylated precursors of [18F]Rho6G-DEG-F amenable to 18F-labeling were obtained either through a two-step synthesis from rhodamine 6G lactone (33% yield), or in one step from rhodamine 575 (64% yield), then purified by preparative C18 chromatography. Manual synthesis of [18F]Rho6G-DEG-F was achieved in a single radiochemical step from either the tosylate salt or the tosylate/formate double salt in DMSO under standard nucleophillic aliphatic 18F-fluorination conditions (K[18F]F/K2CO3/Kryptofix 2.2.2.). Incorporation of the [18F]F- was found to be satisfactory (≥34% by TLC), despite the protic character of the precursor molecules. [18F]Rho6G-DEG-F was manually synthesized in final decay-corrected radiochemical yields of 11-26% (tosylate salt) and 9-21% (tosylate/formate double salt). The protocol was transferred to an automated synthesis unit, where the product was obtained in 3-9% radiochemical yield (n=3) decay corrected to start-of-synthesis, >99% radiochemical purity, and a molar activity of 122-267 GBq/µmol (3.3-7.2 Ci/µmol).

Histidine residues underlie Congo red binding to A beta analogs.

The binding mechanism of Congo red (CR) to Alzheimer's disease (AD) amyloid fibrils (A beta) in terms of binding affinity and number of sites was quantitated from absorption spectroscopy (at 200-700 nm) by measuring the concentration of CR bound (CR-B) to AD A beta assemblies as a function of CR concentration and pH in 80% ethanol. The rationale for the use of this high concentration of ethanol derives from its use in histological screens for amyloid in tissue sections. Moreover, free CR can be separated from bound CR by filtration in ethanolic but not aqueous medium. The A beta analogs studied here included: (1) peptides having different lengths: A beta1-40, A beta11-28, A beta13-28, A beta19-28, A beta11-25; (2) wildtype, control sequences of A beta1-40 and sequences having different natural amino acid substitutions: primate Pr1-40, rodent Ro1-40, hereditary cerebral haemorrhage with amyloidosis, Dutch type (HCHWA-D) Du1-40, primate reverse sequence Pr40-1; and (3) A beta11-25 sequences having different substitutions: H13D, H14D, and D23K. Negative-staining showed that A beta1-40 fibrils in buffer were indistinguishable from those in buffered ethanolic medium. For all amyloid analogs except A beta19-28, which has no histidine residues and showed no CR binding over the entire pH range 4.0-9.5, CR-B decreased as a function of increasing pH. The decrease was steepest at about pH 5 and became zero above pH 7. For analogs having the same number of histidines, CR-B fell on the same binding curve, indicating that histidine residues are the likely binding sites for CR in this medium. The pH titration of the binding was parameterized by the stoichiometry of dye to the sites, the number of histidines per molecule, the binding dissociation constant Kd, and the apparent proton dissociation constant pK of the histidine; and the calculated pH-titration curves were found to fit the observed ones. For the peptides having 1-3 histidines the average pK was 5.0-5.5, which was similar to the expected pK of histidine in low dielectric medium (80% ethanol), and the Kd's were 2.8-5.9 microM. That histidine residues underlie CR binding in A beta amyloid is consistent with previous findings that A beta peptides sediment as fibrillar assemblies at pH-3-7 and bind Congo red over the same pH range in aqueous medium. Further, the conformation near the binding motif His13-His14-Gln15-Lys16 in A beta assemblies is not greatly altered in 80% ethanol.

Rapid renal single-photon emission tomography by continuous infusion of iridium-191m.

Continuous infusion of iridium-191m (t1/2 = 5 s), produced with an 191Os/191mIr generator, was used to obtain rapid high-resolution single-photon emission tomography (SPET) of renal blood flow in the rabbit. SPET scans of the abdomen were obtained with a triple-detector SPET system (MS3, Siemens Gammasonics). The generator was eluted at a flow rate of 3 ml/min, which delivered a steady-state dose of 170 MBq (4.5 mCi) of 191mIr. The total 191Os breakthrough was 850 kBq (23 microCi). A 5-min SPET acquisition recorded a total of 2.8 million counts, resulting in images of high technical quality. Volume-rendered images clearly showed the abdominal aorta, splenic artery, spleen, renal arteries, kidneys and splanchnic vasculature. Tomographic slices through the kidneys revealed tracer primarily within the renal cortices without visualization of the collecting system. The estimated effective dose equivalent for a 5 min infusion of 191mIr at a steady-state dose of 170 MBq is 0.74 mSv compared with 2.7 mSv from a 170 MBq dose of 99mTc-DMSA. This study demonstrates the feasibility of high-resolution SPET of regional renal perfusion in the rabbit by continuous intravenous infusion of 191mIr. The renal distribution of continuously infused 191mIr is largely within the cortices, with minimal or no detectable activity in the region of the renal pelvicalyceal system. Using this technique, cortical renal SPET can be completed much more rapidly (< 5 min) than with conventional renal cortical imaging agents, which suggests that this technique could be applied to the observation of rapid changes in renal perfusion such as those resulting from pharmacologic intervention, obviating the need for the patient to return for additional visits. Additional studies are required to (a) validate the methodology in larger animals prior to considering the potential for use in human beings, (b) optimize the generator design for continuous infusion, and (c) evaluate the changes in the distribution of 191mIr that occur in animal models of altered renal perfusion.

Synthesis and biodistribution of 64Cu-labeled monocationic diiminedioxime copper(II) complexes.

Monocationic copper(II) complexes of three derivatives of the diiminedioxime ligand 2,10-dioximino-3,9-dimethyl-4,8-diazaundeca-3,8-diene were labeled with 64Cu in high radiochemical yield, and the biodistribution of the complexes was measured in mice. The concentration of the complexes in the heart was low, but the partition coefficients of the complexes are less than optimal for a myocardial perfusion agent. All three complexes are resistant to reduction by glutathione in vitro. This suggests that more lipophilic derivatives of these compounds merit further investigation as possible myocardial perfusion agents.

Comparison of uptake of 99mTc-alkylisonitriles in the rat 9L gliosarcoma tumor model.

The accumulation of three 99mTc(I) alkyl isonitriles was compared in vitro and in vivo using 9L gliosarcoma cells. In vitro, the uptake of 99mTc-EIBI and 99mTc-EPI was higher than that of 99mTc-MIBI. In vivo, however, there was no difference in the tumor concentration at 15 or 60 min postinjection and only a small difference at 24 h. The differences in uptake observed in vitro are apparently offset in vivo by differences in delivery of the tracers to the tumor.

Ictal and interictal technetium-99m-bicisate brain SPECT in children with refractory epilepsy.

UNLABELLED: Identification of epileptogenic foci in patients with refractory epilepsy remains a significant diagnostic challenge. Magnetic resonance imaging studies frequently fail to reveal an anatomic origin for the seizures, and scalp electroencephalography is often limited to identification of the involved hemisphere. Functional imaging modalities such as PET and SPECT are more promising tools for this application because they reflect the functional pathology associated with the seizure. These changes are more pronounced ictally, but until recently, no radiopharmaceutical was available that could be used routinely for ictal SPECT. The present study was therefore undertaken to determine whether 99mTc-bicisate could be used in ictal SPECT in pediatric patients with refractory epilepsy, to compare the patterns of ictal and interictal blood flow in these patients and to compare the localization information provided by ictal SPECT with that available from other techniques. METHODS: Technetium-99m-bicisate/SPECT was compared prospectively with scalp EEG for its ability to identify a possible seizure focus in pediatric patients with refractory epilepsy. Ictal and interictal SPECT studies were performed in 10 patients (3-19 yr old, mean age 10.9 +/- 4.3 yr; 7 female, 3 male) in whom MRI scans revealed no lesions that might be responsible for the seizures. RESULTS: Ictal SPECT was performed in all patients, and all ictal studies revealed focal perfusion abnormalities. By comparison, four of the interictal SPECT studies showed regional hypoperfusion that corresponded to the regions of hyperperfusion in the ictal studies, and three showed regional hyperperfusion corresponding to the hyperperfused regions in the ictal studies. Three interictal studies revealed no abnormal perfusion. Scalp EEG provided localization information in five patients. CONCLUSION: These initial results suggest that ictal SPECT with 99mTc-bicisate is a more promising tool for the identification of epileptogenic foci than interictal SPECT or scalp EEG in patients without focal abnormalities on MRI.

An improved 191Os/191mIr generator using a hybrid anion exchanger.

Iridium-191m is an attractive radionuclide for first-pass radionuclide angiography, but development of an 191Os/191mIr generator with high 191mIr yield has proven difficult. The use of trans-dioxobisoxalatoosmate(VI) as a parent species results in a higher initial yield (20 to 25%/mL), but the yield decreases over time. Using an anion-exchange column of tridodecylmethylammonium chloride-treated silica gel and AG MP-1 resin, we have developed an improved 191Os/191mIr generator with higher initial yield (25 to 30%/mL) and a slower rate of decrease than the previous design.

Tumor uptake of 99mTc-MIBI and 201Tl by a 9L gliosarcoma brain tumor model in rats.

There have been several recent case reports of the accumulation of 99mTc-MIBI [hexakismethoxyisobutylisonitriletechnetium(I), Cardiolite, Sestamibi] in tumors, but no reports of the uptake of this radiopharmaceutical in an animal model. To address this question, the biodistributions of 99mTc-MIBI and 201Tl were compared in Fisher rats bearing 9L gliosarcomas. The results showed that, although the absolute uptake of the tracers by the tumor is relatively low (< 1% ID/g), the tumor-to-normal brain ratios are greater than 6:1 because of low uptake by normal brain. The tumor-to-normal brain ratio of 99mTc-MIBI exceeds that of other currently available 99mTc radiopharmaceuticals suggesting that 99mTc-MIBI may be of particular value in the clinical evaluation of brain tumors and that further investigation of this class of compounds as tumor-avid radiopharmaceuticals is necessary.

Thallium-201 versus technetium-99m-MIBI SPECT in evaluation of childhood brain tumors: a within-subject comparison.

We previously found that 201TI SPECT is a highly specific agent for detection of metabolic activity of childhood brain tumors. To compare the relative diagnostic accuracy of 201TI and a technetium-based tumor-avid agent, we have obtained SPECT in 19 children using 201TI (37-111 MBq) followed immediately by 99mTc-methoxyisobutylisonitrile (MIBI) (370-740 MBq) intravenously. Moderate to intense focal uptake of both tracers characterized true positive cases (n = 6). Lesion boundaries were better defined by MIBI. Uptake of MIBI by choroid plexus occurred despite pretreatment with potassium perchlorate (6 mg/kg) and complicated interpretation of deep/paraventricular lesions. Preliminary assessment indicated sensitivity approximately 67% (TI and MIBI); specificity approximately 91% (TI); approximately 100% (MIBI). Two tumors (medulloblastoma, dysgerminoma) were TI/MIBI nonavid. Semi-quantitative assessment of tracer uptake was made using a ratio of radioactivity in tumor-containing areas compared to uninvolved brain. Ratio values were (mean +/- s.d.) 7.88 +/- 7.70 (TI) and 27.1 +/- 36.41 (MIBI). The spectrum of tumor avidity is similar for TI and MIBI. Clearer identification of boundaries by MIBI may be an advantage in applications, e.g., radiotherapy port planning.

Evaluation of osmium(II)-nitrosyl complexes as a method to increase the yield of the 191Os-191mIr generator.

The nitrosyl complexes pentachloronitrosylosmate(II), [OsCl5(NO)]2-, and hydroxytetranitronitrosylosmate(II), [Os(OH)(NO2)4(NO)]2-, were evaluated as parent species for use on the 191Os-191mIr generator in an attempt to increase the 191mIr yield of the generator by providing a direct route to a chemically stable 191mIr daughter. The uptake of the 191Os-labeled complexes by the inorganic ion-exchangers ZrO2, SnO2, PbS, MnO2 and Al2O3 and the organic resin AG MP-1 was measured and prototype generators were prepared using those exchangers that demonstrated greater than 90% uptake of the 191Os-labeled complexes. The 191mIr(III)-nitrosyl complexes produced subsequent to beta- decay of the 191Os-nitrosyl parent complexes were found to undergo secondary chemical reactions to form nitro (NO2-) complexes that were tightly retained on the ion exchanger limiting 191mIr yield to less than 5%.

SPECT imaging of pediatric brain tumor with hexakis (methoxyisobutylisonitrile) technetium (I).

Technetium-99m-Hexamibi [Hexakis (methoxyisobutylisonitrile) technetium (i)] was developed as a myocardial perfusion agent with biologic properties similar to those of thallium-201 (201TI). As 201TI has recently been observed to be of value for the diagnosis of brain tumors when used in conjunction with single-photon emission computed tomography (SPECT) imaging technology, the possibility that the biologic similarity of the two radiopharmaceuticals extended to their affinity for tumors was tested. A 5-yr-old female patient with a brain stem astrocytoma showed marked focal uptake of 99mTc-Hexamibi at the site of tumor recurrence as defined by biopsy and prior 201TI/SPECT study. Tumor-to-normal cortex radioactivity ratios for the 99mTc-Hexamibi/SPECT study were 132:1 and the spatial resolution of the 99mTc-Hexamibi images was high. This observation suggests that 99mTc-Hexamibi merits further study as a potential agent for SPECT imaging of human brain tumors.

Blunt aortic trauma: signs of high risk.

In the last 10 years, our center has managed 60 cases of aortic rupture from blunt chest trauma. Nineteen patients died (32%), 11 of whom were moribund on admission. Two patients out of ten who had undergone aortography at other institutions arrived at our hospital with massive bleeding in the left chest and died despite immediate operation. Six patients exsanguinated 1 to 2 1/2 hours after admission while aortography was being arranged or performed, and review of these cases to identify clinical signs of high risk revealed that left hemothorax, pseudocoarctation, and/or supraclavicular hematoma were present in five of the six. It appeared that the survival rate of patients suspected of blunt aortic trauma who had any of these clinical signs might be improved if they were taken directly to the operating room. To investigate this possibility we reviewed all cases from the past 10 years (excluding patients moribund on arrival or who had aortography elsewhere) in whom suspicion of aortic trauma led to aortography or surgery. Thirteen of the 17 patients (76%) with one or more signs of high risk had torn the aortic isthmus, compared to 26 of 154 patients (17%) without these signs. Five of the high-risk group (29%) exsanguinated, compared to one (less than 1%) of the others. No patient in this series died from unsuspected aortic trauma, which we attribute to the liberal use of aortography. Except for the patients with exsanguinating hemorrhage preoperatively, there were no operative or postoperative deaths.(ABSTRACT TRUNCATED AT 250 WORDS)

Synthesis and biological properties of the lipophilic technetium-99m complex 99mTc(acac)3.

In the development of technetium-99m radiopharmaceuticals for the evaluation of regional cerebral perfusion, one series of complexes that has remained unexplored is the neutral lipophilic tris complexes formed with beta-diketonato ligands. The prototype complex of this series, tris(2,4-pentanedionato) technetium(III), has been prepared via a new synthetic route and chemically characterized using 99Tc and the biodistribution of the no-carrier-added 99mTc complex has been determined. The 99mTc complex was found to be distributed throughout the body with persistent high blood levels indicative of a high degree of protein binding. The primary route of excretion was the hepatobiliary system as indicated by the appearance of 99mTc in the gut and feces at longer sample times post-injection. Although this complex was not retained by the brain, it does provide a starting point from which a more effective agent might be developed.

An osmium-191/iridium-191m radionuclide generator using an oxalato osmate parent complex.

A new osmium-191/iridium-191m (191Os/191mIr) radionuclide generator has been developed that offers high 191mIr yield (greater than 20%/ml) and low 191Os breakthrough (less than 5 X 10(-4)%/ml) when eluted with a solution of 0.001 M oxalic acid and 0.9% (normal) saline. This is the first 191Os/191mIr generator that combines the advantages of high 191mIr yield, extremely low 191Os breakthrough, and an eluate that does not require buffering prior to injection. These improvements in performance were accomplished through use of the chelate transdioxobisoxalatoosmate(VI) as the parent complex on the generator. The clinical result of the combination of higher yield and lower breakthrough is a 100-fold decrease in the estimated patient radiation dose compared with the same study performed with technetium-99m (99mTc), and the injectable eluate makes the generator easier to use. Acute and subacute toxicity studies performed on this generator eluate have shown no adverse effects attributable to the eluate.

Evaluation of the renal clearance of technetium-99m PAHIDA in dogs.

The renal clearance of the technetium-99m complex of para[(biscarboxylmethyl)-aminomethylcarboxyamino]hippuric acid ([99mTc]PAHIDA), has been previously studied in rodents and falls between that of [99mTc]DTPA (diethylenetriaminepentaacetic acid) and iodine-131 (131I) orthoiodohippuran (OIH). To investigate the effect of species variation, the plasma clearance of [99mTc]PAHIDA was investigated in dogs. The plasma disappearance of the renal agent approached that of [99mTc]DTPA and was significantly less than that of OIH. Despite the structural similarities of the PAHIDA ligand and aminohippurate, the [99mTc]PAHIDA complex undergoes little, if any, tubular secretion in the canine kidney.

Comparison of ultrashort-lived iridium-191m with technetium-99m for first pass radionuclide angiocardiographic evaluation of right and left ventricular function in adults.

Ultrashort-lived iridium-191m (Ir-191m, physical half-life = 5.0 seconds) has been used in angiocardiography, primarily in pediatric patients. A theoretical obstacle to more widespread use of Ir-191m is the belief that its physical half-life is too short to permit evaluation of left ventricular function in adult patients. To evaluate its usefulness in adults, first pass ejection fractions of the left and right ventricles determined with use of Ir-191m and technetium-99m (Tc-99m) were compared in 33 adult patients. An osmium-191m----iridium-191m (Os-191----Ir-191m) generator was employed to deliver doses of 150 to 250 mCi (5.5 to 9.2 GBq) of Ir-191m for intravenous injection. The whole body radiation absorbed dose with Ir-191m was 15 to 25 mrad. High quality angiocardiograms were obtained with both Tc-99m and Ir-191m. Total counts per image for the right ventricle were 51,000 +/- 8,000 (mean +/- SD) for Ir-191m and 30,000 +/- 8,000 for Tc-99m. The left ventricular counts were comparable for both radiotracers (25,000 +/- 7,000 for Ir-191m and 25,000 +/- 8,000 for Tc-99m). Right ventricular ejection fractions were similar: 44 +/- 8% for Ir-191m and 47 +/- 9% for Tc-99m. The correlation coefficient was 0.93 with a standard deviation of the regression of 3.1% ejection fraction units. The left ventricular ejection fractions were also similar: 45 +/- 14% for Ir-191m and 46 +/- 13% for Tc-99m. The left ventricular ejection fraction correlation coefficient was 0.96 with a standard deviation of the regression of 3.7%.(ABSTRACT TRUNCATED AT 250 WORDS)

The development of an 191Os----191mIr generator using an osmium chelate parent complex--I. Trans-dioxobismalonatoosmate(VI).

A 191Os----191mIr generator has been developed that has higher 191mIr yield and lower 191Os breakthrough than previous designs. These improvements have been realized through the use of the osmium chelate complex trans-dioxobismalonatoosmate(VI) as the parent species on the generator. The new generator provides an initial 191mIr yield of 40%/mL and 191Os breakthrough of 2-3 X 10(-3)% when eluted with a solution of 0.05 M malonic acid/0.10 M sodium chloride at pH 4. Other advantages of the new design include faster clearance of the 191Os breakthrough products and simpler assembly.