Measurement of the arterial concentration of Gd-DTPA using MRI: a step toward quantitative perfusion imaging

A noninvasive method using an inversion recovery turbo-FLASH for dynamic measurement of the arterial input function represented by the bolus passage of Gd-DTPA in the descending aorta is presented, and the results are compared with the input function obtained by arterial blood samples. A good accordance between the two input functions was found, indicating that it is possible to measure the input function to the myocardium using MRI. A variation between the two concentration curves of 5% at upslope, 2.7% at peak point, and < 7% at downslope was found. The study also indicates that a short inversion time < 250 ms has to be used to ensure correct measurement of peak concentration.

Detection and quantitation of gadolinium chelates in human serum and urine by high-performance liquid chromatography and post-column derivatization of gadolinium with Arsenazo III

A narrow-bore high-performance liquid chromatography method was developed for simultaneous separation of gadolinium diethylenetriaminepentaacetic acid (GdDTPA), the monomethylamide (GdDTPA-MMA) and the bis-methylamide (GdDTPA-BMA) in human serum and urine. The Gd complexes were detected at 658 nm after post-column derivatization with Arsenazo III. The serum samples were ultrafiltrated, whereas the urine samples were centrifuged and diluted before analysis. With an injection volume of 10 microliters on a 2.1 mm ID reversed-phase column, the limit of detection of GdDTPA-BMA was calculated as 0.3 microM and 1.1 microM in serum and urine, respectively. The method was validated with respect to GdDTPA-BMA with a limit of quantification set to 2 microM and 10 microM in serum and urine, respectively. The best fit of the calibration curve was obtained using non-linear regression according to the equation Y = A+BX+CX2 in the concentration ranges 2-800 microM and 10-2000 microM of GdDTPA-BMA in serum and urine, respectively. The precision of the method was found to range from 1 to 4% RSD. The recoveries of GdDTPA-BMA spiked in serum and urine were higher than 95% with an RSD equal to or less than 4%. The serum samples were stable for at least 5 months when stored at -70 degrees C, and the urine samples were stable for a least 6 months when stored at -20 degrees C.

Electrophoretic method for the quantitative determination of a benzyl-DTPA ligand in DTPA monoclonal antibody conjugates

A simple electrophoretic IEF procedure was developed for the quantitation of bifunctional DTPA ligand molecules in DTPA-protein conjugates. From a calibration plot of pI versus substitution ratios of reference conjugates, the concentrations of DTPA conjugated to protein were determined. Molar ratios of DTPA to protein agreed satisfactorily with the ratios obtained by a spectrophotometric technique using a colored yttrium(III) complex of arsenazo III. The IEF method was successfully applied on preparations of benzyl-DTPA to mAbs MOPC-21, SC-20 (aCEA), and human serum albumin.

Metabolism of receptor targeted 111In-DTPA-glycoproteins: identification of 111In-DTPA-epsilon-lysine as the primary metabolic and excretory product

The hepatic and renal retention of indium-111 (111In) from 111In-labeled polypeptides has been the subject of many investigations. Because the lysosome is a common intracellular destination for the degradation of polypeptides, we studied the lysosomal metabolism of 111In-DTPA-labeled glycoproteins targeted to cell surface receptors in vitro and in vivo. We found that 111In-DTPA-glycoproteins were degraded to 111In-DTPA-epsilon-lysine, which was slowly released from cells and recovered intact in urine and feces. These results suggest a mechanism for 111In retention at target and non-target sites.

Determination of non-protein-bound iron in human synovial fluid by high-performance liquid chromatography with electrochemical detection

Non-protein-bound iron in human synovial fluid was determined using high-performance liquid chromatography with electrochemical detection. The procedure was based on the separation of the iron-diethylenetriaminepentaacetic acid (DTPA) complex formed directly on a chromatographic column containing an anion-exchange resin followed by electrochemical detection. The method enabled more than 0.1 microM Fe(III) to be determined with an injection volume of 10 microliters. A mixture of synovial fluid, 20 microM DTPA and acetate buffer was incubated in the presence and absence of superoxide (O2-) generated by a xanthine-xanthine oxidase system and was ultrafiltered through a 30,000 molecular mass cut-off filter. No iron was detected in the ultrafiltrate at physiological pH. However, the presence of iron was observed in the ultrafiltrate at low pH, and O2- facilitated the release of iron into the synovial fluid. This result suggested that in an inflamed joint with generated O2- and decreased pH, iron may be released into the synovial fluid.

Hepatic kinetics and magnetic resonance imaging of gadolinium ethoxybenzyl diethylenetriaminepentacetic acid (Gd-EOB-DTPA) in dogs

This complex study was designed to measure the transport and excretion characteristics of gadolinium ethoxybenzyl diethylenetriaminepentacetic acid (Gd-EOB-DTPA) in dog's livers following bolus and infusion. Simultaneous T1 magnetic resonance imaging was performed to measure maximum signal enhancement. Anaesthetized dogs had cannulation of the common bile duct and urinary bladder for collections and cannulation of the femoral artery and vein for monitoring, blood sampling and infusion. Gd-EOB-DTPA was administered by bolus (range 12.5-200 mumol/kg) and infusion (range 0.4-6.4 mumol/min per kg). An hepatic transport maximum 0.09-0.15 mumol/min/kg was achieved with a blood concentration of 0.03-0.06 mumol/mL. Marked hepatic affinity for Gd-EOB-DTPA was demonstrated with measurements of liver concentration. Maximum T1 signal enhancement was achieved with blood Gd-EOB-DTPA concentration of 0.02-0.03 mumol/mL and a liver concentration of 1-2 mumol/g. The transport maximum for Gd-EOB-DTPA in the dog was similar to that for ipodate and iodipamide and effective imaging was achieved with sub-maximal doses. The maximum signal enhancement at blood concentrations less than required for maximum transport suggest a wide latitude for effective clinical imaging.

Evaluation of copper-labeled bifunctional chelate-albumin conjugates for blood pool imaging

62Cu(T1/2 = 9.8 min) is a generator-produced positron-emitting radionuclide with a half-life amenable to blood-pool imaging with PET. Three bifunctional chelates [cyclic anhydride of diethylenetriaminepentaacetic acid (cDTPAA), 6-bromoacetamidobenzyl-1,4,8,11-tetraazacyclotetradecane-N,N ',N", N"'-tetraacetic acid (BAT), and p-carboxyethylphenylglyoxal-bis-(4N-methyl-thiosemicarbazone (CE-DTS)] were conjugated to HSA and labeled with 67Cu. The labeling efficiency of 67Cu-DTS-HSA was > 90%, whereas the labeling yields of 67Cu-DTPA-HSA and 67Cu-benzyl-TETA-HSA were less than 70%. Blood clearance and biodistribution of these three 67Cu-labeled conjugates were determined in rats. Of the three 67Cu-labeled bifunctional chelate-HSA conjugates, 67Cu-benzyl-TETA-HSA remained in the blood pool the longest, achieving stable blood levels at times longer than 24 h post-injection. The 67Cu radioactivity cleared the blood within 60 min post-injection of 67Cu-DTS-HSA, and within 10 min after administration of 67Cu-DTPA-HSA, indicating the dissociation of Cu2+ from these conjugates. Copper-labeled DTS-HSA achieved stable blood concentrations for at least 30 min post-injection and was therefore evaluated as a vascular imaging agent. DTS-HSA and benzyl-TETA-HSA were labeled with 62Cu and administered to a dog for blood-pool imaging using PET. Images were nearly identical to an image taken after administration of C15O. Because of the high labeling efficiency, DTS-HSA can be labeled with 62Cu without purification, making it more practical than 62Cu-benzyl-TETA-HSA as a blood-pool imaging agent.(ABSTRACT TRUNCATED AT 250 WORDS)

Spectrophotometric method for the determination of a bifunctional DTPA ligand in DTPA-monoclonal antibody conjugates

A simple spectrophotometric method was developed to quantitate micromolar concentrations of a bifunctional DTPA ligand in DTPA monoclonal antibody (mAb) conjugates. Titration of a brightly colored 1:2 yttrium (III) complex of arsenazo III with the ligand 1B4M-DTPA obeyed Beer's law over the concentration range 0-2.0 microM 1B4M-DTPA at 652 nm. From a calibration plot of absorbance versus 1B4M molarity, concentrations of 1B4M-DTPA conjugated to mAb were determined. Mole ratios of 1B4M-DTPA to mAb agreed satisfactorily with the ratios obtained by a radioanalytical technique using carbon-14-labeled 1B4M-DTPA and a binding assay using 111In. The spectrophotometric method was applied successfully to the preparation of 1B4M-DTPA mAb anti-TAC, a mAb conjugate used in clinical trials of 90Y radioimmunotherapy.

Investigations of N-linked macrocycles for 111In and 90Y labeling of proteins

To simplify the synthesis of macrocyclic chelators, commercially available macrocyclic amines were condensed with halogenated acetic acid to prepare the five chelators 12N4 (DOTA), 14N4 (TETA), 15N4, 9N3 and 12N3. Only 12N4 and 9N3 showed efficient labeling of the free chelator with 111In and 90Y. Serum stability studies at 37 degrees C with In-labeled DTPA, 12N4 and 9N3 showed no loss of label over 2 days whereas, with 90Y, only 12N4 showed stabilities comparable to DTPA. The 12N4 chelator was derivatized by attaching biotin on one N-acetate group to stimulate the attachment to protein. The serum stability for both 111In and 90Y was identical to that of biotin derivatized DTPA and lower than that of the free chelators. Biodistribution studies in normal mice of a model protein (avidin) labeled with 90Y via biotinylated 12N4 and biotinylated DTPA showed identical distribution at 1 day except in bone where the %ID/g for the macrocyclic-conjugated protein (3.4 +/- 0.5, N = 8) was significantly (P less than 0.001) lower than that of the DTPA-conjugated protein (9.4 +/- 0.9, N = 7). In conclusion, macrocycles may be readily synthesized from the macrocyclic amines and several show useful stabilities with In and Y. When N-linked to a protein, the Y biodistribution was found to be superior to that of the corresponding DTPA-coupled protein.

Characterization of antibody-chelator conjugates: determination of chelator content by terbium fluorescence titration

Fluorescence titrations were performed by adding varying mole ratios of terbium(III) to antibody conjugates formed by benzyl isothiocyanate derivatives of three different polyaminopolycarboxylate chelators (NTA, EDTA, and DTPA) and the results compared to values for average chelator content obtained by cobalt-57 binding assays. For two different murine monoclonal antibodies, the average chelator content obtained by terbium fluorescence titration correlated closely with that measured by the cobalt-57 binding assay. It is concluded that lanthanide fluorescence titrations provide a useful alternative to radiometal binding assays for the determination of chelator content in protein-chelator conjugates.

Evaluation of kidney function in renal transplant patients receiving long-term cyclosporine

We prospectively assessed renal function in a group of 29 renal transplant patients receiving cyclosporine (CsA) in order to determine the course of their renal function over time and the relationship between different markers of glomerular function. We measured serum creatinine, DPTA, and creatinine clearances, and urinary albumin excretion. The clinical course of 24 patients (83%) permitted repeat studies over a period of 32 +/- 1 (SEM) months, and in these patients DTPA clearance, creatinine clearance, and the serum creatinine concentration did not vary with time. Five of the patients (17%) lost their grafts and returned to dialysis. On initial evaluation patients who lost their grafts had a lower DPTA clearance than those whose function was maintained (29 +/- 3 v 46 +/- 2 mL/min/1.73 m2 body surface area [BSA], respectively, P less than 0.005) and all of them had a DTPA clearance of less than 40 mL/min/1.73 m2 BSA. There was an inverse correlation between the log of the urinary albumin excretion and the DTPA clearance (n = 33, r = -0.59, P less than 0.001), a direct correlation with the serum creatinine concentration (N = 33, r = 0.89, P less than 0.0001), but no correlation with time after transplantation. Thus, despite the continued use of CsA, renal function over time was stable in patients who underwent repeated studies, as was the relationship between the DTPA clearance and the clinically used markers of transplant function, the serum creatinine concentration, and the creatinine clearance.

Technetium-99m DTPA does not break down during ultrasound nebulization

For several years aerosolized 99Tcm-DTPA has been used for studies of pulmonary permeability. Comparable results have been obtained regardless of the 99Tcm-DTPA having been nebulized in an ultrasound nebulizer or a jet nebulizer. It was therefore surprising when in a recent study it was observed that more than 90% of a commercially available 99Tcm-DTPA (Squibb) was dissociated into 99TcmO4- and DTPA during ultrasound nebulization. To verify this observation we performed chromatography of seven commercially available DTPA-labelling kits (including that of Squibb). Four different test preparations of each of the kits were analysed: (1) stock solution of 99Tcm-DTPA; (2) heated (80 degrees C) 99Tcm-DTPA; (3) 99Tcm-DTPA nebulized by a DeVilbiss ultrasound nebulizer; (4) 99Tcm-DTPA nebulized by a Varic ultrasound nebulizer. In no case were we able to demonstrate more than 1.0% reduced pertechnetate (99TcmO2) or more than 0.9% free 99TcmO4- after either heating or ultrasound nebulization. A maximum of 5.6% 99TcmO2 could be demonstrated in the stock solution if chromatography was done immediately after the preparation, but only 15 min later no more than 0.9% 99TcmO2 was present. We conclude that there is no essential chemical breakdown of 99Tcm-DTPA during ultrasound nebulization. Caution should be taken not to use the 99Tcm-DTPA until 15 min after its preparation.

Indirect spectrophotometric determination of BIDA, DISIDA, DTPA and MDP in labelled compounds

N-(4-(n-butyl)-acetanilide)iminodiacetic acid (BIDA), N-(2,6-diisopropylacetanilide)iminodiacetic acid (DISIDA), diethylenetriaminepentaacetic acid (DTPA) and methylene diphosphonic acid (MDP) are used in labelling kits. The contents of BIDA, DISIDA or MDP of the 99mTc-labelled compounds can be determined (indirectly) spectrophotometrically with copper, eriochrome cyaanine R (ECC) and dodecylethyldimethylammonium bromide (DEDA) in a sodium barbital buffered system at pH 8.5. The calibration curves obey Beer's Law from 0 to 40 micrograms/25 mL for BIDA and DISIDA, 0 to 60 micrograms/25 mL for DTPA and 0 to 100 micrograms/10 mL for MDP.

Chemical breakdown of technetium-99m DTPA during nebulization

Aerosols of 99mTc diethylenetriaminepentaacetic acid ([99mTc]DTPA) used for measuring lung permeability and lung ventilation require a radioaerosol delivery system to produce an aerosol with reproducible size and radiochemical purity. To test how well nebulizers meet this requirement, radiochemical purity of aerosols produced with a jet and an ultrasonic nebulizer was evaluated. The activity median aerodynamic diameter (AMAD) and geometric standard deviation (sigma g) of radioaerosols were 0.46 micron (sigma g = 1.6) for the jet nebulizer and 0.70 micron (sigma g = 1.7) for the ultrasonic nebulizer. Paper and liquid chromatographic assays were obtained on the [99mTc]DTPA aerosol solute produced with each nebulizer. The results of these tests showed major differences in radiochemical purity. Aerosols produced in the jet nebulizer consistently showed greater than 90% of the radioactivity bound to the DTPA ligand whereas aerosols produced in the ultrasonic nebulizer showed less than 10% of the radioactivity bound to DTPA. The results support the need to test radiochemical purity of aerosols before using an aerosol nebulizer for pulmonary imaging and clearance studies.

A method for direct quantification of the amount of DTPA in 111In monoclonal antibody preparations

The bicyclic anhydride of DTPA-1-14C (BADTPA-1-14C) was synthesized and reacted with an antibody to human melanoma associated antigen (MAA) and with one to human class II major histocompatibility complex antigen (HLA-DR). DTPA-1-C incorporation per mole of anti MAA at molar ratios of 1:1 to 200:1 ranged from 0.5 to 25, while immunoreactivity ranged from 49 to 9%. With antibody to HLA-DR, results were similar. Anti MAA, but not anti HLA-DR, demonstrated polymerization upon conjugation. BADTPA-1-14C provides a convenient and accurate method for measuring the amount of DTPA in monoclonal antibody preparations and its effect on immunoreactivity.

Optimization of the DTPA mixed-anhydride reaction with antibodies at low concentration

Diethylenetriaminepentaacetic acid (DTPA) was conjugated with antibody to human serum albumin (Ab) at low concentration (300 micrograms/ml, 2.0 microM) via the DTPA carboxycarbonyl mixed-anhydride method. To study parameters determining the balance between the degree of conjugation and the antibody-binding activity of Ab, a known concentration of the anhydride prepared at isobutylchloroformate (IBC)-to-DTPA ratios of 1, 2.1, or 4.2 was reacted with Ab. The percentage yields of the anhydride were determined by spectrophotometric and gravimetric titration. By the former method the percentage yields, based on DTPA concentration, were 18, 24, and 220, respectively, when the IBC-to-DTPA ratios were 1, 2.1, and 4.2. The corresponding percentage yields were 17, 39, and 262 when determined by the latter method. When the anhydride was prepared at an IBC-to-DTPA ratio of 2.1, an optimum conjugation giving three indium atoms per Ab was obtained, with 64% retention of antibody-binding activity. For an IBC-to-DTPA ratio of 1, the antibody retained almost 100% binding activity but the number of indium atoms incorporated (0.2) was too small. For an IBC-to-DTPA ratio of 4.2, up to 22 indium atoms were incorporated but antibody-binding activity was completely destroyed.

Evaluation of five miniature chromatography systems for determining labeling efficiency of technetium Tc 99m pentetate

The reliability and reproducibility of five miniature chromatography systems for the radiochemical purity of 99mTc-labeled technetium Tc 99m pentetate was evaluated. Radiochemical purity of technetium Tc 99m pentetate was determined 15-30 minutes after preparation once a month for nine consecutive months. A reference value was determined by gel filtration or by conventional-length paper chromatography and thin-layer chromatography. Radiochemical purity was determined simultaneously by five miniature chromatography systems. The miniature systems included an in-house system and commercial systems distributed by Ackerman Nuclear, Ashley Innovations, Atomic Products, and Technical Advancement. Each miniature system was tested in duplicate. A follow-up comparison of the Ackerman Nuclear and in-house systems was performed for an additional nine months. Labeling efficiency by the reference method was greater than 97% for all nine months. The miniature systems gave results that were comparable in most months. Very low labeling efficiency occurred with the Ackerman Nuclear system in month 9. The follow-up comparison produced only one unconfirmed result for the Ackerman Nuclear system that would have caused a laboratory to erroneously discard a batch of technetium Tc 99m pentetate. The miniature chromatography systems evaluated generally will give reliable and reproducible results for the radiochemical purity of technetium Tc 99m pentetate for nine months after receipt of the systems.

Quantitative chromatographic method for the determination of low levels of nitrilotriacetic and ethylenediaminetetraacetic acids in diethylenetriaminepentaacetic acid

A quantitative method for determination of low levels (0.05%, w/w) of nitrilotriacetic and ethylenediaminetetraacetic acids in diethylenetriaminepentaacetic acid is described. Palmitic acid is added to the chelator as an internal standard before esterification with methanol containing 2%(v/v)H2SO4. The methyl esters of palmitic, nitrilotriacetic, and ethylenediaminetetraacetic acids are first separated from diethylenetriaminepentaacetate by silicic acid column chromatography and are subsequently quantitated by gas-liquid chromatography. The method is both accurate and reproducible with less than 10% relative error. Thin-layer chromatographic separations of the methyl esters, and quantitation at the 1% level, are also described.