Developing a robust LC-MS/MS method to quantify Zn-DTPA, a zinc chelate in human plasma and urine.

Quantitation of Zn-DTPA (zinc diethylenetriamene pentaacetate, a metal chelate) in complex biological matrix is extremely challenging on account of its special physiochemical properties. This study aimed to develop a robust and specific liquid chromatography-tandem mass spectrometry (LC-MS/MS) method for determination of Zn-DTPA in human plasma and urine. The purified samples were separated on Proteonavi (250 × 4.6 mm, 5 µm; Shiseido, Ginza, Tokyo, Japan) and a C18 guard column. The mobile phase consisted of methanol-2 mm ammonium formate (pH 6.3)-ammonia solution (50:50:0.015, v/v/v), flow rate 0.45 mL/min. The linear concentration ranges of the calibration curves for Zn-DTPA were 1-100 µg/mL in plasma and 10-2000 µg/mL in urine. The intra- and inter-day precisions for quality control (QC) samples were from 1.8 to 14.6% for Zn-DTPA and the accuracies for QC samples were from -4.8 to 8.2%. This method was fully validated and successfully applied to the quantitation of Zn-DTPA in plasma and urine samples of a healthy male volunteer after intravenous infusion administration of Zn-DTPA. The result showed that the concentration of Zn-DTPA in urine was about 20 times that in plasma, and Zn-DTPA was completely (94.7%) excreted through urine in human.

L-arginine supplementation prevents increases in intestinal permeability and bacterial translocation in male Swiss mice subjected to physical exercise under environmental heat stress.

Dietary supplementation with l-arginine has been shown to improve the intestinal barrier in many experimental models. This study investigated the effects of arginine supplementation on the intestinal permeability and bacterial translocation (BT) induced by prolonged physical exercise under heat stress. Under anesthesia, male Swiss mice (5-wk-old) were implanted with an abdominal sensor to record their core body temperature (T(core)). After recovering from surgery, the mice were divided into 3 groups: a non-supplemented group that was fed the standard diet formulated by the American Institute of Nutrition (AIN-93G; control), a non-supplemented group that was fed the AIN-93G diet and subjected to exertional hyperthermia (H-NS), and a group supplemented with l-arginine at 2% and subjected to exertional hyperthermia (H-Arg). After 7 d of treatment, the H-NS and H-Arg mice were forced to run on a treadmill (60 min, 8 m/min) in a warm environment (34°C). The control mice remained at 24°C. Thirty min before the exercise or control trials, the mice received a diethylenetriamine pentaacetic acid (DTPA) solution labeled with technetium-99m ((99m)Tc-DTPA) or (99m)Tc-Escherichia coli by gavage to assess intestinal permeability and BT, respectively. The H-NS mice terminated the exercise with T(core) values of ∼40°C, and, 4 h later, presented a 12-fold increase in the blood uptake of (99m)Tc-DTPA and higher bacterial contents in the blood and liver than the control mice. Although supplementation with arginine did not change the exercise-induced increase in T(core), it prevented the increases in intestinal permeability and BT caused by exertional hyperthermia. Our results indicate that dietary l-arginine supplementation preserves the integrity of the intestinal epithelium during exercise under heat stress, acting through mechanisms that are independent of T(core) regulation.

Effects of nitric oxide synthase inhibition on glutamine action in a bacterial translocation model.

Glutamine may be a precursor for NO synthesis, which may play a crucial role in bacterial translocation (BT). The goal of the present study was to investigate the potential effects of glutamine on BT and the immunological response in an experimental model of NO synthase inhibition by NG-nitro-L-arginine methyl ester (l-NAME). Mice were randomly assigned to four groups: sham; intestinal obstruction (IO); IO+500 mg/kg per d glutamine (GLN); IO+GLN plus 10 mg/kg per d l-NAME (GLN/LN). The groups were pretreated for 7 d. BT was induced by ileal ligation and was assessed 18 h later by measuring the radioactivity of 99mTc-Escherichia coli in the blood and organs. Mucosal damage was determined using a histological analysis. Intestinal permeability (IP) was assessed by measuring the levels of 99mTc-diethylenetriaminepentaacetic acid in the blood at 4, 8 and 18 h after surgery. IgA and cytokine concentrations were determined by ELISA in the intestinal fluid and plasma, respectively. BT was increased in the GLN/LN and IO groups than in the GLN and sham groups. IP and intestinal mucosa structure of the sham, GLN and GLN/LN groups were similar. The GLN group had the highest levels of interferon-γ, while IL-10 and secretory IgA levels were higher than those of the IO group but similar to those of the GLN/LN group. The present results suggest that effects of the glutamine pathway on BT were mediated by NO. The latter also interferes with the pro-inflammatory systemic immunological response. On the other hand, IP integrity preserved by the use of glutamine is independent of NO.

Estimating glomerular filtration rate in kidney transplantation: is the new chronic kidney disease epidemiology collaboration equation any better?

BACKGROUND: The new Chronic Kidney Disease Epidemiology Collaboration (CKD-EPI) equation was developed to address the systematic underestimation of the glomerular filtration rate (GFR) by the Modification of Diet in Renal Disease (MDRD) Study equation in patients with a relatively well-preserved kidney function. The performance of the new equation for kidney transplant recipients (KTRs) is unknown. METHODS: We used the plasma clearance of (99m)Tc-diethylenetriamine pentaacetic acid to measure the GFR in a cohort of 207 stable KTRs and estimated the GFR with the new CKD-EPI equation. RESULTS: The mean bias for the CKD-EPI equation of -4.5 mL x min(-1) x (1.73 m(2))(-1) was lower than that of the 4-variable MDRD Study equation; however, the 2 equations showed similar variation of individual biases around the mean or median bias, so that only modest improvement was seen in the overall percentage of GFR estimates within 30% of the measured GFR (84% vs 77% for the CKD-EPI vs MDRD Study equations, respectively). In the cohort with a GFR >60 mL x min(-1) x (1.73 m(2))(-1) (n = 98), the CKD-EPI bias was much less than that of the MDRD Study equation [-7.4 mL x min(-1) x (1.73 m(2))(-1) vs -14.3 mL x min(-1) x (1.73 m(2))(-1)], and an accuracy of + or - 30% was seen for 89% of GFR estimates, compared with 77% with the MDRD Study equation. The variation of the individual biases around the mean bias remained substantial [SD = 13.7 mL x min(-1) x (1.73 m(2))(-1)]. CONCLUSIONS: The CKD-EPI equation shows improved estimation ability, and we recommend that it replace the MDRD Study equation as the currently preferred creatinine-based estimating equation for KTRs. The precision of GFR estimates obtained with the CKD-EPI equation remains suboptimal, however, and we recommend that research on other markers of GFR, such as cystatin C and beta-trace protein, be pursued.

Renal function in infants with sickle cell anemia: baseline data from the BABY HUG trial.

OBJECTIVES: To examine the feasibility and accuracy of glomerular filtration rate (GFR) measurements in infants with sickle cell anemia (SCA). STUDY DESIGN: The NHLBI/NICHD-sponsored Phase III randomized double-blinded placebo-controlled trial (BABY HUG) tests the hypothesis that hydroxyurea can prevent chronic organ damage in SCA. GFR elevation is a coprimary endpoint, measured quantitatively by technetium 99m-labeled diethylenetriaminepentaacetic acid (DTPA) plasma clearance and estimated by the Schwartz equation with height and creatinine. RESULTS: Baseline DTPA GFR measurement was attempted in 191 infants; 176 of 184 completed studies (96%) were interpretable. Average age (mean +/- 1SD) was 13.7 +/- 2.6 months. Average DTPA GFR was 125.2 +/- 34.4 (range 40.2-300.9, normal 91.5 +/- 17.8 mL/min/1.73m(2)), while Schwartz estimates were higher at 184.4 +/- 55.5 mL/min/1.73m(2). DTPA GFR was correlated with Schwartz GFR (r(2) = 0.0658, P = .0012); also with age, weight, height, and kidney volume (all P < .002); but not with hemoglobin, HbF, white blood cell count, reticulocytes, medical events, or splenic function. CONCLUSIONS: Quantitative GFR measurement is feasible but variable among infants with SCA. Schwartz GFR estimates are not highly correlated with quantitative DTPA GFR values. Baseline GFR measurements suggest that renal dysfunction in SCA, evidenced by glomerular hyperfiltration, begins during infancy.

A systematic study on the utility of CHX-A''-DTPA-NCS and NOTA-NCS as bifunctional chelators for 177Lu radiopharmaceuticals.

This paper describes the evaluation of [(R)-2-Amino-3-(4-isothiocyanatophenyl)propyl]-trans-(S,S)-cyclohexane-1,2-diamine-pentaacetic acid (CHX-A''-DTPA-NCS) and 2-S-(4-isothiocyanatobenzyl)-1,4,7-triazacyclononane-1,4,7-triacetic acid (NOTA-NCS) as bifunctional chelators for 177Lu. While 177Lu-CHX-A''-DTPA-NCS could be obtained in high yields at equimolar ratios of lutetium to CHX-A''-DTPA-NCS, >95% yield of 177Lu-NOTA-NCS could be achieved at 1:2M ratio of lutetium to NOTA-NCS. Trace metals reduced the yields of 177Lu-NOTA-NCS significantly as compared to 177Lu-CHX-A''-DTPA-NCS. In vitro stability of 177Lu-CHX-A''-DTPA-NCS was also superior to 177Lu-NOTA-NCS. It could be concluded from this study that among the two chelators evaluated, CHX-A''-DTPA-NCS is more appropriate for preparation of 177Lu radiopharmaceuticals.

A comparison of biodistribution between 111In-DTPA octreotide and 111In-DOTATOC in rats bearing pancreatic tumors.

111In-DTPA octreotide (DTPAOC) has been used for detecting somatostatin receptor positive tumor for years. In-111 DOTA-Tyr3-octreotide (DOTATOC) is newly developed for diagnostic and therapeutic purposes. In this study, we compared the biodistribution and tumor uptake ratio after injection of In-111 DTPAOC and In-111 DOTATOC in rats. Twelve rats bearing pancreatic tumors were divided into two groups: six rats were sacrificed at 4 hr after injection of 3.7 MBq of In-111 DTPAOC and another 6 rats were sacrificed at the same time after injection of 3.7 MBq of In-111 DOTATOC. Samples of various organs were obtained and counted to calculate the tissue concentration. In addition, 12 rats bearing pancreatic tumors were scanned at 4, 24, and 48 hr after injection of 37 MBq of In-111 DTPAOC or In-111 DOTATOC. The tumor uptake ratios (T/N ratio) were calculated. The biodistribution data showed that the activity in the tumor as well as in the kidney was significantly higher in the In-111 DOTATOC group than in the In-111 DTPAOC group, although both radiopharmaceuticals had the expected high affinity to the tumor. The T/N ratios in the In-111 DOTATOC group were also significantly higher than those in the In-111 DTPAOC group at 24 hr after injection. We conclude that In-111 DOTATOC showed lower clearance than In-111 DTPAOC in the rats bearing pancreatic tumors, although both of these radiopharmaceuticals showed expected high tumor uptake.

Species-dependent chelation of (241)Am by DTPA Di-ethyl ester.

Diethylenetriaminepentaacetic acid (DTPA) is an FDA-approved chelating agent for enhancing the elimination of transuranic elements such as americium from the body. Early access to therapy minimizes deposition of these radionuclides in tissues such as the bone. Due to its poor oral bioavailability, DTPA is administered as an IV injection, delaying access. Therefore, a diethyl-ester analog of DTPA, named C2E2, was synthesized as a means to increase oral absorption. As a hexadentate ligand, it was hypothesized that C2E2 was capable of binding americium directly. Therefore, the protonation constants and americium stability constant for C2E2 were determined by potentiometric titration and a solvent extraction method, respectively. C2E2 was shown to bind americium with a log K of 19.6. The concentrations of C2E2, its metabolite C2E1, and DTPA required to achieve effective binding in rat, beagle, and human plasma were studied in vitro. Dose response curves for each ligand were established, and the 50% maximal effective concentrations were determined for each species. As expected, higher concentrations of C2E2 were required to achieve the same degree of binding as DTPA. The results indicated that chelation in beagle plasma is more representative of the human response than rats. Finally, the pharmacokinetics of C2E2 were investigated in beagles, and the data was fit to a two-compartment model with elimination from the central compartment, along with first-order absorption. Based on the in vitro data, a 100 mg kg dose of C2E2 can be expected to have an effective duration of action of 3.8 h in beagles.

Comparison of three remote radiolabelling methods for long-circulating liposomes.

Long-circulating liposomes (LCL) are often used as a drug carrier system to improve the therapeutic index of water-soluble drugs. To track these LCL in vivo, they can be radiolabelled with (111)In-oxine. For this labelling method, generally DTPA is encapsulated in the aqueous phase of LCL (DTPA-LCL). Alternatively, LCL can be labelled with (111)InCl3 after incorporation of DTPA-conjugated DSPE in the lipid bilayer (DTPA-DSPE LCL). Here, we compared the in vitro properties of DTPA-DSPE LCL with those of DTPA LCL and empty LCL. Additionally, we compared the in vivo performance of DTPA-DSPE LCL with those of DTPA LCL in mice. DTPA LCL (88 nm) and empty LCL (84 nm) were labelled with (111)In-oxine, and DTPA-DSPE LCL (83 nm) were labelled with (111)InCl3. Labelling efficiency at increasing specific activity was determined. In vitro stability of (111)In-labelled LCL was determined in human serum at 37 °C. The in vivo properties of (111)In-labelled LCL were determined in mice with a Staphylococcus aureus infection in the thigh muscle. Image acquisition, blood sampling and biodistribution studies were performed 1, 4 (blood sampling only), 24, 48 and 72 h p.i. of (111)In-labelled LCL. DTPA-DSPE LCL could be labelled efficiently at a much higher specific activity compared to DTPA LCL and empty LCL: > 90% at 15 GBq/mmol, > 90% at 150 MBq/mmol and 60­65% at 150 MBq/mmol, respectively. (111)In-labelled DTPA-DSPE LCL and DTPA LCL were stable in human serum, regarding label retention, for at least 48 h at 37 °C (> 98% retention of the radiolabel). In contrast, only 68% radiolabel was retained in empty LCL after 48 h. In vivo targeting of (111)In-DTPA-DSPE LCL to the abscess was comparable to targeting of (111)In-DTPA LCL (3.5 ± 0.9%ID/g and 3.4 ± 0.9%ID/g abscess uptake respectively, 48 h p.i.). In conclusion, labelling of DTPA-DSPE LCL with (111)InCl3 represents a robust, easy and fast procedure which is preferred over the more laborious conventional labelling of DTPA-LCL with (111)In-oxine.

Single-fraction irradiation has no effect on uptake of radiolabeled pegylated liposomes in a tumor xenograft model.

PURPOSE: These studies were performed with the intention of examining the effect of single-fraction doses of radiotherapy (RT) on the tumor deposition of radiolabeled pegylated liposomes in an animal xenograft tumor model. METHODS AND MATERIALS: Human KB head-and-neck xenograft tumors were established in female nude mice. The effect of single fraction tumor RT doses (5, 10, 15, and 20 Gy) on the tumor uptake of intravenously administered (111)In-DTPA-labeled pegylated liposomes (IDLPL) was examined using two protocols: (1) to test the effect of RT delivered 30 min before liposome injection on the time course of tumor uptake over a 96-h period; (2) to test the effect of RT at times ranging from 72-h to 1-h before liposome injection on the levels of liposome uptake at 24 h. Tumor and normal tissue/organ (blood, liver, spleen, lung, and kidney) liposome uptake was determined by dissection and quantitation in a gamma counter. RESULTS: There was no demonstrable effect of RT on tumor uptake of IDLPL (p > 0.1 for all comparisons). Reassuringly, neither was there an effect of RT on the pharmacokinetics and biodistribution of radiolabeled liposomes to normal tissues. CONCLUSIONS: Single fraction doses of RT appear to have no effect on tumor or normal tissue biodistribution and pharmacokinetics of radiolabeled pegylated liposomes in this animal model.

Measurement of glomerular filtration rate with technetium-99m DTPA: comparison of plasma clearance techniques.

We have compared several techniques for measuring [99mTc]DTPA plasma clearance following single injection to estimate glomerular filtration rate (GFR). Half hourly measurements of disappearance of plasma activity were used to calculate a reference GFR corrected for one-pool assumption and body surface area. Alternative methods involving (i) single blood sample, (ii) two blood samples, (iii) external detector clearance rate, and (iv) a combination of (i) and (iii) were then compared. Closest correlations were obtained with (i) two blood samples at 2 hr and 4 hr (s.e.e. 2.8 ml/min) and (i.v.) external rate constant from 2-5 hr with a blood sample at 3 hr (s.e.e. 3.0 ml/min). Correlations with single blood sample were closest at 3 hr and 4 hr postinjection (s.e.e. 5.4 and 4.5 ml/min, respectively). External detector disappearance rate constant alone was least accurate (s.e.e. greater than 10 ml. min).

Technetium-99m DTPA uptake and transit in bone: effect on blood clearance in rabbits.

The purpose of this study is to explain the initial "plateau" distribution of [99mTc]DTPA in the forearm found when using serial external counting for kidney clearance measurements. A study by a MIRD task group, McAfee et al. 1979 (1), measured the biologic distribution of [99mTc]DTPA(Sn) in most body tissues but omitted bone, which we believe is a major contributor to this initial "plateau". Using MIRD criteria, measurements were carried out on rabbit humeri and these were compared with results obtained from human subjects. It would appear that initial accumulation of the compound by interstitial bone is the reason for the "plateau" and explains why blood sampling for GFR studies should not be undertaken over the first 2 hr. In addition, the results of this study provide valuable information relevant to bone perfusion studies and the biologic distribution and concentration of i.v. administered drugs during the first 2 hr postinjection.

Uptake of [111In-DTPA0]octreotide in the rat kidney is inhibited by colchicine and not by fructose.

UNLABELLED: The high renal uptake of radiolabeled somatostatin analogs is dose limiting. Lowering this uptake permits higher radioactivity doses and, thus, tumor doses to be administered. We tested the effects of the microtubule drug colchicine on renal uptake of [(111)In-DTPA(0)]octreotide. Also, the effects of fructose were tested. METHODS: Organ radioactivity 24 h after injection of [(111)In-DTPA(0)]octreotide was determined in rats. RESULTS: Coinjection of 1 mg of colchicine per kilogram did not influence renal uptake of [(111)In-DTPA(0)]octreotide, whereas this dose administered 5 h before [(111)In-DTPA(0)]octreotide resulted in significant renal uptake reduction (63%). D-Lysine plus colchicine reduced the uptake by 76% (P < 0.01 vs. D-lysine alone). Liver and blood radioactivity levels were significantly elevated by colchicine. Fructose did not affect the biodistribution of [(111)In-DTPA(0)]octreotide. CONCLUSION: Renal uptake of [(111)In-DTPA(0)]octreotide is dependent on microtubule function in rats. The addition of colchicine to amino acid protocols may permit administration of higher doses, improving the therapeutic window of peptide receptor radionuclide therapy.

A comparison of clearance and arteriovenous extraction techniques for measurements of renal hemodynamic functions.

No previous studies have directly compared timed urine collections (UV/P) vs. arteriovenous (A-V) extraction methods for determination of renal function in whole kidney preparations. We examined different markers and techniques for assessing renal plasma flow (RPF), filtration fraction (FF), and glomerular filtration rate (GFR) in both steady-state and rapidly changing conditions following 2 ml/kg bolus intravenous injections of either Renografin 76% (meglumine/sodium diatrizoate-76%) or hypertonic mannitol 25%. During steady-state conditions, excellent correlations were obtained when comparing markers and techniques. Thus, timed urinary clearances of inulin vs. 99m-technetium DTPA (Tc) had a correlation coefficient (R) of .96 (P less than .01; n = 16), and the A-V extraction technique of inulin vs. Tc as determinants of GFR showed a correlation of R = .98 (P less than .01; n = 15). The timed urinary clearance of inulin vs. the A-V extraction of inulin for glomerular filtration gave a correlation of R = .93 (P less than .01; n = 15). The clearance of para-aminohippurate (PAH) divided by the extraction of PAH vs. flow determinations using the electromagnetic flowmeter gave a correlation of R = .92 (P less than .01; n = 16). The anticipated decrease in GFR following contrast medium and hypertonic mannitol was observed using the A-V extraction technique, whereas an artifactual, exaggerated increase in GFR was observed using the timed urine collection technique. Similarly, we noted an exaggerated increase in RPF using CPAH/EPAH as the methodology. We conclude that rapid changes in renal hemodynamics may be measured accurately using the A-V extraction technique but not with clearance techniques requiring timed urine collections.

Sequential changes in lung metabolism, permeability, and edema after ANTU.

Lung injury and pulmonary edema were induced in rats after intraperitoneal injection of 10 mg/kg alpha-naphthylthiourea (ANTU). The time course of development of lung injury was assessed by the clearance of 99mTc-diethylenetriamine pentaacetate (99mTcDTPA) from the lung into the blood, the pharmacokinetics of tritiated prostaglandin E2 [( 3H]PGE2) in the isolated perfused lung, and by increase in the weight ratio (wet-to-dry) of lung. Two hours after ANTU administration, the clearance of 99mTcDTPA was significantly faster than in untreated animals and implied an increase in permeability of the alveolar-capillary barrier. This change preceded the increase in wet-to-dry weight ratio of lung, which was not significant until 5 h after ANTU administration. The pharmacokinetics of [3H]PGE2 were significantly altered after ANTU and these changes persisted beyond the time when both lung weight ratio and 99mTcDTPA clearance had recovered to normal values. We conclude that both 99mTcDTPA clearance and PGE2 pharmacokinetics change in ANTU-induced lung injury but with different time courses. In the progressive phase of lung injury due to ANTU, the early change in clearance of 99mTcDTPA suggests that an increased permeation of the alveolar capillary barrier by this small molecule precedes pulmonary edema due to an increased colloid permeability of the barrier. Abnormal metabolism in the pulmonary microvasculature persists when the permeability defect and edema have recovered.

Monoexponential analysis of plasma disappearance of 99mTc-DTPA and 131I-iodohippurate: a reliable method for measuring changes of renal function.

Glomerular filtration rate and effective renal plasma flow were measured in 170 subjects using monoexponential analysis of plasma disappearance curves for 99mTc-DTPA and 131I-iodohippurate after single injection. In the current study population, glomerular filtration rate and effective renal plasma flow decreased with increasing age, were less in females than in males, and were less in hypertensives than in normotensives. Differences in glomerular filtration rate according to age and sex in the current study were similar to those reported using traditional creatinine clearance methodology. Monoexponential treatment of plasma isotope disappearance gave reproducible values for both glomerular filtration rate and effective renal plasma flow when measured either during the day or on a daily basis. Intraindividual coefficient of variation was less than 10% for both 99mTc-DTPA and 131I-iodohippurate clearances derived from monoexponential analysis. These results demonstrate that monoexponential analysis of plasma disappearance curves for 99mTc-DTPA and 131I-iodohippurate after a single injection is a useful method for evaluating changes in renal hemodynamics either during chronic drug therapy or acutely after single dose administration.

The effect of surgery with cardiopulmonary bypass on alveolar-capillary barrier function in human beings.

We measured the rate of clearance of technetium 99m-labeled diethylenetriamine pentaacetate (99mTcDTPA) (molecular weight, 492 daltons) from the lung into the blood (T1/2LB) in 9 patients before and after operation with cardiopulmonary bypass (CPB). Two hours postoperatively, T1/2LB fell from 49.3 +/- 13.6 minutes (mean +/- standard deviation) to 24.0 +/- 12.8 minutes (p less than 0.001). In addition, alveolar-arterial oxygen tension difference P(A-a)O2 had increased from 73 +/- 28 mm Hg to 164 +/- 37 mm Hg (p less than 0.001). The rates of clearance of 99mTcDTPA had returned to preoperative times by 7 days after operation, although there was still a significant (p less than 0.05) elevation in P(A-a)O2. Postoperative respiratory failure developed in 1 patient. The only abnormality of lung function detected preoperatively was an increased clearance rate for 99mTcDTPA (T1/2LB, 18 minutes). This study has shown an increased clearance from the lung of a low-molecular-weight molecule following operation with CPB. This finding should allow a more rational approach to elucidating the mechanisms of injury to the gas-blood interface in the lung following this type of operation.

A molecular CT blood pool contrast agent.

RATIONALE AND OBJECTIVES: A molecular-based computed tomographic (CT) contrast agent with prolonged vascular residence time is needed for vascular and tumor imaging. No particulate agents have reached clinical practice due to nonspecific macrophage activation. The authors' objective was to synthesize a water-soluble macromolecular agent. MATERIALS AND METHODS: Dysprosium-DTPA-dextran was synthesized through activation of the hydroxyl units of dextran PM40 with allylbromine and subsequent reaction with amino ethanethiol to produce amino-terminated leashes. These leashes were then coupled to DTPA by means of the mixed anhydride method. Complexation of dysprosium by DTPA-dextran was achieved in an acidic solution of 0.2 M dysprosium chloride. One rabbit with a VX2 tumor was imaged with [Dy]DTPA-dextran (0.5 mL, 3.1 g, 1.15 mmol of dysprosium per kilogram). Transaxial scans were acquired through the liver and tumor for 45 minutes. A second healthy rabbit was imaged with Optiray-320 (6.0 mL, 5.0 mmol of iodine per kilogram) at 1-minute intervals for 10 minutes and again at 20 minutes. RESULTS: Each dextran PM40 molecule (diameter, 8.8 nm) contained 95 [Dy]DTPA groups, increasing its average molecular weight from 40,500 to 101,537 g/mol. The baseline-corrected inferior vena cava (IVC) enhancement for [Dy]DTPA-dextran decreased, with an 8-minute half-time during the first 15 minutes followed by a nearly zero slope for the rest of the observation period. The IVC remained brighter than liver throughout the observation period. The solid portion of the tumor was enhanced by 5-10 CT numbers, rendering areas of necrosis more apparent. The baseline-corrected IVC curve for Optiray-320 also demonstrated two phases, with half-times of 2.5 and 45 minutes. The IVC became less dense than liver within 5-8 minutes. CONCLUSION: [Dy]DTPA-dextran is water soluble and can be synthesized without intermolecular cross-linking to carry a high load of dysprosium. It provides blood pool enhancement characteristics with a long intravascular dwell time.

Labeling of biotin with [166Dy]Dy/166Ho as a stable in vivo generator system.

The aim of this work was to synthesize [166Dy]Dy/166Ho-DTPA-Biotin to evaluate its potential as a new radiopharmaceutical for targeted radiotherapy. Dysprosium-166 (166Dy) was obtained by neutron irradiation of enriched 164Dy(2)O(3) in a Triga Mark III reactor. The labeling was carried out in aqueous media at pH 8.0 by addition of [166Dy]DyCl(3) to diethylenetriaminepentaacetic-alpha,omega-bis(biocytinamide) (DTPA-Biotin). Radiochemical purity was determined by high-performance liquid chromatography (HPLC) and TLC. The biological integrity of labeled biotin was studied evaluating its avidity for avidin in an agarose column and by size-exclusion HPLC analysis of the radiolabeled DTPA-Biotin with and without the addition of avidin. Stability studies against dilution were carried out by diluting the radiocomplex solution with saline solution and with human serum at 37 degrees C for 24 h. The [166Dy]Dy/166Ho-labeled biotin was obtained with a 99.1+/-0.6% radiochemical purity. In vitro studies demonstrated that [166Dy]Dy/166Ho-DTPA-Biotin is stable after dilution in saline and in human serum and no translocation of the daughter nucleus occurs subsequent to beta(-) decay of 166Dy that could produce release of 166Ho(3+). Avidity of labeled biotin for avidin was not affected by the labeling procedure. Biodistribution studies in normal mice showed that the [166Dy]Dy/166Ho-DTPA-Biotin has a high renal clearance. In conclusion, the radiolabeled biotin prepared in this investigation has adequate properties to work as a stable in vivo generator system for targeted radiotherapy.

Comparative evaluation of renoscintigraphic properties and plasma clearance of 99MTc-DADS (99mTc-N,N'-bis/mercaptoacetamido ethylenediamine), 99mTc-DTPA and 131I-o-hippuran.

Plasma clearance of 99mTc-N,N'-bis (1,2-mercaptoacetamido) ethylenediamine (DADS), 99mTc-DTPA and 131I-o-hippuran (OIH) was determined in rabbits from blood-concentration decay curves after single i.v. injection of the compounds. Dynamic scintigraphy was performed using the same three compounds, and "activity" curves were compared as observed over kidney ROIs. Both clearance values and renoscintigraphic curves were similar for 99mTc-DADS and 99mTc-DTPA but evidently different from those of OIH. Biliary excretion of 99mTc-DADS was also observed. It appears that, in contrast to other authors, 99mTc-DADS cannot serve as a substitute for 131I-o-hippuran.