Imaging of experimental colitis with a radiolabeled leukotriene B4 antagonist.

UNLABELLED: The use of radiolabeled leukocytes is considered the gold standard for scintigraphic imaging of inflammatory bowel disease. The disadvantages of (99m)Tc-hexamethylpropyleneamine oxime (HMPAO)-leukocytes, however, encourage the search for new imaging agents with at least similar diagnostic accuracy but without the laborious preparation and subsequent risk of contamination. In this study we investigated the imaging characteristics of a new imaging agent that specifically binds to the leukotriene B(4) (LTB(4)) receptors expressed on neutrophils. Imaging characteristics of the (111)In-labeled LTB(4) antagonist (DPC11870) were compared with those of (18)F-FDG and (99m)Tc-HMPAO-granulocytes in a rabbit model of experimental colitis. METHODS: Acute colitis was induced in New Zealand White (NZW) rabbits by infusion of trinitrobenzene sulfonic acid in the descending colon. Forty-eight hours after induction of colitis, all animals were injected intravenously with (99m)Tc-granulocytes, (18)F-FDG, or (111)In-DPC11870. The pharmacokinetics and biodistribution were studied by serial scintigraphic imaging and by ex vivo counting of dissected tissues. RESULTS: All 3 radiopharmaceuticals showed the inflamed colon as early as 1 h after injection. However, compared with (99m)Tc-granulocytes, both (111)In-DPC11870 and (18)F-FDG were superior in revealing the inflamed lesions. The biodistribution data showed that uptake of (111)In-DPC11870 in the inflamed colon was highest (0.72 +/- 0.18 percentage injected dose per gram [%ID/g]), followed by uptake of (99m)Tc-granulocytes (0.40 +/- 0.11 %ID/g) and of (18)F-FDG (0.16 +/- 0.04 %ID/g). Because of low activity concentrations in the noninflamed colon, the radiolabeled LTB(4) antagonist also revealed the highest ratio of affected colon to unaffected colon (11.6 for (111)In-DPC11870, 5.5 for (99m)Tc-granulocytes, and 4.1 for (18)F-FDG). CONCLUSION: The radiolabeled LTB(4) antagonist DPC11870 clearly delineated acute colitis lesions in NZW rabbits within 1 h after injection. Because of high uptake in the inflamed lesions and a low activity concentration in the noninflamed colon, images acquired with (111)In-DPC11870 were better than those acquired with (99m)Tc-granulocytes or (18)F-FDG.

Anaerobic 90Y- and 177Lu-labeling of a DOTA-conjugated nonpeptide vitronectin receptor antagonist.

This study describes the discovery and development of an anaerobic formulation for the routine preparation of (90)Y and (177)Lu complexes ((90)Y-TA138 and (177)Lu-TA138) of a DOTA-conjugated nonpeptide vitronectin receptor antagonist (TA138: 3-sulfon-N-[[4,7,10-tris(carboxymethyl)1,4,7,10-tetraazacyclododec-1-yl]acetyl]-l-alanyl-N-[2-[4-[[[(1S)-1-carboxy-2[[[1,4-dihydro-7-[(1H-imidazol-2-ylamino]meth-yl]-1-methyl-4-oxo-3-quinolinyl]carbonyl]amino]ethyl]amino]-sulfonyl]-3,5-dimethylphenoxy]-1-oxobutyl]amino]ethyl]-3-sulfo-l-alaninamide). Since (90)Y-TA138 and (177)Lu-TA138 are very sensitive to radiolytic degradation, exclusion of oxygen is necessary during the radiolabeling. Using the anaerobic formulation, (90)Y-TA138 and (177)Lu-TA138 can be prepared in high yield and high specific activity. The anaerobic formulation described in this study is particularly useful for (90)Y- and (177)Lu-labeling of DOTA-conjugated small biomolecules, which are sensitive to the radiolytic degradation during radiolabeling.

A bivalent leukotriene B(4) antagonist for scintigraphic imaging of infectious foci.

UNLABELLED: Several radiolabeled chemotactic peptides have been tested for their suitability to show infection and inflammation. Leukotriene B(4) (LTB(4)) receptor-binding ligands could be useful agents for revealing neutrophilic infiltrations because the LTB(4) receptor is abundantly expressed on neutrophils after an inflammatory stimulus. In this study, we investigated the in vivo and in vitro characteristics of a new hydrophilic (111)In-labeled LTB(4) antagonist. METHODS: The LTB(4) antagonist DPC11870-11 was labeled with (111)In and intravenously injected into New Zealand White rabbits with Escherichia coli infection in the left thigh muscle. The pharmacokinetics and biodistribution were studied by serial scintigraphic imaging (0-24 h after injection) and by ex vivo counting of dissected tissues (6 and 24 h after injection). The receptor-mediated in vivo localization of the compound was investigated in 3 rabbits that received an excess of nonradioactive indium-labeled agent 2 min before the administration of the (111)In-labeled LTB(4) antagonist. RESULTS: In rabbits with intramuscular E. coli infection, the abscess was visualized as early as 2 h after injection. Accumulation in the abscess increased with time, resulting in excellent images at 6 h after injection. Blood clearance was rapid in the first hours after injection (alpha-half-life = 30 +/- 6 min, 85%; beta-half-life = 25.7 +/- 0.8 h, 15%). Abscess-to-background ratios, as derived from the region-of-interest analysis, increased to 34 +/- 7 at 24 h after injection. The images of both groups showed moderate uptake in the liver, spleen, kidneys, and bone marrow. No activity was seen in the bladder, indicating almost complete retention in the kidneys. The uptake in the abscess could be blocked completely by injection of an excess of nonradioactive agent, indicating a specific receptor-ligand interaction of the radiolabeled agent in the infected tissue. Biodistribution data showed that after saturation of the LTB(4) receptor, the abscess uptake, in percentage injected dose per gram, was significantly reduced (0.03 +/- 0.02 vs. 0.24 +/- 0.06, P = 0.008). CONCLUSION: The modified LTB(4) antagonist showed infectious foci rapidly after injection because of specific receptor-ligand interaction. Because of the high abscess-to-background ratios that were obtained and the fact that no accumulation of radioactivity was observed in the gastrointestinal tract, this compound has excellent characteristics for revealing infectious and inflammatory foci.

Comparison of yttrium and indium complexes of DOTA-BA and DOTA-MBA: models for (90)Y- and (111)In-labeled DOTA-biomolecule conjugates.

Yttrium and indium complexes of 1,4,7,10-tetraaza-4,7,10-tris(carboxymethyl)-1-cyclododecylacetylbenzylamine (DOTA-BA) and 1,4,7,10-tetraaza-4,7,10-tris(carboxymethyl)-1-cyclododecylacetyl-R-(+)-alpha-methylbenzylamine (DOTA-MBA) were prepared in order to study solution structures of (90)Y- and (111)In-labeled DOTA-biomolecule conjugates. (90)Y and (111)In complexes M(L) (M = (90)Y and (111)In; L = DOTA-BA and DOTA-MBA) were prepared from the reaction of MCl(3) with DOTA-BA and DOTA-MBA, respectively, in ammonium acetate buffer. A reverse phase HPLC method revealed that both (90)Y and (111)In complexes show only one radiometric peak in their radio-HPLC chromatograms. It was also found that (111)In(DOTA-BA) and (111)In(DOTA-MBA) are more hydrophilic than their corresponding (90)Y analogues, suggesting different coordination spheres in (111)In and (90)Y complexes of the same DOTA conjugate. Complexes M(L) (M = Y and In; L = DOTA-BA and DOTA-MBA) were prepared and characterized by HPLC, LC-MS, and NMR ((1)H and (13)C) methods. The HPLC concordance experiments for (90)Y(DOTA-MBA)/Y(DOTA-MBA) and (111)In(DOTA-MBA)/In(DOTA-MBA) show that the same complex is prepared at both tracer and macroscopic levels. The NMR data ((1)H and (13)C) clearly demonstrates that Y(DOTA-BA) and Y(DOTA-MBA) exist in solution as one predominant isomer. VT NMR data ((1)H and (13)C) show that In(DOTA-BA) and In(DOTA-MBA) are fluxional at room temperature while Y(DOTA-BA) and Y(DOTA-MBA) become fluxional only at elevated temperatures. The fluxionality of these complexes is due to rapid rotation of acetate/acetamide chelating arms and inversion of ethylenic groups of the macrocyclic ring.