Sandra A. Barrow

Rapid detection of Parkinson's disease by SPECT with altropane: A selective ligand for dopamine transporters

Increasing evidence indicates that dopamine (DA) transporter density declines in Parkinsons disease (PD). 2β‐Carbomethoxy‐3β‐(4‐fluorophenyl)‐n‐(1‐iodoprop‐1‐en‐3‐yl) nortropane (IACFT, Altropane™) is a cocaine analog with high affinity and selectivity for dopamine transporter (DAT) sites in the striatum. In this study, single photon emission computed tomography (SPECT) with [123I]altropane was used to measure DAT density in seven healthy volunteers (five males, age 37–75, and two females, ages 26 and 39) and eight male patients with Parkinsons disease (age 14–79, Hoehn and Yahr stage: 1.5–3 (n = 5) and 4–5 (n = 3)). Dynamic SPECT images and arterial blood samples were acquired over 1.5–2 hr and plasma radioactivity was analyzed chromatographically to obtain metabolite corrected arterial input functions. Binding potential (BP, B′max/KD) for striatal (Str) DAT sites was calculated by two methods using occipital cortex (Occ) as a reference. In the first method, tissue time–activity curves (TAC) and metabolite corrected arterial input functions were analyzed by a linear graphical method developed for reversible receptor ligands. In the second method, the expression (StrTAC − OccTAC) was fitted to a gamma variate function and the maximum divided by OccTAC at the same time was used to estimate BP. In five of the PD patients, the SPECT data were compared with the results of PET with [18F] 6‐fluoro DOPA (FD‐PET). Plasma analysis indicated that [123I]altropane is rapidly converted to polar metabolites. SPECT images in healthy volunteers showed that [123I]altropane accumulated rapidly and selectively in the striatum and yielded excellent quality images within 1 h after injection. Both methods of analysis revealed a 7.6%/decade reduction in BP and average striatal values (corrected to age 25) were 1.83 ± 0.22 and 2.09 ± 0.20 by methods 1 and 2. In all the PD patients, striatal accumulation was markedly reduced and the pattern of loss was similar to that reported for DA; most profound in the posterior putamen with relative sparing of the caudate nuclei. A comparable pattern was observed with FD‐PET. For total striatum, age‐corrected BP was significantly (P < 0.001) reduced; 0.83 ± 0.06 (method 1), 0.84 ± 0.07 (method 2). BPs measured by the two methods were remarkably similar and highly correlated r2 = 0.88, (P < 0.001). These results indicate that [123I]altropane is an excellent SPECT ligand for imaging the DAT/DA neurons in human brain. The high selectivity and rapid striatal accumulation of the ligand allows for accurate quantitation of DAT sites in less than 2 hr. The results further demonstrate that [123I]altropane is an effective marker for PD. Synapse 29:128–141, 1998.

Comparison of the infection imaging properties of a 99mTc labeled chemotactic peptide with 111In IgG.

The biodistribution and infection imaging properties of a 99mTc labeled hydrazino nicotinamide (HYNIC) derivatized chemotactic peptide analog (For-Met-Leu-Phe-Lys-HYNIC) and 111In-DTPA-IgG were compared in rabbits with Escherichia coli infection. Six New Zealand white rabbits were injected in the left posterior thigh with a suspension of E. coli. Twenty four hours later, the animals were injected with: 1.0 mCi of 99mTc labeled peptide plus 0.1 mCi of 111In-DTPA-IgG. At 2-3 and 16-18 h, dual photon scintigrams were acquired and the images were corrected for crossover between the two windows. After recording the final images, the animals were sacrificed and biodistribution was determined. At both imaging times the biodistributions of the two reagents were markedly different. The highest concentrations of 111In-DTPA-IgG were detected in blood pool structures, liver and kidney. In contrast localization of 99mTc labeled peptide was greatest in spleen, lung and liver (consistent with binding to leukocytes). In general, the sites of infection were better visualized with the radiolabeled peptide and T/B ratios increased with time (P < 0.01). At both times, the T/Bs for 99mTc-peptide were higher (P < 0.01); 3.54 +/- 0.47 vs 2.52 +/- 0.38 at 2-3 h and 6.88 +/- 0.79 vs 3.78 +/- 0.36 at 16-18 h. These results indicate that although both radiopharmaceuticals localize at sites of infection, the radiolabeled peptide are superior reagents for the rapid detection of focal sites of infection. However, since the mechanisms of localization are different the combined use of both agents could have value in the general evaluation of infection/inflammation.

99mTc-labeled chemotactic peptides: Influence of coligand on distribution of molecular species and infection imaging properties. Synthesis and structural characterization of model complexes with the {Re(η2-HNNC5H4N)(η1-NNC5H4N)} core

Abstract 99m Tc-labeled hydrazino nicotinamide (HYNIC) derivatized chemotactic peptides are useful infection imaging agents. However, the reagent that is used for radiolabeling (‘coligand’) can have profound effects on biodistribution. In this study, the distribution of molecular species formed with a variety of coligands was correlated with infection localization and biodistribution in E. coli infected rabbits. Five 99m Tc-coligand complexes (mannitol, glucamine, glucarate, tricine and glucoheptonate) were used to label f-MLFK-HYNIC and radiolabeled species were characterized by reverse phase HPLC. One mCi of each 99m Tc-coligand–peptide complex was injected into rabbits 24 h after infection and imaging was performed 3–4 and 16–17 h later. After acquiring the final images, the animals were euthanized and biodistribution was measured. With all five coligands, 99m Tc-labeled peptide was obtained in >90% radiochemical purity. Multiple radiolabeled species were obtained with each reagent; however, mannitol yielded the most homogeneous product. Model studies on the robust {Re(η 2 -HNNC 5 H 4 N)(η 1 -NNC 5 H 4 )} core demonstrate that ligands such as mannitol, tricine, tris(hydroxymethyl)propane, glucarate-a, glucarate-b, and glucoheptonate yield intractable mixtures of products as a consequence of the ambidentate nature of these ligands and their facile displacement by other donor groups, including solvent molecules. In contrast, dihydroxylic ligands with an additional imine functionality and a meridional geometric preference yield monophasic materials upon reaction with [ReCl 3 (η 1 -NNC 5 H 4 NH)(η 2 -HNNC 5 H 4 N)]. Both [Re{η 3 -C 5 H 3 N-2,6-(CH 2 O) 2 }(η 1 -NNC 5 H 4 N)(η 2 -HNNC 5 H 4 N)] ( 1 ) and [Re{η 3 -OC 6 H 4 C(H)NC 6 H 4 O}(η 1 -NNC 5 H 4 N)(η 2 -HNNC 5 H 4 N)] ( 2 ) exhibit distorted octahedral geometries with a meridional disposition of the bidentate pyridinediazene and pyridinediazenido(1−) ligands and the three remaining meridional positions occupied by the two oxygen and the nitrogen donors of the tridentate coligand. Image analysis demonstrated that 99m Tc-mannitol-f-MLFK-HYNIC produced the highest target to background ratios (T/B). The T/B values were: 3.91±0.99, 6.15±1.07, 2.8±1.07, 2.57±1.07, 3.41±1.07 and 1.8±1.07 at 3–4 h and 11.9±0.99, 3.94±1.07, 3.79±1.07, 4.81±1.17, 7.0±1.31 and 5.32±1.07 at 16–17 h for mannitol, tricine, glucamine, glucarate-a, glucarate-b, and glucoheptonate, respectively. At both imaging times, 99m Tc-mannitol-f-MLFK-HYNIC had the lowest relative levels of accumulation in bowel. Biodistribution measurements demonstrated that the mannitol preparation had the highest level of accumulation (%ID g −1 ) in infected tissue; mannitol>glucoheptonate=glucarate-b>glucarate-a>glucamine>tricine; P 99m Tc-mannitol-f-MLFK-HYNIC was ∼50:1. These results support our previous findings in rats that coligands can markedly effect the biodistribution and infection localization of 99m Tc-labeled HYNIC chemotactic peptides. For infection imaging, the mannitol preparation had the most favorable combination of accumulation in infected tissue, T/B ratio and biodistribution in uninfected organs.

Detection of acute bacterial infection within soft tissue injuries using a 99mTc-labeled chemotactic peptide

OBJECTIVE Infection imaging with a 99mTc-labeled chemotactic peptide was evaluated in a rabbit model of Escherichia coli infections in burned tissue. MATERIALS AND METHODS The peptide was radiolabeled with 99mTc via the hydrazino nicotinamide derivative. Three groups of six animals were studied: (group A) unilateral infected burns; (group B) bilateral burns with unilateral infection; and (group C) uninfected burns. Twenty-four hours after injury, groups A and B were infected, and 8 hours later, all animals were injected with approximately 0.50 mCi of 99mTc-peptide. MEASUREMENTS AND MAIN RESULTS In groups A and B, excellent images of the infections were obtained at 3 to 4 and 16 to 18 hours after injection of the peptide. At 3 to 4 hours after injection, the target-to-background ratios (T/B) were 3.12 +/- 0.28 for group A and 4.33 +/- 0.61 for group B (p = n.s.). At 16 to 18 hours, the T/B ratios increased significantly (p < 0.01): group A = 8.10 +/- 1.03 and B = 7.70 +/- 1.25. The T/B ratio for group C was only slightly greater than unity. CONCLUSIONS These results indicate that 99mTc-labeled chemotactic peptides are effective radiopharmaceuticals for the rapid detection of focal sites of infection within thermally injured tissues.

Previous burn injury predisposes mice to lipopolysaccharide-induced changes in glucose metabolism.

In mice, it has been demonstrated that at 7 days after burn injury, injection of lipopolysaccharide (LPS) is more lethal than the same dose at 1 day after injury. In the present study, we examined the effect of LPS injection to mice burned 7 days previously on glucose metabolism ([18F] 2-fluoro-2-deoxy-D-glucose [18FDG] uptake) in vivo. CD-1 male mice (25–28 g, Charles River Breeding Laboratories, Wilmington, MA) were anesthetized, backs shaven, and subjected to dorsal full thickness burn on 25% TBSA. Sham-treated animals were used as controls. Six days after burn injury, all mice were fasted overnight. One half of the burned and sham controls were subsequently injected IP with LPS (10 mg/kg; Escherichia coli). The remaining animals were injected with saline IP. Two hours later, all mice were injected IV with 50 &mgr;Ci of 18F FDG. One hour later, the animals were euthanized, and biodistribution was measured. Tissues were weighed, and radioactivity was measured with a well-type &ggr; counter. Results were expressed as %dose/g tissue, mean ± SEM. The combination of burn 7 days previously and LPS significantly increased mortality compared to animals with burn alone, LPS alone, or sham controls. Burn injury 7 days previously caused a significant decrease in 18FDG uptake by the brain compared to sham controls. The combination of LPS and burn injury 7 days previously produced a significant increase in 18FDG uptake by brown adipose tissue and heart compared with either treatment separately. LPS produced a significant increase in 18FDG uptake by lung, spleen, and gastrointestinal tract of the sham animals, changes that were different in mice burned 7 days previously and injected with LPS. The present results suggest that burn injury 7 days previously predisposes mice to alterations in 18FDG uptake produced by LPS. These changes may relate, in part, to the increased lethality of LPS injection in previously burned mice.