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Radiosynthesis, In Vivo Biological Evaluation, and Imaging of Brain Lesions with [123I]-CLINME, a New SPECT Tracer for the Translocator Protein.

Mattner F, Quinlivan M, Greguric I, Pham T, Liu X, Jackson T, Berghofer P, Fookes CJ, Dikic B, Gregoire MC, Dolle F, Katsifis A - Dis. Markers (2015)

Bottom Line: The striatum lesion was confirmed and correlated with TSPO expression in astrocytes and activated microglia by immunohistochemistry and autoradiography.Moreover, TSPO changes observed by SPECT imaging were confirmed by immunofluorescence, immunochemistry, and autoradiography.These results indicated that [(123)I]-CLINME is a promising candidate for the quantification and visualization of TPSO expression in activated astroglia using SPECT.

View Article: PubMed Central - PubMed

Affiliation: Life Sciences Division, Australian Nuclear Science and Technology Organisation, New Illawarra Road, Lucas Heights, NSW 2234, Australia ; Department of Molecular Imaging, Royal Prince Alfred Hospital, Camperdown, NSW 2050, Australia.

ABSTRACT
The high affinity translocator protein (TSPO) ligand 6-chloro-2-(4'-iodophenyl)-3-(N,N-methylethyl)imidazo[1,2-a]pyridine-3-acetamide (CLINME) was radiolabelled with iodine-123 and assessed for its sensitivity for the TSPO in rodents. Moreover neuroinflammatory changes on a unilateral excitotoxic lesion rat model were detected using SPECT imaging. [(123)I]-CLINME was prepared in 70-80% radiochemical yield. The uptake of [(123)I]-CLINME was evaluated in rats by biodistribution, competition, and metabolite studies. The unilateral excitotoxic lesion was performed by injection of α-amino-3-hydroxy-5-methylisoxazole-4-propionic acid unilaterally into the striatum. The striatum lesion was confirmed and correlated with TSPO expression in astrocytes and activated microglia by immunohistochemistry and autoradiography. In vivo studies with [(123)I]-CLINME indicated a biodistribution pattern consistent with TPSO distribution and the competition studies with PK11195 and Ro 5-4864 showed that [(123)I]-CLINME is selective for this site. The metabolite study showed that the extractable radioactivity was unchanged [(123)I]-CLINME in organs which expresses TSPO. SPECT/CT imaging on the unilateral excitotoxic lesion indicated that the mean ratio uptake in striatum (lesion:nonlesion) was 2.2. Moreover, TSPO changes observed by SPECT imaging were confirmed by immunofluorescence, immunochemistry, and autoradiography. These results indicated that [(123)I]-CLINME is a promising candidate for the quantification and visualization of TPSO expression in activated astroglia using SPECT.

No MeSH data available.


Measures of relative optical density (ROD) following in vitro autoradiography with 16 nM [125I]-CLINME and effect of 20 μM of PK11195, CLINME, or flumazenil (a). Representative autoradiograms showing a region of very high activity in the unilateral dorsal striatum (with extension dorsally into the cortex). Specific binding in the lining of the lateral ventricles can also be observed (b). ∗P < 0.05 ipsilateral versus contralateral; §P < 0.05 versus [125I]-CLINME alone.
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fig6: Measures of relative optical density (ROD) following in vitro autoradiography with 16 nM [125I]-CLINME and effect of 20 μM of PK11195, CLINME, or flumazenil (a). Representative autoradiograms showing a region of very high activity in the unilateral dorsal striatum (with extension dorsally into the cortex). Specific binding in the lining of the lateral ventricles can also be observed (b). ∗P < 0.05 ipsilateral versus contralateral; §P < 0.05 versus [125I]-CLINME alone.

Mentions: In tissue harvested immediately following SPECT imaging, autoradiography with 16 nM [125I]-CLINME also showed significantly increased radioligand binding in the lesioned striatum compared to the contralateral one (Figure 6). This differential in [125I]-CLINME binding was eliminated by coincubation of [125I]-CLINME with 20 μM of either CLINME or PK11195. Coincubation with 20 μM flumazenil on the other hand had no effect on the differential binding of [125I]-CLINME. Analysis of the ipsilateral data across the different incubation conditions shows that the two TSPO drugs greatly and significantly decreased the measured ROD in these ROIs, whilst coincubation with flumazenil produced a small, nonsignificant reduction. In the contralateral striatum, all 3 coincubation conditions resulted in significantly decreased ROD compared to incubation with 16 nM [125I]-CLINME alone, although these decreases were of a smaller magnitude than those observed ipsilaterally.


Radiosynthesis, In Vivo Biological Evaluation, and Imaging of Brain Lesions with [123I]-CLINME, a New SPECT Tracer for the Translocator Protein.

Mattner F, Quinlivan M, Greguric I, Pham T, Liu X, Jackson T, Berghofer P, Fookes CJ, Dikic B, Gregoire MC, Dolle F, Katsifis A - Dis. Markers (2015)

Measures of relative optical density (ROD) following in vitro autoradiography with 16 nM [125I]-CLINME and effect of 20 μM of PK11195, CLINME, or flumazenil (a). Representative autoradiograms showing a region of very high activity in the unilateral dorsal striatum (with extension dorsally into the cortex). Specific binding in the lining of the lateral ventricles can also be observed (b). ∗P < 0.05 ipsilateral versus contralateral; §P < 0.05 versus [125I]-CLINME alone.
© Copyright Policy - open-access
Related In: Results  -  Collection

Show All Figures
getmorefigures.php?uid=PMC4496498&req=5

fig6: Measures of relative optical density (ROD) following in vitro autoradiography with 16 nM [125I]-CLINME and effect of 20 μM of PK11195, CLINME, or flumazenil (a). Representative autoradiograms showing a region of very high activity in the unilateral dorsal striatum (with extension dorsally into the cortex). Specific binding in the lining of the lateral ventricles can also be observed (b). ∗P < 0.05 ipsilateral versus contralateral; §P < 0.05 versus [125I]-CLINME alone.
Mentions: In tissue harvested immediately following SPECT imaging, autoradiography with 16 nM [125I]-CLINME also showed significantly increased radioligand binding in the lesioned striatum compared to the contralateral one (Figure 6). This differential in [125I]-CLINME binding was eliminated by coincubation of [125I]-CLINME with 20 μM of either CLINME or PK11195. Coincubation with 20 μM flumazenil on the other hand had no effect on the differential binding of [125I]-CLINME. Analysis of the ipsilateral data across the different incubation conditions shows that the two TSPO drugs greatly and significantly decreased the measured ROD in these ROIs, whilst coincubation with flumazenil produced a small, nonsignificant reduction. In the contralateral striatum, all 3 coincubation conditions resulted in significantly decreased ROD compared to incubation with 16 nM [125I]-CLINME alone, although these decreases were of a smaller magnitude than those observed ipsilaterally.

Bottom Line: The striatum lesion was confirmed and correlated with TSPO expression in astrocytes and activated microglia by immunohistochemistry and autoradiography.Moreover, TSPO changes observed by SPECT imaging were confirmed by immunofluorescence, immunochemistry, and autoradiography.These results indicated that [(123)I]-CLINME is a promising candidate for the quantification and visualization of TPSO expression in activated astroglia using SPECT.

View Article: PubMed Central - PubMed

Affiliation: Life Sciences Division, Australian Nuclear Science and Technology Organisation, New Illawarra Road, Lucas Heights, NSW 2234, Australia ; Department of Molecular Imaging, Royal Prince Alfred Hospital, Camperdown, NSW 2050, Australia.

ABSTRACT
The high affinity translocator protein (TSPO) ligand 6-chloro-2-(4'-iodophenyl)-3-(N,N-methylethyl)imidazo[1,2-a]pyridine-3-acetamide (CLINME) was radiolabelled with iodine-123 and assessed for its sensitivity for the TSPO in rodents. Moreover neuroinflammatory changes on a unilateral excitotoxic lesion rat model were detected using SPECT imaging. [(123)I]-CLINME was prepared in 70-80% radiochemical yield. The uptake of [(123)I]-CLINME was evaluated in rats by biodistribution, competition, and metabolite studies. The unilateral excitotoxic lesion was performed by injection of α-amino-3-hydroxy-5-methylisoxazole-4-propionic acid unilaterally into the striatum. The striatum lesion was confirmed and correlated with TSPO expression in astrocytes and activated microglia by immunohistochemistry and autoradiography. In vivo studies with [(123)I]-CLINME indicated a biodistribution pattern consistent with TPSO distribution and the competition studies with PK11195 and Ro 5-4864 showed that [(123)I]-CLINME is selective for this site. The metabolite study showed that the extractable radioactivity was unchanged [(123)I]-CLINME in organs which expresses TSPO. SPECT/CT imaging on the unilateral excitotoxic lesion indicated that the mean ratio uptake in striatum (lesion:nonlesion) was 2.2. Moreover, TSPO changes observed by SPECT imaging were confirmed by immunofluorescence, immunochemistry, and autoradiography. These results indicated that [(123)I]-CLINME is a promising candidate for the quantification and visualization of TPSO expression in activated astroglia using SPECT.

No MeSH data available.