Effect of Animal Condition and Fluvoxamine on the Result of [(18)F]N-3-Fluoropropyl-2β-carbomethoxy-3β-(4-iodophenyl) Nortropane ([(18)F]FP-CIT) PET Study in Mice

Synthesis and initial evaluation of radioiodine-labelled deuterated tropane derivatives targeting dopamine transporter

The dopamine transporter (DAT) is closely related to a variety of neurological disorders including Parkinson's disease (PD) and other neurodegenerative diseases. In vivo imaging of DAT with radio-labelled tracers has become a powerful technique in related disorders. The radioiodine-labelled tropane derivative [123I]FP-CIT ([123I]1a) is widely used in clinical single photon emission computed tomography (SPECT) imaging as a DAT imaging agent. To develop more metabolically stable DAT radioligands for accurate imaging, this work compared two novel deuterated tropane derivatives ([131I]1c-d) with non-deuterated tropane derivatives ([131I]1a-b). [131I]1a-d were obtained in high radiochemical purity (RCP) above 99 % with molar activities of 7.0-10.0 GBq/μmol. The [131I]1a and [131I]1c exhibited relatively higher affinity to DAT (Ki: 2.0-3.12 nM) than [131I]1b and [131I]1d. Biodistribution results showed that [131I]1c consistently exhibited a higher ratio of the target to non-target (striatum/cerebellum) than [131I]1a. Furthermore, metabolism studies indicated that the in vivo metabolic stability of [131I]1c was superior to that of [131I]1a. Ex vivo autoradiography showed that [131I]1c selectively localized on DAT-rich striatal regions and the specific signal could be blocked by DAT inhibitor. These results indicated that [131I]1c might be a potential probe for DAT SPECT imaging in the brain.

18F-FP-CIT dopamine transporter PET findings in the striatum and retina of type 1 diabetic rats

PURPOSE

Noninvasive methods used in clinic to accurately detect DA neuron loss in diabetic brain injury and diabetic retinopathy have not been reported up to now. ¹⁸F-FP-CIT is a promising dopamine transporter (DAT) targeted probe. Our study first applies ¹⁸F-FP-CIT PET imaging to assess DA neuron loss in the striatum and retina of T1DM rat model.

METHODS

T1DM rat model was induced by a single intraperitoneal injection of streptozotocin (STZ) (65 mg kg^-1, ip). ¹⁸F-FP-CIT uptake in the striatum and retina was evaluated at 4 weeks, 8 weeks and 12 weeks after STZ injection. The mean standardized uptake value (SUVmean) and the maximum standardized uptake value (SUVmax) were analyzed. Western blot was performed to confirm the DAT protein levels in the striatum and retina.

RESULTS

PET/CT results showed that the SUV of ¹⁸F-FP-CIT was significantly reduced in the diabetic striatum and retina compared with the normal one from 4-week to 12-week (p < 0.0001). Western blots showed that DAT was significantly lower in the diabetic striatum and retina compared to the normal one for all three time points (p < 0.05). The results from Western blots confirmed the findings in PET imaging studies.

CONCLUSIONS

DA neuron loss in the striatum and retina of T1DM rat model can be non-invasively detected with PET imaging using ¹⁸F-FP-CIT targeting DAT. ¹⁸F-FP-CIT PET imaging may be a useful tool used in clinic for DR and diabetic brain injury diagnosis in future. The expression level of DAT in striatum and retina may act as a new biomarker for DR and diabetic brain injury diagnosis.

Tc‑99m Ser‑Asp‑Val‑Glu‑Cys‑Gly: A novel Tc‑99m labeled hexapeptide for molecular and non‑invasive tumor imaging

In a ProteoChip‑based screening system and subsequent studies, serine‑aspartic acid‑valine (SDV) was demonstrated to specifically bind to integrin αvβ3. An SDV‑containing peptide could target the tumor vessel and it may be an effective replacement for molecular imaging of the tumor. In the present study, a hexapeptide, SDV‑glutamic acid‑cysteine‑glycine (ECG), was developed and evaluated its diagnostic performance as a tumor imaging agent in tumor‑bearing mice. The hexapeptide SDV‑ECG was synthesized using Fmoc solid‑phase peptide synthesis. Following radiolabeling procedures with technetium‑99m, the Tc‑99m SDV‑ECG complexes were prepared at high yields (>97%). The uptake of Tc‑99m SDV‑ECG within HT‑1080 tumor cells (integrin αvβ3‑positive) was confirmed by in vitro studies. γ‑camera imaging revealed substantial uptake of Tc‑99m SDV‑ECG in the HT‑1080 cell line tumor murine model. With the co‑injection of excess SDV, tumoral uptake was blocked. Furthermore, HT‑29 tumor cells (integrin αvβ3‑negative) and inflammatory lesions demonstrated minimal uptake of Tc‑99m SDV‑ECG. In the present study, Tc‑99m SDV‑ECG was developed as a novel Tc‑99m agent for tumor imaging. The current in vitro and in vivo studies demonstrated specific functions of Tc‑99m SDV‑ECG in tumor imaging.

Tc-99m Glu-Cys-Gly-His-Gly-Lys (ECG-HGK), a novel Tc-99m labeled hexapeptide for molecular tumor imaging

Domain 5 of kinin-free high molecular weight kininogen inhibits the adhesion of many tumor cell lines, and it has been reported that the histidine-glycine-lysine (HGK)-rich region might be responsible for inhibition of cell adhesion. The authors developed HGK-containing hexapeptide, glutamic acid-cysteine-glycine (ECG)-HGK, and evaluated the utility of Tc-99m ECG-HGK for tumor imaging. Hexapeptide, ECG-HGK was synthesized using Fmoc solid-phase peptide synthesis. Radiolabeling efficiency was evaluated. The uptake of Tc-99m ECG-HGK within HT-1080 cells was evaluated in vitro. In HT-1080 tumor-bearing mice, gamma imaging and biodistribution studies were performed. The complexes Tc-99m ECG-HGK was prepared in high yield. The uptake of Tc-99m ECG-HGK within the HT-1080 tumor cells had been demonstrated by in vitro studies. The gamma camera imaging in the murine model showed that Tc-99m ECG-HGK was accumulated substantially in the HT-1080 tumor (tumor-to-muscle ratio = 5.7 ± 1.4 at 4 h), and the tumoral uptake was blocked by the co-injection of excess HGK (tumor-to-muscle ratio = 2.8 ± 0.6 at 4 h). In the present study, Tc-99m ECG-HGK was developed as a new tumor imaging agents. Our in vitro and in vivo studies revealed specific function of Tc-99m ECG-HGK for tumor imaging.

The Effect of SSRIs on the Binding of (18)F-FP-CIT in Parkinson Patients: A Retrospective Case Control Study

PURPOSE

(18)F-FP-CIT [(18)F-fluorinated N-3-fluoropropyl-2-beta-carboxymethoxy-3-beta-(4-iodophenyl) nortropane] is useful for detecting striatal dopamine transporter (DAT). Since FP-CIT shows relatively high affinities for DAT and serotonin transporter (SERT), its binding can be influenced by selective serotonin reuptake inhibitors (SSRIs). We aimed to evaluate the effect of SSRIs on the binding of (18)F-FP-CIT.

METHODS

In our (18)F-FP-CIT positron emission tomography (PET) data pool, images of 24 drug-naive Parkinson's disease (PD) patients (62.6 ± 10.6 years), 111 PD patients taking SSRIs [escitalopram (n = 19) and fluvoxamine (n = 20)] or clonazepam (n = 72), and 10 normal people were reviewed. PET images acquired 3 h after (18)F-FP-CIT injection were analyzed by an automated method using a predefined volume of interest (VOI) set of the striatum (ST), occipital cortex (OC), raphe nuclei (RN), and cerebellar cortex (CB). The uptake ratios (URs) of each VOI to the CB were compared among the groups.

RESULTS

The ST/CB URs of all PD groups were significantly lower than that of normal group. When adjusted for drug severity, ST/CB URs were higher in drug-naive group but had no difference among antidepressant groups. Whereas OC/CB URs were not different among groups (p > 0.05), RN/CB URs were significantly lower in SSRI groups than in non-SSRI groups (p < 0.001) and showed similar results when adjusted for disease severity.

CONCLUSIONS

PD patients taking SSRIs showed significantly decreased URs in the RN but not the OC. When adjusted for Hoehn and Yar (HY) score, ST URs were not different among antidepressant groups. This result suggests that the OC may be used as a reference region for the quantification of DAT binding in (18)F-FP-CIT PET images of PD patients taking SSRIs.

Automated Analysis of (123)I-beta-CIT SPECT Images with Statistical Probabilistic Anatomical Mapping

BACKGROUND

Population-based statistical probabilistic anatomical maps have been used to generate probabilistic volumes of interest for analyzing perfusion and metabolic brain imaging. We investigated the feasibility of automated analysis for dopamine transporter images using this technique and evaluated striatal binding potentials in Parkinson's disease and Wilson's disease.

MATERIALS AND METHODS

We analyzed 2β-Carbomethoxy-3β-(4-(123)I-iodophenyl)tropane ((123)I-beta-CIT) SPECT images acquired from 26 people with Parkinson's disease (M:F = 11:15, mean age = 49 ± 12 years), 9 people with Wilson's disease (M: F = 6:3, mean age = 26 ± 11 years) and 17 normal controls (M:F = 5:12, mean age = 39 ± 16 years). A SPECT template was created using striatal statistical probabilistic map images. All images were spatially normalized onto the template, and probability-weighted regional counts in striatal structures were estimated. The binding potential was calculated using the ratio of specific and nonspecific binding activities at equilibrium. Voxel-based comparisons between groups were also performed using statistical parametric mapping.

RESULTS

Qualitative assessment showed that spatial normalizations of the SPECT images were successful for all images. The striatal binding potentials of participants with Parkinson's disease and Wilson's disease were significantly lower than those of normal controls. Statistical parametric mapping analysis found statistically significant differences only in striatal regions in both disease groups compared to controls.

CONCLUSION

We successfully evaluated the regional (123)I-beta-CIT distribution using the SPECT template and probabilistic map data automatically. This procedure allows an objective and quantitative comparison of the binding potential, which in this case showed a significantly decreased binding potential in the striata of patients with Parkinson's disease or Wilson's disease.