In vivo evaluation of [123I]mZIENT as a SPECT radioligand for the serotonin transporter

IntroductionIn vivo imaging of the serotonin transporter continues to be a valuable tool in drug development and in monitoring diseases that alter serotonergic function. The purposes of this study were to: 1) evaluate the test/retest reproducibility of [¹²³I] 2β-Carbomethoxy-3β-(3′-((Z)-2-iodoethenyl)phenyl)nortropane ([¹²³I]mZIENT); and 2) to assess displacement of [¹²³I]mZIENT following administration of SERT specific drugs.MethodsSix female baboons (Papio anubis) were scanned following i.v. administration of [¹²³I]mZIENT. The regional binding potential (BP_nd) was determined using a simplified reference tissue model, with the cerebellum used as a reference region. The test/retest reproducibility of BP_nd was determined following repeated injection of [¹²³I]mZIENT on a different day. To assess the displacement of [¹²³I]mZIENT from SERT, citalopram (0.01–5 mg/kg) or sertraline (0.01–0.5 mg/kg) was given as iv bolus at ~ 4 h following administration of [¹²³I]mZIENT.ResultsThe test/retest variability of BP_nd was less than 10% for all SERT-rich brain regions. Estimates of ED50 for displacement of [¹²³I]mZIENT in SERT-rich regions were consistent with previous reports for the [¹¹C] analog of [¹²³I]mZIENT. Both citalopram and sertraline displaced [¹²³I]mZIENT from SERT in a dose-dependent manner, with maximal observed displacements of greater than 80% in the diencephalon and greater than 75% in brainstem for both citalopram and sertraline.Conclusions[¹²³I] mZIENT demonstrates good test–retest reproducibility; and initial displacement studies suggest that this compound is highly selective for SERT. Overall, this radioligand has favorable characteristics for use in drug development studies and/or longitudinal studies interrogating SERT.     

[123I]Iodobenzamide binding to the rat dopamine D2 receptor in competition with haloperidol and endogenous dopamine—an in vivo imaging study with a dedicated small animal SPECT

Purpose This study assessed [¹²³I]iodobenzamide binding to the rat dopamine D₂ receptor in competition with haloperidol and endogenous dopamine using a high-resolution small animal SPECT.Methods Subsequent to baseline quantifications of D₂ receptor binding, imaging studies were performed on the same animals after pre-treatment with haloperidol and methylphenidate, which block D₂ receptors and dopamine transporters, respectively.Results Striatal baseline equilibrium ratios (V₃) of [¹²³I]iodobenzamide binding were 1.42±0.31 (mean±SD). After pre-treatment with haloperidol and methylphenidate, V₃ values decreased to 0.54±0.46 (p<0.0001) and 0.98±0.48 (p=0.009), respectively.Conclusion The decrease in [¹²³I]iodobenzamide binding induced by pre-treatment with haloperidol reflects D₂ receptor blockade, whereas the decrease in receptor binding induced by pre-treatment with methylphenidate can be interpreted in terms of competition between [¹²³I]IBZM and endogenous dopamine. Findings show that multiple in vivo measurements of [¹²³I]iodobenzamide binding to D₂ receptors in competition with exogenous and endogenous ligands are feasible in the same animal. This may be of future relevance for the in vivo evaluation of novel radioligands as well as for studying the interrelations between pre- and/or postsynaptic radioligand binding and different levels of endogenous dopamine.     

Quantitation of dopamine transporter blockade by methylphenidate: first in vivo investigation using [123I]FP-CIT and a dedicated small animal SPECT

Purpose The aim of this study was to investigate the feasibility of assessing dopamine transporter binding after treatment with methylphenidate in the rat using a recently developed high-resolution small animal single-photon emission computed tomograph (TierSPECT) and [¹²³I]FP-CIT.Methods [¹²³I]FP-CIT was administered intravenously 1 h after intraperitoneal injection of methylphenidate (10 mg/kg) or vehicle. Animals underwent scanning 2 h after radioligand administration. The striatum was identified by superimposition of [¹²³I]FP-CIT scans with bone metabolism and perfusion scans obtained with ^99mTc-DPD and ^99mTc-tetrofosmin, respectively. As these tracers do not pass the blood–brain barrier, their distribution permits the identification of extracerebral anatomical landmarks such as the orbitae and the harderian glands. The cerebellum was identified by superimposing [¹²³I]FP-CIT scans with images of brain perfusion obtained with ^99mTc-HMPAO.Results Methylphenidate-treated animals and vehicle-treated animals yielded striatal equilibrium ratios (V₃) of 0.24±0.26 (mean ± SD) and 1.09±0.42, respectively (t test, two-tailed, p<0.0001). Cortical V₃ values amounted to 0.05±0.28 (methylphenidate) and 0.3±0.39 (saline, p=0.176). This first in vivo study of rat dopamine transporter binding after pre-treatment with methylphenidate showed a mean reduction of 78% in striatal [¹²³I]FP-CIT accumulation.Conclusion The results can be interpreted in terms of a pharmacological blockade in the rat striatum and show that in vivo quantitation of dopamine transporter binding is feasible with [¹²³I]FP-CIT and the TierSPECT. This may be of future relevance for in vivo investigations on rat models of attention deficit/hyperactivity disorder. Furthermore, our findings suggest that investigations in other animal models, e.g. of Parkinsons and Huntingtons disease, may be feasible using SPECT radioligands and small animal imaging systems.     

Increased Brainstem Serotonergic Transporter Availability in Adult Migraineurs: an [<Superscript>18</Superscript>F]FP-CIT PET Imaging Pilot Study

Purpose

Recent studies have proposed central serotonergic dysfunction as a major pathophysiology of migraine. We investigated serotonin transporter (SERT) availability in migraineurs using F-18-N-(3-fluoropropyl)-2β-carbomethoxy-3β-(4-iodophenyl) nortropane ([¹⁸F]FP-CIT) positron emission tomography (PET).

Methods

Brain [¹⁸F]FP-CIT PET images were obtained in eight women with migraine during headache free phase and 12 healthy adult women, 120 min after injection of 185 MBq. Non-displaceable binding potential (BP_ND) of [¹⁸F]FP-CIT, which is an estimate of SERT availability, was calculated at the brainstem and compared with clinical parameters.

Results

BP_ND at the brainstem was significantly higher in adult migraineurs (n = 6, 1.15 ± 0.17) than healthy subjects (0.95 ± 0.14) (p = 0.04). Healthy subjects demonstrated negative correlation between brainstem BP_ND and age (r = −0.64, p = 0.02), whereas this age-related decline pattern was not found in the migraineurs. Severity of migraine attack was significantly correlated with brainstem BP_ND (r = 0.66, p = 0.02), when age and duration of illness were corrected.

Conclusions

Increased SERT availability in the brainstem of adult migraineurs indicates low serotonin neurotransmission during headache-free phase. Patients who experience more painful headaches have lower serotonin neurotransmission. [¹⁸F]FP-CIT PET is a useful in vivo imaging technique for evaluating brainstem SERT availability in migraineurs.     

Clinical correlation of the binding potential with <Superscript>123</Superscript>I-FP-CIT in de novo idiopathic Parkinson’s disease patients

Purpose  The aim of this study was to evaluate the accuracy of different single-photon emission computed tomography (SPECT) reconstruction techniques in measuring striatal N-ω-fluoropropyl-2β-carbomethoxy-3β-4-[¹²³I]iodophenyl-nortropane (¹²³I-FP-CIT) binding in de novo Parkinson’s disease (PD) patients, in order to find a correlation with clinical scales of disease severity in the initial phases of disease. Methods  Thirty-six de novo PD patients underwent ¹²³I-FP-CIT SPECT and MRI scan. SPECT data were reconstructed with filtered back projection (FBP), with an iterative algorithm (ordered subset expected maximization, OSEM) and with a method previously developed in our institution, called least-squares (LS) method. The ratio of specific to non-specific striatal ¹²³I-FP-CIT binding (binding potential, BP) was used as the outcome measure with all the reconstruction methods (BP_FBP, BP_OSEM, BP_LS). Results  The range of values of striatal BP_LS was significantly greater than BP_FBP and BP_OSEM. For all striatal regions, estimates of BP_FBP correlated well with BP_OSEM (r = 0.84) and with BP_LS (r = 0.64); BP_OSEM correlated significantly with BP_LS (r = 0.76). A good correlation was found between putaminal BP_LS and Hoen and Yahr, Unified PD Rating Scale (UPDRS) and lateralized UPDRS motor scores (r = −0.46, r = −0.42, r = −0.39, respectively). Neither putaminal BP_FBP nor putaminal BP_OSEM correlated with any of these motor scores. Conclusions  In de novo PD patients, ¹²³I-FP-CIT BP values derived from FBP and OSEM reconstruction techniques do not permit to differentiate PD severity. The LS method instead finds a correlation between striatal BP and disease severity scores. The results of this study support the use of ¹²³I-FP-CIT BP values estimated with the LS method as a biomarker of PD severity.     

Single-photon emission tomography imaging of serotonin transporters in the nonhuman primate brain with [123I]ODAM

We have described previously a selective serotonin transporter (SERT) radioligand, [¹²³I]IDAM. We now report a similarly potent, but more stable IDAM derivative, 5-iodo-2-[2-[(dimethylamino)methyl]phenoxy]benzyl alcohol ([¹²³I]ODAM). The imaging characteristics of this radioligand were studied and compared against [¹²³I]IDAM. Dynamic sequences of single-photon emission tomography (SPET) scans were obtained on three female baboons after injection of 375 MBq of [¹²³I]ODAM. Displacing doses (1 mg/kg) of the selective SERT ligand (+)McN5652 were administered 120 min after injection of [¹²³I]ODAM. Total integrated brain uptake of [¹²³I]ODAM was about 30% higher than [¹²³I]IDAM. After 60–120 min, the regional distribution of tracer within the brain reflected the characteristic distribution of SERT. Peak specific binding in the midbrain occurred 120 min after injection, with an equilibrium midbrain to cerebellar ratio of 1.50±0.08, which was slightly lower than the value for [¹²³I]IDAM (1.80± 0.13). Both the binding kinetics and the metabolism of [¹²³I]ODAM were slower than those of [¹²³I]IDAM. Following injection of a competing SERT ligand, (+)McN5652, the tracer exhibited washout from areas with high concentrations of SERT, with a dissociation kinetic rate constant k _off=0.0085±0.0028 min^–1 in the midbrain. Similar studies using nisoxetine and methylphenidate showed no displacement, consistent with its low binding affinity to norepinephrine and dopamine transporters, respectively. These results suggest that [¹²³I]ODAM is suitable for selective SPET imaging of SERT in the primate brain, with higher uptake and slower kinetics and metabolism than [¹²³I]IDAM, but also a slightly lower selectivity for SERT. Received 1 May and in revised form 31 May 1999     

Single-photon emission tomography imaging of serotonin transporters in the non-human primate brain with the selective radioligand [123I]IDAM

A new radioligand, 5-iodo-2-[[2–2-[(dimethylamino)methyl]phenyl]thio]benzyl alcohol ([¹²³I]IDAM), has been developed for selective single-photon emission tomography (SPET) imaging of SERT. In vitro binding studies suggest a high selectivity of IDAM for SERT (K _i=0.097 nM), with considerably lower affinities for norepinephrine and dopamine transporters (NET K _i= 234 nM and DAT K _i>10 μM, respectively). In this study the biodistribution of SERT in the baboon brain was investigated in vivo using [¹²³I]IDAM and SPET imaging. Dynamic sequences of SPET scans were performed on three female baboons (Papio anubis) after injection of 555 MBq of [¹²³I]IDAM. Displacing doses (1 mg/kg) of the selective SERT ligand (+)McN5652 were administered 90–120 min after injection of [¹²³I]IDAM. Similar studies were performed using a NET inhibitor, nisoxetine, and a DAT blocker, methylphenidate. After 60–120 min, the regional distribution of tracer within the brain reflected the characteristic distribution of SERT, with the highest uptake in the midbrain area (hypothalamus, raphe nucleus, substantia nigra), and the lowest uptake in the cerebellum (an area presumed free of SERT). Peak specific binding in the midbrain occurred at 120 min, with a ratio to the cerebellum of 1.80±0.13. At 30 min, 85% of the radioactivity in the blood was metabolite. Following injection of a competing SERT ligand, (+)McN5652, the tracer exhibited rapid washout from areas with high concentrations of SERT (dissociation rate constant in the midbrain, averaged over three baboons, k _off=0.025±0.002 min^–1), while the cerebellar activity distribution was undisturbed (washout rate 0.0059± 0.0003 min^–1). Calculation of tracer washout rate pixel-by-pixel enabled the generation of parametric images of the dissociation rate constant. Similar studies using nisoxetine and methylphenidate had no effect on the distribution of [¹²³I]IDAM in the brain. These results suggest that [¹²³I]IDAM is suitable for selective SPET imaging of SERT in the primate brain, with high contrast, favorable kinetics, and negligible binding to either NET or DAT. Received: 1 February and in revised form 2 March 1999     

Mass dose effects and in vivo affinity in brain PET receptor studies--a study of cerebral 5-HT4 receptor binding with [11C]SB207145

Attention to tracer dose principles is crucial in positron emission tomography (PET), and deviations can induce serious errors. In this study, we devise a method for determining receptor occupancy of the mass dose of the radioligand itself and the in vivo affinity.

Methods

The approach was used for [¹¹C]SB207145, a new PET radioligand for imaging the cerebral 5-HT₄ receptors in humans. Test–retest PET studies with varying specific activities of [¹¹C]SB207145 were conducted in seven healthy subjects, and the output parameter regional BP_ND was modeled. Individual occupancy plots were first computed to estimate the mass dose that saturates 50% of receptors (ID₅₀), and subsequently, the maximal mass dose that can be injected (arbitrarily set at an occupancy <5%) was calculated. Scatchard plots were computed to estimate the in vivo K_D.

Results

Increasing the mass dose resulted in a decrease in BP_ND, whilst the relative cerebellar uptake was unchanged. The ID₅₀ was 85.4±30.2 μg, and the upper mass dose limit was 4.5±1.6 μg, which does not require ultrahigh specific activity. The estimated in vivo K_D was 2.8 nM (range 1.0–4.8), without any regional differences.

Conclusion

The presented method for estimating the upper mass dose limit is suggested as part of validation of PET radioligands.     

Microautoradiography of [123I]ADAM in mice treated with fluoxetine and serotonin reuptake inhibitors

A radiopharmaceutical, (123)I-labeled 2-((2-((dimethylamino)methyl)phenyl)thio)-5-iodophenylamine ([(123)I]ADAM), has been developed recently for evaluation of how serotonin transporters (SERT) function in the brain. However, the detailed biodistribution and specific binding in certain brain areas are not well investigated. In this study, both phosphor plate imaging and microautoradiography were applied to explore the binding characteristics of [(123)I]ADAM in SERT neurons. The effect of two psychotropics and one narcotic on the binding of [(123)I]ADAM to SERT was also studied. Fluoxetine and desipramine, both are psychotropics and specific SERT ligands and decreased the affinity of [(123)I]ADAM, while p-chloroamphetamine (PCA), a narcotic, destroyed most of serotonergic neurons, as well as reducing the concentration of serotonin and the number of SERT in the brain as shown by the biodistribution of [(123)I]ADAM. Significant and selective accumulation of [(123)I]ADAM in the areas from midbrain to brain stem in normal mice with maximum target-to-background ratio was found at 90 minutes postinjection. A rapid clearance of [(131)I]ADAM at 120 minutes postinjection was found in the CA1, CA3 and ThN brain areas. In addition, the inhibition effect on binding ability of [(123)I]ADAM to SERT by the psychotropics and the narcotic was found to have the order of: PCA > fluoxetine > desipramine.     

Comparison of [123I]ß-CIT and [123I]IPCIT as single-photon emission tomography radiotracers for the dopamine transporter in nonhuman primates

Single-photon emission tomographic (SPET) imaging with the radiotracer [¹²³I]2-carbomethoxy-3-(4-iodophenyl)tropane ([¹²³I]-CIT) has been reported to be a useful in vivo measure of dopamine (DA) transporters. However, in addition to its high DA transporter affinity,-CIT also binds with high affinity to serotonin (5-HT) transporters. 2-Carboisopropoxy-3-(4-iodophenyl)tropane (IPCIT) has been demonstrated by in vitro studies to have higher selectivity for the DA transporter. We compared [¹²³I]-CIT and [¹²³I]IPCIT SPET imaging and plasma metabolite analyses in baboons to evaluate the potential advantages of [¹²³I]IPCIT for quantitative in vivo measurements of DA transporter densities. Both tracers had low levels (2% of total plasma¹²³I activity) of lipophilic radiolabeled metabolites at 420 min. [¹²³I]IPCIT had significantly higher binding to plasma proteins. The average percent free (nonprotein bound) [¹²³I]-CIT and [¹²³I]IPCIT were 52%±7% and 14%±6%, respectively. Region of interest uptake data were normalized by injected dose and body weight. Consistent with the high density of 5-HT transporters in the midbrain and the lower 5-HT transporter affinity of IPCIT, the normalized peak specific midbrain uptake of [¹²³I]-CIT (1.7±0.5) was higher than that of [¹²³I]IPCIT (0.4±0.2). Consistent with its greater lipophilicity, [¹²³I]IPCIT had higher nonspecific uptake, such that normalized cerebellar uptake of [¹²³I]IPCIT was about twice that of [¹²³I]-CIT. The ratio of specific to nonspecific uptake in striatum was greater for [¹²³I]-CIT compared to [¹²³I]IPCIT; however, striatal binding potentials and distribution volumes were not significantly different. In conclusion, [¹²³I]IPCIT demonstrated in vivo a higher DA transporter selectivity and higher level of nonspecific uptake.     

Reproducibility of [<Superscript>123</Superscript>I]PE2I binding to dopamine transporters with SPECT

Purpose The iodinated cocaine derivative [¹²³I]PE2I is a new selective ligand for in vivo studies of the dopamine transporter (DAT) with SPECT. Recently, a bolus/infusion (B/I) protocol for [¹²³I]PE2I measurements of DAT density was established [Pinborg LH et al. J Nucl Med 2005;46:1119–271]. The aims of this study were, firstly, to evaluate the test–retest variability using the B/I protocol and, secondly, to evaluate the B/I approach in a new group of healthy subjects using two outcome parameters, BP₁ (C_ROI/C_plasma) and BP₂ (C_ROI/C_REF). Methods Seven healthy subjects were subjected to [¹²³I]PE2I SPECT scanning twice. For both studies, the two outcome parameters BP₁ and BP₂ were calculated based on two different methods for region of interest (ROI) delineation, namely manual delineation and probability map-based automatic delineation with MRI co-registration. Results With manual delineation, striatal test–retest variability (absolute difference between first and second scan as a percentage of the mean) of BP₁ and BP₂ was 13.9% (range 1.8–35.7%) and 4.1% (range 0.5–9.7%) respectively. The probability map-based automatic delineation resulted in striatal test–retest variability of 17.2% (range 4.3–40.5%) and 5.2% (range 0.1–10.9%) respectively. The B/I approach provided stable brain activity from 120 to 180 min post injection in both high- and low-count regions with a mean % change/hour in striatal BP₂ of 10.6. Conclusion [¹²³I]PE2I SPECT with the B/I approach yields a highly reproducible measure of striatal dopamine transporter binding. The appropriateness of a B/I protocol with a B/I ratio of 2.7 h (i.e. with a bolus worth 2.7 h of infusion) was confirmed in an independent sample of healthy subjects.     

Serotonin transporter binding with [<Superscript>123</Superscript>I]β-CIT SPECT in major depressive disorder versus controls: effect of season and gender

Purpose  The serotonin system is undoubtedly involved in the pathogenesis of major depressive disorder (MDD). More specifically the serotonin transporter (SERT) serves as a major target for antidepressant drugs. There are conflicting results about SERT availability in depressed patients versus healthy controls. We aimed to measure SERT availability and study the effects of age, gender and season of scanning in MDD patients in comparison to healthy controls. Methods  We included 49 depressed outpatients (mean±SD 42.3 ± 8.3 years) with a Hamilton depression rating scale score above 18, who were drug-naive or drug-free for ≥4 weeks, and 49 healthy controls matched for age (±2 years) and sex. Subjects were scanned with single photon emission computed tomography (SPECT) using [¹²³I]β-CIT. SERT availability was expressed as specific to nonspecific binding ratios (BP_ND) in the midbrain and diencephalon with cerebellar binding as a reference. Results  In crude comparisons between patients and controls, we found no significant differences in midbrain or diencephalon SERT availability. In subgroup analyses, depressed males had numerically lower midbrain SERT availability than controls, whereas among women SERT availability was not different (significant diagnosis×gender interaction; p = 0.048). In the diencephalon we found a comparable diagnosis×gender interaction (p = 0.002) and an additional smoking×gender (p = 0.036) interaction. In the midbrain the season of scanning showed a significant main effect (p = 0.018) with higher SERT availability in winter. Conclusion  Differences in SERT availability in the midbrain and diencephalon in MDD patients compared with healthy subjects are affected by gender. The season of scanning is a covariate in the midbrain. The diagnosis×gender and gender×smoking interactions in SERT availability should be considered in future studies of the pathogenesis of MDD.     

Differential kinetics of [123I]β-CIT binding to dopamine and serotonin transporters

Iodine-123-labelled 3-(4-iodophenyl)tropane-2-carboxylic acid ([¹²³I]-CIT) labels both the dopamine transporter (DAT) and the serotonin transporter (5-HTT) and this ligand is able to clarify pathological changes in both dopaminergic and serotonergic systems. However, the differential kinetics of -CIT binding to DAT and 5-HTT has not been clarified fully. In this study we examined time-activity curves of [¹²³I]-CIT in individual regions in the rat brain. Using cerebellum as the reference region,k ₃ andk ₄ values were estimated by a two-compartment kinetic analysis. In the striatum, the kinetics was slowest among all brain areas. In this area specific binding reached its peak 4 h after the injection. In the hypothalamus, specific binding reached its peak 1 h after the injection and its amount did not change until 4 h after the injection. In the occipital cortex, the binding and washout of the ligand were fastest among all brain regions. Estimatedk ₃ values were 0.040±0.003 in the striatum, 0.019±0.002 in the hypothalamus and 0.082±0.011 in the occipital cortex (min^–t, mean ±SD). Estimatedk ₄ values were 0.0034±0.0005 in the striatum, 0.0071±0.0009 in the hypothalamus and 0.083±0.013 in the occipital cortex (min^–1, mean ±SD). Therefore binding kinetics of [¹²³I]-CIT in the region rich in DAT is apparently different from that in the region rich in 5-HTT. These results will provide fundamental data to image both DAT and 5-HTT in one series of examinations with [¹²³I]-CIT.     

The relationship between the dopaminergic system and depressive symptoms in cervical dystonia

Purpose

Cervical dystonia (CD) is associated with tremor/jerks (50%) and psychiatric complaints (17–70%). The dopaminergic system has been implicated in the pathophysiology of CD in animal and imaging studies. Dopamine may be related to the motor as well as non-motor symptoms of CD. CD is associated with reduced striatal dopamine D_2/3 (D2/3) receptor and increased dopamine transporter (DAT) binding. There are differences in the dopamine system between CD patients with and without jerks/tremor and psychiatric symptoms.

Methods

Patients with CD and healthy controls underwent neurological and psychiatric examinations. Striatal DAT and D2/3 receptor binding were assessed using [¹²³I]FP-CIT and [¹²³I]IBZM SPECT, respectively. The ratio of specific striatal to non-specific binding (binding potential; BP_ND) was the outcome measure.

Results

Twenty-seven patients with CD and 15 matched controls were included. Nineteen percent of patients fulfilled the criteria for a depression. Striatal DAT BP_ND was significantly lower in depressed versus non-depressed CD patients. Higher DAT BP_ND correlated significantly with higher scores on the Unified Myoclonus Rating Scale (UMRS). The striatal D2/3 receptor BP_ND in CD patients showed a trend towards lower binding compared to controls. The D2/3 BP_ND was significantly lower in depressed versus non-depressed CD patients. A significant correlation between DAT and D2/3R BP_ND was found in both in patients and controls.

Conclusions

Alterations of striatal DAT and D2/3 receptor binding in CD patients are related mainly to depression. DAT BP_ND correlates significantly with scores on the UMRS, suggesting a role for dopamine in the pathophysiology of tremor/jerks in CD.

     

Dual-isotope single-photon emission computed tomography for dopamine and serotonin transporters in normal and parkinsonian monkey brains

IntroductionParkinson's disease (PD) affects both dopaminergic and serotonergic systems. In this study, we simultaneously evaluated dopamine and serotonin transporters in primates using dual-isotope single-photon emission computed tomography (SPECT) imaging and compared the results with traditional single-isotope imaging.MethodsFour healthy and one 6-OHDA-induced PD monkeys were used for this study. SPECT was performed over 4 h after individual or simultaneous injection of [^99mTc]TRODAT-1 (a dopamine transporter imaging agent) and [¹²³I]ADAM (a serotonin transporter imaging agent).ResultsThe results showed that the image quality and uptake ratios in different brain regions were comparable between single- and dual-isotope studies. The striatal [^99mTc]TRODAT-1 uptake in the PD monkey was markedly lower than that in normal monkeys. The uptake of [¹²³I]ADAM in the midbrain of the PD monkey was comparable to that in the normal monkeys, but there were decreased uptakes in the thalamus and striatum of the PD monkey.ConclusionsOur results suggest that dual-isotope SPECT using [^99mTc]TRODAT-1 and [¹²³I]ADAM can simultaneously evaluate changes in dopaminergic and serotonergic systems in a PD model.     

Effects of rs591323 on serotonin transporter availability in healthy male subjects

Objectives

We aimed to investigate the association between genetic factors of SNPs dopamine transporter (DAT) and serotonin transporter (SERT) availabilities in healthy controls.

Methods

The study population consisted of healthy controls with screening ¹²³I-FP-CIT single-photon emission computed tomography. Specific binding of ¹²³I-FP-CIT regarding DAT and SERT was calculated using a region of interest analysis. VOI template was applied to measure specific binding ratios (SBRs) of caudate nucleus, putamen, striatum, midbrain, and pons.

Results

One hundred sixty healthy controls (male 106, female 54, 61.0?±?11.5 years) were included in this study. Sex difference did not exist in DAT availabilities of caudate nucleus (p?=?0.5344), putamen (p?=?0.5006), and striatum (p?=?0.5056). However, male subjects had higher SERT availabilities of both midbrain (p?=?0.0436), and pons (p?=?0.0061). Therefore, we analyzed the effect of SNP on DAT availabilities of subjects in all, and that on SERT availabilities of males and females separately. None of 19 SNPs included in this study showed the effect on DAT availabilities. However, rs591323 in Fibroblast Growth Factor 20 on chromosome 8 had a significant impact on SERT availability of both midbrain (p?=?0.0056) and pons (p?=?0.0007).

Conclusion

SNP rs591323 of risk loci for Parkinson’s disease is associated with SERT availability of healthy male subjects.

     

The effects of <Emphasis Type="Italic">d</Emphasis>-amphetamine on extrastriatal dopamine D<Subscript>2</Subscript>/D<Subscript>3</Subscript> receptors: a randomized,double-blind,placebo-controlled PET study with [<Superscript>11</Superscript>C]FLB 457 in healthy subjects

Purpose  The dopamine D₂/D₃ receptor ligand [¹¹C]FLB 457 and PET enable quantification of low-density extrastriatal D₂/D₃ receptors, but it is uncertain whether [¹¹C]FLB 457 can be used for measuring extrastriatal dopamine release. Methods  We studied the effects of d-amphetamine (0.3 mg/kg i.v.) on extrastriatal [¹¹C]FLB 457 binding potential (BP_ND) in a randomized, double-blind, placebo-controlled study including 24 healthy volunteers. Results  The effects of d-amphetamine on [¹¹C]FLB 457 BP_ND and distribution volume (V_T) in the frontal cortex were not different from those of placebo. Small decreases in [¹¹C]FLB 457 BP_ND were observed only in the posterior cingulate and hippocampus. The regional changes in [¹¹C]FLB 457 BP_ND did not correlate with d-amphetamine-induced changes in subjective ratings of euphoria. Conclusion  This placebo-controlled study showed that d-amphetamine does not induce marked changes in measures of extrastriatal dopamine D₂/D₃ receptor binding. Our results indicate that [¹¹C]FLB 457 PET is not a useful method for measuring extrastriatal dopamine release in humans.     

The stereoisomers of 17α-[123I]iodovinyloestradiol and its 11α-methoxy derivative evaluated for their oestrogen receptor binding in human MCF-7 cells and rat uterus,and their distribution in immature rats

We studied the potential of both stereoisomers of 17-[¹²³I]iodovinyloestradiol (E- andZ-[¹²³I]IVE) and of 11-methoxy-17-[¹²³I]iodovinyloestradiol (E-andZ-[¹²³I]MIVE) as suitable radioligands for the imaging of oestrogen receptor(ER)-positive human breast tumours. The 17-[¹²³I]iodovinyloestradiols were prepared stereospecifically by oxidative radio-iododestannylation of the corresponding 17-tri-n-butylstannylvi-nyloestradiol precursors. Competitive binding studies were performed in order to determine the relative binding affinity (RBA) of the unlabelled 17-iodovinyloes-tradiols for the ER in both human MCF-7 breast tumour cells and rat uterine tissue, compared with that of diethylstilboestrol (DES). Target tissue uptake, retention and uptake selectivity of their¹²³I-labelled analogues were studied in immature female rats. All four 17-iodovi-nyloestradiols showed high affinity for the ER in human MCF-7 cells, as well as rat uterus. Their RBA for the ER showed the following order of decreasing potency: RBA of DES >Z-IVE >Z-MIVE >E-MIVE E-IVE. Neither of these 17-iodovinyloestradiols showed any significant binding to the sex hormone binding globulin in human plasma. The biodistribution studies showed ER-mediated uptake in the uterus, ovaries and pituitary, that ofE- andZ-[¹²³I]MIVE being higher than that ofE- andZ-[¹²³I]IVE. High target-to-non-target tissue uptake ratios, especially at longer periods after injection (up to 24 h), were exhibited by both isomers of [¹²³I]MIVE. The uterus-to-blood uptake ratio was higher for^E-[¹²³I]MIVE. However, the uterus-to-fat uptake ratio appeared to be higher for theZ-isomer of [¹²³I]MIVE, especially at 24 h after injection. Metabolic properties and temperature effects, which play a more important role in vivo, probably cause the discrepancies seen between in vitro and in vivo binding results. On the basis of their in vitro binding properties and in vivo distribution characteristics we conclude thatE- andZ-[¹²³I]MIVE could be suitable radioligands for the diagnostic imaging of ER in human breast cancer. Therefore, further studies with these radioligands in mature normal and tumour-bearing rats are warranted.     

The uptake of 3′-deoxy-3′-[18F]fluorothymidine into L5178Y tumours in vivo is dependent on thymidine kinase 1 protein levels

Purpose The aim of this study was to investigate the role of thymidine kinase 1 (TK₁) protein in 3-deoxy-3-[¹⁸F]fluorothymidine ([¹⁸F]FLT) positron emission tomography (PET) studies.Methods We investigated the in vivo kinetics of [¹⁸F]FLT in TK₁+/– and TK₁–/– L5178Y mouse lymphoma tumours that express different levels of TK₁ protein.Results [¹⁸F]FLT-derived radioactivity, measured by a dedicated small animal PET scanner, increased within the tumours over 60 min. The area under the normalised tumour time–activity curve were significantly higher for the TK₁+/– compared with the –/– variant (0.89±0.02 vs 0.79±0.03 MBq ml^–1 min, P=0.043; n=5 for each tumour type). Ex vivo gamma counting of tissues excised at 60 min p.i. (n=8) also revealed significantly higher tumour [¹⁸F]FLT uptake for the TK₁+/– variant (6.2±0.6 vs 4.6±0.4%ID g^–1, P=0.018). The observed differences between the cell lines with respect to [¹⁸F]FLT uptake were in keeping with a 48% higher TK₁ protein in the TK₁+/– tumours versus the –/– variant (P=0.043). On average, there were no differences in ATP levels between the two tumour variants (P=1.00). A positive correlation between [¹⁸F]FLT accumulation and TK₁ protein levels (r=0.68, P=0.046) was seen. Normalisation of the data for ATP content further improved the correlation (r=0.86, P=0.003).Conclusion This study shows that in vivo [¹⁸F]FLT kinetics depend on TK₁ protein expression. ATP may be important in realising this effect. Thus, [¹⁸F]FLT-PET has the potential to yield specific information on tumour proliferation in diagnostic imaging and therapy monitoring.     

Quantification of serotonin transporters in nonhuman primates using [(123)I]ADAM and SPECT.

We reported recently a highly selective radioligand, 2-([2-([dimethylamino]methyl)phenyl]thio)-5-[(123)I]iodophenylamine (ADAM), for SPECT imaging of serotonin transporters (SERT). In this article we describe the kinetic modeling of [(123)I]ADAM and its ability to quantitatively and reproducibly measure the concentrations of SERT in the nonhuman primate brain. We also investigate simplified models of tracer behavior that do not require invasive arterial blood sampling. METHODS: Three female baboons each underwent 3 [(123)I]ADAM SPECT studies. The studies consisted of a dynamic sequence of seventy-two 5-min scans after injection of 330 +/- 50 MBq (mean +/- SD) [(123)I]ADAM. Rapid arterial blood samples were obtained and corrected for the presence of labeled metabolites. Dynamic imaging and metabolite-corrected plasma data were analyzed using graphic analysis to give the distribution volumes (DVs) of different brain regions. DV ratios (DVRs) of target to cerebellum were derived and compared against a kinetic reference tissue model and simple target-to-background ratio. RESULTS: Averaged over all 9 scans, the mean DV in the midbrain was 4.86 +/- 1.06 mL/mL and the mean DV in the cerebellum was 2.25 +/- 0.48 mL/mL. The mean test-retest repeatability of the midbrain DV was 14.5%. The reference tissue model gave a mean midbrain DVR of 2.01 +/- 0.17 and correlated strongly with the DVR calculated from the full kinetic model (correlation coefficient [R(2)] = 0.94; P < 0.001), but with much improved repeatability (test-retest, 5.4%; intersubject variability, 5.2%). Similarly, the simple ratio method gave strong correlations with the full kinetic model (R(2) = 0.89; P < 0.001) and a test-retest of 7.6%. CONCLUSION: Accurate, repeatable quantification of SERT in the nonhuman primate brain is possible using kinetic modeling of dynamic [(123)I]ADAM SPECT scans. Simplified models, which do not require arterial blood sampling, gave accurate results that correlated strongly with the full kinetic model. The test-retest reliability of the simplified reference region models was excellent. Quantification of SERT is possible using full kinetic modeling and also with simpler reference region methods.