Imaging of the prostate-specific membrane antigen (PSMA) has become an important tool for managing patients with recurrent prostate cancer, and one of the most frequently employed radiopharmaceuticals is [68Ga]Ga-PSMA-11. Herein, we summarize the preclinical development and the clinical applications of [68Ga]Ga-PSMA-11 and present side-by-side comparisons with other radiopharmaceuticals or imaging modalities, in order to assist imagers and clinicians in recommending, performing, and interpreting the results of [68Ga]Ga-PSMA-11 PET scans in patients with prostate cancer.

The M-1 muscarinic acetylcholine receptor (mAChR) plays an important role in learning and memory, and therefore is a target for development of drugs for treatment of cognitive impairments in Alzheimer disease and schizophrenia. The availability of M-1-selective radiotracers for PET will help in developing therapeutic agents by providing an imaging tool for assessment of drug dose-receptor occupancy relationship. Here we report the synthesis and evaluation of C-11-LSN3172176 (ethyl 4-(6-(methyl-C-11)-2-oxoindolin-1-yl)[1,4'-bipiperidine]-1'-carboxylate) in nonhuman primates. Methods: C-11-LSN3172176 was radiolabeled via the Suzuki-Miyaura crosscoupling method. PET scans in rhesus macaques were acquired for 2 h with arterial blood sampling and metabolite analysis to measure the input function. Blocking scans with scopolamine (50 mu g/kg) and the M-1-selective agent AZD6088 (0.67 and 2 mg/kg) were obtained to assess tracer binding specificity and selectivity. Regional brain time-activity curves were analyzed with the 1-tissue-compartment model and the multilinear analysis method (MA1) to calculate regional distribution volume. Nondisplaceable binding potential values were calculated using the cerebellum as a reference region. Results: C-11-LSN3172176 was synthesized with greater than 99% radiochemical purity and high molar activity. In rhesus monkeys, C-11-LSN3172176 metabolized rapidly (29% +/- 6% parent remaining at 15 min) and displayed fast kinetics and extremely high uptake in the brain. Imaging data were modeled well with the 1-tissue-compartment model and MA1 methods. MA1-derived distribution volume values were high (range, 10-81 mL/cm(3)) in all known M-1 mAChR-rich brain regions. Pretreatment with scopolamine and AZD6088 significantly reduced the brain uptake of C-11-LSN3172176, thus demonstrating its binding specificity and selectivity in vivo. The cerebellum appeared to be a suitable reference region for derivation of nondisplaceable binding potential, which ranged from 2.42 in the globus pallidus to 8.48 in the nucleus accumbens. Conclusion: C-11-LSN3172176 exhibits excellent in vivo binding and imaging characteristics in nonhuman primates and appears to be the first appropriate radiotracer for PET imaging of human M-1 AChR.

The myriad physiological functions of γ-amino butyric acid (GABA) are mediated by the GABA-benzodiazepine receptor complex comprising of the GABAA, GABAB, and GABAC groups. The various GABAA subunits with region-specific distributions in the brain subserve different functional and physiological roles. For example, the sedative and anticonvulsive effects of classical benzodiazepines are attributed to the α1 subunit, and the α2 and α3 subunits mediate the anxiolytic effect. To optimize pharmacotherapies with improved efficacy and devoid of undesirable side effects for the treatment of anxiety disorders, subtype-selective imaging radiotracers are required to assess target engagement at GABA sites and determine the dose–receptor occupancy relationships. The goal of this work was to characterize, in nonhuman primates, the in vivo binding profile of a novel positron emission tomography (PET) radiotracer, [11C]ADO, which has been indicated to have functional selectivity for the GABAA α2/α3 subunits. High specific activity [11C]ADO was administrated to 3 rhesus monkeys, and PET scans of 120-minute duration were performed on the Focus-220 scanner. In the blood, [11C]ADO metabolized at a fairly rapid rate, with ∼36% of the parent tracer remaining at 30 minutes postinjection. Uptake levels of [11C]ADO in the brain were high (peak standardized uptake value of ∼3.0) and consistent with GABAA distribution, with highest activity levels in cortical areas, intermediate levels in cerebellum and thalamus, and lowest uptake in striatal regions and amygdala. Tissue kinetics was fast, with peak uptake in all brain regions within 20 minutes of tracer injection. The one-tissue compartment model provided good fits to regional time–activity curves and reliable measurement of kinetic parameters. The absolute test–retest variability of regional distribution volumes (VT) was low, ranging from 4.5% to 8.7%. Pretreatment with flumazenil (a subtype nonselective ligand, 0.2 mg/kg, intravenous [IV], n = 1), Ro15-4513 (an α5-selective ligand, 0.03 mg/kg, IV, n = 2), and zolpidem (an α1-selective ligand, 1.7 mg/kg, IV, n = 1) led to blockade of [11C]ADO binding by 96.5%, 52.5%, and 76.5%, respectively, indicating the in vivo binding specificity of the radiotracer. Using the nondisplaceable volume of distribution (VND) determined from the blocking studies, specific binding signals, as measured by values of regional binding potential (BPND), ranged from 0.6 to 4.4, which are comparable to those of [11C]flumazenil. In conclusion, [11C]ADO was demonstrated to be a specific radiotracer for the GABAA receptors with several favorable properties: high brain uptake, fast tissue kinetics, and high levels of specific binding in nonhuman primates. However, subtype selectivity in vivo is not obvious for the radiotracer, and thus, the search for subtype-selective GABAA radiotracers continues.

The sigma(1) receptors (S1Rs) are implicated in a variety of diseases including Alzheimer disease and cancer. Previous PET S1R radiotracers are characterized by slow kinetics or off-target binding that impedes their use in humans. Here, we report the first PET imaging evaluation in rhesus monkeys of 4 F-18-labeled spirocyclic piperidine-based PET radiotracers (F-18-1 to F-18-4). Methods: Baseline scans for the 4 radiotracers were obtained on an adult male rhesus monkey. Blocking scans were obtained with the S1R-selective agonist SA4503 to assess binding specificity of F-18-2 and F-18-4. Arterial input functions were measured, and binding parameters were determined with kinetic modeling analysis. Results: In the rhesus brain, all 4 radiotracers showed high and fast uptake. Tissue activity washout was rapid for F-18-2 and F-18-4, and much slower for F-18-1 and F-18-3, in line with their respective in vitro S1R-binding affinities. Both the 1-tissue-compartment and multilinear analysis-1 kinetic models provided good fits of time-activity curves and reliable estimates of distribution volume. Regional distribution volume values were highest in the cingulate cortex and lowest in the thalamus for all radiotracers. F-18-4 showed greater differential uptake across brain regions and 3-fold-higher binding potential than F-18-2. SA4503 at the dose of 0.5 mg/kg blocked approximately 85% (F-18-2) and 95% (F-18-4) of radiotracer binding. Conclusion: Tracers F-18-2 and F-18-4 displayed high brain uptake and fast tissue kinetics, with F-18-4 having higher specific binding signals than F-18-2 in the same monkey. Taken together, these data indicate that both F-18-2 and F-18-4 possess the requisite kinetic and imaging properties as viable PET tracers for imaging S1R in the human brain.

INTRODUCTION:Tobacco smoking leads to increased numbers of β2*-containing nicotinic acetylcholine receptors (β2*-nAChRs) throughout the brain, which return to nonsmoker levels over extended abstinence. The goal of the current study was to determine whether the degree of tobacco smoking-induced changes in β2*-nAChR availability is genetically influenced.METHODS:In this study, 113 European Americans participated in one or two [(123)I]5-IA-85380 single photon emission computed tomography (SPECT) brain scans. Smokers (n = 58) participated in one scan at 7-9 days of abstinence and those who remained abstinent (n = 27) were imaged again at 6-8 weeks of abstinence. Age- and sex-matched nonsmokers (n = 55) participated in one scan. Blood samples were collected for DNA analysis and genotyped for single nucleotide polymorphisms (SNPs) in the CHRNA4 and ANKK1 gene loci. β2*-nAChR availability was measured in the thalamus, striatum, cortical regions, and cerebellum.RESULTS:The CHRNA4 SNP rs2236196 and ANKK1 SNP rs4938015 were associated with significantly higher cerebellar and cortical β2*-nAChR availability in smokers versus nonsmokers for specific genotypes. There were no significant differences by carrier status in the change in β2*-nAChR availability in smokers from 7-9 days to 6-8 weeks of abstinence.CONCLUSION:This study provides evidence for genetic regulation of tobacco smoking-induced changes in β2*-nAChR availability and suggests that β2*-nAChR availability could be an endophenotype mediating influences of CHRNA4 variants on nicotine dependence. These results highlight individual differences in the neurochemistry of nicotine dependence and may suggest the need for individualized programs for smoking cessation.IMPLICATIONS:This study demonstrates genetic regulation of smoking-induced changes in β2*-nAChRs throughout the brain and highlights the need for personalized programs for smoking cessation.

The positron emission tomography (PET) radioligand (−)-[18F]flubatine is specific to α4β2⁎ nicotinic acetylcholine receptors (nAChRs) and has promise for future investigation of the acetylcholine system in neuropathologies such as Alzheimer's disease, schizophrenia, and substance use disorders. The two goals of this work were to develop a simplified method for α4β2⁎ nAChR quantification with bolus plus constant infusion (B/I) (−)-[18F]flubatine administration, and to assess the radioligand's sensitivity to acetylcholine fluctuations in humans. Healthy human subjects were imaged following either bolus injection (n = 8) or B/I (n = 4) administration of (−)-[18F]flubatine. The metabolite-corrected input function in arterial blood was measured. Free-fraction corrected distribution volumes (VT/fP) were estimated with modeling and graphical analysis techniques. Next, sensitivity to acetylcholine was assessed in two ways: 1. A bolus injection paradigm with two scans (n = 6), baseline (scan 1) and physostigmine challenge (scan 2; 1.5 mg over 60 min beginning 5 min prior to radiotracer injection); 2. A single scan B/I paradigm (n = 7) lasting up to 240 min with 1.5 mg physostigmine administered over 60 min beginning at 125 min of radiotracer infusion. Changes in VT/fP were measured. Baseline VT/fP values were 33.8 ± 3.3 mL/cm3 in thalamus, 12.9 ± 1.6 mL/cm3 in cerebellum, and ranged from 9.8 to 12.5 mL/cm3 in other gray matter regions. The B/I paradigm with equilibrium analysis at 120 min yielded comparable VT/fP values with compartment modeling analysis of bolus data in extrathalamic gray matter regions (regional means < 4% different). Changes in VT/fP following physostigmine administration were small and most pronounced in cortical regions, ranging from 0.8 to 4.6% in the two-scan paradigm and 2.8 to 6.5% with the B/I paradigm. These results demonstrate the use of B/I administration for accurate quantification of (−)-[18F]flubatine VT/fP in 120 min, and suggest possible sensitivity of (−)-[18F]flubatine binding to physostigmine-induced changes in acetylcholine levels.

Introduction: The PET radiotracer [F-18]FMISO has been used in the clinic to image hypoxia in tumors. The aim of the present study was to optimize the radiochemical parameters for the preparation of [F-18]FMISO using a microfluidic reaction system. The main parameters evaluated were (1) precursor concentration, (2) reaction temperature, and (3) flow rate through the microfluidic reactor. Optimized conditions were then applied to the batch production of [F-18]FMISO for clinical research use.Methods: For the determination of optimal reaction conditions within a flow-through microreactor synthesizer, 5-400 mu L. the precursor and dried [F-18]fluoride solutions in acetonitrile were simultaneously pushed through the temperature-controlled reactor (60-180 degrees C) with defined flow rates (20-120 mu L/min). Radiochemical incorporation yields to form the intermediate species were determined using radio-TLC. Hydrolysis to remove the protecting group was performed following standard vial chemistry to afford [F-18]FMISO.Results: Optimum reaction parameters for the microfluidic set-up were determined as follows: 4 mg/mL of precursor, 170 degrees C, and 100 mu L/min pump rate per reactant (200 mu L/min reaction overall flow rate) to prepare the radiolabeled intermediate. The optimum hydrolysis condition was determined to be 2 N HCl for 5 min at 100 degrees C. Large-scale batch production using the optimized conditions gave the final, ready for human injection [F-18]FMISO product in 28.4 +/- 3.0% radiochemical yield, specific activity of 119 +/- 26 GBq/mu mol, and >99% radio-chemical and chemical purity at the end of synthesis (n = 4).Conclusion: By using the NanoTek microfluidic synthesis system, [F-18]FMISO was successfully prepared with good specific activity and high radiochemical purity for human use. The product generated from large-scale batch production using flow chemistry is currently being used in clinical research. (C) 2015 Elsevier Inc. All rights reserved.

Understanding the effects of tobacco smoking on neuroadaptations in GABA(A) receptor levels over alcohol withdrawal will provide critical insights for the treatment of comorbid alcohol and nicotine dependence. We conducted parallel studies in human subjects and nonhuman primates to investigate the differential effects of tobacco smoking and nicotine on changes in GABA(A) receptor availability during acute and prolonged alcohol withdrawal. We report that alcohol withdrawal with or without concurrent tobacco smoking/nicotine consumption resulted in significant and robust elevations in GABA(A) receptor levels over the first week of withdrawal. Over prolonged withdrawal, GABA(A) receptors returned to control levels in alcohol-dependent nonsmokers, but alcohol-dependent smokers had significant and sustained elevations in GABA(A) receptors that were associated with craving for alcohol and cigarettes. In nonhuman primates, GABA(A) receptor levels normalized by 1 mo of abstinence in both groups-that is, those that consumed alcohol alone or the combination of alcohol and nicotine. These data suggest that constituents in tobacco smoke other than nicotine block the recovery of GABA(A) receptor systems during sustained alcohol abstinence, contributing to alcohol relapse and the perpetuation of smoking.

Background: Schizophrenia is associated with very high rates of tobacco smoking. The latter may be related to an attempt to self-medicate symptoms and/or to alterations in function of high-affinity beta(2)-subunit-containing nicotinic acetylcholine receptors (beta(2)*-nAChRs).Methods: Smoking and nonsmoking subjects with schizophrenia (n = 31) and age-, smoking-, and sex-matched comparison subjects (n = 31) participated in one [I-123]5-IA-85380 single photon emission computed tomography scan to quantify beta(2)*-nAChR availability. Psychiatric, cognitive, nicotine craving, and mood assessments were obtained during active smoking, as well as smoking abstinence.Results: There were no differences in smoking characteristics between smokers with and without schizophrenia. Subjects with schizophrenia had lower beta(2)*-nAChR availability relative to comparison group, and nonsmokers had lower beta(2)*-nAChR availability relative to smokers. However, there was no smoking by diagnosis interaction. Relative to nonsmokers with schizophrenia, smokers with schizophrenia had higher beta(2)*-nAChR availability in limited brain regions. In smokers with schizophrenia, higher beta(2)*-nAChR availability was associated with lower negative symptoms of schizophrenia and better performance on tests of executive control. Chronic exposure to antipsychotic drugs was not associated with changes in beta(2)*-nAChR availability in schizophrenia.Conclusions: Although subjects with schizophrenia have lower beta(2)*-nAChR availability relative to comparison group, smokers with schizophrenia appear to upregulate in the cortical regions. Lower receptor availability in smokers with schizophrenia in the cortical regions is associated with a greater number of negative symptoms and worse performance on tests of executive function, suggesting smoking subjects with schizophrenia who upregulate to a lesser degree may be at risk for poorer outcomes.

ABSTRACT Objective 18 F‐(‐)‐NCFHEB (also known as 18 F‐(‐)‐Flubatine) is a new radioligand to image α4β2* nicotinic acetylcholine receptors in vivo with positron emission tomography (PET), with faster kinetics than previous radioligands such as 18 F‐2‐F‐A85380. The goal of this study was to assess the sensitivity of 18 F‐(‐)‐NCFHEB‐PET to increases in synaptic acetylcholine concentration induced by acetylcholinesterase inhibitors. Methods Two rhesus monkeys were scanned four times each on a Focus 220 scanner: first at baseline, then during two bolus plus infusions of physostigmine (0.06–0.28 mg/kg), and finally following a bolus injection of donepezil (0.25 mg/kg). The arterial input function and the plasma free fraction f P were measured. 18 F‐(‐)‐NCFHEB volume of distribution V T was estimated using the multilinear analysis MA1 and then normalized by plasma free fraction f P . Results 18 F‐(‐)‐NCFHEB f P was 0.89 ± 0.04. At baseline, 18 F‐(‐)‐NCFHEB V T / f P ranged from 7.9 ± 1.3 mL plasma/cm 3 tissue in the cerebellum to 34.3 ± 8.4 mL plasma/cm 3 tissue in the thalamus. Physostigmine induced a dose‐dependent reduction of 18 F‐(‐)‐NCFHEB V T / f P of 34 ± 9% in the putamen, 32 ± 8% in the thalamus, 25 ± 8% in the cortex, and 23 ± 10% in the hippocampus. With donepezil, 18 F‐(‐)‐NCFHEB V T / f P was reduced by 24 ± 2%, 14 + 3% and 14 ± 5%, 10 ± 6% in the same regions. Conclusion 18 F‐(‐)‐NCFHEB can be used to detect changes in synaptic acetylcholine concentration and is a promising tracer to study acetylcholine dynamics with shorter scan durations than previous radioligands. Synapse 68:556–564, 2014 . © 2014 Wiley Periodicals, Inc.

INTRODUCTION:The aims of the present study were to develop an optimized microfluidic method for the production of the selective nicotinic acetylcholine α4β2 receptor radiotracer [(18)F]-(-)-NCFHEB ([(18)F]-Flubatine) and to investigate its receptor binding profile and pharmacokinetic properties in rhesus monkeys in vivo. METHODS:[(18)F]-(-)-NCFHEB was prepared in two steps, a nucleophilic fluorination followed by N-Boc deprotection. PET measurements were performed in rhesus monkeys including baseline and preblocking experiments with nicotine (0.24 mg/kg). Radiometabolites in plasma were measured using HPLC. RESULTS:[(18)F]-(-)-NCFHEB was prepared in a total synthesis time of 140 min. The radiochemical purity in its final formulation was >98% and the mean specific radioactivity was 97.3 ± 16.1 GBq/μmol (n = 6) at end of synthesis (EOS). In the monkey brain, radioactivity concentration was high in the thalamus, moderate in the putamen, hippocampus, frontal cortex, and lower in the cerebellum. Nicotine blocked 98-100% of [(18)F]-(-)-NCFHEB specific binding, and the non-displaceable distribution volume (VND) was estimated at 5.9 ± 1.0 mL/cm(3) (n = 2), or 6.6 ± 1.1 mL/cm(3) after normalization by the plasma free fraction fP. Imaging data are amenable to kinetic modeling analysis using the multilinear analysis (MA1) method, and model-derived binding parameters display good test-retest reproducibility. In rhesus monkeys, [(18)F]-(-)-NCFHEB can yield robust regional binding potential (BPND) values (thalamus = 4.1 ± 1.5, frontal cortex = 1.2 ± 0.2, putamen = 0.96 ± 0.45, and cerebellum = 0.10 ± 0.29). CONCLUSION:An efficient microfluidic synthetic method was developed for preparation of [(18)F]-(-)-NCFHEB. PET examination in rhesus monkeys showed that [(18)F]-(-)-NCFHEB entered the brain readily and its regional radioactivity uptake pattern was in accordance with the known distribution of α4β2 receptors. Estimated non-displaceable binding potential (BPND) values in brain regions were better than those of [(18)F]2-FA and comparable to [(18)F]AZAN. These results confirm previous findings and support further examination of [(18)F]-(-)-NCFHEB in humans.

Background: The cholinergic system is substantially altered in individuals with major depression and is partially restored when depression remits. We quantified the availability of beta(2)-subunit-containing nicotinic acetylcholine receptors (beta(2)*-nAChR) in subjects with bipolar disorder.Methods: Twenty-five subjects with bipolar disorder (15 depressed, 10 euthymic) and 25 sex-and age-matched control subjects had a [I-123]5IA-85380 single photon emission computed tomography scan to quantify beta(2)*-nAChR VT/fP (total volume of distribution, corrected for individual differences in metabolism and protein binding of the radiotracer). Average VT/fP was compared between groups and correlated with clinical characteristics. Postmortem analysis of beta(2)*-nAChRs was conducted using equilibrium binding with [I-125]5IA in subjects with bipolar disorder and matched control subjects.Results: We showed significantly lower beta(2)*-nAChR availability (20%-38%) in subjects with bipolar depression compared with euthymic and control subjects across all brain regions assessed (frontal, parietal, temporal, and anterior cingulate cortex, hippocampus, amygdala, thalamus, striatum). The postmortem binding study in which endogenous acetylcholine was washed out did not show a statistically significant difference in beta(2)*-nAChR number in temporal cortex of the bipolar depressed and control groups (15% difference; p = .2).Conclusions: We show that the alteration in the cholinergic system observed during a depressive episode appears to resolve during euthymia. We suggest that lower VT/fP observed in vivo may be due to a combination of higher endogenous acetylcholine levels during depression, which could compete with radiotracer binding to the receptor in vivo, and lower receptor number in bipolar depression. Identification of differences in cholinergic signaling in subjects with bipolar depression may improve our understanding of its etiology and reveal new treatment targets.

In vivo estimation of β2-nicotinic acetylcholine receptor availability with molecular neuroimaging is complicated by competition between the endogenous neurotransmitter acetylcholine and the radioligand 123I-3-[2(S)-2-azetidinylmethoxy]pyridine (123I-5-IA). We examined whether binding of 123I-5-IA is sensitive to increases in extracellular levels of acetylcholine in humans, as suggested in nonhuman primates. Methods: Six healthy subjects (31 ± 4 y) participated in a 123I-5-IA SPECT study. After baseline scans, physostigmine (1–1.5 mg) was administered intravenously over 60 min, and 9 additional scans were obtained. Results: We observed a significant reduction in the total volume of distribution after physostigmine administration (29% ± 17% in the cortex, 19% ± 15% in the thalamus, 19% ± 15% in the striatum, and 36% ± 30% in the cerebellum; P < 0.05). This reduction reflected a combination of a region-specific 7%–16% decrease in tissue concentration of tracer and a 9% increase in plasma parent concentration. Conclusion: These data suggest that increases in acetylcholine compete with 123I-5-IA for binding to β2-nicotinic acetylcholine receptor. Additional validation of this paradigm is warranted, but it may be used to interrogate changes in extracellular acetylcholine.

412 Objectives The cholinergic system plays an important role in medical and psychiatric disorders. Here, we evaluate the suitability of the recently developed PET ligand [18F](-)-norchloro-fluorohomoepibatidine ([18F]NCFHEB) to image α4β2 nicotinic acetylcholine (ACh) receptors in rhesus monkeys, and assess its sensitivity to physostigmine-induced increases in endogenous ACh. Methods PET data were acquired for 2 h. The arterial input function and plasma free fraction fP were measured. Rhesus monkeys underwent test and retest scans, a blocking scan with nicotine (0.24 mg/kg, iv) and two scans after physostigmine (0.06-0.28 mg/kg, iv). Regional normalized distribution volumes (VT/fP) were quantified using the multilinear analysis MA1 method. Results [18F]NCFHEB radiochemical purity was >98% and specific activity at the end of synthesis was 2.5±0.6 mCi/nmol (n=5). [18F]NCFHEB had high plasma free fraction (0.89±0.04, n=10) and rapid metabolism, with a parent fraction of 43±7 and 14±2% at 30 and 90 min postinjection. Baseline [18F]NCFHEB VT/fP values were 7.4±1.0 (cerebellum), 13±1.0 (hippocampus), 15±1.8 (frontal cortex), 13±1.6 (putamen), and 33±5.3 (thalamus) mL/cm3 (n=4). Test-retest variability of VT/fP ranged from 9% (thalamus) to 15% (cerebellum) (11% average for all regions). From blockade studies with nicotine, [18F]NCFHEB normalized nondisplaceable distribution volume (VND/fP) was 6.7±1.2 mL/cm3 (n=2) for all brain regions. Physostigmine-induced increases in ACh reduced [18F]NCFHEB VT/fP by 17±10% (cerebellum), 20±7% (hippocampus), 22±7% (frontal cortex), 30±6% (putamen) and 31±7% (thalamus) (n=4). Conclusions This first-time evaluation of [18F]NCFHEB in rhesus monkeys confirmed several favorable properties including high free fraction in plasma and specific binding in brain, good test-retest reproducibility and sensitivity to increases in endogenous ACh. These results support the use of this tracer in human studies of the cholinergic system in healthy and diseased brain. Research Support VA PTSD Center and NIH (K01 MH092681, K02 DA031750)

OBJECTIVE:Nicotine promotes smoking partly by binding to β2-containing nicotinic acetylcholine receptors (β2*-nAChRs) in the brain. Smoking one tobacco cigarette results in occupation of 80% of β2*-nAChRs for more than 6 hours. This likely contributes to maintenance of smoking dependence and cessation difficulty. Developing nicotine vaccines could improve treatments. The authors used [123I]5-I-A-85380 single photon emission computed tomography (SPECT) to evaluate the effect of 3'-AmNic-rEPA on the amount of nicotine that binds to β2*-nAChRs in smokers' brain cortical and subcortical regions.METHOD:Eleven smokers who smoked an average of 19 cigarettes per day, had smoked for 10 years on average, and met criteria for nicotine dependence were given SPECT scans on two days: before and after immunization with 4-400 μg of 3'-AmNic-rEPA. On scan days, three 30-minute baseline emission scans were followed by intravenous administration of nicotine (1.5 mg/70 kg body weight) and up to nine 30-minute emission scans.RESULTS:β2*-nAChR availability was quantified as VT/fP (total distribution volume divided by free plasma concentration), and nicotine binding was derived by the Lassen plot approach. Immunization led to a 12.5% reduction in nicotine binding. Nicotine bound to β2*-nAChRs correlated positively with nicotine injected before but not after vaccination. The daily number of cigarettes and desire for a cigarette decreased after vaccination.CONCLUSIONS:This proof-of-concept study demonstrates that immunization with nicotine vaccine can reduce the amount of nicotine binding to β2*-nAChRs and disrupt the relationship between administered nicotine and nicotine available to occupy β2*-nAChRs.

BACKGROUND:Modulation of nicotinic acetylcholine receptors (nAChRs), specifically those containing the β2 subunit, may be effective in treating patients with major depressive disorder. Using [123I]5-I-A-85380 single photon emission computed tomography (SPECT), the authors studied the availability of β2-subunit-containing nAChRs (β2*-nAChRs) in depressed patients. To understand its molecular basis, the authors also studied β2*-nAChR binding in postmortem brain samples from depressed subjects.METHOD:The participants were 23 medication-free, nonsmoking subjects with familial, early-onset depression (eight acutely ill and 15 recovered) and 23 age- and gender-matched nonsmoking comparison subjects. Each received one [123I]5-I-A-85380 SPECT scan and an MRI scan. The availability of β2*-nAChRs was quantified as VT/fP. Postmortem analysis of β2*-nAChR binding was conducted with [123I]5-I-A-85380 on prefrontal cortex samples from 14 depressed subjects and 14 age-matched comparison subjects.RESULTS:The β2*-nAChR availability in both the acutely ill and recovered depressed subjects was significantly lower across all brain regions than in the respective comparison subjects, and it was lower in the acutely ill subjects than in those who were recovered. In the depressed patients, β2*-nAChR availability was significantly correlated with lifetime number of depressive episodes, trauma score, and anxiety score. There were no differences in β2*-nAChR number between groups in the postmortem study.CONCLUSIONS:Depressed patients have lower β2*-nAChR availability than do healthy subjects. The difference between β2*-nAChR availability in vivo and in post-mortem samples may be analogous to data with dopaminergic PET ligands and dopamine receptor availability; lower receptor availability for the SPECT ligand could be caused by greater endogenous acetylcholine.