Biodistribution and radiation dosimetry of the α7 nicotinic acetylcholine receptor ligand [11C]CHIBA-1001 in humans

doi:10.1016/j.nucmedbio.2010.09.007

Nuclear Medicine and Biology

Volume 38, Issue 3, April 2011, Pages 443-448

https://doi.org/10.1016/j.nucmedbio.2010.09.007 Get rights and content

Abstract

Introduction

4-[¹¹C]Methylphenyl 2,4-diazabicyclo[3.2.2]nonane-2-carboxylate ([¹¹C]CHIBA-1001) is a newly developed positron emission tomography (PET) ligand for mapping α₇ nicotinic acetylcholine receptors. We investigated whole-body biodistribution and radiation dosimetry of [¹¹C]CHIBA-1001 in humans and compared the results with those obtained in mice.

Methods

Dynamic whole-body PET was carried out for three human subjects after administering a bolus injection of [¹¹C]CHIBA-1001. Emission scans were collected in two-dimensional mode over five bed positions. Regions of interest were placed over 12 organs. Radiation dosimetry was estimated from the residence times of these source organs using the OLINDA program. Biodistribution data from mice were also used for the prediction of radiation dosimetry in humans, and results with and those without accommodation of different proportions of organ-to-total-body mass were compared with the results from the human PET study.

Results

In humans, the highest accumulation was observed in the liver, whereas in mice, the highest accumulation was observed in the urinary bladder. The estimated effective dose from the human PET study was 6.9 μSv/MBq, and that from mice was much underestimated.

Conclusion

Effective dose estimates for [¹¹C]CHIBA-1001 were compatible with those associated with other common nuclear medicine tests. Absorption doses among several organs were considerably different between the human and mouse studies. Human dosimetry studies for the investigation of radiation safety are desirable as one of the first clinical trials of new PET probes before their application in subsequent clinical investigations.

Introduction

α₇ Nicotinic acetylcholine receptors (nAChRs) are one of the predominant nAChR subtypes in the brain. They play an important part in the pathophysiology of neurological and psychiatric diseases, such as schizophrenia, Alzheimer's disease and dementia with Lewy bodies [1], [2], [3], [4], [5]. It is therefore of great interest to examine whether α₇ nAChRs are altered in the living brain of these neuropsychiatric diseases. So far, a number of new radioligands for visualizing α₇ nAChRs in the living human brain, including anabaseine derivatives [6], 1-azabicyclo[2.2.2]octane derivatives [7], [8], [9], [10], 1,4-diazabicyclo[3.2.2]nonane derivatives [11], [12] and 3,7-diazabicyclo[3.3.0]octane derivatives [13], have been reported [14]. Among them, to the best of our knowledge, 4-[¹¹C]methylphenyl 2,4-diazabicyclo[3.2.2]nonane-2-carboxylate ([¹¹C]CHIBA-1001) is the only available PET ligand for human use [15].

[¹¹C]CHIBA-1001 is a methylated derivative of the selective α₇ partial agonist SSR180711 and was originally developed by Hashimoto et al. [11]. An in vitro binding study showed that high affinity of CHIBA-1001 for α₇ nAChR (IC₅₀=45.8 nM for [¹²⁵I]α-bungarotoxin binding) was much lower than those for 28 other receptors, including α₄β₂ nAChR. [¹¹C]CHIBA-1001 distribution in the monkey brain measured by PET was consistent with the regional distribution of α₇ nAChRs, and the brain uptake of [¹¹C]CHIBA-1001 was dose-dependently blocked by pretreatment with SSR180711 but was not with the selective α₄β₂ nAChR agonist A-85380 [11]. Although radioligands with sub-nanomolar in vitro affinity (below 0.02–0.3 nM) will be required for α₇-specific imaging, these positive in vivo findings prompted us to undertake preclinical and first clinical studies of [¹¹C]CHIBA-1001 [15].

We further investigated the pharmacological safety and radiation dosimetry of [¹¹C]CHIBA-1001. The ligand was synthesized by palladium-mediated Stille cross-coupling reactions, which produce toxic tin-containing contaminants. We confirmed that contamination of tin in the final product was under detectable range (<10 μg/L) by ICP-MS analysis. Moreover, final products did not include other undesirable compounds, such as starting materials tri(o-tolyl)phosphine and tributylstannyl iodide. Acute toxicity testing in rats using standard CHIBA-1001 at a dose of 3.20 mg/kg body (>41,000-fold clinical equivalent dose) and three lots of [¹¹C]CHIBA-1001 preparations in a dose range of 1.63–4.11 μg/kg body showed no abnormal signs, including body weight gain, clinical signs and postmortem macroscopic examination results. No mutagenic activity was also observed for CHIBA-1001 in the standard Ames test. The radiation-absorbed dose estimated was low enough for clinical use. The effective dose according to the risk-weighting factors of Publication 60 of the International Commission on Radiological Protection [16] was estimated at 3.8 μSv/MBq. The first human PET study was successfully performed with high levels of brain uptake and no pharmacological side effect at the dose required for adequate PET imaging [15]. However, peripheral metabolism of [¹¹C]CHIBA-1001 in humans was significantly different from that in rodents and monkeys. The findings suggest pharmacokinetic differences of radiotracers between species [17], which might result in inadequate prediction of radiation dosimetry of [¹¹C]CHIBA-1001 in animal studies [15]. Here, we investigated the biodistribution and radiation dosimetry of [¹¹C]CHIBA-1001 in humans using whole-body PET scans before proceeding to clinical studies. We then compared the results with those from a previous murine study [15].

Section snippets

Synthesis of [¹¹C]CHIBA-1001

The synthesis of [¹¹C]CHIBA-1001 has been described previously [15]. The average specific activity in human PET studies was 53.1±25.8 TBq/mmol.

Human PET study

This study was approved by the ethics committees of the Tokyo Metropolitan Institute of Gerontology (Tokyo, Japan) and Chiba University Graduate School of Medicine (Chiba, Japan). Written informed consent was obtained from each subject after the procedures had been fully explained.

Three healthy male volunteers participated in this study (age range=22–24

Results

The whole-body distribution of [¹¹C]CHIBA-1001 in the third subject is shown in Fig. 1. Fig. 2 gives the typical decay-corrected radioactivity time–activity curves of high-uptake (Fig. 2A) and low-uptake (Fig. 2B) source organs of the same subject. At the first frame, the lungs showed the highest uptake of radioactivity, which rapidly decreased thereafter. The highest accumulation was observed in the liver, which indicated an accumulative pattern until ∼90 min. Radioactivity disappeared more

Discussion

In this study, we studied the biodistribution and dosimetry of [¹¹C]CHIBA-1001 using dynamic whole-body PET in humans and compared them with those estimated from a tissue dissection study in mice. The most significant finding is the fact that the target organs for radiation were different in the two estimates. In the human study, the main route of elimination was the hepatobiliary and gastrointestinal system, which resulted in the highest absorbed dose being in the small intestine. In the mouse

Conclusions

We evaluated the whole-body distribution and radiation dosimetry of [¹¹C]CHIBA-1001, a novel PET ligand for α₇ nAChRs. The estimated effective dose of [¹¹C]CHIBA-1001 in humans was 6.9 μSv/MBq. From the perspective of radiation safety, [¹¹C]CHIBA-1001 is feasible in clinical studies. The data on organ distribution in mice and subsequent extrapolation could not predict dosimetry in humans because of the pharmacokinetic differences between the two species. These results emphasize that human

Acknowledgments

This work was supported by a grant from the Program for Promotion of Fundamental Studies in Health Sciences of the National Institute of Biomedical Innovation of Japan (Grant ID 06–46; to K.H. and K.I.). We thank Mr. Kunpei Hayashi and Ms. Hiroko Tsukinari for their excellent technical assistance.

References (25)

CourtJ. et al.
Nicotinic receptor abnormalities in Alzheimer's disease
Biol Psychiatry
(2001)
FreedmanR. et al.
Evidence in postmortem brain tissue for decreased numbers of hippocampal nicotinic receptors in schizophrenia
Biol Psychiatry
(1995)
WangH.Y. et al.
β-Amyloid(1–42) binds to α₇ nicotinic acetylcholine receptor with high affinity. Implications for Alzheimer's disease pathology
J Biol Chem
(2000)
KimS.W. et al.
Synthesis and positron emission tomography studies of C-11-labeled isotopomers and metabolites of GTS-21, a partial α7 nicotinic cholinergic agonist drug
Nucl Med Biol
(2007)
OgawaM. et al.
Synthesis and evaluation of [¹²⁵I]I-TSA as a brain nicotinic acetylcholine receptor α₇ subtype imaging agent
Nucl Med Biol
(2006)
OgawaM. et al.
Synthesis and evaluation of new imaging agent for central nicotinic acetylcholine receptor α₇ subtype
Nucl Med Biol
(2010)
CourtJ. et al.
Neuronal nicotinic receptors in dementia with Lewy bodies and schizophrenia: α-bungarotoxin and nicotine binding in the thalamus
J Neurochem
(1999)
HashimotoK. et al.
α₇ Nicotinic receptor agonists as potential therapeutic drugs for schizophrenia
Curr Med Chem CNS Agents
(2005)
PomperM.G. et al.
Synthesis and biodistribution of radiolabeled α₇ nicotinic acetylcholine receptor ligands
J Nucl Med
(2005)
DolleF. et al.
Synthesis and preliminary evaluation of a carbon-11-labeled agonist of the α₇ nicotinic acetylcholine receptor
J Labelled Compd Radiopharm
(2001)

HashimotoK. et al.

[¹¹C]CHIBA-1001 as a novel PET ligand for α7 nicotinic receptors in the brain: a PET study in conscious monkeys

PLoS ONE

(2008)

Deuther-ConradW. et al.

Molecular imaging of α₇ nicotinic acetylcholine receptors: design and evaluation of the potent radioligand [¹⁸F]NS10743

Eur J Nucl Med Mol Imaging

(2009)

Cited by (31)

The dual role of alpha7 nicotinic acetylcholine receptor in inflammation-associated gastrointestinal cancers
2020, Heliyon
Alpha7 nicotinic acetylcholine receptor (α7nAChR) is one of the main subtypes of nAChRs that modulates various cancer-related properties including proliferative, anti-apoptotic, pro-angiogenic and pro-metastatic activities in most of the cancers. It also plays a crucial role in inflammation control through the cholinergic anti-inflammatory pathway in numerous pathophysiological contexts. Such diverse physiological and pathological functions that initiate from this receptor may have significant impacts in determining the outcome of different cancers. Various tissues of gastrointestinal (GI) cancers such as gastric, colorectal, pancreatic and liver cancers have shown the up-regulated expression of α7nAChR as compared to normal adjacent tissues. According to the well-established connection between inflammation and tumorigenesis in the digestive system, there are mounting studies demonstrated either stimulatory or inhibitory effects of α7nAChR signaling in the development of GI cancers. To date, the precise underlying mechanisms related to this receptor in patients with GI cancers have not been fully elucidated. Regarding the paradoxical modulatory effects of this receptor in carcinogenesis, in this review, we aim to summarize the accumulated evidence about the involvement of α7nAChR in inflammation-associated GI cancers. It seems that the complex influences of α7nAChR may be a promising target in designing novel strategies in the treatment of such pathologic conditions.
Small interfering RNA targeting alpha7 nicotinic acetylcholine receptor sensitizes hepatocellular carcinoma cells to sorafenib
2020, Life Sciences
Citation Excerpt :
It modulates numerous cancer-related properties in most of the cancers [9,10]. In a recent study, it has been shown that in humans, the greatest amount of α7nAChR recognized in the liver and this finding demonstrated the importance of α7 receptor-related functions in this organ [11]. Previously, it was indicated that α7nAChR-mediated mechanisms may lead to an exaggerated progression of HCC [12].
It has been demonstrated that reduced expression of alpha7 nicotinic acetylcholine receptor (α7nAChR) led to reduced chemotherapeutic drugs resistance in various cancer cells. However, whether small interfering RNA (siRNA) mediated knockdown of α7nAChR can reduce sorafenib (SOR) resistance in HCC cells remains to be determined.
The effects of α7nAChR-siRNA in combination with SOR treatment was analyzed in human (HepG2) and mouse (Hepa 1–6) HCC cell lines. The MTT, DAPI staining and flow cytometry assays were applied to measure the cell viability, apoptosis and cell cycle progression of the cells. Also, the changes in the mRNA and protein levels of the α7nAChR were measured by quantitative real-time PCR and western blot analysis, respectively.
The results revealed that SOR increased both mRNA and protein levels of α7nAChR in HCC cells. Treatment with α7nAChR-siRNA abolished these effects. Also, SOR treatment in combination with α7nAChR-siRNA significantly sensitizes HCC cells to SOR cytotoxicity. This combination therapy significantly induced HCC cells apoptosis compared to SOR alone.
These experimental results indicate that knockdown of α7nAChR by siRNA increased the SOR antitumor activity of HCC cells and suggests that this additive combination is a promising drug candidate for HCC therapy.
Dexmedetomidine-mediated protection against septic liver injury depends on TLR4/MyD88/NF-κB signaling downregulation partly via cholinergic anti-inflammatory mechanisms
2019, International Immunopharmacology
Uncontrolled inflammatory responses exacerbate the pathogenesis of septic acute liver injury (ALI), posing a lethal threat to the host. Dexmedetomidine (DEX) has been reported to possess protective properties in inflammatory conditions. This study aimed to investigate whether DEX pretreatment exhibits hepatoprotection against ALI induced by lipopolysaccharide (LPS) in rats and determine its possible molecular mechanism.
Septic ALI was induced by intravenous injection of LPS. The rats received DEX intraperitoneally 30 min before LPS administration. α-Bungarotoxin (α-BGT), a specific α7 nicotinic acetylcholine receptor (α7nAChR) antagonist, was administered intraperitoneally 1 h before LPS exposure. The role of the vagus nerve was verified by performing unilateral cervical vagotomy or sham surgery before sepsis.
The expression of α7nAChR, toll-like receptor 4 (TLR4), high mobility group box 1 (HMGB1), and cleaved caspase-3 increased, peaking 24 h during sepsis. DEX enhanced α7nAChR activation and reduced TLR4 expression upon challenge with LPS. DEX significantly prevented LPS-induced ALI, which was associated with increased survival, the mitigation of pathological changes, the attenuation of inflammatory cytokine expression and apoptosis, and the downregulation of TLR4/MyD88/NF-κB pathway. Moreover, the hepatoprotective effect of DEX was abolished by α-BGT. Further investigation established that vagotomy, compared to sham surgery, triggered more severe pathogenic manifestations and higher proinflammatory cytokine levels. The inhibitory effects of DEX were shown in sham-operated rats but not in vagotomized rats.
Our data highlight the pivotal function of α7nAChR and intact vagus nerves in protecting against LPS-induced ALI through inhibiting the TLR4/MyD88/NF-κB signaling pathway upon pretreatment with DEX.
Potential of α7 nicotinic acetylcholine receptor PET imaging in atherosclerosis
2017, Methods
Atherosclerotic events are usually acute and often strike otherwise asymptomatic patients. Although multiple clinical risk factors have been associated with atherosclerosis, as of yet no further individual prediction can be made as to who will suffer from its consequences based on biomarker analysis or traditional imaging methods like CT, MRI or angiography.
Previously, non-invasive imaging with ¹⁸F-fluorodeoxyglucose (¹⁸F-FDG) PET was shown to potentially fill this niche as it offers high sensitive detection of metabolic processes associated with inflammatory changes in atherosclerotic plaques. However, ¹⁸F-FDG PET imaging of arterial vessels suffers from non-specificity and has still to be proven to reliably identify vulnerable plaques, carrying a high risk of rupture. Therefore, it may be regarded only as a secondary marker for monitoring treatment effects and it does not offer alternative treatment options or direct insight in treatment mechanisms.
In this review, an overview is given of the current status and the potential of PET imaging of inflammation and angiogenesis in atherosclerosis in general and special emphasis is given to imaging of α7 nicotinic acetylcholine receptors (α7 nAChRs). Due to the gaps that still exist in our understanding of atherogenesis and the limitations of the available PET tracers, the search continues for a more specific radioligand, able to differentiate between stable atherosclerosis and plaques prone to rupture. The potential role of the α7 nAChR as imaging marker for plaque vulnerability is explored. Today, strong evidence exists that nAChRs are involved in the atherosclerotic disease process. They are suggested to mediate the deleterious effects of the major tobacco component, nicotine, a nAChR agonist.
Mainly based on in vitro data, α7 nAChR stimulation might increase plaque burden via increased neovascularization. However, in animal studies, α7 nAChR manipulation appears to reduce plaque size due to its inhibitory effects on inflammatory cells. Thus, reliable identification of α7 nAChRs by in vivo imaging is crucial to investigate the exact role of α7 nAChR in atherosclerosis before any therapeutic approach in the human setting can be justified.
In this review, we discuss the first experience with α7 nAChR PET tracers and developmental considerations regarding the “optimal” PET tracer to image vascular nAChRs.
A high-yield automated radiosynthesis of the alpha-7 nicotinic receptor radioligand [<sup>18</sup>F]NS10743
2015, Applied Radiation and Isotopes
Citation Excerpt :
Among the assessed structural classes, the 1,4-diazabicyclo[3.2.2]nonane scaffold bearing compounds currently represent the most promising α7 nAChR-ligand class regarding affinity and selectivity (Fig. 1). As example, even though [11C]CHIBA-1001 complies with the desirable characteristics of PET α7 nAChRs radiotracers across species, proof of selectivity in clinical trials is still missing (Hashimoto et al., 2008; Sakata et al., 2011). [ 11C]NS14492 and the indole derivative [18F]NS14490 developed by our group showed insufficient binding potential (BP~0.5) for PET imaging (Ettrup et al., 2011; Rötering et al., 2013).
[¹⁸F]NS10743, a promising and highly competitive α7 nAChR radioligand has been synthesized so far by microwave irradiation using a manual single-mode device followed by a palladium-catalyzed reduction of remaining nitro-precursor for HPLC separation purposes. For further preclinical and clinical use, regulated production of [¹⁸F]NS10743 by fully automated radiosynthesis is a crucial requirement. Therefore, we chose a commercial synthesis module and developed the automated radiosynthesis of [¹⁸F]NS10743. Besides evaluation of several radiosynthesis procedures, we performed an extensive HPLC study for quantitative separation of [¹⁸F]NS10743 from the corresponding nitro precursor. After implementation of the optimized procedure on a TRACERlab^TM FX F-N synthesis module, [¹⁸F]NS10743 was obtained in high radiochemical purity (≥99%) with an overall radiochemical yield of 32.2±7% (n=3). The specific activities at the end of the synthesis were 571±17 GBq/µmol (n=3).
Activation of central muscarinic receptor type 1 prevents development of endotoxin tolerance in rat liver
2014, European Journal of Pharmacology
Citation Excerpt :
It appears that the alpha7 nicotinic acetylcholine (α7nACh) receptor is the main target of vagus nerve-mediated cholinergic anti-inflammatory pathway in a variety of tissues including liver (Wang et al., 2003). Recent studies showed that the highest accumulation of a radio-labeled α7nAChR ligand was observed in the liver in humans (Sakata et al., 2011). Hypo-responsiveness to chronic endotoxin exposure (endotoxin tolerance) has also been reported in liver (Fernández et al., 2002), however, the role of central anti-inflammatory pathway in pathophysiology of hepatic endotoxin tolerance is unknown.
Endotoxin tolerance is a mechanism in which cells receiving low doses of endotoxin, enter a transient phase with less inflammatory response to the next endotoxin challenges. Central nervous system is known to modulate systemic inflammation through activation of the cholinergic system; however, the role of central anti-inflammatory pathway in pathophysiology of hepatic endotoxin tolerance is unknown. Our study was designed to assess the effect central muscarinic type 1 receptor (M₁) activation on development of endotoxin tolerance in rat liver. Endotoxin tolerance was induced by daily intraperitoneal injection of endotoxin (1 mg/kg) for 5 days. Animals were randomly divided into two groups which received intracerebroventricular injection of either MCNA-343 (an M₁ agonist, 5 ng/kg) or saline 1 h after intraperitoneal injection of saline or endotoxin. The responsiveness to endotoxin was assessed by measuring hepatic MCP-1 (monocyte chemotactic protein-1), iNOS (inducible nitric oxide synthase) and TNF-α (tumor necrosis-α) mRNA expression 3 h after intraperitoneal administration of endotoxin using quantitative RT-PCR. A significant reduction in hepatic expression of MCP-1, iNOS and TNF-α was observed in rats with 5 days endotoxin challenge in comparison with rats given a single dose of endotoxin. There was no significant difference in hepatic expression of MCP-1, iNOS or TNF-α between acute and chronic LPS-treated groups in rats given MCNA-343. Central MCNA-343 stimulation could prevent the induction of hepatic endotoxin tolerance in animals receiving repeated doses of endotoxin. This indicates that M₁ cholinergic receptor activation in the central nervous system can modulate endotoxin tolerance in rat liver.

View all citing articles on Scopus

View full text

Biodistribution and radiation dosimetry of the α7 nicotinic acetylcholine receptor ligand [11C]CHIBA-1001 in humans

Abstract

Introduction

Methods

Results

Conclusion

Introduction

Section snippets

Synthesis of [11C]CHIBA-1001

Human PET study

Results

Discussion

Conclusions

Acknowledgments

Biol Psychiatry

Biol Psychiatry

J Biol Chem

Nucl Med Biol

Nucl Med Biol

Nucl Med Biol

Neuronal nicotinic receptors in dementia with Lewy bodies and schizophrenia: α-bungarotoxin and nicotine binding in the thalamus

J Neurochem

α7 Nicotinic receptor agonists as potential therapeutic drugs for schizophrenia

Curr Med Chem CNS Agents

Synthesis and biodistribution of radiolabeled α7 nicotinic acetylcholine receptor ligands

J Nucl Med

Synthesis and preliminary evaluation of a carbon-11-labeled agonist of the α7 nicotinic acetylcholine receptor

J Labelled Compd Radiopharm

[11C]CHIBA-1001 as a novel PET ligand for α7 nicotinic receptors in the brain: a PET study in conscious monkeys

PLoS ONE

Molecular imaging of α7 nicotinic acetylcholine receptors: design and evaluation of the potent radioligand [18F]NS10743

Eur J Nucl Med Mol Imaging

Biodistribution and radiation dosimetry of the α₇ nicotinic acetylcholine receptor ligand [¹¹C]CHIBA-1001 in humans

Synthesis of [¹¹C]CHIBA-1001

α₇ Nicotinic receptor agonists as potential therapeutic drugs for schizophrenia

Synthesis and biodistribution of radiolabeled α₇ nicotinic acetylcholine receptor ligands

Synthesis and preliminary evaluation of a carbon-11-labeled agonist of the α₇ nicotinic acetylcholine receptor

[¹¹C]CHIBA-1001 as a novel PET ligand for α7 nicotinic receptors in the brain: a PET study in conscious monkeys

Molecular imaging of α₇ nicotinic acetylcholine receptors: design and evaluation of the potent radioligand [¹⁸F]NS10743