Logo: to the web site of Uppsala University

Primary aldosteronism (PA) is a common, potentially reversible, cause of hypertension. Distinguishing unilateral from bilateral PA is critical when deciding who should be offered surgery (unilateral adrenalectomy). Recent studies have shown that PET/CT with [¹¹C]metomidate can accurately identify unilateral PA, with localization of the causative aldosterone-producing adenoma (APA). However, the availability of [¹¹C]metomidate is limited to centers with an on-site cyclotron. Here, we report an early-phase human study with the ¹⁸F-labeled analog, para-chloro-2-[¹⁸F]fluoroethyletomidate ([¹⁸F]CETO).

Methods: We conducted a phase I/IIa, single-center, open-label, microdosing study. The primary objective was to evaluate the safety of up to 2 administrations of [¹⁸F]CETO in 6 patients with PA (3 unilateral disease, 3 bilateral disease) and 5 healthy volunteers. Safety evaluation included assessment of adrenal function after the first [¹⁸F]CETO administration. The biodistribution of [¹⁸F]CETO was assessed in a 90-min dynamic PET acquisition. In patients with PA, the effect of pretreatment with oral dexamethasone on [¹⁸F]CETO uptake by normal adrenal tissue and APAs was also assessed.

Results: Eleven participants were recruited to the trial, including 6 patients and 5 healthy volunteers. No subjects experienced serious adverse events or reactions, and all participants had normal adrenal function after [¹⁸F]CETO administration. [¹⁸F]CETO demonstrated high selectivity for the adrenal glands with low uptake in other tissues. Visualization of APAs was enhanced after dexamethasone pretreatment, which suppressed [¹⁸F]CETO uptake by normal adrenal tissue.

Conclusion: [¹⁸F]CETO is a safe radiopharmaceutical for PET imaging of the adrenal glands, with no observed adverse reactions or impairment of adrenal function in this study. [¹⁸F]CETO demonstrates selective high affinity for adrenal tissue, particularly APAs. Distinction between APAs and normal adrenal tissue is enhanced by dexamethasone pretreatment to suppress [¹⁸F]CETO uptake by normal glands. This positions [¹⁸F]CETO as a promising imaging tool for evaluation in the context of PA.

BACKGROUND: Neutrophil granulocytes are important parts of the defence against bacterial infections. Their action is a two-edged sword, the mediators killing the intruding bacteria are at the same time causing tissue damage. Neutrophil activation is part of the dysregulated immune response to infection defining sepsis and neutrophil elastase is one of the powerful proteases causing both effects and damage. Inhibition of neutrophil elastase has been tried in sepsis and ARDS, so far with inconclusive results.

METHODS: We used positron emission tomography (PET) combined with computed tomography (CT) and the selective and specific neutrophil elastase inhibitor PET-tracer [¹¹C]GW457427 ([¹¹C]NES), in an intensive care unit porcine Escherichia coli sepsis model with the primary aim to visualise the biodistribution of neutrophil elastase in the initial acute phase of the septic reaction. Repeated PET-CT investigations were performed before and after induction of sepsis.

RESULTS: At baseline [¹¹C]NES uptake was found in the bone marrow, spleen and liver. The uptake in the bone marrow was markedly increased two hours into the sepsis, whereas in spleen and liver the uptake was not as markedly changed compared to baseline. At 4 h after the sepsis induction [¹¹C]NES in the bone marrow decreased while the uptake increased in the spleen, liver and lungs.

CONCLUSION: The neutrophil elastase PET-tracer [¹¹C]NES is a novel and unique instrument to study the acute innate neutrophil immune response in sepsis and associated vital organ failure. We here present images and quantitative data of the neutrophil elastase distribution the first hours of acute experimental sepsis. Surprisingly, a pronounced increase of neutrophil elastase was found in the bone marrow 2 h into the sepsis reaction followed at 4 h by increase in the liver, spleen and lungs and a concomitant reduction of the tracer uptake in bone marrow.

¹⁸F-labelling of nitrogen-containing arenes via copper-mediated radiofluorination (CMRF) was investigated. The studies targeted the analogues of the anti-cancer drug melflufen with an alkylating bis(2-chloroethyl)amino pharmacophore. Studies of the melflufen analogues and various model compounds indicated that the copper mediated boron–fluorine-18 exchange reaction is affected differently by the three nitrogen-containing groups in the target compound. The largest inhibitory effects on the fluorine labelling process were exerted by the tertiary amine based bis(2-chloroethyl)amino pharmacophore. The best results were achieved by applying bipyridyl ligands for the copper mediator.

Primary aldosteronism (PA) is the leading secondary cause of hypertension. Determining whether one (unilateral) or both (bilateral) adrenal glands are the source of PA in a patient remains challenging, and yet it is a critical step in the decision whether to recommend potentially curative surgery (adrenalectomy) or lifelong medical therapy (typically requiring multiple drugs). Recently, we have developed a fluorine-18 radiopharmaceutical [(18) F]CETO to permit greater access to PA molecular imaging. Herein, we report an automated synthesis of this radiotracer. To manufacture the radiopharmaceutical routinely for clinical PET studies, we implemented an automated radiosynthesis method on a Synthra RNplus (c) synthesiser for which Cl-tosyletomidate was used as the precursor for radiolabelling via nucleophilic [(18) F]fluorination. [(18) F]CETO was produced with 35 +/- 1% (n = 7), decay corrected and 25 +/- 4% (n = 7) non-decay corrected radiochemical yield with molar activities ranging from 150 to 400 GBq/mu mol. The GMP compliant manufacturing process produces a sterile formulated [(18) F]CETO injectable solution for human use as demonstrated by the results of quality control. Automation of the radiosynthesis of [(18) F]CETO should facilitate uptake by other adrenal centres and increase access to molecular imaging in PA.

Background: In preclinical studies, the positron emission tomography (PET) imaging with [C-11]UCB-A provided promising results for imaging synaptic vesicle protein 2A (SV2A) as a proxy for synaptic density. This paper reports the first-in-human [C-11]UCB-A PET study to characterise its kinetics in healthy subjects and further evaluate SV2A-specific binding.

Results: Twelve healthy subjects underwent 90-min baseline [C-11]UCB-A scans with PET/MRI, with two subjects participating in an additional blocking scan with the same scanning procedure after a single dose of levetiracetam (1500 mg). Our results indicated abundant [C-11]UCB-A brain uptake across all cortical regions, with slow elimination. Kinetic modelling of [C-11]UCB-A PET using various compartment models suggested that the irreversible two-tissue compartment model best describes the kinetics of the radioactive tracer. Accordingly, the Patlak graphical analysis was used to simplify the analysis. The estimated SV2A occupancy determined by the Lassen plot was around 66%. Significant specific binding at baseline and comparable binding reduction as grey matter precludes the use of centrum semiovale as reference tissue.

Conclusions: [C-11]UCB-A PET imaging enables quantifying SV2A in vivo. However, its slow kinetics require a long scan duration, which is impractical with the short half-life of carbon-11. Consequently, the slow kinetics and complicated quantification methods may restrict its use in humans.

Background: Type 1 diabetes (T1D) is an autoimmune disease characterized by a progressive β-cell destruction. There are no clinically established methods for quantifying endocrine cells of the pancreas and current knowledge is almost exclusively based on autopsy material and functional measurements. Based on the expression of the γ-aminobutyric acid A receptors (GABA_ARs) in pancreatic islets and the fact that GABA_AR agonists are being explored as treatment for T1D, we hypothesized that the positron emission tomography (PET) tracer [¹¹C]flumazenil ([¹¹C]FMZ) could serve as a marker of the endocrine mass of the pancreas. The in vivo uptake of [¹¹C]FMZ in pig pancreas was evaluated by PET/CT, either tracer alone or after blockade of GABA_AR by unlabeled flumazenil. The pancreatic binding of [¹¹C]FMZ was investigated in vitro with frozen sections of pig pancreas as well as human organ donors, in addition to isolated mouse and human islets and exocrine preparations. The expression of GABA_AR subunits in pig, human and mouse pancreas was explored by immunohistochemistry.

Results: Strong specific in vivo uptake of [¹¹C]FMZ was observed in the pig brain as expected, but in the pancreas the signal was moderate and only partially reduced by blockade. In vitro experiments revealed a positive but weak and variable binding of [¹¹C]FMZ in islets compared to exocrine tissue in the mouse, pig and human pancreas. In pig and mouse pancreatic islets we identified the GABA_AR subunits β2 and γ2 but not α2. In the human pancreas from non-diabetic donors, we have identified the α2, β2 (although weak) and γ2 subunits, whereas from a T2D donor the α2 subunit was missing.

Conclusions: Our findings suggest that [¹¹C]FMZ bind to GABA_ARs in the islets, but not with a sufficient contrast or magnitude to be implemented as an in vivo PET marker for the endocrine mass of the pancreas. However, GABA_ARs with different subunits are widely expressed in the endocrine cells within the pancreas in pig, human and mouse. Hence, the GABA_AR could still be a potential imaging target for the endocrine cells of the pancreas but would require tracers with higher affinity and selectivity for individual GABA_AR subunits.

Background [C-11]metomidate, a methyl ester analogue of etomidate, is used for positron emission tomography of adrenocortical cancer, and has been tested in recent clinical trials for lateralization in primary aldosteronism (PA). However, in PA, visualization as well as uptake quantification are hampered by the tracer's rather high non-specific liver uptake, and its overall clinical usefulness is also limited by the short 20-minute half-life of carbon-11. Therefore, we evaluated para-chloro-2-[F-18]fluoroethyl-etomidate, [F-18]CETO, a fluorine-18 (T-1/2=109.8 min) analogue, as a potential new adrenocortical PET tracer. The aim of this study was to assess radiation dosimetry of [F-18]CETO. Results [F-18]CETO showed a high uptake in adrenal glands, still increasing at 5 h post injection. Adrenal glands (absorbed dose coefficients 0.100 +/- 0.032 mGy/MBq in males and 0.124 +/- 0.013 mGy/MBq in females) received the highest absorbed dose. The effective dose coefficient was 20 mu Sv/MBq. Conclusions[F-18]CETO has a favourable biodistribution in humans for adrenal imaging. The effective dose for a typical clinical PET examination with 200 MBq [F-18]CETO is 4 mSv. Trial registration ClinicalTrials.gov, NCT05361083 Retrospectively registered 29 April 2022. at, URL: https://clinicaltrials.gov/ct2/show/NCT05361083.

Background

Alveolar macrophages activation to the pro-inflammatory phenotype M1 is pivotal in the pathophysiology of Ventilator-Induced Lung Injury (VILI). Increased lung strain is a known determinant of VILI, but a direct correspondence between regional lung strain and macrophagic activation remains unestablished. [⁶⁸Ga]Ga-DOTA-TATE is a Positron Emission Tomography (PET) radiopharmaceutical with a high affinity for somatostatin receptor subtype 2 (SSTR2), which is overexpressed by pro-inflammatory-activated macrophages. Aim of the study was to determine, in a porcine model of VILI, whether mechanical strain correlates topographically with distribution of activated macrophages detected by [⁶⁸Ga]Ga-DOTA-TATE uptake.

Methods

Seven anesthetized pigs underwent VILI, while three served as control. Lung CT scans were acquired at incremental tidal volumes, simultaneously recording lung mechanics. [⁶⁸Ga]Ga-DOTA-TATE was administered, followed by dynamic PET scans. Custom MatLab scripts generated voxel-by-voxel gas volume and strain maps from CT slices at para-diaphragmatic (Para-D) and mid-thoracic (Mid-T) levels. Analysis of regional Voxel-associated Normal Strain (VoStrain) and [⁶⁸Ga]Ga-DOTA-TATE uptake was performed and a measure of the statistical correlation between these two variables was quantified using the linear mutual information (LMI) method.

Results

Compared to controls, the VILI group exhibited statistically significant higher VoStrain and Standardized Uptake Value Ratios (SUVR) both at Para-D and Mid-T levels. Both VoStrain and SUVR increased along the gravitational axis with an increment described by statistically different regression lines between VILI and healthy controls and reaching the peak in the dependent regions of the lung (for strain in VILI vs. control was at Para-D: 760 ± 210 vs. 449 ± 106; at Mid-T level 497 ± 373 vs. 193 ± 160; for SUVR, in VILI vs. control was at Para-D: 2.2 ± 1.3 vs. 1.3 ± 0.1; at Mid-T level 1.3 ± 1.0 vs. 0.6 ± 0.03). LMI in both Para-D and Mid-T was statistically significantly higher in VILI than in controls.

Conclusions

In this porcine model of VILI, we found a topographical correlation between lung strain and [⁶⁸Ga]Ga-DOTA-TATE uptake at voxel level, suggesting that mechanical alteration and specific activation of inflammatory cells are strongly linked in VILI. This study represents the first voxel-by-voxel examination of this relationship in a multi-modal imaging analysis.

Background: Of interest to women's mental health, a wealth of studies suggests sex differences in nicotine addiction and treatment response, but their psychoneuroendocrine underpinnings remain largely unknown. A pathway involving sex steroids could indeed be involved in the behavioural effects of nicotine, as it was found to inhibit aromatase in vitro and in vivo in rodents and non-human primates, respectively. Aromatase regulates the synthesis of oestrogens and, of relevance to addiction, is highly expressed in the limbic brain.

Methods: The present study sought to investigate in vivo aromatase availability in relation to exposure to nicotine in healthy women. Structural magnetic resonance imaging and two [11C]cetrozole positron emission tomography (PET) scans were performed to assess the availability of aromatase before and after administration of nicotine. Gonadal hormones and cotinine levels were measured. Given the region-specific expression of aromatase, a ROI -based approach was employed to assess changes in [11C]cetrozole non-displaceable binding potential.

Results: The highest availability of aromatase was found in the right and left thalamus. Upon nicotine exposure, [11C]cetrozole binding in the thalamus was acutely decreased bilaterally (Cohen's d =-0.99). In line, cotinine levels were negatively associated with aromatase availability in the thalamus, although as non-significant trend.

Conclusions: These findings indicate acute blocking of aromatase availability by nicotine in the thalamic area. This suggests a new putative mechanism mediating the effects of nicotine on human behaviour, particularly relevant to sex differences in nicotine addiction.

Purpose

[¹¹C]Metomidate positron emission tomography (PET) is currently used for staging of adrenocortical carcinoma and for lateralization in primary aldosteronism (PA). Due to the short half-life of carbon-11 and a high non-specific liver uptake of [¹¹C]metomidate there is a need for improved adrenal imaging methods. In a previous pre-clinical study para-chloro-2-[¹⁸F]fluoroethyletomidate has been proven to be a specific adrenal tracer. The objective is to perform a first evaluation of para-chloro-2-[¹⁸F]fluoroethyletomidate positron emission computed tomography ([¹⁸F]CETO-PET/CT) in patients with adrenal tumours and healthy volunteers.

Methods

Fifteen patients underwent [¹⁸F]CETO-PET/CT. Five healthy volunteers were recruited for test-retest analysis and three out of the five underwent additional [¹⁵O]water PET/CT to measure adrenal blood flow. Arterial blood sampling and tracer metabolite analysis was performed. The kinetics of [¹⁸F]CETO were assessed and simplified quantitative methods were validated by comparison to outcome measures of tracer kinetic analysis.

Results

Uptake of [¹⁸F]CETO was low in the liver and high in adrenals. Initial metabolization was rapid, followed by a plateau. The kinetics of [¹⁸F]CETO in healthy adrenals and all adrenal pathologies, except for adrenocortical carcinoma, were best described by an irreversible single-tissue compartment model. Standardized uptake values (SUV) correlated well with the uptake rate constant K₁. Both K₁ and SUV were highly correlated to adrenal blood flow in healthy controls. Repeatability coefficients of K₁, SUV_65–70, and SUV₁₂₀ were 25, 22, and 17%.

Conclusions

High adrenal uptake combined with a low unspecific liver uptake suggests that ¹⁸F]CETO is a suitable tracer for adrenal imaging. Adrenal SUV, based on a whole-body scan at 1 h p.i., correlated well with the net uptake rate K_i.

Trial registration

ClinicalTrials.gov, NCT05361083 Retrospectively registered 29 April 2022. at, https://clinicaltrials.gov/ct2/show/NCT05361083