Non-invasive imaging of sympathetic innervation of the pancreas in individuals with type 2 diabetes.

AIMS/HYPOTHESIS: Compromised pancreatic sympathetic innervation has been suggested as a factor involved in both immune-mediated beta cell destruction and endocrine dysregulation of pancreatic islets. To further explore these intriguing findings, new techniques for in vivo assessment of pancreatic innervation are required. This is a retrospective study that aimed to investigate whether the noradrenaline (norepinephrine) analogue 11C-hydroxy ephedrine (11C-HED) could be used for quantitative positron emission tomography (PET) imaging of the sympathetic innervation of the human pancreas. METHODS: In 25 individuals with type 2 diabetes and 64 individuals without diabetes, all of whom had previously undergone 11C-HED-PET/CT because of pheochromocytoma or paraganglioma (or suspicion thereof), the 11C-HED standardised uptake value (SUVmean), 11C-HED specific binding index (SBI), pancreatic functional volume (FV, in ml), functional neuronal volume (FNV, calculated as SUVmean × FV), specific binding index with functional volume (SBI FV, calculated as SBI × FV) and attenuation on CT (HU) were investigated in the entire pancreas, and additionally in six separate anatomical pancreatic regions. RESULTS: Generally, 11C-HED uptake in the pancreas was high, with marked individual variation, suggesting variability in sympathetic innervation. Moreover, pancreatic CT attenuation (HU) (p<0.001), 11C-HED SBI (p=0.0049) and SBI FV (p=0.0142) were lower in individuals with type 2 diabetes than in individuals without diabetes, whereas 11C-HED SUVmean (p=0.15), FV (p=0.73) and FNV (p=0.30) were similar. CONCLUSIONS/INTERPRETATION: We demonstrate the feasibility of using 11C-HED-PET for non-invasive assessment of pancreatic sympathetic innervation in humans. These findings warrant further prospective evaluation, especially in individuals with theoretical defects in pancreatic sympathetic innervation, such as those with type 1 diabetes.

Effects of 6 weeks of treatment with dapagliflozin, a sodium-glucose co-transporter-2 inhibitor, on myocardial function and metabolism in patients with type 2 diabetes: A randomized, placebo-controlled, exploratory study.

AIM: To explore the early effects of dapagliflozin on myocardial function and metabolism in patients with type 2 diabetes without heart failure. MATERIALS AND METHODS: Patients with type 2 diabetes on metformin treatment were randomized to double-blind, 6-week placebo or dapagliflozin 10 mg daily treatment. Investigations included cardiac function and structure with myocardial resonance imaging; cardiac oxygen consumption, perfusion and efficiency with [11 C]-acetate positron emission tomography (PET); and cardiac and hepatic fatty acid uptake with [18 F]-6-thia-heptadecanoic acid PET, analysed by ANCOVA as least square means with 95% confidence intervals. RESULTS: Evaluable patients (placebo: n = 24, dapagliflozin: n = 25; 53% males) had a mean age of 64.4 years, a body mass index of 30.2 kg/m2 and an HbA1c of 6.7%. Body weight and HbA1c were significantly decreased by dapagliflozin versus placebo. Dapagliflozin had no effect on myocardial efficiency, but external left ventricular (LV) work (-0.095 [-0.145, -0.043] J/g/min) and LV oxygen consumption were significantly reduced (-0.30 [-0.49, -0.12] J/g/min) by dapagliflozin, although the changes were not statistically significant versus changes in the placebo group. Change in left atrial maximal volume with dapagliflozin versus placebo was -3.19 (-6.32, -0.07) mL/m2 (p = .056). Peak global radial strain decreased with dapagliflozin versus placebo (-3.92% [-7.57%, -0.28%]; p = .035), while peak global longitudinal and circumferential strains were unchanged. Hepatic fatty acid uptake was increased by dapagliflozin versus placebo (0.024 [0.004, 0.044] µmol/g/min; p = .018), while cardiac uptake was unchanged. CONCLUSIONS: This exploratory study indicates reduced heart work but limited effects on myocardial function, efficiency and cardiac fatty acid uptake, while hepatic fatty acid uptake increased, after 6 weeks of treatment with dapagliflozin.

Recent Progress in the Molecular Imaging of Nonalcoholic Fatty Liver Disease.

Pathological fibrosis of the liver is a landmark feature in chronic liver diseases, including nonalcoholic fatty liver disease (NAFLD) and nonalcoholic steatohepatitis (NASH). Diagnosis and assessment of progress or treatment efficacy today requires biopsy of the liver, which is a challenge in, e.g., longitudinal interventional studies. Molecular imaging techniques such as positron emission tomography (PET) have the potential to enable minimally invasive assessment of liver fibrosis. This review will summarize and discuss the current status of the development of innovative imaging markers for processes relevant for fibrogenesis in liver, e.g., certain immune cells, activated fibroblasts, and collagen depositions.

Non-Invasive Imaging Methodologies for Assessment of Radiation Damage to Bone Marrow and Kidneys from Peptide Receptor Radionuclide Therapy.

BACKGROUND/AIMS: Peptide receptor radionuclide therapy (PRRT) is becoming clinical routine for management of neuroendocrine tumours. The number of PRRT cycles is correlated with treatment effect but theoretically limited by off-target radiation damage to kidneys and bone marrow. New imaging biomarkers for assessment of PRRT tissue damage would enable evaluation of novel renal and bone marrow protective agents, as well as personalised PRRT treatment regiments. METHODS: Mice treated with [177Lu]Lu-DOTA-TATE PRRT or vehicle were examined at baseline and following treatment with [18F]fluorothymidine (FLT) positron emission tomography (PET) and technetium-99m-mercapto-acetyl-tri-glycine ([99mTc]Tc-Mag3) single-photon emission tomography (SPECT) to assess dynamic changes in bone marrow proliferation and renal function, respectively. RESULTS: Bone marrow proliferation as assessed by [18F]FLT was decreased 2 days after PRRT treatment, but not vehicle, compared to baseline (target-to-background ratio [TBRmax] baseline:1.69 ± 0.29 vs. TBRmax PRRT: 0.91 ± 0.02, p < 0.01). Renal function as assessed by [99mTc]Tc-Mag3 SPECT was similarly decreased 2 days following PRRT compared to vehicle (fractional uptake rate [FUR] vehicle: 0.030 ± 0.014 s-1 vs. FUR PRRT: 0.0051 ± 0.0028 s-1, p < 0.01). CONCLUSION: [18F]FLT PET and [99mTc]Tc-Mag3 SPECT are promising techniques for assessing bone marrow and renal injury from [177Lu]Lu-DOTA-TATE PRRT and may potentially improve patient management by allowing evaluation of protective interventions as well as enabling personalised PRRT treatments.

GPR44 as a Target for Imaging Pancreatic Beta-Cell Mass.

PURPOSE OF REVIEW: Quantitative markers for beta-cell mass (BCM) in human pancreas are currently lacking. Medical imaging using positron emission tomography (PET) markers for beta-cell restricted targets may provide an accurate and non-invasive measurement of BCM, to assist diagnosis and treatment of metabolic disease. GPR44 was recently discovered as a putative marker for beta cells and this review summarizes the developments so far. RECENT FINDINGS: Several small molecule binders targeting GPR44 have been radiolabeled for PET imaging and evaluated in vitro and in small and large animal models. 11C-AZ12204657 and 11C-MK-7246 displayed a dose-dependent and GPR44-mediated binding to beta cells both in vitro and in vivo, with negligible uptake in exocrine pancreas. GPR44 represents an attractive target for visualization of BCM. Further progress in radioligand development including clinical testing is expected to clarify the role of GPR44 as a surrogate marker for BCM in humans.

Metabolically Active Brown Adipose Tissue Is Found in Adult Subjects with Type 1 Diabetes.

Type 1 diabetes (T1D) is characterized by the loss of insulin-producing cells and hence insulin secretion and metabolic control. In addition to insulin, there are a number of hormones and cytokines that influence metabolism, and many of these can be secreted from brown adipose tissue (BAT). However, the presence and activity of BAT in T1D have not been studied, despite the fact that preclinical studies have shown that transplantation of BAT in mouse models of T1D can restore metabolic control. The metabolic activity of BAT, white adipose tissue (WAT), and skeletal muscle was investigated in patients with T1D (n = 11) by 2-deoxy-2-(18F)fluoro-D-glucose PET/CT after cold stimulation. Functional BAT was detected in 4 out of 11 individuals with T1D with a prevalence of 36%. The glucose utilization rate in the supraclavicular BAT regions ranged from 0.75-38.7 µmol × min-1 × 100 g-1. The glucose utilization per gram tissue was higher in BAT when compared with both WAT (p = 0.049) and skeletal muscle (p = 0.039). However, no correlation between BAT activity and metabolic control or insulin requirements was found. In conclusion, for the first time, cold-induced BAT was detected in patients with T1D with a wide range in metabolic activity. Contrary to findings in animal models, the metabolic activity of BAT had negligible impact on insulin requirements or metabolic control in T1D under normal physiological conditions.

Detection and quantification of beta cells by PET imaging: why clinical implementation has never been closer.

In this issue of Diabetologia, Alavi and Werner ( https://doi.org/10.1007/s00125-018-4676-1 ) criticise the attempts to use positron emission tomography (PET) for in vivo imaging of pancreatic beta cells, which they consider as 'futile'. In support of this strong statement, they point out the limitations of PET imaging, which they believe render beta cell mass impossible to estimate using this method. In our view, the Alavi and Werner presentation of the technical limitations of PET imaging does not reflect the current state of the art, which leads them to questionable conclusions towards the feasibility of beta cell imaging using this approach. Here, we put forward arguments in favour of continuing the development of innovative technologies enabling in vivo imaging of pancreatic beta cells and concisely present the current state of the art regarding putative technical limitations of PET imaging. Indeed, far from being a 'futile' effort, we demonstrate that beta cell imaging is now closer than ever to becoming a long-awaited clinical reality.

Transplantation of macroencapsulated human islets within the bioartificial pancreas ßAir to patients with type 1 diabetes mellitus.

Macroencapsulation devices provide the dual possibility of immunoprotecting transplanted cells while also being retrievable, the latter bearing importance for safety in future trials with stem cell-derived cells. However, macroencapsulation entails a problem with oxygen supply to the encapsulated cells. The ßAir device solves this with an incorporated refillable oxygen tank. This phase 1 study evaluated the safety and efficacy of implanting the ßAir device containing allogeneic human pancreatic islets into patients with type 1 diabetes. Four patients were transplanted with 1-2 ßAir devices, each containing 155 000-180 000 islet equivalents (ie, 1800-4600 islet equivalents per kg body weight), and monitored for 3-6 months, followed by the recovery of devices. Implantation of the ßAir device was safe and successfully prevented immunization and rejection of the transplanted tissue. However, although beta cells survived in the device, only minute levels of circulating C-peptide were observed with no impact on metabolic control. Fibrotic tissue with immune cells was formed in capsule surroundings. Recovered devices displayed a blunted glucose-stimulated insulin response, and amyloid formation in the endocrine tissue. We conclude that the ßAir device is safe and can support survival of allogeneic islets for several months, although the function of the transplanted cells was limited (Clinicaltrials.gov: NCT02064309).

Combined PET and microdialysis for in vivo estimation of drug blood-brain barrier transport and brain unbound concentrations.

Methods to investigate blood-brain barrier transport and pharmacologically active drug concentrations in the human brain are limited and data translation between species is challenging. Hence, there is a need to further develop the read-out of techniques like positron emission tomography (PET) for studying neuropharmacokinetics. PET has a high translational applicability from rodents to man and measures total drug concentrations in vivo. The aim of the present study was to investigate the possibility of translating total drug concentrations, acquired through PET, to unbound concentrations, resembling those measured in the interstitial fluid by microdialysis sampling. Simultaneous PET scanning and brain microdialysis sampling were performed in rats throughout a 60min infusion of [N-methyl-11C]oxycodone in combination with a therapeutic dose of oxycodone and during a 60min follow up period after the end of infusion. The oxycodone concentrations acquired with PET were converted into unbound concentrations by compensating for brain tissue binding and brain intracellular distribution, using the unbound volume of distribution in brain (Vu,brain), and were compared to microdialysis measurements of unbound concentrations. A good congruence between the methods was observed throughout the infusion. However, an accumulating divergence in the acquired PET and microdialysis data was apparent and became more pronounced during the elimination phase, most likely due to the passage of radioactive metabolites into the brain. In conclusion, the study showed that PET can be used to translate non-invasively measured total drug concentrations into unbound concentrations as long as the contribution of radiolabelled metabolites is minor or can be compensated for.

Pancreatic perfusion and subsequent response to glucose in healthy individuals and patients with type 1 diabetes.

AIMS/HYPOTHESIS: The aim of this study was to investigate pancreatic perfusion and its response to a glucose load in patients with type 1 diabetes mellitus compared with non-diabetic ('healthy') individuals. METHODS: Eight individuals with longstanding type 1 diabetes and ten sex-, age- and BMI-matched healthy controls underwent dynamic positron emission tomography scanning with (15)O-labelled water before and after intravenous administration of glucose. Perfusion in the pancreas was measured. Portal and arterial hepatic perfusion were recorded as references. RESULTS: Under fasting conditions, total pancreatic perfusion was on average 23% lower in the individuals with diabetes compared with healthy individuals. Glucose increased total pancreatic and portal hepatic blood perfusion in healthy individuals by 48% and 38%, respectively. In individuals with diabetes there was no significant increase in either total pancreatic or portal hepatic perfusion. CONCLUSIONS/INTERPRETATION: Individuals with type 1 diabetes have reduced basal pancreatic perfusion and a severely impaired pancreatic and splanchnic perfusion response to intravenous glucose stimulation.

In vivo imaging of beta cells with radiotracers: state of the art, prospects and recommendations for development and use.

Radiotracer imaging is characterised by high in vivo sensitivity, with a detection limit in the lower picomolar range. Therefore, radiotracers represent a valuable tool for imaging pancreatic beta cells. High demands are made of radiotracers for in vivo imaging of beta cells. Beta cells represent only a small fraction of the volume of the pancreas (usually 1-3%) and are scattered in the tiny islets of Langerhans throughout the organ. In order to be able to measure a beta cell-specific signal, one has to rely on highly specific tracer molecules because current in vivo imaging technologies do not allow the resolution of single islets in humans non-invasively. Currently, a considerable amount of preclinical data are available for several radiotracers and three are under clinical evaluation. We summarise the current status of the evaluation of these tracer molecules and put forward recommendations for their further evaluation.

Molecular imaging of EGFR and CD44v6 for prediction and response monitoring of HSP90 inhibition in an in vivo squamous cell carcinoma model.

PURPOSE: Heat shock protein 90 (HSP90) is essential for the activation and stabilization of numerous oncogenic client proteins. AT13387 is a novel HSP90 inhibitor promoting degradation of oncogenic proteins upon binding, and may also act as a radiosensitizer. For optimal treatment there is, however, the need for identification of biomarkers for patient stratification and therapeutic response monitoring, and to find suitable targets for combination treatments. The aim of this study was to assess the response of surface antigens commonly expressed in squamous cell carcinoma to AT13387 treatment, and to find suitable biomarkers for molecular imaging and radioimmunotherapy in combination with HSP90 inhibition. METHODS: Cancer cell proliferation and radioimmunoassays were used to evaluate the effect of AT13387 on target antigen expression in vitro. Inhibitor effects were then assessed in vivo in mice-xenografts. Animals were treated with AT13387 (5 × 50 mg/kg), and were imaged with PET using either (18)F-FDG or (124)I-labelled tracers for EGFR and CD44v6, and this was followed by ex-vivo biodistribution analysis and immunohistochemical staining. RESULTS: AT13387 exposure resulted in high cytotoxicity and possible radiosensitization with IC50 values below 4 nM. Both in vitro and in vivo AT13387 effectively downregulated HSP90 client proteins. PET imaging with (124)I-cetuximab showed a significant decrease of EGFR in AT13387-treated animals compared with untreated animals. In contrast, the squamous cell carcinoma-associated biomarker CD44v6, visualized with (124)I-AbD19384 as well as (18)F-FDG uptake, were not significantly altered by AT13387 treatment. CONCLUSION: We conclude that AT13387 downregulates HSP90 client proteins, and that molecular imaging of these proteins may be a suitable approach for assessing treatment response. Furthermore, radioimmunotherapy targeting CD44v6 in combination with AT13387 may potentiate the radioimmunotherapy outcome due to radiosensitizing effects of the drug, and could potentially lead to a lower dose to normal tissues.

[11C]Carfentanil Binds Preferentially to µ-Opioid Receptor Subtype 1 Compared to Subtype 2.

The positron emission tomography (PET) ligand [(11)C]carfentanil is a selective agonist for µ-opioid receptors and has been used for studying µ-opioid receptors in the human brain. However, it is unknown if [(11)C]carfentanil binding differentiates between subtype receptors µ1 and µ2. In this study, we investigated whether µ1 and µ2 can be studied separately through receptor subtype-selective inhibition of [(11)C]carfentanil by pharmacologic intervention. [(11)C]Carfentanil binding characteristics on rat brain sections were assessed either alone or in the presence of the µ-receptor inhibitor cyprodime or the µ1-specific inhibitor naloxonazine. [(11)C]Carfentanil binding in the living rat brain was similarly studied by small animal PET/computed tomography during baseline conditions or following displacement by cyprodime or naloxonazine. Autoradiography binding studies on rat brain sections demonstrated that [(11)C]carfentanil has higher affinity and binding potential for µ1 than for µ2. [(11)C]Carfentanil binding to µ2 in vivo could not be detected following specific blocking of µ1, as predicted from the low binding potential for µ2 as measured in vitro. [(11)C]Carfentanil binding is preferential for µ1 compared to µ2 in vitro and in vivo. Clinical studies employing [(11)C]carfentanil are therefore likely biased to measure µ1 rather than µ2.

Positron emission tomography imaging of the glucagon-like peptide-1 receptor in healthy and streptozotocin-induced diabetic pigs.

PURPOSE: The glucagon-like peptide-1 receptor (GLP-1R) has been proposed as a target for molecular imaging of beta cells. The feasibility of non-invasive imaging and quantification of GLP-1R in pancreas using the positron emission tomography (PET) tracer [(68)Ga]Ga-DO3A-VS-Cys(40)-Exendin-4 in non-diabetic and streptozotocin (STZ)-induced diabetic pigs treated with insulin was investigated. METHODS: Non-diabetic (n = 4) and STZ-induced diabetic pigs (n = 3) from the same litter were examined. Development of diabetes was confirmed by blood glucose values, clinical examinations and insulin staining of pancreatic sections post mortem. Tissue perfusion in the pancreas and kidneys was evaluated by [(15)O]water PET/computed tomography (CT) scans. The in vivo receptor specificity of [(68)Ga]Ga-DO3A-VS-Cys(40)-Exendin-4 was assessed by administration of either tracer alone or by competition with 3-6.5 µg/kg of Exendin-4. Volume of distribution and occupancy in the pancreas were quantified with a single tissue compartment model. RESULTS: [(15)O]water PET/CT examinations showed reduced perfusion in the pancreas and kidneys in diabetic pigs. [(68)Ga]Ga-DO3A-VS-Cys(40)-Exendin-4 uptake in the pancreas of both non-diabetic and diabetic pigs was almost completely abolished by co-injection of unlabeled Exendin-4 peptide. [(68)Ga]Ga-DO3A-VS-Cys(40)-Exendin-4 uptake did not differ between non-diabetic and diabetic pigs. In all animals, administration of the tracer resulted in an immediate increase in the heart rate (HR). CONCLUSION: Pancreatic uptake of [(68)Ga]Ga-DO3A-VS-Cys(40)-Exendin-4 was not reduced by destruction of beta cells in STZ-induced diabetic pigs.

Gallium-68-labeled affibody molecule for PET imaging of PDGFRß expression in vivo.

Platelet-derived growth factor receptor ß (PDGFRß) is a transmembrane tyrosine kinase receptor involved, for example, in angiogenesis. Overexpression and excessive signaling of PDGFRß has been observed in multiple malignant tumors and fibrotic diseases, making this receptor a pharmaceutical target for monoclonal antibodies and tyrosine kinase inhibitors. Successful targeted therapy requires identification of responding patients. Radionuclide molecular imaging would enable determination of the PDGFRß status in all lesions using a single noninvasive repeatable procedure. Recently, we have demonstrated that the affibody molecule Z09591 labeled with (111)In can specifically target PDGFRß-expressing tumors in vivo. The use of positron emission tomography (PET) as an imaging technique would provide superior resolution, sensitivity, and quantitation accuracy. In this study, a DOTA-conjugated Z09591 was labeled with the generator-produced positron emitting radionuclide (68)Ga (T1/2 = 67.6 min, Eß + max = 1899 keV, 89% ß(+)). (68)Ga-DOTA-Z09591 retained the capacity to specifically bind to PDGFRß-expressing U-87 MG glioma cells. The half-maximum inhibition concentration (IC50) of (68)Ga-DOTA-Z09591 (6.6 ± 1.4 nM) was somewhat higher than that of (111)In-DOTA-Z09591 (1.4 ± 1.2 nM). (68)Ga-DOTA-Z09591 demonstrated specific (saturable) targeting of U-87 MG xenografts in immunodeficient mice. The tumor uptake at 2 h after injection was 3.7 ± 1.7% IA/g, which provided a tumor-to-blood ratio of 8.0 ± 3.1. The only organ with higher accumulation of radioactivity was the kidney. MicroPET imaging provided high-contrast imaging of U-87 MG xenografts. In conclusion, the (68)Ga-labeled affibody molecule Z09591 is a promising candidate for further development as a probe for imaging PDGFRß expression in vivo using PET.

Introduction of a fatty acid chain modification to prolong circulatory half-life of a radioligand towards glucose-dependent insulinotropic polypeptide receptor.

BACKGROUND: The beneficial role of glucose-dependent insulinotropic polypeptide receptor (GIPR) in weight control and maintaining glucose levels has led to the development of several multi-agonistic peptide drug candidates, targeting GIPR and glucagon like peptide 1 receptor (GLP1R) and/or the glucagon receptor (GCGR). The in vivo quantification of target occupancy by these drugs would accelerate the development of new drug candidates. The aim of this study was to evaluate a novel peptide (GIP1234), based on previously reported ligand DOTA-GIP-C803, modified with a fatty acid moiety to prolong its blood circulation. It would allow higher target tissue exposure and consequently improved peptide uptake as well as in vivo PET imaging and quantification of GIPR occupancy by novel drugs of interest. METHOD: A 40 amino acid residue peptide (GIP1234) was synthesized based on DOTA-GIP-C803, in turn based on the sequences of endogenous GIP and Exendin-4 with specific amino acid modifications to obtain GIPR selectivity. A palmitoyl fatty acid chain was furthermore added at Lys14 via a glutamic acid linker to prolong its blood circulation time by the interaction with albumin. GIP1234 was conjugated with a DOTA chelator at the C-terminal cysteine residue to achieve 68Ga radiolabeling. The resulting PET probe, [68Ga]Ga-DOTA-GIP1234 was evaluated for receptor binding specificity and selectivity using HEK293 cells transfected with human GIPR, GLP1R, or GCGR. Blocking experiments with tirzepatide (2 µM) were conducted using huGIPR HEK293 cells to investigate binding specificity. Ex vivo and in vivo organ distribution of [68Ga]Ga-DOTA-GIP1234 was studied in rats and a pig in comparison to [68Ga]Ga-DOTA-C803-GIP. Binding of [68Ga]Ga-DOTA-GIP1234 to albumin was assessed in situ using polyacrylamide gel electrophoresis (PAGE). The stability was tested in formulation buffer and rat blood plasma. RESULTS: [68Ga]Ga-DOTA-GIP1234 was synthesized with non-decay corrected radiochemical yield of 88 ± 3.7 % and radiochemical purity of 97.8 ± 0.8 %. The molar activity for the radiotracer was 8.1 ± 1.1 MBq/nmol. [68Ga]Ga-DOTA-GIP1234 was stable and maintained affinity to huGIPR HEK293 cells (dissociation constant (Kd) = 40 ± 12.5 nM). The binding of [68Ga]Ga-DOTA-GIP1234 to huGCGR and huGLP1R cells was insignificant. Pre-incubation of huGIPR HEK293 cell sections with tirzepatide resulted in the decrease of [68Ga]Ga-DOTA-GIP1234 binding by close to 90 %. [68Ga]Ga-DOTA-GIP1234 displayed slow blood clearance in pigs with SUV = 3.5 after 60 min. Blood retention of the tracer in rat was 2-fold higher than that of [68Ga]Ga-DOTA-C803-GIP. [68Ga]Ga-DOTA-GIP1234 also demonstrated strong liver uptake in both pig and rat combined with decreased renal excretion. The concentration dependent binding of [68Ga]Ga-DOTA-GIP1234 to albumin was confirmed in situ by PAGE. CONCLUSION: [68Ga]Ga-DOTA-GIP1234 demonstrated nanomolar affinity and selectivity for huGIPR in vitro. Addition of a fatty acid moiety prolonged blood circulation time and tissue exposure in both rat and pig in vivo. However, the liver uptake was also increased which may make PET imaging of abdominal tissues such as pancreas challenging. The investigation of the influence of fatty acid moiety on the biological performance of the peptide ligand paved the way for further rational design of GIPR ligand analogues with improved characteristics.

Noninvasive PET Detection of CD69-Positive Immune Cells Before Signs of Clinical Disease in Inflammatory Arthritis.

Rheumatoid arthritis (RA) is the most common inflammatory joint disease, and early diagnosis is key for effective disease management. CD69 is one of the earliest cell surface markers seen at the surface of activated immune cells, and CD69 is upregulated in synovial tissue in patients with active RA. In this study, we evaluated the performance of a CD69-targeting PET agent, [68Ga]Ga-DOTA-ZCAM241, for early disease detection in a model of inflammatory arthritis. Methods: A model of inflammatory arthritis was induced by transferring splenocytes from KRN T-cell receptor transgenic B6 mice into T-cell-deficient I-Ag7 major histocompatibility complex class II-expressing recipient mice. The mice were examined longitudinally by [68Ga]Ga-DOTA-ZCAM241 PET/CT before and 3, 7, and 12 d after induction of arthritis. Disease progression was monitored by clinical parameters, including measuring body weight and scoring the swelling of the paws. The uptake of [68Ga]Ga-DOTA-ZCAM241 in the paws was analyzed and expressed as SUVmean Tissue biopsy samples were analyzed for CD69 expression by flow cytometry or immunostaining for a histologic correlate. A second group of mice was examined by a nonbinding, size-matched Affibody molecule as the control. Results: Clinical symptoms appeared 5-7 d after induction of arthritis. The uptake of [68Ga]Ga-DOTA-ZCAM241 in the joints was negligible at baseline but increased gradually after disease induction. An elevated PET signal was found on day 3, before the appearance of clinical symptoms. The uptake of [68Ga]Ga-DOTA-ZCAM241 correlated with the clinical score and disease severity. The presence of CD69-positive cells in the joints and lymph nodes was confirmed by flow cytometry and immunostaining. The uptake of the nonbinding tracer that was the negative control also increased gradually with disease progression, although to a lesser extent than with [68Ga]Ga-DOTA-ZCAM241 Conclusion: The uptake of [68Ga]Ga-DOTA-ZCAM241 in the inflamed joints preceded the clinical symptoms in the KRN T-cell transfer model of inflammatory arthritis, in accordance with immunostaining for CD69. [68Ga]Ga-DOTA-ZCAM241 is thus a promising PET imaging marker of activated immune cells in tissue during RA onset.

Non-invasive PET imaging of liver fibrogenesis using a RESCA-conjugated Affibody molecule.

Non-invasive assessment of fibrogenic activity, rather than fibrotic scars, could significantly improve the management of fibrotic diseases and the development of anti-fibrotic drugs. This study explores the potential of an Affibody molecule (Z09591) labeled with the Al(18)F-restrained complexing agent (RESCA) method as a tracer for the non-invasive detection of fibrogenic cells. Z09591 was functionalized with the RESCA chelator for direct labeling with [18F]AlF. In vivo positron emission tomography/magnetic resonance imaging scans on U-87 tumor-bearing mice exhibited high selectivity of the resulting radiotracer, [18F]AlF-RESCA-Z09591, for platelet-derived growth factor receptor ß (PDGFRß), with minimal non-specific background uptake. Evaluation in a mouse model with carbon tetrachloride-induced fibrotic liver followed by a disease regression phase, revealed the radiotracer's high affinity and specificity for fibrogenic cells in fibrotic livers (standardized uptake value [SUV] 0.43 ± 0.05), with uptake decreasing during recovery (SUV 0.29 ± 0.03) (p < 0.0001). [18F]AlF-RESCA-Z09591 accurately detects PDGFRß, offering non-invasive assessment of fibrogenic cells and promising applications in precise liver fibrogenesis diagnosis, potentially contributing significantly to anti-fibrotic drug development.

Radiotracers for Imaging of Fibrosis: Advances during the Last Two Decades and Future Directions.

Fibrosis accompanies various pathologies, and there is thus an unmet medical need for non-invasive, sensitive, and quantitative methods for the assessment of fibrotic processes. Currently, needle biopsy with subsequent histological analysis is routinely used for the diagnosis along with morphological imaging techniques, such as computed tomography (CT), magnetic resonance imaging (MRI), and ultrasound (US). However, none of these imaging techniques are sufficiently sensitive and accurate to detect minor changes in fibrosis. More importantly, they do not provide information on fibrotic activity on the molecular level, which is critical for fundamental understanding of the underlying biology and disease course. Molecular imaging technology using positron emission tomography (PET) offers the possibility of imaging not only physiological real-time activity, but also high-sensitivity and accurate quantification. This diagnostic tool is well established in oncology and has exhibited exponential development during the last two decades. However, PET diagnostics has only recently been widely applied in the area of fibrosis. This review presents the progress of development of radiopharmaceuticals for non-invasive detection of fibrotic processes, including the fibrotic scar itself, the deposition of new fibrotic components (fibrogenesis), or the degradation of existing fibrosis (fibrolysis).

In Vivo Visualization and Quantification of Neutrophil Elastase in Lungs of COVID-19 Patients: A First-in-Humans PET Study with 11C-NES.

Coronavirus disease 2019 (COVID-19) can cause life-threatening lung inflammation that is thought to be mediated by neutrophils. The aim of the present work was to evaluate a novel PET tracer for neutrophil elastase (NE). Methods: In this first-in-humans study, 4 patients with hypoxia due to COVID-19 and 2 healthy controls were investigated with PET using 11C-NES and 15O-water for visualization and quantification of NE and perfusion in the lungs, respectively. Results: 11C-NES accumulated selectively in lung areas with COVID-19 opacities on CT scans, suggesting high levels of NE there. In the same areas, perfusion was severely reduced in comparison to healthy lung tissue as measured with 15O-water. Conclusion: The data suggest that NE is associated with severe lung inflammation in COVID-19 patients and that inhibition of NE could potentially reduce the acute inflammatory process and improve the condition.