Glucagon-like peptide-1 receptor imaging for localization of insulinomas

Diagnostic Challenges in Difficult-to-Localize Insulinomas: A Case Report and Review of Literature

Non-somatostatin receptor expressing hypovascular insulinomas can be challenging to prove through imaging. This case highlights the utility of a structured approach to molecular imaging in patients with confirmed endogenous hyperinsulinemia. A 54-year-old woman was admitted because of a sudden loss of consciousness. Her relative reported that she complained of dizziness, intense sweating, blurry vision, and upper extremity tingling before becoming unresponsive for 20 min, after which the patient had little recollection of the event. She experienced similar episodes of shorter duration, trouble recalling everyday events, and unintentional weight gain of over 10 kg during the previous two years. Abdominal magnetic resonance imaging (MRI) and multidetector computerized tomography (MDCT) were unremarkable. Selective arterial calcium stimulation significantly increased hepatic venous insulin concentrations when the superior mesenteric and gastroduodenal arteries were stimulated. Technetium-99m (99mTc) octreotide single-photon emission computed tomography (SPECT) did not localize the lesion. Gallium-68 DOTA-Exendin-4 PET/CT acquisition was performed. A single intense 2 cm hyperperfused pancreatic lesion was located anteriorly in the head of the pancreas. Earlier targeted PET/CT imaging and recognition of significant neuropsychiatric symptoms attributable to the patient's hypoglycemic state might have accelerated the resolution of her condition and obviated the need for unnecessary testing.

Trends in Presentation and Management of Endogenous Hyperinsulinaemic Hypoglycaemia Over the Last Three Decades at a Tertiary Care Centre (1992-2022)

Introduction

Endogenous hyperinsulinaemic hypoglycaemia (EHH) is characterized by inappropriate insulin secretion from pancreatic beta cells despite low blood glucose concentrations. We aimed to evaluate the secular changes in presentation and management of EHH due to insulinoma/non-insulinoma pancreatogenous hypoglycaemia syndrome (NIPHS) at our centre.

Methods

This was a single-centre ambispective study (2014-2022). The clinical, biochemical, hormonal and radiological parameters (n = 63) collected as part of this study were compared with our earlier studies (1992-2005, n = 31; and 2006-2013, n = 35) and with other centres across the world.

Results

A total of 63 patients (39 males) with a preoperative diagnosis of EHH (insulinoma, n = 58; and NIPHS, n = 5) and a mean age of 40.7 years were studied. The mean lag time from the onset of symptoms to diagnosis decreased from 4.6 years during the first study period to 1.9 years during this study period. However, the majority presented with fasting hypoglycaemia of 98.4%, and both fasting and postprandial hypoglycaemia of 32%. Exclusive postprandial hypoglycaemia was present in 1.7% of insulinoma. A histopathological diagnosis of insulinoma was made in 52 patients and nesidioblastosis in two patients. Intraoperative ultrasonography (IOUS) and intraoperative palpation (IOP) yielded 100% sensitivity, while endoscopic ultrasonography (EUS) and 68Ga-DOTA-Exendin-4 positron emission tomography/computed tomography (PET/CT) yielded sensitivity of 86% and 85%, respectively, for localizing insulinoma. Resolution of hypoglycaemia was noted in 53 of 57 (93%) patients who underwent surgery with a preoperative diagnosis of insulinoma.

Conclusion

We observed a trend towards earlier diagnosis of EHH, increased patient numbers and availability of nuclear imaging techniques for preoperative localization in the last decade compared to earlier.

Recent developments in the diagnosis of pancreatic neuroendocrine neoplasms

INTRODUCTION

Pancreatic Neuroendocrine Neoplasms (PanNENs) are characterized by a highly heterogeneous clinical and biological behavior, making their diagnosis challenging. PanNENs diagnostic work-up mainly relies on biochemical markers, pathological examination, and imaging evaluation. The latter includes radiological imaging (i.e. computed tomography [CT] and magnetic resonance imaging [MRI]), functional imaging (i.e. 68Gallium [68 Ga]Ga-DOTA-peptide PET/CT and Fluorine-18 fluorodeoxyglucose [18F]FDG PET/CT), and endoscopic ultrasound (EUS) with its associated procedures.

AREAS COVERED

This review provides a comprehensive assessment of the recent advancements in the PanNENs diagnostic field. PubMed and Embase databases were used for the research, performed from inception to October 2023.

EXPERT OPINION

A deeper understanding of PanNENs biology, recent technological improvements in imaging modalities, as well as progresses achieved in molecular and cytological assays, are fundamental players for the achievement of early diagnosis and enhanced preoperative characterization of PanNENs. A multimodal diagnostic approach is required for a thorough disease assessment.

Ectopic insulinoma: a systematic review

Knowledge of ectopic insulinomas comes from single cases. We performed a systematic review through PubMed, Web of Science, Embase, eLibrary and ScienceDirect of all cases reported in the last four decades. We also describe one unreported patient. From 28 patients with ectopic insulinoma, 78.6% were female and mean age was 55.7 ± 19.2 years. Hypoglycaemia was the first symptom in 85.7% while 14.3% complained of abdominal pain or genital symptoms. Median tumour diameter was 27.5 [15-52.5] mm and it was localised by CT (73.1%), MRI (88.9%), [68Ga]Ga-DOTA-exedin-4 PET/CT (100%), 68Ga-labelled-DOTA-conjugated somatostatin analogue PET/TC (100%), somatostatin receptor scintigraphy (40%) and endoscopic ultrasound (50%). Ectopic insulinomas were located at duodenum (n = 3), jejunum (n = 2), and one respectively at stomach, liver, appendix, rectum, mesentery, ligament of Treitz, gastrosplenic ligament, hepatoduodenal ligament and splenic hilum. Seven insulinomas were affecting the female reproductive organs: ovary (n = 5), cervix (n = 2) and remaining tumours were at retroperitoneum (n = 3), kidney (n = 2), spleen (n = 1) and pelvis (n = 1). 89.3% underwent surgery (66.7% surgery vs. 33.3% laparoscopy) and 16% underwent an ineffective pancreatectomy. 85.7% had localized disease at diagnosis and 14.3% developed distant metastasis. Median follow-up time was 14.5 [4.5-35.5] months and mortality was reported in 28.6% with median time until death of 60 [5-144] months. In conclusion, ectopic insulinomas are presented as hypoglycaemia with female preponderance. Functional imaging [68Ga]Ga-DOTA-exedin-4 PET/CT and 68Ga-labelled-DOTA-conjugated somatostatin analogue PET/TC have very high sensitivity. Clinicians should be alert to the possibility of extra-pancreatic insulinomas when classic diagnostic tests and intraoperative pancreas exploration failed to locate the tumour.

Theranostic in GLP-1R molecular imaging: challenges and emerging opportunities

Theranostic in nuclear medicine combines diagnostic imaging and internal irradiation therapy using different therapeutic nuclear probes for visual diagnosis and precise treatment. GLP-1R is a popular receptor target in endocrine diseases, non-alcoholic steatohepatitis, tumors, and other areas. Likewise, it has also made breakthroughs in the development of molecular imaging. It was recognized that GLP-1R imaging originated from the study of insulinoma and afterwards was expanded in application including islet transplantation, pancreatic β-cell mass measurement, and ATP-dependent potassium channel-related endocrine diseases. Fortunately, GLP-1R molecular imaging has been involved in ischemic cardiomyocytes and neurodegenerative diseases. These signs illustrate the power of GLP-1R molecular imaging in the development of medicine. However, it is still limited to imaging diagnosis research in the current molecular imaging environment. The lack of molecular-targeted therapeutics related report hinders its radiology theranostic. In this article, the current research status, challenges, and emerging opportunities for GLP-1R molecular imaging are discussed in order to open a new path for theranostics and to promote the evolution of molecular medicine.

Reducing kidney uptake of radiolabelled exendin-4 using variants of the renally cleavable linker MVK

BACKGROUND

Peptidic radiotracers are preferentially excreted through the kidneys, which often results in high persistent renal retention of radioactivity, limiting or even preventing therapeutic clinical translation of these radiotracers. Exendin-4, which targets the glucagon-like-peptide 1 receptor (GLP-1R) overexpressed in insulinomas and in congenital hyperinsulinism, is an example thereof. The use of the tripeptide MVK, which is readily cleaved between methionine and valine by neprilysin at the renal brush border membrane, already showed promising results in reducing kidney uptake as reported in the literature. Based on our previous findings we were interested how linker variants with multiple copies of the MV-motive influence renal washout of radiolabelled exendin-4.

RESULTS

Three exendin-4 derivatives, carrying either one MVK, a MV-MVK or a MVK-MVK linker were synthesized and compared to a reference compound lacking a cleavable linker. In vivo results of a biodistribution in GLP-1R overexpressing tumour bearing mice at 24 h post-injection demonstrated a significant reduction (at least 57%) of renal retention of all 111In-labeled exendin-4 compounds equipped with a cleavable linker compared to the reference compound. While the insertion of the single linker MVK led to a reduction in kidney uptake of 70%, the dual approach with the linker MV-MVK slightly, but not significantly enhanced this effect, with 77% reduction in kidney uptake compared to the reference. In vitro IC50 and cell uptake studies were conducted and demonstrated that though the cleavable linkers negatively influenced the affinity towards the GLP-1R, cell uptake remained largely unaffected, except for the MV-MVK cleavable linker conjugate, which displayed lower cell uptake than the other compounds. Importantly, the tumour uptake in the biodistribution study was not significantly affected with 2.9, 2.5, 3.2 and 1.5% iA/g for radiolabelled Ex4, MVK-Ex4, MV-MVK-Ex4 and MVK-MVK-Ex4, respectively.

CONCLUSION

Cleavable linkers are highly efficient in reducing the radioactivity burden in the kidney. Though the dual linker approach using the instillation of MV-MVK or MVK-MVK between exendin-4 and the radiometal chelator did not significantly outperform the single cleavable linker MVK, further structural optimization or the combination of different cleavable linkers could be a stepping stone in reducing radiation-induced nephrotoxicity.

18F-labeled PEGylated exendin-4 imaging noninvasively differentiates insulinoma from an accessory spleen: the first case report of [18F]FB(ePEG12)12-exendin-4 positron emission tomography/computed tomography for insulinoma

Background

Insulinomas are the most common functioning pancreatic neuroendocrine neoplasms, and these tumors induce hypoglycemia due to hyperinsulinemia. Hypoglycemia caused by insulinomas can cause seizures, coma or death due to the delayed diagnosis. The only curative treatment is surgical resection. To perform curative surgical resection of insulinomas, preoperative localization is crucial. However, localization of insulinomas is often challenging using conventional imaging methods such as computed tomography (CT) and magnetic resonance imaging. Although endoscopic ultrasound (EUS) fine-needle aspiration and selective arterial calcium stimulation test, which can reflect the endocrine character of the tumor, are performed in such cases, these modalities are invasive and require operator-dependent techniques. Additionally, somatostatin receptor (SSTR)-targeted imaging has a relatively low sensitivity for detecting insulinomas due to its low SSTR type 2 expression. Thus, there is an urgent need for developing a noninvasive diagnostic technique which is specific for detecting insulinomas. Consequently, glucagon-like peptide-1 receptor-targeted imaging has recently emerged and gained a wide interest. Recently, we have developed a novel 18F-labeled exendin-4-based probe conjugated with polyethylene glycol, [18F]FB(ePEG12)12-exendin-4 (18F-exendin-4), for positron emission tomography (PET) imaging. Here we report a case of insulinoma in which 18F-exendin-4 PET/CT noninvasively provided critical information for localization.

Case description

This is a case of a 58-year-old male with symptomatic hypoglycemia for 10 years; however, a preoperative diagnosis of insulinoma was not established due to the difficulty in differentiating it from an accessory spleen using conventional imaging. Moreover, the patient requested to avoid invasive diagnostic procedures including EUS. 18F-exendin-4 PET/CT revealed significant uptakes in the pancreatic tail whereas no apparent uptakes were observed in the spleen; thus, curative laparoscopic enucleation of the pancreatic tail was performed. The diagnosis of insulinoma was confirmed via histopathological examination. This is the first case report of insulinoma diagnosed using 18F-exendin-4 PET/CT.

Conclusion

In this case, PET information led to curative resection through enucleation of the pancreas. 18F-exendin-4 PET/CT may serve as a useful noninvasive clinical tool for insulinoma localization.

Insulinoma in Patient With Nonalcoholic Steatohepatitis

An insulinoma is a rare neuroendocrine tumor characterized by inappropriate secretion of insulin with resultant hypoglycemia and concomitant symptoms. Symptoms include diaphoresis, tremor, palpitations, tachycardia, visual disturbances, weakness, confusion, syncope, seizures, and even coma. Enteropancreatic neoplasms are rare in general but among them, insulinomas are among the more common neuroendocrine tumors though they still have a very low incidence. They can be benign or malignant, however, the latter is exceptionally rare. In the case of malignancy, such spread usually includes metastasis to the liver and surrounding nodes. They can also be sporadic or occur in association with other inherited conditions. Herein, we present a case of insulinoma in a 51-year-old female.

Role of Exendin-4 Functional Imaging in Diagnosis of Insulinoma: A Systematic Review

BACKGROUND

Insulinomas are the most common neuroendocrine neoplasms of the pancreas. Diagnosis is made through patient clinical presentation with hypoglycemia symptoms and imaging, such as EUS, CT, MRI, and functional imaging. Exendin-4 PET/CT (and SPECT/CT) is a new prominent radiotracer developed to image insulinomas. The aim of the study is to evaluate whether exendin-4 imaging is a useful tool in imaging for insulinoma patients when other imaging methods do not reach them.

METHODS

MEDLINE research conducted on PubMed, Scopus, and Web of Science gathered a total of 501 papers. Studies that evaluated exendin-4 SPECT and PET in insulinoma patients were screened and assessed through QUADAS-2 for risk of bias and applicability concerns' assessment. Sensitivity, specificity, and accuracy were reported when available.

RESULTS

A total of 13 studies were deemed eligible for a QUADAS 2 review. Studies included ranged from 2009 to 2022. The most-used tracer was ⁶⁸Ga-DOTA-exendin-4 in PET and ¹¹¹In-DTPA-exendin-4 in SPECT. Exendin-4 labeled with ⁹⁹mTc was also reported. The QUADAS-2 risk of bias assessment was overall low, with some unclear reports in the reference and index domains. Only two domains were at high risk of bias because of an explicated non-blind imaging review. Applicability concerns for bias were low in all domains. Reported sensitivities ranged from 95% to 100% and specificities from 20% to 100%.

CONCLUSIONS

exendin-4 imaging is a sensitive functional imaging tracer in both SPECT and PET applications, especially in suspicion of benign insulinomas located where endoscopic ultrasound cannot reach, being more sensitive than morfostructural imaging.

Diagnostic work-up and advancement in the diagnosis of gastroenteropancreatic neuroendocrine neoplasms

Neuroendocrine neoplasms (NENs) are a heterogeneous group of neoplasms ranging from well-differentiated, slowly growing tumors to poorly differentiated carcinomas. These tumors are generally characterized by indolent course and quite often absence of specific symptoms, thus eluding diagnosis until at an advanced stage. This underscores the importance of establishing a prompt and accurate diagnosis. The gold-standard remains histopathology. This should contain neuroendocrine-specific markers, such as chromogranin A; and also, an estimate of the proliferation by Ki-67 (or MIB-1), which is pivotal for treatment selection and prognostication. Initial work-up involves assessment of serum Chromogranin A and in selected patients gut peptide hormones. More recently, the measurement of multiple NEN-related transcripts, or the detection of circulating tumor cells enhanced our current diagnostic armamentarium and appears to supersede historical serum markers, such as Chromogranin A. Standard imaging procedures include cross-sectional imaging, either computed tomography or magnetic resonance, and are combined with somatostatin receptor scintigraphy. In particular, the advent of ¹¹¹In-DTPA-octreotide and more recently PET/CT and ⁶⁸Ga-DOTA-Octreotate scans revolutionized the diagnostic landscape of NENs. Likewise, FDG PET represents an invaluable asset in the management of high-grade neuroendocrine carcinomas. Lastly, endoscopy, either conventional, or more advanced modalities such as endoscopic ultrasound, capsule endoscopy and enteroscopy, are essential for the diagnosis and staging of gastroenteropancreatic neuroendocrine neoplasms and are routinely integrated in clinical practice. The complexity and variability of NENs necessitate the deep understanding of the current diagnostic strategies, which in turn assists in offering optimal patient-tailored treatment. The current review article presents the diagnostic work-up of GEP-NENs and all the recent advances in the field.

68Ga-DOTATATE PET/CT imaging for insulinoma in MEN1 patient with endogenous hyperinsulinemic hypoglycemia: A case report

RATIONALE

Multiple endocrine neoplasia type 1 (MEN1) syndrome is a rare and complicated disease that is associated with several endocrine tumors. Here, we report a case of MEN1 associated with insulinoma, parathyroid, and pituitary tumors by 68Ga-DOTATATE positron emission tomography/computed tomography (PET/CT).

PATIENT CONCERNS

A 49-year-old woman presented with intermittent hypoglycemia for more than a year and developed indistinct consciousness without an apparent trigger.

DIAGNOSES

Biochemical results showed abnormally high serum insulin and parathyroid hormone levels. She underwent an Abdominal magnetic resonance imaging revealed a small nodule in the uncinate process of the pancreas, but it did not clarify the nature of the small nodule. Pituitary magnetic resonance imaging scan revealed a micropituitary tumor, and parathyroid imaging showed no abnormalities. 18F-FDG PET/CT showed no apparent abnormal 18F-FDG uptake in the whole body. In contrast, 68Ga-DOTATATE PET/CT imaging showed pathological radiotracer uptake in the pancreatic uncinate process, accompanied by mild radiotracer uptake in the pituitary gland, and no apparent abnormal radiotracer uptake in the parathyroid area.

INTERVENTIONS

The patient underwent echoendoscopy for pancreatic uncinate process lesions and surgical resection.

OUTCOMES

Histological analysis was suggested of insulinoma of pancreatic neuroendocrine tumor, the Ki-67 index was low (only 1% being positive).

LESSONS

This case demonstrates that 68Ga-DOTATATE can be used for the detection of MEN1-related tumors and preoperative localization of small and low-grade insulinomas by PET/CT.

Molecular Imaging in neuroendocrine neoplasias

Molecular imaging, which uses molecular targets due to the overexpression of specific peptide hormone receptors on the tumour surface, has become an indispensable diagnostic technique. Neuroendocrine neoplasms (NENs) especially differentiated NENs or neuroendocrine tumours (NETs) are a rare group of heterogeneous tumours, characterized by the expression of hormone receptors on the tumour cell surface. This property makes them receptive to diagnostic and therapeutic approaches (theranostics) using radiolabelled peptides. Amongst the known hormone receptors, somatostatin receptors (SSTR) are expressed on the majority of NETs and are therefore the most relevant receptors for theranostic approaches. Current research aims to medically upregulate their expression, while other focuses are on the use of different radiopeptides (64Cu and 67Cu) or somatostatin-antagonists instead of the established somatostatin agonists. The GLP-1 receptor is another clinically relevant target, as GLP-1-R imaging has become the new standard for the localisation of insulinomas. For staging and prognostic evaluation in dedifferentiated NENs, 18F-FDG-imaging is useful, but lacks a therapeutic counterpart. Further options for patients with insufficient expression of SSTR involve metaiodobenzylguanidine (MIBG) and the molecular target C-X-C motif chemokine receptor-4 (CXCR4). New targets such as the glucose-dependant insulinotropic polypeptide receptor (GIPR) and the fibroblast activation protein (FAP) have been identified in NENs recently and await further evaluation. For medullary thyroid cancer 18-F-DOPA imaging is standard, however this technique is rather second line for other NENs. In this area, the discovery of minigastrin, which targets the cholecystokinin-2 (CCK2) receptors in medullary thyroid carcinoma and foregut NENs, may improve future management. This review aims to provide an overview of the most commonly used functional imaging modalities for theranostics in NENs today and in the possible future.

New insights in diagnosis and treatment of gastroenteropancreatic neuroendocrine neoplasms

Gastroenteropancreatic neuroendocrine neoplasms (GEP-NENs) are rare epithelial neoplasms derived from pluripotent endocrine cells along the gastrointestinal tract and pancreas. GEP-NENs are classified into well-differentiated neuroendocrine tumors and poorly differentiated neuroendocrine carcinomas. Despite overlapping morphological features, GEP-NENs vary in molecular biology, epigenetic, clinical behavior, treatment response, and prognosis features and remain an unmet clinical challenge. In this review, we introduce recent updates on the histopathologic classification, including the tumor grading and staging system, molecular genetics, and systemic evaluation of the diagnosis and treatment of GEP-NENs at different anatomic sites, together with some insights into the diagnosis of challenging and unusual cases. We also discuss the application of novel therapeutic approaches for GEP-NENs, including peptide receptor radionuclide therapy, targeted therapy, and immunotherapy with immune checkpoint inhibitors. These findings will help improve patient care with precise diagnosis and individualized treatment of patients with GEP-NENs.

68Ga-Exendin-4 PET/CT Differentiates Insulinoma From Accessory Spleen in a Patient Presenting Indeterminate MRI and 68Ga-DOTATATE PET/CT Findings

ABSTRACT

A 55-year-old woman with endogenous hyperinsulinemia hypoglycemia was clinically diagnosed with insulinoma. Contrast-enhanced MRI revealed an inconclusive hypointense lesion in the pancreatic tail, and the enhancement pattern does not support the diagnosis of insulinoma. 68Ga-DOTATATE PET/CT showed intense radioactivity in this nodule, similar to the radioactivity of the adjacent spleen. Therefore, the diagnosis of accessory spleen cannot be excluded. Follow-up with 68Ga-exendin-4 PET/CT also showed intense uptake in this nodule, but no significant uptake in the spleen was observed at this time. Therefore, the insulinoma was unmasked from the spleen, excluding the diagnosis of accessory spleen, and allowing curative surgery.

Development and Validation of an Analytical HPLC Method to Assess Chemical and Radiochemical Purity of [68Ga]Ga-NODAGA-Exendin-4 Produced by a Fully Automated Method

Background: Glucagon-like peptide 1 receptor (GLP-1R) is preferentially expressed in pancreatic islets, especially in β-cells, and highly expressed in human insulinomas and gastrinomas. In recent years several GLP-1R-avid radioligands have been developed to image insulin-secreting tumors or to provide a tentative quantitative in vivo biomarker of pancreatic β-cell mass. Exendin-4, a 39-amino acid peptide with high binding affinity to GLP-1R, has been labeled with Ga-68 for imaging with positron emission tomography (PET). Preparation conditions may influence the quality and in vivo behavior of tracers. Starting from a published synthesis and quality controls (QCs) procedure, we have developed and validated a new rapid and simple UV-Radio-HPLC method to test the chemical and radiochemical purity of [68Ga]Ga-NODAGA-exendin-4, to be used in the clinical routine. Methods: Ga-68 was obtained from a 68Ge/68Ga Generator (GalliaPharma®) and purified using a cationic-exchange cartridge on an automated synthesis module (Scintomics GRP®). NODAGA-exendin-4 contained in the reactor (10 µg) was reconstituted with HEPES and ascorbic acid. The reaction mixture was incubated at 100 °C. The product was purified through HLB cartridge, diluted, and sterilized. To validate the proposed UV-Radio-HPLC method, a stepwise approach was used, as defined in the guidance document released by the International Conference on Harmonization of Technical Requirements of Pharmaceuticals for Human Use (ICH), adopted by the European Medicines Agency (CMP/ICH/381/95 2014). The assessed parameters are specificity, linearity, precision (repeatability), accuracy, and limit of quantification. Therefore, a range of concentrations of Ga-NODAGA-exendin-4, NODAGA-exendin-4 (5, 4, 3.125, 1.25, 1, and 0.75 μg/mL) and [68Ga]Ga-NODAGA-exendin-4 were analyzed. To validate the entire production process, three consecutive batches of [68Ga]Ga-NODAGA-exendin-4 were tested. Results: Excellent linearity was found between 5-0.75 μg/mL for both the analytes (NODAGA-exendin-4 and 68Ga-NODAGA-exendin-4), with a correlation coefficient (R2) for calibration curves equal to 0.999, average coefficients of variation (CV%) < 2% (0.45% and 0.39%) and average per cent deviation value of bias from 100%, of 0.06% and 0.04%, respectively. The calibration curve for the determination of [68Ga]Ga-NODAGA-exendin-4 was linear with a R2 of 0.993 and CV% < 2% (1.97%), in accordance to acceptance criteria. The intra-day and inter-day precision of our method was statistically confirmed using 10 μg of peptide. The mean radiochemical yield was 45 ± 2.4% in all the three validation batches of [68Ga]Ga-NODAGA-exendin-4. The radiochemical purity of [68Ga]Ga-NODAGA-exendin-4 was >95% (97.05%, 95.75% and 96.15%) in all the three batches. Conclusions: The developed UV-Radio-HPLC method to assess the radiochemical and chemical purity of [68Ga]Ga-NODAGA-exendin-4 is rapid, accurate and reproducible like its fully automated production. It allows the routine use of this PET tracer as a diagnostic tool for PET imaging of GLP-1R expression in vivo, ensuring patient safety.

GLP2-GLP2R signal affects the viability and EGFR-TKIs sensitivity of PC9 and HCC827 cells

Background

The resistance to epidermal growth factor receptor (EGFR)- tyrosine kinase inhibitors (TKIs) therapy is currently the major clinical challenge in the treatment of lung cancer. This study aims to reveal the role of glucagon-like peptide (GLP) 2 and GLP-2 receptor (GLP2R) signaling on the EGFR-TKIs and cisplatin resistance of lung cancer cells.

Methods

The common differentially expressed genes in PC9 and HCC827 cells that were individually resistant to one of the three EGFR-TKIs (dacomitinib, osimertinib and afatinib) were screened. The data were from GSE168043 and GSE163913. The expression of GLP2R in drug-resistant cells was detected by western blot. The effect of GLP2R expression down- or up-regulation on resistance to dacomitinib, osimertinib, afatinib or cisplatin was measured by CCK-8 and flow cytometry assays. The long-acting analog of GLP-2, teduglutide, treated the parental cells.

Results

A total of 143 common differentially expressed genes were identified. Compared with the parent cells, the GLP2R expression in drug-resistant cell lines was significantly up-regulated. The exogenous expression of GLP2R in parental cells enhanced cell viability, while knockdown of GLP2R levels in drug-resistant cell lines inhibited cell viability. In addition, teduglutide treatment also enhanced the viability of lung cancer cells.

Conclusion

GLP2-GLP2R signal may change the sensitivity of cells to EGFR-TKIs and cisplatin. The development of GLP-2 or GLP2R inhibitors may be beneficial to the clinical treatment of lung cancer.

Exendin-4-Conjugated Manganese Magnetism-Engineered Iron Oxide Nanoparticles as a Potential Magnetic Resonance Imaging Contrast Agent for Tracking Transplanted β-Cells

To specifically detect and trace transplanted islet β-cells by magnetic resonance imaging (MRI), we conjugated manganese magnetism-engineered iron oxide nanoparticles (MnMEIO NPs) with exendin-4 (Ex4) which specifically binds glucagon-like peptide-1 receptors on the surface of β-cells. The size distribution of MnMEIO and MnMEIO-Ex4 NPs were 67.8 ± 1.3 and 70.2 ± 2.3 nm and zeta potential 33.3 ± 0.5 and 0.6 ± 0.1 mV, respectively. MnMEIO and MnMEIO-Ex4 NPs with iron content ≤ 40 μg/mL did not affect MIN6 β-cell viability and insulin secretion. Positive iron staining was found in MIN6 β-cells loaded with MnMEIO-Ex4 NPs but not in those with MnMEIO NPs. A transmission electron microscope confirmed MnMEIO-Ex4 NPs were distributed in the cytoplasm of MIN6. In vitro MR images revealed a loss of signal intensity in MIN6 β-cells labeled with MnMEIO-Ex4 NPs but not with MnMEIO NPs. After transplantation of islets labeled with MnMEIO-Ex4, the graft under kidney capsule could be visualized on MRI as persistent hypointense areas up to 17 weeks. Moreover, histology of the islet graft showed positive staining for insulin, glucagon and iron. Our results indicate MnMEIO-Ex4 NPs are safe and effective for the detection and long-term monitoring of transplanted β-cells by MRI.

New Directions in Imaging Neuroendocrine Neoplasms

Purpose of Review

Accurate imaging is crucial for correct diagnosis, staging, and therapy of neuroendocrine neoplasms (NENs). The search for the optimal imaging technique has triggered rapid development in the field. This review aims at giving an overview on contemporary imaging methods and providing an outlook on current progresses.

Recent Findings

The discovery of molecular targets due to the overexpression of specific peptide hormone receptors on the NEN’s surface has triggered the development of multiple radionuclide imaging modalities. In addition to the established imaging technique of targeting somatostatin receptors, several alternative radioligands have been developed. Targeting the glucagon-like peptide-1 receptor by exendin-4 has a high sensitivity in localizing insulinomas. For dedifferentiated NENs, new molecular targets such as the C-X-C motif chemokine-receptor-4 have been evaluated. Other new targets involve the fibroblast activation protein and the cholecystokinin-2 receptors, where the ligand minigastrin opens new possibilities for the management of medullary thyroid carcinoma.

Summary

Molecular imaging is an emerging field that improves the management of NENs.

The β Cell in Diabetes: Integrating Biomarkers With Functional Measures

The pathogenesis of hyperglycemia observed in most forms of diabetes is intimately tied to the islet β cell. Impairments in propeptide processing and secretory function, along with the loss of these vital cells, is demonstrable not only in those in whom the diagnosis is established but typically also in individuals who are at increased risk of developing the disease. Biomarkers are used to inform on the state of a biological process, pathological condition, or response to an intervention and are increasingly being used for predicting, diagnosing, and prognosticating disease. They are also proving to be of use in the different forms of diabetes in both research and clinical settings. This review focuses on the β cell, addressing the potential utility of genetic markers, circulating molecules, immune cell phenotyping, and imaging approaches as biomarkers of cellular function and loss of this critical cell. Further, we consider how these biomarkers complement the more long-established, dynamic, and often complex measurements of β-cell secretory function that themselves could be considered biomarkers.

Theranostics in neuroendocrine tumors: an overview of current approaches and future challenges

Neuroendocrine neoplasms (NENs) comprise a heterogeneous group of tumors, mainly localized in the gastrointestinal system. What characterizes NENs is the expression of hormone receptors on the tumor cell surface, making them accessible for diagnostic and therapeutic approaches (theranostics) using radiolabelled peptides. Somatostatin receptors subtype-two (SST2) play an important role in NENs since they are overexpressed and homogeneously distributed at the surface of the majority of NENs. Accordingly, targeting SST2 for diagnostic and therapeutic purposes has been established. Current research aims at upregulating its expression by epigenetic treatment or improving its targeting via use of alternative radioligands. In addition, recent data suggest a future role of SST antagonists as a diagnostic tool and a potential therapeutic option. Another promising target is the glucagon-like peptide-1 (GLP-1) receptor. Targeting GLP-1R using exendin-4 (GLP-1 analogue) has a high sensitivity for the localization of the often SST2-negative sporadic insulinomas and insulinomas in the context of multiple endocrine neoplasia type-1. Further options for patients with insufficient expression of SST2 involve metaiodobenzylguanidine (MIBG) and the molecular target C-X-C motif chemokine receptor-4 (CXCR4), which have been evaluated for potential theranostic approach in symptomatic NENs or dedifferentiated tumors. Recently, new targets such as the glucose-dependent insulinotropic polypeptide receptor (GIPR) and the fibroblast activation protein (FAP) have been identified in NENs. Finally, minigastrin - a ligand targeting the cholecystokinin-2 (CCK2) receptors in medullary thyroid carcinoma and foregut neuroendocrine tumors - may improve future management of these diseases with currently limited therapeutic options. This review summarises the current approaches and future challenges of diagnostic and therapeutic evaluations in neuroendocrine neoplasms.

Distinctive detection of insulinoma using [18F]FB(ePEG12)12-exendin-4 PET/CT

Specifying the exact localization of insulinoma remains challenging due to the lack of insulinoma-specific imaging methods. Recently, glucagon-like peptide-1 receptor (GLP-1R)-targeted imaging, especially positron emission tomography (PET), has emerged. Although various radiolabeled GLP-1R agonist exendin-4-based probes with chemical modifications for PET imaging have been investigated, an optimal candidate probe and its scanning protocol remain a necessity. Thus, we investigated the utility of a novel exendin-4-based probe conjugated with polyethylene glycol (PEG) for [¹⁸F]FB(ePEG12)12-exendin-4 PET imaging for insulinoma detection. We utilized [¹⁸F]FB(ePEG12)12-exendin-4 PET/CT to visualize mouse tumor models, which were generated using rat insulinoma cell xenografts. The probe demonstrated high uptake value on the tumor as 37.1 ± 0.4%ID/g, with rapid kidney clearance. Additionally, we used Pdx1-Cre;Trp53^R172H;Rb^f/f mice, which developed endogenous insulinoma and glucagonoma, since they enabled differential imaging evaluation of our probe in functional pancreatic neuroendocrine neoplasms. In this model, our [¹⁸F]FB(ePEG12)12-exendin-4 PET/CT yielded favorable sensitivity and specificity for insulinoma detection. Sensitivity: 30-min post-injection 66.7%, 60-min post-injection 83.3%, combined 100% and specificity: 30-min post-injection 100%, 60-min post-injection 100%, combined 100%, which was corroborated by the results of in vitro time-based analysis of internalized probe accumulation. Accordingly, [¹⁸F]FB(ePEG12)12-exendin-4 is a promising PET imaging probe for visualizing insulinoma.

Glucagon-like Peptide-1 Receptor as Emerging Target: Will It Make It to the Clinic?

The glucagon-like peptide-1 receptor (GLP-1R) is an emerging target due to its high expression in benign insulinomas as well as in islet cell hypertrophia/hyperplasia (nesidioblastosis) and pancreatic β-cells. In 2008, occult insulinomas were localized for the first time in men using the metabolically stable radiolabeled glucagon-like peptide-1 (GLP-1) agonist [Lys40(Ahx-DTPA-111In)NH2]-exendin-4 (111In-DTPA-exendin-4). Afterward, several radiopharmaceuticals for GLP-1R PET/CT imaging were synthesized and evaluated, for example, [Nle14,Lys40(Ahx-DOTA-68Ga)NH2]-exendin-4 (68Ga-DOTA-exendin-4), [Cys40(MAL-NOTA-68Ga)NH2]-exendin-4 (68Ga-NOTA-exendin-4), and [Lys40(NODAGA-68Ga)NH2]-exendin-4 (68Ga-NODAGA-exendin-4). Several prospective comparison studies provided evidence that GLP-1R PET/CT is significantly more sensitive than contrast-enhanced MRI (ceMRI), contrast-enhanced CT (ceCT), GLP-1R SPECT/CT, somatostatin receptor PET/CT, and SPECT/CT in the detection of benign insulinomas, and insulinomas in the context of multiple endocrine neoplasia type 1. As a result, the European Neuroendocrine Tumor Society guidelines recommend GLP-1R imaging or selective intraarterial calcium stimulation and venous sampling (ASVS) in patients for whom there is a clinical suspicion of having an insulinoma but who have a negative ceMRI/ceCT or negative endoscopic ultrasound. Furthermore, there is growing evidence that GLP-1R PET/CT can visualize and localize adult nesidioblastosis. This is clinically relevant as the distinction between focal and diffuse nesidioblastosis is critical in directing a therapeutic strategy in these patients. Prospective studies have proven the clinical relevance of GLP-1R imaging as it is often the only imaging modality able to localize the insulinoma or nesidioblastosis. It is therefore likely that this noninvasive imaging modality will replace the invasive localization of insulinomas using ASVS. More experimental indications for GLP-1R imaging include the diagnosis of an insulinoma/nesidioblastosis in patients with postprandial hypoglycemia after bariatric bypass surgery and monitoring β-cells in patients with brittle type 1 diabetes after islet-cell transplantation. We believe that these indications and possibly future indications will bring GLP-1R imaging to the clinic.

Multiple endocrine neoplasia type 1 (MEN-1) and neuroendocrine neoplasms (NENs)

Neuroendocrine neoplasms (NENs) are relatively rare neoplasms with 6.4-times increasing age-adjusted annual incidence during the last four decades. NENs arise from neuroendocrine cells, which release hormones in response to neuronal stimuli and they are distributed into organs and tissues. The presentation and biological behaviour of the NENs are highly heterogeneous, depending on the organ. The increased incidence is mainly due to increased awareness and improved detection methods both in the majority of sporadic NENs (non-inherited), but also the inherited groups of neoplasms appearing in at least ten genetic syndromes. The most important one is multiple endocrine neoplasia type 1 (MEN-1), caused by mutations in the tumour suppressor gene MEN1. MEN-1 has been associated with different tumour manifestations of NENs e.g. pancreas, gastrointestinal tract, lungs, thymus and pituitary. Pancreatic NENs tend to be less aggressive when arising in the setting of MEN-1 compared to sporadic pancreatic NENs. There have been very important improvements over the past years in both genotyping, genetic counselling and family screening, introduction and validation of various relevant biomarkers, as well as newer imaging modalities. Alongside this development, both medical, surgical and radionuclide treatments have also advanced and improved morbidity, quality of life and mortality in many of these patients. Despite this progress, there is still space for improving insight into the genetic and epigenetic factors in relation to the biological mechanisms determining NENs as part of MEN-1. This review gives a comprehensive update of current evidence for co-occurrence, diagnosis and treatment of MEN-1 and neuroendocrine neoplasms and highlight the important progress now finding its way to international guidelines in order to improve the global management of these patients.

GLP-1 peptide analogs for targeting pancreatic beta cells

Loss or dysfunction of the pancreatic beta cells or insulin receptors leads to diabetes mellitus (DM). This usually occurs over many years; therefore, the development of methods for the timely detection and clinical intervention are vital to prevent the development of this disease. Glucagon-like peptide-1 receptor (GLP-1R) is the receptor of GLP-1, an incretin hormone that causes insulin secretion in a glucose-dependent manner. GLP-1R is highly expressed on the surface of pancreatic beta cells, providing a potential target for bioimaging. In this review, we provide an overview of various strategies, such as the development of GLP-1R agonists (e.g., exendin-4), and GLP-1 sequence modifications for GLP-1R targeting for the diagnosis and treatment of pancreatic beta cell disorders. We also discuss the challenges of targeting pancreatic beta cells and strategies to address such challenges.

Ectopic insulinoma diagnosed by 68Ga-Exendin-4 PET/CT: A case report and review of literature

RATIONALE

Ectopic insulinomas are extremely rare and challenging to diagnose for clinicians. Precise preoperative localization is essential to successful treatment.

PATIENT CONCERNS

A 23-year-old man presented with a 1-year history of recurrent hypoglycemia.

DIAGNOSIS

Examinations in the local hospital did not reveal any pancreatic lesion. After admission, a fasting test and a 5-hour oral glucose tolerance test (OGTT) suggested a diagnosis of endogenous hyperinsulinemic hypoglycemia. Enhanced volume perfusion computed tomography (VPCT) revealed 2 nodules in the tail of the pancreas, a nodule in the gastric antrum, and a nodule in the hilum of the spleen. To differentiate which nodule was responsible for hypoglycemia, we performed 68Ga-Exendin-4 PET/CT and 68Ga-DOTATATE PET/CT which helped to make a conclusive diagnosis that the lesion in the gastric antrum was an ectopic insulinoma.

INTERVENTIONS

The patient was cured with minimally invasive laparoscopic resection of the tumor.

OUTCOMES

The symptoms were relieved and the blood glucose level remained normal after surgery.

CONCLUSIONS

This case shows that 68Gallium-exendin-4 PET/CT is useful for precise localization and thereby successful treatment of insulinoma, especially for occult insulinomas and those derived from an ectopic pancreas.

Feasibility of a scale-down production of [68Ga]Ga-NODAGA-Exendin-4 in a hospital based radiopharmacy

BACKGROUND

Glucagon-like peptide 1 receptor (GLP-1R) is preferentially expressed in β-cells, but it is highly expressed in human insulinomas and gastrinomas. Several GLP-1 receptor-avid radioligands have been developed to image insulin-secreting tumors or to provide a quantitative in vivo biomarker of pancreatic β-cell mass. Exendin-4 is a high affinity ligand of the GLP1-R, which is a candidate for being labeled with a PET isotope and used for imaging purposes.

OBJECTIVE

Here, we report the development and validation results of a semi manual procedure to label [Lys40,Nle14(Ahx-NODAGA)NH2]exendin-4, with Ga-68.

METHODS

A ⁶⁸Ge/⁶⁸Ga Generator (GalliaPharma®,Eckert and Ziegler) was eluted with 0.1M HCl on an automated synthesis module (Scintomics GRP®). The peptide contained in the kit vial (Radioisotope Center POLATOM) in different amounts (10-20-30 µg) was reconstituted with 2-[4-(2-hydroxyethyl)piperazin-1-yl]ethansulfonic acid (HEPES) solution and 68GaCl3 (400-900 MBq), followed by 10 min incubation at 95°C. The reaction solution was then purified through an Oasis HLB column. The radiopharmaceutical product was tested for quality controls (CQs), in accordance with the European Pharmacopoeia standards.

RESULTS

The synthesis of ⁶⁸Ga]Ga-NODAGA-Exendin-4 provided optimal results with 10 µg of peptide, getting the best radiochemical yield (23.53 ± 2.4 %), molar activity (100 GBq/µmol) and radiochemical purity (91.69 %).

CONCLUSION

The study developed an imaging tool [⁶⁸Ga]Ga-NODAGA-Exendin-4, avoiding pharmacological effects of exendin-4, for the clinical community.

Imaging of Insulinoma by Targeting Glucagonlike Peptide-1 Receptor

"Glucagonlike peptide-1 (GLP-1) receptor imaging, using radiolabeled exendin-4, was recently established for detecting insulinoma in patients with hyperinsulinemic hypoglycemia. It has proven to be a sensitive and specific method for preoperative localization of insulinoma. This review introduces the development, clinical research, and perspective of GLP-1 receptor imaging mainly in insulinoma.

First-in-Human Evaluation of Positron Emission Tomography/Computed Tomography With [18F]FB(ePEG12)12-Exendin-4: A Phase 1 Clinical Study Targeting GLP-1 Receptor Expression Cells in Pancreas

Pancreatic β-cell mass (BCM) has a central importance in the pathophysiology of diabetes mellitus. Recently, pancreatic β-cell-specific imaging, especially positron emission tomography (PET) with exendin-based probes, has emerged for non-invasive evaluation of BCM. We developed a novel exendin-based probe labeled with fluorine-18, [¹⁸F]FB(ePEG12)12-exendin-4 (¹⁸F-Ex4) for PET imaging. We subsequently conducted a first-in-human phase 1 study of ¹⁸F-Ex4 PET/computed tomography (CT) and investigated the safety and utility for visualizing the pancreas. Six healthy male subjects were enrolled in this study. A low dose (37.0 MBq) of ¹⁸F-Ex4 PET/CT was administered (first cohort: n = 2), and subsequently a higher dose (74.0 MBq) was administered (second cohort: n = 4). In the first and second cohorts, 38.6 ± 4.8 and 71.1 ± 4.8 MBq of ¹⁸F-Ex4 were administered, respectively. No serious adverse events were observed in both groups. Only one participant in the first cohort showed transient hypoglycemia during the PET scans. ¹⁸F-Ex4 PET/CT successfully visualized the pancreas in all participants. The mean standardized uptake value of the pancreas was found to be higher than that in the surrounding organs, except for the bladder and kidney, during the observation. Dosimetry analyses revealed the effective systemic doses of ¹⁸F-Ex4 as 0.0164 ± 0.0019 mSv/MBq (first cohort) and 0.0173 ± 0.0020 mSv/MBq (second cohort). ¹⁸F-Ex4 PET/CT demonstrated the safety and utility for non-invasive visualization of the pancreas in healthy male subjects. ¹⁸F-Ex4 is promising for clinical PET imaging targeting pancreatic β cells.

Radiolabeled Peptides and Antibodies in Medicine

Radiolabeled peptides are a relatively new, very specific radiotracer group, which is still expanding. This group is very diverse in terms of peptide size. It contains very small structures containing several amino acids and whole antibodies. Moreover, radiolabeled peptides are diverse in terms of the binding aim and therapeutic or diagnostic applications. The majority of this class of radiotracers is utilized in oncology, where the same structure can be used in therapy and diagnostic imaging by varying the radionuclide. In this study, we collected new reports of radiolabeled peptide applications in diagnosis and therapy in oncology and other fields of medicine. Radiolabeled peptides are also increasingly being used in rheumatology, cardiac imaging, or neurology. The studies collected in this review concern new therapeutic and diagnostic procedures in humans and new structures tested on animals. We also performed an analysis of clinical trials, which concerns application of radiolabeled peptides and antibodies that were reported in the clinicaltrials.gov database between 2008 and 2018.

Pitfalls in the Detection of Insulinomas With Glucagon-Like Peptide-1 Receptor Imaging

PURPOSE

Physiological pancreaticoduodenal uptake of radiolabeled exendin-4 in Brunner glands of the proximal duodenum is the most common pitfall for false interpretation of glucagon-like peptide-1 receptor (GLP-1R) imaging. The aim of this study was to analyze the pancreaticoduodenal uptake in GLP-1R PET/CT and SPECT/CT images and to identify additional potential reading pitfalls in patients with suspected insulinoma.

METHODS

A post hoc analysis of a prospective study, including 52 consecutive patients, was performed. All patients underwent 1 Ga-exendin-4 PET/CT and 2 In-exendin-4 SPECT/CT scans (4 and 72 hours postinjection) in a randomized crossover order. Three board-certified nuclear medicine physicians read all scans independently. They were unaware of other results. Reference standard was surgery with histopathological confirmation of an insulinoma/nesidioblastosis and normalization of blood glucose levels after surgery.

RESULTS

There were no false-positive readings. However, there were a number of false-negative PET/CT and SPECT/CT readings, respectively: (1) due to false interpretation of uptake in the pancreaticoduodenal region (falsely interpreted as physiological uptake in Brunner glands instead of an insulinoma in 0.6% vs 9.0%), (2) due to ectopic insulinoma (0% vs 2.6%), (3) due to small insulinoma (1.9% vs 5.1%), (4) due to insulinoma overlap with kidneys (1.9% vs 4.5%), and (5) due to nesidioblastosis (0.6% and 1.9%). Pitfalls were identified in all GLP-1R PET/CT and SPECT/CT scans.

CONCLUSIONS

Peripancreatic uptake, small size of an insulinoma, insulinoma overlap with kidneys, and presence of nesidioblastosis are potential pitfalls in GLP-1R imaging, which can lead to false reading results.

Detection of Insulinomas Using Dual-Time-Point 68Ga-DOTA-Exendin 4 PET/CT

PURPOSE

Insulinomas are predominantly benign neuroendocrine tumors originating from beta cells within the islets of Langerhans of the endocrine pancreas. Because surgical resection represents the only curative therapy option, exact tumor localization and discrimination of insulinomas from focal or diffuse manifestations of congenital hyperinsulinism are crucial for optimal treatment strategies. We investigated the diagnostic value of glucagon-like peptide 1 receptor PET/CT using Ga-DOTA-exendin 4 for detecting insulinomas and compared the diagnostic value of PET scans performed at 2 time points.

METHODS

In 10 patients with clinically and biochemically suspected insulinoma, PET/CT was performed at 1 hour (PET1) and 2 hours (PET2) after injection of Ga-DOTA-exendin 4. In this retrospective analysis, tracer uptake was visually assessed in both scans by 2 independent readers. SUVmax and tumor-to-background ratio (TBR) of focal lesions were assessed. Imaging results were compared with histopathologic findings, if patients underwent resection.

RESULTS

Increased focal Ga-DOTA-exendin 4 uptake was observed in 8 of 10 patients concordantly by both readers. Seven patients with focal uptake underwent surgery with tumor enucleation and histopathologic proof of insulinoma (7/8). Two of 10 patients without focal uptake were considered to suffer from diffuse form of congenital hyperinsulinism and consequently received medical treatment. A significant increase of tumoral SUVmax on PET2 (PET1: SUVmax 20.2 ± 8.2 g/mL; PET2: SUVmax 24.7 ± 7.9 g/mL; P = 0.0018) did not result in a significant improvement in TBR (PET1: TBR 4.9 ± 1.7; PET2: TBR 4.3 ± 1.2; P = 0.2892).

CONCLUSIONS

Focal uptake of Ga-DOTA-exendin 4 reliably indicated insulinomas as histopathologically confirmed in all patients undergoing consecutive surgery. The diagnostic value of PET2 was not found to be superior to PET1, indicating that a single 1-hour Ga-DOTA-exendin 4 PET/CT scan is a sufficient and convenient approach for patient care.

Current Progress and Perspective: Clinical Imaging of Islet Transplantation

Islet transplantation has great potential as a cure for type 1 diabetes. At present; the lack of a clinically validated non-invasive imaging method to track islet grafts limits the success of this treatment. Some major clinical imaging modalities and various molecular probes, which have been studied for non-invasive monitoring of transplanted islets, could potentially fulfill the goal of understanding pathophysiology of the functional status and viability of the islet grafts. In this current review, we summarize the recent clinical studies of a variety of imaging modalities and molecular probes for non-invasive imaging of transplanted beta cell mass. This review also includes discussions on in vivo detection of endogenous beta cell mass using clinical imaging modalities and various molecular probes, which will be useful for longitudinally detecting the status of islet transplantation in Type 1 diabetic patients. For the conclusion and perspectives, we highlight the applications of multimodality and novel imaging methods in islet transplantation.

Association of glucagon-like peptide-1 receptor-targeted imaging probe with in vivo glucagon-like peptide-1 receptor agonist glucose-lowering effects

Aims/Introduction

Glucagon‐like peptide‐1 receptor agonists (GLP‐1RA) are used for treatment of type 2 diabetes mellitus worldwide. However, some patients do not respond well to the therapy, and caution must be taken for certain patients, including those with reduced insulin secretory capacity. Thus, it is clinically important to predict the efficacy of GLP‐1RA therapy. GLP‐1R‐targeted imaging has recently emerged to visualize and quantify β‐cells. We investigated whether GLP‐1R‐targeted imaging can predict the efficacy of GLP‐1RA treatment.

Materials and Methods

We developed ¹¹¹Indium‐labeled exendin‐4 derivative (¹¹¹In‐Ex4) as a GLP‐1R‐targeting probe. Diabetic mice were selected from NONcNZO10/LtJ male mice that were fed for different durations with 11% fat chow. After 3‐week administration of dulaglutide as GLP‐1RA therapy, mice with non‐fasting blood glucose levels <300 mg/dL and >300 mg/dL were defined as responders and non‐responders, respectively. In addition, ex vivo¹¹¹In‐Ex4 pancreatic accumulations (¹¹¹In‐Ex4 pancreatic values) were examined.

Results

The non‐fasting blood glucose levels after treatment were 172.5 ± 42.4 mg/dL in responders (n = 4) and 330.8 ± 20.7 mg/dL in non‐responders (n = 5), respectively. Ex vivo¹¹¹In‐Ex4 pancreatic values showed significant correlations with post‐treatment glycohemoglobin and glucose area under curve during an oral glucose tolerance test (R² = 0.76 and 0.80; P < 0.01 and <0.01, respectively). The receiver operating characteristic area under curve for identifying responders by ex vivo¹¹¹In‐Ex4 pancreatic values was 1.00 (P < 0.01).

Conclusion

Ex vivo¹¹¹In‐Ex4 pancreatic values reflected dulaglutide efficacy, suggesting clinical possibilities for expanding GLP‐1R‐targeted imaging applications.

Exendin-4 analogs in insulinoma theranostics

Insulinomas, neuroendocrine tumors arising from pancreatic beta cells, often show overexpression of the glucagon‐like peptide‐1 receptor. Therefore, imaging with glucagon‐like peptide analog exendin‐4 can be used for diagnosis and preoperative localization. This review presents an overview of the development and clinical implementation of exendin‐based tracers for nuclear imaging, and the potential use of exendin‐4 based tracers for optical imaging and therapeutic applications such as peptide receptor radionuclide therapy or targeted photodynamic therapy.

Receptor-Targeted Photodynamic Therapy of Glucagon-Like Peptide 1 Receptor-Positive Lesions

Treatment of hyperinsulinemic hypoglycemia is challenging. Surgical treatment of insulinomas and focal lesions in congenital hyperinsulinism is invasive and carries major risks of morbidity. Medication to treat nesidioblastosis and diffuse congenital hyperinsulinism has varying efficacy and causes significant side effects. Here, we describe a novel method for therapy of hyperinsulinemic hyperglycemia, highly selectively killing β-cells by receptor-targeted photodynamic therapy (rtPDT) with exendin-4-IRDye700DX, targeting the glucagon-like peptide 1 receptor (GLP-1R). Methods: A competitive binding assay was performed using Chinese hamster lung (CHL) cells transfected with the GLP-1R. The efficacy and specificity of rtPDT with exendin-4-IRDye700DX were examined in vitro in cells with different levels of GLP-1R expression. Tracer biodistribution was determined in BALB/c nude mice bearing subcutaneous CHL-GLP-1R xenografts. Induction of cellular damage and the effect on tumor growth were analyzed to determine treatment efficacy. Results: Exendin-4-IRDye700DX has a high affinity for the GLP-1R, with a half-maximal inhibitory concentration of 6.3 nM. rtPDT caused significant specific phototoxicity in GLP-1R–positive cells (2.3% ± 0.8% and 2.7% ± 0.3% remaining cell viability in CHL-GLP-1R and INS-1 cells, respectively). The tracer accumulates dose-dependently in GLP-1R–positive tumors. In vivo, rtPDT induces cellular damage in tumors, shown by strong expression of cleaved caspase-3, and leads to a prolonged median survival of the mice (36.5 vs. 22.5 d, respectively; P < 0.05). Conclusion: These data show in vitro as well as in vivo evidence of the potency of rtPDT using exendin-4-IRDye700DX. This approach might in the future provide a new, minimally invasive, highly specific treatment method for hyperinsulinemic hypoglycemia.

Brunner's Gland Hyperplasia in a Patient after Roux-Y Gastric Bypass: An Important Pitfall in GLP-1 Receptor Imaging

Severe cases of postprandial hypoglycaemia after bariatric surgery can be a diagnostic and therapeutic challenge. The diagnostic role of ⁶⁸Ga-DOTA-Exendin-4 PET/CT in postbariatric hypoglycaemia for further treatment decisions is unclear. We present a case of a 50-year-old woman with frequent and severe postprandial hypoglycaemic (≤2.5 mmol/L) episodes starting three years after Roux-Y gastric bypass. Despite strict dietary adherence and several medical therapies, the patient remained severely affected, and ⁶⁸Ga-DOTA-Exendin-4 PET/CT was performed to exclude atypical presentation of an insulinoma or nesidioblastosis. No pancreatic abnormalities were found, but intensive tracer accumulation in the first and second part of the duodenum was detected, which proved to be hyperplastic Brunner's glands on histology and were strongly positive for the glucagon-like peptide-1 receptor. This case provides histopathological verification that duodenal ⁶⁸Ga-DOTA-Exendin-4 uptake is caused by uptake in Brunner's glands and points to a potential relationship between bariatric surgery and Brunner's glands.

Innovative imaging of insulinoma: the end of sampling? A review

Receptors for the incretin glucagon-like peptide-1 (GLP-1R) have been found overexpressed in selected types of human tumors and may, therefore, play an increasingly important role in endocrine gastrointestinal tumor management. In particular, virtually all benign insulinomas express GLP-1R in high density. Targeting GLP-1R with indium-111, technetium-99m or gallium-68-labeled exendin-4 offers a new approach that permits the successful localization of small benign insulinomas. It is likely that this new non-invasive technique has the potential to replace the invasive localization of insulinomas by selective arterial stimulation and venous sampling. In contrast to benign insulinomas, malignant insulin-secreting neuroendocrine tumors express GLP-1R in only one-third of the cases, while they more often express the somatostatin subtype 2 receptors. Importantly, one of the two receptors appears to be always overexpressed. In special cases of endogenous hyperinsulinemic hypoglycemia (EHH), that is, in the context of MEN-1 or adult nesidioblastosis GLP-1R imaging is useful whereas in postprandial hypoglycemia in the context of bariatric surgery, GLP-1R imaging is probably not helpful. This review focuses on the potential use of GLP-1R imaging in the differential diagnosis of EHH.

La néoplasie endocrinienne multiple de type 1 : mise au point après le congrès de l’ENETS 2019

Multiple Endocrine Neoplasia Type 1 (NEM1) is related to mutations of the menin gene. It is an autosomal dominant disease. Its prevalence is about 1/30 000 with a hugh penetrance. There is no genotype-phenotype correlation. This hereditary syndrome is characterized by the presence of tumors of the endocrine system (parathyroid, endocrine pancreas, pituitary and adrenal gland). Other disorders have also been described (bronchial and thymic carcinoid tumor, breast cancer, skin lesions). Management must take into account the specificities of these pathologies in NEM1 compared to sporadic forms (young age at diagnosis, multiple lesions within the same gland, multi-focal disease). © 2019 Published by Elsevier Masson SAS. All rights reserved. Cet article fait partie du numéro supplément Les Must de l'Endocrinologie 2019 réalisé avec le soutien institutionnel de Ipsen-Pharma.

Targeted Optical Imaging of the Glucagonlike Peptide 1 Receptor Using Exendin-4-IRDye 800CW

The treatment of choice for insulinomas and focal lesions in congenital hyperinsulinism (CHI) is surgery. However, intraoperative detection can be challenging. This challenge could be overcome with intraoperative fluorescence imaging, which provides real-time lesion detection with a high spatial resolution. Here, a novel method for targeted near-infrared (NIR) fluorescence imaging of glucagonlike peptide 1 receptor (GLP-1R)–positive lesions, using the GLP-1 agonist exendin-4 labeled with IRDye 800CW, was examined in vitro and in vivo. Methods: A competitive binding assay was performed using Chinese hamster lung (CHL) cells transfected with GLP-1R. Tracer biodistribution was determined in BALB/c nude mice bearing subcutaneous CHL-GLP-1R xenografts. In vivo NIR fluorescence imaging of CHL-GLP-1R xenografts was performed. Localization of the tracer in the pancreatic islets of BALB/c nude mice was examined using fluorescence microscopy. Laparoscopic imaging was performed to detect the fluorescent signal of the tracer in the pancreas of mini pigs. Results: Exendin-4-IRDye 800CW binds GLP-1R with a half-maximal inhibitory concentration of 3.96 nM. The tracer accumulates in CHL-GLP-1R xenografts. Subcutaneous CHL-GLP-1R xenografts were visualized using in vivo NIR fluorescence imaging. The tracer accumulates specifically in the pancreatic islets of mice, and a clear fluorescent signal was detected in the pancreas of mini pigs. Conclusion: These data provide the first in vivo evidence of the feasibility of targeted fluorescence imaging of GLP-1R–positive lesions. Intraoperative lesion delineation using exendin-4-IRDye 800CW could benefit open as well as laparoscopic surgical procedures for removal of insulinomas and focal lesions in CHI.

Single Photon Emission Computed Tomography Tracer

Single photon emission computed tomography (SPECT) is the state-of-the-art imaging modality in nuclear medicine despite the fact that only a few new SPECT tracers have become available in the past 20 years. Critical for the future success of SPECT is the design of new and specific tracers for the detection, localization, and staging of a disease and for monitoring therapy. The utility of SPECT imaging to address oncologic questions is dependent on radiotracers that ideally exhibit excellent tissue penetration, high affinity to the tumor-associated target structure, specific uptake and retention in the malignant lesions, and rapid clearance from non-targeted tissues and organs. In general, a target-specific SPECT radiopharmaceutical can be divided into two main parts: a targeting biomolecule (e.g., peptide, antibody fragment) and a γ-radiation-emitting radionuclide (e.g., ^99mTc, ¹²³I). If radiometals are used as the radiation source, a bifunctional chelator is needed to link the radioisotope to the targeting entity. In a rational SPECT tracer design, these single components have to be critically evaluated in order to achieve a balance among the demands for adequate target binding, and a rapid clearance of the radiotracer. The focus of this chapter is to depict recent developments of tumor-targeted SPECT radiotracers for imaging of cancer diseases. Possibilities for optimization of tracer design and potential causes for design failure are discussed and highlighted with selected examples.

Advances in GLP-1 receptor targeting radiolabeled agent development and prospective of theranostics

In the light of theranostics/radiotheranostics and prospective of personalized medicine in diabetes and oncology, this review presents prior and current advances in the development of radiolabeled imaging and radiotherapeutic exendin-based agents targeting glucagon-like peptide-1 receptor. The review covers chemistry, preclinical, and clinical evaluation. Such critical aspects as structure-activity-relationship, stability, physiological potency, kidney uptake, and dosimetry are discussed.

Diagnostic value of ASVS for insulinoma localization: A systematic review and meta-analysis

BACKGROUND

Previous studies on the diagnostic value of arterial calcium stimulation with hepatic venous sampling (ASVS) for the localization of insulinoma have reported inconsistent results. Here, we performed a meta-analysis of the relevant published studies.

METHODS

PubMed, Embase, Web of Science, the Cochrane Library, and Wanfang Data were searched for studies on the diagnostic value of ASVS in insulinoma localization published up to May 2019. We calculated the sensitivity, specificity, positive likelihood ratio (PLR), negative likelihood ratio (NLR), diagnostic odds ratio (DOR), and receiver operating characteristic (ROC) curve of ASVS in the localization of insulinoma.

RESULTS

We included ten studies involving 337 patients in the study. The pooled sensitivity, specificity, PLR, and NLR were 0.93 (95% confidence interval [CI]: 0.83-0.97), 0.86 (95%CI: 0.75-0.93), 6.8(95%CI: 3.7-12.7), and 0.08 (95%CI: 0.03-0.19), respectively. The DOR was 84 (95%CI: 30-233), and the area under the ROC curve was 0.96 (95%CI: 0.94-0.97).The results of the heterogeneity of the studies (P = 0.00, I2 = 80.17) were calculated using forest plots of the DOR.

CONCLUSION

ASVS is of significant value in localization of insulinoma. If a qualitative diagnosis of insulinoma is definite and the imaging examination results are negative, ASVS should be performed to confirm the localization of insulinoma.

PET-Based Human Dosimetry of 68Ga-NODAGA-Exendin-4, a Tracer for β-Cell Imaging

⁶⁸Ga-NODAGA-exendin-4 is a promising tracer for β-cell imaging using PET/CT. Possible applications include preoperative visualization of insulinomas and discrimination between focal and diffuse forms of congenital hyperinsulinism. There is also a significant role for this tracer in extending our knowledge on the role of β-cell mass in the pathophysiology of type 1 and type 2 diabetes by enabling noninvasive quantification of tracer uptake as a measure for β-cell mass. Calculating radiation doses from this tracer is important to assess its safety for use in patients (including young children) with benign diseases and healthy individuals. Methods: Six patients with hyperinsulinemic hypoglycemia were included. After intravenous injection of 100 MBq of the tracer, 4 successive PET/CT scans were obtained at 30, 60, 120, and 240 min after injection. Tracer activity in the pancreas, kidneys, duodenum, and remainder of the body were determined, and time-integrated activity coefficients for the measured organs were calculated. OLINDA/EXM software, version 1.1, was applied to calculate radiation doses using the reference adult male and female models and to estimate radiation doses to children. Results: The mean total effective dose for adults was very low (0.71 ± 0.07 mSv for a standard injected dose of 100 MBq). The organ with the highest absorbed dose was the kidney (47.3 ± 10.2 mGy/100 MBq). The estimated effective dose was 2.32 ± 0.32 mSv for an injected dose of 20 MBq in newborns. This dose decreased to 0.77 ± 0.11 mSv/20 MBq for 1-y-old children and 0.59 ± 0.05 mSv for an injected dose of 30 MBq in 5-y-old children. Conclusion: Our human PET/CT-based dosimetric calculations show that the effective radiation doses from the novel tracer ⁶⁸Ga-NODAGA-exendin-4 are very low for adults and children. The doses are lower than reported for other polypeptide tracers such as somatostatin analogs (2.1–2.6 mSv/100 MBq) and are beneficial for application as a research tool, especially when repeated examinations are needed.

Endogenous hyperinsulinism: diagnostic and therapeutic difficulties

Endogenous hyperinsulinism is an abnormal clinical condition that involves excessive insulin secretion, related in 55% of cases to insulinoma. Other causes are possible such as islet cell hyperplasia, nesidioblastosis or antibodies to insulin or to the insulin receptor. Differentiation between these diseases may be difficult despite the use of several morphological examinations. We report six patients operated on for endogenous hyperinsulinism from 1^st January 2000 to 31^st December 2015. Endogenous hyperinsulinism was caused by insulinoma in three cases, endocrine cells hyperplasia in two cases and no pathological lesions were found in the last case. All patients typically presented with adrenergic and neuroglycopenic symptoms with a low blood glucose level concomitant with high insulin and C-peptide levels. Computed tomography showed insulinoma in one case out of two. MRI was carried out four times and succeeded to locate the lesion in the two cases of insulinoma. Endoscopic ultrasound showed one insulinoma and provided false positive findings three times out of four. Intra operative ultrasound succeeded to localize the insulinoma in two cases but was false positive in two cases. Procedures were one duodenopancreatectomy, two left splenopancreatectomy and two enucleations. For the sixth case, no lesion was radiologically objectified. Hence, a left blind pancreatectomy was practised but the pathological examination showed normal pancreatic tissue. Our work showed that even if morphological examinations are suggestive of insulinoma, other causes of endogenous hyperinsulinism must be considered and therefore invasive explorations should be carried out.

[68Ga]Ga-NOTA-MAL-Cys39-exendin-4, a potential GLP-1R targeted PET tracer for the detection of insulinoma

Glucagon-like peptide-1 receptor (GLP-1R) is a kind of G protein coupled receptor which regulates the insulin secretion and serves as potential target in the diagnosis of functional pancreas neuroendocrine tumor. The aim of this study was to evaluate the feasibility of GLP-1R targeted tracer [⁶⁸Ga]Ga-NOTA-MAL-Cys³⁹-exendin-4 in the detection of insulinoma.

METHODS

NOTA-MAL-Cys³⁹-exendin-4 was synthesized and then radiolabeled with gallium-68 in iQS® Ga-68 Fluidic Labeling Module. The in vitro binding affinity and cell uptake studies were evaluated in INS-1 cells. The in vivo micro-PET/CT imaging and biodistribution studies were performed on INS-1 xenograft tumor models.

RESULTS

[⁶⁸Ga]Ga-NOTA-MAL-Cys³⁹-exendin-4 can be efficiently radiolabelled with a yield of about 85% (non-decay corrected) and radiochemical purity of >95% with a favorable stability. The molar activity was at least 145.5 GBq/μmol. The affinity (IC50) for [⁶⁸Ga]Ga-NOTA-MAL-Cys³⁹-exendin-4 was 12.99 ± 0.81 nM. Micro-PET/CT images showed intense tumor uptake with good contrast to background. Biodistribution study showed the predominant uptake was in the kidney, followed by pancreas, and the liver and spleen just showed mild uptake in the blood-pool phase with rapid clearance. At 1 h post- injection, the tumor to blood, muscle and pancreas ratios were 30.64, 40.21 and 6.46, respectively. Blocking studies showed significantly decreased tumor uptake, which further confirmed binding affinity of [⁶⁸Ga]Ga-NOTA-MAL-Cys³⁹-exendin-4 to GLP-1R.

CONCLUSION

[⁶⁸Ga]Ga-NOTA-MAL-Cys³⁹-exendin-4 was easily synthesized with high yield, favorable biodistribution and high affinity to islet tumor cell, making the tracer may have great potential in the detection of GLP-1R positive tumor such as an insulinoma.