99mTc Labeled Glucagon-Like Peptide-1-Analogue (99mTc-GLP1) Scintigraphy in the Management of Patients with Occult Insulinoma

Serotonin transporter imaging agent as a probe for β-cells of pancreas

OBJECTIVE

Diabetes mellitus (DM) is one of the major diseases in the world. Nuclear medicine imaging may be able to detect functional status of pancreatic β cells in vivo, which might elucidate the pathological mechanisms of diabetes and develop individualized treatment plans. In this study, we evaluated the ability of [125I]ADAM, a serotonin transporter (SERT) imaging agent, as a probe for detecting pancreatic β-cell mass (BCM).

METHODS

In vitro cell studies were evaluated in INS-1 cells (rat islet β cell line). Biodistribution studies were performed in male normal Sprague-Dawley rats and alloxan-induced type 1 diabetes mellitus (T1DM) rats. Distribution and expression of SERT protein in pancreas of rats were also measured by immunofluorescence staining and Western blot.

RESULTS

In vitro cell studies showed that the concentration of [125I]ADAM associated with the INS-1 cells was increased gradually with incubation time, and the SERT specific inhibitor, escitalopram, exhibited the inhibitory effect on this interaction. Biodistribution studies also showed that the uptake of [125I]ADAM in the pancreas of normal rats was decreased in the presence of escitalopram. However, in the T1DM rat model with a significant β cells reduction, the uptake of pancreas was increased when compared with the control. Through immunofluorescence staining and Western blot, it was found that both the endocrine and exocrine cells of the normal pancreas expressed SERT protein, and the level of SERT protein in the exocrine cells was higher than islets. In the diabetic state, the expression of SERT in the exocrine cells was further increased.

CONCLUSIONS

The SERT imaging agent, [125I]ADAM, at the present form will not be suitable for imaging β cells, specifically because there were extraordinarily high non-specific signals contributing from the exocrine cells of pancreas. In addition, we noticed that the level of SERT expression was abnormally elevated in the diabetic state, which might provide an unexpected target for studying the pathological mechanisms of diabetes.

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.

Diffuse, Adult-Onset Nesidioblastosis/Non-Insulinoma Pancreatogenous Hypoglycemia Syndrome (NIPHS): Review of the Literature of a Rare Cause of Hyperinsulinemic Hypoglycemia

Differential diagnosis of hypoglycemia in the non-diabetic adult patient is complex and comprises various diseases, including endogenous hyperinsulinism caused by functional β-cell disorders. The latter is also designated as nesidioblastosis or non-insulinoma pancreatogenous hypoglycemia syndrome (NIPHS). Clinically, this rare disease presents with unspecific adrenergic and neuroglycopenic symptoms and is, therefore, often overlooked. A combination of careful clinical assessment, oral glucose tolerance testing, 72 h fasting, sectional and functional imaging, and invasive insulin measurements can lead to the correct diagnosis. Due to a lack of a pathophysiological understanding of the condition, conservative treatment options are limited and mostly ineffective. Therefore, nearly all patients currently undergo surgical resection of parts or the entire pancreas. Consequently, apart from faster diagnosis, more elaborate and less invasive treatment options are needed to relieve the patients from the dangerous and devastating symptoms. Based on a case of a 23-year-old man presenting with this disease in our department, we performed an extensive review of the medical literature dealing with this condition and herein presented a comprehensive discussion of this interesting disease, including all aspects from epidemiology to therapy.

Peptide-based diagnostic and therapeutic agents: Where we are and where we are heading?

Peptides are increasingly present in all branches of medicine as innovative drugs, imaging agents, theragnostic, and constituent moieties of other sophisticated drugs such as peptide-drug conjugates. Due to new developments in chemical synthesis strategies, computational biology, recombinant technology, and chemical biology, peptide drug development has made a great progress in the last decade. Numerous natural peptides and peptide mimics have been obtained and studied, covering multiple therapeutic areas. Even though peptides have been investigated across the wide therapeutic spectrum, oncology, metabolism, and endocrinology are the most frequent medical indications of them. This review summarizes the current use of and the emerging new opportunities of peptides for diagnosis and treatment of various diseases.

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.

Peptide receptor radionuclide therapy as a tool for the treatment of severe hypoglycemia in patients with primary inoperable insulinoma

Objectives

Severe hypoglycemia in a course of inoperable insulinoma may be life-threating and often it is not well controlled, even by high doses of diazoxide requiring second line treatment. Among available methods PRRT is characterized by relatively low toxicity and is connected with favorable antitumor effect. The aim of the study was an evaluation of the PRRT effectiveness in control of hypoglycemia in patients with primary inoperable insulinoma.

Methods

Three patients (female with metastatic insulinoma, male with primary inoperable pancreatic tumor, female with MEN1 syndrome and hepatic metastases) were treated with PRRT due to severe hypoglycemia poorly controlled by diazoxide in course of primary inoperable insulinoma.

Results

Patient 1 baseline fasting glucose concentration increased from 2.4 mmol/L [3.30–5.60] to 5.9 mmol/L after PRRT. In patient 2 fasting glucose level 2.30 mmol/L increased after PRRT to 7.0 mmol/L, while baseline insulin level initially 31.15 uU/mL [2.6–24.9] decreased to 15.4 uU/mL. In patients 3, baseline fasting glucose level 2.5 mmol/L increased after PRRT to 7.9 mmol/L, and insulin decreased from 57.9 uU/mL to 6.3 uU/mL. In imaging there was partial response (PR) in patient 1 and 2 and stabilization of the tumor size in patient 3. In patient 2 reduction of tumor infiltration let for curative surgery performed 4 months after PPRT.

Conclusions

PRRT may be effective as a first or second line treatment in management of hypoglycemia for patients with hormonally active inoperable insulinoma.

Hyperinsulinemic Hypoglycemia in Three Generations of a Family with Glucokinase Activating Mutation, c.295T>C (p.Trp99Arg)

Familial Hyperinsulinemic Hypoglycemia (FHH) is a very rare disease with heterogeneous clinical manifestations. There are only a few reports of heterozygous activating mutations of glucokinase (GCK) attributable to FHH, with no reports describing effects in the course in pregnancy with affected mother/affected child. A large kindred with FHH and GCK:c.295T>C (p.Trp99Arg) pathogenic variant was identified in which four family members from three generations were affected. The clinical follow up in one clinical center lasted up to 30 years, with different times of diagnosis ranging from neonate period to adulthood. The severity of hypoglycemia was mild/severe and fasting was the trigger for hypoglycemia. Response to diazoxide varied from good, in the neonate, to moderate/poor, in childhood/adulthood; however, this was biased by poor compliance. Treatment with somatostatin analogues was discontinued due to side effects. Over time, patients developed clinical adaptation to very low glucose levels. During pregnancy, episodes of severe hypoglycemia in the first trimester were observed, which responded very well to steroids. The clinical course of the GCK:c.295T>C (p.Trp99Arg) mutation varied in the same family, with the development of clinical adaptation to very low glucose levels over time. Treatment with steroids might prevent hypoglycemia during pregnancy in an affected mother.

Exendin-4-based imaging in insulinoma localization: Systematic review and meta-analysis

BACKGROUND AND CONTEXT

Glucagon-like peptide-1 receptor (GLP-1 R) based imaging has shown higher sensitivity for insulinoma localization as compared to other anatomic/functional imaging.

METHODOLOGY

We reviewed the published English literature for GLP-1 R targeted imaging in insulinoma in PubMed until August 2020 in accordance with PRISMA guidelines using the MeSH terms "((Exendin-4 PET/CT) OR (Exendin-4 SPECT/CT) OR (GLP-1 R imaging)) AND (Insulinoma)". An individual patient data-metanalysis (IPD-MA) was performed, and performance parameters were calculated for the histopathological diagnosis of insulinoma.

MAIN OUTCOME MEASURES

True-positive (TP), false-positive (FP), false-negative (FN), true-negative (TN), sensitivity (Sn), specificity (Sp), positive predictive value (PPV) and negative predictive value (NPV) for insulinoma localization.

RESULTS

A total of 179 cases (316 lesions) from 16 publications were included for IPD-MA. For insulinoma localization, exendin-4-PET/CT (Sn & PPV: 94%) performed better than exendin-4-SPECT/CT (Sn: 63%, PPV: 94%). The Sn was lower in malignant insulinoma cases whereas the Sp was higher in cases with MEN-1 syndrome. With exendin-4-based imaging, FP uptakes in Brunner's gland, normal pancreas, and other β-cell pathologies and FN results in pancreatic tail lesions and malignancy were seen in a few patients. TN results suggested the correct diagnosis of other endogenous hyperinsulinemic hypoglycaemia (EHH) subtypes.

CONCLUSION

For insulinoma localization, exendin-4 PET/CT should be preferred over exendin-4 SPECT/CT because of higher sensitivity and specificity. FP uptakes in Brunner's gland, normal pancreas, and other β-cell pathologies and FN results in tail lesions, and malignant insulinomas are limitations. Higher specificity for insulinoma localization is particularly useful in patients with MEN-1 syndrome.

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.

Heterogeneity of the Clinical Presentation of the MEN1 LRG_509 c.781C>T (p.Leu261Phe) Variant Within a Three-Generation Family

Multiple neuroendocrine neoplasia type 1 (MEN1) is a rare genetic disorder with an autosomal dominant inheritance, predisposing carriers to benign and malignant tumors. The phenotype of MEN1 syndrome varies between patients in terms of tumor localization, age of onset, and clinical aggressiveness, even between affected members within the same family. We describe a heterogenic phenotype of the MEN1 variant c.781C>T (LRG_509t1), which was previously reported only once in a family with isolated hyperparathyroidism. A heterozygous missense variant in exon 4 of the gene was identified in the sequence of the MEN1 gene, i.e., c.781C>T, leading to the amino acid change p.Leu261Phe in a three-generation family. In the screened family, 5/6 affected members had already developed hyperparathyroidism. In the index patient and two other family members, an aggressive course of pancreatic neuroendocrine tumor (insulinoma and non-functioning neuroendocrine tumors) with dissemination was diagnosed. In the index patient, late diagnosis and slow progression of the disseminated neuroendocrine tumor have been observed (24 years of follow-up). The very rare variant of MEN1, LRG_509t1 c.781C>T /p.Leu261Phe (LRG_509p1), diagnosed within a three-generation family has a heterogenic clinical presentation. Further follow-up of the family members should be carried out to confirm the spectrum and exact time of clinical presentation.

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.

Indirectly radioiodinated exendin-4 as an analytical tool for in vivo detection of glucagon-like peptide-1 receptor in a disease setting

OBJECTIVE

Glucagon-like peptide-1 receptor agonist (GLP-1RA) has been reported to have therapeutic effects on diabetes and various diseases. Precise detection of GLP-1 receptor (GLP-1R) can be useful to diagnose and elucidate the mechanism of such diseases. Here we aimed to develop an imaging probe based on GLP-1RA that has high molar activity and sensitivity for detection of low-level GLP-1R expression in non-pancreatic diseases.

METHODS

We selected the agonist exenatide (Ex4) as the parent peptide of a GLP-1R targeting probe and prepared Cys-Ex4 by addition of an N-terminal Cys residue and labeling with the prosthetic agent N-(3-[125I]iodophenyl)maleimide ([125I]IPM) to generate [125I]Ex4ipm. We evaluated the affinity of [125I]Ex4ipm for GLP-1R, as well as cellular binding profiles in insulinoma and prostate cancer cell lines, and in vivo biodistributions in normal and tumor-bearing mice to assess GLP-1R-dependent accumulation of radioactivity in tissues.

RESULTS

[125I]Ex4ipm was easily synthesized with high radiochemical yield (73%), radiochemical purity (> 99%), and molar activity (81 GBq/µmol) via a thiol/maleimide reaction. Following administration to mice, [125I]Ex4ipm accumulated to high levels in the pancreas (23.3% ID/g), with radioactivity co-localizing in areas having insulin-positive β cells. High amounts of radioactivity also accumulated in insulinomas that overexpressed GLP-1R (27.5% ID/g). In contrast, low amounts of [125I]Ex4ipm accumulation, corresponding to low expression levels of GLP-1R, were observed in prostate cancer cells and xenografts used as a model of non-pancreatic applications.

CONCLUSION

Our results suggested that [123I]Ex4ipm could be valuable for GLP-1R imaging in diabetes, insulinomas, and various diseases related to GLP-1R.

Utility of 68 Ga-DOTA-Exendin-4 positron emission tomography-computed tomography imaging in distinguishing between insulinoma and nesidioblastosis in patients with confirmed endogenous hyperinsulinaemic hypoglycaemia

BACKGROUND

Because management is very different, it is important to differentiate between small focal insulinomas and diffuse pancreatic dysplasia (nesidioblastosis) in patients with confirmed endogenous hyperinsulinaemic hypoglycaemia (EHH). Most insulinomas highly express glucagon-like peptide-1 receptors enabling positron emission tomography-computed tomography imaging with its radiolabelled analogue; ⁶⁸ Ga-DOTA-Exendin-4 (Exendin).

AIM

To determine: (i) the utility of Exendin in EHH patients in a clinical setting; and (ii) whether the degree of Exendin uptake differentiates non-insulinoma pancreatogenous hypoglycaemia syndrome (NIPHS) from post-gastric bypass hypoglycaemia (PGBH).

METHODS

This retrospective study reviewed the clinical, biochemistry and prior imaging findings in confirmed EHH patients referred for Exendin. Accuracy of Exendin was based on surgical findings and treatment outcomes. Finally, average Exendin uptake (SUVmax) of five PGBH studies was compared with the SUVmax of a key NIPHS case report.

RESULTS

Twenty of 25 consecutive patients had confirmed EHH. Exendin located insulinomas in eight of nine patients enabling successful surgical excision with rapid and durable cure. Exendin correctly identified diffuse nesidioblastosis in two of three cases requiring partial pancreatectomy for hypoglycaemia control. All three relapsed within 1.7 years with one needing completion pancreatectomy. Establishing the cause in the remainder relied on other investigations, clinical correlation and response to empirical treatment. Finally, Exendin SUVmax could not distinguish between NIPHS and PGBH.

CONCLUSION

In EHH patients, Exendin accurately identifies the site of insulinoma and thereby differentiates it from nesidioblastosis but negative findings should not be ignored. Exendin is unlikely to differentiate between normal pancreatic uptake, NIPHS and PGBH.

Exendin-4-based imaging in endogenous hyperinsulinemic hypoglycaemia cohort: A tertiary Endocrine centre experience

CONTEXT

Insulinoma needs accurate preoperative localization for minimally invasive surgery. Exendin-4-based imaging has shown promising results.

OBJECTIVE

To evaluate performance parameters of exendin-4-based imaging in insulinoma localization and compare with other imaging modalities.

DESIGN

Retrospective cross-sectional study.

PATIENTS

We report 14 patients with endogenous hyperinsulinemic hypoglycaemia (EHH) managed at our centre; in whom, the final diagnosis was insulinoma (n = 11), Munchausen syndrome (MS) (n = 2) and inconclusive (n = 1). Retrospective reporting of CECT, ⁶⁸ Ga-DOTATATE PET/CT and ⁶⁸ Ga-NODAGA-exendin-4-PET/CT was done. With per-lesion analysis, performance parameters were calculated for the histopathological diagnosis of insulinoma.

MAIN OUTCOME MEASURES

True positive (TP), false positive (FP), false negative (FN), true negative (TN), sensitivity (Sn), specificity (Sp), positive predictive value (PPV), negative predictive value (NPV) for insulinoma localization.

RESULTS

In our cohort, 12 histopathologically proven insulinoma lesions [(TP): 11 primary lesions, 1 metastasis] were detected in 11 patients, whereas two patients had MS (TN). Sn and PPV were 75% and 100%, 33.3% and 80% and 83.3% and 71.4% for CECT, ⁶⁸ Ga-DOTATATE PET/CT and ⁶⁸ Ga-NODAGA-exendin-4-PET/CT, respectively. With exendin-4-based imaging, FP uptake in normal pancreatic tissue and FN results in the pancreatic tail lesion was seen. In one patient, TN result suggested the correct diagnosis of MS.

CONCLUSION

⁶⁸ Ga-NODAGA-exendin-4-PET/CT has higher sensitivity than ⁶⁸ Ga-DOTATATE PET/CT and CECT for insulinoma localization. FP uptake in normal pancreas and FN result in tail lesions are limitations of currently utilized exendin-4-based imaging.

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.

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.

Synthesis and in vivo behaviour of an exendin-4-based MRI probe capable of β-cell-dependent contrast enhancement in the pancreas

Global rates of diabetes mellitus are increasing, and treatment of the disease consumes a growing proportion of healthcare spending across the world. Pancreatic β-cells, responsible for insulin production, decline in mass in type 1 and, to a more limited degree, in type 2 diabetes. However, the extent and rate of loss in both diseases differs between patients resulting in the need for the development of novel diagnostic tools, which could quantitatively assess changes in mass of β-cells over time and potentially lead to earlier diagnosis and improved treatments. Exendin-4, a potent analogue of glucagon-like-peptide 1 (GLP-1), binds to the receptor GLP-1R, whose expression is enriched in β-cells. GLP-1R has thus been used in the past as a means of targeting probes for a wide variety of imaging modalities to the endocrine pancreas. However, exendin-4 conjugates designed specifically for MRI contrast agents are an under-explored area. In the present work, the synthesis and characterization of an exendin-4-dota(ga)-Gd(iii) complex, GdEx, is reported, along with its in vivo behaviour in healthy and in β-cell-depleted C57BL/6J mice. Compared to the ubiquitous probe, [Gd(dota)]-, GdEx shows selective uptake by the pancreas with a marked decrease in accumulation observed after the loss of β-cells elicited by deleting the microRNA processing enzyme, DICER. These results open up pathways towards the development of other targeted MRI contrast agents based on similar chemistry methodology.

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.

The role of multimodal imaging in guiding resectability and cytoreduction in pancreatic neuroendocrine tumors: focus on PET and MRI

Pancreatic neuroendocrine tumors (pNETs) are rare neoplasms that secrete peptides and neuro-amines. pNETs can be sporadic or hereditary, syndromic or non-syndromic with different clinical presentations and prognoses. The role of medical imaging includes locating the tumor, assessing its extent, and evaluating the feasibility of curative surgery or cytoreduction. Pancreatic NETs have very distinctive phenotypes on CT, MRI, and PET. PET have been demonstrated to be very sensitive to detect either well-differentiated pNETs using ⁶⁸Gallium somatostatin receptor (SSTR) radiotracers, or more aggressive undifferentiated pNETS using ¹⁸F-FDG. A comprehensive interpretation of multimodal imaging guides resectability and cytoreduction in pNETs. The imaging phenotype provides information on the differentiation and proliferation of pNETs, as well as the spatial and temporal heterogeneity of tumors with prognostic and therapeutic implications. This review provides a structured approach for standardized reading and reporting of medical imaging studies with a focus on PET and MR techniques. It explains which imaging approach should be used for different subtypes of pNET and what a radiologist should be looking for and reporting when interpreting these studies.

Biomedical applications of radioiodinated peptides

The overexpression of peptide receptors in certain tumors as compared to endogeneous expression levels represents the molecular basis for the design of peptide-based tools for targeted nuclear imaging and therapy. Receptor targeting with radiolabelled peptides became a very important imaging and/or therapeutic approach in nuclear medicine and oncology. A great variety of peptides has been radiolabelled with clinical relevant radionuclides, such as radiometals and radiohalogens. However, to the best of our knowledge concise and updated reviews providing information about the biomedical application of radioiodinated peptides are still missing. This review outlines the synthetic efforts in the preparation of radioiodinated peptides highlighting the importance of radioiodine in nuclear medicine, giving an overview of the most relevant radioiodination strategies that have been employed and describes relevant examples of their use in the biomedical field.

Tumor targeting with 99m Tc radiolabeled peptides: Clinical application and recent development

Targeting overexpressed receptors on the cancer cells with radiolabeled peptides has become very important in nuclear oncology in the recent years. Peptides are small and have easy preparation and easy radiolabeling protocol with no side-effect and toxicity. These properties made them a valuable tool for tumor targeting. Based on the successful imaging of neuroendocrine tumors with ¹¹¹ In-octreotide, other receptor-targeting peptides such as bombesin (BBN), cholecystokinin/gastrin analogues, neurotensin analogues, glucagon-like peptide-1, and RGD peptides are currently under development or undergoing clinical trials. The most frequently used radionuclides for tumor imaging are ^99m Tc and ¹¹¹ In for single-photon emission computed tomography and ⁶⁸ Ga and ¹⁸ F for positron emission tomography imaging. This review presents some of the ^99m Tc-labeled peptides, with regard to their potential for radionuclide imaging of tumors in clinical and preclinical application.

Imaging of pancreatic neuroendocrine tumors: recent advances, current status, and controversies

INTRODUCTION

Recently, there have been a number of advances in imaging pancreatic neuroendocrine tumors (panNETs), as well as other neuroendocrine tumors (NETs), which have had a profound effect on the management and treatment of these patients, but in some cases are also associated with controversies. Areas covered: These advances are the result of numerous studies attempting to better define the roles of both cross-sectional imaging, endoscopic ultrasound, with or without fine-needle aspiration, and molecular imaging in both sporadic and inherited panNET syndromes; the increased attempt to develop imaging parameters that correlate with tumor classification or have prognostic value; the rapidly increasing use of molecular imaging in these tumors and the attempt to develop imaging parameters that correlate with treatment/outcome results. Each of these areas and the associated controversies are reviewed. Expert commentary: There have been numerous advances in all aspects of the imaging of panNETs, as well as other NETs, in the last few years. The advances are leading to expanded roles of imaging in the management of these patients and the results being seen in panNETs/GI-NETs with these newer techniques are already being used in more common tumors.

Insulinoma presenting with post-prandial hypoglycaemia following fundoplication

Insulinomas are rare neuroendocrine tumours that classically present with fasting hypoglycaemia. This case report discusses an uncommon and challenging case of insulinoma soon after upper gastrointestinal surgery. A 63-year-old man presented with 6 months of post-prandial hypoglycaemia beginning after a laparoscopic revision of Toupet fundoplication. Hyperinsulinaemic hypoglycaemia was confirmed during a spontaneous episode and in a mixed-meal test. Localisation studies including magnetic resonance imaging (MRI), endoscopic ultrasound (EUS) and gallium dotatate positron emission tomography (⁶⁸Ga Dotatate PET) were consistent with a small insulinoma in the mid-body of the pancreas. The lesion was excised and histopathology was confirmed a localised well-differentiated neuroendocrine pancreatic neoplasm. There have been no significant episodes of hypoglycaemia since. This case highlights several key points. Insulinoma should be sought in proven post-prandial hyperinsulinaemic hypoglycaemia - even in the absence of fasting hypoglycaemia. The use of nuclear imaging targeting somatostatin and GLP1 receptors has improved accuracy of localisation. Despite these advances, accurate surgical resection can remain challenging.

Learning points

Hypoglycaemia is defined by Whipple's triad and can be provoked by fasting or mixed-meal tests.Although uncommon, insulinomas can present with post-prandial hypoglycaemia.In hypoglycaemia following gastrointestinal surgery (i.e. bariatric surgery or less commonly Nissen fundoplication) dumping syndrome or non-insulinoma pancreatogenous hypoglycaemia syndrome (NIPHS) should be considered.Improved imaging techniques including MRI, endoscopic ultrasound and functional nuclear medicine scans aid localisation of insulinomas.Despite advances in imaging and surgical techniques, accurate resection of insulinomas remains challenging.

The future: diagnostic and imaging advances in MEN1 therapeutic approaches and management strategies

Prospective randomized data are lacking, but current clinical expert guidelines recommend annual screening examinations, including laboratory assessments and various imaging modalities (e.g. CT, MRI, scintigraphy and EUS) for patients with multiple endocrine neoplasia type 1 (MEN1). Routine screening is proposed to detect and localize neuroendocrine manifestations as early as possible. The goal is timely intervention to improve quality of life and to increase life expectancy by preventing the development of life-threatening hormonal syndromes and/or metastatic disease. In recent years, some studies compared different and new imaging methods regarding their sensitivity and utility in MEN1 patients. This present article reviews the proposed diagnostic tools for MEN1 screening as well as potential future perspectives.

Fully automated GMP production of [68Ga]Ga-DO3A-VS-Cys40-Exendin-4 for clinical use

[68Ga]Ga-DO3A-VS-Cys40-Exendin-4/PET-CT targeting glucagon like peptide-1 receptor (GLP-1R) has previously demonstrated its potential clinical value for the detection of insulinomas. The production and accessibility of this radiopharmaceutical is one of the critical factors in realization of clinical trials and routine clinical examinations. Previously, the radiopharmaceutical was prepared manually, however larger scale of clinical trials and healthcare requires automation of the production process in order to limit the operator radiation dose as well as improve tracer manufacturing robustness and on-line documentation for enhanced good manufacturing practice (GMP) compliance. A method for 68Ga-labelling of DO3A-VS-Cys40-Exendin-4 on a commercially available synthesis platform was developed. Equipment such as 68Ge/68Ga generator, synthesis platform, and disposable cassettes for 68Ga-labelling used in the study was purchased from Eckert & Ziegler. DO3A-VS-Cys40-Exendin-4 was synthesized in-house. The parameters such as time, temperature, precursor concentration, radical scavenger, buffer concentration, pH, product purification step were investigated and optimised. Reproducible and GMP compliant automated production of [68Ga]Ga-DO3A-VS-Cys40-Exendin-4 was developed. Exendin-4 comprising methionine amino acid residue was prone to oxidation which was strongly influenced by the elevated temperature, radioactivity amount, and precursor concentration. The suppression of the oxidative radiolysis was achieved by addition of ethanol, dihydroxybenzoic acid and ascorbic acid to the reaction buffer as well as by optimizing heating temperature. The non-decay corrected radiochemical yield was 43±2% with radiochemical purity of over 90% wherein the individual impurity signals in HPLC chromatogram did not exceed 5%. Automated production and quality control methods were established for paving the pathway for broader clinical use of [68Ga]Ga-DO3A-VS-Cys40-Exendin-4.

Recurrent insulinoma in a 10-year-old boy with Down's syndrome

An insulinoma is a rare tumour with an incidence of four cases per million per year in adults. The incidence in children is not established. There is limited literature available in children with insulinoma, and only one case is reported in association with Down’s syndrome in adults. Insulinoma diagnosis is frequently missed in adults as well as in children. The Whipple triad is the most striking feature although it has limited application in young children. Hypoglycaemia with elevated insulin, C-peptide and absent ketones is highly suggestive of hyperinsulinism. We present a case of 10-year-old boy with Down’s syndrome with recurrent insulinoma. He was initially misdiagnosed as having an adrenal insufficiency and developed cushingoid features and obesity secondary to hydrocortisone treatment and excessive sugar intake. The tumour was successfully localised in the head of the pancreas with an MRI and octreotide scan on first presentation. Medical treatment with diazoxide and octreotide could not achieve normal blood glucose levels. The insulinoma was laparoscopically enucleated and pathological examination confirmed a neuroendocrine tumour. Subsequently, he had complete resolution of symptoms. He had a recurrence after 2 years with frequent episodes of hypoglycaemia. The biochemical workup was suggestive of hyperinsulinism. MRI and PET scan confirmed the recurrence at the same site (head of the pancreas). He had an open laparotomy for insulinoma resection. The pathology was consistent with benign insulinoma, and subsequently, he had complete resolution of symptoms.

Molecular imaging in the investigation of hypoglycaemic syndromes and their management

There has been recent progress in molecular imaging using a variety of cellular targets for the investigation of adult non-diabetic hypoglycaemic syndromes and its integration into patient management. These targets include peptide receptors (somatostatin receptors (SSTRs) and glucagon-like peptide-1 receptor (GLP-1R)) the amine precursor uptake and decarboxylation system utilising the diphydroxyphenylaline (DOPA) analogue 6-[¹⁸F]-l-fluoro-l-3,4-dihydroxyphenylalanine (¹⁸F-FDOPA), and glycolytic metabolism with 2-[¹⁸F]fluoro-2-deoxy-d-glucose (FDG). Accurate preoperative localisation and staging is critical to enable directed surgical excision or enucleation with minimal morbidity and preservation of residual pancreatic function. Benign insulinoma has near ubiquitous dense GLP-1R expression enabling accurate localisation with radiolabelled-exendin-4 compounds (e.g. ⁶⁸Ga-NOTA-exendin-4 PET/CT), whilst the rarer and more difficult to manage metastatic insulinoma typically express SSTR and is preferably imaged with radiolabelled-SSTR analogues such as ⁶⁸Ga-DOTA-octreotate (DOTATATE) PET/CT for staging and assessment of suitability for peptide receptor radionuclide therapy (PRRT). Similar to other metastatic neuroendocrine tumours, FDG PET/CT is used in the setting of higher-grade metastatic insulinoma to provide important prognostic information that can guide treatment and determine suitability for PRRT. Interestingly, these three tracers appear to represent a spectrum of differentiation, which we conceptually describe as the 'triple-flop' phenomenon, with GLP-1R > SSTR > FDG in benign insulinoma and the opposite in higher-grade disease. This paper will review the clinical syndromes of adult hypoglycaemia (including a practical overview of the differential diagnoses to be considered), comparison of techniques for insulinoma localisation with emphasis on molecular imaging before discussing its implications for management of metastatic insulinoma.

Current Status of Radiopharmaceuticals for the Theranostics of Neuroendocrine Neoplasms

Nuclear medicine plays a pivotal role in the management of patients affected by neuroendocrine neoplasms (NENs). Radiolabeled somatostatin receptor analogs are by far the most advanced radiopharmaceuticals for diagnosis and therapy (radiotheranostics) of NENs. Their clinical success emerged receptor-targeted radiolabeled peptides as an important class of radiopharmaceuticals and it paved the way for the investigation of other radioligand-receptor systems. Besides the somatostatin receptors (sstr), other receptors have also been linked to NENs and quite a number of potential radiolabeled peptides have been derived from them. The Glucagon-Like Peptide-1 Receptor (GLP-1R) is highly expressed in benign insulinomas, the Cholecystokinin 2 (CCK2)/Gastrin receptor is expressed in different NENs, in particular medullary thyroid cancer, and the Glucose-dependent Insulinotropic Polypeptide (GIP) receptor was found to be expressed in gastrointestinal and bronchial NENs, where interestingly, it is present in most of the sstr-negative and GLP-1R-negative NENs. Also in the field of sstr targeting new discoveries brought into light an alternative approach with the use of radiolabeled somatostatin receptor antagonists, instead of the clinically used agonists. The purpose of this review is to present the current status and the most innovative strategies for the diagnosis and treatment (theranostics) of neuroendocrine neoplasms using a cadre of radiolabeled regulatory peptides targeting their receptors.