68Ga DOTA-Exendin PET/CT for Detection of Insulinoma in a Patient With Persistent Hyperinsulinemic Hypoglycemia

Malignant Insulinoma: Diagnostic Difficulties and Treatment Strategies in a Case of Persistent Hypoglycemia

Hypoglycemia in non-diabetic individuals is a rare but critical condition that often signals an underlying pathology. Insulinoma, a rare neuroendocrine tumor of the pancreas, is a key differential diagnosis. As the most common functional pancreatic neuroendocrine tumors, insulinomas originate from pancreatic islet cells and are predominantly benign. However, malignant cases, although rare, represent a significant diagnostic challenge. Here, we report a 67-year-old female with recurrent hypoglycemic episodes presenting as diaphoresis and palpitations, alleviated by glucose intake. Initial tests revealed critically low blood sugar levels and elevated fasting insulin and C-peptide. Despite a normal abdominal CT, a PET-CT scan identified an exophytic pancreatic lesion with metastases to retroperitoneal lymph nodes, and malignancy was confirmed by histopathological examination. This case highlights the necessity of considering insulinoma in the differential diagnosis of unexplained hypoglycemia. Accurate and timely diagnosis, along with appropriate imaging and management, is crucial for effective treatment and improved patient outcomes.

[Search for new immunohistochemical and circulating markers of insulinoma]

BACKGROUND

Insulinoma is a neuroendocrine tumor, the main manifestation of which is hypoglycemia. However, the symptoms of hypoglycemia can be non-specific for a long time, especially outside provocative conditions, and quite often the tumor manifests from a life-threatening condition - hypoglycemic coma. In this regard, timely laboratory diagnosis of insulinoma and determination of its aggressive course is one of the priorities in modern researches.

AIM

Search for new immunohistochemical (IHC) and circulating markers (CM) of insulinoma, including its aggressive course.

MATERIALS AND METHODS

The patients examined at the Endocrinology Research Centre in the period 2017-2022 and operated on for an insulin-producing tumor were included. Before surgery and 2-12 months after it, blood sampling was performed with the determination of targeted marker proteins. Some patients underwent an extended IHC examination of the tumor, surrounding tissue and islets of Langerhans with primary antibodies to target marker proteins with an assessment of the degree of their expression. To determine the aggressive course of the tumor, the degree of malignancy (Grade), the number of tumors and signs of recurrence were characterized.

RESULTS

Based on the analysis of literature and pathogenetic characteristics of insulinoma, the following candidates for targeted marker proteins were selected: cocaine and amphetamine-regulated transcript (CART), chromogranin B (CrB), neuroendocrine secretory protein 55 (NESP55), glucagon-like peptide 1 (GLP1), arylalkylamine-N-acetyltransferase (AA-NAT), melatonin, and, exclusively for IHC research, protein D52 (TPD52), as well as receptors for glucagon-like peptide-1 (rGLP1) and melatonin (MTNR1b). 41 patients were included in the study, of which 10 patients underwent an extended IHC study. In patients with both aggressive and non-aggressive insulinoma after surgical treatment, CM levels did not change significantly and in individual patients they could both increase and decrease, including those patients with the expression of the corresponding marker in tumor tissue. It was shown that CART was expressed only in the tumor (in 4/10 of cases), while MTNR1b and rGLP1 were expressed in the tumor (in 6/10 and 10/10, respectively) and the islets of Langerhans (in 5/9 and 9/9, respectively). The association of marker expression with the aggressiveness of the course of insulinoma has not been revealed.

CONCLUSION

The markers CART, MTNR1b and rGLP1 are of primary interest for further study in a larger sample of patients with insulinoma. Other markers (TPD52, XgB, NESP55, melatonin, AA-NAT) have not been shown to be associated with an insulin-producing tumor, therefore they are not promising for future researches. At the same time, it is necessary to continue research aimed at finding new both circulating and IHC markers in order to early diagnose the manifestation of the disease and its recurrence, and more accurately determine the malignant and proliferative potential of the tumor.

68Ga-DOTA-Exendin-4 PET/CT Demonstrated a Higher Detection Efficacy for Double-Primary Insulinomas Than MRI: A Case Report

ABSTRACT

We presented a 20-year-old woman with gradually increasing lethargy and multiple episodes of dizziness for 5 months. The laboratory examination revealed decreasing level of blood glucose and elevated levels of fasting plasma insulin and C-peptide. The MRI identified a focal nodule in the tail of the pancreas. 68Ga-DOTA-exendin-4 PET/CT revealed 2 intense focal tracer uptakes in the tail of the pancreas, one of which corresponded to the lesion revealed on MRI. The immunohistochemical results of resected samples confirmed the diagnosis of double-primary insulinomas. 68Ga-DOTA-exendin-4 PET/CT demonstrated excellent localization and characterization for double-primary insulinomas in the tail of the pancreas.

Nuclear Medicine and Radiological Imaging of Pancreatic Neuroendocrine Neoplasms: A Multidisciplinary Update

Pancreatic neuroendocrine neoplasms (panNENs) are part of a large family of tumors arising from the neuroendocrine system. PanNENs show low-intermediate tumor grade and generally high somatostatin receptor (SSTR) expression. Therefore, panNENs benefit from functional imaging with ⁶⁸Ga-somatostatin analogues (SSA) for diagnosis, staging, and treatment choice in parallel with morphological imaging. This narrative review aims to present conventional imaging techniques and new perspectives in the management of panNENs, providing the clinicians with useful insight for clinical practice. The ⁶⁸Ga-SSA PET/CT is the most widely used in panNENs, not only fr diagnosis and staging purpose but also to characterize the biology of the tumor and its responsiveness to SSAs. On the contrary, the ¹⁸F-Fluordeoxiglucose (FDG) PET/CT is not employed systematically in all panNEN patients, being generally preferred in G2-G3, to predict aggressiveness and progression rate. The combination of ⁶⁸Ga-SSA PET/CT and ¹⁸F-FDG PET/CT can finally suggest the best therapeutic strategy. Other radiopharmaceuticals are ⁶⁸Ga-exendin-4 in case of insulinomas and ¹⁸F-dopamine (DOPA), which can be helpful in SSTR-negative tumors. New promising but still-under-investigation radiopharmaceuticals include radiolabeled SSTR antagonists and ¹⁸F-SSAs. Conventional imaging includes contrast enhanced CT and multiparametric MRI. There are now enriched by radiomics, a new non-invasive imaging approach, very promising to early predict tumor response or progression.

Molecular imaging phenotyping for selecting and monitoring radioligand therapy of neuroendocrine neoplasms

Neuroendocrine neoplasia (NEN) is an umbrella term that includes a widely heterogeneous disease group including well-differentiated neuroendocrine tumours (NETs), and aggressive neuroendocrine carcinomas (NECs). The site of origin of the NENs is linked to the intrinsic tumour biology and is predictive of the disease course. It is understood that NENs demonstrate significant biologic heterogeneity which ultimately translates to widely varying clinical presentations, disease course and prognosis. Thus, significant emphasis is laid on the pre-therapy evaluation of markers that can help predict tumour behavior and dynamically monitors the response during and after treatment. Most well-differentiated NENs express somatostatin receptors (SSTRs) which make them appropriate for peptide receptor radionuclide therapy (PRRT). However, the treatment outcomes of PRRT depend heavily on the adequacy of patient selection by molecular imaging phenotyping not only utilizing pre-treatment SSTR PET but ¹⁸F-Fluorodeoxyglucose (¹⁸F-FDG) PET to provide insights into the intra- or inter-tumoural heterogeneity of the metastatic disease. Molecular imaging phenotyping may go beyond patient selection and provide useful information during and post-treatment for monitoring of temporal heterogeneity of the disease and dynamically risk-stratify patients. In addition, advances in the understanding of genomic-phenotypic classifications of pheochromocytomas and paragangliomas led to an archetypical example in precision medicine by utilizing molecular imaging phenotyping to guide radioligand therapy. Novel non-SSTR based peptide receptors have also been explored diagnostically and therapeutically to overcome the tumour heterogeneity. In this paper, we review the current molecular imaging modalities that are being utilized for the characterization of the NENs with special emphasis on their role in patient selection for radioligand therapy.

Somatostatin Receptor Imaging and Theranostics: Current Practice and Future Prospects

A new era of precision diagnostics and therapy for patients with neuroendocrine neoplasms began with the approval of somatostatin receptor (SSTR) radiopharmaceuticals for PET imaging followed by peptide receptor radionuclide therapy (PRRT). With the transition from SSTR-based γ-scintigraphy to PET, the higher sensitivity of the latter raised questions regarding the direct application of the planar scintigraphy-based Krenning score for PRRT eligibility. Also, to date, the role of SSTR PET in response assessment and predicting outcome remains under evaluation. In this comprehensive review article, we discuss the current role of SSTR PET in all aspects of neuroendocrine neoplasms, including its relation to conventional imaging, selection of patients for PRRT, and the current understanding of SSTR PET-based response assessment. We also provide a standardized reporting template for SSTR PET with a brief discussion.

18F-6-Fluoro-l-Dopa PET/CT Imaging of Congenital Hyperinsulinism

Congenital hyperinsulinism is characterized by persistent hypoglycemia due to inappropriate excess secretion of insulin resulting in hyperinsulinemic hypoglycemia. The clinical course varies from mild to severe, with a significant risk for brain damage. Imaging plays a valuable role in the care of infants and children with severe hypoglycemia unresponsive to medical therapy. 18F-6-fluoro-l-dopa PET/CT is the method of choice for the detection and localization of a focal lesion of hyperinsulinism. Surgical resection of a focal lesion can lead to a cure with limited pancreatectomy. This article reviews the role of 18F-6-fluoro-l-dopa PET/CT in the management of this vulnerable population.

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.

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.

Role of PET/CT and Therapy Management of Pancreatic Neuroendocrine Tumors

Pancreatic neuroendocrine neoplasms (panNENs) are heterogeneous neoplasms with neuroendocrine differentiation that show peculiar clinical and histomorphological features, with variable prognosis. In recent years, advances in knowledge regarding the pathophysiology and heterogeneous clinical presentation, as well as the availability of different diagnostic procedures for panNEN diagnosis and novel therapeutic options for patient clinical management, has led to the recognition of the need for an active multidisciplinary discussion for optimal patient care. Molecular imaging with positron emission tomography/computed tomography (PET/CT) has become indispensable for the management of panNENs. Several PET radiopharmaceuticals can be used to characterize either panNEN receptor expression or metabolism. The aim of this review is to offer an overview of all the currently used radiopharmaceuticals and of the new upcoming tracers for pancreatic neuroendocrine tumors (panNETs), and their clinical impact on therapy management. [68Ga]Ga-DOTA-peptide PET/CT (SSA-PET/CT) has high sensitivity, specificity, and accuracy and is recommended for the staging and restaging of any non-insulinoma well-differentiated panNEN cases to carry out detection of unknown primary tumor sites or early relapse and for evaluation of in vivo somatostatin receptors expression (SRE) to select patient candidates for peptide receptor radiometabolic treatment (PRRT) with 90Y or 177Lu and/or cold analogs. SSA-PET/CT also has a strong impact on clinical management, leading to a change in treatment in approximately a third of the cases. Its role for treatment response assessment is still under debate due to the lack of standardized criteria, even though some semiquantitative parameters seem to be able to predict response. [18F]FDG PET/CT generally shows low sensitivity in small growing and well-differentiated neuroendocrine tumors (NET; G1 and G2), while it is of utmost importance in the evaluation and management of high-grade NENs and also provides important prognostic information. When positive, [18F]FDG PET/CT impacts therapeutical management, indicating the need for a more aggressive treatment regime. Although FDG positivity does not exclude the patient from PRRT, several studies have demonstrated that it is certainly useful to predict response, even in this setting. The role of [18F]FDOPA for the study of panNET is limited by physiological uptake in the pancreas and is therefore not recommended. Moreover, it provides no information on SRE that has crucial clinical management relevance. Early acquisition of the abdomen and premedication with carbidopa may be useful to increase the accuracy, but further studies are needed to clarify its utility. GLP-1R agonists, such as exendin-4, are particularly useful for benign insulinoma detection, but their accuracy decreases in the case of malignant insulinomas. Being a whole-body imaging technique, exendin-PET/CT gives important preoperative information on tumor size and localization, which is fundamental for surgical planning as resection (enucleation of the lesion or partial pancreatic resection) is the only curative treatment. New upcoming tracers are under study, such as promising SSTR antagonists, which show a favorable biodistribution and higher tumor-to-background ratio that increases tumor detection, especially in the liver. [68Ga]pentixafor, an in vivo marker of CXCR4 expression associated with the behavior of more aggressive tumors, seems to only play a limited role in detecting well-differentiated NET since there is an inverse expression of SSTR2 and CXCR4 in G1 to G3 NETs with an elevation in CXCR4 and a decrease in SSTR2 expression with increasing grade. Other tracers, such as [68Ga]Ga-PSMA, [68Ga]Ga-DATA-TOC, [18F]SiTATE, and [18F]AlF-OC, are also under investigation.

Hyperinsulinemic hypoglycemia in children and adolescents: Recent advances in understanding of pathophysiology and management

Hyperinsulinemic hypoglycemia (HH) is characterized by unregulated insulin release, leading to persistently low blood glucose concentrations with lack of alternative fuels, which increases the risk of neurological damage in these patients. It is the most common cause of persistent and recurrent hypoglycemia in the neonatal period. HH may be primary, Congenital HH (CHH), when it is associated with variants in a number of genes implicated in pancreatic development and function. Alterations in fifteen genes have been recognized to date, being some of the most recently identified mutations in genes HK1, PGM1, PMM2, CACNA1D, FOXA2 and EIF2S3. Alternatively, HH can be secondary when associated with syndromes, intra-uterine growth restriction, maternal diabetes, birth asphyxia, following gastrointestinal surgery, amongst other causes. CHH can be histologically characterized into three groups: diffuse, focal or atypical. Diffuse and focal forms can be determined by scanning using fluorine-18 dihydroxyphenylalanine-positron emission tomography. Newer and improved isotopes are currently in development to provide increased diagnostic accuracy in identifying lesions and performing successful surgical resection with the ultimate aim of curing the condition. Rapid diagnostics and innovative methods of management, including a wider range of treatment options, have resulted in a reduction in co-morbidities associated with HH with improved quality of life and long-term outcomes. Potential future developments in the management of this condition as well as pathways to transition of the care of these highly vulnerable children into adulthood will also be discussed.

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.

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.

68Ga-DOTA-Exendin PET-MRI Fusion Imaging in a Case of Insulinoma

Persistent hyperinsulinemic hypoglycemia in adults is most commonly caused by insulinomas, which pose a diagnostic challenge to physicians, surgeons, and radiologists and require multimodality imaging for precise localization and staging. PET tracers such as F-FDOPA and glucagon-like peptide 1 receptor analogs have been used for imaging insulinomas. Glucagon-like peptide 1 receptor analogs have recently shown promising results in preoperative localization of these tumors, as all insulinomas express glucagon-like peptide 1 receptors. Ga-DOTA-Exendin PET and MRI done in the present case helped in precise localization and management of the culprit lesion, whereas contrast-enhanced CT and F-FDOPA PET failed to do so.