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

The construction of long-acting exendin-4 analog and its hypoglycemic effect in diabetic mice

Exendin-4 is a glucagon-like polypeptide-1 (GLP-1) analog derived from lizard venom, but its short half-life affects drug administration compliance. An anti-HSA nanobody with a smaller size to guide the peptide coupling to Human Serum Albumin(HSA) in vivo may be a feasible strategy for constructing inexpensive, long-acting exendin-4 analogs. For this purpose, a fusion protein (exendin-4-(G4S)3-sdAbHSA), in which a humanized anti-HSA nanobody to the C-terminal of exendin-4 through the (Gly4Ser)3 flexible joint, was constructed. The target gene was designed according to the preferred codons and cloned into expression vector pET21b of Escherichia coli. The fusion protein could be efficiently expressed as a soluble protein, and purified to a purity over 98% by two steps of chromatography columns. In the streptozotocin-induced mouse diabetes model, the purified product had similar hypoglycemic activity as exendin-4, but dropped to the lowest value from 1 to 2 h to more than 8-10 h. The results show that this construction form does not interfere with the binding of exendin-4 to GLP-1 receptor, and can significantly prolong its half-life in vivo. This study has important reference value for constructing long-acting exendin-4 analogs and establishing efficient and green production process.

Noninvasive evaluation of donor and native pancreases following simultaneous pancreas-kidney transplantation using positron emission tomography/computed tomography

It is crucial to develop practical and noninvasive methods to assess the functional beta-cell mass in a donor pancreas, in which monitoring and precise evaluation is challenging. A patient with type 1 diabetes underwent noninvasive imaging following simultaneous kidney-pancreas transplantation with positron emission tomography/computed tomography (PET/CT) using an exendin-based probe, [18 F]FB(ePEG12)12-exendin-4. Following transplantation, PET imaging with [18 F]FB(ePEG12)12-exendin-4 revealed simultaneous and distinct accumulations in the donor and native pancreases. The pancreases were outlined at a reasonable distance from the surrounding organs using [18 F]FB(ePEG12)12-exendin-4 whole-body maximum intensity projection and axial PET images. At 1 and 2 h after [18 F]FB(ePEG12)12-exendin-4 administration, the mean standardized uptake values were 2.96 and 3.08, respectively, in the donor pancreas and 1.97 and 2.25, respectively, in the native pancreas. [18 F]FB(ePEG12)12-exendin-4 positron emission tomography imaging allowed repeatable and quantitative assessment of beta-cell mass following simultaneous kidney-pancreas transplantation.

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.

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.

Unmasked insulinoma occasioned by severe hypoglycemic coma immediately postpartum: a case report

BACKGROUND

Insulinoma in women during pregnancy and postpartum is very rare; approximately 65% of cases are diagnosed early in pregnancy and ~ 35% immediately after delivery, few being found in middle or late pregnancy, likely due to increased insulin resistance seen after early-stage pregnancy. We successfully treated a case of insulinoma in which severe hypoglycemic coma immediately after delivery occasioned detailed investigation and diagnosis.

CASE PRESENTATION

Our patient experienced hypoglycemic coma in the 3rd month of pregnancy (initially considered due to her hyperemesis gravidarum) that improved spontaneously during the gestational period. No abnormalities of plasma glucose or body weight were found in regular checkups during her pregnancy; however, recurrence of hypoglycemic coma after delivery led us to suspect insulinoma. While contrast enhanced computer tomography and endoscopic ultrasonography (EUS) initially failed to detect a tumor in the pancreas, selective arterial calcium stimulation test revealed an insulin-secreting tumor localized in the pancreatic body. She then underwent spleen-preserving distal pancreatectomy; a 10-mm tumor positive for chromogranin A, synaptophysin and insulin was identified.

CONCLUSIONS

Although pregnancy can mask insulinoma-associated symptoms and make diagnosis challenging, hypoglycemic episodes during early pregnancy, which were observed in this case, are suggestive of insulinoma. Importantly, in this case, accurate preoperative localization of the tumor enabled prompt curative surgery after delivery. Thus, clinical vigilance for the occurrence of insulinoma and its localization is appropriate for pregnant women suffering severe hypoglycemia.

Noninvasive quantitative evaluation of viable islet grafts using 111 In-exendin-4 SPECT/CT

Islet transplantation (IT) is an effective β-cell replacement therapy for patients with type 1 diabetes; however, the lack of methods to detect islet grafts and evaluate their β-cell mass (BCM) has limited the further optimization of IT protocols. Therefore, the development of noninvasive β-cell imaging is required. In this study, we investigated the utility of the ¹¹¹ Indium-labeled exendin-4 probe {[Lys12(111In-BnDTPA-Ahx)] exendin-4} (¹¹¹ In exendin-4) to evaluate islet graft BCM after intraportal IT. The probe was cultured with various numbers of isolated islets. Streptozotocin-induced diabetic mice were intraportally transplanted with 150 or 400 syngeneic islets. After a 6-week observation following IT, the ex-vivo liver graft uptake of ¹¹¹ In-exendin-4 was compared with the liver insulin content. In addition, the in-vivo liver graft uptake of ¹¹¹ In exendin-4 using SPECT/CT was compared with that of liver graft BCM measured by a histological method. As a result, probe accumulation was significantly correlated with islet numbers. The ex-vivo liver graft uptake in the 400-islet-transplanted group was significantly higher than that in the control and the 150-islet-transplanted groups, consistent with glycemic control and liver insulin content. In conclusion, in-vivo SPECT/CT displayed liver islet grafts, and uptakes were corroborated by histological liver BCM. ¹¹¹ In-exendin-4 SPECT/CT can be used to visualize and evaluate liver islet grafts noninvasively after intraportal IT.

New PET Radiotracers for the Imaging of Neuroendocrine Neoplasms

Neuroendocrine neoplasms (NEN) are a heterogeneous group of tumours derived from cells of neuroendocrine origin and can potentially arise everywhere in the human body. The diagnostic assessment of NEN can be performed using a variety of PET radiopharmaceuticals. Well-differentiated NEN (NET) present a high expression of SSTR (somatostatin receptors) and can therefore be studied with 68Ga-DOTA-peptides ([68Ga]Ga-DOTANOC, [68Ga]Ga-DOTATOC, [68Ga]Ga-DOTATATE). Current guidelines recommend the use of SSTR imaging to assess disease extension at staging/restaging, follow-up, assessment of response to therapy and selection of patients who may benefit from radionuclide therapy (PRRT). [18F]F-FDG is used for the assessment of high-grade tumours (high-grade G2, G3 and NEC) and in every case, there is one or more mismatched lesions between diagnostic CT (positive) and SSTR-PET/CT (negative). [18F]F-DOPA is currently used for the assessment of medullary thyroid carcinoma, neuroblastoma, primary pheochromocytoma and abdominal paraganglioma. In recent years, however, several new tracers were designed exploiting the many potential targets of the neuroendocrine cell and were employed in clinical trials for both imaging and therapy. Currently, the real-life clinical impact of these tracers is still mostly not known; however, the favourable biodistribution (e.g. [68Ga]Ga-FAPI, SSTR antagonists) and the possibility to use new theranostic pairs may provide novel diagnostic as well as therapeutic options (e.g. [68Ga]Ga-PSMA, [64Cu]Cu-SARTATE, [68Ga]Ga-CXCR4) for NEN patients.

Noninvasive Evaluation of GIP Effects on β-Cell Mass Under High-Fat Diet

Pancreatic β-cell mass (BCM) has an importance in the pathophysiology of diabetes mellitus. Recently, glucagon-like peptide-1 receptor (GLP-1R)-targeted imaging has emerged as a promising tool for BCM evaluation. While glucose-dependent insulinotropic polypeptide/gastric inhibitory polypeptide (GIP) is known to be involved in high-fat diet (HFD)-induced obesity, the effect of GIP on BCM is still controversial. In this study, we investigated indium 111 (¹¹¹In)-labeled exendin-4 derivative ([Lys¹²(¹¹¹In-BnDTPA-Ahx)]exendin-4) single-photon emission computed tomography/computed tomography (SPECT/CT) as a tool for evaluation of longitudinal BCM changes in HFD-induced obese mice, at the same time we also investigated the effects of GIP on BCM in response to HFD using GIP-knockout (GIP^-/-) mice. ¹¹¹In-exendin-4 SPECT/CT was able to distinguish control-fat diet (CFD)-fed mice from HFD-fed mice and the pancreatic uptake values replicated the BCM measured by conventional histological methods. Furthermore, BCM expansions in HFD-fed mice were demonstrated by time-course changes of the pancreatic uptake values. Additionally, ¹¹¹In-exendin-4 SPECT/CT demonstrated the distinct changes in BCM between HFD-fed GIP^-/- (GIP^-/-+HFD) and wild-type (WT+HFD) mice; the pancreatic uptake values of GIP^-/-+HFD mice became significantly lower than those of WT+HFD mice. The different changes in the pancreatic uptake values between the two groups preceded those in fat accumulation and insulin resistance. Taken together with the finding of increased β-cell apoptosis in GIP^-/-+HFD mice compared with WT+HFD mice, these data indicated that GIP has preferable effects on BCM under HFD. Therefore, ¹¹¹In-exendin-4 SPECT/CT can be useful for evaluating increasing BCM and the role of GIP in BCM changes under HFD conditions.

The Current State of Beta-Cell-Mass PET Imaging for Diabetes Research and Therapies

Diabetes is a chronic metabolic disease affecting over 400 million people worldwide and one of the leading causes of death, especially in developing nations. The disease is characterized by chronic hyperglycemia, caused by defects in the insulin secretion or action pathway. Current diagnostic methods measure metabolic byproducts of the disease such as glucose level, glycated hemoglobin (HbA1c), insulin or C-peptide levels, which are indicators of the beta-cell function. However, they inaccurately reflect the disease progression and provide poor longitudinal information. Beta-cell mass has been suggested as an alternative approach to study disease progression in correlation to beta-cell function, as it behaves differently in the diabetes physiopathology. Study of the beta-cell mass, however, requires highly invasive and potentially harmful procedures such as pancreatic biopsies, making diagnosis and monitoring of the disease tedious. Nuclear medical imaging techniques using radiation emitting tracers have been suggested as strong non-invasive tools for beta-cell mass. A highly sensitive and high-resolution technique, such as positron emission tomography, provides an ideal solution for the visualization of beta-cell mass, which is particularly essential for better characterization of a disease such as diabetes, and for estimating treatment effects towards regeneration of the beta-cell mass. Development of novel, validated biomarkers that are aimed at beta-cell mass imaging are thus highly necessary and would contribute to invaluable breakthroughs in the field of diabetes research and therapies. This review aims to describe the various biomarkers and radioactive probes currently available for positron emission tomography imaging of beta-cell mass, as well as highlight the need for precise quantification and visualization of the beta-cell mass for designing new therapy strategies and monitoring changes in the beta-cell mass during the progression of diabetes.

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.