Noninvasive Evaluation of GPR119 Agonist Effects on β-Cell Mass in Diabetic Male Mice Using 111In-Exendin-4 SPECT/CT

Impact of Prevascularization on Immunological Environment and Early Engraftment in Subcutaneous Islet Transplantation

BACKGROUND

The utilization of islet-like cells derived from pluripotent stem cells may resolve the scarcity of islet transplantation donors. The subcutaneous space is a promising transplantation site because of its capacity for graft observation and removal, thereby ensuring safety. To guarantee subcutaneous islet transplantation, physicians should ensure ample blood supply. Numerous methodologies, including prevascularization, have been investigated to augment blood flow, but the optimal approach remains undetermined.

METHODS

From C57BL/6 mice, 500 syngeneic islets were transplanted into the prevascularized subcutaneous site of recipient mice by implanting agarose rods with basic fibroblast growth factor at 1 and 2 wk. Before transplantation, the blood glucose levels, cell infiltration, and cytokine levels at the transplant site were evaluated. Furthermore, we examined the impact of the extracellular matrix capsule on graft function and the inflammatory response.

RESULTS

Compared with the 1-wk group, the 2-wk group exhibited improved glycemic control, indicating that longer prevascularization enhanced transplant success. Flow cytometry analysis detected immune cells, such as neutrophils and macrophages, in the extracellular matrix capsules, whereas cytometric bead array analysis indicated the release of inflammatory and proinflammatory cytokines. Treatment with antitumor necrosis factor and anti-interleukin-6R antibodies in the 1-wk group improved graft survival, similar to the 2-wk group.

CONCLUSIONS

In early prevascularization before subcutaneous transplantation, neutrophil and macrophage accumulation prevented early engraftment owing to inflammatory cytokine production.

GPR119 agonists for type 2 diabetes: past failures and future hopes for preclinical and early phase candidates

INTRODUCTION

Type 2 diabetes (T2D) is metabolic disorder associated with a decrease in insulin activity and/or secretion from the β-cells of the pancreas, leading to elevated circulating glucose. Current management practices for T2D are complex with varying long-term effectiveness. Agonism of the G protein-coupled receptor GPR119 has received a lot of recent interest as a potential T2D therapeutic.

AREAS COVERED

This article reviews studies focused on GPR119 agonism in animal models of T2D and in patients with T2D.

EXPERT OPINION

GPR119 agonists in vitro and in vivo can potentially regulate incretin hormone release from the gut, then pancreatic insulin release which regulates blood glucose concentrations. However, the success in controlling glucose homeostasis in rodent models of T2D and obesity, failed to translate to early-stage clinical trials in patients with T2D. However, in more recent studies, acute and chronic dosing with the GPR119 agonist DS-8500a had increased efficacy, although this compound was discontinued for further development. New trials on GPR119 agonists are needed, however it may be that the future of GPR119 agonists lie in the development of combination therapy with other T2D therapeutics.

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.

Cellular Senescence in Diabetes Mellitus: Distinct Senotherapeutic Strategies for Adipose Tissue and Pancreatic β Cells

Increased insulin resistance and impaired insulin secretion are significant characteristics manifested by patients with type 2 diabetes mellitus (T2DM). The degree and extent of these two features in T2DM vary among races and individuals. Insulin resistance is accelerated by obesity and is accompanied by accumulation of dysfunctional adipose tissues. In addition, dysfunction of pancreatic β-cells impairs insulin secretion. T2DM is significantly affected by aging, as the β-cell mass diminishes with age. Moreover, both obesity and hyperglycemia-related metabolic changes in developing diabetes are associated with accumulation of senescent cells in multiple organs, that is, organismal aging. Cellular senescence is defined as a state of irreversible cell cycle arrest with concomitant functional decline. It is caused by telomere shortening or senescence-inducing stress. Senescent cells secrete proinflammatory cytokines and chemokines, which is designated as the senescence-associated secretory phenotype (SASP), and this has a negative impact on adipose tissues and pancreatic β-cells. Recent advances in aging research have suggested that senolysis, the removal of senescent cells, can be a promising therapeutic approach to prevent or improve aging-related diseases, including diabetes. The attenuation of a SASP may be beneficial, although the pathophysiological involvement of cellular senescence in diabetes is not fully understood. In the clinical application of senotherapy, tissue-context-dependent senescent cells are increasingly being recognized as an issue to be solved. Recent studies have observed highly heterogenic and complex senescent cell populations that serve distinct roles among tissues, various stages of disease, and different ages. For example, in high-fat-diet induced diabetes with obesity, mouse adipose tissues display accumulation of p21Cip1-highly-expressing (p21high) cells in the early stage, followed by increases in both p21high and p16INK4a-highly-expressing (p16high) cells in the late stage. Interestingly, elimination of p21high cells in visceral adipose tissue can prevent or improve insulin resistance in mice with obesity, while p16high cell clearance is less effective in alleviating insulin resistance. Importantly, in immune-deficient mice transplanted with fat from obese patients, dasatinib plus quercetin, a senolytic cocktail that reduces the number of both p21high and p16high cells, improves both glucose tolerance and insulin resistance. On the other hand, in pancreatic β cells, p16high cells become increasingly predominant with age and development of diabetes. Consistently, elimination of p16high cells in mice improves both glucose tolerance and glucose-induced insulin secretion. Moreover, a senolytic compound, the anti-Bcl-2 inhibitor ABT263 reduces p16INK4a expression in islets and restores glucose tolerance in mice when combined with insulin receptor antagonist S961 treatment. In addition, efficacy of senotherapy in targeting mouse pancreatic β cells has been validated not only in T2DM, but also in type 1 diabetes mellitus. Indeed, in non-obese diabetic mice, treatment with anti-Bcl-2 inhibitors, such as ABT199, eliminates senescent pancreatic β cells, resulting in prevention of diabetes mellitus. These findings clearly indicate that features of diabetes are partly determined by which or where senescent cells reside in vivo, as adipose tissues and pancreatic β cells are responsible for insulin resistance and insulin secretion, respectively. In this review, we summarize recent advances in understanding cellular senescence in adipose tissues and pancreatic β cells in diabetes. We review the different potential molecular targets and distinctive senotherapeutic strategies in adipose tissues and pancreatic β cells. We propose the novel concept of a dual-target tailored approach in senotherapy against diabetes.

Imaging in experimental models of diabetes

Translational medicine, experimental medicine and experimental animal models, in particular mice and rats, represent a multidisciplinary field that has made it possible to achieve, in the last decades, important scientific progress. In this review, we have summarized the most frequently used imaging animal models, such as ultrasound (US), micro-CT, MRI and the optical imaging methods, and their main implications in diagnostic and therapeutic fields, with a particular focus on diabetes mellitus, a multifactorial disease extremely widespread among the general population.

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.

Preservation effect of imeglimin on pancreatic β-cell mass: Noninvasive evaluation using 111In-exendin-4 SPECT/CT imaging and the perspective of mitochondrial involvements

Progressive loss of β-cell mass (BCM) has a pernicious influence on type 2 diabetes mellitus (T2DM); evaluation of BCM has conventionally required an invasive method that provides only cross-sectional data. However, a noninvasive approach to longitudinal assessment of BCM in living subjects using an indium 111-labeled exendin-4 derivative ([Lys12(¹¹¹In-BnDTPA-Ahx)]exendin-4) (¹¹¹In-exendin-4) has been developed recently. Imeglimin is a novel antidiabetic agent that is reported to improve glycemic control and glucose-stimulated insulin secretion (GSIS) via augmentation of mitochondrial function. However, the influence of imeglimin on BCM is not fully understood. We have investigated the effects of imeglimin on BCM in vivo in prediabetic db/db mice using a noninvasive ¹¹¹In-exendin-4 single-photon emission computed tomography/computed tomography (SPECT/CT) technique. During the 5-week study period, imeglimin treatment attenuated the progression of glucose intolerance, and imeglimin-treated mice retained greater BCM than control, which was consistent with the results of ¹¹¹In-exendin-4 SPECT/CT scans. Furthermore, immunohistochemical analysis revealed reduced β-cell apoptosis in the imeglimin-treated db/db mice, and also lowered release of cytosolic cytochrome c protein in the β cells. Furthermore, electron microscopy observation and membrane potential measurement revealed improved structural integrity and membrane potential of the mitochondria of imeglimin-treated islets, respectively. These results demonstrate attenuation of progression of BCM loss in prediabetic db/db mice partly via inhibition of mitochondria-mediated apoptosis.

Development of novel radioiodinated exendin-4 derivatives targeting GLP-1 receptor for detection of β-cell mass

In subjects with type 2 diabetes mellitus (T2DM), pancreatic β-cell mass decreases; however, it is unknown to what extent this decrease contributes to the pathophysiology of T2DM. Therefore, the development of a method for noninvasive detection of β-cell mass is underway. We previously reported that glucagon-like peptide-1 receptor (GLP-1R) is a promising target molecule for β-cell imaging. In this study, we attempted to develop a probe targeting GLP-1R for β-cell imaging using single-photon emission computed tomography (SPECT). For this purpose, we selected exendin-4 as the lead compound and radiolabeled lysine at residue 12 in exendin-4 or additional lysine at the C-terminus using [¹²³I]iodobenzoylation. To evaluate in vitro receptor specificity, binding assay was performed using dispersed mouse islet cells. Biodistribution study was performed in normal ddY mice. Ex vivo autoradiography was performed in transgenic mice expressing green fluorescent protein under control of the mouse insulin I gene promoter. Additionally, SPECT imaging was performed in normal ddY mice. The affinity of novel synthesized derivatives toward pancreatic β-cells was not affected by iodobenzoylation. The derivatives accumulated in the pancreas after intravenous administration specifically via GLP-1R expressed on the pancreatic β-cells. Extremely high signal-to-noise ratio was observed during evaluation of biodistribution of [¹²³I]IB12-Ex4. SPECT images using normal mice showed that [¹²³I]IB12-Ex4 accumulated in the pancreas with high contrast between the pancreas and background. These results indicate that [¹²³I]IB12-Ex4 for SPECT is useful for clinical applications because of its preferable kinetics in vivo.

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.

Targeting the GPR119/incretin axis: a promising new therapy for metabolic-associated fatty liver disease

In the past decade, G protein-coupled receptors have emerged as drug targets, and their physiological and pathological effects have been extensively studied. Among these receptors, GPR119 is expressed in multiple organs, including the liver. It can be activated by a variety of endogenous and exogenous ligands. After GPR119 is activated, the cell secretes a variety of incretins, including glucagon-like peptide-1 and glucagon-like peptide-2, which may attenuate the metabolic dysfunction associated with fatty liver disease, including improving glucose and lipid metabolism, inhibiting inflammation, reducing appetite, and regulating the intestinal microbial system. GPR119 has been a potential therapeutic target for diabetes mellitus type 2 for many years, but its role in metabolic dysfunction associated fatty liver disease deserves further attention. In this review, we discuss relevant research and current progress in the physiology and pharmacology of the GPR119/incretin axis and speculate on the potential therapeutic role of this axis in metabolic dysfunction associated with fatty liver disease, which provides guidance for transforming experimental research into clinical applications.

Targeting lipid GPCRs to treat type 2 diabetes mellitus - progress and challenges

Therapeutic approaches to the treatment of type 2 diabetes mellitus that are designed to increase insulin secretion either directly target β-cells or indirectly target gastrointestinal enteroendocrine cells (EECs), which release hormones that modulate insulin secretion (for example, incretins). Given that β-cells and EECs both express a large array of G protein-coupled receptors (GPCRs) that modulate insulin secretion, considerable research and development efforts have been undertaken to design therapeutic drugs targeting these GPCRs. Among them are GPCRs specific for free fatty acid ligands (lipid GPCRs), including free fatty acid receptor 1 (FFA1, otherwise known as GPR40), FFA2 (GPR43), FFA3 (GPR41) and FFA4 (GPR120), as well as the lipid metabolite binding glucose-dependent insulinotropic receptor (GPR119). These lipid GPCRs have demonstrated important roles in the control of islet and gut hormone secretion. Advances in lipid GPCR pharmacology have led to the identification of a number of synthetic agonists that exert beneficial effects on glucose homeostasis in preclinical studies. Yet, translation of these promising results to the clinic has so far been disappointing. In this Review, we present the physiological roles, pharmacology and clinical studies of these lipid receptors and discuss the challenges associated with their clinical development for the treatment of type 2 diabetes mellitus.

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.

Non-invasive Beta-cell Imaging: Visualization, Quantification, and Beyond

Pancreatic beta (β)-cell dysfunction and reduced mass play a central role in the development and progression of diabetes mellitus. Conventional histological β-cell mass (BCM) analysis is invasive and limited to cross-sectional observations in a restricted sampling area. However, the non-invasive evaluation of BCM remains elusive, and practical in vivo and clinical techniques for β-cell-specific imaging are yet to be established. The lack of such techniques hampers a deeper understanding of the pathophysiological role of BCM in diabetes, the implementation of personalized BCM-based diabetes management, and the development of antidiabetic therapies targeting BCM preservation and restoration. Nuclear medical techniques have recently triggered a major leap in this field. In particular, radioisotope-labeled probes using exendin peptides that include glucagon-like peptide-1 receptor (GLP-1R) agonist and antagonist have been employed in positron emission tomography and single-photon emission computed tomography. These probes have demonstrated high specificity to β cells and provide clear images accurately showing uptake in the pancreas and transplanted islets in preclinical in vivo and clinical studies. One of these probes, ¹¹¹indium-labeled exendin-4 derivative ([Lys¹²(¹¹¹In-BnDTPA-Ahx)]exendin-4), has captured the longitudinal changes in BCM during the development and progression of diabetes and under antidiabetic therapies in various mouse models of type 1 and type 2 diabetes mellitus. GLP-1R-targeted imaging is therefore a promising tool for non-invasive BCM evaluation. This review focuses on recent advances in non-invasive in vivo β-cell imaging for BCM evaluation in the field of diabetes; in particular, the exendin-based GLP-1R-targeted nuclear medicine techniques.

Beta Cell Imaging-From Pre-Clinical Validation to First in Man Testing

There are presently no reliable ways to quantify human pancreatic beta cell mass (BCM) in vivo, which prevents an accurate understanding of the progressive beta cell loss in diabetes or following islet transplantation. Furthermore, the lack of beta cell imaging hampers the evaluation of the impact of new drugs aiming to prevent beta cell loss or to restore BCM in diabetes. We presently discuss the potential value of BCM determination as a cornerstone for individualized therapies in diabetes, describe the presently available probes for human BCM evaluation, and discuss our approach for the discovery of novel beta cell biomarkers, based on the determination of specific splice variants present in human beta cells. This has already led to the identification of DPP6 and FXYD2ga as two promising targets for human BCM imaging, and is followed by a discussion of potential safety issues, the role for radiochemistry in the improvement of BCM imaging, and concludes with an overview of the different steps from pre-clinical validation to a first-in-man trial for novel tracers.

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.