Development of a water-soluble fluorescent Al3+ probe based on phenylsulfonyl-2-pyrone in biological systems

BACKGROUND

Al exists naturally in the environment and is an important component in acidic soils, which harm almost all plants. Furthermore, Al is widely used in food additives, cosmetics, and medicines, resulting in living organisms ingesting traces of Al orally or dermally every day. Accordingly, Al accumulates in the body, which can cause negative bioeffects and diseases, and this concern is gaining increasing attention. Therefore, to detect and track Al in the environment and in living organisms, the development of novel Al-selective probes that are water-soluble and exhibit fluorescence at long wavelengths is necessary.

RESULTS

In this study, an Al3+-selective fluorescent probe PSP based on a novel pyrone molecule was synthesized and characterized to detect and track Al in biological systems. PSP exhibited fluorescence enhancement at 580 nm in the presence of Al3+ in aqueous media. Binding analysis using Job's plot and structural analysis using 1H NMR showed that PSP formed a 1:1 complex with Al3+ at the two carbonyl groups of the dimethyl malonate of the pyrone ring. Upon testing in biological systems, PSP showed good cell membrane permeability, detected intracellular Al3+ in human breast cancer cells (MDA-MB-231), and successfully imaged accumulated Al3+ in Microcystis aeruginosa and the larvae of Rheocricotopus species.

SIGNIFICANCE

The novel Al3+-selective fluorescent probe PSP is highly effective and is expected to aid in elucidating the role of Al3+ in the environment and living organisms.

The clinical utility of comprehensive measurement of autoimmune disease-related antibodies in patients with advanced solid tumors receiving immune checkpoint inhibitors: a retrospective study

BACKGROUND

The comprehensive measurement of autoimmune disease-related antibodies (Abs) before immune checkpoint inhibitor (ICI) treatment may be useful for predicting the development of immune-related adverse events (irAEs); however, the clinical utility is not well known.

MATERIALS AND METHODS

We retrospectively analyzed patients with advanced solid tumors treated with ICI monotherapy or doublet combination therapy between July 2014 and December 2020 at single institute. Anti-nuclear antibody (ANA), anti-thyroglobulin (Tg) Ab, anti-thyroid peroxidase (TPO) Ab, anti-glutamic acid decarboxylase (GAD) Ab, anti-acetylcholine esterase receptor (AchR) Ab, and platelet-associated immunoglobulin G (PA-IgG) Ab were comprehensively measured for the screening before ICI therapy.

RESULTS

Of 275 registered patients (median age, 70 years; male, 64.4%; Eastern Cooperative Oncology Group performance status of 0 or 1, 88.7%; and prior regimen of 0-1/≥2, 88.7%/11.3%), 128 non-small-cell lung cancer, 35 gastric cancer, 33 head and neck cancer, 24 melanoma, 19 renal cell carcinoma, 13 urothelial carcinoma, 12 esophageal cancer, 5 malignant mesothelioma of pleura, 2 endometrial cancer, and 4 other cancer were included. The number of patients with positive ANA, Tg, TPO, PA-IgG, GAD, and AchR Abs was 52 (24.9%), 38 (14.5%), 11 (10.1%), 6 (3.5%), 5 (2.0%), and 1 (0.5%), respectively. There was no association between the development of any irAEs and Abs positivity, while thyroid dysfunction developed more frequently among patients with than without Tg Ab or TPO Ab (39.5% versus 12.5%, P < 0.01; 45.5% versus 14.3%, P = 0.02).

CONCLUSIONS

The clinical utility of comprehensive measurement of autoimmune disease-related Abs before introduction of ICI therapy was limited for predicting irAE. However, Tg and TPO Abs were risk factors as regards the development of ICI-induced thyroid dysfunction.

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.

Development of Gold Nanorods Conjugated with Radiolabeled Anti-human Epidermal Growth Factor Receptor 2 (HER2) Monoclonal Antibody as Single-Photon Emission Computed Tomography/Photoacoustic Dual-Imaging Probes Targeting HER2-Positive Tumors

Surgery remains one of the main treatments of cancer and both precise pre- and intraoperative diagnoses are crucial in order to guide the operation. We consider that using an identical probe for both pre- and intra-operative diagnoses would bridge the gap between surgical planning and image-guided resection. Therefore, in this study, we developed gold nanorods (AuNRs) conjugated with radiolabeled anti-human epidermal growth factor receptor 2 (HER2) monoclonal antibody, and investigated their feasibility as novel HER2-targeted dual-imaging probes for both single photon emission computed tomography (SPECT) (preoperative diagnosis) and photoacoustic (PA) imaging (intraoperative diagnosis). To achieve the purpose, AuNRs conjugated with different amount of trastuzumab (Tra) were prepared, and Tra-AuNRs were labeled with indium-111. After the evaluation of binding affinity to HER2, cell binding assay and biodistribution studies were carried out for optimization. AuNRs with moderate trastuzumab conjugation (Tra2-AuNRs) were proposed as the novel probe and demonstrated significantly higher accumulation in NCI-N87 (HER2 high-expression) tumors than in SUIT2 (low-expression) tumors 96 h post-injection along with good affinity towards HER2. Thereafter, in vitro PA imaging and in vivo SPECT imaging studies were performed. In in vitro PA imaging, Tra2-AuNRs-treated N87 cells exhibited significant PA signal increase than SUIT2 cells. In in vivo SPECT, signal increase in N87 tumors was more notable than that in SUIT2 tumors. Herein, we report that the Tra2-AuNRs enabled HER2-specific imaging, suggesting the potential as a robust HER2-targeted SPECT and PA dual-imaging probe.

Increased [18F]FMISO accumulation under hypoxia by multidrug-resistant protein 1 inhibitors

Background

[¹⁸F]Fluoromisonidazole ([¹⁸F]FMISO) is a PET imaging probe widely used for the detection of hypoxia. We previously reported that [¹⁸F]FMISO is metabolized to the glutathione conjugate of the reduced form in hypoxic cells. In addition, we found that the [¹⁸F]FMISO uptake level varied depending on the cellular glutathione conjugation and excretion ability such as enzyme activity of glutathione-S-transferase and expression levels of multidrug resistance-associated protein 1 (MRP1, an efflux transporter), in addition to the cellular hypoxic state. In this study, we evaluated whether MRP1 activity affected [¹⁸F]FMISO PET imaging.

Methods

FaDu human pharyngeal squamous cell carcinoma cells were pretreated with MRP1 inhibitors (cyclosporine A, lapatinib, or MK-571) for 1 h, incubated with [¹⁸F]FMISO for 4 h under hypoxia, and their radioactivity was then measured. FaDu tumor-bearing mice were intravenously injected with [¹⁸F]FMISO, and PET/CT images were acquired at 4 h post-injection (1st PET scan). Two days later, the same mice were pretreated with MRP1 inhibitors (cyclosporine A, lapatinib, or MK-571) for 1 h, and PET/CT images were acquired (2nd PET scan).

Results

FaDu cells pretreated with MRP1 inhibitors exhibited significantly higher radioactivity than those without inhibitor treatment (cyclosporine A: 6.91 ± 0.27, lapatinib: 10.03 ± 0.47, MK-571: 10.15 ± 0.44%dose/mg protein, p < 0.01). In the in vivo PET study, the SUV_mean ratio in tumors [calculated as after treatment (2nd PET scan)/before treatment of MRP1 inhibitors (1st PET scan)] of the mice treated with MRP1 inhibitors was significantly higher than those of control mice (cyclosporine A: 2.6 ± 0.7, lapatinib: 2.2 ± 0.7, MK-571: 2.2 ± 0.7, control: 1.2 ± 0.2, p < 0.05).

Conclusion

In this study, we revealed that MRP1 inhibitors increase [¹⁸F]FMISO accumulation in hypoxic cells. This suggests that [¹⁸F]FMISO-PET imaging is affected by MRP1 inhibitors independent of the hypoxic state.

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.

Sensitive Photoacoustic/Magnetic Resonance Dual Imaging Probe for Detection of Malignant Tumors

In order to completely remove tumors in surgeries, probes are needed both preoperatively and intraoperatively. For tumor diagnosis, magnetic resonance imaging (MRI) has been widely used as a precise preoperative method, and photoacoustic imaging (PAI) is a recently emerged intraoperative (or preoperative) method, which detects ultrasonic waves thermoelastically induced by optical absorbers irradiated by laser. Iron oxide nanoparticles (IONPs) can be used as both MR and PA imaging probes. In order to improve the sensitivity of IONPs as MR/PA imaging probes, we newly prepared liposomes encapsulated with a number of IONPs (Lipo-IONPs). Interestingly, Lipo-IONPs showed 2.6 and 3.8-times higher PA and MR signals, respectively, compared to dispersed IONPs at the same concentration. Furthermore, trastuzumab (Tra) (anti-human epidermal growth factor receptor 2 (EGFR2; HER2) monoclonal antibody) was introduced onto the surface of liposomes for detection of HER2 related to tumor malignancy. In an cellular uptake study, Tra-Lipo-IONPs were taken up by HER2-positive tumor cells and HER2-specific MR/PA dual imaging was achieved. Finally, a biodistribution study using radiolabeled Tra-Lipo-IONPs showed HER2-specific tumor accumulation. In conclusion, we demonstrated the usefulness of Lipo-IONPs as platforms for sensitive MR/PA dual imaging and the possibility of HER2-specific tumor MR/PA imaging using Tra-Lipo-IONPs.

Activatable Fluorescence Imaging of Macrophages in Cerebral Aneurysms Using Iron Oxide Nanoparticles Conjugated With Indocyanine Green

Background and Purpose

Chronic inflammation is involved in the formation and enlargement of cerebral aneurysms (CAs), with macrophages playing a key role in the process. The present study evaluated visualization of macrophages present in CAs using an activatable fluorescent probe (IONP-ICG) comprising an iron oxide nanoparticles (IONPs) conjugated with indocyanine green (ICG).

Methods

IONP-ICG was intravenously administered to 15-week-old CA model rats (n = 8), and ex vivo near-infrared fluorescence (NIRF) imaging and histological assessment of exposed CAs and cerebral arteries were performed 48 h later. Similar evaluations were performed in the control group, which included CA model rats given IONPs or ICG (n = 8 each).

Results

ICG-derived NIRF signals were detected in three IONP-ICG group rats but not in IONP or ICG control groups. Among the three rats that exhibited signals, NIRF signal accumulation was observed in the CA of two rats and at the site of hemodynamic stress in the left posterior cerebral artery in one rat. Histologically, NIRF signals correlated strongly with macrophage localization. A total of 13 CAs formed in the IONP-ICG group. The number of macrophages in the CA wall was significantly greater in the two CAs that exhibited NIRF signals compared to the remaining 11 CAs that did not (P = 0.037). Moreover, all 11 CAs that did not exhibit NIRF signals were iron-negative, while the two CAs that exhibited NIRF signals were both iron-positive (P = 0.013).

Conclusion

NIRF imaging using an activatable IONP-ICG probe is feasible for detecting the macrophage-rich regions in CAs and the cerebral artery wall, which is considered an early lesion in the process of CA formation.

Spatial Patterns of Amyloid Deposition in Patients with Chronic Focal or Diffuse Traumatic Brain Injury Using 18F-FPYBF-2 PET

AIM

Amyloid-β (Aβ) accumulation, accelerated by traumatic brain injury (TBI), may play a crucial role in neurodegeneration in chronic-stage TBI. The injury type could influence Aβ dynamics because of TBI's complex, heterogeneous nature. We, therefore, investigated spatial patterns of amyloid deposition according to injury type after TBI using 5-(5-(2-(2-(2-[F]-fluoroethoxy)ethoxy)ethoxy)benzofuran-2-yl)-N-methylpyridin-2-amine (¹⁸F-FPYBF-2) positron emission tomography (PET).

METHODS

Altogether, 20 patients with chronic TBI [12 with focal injury, 8 with diffuse axonal injury (DAI)] underwent ¹⁸F-FPYBF-2 PET, structural magnetic resonance imaging (MRI), and neuropsychological examination. Additionally, 50 healthy controls underwent either ¹⁸F-FPYBF-2 PET (n=30) or structural MRI (n=20).

RESULTS

Standardized uptake value ratio (SUVR) on PET images and regional brain volumes were measured in four cortical (frontal, parietal, occipital, temporal) and subcortical (combined caudate, putamen, pallidum, thalamus) regions. Patients with DAI showed significantly increased (compared with controls) SUVR in occipital and temporal cortices and decreased brain volume in occipital cortex (corrected p < 0.05). Although patients with focal injury showed decreased SUVR in all regions except occipital cortex, there were no significant differences (compared with controls) in the SUVR in any regions. There were no significant correlations between increased SUVR and neuropsychological impairments in patients with DAI.

CONCLUSION

Varying spatial patterns of amyloid deposition suggest amyloid pathology diversity depending on the injury type in chronic-TBI patients.

Development and characterization of a 68Ga-labeled A20FMDV2 peptide probe for the PET imaging of αvβ6 integrin-positive pancreatic ductal adenocarcinoma

Pancreatic ductal adenocarcinoma (PDAC) is known to be one of the most lethal cancers. Since the majority of patients are diagnosed at an advanced stage, development of a detection method for PDAC at an earlier stage of disease progression is strongly desirable. Integrin αVβ6 is a promising target for early PDAC detection because its expression increases during precancerous changes. The present study aimed to develop an imaging probe for positron emission tomography (PET) which targets αVβ6 integrin-positive PDAC. We selected A20FMDV2 peptide, which binds specifically to αvβ6 integrin, as a probe scaffold, and 68Ga as a radioisotope. A20FMDV2 peptide has not been previously labeled with 68Ga. A cysteine residue was introduced to the N-terminus of the probe at a site-specific conjugation of maleimide-NOTA (mal-NOTA) chelate. Different numbers of glycine residues were also introduced between cysteine and the A20FMDV2 sequence as a spacer in order to reduce the steric hindrance of the mal-NOTA on the binding probe to αVβ6 integrin. In vitro, the competitive binding assay revealed that probes containing a 6-glycine linker ([natGa]CG6 and [natGa]Ac-CG6) showed high affinity to αVβ6 integrin. Both probes could be labeled by 67/68Ga with high radiochemical yield (>50%) and purity (>98%). On biodistribution analysis, [67Ga]Ac-CG6 showed higher tumor accumulation, faster blood clearance, and lower accumulation in the surrounding organs of pancreas than did [67Ga]CG6. The αVβ6 integrin-positive xenografts were clearly visualized by PET imaging with [68Ga]Ac-CG6. The intratumoral distribution of [68Ga]Ac-CG6 coincided with the αVβ6 integrin-positive regions detected by immunohistochemistry. Thus, [68Ga]Ac-CG6 is a useful peptide probe for the imaging of αVβ6 integrin in PDAC.

Noninvasive longitudinal quantification of β-cell mass with [111In]-labeled exendin-4

Currently, quantifying β-cell mass (BCM) requires harvesting the pancreas. In this study, we investigated a potential noninvasive method to quantify BCM changes longitudinally using [Lys12(111In-BnDTPA-Ahx)]exendin-4 ([111In]-Ex4) and single-photon emission computed tomography (SPECT). We used autoradiography and transgenic mice expressing green fluorescent protein under the control of mouse insulin 1 gene promotor to evaluate the specificity of [111In]-Ex4 toward β cells. Using nonobese diabetic (NOD) mice, we injected [111In]-Ex4 (3.0 MBq) intravenously and performed SPECT 30 min later, repeating this at a 2-wk interval. After the second scan, we harvested the pancreas and calculated BCM from immunohistochemically stained pancreatic sections. Specific accumulation of [111In]-Ex4 in β cells was confirmed by autoradiography, with a significant correlation (r = 0.94) between the fluorescent and radioactive signal intensities. The radioactive signal from the pancreas in the second SPECT scan significantly correlated (r = 0.89) with BCM calculated from the immunostained pancreatic sections. We developed a regression formula to estimate BCM from the radioactive signals from the pancreas in SPECT scans. BCM can be quantified longitudinally and noninvasively by SPECT imaging with [111In]-Ex4. This technique successfully demonstrated longitudinal changes in BCM in NOD mice before and after onset of hyperglycemia.-Fujita, N., Fujimoto, H., Hamamatsu, K., Murakami, T., Kimura, H., Toyoda, K., Saji, H., Inagaki, N. Noninvasive longitudinal quantification of β-cell mass with [111In]-labeled exendin-4.

Development of 99mTc radiolabeled A85380 derivatives targeting cerebral nicotinic acetylcholine receptor: Novel radiopharmaceutical ligand 99mTc-A-YN-IDA-C4

Nicotinic acetylcholine receptors (nAChRs) are pentameric ligand-gated ion channels that have been implicated in higher brain functions. To elucidate the functional mechanisms underlying nAChRs and contribute significantly to development of drugs targeting neurological and neuropsychiatric diseases, non-invasive nuclear medical imaging can be used for evaluation. In addition, technetium-99m (^99mTc) is a versatile radionuclide used clinically as a tracer in single-photon emission computed tomography. Because A85380 is known as a potent α4β2-nAChR agonist, we prepared A85380 derivatives labeled with ^99mTc using a bifunctional chelate system. A computational scientific approach was used to design the probe efficiently. We used non-radioactive rhenium (Re) for a ^99mTc analog and found that one of the derivatives, Re-A-YN-IDA-C4, exhibited high binding affinity at α4β2-nAChR in both the docking simulation (-19.3 kcal/mol) and binding assay (Ki = 0.4 ± 0.04 nM). Further, ^99mTc-A-YN-IDA-C4 was synthesized using microwaves, and its properties were examined. Consequently, we found that ^99mTc-A-YN-IDA-C4, with a structure optimized by using computational chemistry techniques, maintained affinity and selectivity for nAChR in vitro and possessed efficient characteristics as a nuclear medicine molecular imaging probe, demonstrated usefulness of computational scientific approach for molecular improvement strategy.

18F-labeled benzimidazopyridine derivatives for PET imaging of tau pathology in Alzheimer's disease

Hyperphosphorylated tau proteins are one of the neuropathological hallmarks in the Alzheimer's disease (AD) brain. The in vivo imaging of tau aggregates with nuclear medical imaging probes is helpful for the further comprehension of and medical intervention in the AD pathology. For tau-selective PET imaging, we newly designed and synthesized ¹⁸F-labeled benzimidazopyridine (BIP) derivatives with fluoroalkylamino groups, [¹⁸F]IBIPF1 and [¹⁸F]IBIPF2, and evaluated their utilities as tau imaging probes. They both bound selectively to tau against amyloid β (Aβ) aggregates in AD brain sections in vitro, and showed good pharmacokinetics in mouse brains in vivo. Notably, [¹⁸F]IBIPF1 exhibited high tau-selectivity (Tau/Aβ ratio = 34.8), high brain uptake (6.22% ID/g at 2 min postinjection), and subsequent washout (2.77% ID/g at 30 min postinjection). In vivo analysis of radiometabolites indicated that [¹⁸F]IBIPF1 was stable against metabolism in the mouse brain. These encouraging preclinical results suggest that further structural optimization based on the BIP scaffold may lead to the development of more useful tau imaging probes.

Synthesis of a Novel Pyrazine⁻Pyridone Biheteroaryl-Based Fluorescence Sensor and Detection of Endogenous Labile Zinc Ions in Lung Cancer Cells

A small extent of endogenous labile zinc is involved in many vital physiological roles in living systems. However, its detailed functions have not been fully elucidated. In this study, we developed a novel biheteroaryl-based low molecular weight fluorescent sensor, 3-(phenylsulfonyl)-pyrazine–pyridone (5b), and applied it for the detection of endogenous labile zinc ions from lung cancer cells during apoptosis. The electron-withdrawing property of the sulfonyl group between the phenyl ring as an electron donor and the pyridone ring as a fluorophore inhibited the intramolecular charge transfer state, and the background fluorescence of the sensor was decreased in aqueous media. From the structure–fluorescence relationship analysis of the substituent effects with/without Zn²⁺, compound 5b acting as a sensor possessed favorable properties, including a longer emission wavelength, a large Stokes shift (over 100 nm), a large fluorescence enhancement in response to Zn²⁺ under physical conditions, and good cell membrane permeability in living cells. Fluorescence imaging studies of human lung adenocarcinoma cells (A549) undergoing apoptosis revealed that compound 5b could detect endogenous labile zinc ions. These experiments suggested that the low molecular weight compound 5b is a potential fluorescence sensor for Zn²⁺ toward understanding its functions in living systems.

Development of the 99mTc-Hydroxamamide Complex as a Probe Targeting Carbonic Anhydrase IX

Carbonic anhydrase IX (CA-IX) is regarded as a favorable target for in vivo imaging because of its specific expression in hypoxic regions of tumors. Hypoxia assists tumor propagation and growth and is resistant to chemotherapy and radiotherapy. Here, we designed and synthesized [^99mTc]hydroxamamide ([^99mTc]Ham) and [^99mTc]methyl-substituted-hydroxamamide ([^99mTc]MHam) complexes including a bivalent CA-IX ligand, sulfonamide (SA), and ureidosulfonamide (UR). In a cell binding assay, [^99mTc]Ham complexes with bivalent SA ([^99mTc]SAB2A and [^99mTc]SAB2B) and UR ([^99mTc]URB2A and [^99mTc]URB2B) showed significantly greater uptake into CA-IX high-expressing (HT-29) cells than that into CA-IX low-expressing cells. Since the binding affinity of [^99mTc]URB2A and [^99mTc]URB2B for CA-IX was significantly higher than that of [^99mTc]SAB2A and [^99mTc]SAB2B, we additionally synthesized [^99mTc]MURB2 (a [^99mTc]MHam complex with bivalent UR) and evaluated the CA-IX-specific binding affinity of [^99mTc]URB2A, [^99mTc]URB2B, and [^99mTc]MURB2. Their uptake into HT-29 cells was reduced by the addition of a CA inhibitor, acetazolamide, suggesting their CA-IX-specific binding affinity. A biodistribution study in HT-29 tumor-bearing mice was carried out using [^99mTc]URB2A and [^99mTc]MURB2 with the highest specificity for HT-29 cells. [^99mTc]URB2A showed moderate tumor uptake and reduction by coinjection with acetazolamide; however, the tumor/blood ratio was insufficient for in vivo imaging. These results provided key information for the design of novel Ham-based imaging probes targeting CA-IX.

Initial evaluation of PET/CT with 18 F-FSU-880 targeting prostate-specific membrane antigen in prostate cancer patients

This first‐in‐man study was carried out to evaluate the safety, whole‐body distribution, dose estimation, and lesion accumulation of ¹⁸F‐FSU‐880, a newly developed probe targeting prostate‐specific membrane antigen. Six prostate cancer patients with known metastatic lesions underwent serial whole‐body PET/computed tomography (CT) with ¹⁸F‐FSU‐880. Blood and urine were analyzed before and after PET/CT. Accumulation of ¹⁸F‐FSU‐880 in organs and metastatic lesions in serial PET images were evaluated by measuring the standardized uptake values. From the biodistribution data, the organ doses and whole‐body effective dose were calculated using OLINDA/EXM software was developed by Dr. Michael Stabin of Vanderbilt University, Nashville, Tennessee, USA. ¹⁸F‐FSU‐880 PET/CT could be carried out without significant adverse effects. High physiological uptake was observed in the salivary/lachrymal glands and kidneys. The effective dose was calculated to be 0.921 × 10⁻²mSv/MBq. Known metastatic lesions were clearly visualized with high image contrast that increased with time, except in 1 patient, whose bone metastases were well‐controlled and inactive. The PET/CT with ¹⁸F‐FSU‐880 could be carried out safely and could clearly visualize active metastatic lesions. The present results warrant further clinical studies with a larger number of cases to verify the clinical utility of ¹⁸F‐FSU‐880 PET/CT in the management of prostate cancer patients.

Characterization of Novel 18F-Labeled Phenoxymethylpyridine Derivatives as Amylin Imaging Probes

Deposition of islet amyloid consisting of amylin constitutes one of pathological hallmarks of type 2 diabetes mellitus (T2DM), and it may be involved in the development and progression of T2DM. However, the details about the relationship between the deposition of islet amyloid and the pathology of T2DM remain unclear, since no useful imaging tracer enabling the visualization of pancreatic amylin is available. In the present study, we synthesized and evaluated six novel ¹⁸F-labeled phenoxymethylpyridine (PMP) derivatives as amylin imaging probes. All ¹⁸F-labeled PMP derivatives showed not only affinity for islet amyloid in the post-mortem T2DM pancreatic sections but also excellent pharmacokinetics in normal mice. Furthermore, ex vivo autoradiographic studies demonstrated that [¹⁸F]FPMP-5 showed intense labeling of islet amyloids in the diabetes model mouse pancreas in vivo. The preclinical studies suggested that [¹⁸F]FPMP-5 may have potential as an imaging probe that targets amylin aggregates in the T2DM pancreas.

Synthesis and evaluation of a [18F]formyl-Met-Leu-Phe derivative: A positron emission tomography imaging probe for bacterial infections

The tripeptide formyl-Met-Leu-Phe (fMLF) is a prototype of N-formylated chemotactic peptides for neutrophils owing to its ability to bind and activate the G protein-coupled formyl peptide receptor (FPR). Here, we developed an ¹⁸F-labeled fMLF derivative targeting FPR as a positron emission tomography (PET) imaging probe for bacterial infections. The study demonstrates that the fMLF derivative fMLFXYk(FB)k (X = Nle) has a high affinity for FPR (Ki = 0.62 ± 0.13 nM). The radiochemical yield and purity of [¹⁸F]fMLFXYk(FB)k were 16% and >96%, respectively. The in vivo biodistribution study showed that [¹⁸F]fMLFXYk(FB)k uptake was higher in the bacterial infected region than in the non-infected region. We observed considerably higher infection-to-muscle ratio of 4.6 at 60 min after [¹⁸F]fMLFXYk(FB)k injection. Furthermore, small-animal PET imaging studies suggested that [¹⁸F]fMLFXYk(FB)k uptake in the bacterial infected region was clearly visualized 60 min after injection.

Novel fluorescence probes based on the chalcone scaffold for in vitro staining of β-amyloid plaques

The β-amyloid (Aβ) plaque is one of the neuropathological hallmarks in the Alzheimer's disease brain. The detection of Aβ plaques with fluorescence probes is useful for preclinical studies of Alzheimer's disease. In this study, we developed four novel fluorescence probes based on chalcone scaffold. In an in vitro binding study, all FCH derivatives showed moderate binding affinity for Aβ(1-42) aggregates (K_i = 72-114 nM). The fluorescence intensities of FCH-3 and FCH-4 dramatically changed in the presence of Aβ(1-42) aggregates (6.7 and 14.2 fold), but the changes of FCH-1 and FCH-2 were minor (2.0 and 2.4 fold). In a fluorescence staining study using Tg2576 mouse brain sections, FCH-3 and FCH-4 clearly visualized Aβ plaques, but FCH-1 and FCH-2 did not stain. Taken together, all FCH derivatives could bind to Aβ aggregates, but only FCH-3 and FCH-4 may be useful fluorescence probes for in vitro staining of Aβ plaques.

Establishment of a method for in-vivo SPECT/CT imaging analysis of 111In-labeled exendin-4 pancreatic uptake in mice without the need for nephrectomy or a secondary probe

INTRODUCTION

Radiolabeled exendin derivatives have been developed to visualize and quantify pancreatic beta cells. However, there are currently no established methods for analyzing in-vivo SPECT/CT images to quantify probe accumulation in the pancreas in rodent models. In this study, we aimed to establish an analytical method for murine in-vivo SPECT/CT imaging.

METHODS

First, we investigated the correlation between radioactivity measured by curiemeter and uptake calculated from SPECT/CT images of pancreata harvested after probe injection. Second, ROI volume necessary for reliable estimation of pancreatic uptake value was also examined. Third, the influence of high renal uptake on analysis was investigated with SPECT/CT imaging of harvested kidneys. Fourth, we compared pancreatic uptake values and ROI volumes estimated from in-vivo SPECT/CT images of pre- and post-nephrectomy mice. Finally, we assessed the correlation between the pancreatic uptake values from in-vivo SPECT/CT image analysis and radioactivity of harvested pancreata determined with a curiemeter.

RESULTS

Radioactivity of harvested pancreata measured by curiemeter and uptake values derived from SPECT/CT imaging of harvested pancreas showed an almost perfect correlation (r = 0.99, p < 0.001). Analysis using ROIs with >40% of the volume of the whole pancreas enabled reliable estimates of uptake (%CV < 10%). Exclusion of the perirenal space 2.7 mm from the kidney surface removed the influence of high renal uptake. Setting the uptake value of post-nephrectomy pancreatic ROIs as 100%, the uptake estimated from pre-nephrectomy images was comparable (102.9 ± 2.2%). A strong correlation was observed between pancreatic radioactivity measured by curiemeter and the uptake value derived from in-vivo SPECT/CT imaging (r = 0.90, p < 0.001).

CONCLUSION

Our analytical method without nephrectomy or additional probes enables reliable quantification of the pancreatic uptake of ¹¹¹In-labeled exendin-4 using in-vivo SPECT/CT imaging. The quantification of rodent BCM with our method would be helpful to drug development.

Core Binding Site of a Thioflavin-T-Derived Imaging Probe on Amyloid β Fibrils Predicted by Computational Methods

Development of new diagnostic imaging probes for Alzheimer's disease, such as positron emission tomography (PET) and single photon emission computed tomography (SPECT) probes, has been strongly desired. In this study, we investigated the most accessible amyloid β (Aβ) binding site of [¹²³I]IMPY, a Thioflavin-T-derived SPECT probe, using experimental and computational methods. First, we performed a competitive inhibition assay with Orange-G, which recognizes the KLVFFA region in Aβ fibrils, suggesting that IMPY and Orange-G bind to different sites in Aβ fibrils. Next, we precisely predicted the IMPY binding site on a multiple-protofilament Aβ fibril model using computational approaches, consisting of molecular dynamics and docking simulations. We generated possible IMPY-binding structures using docking simulations to identify candidates for probe-binding sites. The binding free energy of IMPY with the Aβ fibril was calculated by a free energy simulation method, MP-CAFEE. These computational results suggest that IMPY preferentially binds to an interfacial pocket located between two protofilaments and is stabilized mainly through hydrophobic interactions. Finally, our computational approach was validated by comparing it with the experimental results. The present study demonstrates the possibility of computational approaches to screen new PET/SPECT probes for Aβ imaging.

Structure-Activity Relationships of Radioiodinated Benzoimidazopyridine Derivatives for Detection of Tau Pathology

It is generally accepted that neurofibrillary tangles consisting of tau proteins are involved in the pathogenesis of Alzheimer's disease (AD). For selective detection of tau pathology, we synthesized and evaluated radioiodinated benzoimidazopyridine (BIP) derivatives with an alkylamino group as tau imaging probes. In vitro selectivity to tau aggregates and in vivo pharmacokinetics of BIP derivatives varied markedly, being strongly dependent on the alkylamino group. In in vitro autoradiography with AD brain sections, the BIP derivative with a dimethylamino group (BIP-NMe₂) showed the highest selectivity to tau aggregates. Regarding the biodistribution using normal mice, the BIP derivative with an ethylamino group (BIP-NHEt) showed the highest uptake (6.04% ID/g at 2 min postinjection) into and rapid washout (0.12% ID/g at 60 min postinjection) from the brain. These results suggest that the introduction of an optimal alkylamino group into the BIP scaffold may lead to the development of more potential tau imaging probes.

Cancer radiotheranostics targeting carbonic anhydrase-IX with 111In- and 90Y-labeled ureidosulfonamide scaffold for SPECT imaging and radionuclide-based therapy

Hypoxic cells dynamically translocate during tumor growth and after radiotherapy. The most desirable direction for therapy targeting hypoxic cells is combining imaging and therapy (theranostics), which may help realize personalized medicine. Here, we conducted cancer radiotheranostics targeting carbonic anhydrase-IX (CA-IX), which is overexpressed in many kinds of hypoxic cancer cells, using low-molecular-weight 111In and 90Y complexes with a bivalent ureidosulfonamide scaffold as the CA-IX-binding moiety ([111In/90Y]US2). Methods: The targeting ability of [111In]US2 was evaluated by in vivo biodistribution study in CA-IX high-expressing (HT-29) tumor-bearing mice. In vivo imaging of HT-29 tumors was carried out using single photon emission computed tomography (SPECT). [90Y]US2 was administered to HT-29 tumor-bearing mice to evaluate cancer therapeutic effects. Results: [111In]US2 highly and selectively accumulated within HT-29 tumors (4.57% injected dose/g tumor at 1 h postinjection), was rapidly cleared from the blood pool and muscle after 4 h based on a biodistribution study, and visualized HT-29 tumor xenografts in mice at 4 h postinjection with SPECT. Radionuclide-based therapy with [90Y]US2 significantly delayed HT-29 tumor growth compared with that of untreated mice (P = 0.02 on day 28, Student's t-test), without any critical hematological toxicity due to its rapid pharmacokinetics. Conclusion: These results indicate that cancer radiotheranostics with [111In/90Y]US2 provides a novel strategy of theranostics for cancer hypoxia.

Comparison of 125I- and 111In-labeled peptide probes for in vivo detection of oxidized low-density lipoprotein in atherosclerotic plaques

OBJECTIVE

Oxidized low-density lipoprotein (OxLDL) plays a pivotal role in atherosclerotic plaque destabilization, which suggests its potential as a nuclear medical imaging target. We previously developed radioiodinated ¹²⁵I-AHP7, a peptide probe carrying a 7-residue sequence from the OxLDL-binding protein Asp-hemolysin, for specific OxLDL imaging. Although ¹²⁵I-AHP7 recognized OxLDL, it had low stability. Thus, to improve stability, we designed radiolabeled 22-residue peptide probes, ¹²⁵I-AHP22 and ¹¹¹In-AHP22, which include the entire AHP7 sequence, and evaluated the stability, activity, and applications of these probes in vitro and in vivo.

METHODS

Probes consisting of a 21-residue peptide derived from the Asp-hemolysin sequence and an N-terminal Cys or aminohexanoic acid for labeling with ¹²⁵I-N-(3-iodophenyl)maleimide or ¹¹¹In diethylene triamine pentaacetic acid were termed ¹²⁵I-AHP22 and ¹¹¹In-AHP22. An in vitro-binding inhibition assay with OxLDL was performed using ¹²⁵I-AHP7 as a radiotracer. Radioactivity accumulation in the atherosclerotic aorta and plasma intact fraction was evaluated 30 min after intravenous administration of probes in myocardial infarction-prone Watanabe heritable hyperlipidemic (WHHLMI) rabbits.

RESULTS

¹²⁵I-AHP22 and ¹¹¹In-AHP22 were synthesized in ~ 360 and 60 min, respectively, with > 98% radiochemical purities after RP-HPLC purification. An in vitro-binding assay revealed similar or greater inhibition of OxLDL binding by both In-AHP22 and I-AHP22 compared to I-AHP7. The fraction of intact ¹²⁵I-AHP22 and ¹¹¹In-AHP22 in plasma was estimated to be approximately tenfold higher than that of ¹²⁵I-AHP7. Both probes were rapidly cleared from the blood. ¹¹¹In-AHP22 had a 2.3-fold higher accumulation in WHHLMI rabbit aortas compared to control rabbits, which was similar to ¹²⁵I-AHP7. However, ¹²⁵I-AHP22 accumulated to similar levels in aortas of WHHLMI and control rabbits due to high nonspecific accumulation in normal aortas that could be due to high lipophilicity.

CONCLUSIONS

¹¹¹In-AHP22, easily prepared within 1 h, showed moderate affinity for OxLDL, high stability in vivo, and high accumulation in atherosclerotic aortas. ¹¹¹In-AHP22 could be a potential lead compound to develop future effective OxLDL imaging probes.

18F-FPYBF-2, a new F-18-labelled amyloid imaging PET tracer: first experience in 61 volunteers and 55 patients with dementia

Objective

Recently, we developed a benzofuran derivative for the imaging of β-amyloid plaques, 5-(5-(2-(2-(2-¹⁸F-fluoroethoxy)ethoxy)ethoxy)benzofuran-2-yl)-N-methylpyridin-2-amine (¹⁸F-FPYBF-2) (Ono et al., J Med Chem 54:2971–9, 2011). The aim of this study was to assess the feasibility of ¹⁸F-FPYBF-2 as an amyloid imaging PET tracer in a first clinical study with healthy volunteers and patients with various dementia and in comparative dual tracer study using ¹¹C-Pittsburgh Compound B (¹¹C-PiB).

Methods

61 healthy volunteers (age: 53.7 ± 13.1 years old; 19 male and 42 female; age range 24–79) and 55 patients with suspected dementia [Alzheimer’s Disease (AD); early AD: n = 19 and moderate stage AD: n = 8, other dementia: n = 9, mild cognitive impairment (MCI): n = 16, cognitively normal: n = 3] for first clinical study underwent static head PET/CT scan using ¹⁸F⁻FPYBF-2 at 50–70 min after injection. 13 volunteers and 14 patients also underwent dynamic PET scan at 0–50 min at the same instant. 16 subjects (volunteers: n = 5, patients with dementia: n = 11) (age: 66.3 ± 14.2 years old; 10 males and 6 females) were evaluated for comparative study (50–70 min after injection) using ¹⁸F-FPYBF-2 and ¹¹C-PiB on separate days, respectively. Quantitative analysis of mean cortical uptake was calculated using Mean Cortical Index of SUVR (standardized uptake value ratio) based on the established method for ¹¹C-PiB analysis using cerebellar cortex as control.

Results

Studies with healthy volunteers showed that ¹⁸F-FPYBF-2 uptake was mainly observed in cerebral white matter and that average Mean Cortical Index at 50–70 min was low and stable (1.066 ± 0.069) basically independent from age or gender. In patients with AD, ¹⁸F-FPYBF-2 uptake was observed both in cerebral white and gray matter, and Mean Cortical Index was significantly higher (early AD: 1.288 ± 0.134, moderate AD: 1.342 ± 0.191) than those of volunteers and other dementia (1.018 ± 0.057). In comparative study, the results of ¹⁸F-FPYBF-2 PET/CT were comparable with those of ¹¹C-PiB, and the Mean Cortical Index (¹⁸F-FPYBF-2: 1.173 ± 0.215; ¹¹C-PiB: 1.435 ± 0.474) showed direct proportional relationship with each other (p < 0.0001).

Conclusions

Our first clinical study suggest that ¹⁸F-FPYBF-2 is a useful PET tracer for the evaluation of β-amyloid deposition and that quantitative analysis of Mean Cortical Index of SUVR is a reliable diagnostic tool for the diagnosis of AD.

Electronic supplementary material

The online version of this article (10.1007/s12149-018-1236-1) contains supplementary material, which is available to authorized users.

Evaluation of 18F-labeled exendin(9-39) derivatives targeting glucagon-like peptide-1 receptor for pancreatic β-cell imaging

β-cell mass (BCM) is known to be decreased in subjects with type-2 diabetes (T2D). Quantitative analysis for BCM would be useful for understanding how T2D progresses and how BCM affects treatment efficacy and for earlier diagnosis of T2D and development of new therapeutic strategies. However, a noninvasive method to measure BCM has not yet been developed. We developed four ¹⁸F-labeled exendin(9-39) derivatives for β-cell imaging by PET: [¹⁸F]FB9-Ex(9-39), [¹⁸F]FB12-Ex(9-39), [¹⁸F]FB27-Ex(9-39), and [¹⁸F]FB40-Ex(9-39). Affinity to the glucagon-like peptide-1 receptor (GLP-1R) was evaluated with dispersed islet cells of ddY mice. Uptake of exendin(9-39) derivatives in the pancreas as well as in other organs was evaluated by a biodistribution study. Small-animal PET study was performed after injecting [¹⁸F]FB40-Ex(9-39). FB40-Ex(9-39) showed moderate affinity to the GLP-1R. Among all of the derivatives, [¹⁸F]FB40-Ex(9-39) resulted in the highest uptake of radioactivity in the pancreas 30 min after injection. Moreover, it showed significantly less radioactivity accumulated in the liver and kidney, resulting in an overall increase in the pancreas-to-organ ratio. In the PET imaging study, pancreas was visualized at 30 min after injection of [¹⁸F]FB40-Ex(9-39). [¹⁸F]FB40-Ex(9-39) met the basic requirements for an imaging probe for GLP-1R in pancreatic β-cells. Further enhancement of pancreatic uptake and specific binding to GLP-1R will lead to a clear visualization of pancreatic β-cells.

Flumioxazin metabolism in pregnant animals and cell-based protoporphyrinogen IX oxidase (PPO) inhibition assay of fetal metabolites in various animal species to elucidate the mechanism of the rat-specific developmental toxicity

Flumioxazin, an N-phenylimide herbicide, inhibits protoporphyrinogen oxidase (PPO), a key enzyme in heme biosynthesis in mammals, and causes rat-specific developmental toxicity. The mechanism has mainly been clarified, but no research has yet focused on the contribution of its metabolites. We therefore conducted in vivo metabolism studies in pregnant rats and rabbits, and found 6 major known metabolites in excreta. There was no major rat-specific metabolite. The most abundant component in rat fetuses was APF, followed by flumioxazin and 5 identified metabolites. The concentrations of flumioxazin and these metabolites in fetuses were lower in rabbits than in rats. In vitro PPO inhibition assays with rat and human liver mitochondria showed that flumioxazin is a more potent PPO inhibitor than the metabolites. There were no species differences in relative intensity of PPO inhibition among flumioxazin and these metabolites. Based on the results of these in vivo and in vitro experiments, we concluded that flumioxazin is the causal substance of the rat-specific developmental toxicity. As a more reliable test system for research on in vitro PPO inhibition, cell-based assays with rat, rabbit, monkey, and human hepatocytes were performed. The results were consistent with those of the mitochondrial assays, and rats were more sensitive to PPO inhibition by flumioxazin than humans, while rabbits and monkeys were almost insensitive. From these results, the species difference in the developmental toxicity was concluded to be due to the difference in sensitivity of PPO to flumioxazin, and rats were confirmed to be the most sensitive of these species.

Construction of nanostructured DNA harbouring phosphorodiamidate morpholino oligonucleotide for controlled tissue distribution in mice

Phosphorodiamidate morpholino oligonucleotides (PMOs) are a class of antisense oligonucleotides used in the treatment of neuromuscular diseases. Their major drawbacks are high blood clearance and poor cellular delivery. Previously, we demonstrated that tripod-like nanostructured DNA, or tripodna, was efficiently taken up by macrophages and dendritic cells. In this study, we used iodine-125(¹²⁵I)-labelled PMOs, designed a tripodna harbouring an ¹²⁵I-PMO (¹²⁵I-PMO/tripodna), and evaluated whether this tripodna could control the pharmacokinetic properties of PMO. Gel electrophoresis showed that ¹²⁵I-PMO was almost completely incorporated into the tripodna. Compared to ¹²⁵I-PMO, ¹²⁵I-PMO/tripodna was more efficiently taken up by macrophage-like RAW264.7 cells. Moreover, after intravenous injection into mice, the area under the plasma concentration-time curve of ¹²⁵I-PMO/tripodna was significantly larger than that of ¹²⁵I-PMO. The distribution of ¹²⁵I-PMO/tripodna in the liver and spleen at 24 h was 32- and 51-fold higher than that of ¹²⁵I-PMO, respectively. The fractionation of liver cells revealed that non-parenchymal cells were the major cells contributing to the hepatic uptake of ¹²⁵I-PMO/tripodna. These results indicate that tripodna has the potential to deliver PMO, particularly to the liver and spleen.

In Vivo HER2-Targeted Magnetic Resonance Tumor Imaging Using Iron Oxide Nanoparticles Conjugated with Anti-HER2 Fragment Antibody

PURPOSE

The feasibility of iron oxide nanoparticles (IONPs) conjugated with anti-epidermal growth factor receptor 2 (HER2) single-chain antibody (scFv-IONPs) as novel HER2-targeted magnetic resonance (MR) contrast agents was investigated.

PROCEDURES

The scFv-IONPs were prepared and identified. For in vitro MRI, NCI-N87 (HER2 high expression) and SUIT2 (low expression) cells were incubated with scFv-IONPs. For in vivo MRI, NCI-N87 and SUIT2 tumor-bearing mice were intravenously injected with scFv-IONPs and imaged before and 24 h post-injection.

RESULTS

The scFv-IONPs demonstrated high transverse relaxivity (296.3 s^-1 mM^-1) and affinity toward HER2 (K_D = 11.7 nM). In the in vitro MRI, NCI-N87 cells treated with scFv-IONPs exhibited significant MR signal reduction (44.6 %) than SUIT2 cells (6.8 %). In the in vivo MRI, decrease of MR signals in NCI-N87 tumors (19.3 %) was more notable than that in SUIT2 tumors (6.2 %).

CONCLUSIONS

The scFv-IONPs enabled HER2-specific tumor MR imaging, suggesting the potential of scFv-IONPs as a robust HER2-targeted MR contrast agent.

Synthesis and biological evaluation of an 111In-labeled exendin-4 derivative as a single-photon emission computed tomography probe for imaging pancreatic β-cells

A non-invasive method of pancreatic β-cell mass measurement is needed to enhance our understanding of the pathogenesis of diabetes, facilitate the early diagnosis of this disease, and promote the development of novel therapeutics. Here, we described the synthesis of a novel indium-111 (¹¹¹In) exendin-4 derivative, [Lys¹²(In-BnDTPA-Ahx)]exendin-4, through a process involving isothiocyanate-benzyl-DTPA (BnDTPA) and 6-aminohexanoic acid (Ahx) attached to an ɛ-amino group at the lysine-12 residue. We further evaluated the potential use of this derivative as a SPECT probe for pancreatic β-cell imaging. An in vitro binding assay revealed that [Lys¹²(^natIn-BnDTPA-Ahx)]exendin-4 has a high affinity for GLP-1 receptors (IC₅₀=0.43nM). In biodistribution experiments involving normal mice, high [Lys¹²(¹¹¹In-BnDTPA-Ahx)]exendin-4 uptake was observed in the pancreas (21.8 ± 4.0%ID/g) and was maintained for 2h after injection. Pre-injection of excess exendin(9-39) markedly reduced the pancreatic uptake of [Lys¹²(¹¹¹In-BnDTPA-Ahx)]exendin-4 (95.2%), indicating that the uptake of this tracer is specific and mediated by GLP-1 receptors. Ex vivo autoradiography experiments involving pancreatic sections from MIP-GFP mice confirmed the accumulation of [Lys¹²(¹¹¹In-BnDTPA-Ahx)]exendin-4 in pancreatic β-cells. Finally, in mice, [Lys¹²(¹¹¹In-BnDTPA-Ahx)]exendin-4 SPECT/CT yielded clear images of the pancreas at 30min post-injection. In conclusion, SPECT with [Lys¹²(¹¹¹In-BnDTPA-Ahx)]exendin-4 enables to visualize β-cells in vivo non-invasively.

Novel Benzothiazole Derivatives as Fluorescent Probes for Detection of β-Amyloid and α-Synuclein Aggregates

Deposits of β-amyloid (Aβ) and α-synuclein (α-syn) are the hallmark of Alzheimer's disease (AD) and Parkinson's disease (PD), respectively. The detection of these protein aggregates with fluorescent probes is particularly of interest for preclinical studies using fluorescence microscopy on human brain tissue. In this study, we newly designed and synthesized three push-pull benzothiazole (PP-BTA) derivatives as fluorescent probes for detection of Aβ and α-syn aggregates. Fluorescence intensity of all PP-BTA derivatives significantly increased upon binding to Aβ(1-42) and α-syn aggregates in solution. In in vitro saturation binding assays, PP-BTA derivatives demonstrated affinity for both Aβ(1-42) (K_d = 40-148 nM) and α-syn (K_d = 48-353 nM) aggregates. In particular, PP-BTA-4 clearly stained senile plaques composed of Aβ aggregates in the AD brain section. Moreover, it also labeled Lewy bodies composed of α-syn aggregates in the PD brain section. These results suggest that PP-BTA-4 may serve as a promising fluorescent probe for the detection of Aβ and α-syn aggregates.

Accelerated growth of B16BL6 tumor in mice through efficient uptake of their own exosomes by B16BL6 cells

Exosomes are extracellular vesicles released by various cell types and play roles in cell-cell communication. Several studies indicate that cancer cell-derived exosomes play important pathophysiological roles in tumor progression. Biodistribution of cancer cell-derived exosomes in tumor tissue is an important factor for determining their role in tumor proliferation; however, limited studies have assessed the biodistribution of exosomes in tumor tissues. In the present study, we examined the effect of cancer-cell derived exosomes on tumor growth by analyzing their biodistribution. Murine melanoma B16BL6-derived exosomes increased the proliferation and inhibited the apoptosis of B16BL6 cells, which was associated with an increase and decrease in the levels of proliferation- and apoptosis-related proteins, respectively. GW4869-induced inhibition of exosome secretion decreased the proliferation of B16BL6 cells, and treatment of GW4869-treated cells with B16BL6-derived exosomes restored their proliferation. Next, we treated B16BL6 tumors in mice with B16BL6-derived exosomes and examined the biodistribution and cellular uptake of these exosomes. After the intratumoral injection of radiolabeled B16BL6-derived exosomes, most radioactivity was detected within the tumor tissues of mice. Fractionation of cells present in the tumor tissue showed that fluorescently labeled exosomes were mainly taken up by B16BL6 cells. Moreover, intratumoral injection of B16BL6-derived exosomes promoted tumor growth, whereas intratumoral injection of GW4869 suppressed tumor growth. These results indicate that B16BL6 cells secrete and take up their own exosomes to induce their proliferation and inhibit their apoptosis, which promotes tumor progression.

18F-Labeled Pyrido[3,4-d]pyrimidine as an Effective Probe for Imaging of L858R Mutant Epidermal Growth Factor Receptor

In nonsmall-cell lung carcinoma patients, L858R mutation of epidermal growth factor receptor (EGFR) is often found, and molecular target therapy using EGFR tyrosine kinase inhibitors is effective for the patients. However, the treatment frequently develops drug resistance by secondary mutation, of which approximately 50% is T790M mutation. Therefore, the ability to predict whether EGFR will undergo secondary mutation is extremely important. We synthesized a novel radiofluorinated 4-(anilino)pyrido[3,4-d]pyrimidine derivative ([¹⁸F]APP-1) and evaluated its potential as a positron emission tomography (PET) imaging probe to discriminate the difference in mutations of tumors. EGFR inhibition assay, cell uptake, and biodistribution study showed that [¹⁸F]APP-1 binds specifically to the L858R mutant EGFR but not to the L858R/T790M mutant. Finally, on PET imaging study using [¹⁸F]APP-1 with tumor-bearing mice, the H3255 tumor (L858R mutant) was more clearly visualized than the H1975 tumor (L858R/T790M mutant).

Development of 111In-labeled exendin(9-39) derivatives for single-photon emission computed tomography imaging of insulinoma

Insulinoma is a tumor derived from pancreatic β-cells, and the resulting hyperinsulinemia leads to characteristic hypoglycemia. Recent studies have reported the frequent overexpression of glucagon-like peptide-1 receptor (GLP-1R) in human insulinomas, suggesting that the binding of a radiolabeled compound to GLP-1R is useful for the imaging of such tumors. Exendin(9-39), a fragment peptide of exendin-3 and -4, binds GLP-1R with high affinity and acts as an antagonist. Accordingly, radiolabeled exendin(9-39) derivatives have also been investigated as insulinoma imaging probes that might be less likely to induce hypoglycemia. In this study, we synthesized a novel indium-111 (¹¹¹In)-benzyl-diethylenetriaminepentaacetic acid (¹¹¹In-BnDTPA)-conjugated exendin(9-39), ¹¹¹In-BnDTPA-exendin(9-39), and evaluated its utility as a probe for the SPECT imaging of insulinoma. natIn-BnDTPA-exendin(9-39) exhibited a high affinity for GLP-1R (IC₅₀=2.5nM), stability in plasma, and a specific activity that improved following reactions with a solvent and solubilizer. Regarding the in vivo biodistribution of ¹¹¹In-BnDTPA-exendin(9-39) in INS-1 tumor-bearing mice, high uptake levels were observed in tumors (14.6%ID/g at 15min), with corresponding high tumor-to-blood (T/B), tumor-to-muscle (T/M), and tumor-to-pancreas (T/P) ratios (T/B=2.55, T/M=22.7, T/P=2.7 at 1h). The pre-administration of excess nonradioactive exendin(9-39) significantly reduced accumulation in both the tumor and pancreas (76% and 68% inhibition, respectively) at 1h after ¹¹¹In-BnDTPA-exendin(9-39) injection, indicating that the GLP-1R mediated a majority of ¹¹¹In-BnDTPA-exendin(9-39) uptake in the tumor and pancreas. Finally, ¹¹¹In-BnDTPA-exendin(9-39) SPECT/CT studies in mice yielded clear images of tumors at 30min post-injection. These results suggest that ¹¹¹In-BnDTPA-exendin(9-39) could be a useful SPECT molecular imaging probe for the detection and exact localization of insulinomas.