Detection of Intestinal Inflammation by Vascular Adhesion Protein-1-Targeted [68Ga]Ga-DOTA-Siglec-9 Positron Emission Tomography in Murine Models of Inflammatory Bowel Disease

PURPOSE

Inflammatory bowel disease (IBD) can be imaged with positron emission tomography (PET), but existing PET radiopharmaceuticals have limited diagnostic accuracy. Vascular adhesion protein-1 (VAP-1) is an endothelial cell surface molecule that controls leukocyte extravasation into sites of inflammation. However, the role of inflammation-induced VAP-1 expression in IBD is still unclear. Therefore, this study investigated the utility of VAP-1-targeted [68Ga]Ga-DOTA-Siglec-9 positron emission tomography/computed tomography (PET/CT) for assessing inflammation in two mouse models of IBD.

PROCEDURES

Studies were performed using K8-/- mice that develop a chronic colitis-phenotype and C57Bl/6NCrl mice with acute intestinal inflammation chemically-induced using 2.5% dextran sodium sulfate (DSS) in drinking water. In both diseased and control mice, uptake of the VAP-1-targeting peptide [68Ga]Ga-DOTA-Siglec-9 was assessed in intestinal regions of interest using in vivo PET/CT, after which ex vivo gamma counting, digital autoradiography, and histopathological analyses were performed. Immunofluorescence staining was performed to determine VAP-1-expression in the intestine, including in samples from patients with ulcerative colitis.

RESULTS

Intestinal inflammation could be visualized by [68Ga]Ga-DOTA-Siglec-9 PET/CT in two murine models of IBD. In both models, the in vivo PET/CT and ex vivo studies of [68Ga]Ga-DOTA-Siglec-9 uptake were significantly higher than in control mice. The in vivo uptake was increased on average 1.4-fold in the DSS model and 2.0-fold in the K8-/- model. Immunofluorescence staining revealed strong expression of VAP-1 in the inflamed intestines of both mice and patients.

CONCLUSIONS

This study suggests that the VAP-1-targeting [68Ga]Ga-DOTA-Siglec-9 PET tracer is a promising tool for non-invasive imaging of intestinal inflammation. Future studies in patients with IBD and evaluation of the potential value of [68Ga]Ga-DOTA-Siglec-9 in diagnosis and monitoring of the disease are warranted.

High folate receptor expression in gliomas can be detected in vivo using folate-based positron emission tomography with high tumor-to-brain uptake ratio divulging potential future targeting possibilities

Introduction

Non-invasive imaging techniques such as positron emission tomography (PET) are extremely important for cancer detection and characterization especially for difficult to biopsy or extremely delicate organs such as the brain. The folate analogue 1,4,7-triazacylononane-1,4,7-triacetic acid-conjugated folate radiolabeled with aluminum fluoride-18 ([¹⁸F]FOL) has been previously shown to accumulate preferentially in tumor cells with an overexpression of folate receptors (FRs) and here was investigated for its ability to detect orthotopic gliomas in a rat model. In addition, we studied the expression of FRs in human glioblastoma samples to investigate if an analogous relationship may exist.

Methods

Nine BDIX rats were injected with BT4C rat glioma cells into the right hemisphere of the brain. Animals were imaged with gadolinium-enhanced magnetic resonance imaging at on days prior to PET/computed tomography (CT) imaging. Animals were divided into two groups, and were PET/CT imaged with either [¹⁸F]FOL or 2-deoxy-2-18F-fluoro-D-glucose ([¹⁸F]FDG) on 19 and 32-days post glioma grafting. Two subjects were also PET/CT imaged with [¹⁸F]FOL on day 16. Biodistribution was studied and brains were cryosectioned for autoradiography, immunofluorescence, and histological studies. Patient-derived paraffin-embedded glioblastomas were sectioned and stained with similar methods.

Results

PET imaging showed an increase of [18F]FOL tumor-to-brain uptake ratio (TBR) over the study duration from day 16/19 (3.3 ± 0.9) increasing to 5.7 ± 1.0 by day 32. [¹⁸F]FDG PET-imaged rats had a consistent TBR of 1.6 ± 0.1 throughout the study. Ex vivo autoradiography results revealed an exceptionally high TBR of 116.1 ± 26.9 for [¹⁸F]FOL while the [18F]FDG values were significantly lower giving 2.9 ± 0.6 (P<0.0001). Immunostaining demonstrated an increased presence of FR-α in the BT4C gliomas versus the contralateral brain tissue, while FR-β was present only on glioma periphery. Human sections assayed showed similar FRs expression characteristics.

Conclusion

This study shows upregulation of FR-α inside glioma regions in both human and animal tissue, providing a biochemical basis for the observed increased [¹⁸F]FOL uptake in animal PET images. These results suggest that FRs targeting imaging and therapeutic compounds may possess clinically relevant translational abilities for the detection and treatment of gliomas.

Preclinical Evaluation of a Humanized Antibody Against Common Lymphatic Endothelial and Vascular Endothelial Receptor-1,89Zr-Desferrioxamine-Bexmarilimab, in a Rabbit Model of Renal Fibrosis

Bexmarilimab is a new humanized monoclonal antibody against common lymphatic endothelial and vascular endothelial receptor-1 (CLEVER-1) and is in clinical trials for macrophage-guided cancer immunotherapy. In addition being associated with cancer, CLEVER-1 is also associated with fibrosis. To facilitate prospective human PET studies, we preclinically evaluated ⁸⁹Zr-labeled bexmarilimab in rabbits. Methods: Bexmarilimab was conjugated with desferrioxamine (DFO) and radiolabeled with ⁸⁹Zr. Retained immunoreactivity was confirmed by flow cytometry. The distribution kinetics of intravenously administered ⁸⁹Zr-DFO-bexmarilimab (0.1 mg/kg) were determined for up to 7 d in a rabbit model of renal fibrosis mediated by unilateral ureteric obstruction. The in vivo stability of ⁸⁹Zr-DFO-bexmarilimab was evaluated by sodium dodecyl sulfate-polyacrylamide gel electrophoresis in combination with autoradiography. Additionally, we estimated the human radiation dose from data obtained in healthy rabbits. Results: ⁸⁹Zr-DFO-bexmarilimab cleared rapidly from the blood circulation and distributed to the liver and spleen. At 24 h after injection, PET/CT, ex vivo γ-counting, and autoradiography demonstrated that there was significantly higher ⁸⁹Zr-DFO-bexmarilimab uptake in unilateral ureteric obstruction-operated fibrotic renal cortex, characterized by abundant CLEVER-1-positive cells, than in contralateral or healthy kidneys. The estimated effective dose for a 70-kg human was 0.70 mSv/MBq. Conclusion: The characteristics of ⁸⁹Zr-DFO-bexmarilimab support future human PET studies to, for example, stratify patients for bexmarilimab treatment, evaluate the efficacy of treatment, or monitor disease progression.

[68Ga]Ga-DOTA-Siglec-9 Detects Pharmacodynamic Changes of FAP-Targeted IL2 Variant Immunotherapy in B16-FAP Melanoma Mice

Vascular adhesion protein-1 (VAP-1) is an inflammation-inducible adhesion molecule, which supports contact between leukocytes and inflamed endothelium. There is evidence that VAP-1 is involved in the recruitment of leukocytes to melanoma tumors. Interleukin-2 (IL-2)-based immunotherapy is an efficient therapy that promotes immune system activity against cancers but is associated with toxicity. In the present study, we evaluated the feasibility of PET/CT imaging using the radiotracer [⁶⁸Ga]Ga-DOTA-Siglec-9, which is targeted to VAP-1, to monitor pharmacodynamic effects of a novel FAP-IL2v immunocytokine (a genetically engineered variant of IL-2 fused with fibroblast activation protein) in the B16-FAP melanoma model. At 9 days after the inoculation of B16-FAP melanoma cells, mice were studied with [⁶⁸Ga]Ga-DOTA-Siglec-9 PET/CT as a baseline measurement. Immediately after baseline imaging, mice were treated with FAP-IL2v or vehicle, and treatment was repeated 3 days later. Subsequent PET/CT imaging was performed 3, 5, and 7 days after baseline imaging. In addition to in vivo PET imaging, ex vivo autoradiography, histology, and immunofluorescence staining were performed on excised tumors. B16-FAP tumors were clearly detected with [⁶⁸Ga]Ga-DOTA-Siglec-9 PET/CT during the follow-up period, without differences in tumor volume between FAP-IL2v-treated and vehicle-treated groups. Tumor-to-muscle uptake of [⁶⁸Ga]Ga-DOTA-Siglec-9 was significantly higher in the FAP-IL2v-treated group than in the vehicle-treated group 7 days after baseline imaging, and this was confirmed by tumor autoradiography analysis. FAP-IL2v treatment did not affect VAP-1 expression on the tumor vasculature. However, FAP-IL2v treatment increased the number of CD8⁺ T cells and natural killer cells in tumors. The present study showed that [⁶⁸Ga]Ga-DOTA-Siglec-9 can detect B16-FAP tumors and allows monitoring of FAP-IL2v treatment.

68Ga-Citrate Positron Emission Tomography of Healthy Men: Whole-Body Biodistribution Kinetics and Radiation Dose Estimates

⁶⁸Ga-citrate has one of the simplest chemical structures of all ⁶⁸Ga-radiopharmaceuticals, and its clinical use is justified by the proven medical applications using its isotope-labeled compound ⁶⁷Ga-citrate. To support broader application of ⁶⁸Ga-citrate in medical diagnosis, further research is needed to gain clinical data from healthy volunteers. In this work, we studied the biodistribution of ⁶⁸Ga-citrate and subsequent radiation exposure from it in healthy males. Methods: ⁶⁸Ga-citrate was prepared with an acetone-based radiolabeling procedure compliant with Good Manufacturing Practices. Six healthy males (age 41 ± 12 years, mean ± SD) underwent sequential whole-body PET/CT scans after an injection of 204 ± 8 MBq of ⁶⁸Ga-citrate. Serial arterialized venous blood samples were collected during PET imaging and the radioactivity concentration was measured with a gamma counter. Urinary voids were collected and measured. The Medical Internal Radiation Dose (MIRD) bladder-voiding model with a 3.5 hour voiding interval was used. A model using a 70 kg adult male and MIRD schema was used to estimate absorbed doses in target organs and effective doses. Calculations were performed using OLINDA/EXM 2.0 software. Results: Radioactivity clearance from the blood was slow, and relatively high radioactivity concentrations were observed over the whole of the 3 hour measuring period. Although radioactivity excretion via urine was rather slow (biological half-time, 69 ± 24 hours), the highest decay-corrected concentrations in urinary bladder contents were measured at 90 and 180 minute time points. Moderate concentrations were also seen in kidneys, liver, and spleen. The source organs showing the largest residence times were muscle, liver, lung, and heart contents. The heart wall received the highest absorbed dose of 0.077 ± 0.008 mSv/MBq. The mean effective dose (ICRP 103) was 0.021 ± 0.001 mSv/MBq. Conclusion: PET imaging with ⁶⁸Ga-citrate is associated with modest radiation exposure. A 200 MBq injection of ⁶⁸Ga-citrate results in an effective radiation dose of 4.2 mSv, which is in the same range as other ⁶⁸Ga-labeled tracers. This suggests the feasibility of clinical studies using ⁶⁸Ga-citrate imaging in humans and the possibility of performing multiple scans in the same subjects across the course of a year.

The circadian gene Cryptochrome 2 influences stress-induced brain activity and depressive-like behavior in mice

Cryptochrome 2 (Cry2) is a core clock gene important for circadian regulation. It has also been associated with anxiety and depressive-like behaviors in mice, but the previous findings have been conflicting in terms of the direction of the effect. To begin to elucidate the molecular mechanisms of this association, we carried out behavioral testing, PET imaging, and gene expression analysis of Cry2^-/- and Cry2^+/+ mice. Compared to Cry2^+/+ mice, we found that Cry2^-/- mice spent less time immobile in the forced swim test, suggesting reduced despair-like behavior. Moreover, Cry2^-/- mice had lower saccharin preference, indicative of increased anhedonia. In contrast, we observed no group differences in anxiety-like behavior. The behavioral changes were accompanied by lower metabolic activity of the ventro-medial hypothalamus, suprachiasmatic nuclei, ventral tegmental area, anterior and medial striatum, substantia nigra, and habenula after cold stress as measured by PET imaging with a glucose analog. Although the expression of many depression-associated and metabolic genes was upregulated or downregulated by cold stress, we observed no differences between Cry2^-/- and Cry2^+/+ mice. These findings are consistent with other studies showing that Cry2 is required for normal emotional behavior. Our findings confirm previous roles of Cry2 in behavior and extend them by showing that the effects on behavior may be mediated by changes in brain metabolism.

Hydroxysteroid (17β) dehydrogenase 12 is essential for metabolic homeostasis in adult mice

Hydroxysteroid 17β dehydrogenase 12 (HSD17B12) is suggested to be involved in the elongation of very long chain fatty acids. Previously, we have shown a pivotal role for the enzyme during mouse development. In the present study we generated a conditional Hsd17b12 knockout (HSD17B12cKO) mouse model by breeding mice homozygous for a floxed Hsd17b12 allele with mice expressing the tamoxifen-inducible Cre recombinase at the ROSA26 locus. Gene inactivation was induced by administering tamoxifen to adult mice. The gene inactivation led to a 20% loss of body weight within 6 days, associated with drastic reduction in both white (83% males, 75% females) and brown (65% males, 60% females) fat, likely due to markedly reduced food and water intake. Furthermore, the knockout mice showed sickness behavior and signs of liver toxicity, specifically microvesicular hepatic steatosis and increased serum alanine aminotransferase (4.6-fold in males, 7.7-fold in females). The hepatic changes were more pronounced in females than males. Proinflammatory cytokines, such as interleukin-6 (IL-6), IL-17, and granulocyte colony-stimulating factor, were increased in the HSD17B12cKO mice indicating an inflammatory response. Serum lipidomics study showed an increase in the amount of dihydroceramides, despite the dramatic overall loss of lipids. In line with the proposed role for HSD17B12 in fatty acid elongation, we observed accumulation of ceramides, dihydroceramides, hexosylceramides, and lactosylceramides with shorter than 18-carbon fatty acid side chains in the serum. The results indicate that HSD17B12 is essential for proper lipid homeostasis and HSD17B12 deficiency rapidly results in fatal systemic inflammation and lipolysis in adult mice.

First-in-Humans Study of 68Ga-DOTA-Siglec-9, a PET Ligand Targeting Vascular Adhesion Protein 1

Sialic acid–binding immunoglubulinlike lectin 9 (Siglec-9) is a ligand of vascular adhesion protein 1. A ⁶⁸Ga-labeled peptide of Siglec-9, ⁶⁸Ga-DOTA-Siglec-9, holds promise as a novel PET tracer for imaging of inflammation. This first-in-humans study investigated the safety, tolerability, biodistribution, and radiation dosimetry of this radiopharmaceutical. Methods: Six healthy men underwent dynamic whole-body PET/CT. Serial venous blood samples were drawn from 1 to 240 min after intravenous injection of 162 ± 4 MBq of ⁶⁸Ga-DOTA-Siglec-9. In addition to γ-counting, the plasma samples were analyzed by high-performance liquid chromatography to detect intact tracer and radioactive metabolites. Radiation doses were calculated using the OLINDA/EXM software, version 2.2. In addition, a patient with early rheumatoid arthritis was studied with both ⁶⁸Ga-DOTA-Siglec-9 and ¹⁸F-FDG PET/CT to determine the ability of the new tracer to detect arthritis. Results:⁶⁸Ga-DOTA-Siglec-9 was well tolerated by all subjects. ⁶⁸Ga-DOTA-Siglec-9 was rapidly cleared from the blood circulation, and several radioactive metabolites were detected. The organs with the highest absorbed doses were the urinary bladder wall (0.38 mSv/MBq) and kidneys (0.054 mSv/MBq). The mean effective dose was 0.022 mSv/MBq (range, 0.020–0.024 mSv/MBq). Most importantly, however, ⁶⁸Ga-DOTA-Siglec-9 was comparable to ¹⁸F-FDG in detecting arthritis. Conclusion: Intravenous injection of ⁶⁸Ga-DOTA-Siglec-9 was safe and biodistribution was favorable for testing of the tracer in larger group of patients with rheumatoid arthritis, as is planned for the next phase of clinical trials. The effective radiation dose of ⁶⁸Ga-DOTA-Siglec-9 was within the same range as the effective radiation doses of other ⁶⁸Ga-labeled tracers. Injection of 150 MBq of ⁶⁸Ga-DOTA-Siglec-9 would expose a subject to 3.3 mSv. These findings support the possible repeated clinical use of ⁶⁸Ga-DOTA-Siglec-9, such as in trials to elucidate the treatment efficacy of novel drug candidates.

Does the cis/trans configuration of peptide bonds in bioactive tripeptides play a role in ACE-1 enzyme inhibition?

Background

The milk casein-derived bioactive tripeptides isoleucine-proline-proline (IPP) and valine-proline-proline (VPP) have been shown to prevent development of hypertension in animal models and to lower blood pressure in moderately hypertensive subjects in most but not all clinical trials. Inhibition of angiotensin-converting enzyme 1 (ACE-1) has been suggested as the explanation for these antihypertensive and beneficial vascular effects. Previously, human umbilical vein endothelial cells (HUVEC) have not been used to test ACE-1 inhibiting properties of casein derived tripeptides in vasculature.

Purpose

We focused on the cis/trans configurations of the peptide bonds in proline-containing tripeptides in order to discover whether the different structural properties of these peptides influence their activity in ACE-1 inhibition. We hypothesized that the configuration of proline-containing peptides plays a significant role in enzyme inhibition.

Methods

AutoDock 4.2 docking software was used to predict suitable peptide bond configurations of the tripeptides. Besides modeling studies, we completed ACE-1 activity measurements in vitro using HUVEC cultures.

Results

In HUVEC cells, both IPP and VPP inhibited ACE-1. Based on molecular docking studies, we propose that in ACE-1 inhibition IPP and VPP share a similar cis configuration between the first aliphatic (isoleucine or valine) and the second (proline) amino acid residues and more different configurations between two proline residues. In vivo experiments are needed to validate the significance of the present findings.