High-Affinity and Proteolytically Stable Peptidic Fluorescent NTSR Ligands.

Labeled ligands for the neurotensin receptor 1 (NTSR), which is expressed in the CNS, the gastrointestinal tract, and in malignant tumors, are needed to investigate NTSR-ligand binding and NTSR expression. Aiming for fluorescence-labeled neurotensin(8-13)-derived NTSR ligands with high affinity and proteolytic stability, several previous approaches were combined: (1) replacement of Arg by an amino-functionalized carbamoylated arginine, allowing conjugation to a fluorophore, (2) -methylation of Arg and replacement of Tyr by β,β-dimethyl-l-Tyr, conferring proteolytic stability, and (3) replacement of Leu by trimethylsilyl-Ala, boosting binding affinity. This strategy gave fluorescent NTSR ligands with unprecedented NTSR binding affinity (5-TAMRA-labeled ligand : 0.

Tc-Labeled Diarylpyrazoles for Single-Emission Computer Tomography Imaging of Neurotensin Receptor-Positive Tumors: A Comparative Preclinical Study.

Neurotensin receptors (NTSRs), members of the G protein-coupled receptor (GPCR) family, have been found to be overexpressed in several types of human cancers, including breast, colon, lung, liver, prostate, and pancreatic cancer. In particular, NTSR1 is overexpressed in at least 75% of pancreatic ductal adenocarcinomas. The aim of the present study was the development and evaluation of new Tc-labeled nonpeptide NTSR1-antagonists for SPECT imaging of NTSR-positive tumors.

Heteroaryl derivatives of suvorexant as OX1R selective PET ligand candidates: Cu-mediated F-fluorination of boroxines, in vitro and initial in vivo evaluation.

Background: The orexin receptor (OXR) plays a role in drug addiction and is aberrantly expressed in colorectal tumors. Subtype-selective OXR PET ligands suitable for in vivo use have not yet been reported. This work reports the development of F-labeled OXR PET ligand candidates derived from the OXR antagonist suvorexant and the OX1R-selective antagonist JH112.

Radiosynthesis and Preclinical Evaluation of F-Labeled Estradiol Derivatives with Different Lipophilicity for PET Imaging of Breast Cancer.

About 75% of breast tumors show an overexpression of the estradiol receptor (ER), making it a valuable target for tumor diagnosis and therapy. To date, 16-[F]fluoroestradiol (FES) is the only FDA-approved imaging probe for the positron emission tomography (PET) imaging of ER-positive (ER breast cancer. However, FES has the drawback of a high retention in the liver.

Structure-guided discovery of orexin receptor-binding PET ligands.

Molecular imaging using positron emission tomography (PET) can serve as a promising tool for visualizing biological targets in the brain. Insights into the expression pattern and the in vivo imaging of the G protein-coupled orexin receptors OX1R and OX2R will further our understanding of the orexin system and its role in various physiological and pathophysiological processes. Guided by crystal structures of our lead compound JH112 and the approved hypnotic drug suvorexant bound to OX1R and OX2R, respectively, we herein describe the design and synthesis of two novel radioligands, [F]KD23 and [F]KD10.

In Vitro Assessment of Lu-Labeled Trastuzumab-Targeted Mesoporous Carbon@Silica Nanostructure for the Treatment of HER2-Positive Breast Cancer.

This study assessed the effectiveness of a trastuzumab-targeted Lu-labeled mesoporous Carbon@Silica nanostructure (DOTA@TRA/MC@Si) for HER2-positive breast cancer treatment, focusing on its uptake, internalization, and efflux in breast cancer cells. The synthesized PEI-MC@Si nanocomposite was reacted with DOTA-NHS-ester, confirmed by the Arsenazo(III) assay. Following this, TRA was conjugated to the DOTA@PEI-MC@Si for targeting.

CD200 fibroblasts form a pro-resolving mesenchymal network in arthritis.

Fibroblasts are important regulators of inflammation, but whether fibroblasts change phenotype during resolution of inflammation is not clear. Here we use positron emission tomography to detect fibroblast activation protein (FAP) as a means to visualize fibroblast activation in vivo during inflammation in humans. While tracer accumulation is high in active arthritis, it decreases after tumor necrosis factor and interleukin-17A inhibition.

Bioconjugation of a Fibroblast Activation Protein Targeted Interleukin-4.

Interleukin-4 (IL-4) is an immune-modulating therapeutic with growing potential for the treatment of inflammatory diseases. Current challenges of IL-4 therapy include a low serum half-life and pleiotropic activity, suggesting effective targeting of IL-4. To develop an interleukin-4 bioconjugate with rapid targeting to inflammatory disease sites, we report the chemical synthesis, bioconjugation, and characterization of a murine interleukin-4 (mIL-4) conjugate decorated with a fibroblast activation protein inhibitor (FAPI).

N-glycosylation Regulates Intrinsic IFN-γ Resistance in Colorectal Cancer: Implications for Immunotherapy.

Background & Aims: Advanced colorectal carcinoma (CRC) is characterized by a high frequency of primary immune evasion and refractoriness to immunotherapy. Given the importance of interferon (IFN)-γ in CRC immunosurveillance, we investigated whether and how acquired IFN-γ resistance in tumor cells would promote tumor growth, and whether IFN-γ sensitivity could be restored.

Methods: Spontaneous and colitis-associated CRC development was induced in mice with a specific IFN-γ pathway inhibition in intestinal epithelial cells.

Neurotensin analogs by fluoroglycosylation at N-carbamoylated arginines for PET imaging of NTS1-positive tumors.

Since neurotensin (NT) receptors of subtype-1 (NTS1) are expressed by different types of malignant tumors, such as pancreatic adenocarcinoma, colorectal and prostate carcinoma, they represent an interesting target for tumor imaging by positron emission tomography (PET) and endoradiotherapy. Previously reported neurotensin-derived NTS1 ligands for PET were radiolabeled by modification and prelongation of the N-terminus of NT(8-13) peptide analogs. In this study, we demonstrate that modifying Arg or Arg by N-carbamoylation and subsequent fluoroglycosylation provides a suitable approach for the development of NT(8-13) analogs as PET imaging agents.

Non-Invasive Characterization of Experimental Bone Metastasis in Obesity Using Multiparametric MRI and PET/CT.

The growth of primary tumors and metastases is associated with excess body fat. In bone metastasis formation, the bone marrow microenvironment, and particularly adipocytes, play a pivotal role as growth mediators of disseminated tumor cells in the bone marrow. The aim of the present study is to non-invasively characterize the pathophysiologic processes in experimental bone metastasis resulting from accelerated tumor progression within adipocyte-rich bone marrow using multimodal imaging from magnetic resonance imaging (MRI) and positron emission tomography/computed tomography (PET/CT).

Sweetening Pharmaceutical Radiochemistry by F-Fluoroglycosylation: Recent Progress and Future Prospects.

In the field of F-chemistry for the development of radiopharmaceuticals for positron emission tomography (PET), various labeling strategies by the use of prosthetic groups have been implemented, including chemoselective F-labeling of biomolecules. Among those, chemoselective F-fluoroglycosylation methods focus on the sweetening of pharmaceutical radiochemistry by offering a highly valuable tool for the synthesis of F-glycoconjugates with suitable in vivo properties for PET imaging studies. A previous review covered the various F-fluoroglycosylation methods that were developed and applied as of 2014 (Maschauer and Prante, BioMed.

F-Fluorination Using Tri--Butanol Ammonium Iodide as Phase-Transfer Catalyst: An Alternative Minimalist Approach.

The F syntheses of tracers for positron emission tomography (PET) typically require several steps, including extraction of [F]fluoride from H[O]O, elution, and drying, prior to nucleophilic substitution reaction, being a laborious and time-consuming process. The elution of [F]fluoride is commonly achieved by phase transfer catalysts (PTC) in aqueous solution, which makes azeotropic drying indispensable. The ideal PTC is characterized by a slightly basic nature, its capacity to elute [F]fluoride with anhydrous solvents, and its efficient complex formation with [F]fluoride during subsequent labeling.

Bivalent ligands promote endosomal trafficking of the dopamine D3 receptor-neurotensin receptor 1 heterodimer.

Bivalent ligands are composed of two pharmacophores connected by a spacer of variable size. These ligands are able to simultaneously recognize two binding sites, for example in a G protein-coupled receptor heterodimer, resulting in enhanced binding affinity. Taking advantage of previously described heterobivalent dopamine-neurotensin receptor ligands, we demonstrate specific interactions between dopamine D3 (DR) and neurotensin receptor 1 (NTSR1), two receptors with expression in overlapping brain areas that are associated with neuropsychiatric diseases and addiction.

Multimodal Bone Metastasis-associated Epidermal Growth Factor Receptor Imaging in an Orthotopic Rat Model.

Purpose To develop multimodality imaging techniques for measuring epidermal growth factor receptor (EGFR) as a therapy-relevant and metastasis-associated molecular marker in triple-negative mammary adenocarcinoma metastases. Materials and Methods An orthotopic bone metastasis EGFR-positive, triple-negative breast cancer (TNBC) model in rats was used for bioluminescence imaging, SPECT/CT, PET/CT, and MRI with quantitative analysis of transcripts ( = 22 rats). Receptor-specific MRI of EGFR expression in vivo was performed by acquiring spin-echo T1-weighted images after sequential administration of a pair of anti-EGFR antigen binding fragments, F(ab'), conjugated to either horseradish peroxidase or glucose oxidase, which have complementing activities, as well as paramagnetic (gadolinium[III]-mono-5-hydroxytryptamide of 2,2',2''-(10-(2,6-dioxotetrahydro-2H-pyran-3-yl)-1,4,7,10-tetraazacyclododecane-1,4,7-triyl)triacetic acid, or Gd-5HT-DOTAGA) or positron-emitting (gallium 68-5HT-DOTAGA) substrates for MRI and PET/CT imaging, respectively.

Pharmacological Characterization of Low-to-Moderate Affinity Opioid Receptor Agonists and Brain Imaging with F-Labeled Derivatives in Rats.

The 3,4-dichloro--(1-(dimethylamino)cyclohexyl)methyl benzamide scaffold was studied as a template for F-positron emission tomography (F-PET) radiotracer development emphasizing sensitivity to changes in opioid receptor (OR) occupancy over high affinity. Agonist potency, binding affinity, and relevant pharmacological parameters of 15 candidates were investigated. Two promising compounds and with μ-OR (MOR) selective agonist activity in the moderate range (EC = 1-100 nM) were subjected to F-fluorination, autoradiography, and small-animal PET imaging.

Disentangling inflammatory from fibrotic disease activity by fibroblast activation protein imaging.

Objectives: To date, there is no valuable tool to assess fibrotic disease activity in humans in vivo in a non-invasive way. This study aims to uncouple inflammatory from fibrotic disease activity in fibroinflammatory diseases such as IgG-related disease.

Methods: In this cross-sectional clinical study, 27 patients with inflammatory, fibrotic and overlapping manifestations of IgG-related disease underwent positron emission tomography (PET) scanning with tracers specific for fibroblast activation protein (FAP; Ga-FAP inhibitor (FAPI)-04), F-fluorodeoxyglucose (FDG), MRI and histopathological assessment.

Synthesis, Radiosynthesis and Biological Evaluation of Buprenorphine-Derived Phenylazocarboxamides as Novel μ-Opioid Receptor Ligands.

Targeted structural modifications have led to a novel type of buprenorphine-derived opioid receptor ligand displaying an improved selectivity profile for the μ-OR subtype. On this basis, it is shown that phenylazocarboxamides may serve as useful bioisosteric replacements for the widely occurring cinnamide units, without loss of OR binding affinity or subtype selectivity. This study further includes functional experiments pointing to weak partial agonist properties of the novel μ-OR ligands, as well as docking and metabolism experiments.

Development of F-Fluoroglycosylated PSMA-Ligands with Improved Renal Clearance Behavior.

The prostate-specific membrane antigen (PSMA) is a type II transmembrane glycoprotein that is highly expressed in the malignant human prostate epithelium. Therefore, PSMA has emerged as a very attractive target for developing radiopharmaceuticals for the diagnosis, e.g.

Identification of Boronic Acid Derivatives as an Active Form of N-Alkylaminoferrocene-Based Anticancer Prodrugs and Their Radiolabeling with F.

N-Alkylaminoferrocene (NAAF)-based prodrugs are activated in the presence of elevated amounts of reactive oxygen species (ROS), which corresponds to cancer specific conditions, with formation of NAAF and p-quinone methide. Both products act synergistically by increasing oxidative stress in cancer cells that causes their death. Though it has already been demonstrated that the best prodrugs of this type retain their antitumor activity in vivo, the effects were found to be substantially weaker than those observed in cell cultures.

Radiosynthesis of an F-fluoroglycosylated aminoferrocene for in-vivo imaging of reactive oxygen species activity by PET.

The imaging of reactive oxygen species (ROS) at the molecular level with high sensitivity and specificity by positron emission tomography (PET) could be of enormous interest to increase our knowledge about ROS activity and signalling, especially in tumours. The aim of this research was to optimise the click chemistry-based radiosynthesis of an F-labelled aminoferrocene glycoconjugate that was derived from an N-alkylaminoferrocene lead structure known to have anticancer activity in vitro. Applying the solvent system phosphate buffer/THF (12/5), Cu(OAc) and sodium ascorbate as reducing agent at 60°C, the alkyne 1 reacted with the F-labelled glycosyl azide [ F]2 in the presence of carrier 3 (47μM) to obtain carrier-added [ F]4 in a radiochemical yield of 85%.

[F]Fluorophenylazocarboxylates: Design and Synthesis of Potential Radioligands for Dopamine D3 and μ-Opioid Receptor.

F-Labeled building blocks from the type of [F]fluorophenylazocarboxylic--butyl esters offer a rapid, mild, and reliable method for the F-fluoroarylation of biomolecules. Two series of azocarboxamides were synthesized as potential radioligands for dopamine D3 and the μ-opioid receptor, revealing compounds and with single-digit and sub-nanomolar affinity for the D3 receptor and compound with only micromolar affinity for the μ-opioid receptor, but enhanced selectivity for the μ-subtype in comparison to the lead compound AH-7921. A "minimalist procedure" without the use of a cryptand and base for the preparation of 4-[F]fluorophenylazocarboxylic--butyl ester was established, together with the radiosynthesis of methyl-, methoxy-, and phenyl-substituted derivatives ().