Synthesis and biological evaluation of technetium-99m labeled galactose derivatives as potential asialoglycoprotein receptor probes in a hepatic fibrosis mouse model

Advances in Noninvasive Molecular Imaging Probes for Liver Fibrosis Diagnosis

Liver fibrosis is a wound-healing response to chronic liver injury, which may lead to cirrhosis and cancer. Early-stage fibrosis is reversible, and it is difficult to precisely diagnose with conventional imaging modalities such as magnetic resonance imaging, positron emission tomography, single-photon emission computed tomography, and ultrasound imaging. In contrast, probe-assisted molecular imaging offers a promising noninvasive approach to visualize early fibrosis changes in vivo, thus facilitating early diagnosis and staging liver fibrosis, and even monitoring of the treatment response. Here, the most recent progress in molecular imaging technologies for liver fibrosis is updated. We start by illustrating pathogenesis for liver fibrosis, which includes capillarization of liver sinusoidal endothelial cells, cellular and molecular processes involved in inflammation and fibrogenesis, as well as processes of collagen synthesis, oxidation, and cross-linking. Furthermore, the biological targets used in molecular imaging of liver fibrosis are summarized, which are composed of receptors on hepatic stellate cells, macrophages, and even liver collagen. Notably, the focus is on insights into the advances in imaging modalities developed for liver fibrosis diagnosis and the update in the corresponding contrast agents. In addition, challenges and opportunities for future research and clinical translation of the molecular imaging modalities and the contrast agents are pointed out. We hope that this review would serve as a guide for scientists and students who are interested in liver fibrosis imaging and treatment, and as well expedite the translation of molecular imaging technologies from bench to bedside.

Research progress on asialoglycoprotein receptor-targeted radiotracers designed for hepatic nuclear medicine imaging

Asialoglycoprotein receptor (ASGPR) specifically recognizes glycans terminated with β-d-galactose or N-acetylgalactosamine. Its exclusive expression in mammalian hepatocytes renders it an ideal hepatic-targeted biomarker. To date, ASGPR-targeted ligands have been actively developed for drug delivery and hepatic imaging. This review provides a comprehensive summary of the progress achieved to-date in the field of developing ASGPR-targeted nuclear medicine imaging (NMI) radiotracers, highlighting the recent advancements over the last decade in terms of structure, radionuclides and labeling strategies. The biodistribution patterns, imaging characteristics, challenges and future prospective are discussed.

PET/SPECT Molecular Probes for the Diagnosis and Staging of Nonalcoholic Fatty Liver Disease

Nonalcoholic fatty liver disease (NAFLD) is a significant public health challenge afflicting approximately 1 billion individuals both in the Western world and in the East world. While liver biopsy is considered as gold standard in the diagnosis and staging of liver fibrosis, noninvasive imaging technologies, including ultrasonography, computed tomography, single-photon emission computed tomography (SPECT), magnetic resonance imaging, and positron emission tomography (PET) could offer more sensitive, comprehensive, and quantitative measurement for NAFLD. In this review, we focus on recent development and applications of PET/SPECT molecular probes that enable multispatial/temporal visualization and quantification of physiopathological progress at the molecular level in the NAFLD. We shall also discuss the limitations of current radioligands and future direction for PET/SPECT probe development.

Hexavalent lactoside labeled with [18F]AlF for PET imaging of asialoglycoprotein receptor

Several methods have been developed to label compounds with ¹⁸F. However, in general these are laborious and require a multistep synthesis. A method based on the chelation of ¹⁸F-aluminum fluoride ([¹⁸F]AlF) by 1,4,7-triazacyclononane-1,4,7-triacetic acid (NOTA) was developed recently. The present work was aimed to radiolabel hexavalent lactoside (NOTA-HL) by [¹⁸F]AlF method for PET imaging of asialoglycoprotein receptor (ASGPR).

METHODS

hexavalent lactoside was conjugated with the NOTA chelate and labeled with ¹⁸F in a one-pot method. The labeling procedure was investigated with different amounts of NOTA-HL and aluminum concentration. Radiochemical yield and radiochemical purity were determined by radio-TLC and radio-HPLC respectively. In vitro stability study of [¹⁸F]AlF-HL were carried out. PET/CT imaging of normal mice injected with [¹⁸F]AlF-NOTA-HL was performed.

RESULTS

The Radiochemical yield of [¹⁸F]AlF-NOTA-HL was higher with more precursor and optimal Al⁺ concentration. The radiochemical purity of labeled product was >95% after purified by Sep-Pak cartridge to remove unbound [¹⁸F]AlF. The radiolabeling, including purification, was performed in 30 min [¹⁸F]AlF-NOTA-HL exhibited good in vitro stability. PET studies in normal mice revealed high specific accumulation of activity in the liver.

CONCLUSION

NOTA-HL could be labeled rapidly and efficiently with aqueous ¹⁸F using AlF method. [¹⁸F]AlF-NOTA-HL would provide another efficient approach for PET imaging of ASGPR.

Use of 111In-Hexavalent Lactoside for Liver Reserve Estimation in Rodents with Thioacetamide-Induced Hepatic Fibrosis

Many biochemical tests detecting the presence of liver disease are not liver-specific and may be abnormal in nonhepatic conditions. The asialoglycoprotein receptor (ASGPR) is a hepatocyte-specific receptor for Gal/GalNAc-terminated glycopeptide or glycoprotein. The number of these receptors decreases in patients with chronic liver diseases. Here, we aimed to evaluate the use of ¹¹¹In-hexavalent lactoside, a known ASGPR imaging biomarker, as a more sensitive probe to detect small changes in liver reserve in animal models of chronic liver injury. Thioacetamide (TAA) treatment via intraperitoneal injection every 2 days in BALB/c mice continued for 1, 2, 3, or 4 months. The liver fibrosis stages were determined by Sirius Red staining and were based on the METAVIR classification method. Serum transaminase enzymes (alanine transaminase (ALT) and aspartate transaminase (AST)), alkaline phosphatase, albumin, and bilirubin were measured using a FUJI FDC3500 i/s analyzer. The ASGPR staining was performed by immunohistocytochemical stain. The percentages of fibrosis and ASGPR were calculated using ImageJ software after collagen staining and anti-ASGPR staining, respectively. A nanoSPECT/CT was used for molecular imaging and liver uptake measurement. We observed fibrosis grades of F0-F1 in mice treated with TAA for 1 month, F2 in mice treated for 2 months, F3-F4 in mice treated for 3 months, and F4 in mice treated for 4 months. The levels of ALT and albumin were not significantly different in the TAA groups from those in the controls. Although the average levels of AST, alkaline phosphatase, and bilirubin in the TAA groups were different from those in the control group, there was little difference between TAA groups. More sensitive distinctions among TAA groups were detected in ¹¹¹In-hexavalent lactoside uptake of ASGPR, ASGPR staining, and fibrosis % than when using the conventional AST, ALT, albumin, alkaline phosphatase, and bilirubin tests. The absorption and distribution of ¹¹¹In-hexavalent lactoside were lower in the chronic hepatitis models than the normal controls. The liver reserves measured by ¹¹¹In-hexavalent lactoside uptake were 71.7 ± 7.5% and 50.9 ± 5.6% after 1 and 2 months, respectively, of TAA treatment. As an ASGPR biomarker, ¹¹¹In-hexavalent lactoside has higher sensitivity than traditional liver function tests and collagen stain to provide more objective data for evaluating compensated cirrhosis or changes in liver damage. ASGPR staining can reflect the regenerated hepatocytes, but the need for a biopsy limits its use. ¹¹¹In-hexavalent lactoside measurement is comparable with ASGPR staining, which suggests that ¹¹¹In-hexavalent lactoside measurement will be more useful as a practical, noninvasive test of chronic liver injury.

Synthesis and biological evaluation of novel mono- and bivalent ASGP-R-targeted drug-conjugates

Asialoglycoprotein receptor (ASGP-R) is a promising biological target for drug delivery into hepatoma cells. Nevertheless, there are only few examples of small-molecule conjugates of ASGP-R selective ligand equipped by a therapeutic agent for the treatment of hepatocellular carcinoma (HCC). In the present work, we describe a convenient and versatile synthetic approach to novel mono- and multivalent drug-conjugates containing N-acetyl-2-deoxy-2-aminogalactopyranose and anticancer drug - paclitaxel (PTX). Several molecules have demonstrated high affinity towards ASGP-R and good stability under physiological conditions, significant in vitro anticancer activity comparable to PTX, as well as good internalization via ASGP-R-mediated endocytosis. Therefore, the conjugates with the highest potency can be regarded as a promising therapeutic option against HCC.

Small Molecule Radiopharmaceuticals - A Review of Current Approaches

Radiopharmaceuticals are an integral component of nuclear medicine and are widely applied in diagnostics and therapy. Though widely applied, the development of an “ideal” radiopharmaceutical can be challenging. Issues such as specificity, selectivity, sensitivity, and feasible chemistry challenge the design and synthesis of radiopharmaceuticals. Over time, strategies to address the issues have evolved by making use of new technological advances in the fields of biology and chemistry. This review presents the application of few advances in design and synthesis of radiopharmaceuticals. The topics covered are bivalent ligand approach and lipidization as part of design modifications for enhanced selectivity and sensitivity and novel synthetic strategies for optimized chemistry and radiolabeling of radiopharmaceuticals.

Molecular changes in hepatic metabolism and transport in cirrhosis and their functional importance

Liver cirrhosis is the common endpoint of many hepatic diseases and represents a relevant risk for liver failure and hepatocellular carcinoma. The progress of liver fibrosis and cirrhosis is accompanied by deteriorating liver function. This review summarizes the regulatory and functional changes in phase I and phase II metabolic enzymes as well as transport proteins and provides an overview regarding lipid and glucose metabolism in cirrhotic patients. Interestingly, phase I enzymes are generally downregulated transcriptionally, while phase II enzymes are mostly preserved transcriptionally but are reduced in their function. Transport proteins are regulated in a specific way that resembles the molecular changes observed in obstructive cholestasis. Lipid and glucose metabolism are characterized by insulin resistance and catabolism, leading to the disturbance of energy expenditure and wasting. Possible non-invasive tests, especially breath tests, for components of liver metabolism are discussed. The heterogeneity and complexity of changes in hepatic metabolism complicate the assessment of liver function in individual patients. Additionally, studies in humans are rare, and species differences preclude the transferability of data from rodents to humans. In clinical practice, some established global scores or criteria form the basis for the functional evaluation of patients with liver cirrhosis, but difficult treatment decisions such as selection for transplantation or resection require further research regarding the application of existing non-invasive tests and the development of more specific tests.