[68Ga]NOTA-Galactosyl Human Serum Albumin: a Tracer for Liver Function Imaging with Improved Stability

Combined PET and near-infrared fluorescence probe based on lapatinib targeting HER2 for in vivo tumor imaging

Combination of PET and optical imaging techniques holds significant potential for complete tumor resection to optimize patient outcomes. In this study, we combined two lapatinib-based molecular probes for detecting HER2-overexoression tumors through PET and near-infrared (NIR) fluorescence imaging. HER2 receptor had been confirmed to be overexpressed in many types of tumors and had become a specific target for molecular imaging. The radiolabeled probe [68Ga] Ga-NOTA-lapatinib demonstrated superior imaging performance in micro-PET scans, achieving clear differentiation of subcutaneous tumors from adjacent tissues. Complementarily, the NIR fluorescent probe LP-S exhibited prolonged tumor retention (>72 h) with distinct signal demarcation between malignant and normal tissues in ex vivo analyses. Fluorescence microscopy further validated specific intra-tumoral accumulation of the probe at cellular resolution. This synchronized dual-probe strategy, leveraging identical targeting moieties, established a robust platform for multimodality cancer imaging that bridges preoperative detection with intraoperative visualization.

68Ga-Labeled Glycopeptides as Effective Tools for Liver Function Imaging

[99mTc]Tc-GSA, an albumin-based glycoprotein, is routinely used in Japan to measure the asialoglycoprotein receptor (ASGR) density via single photon emission tomography. Here we describe the development of 68Ga-labeled peptide-based alternatives. Peptides were assembled on a solid support using a fragment coupling strategy. Glycosylation was carried out via a click chemistry approach resulting in a set of three peptides with increasing amounts of d-galactose (n = 3, 6, and 9) as well as one glycopeptide bearing nine N-acetylgalactosamine residues. 68Ga-labeling of all compounds could be achieved in high radiochemical yields (>95%). Radiotracers exhibited high hydrophilicity, good metabolic stability in human serum and protein binding between 12 and 22%. The IC50 values improved in the series tri-, hexa-, and nonamer with an IC50 of 50 ± 30 pM for the latter one. In analogy, the in vivo biodistribution studies revealed increased liver uptake in the series of [68Ga]Ga-NODAGA-TriLysan (9.4 ± 2.0% ID/g, 30 min p.i.), [68Ga]Ga-NODAGA-HexaLysan (55.5 ± 7.4% ID/g, 30 min p.i.), and [68Ga]Ga-NODAGA-NonaLysan (79.6 ± 8.0% ID/g, 30 min p.i.). [68Ga]Ga-NODAGA-GalNAc-NonaLysan reached comparable liver uptake to [68Ga]Ga-NODAGA-NonaLysan, but showed higher accumulation in nontarget organs. The impressive imaging properties of [68Ga]Ga-NODAGA-NonaLysan were also confirmed by the PET/MR imaging studies in mice. Hence, [68Ga]Ga-NODAGA-NonaLysan represents a new PET radiopharmaceutical with even better imaging properties than [99mTc]Tc-GSA.

Advancements of non‐invasive imaging technologies for the diagnosis and staging of liver fibrosis: Present and future

Liver fibrosis is a reparative response triggered by liver injury. Non‐invasive assessment and staging of liver fibrosis in patients with chronic liver disease are of paramount importance, as treatment strategies and prognoses depend significantly on the degree of fibrosis. Although liver fibrosis has traditionally been staged through invasive liver biopsy, this method is prone to sampling errors, particularly when biopsy sizes are inadequate. Consequently, there is an urgent clinical need for an alternative to biopsy, one that ensures precise, sensitive, and non‐invasive diagnosis and staging of liver fibrosis. Non‐invasive imaging assessments have assumed a pivotal role in clinical practice, enjoying growing popularity and acceptance due to their potential for diagnosing, staging, and monitoring liver fibrosis. In this comprehensive review, we first delved into the current landscape of non‐invasive imaging technologies, assessing their accuracy and the transformative impact they have had on the diagnosis and management of liver fibrosis in both clinical practice and animal models. Additionally, we provided an in‐depth exploration of recent advancements in ultrasound imaging, computed tomography imaging, magnetic resonance imaging, nuclear medicine imaging, radiomics, and artificial intelligence within the field of liver fibrosis research. We summarized the key concepts, advantages, limitations, and diagnostic performance of each technique. Finally, we discussed the challenges associated with clinical implementation and offer our perspective on advancing the field, hoping to provide alternative directions for the future research.

[68Ga]Ga-NODAGA-TriGalactan, a low molecular weight tracer for the non-invasive imaging of the functional liver reserve

BACKGROUND

Determination of the functional liver mass is important in a variety of clinical settings including liver surgery and transplantation. [99mTc]Tc-diethylenetriamine-pentaacetic acid galactosyl human serum albumin (99mTc-GSA) is a radiotracer targeting the asialoglycoprotein receptor (ASGR) and is routinely used in Japan for this purpose. Here we describe the development and evaluation of [68Ga]Ga-NODAGA-TriGalactan a low molecular weight PET-tracer targeting this structure.

RESULTS

For synthesis TRIS as branching unit and NODAGA as chelator for labelling with [68Ga]Ga are included. Three galactose moieties are conjugated via a click chemistry approach resulting in the desired labelling precursor.68Ga-labelling could be accomplished in high radiochemical yield and purity. [68Ga]Ga-NODAGA-TriGalactan is very hydrophilic and revealed high plasma stability and low plasma protein binding. Fluorescence imaging showed binding on ASGR-positive organoids and the IC50-value was in the nanomolar range. Most importantly, both biodistribution as well as animal imaging studies using normal mice demonstrated high liver uptake with rapid elimination from all other organs leading to even higher liver-to-background ratios as found for 99mTc-GSA.

CONCLUSION

[68Ga]Ga-NODAGA-TriGalactan shows high in vitro stability and selectively binds to the ASGR allowing imaging of the functional liver mass with high contrast. Thus, our first generation compound resulted already in an alternative to 99mTc-GSA for imaging the functional liver reserve and might allow the broader use of this imaging technique.

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.

68 Ga-labeled, imatinib encapsulated, theranostic liposomes: Formulation, characterization, and in vitro evaluation of anticancer activity

Cancer is still a global health problem. Among cancer types, breast cancer is the most frequently diagnosed one, and it causes a high mortality rate if not diagnosed in the early stages. In our study, imatinib encapsulated, nanosized, neutral/cationic liposome formulations were prepared as theranostic agents for breast cancer. After the characterization studies in which all liposomes exhibited proper profile owing to their particle size between 133 and 250 nm, polydispersity index values lower than 0.4, neutral and cationic zeta potential values, and high drug encapsulation efficiency, controlled drug release behaviors with zero-order kinetic were obtained. The higher than 90% radiolabeling efficiency values were obtained thanks to the determination of optimum radiolabeling condition (80°C temperature, 5 mCi radioactivity, and 10 min incubation period). According to the resazurin assay evaluating the cytotoxic profile of liposomes on MCF7 cells, neutral empty liposome was found as biocompatible, while both cationic liposomes (empty and drug-loaded ones) exhibited high nonspecific cytotoxicity at even low drug concentration due to the existence of stearyl amine in the formulations. However, dose-dependent cytotoxic effect and the highest cellular binding capacity were obtained by imatinib loaded neutral liposomes. In conclusion, 68 Ga-radiolabeled, imatinib-loaded, neutral, nanosized liposome formulation is the most promising one as a theranostic agent among all formulations.

Automated GMP Production and Preclinical Evaluation of [68Ga]Ga-TEoS-DAZA and [68Ga]Ga-TMoS-DAZA

[⁶⁸Ga]Ga-TEoS-DAZA and [⁶⁸Ga]Ga-TMoS-DAZA are two novel radiotracers suitable for functional PET liver imaging. Due to their specific liver uptake and biliary excretion, the tracers may be applied for segmental liver function quantification, gall tree imaging and the differential diagnosis of liver nodules. The purpose of this study was to investigate problems that occurred initially during the development of the GMP compliant synthesis procedure and to evaluate the tracers in a preclinical model. After low radiolabeling yields were attributed to precursor instability at high temperatures, an optimized radiolabeling procedure was established. Quality controls were in accordance with Ph. Eur. requirements and gave compliant results, although the method for the determination of the ⁶⁸Ga colloid is partially inhibited due to the presence of a radioactive by-product. The determination of logP revealed [⁶⁸Ga]Ga-TEoS-DAZA (ethoxy bearing) to be more lipophilic than [⁶⁸Ga]Ga-TMoS-DAZA (methoxy bearing). Accordingly, biodistribution studies in an in ovo model showed a higher liver uptake for [⁶⁸Ga]Ga-TEoS-DAZA. In dynamic in ovo PET imaging, rapid tracer accumulation in the liver was observed. Similarly, the activity in the intestines rose steadily within the first hour p.i., indicating biliary excretion. As [⁶⁸Ga]Ga-TEoS-DAZA and [⁶⁸Ga]Ga-TMoS-DAZA can be prepared according to GMP guidelines, transition into the early clinical phase is now possible.

Asialoglycoprotein Receptor-Targeted Superparamagnetic Perfluorooctylbromide Nanoparticles

Background

The decrease in asialoglycoprotein receptor (ASGPR) levels is observed in patients with chronic liver disease and liver tumor. The aim of our study was to develop ASGPR-targeted superparamagnetic perfluorooctylbromide nanoparticles (M-PFONP) and wonder whether this composite agent could target buffalo rat liver (BRL) cells in vitro and could improve R2^∗ value of the rat liver parenchyma after its injection in vivo.

Methods

GalPLL, a ligand of ASGPR, was synthesized by reductive amination. ASGPR-targeted M-PFOBNP was prepared by a film hydration method coupled with sonication. Several analytical methods were used to investigate the characterization and safety of the contrast agent in vitro. The in vivo MR T2^∗ mapping was performed to evaluate the enhancement effect in rat liver.

Results

The optimum concentration of Fe₃O₄ nanoparticles inclusion in GalPLL/M-PFOBNP was about 52.79 µg/mL, and the mean size was 285.6 ± 4.6 nm. The specificity of GalPLL/M-PFOBNP for ASGPR was confirmed by incubation experiment with fluorescence microscopy. The methyl thiazolyl tetrazolium (MTT) test showed that there was no significant difference in the optical density (OD) of cells incubated with all GalPLL/M-PFOBNP concentrations. Compared with M-PFOBNP, the increase in R2^∗ value of the rat liver parenchyma after GalPLL/M-PFOBNP injection was higher.

Conclusions

GalPLL/M-PFOBNP may potentially serve as a liver-targeted contrast agent for MR receptor imaging.

Triantennary GalNAc Molecular Imaging Probes for Monitoring Hepatocyte Function in a Rat Model of Nonalcoholic Steatohepatitis

Nonalcoholic steatohepatitis (NASH) is a progressive form of nonalcoholic fatty liver disease that can lead to irreversible liver cirrhosis and cancer. Early diagnosis of NASH is vital to detect disease before it becomes life-threatening, yet noninvasively differentiating NASH from simple steatosis is challenging. Herein, bifunctional probes have been developed that target the hepatocyte-specific asialoglycoprotein receptor (ASGPR), the expression of which decreases during NASH progression. The results show that the probes allow longitudinal, noninvasive monitoring of ASGPR levels by positron emission tomography in the newly developed rat model of NASH. The probes open new possibilities for research into early diagnosis of NASH and development of drugs to slow or reverse its progression.

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.

Metal-Based Complexes as Pharmaceuticals for Molecular Imaging of the Liver

This article reviews the use of metal complexes as contrast agents (CA) and radiopharmaceuticals for the anatomical and functional imaging of the liver. The main focus was on two established imaging modalities: magnetic resonance imaging (MRI) and nuclear medicine, the latter including scintigraphy and positron emission tomography (PET). The review provides an overview on approved pharmaceuticals like Gd-based CA and ^99mTc-based radiometal complexes, and also on novel agents such as ⁶⁸Ga-based PET tracers. Metal complexes are presented by their imaging modality, with subsections focusing on their structure and mode of action. Uptake mechanisms, metabolism, and specificity are presented, in context with advantages and limitations of the diagnostic application and taking into account the respective imaging technique.

Development of a Novel Imaging Agent for Determining Albumin Uptake in Solid Tumors

Purpose

The purpose of this study was to investigate the albumin-binding compound ¹¹¹In-C4-DTPA as an imaging agent for the detection of endogenous albumin accumulation in tumors.

Methods

¹¹¹In-C4-DTPA was injected in healthy nude mice for pharmacokinetic and biodistribution studies (10 min, 1, 6, 24, and 48 h, n = 4) and subsequently in tumor-bearing mice for single-photon emission computed tomography/X-ray-computed tomography (SPECT/CT) imaging studies. Four different human tumor xenograft models (LXFL529, OVXF899, MAXFTN401, and CXF2081) were implanted subcutaneously unilaterally or bilaterally (n = 4-8). After intravenous administration of ¹¹¹In-C4-DTPA, SPECT/CT images were collected over 72 h at 4-6 time points. Additionally, gamma counting was performed for the blood, plasma, lungs, heart, liver, spleen, kidneys, muscle, and tumors at 72 h post-injection.

Results

¹¹¹In-C4-DTPA bound rapidly to circulating albumin upon injection, and the radiolabeled albumin conjugate thus formed was stable in murine and human serum. SPECT/CT images demonstrated a time-dependent uptake with a maximum of 2.7-3.8% ID/cm³ in the tumors at approximately 24 h post-injection and mean tumor/muscle ratios in the range of 3.2-6.2 between 24 and 72 h post-injection. The kidneys and bladder were the predominant elimination organs. Gamma counting at 72 h post-injection showed 1.3-2.5% ID/g in the tumors and mean tumor/muscle ratios in the range of 4.9-9.4.

Conclusion

¹¹¹In-C4-DTPA bound rapidly to circulating albumin upon injection and showed time-dependent uptake in the tumors demonstrating a potential for clinical application as a companion imaging diagnostic for albumin-binding anticancer drugs.

Aggregation-induced emission based PET probe for liver function imaging

A novel aggregation-induced emission based PET probe for liver function imaging was developed.