Synthesis and biological evaluation of a novel ⁶⁸Ga-labeled GalNAc-PET probe for asialoglycoprotein receptor imaging

Purpose: The asialoglycoprotein receptor (ASGPR), expressed exclusively on mammalian hepatocyte membranes, recognizes ligands terminated with beta-D-galactose (Gal) and N-acetylglucosamine (GalNAc). This study aims to develop a Ga-68-labeled monovalent GalNAc derivative that particularly interacts with ASGPR. It also aims to assess the potential utility of this derivative in visualizing ASGPR-related liver dysfunction using positron emission tomography (PET)/ computed tomography (CT) imaging. Methods: The PET imaging probe Ga-68-NOTA-GalNAc was developed and characterized with regard to radiochemical purity, biocompatibility, biodistribution patterns, and specific ASGPR-targeting ability. Groups of normal mice, mice with acute liver injury (ALI) induced by CCl4, mice with early-stage liver fibrosis induced by CCl4, mice with nonalcoholic fatty liver disease (NAFLD), and orthotopic HepG2 hepatoma-bearing mice were imaged with Ga-68-NOTA-GalNAc PET to evaluate the potential of this technique in monitoring ASGPR-related liver dysfunction. Results: Ga-68-NOTA-GalNAc, a hydrophilic compound with high radiochemical purity (>99 %) and good liver targeting ability, particularly binds ASGPR on the surface of hepatocytes with moderate affinity (KD = 6.82 mu M). Compared with control, ASGPR-related liver dysfunction groups, even the group of mice with ALI (P <0.0001), revealed sensitive distinctions in the liver uptake value of Ga-68-NOTA-GalNAc. The Ga-68-NOTA-GalNAc absorbed in the livers of mice with early-stage liver fibrosis and NAFLD group is significantly less than that absorbed in the livers of mice in the normal group (P <0.0001). Hepatoma can be visualized in orthotopic HepG2 hepatoma-bearing mice because of different radioactivity accumulated in the nontumor region and lesion region, corresponding to the ASGPR expression confirmed with immunohistochemical staining. Conclusion: Ga-68-NOTA-GalNAc has the potential to be a specific, noninvasive, and sensitive PET imaging agent for ASGPR-related liver dysfunction.