Stimulation of liver-directed cholesterol flux in mice by novel N-acetylgalactosamine-terminated glycolipids with high affinity for the asialoglycoprotein receptor

Synthesis and Evaluation of New Trivalent Ligands for Hepatocyte Targeting via the Asialoglycoprotein Receptor

Since the asialoglycoprotein receptor (also known as the "Ashwell-Morell receptor" or ASGPR) was discovered as the first cellular mammalian lectin, numerous drug delivery systems have been developed and several gene delivery systems associated with multivalent ligands for liver disease targeting are undergoing clinical trials. The success of these systems has facilitated the further study of new ligands with comparable or higher affinity and less synthetic complexity. Herein, we designed two novel trivalent ligands based on the esterification of tris(hydroxymethyl) aminomethane (TRIS) followed by the azide-alkyne Huisgen cycloaddition with azido N-acetyl-d-galactosamine. The presented triazolyl glycoconjugates exhibited good binding to ASGPR, which was predicted using in silico molecular docking and assessed by a surface plasmon resonance (SPR) technique. Moreover, we demonstrated the low level of in vitro cytotoxicity, as well as the optimal spatial geometry and the required amphiphilic balance, for new, easily accessible ligands. The conjugate of a new ligand with Cy5 dye exhibited selective penetration into HepG2 cells in contrast to the ASGPR-negative PC3 cell line.

Development of lipid nanoparticle formulations of siRNA for hepatocyte gene silencing following subcutaneous administration

Recently developed lipid nanoparticle (LNP) formulations of siRNA have proven to be effective agents for hepatocyte gene silencing following intravenous administration with at least three LNP-siRNA formulations in clinical trials. The aim of this work was to develop LNP-siRNA systems for hepatocyte gene silencing that can be administered subcutaneously (s.c.). Three parameters were investigated, namely LNP size, residence time of the polyethylene glycol (PEG)-lipid coating and the influence of hepatocyte-specific targeting ligands. LNP sizes were varied over the range of 30 to 115 nm in diameter and PEG-lipid that dissociates rapidly (PEG-DMG) and slowly (PEG-DSG) were employed. In mice, results show that large (~80 nm) LNP exhibited limited accumulation in the liver and poor Factor VII (FVII) gene silencing at 1mg siRNA/kg body weight. Conversely, small (~30 nm) LNP systems showed maximal liver accumulation yet still had minimal activity. Interestingly, intermediate size (~45 nm) LNP containing PEG-DSG exhibited nearly equivalent liver accumulation as the smaller systems following s.c. administration but reduced FVII levels by 80% at 1mg siRNA/kg body weight. Smaller systems (~35 nm diameter) containing either PEG-DMG or PEG-DSG were less active; however addition of 0.5 mol.% of a GalNAc-PEG lipid to these smaller systems improved activity to levels similar to that observed for the ~45 nm diameter systems. In summary, this work shows that appropriately designed LNP-siRNA systems can result in effective hepatocyte gene silencing following s.c administration.

Evaluating the potential of a new isotope-labelled glyco-ligand for estimating the remnant liver function of schistosoma-infected mice

A new glyco-derivative compound (OCTAM) was developed and labelled with isotope to form (188) Re-OCTAM as a candidate nuclear medicine imaging agent for testing the liver function. We evaluated the potential of isotope-labelled OCTAM for estimating the remnant liver function in vitro and in vivo schistosoma-infected mice. The affinity of OCTAM to liver asialoglycoprotein receptors (ASGPR) was assessed by competitive inhibition assay in vitro. In vivo assessments were performed to score the remnant liver function in mice at different schistosomal infection stages. OCTAM binds specifically to ASGPR and showed competitive inhibition of anti-ASGPR antibody binding to hepatocytes, and was higher than that of other galactosyl ligands. Micro-SPECT/CT images of uninfected mice revealed strong liver uptake. Quantified serial images of mice infected for 9, 12 and 18 weeks showed delayed liver uptake, and the retention of uptake was inversely correlated with stage and grade of schistosoma infection. Pathological and biochemical analysis demonstrated that gradually accumulating liver injury caused by infection significantly influenced uptake of (188) Re-OCTAM. Hepatic ASGPR expression diminished only in the chronic infection stage. This study demonstrated that the isotope-labelled OCTAM could accumulate in the liver, might have potential as an imaging agent for in vivo hepatic function evaluation of schistosomiasis.

Detection of circulating tumor cells in patients with hepatocellular carcinoma using an improved asialoglycoprotein receptor-based separation method

AIM: To introduce a novel magnetic cell separation system which allows for immunomorphological identification and enumeration of circulating tumor cells (CTCs) in patients with hepatocellular carcinoma (HCC).

METHODS: The asialoglycoprotein receptor (ASGPR) is a transmembrane protein expressed exclusively on the surface of hepatocytes. We have recently developed a sensitive and specific system mediated by the interaction of the ASGPR with its ligand to magnetically separate CTCs in HCC patients. In the system, HCC cells were bound by biotinylated asialofetuin, an ASGPR ligand, and subsequently labeled by anti-biotin antibody-coated magnetic beads, followed by magnetic separation. The separated HCC cells were then identified by immunofluorescence staining using the hepatocyte-specific antibody Hep Par 1. In this study, we used EDTA instead of heparin for anticoagulation because heparin could cause the presence of gels in cell suspension, which affected the passage of cells through the separation column and reduced the separation efficiency. The recovery, specificity and sensitivity of the HCC CTC separation and detection system were determined by performing Hep3B cell spiking experiments.

RESULTS: Calcium chelating agent EDTA was used for anticoagulation instead of heparin in some steps of the original method and gel phenomenon no longer appeared in the cell suspension. The cell spiking experiments showed that when there were 10, 30, 90, 270 and 810 Hep3B cells spiked into five milliliters of peripheral blood from healthy volunteers, the average recovery was ≥ 70% at each spiking level and the recovery of the modified method was higher than that of the original method (P < 0.05).

CONCLUSION: We have developed a new tool that allows for highly sensitive and specific separation and detection of CTCs in HCC patients. It may be clinically useful for diagnosis and monitoring of HCC. The cell spiking experiments showed that the recovery of the modified method was higher than that of the original method.