Conjugates of nucleoside analogs with lactosaminated human albumin to selectively increase the drug levels in liver blood: requirements for a regional chemotherapy

Artificial Glycoproteins as a Scaffold for Targeted Drug Therapy

Akin to a cellular "fingerprint," the glycocalyx is a glycan-enriched cellular coating that plays a crucial role in mediating cell-to-cell interactions. To gain a better understanding of the factors that govern in vivo recognition, artificial glycoproteins were initially created to probe changes made to the accumulation and biodistribution of specific glycan assemblies through biomimicry. As a result, the organ-specific accumulation for a variety of glycoproteins decorated with simple and/or complex glycans was identified. Additionally, binding trends with regard to cancer cell selectivity were also investigated. To exploit the knowledge gained from these studies, numerous groups thus became engaged in developing targeted drug methodologies based on the use of artificial glycoproteins. This has either been done through adopting the glycoprotein scaffold as a drug carrier, or to directly glycosylate therapeutic proteins/enzymes to localize their biological activity. The principle aim of this Review is to present the foundational research that has driven artificial glycoprotein-based targeting and subsequent adaptations with potential therapeutic applications.

Albumin-drug conjugates in the treatment of hepatic disorders

INTRODUCTION

This review deals with the use of serum albumin (SA) as a carrier for the selective delivery of drugs to liver cells.

AREAS COVERED

The synthesis and properties of the SA conjugates prepared to enhance the performance of the drugs used in the treatment of viral hepatitis, hepatocellular carcinoma (HCC), liver micrometastases and hepatic fibrosis are reported.

EXPERT OPINION

Studies in humans and laboratory animals demonstrated the capacity of SA conjugates to accomplish a liver targeting of the drugs, but at the same time underscored their limits and drawbacks, which can explain why to date these complexes did not reach a practical application. The major drawback is the need of administration by intravenous route, which prevents long-term daily treatments as required by some liver pathologies, such as chronic virus hepatitis and fibrosis. At present, only a conjugate carrying doxorubicin and addressed to the treatment of HCC showed in laboratory animals a solid potentiality to improve the value of the coupled drug. In the future, conjugation to SA could remain a successful strategy to permit the administration of drugs with rapid resolutive effects inside liver cells without causing severe extrahepatic adverse reactions.

Lactosaminated human albumin, a hepatotropic carrier of drugs

A selective delivery of drugs to liver can be obtained by conjugation with galactosyl terminating macromolecules. The conjugates selectively enter hepatocytes after interaction of the carrier galactose residues with the asialoglycoprotein receptor (ASGP-R) present only on these cells. Within hepatocytes the conjugates are transported to lysosomes where the drug is set free from the carrier, becoming concentrated in liver cells. The present article reviews the liver targeting of drugs obtained with lactosaminated albumin (L-SA), a neoglycoprotein exposing galactosyl residues. We report: (1) experiments which demonstrate the antiviral efficacy of the L-H(human)SA-ara-AMP conjugate in laboratory animals and in humans with viral hepatitis; (2) the property of a L-HSA conjugate with fluorodeoxyuridine to produce concentrations of the drug higher in hepatic sinusoids than in systemic circulation, with the potential of accomplishing a loco-regional, noninvasive treatment of liver micrometastases; (3) the increased anticancer activity of doxorubicin (DOXO) when coupled to L-HSA on all the forms of chemically induced rat hepatocellular carcinomas including those which do not express the ASGP-R.

Norcantharidin-associated galactosylated chitosan nanoparticles for hepatocyte-targeted delivery

In this study a new chitosan (CS) derivative, galactosylated chitosan (GC), was synthesized and used to prepare norcantharidin-associated GC nanoparticles (NCTD-GC NPs) by taking advantage of the ionic cross-linkage between the molecules of the anti-hepatocarcinoma medicine NCTD and of the GC as carrier. NCTD-GC NPs were obtained with average particle size of 118.68 +/- 3.37 nm, entrapment efficiency of 57.92 +/- 0.40%, and drug-loading amount of 10.38 +/- 0.06%. Several important factors influencing the entrapment efficiency, drug-loading amount, and particle size of NCTD-GC NPs were studied. The characteristics of sustained and pH-sensitive release of NCTD from NCTD-GC NPs in vitro were studied. In addition, in vitro cellular uptake and cytotoxicity of nanoparticles to hepatoma cell lines SMMC-7721 and HepG2 were also investigated. In vitro, and compared to CS-based NCTD-CS NPs, NCTD-GC NPs demonstrated satisfactory compatibility with hepatoma cells and strong cytotoxicity against hepatocellular carcinoma cells. In vivo antitumor activity of NCTD-GC NPs was evaluated in mice bearing H22 liver tumors. NCTD-GC NPs displayed tumor inhibition effect in mice, better than either the free NCTD or the NCTD-CS NPs. As a hepatocyte-targeting carrier, GC NPs are potentially promising for clinical applications.

FROM THE CLINICAL EDITOR

In this paper, a galactosylated chitosan (GC), was synthesized and norcantharidin (NCTD)-associated galactosylated chitosan nanoparticles (NCTDGC NPs) were generated by coupling NCTD--an anti-hepatocarcinoma drug--and GC as carrier. Compared to chitosan nanoparticles, NCTD-GC-NPs demonstrated satisfactory compatibility with hepatoma cells and strong cytotoxicity against the cells.

N/A

N/A

Doxorubicin coupled to lactosaminated human albumin remains confined within mouse liver cells after the intracellular release from the carrier

BACKGROUND

The hepatocyte receptor for asialoglycoproteins, which binds and internalises galactosyl terminating peptides, was found to be expressed also on the cells of the majority of hepatocarcinomas.

AIMS

To verify whether doxorubicin coupling to lactosaminated albumin, a galactosyl terminating neoglycoprotein, produces selective drug accumulation in hepatocytes with reduced concentrations in extra-hepatic tissues, thus facilitating the use of the drug in hepatocarcinoma treatment.

METHODS

Doxorubicin concentrations were measured in organs of mice injected with the free or coupled drug.

RESULTS

In mice injected with the coupled drug, the ratios between doxorubicin concentrations in liver and those in heart, intestine, spleen and kidney were 8-14 times higher than in animals that received the same dose of the free drug.

CONCLUSIONS

Due to the very efficient liver targeting of doxorubicin, the lactosaminated human albumin-doxorubicin conjugate appears to have the potential of improving the chemotherapy of hepatocellular carcinomas through the asialoglycoprotein receptor.

Synthesis and physicochemical characteristics of a liver-targeted conjugate of fluorodeoxyuridine monophosphate with lactosaminated human albumin

In previous experiments fluorodeoxyuridine monophosphate (FUdRMP) was conjugated with lactosaminated human albumin (L-HSA). Fluorodeoxyuridine (FUdR) is an anticancer agent and L-HSA is a hepatotropic carrier of drugs obtained by the covalent linkage of lactose residues to the albumin molecule. The conjugate was synthesised via the imidazolide of FUdRMP at alkaline pH. Peripheral venous administration of L-HSA-FUdRMP produced enhanced FUdR levels in hepatic blood and might accomplish a non-invasive loco-regional chemotherapy of liver micrometastases. In the present paper some physicochemical characteristics of L-HSA-FUdRMP are reported. Polyacrylamide gel electrophoresis indicated that the coupling reaction did not cause covalent aggregation of the L-HSA molecules. 31P NMR spectra of the conjugate showed that FUdRMP was linked to L-HSA by phosphoamide bonds to lysine and histidine residues, and the area of the peak due to the lysine bond represented more than 80% of the spectrum of L-HSA-FUdRMP. MALDI analysis revealed a partial degradation of the peptide backbone of the conjugate which could not be detected using other methods of analysis. The degradation was not caused by the coupling of lactose molecules to albumin, but rather a consequence of FUdRMP conjugation with L-HSA. This fragmentation was dependent on the pH of the medium used for the FUdRMP coupling reaction. By decreasing the pH to 7.5, conjugates were obtained with a lower drug load but with a substantially reduced fragmentation, which should be preferred for a clinical use of L-HSA-FUdRMP.