Inhibition of hepatitis B virus replication by vidarabine monophosphate conjugated with lactosaminated serum albumin

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.

The antitumor activity of a lactosaminated albumin conjugate of doxorubicin in a chemically induced hepatocellular carcinoma rat model compared to sorafenib

BACKGROUND

Worldwide, consistent survival benefit for chemotherapy in hepatocellular carcinoma (HCC) is a golden goal for concerned researchers. Nexavar^® (sorafenib) is the only approved agent that achieved touchable successes in this regard. Thus, there is a pressing medical need for new promising drugs to improve HCC therapy.

AIMS

our designed lactosaminated albumin conjugate of doxorubicin (L-HSA-DOXO) that rapidly and preferentially accumulates in the liver is compared, for the first time at its MTD, with doxorubicin and sorafenib, not only for antitumor efficacy but also for overall survival.

METHODS

HCC was induced in male Wistar rats with N-nitrosodiethylamine added to drinking water (100mg/L) for 8 weeks. Endpoints were antitumor efficacy, tolerability and overall survival.

RESULTS

L-HSA-DOXO proved to be superior at least over doxorubicin in the majority of assessed endpoints. Circulating AFP-L3% was diminished in L-HSA-DOXO (14.5%) and sorafenib (18.4%) groups compared to DENA (31.1%) and doxorubicin (29.5%) groups. This superiority was further confirmed by Western blot analyses of some novel HCC biomarkers. Survival study reinforced consistent benefits of both L-HSA-DOXO and sorafenib.

CONCLUSIONS

L-HSA-DOXO shows at least comparable activity to sorafenib which clinically achieves only ∼3 months overall survival benefit. Combination of these two agents could act beneficially or synergistically via two different modes of action to fight HCC.

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.

Efficacy of doxorubicin coupled to lactosaminated albumin on rat hepatocellular carcinomas evaluated by ultrasound imaging

BACKGROUND/AIMS

Doxorubicin was conjugated with lactosaminated human albumin, a hepatotropic drug carrier, in order to increase its efficacy in the treatment of hepatocellular carcinoma. In rats bearing hepatocellular carcinomas induced by diethylnitrosamine, lactosaminated human albumin coupled doxorubicin enhanced the drug concentrations in the tumours and lowered those in extrahepatic tissues. The aim of the present study was to investigate the effects of lactosaminated human albumin coupled doxorubicin on the growth of established rat hepatocellular carcinomas induced by diethylnitrosamine.

METHODS

Lactosaminated human albumin coupled doxorubicin and the free drug were i.v. administered to rats twice a week for 4 weeks at the single dose of 1 microg/g. Growth of individual tumours was followed through time by ultrasonography.

RESULTS

In the control animals injected with saline the mean area of the tracked tumours significantly increased during the whole period of treatment. In the group of rats treated with lactosaminated human albumin coupled doxorubicin the mean area of the followed hepatocellular carcinomas remained practically unchanged. The free drug inhibited tumour growth only in the first period of drug administration. Lactosaminated human albumin coupled doxorubicin also hindered the development of new neoplastic nodules, which was unaffected by the free drug.

CONCLUSIONS

The results support lactosaminated human albumin coupled doxorubicin as a promising agent for a systemic chemotherapy of hepatocellular carcinomas to treat noncurable patients.

A conjugate of doxorubicin with lactosaminated albumin enhances the drug concentrations in all the forms of rat hepatocellular carcinomas independently of their differentiation grade

BACKGROUND/AIMS

Doxorubicin (DOXO) was coupled to lactosaminated human serum albumin (L-HSA) in order to enhance the drug concentration in the well differentiated hepatocellular carcinomas (HCCs), which can accumulate L-HSA through the asialoglycoprotein receptor. In the present experiments we compared the DOXO concentrations produced by this conjugate (L-HSA-DOXO) and by the uncoupled drug in the well, moderately, and poorly differentiated rat HCCs.

METHODS

The same dose (1 microg/g) of free or L-HSA coupled-DOXO was injected in rats with HCCs induced by diethylnitrosamine. At different times, the animals were killed and the neoplastic nodules of liver were isolated. Their differentiation grade was determined histologically and their DOXO content was measured.

RESULTS

Unexpectedly, we found that also in the poorly differentiated forms of HCCs, which display no or only a poor capacity of accumulating L-HSA, the conjugate raised DOXO levels that were approximately twofold higher than those produced by the free drug.

CONCLUSIONS

The conjugate L-HSA-DOXO could improve the potential of DOXO in the treatment of all HCCs, including the poorly differentiated tumors that are the common forms in the advanced disease for which an effective chemotherapy is particularly needed.

Doxorubicin coupled to lactosaminated albumin: Effects on rats with liver fibrosis and cirrhosis

BACKGROUND

The conjugate of doxorubicin with lactosaminated human albumin has the potential of increasing the doxorubicin efficacy in the treatment of hepatocellular carcinomas expressing the asialoglycoprotein receptor. However, coupled doxorubicin also accumulates in the liver, which might damage hepatocytes.

AIMS

To verify whether coupled doxorubicin impairs liver function in rats with liver fibrosis and cirrhosis.

METHODS

Coupled doxorubicin was administered using the same schedule which exerted an antineoplastic effect on rat hepatocellular carcinomas (4-weekly injections of doxorubicin at 1 microg/g). Liver fibrosis/cirrhosis was produced by carbon tetrachloride (CCl4) poisoning. Liver samples were studied histologically. Serum parameters of liver function and viability were determined.

RESULTS

In normal rats, administration of coupled doxorubicin neither caused microscopic changes of hepatocytes nor modified serum liver parameters. In rats with fibrosis/cirrhosis, although a selective doxorubicin accumulation within the liver followed coupled doxorubicin administration, the drug did not have a detrimental effect on the histology of the liver and, among serum liver tests, only alanine aminotransferase and aspartate aminotransferase levels were moderately modified.

CONCLUSIONS

Coupled doxorubicin can be administered to rats with liver fibrosis/cirrhosis without inducing a severe liver damage. If further studies will confirm the efficacy and safety of this compound, coupled doxorubicin therapy may open a new perspective in the treatment of hepatocellular carcinoma.

Novel delivery methods for treatment of viral hepatitis: an update

Viral hepatitis represents the most common cause of chronic liver disease worldwide. Currently approved therapies for chronic hepatitis B include IFN, an immune modulator, and nucleoside analogues lamivudine and adefovir. For chronic hepatitis C, a combination of pegylated IFN-alpha and ribavirin represents the standard treatment. However, currently available treatments for both these viruses are effective only in a limited number of patients, are costly, prolonged, associated with significant side effects and require a substantial commitment from the patients and healthcare providers. A number of novel antiviral treatments, together with strategies to enhance the response to current therapies, are being explored at present. For all new therapies, as well as for improving existing treatments, selective delivery of medications into liver cells would be desirable to enhance antiviral activity and avoid systemic side effects. New achievements in the field of drug and gene delivery against chronic hepatitis to the liver are reviewed here.

Doxorubicin coupled to lactosaminated albumin inhibits the growth of hepatocellular carcinomas induced in rats by diethylnitrosamine

BACKGROUND/AIMS

The hepatocyte receptor for asialoglycoproteins internalizes galactosyl terminating macromolecules which can be used as hepatotropic drug carriers. Since this receptor is also expressed on the cells of well differentiated human hepatocellular carcinomas (HCCs), we studied whether conjugation of doxorubicin (DOXO) with lactosaminated human albumin (L-HSA) increases the drug efficacy on HCCs induced in rats by diethylnitrosamine (DENA).

METHODS

DENA was given in the drinking water for 8 weeks. One week after the last day of DENA administration, animals were randomly assigned to three groups. Each group was administered with either saline, free or coupled DOXO (1 microg/g). Rats received 4 weekly intravenous injections. One week after the last administration, rats were killed and HCC development was evaluated by counting the tumor nodules on the surface of hepatic lobes.

RESULTS

In rats treated with L-HSA coupled DOXO the number of neoplastic nodules was significantly lower (P < 0.05) than that counted in animals injected with saline or with free DOXO. Coupled DOXO did not decrease body rat weight, which was markedly reduced by the free drug.

CONCLUSIONS

Conjugation with L-HSA increased the antineoplastic efficacy and decreased the systemic toxicity of DOXO administered to rats with HCCs produced by DENA.

Enhanced uptake of lactosaminated human albumin by rat hepatocarcinomas: implications for an improved chemotherapy of primary liver tumors

BACKGROUND/AIMS

The hepatocyte receptor for asialoglycoproteins (ASGP-R) internalizes macromolecules exposing galactosyl residues (MEGRs) which can be used as liver-addressed drug carriers. This receptor was also found on the cells of the large majority of well differentiated hepatocarcinomas (HCCs). The aim of the present experiments was to ascertain whether ASGP-R of HCCs is functionally active and these tumors can internalize higher quantities of MEGRs than extra-hepatic tissues.

METHODS

We injected radioactive lactosaminated human albumin (L-HSA) in rats with HCCs produced by nitroso-diethylamine and measured the radioactivity of tumors, surrounding liver, heart, intestine and kidney. L-HSA is a MEGR successfully used in humans as a hepatotropic drug carrier.

RESULTS

The levels of radioactivity of HCCs were two to three times lower than those of surrounding liver, but several times higher than those of extra-hepatic tissues. L-HSA accumulation in the tumors mainly occurred via the ASGP-R, as indicated by the 20 times lower penetration of non-lactosaminated HSA. L-HSA uptake by the well-differentiated tumors were four times higher compared with that by the poorly differentiated forms.

CONCLUSIONS

The present results suggest that in the chemotherapy of HCCs expressing the ASGP-R the extra-hepatic toxicity of anticancer agents can be reduced by conjugation to L-HSA.

A novel method for coupling doxorubicin to lactosaminated human albumin by an acid sensitive hydrazone bond: synthesis, characterization and preliminary biological properties of the conjugate

The expression of the asialoglycoprotein receptor on the cells of the large majority of the well differentiated hepatocellular carcinomas can be exploited to improve the chemotherapy of these tumours by coupling anticancer agents to macromolecules taken up by the receptor. In line with this approach, in previous experiments we coupled doxorubicin (DOXO) to lactosaminated human albumin (L-HSA) using the (6-maleimidocaproyl)hydrazone derivative of the drug as an acid sensitive linker. Encouraging results were obtained in laboratory animals using L-HSA-DOXO. This conjugate, however, has the disadvantage of a difficult synthesis, which requires protein thiolation with iminothiolane and can hinder its preparation on a large scale. Here we describe a very simple method of coupling. The HS-groups required for the reaction with the maleimide moiety of DOXO-EMCH are made available in L-HSA by a cleavage of the protein disulphides achieved with tris(2-carboxyethyl) phosphine (TCEP). Contrary to thiolic reducing agents, the use of TCEP eliminates the need of an inert atmosphere and allows a one-step coupling reaction, without purification of the reduced protein before the addition of DOXO-EMCH. As the previous L-HSA-DOXO conjugate, the new conjugate accomplishes a very efficient liver targeting of the drug. This novel method of synthesis should facilitate the preparation of L-HSA-DOXO in the amounts required for clinical studies.

Liver-Targeted Drug Delivery Using HepDirect Prodrugs

Targeting drugs to specific organs, tissues, or cells is an attractive strategy for enhancing drug efficacy and reducing side effects. Drug carriers such as antibodies, natural and manmade polymers, and labeled liposomes are capable of targeting drugs to blood vessels of individual tissues but often fail to deliver drugs to extravascular sites. An alternative strategy is to use low molecular weight prodrugs that distribute throughout the body but cleave intracellularly to the active drug by an organ-specific enzyme. Here we show that a series of phosphate and phosphonate prodrugs, called HepDirect prodrugs, results in liver-targeted drug delivery following a cytochrome P450-catalyzed oxidative cleavage reaction inside hepatocytes. Liver targeting was demonstrated in rodents for MB06866 [(2R,4S)-9-[2-[4-(3-chlorophenyl)-2-oxo-1,3,2-dioxaphosphorinan-2-yl]methoxyethyl]adenine (remofovir)], a Hep-Direct prodrug of the nucleotide analog adefovir (PMEA), and MB07133 [(2R,4S)-4-amino-1-[5-O-[2-oxo-4-(4-pyridyl)-1,3,2-dioxaphosphorinan-2-yl]-beta-d-arabinofuranosyl]-2(1H)-pyrimidinone], a HepDirect prodrug of cytarabine (araC) 5'-monophosphate. Liver targeting led to higher levels of the biologically active form of PMEA and araC in the liver and to lower levels in the most toxicologically sensitive organs. Liver targeting also confined production of the prodrug byproduct, an aryl vinyl ketone, to hepatocytes. Glutathione within the hepatocytes rapidly reacted with the byproduct to form a glutathione conjugate. No byproduct-related toxicity was observed in hepatocytes or animals treated with HepDirect prodrugs. A 5-day safety study in mice demonstrated the toxicological benefits of liver targeting. These findings suggest that HepDirect prodrugs represent a potential strategy for targeting drugs to the liver and achieving more effective therapies against chronic liver diseases such as hepatitis B, hepatitis C, and hepatocellular carcinoma.

Liver-targeted doxorubicin: effects on rat regenerating hepatocytes

BACKGROUND/AIMS

The conjugate of doxorubicin (DOXO) with lactosaminated human albumin (L-HSA) has the potential of improving DOXO efficacy in the treatment of hepatocellular carcinomas (HCCs) expressing the asialoglycoprotein receptor (ASGP-R). In view of an adjuvant chemotherapy with L-HSA-DOXO after the surgical removal of the tumour, in the present experiments we verified whether DOXO accumulation produced by the conjugate can impair the liver regeneration following hepatic resection in non-cirrhotic liver.

METHODS

Using saline-injected hepatectomised rats as controls, we studied the effects of the conjugate on the ultrastructure of regenerating hepatocytes and evaluated [3H]thymidine incorporation, mitotic index and rate of DNA recovery in the liver remnant.

RESULTS

L-HSA-DOXO caused a selective drug accumulation in liver remnant, with low DOXO levels in extra-hepatic tissues. It did not change the ultrastructure of hepatocytes and did not increase serum alanine aminotransferase. It decreased [3H]thymidine incorporation and mitotic index, causing a moderate delay in hepatic DNA recovery.

CONCLUSIONS

The experiments indicate a substantial resistance of rat regenerating hepatocytes to high intracellular concentrations of DOXO. They support the possibility of using L-HSA-DOXO in an adjuvant chemotherapy after the surgical removal of HCCs which maintain the ASGP-R.

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.

Floxuridine coupling with lactosaminated human albumin to increase drug efficacy on liver micrometastases

BACKGROUND

Conjugates of nucleoside analogues with galactosyl terminating peptides selectively enter hepatocytes through the asialoglycoprotein receptor. After intracellular release from the carrier, the drugs partly exit from hepatic cells into hepatic blood.

AIMS

To establish whether administration of a conjugate of floxuridine with lactosaminated human albumin selectively enhances drug concentrations in hepatic blood. Floxuridine is a fluoropyrimidine active on human colorectal cancer, a tumour which metastasises first to the liver.

METHODS

In rats injected with free or conjugated floxuridine, plasma levels of the drug were determined in hepatic veins and in inferior vena cava, in order to measure drug concentrations in hepatic blood and in the systemic circulation, respectively.

RESULTS

Ratios between floxuridine levels in hepatic veins and those in systemic circulation were found to be seven times higher in rats injected with the conjugate (p=0.000).

CONCLUSIONS

The present results suggest that coupling to lactosaminated albumin might improve the effect of floxuridine in adjuvant chemotherapy of colorectal cancer by exposing the cells of liver micrometastases (nourished by hepatic sinusoids) to enhanced drug concentrations.

Ribavirin conjugated with lactosaminated poly-L-lysine: selective delivery to the liver and increased antiviral activity in mice with viral hepatitis

Ribavirin (RIBV) is a useful drug in the treatment of chronic type C hepatitis but displays a toxicity for red blood cells (RBC), which limits its dosage and necessitates withdrawal in some patients. Selective concentration of RIBV in liver should improve therapeutic results. Liver targeting can be achieved by coupling the drug to galactosyl-terminating peptides, which specifically enter hepatocytes. In the present work, we conjugated RIBV to lactosaminated poly-L-lysine (L-Poly(Lys)), a hepatotropic carrier enabling intramuscular (IM) administration of conjugates. The L-Poly(Lys)-RIBV conjugate had a heavy drug load (312-327 microg of RIBV in 1 mg of conjugate) and was very soluble in 0.9% NaCl (200 mg/mL). The conjugate was devoid of acute toxicity in mouse. When incubated with human or mouse blood, it did not release the drug. After IM administration to mice, the conjugate was selectively taken up by the liver, where the drug was released in a pharmacologically active form. This was demonstrated using mice infected with a strain of murine hepatitis virus (MHV) sensitive to RIBV. Coupled RIBV, IM injected, inhibited MHV replication in liver at a daily dose two to three times lower than that of the free drug. In mice IM injected with a conjugate tritiated in the RIBV moiety, the ratios between the levels of radioactivity in liver and RBC were two times higher than in animals injected with free tritiated RIBV. In conclusion, the present results support the possibility that the chemotherapeutic index of RIBV in chronic type C hepatitis can be increased by conjugation with L-Poly(Lys).

Hepatotropic conjugate of adenine arabinoside monophosphate with lactosaminated poly-L-lysine. Synthesis of the carrier and pharmacological properties of the conjugate

BACKGROUND/AIMS

The hepatotropic conjugate of adenine arabinoside monophosphate with lactosaminated poly-L-lysine (L-Poly(Lys)) must have a high solubility in order to be injected in a small volume compatible with the intramuscular route. In this paper the molecular weights of Poly(Lys) which allowed the synthesis of conjugates with the properties of high solubility and limited loss by the kidney were determined and a procedure for obtaining Poly(Lys) preparations with the required range of polymerization has been described.

METHODS

Conjugates were prepared using Poly(Lys) of different molecular weights obtained by the procedure described here or purchased from a commercial source. Their solubility and renal loss in mice was determined.

RESULTS

Poly(Lys) with molecular weights ranging from 45,000 and 65,000 Da guarantees high solubility and low renal elimination of the conjugates. Conjugate preparations with these properties, intramuscularly administered to woodchuck hepatitis virus-infected woodchucks for 37 days at a daily dose of 5.8 mg/kg exerted a strong antiviral activity. These preparations were devoid of acute toxicity in rat and caused no toxic effects when injected intramuscularly daily for 28 days at a dose ten times higher than that active in woodchucks.

CONCLUSIONS

The results support the possibility of a clinical use of L-Poly(Lys) to obtain liver targeting of adenine arabinoside monophosphate for the treatment of chronic hepatitis B virus infection.

Hepatic purine and pyrimidine metabolism: implications for antiviral chemotherapy of viral hepatitis

The use of nucleoside analogues as antiviral agents is expanding. For most nucleoside analogues, intracellular phosphorylation is the major prerequisite for activity. Antiviral activity may be limited by poor uptake, absence of appropriate activating enzymes, catabolism, and competition from endogenous nucleotides. Appreciation of these factors, which are species-, tissue- and cell-specific is important in the understanding of the pharmacology and toxicology of nucleoside analogues. The use of nucleoside analogues against the agents of viral hepatitis is inherently problematic for many reasons including active hepatic nucleoside catabolism, probable absence of virus-specific activating enzymes, competition from endogenous nucleotides synthesised de novo or derived from RNA turnover, and factors related to mitochondrial toxicity. Despite these drawbacks, some nucleoside analogues have been found efficacious against hepatitis B virus and it is likely that as knowledge of their mechanism of action accumulates, their efficacy can be improved both by rational drug design and by use in combination with other drugs, including interferon.

Selective delivery to the liver of antiviral nucleoside analogs coupled to a high molecular mass lactosaminated poly-L-lysine and administered to mice by intramuscular route

In order to obtain hepatotropic conjugates of antiviral drugs suitable for intramuscular administration, three nucleoside analogs (adenine arabinoside monophosphate, ribavirin and azidothymidine) were coupled to a high molecular mass lactosaminated poly-L-lysine. The conjugates had a high molar ratio drug/conjugate and after intramuscular administration to mice, were selectively taken up by the liver and eliminated by the kidney only in minute quantities. The high molar ratio and low renal elimination are important properties not possessed by conjugates previously prepared by using a small molecular mass lactosaminated poly-L-lysine. The conjugate with adenine arabinoside monophosphate (ara-AMP) was found to be devoid of acute toxicity for mice and in spite of its high molecular dimension (Mn = ca. 72,500) did not induce antibodies in this animal after repeated intramuscular injections. This conjugate could have two advantages over a similar complex of ara-AMP with lactosaminated human albumin currently under clinical trials for the treatment of chronic type B hepatitis which must be injected intravenously: it might provide better patient compliance since it is injectable intramuscularly and could introduce larger amounts of ara-AMP into hepatocytes due to its higher drug/carrier molar ratio.

Receptor mediated glycotargeting

Glycotargeting relies on carrier molecules possessing carbohydrates that are recognized and internalized by cell surface mammalian lectins. Numerous types of glycotargeting vehicles have been designed based on the covalent attachment of saccharides to proteins, polymers and other aglycones. These carriers have found their major applications in antiviral therapy, immunoactivation, enzyme replacement therapy and gene therapy. This review compared different types of glycotargeting agents and the lectins which have been successfully targeted to treat both model and human diseases. It may be concluded that the discovery of new mammalian lectins which endocytose their ligands will lead to the rapid development of new glycotargeting agents founded on the principles of carbohydrate-protein interactions.

Treatment of chronic hepatitis B

Chronic infection with the hepatitis B virus (HBV) is a major cause of worldwide morbidity and mortality. A large number of therapeutic approaches has been tried, including interferon (IFN), nucleoside analogues and immunomodulators. To date controlled clinical trials have shown that only IFN is of long-term value but many patients fail to respond to treatment. New approaches to treating patients with IFN-resistant hepatitis B are currently undergoing clinical and experimental evaluation, and it seems likely that new therapeutic agents will be available in the near future.

A conjugate of lactosaminated poly-L-lysine with adenine arabinoside monophosphate, administered to mice by intramuscular route, accomplishes a selective delivery of the drug to the liver

A conjugate of the antiviral agent adenine arabinoside monophosphate (ara-AMP) with a low molecular mass lactosaminated poly-L-lysine, administered to mice by i.m. route, selectively delivers the drug to the liver. In mice the conjugate is devoid of acute toxicity even at high dose (1.3 mg/g) and injected i.m. for 20 days does not induce antibodies. Moreover it is highly soluble in water; this means that a pharmacologically active dose may be administered in a small volume compatible with the i.m. route. Compared to the similar ara-AMP complex with lactosaminated albumin which must be injected intravenously, the present conjugate might assure a better compliance of patients with hepatitis B virus infection for a long lasting, liver targeted antiviral treatment.

The pathogenesis of vacuoles produced in rat and mouse liver cells by a conjugate of adenine arabinoside monophosphate with lactosaminated albumin

A conjugate of adenine arabinoside monophosphate with lactosaminated albumin produced vacuoles in hepatic cells of rats and mice when given at doses 5-10 times higher than that (35 mg/kg) capable of inhibiting hepatitis B virus replication in patients with chronic hepatitis B. The vacuoles were due to the swelling of secondary lysosomes probably caused by incapacity of the lysosomal enzymes to rapidly digest large amounts of conjugate into products able to cross the lysosomal membrane. Although vacuoles progressively disappeared when conjugate administration was discontinued, the present observation suggests caution in giving the conjugate to man at daily doses higher than 35 mg/kg.

Adenine arabinoside monophosphate and acyclovir monophosphate coupled to lactosaminated albumin reduce woodchuck hepatitis virus viremia at doses lower than do the unconjugated drugs

The woodchuck was selected to study the efficacy of liver-targeted antiviral drugs on hepadnavirus replication. Nineteen woodchucks chronically infected with woodchuck hepatitis virus were treated with adenine arabinoside monophosphate or acyclovir monophosphate, either free or conjugated with the liver-targeting molecule lactosaminated human serum albumin. Circulating woodchuck hepatitis virus DNA levels remained unchanged in untreated animals and in those receiving the carrier lactosaminated human serum albumin alone; in contrast, they were consistently lower after 5 days of treatment with the antiviral drugs. Free and conjugated adenine arabinoside monophosphate were active at doses of 10 and 0.75 mg/kg, respectively, and free and coupled ACVMP were active at doses of 20 and 2.6 mg/kg, respectively. These results indicate that the dosages of adenine arabinoside monophosphate and acyclovir monophosphate required to inhibit hepadnavirus growth can be sharply reduced by coupling the drugs to lactosaminated human serum albumin.

A nonradioactive riboprobe assay for the detection of hepatitis B virus DNA in human sera

Sequences of hepatitis B virus DNA were detected specifically in the sera of infected individuals by a non-radioactive riboprobe nucleic acid hybridization assay. The nucleic acids contained in serum specimens were prepared by an overnight proteinase K-/SDS-digest, phenol/chloroform-extraction and ethanol-precipitation, and immobilized on nylon membranes by the dot-blot technique. Digoxigenin-labelled 1.4 kb RNA-probes were generated by the phage sp 6 RNA-polymerase from a linearized HBV DNA transcription template containing the appropriate promoter. Hybridized probes were detected by alkaline phosphatase-conjugated sheep anti-digoxigenin Fab-fragments, and 5-bromo-4-chloro-3-indolylphosphate (BCIP) and nitroblue tetrazolium salt (NBT) as chromogenic substrates for the subsequent ELISA procedure. With a detection limit of 0.5-1.0 pg HBV DNA and a high specificity, the results were comparable to those obtained by the standard assay employing radioactively labeled DNA-probes.

Perspectives in antiviral chemotherapy

The current progress in antiviral therapy is related to our better understanding of the viral multiplication, with potential targets for specific antiviral action at each step of the multiplication cycle inside the infected cell. Amantadine and Rimantadine are anti-influenza A drugs interfering with the penetration and the release of the virus. Most of the other antiviral drugs which are clinically available have the same target in common, namely the viral DNA polymerase. This holds true for modified nucleosides such as Acycloguanosine (Acyclovir), DHPG, Adenine-Arabinoside, Azidothymidine as well as pyrophosphate derivatives such as phosphonoformic acid. Unfortunately the antiviral chemotherapy must confront 3 obstacles: 1) a possible interference with the normal cellular metabolism, leading to residual cytotoxic side effects; 2) the genetic variability of the viruses, producing drug-resistant mutants and 3) the inability of any antiviral chemotherapeutic agent known to date to eradicate latent viral infection. A new approach of the control of latent infection is suggested with anti sense oligonucleotides of hybridons.

Review article: the management of hepatitis A, B, D and non-A non-B

This paper reviews the modern management of viral hepatitis: hepatitis A, hepatitis B, hepatitis D and non-A non-B hepatitis. It describes the treatment of uncomplicated acute viral hepatitis, complicated acute viral hepatitis, and chronic viral hepatitis. The roles for corticosteroids, synthetic nucleotides, and interferons are reviewed. Finally, passive and active immunization against viral hepatitis are discussed.

Treatment of acute and chronic viral hepatitis

Over the 12 years since the first introduction of interferon for the treatment of chronic hepatitis B, progress has apparently been slow. Nevertheless, it now appears that at least one third of chronic hepatitis virus carriers, particularly those with more severe disease, and a similar, perhaps greater, proportion of those with chronic parenteral non-A, non-B hepatitis, can be successfully treated with alpha-interferon. In the not too distant future, controlled trials of alpha-interferons in these situations will be complete and they will be a yardstick by which other future therapies can be judged. Already a number of trials are in progress to determine which agents might, in addition to interferon, augment the response rates. The situation clinically is analogous to that for tuberculosis in the 1950s and for cancer chemotherapy only a decade or so ago. The prospects of prevention of the progression to cirrhosis, and perhaps in the long term reduction in the incidence of hepatocellular carcinoma, are exciting, and with the introduction of a number of new cytokines available through recombinant technology, each with novel antiviral activities, the future prospects are exciting indeed.