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

Design, synthesis and biological applications of glycopolypeptides

Carbohydrates play essential structural and biochemical roles in all living organisms. Glycopolymers are attractive as well-defined biomimetic analogs to study carbohydrate-dependent processes, and are widely applicable biocompatible materials in their own right. Glycopolypeptides have shown great promise in this area since they are closer structural mimics of natural glycoproteins than other synthetic glycopolymers and can serve as carriers for biologically active carbohydrates. This review highlights advances in the area of design and synthesis of such materials, and their biomedical applications in therapeutic delivery, tissue engineering, and beyond.

Management of tumor growth and angiogenesis in triple-negative breast cancer by using redox nanoparticles

In cancer, angiogenesis is a critical phenomenon of nascent blood vessel development to facilitate the oxygen and nutrient supply prerequisite for tumor progression. Therefore, targeting tumors at the angiogenesis step may be significant to prevent their advanced progression and metastasis. Although angiogenesis inhibitors can limit the further growth of tumors, complete eradication of tumors may not be possible by monotherapy alone. Therefore, a therapeutic regimen targeting both tumor growth and its vasculature is essential. Because reactive oxygen species (ROS) are fundamental to both angiogenesis and tumor growth, the use of antioxidants may be an effective dual approach to inhibit tumors. We previously confirmed that our original antioxidant nitroxide radical-containing nanoparticles (RNPs) such as pH-sensitive RNP^N_, and pH-insensitive RNP^O, effectively attenuates the tumorigenic and metastasis potentials of triple-negative breast cancer. In this study, we further investigated the efficacy of RNPs to limit the tumor progression by inhibiting the ROS-regulated cancer angiogenesis in a triple-negative breast cancer model. Here, we confirmed that RNPs significantly inhibited in vitro angiogenesis, attributed to the downregulation of the ROS-regulated angiogenesis inducer, vascular endothelial growth factor (VEGF) in the breast cancer cell line (MDA-MB231) and human umbilical vein endothelial cells (HUVEC), which was consistent with decreased cellular ROS. TEMPOL, a low-molecular-weight (LMW) control antioxidant, exhibited anti-angiogenic effects accompanied by cytotoxicity to the endothelial cells. In an in vivo xenograft model for breast cancer, RNPs exerted significant anti-tumor effect due to the decreased expression of tumor VEGF, which prevented accumulation of the endothelial cells. It should be noted that such efficacy of RNPs was obtained with negligible off-target effects. On the other hand, TEMPOL, because of its size, exerted anti-angiogenesis effect accompanied with injuries to the kidneys, which corroborated with previous reports. Our findings imply that RNPs are more potential antioxidants than their LMW counterparts, such as TEMPOL, for the management of breast cancers.

Reactive oxygen species-scavenging nanomedicines for the treatment of oxidative stress injuries

This Progress Report describes a development of two types of reactive oxygen species (ROS)-scavenging nanomedicines for the treatment of oxidative stress injuries, referred to as pH-sensitive redox nanoparticle (RNP(N) ) and pH-insensitive redox nanoparticle (RNP(O) ), which are prepared by self-assembling amphiphilic block copolymers possessing nitroxide radicals as a side chain of hydrophobic segment via amine and ether linkages, respectively. Due to a protonation of amino groups in hydrophobic core, RNP(N) disintegrates in low pH environments such as ischemic, inflamed, and tumor tissues, resulting in increased ROS-scavenging activity because of the exposed nitroxide radicals from the core. Utilizing pH-responsiveness of RNP(N) , it shows remarkable therapeutic effects on oxidative stress injuries such as renal and cerebral ischemia-reperfusion injuries after intravenous administration. Moreover, RNP(N) shows an enhancement of the activity of anticancer drugs by suppression of activation of transcription factors in tumor due to the ROS scavenging. On the other hand, orally administered RNP(O) has notable characteristics such as preferential accumulation in mucosa and inflamed area of gastrointestinal tract and no uptake into blood stream. Based on these characters, RNP(O) shows a remarkable therapeutic effect for the gastrointestinal inflammation without any adverse effects. Thus, ROS-scavenging nanomedicines have therapeutic efficacy in numerous oxidative stress diseases.

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.

Nitroxide radicals and nanoparticles: a partnership for nanomedicine radical delivery

This article aims to provide a research update on nitroxide radical compounds for application of anti-oxidative stress therapy. Nitroxide compounds such as 2,2,6,6-tetramethylpyperidine-1-oxyl (TEMPO) can catalytically react with reactive oxygen species (ROS) and are anticipated as new anti-oxidant therapies for several diseases. However, low-molecular-weight nitroxide compounds pose several problems such as nonspecific dispersion in normal tissues, preferential renal clearance and rapid reduction of the nitroxide radical to the corresponding hydroxylamine. Nitroxide radical compounds are also known to show dose-related antihypertensive action accompanied by reflex tachycardia, increased skin temperature, and seizures. The author has recently designed novel nanoparticles, which possess nitroxide radicals in the core for novel bioimaging and nanotherapy. Nitroxide radical-containing nanoparticles (RNP) shows high safety, long blood circulation, magnetic resonance imaging and ESR imaging sensitive character and efficient therapeutic effects to several diseases such as cerebral and renal ischemia reperfusions, ulcerative colitis and Alzheimer’s disease models. RNPs are, thus, promising as new nanotherapeutic materials.

In vitro and in vivo characteristics of core-shell type nanogel particles: optimization of core cross-linking density and surface poly(ethylene glycol) density in PEGylated nanogels

The biocompatibility and body distribution of PEGylated polyamine nanogels composed of chemically cross-linked poly(2-N,N-(diethylamino)ethyl methacrylate) (PEAMA) gel cores surrounded by poly(ethylene glycol) (PEG) chains were investigated to evaluate their feasibility as drug nanocarriers for systemic administration. PEGylated nanogels with different cross-linking densities (1, 2, and 5mol.%) were prepared to evaluate their biocompatibilities by in vitro cytotoxicity assay, hemolysis assay, and in vivo acute toxicity assay. The toxic effect of the PEGylated nanogels derived from polyamine gel cores was significantly reduced when the cross-linking density was increased, and those with a cross-linking density of 5mol.% showed a remarkably high median lethal dose (LD(50)) value >200mgkg(-1),despite the abundance of amino groups in the core. One hour after intravenous injection the PEGylated nanogels were found to have been eliminated from the systemic circulation, and less than 1% of the injected dose (ID) remained in the bloodstream. To improve the blood circulation time by increasing the surface PEG density of the PEGylated nanogels post-PEGylation of the PEGylated nanogels (via the Menschutkin reaction between tertiary amines of the PEAMA gel core and bromobenzyl-terminated short PEG) was carried out. A biodistribution study of these post-PEGylated nanogels revealed that the blood circulation time of the nanogels was definitely prolonged as the PEG content was increased. Therefore, the precise design of PEGylated nanogels with increased cross-linking densities in their polyamine gel cores and increased surface PEG densities seems promising for systemic applications.

Nitroxyl radical-containing nanoparticles for novel nanomedicine against oxidative stress injury

This article discusses the preparation and characterization of pH-sensitive nitroxyl radical-containing nanoparticles (RNPs) possessing nitroxyl radicals in the core and reactive groups on the periphery, and its biomedical application. The RNPs prepared by a self-assembling amphiphilic block copolymers composed of a hydrophilic poly(ethylene glycol) (PEG) segment and a hydrophobic poly(chloromethylstyrene) (PCMS) segment in which the chloromethyl groups were converted to 2,2,6,6-tetramethylpiperidinyloxyls (TEMPOs) via an amination of PEG-b-PCMS block copolymer with 4-amino-TEMPO are initially described. The cumulant average diameter of an RNP is approximately 40 nm, and the RNP has intense electron paramagnetic resonance signals. RNPs show a prolonged blood circulation time by the compartmentalization of nitroxyl radicals into the hydrophobic core, and disintegrate in response to a low pH environment, such as ischemic tissue, resulting in effectively scavenging reactive oxygen species due to an exposure of nitroxyl radicals from the RNP core. Thus, the RNP prepared was found to be effective for cerebral ischemia–reperfusion injury. Therefore, RNPs are promising as high-performance therapeutic nanomedicine for oxidative stress injuries.

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.

Human uridine-cytidine kinase phosphorylation of ribavirin: a convenient method for activation of ribavirin for conjugation to proteins

Ribavirin is a synthetic nucleoside analog that is used for the treatment of hepatitis C virus (HCV) infection. Its primary toxicity is hemolytic anemia, which sometimes necessitates dose reduction or discontinuation of therapy. Selective delivery of ribavirin into liver cells would be desirable to enhance its antiviral activity and avoid systemic side effects. One approach to liver-specific targeting is conjugation of the ribavirin with asialoglycoprotein that is taken up specifically by liver cells. Human uridine-cytidine kinase-1 (UCK-1) was used for ribavirin phosphorylation to its monophosphate form. 1-Ethyl-3-diisopropylaminocarbodiimide (EDC) was used as a coupling agent. The best results were obtained using direct conjugation protocol with a molar ratio of 6.5 ribavirin monophosphate (RMP) molecules per one asialoorosomucoid (AsOR) molecule. Our findings show that ribavirin is a potential substrate of UCK-1, and RMP formed could be chemically coupled to AsOR to form a conjugate for liver specific targeting.

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.

Synergy of bovine lactoferrin with the anti-cytomegalovirus drug cidofovir in vitro

Human cytomegalovirus (HCMV) causes severe morbidity and mortality in immunocompromised patients. Treatment of HCMV infections with conventional antiviral drugs like ganciclovir and cidofovir has major drawbacks (i.e. serious side effects). Therefore, combination therapies using drugs with different antiviral mechanisms should be envisaged. Potential synergy between lactoferrin (LF), an antibacterial, antimycotic and antiviral protein, and the antiviral drugs acyclovir, ganciclovir, foscarnet and cidofovir was investigated, using an in vitro test system with the recombinant RC256 HCMV strain.

RESULTS

Combination of LF with acyclovir and foscarnet resulted in antagonism. When LF and ganciclovir were combined, neither synergy nor antagonism was observed. Strikingly, the combination of LF with cidofovir resulted in marked synergy. The synergistic effect could be explained by inhibition of two subsequent steps in the viral replication cycle: HCMV penetration into the target cells and intracellular synthesis of HCMV DNA. In conclusion, LF might be a potential candidate for combination therapy with cidofovir.

Poly(L-lysine) as a model drug macromolecule with which to investigate secondary structure and membrane transport, part I: Physicochemical and stability studies

Low oral bioavailability of therapeutic peptides and proteins generally results from their poor permeability through biological membranes and enzymatic degradation in the gastrointestinal tract. Since different secondary structures exhibit different physicochemical properties such as hydrophobicity, size and shape, changing the secondary structure of a therapeutic polypeptide may be another approach to increasing its membrane permeation. Poly(L-lysine) was used as a model polypeptide. The objectives of this study were to induce secondary structural changes in poly(L-lysine) and to determine the time course over which a given conformer was retained. In addition, the hydrophobicity of each secondary structure of poly(L-lysine) was assessed. The circular dichroism (CD) studies demonstrated that the conditions employed could successfully induce the desired secondary structural changes in poly(L-lysine). The alpha-helix conformer appeared to be more stable at 25 degrees C whereas the beta-sheet conformer could be preserved at 37 degrees C. On the other hand, the random coil conformer was retained at both temperatures. Significant losses of the alpha-helix and the beta-sheet conformers were observed when the pH was reduced. The change in ionic strength did not affect any of the conformers. The octanol/buffer partitioning studies indicated that the alpha-helix and the beta-sheet conformers exhibited significantly different (P < 0.05) hydrophobicities. In conclusion, variation of pH and temperature conditions can be used to induce secondary structural changes in poly(L-lysine). These changes are reversible when the stimuli are removed. The alpha-helix and the beta-sheet conformers of poly(L-lysine) are more lipophilic than the native random coil conformer. Thus, poly(L-lysine) may represent an ideal model polypeptide with which to further investigate the effects of secondary structure on membrane diffusion or permeation.

Antiviral activities of lactoferrin

Lactoferrin (LF) is an iron binding glycoprotein that is present in several mucosal secretions. Many biological functions have been ascribed to LF. One of the functions of LF is the transport of metals, but LF is also an important component of the non-specific immune system, since LF has antimicrobial properties against bacteria, fungi and several viruses. This review gives an overview of the present knowledge about the antiviral activities and, when possible, the antiviral modes of action of this protein. Lactoferrin displays antiviral activity against both DNA- and RNA-viruses, including rotavirus, respiratory syncytial virus, herpes viruses and HIV. The antiviral effect of LF lies in the early phase of infection. Lactoferrin prevents entry of virus in the host cell, either by blocking cellular receptors, or by direct binding to the virus particles.

Gene therapy of cystic fibrosis (CF) airways: a review emphasizing targeting with lactose

Cystic fibrosis is a disease for which a number of Phase I clinical trials of gene therapy have been initiated. Several factors account for the high level of interest in a gene therapy approach to this disease. CF is the most common lethal inherited disease in Caucasian populations. The lung, the organ that is predominantly responsible for the morbidity and mortality in CF patients, is accessible by a non-invasive method, the inhalation of aerosols. The vectors employed in the Phase I trials have included recombinant adenoviruses, adeno-associated viruses and cationic lipids. While there have been some positive results, the success of the vectors until now has been limited by either immunogenicity or low efficiency. A more fundamental obstacle has been the absence of appropriate receptors on the apical surface of airway epithelial cells. Molecular conjugates with carbohydrate substitution to provide targeting offer several potential advantages. Lactosylated polylysine in which 40% of the lysines have been substituted with lactose has been shown to provide a high efficiency of transfection in primary cultures of CF airway epithelial cells. Other important features include a relatively low immunogenicity and cytotoxicity. Most importantly, the lactosylated polylysine was demonstrated to give nuclear localization in CF airway epithelial cells. Until now, most non-viral vectors did not have the capability to provide nuclear localization. These unique qualities provided by the lactosylation of non-viral vectors, such as polylysine may help to advance the development of molecular conjugates sufficiently to warrant their use in future clinical trials for the gene therapy of inherited diseases of the lung.

Coupling of 5-fluoro 2'-deoxyuridine to lactosaminated poly-l-lysine: an approach to a regional, non-invasive chemotherapy of liver micrometastases

Nucleoside analogs conjugated with galactosyl-terminating peptides selectively enter liver cells and after intracellular release from the carrier partly exit into bloodstream, resulting in higher concentrations in liver blood than in systemic circulation. The aim of the present experiments was to ascertain whether, in mice injected with non-toxic doses of a 5-fluoro 2'-deoxyuridine (FUdR) conjugate with lactosaminated poly-L-lysine (L-poly(LYS)), the drug was released by hepatic cells in high enough amounts to be pharmacologically active on neoplastic cells infiltrating the liver. We observed that L-poly(LYS)-FUdR inhibited the growth of hepatic metastases induced by intrasplenic administration of murine colon carcinoma C-26 cells. L-poly(LYS)-FUdR was not toxic for C-26 cells in vitro, was selectively taken up by mouse liver, and was stable in mouse blood, indicating that the effect on the metastases was due to FUdR (and/or its active metabolites) released in liver blood after the conjugate was taken up by the hepatic cells. These results suggest that L-poly(LYS)-FUdR might be useful in adjuvant chemotherapy of tumors giving liver metastases. The drug released from hepatic cells into liver blood following conjugate administration via the peripheral venous route might accomplish a locoregional, non-invasive treatment of micrometastases nourished by liver sinusoids.

Enhanced liver blood concentrations of adenine arabinoside accomplished by lactosaminated poly-L-lysine coupling: implications for regional chemotherapy of hepatic micrometastases

Conjugates of antiviral and antiblastic nucleoside analogs (NAs) with galactosyl-terminating peptides selectively enter hepatocytes after binding of the carrier galactose residues to the asialoglycoprotein receptor. Since NAs, when set free from the carrier within hepatocytes, partly exit from these cells into the bloodstream, we considered the possibility that administration of galactosyl-terminating conjugates of NAs could result in plasma concentrations of these drugs that would be higher in liver sinusoids than in capillaries of other organs. In the present study we demonstrated the validity of this hypothesis. We injected rats with a conjugate of adenine arabinoside (ara-A) with lactosaminated poly-L-lysine and found that the plasma concentrations of ara-A were >2-fold higher in blood of liver than in systemic circulation. Liver blood was collected from the inferior vena cava after closing below and above the outflows of the hepatic veins. The present result suggests that conjugation with galactosyl-terminating peptides might be a way to selectively increase the concentrations of NAs not only in hepatocytes, which have the asialoglycoprotein receptor, but also in cells infiltrating the liver, such as neoplastic cells of micrometastases nourished by hepatic sinusoids.

Enhanced efficiency of lactosylated poly-L-lysine-mediated gene transfer into cystic fibrosis airway epithelial cells

Lactosylated poly-L-lysine is a nonviral vector that transfers genes into airway epithelial cells, including those from individuals with cystic fibrosis (CF). Substitution of 40% of the epsilon-amino groups of poly-L-lysine with lactosyl residues not only provided a ligand for receptor-mediated endocytosis, but also reduced the toxicity when compared with nonsubstituted poly-L-lysine. Lactosylated poly-L-lysine/pCMVLuc complex is not toxic to cells in amounts that gave the maximum gene expression. The level of gene expression was regulated by using different combinations of chloroquine, glycerol, and E5CA peptide. Using cultured CF cells, chloroquine, combined with E5CA peptide, increased the transfer of the pCMVLuc/ lactosylated poly-L-lysine complex 10,000-fold compared with transfer without additives. In many systems, a high efficiency is of paramount importance and the enhancing agents can be used to modulate the expression of the gene. For example, transfer of pCMVLacZ/lactosylated poly-L-lysine complexes with chloroquine added to the transfection medium gave only 20% transfection efficiency of the reporter gene. However, when chloroquine was combined with glycerol, the efficiency was increased to 90%, thus approaching that reported with viral vectors. This highly efficient vector may be of great value for the future development of gene transfer systems.

Inhibition of [3H]thymidine incorporation into DNA of rat regenerating liver by 2',2'-difluorodeoxycytidine coupled to lactosaminated poly-L-lysine

The expression of asialoglycoprotein receptor (ASGP-R) on human hepatocarcinoma cells might be exploited to reduce the extrahepatic toxicity of DNA synthesis inhibitors by their conjugation with galactosyl- terminating peptides. We conjugated 2',2'-difluorodeoxycytidine (dFdC), an inhibitor of DNA synthesis active on solid tumors, with lactosaminated poly-L-lysine (L-poly(LYS)). In experiments in vitro, L-poly(LYS)-dFdC inhibited proliferation of Hep G2 cells, a human hepatocarcinoma cell line which maintains the ASGP-R. Inhibition was rescued by asialofetuin. To study the pharmacological action of the conjugate in vivo, we used rats 18-24 hr after 2/3 hepatectomy and observed that regenerating hepatocytes expressed ASGP-R on their surface and internalized L-poly(LYS)-dFdC. Conjugate uptake by bone marrow, spleen, and intestine was negligible. We also found that L-poly(LYS)-dFdC inhibited [3H]thymidine incorporation into DNA of regenerating liver. These results indicated that hepatectomized rats were a suitable animal model to study the pharmacological action, on DNA-synthesizing hepatocytes, of conjugates binding to ASGP-R and carrying inhibitors of DNA synthesis. L-poly(LYS)-dFdC also inhibited [3H]thymidine incorporation in bone marrow, spleen, and intestine. Evidence was obtained that inhibition of DNA synthesis in extrahepatic tissues was a consequence of drug release from hepatocytes into blood-stream after the bond with the carrier has been broken down within liver cells. Possible ways of reducing the exit of dFdC from liver cells, thereby obtaining an inhibition of DNA synthesis restricted to dividing hepatocytes, were discussed.

High-efficiency transfer of cystic fibrosis transmembrane conductance regulator cDNA into cystic fibrosis airway cells in culture using lactosylated polylysine as a vector

To find more efficient vectors for the transfer of CFTR cDNA, lactosylated polylysine was explored for transfer into airway epithelial cells in primary culture. The efficacy and high efficiency of transfection were shown by several criteria: expression of both mRNA and protein for CFTR and the functional correction of the Cl- channel activity. Using specific combinations of agents to enhance the transfection, an efficiency of 90% was obtained as detected by in situ hybridization with digoxigenin-labeled probes generated against exon 14 of CFTR. The highest efficiency was observed by adding E5CA peptide (10 microg) and 5% glycerol to the transfection mixture. The degree of transfection could be controlled by the enhancing agents, thus modulating the efficiency of transfection. The highest level of transfection efficiency is equivalent to that reported for viral vectors. None of the agents or their combinations in the concentrations used were cytotoxic to the primary cells. Antibody pAb3145 was used to detect the expression of the CFTR protein in the cells. When an N-terminal GFP-CFTR fusion gene was used to transfect the CF cells a functional correction of the CFTR Cl- channel was detected by patch-clamp electrophysiology. The high efficiency of CFTR gene transfer with lactosylated polylysine leads to the conclusion that lactosylated polylysine is a promising vector to transfer the CFTR gene into human airway cells in culture.

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.