(Glyco)-protein drug carriers with an intrinsic therapeutic activity: The concept of dual targeting

The effects of a hirudin/liposome complex on a diabetic nephropathy rat model

Background

Hirudin, an extract from Hirudo spp., is an anticoagulant used to treat a variety of renal diseases, including diabetic nephropathy (DN). Currently, hirudin has to be used at high dosages to treat DN because it poorly targets the kidneys, although at high dosages it can have severe side effects. Developing a targeted drug delivery system for hirudin, then, could boost its positive therapeutic effects while lowering the risk of side effects. Liposomes have been demonstrated to have significant renal targeting potential, but here we show that a hirudin-loaded liposome is an effective delivery method for patients with DN.

Method

In this study, we prepared a hirudin/liposome complex and tested its efficacy by injecting it into a rat model. We then compared the renal accumulation of hirudin between complex-injected rat models and rat models that received injections of hirudin alone. We also investigated the mechanisms behind the complex’s effects.

Result

The hirudin/liposome complex increased the accumulation of hirudin in kidney tissues and relieved the renal injury in DN rat models. Moreover, the hirudin/liposome complex down-regulated the expression of TGF-β1 and VEGF in the kidneys.

Conclusion

We demonstrated that a hirudin/liposome complex can have a significant positive effect on DN. The mechanism may be that the complex inhibits the expression of VEGF and TGF-β1.

Glycodendrimeric nanoparticulate carriers of primaquine phosphate for liver targeting

In the present study it was intended to deliver primaquine phosphate (PP), a liver schizonticide directly to liver cells using polypropyleneimine (PPI) dendrimers-coated peripherally with galactose. PPI dendrimers were synthesized by consecutive Michael double addition reaction (using ethyelenediamine as core), followed by hydrogenation reaction. Galactose conjugation was carried out by ring opening reactions, followed by Schiff's reaction and reduction to secondary amine in sodium acetate buffer (pH 4.0). IR, NMR, MASS spectroscopy were used for the confirmation of synthesis of uncoated and coated dendrimers. The formulations were made by equilibrium dialysis of dendrimers with the solution of PP. Then the formulations were characterized by TEM for size and shape. Release rate, hemolytic toxicity; bio-distribution and blood level studies were also performed on lyophilized formulations. The results obtained indicated that galactose coating of PPI systems increases the drug entrapment efficiency by 5-15 times depending upon generations. Galactose coating prolonged release up to 5-6 days as compared to 1-2 days for uncoated PPI systems. The hemolytic toxicity, blood level and hematological studies proved these systems to be safer and suitable for sustained drug delivery. Blood level studies proved the suitability of the systems for the prolonged circulations and delivery of PP to liver. The galactose coating of PPI dendrimers can therefore make the PPI systems more effective and suitable for targeted delivery of Primaquine phosphate to liver.

Development of vasculature targeting strategies for the treatment of cancer and chronic inflammatory diseases

Endothelial cells play a pathological role in cancer and chronic inflammation and are therefore attractive targets for therapeutic intervention. This review focuses on endothelial cell specific drug targeting strategies for the treatment of these diseases. The cellular and molecular processes involved in the activation of endothelial cells in angiogenesis and inflammation will be reviewed. Various target epitopes expressed by activated endothelium suitable for targeting purposes, design and development of drug-carrier complexes, drugs of interest which might interfere with endothelial cell activation, as well as in vitro and in vivo experimental approaches to study (intra) cellular drug delivery will be discussed.

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.

Design and synthesis of glycodendrimers

Multivalent neoglycoconjugates with well-defined structures have considerable potential as inhibitors of cell surface protein-carbohydrate interactions and as tools for studying such recognition processes in vitro. In this review, we outline strategies and synthetic methods for making one such class of neoglycoconjugates based on dendrimers--the so-called glycodendrimers. Glycodendrimers can be classified as: (i) carbohydrate-coated; (ii) carbohydrate-centered; and (iii) fully carbohydrate-based. Approaches to their construction have included both the modification of commercially available dendrimers and de novo dendrimer synthesis. Examples from the authors' and other laboratories are drawn upon to illustrate design considerations and the application of dendritic synthetic principles--including divergent and convergent syntheses--for making glycodendrimers. Key coupling reactions for the synthesis of glycodendrimers include: amide and thiourea formation; glycosylation; photoaddition to allyl ethers; and reductive amination. The advantages and disadvantages of using protected and unprotected saccharide building blocks and potential applications for glycodendrimers in both biotechnology and materials science are also discussed.

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.

Successful targeting to rat hepatic stellate cells using albumin modified with cyclic peptides that recognize the collagen type VI receptor

The key pathogenic event in liver fibrosis is the activation of hepatic stellate cells (HSC). Consequently, new antifibrotic therapies are directed toward an inhibition of HSC activities. The aim of the present study was to develop a drug carrier to HSC, which would allow cell-specific delivery of antifibrotic drugs thus enhancing their effectiveness in vivo. We modified human serum albumin (HSA) with 10 cyclic peptide moieties recognizing collagen type VI receptors (C*GRGDSPC*, in which C* denotes the cyclizing cysteine residues) yielding pCVI-HSA. In vivo experiments showed preferential distribution of pCVI-HSA to both fibrotic and normal rat livers (respectively, 62 +/- 6 and 75 +/- 16% of the dose at 10 min after intravenous injection). Immunohistochemical analysis demonstrated that pCVI-HSA predominantly bound to HSC in fibrotic livers (73 +/- 14%). In contrast, endothelial cells contributed mostly to the total liver accumulation in normal rats. In vitro studies showed that pCVI-HSA specifically bound to rat HSC, in particular to the activated cells, and showed internalization of pCVI-HSA by these cells. In conclusion, pCVI-HSA may be applied as a carrier to deliver antifibrotic agents to HSC, which may strongly enhance the effectiveness and tissue selectivity of these drugs. This approach has the additional benefit that such carriers may block receptors that play a putative role in the pathogenesis of liver fibrosis.

Human serum albumin enhances DNA transfection by lipoplexes and confers resistance to inhibition by serum

Cationic liposome-DNA complexes ('lipoplexes') are used as gene delivery vehicles and may overcome some of the limitations of viral vectors for gene therapy applications. The interaction of highly positively charged lipoplexes with biological macromolecules in blood and tissues is one of the drawbacks of this system. We examined whether coating cationic liposomes with human serum albumin (HSA) could generate complexes that maintained transfection activity. The association of HSA with liposomes composed of 1, 2-dioleoyl-3-(trimethylammonium) propane and dioleoylphosphatidylethanolamine, and subsequent complexation with the plasmid pCMVluc greatly increased luciferase expression in epithelial and lymphocytic cell lines above that obtained with plain lipoplexes. The percentage of cells transfected also increased by an order of magnitude. The zeta potential of the ternary complexes was lower than that of the lipoplexes. Transfection activity by HSA-lipoplexes was not inhibited by up to 30% serum. The combined use of HSA and a pH-sensitive peptide resulted in significant gene expression in human primary macrophages. HSA-lipoplexes mediated significantly higher gene expression than plain lipoplexes or naked DNA in the lungs and spleen of mice. Our results indicate that negatively charged HSA-lipoplexes can facilitate efficient transfection of cultured cells, and that they may overcome some of the problems associated with the use of highly positively charged complexes for gene delivery in vivo.

Studies of macromolecular prodrugs of zidovudine

The current problems in controlling severe viral infections such as AIDS as well as the lack of effective and safe therapeutic measures for such diseases have caused interest in systems such as macromolecular prodrugs potentially able to solve heavier drawbacks of conventional antiviral therapy. This review focuses on various approaches proposed in the literature in this field. Neoglycoproteins and synthetic protein-like structure polymers have been mainly proposed. In the first group, the possibility of incorporating into the polymeric structures a determined amount of sugar molecules make them interesting candidates for targeting of infected blood cells. The conjugate of zidovudine (AZT) and an anti-transferrin receptor antibody OX-26 has been proposed for brain targeting. The conjugate of AZT with alpha,beta-poly(N-hydroxyethyl)-DL-aspartamide (PHEA) showed good release properties in a prolonged time.

Albumin modified with mannose 6-phosphate: A potential carrier for selective delivery of antifibrotic drugs to rat and human hepatic stellate cells

The hallmark of liver fibrosis is an increased extracellular matrix deposition, caused by an activation of hepatic stellate cells (HSC). Therefore, this cell type is an important target for pharmacotherapeutic intervention. Antifibrotic drugs are not efficiently taken up by HSC or may produce unwanted side-effects outside the liver. Cell-specific delivery can provide a solution to these problems, but a specific drug carrier for HSC has not been described until now. The mannose 6-phosphate/insulin-like growth factor II (M6P/IGF-II) receptor, which is expressed in particular upon HSC during fibrosis, may serve as a target-receptor for a potential carrier. The aim of the present study was to examine if human serum albumin (HSA) modified with mannose 6-phosphate (M6P) is taken up by HSC in fibrotic livers. A series of M6Px-modified albumins were synthetized: x = 2, 4, 10, and 28. Organ distribution studies were performed to determine total liver uptake. The hepatic uptake of M6Px-HSA increased with increasing M6P density. M6Px-HSA with a low degree of sugar loading (x = 2-10) remained in the plasma and accumulated for 9% +/- 0.5% or less in fibrotic rat livers. An increase in the molar ratio of M6P:HSA to 28:1 caused an increased liver accumulation to 59% +/- 9% of the administered dose. Furthermore, we determined quantitatively the in vivo intrahepatic distribution of M6Px-HSA using double-immunostaining techniques. An increased substitution of M6P was associated with an increased accumulation in HSC; 70% +/- 11% of the intrahepatic staining for M6P28-HSA was found in HSC. We also demonstrate that M6P-modified bovine serum albumin (BSA) accumulates in slices of normal and cirrhotic human livers. After incubation of this neoglycoprotein with human tissue, the protein is found in nonparenchymal liver cells. Because M6P-modified albumins are taken up by HSC in fibrotic livers, this neoglycoprotein can be applied as a selective drug carrier for HSC. This technology may create new opportunities for the pharmacological intervention of liver fibrosis.

Tumor vasculature targeted therapies: getting the players organized

Based on their location and central role in solid tumor growth, tumor vascular endothelial cells may present an attractive target for the delivery of therapeutic drugs or cells. The potency of blocking the tumor blood supply in eradicating solid tumors was demonstrated recently in a mouse model of tumor vasculature targeting (Huang et al., Science 275: 547-550, 1997). For clinical application of such strategies, tumor endothelium specific target epitopes need to be identified. Recent studies on angiogenesis have identified angiogenesis-related molecules as potential target epitopes. Among these are vascular endothelial growth factor (VEGF)/VEGF-receptor complex, alpha(v) integrins, and Tie receptor tyrosine kinases. Besides blockade of their signalling cascades leading to inhibition of angiogenesis, these epitopes may also be instrumental in tumor vessel specific delivery of therapeutics. Data on the efficacy of therapeutic modalities aimed at these, mostly heterogeneously distributed tumor endothelial epitopes are scarce, and sophisticated experimentation is required to rationalize the development of new therapeutic strategies. Importantly, only detailed evaluations in cancer patients will provide the blueprint for the development of clinically effective tumor vascular targeted therapies.