Drug Targeting Systems Research Articles

Targeting antiviral nucleotide analogues to macrophages.

Macrophages are important target cells for human immunodeficiency virus type 1 (HIV-1) infection. We have developed a drug targeting system for the selective delivery of phosphorylated nucleoside analogues to these phagocytosing cells. This system is based on the possibility of encapsulating the phosphorylated drugs into autologous erythrocytes and on the subsequent selective modification of their membranes to promote macrophage recognition and phagocytosis. Targeted delivery of phosphorylated nucleoside analogues to human, feline, and murine macrophages inhibits the infectivity of HIV-1, feline immunodeficiency virus, and LP-BM5 viruses more efficiently than the administration of the corresponding nucleoside analogues. In vivo administration of 2',3'-dideoxycytidine 5'-triphosphate (ddCTP) encapsulated into autologous erythrocytes to LP-BM5-infected mice was found to reduce infectivity and disease progression. Furthermore, the simultaneous administration of AZT or ddC produced additive antiviral effects. The possibility of using red cells as drug targeting systems was useful for the design, synthesis, and delivery of new antiviral nucleoside analogues. As a prototype of these new drugs, di-(thymidine-3'-azido-2',3'-dideoxy-D-riboside)-5'-5'-p1-p2-pyrophospha te (AZTp2AZT) was prepared. Although this drug in solution has the same antiviral activity as AZT, when administered encapsulated into erythrocytes it was several times more efficient in inhibiting the infectivity of human, feline, and murine immunodeficiency viruses. Thus, the availability of a drug targeting system for the selective delivery of antivirals to macrophages offers an additional possibility for the development of new drugs and of new combination antiviral therapies.

Human Serum Albumin as a Probe for Protein Adsorption to Nanopartides: Relevance to Biodistribution

A range of poloxamers and poloxamines were adsorbed to biodegradable poly(lactide-coglycolide) (PLGA) and non-biodegradable polystyrene (PS) particulate systems in order to alter their surface characteristics and produce potential drug targeting systems. Human serum albumin (HSA) was chosen as a model protein to investigate protein adsorption to the above systems and was quantified by two techniques. I125 radiolabelled HSA proved to be a useful probe for determining protein adsorption but was limited by a modification that occurred on storage. Also, HSA eluted from the particle surface was quantified by densitometry following it's development on an SDS-PAGE gel. Both techniques produced similar results. For cleaned coated PS particles it was found that the PEO chain length and the molecular structure of the block copolymer were important in preventing protein adsorption. The presence of excess block copolymer in the uncleaned preparations resulted in further suppression of HSA adsorption, which was thought to be due to their detergent properties. Due to the different results obtained with similarly coated PLGA particles, it was concluded that the block copolymers adsorb onto the surface of me PLGA particles in a different conformation to those adsorbed onto PS particles. Correlating in vivo biodistribution in terms of the prevention of protein (opsonin) adsorption was of only limited success and it was concluded that adsorption data for a single model protein can only be used with caution to predict the in vivo behaviour of colloidal targeting systems.

Macrophage targeting of azidothymidine: a promising strategy for AIDS therapy.

Macrophages play an important role in the immunopathogenesis of AIDS. The objective of this study was to investigate the possibility of specific targeting of antivirals such as azidothymidine (AZT) to macrophages, using nanoparticles as a colloidal drug carrier. The body distribution of AZT bound to nanoparticles and as a control solution was studied in rats after intravenous and peroral administration. 14C-Labeled AZT was bound to nanoparticles in the presence of bis(2-ethylhexyl)sulfosuccinate sodium. The radioactivity was measured in different organs including those containing large numbers of macrophages. After intravenous injection, the concentrations of AZT were up to 18 times higher in organs belonging to the reticuloendothelial system (RES) when the drug was bound to nanoparticles than after injection of an aqueous AZT solution. Likewise, after oral administration the nanoparticle formulation delivered AZT more efficiently to the RES than the aqueous solution. In addition, the blood concentration was significantly higher after oral administration of nanoparticles. These results demonstrate that nanoparticles are a promising drug-targeting system for AZT to the RES organs. The increase in drug availability at the sites containing abundant macrophages may allow a reduction in dosage to avoid systemic toxicity.

Oligonucleotide targeting to alveolar macrophages by mannose receptor-mediated endocytosis

Antisense oligonucleotides (ONs) have proven useful for selective inhibition of gene expression. However, their effective use is limited by inefficient cellular uptake and lack of cellular targeting. In this paper, we report a drug targeting system which utilizes mannose receptor-mediated endocytosis to enhance cellular uptake of ONs in alveolar macrophages (AMs). The system employs a molecular complex consisting of partially substituted mannosylated poly( l-lysine) (MPL), electrostatically linked to a 5′ fluorescently labeled ON. Upon recognition by the macrophage mannose receptors, the MPL was internalized by the receptor-mediated pathway, co-transporting the ON. Our results indicated that the AMs treated with the MPL:ON complex exhibited a significant increase in ON uptake (up to 17-fold) over free ON-treated controls. Effective ON uptake was shown to require the recognition of the mannose moiety since unmodified polylysine was much less effective in promoting ON uptake. Specific internalization of the ON:MPL complex by the mannose receptor pathway was verified by competitive inhibition using mannosylated albumin. Under this condition, the ON complex uptake was inhibited. The requirement of mannose receptors for complex uptake was further demonstrated using a macrophage cell line, J774.1, which expresses a low level of mannose receptors. When treated with the complex, these cells showed no susceptibility to ON uptake, thus suggesting the targeting ability of the carrier system to the AMs. Following cellular internalization, the ON complex appeared largely accumulated in endocytic vesicles. Enhanced endosomal exit of the ON was achieved using a fusogenic peptide derived from the amino terminal sequence of influenza virus hemagglutinin HA2. Cytotoxicity studies showed that at the concentrations effectively enhancing ON uptake, both MPL and the fusogenic peptide caused no toxic effects to the cells, thereby suggesting their potential safety and utilization in vivo.

Trends in Drug Targeting for Cancer Treatment

Various drug delivery and targeting systems and approaches are currently utilized for cancer chemotherapy. Many drugs being developed through biotechnology are also in various stages of clinical trials. The most common approaches with drug delivery and targeting systems have been those using stealth liposomes or microspheres. Recent efforts have been made to use stealth nanoparticles for cancer drug delivery. In the next few years, it is expected that several liposomal products will be on the market. Another approach that has been utilized for some time has been the use of antibody-directed drugs or toxins. Several immunotoxins are currently in phase III trials, and efforts are being made to potentiate their activity with different potentiators. In an effort to understand the intricacies of tumor morphology and the limitations of drug targeting, various mathematical models have been proposed that help in designing appropriate delivery systems for successful tumor targeting. This review considers a number of drug targeting systems, especially microparticulate and colloidal systems, for cancer therapy.

Synthesis of transferrin-mitomycin C conjugate as a receptor-mediated drug targeting system.

Macromolecular conjugates of mitomycin C (MMC) were synthesized by binding an active ester of glutarylated MMC (MMC-G-OSu) to human holo-transferrin (TF). Water-soluble TF-MMC conjugates (TF-G-MMC) were obtained in a good yield (> 95%) by this method. The MMC content of the conjugate increased (0.82-9.49 MMC/w%) with increasing amounts of MMC-G-OSu added to the conjugation mixture. Sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE) analysis showed no aggregation in these conjugates. 125I-TF-G-MMC was bound specifically to the TF receptor on Sarcoma 180 cells; the measurement of equilibrium binding of the 125I-labeled conjugate resulted in a saturation isotherm. The amount of conjugate specifically bound to the TF receptor decreased as the MMC content of the conjugate increased. However, it was found that the conjugate with an MMC content below 10 mol MMC/mol TF still retains a binding activity of more than half that of TF. Therefore, when an optimal chemical modification was chosen, TF could be used as a tumor specific drug carrier.

Synthesis of single- and double-chain fluorocarbon and hydrocarbon β-linked galactose amphiphiles derived from serine

Single- and double-chain β-linked galactose amphiphiles derived from serine were synthesized. Both types of compounds have potential as material for the formulation of liposomal drug carrier and targeting systems and as HIV inhibitors.

Modulated red blood cell survival by membrane protein clustering.

Human and murine blood cells treated with ZnCl2 and bis(sulfosuccinimidyl)suberate (BS3) (a cross linking agent) undergo band 3 clustering and binding of hemoglobin to red blood cell membrane proteins. These clusters induce autologous IgG binding and complement fixation, thus favouring the phagocytosis of ZnCl2/BS3 treated cells by macrophages. The extension of red blood cell opsonization can be easily modulated by changing the ZnCl2 concentration in the 0.1-1.0 mM range thus providing an effective way to affect blood cell recognition by macrophages. In fact, murine erythrocytes treated with increasing ZnCl2 concentrations have proportionally reduced survivals when reinjected into the animal. Furthermore, the organ sequestration of ZnCl2/BS3 treated cells strongly resembles the typical distribution of the senescent cells. Since the ZnCl2/BS3 treatment can also be performed on red blood cells loaded with drugs or other substances, this procedure is an effective drug-targeting system to be used for the delivery of molecules to peritoneal, liver and spleen macrophages.

Immunoliposomes in Vivo

Attachment of antibodies to the surface of liposomes was performed to confer specificity for a certain cell or organ expressing the targeted antigenic determinant. These so-called immunoliposomes are expected to be applied as targeted drug carriers. In this article, the literature concerning in vivo studies of the targeting of immunoliposomes to various sites in the body is reviewed. The anatomical, physiological, and pathological constraints and current progress are described. Moreover, perspectives on the therapeutic feasibility of this drug targeting system are discussed.

Double-Tailed Perfluoroalkylated Glycolipids as Components for Drug Delivery and Targeting Systems. Preliminary Biocompatibility Results

Vesicles are being investigated as drug carriers, especially for enhancing the therapeutic effectiveness of the drug while minimizing its side effects. Drug targeting can be achieved if there is a specific recognition of the vesicle's outer wall by specific cells. With these objectives in mind new glycolipids fitted with fluorinated, hydrogenated or mixed, single and double-tails, containing either a gluco- or a galactopyranose residue in their hydrophilic head, were synthesized and their ability to achieve self-organized supramolecular systems was assessed. Replacement of hydrogen by fluorine in these glycolipids was found to enhance biological tolerance. Thus, a fluorinated single-tailed glycolipid displayed no action on red blood cells at concentrations as high as 50 g/l while its hydrogenated analog was hemolytic at 5 g/l. 100% of survival was obtained one month after intravenous or intraperitoneal injection into mice of isotonic dispersions of single and double-tailed glycolipids at a dose of 500 mg/kg. These glycolipids were innocuous on Namalva cell cultures at a concentration of 0.1 g/l.

New approaches to targeting bioactive compounds

The paper reviews some of the new approaches to the targeting of bioactive compounds. In particular, the results of artificially rendering macromolecules hydrophobic by nonpolar substituents are considered. This principle enabled us to develop a method for suppressing virus reproduction in cells with fatty acylated antiviral antibodies and also to enhance antisense activity of short complementary oligonucleotides. Some ideas for creation of drug-targeting systems based on self-assembling supramolecular complexes have been tested. In this respect, a possibility of using interpolyelectrolyte complexes of nucleic acids with polycations for targeting genetic material into cells is discussed. Within the limits of this concept, a new class of highly selective immunotoxins (‘respecrins’) representing supramolecular protein complexes in which toxin molecules are reversibly masked by antibodies to specific antigens of target cells has been developed.

Inhibition of HIV in vitro by antiviral drug-targeting using nanoparticles

Nanoparticles are known to accumulate in the phagocytic cells of the mononuclear phagocyte system. Therefore, the use of this carrier system for the targeting of antiviral drugs to monocytes/macrophages (MO/MAC) is an attractive concept in the treatment of diseases involving MO/MAC, e.g. infection with HIV. In this study, the ability of macrophages isolated from peripheral blood of healthy blood donors to phagocytose and metabolize human serum albumin microspheres was investigated by transmission electron microscopy. Furthermore, nanoparticles manufactured using human serum albumin or polyhexylcyanoacrylate were loaded with nucleoside analogues (AZT and ddC) and tested for their ability to prevent HIV infection in MO/MAC cultures. Our results demonstrate the effectiveness of this drug-targeting system to one of the major target cells for HIV.

Drug targeting systems for antiviral agents: options and limitations

Drug targeting systems for antiviral agents: options and limitations

Clinical experience of targeted therapy

Drug targeting (i.e. administration of a drug-carrier conjugate which delivers active drug selectively to a particular tissue) has recently evolved into a new subdiscipline of experimental pharmacy/pharmacology. However, clinical experience with targeted therapy is very limited to date. This review summarizes human studies of targeted therapy. Indications for which drug targeting has been attempted include neoplastic disorders, fungal infections, enzyme replacement, hematologic and immune disorders, and iron storage disease. To date, no single drug targeting system is recommendable for routine clinical use, but present results justify further clinical evaluation in a number of situations.

A nondenaturing solid phase pharmaceutical carrier comprised of surface-modified nanocrystalline materials.

Numerous carrier systems have been developed for the controlled delivery of biologically active molecules such as drugs and diagnostic agents. The biophysical interactions between the biologically active molecules and their carriers, however, may denature the former and lead to reduced biological activity. In this study, a model nondenaturing carrier comprised of a nanocrystalline (10 -7 m) tin oxide core and a surface-charge-reducing organic bonding layer (GF292) was synthesized. A subsequently bound protein (human transferrin) showed significant retained conformation by immunoelectron microscopy. In the synthesis of targeted drug systems and vaccines, nanocrystalline cores treated with appropriate surface-modifying agents may be suitable carriers.

Drug delivery and drug targeting systems: latest advances: 30th November/1st December 1989, Royal Lancaster Hotel, London

Drug delivery and drug targeting systems: latest advances: 30th November/1st December 1989, Royal Lancaster Hotel, London

Drug delivery and drug targeting systems: lates advances: 30th November/1st December 1989, Royal Lancaster Hotel, London

Drug delivery and drug targeting systems: lates advances: 30th November/1st December 1989, Royal Lancaster Hotel, London

Immobilised enzymes as drugs

The main objective of the work is to present the state of the art in a relatively new field of biotechnology — the use of immobilised enzymes in applied medicine. Enzyme therapy seems to be promising in the treatment of cardiovascular, oncological, intestinal, viral and hereditary diseases. At the same time there exist many limitations for the everyday clinical use of native enzymes. Enzymes are unstable, have a short lifetime in the circulation, cause toxic and immune reactions, and are costly, etc. These drawbacks can be at least partially eliminated by enzyme immobilisation onto different carriers. Such immobilisation can make enzymes more stable, less antigenic and impart a longer circulation lifetime in the organism. This present contribution reviews the data on natural and synthetic carriers used for enzyme immobilisation, chemistry of enzyme binding, in vitro and in vivo properties of immobilised enzymes as well as their clinical use. Immobilised enzymes can be used as drugs for either local or systemic application (including soluble and insoluble immobilised enzymes for thrombolytic therapy, and for the treatment of both malignant diseases and some in-born enzyme deficiences). Immobilised enzymes can be also used for preparation of artificial cells (based on semipermeable microcapsules, liposomes, cells and cell ghosts). Special attention is paid to the problem of using the immobilisation principles for the construction of drug targeting systems (vector protein and antibody immobilisation, enzyme-polymer-vector conjugates, etc.).

Drug delivery and drug targeting systems: 14–15 December 1987, London, U.K.

Drug delivery and drug targeting systems: 14–15 December 1987, London, U.K.

On the possibility of the unification of drug targeting systems: Studies with liposome transport to the mixtures of target antigens

In order to make the drug targeting system more effective, simple and technological, we suggest creation of drug-bearing conjugates capable of simultaneous binding with different antigenic components of the target via specific antibodies. It is supposed that the targeted therapy should include sequential administration of the mixture of modified antibodies (or other specific vectors) against different components of affected tissue and, upon antibody accumulation in the desired region, administration of modified drugs or drug carrying systems which can recognize and bind with the target via accumulated antibodies due to the interaction between vector modifier and carrier modifier. Using as a model system monolayers consisting of the mixture of extracellular antigens and appropriated antibodies, it was shown that the treatment of the target with the mixture of biotinylated antibodies against all target components and subsequent binding with the target of biotinylated liposomes via avidin permits high liposome accumulation on the monolayer. The binding achieved is always higher than in the case of the utilization of single antibody-bearing liposomes. Besides, the system suggested is very simple and its components can be easily obtained on technological scale in standardized conditions.