Antibody-mediated targeting of liposomes to red cells in vivo

Targeted In Vivo Loading of Red Blood Cells Markedly Prolongs Nanocarrier Circulation

Engineering drug delivery systems for prolonged pharmacokinetics (PK) has been an ongoing pursuit for nearly 50 years. The gold standard for PK enhancement is the coating of nanoparticles with polymers, namely polyethylene glycol (PEGylation), which has been applied in several clinically used products. In the present work, we utilize the longest circulating and most abundant component of blood─the erythrocyte─to improve the PK behavior of liposomes. Antibody-mediated coupling of liposomes to erythrocytes was tested in vitro to identify a loading dose that did not adversely impact the carrier cells. Injection of erythrocyte targeting liposomes into mice resulted in a ∼2-fold improvement in the area under the blood concentration versus time profile versus PEGylated liposomes and a redistribution from the plasma into the cellular fraction of blood. These results suggest that in vivo targeting of erythrocytes is a viable strategy to improve liposome PK relative to current, clinically viable strategies.

Red blood cells: The metamorphosis of a neglected carrier into the natural mothership for artificial nanocarriers

Drug delivery research pursues many types of carriers including proteins and other macromolecules, natural and synthetic polymeric structures, nanocarriers of diverse compositions and cells. In particular, liposomes and lipid nanoparticles represent arguably the most advanced and popular human-made nanocarriers, already in multiple clinical applications. On the other hand, red blood cells (RBCs) represent attractive natural carriers for the vascular route, featuring at least two distinct compartments for loading pharmacological cargoes, namely inner space enclosed by the plasma membrane and the outer surface of this membrane. Historically, studies of liposomal drug delivery systems (DDS) astronomically outnumbered and surpassed the RBC-based DDS. Nevertheless, these two types of carriers have different profile of advantages and disadvantages. Recent studies showed that RBC-based drug carriers indeed may feature unique pharmacokinetic and biodistribution characteristics favorably changing benefit/risk ratio of some cargo agents. Furthermore, RBC carriage cardinally alters behavior and effect of nanocarriers in the bloodstream, so called RBC hitchhiking (RBC-HH). This article represents an attempt for the comparative analysis of liposomal vs RBC drug delivery, culminating with design of hybrid DDSs enabling mutual collaborative advantages such as RBC-HH and camouflaging nanoparticles by RBC membrane. Finally, we discuss the key current challenges faced by these and other RBC-based DDSs including the issue of potential unintended and adverse effect and contingency measures to ameliorate this and other concerns.

Liposomes for malaria management: the evolution from 1980 to 2020

Malaria is one of the most prevalent parasitic diseases and the foremost cause of morbidity in the tropical regions of the world. Strategies for the efficient management of this parasitic infection include adequate treatment with anti-malarial therapeutics and vaccination. However, the emergence and spread of resistant strains of malaria parasites to the majority of presently used anti-malarial medications, on the other hand, complicates malaria treatment. Other shortcomings of anti-malarial drugs include poor aqueous solubility, low permeability, poor bioavailability, and non-specific targeting of intracellular parasites, resulting in high dose requirements and toxic side effects. To address these limitations, liposome-based nanotechnology has been extensively explored as a new solution in malaria management. Liposome technology improves anti-malarial drug encapsulation, bioavailability, target delivery, and controlled release, resulting in increased effectiveness, reduced resistance progression, and fewer adverse effects. Furthermore, liposomes are exploited as immunological adjuvants and antigen carriers to boost the preventive effectiveness of malaria vaccine candidates. The present review discusses the findings from studies conducted over the last 40 years (1980-2020) using in vitro and in vivo settings to assess the prophylactic and curative anti-malarial potential of liposomes containing anti-malarial agents or antigens. This paper and the discussion herein provide a useful resource for further complementary investigations and may pave the way for the research and development of several available and affordable anti-malarial-based liposomes and liposomal malaria vaccines by allowing a thorough evaluation of liposomes developed to date for the management of malaria.

Targeted erythropoietin selectively stimulates red blood cell expansion in vivo

The design of cell-targeted protein therapeutics can be informed by natural protein-protein interactions that use cooperative physical contacts to achieve cell type specificity. Here we applied this approach in vivo to the anemia drug erythropoietin (EPO), to direct its activity to EPO receptors (EPO-Rs) on red blood cell (RBC) precursors and prevent interaction with EPO-Rs on nonerythroid cells, such as platelets. Our engineered EPO molecule was mutated to weaken its affinity for EPO-R, but its avidity for RBC precursors was rescued via tethering to an antibody fragment that specifically binds the human RBC marker glycophorin A (huGYPA). We systematically tested the impact of these engineering steps on in vivo markers of efficacy, side effects, and pharmacokinetics. huGYPA transgenic mice dosed with targeted EPO exhibited elevated RBC levels, with only minimal platelet effects. This in vivo selectivity depended on the weakening EPO mutation, fusion to the RBC-specific antibody, and expression of huGYPA. The terminal plasma half-life of targeted EPO was ∼28.3 h in transgenic mice vs. ∼15.5 h in nontransgenic mice, indicating that huGYPA on mature RBCs acted as a significant drug sink but did not inhibit efficacy. In a therapeutic context, our targeting approach may allow higher restorative doses of EPO without platelet-mediated side effects, and also may improve drug pharmacokinetics. These results demonstrate how rational drug design can improve in vivo specificity, with potential application to diverse protein therapeutics.

Liposomal delivery of a phosphodiesterase 3 inhibitor rescues low oxygen-induced ATP release from erythrocytes of humans with type 2 diabetes

ATP release from erythrocytes in response to low oxygen tension requires an increase in cAMP, the level of which is regulated by phosphodiesterase 3 (PDE3). Such release is defective in erythrocytes of humans with type 2 diabetes (DM2). This study tested a hypothesis that direct delivery of the clinically useful PDE3 inhibitor, cilostazol, to erythrocytes of humans with type 2 diabetes using liposomes would restore low-oxygen tension-induced ATP release. Cilostazol was incorporated into liposomes prepared from dimyristoylphosphatidylcholine (DMPC). Liposome-delivery of cilostazol restored ATP release from DM2 erythrocytes to levels which were not different from that released from non-cilostazol treated healthy erythrocytes under the same conditions. There were no observed adverse effects of the liposomes on either healthy or DM2 erythrocytes. The directed liposomal delivery of PDE inhibitors to erythrocytes may help prevent or slow the development of peripheral vascular disease in individuals with DM2 by restoring an important physiological controller of microvascular perfusion while minimizing side effects associated with systemic delivery of some of these inhibitors.

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Liposomes can deliver phosphodiesterase (PDE) inhibitors to erythrocytes.

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No adverse effect of drug-loaded liposomes on erythrocytes was observed.

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Release of ATP from erythrocytes of patients with type 2 diabetes was investigated.

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Liposome-delivered PDE inhibitors restore the release of ATP in response to low O₂.

Erythrocytes-based synthetic delivery systems: transition from conventional to novel engineering strategies

INTRODUCTION

Erythrocytes (red blood cells [RBCs]) and artificial or synthetic delivery systems such as liposomes, nanoparticles (NPs) are the most investigated carrier systems. Herein, progress made from conventional approach of using RBC as delivery systems to novel approach of using synthetic delivery systems based on RBC properties will be reviewed.

AREAS COVERED

We aim to highlight both conventional and novel approaches of using RBCs as potential carrier system. Conventional approaches which include two main strategies are: i) directly loading therapeutic moieties in RBCs; and ii) coupling them with RBCs whereas novel approaches exploit structural, mechanical and biological properties of RBCs to design synthetic delivery systems through various engineering strategies. Initial attempts included coupling of antibodies to liposomes to specifically target RBCs. Knowledge obtained from several studies led to the development of RBC membrane derived liposomes (nanoerythrosomes), inspiring future application of RBC or its structural features in other attractive delivery systems (hydrogels, filomicelles, microcapsules, micro- and NPs) for even greater potential.

EXPERT OPINION

In conclusion, this review dwells upon comparative analysis of various conventional and novel engineering strategies in developing RBC based drug delivery systems, diversifying their applications in arena of drug delivery. Regardless of the challenges in front of us, RBC based delivery systems offer an exciting approach of exploiting biological entities in a multitude of medical applications.

A nanovector with complete discrimination for targeted delivery to Plasmodium falciparum-infected versus non-infected red blood cells in vitro

Current administration methods of antimalarial drugs deliver the free compound in the blood stream, where it can be unspecifically taken up by all cells, and not only by Plasmodium-infected red blood cells (pRBCs). Nanosized carriers have been receiving special attention with the aim of minimizing the side effects of malaria therapy by increasing drug bioavailability and selectivity. Liposome encapsulation has been assayed for the delivery of compounds against murine malaria, but there is a lack of cellular studies on the performance of targeted liposomes in specific cell recognition and on the efficacy of cargo delivery, and very little data on liposome-driven antimalarial drug targeting to human-infecting parasites. We have used fluorescence microscopy to assess in vitro the efficiency of liposomal nanocarriers for the targeted delivery of their contents to pRBCs. 200-nm liposomes loaded with quantum dots were covalently functionalized with oriented, specific half-antibodies against P. falciparum late form-infected pRBCs. In less than 90min, liposomes dock to pRBC plasma membranes and release their cargo to the cell. 100.0% of late form-containing pRBCs and 0.0% of non-infected RBCs in P. falciparum cultures are recognized and permeated by the content of targeted immunoliposomes. Liposomes not functionalized with antibodies are also specifically directed to pRBCs, although with less affinity than immunoliposomes. In preliminary assays, the antimalarial drug chloroquine at a concentration of 2nM, ≥10 times below its IC(50) in solution, cleared 26.7±1.8% of pRBCs when delivered inside targeted immunoliposomes.

Nanotechnology applied to the treatment of malaria

Despite the fact that we live in an era of advanced technology and innovation, infectious diseases, like malaria, continue to be one of the greatest health challenges worldwide. The main drawbacks of conventional malaria chemotherapy are the development of multiple drug resistance and the non-specific targeting to intracellular parasites, resulting in high dose requirements and subsequent intolerable toxicity. Nanosized carriers have been receiving special attention with the aim of minimizing the side effects of drug therapy, such as poor bioavailability and the selectivity of drugs. Several nanosized delivery systems have already proved their effectiveness in animal models for the treatment and prophylaxis of malaria. A number of strategies to deliver antimalarials using nanocarriers and the mechanisms that facilitate their targeting to Plasmodium spp.-infected cells are discussed in this review. Taking into account the peculiarities of malaria parasites, the focus is placed particularly on lipid-based (e.g., liposomes, solid lipid nanoparticles and nano and microemulsions) and polymer-based nanocarriers (nanocapsules and nanospheres). This review emphasizes the main requirements for developing new nanotechnology-based carriers as a promising choice in malaria treatment, especially in the case of severe cerebral malaria.

Tuftsin-bearing liposomes in treatment of macrophage-based infections

The use of liposomes as drug carriers in treatment of various diseases has been explored extensively for more than 20 years. 'Conventional' liposomes, when administered in vivo by a variety of routes, rapidly accumulate in the mononuclear phagocyte system (MPS). The inherent tendency of the liposomes to concentrate in MPS can be exploited in enhancing the non-specific host defence against infections by entrapping in them the macrophage modulators, and as carriers of antibiotics in treatment of intracellular infections that reside in MPS. This must further be enhanced by grafting on the liposome surface the ligands, e.g. tuftsin, that not only binds specifically to the MPS cells but also enhances their natural killer activity. Keeping this in view, we designed and developed tuftsin-bearing liposomes as drug carriers for the treatment of macrophage-based infections and outline these studies in this overview.

Immunoliposomes for the targeted delivery of antitumor drugs

This review presents an overview of the field of immunoliposome-mediated targeting of anticancer agents. First, problems that are encountered when immunoliposomes are used for systemic anticancer drug delivery and potential solutions are discussed. Second, an update is given of the in vivo results obtained with immunoliposomes in tumor models. Finally, new developments on the utilization of immunoliposomes for the treatment of cancer are highlighted.

Chloroquine encapsulated in malaria-infected erythrocyte-specific antibody-bearing liposomes effectively controls chloroquine-resistant Plasmodium berghei infections in mice

The suitability of liposomes as drug carriers in the treatment of drug-resistant rodent malaria was examined after covalently attaching F(ab')2 fragments of a mouse monoclonal antibody (MAb), MAb F10, raised against the host cell membranes isolated from the Plasmodium berghei-infected mouse erythrocytes, to the liposome surface. The antibody-bearing liposomes thus formed specifically recognized the P. berghei-infected mouse erythrocytes under both in vitro and in vivo conditions. No such specific binding of the liposomes with the infected cells was observed when MAb F10 was replaced by another mouse monoclonal antibody, MAb D2. Upon loading with the antimalarial drug chloroquine, the MAb F10-bearing liposomes effectively controlled not only the chloroquine-susceptible but also the chloroquine-resistant P. berghei infections in mice. The chloroquine delivered in these liposomes intravenously at a dosage of 5 mg/kg of body weight per day on days 4 and 6 postinfection completely cured the animals (75 to 90%) of chloroquine-resistant P. berghei infections. These results indicate that selective homing of chloroquine to malaria-infected erythrocytes may help to cure the chloroquine-resistant malarial infections with low doses of chloroquine.

Improvement of therapeutic effect by using Fab' fragment in the treatment of carcinoembryonic antigen-positive human solid tumors with adriamycin-entrapped immunoliposomes

To improve the therapeutic efficiency adriamycin entrapped in antibody-conjugated liposomes, Fab' fragment was used instead of the whole antibody molecule. The murine monoclonal antibody, 21B2, against human carcinoembryonic antigen (CEA) was digested with pepsin, and the thiol residue of intra-heavy chain produced by reduction of F(ab')2 with dithiothreitol was conjugated to liposomes containing adriamycin. The tissue distribution of adriamycin delivered with these liposomes was studied in BALB/c nu/nu female mice bearing CEA-positive human gastric cancer strain MKN-45. An increase in delivery of adriamycin to the tumor was observed in the mice given liposomes with Fab' fragment as compared to those given liposomes with whole antibody. However, the preferential distribution of adriamycin in liposomes to the reticuloendothelial cells remained the same regardless of the use of Fab' fragment. For investigation of in vivo therapeutic effect, three i.v. injections of free adriamycin or adriamycin in liposomes equivalent to 5 mg/kg were given, and adriamycin in Fab' fragment-conjugated liposomes was found most effective in the inhibition of tumor growth. This was confirmed in terms of actual tumor weights excised and CEA concentration in the blood, as well as by pathological observations. The advantages of using Fab' fragment instead of whole antibody are discussed.

In vitro cytostatic effect of TNF (tumor necrosis factor) entrapped in immunoliposomes on cells normally insensitive to TNF

The cytostatic activity of TNF entrapped in novel immunoliposomes with a specific antibody against target cells is described. A two step conjugation method was used for the preparation of these targeted immunoliposomes. In the first step, liposomes containing N-4-(p-maleimidophenyl)butyryl phosphatidylethanolamine (MPB-PE) were conjugated with a goat anti-mouse IgG Fab' fragment which recognizes the Fc portion of a mouse antibody against the target cell markers. In the second step, the mouse antibody against human tumor cells was conjugated to the liposomes. Using these targeted immunoliposomes, we demonstrated that cells usually insensitive to TNF such as Daudi cells, MT-2 cells and T-24 cells could become sensitive to TNF in vitro. The cytostatic activity of these immunoliposomes was blocked by the addition of a lysosomotropic agent such as NH4Cl or chloroquine. Significant uptake of 125I-TNF into T-24 cells was observed when these immunoliposomes were used, and this uptake of TNF was inhibited by cytochalasin B or chloroquine. Free 125I-TNF was not taken up by these cells.

On the interaction of the liposomal membrane with blood components

Liposome-encapsulated hemoglobin (LEH) has been shown to be a viable candidate as a blood replacement. However, few data have been presented as to how LEH interacts with normal blood components. Liposomes were prepared from egg lecithin, cholesterol, and dicetyl phosphate or phosphatidic acid, and mixed with fresh blood plasma or whole blood. Erythrocyte osmotic fragility, prothrombin time (extrinsic coagulation efficiency), activated partial thromboplastin time (intrinsic coagulation efficiency), plasma clot stability in urea (fibrin stabilizing factor), and clot retraction (platelet activation) were measured. Although liposomes were found to bind extensively to erythrocytes, all tests indicated that the liposomes had no significant adverse effects, provided that normal levels of plasma Ca++ were maintained. The ability of liposomes to absorb Ca++ from the plasma was related directly to the amount of dicetyl phosphate or phosphatidic acid present and thus, presumably, to the presence of negatively charged species in the membrane. The mechanics of deformation of the LEH membrane were investigated by encapsulating Hemoglobin S in liposomes. Liposomes containing Hemoglobin S were found to sickle when deoxygenated, but not liposomes containing normal hemoglobin. Shape analysis of sickled liposomes yielded a deforming stress of 10(6) dynes/cm2, about 50 times greater than the reported limit for shear elasticity of the erythrocyte membrane.

Drug targeting in cancer chemotherapy: a clinical perspective

Drug targeting is a phenomenon which maneuvers the distribution of drug in the body in such a manner that the major fraction of the drug interacts exclusively with the target tissue at a cellular or subcellular level. Numerous strategies have been developed to accomplish this goal; some of them have been tried clinically for improving cancer chemotherapy. This review updates the current status of research in the area of targeted drug delivery, with particular emphasis on its application in the clinical management of carcinomas.

Characterization of in vivo immunoliposome targeting to pulmonary endothelium

Two rat monoclonal antibodies, 34A and 201B, which specifically bind to a surface glycoprotein (gp112) of the pulmonary endothelial cell surface, have been coupled to unilamellar liposomes of approximately 0.25 microns in diameter. The 34A- and 201B-liposomes (monoclonal antibodies 273-34A and 411-201B, respectively), but not antibody-free liposomes and liposomes coupled to 14, a nonspecific monoclonal antibody, accumulate efficiently (approximately 30% injected dose) in the lung of mice which have been injected via the tail vein. Immunoliposome targeting to lung is demonstrated both by using a 125I-labeled lipid marker and an entrapped water-soluble marker. Lung accumulation of 34A-liposomes is completely blocked by a preincubation of free antibody 34A, but not antibody 14, indicating that the immunoliposome accumulation at the target site is immunospecific. Time course studies have revealed that 34A-liposomes bind to lung antigens within 1 min after injection, indicating that the target binding takes place during the first few passages of immunoliposomes through the lung capillary bed. Unbound immunoliposomes are taken up by liver and spleen within 3-5 min after injection. The level of lung accumulation increases significantly as the protein:lipid ratio of the immunoliposome increases. Approximately 50% of injected dose is accumulated in lung for 34A-liposomes, with an average of 935 antibody molecules per liposome. Immunoliposomes of larger size accumulate in lung more significantly than those of smaller size. Injection with higher doses also enhances the level of lung accumulation.(ABSTRACT TRUNCATED AT 250 WORDS)

pH-sensitive, plasma-stable liposomes with relatively prolonged residence in circulation

Acid-sensitive liposomes composed of unsaturated phosphatidylethanolamine (PE) are efficient vehicles for cytoplasmic delivery of the target cells. We have recently shown that liposomes composed of dioleoyl-PE (DOPE) and dipalmitoyl-succinylglycerol (DPSG) retain the acid-sensitivity after exposure to human plasma. In the present work, we have extended these observations to investigate the role of ganglioside GM1 on the blood residence time of these liposomes. Small (d approximately 100 nm) unilamellar liposomes composed of DOPE and DPSG (4:1, molar ratio) became progressively less acid-sensitive when increasing amounts of GM1 were included in the lipid composition. However, partial sensitivity to acid (40-50% release of entrapped contents at pH 4) could be retained up to 5% GM1, even for liposomes which had been exposed to human plasma. Inclusion of GM1 in the lipid composition only slightly increased the release of entrapped contents in the presence of human plasma. The biodistribution of i.v. injected GM1-containing liposomes was studied by following the entrapped 125I-labeled tyraminylinulin marker in Balb/c mice. Inclusion of up to 5% GM1 showed a transient increase in the blood level and a concomitant decrease of liver and spleen uptake of liposomes. Thus, these liposomes are pH-sensitive, plasma-stable and show a relatively prolonged residence time in circulation. They are potentially significant drug carriers in vivo.

Drug delivery systems. 1. site-specific drug delivery using liposomes as carriers

Drug delivery systems, offering controlled delivery of biologically active agents, are rapidly gaining importance in pharmaceutical research and development. To achieve controlled drug delivery, i.e., the administration of drugs so that optimal amount reaches the target site to cure or control the disease state, increasingly sophisticated systems containing different carriers have been developed. Macromolecules represent one of the carriers involved, and they have taken on a significantly prominent role in various modes of administration of therapeutic agents. Among macromolecules, for example, synthetic copolymers, polysaccharides, liposomes, polyanions and antibodies, as drug carriers, liposomes have proved most effective for diseases affecting the reticuloendothelial system and blood cells in particular. Liposomes, which are vesicles consisting of one or more concentrically ordered assemblies of phospholipids bilayers, range in size from a nanometer to several micrometers. Phospholipids such as egg phosphatidylcholine, phosphatidylserine, synthetic dipalmitoyl-DL-alpha-phosphatidylcholine or phosphatidylinositol, have been used in conjunction with cholesterol and positively or negatively charged amphiphiles such as stearylamine or phosphatidic acid. Alteration of surface charge has been shown to enhance drug incorporation and also influence drug release. Because of the multifold characteristics as drug carriers, liposomes have been investigated extensively as carriers of anticancer agents for the past several years. Liposomal entrapments include a variety of pharmacologically active compounds such as antimalarial, antiviral, anti-inflammatory and anti-fungal agents as well as antibiotics, prostaglandins, steroids and bronchodilators to name a few. The liposomal entrapment has been shown to have considerable effect on the pharmacokinetics and tissue distribution of administered drugs. Despite the potential value of liposomes as unique carriers, the major obstacles are the first order targeting of a systemically given liposomes, physical stability and manufacture of the liposomal products and these problems still remain to be overcome. Drug delivery systems evolving in the 1980s have become increasingly dependent on fundamental cell-biology and receptor-mediated endocytotic mechanisms. Drug delivery systems during the 1990s may take advantage of the specificity of receptor-mediated uptake mechanisms as well as polymer chemistry and cell-biology in order to introduce more precise and efficient target-specific delivery systems that are based especially on the liposome technology.

Evaluation of drug delivery following the administration of magnetic albumin microspheres containing adriamycin to the rat

The disposition of adriamycin following its intra-arterial administration in rats as a solution (control) or via magnetic albumin microspheres (treatment group) has been investigated. The rat tail was demarcated into three segments: T1, the pre-target site; T2, the target site; and T3, the post-target site. In both groups, 2.0 mg/kg of adriamycin HCl was injected into the ventral caudal artery in T1 through a T-piece cannula. A magnetic field of 8000 G was directed towards T2. The concentration of adriamycin was measured in the heart, kidney, liver, lung, serum, small intestine, spleen, T1, T2, and T3 as a function of time using an ion-pairing HPLC assay. Areas under the mean adriamycin concentration-time curves were used to determine two indices of drug delivery: the relative tissue exposure and targeting efficiency. It was demonstrated that the magnetically responsive albumin microspheres altered the tissue distribution of adriamycin in rats. Administration of drug via magnetic microspheres was shown to increase the relative drug exposure to both T2 and liver.

Cancer chemotherapy administered by activated carbon particles and liposomes

In cancer chemotherapy, a specific drug delivery system is expected since many anticancer drugs show toxicity against not only cancer cells but also against normal tissues. The dosage form comprising anticancer drugs adsorbed on activated carbon particles or encapsulated in liposomes is developed as a drug-delivery system which enhances the therapeutic efficacy and reduces the adverse effects. The dosage forms are versatile in size and electric charge, so that large amounts of the drugs are distributed to the "targeted" organs or tissues and lesser amounts are distributed to the whole body. The dosage forms are designed to release the drugs slowly for a long time at local sites. Through this process, practical use of the dosage forms as an anticancer drug carrier results in an enhancement of anticancer efficacy on the local lesion and a decrease of systemic toxicity.

Immunospecific targeting of immunoliposomes, F(ab')2 and IgG to red blood cells in vivo

In this report a model to study the fate of target cells in the blood circulation after injection of appropriate immunoliposomes is discussed. The effect of intravenous administration of antimouse RBC immunoliposomes, F(ab')2 or IgG on the fate of intravenously injected 51Cr-labelled mouse RBC (Cr-mRBC) in the mouse and, particularly, in the rat was studied. The immunoliposome was of the Fab'-MPBPE-REV type (Fab'-fragments covalently linked to reverse phase evaporation vesicles by maleimido-4-(p-phenylbutyrate)phosphatidylethanolamine). In the rat model a high blood level (80%) of the injected dose of target cells, Cr-mRBC, was maintained for several hours. The elimination by Fab'-liposomes, F(ab')2 or IgG of Cr-mRBC, and subsequent uptake into liver and spleen was dose dependent. Administration of Fab'-liposomes or F(ab')2 resulted in a preferential uptake into the spleen (above a certain dose also, but much lower, uptake into the liver was observed), while after IgG administration 51Cr-label was mainly recovered in the liver. At equal protein doses (+/- 130 micrograms) Fab'-liposomes induced a faster elimination of the Cr-mRBC and a higher uptake into the spleen than F(ab')2. The potential advantage of the use of drug-loaded immunoliposomes to eliminate target cells from the blood stream and to induce a certain pharmacological effect in the target cells, in comparison with the free antibody administration of F(ab')2 or IgG is discussed.

Pharmacokinetics and chemotherapeutic efficacy of adriamycin encapsulated in immunoliposomes against avian myeloblastosis virus infection

Immunoliposomes were prepared using rabbit anti-AMV gp80 IgG for the targeted chemotherapy of avian myeloblastosis virus infection. Adriamycin was encapsulated into immunoliposomes and used for in vivo studies. Comparative pharmacokinetics of free drug, drug encapsulated in free liposomes and of drug encapsulated in immunoliposomes in the virus-infected cells revealed that (i) the drug encapsulated in liposomes was cleared from the plasma slowly, and (ii) the drug encapsulated in immunoliposomes accumulated in the target tissue, the bone marrow, 5- and 8.5-fold more than the drug encapsulated in free liposomes and free drug, respectively. The drug encapsulated in immunoliposomes inactivated the virus and exhibited more chemotherapeutic efficacy as compared to controls when injected up to 24 h post-infection. However, when injected 48 h post-infection the drug encapsulated in immunoliposomes did not offer any protection against the virus infection. There is no detectable antibody response against immunoliposomes in the infected animals.

Functional drug targeting to erythrocytes in vivo using antibody bearing liposomes as drug vehicles

Covalent attachment of anti-erythrocyte F(ab')2 to the liposome surface has recently been shown to considerably enhance the liposome binding to erythrocytes in vivo. These antibody bearing liposomes have now been found quite effective as vehicles for delivering the antimalarial drug, chloroquine, to erythrocytes in Plasmodium berghei-infected mice. This demonstrates the usefulness of antibody targeted liposomes as carriers for site-specific drug delivery.