Targeting antiretroviral nucleoside analogues in phosphorylated form to macrophages: in vitro and in vivo studies

Clinical progress and advanced research of red blood cells based drug delivery system

Red blood cells (RBCs) are biocompatible carriers that can be employed to deliver different bioactive substances. In the past few decades, many strategies have been developed to encapsulate or attach drugs to RBCs. Osmotic-based encapsulation methods have been industrialized recently, and some encapsulated RBC formulations have reached the clinical stage for treating tumors and neurological diseases. Inspired by the intrinsic properties of intact RBCs, some advanced delivery strategies have also been proposed. These delivery systems combine RBCs with other novel systems to further exploit and expand the application of RBCs. This review summarizes the clinical progress of drugs encapsulated into intact RBCs, focusing on the loading and clinical trials. It also introduces the latest advanced research based on developing prospects and limitations of intact RBCs drug delivery system (DDS), hoping to provide a reference for related research fields and further application potential of intact RBCs based drug delivery system.

Erythrocytes as Carriers: From Drug Delivery to Biosensors

Drug delivery using natural biological carriers, especially erythrocytes, is a rapidly developing field. Such erythrocytes can act as carriers that prolong the drug's action due to its gradual release from the carrier; as bioreactors with encapsulated enzymes performing the necessary reactions, while remaining inaccessible to the immune system and plasma proteases; or as a tool for targeted drug delivery to target organs, primarily to cells of the reticuloendothelial system, liver and spleen. To date, erythrocytes have been studied as carriers for a wide range of drugs, such as enzymes, antibiotics, anti-inflammatory, antiviral drugs, etc., and for diagnostic purposes (e.g. magnetic resonance imaging). The review focuses only on drugs loaded inside erythrocytes, defines the main lines of research for erythrocytes with bioactive substances, as well as the advantages and limitations of their application. Particular attention is paid to in vivo studies, opening-up the potential for the clinical use of drugs encapsulated into erythrocytes.

Red Blood Cell Membrane Processing for Biomedical Applications

Red blood cells (RBC) are actually exploited as innovative drug delivery systems with unconventional and convenient properties. Because of a long in vivo survival and a non-random removal from circulation, RBC can be loaded with drugs and/or contrasting agents without affecting these properties and maintaining the original immune competence. However, native or drug-loaded RBC, can be modified decorating the membrane with peptides, antibodies or small chemical entities so favoring the targeting of the processed RBC to specific cells or organs. Convenient modifications have been exploited to induce immune tolerance or immunogenicity, to deliver antibodies capable of targeting other cells, and to deliver a number of constructs that can recognize circulating pathogens or toxins. The methods used to induce membrane processing useful for biomedical applications include the use of crosslinking agents and bifunctional antibodies, biotinylation and membrane insertion. Another approach includes the expression of engineered membrane proteins upon ex vivo transfection of immature erythroid precursors with lentiviral vectors, followed by in vitro expansion and differentiation into mature erythrocytes before administration to a patient in need. Several applications have now reached the clinic and a couple of companies that take advantage from these properties of RBC are already in Phase 3 with selected applications. The peculiar properties of the RBC and the active research in this field by a number of qualified investigators, have opened new exciting perspectives on the use of RBC as carriers of drugs or as cellular therapeutics.

HIV and the Macrophage: From Cell Reservoirs to Drug Delivery to Viral Eradication

Macrophages serve as host cells, inflammatory disease drivers and drug runners for human immunodeficiency virus infection and treatments. Low-level viral persistence continues in these cells in the absence of macrophage death. However, the cellular microenvironment changes as a consequence of viral infection with aberrant production of pro-inflammatory factors and promotion of oxidative stress. These herald viral spread from macrophages to neighboring CD4⁺ T cells and end organ damage. Virus replicates in tissue reservoir sites that include the nervous, pulmonary, cardiovascular, gut, and renal organs. However, each of these events are held in check by antiretroviral therapy. A hidden and often overlooked resource of the macrophage rests in its high cytoplasmic nuclear ratios that allow the cell to sense its environment and rid it of the cellular waste products and microbial pathogens it encounters. These phagocytic and intracellular killing sensing mechanisms can also be used in service as macrophages serve as cellular carriage depots for antiretroviral nanoparticles and are able to deliver medicines to infectious disease sites with improved therapeutic outcomes. These undiscovered cellular functions can lead to reductions in persistent infection and may potentially facilitate the eradication of residual virus to eliminate disease.

Past, Present, and Future Drug Delivery Systems for Antiretrovirals

The human immunodeficiency virus has infected millions of people and the epidemic continues to grow rapidly in some parts of the world. Antiretroviral (ARV) therapy has provided improved treatment and prolonged the life expectancy of patients. Moreover, there is growing interest in using ARVs to protect against new infections. Hence, ARVs have emerged as our primary strategy in combating the virus. Unfortunately, several challenges limit the optimal performance of these drugs. First, ARVs often require life-long use and complex dosing regimens. This results in low patient adherence and periods of lapsed treatment manifesting in drug resistance. This has prompted the development of alternate dosage forms such as vaginal rings and long-acting injectables that stand to improve patient adherence. Another problem central to therapeutic failure is the inadequate penetration of drugs into infected tissues. This can lead to incomplete treatment, development of resistance, and viral rebound. Several strategies have been developed to improve drug penetration into these drug-free sanctuaries. These include encapsulation of drugs in nanoparticles, use of pharmacokinetic enhancers, and cell-based drug delivery platforms. In this review, we discuss issues surrounding ARV therapy and their impact on drug efficacy. We also describe various drug delivery-based approaches developed to overcome these issues.

Efficacy and Toxicity of Long-Term Administration of 2′,3′-dideoxycytidine in the LP-BM5 Murine-Induced Immunodeficiency Model

The LP-BM5 murine retrovirus-induced immunodeficiency model was used to evaluate the efficacy and toxicity of long-term 2′,3′-dideoxycytidine (DDC) therapy. A mean plasma drug concentration of 0.2 + 0.02 μm of DDC for 3 months was found to reduce splenomegaly, lymphoadenopathy and hypergammaglobulinemia in infected mice. However, DDC also reduced spleen weight in control mice and spleen haemopoiesis in both infected and uninfected animals. In the bone marrow the most prominent feature of DDC treatment was a marked reduction of megakariocytes, while in the liver an hepatocellular vacuolation was evident in uninfected animals. DDC reduced, but did not prevent, LP-BM5 integration in lymph node DNA and Pr 60gag expression in spleen lymphocytes and bone marrow cells. Furthermore, DDC reduced the mitochondrial DNA content and restored the mitogen proliferation of T cells but not that of B cells in infected mice. Thus, DDC appears to be of some, but limited, efficacy in murine AIDS, with a toxicity profile involving more cell types than previously thought.

Inhibition of HIV-1 and LP-BM5 Replication in Macrophages by Dideoxycytidine and Dideoxycytidine 5′-Triphosphate

The antiviral agent 2′,3′-dideoxycytidine (ddC) has been shown to be active against HIV-1 infectivity. However, conflicting results have been reported concerning its efficacy in macrophages. Because macrophages possess low levels of the kinase(s) responsible for ddC phosphorylation, we investigated the ability of ddC and 2′,3′-dideoxycytidine 5′-trisphosphate (ddCTP) to suppress HIV-1 and LP-BM5 replication in these cells. Retrovirus replication was only partially inhibited in the two systems investigated by a high (1 μM) ddC concentration. The direct administration of ddCTP, using autologous red blood cells as a delivery system, was found to inhibit HIV-1 and LP-BM5 replication by more than 90% in macrophages without affecting major cell functions. These data, together with those already reported for FIV [Magnani et al. (1994) AIDS Res Hum Retroviruses 10: 1179-1186], suggest that the anabolic phosphorylation of ddC is an important determinant of its anti-HIV activity and that pharmacological interventions that modulate ddC metabolism may be useful for improving its antiretroviral activity in macrophages.

Drug-loaded erythrocytes: on the road toward marketing approval

Erythrocyte drug encapsulation is one of the most promising therapeutic alternative approaches for the administration of toxic or rapidly cleared drugs. Drug-loaded erythrocytes can operate through one of the three main mechanisms of action: extension of circulation half-life (bioreactor), slow drug release, or specific organ targeting. Although the clinical development of erythrocyte carriers is confronted with regulatory and development process challenges, industrial development is expanding. The manufacture of this type of product can be either centralized or bedside based, and different procedures are employed for the encapsulation of therapeutic agents. The major challenges for successful industrialization include production scalability, process validation, and quality control of the released therapeutic agents. Advantages and drawbacks of the different manufacturing processes as well as success key points of clinical development are discussed. Several entrapment technologies based on osmotic methods have been industrialized. Companies have already achieved many of the critical clinical stages, thus providing the opportunity in the future to cover a wide range of diseases for which effective therapies are not currently available.

Improving bioavailability and biodistribution of anti-HIV chemotherapy

In the context of the treatment of HIV/AIDS, many improvements have been achieved since the introduction of the combination therapy (HAART). Nevertheless, no cure for this disease has been so far possible, because of some particular features of the therapies. Among them, two important ones have been selected and will be the subject of this review. The first main concern in the treatments is the poor drug bioavailability, resulting in repeated administrations and therefore a demanding compliance (drug regimens consist of multiple drugs daily intake, and non-adherence to therapy is among the important reasons for treatment failure). A second important challenge is the need to target the drugs into the so-called reservoirs and sanctuaries, i.e. cells or body compartments where drugs cannot penetrate or are distributed in sub-active concentrations. The lack of antiviral action in these regions allows the virus to lie latent and start to replicate at any moment after therapy suspension. Recent drug delivery strategies addressing these two limitations will be presented in this review. In the first part, strategies to improve the bioavailability are proposed in order to overcome the absorption or the target cell barrier, or to extend the efficacy time of drugs. In the second section, the biodistribution issues are considered in order to target the drugs into the reservoirs and the sanctuaries, in particular the mononuclear phagocyte system and the brain.

Co-opting biology to deliver drugs

The goal of drug delivery is to improve the safety and therapeutic efficacy of drugs. This review focuses on delivery platforms that are either derived from endogenous pathways, long-circulating biomolecules and cells or that piggyback onto long-circulating biomolecules and cells. The first class of such platforms is protein-based delivery systems--albumin, transferrin, and fusion to the Fc domain of antibodies--that have a long-circulation half-life and are designed to transport different molecules. The second class is lipid-based delivery systems-lipoproteins and exosomes-that are naturally occurring circulating lipid particles. The third class is cell-based delivery systems--erythrocytes, macrophages, and platelets--that have evolved, for reasons central to their function, to exhibit a long life-time in the body. The last class is small molecule-based delivery systems that include folic acid. This article reviews the biology of these systems, their application in drug delivery, and the promises and limitations of these endogenous systems for drug delivery.

Macrophage depletion by free bisphosphonates and zoledronate-loaded red blood cells

Bisphosphonates, besides being important drugs for the treatment of various bone diseases, could also be used to induce apoptosis in macrophage-like and cancer cells. However, their activity in vivo is limited by a short plasma half-life and rapid uptake within bone. Therefore, several delivery systems have been proposed to modify their pharmacokinetic profile and biodistribution. Among these, red blood cells (RBCs) represent one of the most promising biological carriers. The aim of this study was to select the best performing compound among Clodronate, Pamidronate, Ibandronate and Zoledronate in killing macrophages and to investigate RBCs as innovative carrier system to selectively target bisphosphonates to macrophages. To this end, the encapsulation of the selected bisphosphonates in autologous RBCs as well as the effect on macrophages, both in vitro and in vivo were studied. This work shows that, among the tested bisphosphonates, Zoledronate has proven to be the most active molecule. Human and murine RBCs have been successfully loaded with Zoledronate by a procedure of hypotonic dialysis and isotonic resealing, obtaining a dose-dependent drug entrapment with a maximal loading of 7.96±2.03, 6.95±3.9 and 7.0±1.89 µmoles of Zoledronate/ml of packed RBCs for human, Swiss and Balb/C murine RBCs, respectively. Engineered RBCs were able to detach human and murine macrophages in vitro, leading to a detachment of 66±8%, 67±8% and 60.5±3.5% for human, Swiss and Balb/C RBCs, respectively. The in vivo efficacy of loaded RBCs was tested in Balb/C mice administering 59 µg/mouse of RBC-encapsulated Zoledronate. By a single administration, depletion of 29.0±16.38% hepatic macrophages and of 67.84±5.48% spleen macrophages was obtained, confirming the ability of encapsulated Zoledronate to deplete macrophages in vivo. In conclusion, RBCs loaded with Zoledronate should be considered a suitable system for targeted delivery to macrophages, both in vitro and in vivo.

Cell-based drug-delivery platforms

Cell systems have recently emerged as biological drug carriers, as an interesting alternative to other systems such as micro- and nano-particles. Different cells, such as carrier erythrocytes, bacterial ghosts and genetically engineered stem and dendritic cells have been used. They provide sustained release and specific delivery of drugs, enzymatic systems and genetic material to certain organs and tissues. Cell systems have potential applications for the treatment of cancer, HIV, intracellular infections, cardiovascular diseases, Parkinson’s disease or in gene therapy. Carrier erythrocytes containing enzymes such us L-asparaginase, or drugs such as corticosteroids have been successfully used in humans. Bacterial ghosts have been widely used in the field of vaccines and also with drugs such as doxorubicin. Genetically engineered stem cells have been tested for cancer treatment and dendritic cells for immunotherapeutic vaccines. Although further research and more clinical trials are necessary, cell-based platforms are a promising strategy for drug delivery.

Targeted therapeutics and nanodevices for vascular drug delivery: quo vadis?

This issue of the journal is dedicated to targeted delivery of therapeutics in the vasculature, an approach that holds promise to optimize treatment of diverse pathological conditions ranging from ischemia and tumor growth to metabolic and genetic diseases. From the standpoint of drug delivery, circulation system represents the natural route to the targets, whereas its components (blood and vascular cells) represent targets, carriers or barriers for drug delivery. Diverse nanodevices and targeted therapeutic agents that are designed and tested in animal and early clinical studies to achieve optimal and precise spatiotemporal control of the pharmacokinetics, destination, metabolism and effect of pharmacological agents will be discussed in this introductory essay and subsequent critical reviews in this series.

Erythrocytes as carriers of antisense PNA addressed against HIV-1 gag-pol transframe domain

PNA(PR2) is a peptide nucleic acid (PNA) complementary to a sequence of the viral protease-encoding gene, effective in blocking HIV release, when used at high doses. Erythrocytes (RBC) were used to target PNA(PR2) to the macrophage compartment. The antiviral activity was assessed in human HIV-infected macrophages both as inhibition of p24 production and reduction of HIV DNA content. PNA(PR2), either added to the medium at a concentration of 100 microM or loaded into RBC at about 40 microM, inhibited p24 production approximately 80% compared with infected samples and reduced HIV DNA content by 83% and 90%, respectively. The results show that (1) a stronger anti-HIV effect is achievable with higher doses of PNA(PR2), both when given free and encapsulated into RBC; (2) the antiviral effect obtained by free PNA(PR2) at a concentration of 100 microM is achievable by encapsulating it into RBC at a concentration of 40 microM, suggesting that RBC can be used as a delivery system to increase the antisense effect of PNA(PR2).

Drug delivery by red blood cells: vascular carriers designed by mother nature

IMPORTANCE OF THE FIELD

Vascular delivery of several classes of therapeutic agents may benefit from carriage by red blood cells (RBC), for example, drugs that require delivery into phagocytic cells and those that must act within the vascular lumen. The fact that several protocols of infusion of RBC-encapsulated drugs are now being explored in patients illustrates a high biomedical importance for the field. AREAS COVERED BY THIS REVIEW: Two strategies for RBC drug delivery are discussed: encapsulation into isolated RBC ex vivo followed by infusion in compatible recipients and coupling therapeutics to the surface of RBC. Studies of pharmacokinetics and effects in animal models and in human studies of diverse therapeutic enzymes, antibiotics and other drugs encapsulated in RBC are described and critically analyzed. Coupling to RBC surface of compounds regulating immune response and complement, affinity ligands, polyethylene glycol alleviating immune response to donor RBC and fibrinolytic plasminogen activators are described. Also described is a new, translation-prone approach for RBC drug delivery by injection of therapeutics conjugated with fragments of antibodies providing safe anchoring of cargoes to circulating RBC, without need for ex vivo modification and infusion of RBC.

WHAT THE READER WILL GAIN

Readers will gain historical perspective, current status, challenges and perspectives of medical applications of RBC for drug delivery.

TAKE HOME MESSAGE

RBC represent naturally designed carriers for intravascular drug delivery, characterized by unique longevity in the bloodstream, biocompatibility and safe physiological mechanisms for metabolism. New approaches for encapsulating drugs into RBC and coupling to RBC surface provide promising avenues for safe and widely useful improvement of drug delivery in the vascular system.

Biological gene delivery vehicles: beyond viral vectors

Gene therapy covers a broad spectrum of applications, from gene replacement and knockdown for genetic or acquired diseases such as cancer, to vaccination, each with different requirements for gene delivery. Viral vectors and synthetic liposomes have emerged as the vehicles of choice for many applications today, but both have limitations and risks, including complexity of production, limited packaging capacity, and unfavorable immunological features, which restrict gene therapy applications and hold back the potential for preventive gene therapy. While continuing to improve these vectors, it is important to investigate other options, particularly nonviral biological agents which include bacteria, bacteriophage, virus-like particles (VLPs), erythrocyte ghosts, and exosomes. Exploiting the natural properties of these biological entities for specific gene delivery applications will expand the repertoire of gene therapy vectors available for clinical use. Here, we review the prospects for nonviral biological delivery vehicles as gene therapy agents with focus on their unique evolved biological properties and respective limitations and potential applications. The potential of these nonviral biological entities to act as clinical gene therapy delivery vehicles has already been shown in clinical trials using bacteria-mediated gene transfer and with sufficient development, these entities will complement the established delivery techniques for gene therapy applications.

Effect of macrophage depletion on viral DNA rebound following antiretroviral therapy in a murine model of AIDS (MAIDS)

In the attempt to eradicate HIV-1 infection, a strategy to eliminate macrophages, one of the most important cellular reservoirs in sustaining virus replication during HAART, could be of great benefit in the suppression of viral rebound. Aware of the ability of clodronate to cause macrophage depletion, the effect of the administration of clodronate encapsulated in erythrocytes on disease progression and on viral rebound was evaluated in a murine model of AIDS (MAIDS). One group of LP-BM5 retroviral complex-infected C57BL/6 mice received oral administrations of azidothymidine and dideoxyinosine daily for 12 weeks; two other groups received in addition, either clodronate-loaded erythrocytes or free clodronate at 7-10 day intervals. At the end of the treatment, the three groups maintained parameters characterizing disease progression similar to those of uninfected mice and showed a significantly lower level of BM5d DNA than infected mice in all organs and cells tested. To assess the viral rebound, some animals were left for an additional 4 month period without any treatment. After this time, the BM5d DNA content in blood leukocytes increased in all groups, but the group having received clodronate-loaded erythrocytes, in addition to transcriptase inhibitors, showed a significant delay in viral rebound.

Prolonged islet allograft survival in diabetic mice upon macrophage depletion by clodronate-loaded erythrocytes

Early impairment of islet function and graft loss strongly limit the success of allogenic islet transplantation in insulin-dependent diabetes. Macrophages play a key role in this process thus the depletion of these cells may strongly affect islet survival. In this study, we have evaluated the effect of the depletion of macrophages in mouse allograft rejection using a new approach based on a single infusion of red blood cells loaded with the synthetic analogue of pyrophosphate clodronate. Graft survival was 19.4+/-0.89 and 20+/-2 days in the two control groups treated with physiological solution and unloaded erythrocytes, respectively; 25+/-1.9 days in the group treated with free-clodronate and 35+/-6 days in the erythrocytes-loaded group. Our results indicate clodronate selectively targeted to the macrophagic cells by a single administration of engineered erythrocytes can significantly prolong islet graft survival and open new therapeutic strategies in islet transplantation.

Inhibition of HIV-1 replication in macrophages by red blood cell-mediated delivery of a heterodinucleotide of lamivudine and tenofovir

Homo- and heterodimers of nucleoside/nucleotide analogues as reverse transcriptase inhibitors are effective on HIV-1-infected human monocyte-derived macrophages (M/M) compared to the single drugs or their combination. Since the combined treatment of lamivudine (3TC) and tenofovir ((R)PMPA) has an antiretroviral efficacy and a synergic effect respect to separate drugs, the heterodinucleotide 3TCpPMPA was synthesized. A single administration of the dimer as free drug or 3TCpPMPA-loaded RBC selectively targeted to M/M was able to almost completely protect macrophages from "de novo" infection.

Cell-based drug delivery

Drug delivery has been greatly improved over the years by means of chemical and physical agents that increase bioavailability, improve pharmacokinetic and reduce toxicities. At the same time, cell based delivery systems have also been developed. These possesses a number of advantages including prolonged delivery times, targeting of drugs to specialized cell compartments and biocompatibility. Here we'll focus on erythrocyte-based drug delivery. These systems are especially efficient in releasing drugs in circulations for weeks, have a large capacity, can be easily processed and could accommodate traditional and biologic drugs. These carriers have also been used for delivering antigens and/or contrasting agents. Carrier erythrocytes have been evaluated in thousands of drug administration in humans proving safety and efficacy of the treatments. Erythrocyte-based delivery of new and conventional drugs is thus experiencing increasing interests in drug delivery and in managing complex pathologies especially when side effects could become serious issues.

Delivery systems to increase the selectivity of antibiotics in phagocytic cells

Many infectious diseases are caused by facultative organisms that are able to survive in phagocytic cells. The intracellular location of these microorganisms protects them from the host defence systems and from some antibiotics with poor penetration into phagocytic cells. One strategy used to improve the penetration of antibiotics into phagocytic cells is the use of carrier systems that deliver these drugs directly to the target cell. Delivery systems such as liposomes, micro/nanoparticles, lipid systems, conjugates, and biological carriers such as erythrocyte ghosts may contribute to increasing the therapeutic efficacy of antibiotics and antifungal agents in the treatment of infections caused by intracellular microorganisms. The main objective of this review is to analyze recent advances and current perspectives in the use of antibiotic delivery systems in the treatment of intracellular infections such as mycobacterial infections, brucellosis, salmonellosis, listeriosis, fungal infections, visceral leishmaniasis, and HIV.

Recent advances in delivery systems for anti-HIV1 therapy

In the last years, different non-biological and biological carrier systems have been developed for anti-HIV1 therapy. Liposomes are excellent potential anti-HIV1 carriers that have been tested with drugs, antisense oligonucleotides, ribozymes and therapeutic genes. Nanoparticles and low-density lipoproteins (LDLs) are cell-specific transporters of drugs against macrophage-specific infections such as HIV1. Through a process of protein transduction, cell-permeable peptides of natural origin or designed artificially allow the delivery of drugs and genetic material inside the cell. Erythrocyte ghosts and bacterial ghosts are a promising delivery system for therapeutic peptides and HIV vaccines. Of interest are the advances made in the field of HIV gene therapy by the use of autologous haematopoietic stem cells and viral vectors for HIV vaccines. Although important milestones have been reached in the development of carrier systems for the treatment of HIV, especially in the field of gene therapy, further clinical trials are required so that the efficiency and safety of these new systems can be guaranteed in HIV patients.

Inhibition of HIV-1 replication in macrophages by a heterodinucleotide of lamivudine and tenofovir

OBJECTIVES

(i) To generate a new heterodinucleotide (3TCpPMPA) comprising the drugs lamivudine and tenofovir which have been shown to act synergistically and (ii) to protect macrophages from 'de novo' HIV-1-infection through its administration.

METHODS

3TCpPMPA was obtained by coupling the morpholidate derivative of tenofovir with the mono n-tri-butylammonium salt of lamivudine 5'-monophosphate. Stability and metabolism were evaluated in vitro and in vivo in mice. 3TCpPMPA was encapsulated into autologous erythrocytes by a procedure of hypotonic dialysis, isotonic resealing and reannealing. 3TCpPMPA-loaded erythrocytes were modified to increase their phagocytosis by human macrophages. Macrophages were infected by HIV-1(Ba-L) and inhibition of HIV-1 replication was assessed by HIV p24(gag) quantification.

RESULTS

Pharmacokinetic studies in mice revealed a rapid disappearance of the heterodinucleotide from circulation (t(1/2)=15 min) without any advantage compared with the administration of single drugs. Adding free 3TCpPMPA to macrophages (18 h), a 90% inhibition of viral replication up to 35 days post-treatment was achieved, while only a 60% inhibition was obtained by the combined treatment 3TC and (R)PMPA. When 3TCpPMPA was selectively targeted to the macrophage compartment by a single addition of loaded erythrocytes, the protection of macrophages from 'de novo' infection (99% protection 3 weeks post-treatment) was nearly complete.

CONCLUSIONS

Erythrocytes loaded with 3TCpPMPA and modified to increase their phagocytosis are able to protect macrophages from 'de novo' HIV-1 infection. 3TCpPMPA acts as an efficient antiviral pro-drug that, once inside macrophages, can be slowly converted into 3TCMP and (R)PMPA protecting these cells for a longer period of time.

Applications of carrier erythrocytes in delivery of biopharmaceuticals

Carrier erythrocytes, resealed erythrocytes loaded by a drug or other therapeutic agents, have been exploited extensively in recent years for both temporally and spatially controlled delivery of a wide variety of drugs and other bioactive agents owing to their remarkable degree of biocompatibility, biodegradability and a series of other potential advantages. Biopharmaceuticals, therapeutically significant peptides and proteins, nucleic acid-based biologicals, antigens and vaccines, are among the recently focused pharmaceuticals for being delivered using carrier erythrocytes. In this article, the potential applications of erythrocytes in drug delivery have been reviewed with a particular stress on the studies and laboratory experiences on successful erythrocyte loading and characterization of the different classes of biopharmaceuticals.

Administration of fludarabine-loaded autologous red blood cells in simian immunodeficiency virus-infected sooty mangabeys depletes pSTAT-1-expressing macrophages and delays the rebound of viremia after suspension of antiretroviral therapy

A major limitation of highly active antiretroviral therapy is that it fails to eradicate human immunodeficiency virus (HIV) infection due to its limited effects on viral reservoirs carrying replication-competent HIV, including monocytes/macrophages (M/M). Therefore, therapeutic approaches aimed at targeting HIV-infected M/M may prove useful in the clinical management of HIV-infected patients. In previous studies, we have shown that administration of fludarabine-loaded red blood cells (RBC) in vitro selectively induces cell death in HIV-infected M/M via a pSTAT1-dependent pathway. To determine the in vivo efficacy of this novel therapeutic strategy, we treated six naturally simian immunodeficiency virus (SIV)-infected sooty mangabeys (SMs) with either 9-[2-(R)-(phosphonomethoxy)propyl]adenine (PMPA) only, fludarabine-loaded RBC only, or PMPA in association with fludarabine-loaded RBC. The rationale of this treatment was to target infected M/M with fludarabine-loaded RBC at a time when PMPA is suppressing viral replication taking place in activated CD4+ T cells. In vivo administration of fludarabine-loaded RBC was well tolerated and did not induce any discernible side effect. Importantly, addition of fludarabine-loaded RBC to PMPA delayed the rebound of viral replication after suspension of therapy, thus suggesting a reduction in the size of SIV reservoirs. While administrations of fludarabine-loaded RBC did not induce any change in the CD4+ or CD8+ T-cell compartments, we observed, in chronically SIV-infected SMs, a selective depletion of M/M expressing pSTAT1. This study suggests that therapeutic strategies based on the administration of fludarabine-loaded RBC may be further explored as interventions aimed at reducing the size of the M/M reservoirs during chronic HIV infection.

Macrophage depletion induced by clodronate-loaded erythrocytes

Given the important role of macrophages in various disorders, the transient and organ specific suppression of their functions may benefit some patients. Until now, liposome-encapsulated bisphosphonate clodronate has been extensively proposed to this end. In this paper, we demonstrate that erythrocytes loaded with clodronate can also be effective in macrophage depletion. Here, clodronate was encapsulated in erythrocytes through hypotonic dialysis, isotonic resealing and reannealing to final concentrations of 4.1 +/- 0.4 and 10.1 +/- 0.8 micromol/ml of human and murine erythrocytes, respectively. The ability of clodronate-loaded erythrocytes to deplete macrophages was evaluated both in vitro and in vivo. In vitro studies on human macrophages showed that a single administration of engineered erythrocytes was able to reduce cell adherence capacity in a time-dependent manner, reaching 50 +/- 4% reduction, 13 days post treatment. The administration of loaded erythrocytes to cultures of murine peritoneal macrophages was able to reduce macrophage adhesion 67 +/- 3%, 48 h post treatment. In vivo, the ability of clodronate-loaded erythrocytes to deplete macrophages was evaluated both in Swiss and C57BL/6 mice. Swiss mice received 125 microg of clodronate through erythrocytes and 6 days post treatment 69 +/- 7% reduction in the number of adherent peritoneal macrophages and 75 +/- 5% reduction in number of spleen macrophages were observed. C57BL/6 mice received 220 microg clodronate by RBC and 3 and 8 days post treatment 65 +/- 7% reduction in the number of spleen macrophages and the complete depletion of liver macrophages were obtained. In summary, our results indicate that clodronate selectively targeted to the phagocytic cells by a single administration of engineered erythrocytes is able to deplete macrophages, even if not completely. The transient suppression of macrophage functions through clodronate-loaded erythrocytes can be used in many biomedical phenomena and research applications.

Factors associated with the performance of carrier erythrocytes obtained by hypotonic dialysis

Carrier erythrocytes containing drugs, enzymes or peptides can be used as a delivery system that allows changes in the kinetic behaviour and selective biodistribution of the substances encapsulated. Hypotonic dialysis is the method most commonly used in the preparation of carrier erythrocytes, but many factors affect the yield and characteristics of the ghost erythrocytes obtained using this method. This review analyses the factors that affect the performance of carrier erythrocytes prepared by hypotonic dialysis. Factors such as the composition and osmolality range of the hypotonic buffer used, the duration of the hypotonic dialysis, temperature, the volume ratio between the erythrocyte suspension and the dialysis buffer, the inclusion in the process of an annealing phase, the composition and osmolality of the resealing buffer, and the conditions under which the final washing of the erythrocytes is carried out may all affect the morphological properties and the later in vivo behaviour of the ghost erythrocytes obtained. Changes in the yield of the encapsulation process, the in vitro drug or enzyme controlled delivery, the pharmacokinetic properties or the in vivo tissue targeting may be modified depending on the conditions under which the preparation of carrier erythrocytes by hypotonic dialysis is carried out. Chemical alterations to the membrane of carrier erythrocytes obtained by hypotonic dialysis with substances such as glutaraldehyde, band 3 cross-linking reagents, trypsin or NHS-biotin, among others, may affect the release rate of the substances encapsulated and may increase the uptake of cells by macrophages both in vitro and in vivo.

Drug, enzyme and peptide delivery using erythrocytes as carriers

Erythrocytes are potential biocompatible vectors for different bioactive substances, including drugs. These can be used successfully as biological carriers of drugs, enzymes and peptides. There are currently diverse methods that permit drug encapsulation in erythrocytes with an appropriate yield. The methods most commonly employed are based on a high-haematocrit dialysis procedure, mainly hypo-osmotic dialysis. Erythrocytes loaded with drugs and other substances allow for different release rates to be obtained. Encapsulation in erythrocytes significantly changes the pharmacokinetic properties of drugs in both animals and humans, enhancing liver and spleen uptake and targeting the reticulo-endothelial system (RES). Amongst other applications, erythrocytes have been used for drug-targeting the RES with aminoglycoside antibiotics; the selective transport to certain organs and tissues of certain antineoplastic drugs, such as methotrexate, doxorubicine, etoposide, carboplatin, etc.; the encapsulation of angiotensin-converting enzyme (ACE) inhibitors, systemic corticosteroids, the encapsulation of new prodrugs with increased duration of action, etc. Erythrocytes are also attractive systems in the sense of their potential ability to deliver proteins and therapeutic peptides. Thus, erythrocytes have been used for the transport of enzymes destined for the correction of metabolic alterations as l-asparaginase, alcohol dehydrogenase (ADH) and aldehyde dehydrogenase (AlDH) among others. Erythrocytes have been used successfully as carriers of anti-HIV peptides, such as AZT, nucleoside analogues, antisense oligonucleotides, antineoplastic peptides, erythropoietin, interleukin 3, etc. Amongst other applications, mention may be made of paramagnetic erythrocytes, encapsulation of MRI contrast agents or the study of the metabolism of the red cell. Although erythrocytes have been applied with different uses in human medicine, their deployment is still very limited due to difficulties involving storage, its exposure to contamination and the absence of a validated industrial procedure for its preparation.

Drug-loaded red blood cell-mediated clearance of HIV-1 macrophage reservoir by selective inhibition of STAT1 expression

Current highly active antiretroviral therapy (HAART) cannot eliminate HIV-1 from infected persons, mainly because of the existence of refractory viral reservoir(s). Beyond latently-infected CD4+-T lymphocytes, macrophages (M/M) are important persistent reservoirs for HIV in vivo, that represent a major obstacle to HIV-1 eradication. Therefore, a rational therapeutic approach directed to the selective elimination of long-living HIV-infected M/M may be relevant in the therapy of HIV infection. Here we report that HIV-1 chronic infection of human macrophages results in the marked increase of expression and phosphorylation of STAT1, a protein involved in the regulation of many functions such as cell growth, differentiation, and maintenance of cellular homeostasis, thereby providing a new molecular target for drug development. A single and brief exposure to 9-(beta-D-arabinofuranosyl)-2-fluoroadenine 5'-monophosphate (FaraAMP, Fludarabine), a potent antileukemic nucleoside analog active against STAT1 expressing cells, selectively kills macrophage cultures infected by HIV-1 without affecting uninfected macrophages. Furthermore, encapsulation of Fludarabine into autologous erythrocytes (RBC) and targeting to macrophages through a single-18 h treatment with drug-loaded RBC, not only abolishes the Fludarabine-mediated toxic effect on non-phagocytic cells, but also enhances the selective killing of HIV-infected macrophages. As a final result, a potent (>98%) and long-lasting (at least 4 weeks without rebound) inhibition of virus release from drug-loaded RBC-treated chronically-infected macrophages was achieved. Taken together, the evidence of HIV-1-induced increase of STAT1, and the availability of a selective drug targeting system, may prove useful in the design of new pharmacological treatments to clear the HIV-1 macrophage reservoir.

Prophylactic fibrinolysis through selective dissolution of nascent clots by tPA-carrying erythrocytes

A fibrinolytic agent consisting of a tissue-type plasminogen activator (tPA) coupled to the surface of red blood cells (RBCs) can dissolve nascent clots from within the clot, in a Trojan horse-like strategy, while having minimal effects on preexisting hemostatic clots or extravascular tissue. After intravenous injection, the fibrinolytic activity of RBC-tPA persisted in the bloodstream at least tenfold longer than did that of free tPA. In a model of venous thrombosis induced by intravenously injected fibrin microemboli aggregating in pulmonary vasculature, soluble tPA lysed pulmonary clots lodged before but not after tPA injection, whereas the converse was true for RBC-tPA. Free tPA failed to lyse occlusive carotid thrombosis whether injected before or after vascular trauma, whereas RBC-tPA circulating before, but not injected after, thrombus formation restored blood flow. This RBC-based drug delivery strategy alters the fibrinolytic profile of tPA, permitting prophylactic fibrinolysis.

Delivery to macrophages and toxic action of etoposide carried in mouse red blood cells

Erythrocytes could be used as physiological carriers of active compounds. Several substances can be loaded into erythrocytes by hypotonic dialysis methods. Furthermore, carrier erythrocyte membrane can be chemically modified in order to promote increased arrival of the loaded compound to macrophages. In this work, we have prepared erythrocytes loaded with etoposide. We found conditions to obtain high etoposide encapsulation yields with minor alteration of some cell parameters of these carrier erythrocytes. Etoposide loaded into erythrocytes is mainly localised in the cytoplasmic compartment. Membrane modification of etoposide-loaded erythrocytes with band 3 crosslinkers produces an increased incorporation of the drug into macrophages mainly by phagocytosis process. The toxic effect of etoposide conveyed in these carrier erythrocytes determined as DNA fragmentation in macrophages was higher than that shown by free etoposide added at the same concentration in the culture medium to macrophages. These results seem to indicate the usefulness of this model to deliver this anti-tumour compound to macrophages, which might be useful in therapy.

Erythrocyte-mediated delivery of drugs, peptides and modified oligonucleotides

An important determinant for the success of every new therapy is the ability to deliver the molecules of interest to the target cells or organ. This selective delivery is even more complex when the therapeutic agents are peptides, modified oligonucleotides or genes. In this paper we summarize the possibility of using autologous erythrocytes for the delivery and targeting of new and conventional therapeutics. In fact, a number of macromolecules can be encapsulated by different procedures into human erythrocytes. These modified cells can then be re-infused into the same or a compatible recipient where they can circulate for several weeks. However, drug-loaded erythrocytes can also be modified to be selectively recognized by tissue macrophages. These phagocyte cells recognize the modified drug-loaded erythrocytes which are able to release their content into the macrophage. The feasibility and safety of the use of erythrocytes as drug delivery systems was evaluated in 10 cystic fibrosis patients, where a sustained release of corticosteroids from dexamethasone 21-phosphate-loaded erythrocytes was obtained. In vitro human erythrocytes were found to be able to deliver ubiquitin analogues and modified oligonucleotides to macrophages. Thus, drug-loaded erythrocytes are safe and useful carriers of new and conventional therapeutics and can be advantageous delivery systems for new clinical applications where proteins and oligonucleotides are therapeutic agents.

Efficacy of macrolides used in combination with ethambutol, with or without other drugs, against Mycobacterium avium within human macrophages

The activities of clarithromycin or roxithromicin used in combination with other antimicrobial drugs were tested in human macrophages experimentally infected with 23 strains of Mycobacterium avium. Overall, clarithromycin-ethambutol-rifampicin was the most active combination tested. The reduction in intracellular viable bacilli was found to be more than 1 log(10) for 95% and more than 2 logs(10) for 65% of the strains. The second most active combination was roxithromycin-ethambutol-rifampicin, which was found to be bactericidal for about 80% and highly bactericidal for 20% of the strains. Others combinations were only bacteriostatic or weakly bactericidal for many of the strains. The addition of a third drug did not necessarily promote enhanced bacterial killing inside the macrophage.

Inhibition of HIV-1 replication in macrophages by red blood cell-mediated delivery of a heterodinucleotide of azidothymidine and 9-(R)-2-(phosphono methoxypropyl)adenine

Monocyte-derived macrophages (M/M) are considered important in vivo reservoirs for different kinds of viruses, including HIV. Hence, therapeutic strategies are urgently needed to protect these cells from virus infection or to control viral replication. In this paper, we report the synthesis, target delivery and in vitro efficacy of a new heterodinucleotide (AZTpPMPA), able to inhibit HIV-1 production in human macrophages. AZTpPMPA consists of two established anti-HIV drugs [zidovudine (AZT) and tenofovir (PMPA)] chemically coupled together by a phosphate bridge. This drug is not able to prevent p24 production when administered for 18 h to M/M experimentally infected with HIV-1 Bal (inhibition 27%), but can almost completely suppress virus production when given encapsulated into autologous erythrocytes (inhibition of p24 production 97%). AZTpPMPA is slowly converted to PMPA, AZT monophosphate and AZT (36 h half-life at 37 degrees C) by cell-resident enzymes. Thus AZTpPMPA should be considered a new prodrug of AZT and PMPA that is able to provide stechiometric amounts of both nucleoside analogues to macrophage cells and to overcome the low phosphorylating activity of M/M for AZT and the modest permeability of PMPA.

New drug combinations for the treatment of murine AIDS and macrophage protection

The failure of highly active antiretroviral therapies (HAART) is mainly due to the existence of latent infected reservoirs, such as macrophages and resting CD4+ T cells. In this paper, we report the results that we obtained in a murine model of AIDS by alternating the administration of the lympholitic drug 2-Fluoro-ara-AMP (Fludarabine) to eliminate the infected cells, with that of Azidothymidine (AZT) plus reduced glutathione (GSH) encapsulated in erythrocytes, to protect lymphocytes and macrophages not yet infected, respectively. Two groups of infected mice were treated as follows: one group was treated by alternating the administration of Fludarabine and AZT (treatment A), while the other group received the same treatment plus GSH-loaded erythrocytes given with AZT (treatment A + L-RBC). Fludarabine was administered intraperitoneally, AZT in the drinking water and GSH was encapsulated in erythrocytes by a procedure of hypotonic dialysis and isotonic resealing. The results obtained show that GSH-loaded erythrocytes provide additive effects in all the parameters examined. Alternation of a lympholitic drug and antiretroviral drug is effective in reducing the progression of murine AIDS. Addition of a system to protect macrophages provides additive effects in almost all the parameters considered, confirming that combination therapies aimed at protecting different infectable cell compartments are better than treatments protecting mainly lymphocytes.

Selective inhibition of NF-kB activation and TNF-alpha production in macrophages by red blood cell-mediated delivery of dexamethasone

Glucocorticoids are a widely used class of anti-inflammatory and immunosuppressive drugs, but their therapeutic use is limited by endocrine and metabolic side effects that they produce when given systemically. Since cells of the monocyte/macrophage lineage play an important role in the pathogenesis of several autoimmune and inflammatory diseases, a drug-delivery system which targets phagocytic cells was studied. We had previously demonstrated that dexamethasone, a potent glucocorticoid analogue, can be encapsulated in erythrocytes and selectively delivered to macrophages. In addition, lipopolysaccharide (LPS) stimulation of dexamethasone-targeted macrophages results in the suppression of TNF-alpha secretion. In this paper we demonstrate that the administration of dexamethasone to macrophages by means of opsonized red blood cells allows efficient interference with NF-kB activation. This NF-kB repression was in part mediated by induction of IkBalpha gene transcription and, as a consequence, by an increased rate of IkBalpha protein synthesis. Furthermore, NF-kB inactivation correlated with downmodulation of TNF-alpha mRNA expression, demonstrating that suppression of TNF-alpha production in dexamethasone-targeted cells occurs at the transcriptional level.

Efficient inhibition of macrophage TNF-alpha production upon targeted delivery of K48R ubiquitin

K48R ubiquitin (K48R-Ub) is an analogue of native ubiquitin that does not form polyubiquitin chain conjugates. Targeted delivery of this recombinant mutant ubiquitin to human macrophages results in an intracellular increase in the ubiquitin analogue. IkappaBalpha polyubiquitination and degradation were significantly inhibited in K48R-Ub targeted macrophages upon stimulation with lipopolysaccharide. The ability to reduce IkappaBalpha degradation was also associated with a reduced production of TNF-alpha, the gene of which is under NF-kappaB control. At a concentration of 0.1 microM, dexamethasone was less effective than K48R-Ub in preventing IkappaBalpha depletion and TNF-alpha release. These data suggest that ubiquitin analogues are potent suppressors of TNF-alpha release in macrophages.

Heterodimer-loaded erythrocytes as bioreactors for slow delivery of the antiviral drug azidothymidine and the antimycobacterial drug ethambutol

Disseminated infection with Mycobacterium avium complex (MAC) remains the most common serious bacterial infection in patients with advanced AIDS. The organisms that make up this complex are found ubiquitously in the environment, yet rarely cause disseminated disease in nonimmunocompromised human patients; on the contrary, up to 50% of patients with AIDS may ultimately develop the pathology. Hence, therapeutic strategies able to inhibit HIV and Mycobacterium replication are needed. Because of the rapid plasma elimination and toxicity of the most commonly used drugs, daily multiple-drug therapies must often be continued throughout life, frequently causing major side effects and, as a consequence, poor patient compliance. Therefore, alternative strategies that reduce the toxicity of the drugs and allow prolonged application intervals are sorely needed. Since erythrocytes (RBCs) can behave as bioreactors able to convert impermeant prodrugs to membrane-releasable active drugs, new compounds (AZTpEMB, AZTpEMBpAZT, and AZTp2EMB) consisting of both an antiretroviral and an antimicrobial drug were designed and synthesized. Among these, only AZTp2EMB was hydrolyzed by erythrocyte enzymes and could be encapsulated inside RBCs. AZTp2EMB-loaded RBCs slowly released AZT and EMB in culture medium, reducing its concentration by one-half about every 48 hr of incubation at 37 degrees C. Moreover, when AZTp2EMB-loaded erythrocytes were incubated for 6 days in the presence of human macrophages infected with Mycobacterium avium (M. avium) a marked bactericidal effect (>1 log) was observed. Thus, AZTp2EMB-loaded erythrocytes could be used as endogenous bioreactors for AZT and EMB delivery in the treatment of HIV and M. avium infection.

Macrophage protection against human immunodeficiency virus or herpes simplex virus by red blood cell-mediated delivery of a heterodinucleotide of azidothymidine and acyclovir

Human herpesvirus (HSVs) are distributed worldwide and are among the most frequent causes of viral infection in HIV-1-immunocompromised patients. Hence, therapeutic strategies able to inhibit HSV-1 and HIV-1 replication are sorely needed. Until now, the most common therapies against HSV-1 and HIV-1 infectivity have been based on the administration of nucleoside analogs; however, to be active, these antiviral drugs must be converted to their triphosphorylated derivatives by viral and/or cellular kinases. At the cellular level, the main problems involved in the use of such drugs are their limited phosphorylation in some cells (e.g., antiretroviral drugs in macrophages) and the cytotoxic side effects of nucleoside analog triphosphates. To overcome these limitations, a new heterodinucleotide (AZTp2ACV) consisting of both an antiretroviral and an antiherpetic drug, bound by a pyrophosphate bridge, was designed and synthesized. The impermeant AZTp2ACV was encapsulated into autologous erythrocytes modified to increase their recognition and phagocytosis by human macrophages. Once inside macrophages, metabolic activation of the drug occurred. The addition of AZTp2ACV-loaded erythrocytes to human macrophages provided effective and almost complete in vitro protection from HIV-1 and HSV-1 replications, respectively. Therefore, AZTp2ACV acts as an efficient antiviral prodrug following selective targeting to macrophages by means of loaded erythrocytes.

Inhibition of murine AIDS by a new azidothymidine homodinucleotide

A new antiretroviral drug (azidothymidine homodinucleotide, AZTp2AZT), designed for the protection of macrophages against retroviral infection, was evaluated in a murine retrovirus-induced immunodeficiency model of AIDS (MAIDS) alone and in combination with oral azidothymidine (AZT). C57BL/6 mice were infected with the retroviral complex LP-BM5 and treated for 3 months by weekly administrations of 15 nmol of AZTp2AZT encapsulated into autologous erythrocytes for macrophage protection. AZTp2AZT treatment was found to reduce lymphoadenopathy (48%), splenomegaly (26%), and BM5d proviral DNA content in lymph nodes, spleen, and brain of 37%, 40%, and 36%, respectively, compared with untreated animals. AZT administration in drinking water (0.25 mg/ml) was more effective than administration of AZTp2AZT encapsulated into erythrocytes in reducing lymphoadenopathy, splenomegaly, gammaglobulinemia, and proviral DNA content in lymph nodes, but it caused a reduction in erythrocyte count and hematocrit levels. Although combined treatments do not provide additive responses in the several parameters investigated, they were found to be much more effective in reducing the proviral DNA content in brain (67%) than were monotherapies. Furthermore, no apparent signs of hematotoxicity were observed. Thus, macrophage delivery of antiviral drugs may contribute to brain protection from retroviral infections by mechanisms other than those exerted by oral AZT administration.

Influence of osmotic stress on protein methylation in resealed erythrocytes

Resealed erythrocytes are a useful means of targeting exogenous proteins or extending their activity. We tested human resealed erythrocytes as a model system for studying protein methyl esterification, a reaction involved in the processing of spontaneously deamidated/isomerized polypeptides. Our results show that resealed erythrocytes are still active in the metabolic processes that lead to the formation of methyl-esterified proteins. The methylation pattern of endogenous membrane proteins appeared to be similar to that of normal erythrocytes, with bands 2.1, 3, 4.1 and 4.2 as the major methyl acceptors. We detected methyl esterification of ovalbumin, as an exogenous substrate trapped within resealed erythrocytes. Methyl incorporation was almost completely inhibited by simultaneously loading red cells with adenosine and homocysteine thiolactone, in vivo precursors of the transmethylation inhibitor S-adenosylhomocysteine. We investigated the effects of repeated resealing procedures on methyl acceptability of endogenous membrane proteins. We found that methyl-incorporation levels increased, despite an apparent conserved protein composition of the membrane. This result suggests that osmotic stress to the membrane may be responsible for increased protein methylation due to the appearance of new sites or an increased accessibility of existing sites.

Red blood cells mediated delivery of 9-(2-phosphonylmethoxyethyl)adenine to primary macrophages: efficiency metabolism and activity against human immunodeficiency virus or herpes simplex virus

Red blood cells (RBC) may act as selective carriers of drugs to macrophages, an important reservoir of viruses such as human immunodeficiency virus (HIV) and herpes simplex virus type 1 (HSV-1). We therefore assessed the incorporation of 9-(2-phosphonylmethoxyethyl)adenine (PMEA), a potent inhibitor of HIV and HSV-1) into RBC, its delivery to macrophages and its activity against HIV or HSV-1. Loading of PMEA in artificially aged opsonized RBC affords significant levels of intracellular PMEA. RBC metabolize PMEA to its active congener PMEA-diphosphate, although with low efficiency. Exposure of macrophages to RBC-encapsulated PMEA inhibits the replication of both HIV and HSV-1 (about 90% inhibition at the highest RBC:macrophages ratios) even if RBC were removed before virus challenge. By contrast, the antiviral activity of free PMEA removed before virus challenge was irrelevant at concentrations up to 150-fold higher than the 50% effective concentration (EC50). Finally, the antiviral effect of RBC-encapsulated PMEA correlates with PMEA levels in macrophages about 500-fold higher than those achieved by free PMEA (at concentrations 10-fold higher than the EC50). The efficacy of RBC-mediated delivery to macrophages of PMEA (and perhaps of compounds with shorter intracellular half-lives) warrants further studies in infectious diseases involving phagocytizing cells as main targets of the pathogen.

Inhibition of murine AIDS by combination of AZT and dideoxycytidine 5'-triphosphate

SUMMARY

A combination of antiretroviral drugs acting on different cell types (lymphocytes and macrophages) was evaluated in a murine retrovirus-induced immunodeficiency model of AIDS (MAIDS). In a first experiment, C57BL/6 mice were infected with a single i.p. administration of LP-BM5 and treated with 0.125 or 0.25 mg/ml AZT in drinking water for 3 months. AZT treatment was found to reduce lymphadenopathy (60 and 65 percent, respectively), splenomegaly (37 and 50 percent, respectively), and hypergammaglobulinemia (6 and 50 percent, respectively). Furthermore, at the highest AZT concentration, BM5d proviral DNA content in lymph nodes and in the spleen showed a reduction of 78 and 70 percent, respectively, compared to untreated animals. In a second experiment, infected mice were treated with AZT (0.25 mg/ml in drinking water) and with 2',3'-dideoxycytidine 5'-triphosphate (ddCTP) encapsulated into autologous erythrocytes for macrophage protection. Combined treatments resulted in a further reduction of lymphadenopathy (a further 33 percent with respect to the single treatment of AZT) and splenomegaly (a further 28 percent respect to the single treatment of AZT) but not of gammaglobulinemia. Proviral DNA in lymph nodes and spleen showed a reduction of 82 and 77 percent, respectively, compared to infected mice. Stimulation index of T cells was also significantly increased in animals receiving both treatments versus AZT only. In conclusion, the selective administration of antiviral drugs that preferentially protect different cell types seems to provide additional advantages compared to single-agent therapy.

Synthesis and targeted delivery of an azidothymidine homodinucleotide conferring protection to macrophages against retroviral infection

The infectivity and replication of human (HIV-1), feline (FIV), and murine (LP-BM5) immunodeficiency viruses are all inhibited by several nucleoside analogues after intracellular conversion to their triphosphorylated derivatives. At the cellular level, the main problems in the use of these drugs concern their limited phosphorylation in some cells (e.g., macrophages) and the cytotoxic side effects of nucleoside analogue triphosphates. To overcome these limitations a new nucleoside analogue homodinucleotide, di(thymidine-3'-azido-2',3'-dideoxy-D-riboside)-5'-5'-p1-p2-pyrophosphat e (AZTp2AZT), was designed and synthesized. AZTp2AZT was a poor in vitro inhibitor of HIV reverse transcriptase, although it showed antiviral and cytotoxic activities comparable to those of the parent AZT when added to cultures of a HTLV-1 transformed cell line. AZTp2AZT encapsulated into erythrocytes was remarkably stable. Induction of erythrocyte-membrane protein clusterization and subsequent phagocytosis of AZTp2AZT-loaded cells allowed the targeted delivery of this impermeant drug to macrophages where its metabolic activation occurs. The addition of AZTp2AZT-loaded erythrocytes to human, feline, and murine macrophages afforded almost complete in vitro protection of these cells from infection by HIVBa-L, FIV, and LP-BM5, respectively. Therefore, AZTp2AZT, unlike the membrane-diffusing azidothymidine, acts as a very efficient antiretroviral prodrug following selective targeting to macrophages by means of loaded erythrocytes.

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.