A new treatment strategy for hemophilia B: incorporation of factor IX into red cell ghosts

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.

Erythrocyte-based drug delivery

The use of a physiological carrier to deliver therapeutics throughout the body to both improve their efficacy while minimising inevitable adverse side effects, is an extremely fascinating perspective. The behaviour of erythrocytes as a delivery system for several classes of molecules (i.e., proteins, including enzymes and peptides, therapeutic agents in the form of nucleotide analogues, glucocorticoid analogues) has been studied extensively as they possess several properties, which make them unique and useful carriers. Furthermore, the possibility of using carrier erythrocytes for selective drug targeting to differentiated macrophages increases the opportunities to treat intracellular pathogens and to develop new drugs. Finally, the availability of an apparatus that permits the encapsulation of drugs into autologous erythrocytes has made this technology available in many clinical settings and competitive with other drug delivery systems.

Erythrocytes as carriers of chemotherapeutic agents for targeting the reticuloendothelial system

The object of this work was to define a model using hypotonically loaded erythrocytes as a vehicle to target drugs to the reticuloendothelial system (RES). The optimum hemolytic event was found to occur at 100 mOsm/kg using a 0.5-min exposure at 0 degrees C. Approximately one third of the total volume of the cells could be replaced with hypotonic drug solutions under these conditions. Although cytosine-beta-D-arabinofuranoside, ara C, is membrane permeable and could not be entrapped in the erythrocytes, phosphorylation of this nucleoside antimetabolite enabled it to be loaded efficiently. Actinomycin D could be loaded and retained within the cells at 0 degrees C, but 90% of this loaded drug leaked out of the erythrocytes in 1 min at 37 degrees C. Actinomycin D-DNA complexes, however, could be loaded and retained for longer periods. In this case, 50% of the DNA-bound drug was retained in the cells for one hour at 37 degrees C. It was found that the glycopeptide antitumor antibiotic, bleomycin, could be entrapped and retained in the cells without appreciable leakage. It was possible to load a human therapeutic dose of this drug in 1-2 ml of packed cells. Furthermore, it was demonstrated that bleomycin entrapped in erythrocytes was significantly more effective than the same dose of free drug in suppressing the phagocytic function of the RES in Balb/C and C3H mice. The rationale is discussed for the possible use of these drugs, entrapped in erythrocytes, for the production of RES blockade in the treatment of disorders in man.