Drug-induced endocytosis and entrapment in red cells and ghosts.

Induction of endocytosis in intact human RBC can be achieved by treating RBC in vitro with several classes of amphipathic cations. Perhaps 1-2% of the 90 fl volume of the red cell will then consist of any material suspended or dissolved in the bulk supernatant medium. This amount could be increased if the material in question also binds selectively to the outer surface of the red cell's plasma membrane. Such a red cell, now rendered spherostomatocytic if reinjected into the circulation, would be removed by the monocytes-macrophages concentrated in spleen and to a lesser extent in liver, lymph nodes, and bone marrow. Conceivably, one could deliver a significant amount of drug or other agent to monocytes-macrophages in these sites. Endocytosis can also be induced in white ghosts and the resulting vacuoles are not accessible to small molecules. The targeting of white ghosts has not been subjected to extensive study but such ghosts containing material included in their endocytic vacuoles could be used to deliver agents to the recipient's monocyte-macrophage system.