Liposomally activated macrophages; subsequent interaction with L1210 leukemic cells

The coincubation of liposomes with mouse leukemia cells or fibroblasts can cause a wide range of effects on their viability. These effects are not particularly specific in terms of destroying the leukemic cells. However, it was observed that the combination of phosphoryl‐choline‐cholesterol (PC‐CHOL)1‐liposomes, which are not toxic by themselves, with alkyl‐lysophospholipids as components of the liposome, can produce the desired specific cytotoxicity for leukemic cells. In this report we show that the cytotoxic effect of vinca alkaloid entrapped in PC‐CHOL‐liposomes was enhanced by syngeneic mouse bone marrow macrophages. In addition, alkyl‐lysophospholipids, which are known to be potent macrophage activators, augment the cytotoxicity. Thus, the macrophage could act as a carrier for liposome‐entrapped drug and, on the other hand, the liposomes partly composed of macrophage activating alkyl‐lysophos‐pholipid and loaded with chemotherapeutic drug seem to be ideal carriers of two effector mechanisms for attacking leukemic cells.