Specific interaction of myeloma tumor cells with hapten-bearing liposomes containing methotrexate and carboxyfluorescein.

Hapten-bearing liposomes containing methotrexate and the fluorescent solute carboxyfluorescein were incubated with murine myeloma tumor cells expressing surface immunoglobulin with affinity for the hapten. Liposomes bearing the dinitrophenyl hapten became bound to MOPC 315 myeloma tumor cells, and liposomes bearing the phosphorylcholine hapten became bound in much larger amounts to TEPC 15 cells. In each case, fluorescence microscopy showed a patchy surface pattern, indicating intact liposomes at the cell surface. Few liposomes were bound to cells in the presence of excess soluble hapten or to cells lacking the relevant surface immunoglobulin. Cell-associated liposomes were quantitated by use of the fluorescence-activated cell sorter, and the pharmacological effect of the methotrexate was assessed from measurement of incorporation of radiolabeled deoxyuridine into the cells. Little inhibition of deoxyuridine incorporation was observed, because contents of the bound liposomes did not enter the cytoplasmic compartments of the cells.