Antibody directed targeting of methotrexate-containing small unilamellar vesicles

The potential of antibody-linked SUVs containing MTX in anticancer therapy was investigated. The SUVs, mean diameter 50 +/- 20 nm, were prepared by probe sonication of MTX-containing MLVs and were covalently linked either to a RAMG or NRG. After incubation with M21 melanoma cells for 2 h, RAMG-linked SUVs showed 2 and 4 times more binding than NRG-linked MTX-containing SUVs or MTX-containing SUVs unlinked to any Ig. Furthermore, on incubating M21 melanoma cells with RAMG-linked 3H MTX-containing SUVs for 2, 4, and 8 h at 4 degrees C or 37 degrees C, a higher radioactivity was associated with cells at 37 degrees C than at 4 degrees C. Membrane immunofluorescence revealed aggregation of and cap formation by RAMG-linked SUVs after 2 h (37 degrees C) and endocytosis at 4 and 8 h at 37 degrees C. Electron microscopic and autoradiographic studies confirmed aggregation of 3H MTX-containing SUVs around and on the surface of M21 cells. Electron microscopy also revealed these SUVs inside invaginations of and under the plasma membrane of melanoma cells. A colony inhibition assay showed that RAMG-linked, MTX-containing SUVs were 60 times, 8 times, and 4.5 times more growth inhibitory than free MTX, NRG-linked MTX-containing SUV, and MTX-containing SUVs unlinked to any Ig, but not toxic to a human kidney cancer line (that did not react with RAMG).