Interaction of 99mTc-labeled liposomes with Walker tumour cells in vitro. Liposome-mediated introduction of thaliblastine into resistant Walker tumour cells.

A method for labeling phospholipid vesicles (liposomes) with 99mTc-pertechnetate is described. The labeling methodology involves the chemical reduction of sodium 99mTc-pertechnetate by stannous chloride, which produces a 99mTc-SnCl2 complex with high binding capacity to phospholipids. Binding studies in vitro showed that Walker tumour cells can incorporate large amounts of 99mTc-labeled liposomes without cytotoxic effects. Fusion of liposomes with the cell plasma membrane may represent an important pathway for lipid incorporation. A Walker cell line resistant to thaliblastine, on treatment with the antitumour alkaloid thaliblastine entrapped in liposomes, showed a marked growth inhibition at concentrations that had little effect when used as free drug. The usefulness of 99mTc-labeled liposomes for kinetic binding studies with tumour cells in cultures and their possible use as carriers of cytotoxic agents in selective cancer chemotherapy, are discussed.