Anti-laminin receptor antibody targeting of liposomes with encapsulated doxorubicin to human breast cancer cells in vitro.

The tumor cell laminin receptor is a cell-surface protein that binds laminin with high affinity (Kd = 1.0 nM). The putative ligand-binding domain of the laminin receptor has been molecularly cloned and sequenced. In the present study, we used the predicted amino acid sequence of the laminin receptor to generate synthetic peptide antigens and produced immunoglobulin M (IgM) anti-laminin receptor monoclonal antibodies. The disulfide bond group of the IgM molecule was used to couple the antibodies to the surface of liposomes encapsulating doxorubicin. The anti-laminin receptor monoclonal antibodies coupled to the liposomes bound avidly to the surface of MDA-MB-435S (MDA-435) human breast carcinoma cells, which have high numbers of laminin receptors. These antibody-coupled liposomes exhibited a low degree of binding to Hs 578Bst (Hs 578) normal human breast epithelial cells, which express a low number of laminin receptors. Excess liposomes competed for the binding of unbound laminin to the tumor cell surface, and excess laminin competed for binding with the liposomes. Antibody-coupled liposomes encapsulating doxorubicin were specifically more efficient in inhibiting colony formation by MDA-435 cells in vitro than unbound doxorubicin or liposomes without anti-laminin receptor monoclonal antibodies. Unbound doxorubicin inhibited thymidine uptake by 10%-20% in both Hs 578 and MDA-435 cells, whereas the antibody-coupled liposomes encapsulating doxorubicin inhibited thymidine uptake by 90% in MDA-435 cells but only 15% in Hs 578 cells. Thus, use of anti-laminin receptor monoclonal antibodies coupled with liposomes encapsulating doxorubicin represents a new strategy for selective targeting of doxorubicin to carcinoma cells with exposed laminin receptors.