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Receptor-mediated endocytosis of antibody-opsonized liposomes by tumor cells
Abstract:
Specific receptor-mediated delivery of the contents of small, sonicated liposomes was studied with three murine tumor cell types: an IgG Fc receptor-negative nonphagocytic line (EL4); an Fc receptor-positive phagocytic line (P388D1); and an Fc receptor-positive nonphagocytic line (P388). The liposomes (formed from phosphatidylcholines, cholesterol, and dinitrophenyl-substituted phosphatidylethanolamine) contained carboxyfluorescein as a fluorescent marker and methotrexate as a pharmacologic agent. Binding and internalization of the liposomes were observed by fluorescence microscopy and measured by flow microfluorometry. The hapten-derivatized lipid was used as a binding point on the liposome for the antibody-combining site of the immunoglobulin. In the presence of IgG anti-dinitrophenyl, but not F(ab')2 or IgA anti-dinitrophenyl, liposomes bound to the Fc receptor-bearing cells. The liposomes underwent endocytosis by the P388D1 cells and, to a lesser extent, by the P388 cells. As measured by depression of [3H]deoxyuridine incorporation, methotrexate in IgG-opsonized liposomes had a much greater pharmacologic effect on the P388D1 cells than did the same amount in unopsonized liposomes or in free solution. This observation indicates that an appropriately chosen drug, incorporated in liposomes, can exert its effect on a cytoplasmic target after endocytosis. P388 cells showed a moderate effect of the drug in liposomes. Neither P388 nor P388D1 cells bound or ingested unopsonized liposomes, and the Fc receptor-negative EL4 line neither bound nor ingested opsonized liposomes. The data demonstrate specific interaction of opsonized liposomes with the cells' IgG Fc receptor.
Insights
Liposomes targeted to the IgG Fc receptor deliver drugs effectively into tumor cells. This specific receptor-mediated delivery enhances drug efficacy, particularly in phagocytic cells, demonstrating a promising approach for targeted cancer therapy.
Area of Science:
- Biotechnology
- Drug Delivery Systems
- Immunology
Background:
- Liposomes are versatile nanocarriers for drug delivery.
- Targeted delivery aims to enhance therapeutic efficacy and reduce side effects.
- Fc receptors play a role in cellular uptake and immune responses.
Purpose of the Study:
- To investigate specific receptor-mediated delivery of liposomes into murine tumor cells.
- To evaluate the role of the IgG Fc receptor in liposome binding and internalization.
- To assess the enhanced pharmacologic effect of liposome-encapsulated drugs via targeted delivery.
Main Methods:
- Utilized three murine tumor cell lines with varying Fc receptor expression and phagocytic capabilities.
- Formulated liposomes containing a fluorescent marker and methotrexate.
- Employed fluorescence microscopy and flow microfluorometry to quantify liposome binding and uptake.
- Assessed drug efficacy by measuring [3H]deoxyuridine incorporation.
Main Results:
- IgG-opsonized liposomes specifically bound to Fc receptor-positive cells (P388D1 and P388).
- Liposomes were internalized via endocytosis by P388D1 and, to a lesser extent, P388 cells.
- Methotrexate in IgG-opsonized liposomes showed significantly greater efficacy against P388D1 cells compared to unopsonized liposomes or free drug.
- Fc receptor-negative EL4 cells did not bind or internalize liposomes, confirming specificity.
Conclusions:
- Specific binding and internalization of liposomes are mediated by the IgG Fc receptor.
- IgG Fc receptor-mediated endocytosis facilitates the delivery of liposomal contents into tumor cells.
- Targeted liposomal drug delivery via the IgG Fc receptor enhances intracellular drug efficacy.