For cancer chemotherapy, avoiding the side effects of chemotherapeutic agents is difficult. Multidrug resistance is one of the major obstacles to successful cancer chemotherapy. P-Glycoprotein (P-gp) serves as an efflux pump and plays a key role in the multidrug resistance. We examined the effect of MRK-16, a monoclonal antibody against P-gp, modified liposomes (MRK-Lip) on the human myelogenous leukemia K-562 cells and its adriamycin resistance cell line K-562/ADM cells to avoid the side effects and to reverse the multidrug resistance. The uptake of vincristine (VCR) by K-562/ADM cells was lower than that by K-562 cells. This low uptake was increased in the presence of verapamil and MRK-16, however, it was not increased in the presence of control antibody, IgG2A. The binding of MRK-Lip to K-562/ADM cells was higher than that of IgG2A-modified liposome (IgG-Lip) and liposome without modification (Cont-Lip). Moreover, the cytotoxicity of VCR-encapsulated MRK-Lip to K-562/ADM cells was higher than that of VCR-encapsulated IgG-Lip and Cont-Lip. These results suggest that the interaction between liposomes and multidrug resistance cells was increased by the modification of liposomes with MRK-16. Consequently, the usefulness of MRK-Lip in cancer chemotherapy as a potent carrier was suggested.
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