Cellular and Tissue Distribution of MRK20 Murine Monoclonal Antibody‐defined 85‐kDa Protein in Adriamycin‐resistant Cancer Cell Lines

A murine monoclonal antibody (MAb) specific to adriamycin‐resistant K‐562 (K‐562/ADM) cells, MRK20, was found to react strongly with an 85‐kDa protein present in K‐562/ADM and adriamycin‐resistant ovarian cancer (2780(AD)) cells. This protein was present at only very low levels in parental cells (K‐562 and A2780), methotrexate‐resistant K‐562 cells (K‐562/MTX3, K‐562/MTX4 and K‐562/MTX5) and cisplatin‐resistant ovarian cells (KFr). Immunoelectron microscopically, the protein was found to be located on the cell membrane of K‐562/ADM and 2780(AD) cells. Furthermore, the presence of the protein in various cell lines, normal tissues and surgical materials from patients given no anti‐cancer agents was examined by immunocytochemistry and flow cytometry. MRK20 reacted with granulocytes, monocytes and endothelial cells in various tissues, but did not react with tissue macrophages. This 85‐kDa protein recognized by MRK20 seems to be the second multidrug‐resistance gene‐encoded product appearing in adriamycin‐resistant cancer cells, following the characterization of 170‐180‐kDa glycoprotein, and may be important for elucidating the multidrug‐resistance mechanism relevant to adriamycin and Vinca alkaloids.