High-level expression of P-glycoprotein and 85 kD protein as assessed by flow cytometry and immunocytochemistry in leukemias and malignant lymphomas.

Acquired resistance developed after chemotherapy is characterized by lower sensitivity to anticancer agents. We utilized two monoclonal antibodies (MABs): MRK16 which recognized 170 to 180 kD P-glycoprotein and MRK20 which recognized 85 kD protein, to investigate the frequency of multidrug-resistant cancer cells appearing during treatment of 23 cases of leukemias and 27 cases of malignant lymphomas. The reactivities of these MABs with lymphocytes and blastic cells were examined by flow cytometry and immunocytochemistry. The following findings were obtained. First, among 50 cases, increases in MRK16-reactive cells and MRK20-reactive cells were noted in 17 cases (34%) and 28 cases (56%), respectively. Second, the increase of MRK16-positive cells in three cases and the increase of MRK20-positive cells in two cases were correlated with dosages of the corresponding anticancer drugs used. Although we investigated the total amounts of anti-cancer drugs used, we were not able to detect exactly when P-glycoprotein recognized by MRK16 and the 85 kDa protein recognized by MRK20 appeared in these resistant cells during treatment. More cases will be required to investigate the significance between treatment and reactivity of MRK16 or MRK20 with leukemia or lymphomas cells.