P170 glycoprotein expression and impaired anthracycline retention in chronic myeloid leukaemia

Chronic myeloid leukaemia (CML) is a well known model of a disease refractory to chemotherapy, including anthracyclines and other drugs that are believed to be pumped out of the cells by a 170 Kd transmembrane glycoprotein (P170). In 35 cases of Ph+ CML we investigated the reactivity of leukaemic cells to a P170-directed monoclonal antibody (MRK-16), by means of flow cytometry. P170 overexpression was found in 4/14 (29%) chronic phase CML cases and in 16/23 (70%) accelerated and blastic phase CML cases (P = 0.01). The same cells were assayed for their ability to retain Daunorubicin and Idarubicin after 2-hours in vitro incubation with 1000 ng/ml of either drug. It was found that anthracycline cell concentration was negatively related with the degree of the reactivity to MRK-16. In accelerated and blastic phase, CML cells simultaneously expressed P170 and the stem cell related marker, CD34. These data confirm that Ph+ leukaemic cells overexpress P170, show that P170 overexpression is functionally relevant, and suggest that P170-related multidrug resistance may be an important factor for chemotherapy failure in Ph+ CML.