Repetitive analyses of P-glycoprotein in chronic myeloid leukaemia

P-glycoprotein, a pump located in the plasma cell membrane, extrudes severa l clinically important drugs from the cell, and hence causes multidrug resi stance. Reversing clinical drug resistance is possible by using agents that inhibit the activity of P-glycoprotein. We describe the results of sequent ial flow cytometric determinations of P-glycoprotein expression and activit y in two patients suffering from acute lymphoblastic transformation of chro nic myeloid leukaemia. Neither P-glycoprotein expression, nor its activity could be detected in the initial sample of the first patient. In the second patient, no P-glycoprotein expression was found at diagnosis. However, aft er chemotherapy containing P-glycoprotein substrates, a significant express ion was found in both patients and the functional flow cytometric test was positive. In order to achieve an accurate selection of patients that might benefit from the clinical use of P-gp inhibitors, repeated analyses are ind icated in each patient suffering from acute leukaemia, during the course of the illness.