Quantification of P-glycoprotein in chronic lymphocytic leukemia by flow cytometry

The P-glycoprotein (P-gp) was investigated in 40 patients with chronic lymphocytic leukemia by immunological, functional and quantitative assays. The proportion of positive cases with the anti-Pgp McAb UIC2 was 30% and increased to 64% after neuraminidase treatment (p = 0.002). Fifty-six per cent of cases were positive with the functional test with rhodamine 123 and verapamil. A negative correlation was found between the number of cells stained with the McAb and the functional test (p = 0.006). The mean of P-gp molecules was 2509 +/- 2805 molecules per cell; these values were higher than in the control K562 cell line in the majority of cases. The number of positive cases and P-gp molecules were higher in treated than in untreated patients (p = 0.01 and 0.07). There were no significant differences with respect to response to treatment, but a higher number of P-gp molecules was found in non-responders. When the results of the functional test were put together with the quantification assay this allowed the detection of 71% non-responders. Our findings suggest that quantification of the P-gp could be of value in the assessment of possible drug resistance in CLL.