COMPARISON OF 2 METHODS TO DETECT P-GLYCOPROTEIN IN PATIENTS WITH CHRONIC LYMPHOCYTIC-LEUKEMIA

P-glycoprotein (Pgp) is a transmembrane protein associated with multip le drug resistance. Pgp can be detected by several monoclonal antibodi es or its activity inferred by measuring drug uptake. We compared two methods for quantitating Pgp in 32 patients with chronic lymphocytic l eukaemia. The monoclonal antibody 4E3, which recognizes an external ep itope of Pgp, was detected by flow cytometry. Intracellular daunorubic in (DNR) accumulation was measured by flow cytometry in the presence ( treated) and absence (control) of cyclosporin, an agent known to inhib it Pgp. Correlation between the degree of positivity on the drug uptak e assay and Pgp detected by monoclonal antibody 4E3 was poor (r = 0.06 ). No association with previous drug exposure or lymphocyte doubling t ime and Pgp positivity was found in this series of patients. Poor corr elation between assays might reflect a lack of sensitivity of the DNR uptake assay. Drug accumulation may be influenced by other cellular ef flux pumps unrelated to Pgp, making the DNR assay non-specific.