EXPRESSION OF THE MULTIDRUG-RESISTANCE P-GLYCOPROTEIN IN NEWLY-DIAGNOSED ADULT ACUTE LYMPHOBLASTIC-LEUKEMIA - ABSENCE OF CORRELATION WITH RESPONSE TO TREATMENT

We analyzed P glycoprotein (PGP) expression and its correlation with h ematological parameters and outcome in 50 cases of newly diagnosed adu lt acute lymphoblastic leukemia (ALL). PGP expression was evaluated by flow cytometry using MRK16 monoclonal antibody (MoAb) and/or immunocy tochemistry on marrow slides, using JSB1 MoAb. Thirty-two of the 50 pa tients (64%) were PGP positive by at least one of the two methods, whi ch gave concordant results in 15 of the 18 cases in which they were bo th used. No correlation between PGP expression and clinical and hemato logical parameters including WBC counts, immunophenotype and karyotype was seen, although there was a trend for more frequent CD34 expressio n in PGP-positive cases. All patients were treated with intensive chem otherapy. We found no difference in complete remission (CR) rate, actu arial disease-free survival and survival in PGP-positive and POP-negat ive cases. Our findings suggest that the clinical significance of PGP expression is less clear in ALL than in AML. Wider use of functional t echniques of evaluation of mdr1 gene expression, which assess the 'pum ping' activity of PGP, and their correlation with quantitative analysi s of mdr1 mRNA and protein, would probably improve knowledge of the ro le of PGP in ALL. Analysis of other mechanisms of drug resistance, esp ecially multidrug resistance-associated protein (MRP) expression, woul d also be useful.