EXPRESSION OF MDR1, MRP, TOPOISOMERASE-II-ALPHA/BETA, AND CYCLIN-A IN PRIMARY OR RELAPSED STATES OF ACUTE LYMPHOBLASTIC LEUKEMIAS

In a series of 60 ALL, samples drawn during different stages of the disease we used a cDNA-PCR approach to analyse the relative mRNA levels of the MDR-associated genes encoding mdr1/P-glycoprotein mrp, and the topoisomerase II isozymes alpha and beta. Expression analysis of the cyclin A gene was included to examine cellular proliferation activity. The expression of gapdh served as an internal standard. Calculating the mean values we found: (i) a distinctly lower mdr1 gene expression in primary ALL and first relapses compared to bone marrow from healthy donors, (ii) no change in mdr1 and mrp, but a decreased topoisomerase II alpha( gene expression in first relapses of ALL compared to the primary leukaemia, and (iii) increased mdr1 and mrp levels combined to decreased topoisomerase II alpha levels in recurrent relapses of ALL showing significant correlations (mdr1/mrp: r(s) = +0.6833, P < 0.05; mdr1/ topoII alpha: r(s) = -0.6727, P < 0.05). The expression of the topoisomerase II alpha gene was correlated to that of cyclin A, indicating a link of its expression to cellular proliferation. Our findings suggest that a multifactorial MDR including mrp appears particularly in recurrent relapses of ALL, which often do not respond to chemotherapy. Nonetheless, some individual samples showed gene expression levels very different from the mean values calculated for a particular state of the leukaemia, indicating the need of an individual expression analysis of MDR-associated genes.