PGP AND MRP ACTIVITIES USING CALCEIN-AM ARE PROGNOSTIC FACTORS IN ADULT ACUTE MYELOID-LEUKEMIA PATIENTS

Thirteen cell lines with different levels of Pgp and MRP expression we re used to assess the ability of calcein acetoxymethyl ester (calcein- AM) uptake and calcein efflux to measure Pgp and MRP functions, respec tively. There was a good correlation between MRP expression and the mo dulatory effect of probenecid (a specific modulator of MRP) on the cal cein efflux (r = .91, P = .0003) and between Pgp expression and the mo dulatory effect of CsA on calcein-AM uptake (r = .96, P < .0001). In l ight of the high correlations for both proteins, we tested calcein-AM uptake and efflux in fresh myeloid leukemic cells. In 53 acute myeloid leukemia (AML) patients, there was also a good correlation between MR P expression (measured by reverse transcription-polymerase chain react ion and by MRPm6 expression by flow cytometry) and the modulatory effe ct of probenecid on the calcein fluorescence (r = .92, P < .0001) and between Pgp expression as measured by UIC2 antibody binding on flow cy tometry and the modulatory effect of cyclosporin A on calcein AM uptak e (r = .83, P < .0001). Pgp activity was higher in CD34(+) leukemia th an in CD34(-) leukemia (2.26 +/- 1.50 v 1.46 +/- 1.21, respectively; P = .003), and MRP activity was higher in CD34(-) leukemia than in CD34 (+) leukemia (1.77 +/- 0.40 v 1.4 +/- 0.29, respectively; P = .004). P gp expression and activity (P = .004 and P = .01, respectively) and MR P activity (P = .03) but not MRP expression were prognostic factors fo r achievement of complete remission. These results suggest that functi onal testing (with calcein-AM +/- modulators) for the presence of both MRP and Pgp activities is of prognostic value and that MRP contribute s to drug resistance in AML. (C) 1998 by The American Society of Hemat ology.