Expression and activity of breast cancer resistance protein (BCRP) in de novo and relapsed acute myeloid leukemia

Abstract

Overexpression of the breast cancer resistance protein (BCRP) efflux pump in human cancer cell lines results in resistance to a variety of cytostatic agents. The aim of this study was to analyze BCRP protein expression and activity in acute myeloid leukemia (AML) samples and to determine whether it is upregulated due to clonal selection at relapse/refractory disease. BCRP protein expression was measured flow cytometrically with the monoclonal antibodies BXP-34 and BXP-21 in 20 paired samples of de novo and relapsed/refractory AML. BXP-34/immunoglobulin G1 ratios were observed of 1.6 ± 0.5 (mean ± SD, range 0.8-2.7) and BXP-21/immunoglobulin G2a ratios of 4.9 ± 3.0 (range 1.1-14.5) in the patient samples versus 9.8 ± 6.8 and 6.5 ± 2.4, respectively, in the MCF-7 cell line. BCRP activity was determined flow cytometrically by measuring mitoxantrone accumulation in absence and presence of the inhibitor fumitremorgin C. Mitoxantrone accumulation, expressed as mean fluorescence intensity (MFI), varied between 44 and 761 MFI (227 ± 146 MFI) and correlated inversely with BCRP expression (r = -0.58, P