Breast Cancer Resistance Protein (BCRP) in Adult Acute Lymphoblastic Leukemia Patients.

The transporter breast cancer resistance protein (BCRP) is a member of the ATP-binding cassette which has been recently described as a protein involved in the multidrug resistance (MDR) phenotype. There are currently no reports concerning the role of this protein in adult acute lymphoblastic leukemia (ALL). The aim of this study was to evaluate the frequency of BCRP expression, its correlation with other MDR-related proteins and their prognostic role in 93 untreated adult ALL patients enrolled in the GIMEMA protocols LAL 0496 and LAL 2000. BCRP protein expression was detected by flow cytometry using the monoclonal antibody BXP-34 (Kamiya, Seattle, WA) and the analysis was performed by the Kolmogorov-Smirnov (KS) statistic test (D-value). Detection of BCRP in the cell lines MCF7 pcDNA3 and MDA231 pcDNA3 showed a D-value of 0.12 ± 0.11 and 0.09 ± 0.06, respectively (negative controls). In contrast, the cell lines MCF7 pcDNA3 clone 8 and MDA231 pcDNA3 clone 23 overexpressed BCRP with a D-value of 0.44 ± 0.21 and 0.33 ± 0.11, respectively (positive controls). Analysis of primary ALL samples showed a BCRP expression (D-value >0.20) in 70/93 (75.3%) cases, with a mean value of 0.33 ± 0.19 (range 0.00-0.87, median 0.33) in the overall population analyzed. BCRP expression resulted higher (mean 0.34 ± 0.03) in samples from patients with WBC counts ≥100 x 10⁹/L compared to the values (mean 0.26 ± 0.13) found in those with lower WBC counts (P=0.06). No significant difference was found between BCRP expression and the clinical characteristics of the patients. The analysis was then extended to the Multidrug Resistance Associated protein (MRP1) and to the MDR1/P-glycoprotein-170 (MDR1). A D-value ≥0.20 and ≥0.05 was found in 53.4% (39/73) and 30.2% (26/86) of cases, respectively. Samples analyzed for both BCRP and MRP1 expression (73/93) showed a significant correlation (R² = 0.25; P=0.0001): 12.3% of samples were negative for both proteins, while 43.8% expressed both BCRP and MRP1 proteins. In addition, MRP1 negative samples showed lower BCRP levels (mean 0.30, range 0–0.60) compared to MRP1 positive cases (mean 0.38, range 0–0.87) (P=0.017). BCRP expression did not correlate with MDR1 expression. None of these MDR markers correlated separately with achievement of complete remission (CR). In contrast, BCRP/MRP1 co-expression correlated significantly (P=0.034) with failure to respond to induction treatment: 47.8% (11/23) of BCRP+/MRP1+ patients failed to achieve CR, while 78.4% (29/37) of cases negative for only one protein (BCRP-/MRP1+ or BCRP+/MRP1−) or for both (BCRP-/MRP1-) responded to induction treatment. Multivariate analysis (Backward method) confirmed the unfavorable prognostic role on CR of these two proteins concomitantly expressed (P=0.029; OR 0.27, 95% CI, 0.081–0.87). In conclusion, our study shows that BCRP is expressed in a significant proportion of adult ALL. The co-expression of BCRP and MRP1 plays an unfavorable prognostic role on achievement of CR in ALL. These data suggest that the resistance phenotype may be the result of the combined effects of several transporter proteins involved in the MDR process and therefore detection of all these proteins may better predict clinical response to induction treatment.