Breast Cancer Resistance Protein (BCRP) Expression Affects Event-Free Survival in Adult Acute Lymphoblastic Leukemia Patients Uniformly Treated According to the GIMEMA LAL 2000 Protocol.

There are currently no reports concerning the role of the transporter breast cancer resistance protein (BCRP) 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 118 untreated adult ALL patients uniformly treated according to the GIMEMA protocol LAL2000. BCRP protein expression was detected by flow cytometry using the MoAb BXP-34 (Kamiya, WA); results were analyzed according to the KS statistic test (D-value). Detection of BCRP in the cell lines MCF7pcDNA3 and MDA231pcDNA3 showed a D-value of 0.12±0.11 and 0.09±0.06, respectively. In contrast, the cell lines MCF7pcDNA3clone 8 and MDA231pcDNA3clone23 that overexpress BCRP were characterized by a D-value of 0.44±0.21 and 0.33±0.11, respectively. Analysis of primary ALL samples showed a BCRP expression (D-value≥ 0.20) in 86/118 (72.9%) cases, with a mean value of 0.36±0.22 (range 0.00–0.87, median 0.37) in the overall population. BCRP expression resulted associated with age (P=0.054). No significant difference was found with other clinical characteristics. The multidrug resistance associated protein (MRP1) (MoAb MRPm6) resulted expressed in 70.1% of samples (D-value≥ 0.20); the MDR1/Pglycoprotein-170 (MDR1) (MoAb MRK16) was present in 28.2% of cases (D-value≥ 0.05). Samples analyzed for both BCRP and MRP1 expression (115/118) showed a significant correlation (R=0.56; P=0.0001): 15.6% of cases were negative for both proteins, while 61.7% expressed both BCRP and MRP1. BCRP expression did not correlate with MDR1 expression. None of these proteins separately influenced the achievement of complete remission (CR). In contrast, BCRP/MRP1 co-expression was associated (P=0.091) with failure to respond to induction treatment: 31% (18/58) of BCRP+/MRP1+ patients failed to achieve CR, while 84.2% (32/38) of cases negative for only one protein or for both responded to induction treatment. Kaplan-Meier analysis was then performed for event-free survival (EFS): among 99 evaluable patients a significant difference (P=0.03) was observed with a median EFS of 8.4 months (95%CI, 5.63–11.28) in BCRP+ cases (72) compared to BCRP- patients (27) for whom median EFS has not been achieved. Multivariate analysis confirmed the unfavorable prognostic role of BCRP positive cases on EFS (P=0.072;OR1.87, 95% CI, 0.94–3.70). In summary, our study shows that adult ALL frequently express BCRP. In patients treated with the GIMEMA LAL 2000 protocol EFS was unfavorably affected by BCRP expression, while co-expression of MRP1 and BCRP was associated with failure to induction treatment. The expression of these proteins may contribute to explain the overall poor outcome of adult ALL patients, suggesting that therapeutic strategies based on overcoming drug resistance remain an important goal to be pursued.