9429

ABCG2

ABC15|ABCP|BCRP|BCRP1|BMDP|CD338|CDw338|EST157481|MRX|MXR|MXR1;ATP-binding cassette, sub-family G (WHITE), member 2;ABCG2;ATP-binding cassette, sub-family G (WHITE), member 2

ABC transporter|ATP-binding cassette sub-family G member 2|ATP-binding cassette transporter G2|breast cancer resistance protein|mitoxantrone resistance protein|mitoxantrone resistance-associated protein|multi drug resistance efflux transport ATP-binding c

4q22

protein-coding

The breast cancer resistance protein (BCRP), also known as mitoxantrone resistance protein (MXR) or placenta ABC protein (ABC-P), is the second member of the ABCG subfamily of ABC transport proteins (gene symbol ABCG2). BCRP has been detected in acute myeloid leukaemia and in breast, colon and gastric cancer but there has been no reports regarding BCRP expression in acute lymphoblastic leukaemia (ALL). We report the first results of BCRP expression in childhood ALL. Sixty-seven children (47 initial stage, 20 relapses) with ALL were analysed for BCRP gene expression by TaqMan real-time polymerase chain reaction. The expression of BCRP in mononuclear cells obtained from the bone marrow (BM) and peripheral blood (PB) of healthy donors was also investigated. There was no relationship between BCRP expression and age, sex, initial blast cell count, prednisolone response or BM response on d 15 and 33. Patients with T-lineage ALLshowed a lower expression of BCRP (P = 0.044). Kaplan-Meier analysis of the relapse-free interval showed no prognostic significance of BCRP expression when different levels of BCRP expression were used as cut-off points. No significant difference in expression of BCRP mRNA was measured between initial-stage and relapsed-stage ALL or between normal MNC obtained from BM and ALL patients. The results indicate a low expression of BCRP in childhood ALL. Relationships between BCRP and clinical, molecular or in vivo resistance characteristics of the patients were not observed.

Breast cancer resistance protein (BCRP), also known as mitoxantrone resistance protein (MRX) or placenta ABC protein (ABC-P), is the second member of the ABCG subfamily of ABC transport proteins (gene symbol ABCG2). Transfection and enforced expression of BCRP in drug-sensitive cells confers resistance to mitoxantrone, doxorubicin, daunorubicin and topotecan. In this study the expression of BCRP gene was measured using TaqMan real-time PCR in 59 children with newly diagnosed AML. Nine patients were also analyzed in relapse. The median of BCRP gene expression was more than 10 times higher in patients who did not achieve remission after the first phase of chemotherapy (n = 24) as compared to patients who did achieve remission at this stage (n = 21; P = 0.012). In first relapse the expression of the BCRP gene was higher than at diagnosis (P = 0.038). Although high levels of BCRP gene expression were more frequent in subtypes of AML with a favorable prognosis, we found that within both risk groups (high and low risk), patients who expressed high levels of BCRP had a worse prognosis (P =0.023). Our results strongly suggest that the expression of the BCRP gene reduces the response to chemotherapy in AML and that BCRP expression is higher at the time of relapse.

OBJECTIVES: To evaluate and compare the profile of expression of genes related to drug resistance in brain tumors and to analyze the impact of the increased expression of these genes on overall survival. METHODS: Eighty microdissected brain tumor samples from 79 patients were analyzed by RQ-PCR for the genes MDR1,MRP1, MRP3, LRP and BCRP. Protein expression was assessed by immunohistochemistry for MRP1 and LRP genes. pediatric cases (0 to 20 years): 46 (17F:29M, median age7.3 +/- 5.9 years); adult tumors: 33 (17F:16M, median age 46.6 +/- 14.5 years). Histological diagnoses: 21 astrocytomas I and II, 28 astrocytomas III and glioblastomas, 17 medulloblastomas, 8 ependymomas, and 6 oligodendrogliomas. RESULTS: glial tumors expressed higher MDR1 (P = 0.003) and BCRP (P = 0.03) levels than embryonic tumors. Low-grade astrocytomas expressed high MDR1 (P = 0.001), MRP3 (P = 0.01) and LRP (P = 0.02) levels. The MRP1 gene was preferentially expressed by medulloblastomas (P = 0.04) and ependymomas (P = 0.04); ependymomas also presented an increase of LRP (P = 0.02). The mRNA levelsof MRP1 and LRP genes were associated to protein expression. The profile of geneexpression of primary pilocytic astrocytomas of the hypothalamus and of the other locations was similar. Increased expression of resistance genes, separately or jointly, was not correlated with shorter overall survival in patients with medulloblastomas/PNET and malignant gliomas. CONCLUSIONS: Drug resistance genes do not explain the higher sensitivity of gliomas of the hypothalamus/pituitary/optic pathways to chemotherapy. The increased expression of resistance genes had no impact on the overall survival of patients with medulloblastomas/PNET and high grade gliomas. High MDR1, MRP3 and LRP levels maybe implicated in the primary resistance of pilocytic astrocytomas to chemotherapy.

Renal cancers are as one of the most common drug resistant neoplasms affecting children and multidrug resistance (MDR) happened to be an important reason for the failure of chemotherapy in refractory cancers of childhood. MDR can be intrinsic or acquired, depending on the time of its occurrence, either at diagnosis or during chemotherapy. Renal cancers often have intrinsic form of MDRbecause of de novo expression of P-glycoprotein (P-gp) in renal cells. Molecularinvestigations on MDR during the past two decades have led to the isolation and characterization of genes coding for P-gp, multidrug resistance-associated protein (MRP), lung resistance-related protein (LRP), breast cancer resistance protein (BCRP/MXR), drug resistance-associated protein (DRP), and ATP-binding cassette protein (ABCP). Several molecular probes, primer pairs, and monoclonal antibodies have been developed over the years to quantify the regulation and expression of these drug resistance markers in tumor cells. Methodologies have also been standardized to estimate the gene amplification, mRNA and protein expression, and functionality of drug resistance proteins in clinical specimens from cancer patients. Because of the recent developments in microarray technology, DNA and protein arrays against drug resistant genes are available commercially now. This review includes techniques for detection and quantification of the expression and function of these drug resistance genes in childhood renal tumors. Since these markers have clinical significance, currently available technology warrants the application of these markers in clinical oncology. Moreover, the first, second and third generation drug resistance modifiers have been developed over the past several years for overcoming drug resistance problem in tumor cells. Unfortunately, these reversing agents are yetto be proved successful clinically. Since treatment protocols are usually adopted from adult tumor patients into childhood population, clinical trials with modifying agents are yet to be undertaken and/or concluded in pediatric renal cancer patients. More clinical studies may be required to analyze the genes involved in the MDR of childhood renal cancer patients and trials have to be undertaken to evaluate the efficacy of MDR modifying agents in them, at least inparallel with adult patients.

The aim of this prospective study was to analyze the expression of messenger RNAof genes, such as MDR1, MRP1, BCRP, and LRP, implicated in the mechanism of multidrug resistance (MDR) in relation to the response to induction chemotherapyand relapse and these genes' correlation with each other and with pretreatment laboratory and clinical characteristics. We prospectively studied 49 children (26 boys and 23 girls) with acute lymphoblastic leukemia (ALL) (median age, 5.5 years; range, 15 months to 12.5 years) who were treated with the BFM95 chemotherapy protocol. We used bone marrow mononuclear cells from 7 healthy children as controls. The expression of MDR genes and the beta-actin housekeeping gene was detected by the reverse transcription-polymerase chain reaction with the appropriate primers. The mean expression of each MDR gene was significantly higher in the patients than in the control group (P < .01). We found statistically significant correlations between MRP1 and LRP expression and between MRP1 or LRP expression and MDR1 expression (P < .05). High expression for the MDR1 gene was found in 18 patients (36.7%), and their prognoses were significantly worse than those with low expression (event-free survival, 55.56% versus 86.67%; P = .03, log-rank test). expression of each of the MDR genes was independent of the initial white blood cell count, immunophenotype, National cancer Institute risk classification, and prednisone response. Interestingly, MDR1 expression was significantly higher at relapse than at diagnosis for 4 sample pairs. Evaluation of MDR1 expression at diagnosis of childhood ALL may contribute to the early identification of patients at risk of treatment failure.

Resistance to chemotherapy is an obstacle to the successful treatment of oncohematological malignances. Failure of therapeutic treatment may be due to the development of multidrug resistance (MDR), the mechanisms of which include upregulation of membrane-resident transporters that efflux chemotherapeutic drugs from tumor cells. Deregulation may occur at different levels: gene or protein expression or function depletion. childhood acute lymphoblastic leukemia (ALL) and acute myeloid leukemia (AML) cells and chronic lymphocytic leukemia (CLL) cells of adults were studied. ABCB1 (P-gp) and ABCG2 (BCRP) expression were determined by flow cytometry, rhodamine 123 (Rho123) and mitoxantrone were used for functional activity study of MDR proteins, sensitization of leukemic cells to drugs was quantified by methyl thiazolyl tetrazolium (MTT) assays. Appropriate gene expression was determined using semi-quantitative RT-PCR. No differences between expression of P-gp and BCRP and genes in primary and relapsed acute leukemia (AL) cells as well as in de novo and treated CLL samples were established. Higher expression of P-gp and BCRP proteins was detected in CLL lymphocytes compared to blast cells. Increased P-gp protein expression and function was detected in cells of CLL patients who had more aggressive therapy regimen. Doxorubicine, rubomycinum and L-asparaginase resistance correlates withP-gp overexpression and increased function in pediatric AL whereas vincristine resistance might be associated with P-gp protein expression in AL samples and impared P-gp function in CLL lymphocytes only. A tendency for the decreased doxorubicin cytotoxic activity was shown in BCRP-overexpressing cells both in children and adults leukemia. Multifactorial ANOVA showed that P-gp/MDR1 and BCRP as well as their function could not be used as unconditional and universal predictors of leukemia cell drug resistance in vitro. These results suggest thatstudied MDR transporter-proteins have a limited role per se in vitro and admittedly in vivo drug resistance estimated in leukemia patients or it is not yet fully understood unless would not be studied in aggregate. In any event, theexpression and function studies of the proteins under investigation when singularly considered do not have a crucial significance for impact on drug resistance evaluation in ALL leukemia patients.

INTRODUCTION: Genetic variability affects clinical outcome in pediatric acute lymphocytic leukemia (ALL) patients. Evaluating gene polymorphisms in ABC transporters could help identify relapse risk and predict outcome. MATERIAL AND METHODS: The SNaPshot SNP technique was used to analyze single-nucleotide polymorphisms (SNPs) in the multidrug transporter 1 (MDR1), multidrug resistanceassociated proteins (MRP1, MRP2) and breast cancer resistance protein (BCRP) genes of 82 pediatric ALL patients. The association between the SNPs with risk of ALL events and death as well as with survival was evaluated by the univariate Cox proportional hazard model. RESULTS: The BCRP G34A SNP was the only SNP significantly associated with ALL. Risk factors included pre-treatment WBC counts and post-treatment peripheral and bone marrow leukemic cell counts. We found no association between MDR1 SNPs with these factors. The BCRP C421A C/A and C/C genotypes were significantly associated with low pre-treatment WBC counts while MRP2 G1249A G/G was significantly associated with low levels of post-treatment peripheral and bone marrow leukemic cells. A combination of C1236T, G1249A and/or G34A SNPs was significantly associated with lower EFS and OS. CONCLUSIONS: Polymorphisms associated with risk of ALL and clinical outcome may be potential biomarkers to predict clinical outcome and improve prognosis in childhood ALL.