Increased expression of the breast cancer resistance protein (BCRP) in relapsed or refractory acute myeloid leukemia (AML).

Expression of the multidrug resistance proteins P-glycoprotein, encoded by the MDR1 gene, multidrug resistance-associated protein (MRP1) and the lung resistance-related protein or major vault protein (LRP/MVP) is associated with clinical resistance to chemotherapy in acute myeloid leukemia (AML). Recently, the breast cancer-resistant protein (BCRP), the equivalent of mitoxantrone-resistant protein (MXR) or placental ABC transporter (ABCP), was described in AML. We investigated MDR1, MRP1, LRP/MVP and BCRP mRNA expression simultaneously in 20 paired clinical AML samples from diagnosis and relapse or refractory disease, using quantitative Taqman analysis. In addition, standard assays for P-glycoprotein expression and function were performed. BCRP was the only resistance protein that was expressed at a significantly higher RNA level (median 1.7-fold, P = 0.04) at relapsed/refractory state as compared to diagnosis. In contrast, LRP/MVP mRNA expression decreased as disease evolved (P = 0.02), whereas MDR1 and MRP1 mRNA levels were not different at relapse as compared to diagnosis. Also, at the protein level no difference of MDR1 between diagnosis and relapse was found. A significant co-expression of BCRP and MDR1 was found at diagnosis (r = 0.47, P = 0.04). The present results suggest that BCRP, but not MDR1, MRP1 or LRP/MVP is associated with clinical resistant disease in AML.     

Copper-transporting P-type adenosine triphosphatase (ATP7B) as a cisplatin based chemoresistance marker in ovarian carcinoma: comparative analysis with expression of MDR1, MRP1, MRP2, LRP and BCRP

Intrinsic or acquired resistance to chemotherapy is the major obstacle to overcome in the treatment of patients with solid carcinoma. Cisplatin is one of the most effective chemotherapeutic agents for treating ovarian carcinoma. Recently, copper-transporting P-type adenosine triphosphatase (ATP7B) has been demonstrated as one of the genes responsible for cisplatin resistance in vitro. We hypothesized that the expression of ATP7B gene increases resistance to cisplatin in ovarian carcinoma and a priori knowledge of its expression is important for the choice of therapy. The aim of our study was to assess the role of ATP7B gene in ovarian carcinoma and compare its expression with those of multidrug resistance-related transporters such as MDR1, MRP1, MRP2, LRP and BCRP genes. The transporters' gene expression profiles from 82 patients treated with cisplatin-based chemotherapy after surgery were assessed by RT-PCR. We did not observe any significant correlation between ATP7B gene expression and those of MDR1, MRP1, MRP2, LRP or BCRP. The expression level of ATP7B gene was significantly increased (p < 0.05) in patients with moderately-/poorly-differentiated ovarian carcinomas treated with cisplatin-based chemotherapy, thus ATP7B may serve as an independent prognostic factor in these patients. In contrast, the expression level of MDR1, MRP1, MRP2, LRP and BCRP genes were not prognostic indicators of disease. These findings suggest that ATP7B gene may be considered as a novel chemoresistance marker and that inhibitor(s) of ATP7B might be useful, in patients with ovarian carcinoma treated with cisplatin-based chemotherapy.     

ABC 转运蛋白在肝细胞癌中的表达及意义*

目的:探讨P-gp、MRP1、BCRP 等ABC 转运蛋白在肝细胞癌中的表达及其与临床病理特征的关系。方法:应用RT-PCR 和免疫组织化学方法检测P-gp/MDR1、MRP1、BCRP等mRNA 及蛋白在34例的肝细胞癌、19例癌旁肝组织中的表达。结果:MDR1、MRP1、BCRP等mRNA 在肝癌组的相对表达水平分别为1.15± 0.24、0.64± 0.33、1.07± 0.32,在癌旁肝组织组的相对表达水平分别为0.36± 0.14、0.19± 0.06、0.31± 0.09。MDR1、MRP1、BCRP 在肝细胞癌中低分化组（Ⅲ、Ⅳ级）为1.38± 0.26、0.73± 0.35、1.34± 0.21,在高分化组（Ⅰ、Ⅱ级）分别为0.74± 0.32、0.30± 0.11、0.45± 0.13。P-gp、MRP1、BCRP等的阳性反应产物主要分布于细胞膜和胞浆内;在肝癌组和癌旁肝组织组的阳性表达率分别为82.35% 、58.82% 、79.41% 和42.11% 、26.32% 、36.84% 。P-gp、MRP1、BCRP在肝细胞癌中低分化组（Ⅲ、Ⅳ级）的阳性表达率分别为100% 、81.25% 、100% ,在高分化组（Ⅰ、Ⅱ级）的阳性表达率分别为66.67% 、38.89% 、61.11% 。RT-PCR 及免疫组织化学均显示,P-gp、MDR1、MRP1、BCRP mRNA和蛋白在肝癌组的表达均高于癌旁肝组织组,且在低分化（Ⅲ、Ⅳ级）肝癌组织的表达高于高分化者（Ⅰ、Ⅱ级）,差异有统计学意义（P<0.05）。 MDR1、MRP1、BCRP之间的表达无线性相关。结论:在肝细胞癌中存在原发性多药耐药现象,且多种耐药机制并存。P-gp、MDR1、MRP1、BCRP等与肝细胞癌的耐药有关,在肝癌组的表达高于癌旁肝组织组,且在肝细胞癌中的表达随着肿瘤分化程度的增高而降低,可作为肝细胞癌多药耐药性作用的靶点。      

Expression of LRP Gene in Breast Cancer Patients Correlated with MRP1 as Two Independent Predictive Biomarkers in Breast Cancer

Background: Breast cancer is the most common malignancy in women. Multidrug resistance (MDR) is still a greatobstacle of breast cancer chemotherapy. We have previously shown that multidrug resistance-associated protein 1 (MRP1)is associated with response to neoadjuvant chemotherapy. The lung resistance-related protein (LRP) is identified asa prognostic marker and response to treatment factor which has been studied mainly in hematological malignancy andleukemia. In this study, we aimed to analyze LRP expression and possible correlation between the expression level ofthis gene with MRP1 as a candidate marker for chemotherapy resistance. Materials and Methods: We collected 54breast tumors and adjacent normal tissues from Iranian breast cancer patients and Real time RT-PCR was employed tomeasure the gene expression level in our samples. Results: MRP1 and LRP expression level were significantly lowerin tumor tissues of the patients responding to chemotherapy compared to non-responding patients. No relation betweenthe expression level of either of these genes and clinicopathology markers was found. Conclusion: Our results suggestthat LRP gene expression is correlated to MRP1 in human breast cancer cells and may affect the clinical response totreatment.     

肺癌组织中多药耐药基因及相关蛋白表达的研究

目的:探讨P-糖蛋白(P-glycopro-tein,P-gp)、肺癌耐药蛋白(lung cancer resis-tence protein,LRP)和多药耐药相关蛋白(multidrug resistence protein,MRP)在肺癌组织中的表达及其临床意义。方法:应用SP法检测116例术前未做化疗的肺癌组织中P-gp、LRP和MRP的表达水平。结果:P-gp在腺癌组织中的阳性表达率为78.26%(36/46),小细胞癌为63.64%(7/11),鳞状细胞癌为47.46%(28/59);三者相比差异有统计学意义,P=0.018。LRP在腺癌组织中的阳性表达率为89.13%(41/46),鳞状细胞癌为44.07%(26/59),小细胞癌为27.27%(3/11);三者相比差异有统计学意义,P=0.0001;MRP在不同癌组织中的表达差异无统计学意义,P=0.4165。在腺癌、鳞状细胞癌和小细胞癌组织中同时有两种或两种以上耐药基因产物表达阳性率分别为89.13%(41/46)、49.15%(29/59)和27.28%(3/11),三种类型间比较差异有统计学意义,P=0.0001。结论:不同组织学类型的肺癌存在不同程度的耐药性,检测P-gp、LRP和MRP的协同表达对于指导临床化疗方案的实施有重要意义。     

Multidrug resistance genes in infant acute lymphoblastic leukemia: Ara-C is not a substrate for the breast cancer resistance protein.

Infants with acute lymphoblastic leukemia (ALL) are more resistant to chemotherapeutic drugs than older children with ALL, except for Ara-C. Drug resistance mechanisms in infant ALL, however, remain unknown. Possibly, multidrug resistance (MDR) proteins like P-glycoprotein, MDR-associated protein (MRP1), lung resistance-related protein (LRP/MVP) and the breast cancer resistance protein (BCRP) play a role. Accordingly, we measured the mRNA levels of these proteins in infants (n=13) and non-infants (n=13) with ALL, using quantitative RT-PCR. Infants expressed 2.4-fold less BCRP mRNA (P=0.009) than non-infants with ALL. MDR1, MRP1 and LRP/MVP expression did not differ between both groups. MDR gene expression levels did not correlate to prednisolone, vincristine, daunorubicin or Ara-C cytotoxicity, except for BCRP expression, which correlated with resistance to Ara-C (Rs=0.53, P=0.012), suggesting that Ara-C might be a BCRP substrate. However, culturing patients ALL cells in the presence of the BCRP inhibitor Ko143 had no effect on Ara-C sensitivity. Inhibiting Bcrp1 in the Mdr1a-, Mdr1b- and Mrp1-deficient and Bcrp1-overexpressing mouse cell line Mef3.8/T6400, also did not modulate Ara-C cytotoxicity. Therefore, we conclude that Ara-C is not a substrate for BCRP and that MDR proteins do not play a significant role in drug resistance in infant ALL.     

乳腺癌组织中四种耐药相关蛋白的表达及其临床意义

目的:研究包括P-糖蛋白(P-glycoprotein,PGP)、多药耐药相关蛋白-1(Multidrug resistance-associated protein1,MRP1)、肺耐药相关蛋白(Lung resistance-related protein,LRP)和乳腺癌耐药蛋白(Breast cancer resistance protein,BCRP)在乳腺癌组织中的表达,并评估其在乳腺癌预后中的作用。方法:采用免疫组织化学方法检测50例经手术切除的乳腺癌组织中PGP、MRP1、LRP和BCRP的表达,并分析其与临床、病理特征的关系及其对预后的影响。结果:(1)各种耐药蛋白在乳腺癌组织中均有不同程度的表达,PGP、MRP1、LRP和BCRP的表达率分别为82·0%(41/50)、86·0%(43/50)、80·0%(40/50)和58·0%(29/50);(2)除MRP1表达与淋巴结转移状况有关以及BCRP表达与激素受体有关外(P<0·05),PGP、MRP1、LRP和BCRP表达与月经状况、肿瘤大小、淋巴结转移、组织分级和激素受体状况均无关(P>0·05);(3)Kaplan-Meier生存分析结果表明PGP、MRP1、LRP和BCRP表达均与无病生存期明显相关(P<0·05),但只有PGP表达与总生存期显著相关(P<0·01),而MRP1、LRP和BCRP表达与总生存期无关(P>0·05);(4)Cox多因素分析中,肿瘤大小和腋淋巴结转移与无病生存期和总生存期明显相关(P<0·05),但PGP表达仅与总生存期明显相关(P<0·05)。结论:乳腺癌组织中具有多种耐药蛋白的过度表达,其中PGP有可能成为判断乳腺癌患者预后的独立指标。     

LRP,MRP,MDR1基因在非小细胞肺癌中的表达及其临床意义

目的 探讨肺耐药蛋白（ｌｕｎｇ ｒｅｓｉｓｔａｎｃｅ ｐｒｏｔｅｉｎ,ＬＲＰ）,多药耐药蛋白（ｍｕｌｔｉｄｒｕｇ ｒｅｓｉｓｔａｎｃｅａｓｓｏｃｉａｔｅｄ ｐｒｏｔｅｉｎ,ＭＲＰ）,和多药耐药基因（ｍｕｌｔｉｄｒｕｇ ｒｅｓｉｓｔａｎｅ,ＭＤＲ１）ｍＲＮＡ在非小细胞肺癌（ｎｏｎ－ｓｍａｌｌ ｃｅｌｌ ｃａｎｃｅｒ,ＮＳＣＬＣ）中的共表达及临床意义。方法 ＲＴ－ＰＣＲ检测ＮＳＣＬＣ冰冻组织中上述耐药     

Effects of neoadjuvant chemotherapy on MDR1 and MRP gene expression in primary breast cancer

Objective: To investigate the effects of neoadjuvant chemotherapy on the expression of drug resistance genes, multidrug resistance-1 (MDR1) and multidrug resistance-associated protein (MRP), in patients with primary breast cancer. Methods: MDR1 and MRP expression were detected by semi-quantitative RT-PCR in 20 patients with primary breast cancer, before and after chemotherapy. Results: Before chemotherapy, MDR1 and MRP expression can be detected in 15 cases (75%) and 18 cases (90%) respectively. After chemotherapy, expression of MDR1 is not significantly different from that before chemotherapy, but expression of MRP is significantly different from that before chemotherapy. Conclusion: Expression of drug resistance gene MRP, but not MDR1, is enhanced in patients with primary breast cancer submitted to neoadjuvant chemotherapy.     

MRP、GST-π、TopoⅡα和LRP在胃癌组织中的表达及意义

背景与目的:多药耐药相关蛋白(multidrugresistance-associatedprotein,MRP)、肺耐药蛋白(lungresistanceprotein,LRP)、谷胱甘肽转移酶(glutathione-S-transferase-π,GST-π)和拓扑异构酶Ⅱα(topoisomeraseⅡα,TopoⅡα)均在多药耐药中发挥重要作用。联合检测它们在胃癌组织中的表达,目前国内外报道极少。本研究旨在探讨联合检测MRP、GST-π、TopoⅡα、LRP在胃癌组织中的表达及意义。方法:应用免疫组化SP法检测MRP、GST-π、TopoⅡα、LRP在90例胃癌标本中的表达,采用χ2检验和Fisher精确检验分析它们表达的意义。结果:(1)MRP、GST-π、TopoⅡα、LRP在胃癌组织中的阳性表达率分别为88.9%、91.1%、74.4%和87.7%,均高于在正常胃粘膜组织中的表达(P<0.05)。(2)MRP、GST-π、LRP在高、中分化腺癌中的表达均高于低分化腺癌,而TopoⅡα在高、中分化腺癌中的表达低于低分化腺癌(P<0.05);此四者的表达情况在不同浸润程度及有/无淋巴结转移的胃癌组织之间均无统计学差异(P>0.05)。(3)MRP、GST-π、TopoⅡα、LRP两两间均无相关性。结论:MRP、GST-π、TopoⅡα和LRP均在胃癌原发性多药耐药中起重要作用,它们在胃癌组织中的表达与肿瘤分化程度有关,而与肿瘤浸润程度及是否有淋巴结转移无关。     

P-gp、MRP1、BCRP在晚期NSCLC中的表达及意义

[目的]探讨P-gp、MRP1、BCRP在晚期非小细胞肺癌(NSCLC)中的表达,及其与NSCLC患者临床病理特征及化疗效果的关系。[方法]采用免疫组化SP法检测32例晚期NSCLC患者治疗前肿瘤标本中P-gp、MRP1、BCRP的表达。所有患者接受以铂类为主的化疗方案2个周期,分析P-gp、MRP1、BCRP表达情况与患者临床病理特征及化疗效果的关系。[结果]NSCLC肿瘤中P-gp、MRP1和BCRP阳性表达率分别为46.88%、75.00%和46.88%。腺癌中P-gp表达高于鳞癌;MRP1的表达与年龄有关,60岁以上的患者显示了更高的MRP1表达率。BCRP的表达与化疗效果相关,但P-gp和MRP1的表达与疗效无显著性相关。[结论]BCRP可以作为判断晚期NSCLC患者化疗效果的预测因子。     

Anticancer drug-mediated induction of multidrug resistance-associated genes and protein kinase C isozymes in the T-lymphoblastoid cell line CCRF-CEM and in blasts from patients with acute lymphoblastic leukemias.

The major determinants mediating drug resistance in acute lymphoblastic leukemias (ALL) unresponsive to chemotherapy, are still unclear. For example, it is still unknown whether selection or induction processes are responsible for drug resistance here or whether protein kinase C (PKC) isozymes contribute to the resistant phenotype. Therefore, inducibility of resistance factors or PKC isozymes genes was examined in CCRF-CEM cells treated with diverse anticancer drugs--adriamycin, camptothecin, etoposide or vincristine--at sublethal concentrations for 24 h. MDR1, MRP1, LRP and PKC isozyme alpha, beta(1), beta(2), epsilon, iota, eta, theta, zeta gene expression was determined by cDNA-PCR. We found significant dose-dependent, mostly combined, induction of the MDR1, MRP1 and LRP genes. Significantly enhanced gene expression of the majority of PKC isozyme genes was found after treatment with camptothecin. PKCzeta was upregulated throughout by each anticancer drug applied in this setting. A series of selected CCRF-CEM-derived multidrug resistance (MDR) sublines also showed enhanced expression of the PKC isozymes compared to the parental cell line. MDR1 and PKCeta gene expression levels were correlated highly significantly. Blasts from two patients with ALL during the first week of monotherapy with steroids revealed combined induction of the MDR1, multidrug resistance-associated protein 1 (MRP1), lung cancer resistance-related protein (LRP) and most PKC isozymes, predominantly PKCzeta. Another patient with T-ALL, who failed to respond to four months of intensive chemotherapy, showed an enhanced MRP1 gene expression combined with markedly overexpression of PKCeta and PKCtheta. Furthermore, the camptothecin and etoposide-mediated induction of resistance factors in the CCRF-CEM cell line could be suppressed by staurosporine, a rather unspecific inhibitor of protein kinases. However, selective inhibitors of PKC isozymes (bisindolylmaleimide GO 6850, indolocarbazole GO 6976) produced no significant effects here. Therefore, the PKC isozymes eta, theta and zeta are of interest as potential targets to overcome drug resistance in ALL.     

Lung resistance-related protein as a predictor of clinical outcome in advanced testicular germ-cell tumours

This study was undertaken to investigate the expression and predictive value for outcome of multidrug resistance-associated (MDR) proteins P-glycoprotein (Pgp), MRP1, BCRP, and LRP, in advanced testicular germ-cell tumours (TGCT). Paraffin-embedded sections from 56 previously untreated patients with metastatic TGCT were immunostained for Pgp, MRP1, BCRP, and LRP. All patients received platinum-based chemotherapy after orchidectomy. Immunostaining was related to clinicopathological parameters, response to chemotherapy, and outcome. Strong and intermediate expressions of the different MDR-related proteins were: 27 and 41% (Pgp), 54 and 37% (MRP1), 86 and 7% (BCRP), and 14 and 29% (LRP). P-glycoprotein and MRP1 associated, respectively, to low AFP (P=0.026) and high LDH levels (P=0.014), whereas LRP expression associated with high beta-hCG levels (P=0.003) and stage IV tumours (P=0.029). No correlation was found between Pgp, MRP1, and BCRP expression and response to chemotherapy and survival. In contrast, patients with LRP-positive tumours (strong or intermediate expression) had shorter progression-free (P=0.0006) and overall survival (P=0.0116) than LRP-negative patients, even after individual log-rank adjustments by statistically associated variables. Our data suggest that a positive LRP immunostaining at the time of diagnosis in metastatic TGCT is associated with an adverse clinical outcome.     

Impact of BCRP/MXR, MRP1 and MDR1/P-Glycoprotein on thermoresistant variants of atypical and classical multidrug resistant cancer cells

The impact of the ABC transporters breast cancer resistance protein/mitoxantrone resistance associated transporter (BCRP/MXR), multidrug resistance-associated protein 1 (MRP1) and multidrug resistance gene-1/P-glycoprotein (MDR1/PGP) on the multidrug resistance (MDR) phenotype in chemoresistance and thermoresistance was investigated in the parental human gastric carcinoma cell line EPG85-257P, the atypical MDR subline EPG85-257RNOV, the classical MDR subline EPG85-257RDB and their thermoresistant counterparts EPG85-257P-TR, EPG85-257RNOV-TR and EPG85-257RDB-TR. Within the atypical MDR subline EPG85-257RNOV expression of BCRP/MXR and of MRP1 were clearly enhanced (vs. parental and classical MDR lines). MDR1/PGP expression was distinctly elevated in the classical MDR subline EPG85-257RDB (vs. parental and atypical MDR sublines). In all thermoresistant counterparts basal expression of BCRP/MXR, MRP1 and MDR1/PGP was increased relative to thermosensitive sublines. Although it could be shown that the overexpressed ABC transporters were functionally active, however, no decreased drug accumulations of doxorubicin, mitoxantrone and rhodamine 123 were observed. Thus, expression of BCRP/MXR, MRP1 and MDR1/PGP was found to be dependent on the appropriate type of chemoresistance; correlating with a classical or atypical MDR phenotype. Within the thermoresistant variants, however, the increase in ABC transporter expression did obviously not influence the MDR phenotype.     

Multiple gene expression analysis reveals distinct differences between G2 and G3 stage breast cancers, and correlations of PKC eta with MDR1, MRP and LRP gene expression.

A possible link between protein kinase C (PKC) and P-glycoprotein (P-gp)-mediated-multidrug resistance (MDR) was assumed from studies on MDR cell lines selected in vitro. The functional relevance of PKC for the MDR phenotype remains unclear, and the involvement of a particular PKC isozyme in clinically occurring drug resistance is not known. Recently, we have demonstrated significant correlations between the expression levels of the PKC eta isozyme and the MDR1 or MRP (multidrug resistance-associated protein) genes in blasts from patients with acute myelogenous leukaemia (AML) and in ascites cell aspirates from ovarian cancer patients. To extend these findings to further types of human tumours we analysed specimens from 64 patients with primary breast cancer for their individual expression levels of several MDR-associated genes (MDR1, MRP, LRP (lung cancer resistance-related protein), topoisomerase (Topo) II alpha/IIbeta, cyclin A and the PKC isozyme genes (alpha, beta1, beta2, eta, theta, and mu) by a cDNA-PCR approach. We found significantly enhanced mean values for MRP, LRP and PKC eta gene expression, but significantly decreased Topo II alpha and cyclin A gene expression levels in G2 tumours compared with G3. Remarkably, significant positive correlations between the MDR1, MRP or LRP gene expression levels and PKC eta were determined: MDR1/PKC eta (rs = +0.6451, P < 0.0001) n = 62; MRP/PKC eta (rs = +0.5454, P < 0.0001) n = 63; LRP/PKC eta (rs = +0.5436, P < 0.0001) n = 62; MRP/LRP (rs = +0.7703, P < 0.0001) and n = 62, MDR1/MRP (rs = +0.5042, P < 0.0001) n = 62. Our findings point to the occurrence of a multifactorial MDR in the clinics and to PKC eta as a possible key regulatory factor for up-regulation of a series of MDR-associated genes in different types of tumours.     

非小细胞肺癌MDR1—mRNA,MRP—mRNA及LRP—mRNA表达的研究

目的：观察肺癌组织及癌旁肺组织MDR1－mRNA,MRP-mRNA及LRP－mRNA的表达,方法：采用RT－PCR法检测30例肺癌患者组织和正常肺组织中MDR1－mRNA,MRP-mRNA和LRP－mRNA的表达情况。结果：MDR1－mRNA在肺癌组织及癌旁肺组织的表达阳性率分别为40％及16．67％（P＝0．045）,其表面与细胞分化程度,发期及病理类型无明显关系,MRP－mRNA在肺癌组织及癌旁肺组织的表达分别为43＝．44％及26．67％,低分化者MRP的表达率明显高于中高分化者（P＝0．0004）,其表达与肿瘤类型,临床分期及癌细胞的分化程度无明显关系。30例肺癌组织中MDR1－mRNA,MRP-mRNA,LRP-mRNA共同表达者7例（23．33％）,三者均无表达者10例（33．33％）,三者的一致性达56．67％,结论：MDR1－mRNA,MRP-mRNA,LRP-mRNA在肺癌的耐药中可能起重要作用。     

Prognostic significance of multidrug resistance-related proteins in childhood acute lymphoblastic leukaemia

An important problem in the treatment of children with acute lymphoblastic leukaemia (ALL) is pre-existent or acquired resistance to structurally and functionally unrelated chemotherapeutic compounds. Various cellular mechanisms can give rise to multidrug resistance (MDR). Best studied is the transmembrane protein-mediated efflux of cytotoxic compounds that leads to decreased cellular drug accumulation and toxicity. Several MDR-related efflux pumps have been characterised, including P-glycoprotein (P-gp), multidrug resistance-associated protein 1 (MRP1), breast cancer resistance protein (BCRP) and lung resistance protein (LRP). P-gp expression and/or activity has been associated with unfavourable outcome in paediatric ALL patients, whereas MRP1 and BCRP do not seem to play a major role. LRP might contribute to drug resistance in B-lineage ALL, but larger studies are needed to confirm these results. The present review summarises the current knowledge concerning multidrug resistance-related proteins and focuses on the clinical relevance and prognostic value of these efflux pumps in childhood ALL.