关于乳腺癌耐药蛋白BCRP/ABCG2的研究进展

乳腺癌耐药蛋白是体内重要的跨膜半转运蛋白,是一种依赖ATP酶的半结合转运体,主要负责将内、外源性物质排至细胞外.乳腺癌耐药蛋白在体内分布广泛,胎盘、干细胞、血脑屏障、小肠及肾小管等重要组织中均有表达,是介导肿瘤细胞耐药的重要蛋白,是影响肿瘤药物临床用药个体差异的重要因素之一.本文就乳腺癌耐药蛋白的生理结构、组织分布及对体内药物代谢过程的影响等方面的研究进展作一综述.     

乳腺癌耐药蛋白的研究进展

乳腺癌耐药相关蛋白(BCRP/ABCG2)属于ATP结合盒(Adenosine triphosphate-binding cassette,ABC)膜转运蛋白超家族。它们作为细胞膜上的药物排出泵,可以将一系列细胞毒药物转运至胞外,影响其抗肿瘤作用。在很多血液肿瘤和实体瘤中均检测到ABCG2表达,这意味着ABCG2在肿瘤的多药耐药上发挥重要作用。笔者综述了关于ABCG2的现有研究结果,对其与多药耐药的关系进行了总结。     

乳腺癌耐药蛋白BCRP在肿瘤化疗耐药中的研究进展

ABCG2(三磷酸腺苷(ATP)结合转运蛋白G超家族成员2)是ABC转运体(三磷酸腺苷结合盒转运体)超家族中的一员,因其介导肿瘤药物的化疗耐药中而为人们所熟知。自1998年克隆出ABC转运体家族的多药耐药蛋白(ABCG2/BCRP)后,有关于BCRP的研究论文已超过五千多篇。ABC转运体超家族成员均能引起药物耐药。本文主要对ABCG2的结构、功能、与其有关的底物药、抑制剂以及其对肿瘤药物耐药作用进行综述。     

乳腺癌组织中多药耐药基因的表达及其临床意义

目的探讨多药耐药基因蛋白P-糖蛋白(P-gp)、谷胱甘肽-S-转移酶-π(GST-π)及DNA拓扑异构酶Ⅱ(TopoⅡ)在乳腺癌组织中的表达及其临床意义。方法用免疫组化法检测78例原发乳腺癌组织中P-gp、GST-π及TopoⅡ的表达水平。结果(1)78例乳腺癌组织中P-gp、GST-π和TopoⅡ表达率分别为28.2%、38.5%和52.8%。(2)P-gp和GST-π表达与年龄、肿瘤大小、淋巴结转移、远处转移、临床分期、组织学类型无显著差异(P>0.05),TopoⅡ表达与肿瘤大小、远处转移、临床分期、组织学类型无显著差异(P>0.05),但与年龄、淋巴结转移有显著差异(P<0.05)。P-gp和GST-π的表达呈正相关(P<0.05),P-gp和TopoⅡ的表达呈明显负相关(P<0.05),GST-π和TopoⅡ呈明显负相关(P<0.05)。结论(1)部分乳腺癌患者体内原发存在耐药基因,对抗癌药物已产生耐药性。(2)乳腺癌化疗前检测耐药基因P-gp、GST-π与TopoⅡ,对肿瘤的化疗药物选择具有指导作用,对判断预后及研究耐药逆转提供参考价值。     

乳腺癌耐药蛋白BCRP表达与化疗药物敏感性的关系

目的探讨乳腺癌组织中乳腺癌耐药蛋白表达与临床常用化疗药物敏感性之间的关系。方法选取42例乳腺癌组织标本,采用免疫组织化学S-P法检测标本中BCRP表达,对同一标本应用胶滴肿瘤药敏检测技术进行体外药物敏感性试验。结果乳腺癌组织中BCRP阳性表达率为33.33%(14/42),BCRP阳性表达者中5-氟尿嘧啶、阿霉素耐药组所占比例明显高于BCRP阴性组(P<0.05)。结论 BCRP蛋白表达可以作为预测化疗效果的一个重要参考指标,根据药物敏感试验结果进行药物筛选,实现乳腺癌化疗的个体化,对于提高患者生存质量,具有十分特殊的意义。     

多药耐药蛋白P-糖蛋白的研究进展

肿瘤细胞对化疗药物的耐受性是肿瘤治疗的主要障碍,也是多数肿瘤患者预后不佳的主要原因。有学者认为90％以上恶性肿瘤患者死亡在不同程度上与耐药因素有关。肿瘤产生耐药与多种因素有关,如多药耐药基因的过度表达;谷胱甘肽解毒酶系统活性增高;DNA拓扑异构酶Ⅱ活性增高或性质发生改变;多药耐药相关蛋白基因表达增高等。其中由P-糖蛋白介导的多药耐药最为重要,本文重点介绍与P-糖蛋白有关的多种调控因素及其逆转多药耐药（multir esist—ante,MDR）进展。     

miR-181a对乳腺癌耐药蛋白表达调控作用的研究

目的探讨miRNA-181a对乳腺癌耐药蛋白(BCRP)及其介导的乳腺癌细胞耐药性的调控作用。方法应用生物信息学预测BCRP mRNA-3'UTR与miR-181a的结合位点;荧光素酶报告分析检测miR-181a与BCRP mRNA-3'UTR的结合作用;qRT-PCR和Western blot检测细胞中相关蛋白表达水平。结果与阴性转染组比较,miR-181a mimic与PGL3-BCRP 3'UTR共转染后,荧光素酶活性明显降低(P<0.05)。miR-181a mimic转染到MCF7/MX细胞48 h后,与阴性转染组相比,导致原本miR-181a低表达的MCF-7/MX细胞中miR-181a的表达增加(P<0.05),BCRP mRNA和蛋白表达明显下降(P<0.05),而MRP、P-gp、LRP的mRNA和蛋白水平均无明显改变(P>0.05);MCF-7细胞在miR-181a inhibitor转染48 h后,与阴性转染组相比,miR-181a的表达降低(P<0.05)。同时,BCRP mRNA和蛋白表达明显增加(P<0.05)。而MRP、P-gp、LRP的mRNA和蛋白水平无明显改变(P>0.05)。结论 miR-181a可通过靶向作用于BCRP mRNA-3'UTR区,调控BCRP表达。     

乳腺癌多药耐药机制及其逆转策略研究进展

目的:为乳腺癌的化疗提供参考。方法:查阅近年来国内外相关文献,对乳腺癌多药耐药机制及其逆转策略的研究进展进行归纳和总结。结果与结论:乳腺癌多药耐药产生的机制复杂,化学药物、细胞因子、免疫治疗、基因技术、中药、药物载体等逆转策略能有效逆转乳腺癌耐药。针对不同的乳腺癌耐药分子机制,开发新的逆转剂和逆转策略,有助于解决乳腺癌多药耐药这一难题。     

中药逆转肿瘤多药耐药的研究进展

目的综述逆转肿瘤多药耐药(MDR)的研究进展。方法检索中药提取物或中药单体联合化疗药物逆转肿瘤MDR的研究。结果一些中药提取物或中药单体能使耐药株对化疗药物变得敏感,使耐药蛋白的转运活性下降。结论中药具有逆转肿瘤MDR的活性,其作用机制大多是与耐药相关蛋白相关的。     

多药耐药相关蛋白基因表达与食管及贲门癌的关系

目的 探讨食管癌及贲门癌组织中多药耐药相关蛋白(MRP)基因的表达与其病理特征的关系。方法 应用逆转录酶-多聚酶链反应(RT-PCR)方法,检测了83例食管癌和贲门癌组织及28例患者45枚淋巴结中MRP基因的表达,并与相应癌旁组织进行对照分析。结果 35例食管癌和48例贲门癌组织中MRP阳性率(31.4％和16.7％)与其对应癌旁组织阳性率(5.7％和2％)比较具有显著性差异(P<0.01)。26枚转移淋巴结中,MRP阳性6例(23.1％);19枚非转移淋巴结组织未见MRP。在食管癌和贲门癌侵犯深肌层或纤维层及TNM Ⅲ,Ⅳ期的MRP阳性率(26.6％和28.8％)高于肿瘤侵犯浅肌层以下和TNM Ⅰ,Ⅱ期(10.5％和12.9％),均分布于低分化肿瘤中。对48例术后1～2年的患者随访发现,MRP阳性的肿瘤复发、转移的发生率高于MRP阴性者(P<0.05)。结论 食管、贲门癌组织中MRP基因表达增高,与转移淋巴结组织的MRP基因表达具有一致性,MRP的阳性表达除表现肿瘤的多药耐药外,还提示肿瘤预后不良。     

Combined Effects of Multiple Flavonoids on Breast Cancer Resistance Protein (ABCG2)-Mediated Transport

PURPOSE: The purpose of this study was to determine the dynamic parameter (EC50) of flavonoids apigenin, biochanin A, chrysin, genistein, kaempferol, hesperetin, naringenin, and silymarin for breast cancer resistance protein (BCRP) inhibition when used alone, and to evaluate their potential interactions (additive, synergistic, or antagonistic) with regards to BCRP inhibition when used in multiple-flavonoid combinations. METHODS: The effects of flavonoids on BCRP-mediated transport were examined by evaluating their effects on mitoxantrone accumulation and cytotoxicity in MCF-7 MX100 cells overexpressing BCRP. The EC50 values of these flavonoids for increasing mitoxantrone accumulation were estimated using a Hill equation. The potential interactions among multiple flavonoids with regard to BCRP inhibition were assessed by isobologram and Berenbaum's interaction index methods. RESULTS: The EC50 values of these flavonoids for increasing mitoxantrone accumulation ranged from 0.39+/-0.13 microM to 33.7+/-2.78 microM. Quantitative analysis of the combined effects of multiple flavonoids on mitoxantrone accumulation indicated that these flavonoids act additively in inhibiting BCRP when given as 2-, 3-, 5-, or 8-flavonoid combinations with equimolar concentrations of all constituents. The results of the mitoxantrone cytotoxicity studies were consistent with these findings. CONCLUSIONS: The additive effects of multiple flavonoids for BCRP inhibition suggests that prediction of BCRP-mediated food (herbal product)-drug interactions should also take into consideration the presence of multiple flavonoids and provides a rationale for using "flavonoid cocktails" as a potential approach for multidrug resistance reversal in cancer treatment.     

Lack of Improvement of Oral Absorption of ME3277 by Prodrug Formation Is Ascribed to the Intestinal Efflux Mediated by Breast Cancer Resistant Protein (BCRP/ABCG2)

No HeadingPurpose. ME3229, an ester-type prodrug of a hydrophilic glycoprotein IIb/IIIa antagonist (ME3277), failed to show improved oral absorption. Okudaira et al. (J. Pharmacol. Exp. Ther. 294. 580–587, 2000) provided a piece of evidence that this is ascribed to an efflux system, distinct from P-gp and MRP2, that extrudes ME3277 formed from ME3229 in the intestinal epithelial cells. The aim of the present study is to examine the involvement of breast cancer resistant protein (BCRP/ABCG2) as a cause of low oral absorption of ME3229.Methods. The transport activity of ME3277 in the presence and absence of ATP was determined using a rapid filtration method with the membrane vesicles prepared from LLC-PK1 cells expressing BCRP. The plasma concentrations of ME3229 and its metabolites were compared between Bcrp1^–/– mice and wild-type mice after a single-pass perfusion of small intestine with ME3229.Results. The ATP-dependent uptake of ME3277 was greater in BCRP-expressing membrane vesicles than that in the control vesicles. Furthermore, it was found that after intestinal perfusion with ME3229 for 60 min, the plasma concentrations of ME3277 and PM-5, a metabolite of ME3229, increased 2-fold and 3-fold, respectively, in Bcrp1 knockout mice. It is possible that BCRP acts synergistically with intestinal carboxylesterases.Conclusion. These results suggest that Bcrp1 plays an important role in the intestinal efflux of ME3277 and, probably, PM-10 and PM-11, metabolites of ME3229, and limits its BA after oral administration of ME3229.     

Functional Analysis of SNPs Variants of BCRP/ABCG2

PURPOSE: The aim of the current study was to identify the effect of single nucleotide polymorphisms (SNPs) in breast cancer resistance protein (BCRP/ABCG2) on its localization, expression level, and transport activity. METHODS: The cellular localization was identified using the wild type and seven different SNP variants of BCRP (V12M, Q141K, A149P, R163K, Q166E, P269S, and S441N BCRP) after transfection of their cDNAs in plasmid vector to LLC-PK1 cells. Their expression levels and transport activities were determined using the membrane vesicles from HEK293 cells infected with the recombinant adenoviruses containing these kinds of BCRP cDNAs. RESULTS: Wild type and six different SNP variants of BCRP other than S441N BCRP were expressed on the apical membrane, whereas S441N BCRP showed intracellular localization. The expression levels of Q141K and S441N BCRP proteins were significantly lower compared with the wild type and the other five variants. Furthermore, the transport activity of E1S, DHEAS, MTX, and PAH normalized by the expression level of BCRP protein was almost the same for the wild type, V12M, Q141K, A149P, R163K, Q166E, and P269S BCRP. CONCLUSIONS: These results suggest that Q141K SNPs may associate with a lower expression level, and S441N SNPs may affect both the expression level and cellular localization. It is possible that subjects with these polymorphisms may have lower expression level of BCRP protein and, consequently, a reduced ability to export these substrates.     

Regional expression of the BCRP/ABCG2 transporter in term human placentas

The breast cancer resistance protein (BCRP, ABCG2) is an efflux transporter that removes xenobiotics that cross the placenta back to the maternal circulation, thereby limiting exposure of the fetus to drugs and chemicals. Currently, variability of BCRP expression within the placenta is not known. Ten placentas were collected from healthy women undergoing elective Cesarean sections at term. Villous samples were dissected in defined regions (medial, intermediate, and peripheral) and BCRP mRNA and protein were quantified. There were no regional differences in mRNA expression of housekeeping genes (GAPDH, RPL13a, PRL, 18S). GAPDH had the lowest correlation with BCRP Ct values and was used for BCRP mRNA normalization. No differences in placental BCRP mRNA and protein were observed among the sample sites (<20% variability). Sampling site does not affect the expression of BCRP, supporting the utility of single site sampling protocols to assess the interindividual regulation of this transporter in human placentas.     

Distribution of breast cancer resistance protein (BCRP/ABCG2) mRNA expression along the human GI tract

Human breast cancer resistance protein (BCRP/ABCG2) is an ABC-transporter that is present on the luminal membrane of intestinal epithelial cells and restricts absorption of anticancer drugs such as methotrexate, topotecan, mitoxantrone, and doxorubicin. The exact anatomic distribution of BCRP along the gastrointestinal (GI) tract, however, has not been determined before. The aim of this study was, therefore to investigate BCRP mRNA expression pattern along the GI tract in 14 healthy subjects. Furthermore, BCRP duodenal mRNA expression was compared with MDR1/ABCB1 mRNA. Additionally, BCRP mRNA expression was investigated in two human intestinal cell lines (Caco-2 and LS180). Since previous animal studies have suggested sex specific differences in BCRP expression, we analyzed intestinal BCRP expression with respect to sex. Biopsies were taken from different gut segments (duodenum, terminal ileum and ascending, transverse, descending and sigmoid colon). Gene expression was assessed by quantitative real-time PCR (Taqman). BCRP mRNA expression was maximal in the duodenum and decreased continuously down to the rectum (terminal ileum 93.7%, ascending colon 75.8%, transverse colon 66.6%, descending colon 62.8%, and sigmoid colon 50.1% compared to duodenum, respectively). BCRP expression in the duodenum was comparable to MDR1/ABCB1 gene expression. Caco-2 cells showed a comparable expression of BCRP as human duodenal tissue. Gender specific differences in BCRP expression were not observed. These findings represent the first systematic site-specific analysis of BCRP expression along the GI tract. This information might be helpful to develop target strategies for orally administered anticancer drugs.     

A fluorescence-based in vitro assay for drug interactions with breast cancer resistance protein (BCRP, ABCG2)

Purpose: To establish a fluorescence-based assay for drug interactions with the ABC-export-protein BCRP (ABCG2). Methods: BCRP expression was verified by immunostaining and Western blots in intact porcine brain capillaries, isolated endothelial cells (PBCECs) and in MDCKII-cells over-expressing human wild-type BCRP (MDCKII-hBCRP). Transport of fluorescent mitoxantrone across cells was determined to assess a preferred transport direction. Sensitivity of cultured cells versus mitoxantrone in the absence and in the presence of transport modulators was examined at increasing concentrations of the cytostatic using the AlamarBlue™ assay. In addition, cells were incubated with mitoxantrone in the absence and presence of increasing concentrations of different compounds with the potential to interact with BCRP. Intracellular fluorescence accumulation was measured using a flow cytometer. Results: Isolated capillaries as well as 7-day old PBCECs showed expression of BCRP. Cell sensitivity to mitoxantrone significantly increased in the presence of the BCRP inhibitors KO143 and GF120918. Transport of mitoxantrone across PBCEC monolayers was directed with P_app (apical to basolateral) 5.6 × 10⁻⁶ cm s⁻¹ and with P_app (basolateral to apical) 2.8 × 10⁻⁵ cm s⁻¹. FACS analysis revealed a different extent of fluorescence accumulation dependent on the kind and concentration of BCRP modulating compounds. Conclusions: The mitoxantrone-based assay can be used as a rapid FACS screening system to assess drug interactions with BCRP at the blood-brain barrier and therefore represents a useful tool in drug profiling.     

An update on expression and function of P-gp/ABCB1 and BCRP/ABCG2 in the placenta and fetus

Introduction: P-glycoprotein (P-gp)/ABCB1 and breast cancer resistance protein (BCRP)/ABCG2 are highly expressed in the placenta and fetus throughout gestation and can modulate exposure and toxicity of drugs and xenobiotics to the vulnerable fetus during the sensitive times of growth and development. We aim to provide an update on current knowledge on placental and fetal expressions of the two transporters in different species, and to provide insight on interpreting transporter expression and fetal exposure relative to the concept of fraction of drug transported.

Areas covered: Comprehensive literature review through PubMed (primarily from July 2010 to February 2018) on P-gp and BCRP expression and function in the placenta and fetus of primarily human, mouse, rat, and guinea pig.

Expert opinion: While there are many commonalities in the expression and function of P-gp and BCRP in the placenta and fetal tissues across species, there are distinct differences in expression levels and temporal changes. Further studies are needed to quantify protein abundance of these transporters and functionally assess their activities at various gestational stages. Combining the knowledge of interspecies differences and the concept of fraction of drug transported, we may better predict the magnitude of impact these transporters have on fetal drug exposure.     

Effect of Organic Isothiocyanates on Breast Cancer Resistance Protein (ABCG2)-Mediated Transport

No HeadingPurpose. To investigate the effect of organic isothiocyanates (ITCs), dietary compounds with chemopreventive activity, on breast cancer resistance protein (BCRP)-mediated transport.Methods. The effect of 12 ITCs on the cellular accumulation of mitoxantrone (MX) was measured in both BCRP-overexpressing and BCRP-negative human breast cancer (MCF-7) and large cell lung carcinoma (NCI-H460) cells by flow cytometric analysis. The ITCs showing activity in MX accumulation were examined for their effect on MX cytotoxicity, and the intracellular accumulation of radiolabeled phenethyl isothiocyanate (PEITC) was measured in both BCRP-overexpressing and BCRP-negative NCI-H460 cells.Results. ITCs significantly increased MX accumulation and reversed its cytotoxicity in resistant cells, but had a small or no effect in sensitive cells. The effects of ITCs on MX accumulation and cytotoxicity were ITC-concentration dependent. Significant increases in MX accumulation were observed at ITC concentrations of 10 or 30 gM, and significant reversal of MX cytotoxicity was generally observed at ITC concentrations of 10 M. Intracellular accumulation of radiolabeled PEITC in BCRP-overexpressing cells was significantly lower than that in BCRP-negative cells and was increased significantly by the BCRP inhibitor fumitremorgin C (FTC).Conclusions. Certain ITCs are BCRP inhibitors and PEITC and/or its cellular metabolite(s) may represent BCRP substrates, suggesting the potential for diet-drug interactions.