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。     

瓦他拉尼对乳腺癌耐药蛋白介导的肿瘤多药耐药的逆转研究

目的观察新型激酶抑制剂类抗癌药瓦他拉尼(vatalanib)逆转肿瘤细胞多药耐药(MDR)的效果,研究其对乳腺癌耐药蛋白(BCRP)、P-糖蛋白(P-gp)、多药耐药相关蛋白1(MRP1)的作用,探讨其作用机制。方法应用MTS法或SRB法检测瓦他拉尼对耐药细胞与敏感细胞的细胞毒性和逆转MDR的效果;分别以罗丹明(Rh-123)、米托蒽醌(MX)、阿霉素(ADR)为P-gp、BCRP、MRP1的荧光底物,应用流式细胞术检测该药对P-gp、BCRP、MRP1外排功能的影响;应用Western blot检测该药对耐药细胞中BCRP蛋白表达水平的影响,并研究其对细胞增殖相关信号分子的影响;应用qRT-PCR检测其对耐药细胞中BCRP基因表达水平的影响;通过超速离心法制备BCRP转运蛋白的粗膜,检测瓦他拉尼对BCRP的ATPase活性的影响。结果无毒剂量的瓦他拉尼(5μmol·L-1)可有效逆转BCRP高表达的肿瘤细胞株HEK293/ABCG2对MX、ADR和托泊替康(TOPT)的耐药,而对P-gp高表达的肿瘤细胞株K562/A02和MRP1高表达的肿瘤细胞株HEK293/ABCC1的耐药无逆转作用。该药能够下调耐药肿瘤细胞的BCRP基因和蛋白的表达水平,并具有时间和剂量依赖效应,但对BCRP外排MX的功能无明显抑制作用。该药可以激活BCRP的ATPase活性,但并不改变BCRP的构象,对耐药和敏感细胞中AKT和ERK的表达及其磷酸化水平也均无明显影响。结论瓦他拉尼可有效、特异地逆转BCRP介导的肿瘤MDR,其机制可能是通过下调耐药肿瘤细胞中BCRP基因和蛋白的表达来达到逆转MDR的效果。     

黄酮类化合物对肿瘤多药耐药调节作用的研究进展

多药耐药是临床上化疗失败的重要原因之一。黄酮类化合物存在于多种植物中,具有广泛的药理活性,对P-糖蛋白(P-gp)、多药耐药相关蛋白(MRP)、乳腺癌耐药蛋白(BCRP)等外向转运蛋白的抑制作用使其可能成为肿瘤多药耐药调节剂。文中分别对黄酮类化合物对ABC家族转运蛋白抑制作用的研究概况、作用机制以及构效关系进行综述,为肿瘤多药耐药抑制剂的开发和应用提供重要信息。     

以膜转运蛋白为靶点的胃癌多药耐药研究进展

胃癌是我国病死率最高的常见恶性肿瘤,肿瘤多药耐药（MDR）严重影响临床化疗的效果,而膜转运蛋白如P－糖蛋白（P－gp）、MDR相关蛋白（MRP）、乳腺癌耐药蛋白(BCRP)和肺耐药相关蛋白(LRP)的异常表达是引起肿瘤多药耐药的重要机制之一. 简述上述4种膜转运蛋白在胃癌中的异常表达、耐药机制、临床意义及其逆转药.     

降低细胞膜角蛋白8和乳腺癌耐药蛋白的表达逆转耐药性

目的研究细胞膜角蛋白8(CK8)和乳腺癌耐药蛋白(breast cancer resistant protein,BCRP)作为多靶点治疗逆转耐药的可行性。方法共转染特异的CK8-siRNAs和BCRP-siRNAs至人乳腺癌多药耐药细胞MCF-7/MX,用Western blot方法检测siRNAs对CK8和BCRP蛋白表达的抑制,荧光染色用激光共聚焦显微镜观察细胞膜表面CK8表达量的变化,并用Sulforhodamine B的方法检测转染前后细胞对多种化疗药敏感性的变化。结果MCF-7/MX细胞导入CK8-siRNAs和BCRP-siRNAs后,CK8和BCRP的表达水平均明显降低,且细胞表面CK8染色也明显降低,同时对米托蒽醌等化疗药的敏感性明显提高,耐药表型明显逆转。结论CK8和BCRP在MCF-7/MX耐药细胞中共同高表达且在乳腺癌多药耐药表型的形成中起重要作用,共同抑制CK8和BCRP的表达可以有效逆转乳腺癌的多药耐药,为治疗肿瘤多药耐药提供了一条新的思路。     

外排型转运体介导的抗肿瘤药物多药耐药的研究进展

多药耐药（MDR）是指肿瘤细胞接触一种抗肿瘤药物后,也对其他多种结构不同、功能不同的抗肿瘤药物产生耐药性,其中外排型转运体所介导的MDR是其中至关重要的一部分。外排型转运体是指位于肿瘤细胞生物膜上的具有将抗肿瘤药物从细胞内外排到细胞外的转运体。已知的具有外排作用的转运体有P糖蛋白（P-gp）、多药耐药相关蛋白（MRP）、乳腺癌耐药蛋白（BCRP）和肺耐药蛋白（LRP）。综述这几种外排型转运体的一般性质并着重于阐述逆转这些转运体介导的多药耐药的药物及方法。     

ATP结合盒转运蛋白介导的MDR逆转剂的实验研究现况

多药耐药性(mu ltidrug resistance,MDR)是指人肿瘤细胞对结构各异的化疗药物产生交叉耐药,是肿瘤化疗失败的主要原因之一。为了增强肿瘤细胞对化疗药物的敏感性,积极寻求有效逆转MDR的药物已成为研究重点。体外被证实具有逆转耐药活性的化合物很多,但由于体内要达到体外逆转试验的有效浓度所需剂量过大,毒副作用大,因此限制了临床应用。ATP结合盒转运蛋白家族(ATP-b ind ing cassette,ABC)介导的药物外排机制是目前MDR的主要机制,ABC转运蛋白家族中与多药耐药性相关的转运蛋有P-糖蛋白(P-gp)、多药耐药相关蛋白(MRP)和乳腺癌耐药蛋白(BCRP)。本文对ABC转运蛋白介导的MDR逆转剂的研究进展做一综述。     

倍半萜逆转肿瘤多药耐药机制研究进展

多药耐药（MDR）是指肿瘤细胞对一种抗肿瘤药物产生耐药性的同时,对结构和作用机制完全不同的其他多种抗肿瘤药物产生交叉耐药的现象.肿瘤细胞的多药耐药已经成为肿瘤化疗失败的主要原因之一.MDR由多种途径诱导,其形成机制相当复杂,主要有P-糖蛋白（P-gp）、多药耐药相关蛋白（MRP）、肺耐药相关蛋白（LRP）、乳腺癌耐药蛋白（BCRP）、谷胱甘肽（GSH）和谷胱甘肽-S-转移酶（GST）等含量、活性增加,DNA拓扑异构酶（TOPO） I、Ⅱ含量、活性下降,DNA损伤修复能力增强,肿瘤细胞凋亡抑制,细胞膜能量依赖性内运系统障碍等.由于现今的化学和生物的耐药逆转剂对机体的毒性很大,许多学者的目光转向于天然药物中,从中药中提取其有效成分毒性小、疗效好,而倍半萜类化合物正是目前的研究热点.     

介导肿瘤多药耐药的ATP结合盒转运体的研究进展

多药耐药（MDR）是阻碍肿瘤化疗成功的一大障碍,其机制之一就是耐药的肿瘤细胞高表达三磷酸腺苷（ATP）结合盒（ABC）转运体。依据此机制提出克服肿瘤细胞耐药的策略即开发外排转运体抑制剂,以期逆转MDR。最近的研究发现肿瘤干细胞也可能是通过表达外排转运体天然耐药,这就提供了一个新的抗癌药物作用靶点。对介导肿瘤细胞多药耐药的ABC转运体及其抑制剂的开发作一综述。     

ATP-dependent transport of rosuvastatin in membrane vesicles expressing breast cancer resistance protein.

MDR1/ABCB1, MRP2/ABCC2, and breast cancer resistance protein (BCRP)/ABCG2 are expressed in the liver and intestine and contribute to the disposition of many drugs. Rosuvastatin, a 3-hydroxy-3-methylglutaryl-CoA reductase inhibitor for the treatment of patients with dyslipidemia, is primarily excreted via bile as unchanged drug. The present study was designed to determine whether rosuvastatin is transported by MDR1, MRP2, and BCRP. The apparent permeability value for rosuvastatin across MDR1-Madin-Darby canine kidney cells was low ( approximately 8 nm/s), and no directional transport was observed. Rosuvastatin uptake into control Sf9 membranes and membranes expressing MRP2 was similar in the presence or absence of GSH. In contrast, ATP dramatically stimulated rosuvastatin uptake into membranes expressing BCRP, but not control membranes. Rosuvastatin transport occurred into an osmotically sensitive space and was saturable. An Eadie-Hofstee analysis suggested that there were two transport sites in BCRP, with an apparent K(m) of 10.8 muM for the high affinity site and 307 microM for the low affinity site. These data demonstrate that rosuvastatin is transported efficiently by BCRP and suggest that BCRP plays a significant role in the disposition of rosuvastatin.     

QSAR analysis and molecular modeling of ABCG2-specific inhibitors

In addition to its critical role is controlling drug availability and protecting sensitive organs and stem cells through cellular detoxification, breast cancer resistance protein (BCRP/ABCG2) plays an important role in cancer cell resistance to chemotherapy, together with P-glycoprotein/ABCB1. A main approach to abolish multidrug resistance is to find out specific inhibitors of the drug-efflux activity, able to chemosensitize cancer cell proliferation. Many efforts have been primarily focused on ABCB1, discovered thirty years ago, whereas very few studies have concerned ABCG2, identified much more recently. This review describes the main types of inhibitors presently known for ABCG2, and how quantitative structure-activity relationship analysis among series of compounds may lead to build up molecular models and pharmacophores allowing to design lead inhibitors as future candidates for clinical trials. A special attention is drawn on flavonoids which constitute a structurally-diverse class of compounds, well suited to identify potent ABCG2-specific inhibitors.     

Zafirlukast antagonizes ATP-binding cassette subfamily G member 2-mediated multidrug resistance

ATP-binding cassette (ABC) transporters are present in the majority of human tumors and are involved in multidrug resistance (MDR). Therefore, compounds that inhibit the function of ABC transporters may improve the efficacy of anticancer agents. Previous research has shown that zafirlukast is a reversal drug for multidrug resistance protein (MRP) 1-mediated MDR. In the present study, we assessed whether zafirlukast could be a reversal agent for other ABC transporter-mediated MDR. Using the MTT assay, we found that zafirlukast enhanced the cytotoxicity of several anticancer drugs that are substrates of breast cancer resistance proteins (BCRP/ABCG2), including mitoxantrone and SN-38. Furthermore, zafirlukast could partially reverse P-glycoprotein-mediated (P-gp/ABCB1) and MRP7 (ABCC10)-mediated MDR at nontoxic doses. Studies on [(3)H]-mitoxantrone accumulation and efflux have shown that zafirlukast increases the intracellular accumulation of [(3)H]-mitoxantrone by directly inhibiting ABCG2-mediated drug efflux. Western blot analysis indicated that zafirlukast did not alter the expression of ABCG2. In addition, a docking model predicted the binding conformation of zafirlukast within the transmembrane region of homology-modeled human ABCG2. Our findings suggest a possible strategy to potentially enhance the activity of anticancer drugs using a clinically approved drug with known side effects and drug-drug interactions.     

Inhibitors of cancer cell multidrug resistance mediated by breast cancer resistance protein (BCRP/ABCG2)

Breast cancer resistance protein (BCRP/ABCG2) belongs to the ATP-binding cassette (ABC) transporter superfamily. It is able to efflux a broad range of anti-cancer drugs through the cellular membrane, thus limiting their anti-proliferative effects. Due to its relatively recent discovery in 1998, and in contrast to the other ABC transporters P-glycoprotein (MDR1/ABCB1) and multidrug resistance-associated protein (MRP1/ABCC1), only a few BCRP inhibitors have been reported. This review summarizes the known classes of inhibitors that are either specific for BCRP or also inhibit the other multidrug resistance ABC transporters. Information is presented on structure-activity relationship aspects and how modulators may interact with BCRP.     

Breast cancer resistance protein in pharmacokinetics and drug-drug interactions

Breast cancer resistance protein (BCRP), also known as ABCG2, ABCP and MXR, is a member of the ATP-binding cassette transporter G family. BCRP functions as a biological barrier that extrudes xenobiotics out of cells. The broad substrate specificity and tissue distributions of BCRP in the body make this transporter one of the major efflux transporters in chemotherapy. Recent studies have demonstrated that BCRP exerts a great impact on drug absorption and disposition. This review focuses on the role of BCRP in pharmacokinetics as well as in vitro and in vivo strategies to evaluate hepatic/intestinal BCRP-mediated drug transports and drug-drug interactions. The impacts of polymorphism and gender difference of BCRP are also discussed.     

Multidrug resistance in cancer chemotherapy and xenobiotic protection mediated by the half ATP-binding cassette transporter ABCG2

ABCG2, also termed BCRP/MXR/ABCP, is a half ATP-binding cassette (ABC) transporter expressed on plasma membranes. ABCG2 was independently cloned from placenta as well as cell lines selected for resistance to mitoxantrone or anthracyclines. ABCG2 consists of a nucleotide-binding domain (NBD) at the amino terminus and a transmembrane domain (TMD) at the carboxyl terminus and it is postulated to form a homodimer to perform its biological functions. Over-expression of ABCG2 in cell lines confers resistance on a wide variety of anticancer drugs including mitoxantrone, daunorubicin, doxorubicin, topotecan and epirubicin. The expression of ABCG2 has been implicated in multidrug resistance (MDR) of acute myeloid leukemia and some solid tumors. In addition, ABCG2 can transport several fluorescent dyes or toxins. ABCG2 is found to be expressed in epithelial cells of intestine and colon, liver canaliculi, and renal tubules, where it serves to eliminate the plasma level of orally administered anticancer drugs as well as ingested toxins. ABCG2 is found to be highly expressed in placenta and the luminal surface of microvessel endothelium blood-brain barrier where it may play a role in limiting the penetration of drugs, such as topotecan from the maternal plasma into the fetus and from blood to brain. A variety of inhibitors for ABCG2 including GF120918 may prove useful for sensitizing cancer cells to chemotherapy or altering the distribution of orally administered drug substrates of ABCG2. Interestingly, ABCG2 is also expressed highly in hematopoietic stem cells. However, the function of ABCG2 in stem cells is currently unknown, although it may provide protection to stem cells from a variety of xenobiotics.     

Layer II of placental syncytiotrophoblasts expresses MDR1 and BCRP at the apical membrane in rodents

The purpose of this study is to clarify the subcellular localizations of multidrug resistance protein 1 (MDR1)/ABCB1 and breast cancer resistance protein (BCRP)/ABCG2 in the rodent placental SynT bilayer, i.e., a maternal-facing (SynT-I) layer and a fetal-facing (SynT-II) layer. In double immunofluorescence staining, the signals of MDR1 and BCRP appeared midway between the signals of glucose transporter 1 on the apical membrane of SynT-I and the basal plasma membrane of SynT-II, and mostly overlapped with signals of connexin 26, which forms gap junctions between SynT-I and SynT-II. In detail, median intensities (pixels) of the MDR1 and BCRP signals were significantly closer to the fetal circulation as compared to the location of connexin 26 signals. In double in situ hybridization studies, the signals of Mdr1b mRNA mostly overlapped with those of Syncytin-B, a SynT-II marker. In conclusion, MDR1 and BCRP are expressed on apical membranes of the rodent placental SynT-II layer.     

Independent regulation of apical and basolateral drug transporter expression and function in placental trophoblasts by cytokines, steroids, and growth factors.

Placental ATP binding cassette (ABC) transporters protect placental and fetal tissues by effluxing xenobiotics and endogenous metabolites. We have investigated the effects of cytokines and survival/growth factors, implicated in various placental pathologies, on ABC transporter expression and function in primary placental trophoblast cells. Treatment of primary term trophoblasts in vitro with tumor necrosis factor-alpha (TNF-alpha) or interleukin (IL)-1beta decreased mRNA and protein expression of apical transporters ABCB1/multidrug resistance gene product 1 (MDR1) and ABCG2/breast cancer resistance protein (BCRP) protein by 40 to 50% (P < 0.05). In contrast, IL-6 increased mRNA and protein expression of the basolateral transporter ABCB4/MDR3 (P < 0.05), whereas ABCC1/MRP1 expression was unaltered. Pretreatment of trophoblasts with TNF-alpha over 48 h resulted in significantly decreased BCRP efflux activity (increased mitoxantrone accumulation) with minimal changes in MDR1/3 activity. Epidermal growth factor (EGF) and insulin-like growth factor II, on the other hand, significantly increased BCRP expression at the mRNA and protein level (P < 0.05); EGF treatment also increased BCRP functional activity. Estradiol stimulated BCRP, MDR1, and MDR3 mRNA and protein expression by 40 to 60% and increased MDR1/3 functional activity (P < 0.05). Progesterone had modest positive effects on MRP1 mRNA and MDR1 protein expression (P < 0.05). In conclusion, this study shows that proinflammatory cytokines, sex steroids, and growth factors exert independent effects on expression of apical and basolateral placental ABC transporters in primary trophoblast. Such changes could alter placental drug disposition, increase fetal susceptibility to toxic xenobiotics, and impact on placental viability and function.     

ABCG2: A perspective

ABCG2, or breast cancer resistance protein (BCRP), is an ABC transporter that has been the subject of intense study since its discovery a decade ago. With high normal tissue expression in the brain endothelium, gastrointestinal tract, and placenta, ABCG2 is believed to be important in the protection from xenobiotics, regulating oral bioavailability, forming part of the blood-brain barrier, the blood-testis barrier, and the maternal-fetal barrier. Notably, ABCG2 is often expressed in stem cell populations, where it likely plays a role in xenobiotic protection. However, clues to its epigenetic regulation in various cell populations are only beginning to emerge. While ABCG2 overexpression has been demonstrated in cancer cells after in vitro drug treatment, endogenous ABCG2 expression in certain cancers is likely a reflection of the differentiated phenotype of the cell of origin and likely contributes to intrinsic drug resistance. Notably, research into the transporter's role in cancer drug resistance and its development as a therapeutic target in cancer has lagged. Substrates and inhibitors of the transporter have been described, among them chemotherapy drugs, tyrosine kinase inhibitors, antivirals, HMG-CoA reductase inhibitors, carcinogens, and flavonoids. This broad range of substrates complements the efficiency of ABCG2 as a transporter in laboratory studies and suggests that, while there are redundant mechanisms of xenobiotic protection, the protein is important in normal physiology. Indeed, emerging studies in pharmacology and toxicology assessing polymorphic variants in man, in combination with murine knockout models have confirmed its dynamic role. Work in pharmacology may eventually lead us to a greater understanding of the physiologic role of ABCG2.