Involvement of P-glycoprotein,Multidrug Resistance Protein 2 and Breast Cancer Resistance Protein in the Transport of Belotecan and Topotecan in Caco-2 and MDCKII Cells

Purpose  To investigate the underlying mechanism of low bioavailabilities of the water-soluble camptothecin derivatives, belotecan and topotecan. Methods  The bioavailability of belotecan and topotecan in rats was determined following oral administration of each drug at a dose of 5 mg/kg body weight. The vectorial transport of each drug was measured in Caco-2 and engineered MDCK II cells. Results  The bioavailability of belotecan (11.4%) and topotecan (32.0%) in rats was increased to 61.5% and 40.8%, respectively, by the preadministration of CsA at a dose of 40 mg/kg. Contrary to the absorptive transport, the secretory transport of these drugs across the Caco-2 cell monolayer was concentration-dependent, saturable, and significantly inhibited by the cis presence of verapamil (a P-gp substrate), MK-571 (an MRP inhibitor), bromosulfophthalein (BSP, an MRP2 inhibitor), fumitremorgin C (FTC, a BCRP inhibitor) and cyclosporine A (CsA, an inhibitor of P-gp and BCRP, and a substrate of P-gp) suggesting the involvement of these transporters, which could be further confirmed in MDCKII/P-gp, MDCKII/MRP2 and MDCKII/BCRP cells. Conclusion  The involvement of secretory transporters P-gp, MRP2 and BCRP, particularly for belotecan, as well as a low passive permeability, appears to be responsible for the low bioavailability of belotecan and topotecan. Hong Li and Hyo-Eon Jin have contributed equally to this work.     

Breast Cancer Resistance Protein (BCRP) and Sulfotransferases Contribute Significantly to the Disposition of Genistein in Mouse Intestine

The low bioavailability of genistein has impeded its development into a therapeutic agent. Our earlier studies indicate that glucuronidation is one of the major barriers to genistein oral bioavailability. This study will determine how sulfotransferases and efflux transporters affect its intestinal disposition. A rodent intestinal perfusion model and S9 fractions were used. Sulfate excretion rates were comparable to glucuronide excretion in mouse small intestine but significantly higher than glucuronide excretion in mouse colon, which is different from rat intestinal disposition but similar to disposition in Caco-2 cells. To define efflux transporter(s) involved in sulfate excretion, two organic anion inhibitors (estrone sulfate and dihydroepiandrosterone sulfate) or a multidrug resistance protein inhibitor (MK-571) were used but neither was able to decrease the excretion of genistein sulfates. In contrast, the excretion of genistein sulfate decreased substantially (>90%) in small intestine of breast cancer resistance protein (BCRP) knockout mice and became undetectable in colon of the knockout mice. The excretion rates of genistein glucuronide in the small intestine of BCRP knockout mice were also significant decreased (78%). This study shows clearly that BCRP facilitates the cellular genistein sulfate excretion by removing sulfates to prevent their backward hydrolysis and to limit substrate inhibition, indicating that BCRP plays a dominant role in genistein sulfate excretion and a significant role in genistein glucuronide excretion in the mouse intestine.     

Breast Cancer Resistance Protein-Mediated Efflux of Luteolin Glucuronides in HeLa Cells Overexpressing UDP-Glucuronosyltransferase 1A9

Purpose

UDP-glucuronosyltransferases (UGTs) are responsible for the formation of glucuronides of polyphenolic flavonoids. This study investigated the UGT1A9-mediated glucuronidation of luteolin and the kinetics of luteolin glucuronide efflux.

Method

HeLa cells overexpressing UGT1A9 (HeLa-UGT1A9) were used to determine the kinetics of breast cancer resistance protein (BCRP)-mediated transport of luteolin glucuronides. Human UGT isoforms were used to determine glucuronidation rates.

Results

UGT1A9 was found to catalyze the production of four luteolin glucuronides, including three known monoglucuronides and a novel 3′, 4′-diglucuronide. Ko143, a potent specific inhibitor of BCRP, significantly inhibited efflux of luteolin monoglucuronides from HeLa1A9 cells and increased their intracellular levels in a dose-dependent manner. The formation of luteolin diglucuronide was observed when intracellular concentration of total monoglucuronides went above 0.07 nM.

Conclusions

Intracellular accumulation of diglucuronide was detected at high monoglucuronide concentrations (>0.07 nM). Diglucuronide production is speculated to be a compensatory pathway for luteolin disposition.     

干扰素与维拉帕米逆转乳腺癌细胞耐药作用的研究

目的:研究α-干扰素与维拉帕米对体外培养的乳腺癌细胞多药耐药(MDR)的逆转作用。方法:以对药物敏感的人乳腺癌细胞系MCF-7和经阿霉素(ADM)诱导具有MDR表型的人乳腺癌耐药细胞系MCF-7/ADR为体外试验模型,分别单用及联用α-干扰素与维拉帕米对细胞系进行处理,MTT法检测各组细胞存活率,计算半数抑制浓度(IC50)、耐药倍数和逆转倍数;流式细胞术定量检测细胞表面P-170的表达。结果:α-干扰素与维拉帕米联用后使乳腺癌细胞耐ADM的IC50降低为0.32μmol·L-1,优于二者单用(2.29、1.23μmol·L-1),逆转倍数升高到51.88(二者单用为7.25、13.49),P-170表达低于二者单用。结论:单独应用α-干扰素、维拉帕米均可达到部分逆转MCF-7/ADR对ADM的耐药作用,但二者联用效果更强。     

48例非小细胞肺癌MDR1及MRP基因表达结果分析

目的：探讨多药耐药（MDR1）基因,多药耐药相关蛋白（MRP）基因在非小细胞肺癌（NSCLC）中的表达情况及其与组织类型的关系。方法：用逆转录多聚酶链反应（RT－PCR）方法检测新鲜肺癌组织标本。结果：48例NSCLC标本MDR1,MRP基因阳性表达率分别为62．5％,66．7％,二种基因共同表达率为43．8％,肺鳞癌MRP基因表达明显高于腺癌（P＜0．01）,而鳞癌与腺癌之间MDR1基因表达无显著性差异（P＞0．05）,结论：MDR1,MRP基因可以共同或分别存在于肺癌组织中,肺鳞癌MRP基因表达率较腺癌高。     

Breast Cancer Resistance Protein (ABCG2) Determines Distribution of Genistein Phase II Metabolites: Reevaluation of the Roles of ABCG2 in the Disposition of Genistein

It was recently proposed that the improved oral bioavailability of genistein aglycone and conjugates in Bcrp1(-/-) mice is mainly due to increased intestinal absorption of aglycone and subsequent elevated exposure to conjugation enzymes. Here we tested this proposed mechanism and found that intestinal absorption of genistein aglycone did not increase in Bcrp1(-/-) mice compared with wild-type mice using an in situ mouse intestinal perfusion model and that inhibition of breast cancer resistance protein (BCRP) in Caco-2 cells also did not significantly increase permeability or intracellular concentration of aglycone. Separately, we showed that 5- to 10-fold increases in exposures of conjugates and somewhat lower fold increases (<2-fold) in exposures of aglycone were apparent after both oral and intraperitoneal administration in Bcrp1(-/-) mice. In contrast, the intestinal and biliary excretion of genistein conjugates significantly decreased in Bcrp1(-/-) mice without corresponding changes in aglycone excretion. Likewise, inhibition of BCRP functions in Caco-2 cells altered polarized excretion of genistein conjugates by increasing their basolateral excretion. We further found that genistein glucuronides could be hydrolyzed back to genistein, whereas sulfates were stable in blood. Because genistein glucuronidation rates were 110% (liver) and 50% (colon) higher and genistein sulfation rates were 40% (liver) and 42% (colon) lower in Bcrp1(-/-) mice, the changes in genistein exposures are not mainly due to changes in enzyme activities. In conclusion, improved bioavailability of genistein and increased plasma area under the curve of its conjugates in Bcrp1(-/-) mice is due to altered distribution of genistein conjugates to the systemic circulation.     

Stereoselective Hepatic Disposition of Model Diastereomeric Acyl Glucuronides

Numerous studies have previously been conducted with the impulse-response isolated perfused rat liver (IR-IPRL) to establish the role of both physiological and physicochemical factors in determining solutes' pattern of hepatic disposition, however the impact of optical isomerism on hepatic disposition has hardly been studied using this methodology. In this study, the IR-IPRL was used to assess the extent of stereoselectivity exhibited by the kinetic processes involved in the hepatic disposition of the diastereomeric acyl glucuronides of (R)- and (S)-2-phenylpropionic acid (i.e. (R)- and (S)-PPAG). Moment and model-dependent (distributed model and axial dispersion model) analyses were conducted of the hepatic outflow profiles generated upon bolus administration of (R)-(14)C-PPAG or (S)-(14)C-PPAG and 3H-Sucrose (used as a marker of the hepatic vascular space) into the portal inflow of isolated perfused livers of male Sprague-Dawley rats (n = 4). Significant differences between (R)- and (S)-PPAG were apparent in the pharmacokinetic parameters defining the total hepatic disposition of the two diastereomers, the most marked being the hepatic availabilities, where the value for (S)-PPAG (0.721 +/- 0.059) was significantly lower than that of (R)-PPAG (0.909 +/- 0.042). The distributed and axial dispersion model analyses suggested that the more extensive hepatic extraction of (S)-PPAG was (at least in part) due to the higher sinusoidal membrane permeability-surface area product (PS UPT) of the diastereomer, and this has been considered in light of the emerging evidence regarding the role of hepatocellular membrane transport mechanisms. Furthermore, given the potential immunogenicity of acyl glucuronides (through covalent binding to plasma and intracellular proteins), the results of this study suggest that diastereomeric glucuronides may exhibit differing toxicity due to differences in their access to intracellular proteins.     

肿瘤多药耐药机制及逆转药物的研究进展

导致肿瘤多药耐药的机制很复杂,主要涉及有：ATP结合盒型转运蛋白超家族、DNA甲基化、细胞凋亡、拓扑异构酶Ⅱ、谷胱甘肽解毒系统及相关多药耐药信号通路等,这些机制单独或共同存在而导致耐药。逆转肿瘤多药耐药的方法主要有：化疗增敏剂、中药逆转剂和基因工程技术逆转耐药等。本文就肿瘤多药耐药机制的研究进展及逆转耐药的方法作一综述。     

胃癌细胞的制作对MDR-1免疫组化显示性的影响

目的:探讨胃癌细胞的制片和复染对MDR-1免疫组化显示性的影响.方法:培养胃癌SGC7901和耐药SGC7901/VCR细胞.均制作细胞滴片和爬片,抗MDR-1抗体免疫组化染色,部分标本甲基绿复染,半定量分析免疫反应性.结果:在同一制片中,无论滴片或爬片,复染标本的每种细胞MDR-1免疫反应性高于未复染者(P<0.01);对于同一种细胞不论是否复染,细胞滴片标本的MDR-1免疫反应性高于细胞爬片者(P<0.01);在同一制片和染色的情况下,SGC7901和SGC7901/VCR细胞的MDR-1表达水平不同(P<0.01),但变化趋势一致.结论:胃癌细胞的滴片比爬片有更好的MDR-1免疫组化显示性.     

乳腺癌耐药蛋白（BCRP/ABCG2）的研究进展

肿瘤细胞的多药耐药严重影响肿瘤化疗的疗效,研究肿瘤细胞耐药相关蛋白的生理功能及其转运药物的机制,寻找高效的多药耐药蛋白抑制剂是提高肿瘤化疗效果的重要途径。乳腺癌耐药蛋白（BCRP／ABCG2）是一种介导乳腺癌细胞耐药的重要蛋白,在乳腺癌细胞多药耐药的形成中起关键作用。本文将就BCRP／ABCG2蛋白的结构特点、生理功能、在多药耐药中的作用及其抑制剂等方面的研究进展作一综述。     

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.     

Human Multidrug Resistance Associated Protein 4 Confers Resistance to Camptothecins

Purpose The multidrug resistance associated protein (MRP) 4 is a member of the adenosine triphosphate (ATP)-binding cassette transporter family. Camptothecins (CPTs) have shown substantial anticancer activity against a broad spectrum of tumors by inhibiting DNA topoisomerase I, but tumor resistance is one of the major reasons for therapeutic failure. P-glycoprotein, breast cancer resistance protein, MRP1, and MRP2 have been implicated in resistance to various CPTs including CPT-11 (irinotecan), SN-38 (the active metabolite of CPT-11), and topotecan. In this study, we explored the resistance profiles and intracellular accumulation of a panel of CPTs including CPT, CPT-11, SN-38, rubitecan, and 10-hydroxy-CPT (10-OH-CPT) in HepG2 cells with stably overexpressed human MRP4. Other anticancer agents such as paclitaxel, cyclophosphamide, and carboplatin were also included. Methods HepG2 cells were transfected with an empty vehicle plasmid (V/HepG2) or human MRP4 (MRP4/HepG2). The resistance profiles of test drugs in exponentially growing V/HepG2 and MRP4/HepG2 cells were examined using the 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazonium bromide (MTT) assay with 4 or 48 h exposure time of the test drug in the absence or presence of various MRP4 inhibitors. The accumulation of CPT-11, SN-38, and paclitaxel by V/HepG2 and MRP4/HepG2 cells was determined by validated high-performance liquid chromatography methods. Results Based on the resistance folds from the MTT assay with 48 h exposure time of the test drug, MRP4 conferred resistance to CPTs tested in the order 10-OH-CPT (14.21) > SN-38 carboxylate (9.70) > rubitecan (9.06) > SN-38 lactone (8.91) > CPT lactone (7.33) > CPT-11 lactone (5.64) > CPT carboxylate (4.30) > CPT-11 carboxylate (2.68). Overall, overexpression of MRP4 increased the IC₅₀ values 1.78- to 14.21-fold for various CPTs in lactone or carboxylate form. The resistance of MRP4 to various CPTs tested was significantly reversed in the presence of dl-buthionine-(S,R)-sulfoximine (BSO, a γ-glutamylcysteine synthetase inhibitor), MK571, celecoxib, or diclofenac (all MRP4 inhibitors). In addition, the accumulation of CPT-11 and SN-38 over 120 min in MRP4/HepG2 cells was significantly reduced compared to V/HepG2 cells, whereas the addition of celecoxib, MK571, or BSO significantly increased their accumulation in MRP4/HepG2 cells. There was no significant difference in the intracellular accumulation of paclitaxel in V/HepG2 and MRP4/HepG2 cells, indicating that P-glycoprotein was not involved in the observed resistance to CPTs in this study. MRP4 also conferred resistance to cyclophosphamide and this was partially reversed by BSO. However, MRP4 did not increase resistance to paclitaxel, carboplatin, etoposide (VP-16), 5-fluorouracil, and cyclosporine. Conclusions Human MRP4 rendered significant resistance to cyclophosphamide, CPT, CPT-11, SN-38, rubitecan, and 10-OH-CPT. CPT-11 and SN-38 are substrates for MRP4. Further studies are needed to explore the role of MRP4 in resistance, toxicity, and pharmacokinetics of CPTs and cyclophosphamide.     

Absence of both MDR1 (ABCB1) and Breast Cancer Resistance Protein (ABCG2) Transporters Significantly Alters Rivaroxaban Disposition and Central Nervous System Entry

Rivaroxaban is a novel factor 10a inhibitor, where hepatic metabolism and renal clearance account for its overall disposition. Renal impairment is known to increase rivaroxaban‐associated bleeding risk in patients. As renal rivaroxaban clearance exceeds glomerular filtration rate, we suggested that active secretion by efflux transporters P‐glycoprotein (MDR1) and breast cancer resistance protein (BCRP) contributes to rivaroxaban clearance. The ability of MDR1 and BCRP efflux transporters to mediate rivaroxaban transport in vitro was assessed in polarized cell monolayers. A significantly greater vectorial transport of rivaroxaban was observed in the basal to apical direction in Caco‐2 cells, which was attenuated in the presence of the selective inhibitors. After oral administration of rivaroxaban (2 mg/kg), plasma concentrations did not significantly differ between wild‐type and Mdr1a^def or Bcrp^?/? mice (n = 6 per group). However, rivaroxaban clearance was significantly reduced in Mdr1a/Mdr1b^?/?/Bcrp^?/? mice. Interestingly, rivaroxaban brain‐to‐plasma ratio did not differ in mice lacking only Mdr1a or Bcrp, but more than two times higher in the Mdr1a/Mdr1b^?/?/Bcrp^?/? mice. Rivaroxaban is a shared substrate of MDR1 and BCRP. In vivo, MDR and BCRP function synergistically to modulate rivaroxaban disposition and appear to be particularly relevant to limiting its central nervous system entry. These data have important implications for safety and efficacy of anticoagulation therapy with rivaroxaban as many drugs in clinical use are known MDR1 inhibitors and loss‐of‐function polymorphisms in BCRP are common.     

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.     

Multidrug Resistance Proteins (MRPs) and Cancer Therapy

The ATP-binding cassette (ABC) transporters are members of a protein superfamily that are known to translocate various substrates across membranes, including metabolic products, lipids and sterols, and xenobiotic drugs. Multidrug resistance proteins (MRPs) belong to the subfamily C in the ABC transporter superfamily. MRPs have been implicated in mediating multidrug resistance by actively extruding chemotherapeutic substrates. Moreover, some MRPs are known to be essential in physiological excretory or regulatory pathways. The importance of MRPs in cancer therapy is also implied by their clinical insights. Modulating the function of MRPs to re-sensitize chemotherapeutic agents in cancer therapy shows great promise in cancer therapy; thus, multiple MRP inhibitors have been developed recently. This review article summarizes the structure, distribution, and physiological as well as pharmacological function of MRP1–MRP9 in cancer chemotherapy. Several novel modulators targeting MRPs in cancer therapy are also discussed.KEY WORDS: ABC transporters, cancer chemotherapy, multidrug resistance, multidrug resistance proteins     

Caveolin-1及其与肿瘤多药耐药的研究进展

Caveolin-1(Cav-1)是细胞膜上caveolae的重要组成蛋白,在大多数正常细胞中高表达,通过其绞手架区可与多种信号分子相连接,参与分子运输、细胞黏附和信号转导在内的许多细胞活动.近来研究发现Cav-1与肿瘤细胞的增殖、分化、侵袭、转移、凋亡以及多药耐药(multidrug resistance,MDR)关系密切,且其表达水平存在明显差异,取决于肿瘤的类型、分期和分级.本文就Cav-1蛋白的结构和功能,及其与MDR的关系做一综述,为改善肿瘤治疗中MDR问题提供新思路.     

TPX2蛋白在乳腺癌组织中的表达及意义

目的探讨TPX2蛋白在乳腺癌中的表达及意义。方法用免疫组织化学法检测乳腺癌组织和正常乳腺组织中的TPX2表达情况。结果TPX2在乳腺癌细胞中的阳性表达率为77.5%,在正常乳腺组织中的表达为0,两组差异有统计学意义(P<0.05)。结论TPX2蛋白在乳腺癌中的表达明显高于正常的乳腺组织,其过表达可能对乳腺癌细胞增殖起促进作用。     

肺癌化疗耐药分子标志及其逆转研究

目的:探讨肺癌化疗耐药分子标志及其逆转的临床与基础应用评价。方法:采用国内外相关文献,结合我们在这一领域长期研究,深入归纳与分析。结果与结论:肺癌化疗耐药主要分子标志有多药耐药基因(MDR1)表达增加,多药耐药相关蛋白(MRP)基因表达增加,谷胱甘肽解毒酶系统活性增强和线粒体凋亡途径异常,综合采用逆转耐药分子,耐药基因siRNA和中医药结合的逆转耐药策略,为彻底攻克肺癌耐药奠定坚实研究基础。     

恶性血液病中乳腺癌耐药蛋白基因的表达

目的探讨乳腺癌耐药蛋白(BCRP)基因在恶性血液病中的表达。方法应用半定量逆转录-聚合酶链反应(RT-PCR),β2微球蛋白基因作内参照,以BCRP/β2-MG的比值作为BCRP基因的相对表达水平,检测62例恶性血液病BCRP基因的表达。结果BCRP基因在恶性血液病中,阳性表达率高,表达水平差别较大,由低到高依次为AML、CML、ALL,此外MDS-RAEB和CLL各1例阳性。其中,18例AML(M3除外)中,初次缓解率在BCRP基因表达水平高者明显低于低的患者。结论BCRP基因在恶性血液病中阳性表达率高;BCRP可能与肿瘤的耐药有关,是预后不良的因素之一。     

肿瘤多药耐药逆转剂的研究进展

寻找高效、低毒、具选择性的多药耐药逆转剂是肿瘤化疗中需要解决的难题。本文介绍了P－糖蛋白对多药耐药的作用，并着重报道了一些新的多药耐药逆转剂，它们大多具有逆转的高效性和相对低毒性。本文对一些逆转剂的构效关系亦作了简要阐述。