维吾尔药异常黑胆质成熟剂总黄酮对K562/ADR细胞多药耐药性及耐药相关蛋白表达的影响

目的研究异常黑胆质成熟剂总黄酮(ASMq)对K562/ADR(耐阿霉素的慢性粒细胞株)多药耐药(MDR)及耐药相关蛋白表达的影响。方法不同浓度的总黄酮联合不同浓度的ADR作用于体外培养的K562/ADR细胞株,用CCK-8法检测K562/ADR的存活及不同浓度ASMq的耐药逆转倍数,用Western blot方法分析总黄酮对K562/ADR细胞耐药相关蛋白ABCC-1、ABCB-1、BCL-2表达的影响。不同浓度ASMq对K562/ADR的毒活性及三种蛋白质表达的差异采用t检验,P<0.05为差异有统计学意义。结果 (1)当ASMq达到800μg/ml以上时,随着总黄酮浓度的升高,K562/ADR细胞的OD下降,与ASMq为0μg/ml相比,差异具有统计学意义(P<0.001),且随着ASMq浓度的升高,K562/ADR细胞株的增殖抑制率升高,与低浓度组(200μg/ml)相比,差异亦具有统计学意义(P<0.001)。(2)随着ASMq浓度的升高,其耐药逆转倍数增大。(3)随着ASMq浓度的升高,ABCC-1、ABCB-1表达量下降,差异有统计学意义(P<0.05),而BCL-2表达无明显下降趋势。结论 (1)ASMq可以抑制K562/ADR细胞的增殖。(2)ASMq可实现耐药逆转,且随着ASMq浓度的升高,其逆转倍数增大。(3)ASMq通过下调K562/ADR细胞耐药蛋白ABCC-1、ABCB-1表达的机制,逆转K562/ADR细胞的多药耐药。     

急性淋巴细胞白血病耐药细胞株的建立及耐药机制的研究

目的:构建耐阿霉素的急性淋巴细胞白血病(ALL)细胞株,并探讨其耐药机制。方法:采用阿霉素(ADR)小剂量浓度递增间歇诱导SUP-B15(Ph~+)和RS4;11(Ph~-)细胞,建立SUP-B15/ADR和RS4;11/ADR耐药细胞株;应用CCK-8法检测细胞的活力与增殖;Western blot检测P-糖蛋白(P-gp)的表达;RT-PCR检测MDR1基因的表达。结果:成功构建ALL耐药细胞株SUP-B15/ADR和RS4;11/ADR,耐药指数分别为14.088±0.763和10.473±1.024。冻存的SUP-B15/ADR和RS4;11/ADR细胞复苏后,细胞存活率分别为88.4±1.2%和89.3±1.6%,耐药指数分别为13.976±0.967和10.342±0.846,与冻存前相比差异无统计学意义(P﹥0.05)。撤药培养1个月,2株细胞的耐药指数明显降低,分别为12.893±1.255和9.327±0.321(P﹤0.05)。SUP-B15/ADR和RS4;11/ADR细胞对阿糖胞苷的耐药指数分别为3.459±0.451和3.992±0.795,对依托泊苷的耐药指数分别为3.564±0.365和3.654±0.251。MDR1和P-gp在耐药细胞中的表达较亲本细胞增高。结论:小剂量浓度递增间歇诱导法可成功诱导出ALL耐阿霉素细胞株,其耐药机制是上调MDR1与P-gp的表达。     

人红白血病细胞来源的DC对细胞因子诱导的杀伤细胞逆转多药耐药的影响

目的:探讨人红白血病细胞(K562/ADR)来源的DC与CIK细胞体外共培养后对多药耐药逆转影响。方法:K562敏感株和K562/ADR耐药细胞株,在含细胞因子GM-CSF(1000u/mL)、IL-4(500u/mL)和TNF-α(100ng/mL)的RPMI1640完全培养液中诱导分化成DC。同时将PBMC在细胞因子诱导下培养成细胞因子诱导的杀伤细胞(CIK),与成熟DC进行共培养。采用MTT法测定免疫效应细胞对靶细胞杀伤率、耐药性逆转。流式细胞术检测靶细胞的Pgp表达及细胞内的ADR浓度,RT-PCR检测MDR1基因表达状况。结果:K562/ADR来源的DC与CIK细胞共培养后,细胞增殖速度明显加快,17d以后两者的增殖倍数呈现明显差异。效应细胞对靶细胞的生长抑制率高达78.9%,与单纯CIK细胞相比较显示出高特异免疫杀伤作用。结论:CIK K562/ADR-DC对P-gp高表达K562/ADR耐药细胞株具有特异性的细胞毒作用,有效提高了细胞内的ADR含量,下调了P-gp、mdr-1表达,从而使免疫效应细胞体外逆转多药耐药的效果得以显现。     

白藜芦醇逆转急性髓系白血病细胞HL-60/ADR耐药的凋亡机制

目的:探讨白藜芦醇(Resveratrol,Res)逆转急性髄系白血病细胞HL-60/ADR耐药的凋亡机制。方法:将HL-60/ADR细胞分为对照组(Control)、阿霉素(ADR)处理组、Res处理组和ADR+Res联合处理组4组。应用CCK-8法测定细胞增殖抑制率,流式细胞术检测细胞内阿霉素(ADR)自发荧光强度和细胞凋亡率;RT-PCR法检测耐药基因MRP1、抗凋亡基因BCL-2和促凋亡基因BAX mRNA表达水平,Western blot法测定MRP1、BCL-2和BAX蛋白表达水平。结果:25、50、100和200μmol/L Res作用于HL-60/ADR细胞48 h后,细胞的最大抑制率分别为44%、61%、76%和81%,呈浓度依赖性(r=0.876,P0.05);与ADR组的半数抑制浓度(IC50)(8.534±1.111μmol/L)相比,ADR+Res组HL-60/ADR细胞的IC50(1.591±0.373μmol/L)明显减少(P0.05)。ADR联合Res后HL-60/ADR耐药细胞内ADR自发荧光强度明显增加(P0.05);Res组和ADR+Res组细胞凋亡率均显著增加(P0.05)。Res组和ADR+Res组的MRP1 mRNA、BCL-2 mRNA表达水平显著下降(P0.05),BAX mRNA表达水平明显上升(P0.05)。Res组和ADR+Res组M RP1、BCL-2蛋白表达水平显著下降(P0.05),BAX蛋白明显上升(P0.05)。结论:白藜芦醇具有逆转HL-60/ADR细胞耐药的作用,可能是通过促进HL-60/ADR细胞凋亡、抑制耐药蛋白M RP1而发挥作用,其促凋亡机制与抑制BCL-2和增强BAX表达有关。     

CIK逆转K562/ADR细胞多药耐药作用及其机制探讨

目的 研究细胞因子诱导的杀伤细胞(CIK)体外逆转阿霉素(ADR)耐药细胞株K562/ADR细胞多药耐药(MDR)的作用,并探讨其机制.方法 健康人外周血单个核细胞经细胞因子体外诱导获得CIK,检测其表型和培养上清液细胞因子含量.实验组为CIK作用于K562/ADR细胞48 h后加入ADR;对照1组为CIK作用于K562/ADR细胞48 h,对照2组为ADR作用K562/ADR细胞48 h.采用MTT法检测各组细胞杀伤活性,用流式细胞术检测细胞膜P-糖蛋白(P-gp)含量、细胞内ADR浓度等.结果 实验组对K562/ADR细胞杀伤活性高于对照1组(P＜0.05);且随效靶比增大,杀伤活性增大(P＜0.05);随所加入的ADR浓度增大,杀伤活性无明显变化(P＞0.05).实验组和对照1组的P-gp含量均下降(P＞0.05).实验组细胞内ADR浓度高于仅经ADR作用的对照组2组(P＜0.05),但细胞内ADR浓度与加入的ADR浓度无明显关系(P＞0.05).结论 通过CIK与ADR对K562/ADR细胞的先后作用,降低了其细胞内P-gp的表达,提高了K562/ADR细胞内ADR浓度,增强了ADR对耐药细胞的杀伤活性.为应用生物活性细胞逆转MDR提供理论依据.

Abstract：

Objective To investigate the effects and mechanism of cytokine-induced killer(CIK) cells in reversing multidrug resistance(MDR) and increasing intracellular concentration of adriamycin(ADR)in the K562/ADR cells. Methods Peripheral mononuclear cells (MNCs) were isolated from healthy donors and cultured with combined cytokines to generate CIK. The changes of cell phenotype and cytokines secretion of CIK were determined. K562/ADR cells were divided into three groups: ADR in combination CIK (group Ⅰ ), CIK alone (group Ⅱ ) and ADR alone (groupⅢ) . The viability and proliferation of K562/ADR cells were assayed by MTT assay, the intracellular concentration of ADR and the expression of P-glycoproteins (P-gp) in K562/ADR cells by FCM. Results The cytotoxicity of ADR in group Ⅰ was higher than that in group Ⅱ ( P ＜0.05 ). The cytotoxicity was increased with the E/T ratio increasing( P ＜0.05 ) but had no relation with the concentration of ADR in group Ⅰ (P＞0.05). The expression of P-gp was declined in group Ⅰ and group Ⅱ (P ＞0.05 ). The intracellular concentration of ADR in group Ⅰ was higher than that in group Ⅱ ( P ＜ 0.05 ), and had no relation with the ADR concentration ( P ＞ 0.05 ). Conclusion Pre-treatment with CIK can increase the cytotoxicity and the intracellular concentration of ADR and decrease the expression of P-gp in K562/ADR cells in the ADR and CIK combination group. Acute leukemia patients would be most likely to benefit from the combination of chemotherapy and CIK therapy.     

shRNA干扰MDR1基因逆转胃癌细胞多药耐药性的研究

目的利用短发夹RNA(short hairpin RNA,shRNA)技术沉默多药耐药基因1(multidrug resistance,MDR1),探讨其对SGC7901/L-OHP细胞株多药耐药性的逆转作用。方法采用逐步增加药物浓度法建立耐奥沙利铂(oxaliplatin,L-OHP)的胃癌细胞株SGC7901/L-OHP,用shRNA技术沉默MDR1基因在SGC7901/L-OHP细胞中的表达,以real-time PCR检测细胞中MDR1mRNA的表达,Western blot检测细胞中P糖蛋白(P-glycopmtein,P-gp)的表达,MTT法检测转染后SGC7901/L-OHP细胞对L-OHP和5-FU的敏感性。结果shRNA沉默SGC7901/L-OHP细胞株MDR1基因后,与空白组和阴性质粒组比较,MDR1mRNA表达抑制(P0.01),且P-gp表达下调(P0.05)。干扰后的SGC7901/L-OHP细胞对L-OHP和5-FU的敏感性显著升高(P0.05)。结论shRNA可有效沉默SGC7901/L-OHP胃癌耐药细胞株MDR1基因的表达,提高耐药的胃癌细胞对化疗药的敏感性。     

9-顺式维甲酸联合细胞毒药物对MYCN扩增型神经母细胞瘤细胞毒性及MYCN、MDR1表达的影响

目的:观察9-顺式维甲酸(9-cis retinoic acid,RA)联合细胞毒药物对MYCN扩增型神经母细胞瘤(neuroblastoma,NB)细胞的毒性及MYCN、MDR1表达的影响,为临床合理用药提供依据.方法:RA分别与长春新碱(VCR)、顺铂(CDDP)、足叶乙甙(VP16)、阿霉素(ADR)双药联合或单独作用IMR32细胞株24 h后:(1) CCK-8法测定细胞生长抑制率;(2)流式细胞仪检测细胞凋亡率;(3)实时荧光定量PCR法检测MYCN、MDR1的mRNA表达.结果:(1)细胞生长抑制率:各双药组高于相应单药组(P＜0.01).(2)细胞凋亡率:双药组高于相应单药组(P＜0.01),RA +CDDP高于其他双药组(P＜ 0.05). (3)MYCN表达:各双药组均低于相应单药组(P＜0.05),RA+VCR低于其他双药组(P＜ 0.05);MDR1表达:双药组高于相应单药组(P＜0.05),RA+ADR高于其他双药组(P＜0.01).结论:RA联合细胞毒药物对NB生长抑制、凋亡及下调MYCN表达有协同作用,可上调MDR1表达,综合分析RA与VCR或CDDP的组合可能为临床联合用药提供较合理的选择.     

超声造影剂联合超声介导耐药基因反义寡脱氧核苷酸转染肝癌细胞逆转多药耐药效应的研究

目的 探讨超声造影剂联合超声介导mdr1、mrp基因反义寡脱氧核苷酸(ASODN)转染QGY耐药肝癌细胞对多药耐药(MDR)的逆转.方法 分别将mdr1、mrp-ASODN+超声造影剂+超声辐照转染QGY/CDDP肝癌细胞,检测转染后细胞贴壁率、药物敏感性、耐药基因mRNA表达和相应耐药蛋白表达变化.结果 mdr1-ASODN转染后,细胞贴壁率和耐药基因mRNA表达变化大(P＜0.05),细胞药物敏感性和耐药蛋白P-gp、MRP表达变化小(P＞0.05).实验组(2组)作用更大(P＜0.05).mrp ASODN转染后,细胞贴壁率、药物敏感性、耐药基因的mRNA表达和耐药蛋白P-gp、MRP表达均变化明显(P＜0.05),实验组(2组)作用更大(P＜0.05).结论 mdr1、mrp-ASODN+超声造影剂+超声辐照能够低毒部分逆转肝癌细胞MDR,是潜在肿瘤基因治疗方法.     

环氧合酶2抑制剂塞来昔布对结肠癌多药耐药逆转作用的研究

目的 探讨环氧合酶2(COX-2)抑制剂塞来昔布对结肠癌多药耐药(MDR)的逆转作用.方法 在结肠癌多药耐药细胞株colo320/5-FU中,应用四甲基偶氮唑蓝(MTT)方法检测塞来昔布时5-氟尿嘧啶(5-FU)的耐药逆转倍数;反转录-聚合酶链反应(RT-PCR)方法检测耐药基因的变化;免疫组织化学法检测细胞膜跨膜蛋白p-170(P-gP)的表达.结果 MTT结果显示塞来昔布对结肠癌细胞的耐药产生明显的逆转作用(F=2285.660,P＜0.01),其逆转倍数分别为1.70,3.80,8.48,且呈浓度依赖性.RT-PCR结果显示塞来昔布明显抑制多药耐药基因1(MDR1)mRNA的表达(F=986.776,P＜0.01),且呈浓度依赖性减低,各浓度组之间差异有统计学意义(P＜0.01).免疫荧光结果显示,细胞膜P-gp荧光强度随着塞来昔布浓度的逐渐增高而减弱.结论 选择性COX-2抑制剂塞来昔布对多药耐药细胞株colo320/5-FU具有明显逆转作用,在非细胞毒剂量范围内呈现剂量依赖性,初步机制可能涉及干预多种转录因子的表达而下调MDR1,继而阻滞细胞周期及增加细胞凋亡.     

汉防己甲素、托瑞米芬及其联合应用逆转K562/A02细胞多药耐药的研究

本研究探讨汉防己甲素（Tet）、雌激素受体抑制剂托瑞米芬（Tor）及其联合应用对K562/A02细胞多药耐药的逆转作用。采用噻唑蓝法（MTT）测定阿霉素（ADR）的半数抑制量,RT-PCR法检测MDR1基因mRNA表达水平,FCM检测P-gp的表达和细胞内ADR浓度。结果表明：ADR对K562/A02和K562细胞的IC50分别为57.43和1.16mg/L,Tet（1μmol/L）和Tor（2.5μmol/L）单用及两药联用处理K562/A02细胞时,ADR的IC50值分别为14.12,20.74和9.14mg/L。Tet及Tor单独作用后耐药株MDR1 mRNA下调微弱,联合用药下调效果明显。Tet及Tor均可降低P-gp蛋白的表达,且具有协同作用。Tet及Tor作用后细胞内ADR浓度增加,两药联合作用时效果增强。结论：Tet及Tor均可逆转K562/A02细胞多药耐药,联合作用时效果增强。     

转mdr1基因诱导CIK细胞耐药并保持肿瘤杀伤活性

目的　将多药耐药基因 (mdr1)转入细胞因子诱导的杀伤 (cytokine inducedkiller,CIK)细胞 ,观察其是否产生耐药性并且保持肿瘤杀伤活性。方法　用IFN γ ,CD3单抗 ,IL 2 ,IL 1等细胞因子体外诱导外周血单个核细胞获得CIK细胞。采用电穿孔方法将mdr1基因表达质粒pHamdr转入CIK细胞。转染后 72h提取细胞总RNA ,DNA酶消化残留质粒DNA后进行RT PCR ,鉴定mdr1基因表达 ;流式细胞仪检测细胞膜耐药蛋白 (P gp)表达。四唑蓝比色法 (MTT)检测转基因后CIK细胞对阿霉素和秋水仙碱的耐药性 ;同时检测转染前后CIK细胞对MCF7细胞 (人类乳腺癌细胞系 )的杀伤活性变化。结果　转染mdr1后的CIK细胞mdr1mRNA阳性 ,P gp阳性的CIK细胞为 2 1%～ 37% (平均 2 7% )。转染后CIK细胞获得了多药耐药性 ,对阿霉素的IC50 值较转染前升高了 2 2 .3～ 4 5 .8倍 ,对秋水仙碱的IC50 值升高了 6 .7～ 11.35倍。转染前后CIK细胞对MCF7肿瘤细胞的杀伤活性无明显变化 (P >0 0 5 )。结论　CIK细胞转入mdr1基因后获得了多药耐药性 ,转染后的CIK细胞仍然保持原有的肿瘤细胞杀伤活性。     

Drug-transporter proteins in clinical multidrug resistance.

Upon exposure to chemotherapeutic drugs, mammalian cells can acquire resistance to structurally and functionally unrelated compounds, a property known as multidrug resistance (MDR). One MDR mechanism, i.e. by the overexpression of a plasma membrane protein, P-glycoprotein (P-gp), has been identified at the molecular level. The mdr1 gene-encoded P-gp acts as a drug efflux pump, lowering intracellular drug concentration by active extrusion of drugs from the cell. The role of P-gp in determining clinical resistance to multiple anticancer drugs is likely to be largely different for various tumor types. Recently we selected a monoclonal antibody (mAb LRP56) for strong, granular cytoplasmic reactivity with MDR tumor cell lines without P-gp (over)expression. None or weak reactivity was observed with parental and P-gp positive cell lines. We hypothesize that as yet-undefined drug transport-mediating proteins are inserted in intracellular membranes lining the exocytotic compartment and thus may contribute to clinical multidrug resistance.     

The antipsychotic drug trifluoperazine inhibits DNA repair and sensitizes non small cell lung carcinoma cells to DNA double-strand break induced cell death

Trifluoperazine (TFP), a member of the phenothiazine class of antipsychotic drugs, has been shown to augment the cytotoxicity of the DNA-damaging agent bleomycin. In the present study, we investigated the effect of trifluoperazine on (a) survival of bleomycin-treated human non-small cell lung carcinoma U1810 cells, (b) induction and repair of bleomycin-induced DNA strand breaks, and (c) nonhomologous end-joining (NHEJ), the major DNA double-strand break (DSB) repair pathway in mammalian cells. By using a clonogenic survival assay, we show here that concomitant administration of trifluoperazine at a subtoxic concentration enhances the cytotoxicity of bleomycin. Moreover, trifluoperazine also increases the longevity of bleomycin-induced DNA strand breaks in U1810 cells, as shown by both comet assay and fraction of activity released (FAR)-assay. This action seems to be related to suppression of cellular DNA DSB repair activities because NHEJ-mediated rejoining of DSBs occurs with significantly lower efficiency in the presence of trifluoperazine. We propose that TFP might be capable of inhibiting one or more elements of the DNA DSB repair machinery, thereby increasing the cytotoxicity of bleomycin in lung cancer cells.     

急性白血病患者白血病细胞DNA拓扑异构酶Ⅱ活性与多药耐药？…

探讨急性白血病患白血病细胞ＤＮＡ拓扑异构酶Ⅱ活性与多药耐药的关系。方法：采用溴乙锭荧光法与１７例初治化疗前及２０例化疗后的急性白血病患外周血或骨髓白血病细胞ＤＮＡ ＴｏｐｏⅡ活性进行测定，采用抗多药耐药单抗ＪＳＢ－Ｉ检测１８例化疗后患ｐ－糖蛋白表达，采用ＲＴ－ＰＣＲ法检测ｍｄｒ－１基因表达。     

Possibility of the reversal of multidrug resistance and the avoidance of side effects by liposomes modified with MRK-16, a monoclonal antibody to P-glycoprotein.

For cancer chemotherapy, avoiding the side effects of chemotherapeutic agents is difficult. Multidrug resistance is one of the major obstacles to successful cancer chemotherapy. P-Glycoprotein (P-gp) serves as an efflux pump and plays a key role in the multidrug resistance. We examined the effect of MRK-16, a monoclonal antibody against P-gp, modified liposomes (MRK-Lip) on the human myelogenous leukemia K-562 cells and its adriamycin resistance cell line K-562/ADM cells to avoid the side effects and to reverse the multidrug resistance. The uptake of vincristine (VCR) by K-562/ADM cells was lower than that by K-562 cells. This low uptake was increased in the presence of verapamil and MRK-16, however, it was not increased in the presence of control antibody, IgG2A. The binding of MRK-Lip to K-562/ADM cells was higher than that of IgG2A-modified liposome (IgG-Lip) and liposome without modification (Cont-Lip). Moreover, the cytotoxicity of VCR-encapsulated MRK-Lip to K-562/ADM cells was higher than that of VCR-encapsulated IgG-Lip and Cont-Lip. These results suggest that the interaction between liposomes and multidrug resistance cells was increased by the modification of liposomes with MRK-16. Consequently, the usefulness of MRK-Lip in cancer chemotherapy as a potent carrier was suggested.     

Ixabepilone, a novel microtubule-targeting agent for breast cancer, is a substrate for P-glycoprotein (P-gp/MDR1/ABCB1) but not breast cancer resistance protein (BCRP/ABCG2)

Ixabepilone is the first epothilone to be approved for clinical use. Current data suggest the epothilones have a role in treating taxane-resistant cancers and ixabepilone is unaffected by at least some of the mechanisms underlying chemoresistance. Here, we report a series of cytotoxicity and transport studies to assess the potential role of P-glycoprotein (P-gp) and breast cancer resistance protein (BCRP) in ixabepilone resistance. A significant decrease in ixabepilone-mediated cytotoxicity was observed in Madin-Darby canine kidney cells transfected with human multidrug resistance 1 (MDR1) comparative with the parental cells (IC(50) > 2000 nM versus 90 nM). Overexpression of P-gp also resulted in significantly decreased cell susceptibility to docetaxel, paclitaxel, and vinblastine. Bidirectional transport of ixabepilone across monolayers of porcine kidney-derived cells expressing human MDR1 showed a significantly increased efflux ratio relative to the parental cells. A BCRP-overexpressing cell line was developed by transfecting human embryonic kidney (HEK)-293 cells with BCRP cDNA and confirmed by immunoblotting and bodipy prazosin and mitoxantrone uptake. Neither P-gp nor multidrug resistance protein 2 was detected in the cells by corresponding polyclonal antibodies. This HEK-BCRP cell line demonstrated resistance to docetaxel, paclitaxel, vinblastine, and mitoxantrone, in comparison with the parental cell line (7.3, 4.3, 2.9, and 11.9 resistance factor, respectively). Transport inhibition by BCRP inhibitor fumitremorgin C and broad efflux inhibitor N-(4-[2-(1,2,3,4-tetrahydro-6,7-dimethoxy-2-isoquinolinyl)ethyl]-phenyl)-9,10-dihydro-5-methoxy-9-oxo-4-acridine carboxamide (GF120918) restored drug sensitivity. In contrast, ixabepilone was far less susceptible to BCRP-mediated resistance, resulting in a resistance factor of only 1.2-fold. In summary, these results suggest that P-gp could cause resistance to ixabepilone in tumors and affect the disposition of the drug, but it is unlikely that BCRP mediates any drug resistance to ixabepilone.     

Resistance mechanisms associated with altered intracellular distribution of anticancer agents

The resistance of tumor cells to anticancer agents remains a major cause of treatment failure in cancer patients. The term multidrug resistance (MDR) is used to define a resistance phenotype where cells are resistant to multiple drugs with no obvious structural resemblance and with different molecular targets. It is now clear that MDR is always multifactorial. The intracellular drug distribution is modified in many MDR cell lines, leading to increased drug sequestration in acidic vesicles, such as the trans-Golgi apparatus, recycling endosomes, and lysosomes, followed by transport to the plasma membrane and extrusion into the external medium. Since most anticancer agents target DNA or nuclear enzymes, sequestration of drug in cytoplasmic organelles will lead to decreased drug-target interaction and thereby, decreased cytotoxicity. Altered intracellular drug distribution is usually associated with the expression of drug efflux pumps, such as the P-glycoprotein and the multidrug resistance protein. Another common modification in MDR cells is alkalization of the intracellular pH. The relationship between these different resistance mechanisms is reviewed and a model proposed that suggests why these different resistance mechanisms are co-expressed in multiple cell lines.     

Taxane-based reversal agents modulate drug resistance mediated by P-glycoprotein, multidrug resistance protein, and breast cancer resistance protein

Overexpression of ATP-binding cassette transport proteins, including P-glycoprotein (Pgp), multidrug resistance (MDR) protein (MRP-1), and breast cancer resistance protein (BCRP), is a well-characterized mechanism of MDR in tumor cells. Although the cytotoxic taxanes paclitaxel and docetaxel are substrates for Pgp-mediated efflux, the semisynthetic taxane analogue ortataxel inhibits drug efflux mediated by Pgp as well as, as we recently demonstrated, MRP-1 and BCRP. Nevertheless, ortataxel is not optimal for development as a clinical MDR modulator because of its cytotoxicity [corrected]. We sought to identify noncytotoxic taxane-based broad-spectrum modulators from a library of noncytotoxic taxane-based reversal agents (tRAs) designed by eliminating the C-13 side chain of the taxane molecule, which inhibits microtubule depolymerization. Twenty tRAs, selected based on modulation of paclitaxel cytotoxicity in Pgp-overexpressing MDA435/LCC6(mdr1) cells, were studied for modulation of retention and cytotoxicity of substrates of MRP-1 and BCRP as well as Pgp in established cell lines overexpressing each of these transporters. Four tRAs modulated MRP-1 and 17 modulated BCRP in addition to Pgp. The four broad-spectrum tRAs strongly modulated daunorubicin and mitoxantrone efflux and enhanced their cytotoxicity in cell lines overexpressing the three MDRs, decreasing IC(50) values by as much as 97% [corrected]. These tRAs, especially tRA 98006, have promise for development as clinical broad-spectrum MDR modulators and warrant more preclinical analysis to determine pharmacokinetic interactions and efficacy.