K562／ADM耐药细胞株的建立及其生物学特性的初步观察

我们建立的K562/ADM耐药细胞株,在ADM浓度为2.4μg/m1(4.46μM)中已稳定培养3.5个月,传了30—35代,K562/ADM亦具有多药耐受件(Multidrug Resistance,MDR)的特点,对ADM、VCR、AT—1258和DDP的耐受性分别为K562的114.7、94.0、13.3和7.4倍,但对5—FU不产生交叉耐药。K562和K562/ADM的倍增时间分别为19.2h和52.8h,集落生成率分别为37.5％和11.1％,K562染色体数为34—68,中位数为56;K562/MDM染色体数为32—90,中位数为50,K562/ADM可做为耐药机理和克服耐药措施研究的极好模型。     

潘生丁增强抗肿瘤药物作用的体外实验研究

为观察潘生丁与临床常用抗肿瘤药物阿霉素（ＡＤＭ）、长春新碱（ＶＣＲ）及足叶乙甙（ＶＰ－１６）联合应用的价值，我们选用人肺癌细胞株Ａ５４９进行体外细胞毒试验。可以看到：当阿霉素浓度为０．５μｇ／ｍｌ时，对Ａ５４９的抑制率为２９．７６％，加入０．５～１０μｇ／ｍｌ潘生丁时，其细胞生长抑制率提高了１３．２７％～３１．４２％，对长春新碱、足叶乙甙来说，当加入不同浓度潘生丁（０．５～１０μｇ／ｍｌ）时，其细胞生长抑制率分别提高了１８．４３％～４３．２１％及１６．１３％～２９．４７％。以上试验结果表明：潘生丁具有增强某些抗肿瘤药物（ＡＤＭ、ＶＰ－１６、ＶＣＲ）对肺癌细胞株Ａ５４９的细胞毒作用。     

增加细胞内三氧化二砷浓度恢复耐三氧化二砷的K562细胞对其敏感性的研究

目的 探讨耐受三氧化二砷（ATO）的白血病ATO耐药K562细胞（K562/AS2细胞）内砷浓度与耐药性的关系.方法 亲代敏感K562细胞（K562/S细胞）按照逐步增加ATO浓度诱导,建立K562/AS2细胞.采用原子荧光光谱法检测细胞内砷浓度.采用四甲基偶氮唑蓝（MTT）法检测不同浓度ATO对细胞的毒性作用.结果 1μg/ml ATO培养24、48、72h后,K562/S细胞内的砷浓度比K562/AS2细胞增高[（15.63±0.42） μg/L比0μg/L、（22.27±0.15） μg/L比（3.51±0.12） μg/L、（24.31±0.21） μg/L比（3.61±0.11） μg/L;均P＜0.05].随着ATO浓度的增加及培养时间的延长,K562/AS2细胞内砷浓度逐渐增加（P＜0.05）,在1μg/ml和2μg/ml间砷浓度增加较快.K562/AS2细胞生长抑制率也逐渐增加（P＜0.05）,在1μg/ml和2μg/ml间增加较快.直线相关分析显示,当K562/AS2细胞与ATO接触分别为24、48和72 h时,其细胞生长抑制率均与细胞内ATO浓度呈正相关.结论 增加ATO浓度或延长ATO作用时间均可增加耐药细胞内ATO浓度,细胞内ATO浓度与ATO对细胞的毒性呈正相关,增加细胞内ATO浓度能够增强耐ATO K562细胞对ATO的敏感性.     

TNFα诱导K562/VCR和K562细胞凋亡及逆转其耐药作用的实验研究

目的探讨肿瘤坏死因子α(TNFα)体外诱导K562/VCR及K562细胞凋亡,及其逆转K562/VCR细胞多药耐药(MDR)的作用机制.方法以光镜、电镜、流式细胞仪观察细胞凋亡;流式细胞仪检测P-gp和bcl-2表达.MTT检测药物敏感性.结果 (1)TNFα浓度>100 U/ml,作用时间>48小时,2株细胞均可见典型凋亡现象,以K562/VCR细胞明显.(2)以TNFα 1 000 U/ml处理后,K562/VCR和K562细胞凋亡率分别为29.4%和10.7%.(3)K562/VCR经TNFα 1 000 U/ml处理72小时P-gp表达率从93.6%降至82.4%,bcl-2表达率从32.9%降至7.0%.(4)K562/VCR和K562细胞分别经TNFα 100 U/ml和1 000 U/ml处理后,VCR、Ara-C和VP-16的药物敏感性增加(P<0.05).结论 (1)TNFα可诱导K562/VCR和K562细胞凋亡,以前者更加敏感,且存在时间和剂量依赖性.(2)高浓度TNFα可下调bcl-2表达,但不显著改变P-gp表达.(3)TNFα能增加K562/VCR和K562细胞对VCR、Ara-C和VP-16的药物敏感性,以K562/VCR细胞更明显.(4)TNFα逆转K562/VCR多药耐药是通过诱导细胞凋亡,降低bcl-2表达,而非下调P-gp表达途径实现.     

三种蒽环类抗肿瘤药物对K562/A02细胞体外抑制作用

目的:比较表阿霉素,柔红霉素和吡喃阿霉素对多药耐药细胞株K562/A02体外增殖的抑制作用.方法:利用MTT观察7.5～60μg/ml的表阿霉素或柔红霉素或吡喃阿霉素处理K562/A02细胞后细胞增殖的变化.结果:吡喃阿霉素剂量逐渐增大时,抑制率逐渐增强(P＜0.05).吡喃阿霉素组对K562/A02细胞的抑制率较相同剂量表阿霉素组或柔红霉素组抑制率显著增加(P＜0.01).结论:相同剂量的吡喃阿霉素较表阿霉素或柔红霉素有更强的抑制多药耐药细胞株K562/A02细胞的作用.     

氯丙嗪对耐药细胞系K562/AO2多药耐药逆转作用的研究

目的研究氯丙嗪对耐药细胞系K562/AO2多药耐药逆转作用.方法应用免疫组化观察K562/AO2细胞系的耐药蛋白表达情况,用MTT法测定不同浓度的氯丙嗪对K562/AO2细胞系耐药逆转作用,用流式细胞术测定不同浓度的氯丙嗪与K562/AO2细胞作用后细胞内罗丹明的蓄积情况,用半定量RT-PCR法测定氯丙嗪对K562/AO2细胞多药耐药基因(mdr-1)mRNA表达的影响.结果K562/AO2细胞不但P-gp表达阳性,而且肺耐药相关蛋白(lung resistanceelatedprotein,LRP)表达也阳性;氯丙嗪能增强多柔比星对K562/AO2细胞的杀伤作用(单用ADM组、氯丙嗪0.75 μg/mL+ADM组、氯丙嗪1.5μg/m L+ADM组和氯丙嗪3μg/mL+ADM组对K562/AO2的抑制率分别为5.2%、25.9%、39.1%和74.8%)增加K562/AO2细胞内罗丹明的蓄积(对照组、氯丙嗪0.75 μg/mL组、氯丙嗪1.5 μg/mL组和氯丙嗪3μg/mL组细胞内的荧光强度的均值分别为1.87、10.28、48.75和65.63)对K562/AO2细胞mdr-1 mRNA表达无明显影响(对照组mdr-1和β-actin的面积比为0.41,氯丙嗪组为0.42).结论氯丙嗪对K562/AO2细胞的耐药有较强的逆转作用,并呈剂量依赖关系.     

氯丙嗪对耐药细胞系K562／AO2多药耐药逆转作用的研究

目的：研究氯丙嗪对耐药细胞系K562/AO2多药耐药逆转作用。方法：应用免疫组化观察K562／AO2细胞系的耐药蛋白表达情况，用MTT法测定不同浓度的氯丙嗪对K562/AO2细胞系耐药逆转作用，用流式细胞术测定不同浓度的氯丙嗪与K562／AO2细胞作用后细胞内罗丹明的蓄积情况，用半定量RT—PCR法测定氯丙嗪对K562／AO2细胞多药耐药基因(mdr-1)mRNA表达的影响。结果：K562／AO2细胞不但P-gP表达阳性，而且肺耐药相关蛋白(lung resistanceelated protein．LRP)表达也阳性；氯丙嗪能增强多柔比星对K562／AO2细胞的杀伤作用(单用ADM组、氯丙嗪0．75μg／mL+ADM组、氯丙嗪1．5μg／mL+ADM组和氯丙嗪3μg／mL+ADM组对K562／AO2的抑制率分别为5．2％、25．9％、39．1％和74．8％)；增加K562／AO2细胞内罗丹明的蓄积(对照组、氯丙嗪0．75μg／mL组、氯丙嗪1．5μg/mL组和氯丙嗪3μg／mL组细胞内的荧光强度的均值分别为1．87、10．28、48．75和65．63)；对K562／AO2细胞mdr-1 mRNA表达无明显影响(对照组mdr-1和β-actin的面积比为0．41，氯丙嗪组为0．42)。结论：氯丙嗪对K562／AO2细胞的耐药有较强的逆转作用，并呈剂量依赖关系。     

5-溴汉防己甲素与汉防己甲素对K562/A02细胞多药耐药性逆转作用的比较

背景与目的:5-溴汉防己甲素(5-bromotetrandrine,BrTet)是汉防己甲素(tetrandrine,Tet)的溴化产物,具有逆转P-糖蛋白(P-glyeoprotein,P-gp)介导的肿瘤多药耐药(muhidrug resistance,MDR)的作用。本研究旨在比较BrTet与Tet对人白血病细胞K562/A02多药耐药的逆转作用。方法:采用四甲基偶氮唑蓝法(MTT)法检测不同浓度BrTet对K562细胞和K562/A02细胞的增殖抑制效应;检测阿霉素(adfiamycin,ADM)对K562细胞和K562/A02细胞增殖的抑制作用,以及加用BrTet、Tet时上述抑制作用的变化,并计算半数抑制浓度(IC50)及逆转倍数。Westernblot法检测各组细胞P-gp的表达,流式细胞仪检测各组细胞内ADM的蓄积。结果:K562/A02细胞对ADM的耐药倍数为49.51倍。2.0μmol/L及更低浓度的BrTet和1.5μmol/L及更低浓度的Tet对K562细胞和K562/A02细胞抑制率均小于10%,无明显细胞毒性作用。加入1.0μmol/L的Tet后,K562/A02细胞对ADM的耐药倍数为12.17倍。加入0.25、0.5和1.0μmol/L的BrTet后,K562/A02细胞对ADM的耐药倍数分别为17.88、9.97和4.24倍。1.0"mol/L的BrTet和Tet分别使K562/A02细胞内ADM浓度提高了69.0%和51.6%,使P-gp表达分别下调了51.1%和43.73%,其差异具有统计学意义(P<0.05)。结论:BrTet及Tet均可逆转K562/A02细胞耐药,且前者较后者逆转作用更强,逆转机制与抑制P-gp的表达、增加细胞内抗肿瘤药物浓度有关。     

EGCG降低P糖蛋白表达逆转白血病多药耐药的研究

[目的]探讨表没食子儿茶素没食子酸酯[(-)epigallocatechin-3-gallate,EGCG]对人白血病细胞K562/A02多药耐药性的逆转作用及相关机制.[方法]采用MTT法确定EGCG的非细胞毒性剂量,以及对K562/A02细胞药物敏感性的影响.以流式细胞术测定EGCG作用前后细胞内阿霉素浓度的变化;同时采用半定量逆转录聚合酶链反应(RT-PCR)及Western blot方法分别检测经典多药耐药基因(MDR1)mRNA及其产物P糖蛋白的表达.[结果] EGCG在低于103.2μmol/L时对K562/A02细胞的生长抑制率小于10%.40μmol/L、60μmol/L及80μmol/LEGCG均可增加K562/A02细胞对阿霉素的敏感性,使阿霉素对K562/A02细胞的IC50由原来的113.34μg/ml降低至9.66μg/ml、7.67μg/ml和4.68μg/ml,其逆转倍数分别为11.73、14.77和24.23倍.流式细胞术结果表明EGCG可增加细胞内阿霉素浓度,并呈剂量依赖性.RT-PCR及Western blot结果显示不同浓度的EGCG均可抑制K562/A02细胞MDRlmRNA及P糖蛋白的表达.[结论]EGCG可部分逆转人白血病细胞K562/A02对阿霉素的耐药性,其逆转机制与增加细胞内化疗药物浓度、抑制经典多药耐药基因MDRlmRNA及其产物P糖蛋白的表达有关.     

川芎嗪与β-榄香烯联合应用诱导K562/ADM细胞凋亡及逆转其MDR的实验研究

目的:探讨不同作用机制的川芎嗪(Tetrainethylpyrazine,TMP)与β-榄香烯(β-elemene)联合应用,从多环节逆转耐药细胞K562/ADM的多药耐药(multidrug resistance,MDR),以期进一步提高逆转效果.方法:采用MTT法检测细胞的药敏性及抗药性逆转,流式细胞术及透射电镜检测细胞凋亡,应用SPSS(10.0 Production Pacility)软件包对实验结果进行统计学处理.结果:1)非细胞毒性浓度的TMP(350μg/ml)及β-榄香烯(4.0μg/ml)可显著降低ADM对K562/ADM细胞的IC50(P＜0.01),逆转耐药倍数分别为2.03倍及2.18倍.β-榄香烯(4.0μg/ml)具有诱导该细胞凋亡的作用.2)上述两种药物以非细胞毒性浓度联合应用,对ADM的逆转倍数为4.65倍,明显高于二者单独应用,而且也高于两者单独应用之和.其主要逆转机制是两药的联合应用通过升高细胞内ADM的浓度,诱导该细胞凋亡的途径,实现提高逆转效果的目的.结论:TMP和β-e榄香烯联合应用能明显逆转K562/ADM细胞对ADM的耐药性和诱导该细胞的凋亡.     

Competitive inhibition by verapamil of ATP-dependent high affinity vincristine binding to the plasma membrane of multidrug-resistant K562 cells without calcium ion involvement

Verapamil, a calcium channel blocker, can inhibit the efflux of antitumor agents from multidrug-resistant cells and reverse drug resistance. We have recently reported that the plasma membrane prepared from an adriamycin (ADM)-resistant variant (K562/ADM) of human myelogenous leukemia K562 cells showed ATP/Mg2+-dependent high affinity binding of vincristine (VCR), which is closely related to the drug transport mechanism in this cell line. To clarify how calcium channel blockers inhibit the transport of antitumor agents from the resistant cells, we analyzed the effect of calcium channel blockers and Ca2+ ion on the VCR binding to K562/ADM plasma membrane. The ATP-dependent VCR binding was inhibited by calcium channel blockers (verapamil, nicardipine, and diltiazem), which are known to inhibit drug efflux from the resistant cells. Addition of [ethylenebis(oxyethylenenitrilo)]tetraacetic acid or high concentration of Ca2+ decreased the amount of VCR binding to some extent; however, a substantial amount of VCR still could bind to K562/ADM plasma membrane. The inhibitory effect of verapamil on the VCR binding was observed regardless of the Ca2+ concentration. Klotz plot analysis revealed that the inhibition of the VCR binding to K562/ADM plasma membrane by verapamil was competitive. Dissociation constant (Kd) of VCR and apparent inhibitory constant (Kiapp) of verapamil were calculated to be 0.1 +/- 0.1 microM (SD) and 1 +/- 1 microM, respectively. These results indicate that Ca2+ ion is not required for the VCR binding and that verapamil competitively inhibits the VCR binding without concerning Ca2+ ion. Antitumor agents (vinblastine, actinomycin D, ADM, and colchicine) and other agents known to reverse multidrug resistance (nicardipine, diltiazem, cyclosporin A, quinidine, and trifluoperazine) also inhibited the VCR binding competitively.     

Reversal of multidrug resistance by a novel quinoline derivative,MS-209

MS-209, a novel quinoline derivative, was examined for its reversing effect on multidrug-resistant tumor cells. MS-209 at 1–10 M completely reversed resistance against vincristine (VCR) in vitro in multidrug-resistant variants of mouse leukemia P388 cells (VCR-resistant P388/VCR and Adriamycin (ADM)-resistant P388/ADM) and human leukemia K562 cells (VCR-resistant K562/VCR and ADM-resistant K562/ADM). MS-209 at 1–10 M also completely reversed resistance against ADM in vitro in P388/VCR cells, K562/VCR cells, and K562/ADM cells. In ADM-resistant P388 (P388/ADM) cells, however, ADM resistance was only partially reversed at the MS-209 concentrations tested. MS-209 enhanced the chemotherapeutic effect of VCR in P388/VCR-bearing mice. When MS-209 was given p.o. at 80 mg/kg twice a day (total dose, 160 mg/kg per day) with 100 g/kg VCR, a treated/control (T/C) value of 155% was obtained. MS-209 also enhanced the chemotherapeutic effect of ADM in P388/ADM-bearing mice. The most prominent effects were obtained when MS-209 was given with 2 mg/kg ADM, yielding T/C values of 150%–194% for the combined treatment at an MS-209 dose of 200–450 mg/kg. MS-209 inhibited [³H]-azidopine photolabeling of P-glycoprotein efficiently. Furthermore, the accumulation of ADM in K562/ADM cells was increased more eficiently by MS-209 than by verapamil. These results indicate that MS-209, like verapamil, directly interacts with P-glycoprotein and inhibits the active efflux of antitumor agents, thus overcoming multidrug resistance in vitro and in vivo.This work was supported by grants-in-aid from the Ministry of Education Science and Culture, Japan     

Circumvention of multidrug resistance by a newly synthesized quinoline derivative, MS-073.

Newly synthesized quinoline derivatives were investigated for their efficacy to reverse multidrug resistance (MDR). In this study, one of the most effective quinoline derivatives, MS-073, was compared with verapamil with regard to its ability to overcome MDR in vitro and in vivo. MS-073 at 0.1 microM almost completely reversed in vitro resistance to vincristine (VCR) in VCR-resistant P388 cells. The compound also reversed in vitro VCR, adriamycin (ADM), etoposide, and actinomycin D resistance in ADM-resistant human myelogenous leukemia K562 (K562/ADM) cells, ADM-resistant human ovarian carcinoma A2780 cells, and colchicine-resistant human KB cells. MS-073 administered i.p. daily for 5 days with VCR enhanced the chemotherapeutic effect of VCR in VCR-resistant P388-bearing mice. Increases in life span of 19-50% were obtained by the combination of 100 micrograms/kg of VCR with 3-100 mg/kg of MS-073, as compared to the control. The ability of MS-073 to reverse MDR was remarkably higher, especially at low MS-073 doses, than that of verapamil, both in vitro and in vivo. MS-073 enhanced accumulation of [3H]VCR in K562/ADM cells. Photolabeling of P-glycoprotein with 200 nM [3H]azidopine in K562/ADM plasma membranes was completely inhibited by 10 microM MS-073, indicating that MS-073 reverses MDR by competitively inhibiting drug binding to P-glycoprotein.     

Synergistic effect of cyclosporin A and verapamil in overcoming vincristine resistance of multidrug-resistant cultured human leukemia cells

Reversal of vincristine (VCR) resistance by cyclosporin A (CyA) or the combination of CyA and verapamil (VER) was investigated by using four P-glycoprotein (P-gp)-associated human multidrug-resistant (MDR) cell lines (K562/ADM, KYO-1, HEL and CMK). Drug sensitivity was expressed as 50% inhibitory concentration (IC50). The degree of reversal of resistance was expressed as x-fold decrease by dividing the IC50 value without modifier(s) by that with modifier(s). CyA overcame P-gp-associated MDR significantly in all four MDR cell lines. Reversal of VCR resistance by CyA appeared to be dose-dependent. In the case of low-grade MDR cell lines (KYO-1, HEL and CMK), CyA at the low concentration of 0.5 microgram/ml was still effective. The degree of reversal of VCR resistance in this condition was greater (6.3- to 16-fold decrease) in the low-grade MDR cell lines than in a high-grade MDR cell line (K562/ADM) (2.9-fold decrease). At a high concentration (5 micrograms/ml) of CyA, however, it was greater (240-fold decrease) in the high-grade MDR cell lines than in the low-grade MDR cell line (20- to 100-fold decrease). This indicates that concentration of CyA required for overcoming drug resistance in MDR cells was dependent on the degree of drug resistance. CyA overcame VCR resistance more efficiently than VER. The combination of CyA and VER enhanced reversal of VCR resistance in a supra-additive or at least an additive manner and overcame VCR resistance at low concentrations of both modifiers that are clinically achievable with safety.     

Reversal of multidrug resistance by novel nitrophenyl pyrones, SNF4435C and D.

SNF4435C and D, novel immunosuppressants produced by a strain of Streptomyces spectabilis, were examined for their reversing effects in vitro on various multidrug-resistant (MDR) tumor cells overexpressing P-glycoprotein. These two compounds in the range of 3-10 microM completely reversed the resistance of MDR variant cells, mouse leukemia P388 cells [vincristine (VCR)-resistant P388/VCR and adriamycin (ADM)-resistant P388/ADM], human myelogenous leukemia K562 cells (VCR-resistant K562/VCR and ADM-resistant K562/ADM) and human ovarian cancer A2780 cells (ADM-resistant AD(10)), against VCR. Both compounds moderately potentiated the sensitivity of the MDR cells to ADM but the reversal was not complete. SNF4435C and D significantly increased the intracellular accumulation of VCR in AD(10) cells as potently as verapamil, cyclosporin A (CysA) and FK506, whereas the compounds exerted no effect on the accumulation of VCR in the drug-sensitive parent cells. Moreover, SNF4435C improved the chemotherapeutic efficacy of VCR in the treatment of P388/VCR-bearing mice. When 10 mg/kg SNF4435C was administered intraperitoneally to the mice concurrently with 0.2 mg/kg VCR for every 5 days, a treated/control (T/C) value of 143% was obtained. These results suggest that the compounds are useful candidates or tools for MDR modification in cancer chemotherapy.     

Synergistic Effect of Cyclosporin A and Verapamil in Overcoming Vincristine Resistance of Multidrug-resistant Cultured Human Leukemia Cells

Reversal of vincristine (VCR) resistance by cyclosporin A (CyA) or the combination of CyA and verapamil (VER) was investigated by using four P-glycoprotein (P-gp)-associated human multidrug-resistant (MDR) cell lines (K562/ADM, KYO-1, HEL and CMK). Drug sensitivity was expressed as 50% inhibitory concentration (IC₅₀). The degree of reversal of resistance was expressed as x -fold decrease by dividing the IC₅₀ value without modifier(s) by that with modifier(s). CyA overcame P-gp-associated MDR significantly in all four MDR cell lines. Reversal of VCR resistance by CyA appeared to be dose-dependent. In the case of low-grade MDR cell lines (KYO-1, HEL and CMK), CyA at the low concentration of 0.5 μg/ml was still effective. The degree of reversal of VCR resistance in this condition was greater (6.3- to 16-fold decrease) in the low-grade MDR cell lines than in a high-grade MDR cell line (K562/ADM) (2.9-fold decrease). At a high concentration (5 μg/ml) of CyA, however, it was greater (240-fold decrease) in the high-grade MDR cell lines than in the low-grade MDR cell line (20- to 100-fold decrease). This indicates that concentration of CyA required for overcoming drug resistance in MDR cells was dependent on the degree of drug resistance. CyA overcame VCR resistance more efficiently than VER. The combination of CyA and VER enhanced reversal of VCR resistance in a supra-additive or at least an additive manner and overcame VCR resistance at low concentrations of both modifiers that are clinically achievable with safety.     

Reversal of Multidrug Resistance by Novel Nitrophenyl Pyrones, SNF4435C and D

SNF4435C and D, novel immunosuppressants produced by a strain of Streptomyces spectabilis , were examined for their reversing effects in vitro on various multidrug-resistant (MDR) tumor cells overexpressing P-glycoprotein. These two compounds in the range of 3–10 [jM completely reversed the resistance of MDR variant cells, mouse leukemia P388 cells [vincristine (VCR)-resistant P388/ VCR and adriamycin (ADM)-resistant P388/ADM], human myelogenous leukemia K562 cells (VCR-resistant K562/VCR and ADM-resistant K562/ADM) and human ovarian cancer A2780 cells (ADM-resistant AD10), against VCR. Both compounds moderately potentiated the sensitivity of the MDR cells to ADM but the reversal was not complete. SNF4435C and D significantly increased the intracellular accumulation of VCR in AD10 cells as potently as verapamil, cyclosporin A (CysA) and FK506, whereas the compounds exerted no effect on the accumulation of VCR in the drug-sensitive parent cells. Moreover, SNF4435C unproved the chemotherapeutic efficacy of VCR in the treatment of P388/VCR-bearing mice. When 10 mg/kg SNF4435C was administered intra-peritoneally to the mice concurrently with 0.2 mg/kg VCR for every 5 days, a treated/control (T/C) value of 143% was obtained. These results suggest that the compounds are useful candidates or tools for MDR modification in cancer chemotherapy.     

Reversal of multidrug resistance by an immunosuppressive agent FK-506

Summary FK-506, a novel immunosuppressive agent, was examined for its reversing effect on multidrug-resistant tumor cells. FK-506 at 3 M completely reversed the resistance against vincristine (VCR) in vitro in VCR-resistant mouse leukemia P388 cells (P388/VCR). FK-506 also enhanced the cytotoxicity of VCR in Adriamycin(ADM)-resistant human ovarian cancer A2780 cells (AD₁₀) and ADM-resistant human myelogenous leukemia K562 cells (K562/ADM) in vitro. FK-506 was also effective in modulating sensitivity to ADM in AD₁₀ cells in vitro. FK-506 enhanced the chemotherapeutic effect of VCR in P388/VCR-bearing mice. When 20 mg/kg FK-506 was combined with 200 g/kg VCR, a T/C value of 151% was obtained. Under the protocol used in this study, FK-506 was more potent than cyclosporin A (CsA) and verapamil. FK-506 inhibited [³H]azidopine binding to P-glycoprotein efficiently. The binding of VCR to K562/ADM plasma membrane was inhibited by FK-506 as effectively as by CsA. Moreover, the accumulation of VCR in AD₁₀ cells was increased by FK-506 as efficiently as that of CsA and verapamil. These results indicate that FK-506 directly interacts with P-glycoprotein like CsA and verapamil, inhibits the active efflux of vincristine from resistant cells, increases the vincristine accumulation in resistant cells, and thus overcomes multidrug resistance in vitro and in vivo.Abbreviations VCR vincristine - ADM Adriamycin - CsA cyclosporin A - MTT 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (thiazolyl blue) - T/C mean survival time of treated group of mice divided by mean survival time of control group - T/V mean survival time of treated group of mice divided by mean survival time of the group of mice treated with vincristine alone This work was supported by grants-in-aid for cancer Research from the Ministry of Education, Science and Culture, and from the Ministry of Health and Welfare, Japan     

Comparative Study on Reversal Efficacy of SDZ PSC 833, Cyclosporin a and Verapamil on Multidrug Resistance in vitro and in vivo

A non-immunosuppressive cyclosporin, SDZ PSC 833 (PSC833), shows a reversal effect on multidrug resistance (MDR) by functional modulation of MDR1 gene product, P-glycoprotein. The objective of the present study was to compare the reversal efficacy of three multidrug resistance modulators, PSC833, cyclosporin A (CsA) and verapamil (Vp). PSC833 has approximately 3-10-fold greater potency than CsA and Vp with respect to the restoring effect on reduced accumulation of doxorubicin (ADM) and vincristine (VCR) in ADM-resistant K562 myelogenous leukemia cells (K562/ADM) in vitro and also on the sensitivity of K562/ADM to ADM and VCR in in vitro growth inhibition. The in vivo efficacy of a combination of modifiers (PSC833 and CsA: 50 mg/kg, Vp 100 mg/kg administered p.o. 4 h before the administration of anticancer drugs) with anticancer drugs (ADM 2.5 mg/kg i.p., Q4D days 1, 5 and 9, VCR 0.05 mg/kg i.p., QD days 1-5) was tested in ADM-resistant P388-bearing mice. PSC833 significantly enhanced the increase in life span by more than 80%, whereas CsA and Vp enhanced by less than 50%. This reversal potency, which exceeded that of CsA and Vp, was confirmed by therapeutic experiments using colon adenocarcinoma 26-bearing mice. These results demonstrated that PSC833 has signficant potency to reverse MDR in vitro and in vivo, suggesting that PSC833 is a good candidate for reversing multidrug resistance in clinical situations.     

Reversal mechanism of multidrug resistance by verapamil: direct binding of verapamil to P-glycoprotein on specific sites and transport of verapamil outward across the plasma membrane of K562/ADM cells

The calcium channel blocker verapamil has been shown to reverse multidrug resistance (T. Tsuruo et al., Cancer Res. 41: 1967-1972, 1981), but the mechanism of action of this agent has not been fully elucidated. A radioactive photoactive analogue of verapamil, N-[benzoyl-3,5-3H-(+/-)-5-[(3,4-dimethoxyphenetyl)methylamino]-2- (3,4-dimethoxyphenyl)-2-isopropyl-N-p-azidobenzoylpentylamine, was used to label the plasma membranes of a human myelogenous leukemia cell line (K562), a multidrug-resistant subline selected for resistance to Adriamycin (K562/ADM) and its revertant cell (R1-3). Sodium dodecyl sulfate-polyacrylamide gel electrophoretic fluorograms revealed the presence of an intensely radiolabeled Mr 170,000-180,000 protein in the membranes from K562/ADM but not from the drug-sensitive parental K562 and revertant R1-3 cells. The Mr 170,000-180,000 verapamil acceptor was immunoprecipitated by monoclonal antibody MRK16 specific for P-glycoprotein associated with multidrug resistance, indicating that P-glycoprotein in the plasma membrane is a major target of verapamil in K562/ADM cells. The photolabeling of P-glycoprotein with N-[benzoyl-3,5-3H]-(+/-)-5-[(3,4-dimethoxyphenetyl)methylamino]-2- (3,4-dimethoxyphenyl)-2-isopropyl-N-p-azidobenzoylphentylamine was significantly blocked by other calcium channel blockers, nicardipine and diltiazem, that have been shown to overcome multidrug resistance. In addition, the photolabeling was partially blocked by Adriamycin, vincristine, and colchicine, suggesting that the specific binding sites for verapamil on P-glycoprotein are closely related to the binding sites for these calcium channel blockers and antitumor agents. To determine whether verapamil could be a substrate for P-glycoprotein, the cellular accumulation of [3H]verapamil into K562 and K562/ADM was evaluated. The accumulation of [3H]verapamil in the multidrug-resistant cells was 30% of K562 cells and increased when K562/ADM cells were treated with vincristine and nicardipine at 5 microM, indicating that the P-glycoprotein transports verapamil as well as other antitumor agents in the multidrug-resistant cells. These results suggest that verapamil enhances antitumor agent retention through competition for closely related binding sites on P-glycoprotein.