Reversal of P-glycoprotein-mediated multidrug resistance by the novel tetrandrine derivative W6

Overexpression of ATP-dependent efflux pump P-glycoprotein (P-gp) is the main cause of multidrug resistance (MDR) and chemotherapy failure in cancer treatment. Inhibition of P-gp-mediated drug efflux is an effective way to overcome cancer drug resistance. The present study investigated the reversal effect of the novel tetrandrine derivative W6 on P-gp-mediated MDR. KBv200, MCF-7/adr and their parental sensitive cell lines KB, MCF-7 were used for reversal study. The intracellular accumulation with P-gp substrates of doxorubicin was determined by flow cytometry. The expression of P-gp and ERK1/2 was investigated by western blot and real-time-PCR (RT-PCR) analysis. ATPase activity of P-gp was performed by P-gp-Glo^TM assay systems. In comparison with P-gp-negative parental cells, W6 produced a favorable reversal effect in the MDR cells, as determined using the MTT assay. W6 significantly and dose-dependently increased intracellular accumulation of P-gp substrate doxorubicin (DOX) in P-gp overexpressing KBv200 cells, and also inhibited the ATPase activity of P-gp. W6 inhibited P-gp expression in KBv200 cells in a time-dependent manner, but it had no effect on MDR1 expression. In addition, W6 significantly decreased the ERK1/2 activation in KBv200 cells. Our results showed that W6 effectively reversed P-gp-mediated MDR by inhibiting the transport function and expression of P-gp, demonstrating the potential clinical utility of W6.     

一种新番荔枝内酯单体atemoyacin—B克服肿瘤多药抗药性

目的 探讨ａｔｅｍｏｙａｃｉｎ－Ｂ（Ａｔｅ）克服肿瘤多药抗药性（ＭＤＲ）作用及机制。方法 Ｂｕｌｌａｔａｃｉｎ（Ｂｕｌ）为阳性对照物,细胞毒测定以ＭＴＴ法,Ｐｇｐ功能测定以Ｆｕｒａ２－ＡＭ法,细胞内药物积累测定以荧光分光光度计法;细胞凋亡测定以流式细胞仪法,结果：Ａｔｅ对ＭＣＦ－７／Ｄｏｘ,ＭＣＦ－７,ＫＢＶ２００和ＫＢ细胞的ＩＣ５０分别为１２２,１２０,１．３４,１．２７ｍｍｏｌ．Ｌ＾－１,Ａｔ     

功劳木中异汉防己碱对P-糖蛋白介导的人乳腺癌细胞多药耐药性的逆转作用

本文探讨了异汉防己碱对P-糖蛋白(P-gp)介导的人乳腺癌细胞多药耐药性的逆转作用。首先以RT-PCR和免疫组化方法分别从RNA和蛋白水平检测MCF-7/DOX细胞P-gp表达情况，以明确MCF-7/DOX细胞的耐药特征；然后采用MTT法检测异汉防己碱的内在细胞毒性及其对阿霉素(DOX)的增敏作用，并以RF(reversal fold)值评价其逆转效果；同时应用流式细胞仪(FCM)对细胞内DOX的蓄积量进行了分析；再以免疫组化方法检测异汉防己碱对MCF-7/DOX细胞P-gp表达水平的影响；最后采用罗丹明蓄积和外排试验检测了异汉防己碱对P-gp功能的影响。整个试验以维拉帕米作为阳性对照。实验结果表明：MCF-7/DOX细胞是具有多药耐药表型且P-gp表达阳性的细胞株；无毒剂量异汉防己碱可明显增强DOX对MCF-7/DOX细胞的细胞毒性(RF=3.89)，明显高于维拉帕米(RF=2.54)的逆转活性(P<0.05)，但其几乎不影响DOX对MCF-7细胞的抑制作用；异汉防己碱对MCF-7/DOX细胞P-gp表达水平无明显影响，但其可有效抑制P-gp的药物外排功能。因此，异汉防己碱可有效逆转P-gp介导的人乳腺癌细胞的多药耐药性，它可能成为有效多药耐药逆转剂的候选药物。     

Sensitization of ABCB1 overexpressing cells to chemotherapeutic agents by FG020326 via binding to ABCB1 and inhibiting its function

The effectiveness of chemotherapeutic treatment is usually limited by the overexpression of adenosine triphosphate binding cassette (ABC) transporters, which mediate multidrug resistance (MDR) by acting as efflux pumps to remove chemotherapeutic agents from MDR cancer cells. Thus, the inhibition of ABC transporters may represent a promising strategy to reverse MDR. This study was to characterize the actions of FG020326, a newly synthesized triaryl-substituted imidazole derivative, to reverse MDR in vitro and in vivo. FG020326 significantly potentiated the cytotoxicity of paclitaxel, doxorubicin, and vincristine in the ABCB1 (P-glycoprotein, P-gp) overexpressing cells KBv200 and MCF-7/adr, but not in the ABCB1 negative parental cell lines KB and MCF-7. However, FG020326 did not alter the cytotoxicity of the aforementioned drugs in ABCC1 (MRP1), ABCC4 (MRP4), ABCG2 (BCRP) and LRP overexpressing cell lines, KB-CV60, NIH3T3/MRP4-2, S1-M1-80 and SW1573/2R120, respectively. FG020326, following p.o. administration, was present in concentrations sufficient for reversal of MDR in mice. The co-administration of FG020326 with paclitaxel or vincristine significantly enhanced the antitumor activity of these drugs without significantly increasing toxicity in the mice bearing the KBv200 cell xenografts. In addition, FG020326, at concentrations that reversed MDR, did not significantly affect the activity of CYP3A4 or alter the pharmacokinetic profile of paclitaxel after co-administration with paclitaxel. FG020326 produced a significant concentration-dependent displacement of [³H]azidopine and inhibition of efflux of drug from cells. Furthermore, FG020326 was co-localized with ABCB1 in cell membranes. Hence, FG020326 is characterized as a third generation MDR modulator that holds great promise for the treatment of cancer patients with ABCB1-mediated MDR.     

FG020326-loaded nanoparticle with PEG and PDLLA improved pharmacodynamics of reversing multidrug resistance in vitro and in vivo

Aim： FG020326, a novel imidazole derivative, is a potent multidrug-resistance （MDR） modulator in vitro and in vivo. However, FG020326 is insoluble. PEDLLA-FG020326 is a FG020326-1oaded nanoparticle formed with diblock copolymers of poly （ethylene glycol）-block-poly （D,L-lactic acid） （PEG：PDLLA, PEDLLA） that can solubilize FG020326. This work was intended to evaluate the pharmacodynamics of PEDLLA-FG020326 on reversing MDR in vitro and in vivo. Methods： Cytotoxicity was determined by tetrazolium assay. The intracellular accumulation and efflux of doxorubicin （Dox） were detected by fluorescence spectrophotometry. The function of P-glycoprotein was examined by Rhodamine 123 （Rh123） accumu- lation detected by flow cytometry. The KBv200 cell xenograft model was established to investigate the effect of PEDLLA-FG020326 on reversing MDR in vivo. Resdts： PEDLLA-FG020326 and FG020326 exhibited 56.4- and 35.9-fold activity in reversing KBv200 cells to vincristine （VCR） resistance, respectively and 14.98- and 7.64-fold to Dox resistance, respectively. PEDLLA-FG020326 was much stronger than FG020326, resulting in the increase of Dox and Rh123 accumulation and the decrease of intracellular Dox extrusion in KBv200 cells. Importantly, PEDLLA- FG020326 exhibited more powerful activity than FG020326 in enhancing the effect of VCR against KBv200 cell xenografts in nude mice, but did not appear more toxic. Conclusion： The pharmacodynamics of FG020326 was improved by incorporating it into a micellar nanoparticle formed with PEG-block-PDLLA copolymers.     

脂质体阿霉素逆转肿瘤多药耐药的活性和机制研究

目的 探讨脂质体阿霉素( PLD)逆转肿瘤多药耐药(MDR)的活性及其逆转机制.方法 以噻唑蓝(MTT)方法检测PLD对多药耐药肿瘤细胞MCF-7/ADR及KBv200的耐药逆转活性.结果 PLD在体内具有较强的逆转活性,逆转活性大于公认的强逆转剂维拉帕米的活性;在5.0μmol/L浓度下使多药耐药细胞KBv200对长春新碱的敏感性增加了45倍.PLD浓度依赖性增加(0、2.5、5.0、10 μmol/L)KBv200细胞内的罗丹明蓄积.PLD的心脏毒性、骨髓抑制以及脱发等不良反应显著降低.结论 脂质体阿霉素具有较强的逆转MDR的活性,主要通过持续向肿瘤组织聚集,肿瘤局部药物浓度升高,抗肿瘤的活性增强.     

Dual effect of lobeline on α4β2 rat neuronal nicotinic receptors

Development of agents to overcome multidrug resistance (MDR) is important in cancer chemotherapy, and the overexpression of P-glycoprotein (P-gp) is one of the major mechanisms of MDR. In this paper, we evaluated the effects of two new milbemycin compounds, milbemycin β(14) and secomilbemycin D, isolated from fermentation broth of S. bingchenggensis on reversing MDR of adriamycin-resistant human breast carcinoma (MCF-7/adr) cells. We observed that the both milbemycins (5 μM) showed strong potency to increase adriamycin cytotoxicity toward MCF-7/adr cells with reversal fold (RF) of 13.5 and 10.59, respectively. In addition, the mechanisms of milbemycins on reversing P-gp-mediated MDR demonstrated that they significantly increased the accumulations of adriamycin and Rh123 via inhibiting P-gp efflux in MCF-7/adr cells. Furthermore, the results also revealed that milbemycin β(14) and secomilbemycin D could regulate down the expression of P-gp, but not affect the expression of MDR1 gene. In conclusion, our observations suggest that the two new milbemycin compounds probably represent the promising agents for reversing MDR in cancer therapy.     

Substituted tetrahydroisoquinoline compound B3 inhibited P-glycoprotein-mediated multidrug resistance in-vitro and in-vivo

P-glycoprotein (P-gp) mediated multidrug resistance (MDR) is one of the main obstacles in tumour chemotherapy. A promising approach to reverse MDR is the combined use of nontoxic and potent P-gp inhibitor with conventional anticancer drugs. We have examined the potential of a newly synthesized tetrahydroisoquinoline derivative B3 as a MDR-reversing agent. The MTT (3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide) assay was used to examine the effect of B3 on the cytotoxicity in K562/A02 and MCF-7/ADM cells caused by doxorubicin (adriamycin). Accumulation and efflux of P-gp substrate rhodamine123 in K562/A02 and primary cultured rat brain microvessel endothelial cells (RBMECs) were measured to evaluate the inhibitory effect of B3 on P-gp. The K562/A02 xenograft model in nude mice was established to examine MDR-reversing efficacy of B3 in-vivo. The results indicated that co-administration of B3 resulted in an increase on chemosensitivity of K562/A02 and MCF-7/ADM cells to doxorubicin in a dose-dependent manner. Rhodamine123 accumulation in K562/A02 cells and RBMECs were significantly enhanced after the incubation with various concentrations of B3. Furthermore, B3 inhibited the efflux of rhodamine123 from RBMECs. Co-administration of B3 with doxorubicin significantly decreased weight and volume of tumour in nude mice. In conclusion, B3 is a novel and potent MDR reversal agent with the potential to be an adjunctive agent for tumour chemotherapy.     

The anti-hepatitis drug DDB chemosensitizes multidrug resistant cancer cells <Emphasis Type="Italic">in vitro</Emphasis> and <Emphasis Type="Italic">in vivo</Emphasis> by inhibiting P-gp and enhancing apoptosis

Summary Purpose: DDB (dimethyl-4,4′-dimethoxy-5,6,5′6′-dimethylene dioxybiphenyl-2,2′-dicarboxylate) is a synthetic hepatoprotectant which has been widely used to treat chronic viral hepatitis B patients in China for more than 20 years. In this study, we evaluated DDB as a multidrug resistance (MDR) chemosensitizing agent. Methods: A panel of sensitive and resistant cancer cell lines were treated with various concentration of DDB, and the effect on chemosensitivity and accumulation of anticancer drugs; promotion of apoptosis and P-glycoprotein (P-gp) expression were determined by MTT (Dimethyl thiazolyl-2,5-diphenyltetrazolium bromide) assay, fluorospectrometry and flow cytometry respectively. Drug resistance reversal activity of DDB was also examined in BALB/c nude mice bearing both acquired MDR human nasopharyngeal carcinoma KBv200 and parental KB xenografts. The effect of DDB on the pharmacokinetics of Dox and hematological toxicity induced by Dox was measured in ICR and C₅₇/BL mice, respectively. Results: DDB at nontoxic concentrations of 12.5, 25 and 50 μM partly reversed the resistance to vincristine, doxorubicin, paclitaxel in acquired MDR breast carcinoma MCF-7/Adr cells, KBv200 and intrinsic MDR human hepatocarcinoma Bel₇₄₀₂ cells, whereas no chemosensitizing effect of DDB was observed in sensitive KB and MCF-7 cells. DDB increased the intracellular accumulation of doxorubicin and inhibited surface P-gp expression in MCF-7/Adr cells. Furthermore, it was found that DDB promoted doxorubicin-induced apoptosis of Bel₇₄₀₂ cells through enhanced caspase-3 activation. Co-administration of DDB at 300 and 500 mg/kg orally to nude mice increased the antitumor activity of vincristine to KBv200 xenografts without a significant increase in toxicity. In contrast, Co-administration of DDB did not inhibit the growth of KB xenografts. DDB also markedly reduced the decrease of leukocytes in doxorubicin-treated C₅₇/BL mice. Co-administration of DDB increased Dox concentration in ICR mice bearing S180 sarcoma, but no pharmacokinetical interaction with Dox was observed. Conclusion: These results indicate that DDB has MDR reversal activity by inhibiting P-gp and when used in combination with anti-cancer drugs, it could potentially be used as a clinical treatment for P-gp-mediated MDR cancers.     

番荔枝内酯单体89-2实验治疗KBv200及KB细胞移植瘤的作用

目的番荔枝内酯单体89-2是自阿蒂莫耶番荔枝植物分离获得。本研究旨在探讨89-2对MDR肿瘤的实验治疗作用。方法以MTT法测定细胞毒;KBv200及KB细胞裸鼠移植瘤模型研究89-2对MDR肿瘤的实验治疗作用;以Fura-2-AM法测定P-糖蛋白(P-gp)功能。结果89-2对KBv200及KB细胞的IC₅₀分别为48.7和64.6 nmol·L^-1(P>0.05)。89-2对KB及KBv200细胞裸鼠移植瘤具有相似的剂量依赖性抑制作用,而毒性可以耐受。89-2剂量依赖性地增加KBv200细胞的Fura-2积累。结论89-2体内外均抑制KB和KBv200细胞生长,具有开发前景。     

Reversal of P-glycoprotein-mediated multidrug resistance in vitro by milbemycin compounds in adriamycin-resistant human breast carcinoma (MCF-7/adr) cells

The effects of milbemycin A₄ (MB A₄), milbemycin oxime A₄ (MBO A₄) and milbemycin β₁ (MB β₁) on reversing multidrug resistance (MDR) of tumor cells were firstly conducted according to the following research, including MTT [3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyl tetrazolium bromide] assay, the accumulation of adriamycin, the accumulation and efflux of rhodamine 123 (Rh123), the regulations of MDR1 gene, and expression of P-gp. The three milbemycins (5 μM) showed strong potency to increase adriamycin cytotoxicity toward adriamycin-resistant human breast carcinoma cells MCF-7/adr with reversal fold (RF) of 21.42, 19.06 and 14.89, respectively. In addition, the mechanisms of milbemycins on P-glycoprotein (P-gp)-mediated MDR demonstrated that the milbemycins significantly increased the intracellular accumulations of adriamycin and Rh123 via inhibiting P-gp transport function. Based on the analysis of the P-gp and MDR1 gene expression using flow cytometry and RT-PCR, the results revealed that milbemycin compounds, particularly MB A₄, could regulate down the expression of the P-gp and MDR1 gene. These findings suggest that the milbemycins probably represent promising agents for overcoming MDR in cancer therapy, and especially MB A₄ is better modulator with the lowest toxicity.     

双苄基异喹啉类生物碱粉防己碱与小檗胺逆转多药抗药性的比较研究

比较了2种结构相近的双苄基异喹啉(BBI)生物碱粉防己碱(TTD)、小檗胺(BBM)与维拉帕米(VRP)逆转多药抗药性的作用。结果,TTD,BBM和VRP在多药抗药的MCF-7/Adr和KBv₂₀₀细胞对ADR和VCR均有明显增敏作用,且作用呈剂量依赖性。其中10μmol·L^-1TTD能完全逆转MCF-7/Adr细胞对ADR的抗药性。TTD,BBM和VRP均有增加MCF-7/Adr细胞内阿霉素积累的作用。TTD和BBM在结构上仅有微小差别,但TTD的逆转MDR作用优于VRP10倍,而BBM的作用与VRP相仿。TTD在裸鼠体内MCF-7/Adr实体瘤模型上也证实有明显逆转ADR抗药性的作用。     

Persistent reversal of P-glycoprotein-mediated daunorubicin resistance by tetrandrine in multidrug-resistant human T lymphoblastoid leukemia MOLT-4 cells

Multidrug resistance (MDR) represents a major problem in cancer chemotherapy. P-glycoprotein (P-gp), the drug efflux pump that mediates this resistance, can be inhibited by compounds with a variety of pharmacological functions, thus circumventing the MDR phenotype. The present study was performed to evaluate a unique MDR-reversal feature of a bisbenzylisoquinoline alkaloid tetrandrine (TET) in a P-gp expressing MOLT-4 MDR line (MOLT-4/DNR) established in our laboratory. Cell viability was determined by an MTT assay. P-gp function was characterized by determining the Rh123 accumulation/efflux capacity. P-gp overexpression in resistant MOLT-4/DNR cells was confirmed by flow cytometry analysis after staining with phycoerythrin-conjugated anti-P-gp monoclonal antibody 17F9. Compared to ciclosporin A (CsA), TET exhibited stronger activity to reverse drug resistance to daunorubicin (DNR), vinblastine (VLB) and doxorubicin (DOX) in MOLT-4/DNR cells. TET showed no cytotoxic effects on parental MOLT-4 cells lacking P-gp expression or on the resistant MOLT-4/DNR cells. TET modulated DNR cytotoxicity even after it was washed with the medium for 24 h, while CsA almost completely lost its reversal capability 24 h after washing. TET and CsA similarly increased the accumulation of Rh123 in resistant MOLT-4/DNR cells. However, TET inhibited Rh123 efflux from resistant cells even after washing with the medium, while CsA rapidly lost its ability to inhibit Rh123 efflux after washing. The current study suggests that TET enhances the cytotoxicity of anticancer drugs in the P-gp expressing MDR cell line by modulating P-gp in a different manner to the well-known P-gp inhibitor CsA.     

咯萘啶逆转肿瘤多药耐药及其作用机制

目的:利用mdr1~ 的人白血病和乳腺癌多药耐药(MDR)细胞系K562/A02和MCF-7/ADR研究咯萘啶(pyronaridine,PND)对MDR的逆转作用及其机制.方法:采用MTT法、荧光分光光度法、荧光显微镜法、流式细胞仪法和RT-PCR法分别测定PND单独或与阿霉素(DOX)合用,对肿瘤细胞的生长抑制、诱导凋亡、细胞内药物浓度、mdr1基因表达的影响.结果:PND对敏感及耐药细胞均具有生长抑制作用,半数抑制剂量(IC_(50))根据不同细胞在5.10-18.66μmol/L之间;低毒剂量PND显著增强DOX对耐药细胞的细胞毒和诱导凋亡作用,且增加DOX在耐药细胞内的蓄积及减少罗丹明(Rh123)的外排.RT-PCR结果显示,PND对mdr1基因无下调作用.结论:PND可作为第三代P-糖蛋白(P-gp)抑制剂,通过下调P-gp药物外排泵功能而产生强大的逆转MDR效应.     

Fundamental Relationships Between the Composition of Pluronic Block Copolymers and Their Hypersensitization Effect in MDR Cancer Cells

Purpose. Previous studies have demonstrated that Pluronic block copolymers hypersensitize multiple drug resistant (MDR) cancer cells, drastically increasing the cytotoxic effects of anthracyclines and other anticancer cytotoxics in these cells. This work evaluates the dose dependent effects of these polymers on (i) doxorubicin (Dox) cytotoxicity and (ii) cellular accumulation of P-glycoprotein probe, rhodamine 123 (R123) in MDR cancer cells. Methods. Dox cytotoxicity and R123 accumulation studies are performed on monolayers of drug-sensitive (KB, MCF-7, Aux-Bl) and MDR (KBv, MCF-7/ADR, CH^rC5) cells. Results. Both tests reveal strong effects of Pluronic copolymers observed at concentrations below the critical micelle concentration (CMC) and suggest that these effects are due to the copolymer single chains ('unimers'). Using block copolymers with various lengths of hydrophobic propylene oxide (PO) and hydrophilic ethylene oxide (EO) segments these studies suggest that the potency of Pluronic unimers in MDR cells increases with elevation of the hydrophobicity of their molecule. Optimization of Pluronic composition in R123 accumulation and Dox cytotoxicity studies reveals that Pluronic copolymers with intermediate lengths of PO chains and relatively short EO segments have the highest net efficacy in MDR cells. Conclusions. The relationship between the structure of Pluronic block copolymers and their biological response modifying effects in MDR cells is useful for determining formulations with maximal efficacy with respect to MDR tumors.     

Menadione serves as a substrate for P-glycoprotein: implication in chemosensitizing activity

Based on its chemosensitizing effect, we questioned whether menadione is an inhibitor or a substrate of P-glycoprotein (P-gp). To test this hypothesis, we assessed the effect of menadione on P-gp activity and examined the P-gp-dependency of cellular accumulation and cytotoxicity of menadione as well. Treatment with menadione resulted in the concentration-dependent increase of rhodamine 123 (Rh123) accumulation in P-gp-overexpressing MDCKII/MDR1 and NCI/ADR-RES cells, suggesting that menadione inhibits Rh123 extrusion by P-gp. Compared with MDCKII or MCF-7, intracellular distribution of [³H]-menadione was significantly lower in MDCKII/MDR1 or NCI/ADR-RES cells, which could be restored by the P-gp inhibitors, verapamil and quinidine. Consistent with these results, MDCKII/MDR1 or NCI/ADR-RES cells were more resistant to the cytotoxicity of menadione than MDCKII or MCF-7 cells, respectively. Such resistance was abolished by the combined treatment of verapamil and quinidine in NCI/ADR-RES cells. Our study identified menadione as a substrate of P-gp, which presumably, acts as the mechanism for the chemosensitizing effect. Menadione may be a promising chemotherapeutic enhancer by its ability of circumventing drug resistance, in addition to its own anti-cancer activity.     

CJY, an isoflavone, reverses P-glycoprotein-mediated multidrug-resistance in doxorubicin-resistant human myelogenous leukaemia (K562/DOX) cells

In an effort to develop safe and effective multidrug-resistance (MDR) reversing agents, the effect of CJY, an isoflavone, on the P-glycoprotein (P-gp) function and P-gp-mediated MDR was evaluated in doxorubicin-resistant human myelogenous leukaemia (K562/DOX) cells. The results showed that CJY caused a marked increase in accumulation and a notable decrease in efflux of rhodamine 123 (Rh123). The inhibitory effect of the agent on P-gp function persisted for at least 120 min after removal of 2.5 microM CJY from the incubation medium. The doxorubicin-induced cytotoxicity, apoptosis and cell cycle perturbations were significantly potentiated by CJY. The intracellular accumulation of doxorubicin was also enhanced. The compound exhibited potent effects in-vitro on the reversal of P-gp-mediated MDR, suggesting that it could become a candidate as an effective MDR reversing agent in cancer chemotherapy.     

Influence of ceramide metabolism on P-glycoprotein function in immature acute myeloid leukemia KG1a cells

Previous studies have emphasized the role of glucosylceramide (Glu-Cer) synthase in multidrug resistance (MDR) regulation. However, the mechanism by which the inhibition of this enzyme results in increased drug retention and cytotoxicity remains unclear. In this study, we investigated the respective role of ceramide (Cer) accumulation and Glu-Cer derivatives depletion in MDR reversal effect of 1-phenyl-2-decanoylamino-3-morpholino-1-propanolol (PDMP), a Glu-Cer synthase inhibitor. We show here that treatment with PDMP resulted in increased rhodamine 123 (Rh123) retention and potent chemosensitization of P-glycoprotein (P-gp)-expressing cells, including KG1a cells, KG1a/200 cells, K562/138 cells, and K562/mdr-1 cells. Metabolic studies revealed that PDMP induced not only time-dependent Cer accumulation but also reduction of all glycosylated forms of Cer, including Glu-Cer, lactosylceramide (Lac-Cer), monosialo ganglioside (GM3) and disialo ganglioside (GD3). The influence of these metabolites on P-gp function was investigated by measuring Rh123 retention in PDMP-treated cells. P-gp function was found to be stimulated only by the addition of gangliosides in all resistant cell lines, whereas Glu-Cer, Lac-Cer, and Cer had no effect. Moreover, in KG1a/200 cells, GD3 and, to a lesser extent, GM3 were found to phosphorylate P-gp on serine residues. Altogether, these results suggest that, at least in leukemic cells, gangliosides depletion accounts for PDMP-mediated MDR reversal effect, and that gangliosides are important P-gp regulators perhaps through their capacity to modulate P-gp phosphorylation.     

2—ASG —3—（3‘,5’—双吗啉甲基—4‘—羟基）—苯甲酰吲哚（HWL—12）逆转肿…

AIM: To explore the reversal of multidrug resistance (MDR) by indole derivative HWL-12. METHODS: Cytotoxicity was determined by tetrazolium (MTT) assay. The function of P-gp was examined by Fura 2-AM assay. Cellular accumulation of doxorubicin (Dox) was measured by fluorescence spectrophotometry. RESULTS: HWL-12 10 mumol.L-1 markedly increased Fura-2 accumulation and was 17.2-fold reversal of MDR in MCF-7/ADR cells. The cellular Dox accumulation in MDR cells was increased in the presence of HWL-12 on the MCF-7/ADR cells. No effect was observed for Dox accumulation in the presence of high Ca2+ (addition of CaCl2) or low Ca2+ (addition of egtazic acid). CONCLUSION: HWL-12 has a potent MDR reversal action which was associated with the increase of cellular Dox accumulation in MDR cells and not related with calcium ion concentration.