Increase in doxorubicin cytotoxicity by inhibition of P-glycoprotein activity with lomerizine

Acquired resistance to chemotherapy is a major problem during cancer treatment. One mechanism for drug resistance is overexpression of the MDR (multidrug resistance)1 gene encoding the transmembrane efflux pump, P-glycoprotein (P-gp). Calcium channel blockers such as verapamil, nifedipine and nicardipine have been shown to reverse cellular drug resistance by inhibiting P-gp drug efflux. This study evaluated whether a new calcium channel blocker, lomerizine, influenced doxorubicin (Dox) cytotoxicity and P-gp activity in a P-gp-expressing cell line compared to a non-expressing subline. Verapamil, and even more markedly, lomerizine, increased cellular uptake of calcein transported by P-gp in a P-gp-expressing erythroleukemia cell line, K562-Dox. Ten microM of lomerizine reduced the IC50 of doxorubicin in the K562-Dox from 60000 ng/ml to 800 ng/ml, whereas the IC50 of doxorubicin in the K562 subline was only marginally affected by these drugs. Lomerizine showed greater reduction in P-gp efflux than verapamil at an equimolar concentration. These results suggest that lomerizine has the clinical potential to reverse tumor MDR involving the efflux protein P-gp.     

Discovery of a daunorubicin analogue that exhibits potent antitumor activity and overcomes P-gp-mediated drug resistance

Anthracyclines are considered to be some of the most effective anticancer drugs for cancer therapy. However, drug resistance and cardiotoxicity of anthracyclines limit their clinical application. We hypothesize that direct modifications of the sugar moiety of anthracyclines avert P-glycoprotein (P-gp) recognition and efflux, increase drug intracellular concentration in cancer cells, and thus overcome P-gp-mediated drug resistance. Daunorubicin (DNR) analogues with sugar modifications were synthesized by directly transforming the amino group of DNR to an azido group or triazole group. Molecular docking showed that the lead compound (3'-azidodaunorubicin, ADNR) averts P-gp binding, while daunorubicin (DNR) extensively interacts with multidrug-resistance (MDR) protein through H-bonds and electrostatic interactions. FACS assay demonstrated that these new compounds abolished P-gp drug efflux and accumulated high intracellular concentration in the drug-resistant leukemia K562/Dox. P-gp inhibition by CsA confirmed that these new analogues are no longer P-gp substrates. ADNR exhibited potent anticancer activity in both drug-sensitive (K562) and drug-resistant leukemia cells (K562/Dox), with a 25-fold lower drug resistance index than DNR. An in vivo xenograft model demonstrated that ADNR showed more than 2.5-fold higher maximum growth inhibition rate against drug-resistant cancers and significant improvement for animal survival rate versus DNR. No significant body weight reduction in mice was observed for ADNR at the maximum tolerable dose, as compared to more than 70% body weight reduction for DNR. These data suggest that sugar modifications of anthracyclines avert P-gp binding, abolish P-gp-mediated drug efflux, increase intracellular drug concentration, and thus overcome P-gp-mediated drug resistance in cancer therapy.     

Increase in doxorubicin cytotoxicity by carvedilol inhibition of P-glycoprotein activity

Acquired resistance to chemotherapy is a major problem during cancer treatment. One mechanism for drug resistance is overexpression of the MDR1 (multidrug resistance) gene encoding for the transmembrane efflux pump, P-glycoprotein (P-gp). The calcium channel blocker verapamil has been shown to reverse cellular drug resistance by inhibiting P-gp drug efflux. This study evaluated whether the new antihypertensive drug carvedilol influenced doxorubicin (Dox) cytotoxicity and P-gp activity in a P-gp-expressing cell line compared to a non-expressing subline. Verapamil (10 micromol/L), and even more markedly, carvedilol (10 micromol/L) increased cellular uptake of P-gp-transported calcein of a P-gp-expressing breast cancer cell line (Hs578T-Dox). In the subline (Hs578T) not expressing P-gp, no effects of carvedilol or verapamil on calcein uptake were seen. Carvedilol and verapamil (10 micromol/L) reduced the LD50 (dose which results in the death of half the number of cells) of the Hs578T-Dox subline from 200 mg/L to approx. 10 mg/L Dox, whereas the LD50 of the Hs578T subline was only marginally affected. Carvedilol (10 micromol/L) reduced P-gp activity approximately twice as effectively as verapamil at an equimolar concentration. Carvedilol did not affect pyrogallol cytotoxicity and pyrogallol was without effect on calcein accumulation of the Hs578T-Dox cell line, indicating the lack of antioxidative properties affecting P-gp activity and associated toxicity of the drug. The results suggest that carvedilol has the clinical potential to reverse tumour MDR involving the efflux protein P-gp.     

Mitochondrial localization and activity of P-glycoprotein in doxorubicin-resistant K562 cells

It is now well-established that P-glycoprotein 170 (P-gp), an efflux pump involved in multidrug resistance (MDR) is overexpressed at the plasma membrane of doxorubicin-resistant K562 leukemia cells. Nevertheless, several results suggested: (i) that P-gp-mediated drug efflux was not the only mechanism involved in resistance; (ii) that intracellular compartments could accumulate the drug, preventing it from reaching its nuclear targets; (iii) that agents able to reverse multidrug resistance may lead to intracellular drug redistribution. We have studied the localization of P-gp in mitochondria as well as its functional properties in this compartment. Using several monoclonal antibodies (MoAbs) directed against different P-gp epitopes, a protein was detected in the cytoplasm of two doxorubicin-resistant K562 sublines and, by confocal laser scanning microscopy, this protein was shown to co-localize in the Golgi apparatus and in mitochondria, in equivalent proportions. Purified mitochondria were isolated from K562 cell variants; the presence of a protein of about 170 kDa and reacting with several anti-P-gp antibodies was assessed in MDR cells by Western blotting and flow cytometry. Functional assays have shown that mitochondrial P-gp was involved in doxorubicin accumulation inside the organelle but not in its efflux, suggesting an orientation of P-gp in the mitochondrial membrane inverse to that observed in the plasma membrane. A potential role for mitochondrial P-gp in MDR cells would be to protect the nucleus from doxorubicin. This is the first demonstration of the presence and functional activity of P-gp in mitochondria of MDR cells.     

洛美利嗪逆转K562/ADM细胞多药耐药性

目的研究洛美利嗪(lomerizine,Lom)逆转K562/ADM细胞多药耐药性的作用及机制。方法MTT法检测细胞毒作用,流式细胞仪研究Lom对ADM和长春新碱(vincristine,VCR)的K562/ADM细胞凋亡诱导作用的影响及对罗丹明123(rhodamine 123,Rh123)外排和P-糖蛋白(P-glycoprotein,P-gp)表达的作用。结果Lom明显提高ADM对K562/ADM多药耐药细胞的细胞毒作用及ADM和VCR的凋亡诱导作用,3,10和30 μmol·L^-1 Lom使K562/ADM对ADM的IC₅₀值由79.03 μmol·L^-1分别降至28.14,8.16和3.16 μmol·L^-1。Lom增加胞内ADM的蓄积浓度并抑制Rh123外排;但作用72 h后对K562/ADM细胞P-gp表达无影响。结论Lom通过抑制P-gp的活性逆转K562/ADM细胞的多药耐药性。     

In vitro cellular accumulation and cytotoxicity of liposomal and conventional formulations of daunorubicin and doxorubicin in resistant K562 cells

Previous investigations have indicated the possibility to circumvent multidrug resistance (MDR) by incorporation of an anthracycline into liposomes. We examined the in vitro cytotoxicity and cellular drug accumulation of the anthracyclines daunorubicin and doxorubicin compared with the commercially available liposomal formulations DaunoXome and Caelyx in human myelogenous leukemia K562 cells. The drug-sensitive parental K562/K line was compared with the P-glykoprotein (P-gp)-expressing cell lines K562/Dnr and K562/Vcr. Two cell lines with reduced levels of topoisomerase II (K562/Nov and K562/Ida) were also included. The cytotoxicity was determined by fluorometric microculture cytotoxicity assay and the cellular drug levels were determined by high performance liquid chromatograghy. There was a strong inverse correlation between P-gp levels and cellular drug accumulation (rho = -0.83, p = 0.04) and cytotoxicity (rho = -0.95, p = 0.01) of daunorubicin. Also the cytotoxicity of DaunoXome and doxorubicin was related to P-gp levels (rho = -0.96, p = 0.01 and rho = -0.90, p = 0.07, respectively). Caelyx did not show any cytotoxic effect due to impaired cellular uptake of the pegylated liposome. Regardless of the P-gp levels of the treated cells, DaunoXome showed the same cytotoxic effect despite lower intracellular accumulation (range 22-47%), compared with conventional daunorubicin.     

四氢异喹啉类化合物HZ08逆转白血病K562/DOX细胞多药耐药性的试验研究

目的:探讨四氢异喹啉类化合物HZ08对人白血病多药耐药K562/DOX细胞的逆转作用及其可能的机制。方法:采用MTT法检测HZ08的体外细胞毒性及其对阿霉素(DOX)的增敏作用,采用逆转倍数(RF)值评价其逆转效果;应用流式细胞仪分析细胞内罗丹明123(Rh123)潴留量的变化和DOX浓度,评价P糖蛋白(P-gp)的功能;采用Western blot法及免疫细胞化学法测定mdr1基因产物P-gp的表达;同时以人白血病敏感细胞株K562/S细胞为对照进行比较试验。结果:与K562/S细胞比较,HZ08可明显增强DOX对K562/DOX的细胞毒性,RF值增加;HZ08能浓度相关性地增加K562/DOX细胞对Rh123的摄取以及细胞内Rh123的潴留,明显抑制P-gp介导的Rh123外排;K562/DOX细胞膜上P-gp呈强阳性表达,但HZ08对K562/DOX细胞P-gp表达水平无明显影响;HZ08可显著增加K562/DOX细胞内DOX浓度。结论:HZ08可通过抑制K562/DOX细胞P-gp的功能、增加耐药细胞内DOX的浓度而增强K562/DOX细胞对DOX的敏感性,其可能成为有效的多药耐药逆转剂的候选药物。     

Reversal of P-glycoprotein mediated multidrug resistance in K562 cell line by a novel synthetic calmodulin inhibitor, E6

The overexpression of P-glycoprotein (P-gp) is associated with multidrug resistance (MDR) of tumor cells to a number of chemotherapeutic drugs. P-gp inhibitors have been shown to effectively reverse P-gp-mediated MDR in both in vitro and in vivo. Our previous studies demonstrated that E6, a novel synthetic calmodulin inhibitor, exhibited potent inhibitory effect on P-gp in rat brain microvessel endothelial cells (RBMECs). In the present study, the effect of E6 on MDR in a K562 MDR cell line (K562/DOX) highly expressing P-gp was studied and compared with that of a conventional P-gp inhibitor, verapamil (VER). E6 at concentrations of 1, 3, 10, 30 microM reduced the IC50 value of doxorubicin in K562/DOX cells from 79.19 microM to 35.18, 21.86, 6.31 and 1.97 microM, respectively. However, the IC50 value of doxorubicin in K562 sensitive subline was not significantly changed by E6. Using a DNA content analysis and an annexin V binding assay, the effects of E6 on doxorubicin-induced apoptosis were also examined. The results indicated that E6 effectively reversed the resistance to doxorubicin-induced apoptosis in K562/DOX cells. In addition, co-treatment of E6 and doxorubicin resulted in a remarkably G2/M blocking effect in K562/DOX cells. Furthermore, the treatment of K562/DOX cells with 10 microM E6 led to increased intracellular accumulation and decreased efflux of doxorubicin. Overall, the pharmacological effects of E6 on P-gp-mediated MDR is much stronger than that of positive control drug VER. These results suggested that E6 is a novel and potent MDR reversal agent and may be a potential adjunctive agent for tumor chemotherapy.     

Anthrapyridones, a novel group of antitumour non-cross resistant anthraquinone analogues. Synthesis and molecular basis of the cytotoxic activity towards K562/DOX cells

1. Multidrug resistance (MDR) to antitumour agents, structurally dissimilar and having different intracellular targets, is the major problem in cancer therapy. MDR phenomenon is associated with the presence of membrane proteins which belong to the ATP-binding cassette family transporters responsible for the active drug efflux leading to the decreased intracellular accumulation. 2. The search of new compounds able to overcome MDR is of prime importance. 3. Recently we have synthesized a new family of anthrapyridone compounds. The series contained derivatives modified with appropriate hydrophobic or hydrophylic substituents at the side chain. 4. The interaction of these derivatives with erythroleukemia K562 sensitive and K562/DOX resistant (overexpressing P-glycoprotein) cell lines has been examined. The study was performed using a spectrofluorometric method which allows to continuously follow the uptake and efflux of fluorescent molecules by living cells. 5. It was demonstrated that the increase in the lipophilicity of anthrapyridones favoured the very fast cellular uptake exceeding the rate of P-gp dependent efflux out of the cell. For these derivatives, very high accumulation (the same for sensitive and resistant cells) was observed and the in vitro biological data confirmed that these compounds exhibited comparable cytotoxic activity towards sensitive and P-gp resistant cell line. In contrast, anthrapyridones modified with hydrophylic substituents exhibited relatively low kinetics of cellular uptake. 6. For these derivatives decreased accumulation in resistant cells was observed and the in vitro biological data demonstrated that they were much less active against P-gp resistant cells in comparison to sensitive cells. 7.We also studied, using confocal microscopy, the intracellular distribution of anthrapyridones in NIH-3T3 cells. Our data showed that these compounds were strongly accumulated in the nucleus and lysosomes.     

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.     

A thermally targeted elastin-like polypeptide-doxorubicin conjugate overcomes drug resistance

The ability of cancer cells to become simultaneously resistant to different drugs, a trait known as multidrug resistance, remains a major obstacle for successful anticancer therapy. One major mechanism of resistance involves cellular drug efflux by expression of P-glycoprotein (P-gp), a membrane transporter with a wide variety of substrates. Anthracyclines are especially prone to induction of resistance by the P-gp mechanism. P-gp mediated resistance is often confronted by use of P-gp inhibitors, synthesis of novel analogs, or conjugating drugs to macromolecular carriers in order to circumvent the efflux mechanism. In this report, the effect of free and Elastin-like polypeptide (ELP) bound doxorubicin (Dox) on the viability of sensitive (MES-SA and MCF-7) and multidrug resistant (MES-SA/Dx5 and NCI/ADR-RES) human carcinoma cells was studied in vitro. The resistant MES-SA/Dx5 cells demonstrated about 70 times higher resistance to free Dox than the sensitive MES-SA cells, and the NCI/ADR-RES cells were about 30 fold more resistant than the MCF-7 cells. However, the ELP-bound Dox was equally cytotoxic in both sensitive and resistant cell lines. The ELP-bound Dox was shown to accumulate in MES-SA/Dx5 cells, as opposed to free Dox, which was rapidly pumped out by the P-gp transporter. Since ELP is a thermally responsive carrier, the effect of hyperthermia on the cytotoxicity of the ELP-Dox conjugate was investigated. Both cytotoxicity and apoptosis were enhanced by hyperthermia in the Dox resistant cells. The results suggest that ELP-Dox conjugates may provide a means to thermally target solid tumors and to overcome drug resistance in cancer cells.     

CJZ3, a lomerizine derivative,reverses P‐glycoprotein‐mediated multidrug‐resistance in doxorubicin‐resistant human myelogenous leukemia (K562/DOX) cells

P‐glycoprotein‐mediated drug efflux can yield a multidrug‐resistance (MDR) phenotype that is associated with a poor response to cancer chemotherapy. The development of safe and effective MDR‐reversing agents is an important approach in the clinic. The aim of this study was to examine the effects of CJZ3, a lomerizine derivative, on the inhibition of P‐gp function and P‐gp‐mediated MDR in K562/DOX cells and parental K562 cells. Incubation of K562/DOX cells with CJZ3 caused a marked increase in accumulation and uptake and a notable decrease in efflux of Rh123, No such results were found in parental K562 cells. The inhibitory effect of the agent on P‐gp function was reversible, but it persisted for at least 90 min after removal of 2.5 &µM CJZ3 from the incubation medium. The doxorubicin‐induced cytotoxicity, apoptosis, and cell‐cycle perturbations were significantly potentiated by CJZ3. The intracellular accumulation of doxorubicin was enhanced in the presence of various concentrations of CJZ3. The CJZ3 exhibited potent effects in vitro in the reversal of P‐gp‐mediated MDR, suggesting that the compound may be an effective MDR reversing agent in cancer chemotherapy. Drug Dev. Res. 67:862–869, 2006. © 2007 Wiley‐Liss, Inc.     

Susceptibility of nanoparticle-encapsulated paclitaxel to P-glycoprotein-mediated drug efflux

Overexpression of P-glycoprotein (P-gp) is a key factor contributing to the development of multidrug resistance (MDR) in cancer cells. The objective of the study is to investigate whether a P-gp substrate, paclitaxel, delivered to MDR tumor cells in poly(d,l-lactide-co-glycolide) (PLGA) nanoparticles is susceptible to P-gp – mediated drug efflux. Paclitaxel-loaded nanoparticles were formulated by emulsion-solvent evaporation technique. Nanoparticles had a mean hydrodynamic diameter of about 195 nm, and demonstrated sustained release of paclitaxel. In vitro cell culture studies indicated that paclitaxel nanoparticles result in sustained, dose-dependent and significant cytotoxicity in drug-sensitive MCF-7 tumor cells but not in drug-resistant NCI-ADR/RES cells. Resistance to nanoparticle-encapsulated paclitaxel was reversed by verapamil, a P-gp inhibitor. Further, sustained inhibition of P-gp was necessary for sustaining the cytotoxicity of nanoparticle-encapsulated paclitaxel in drug-resistant cells. Inhibition of P-gp by verapamil did not significantly affect the uptake or retention of nanoparticles in drug-resistant cells. In conclusion, our studies suggest that P-gp substrates, such as paclitaxel, delivered to MDR cells by PLGA nanoparticles, are susceptible to efflux by P-gp. Inhibition of P-gp restores sensitivity to paclitaxel; however, sustained inhibition of P-gp is required for sustained therapeutic efficacy of nanoparticle-encapsulated drug.     

CJX2, an amlodipine derivative,reverses p‐glycoprotein‐mediated multidrug‐resistance in doxorubicin‐resistant human myelogenous leukemia (K562/DOX) cells

P‐glycoprotein‐mediated drug efflux can yield a multidrug‐resistance (MDR) phenotype that is associated with a poor response to cancer chemotherapy. Development of safe and effective MDR‐reversing agents is an important approach in the clinic. The aim of this study was to observe the effects of CJX2, an amlodipine derivative, on the inhibition of P‐gp function and P‐gp‐mediated MDR in K562/DOX cells and parental K562 cells. Based on the flow cytometric technology, the uptake, accumulation, and efflux of rhodamine123 (Rh123) were detected in these cells by measuring Rh123‐associated mean fluorescence intensity (MFI). The effects of CJX2 on the doxorubicin cytotoxicity were evaluated by assaying for MTT (3‐(4,5‐dimethylthiazol)‐2,5‐diphenyltetrazolium bromide) reduction and the reversal fold (RF) values. The DNA content, percentage of apoptosis, and cell cycle analysis were monitored with flow cytometry. Intracellular accumulation of doxorubicin was also assessed by the determination of doxorubicin‐associated MFI. Verapamil was employed as a comparative agent. Incubation of K562/DOX cells with CJX2 caused a marked increase in accumulation, uptake, and a notable decrease in efflux of Rh123. No such results were found in parental K562 cells. The inhibitory effect of the agent on P‐gp function was reversible, but it persisted at least for 90 min after removal of 2.5 µM CJX2 from incubation medium. The doxorubicin‐induced cytotoxicity, apoptosis, and cell cycle perturbations were significantly potentiated by CJX2. The intracellular accumulation of doxorubicin was enhanced in the presence of various concentrations of CJX2. The CJX2 exhibited potent effects in vitro in the reversal of P‐gp‐mediated MDR, suggesting that the compound may become a candidate for an effective MDR‐reversing agent in cancer chemotherapy. Drug Dev. Res. 66:278–285, 2006. © 2006 Wiley‐Liss, Inc.     

氟哌啶醇对人红白血病耐多柔比星细胞株多药耐药性的逆转及其机制

目的　从临床常用药物中探寻逆转肿瘤耐药性的活性物质。方法　应用MTT法测定不同浓度Hal处理的瘤细胞对 0～ 2 0 μmol·L- 1多柔比星 (Dox)的敏感性的影响。RT PCR法分析 12 .5 μmol·L- 1氟哌啶醇 (Hal)处理后多药耐药基因 (MDR1) ,多药耐药相关蛋白 (MRP)和谷胱甘肽S转移酶Pi(GSTπ)mRNA表达的变化。通过流式细胞术观察 0 ,6 .2 5 ,12 .5 ,2 5 μmol·L- 1Hal对细胞内药物蓄积和细胞周期进程的影响。结果　Hal对K5 6 2 /Dox的耐药性具有明显的逆转作用。在 12 .5 ,6 .2 5及 3.12 5 μmol·L- 1时的逆转倍数分别为 8.35 ,4 .2 1及 2 .16。用 12 .5μmol·L- 1Hal处理后 ,MDR1及MRP的mRNA表达水平均呈现时间依赖性明显降低 ,分别较原水平下降76 .3%及 6 4.6 %。药后d 2GSTπmRNA表达下降6 6 .1% ,于d 3回升。Hal处理细胞lh后 ,Dox在细胞内蓄积量明显增加 ,并呈浓度依赖性 ;此外 ,Hal可明显增强Dox对K5 6 2 /Dox细胞的G2 /M阻滞作用 ,12 .5 μmol·L- 1浓度可以使 5 μmol·L- 1Dox的G2 /M阻断由单独应用时的 9.9%± 4 .3%增加到2 3.4 %± 3.0 %。结论　Hal具有较强的逆转K5 6 2 /Dox细胞MDR的作用 ,其逆转机制为多种途径 ,包括相关基因mRNA的表达下调 ,增加细胞内药物蓄积 ,增强Dox对K5 6 2 /Dox在G2     

洛美利嗪衍生物CJZ3对K562/DOX细胞阿霉素耐药的逆转作用

目的研究洛美利嗪衍生物CJZ3对K562/DOX细胞阿霉素耐药的逆转作用。方法应用流式细胞仪和MTT法观察了CJZ3对K562/DOX细胞P-糖蛋白(P-glycoprotein,P-gp)的抑制作用及对K562/DOX细胞阿霉素耐药的逆转作用。结果CJZ3能剂量相关性地增加K562/DOX细胞对罗丹明123(rhodamine123,Rh123)的摄取以及细胞内罗丹明Rh123的累计,明显抑制P-gp介导的Rh123外排,增强阿霉素对K562/DOX细胞的细胞毒作用,提高阿霉素诱导的K562/DOX细胞凋亡率,提高细胞Caspase-3活性,增加K562/DOX细胞内阿霉素水平。结论洛美利嗪衍生物CJZ3体外能明显抑制P-gp的外排功能,逆转P-gp介导的K562/DOX细胞的多药耐药性。     

Analysis of drug transport kinetics in multidrug-resistant cells: implications for drug action

Multidrug resistance (MDR) in model systems is known to be conferred by two different integral proteins--the 170-kDa P-glycoprotein (P-gp) and the 190-kDa multidrug resistance-associated protein (MRP1)--that pump drugs out of MDR cells. The intracellular level of a drug, which influences the drug's cytotoxic effect, is a function of the amount of drug transported inside the cell (influx) and the amount of drug expelled from the cell (efflux). One possible pharmacological approach to overcoming drug resistance is the use of specific inhibitors that enhance the cytotoxicity of known antineoplastic agents. Many compounds have been proven to be very efficient in inhibiting P-gp activity, but only some of them can inhibit MRP1. However, the clinical results obtained so far by this approach have been rather disappointing. The other likely approach is based on the design and synthesis of new non-cross-resistant drugs whose physicochemical properties favor the uptake of such drug by resistant cells. Our recent studies have shown that whereas the P-gp- and MRP1-mediated efflux of different anthracycline-based drugs may not differ considerably, their kinetics of uptake do. Thus, the high uptake of drug by cells may lead to concentrations at the cellular target site high enough to achieve the needed cytotoxicity against MDR cells. Therefore, increased drug lipophilicity might be one factor in improving drug cytotoxicity in MDR cells. In vitro studies have shown that idarubicin, an analogue of daunorub cin, is more effective than daunorubicin and doxorubicin against MDR tumor cell lines and that this increased effectiveness is related in part to the increased lipophilicity of idarubicin. Other studies have also confirmed the strong impact of lipophilicity on the uptake and retention of anthracyclines in MDR cells.     

洛美利嗪对人白血病细胞K562/ADM多药耐药的逆转作用

目的：研究洛美利嗪(lomerizine，Lom)对人白血病细胞K562／ADM多药耐药逆转作用及机制。方法：使用MTT法检测Lom对K562／ADM多药耐药细胞柔红霉素(DNR)细胞毒性的影响，使用荧光分光光度计和流式细胞术分析Lom对K562／ADM多药耐药细胞胞内P—糖蛋白(P—glycoprotein，P—gp)底物—罗丹明123(rhodamine 123，Rh123)的累积情况。结果：Lom能明显提高DNR对K562／ADM多药耐药细胞的细胞毒作用，并可使胞内Rh123的浓度增加。K562敏感细胞株则不受影响。结论：Lom能显地抑制：K562／ADM多药耐药细胞上P—gp的活性，提高P—gp底物的胞内浓度，并增强其他抗癌药的细胞毒作用。     

Effect simultaneous delivery with P-glycoprotein inhibitor and nanoparticle administration of doxorubicin on cellular uptake and in vitro anticancer activity

Multidrug resistance (MDR) is the most common problem of inadequate therapeutic response in tumor cells. Many trials has been developed to overcome drug efflux by P-glycoprotein (P-gp). For instance, co-administration of a number of drugs called chemosensitizers or MDR modulators with a chemotherapeutic agent to inhibit drug efflux. But for optimal synergy, the drug and inhibitor combination may need to be temporally colocalized in the tumor cells. In this study, we encapsulated the Ver and Dox in PLGA nanoparticles to inhibit the P-gp drug efflux in breast cancer. Moreover, the effect of either Dox solution (Dox_S), Dox nanoparticles (Dox_NP), Dox_S + Ver_S, Dox_NP + Ver_S, Dox_NP + Ver_NP or Dox-Ver_NP was evaluated. It was found that co administration of Dox_NP with Ver_NP (70.76%) showed similar cellular uptake of Dox to Dox/Ver combination solution (70.62%). However it is observed that Dox_NP + Ver_NP has the highest apoptotic activity (early apoptotic 13.52 ± 0.06%, late apoptotic 53.94 ± 0.15%) on human breast adenocarcinoma (MCF 7) cells. Hence, it is suggested that Dox_NP + Ver_NP is a promising administration for tumor therapy.