Mechanisms and strategies to overcome multiple drug resistance in cancer

The role of aldehyde dehydrogenase (ALDH) in cancer drug resistance

Chemotherapy in cancer patients is still not satisfactory because of drug resistance. The main mechanism of drug resistance results from the ability of cancer cells to actively expel therapeutic agents via transport proteins of the ABC family. ABCB1 and ABCG2 are the two main proteins responsible for drug resistance in cancers. Recent investigations indicate that aldehyde dehydrogenase (ALDH) can also be involved in drug resistance. Expression of the ABC transporters and ALDH enzymes is observed in normal stem cells, cancer stem cells and drug resistant cancers. Current chemotherapy regimens remove the bulk of the tumour but are usually not effective against cancer stem cells (CSCs) expressing ALDH. As a result, the number of ALDH positive drug resistant CSCs increases after chemotherapy. This indicates that therapies targeting drug resistant CSCs should be developed. A number of therapies targeting CSCs are currently under investigation. These therapies include differentiation therapy using different retinoic acids (RA) as simple agents or in combination with DNA methyltransferase inhibitors (DNMTi) and/or histone deacetylase inhibitors (HDACi). Therapies that target cancer stem cell signaling pathways are also under investigation. A number of natural compounds are effective against cancer stem cells and lead to decreasing numbers of ALDH positive cells and downregulation of the ABC proteins. Combinations of differentiation therapies or therapies targeting CSC signaling pathways with classical cytostatics seem promising. This review discusses the role of ALDH and ABC proteins in the development of drug resistance in cancer and current therapies designed to target CSCs.

Nanostructured lipid carriers as multifunctional nanomedicine platform for pulmonary co-delivery of anticancer drugs and siRNA

We developed, synthesized, and tested a multifunctional nanostructured lipid nanocarrier-based system (NLCS) for efficient delivery of an anticancer drug and siRNA directly into the lungs by inhalation. The system contains: (1) nanostructured lipid carriers (NLC); (2) anticancer drug (doxorubicin or paclitaxel); (3) siRNA targeted to MRP1 mRNA as a suppressor of pump drug resistance; (4) siRNA targeted to BCL2 mRNA as a suppressor of nonpump cellular resistance and (5) a modified synthetic analog of luteinizing hormone-releasing hormone (LHRH) as a targeting moiety specific to the receptors that are overexpressed in the plasma membrane of lung cancer cells. The NLCS was tested in vitro using human lung cancer cells and in vivo utilizing mouse orthotopic model of human lung cancer. After inhalation, the proposed NLCS effectively delivered its payload into lung cancer cells leaving healthy lung tissues intact and also significantly decreasing the exposure of healthy organs when compared with intravenous injection. The NLCS showed enhanced antitumor activity when compared with intravenous treatment. The data obtained demonstrated high efficiency of proposed NLCS for tumor-targeted local delivery by inhalation of anticancer drugs and mixture of siRNAs specifically to lung cancer cells and, as a result, efficient suppression of tumor growth and prevention of adverse side effects on healthy organs.

Shugoshin1 enhances multidrug resistance of gastric cancer cells by regulating MRP1, Bcl-2, and Bax genes

Multidrug resistance (MDR) is a major clinical obstacle in treatment of gastric cancer (GC) and it accounts for the majority of cancer-related mortalities. Shugoshin1 (SGO1) is an important player in appropriate chromosome segregation and is involved in tumorigenesis. In this study, we found endogenous SGO1 overexpression in the multidrug-resistant GC cell lines SGC7901/VCR and SGC7901/ADR compared with their parental cell line SGC7901. By enhancing expression of SGO1, sensitivity of SGC7901 cells to vincristine (VCR), adriamycin, 5-fluorouracil (5-FU), and cisplatin (CDDP) was significantly diminished. Silencing its expression resulted in enhanced sensitivity of SGC7901/VCR and SGC7901/ADR cells to these antitumor drugs. Additionally, we confirmed that SGO1 increased capacity of cells to enable adriamycin (ADR) efflux and inhibit drug-induced apoptosis by regulating MRP 1, Bcl-2, and Bax genes so as to confer a MDR phenotype to GC cells. In brief, these findings suggest that SGO1 promotes MDR of GC cells and may be useful as a novel therapeutic target for preventing or reversing MDR.

5'-ectonucleotidase mediates multiple-drug resistance in glioblastoma multiforme cells

Glioblastoma multiforme (GBM) cells are characterised by their extreme chemoresistance. The activity of multiple-drug resistance (MDR) transporters that extrude antitumor drugs from cells plays the most important role in this phenomenon. To date, the mechanism controlling the expression and activity of MDR transporters is poorly understood. Activity of the enzyme ecto-5'-nucleotidase (CD73) in tumor cells, which hydrolyses AMP to adenosine, has been linked to immunosuppression and prometastatic effects in breast cancer and to the proliferation of glioma cells. In this study, we identify a high expression of CD73 in surgically resected samples of human GBM. In primary cultures of GBM, inhibition of CD73 activity or knocking down its expression by siRNA reversed the MDR phenotype and cell viability was decreased up to 60% on exposure to the antitumoral drug vincristine. This GBM chemosensitization was caused by a decrease in the expression and activity of the multiple drug associated protein 1 (Mrp1), the most important transporter conferring multiple drug resistance in these cells. Using pharmacological modulators, we have recognized the adenosine A(3) receptor subtype in mediation of the chemoresistant phenotype in these cells. In conclusion, we have determined that the activity of CD73 to trigger adenosine signaling sustains chemoresistant phenotype in GBM cells.

Microarray-based detection and expression analysis of ABC and SLC transporters in drug-resistant ovarian cancer cell lines

Multiple drug resistance of cancer cells is multifactorial. A microarray technique may provide information about new candidate genes playing a role in drug resistance. Drug membrane transporters from ABC and SLC families play a main role in this phenomenon. This study demonstrates alterations in ABC and SLC gene expression levels in methotrexate, cisplatin, doxorubicin, vincristine, topotecan and paclitaxel-resistant variant of W1 ovarian cancer cell line. Resistant W1 cell lines were derived by stepwise selection of cells in increasing concentration of drugs. Affymetrix GeneChip(®) Human Genome U219 Array Strip was used for hybridizations. Statistical significance was determined by independent sample t-test. The genes having altered expression levels in drug-resistant sublines were selected and filtered by scater plot. Genes up/downregulated more than threefolds were selected and listed. Among ABC genes, seven were upregulated and three were downregulated. Three genes: ABCB1, ABCB4 and ABCG2 were upregulated very significantly (over tenfold). One ABCA8 was significantly downregulated. Among 38 SLC genes, 18 were upregulated, 16 were downregulated and four were up- or downregulated dependent on the cell line. Expression of 10 SLC genes was changed very significantly (over tenfold). Four genes were significantly increased: SLC6A1, SLC9A2, SLC12A1, SLC16A6 and six genes were significantly decreased: SLC2A14, SLC7A3, SLC7A8, SLC7A11, SLC16A14, SLC38A9. Based on the expression profiles, our results provide a preliminary insight into the relationship between drug resistance and expression of membrane transporters involved in drug resistance. Correlation of specific drug transporter with drug resistance requires further analysis.

Potentiating effect of the flavonolignan (-)-hydnocarpin in combination with vincristine in a sensitive and P-gp-expressing acute lymphoblastic leukemia cell line

The potentiating action of the flavonolignan, (-)-hydnocarpin, in combination with vincristine was evaluated in the 697 acute lymphoblastic leukemia cell line and a P-gp-expressing variant, 697-R. Vincristine at 3 nM caused nearly complete growth inhibition in 697 cells versus a 17% growth inhibition in 697-R cells. When combined with (-)-hydnocarpin at concentrations of 10 and 5 μM, vincristine-mediated growth inhibition in the 697-R cells increased significantly over the sum of the individual agents to 72% (p ≤ 0.0001) and 41% (p = 0.0256), respectively. Vincristine at 1.5 nM (66% growth inhibition) and 0.75 nM (39% growth inhibition) combined with (-)-hydnocarpin at 10 μM (42% growth inhibition) in the 697 cells caused a significant increase in growth inhibition to 83% (p = 0.03) and to 61% (p < 0.0001), respectively, when compared to vincristine treatment as a single agent. To investigate the mechanism for the vincristine re-sensitization caused by (-)-hydnocarpin, the P-gp inhibitory effect of (-)-hydnocarpin was evaluated.

MDR gene expression analysis of six drug-resistant ovarian cancer cell lines

Ovarian cancer is the leading cause of death among gynaecological malignancies. Multiple drug resistance makes cancer cells insensitive to chemotherapy. In this study, we developed six primary ovarian cancer cell lines (W1MR, W1CR, W1DR, W1VR, W1TR, and W1PR) resistant to drugs such as methotrexate, cisplatin, doxorubicin, vincristine, topotecan, and paclitaxel. A chemosensitivity assay MTT test was performed to assess drug cross-resistance. Quantitative real-time polymerase chain reaction and Western blot were also performed to determine mRNA and protein expression of genes involved in chemoresistance. We observed high cross-resistance to doxorubicin, vincristine, and paclitaxel in the cell lines resistant to these agents. We also found a significant correlation between resistance to these drugs and increased expression of P-gp. Two different mechanisms of topotecan resistance were observed in the W1TR and W1PR cell lines. We did not observe any correlation between MRP2 transcript and protein levels. Cell lines resistant to agents used in ovarian cancer treatment remained sensitive to methotrexate. The main mechanisms of drug resistance were due to P-gp expression in the doxorubicin, vincristine, and paclitaxel resistant cell lines and BCRP expression in the topotecan resistant cell line.

Signal transduction pathways and transcriptional mechanisms of ABCB1/Pgp-mediated multiple drug resistance in human cancer cells

Multiple drug resistance (MDR), defined as the ability of tumour cells to survive exposure to many chemotherapeutic agents, is a major cause of treatment failure in human cancers. The membrane transporter P-glycoprotein (Pgp, encoded by the ABCB1 [adenosine triphosphate-binding cassette, subfamily B, member 1] gene) is the main mechanism for decreased intracellular drug accumulation in human MDR cancer. ABCB1/Pgp-mediated MDR involves several signal transduction pathways and transcription factors. Activation of these signal transduction pathways influences the prognosis of MDR human cancer. Signalling pathways involved in ABCB1/Pgp-mediated MDR include the mitogen-activated protein kinase (MAPK), c-Jun NH(2)-terminal kinase (JNK), p38, cyclic adenosine monophosphate-dependent protein kinase, phosphatidylino sitol 3-kinase and protein kinase C signalling pathways. This review summarizes the biological characteristics, target points and signalling cascade mediators of these pathways. Drugs targeted against these pathways may provide new therapies for treatment of ABCB1/Pgp-mediated MDR.

Doxorubicin influences the expression of glucosylceramide synthase in invasive ductal breast cancer

Introduction

Glucosylceramide synthase (GCS) is one enzyme that provides a major route for ceramide clearance. Recent evidence has indicated an important role for GCS in multidrug resistance (MDR) tumors. Doxorubicin (DOX)can modulate the expression of GCS in leukemia and ovary cell lines. However, few studies have investigated their relationship in breast cancer;

Methods

We collected 84 excision biopsies from patients with invasive ductal breast cancer of whom 33 patients had undergone preoperative chemotherapy. Immunohistochemistry was used to analyze the expression of GCS protein and significantly showed that the expression of GCS was higher in the samples from patients treated with preoperative chemotherapy(p = 0.018). In order to investigate the underlying mechanism, breast cancer cell lines were cultured with different concentrations of DOX, and mRNA and protein levels of GCS were then detected;

Results

DOX significantly upregulated the expression of GCS at both the mRNA and protein level in ERα-positive MCF-7 cells.We then block down the Sp1 site of GCS promoter, which inhibited the DOX-mediated increase in GCS expression; and after Erα was inhibited in MCF-7 cells, the up-regulation of GCS by DOX also been inhibited.

Conclusions

In conclusion, our data demonstrated the novel finding that DOX could modulate the expression of GCS through the Sp1 site of GCS promoter in ERα-positive breast cancer cells.

Overview of P-glycoprotein inhibitors: a rational outlook

P-glycoprotein (P-gp), a transmembrane permeability glycoprotein, is a member of ATP binding cassette (ABC) super family that functions specifically as a carrier mediated primary active efflux transporter. It is widely distributed throughout the body and has a diverse range of substrates. Several vital therapeutic agents are substrates to P-gp and their bioavailability is lowered or a resistance is induced because of the protein efflux. Hence P-gp inhibitors were explored for overcoming multidrug resistance and poor bioavailability problems of the therapeutic P-gp substrates. The sensitivity of drug moieties to P-gp and vice versa can be established by various experimental models in silico, in vitro and in vivo. Ever since the discovery of P-gp, the research plethora identified several chemical structures as P-gp inhibitors. The aim of this review was to emphasize on the discovery and development of newer, inert, non-toxic, and more efficient, specifically targeting P-gp inhibitors, like those among the natural herb extracts, pharmaceutical excipients and formulations, and other rational drug moieties. The applications of cellular and molecular biology knowledge, in silico designed structural databases, molecular modeling studies and quantitative structure-activity relationship (QSAR) analyses in the development of novel rational P-gp inhibitors have also been mentioned.

Reversal effects of pantoprazole on multidrug resistance in human gastric adenocarcinoma cells by down-regulating the V-ATPases/mTOR/HIF-1α/P-gp and MRP1 signaling pathway in vitro and in vivo

To investigate reversal effects of pantoprazole (PPZ) on multidrug resistance (MDR) in human gastric adenocarcinoma cells in vivo and in vitro. Human gastric adenocarcinoma cell SGC7901 was cultured in RPMI-1640 medium supplemented with 10% fetal bovine serum and antibiotics in a humidified 5% CO(2) atmosphere at 37°C. Adriamycin (ADR)-resistant cells were cultured with addition of 0.8 µg/ml of ADR maintaining MDR phenotype. ADR was used to calculate ADR releasing index; CCK-8 Assay was performed to evaluate the cytotoxicity of anti-tumor drugs; BCECF-AM pH-sensitive fluorescent probe was used to measure intracellular pH (pHi) value of cells, whereas pH value of medium was considered as extracellular pH (pHe) value; Western blotting and immunofluorescent staining analyses were employed to determine protein expressions and intracellular distributions of vacuolar H(+) -ATPases (V-ATPases), mTOR, HIF-1α, P-glycoprotein (P-gp), and multidrug resistant protein 1 (MRP1); SGC7901 and SGC7901/ADR cells were inoculated in athymic nude mice. Thereafter, effects of ADR with or without PPZ pretreatment were compared by determining the tumor size and weight, apoptotic cells in tumor tissues were detected by TUNEL assay. At concentrations greater than 20 µg/ml, PPZ pretreatment reduced ADR releasing index and significantly enhanced intracellular ADR concentration of SGC7901 (P < 0.01). Similarly, PPZ pretreatment significantly decreased ADR releasing index of SGC7901/ADR dose-dependently (P < 0.01). PPZ pretreatment also decreased cell viabilities of SGG7901 and SGC7901/ADR dose-dependently. After 24-h PPZ pretreatment, administration of chemotherapeutic agents demonstrated maximal cytotoxic effects on SGC7901 and SGC7901/ADR cells (P < 0.05). The resistance index in PPZ pretreatment group was significantly lower than that in non-PPZ pretreatment group (3.71 vs. 14.80). PPZ at concentration >10 µg/ml significantly decreased pHi in SGC7901 and SGC7901/ADR cells and diminished or reversed transmembrane pH gradient (P < 0.05). PPZ pretreatment also significantly inhibited protein expressions of V-ATPases, mTOR, HIF-1α, P-gp, and MRP1, and alter intracellular expressions in parent and ADR-resistant cells (P < 0.05). In vivo experiments further confirmed that PPZ pretreatment could enhance anti-tumor effects of ADR on xenografted tumor of nude mice and also improve the apoptotic index in xenografted tumor tissues. PPZ pretreatment enhances the cytotoxic effects of anti-tumor drugs on SGC7901 and reverse MDR of SGC7901/ADR by downregulating the V-ATPases/mTOR/HIF-1α/P-gp and MRP1 signaling pathway.

Flow cytometry-based assessment of mitoxantrone efflux from leukemic blasts varies with response to induction chemotherapy in acute myeloid leukemia

BACKGROUND

Accurate prediction of chemotherapy drug resistance would aid treatment decisions in acute myeloid leukemia (AML). The aim of this study was to determine if mitoxantrone efflux from AML blasts would correlate with response to induction chemotherapy.

METHODS

Flow cytometry was used to measure the median fluorescence intensity (MFI) for AML blasts incubated with mitoxantrone [an ATP-binding cassette (ABC) transporter substrate] with or without coincubation with cyclosporine A (a broad-spectrum inhibitor of ABC transporters) and a ratio (MFIR) between the inhibited and uninhibited MFI was calculated.

RESULTS

Among 174 AML patient blast samples, the mean MFIR for complete remission (CR) patients was lower than that obtained for induction failure (IF) patients (mean MFIR ± SD 1.62 ± 0.53 for CR after one cycle of chemotherapy vs. 2.22 ± 1.29 for CR after two cycles and 2.59 ± 0.98 for IF, P < 0.001). Logistic regression analysis determined 2.45 as the MFIR threshold above which 29% of patients achieved CR vs. a CR rate of 84% when the MFIR was ≤ 2.45 (P < 0.0001). In AML patients with normal karyotype (n = 80), CR was obtained for 33% of patients with an MFIR > 2.45 vs. 89% of those with MFIR ≤ 2.45 (P < 0.0001). In patients > age 60 (n = 77), 30% vs. 87% of those with MFIR > vs. ≤ 2.45 achieved CR (P < 0.0001).

CONCLUSIONS

This assay of ABC transporter function can potentially predict response to induction chemotherapy in AML.

Special AT-rich sequence binding protein 1 regulates the multidrug resistance and invasion of human gastric cancer cells

Special AT-rich sequence binding protein 1 (SATB1) is a nuclear factor that functions as a global chromatin organizer to regulate gene expression. Recent studies have suggested an oncogenic role of SATB1 in breast cancer. However, the role of SATB1 in gastric cancer, especially in regulating the malignant phenotypes, including multidrug resistance (MDR) and metastasis, remains poorly understood. In this study, the aggressive human gastric cancer cell line SGC7901 and its corresponding MDR variant SGC7901/VCR cells were used as a model. SATB1 expression was examined by RT-PCR and western blot analysis. Results showed that SATB1 was upregulated in SGC7901/VCR cells. An in vitro drug sensitivity assay demonstrated a positive correlation between SATB1 expression levels and drug resistance. Gain and loss of SATB1 function experiments further demonstrated that SATB1 contributes to MDR by inhibiting the accumulation of vincristine (VCR) in gastric cancer cells and protecting the cells from VCR-induced apoptosis. In addition, SATB1 may promote the invasion of gastric cancer cells. The present study provides a novel insight into the oncogenic role of SATB1 in gastric cancer, suggesting that SATB1 is a promising target for the therapy of drug-resistant and invasive gastric cancer.

alpha-Mangostin enhances betulinic acid cytotoxicity and inhibits cisplatin cytotoxicity on HCT 116 colorectal carcinoma cells

Despite the progress in colon cancer treatment, relapse is still a major obstacle. Hence, new drugs or drug combinations are required in the battle against colon cancer. α-Mangostin and betulinic acid (BA) are cytotoxic compounds that work by inducing the mitochondrial apoptosis pathway, and cisplatin is one of the most potent broad spectrum anti-tumor agents. This study aims to investigate the enhancement of BA cytotoxicity by α-mangostin, and the cytoprotection effect of α-mangostin and BA on cisplatin-induced cytotoxicity on HCT 116 human colorectal carcinoma cells. Cytotoxicity was investigated by the XTT cell proliferation test, and the apoptotic effects were investigated on early and late markers including caspases-3/7, mitochondrial membrane potential, cytoplasmic shrinkage, and chromatin condensation. The effect of α-mangostin on four signalling pathways was also investigated by the luciferase assay. α-Mangostin and BA were more cytotoxic to the colon cancer cells than to the normal colonic cells, and both compounds showed a cytoprotective effect against cisplatin-induced cytotoxicity. On the other hand, α-mangostin enhanced the cytotoxic and apoptotic effects of BA. Combination therapy hits multiple targets, which may improve the overall response to the treatment, and may reduce the likelihood of developing drug resistance by the tumor cells. Therefore, α-mangostin and BA may provide a novel combination for the treatment of colorectal carcinoma. The cytoprotective effect of the compounds against cisplatin-induced cytotoxicity may find applications as chemopreventive agents against carcinogens, irradiation and oxidative stress, or to neutralize cisplatin side effects.

Starvation, detoxification, and multidrug resistance in cancer therapy

The selection of chemotherapy drugs is based on the cytotoxicity to specific tumor cell types and the relatively low toxicity to normal cells and tissues. However, the toxicity to normal cells poses a major clinical challenge, particularly when malignant cells have acquired resistance to chemotherapy. This drug resistance of cancer cells results from multiple factors including individual variation, genetic heterogeneity within a tumor, and cellular evolution. Much progress in the understanding of tumor cell resistance has been made in the past 35 years, owing to milestone discoveries such as the identification and characterization of ABC transporters. Nonetheless, the complexity of the genetic and epigenetic rewiring of cancer cells makes drug resistance an equally complex phenomenon that is difficult to overcome. In this review, we discuss how the remarkable changes in the levels of glucose, IGF-I, IGFBP-1 and in other proteins caused by fasting have the potential to improve the efficacy of chemotherapy against tumors by protecting normal cells and tissues and possibly by diminishing multidrug resistance in malignant cells.

Regulation of xenobiotic transporter genes in liver and brain of juvenile thicklip grey mullets (Chelon labrosus) after exposure to Prestige-like fuel oil and to perfluorooctane sulfonate

Xenobiotic transport proteins are involved in cellular defence against accumulation of xenobiotics participating in multixenobiotic resistance (MXR). In order to study the transcriptional regulation of MXR genes in fish exposed to common chemical pollutants we selected the thicklip grey mullet (Chelon labrosus), since mugilids are widespread in highly degraded estuarine environments where they have to survive through development and adulthood. Partial sequences belonging to genes coding for members of 3 different families of ATP binding cassette (ABC) transporter proteins (ABCB1; ABCB11; ABCC2; ABCC3; ABCG2) and a vault protein (major vault protein, MVP) were amplified and sequenced from mullet liver. Their liver and brain transcription levels were examined in juvenile mullets under exposure to perfluorooctane sulfonate (PFOS) and to fresh (F) and weathered (WF) Prestige-like heavy fuel oil for 2 and 16 days. In liver, PFOS significantly up-regulated transcription of abcb1, abcb11 and abcg2 while in brain only abcb11 was up-regulated. Both fuel treatments significantly down-regulated abcb11 in liver at day 2 while abcc2 was only down-regulated by WF. mvp was significantly up-regulated by F and down-regulated by WF at day 2 in the liver. At day 16 only a significant up-regulation of abcb1 in the F group was recorded. Brain abcc3 and abcg2 were down-regulated by both fuels at day 2, while abcb1 and abcc2 were only down-regulated by F exposure. After 16 days of exposure only abcb11 and abcg2 were regulated. In conclusion, exposure to organic xenobiotics significantly alters transcription levels of genes participating in xenobiotic efflux, especially after short periods of exposure. Efflux transporter gene transcription profiling could thus constitute a promising tool to assess exposure to common pollutants.

HIF-1 activation induces doxorubicin resistance in MCF7 3-D spheroids via P-glycoprotein expression: a potential model of the chemo-resistance of invasive micropapillary carcinoma of the breast

Background

Invasive micropapillary carcinoma (IMPC) of the breast is a distinct and aggressive variant of luminal type B breast cancer that does not respond to neoadjuvant chemotherapy. It is characterized by small pseudopapillary clusters of cancer cells with inverted cell polarity. To investigate whether hypoxia-inducible factor-1 (HIF-1) activation may be related to the drug resistance described in this tumor, we used MCF7 cancer cells cultured as 3-D spheroids, which morphologically simulate IMPC cell clusters.

Methods

HIF-1 activation was measured by EMSA and ELISA in MCF7 3-D spheroids and MCF7 monolayers. Binding of HIF-1α to MDR-1 gene promoter and modulation of P-glycoprotein (Pgp) expression was evaluated by ChIP assay and FACS analysis, respectively. Intracellular doxorubicin retention was measured by spectrofluorimetric assay and drug cytotoxicity by annexin V-FITC measurement and caspase activity assay.

Results

In MCF7 3-D spheroids HIF-1 was activated and recruited to participate to the transcriptional activity of MDR-1 gene, coding for Pgp. In addition, Pgp expression on the surface of cells obtained from 3-D spheroids was increased. MCF7 3-D spheroids accumulate less doxorubicin and are less sensitive to its cytotoxic effects than MCF7 cells cultured as monolayer. Finally, HIF-1α inhibition either by incubating cells with 3-(5'-hydroxymethyl-2'-furyl)-1-benzylindazole (a widely used HIF-1α inhibitor) or by transfecting cells with specific siRNA for HIF-1α significantly decreased the expression of Pgp on the surface of cells and increased the intracellular doxorubicin accumulation in MCF7 3-D spheroids.

Conclusions

MCF7 breast cancer cells cultured as 3-D spheroids are resistant to doxorubicin and this resistance is associated with an increased Pgp expression in the plasma membrane via activation of HIF-1. The same mechanism may be suggested for IMPC drug resistance.

Nanohybrid systems of non-ionic surfactant inserting liposomes loading paclitaxel for reversal of multidrug resistance

Three new nanohybrid systems of non-ionic surfactant inserting liposomes loading paclitaxel (PTX) (NLPs) were prepared to overcome multidrug resistance (MDR) in PTX-resistance human lung cancer cell line. Three non-ionic surfactants, Solutol HS 15 (HS-15), pluronic F68 (PF-68) and cremophor EL (CrEL) were inserted into liposomes by film hydration method to form NLPs with an average size of around 110, 180 and 110 nm, respectively. There was an obvious increase of rhodamin 123 (Rh123) accumulation in A549/T cells after treated with nanohybrid systems loading Rh123 (NLRs) when compared with free Rh123 or liposomes loading Rh123 without surfactants (LRs), which indicated the significant inhibition effects of NLRs on drug efflux. The P-gp detection and ATP determination demonstrated that BNLs could not only interfere P-gp expression on the membrane of drug resistant cells, but also decrease ATP level in the cells. The cytotoxicity of NLPs against A549/T cells was higher than PTX loaded liposomes without surfactants (LPs), and the best result was achieved after treated with NLPs2. The apoptotic assay and the cell cycle analysis showed that NLPs could induce more apoptotic cells in drug resistant cells when compared with LPs. These results suggested that NLPs could overcome MDR by combination of drug delivery, P-gp inhibition and ATP depletion, and showed potential for treatment of MDR.

On the selectivity and efficacy of defense peptides with respect to cancer cells

Here, we review potential determinants of the anticancer efficacy of innate immune peptides (ACPs) for cancer cells. These determinants include membrane-based factors, such as receptors, phosphatidylserine, sialic acid residues, and sulfated glycans, and peptide-based factors, such as residue composition, sequence length, net charge, hydrophobic arc size, hydrophobicity, and amphiphilicity. Each of these factors may contribute to the anticancer action of ACPs, but no single factor(s) makes an overriding contribution to their overall selectivity and toxicity. Differences between the anticancer actions of ACPs seem to relate to different levels of interplay between these peptide and membrane-based factors.

Selenium-induced apoptosis-like cell death in Plasmodium falciparum

Plasmodium falciparum has for some time been developing resistance against known anti-malarial drugs, and therefore a new drug is urgently needed. Selenium (Se), an essential trace element, in the form of inorganic Se, selenite (SeO32−), has been reported to have an anti-plasmodial effect, but its mechanism is still unclear. In the present study, we evaluated the anti-plasmodial effect of several Se compounds against P. falciparum in vitro. The anti-plasmodial effect of several Se compounds was analysed and their apoptosis-inducing activity was evaluated by morphological observation, DNA fragmentation assay and mitochondrial function analysis. SeO32−, methylseleninic acid, selenomethionine and selenocystine have anti-plasmodial effects with 50% inhibition concentration at 9, 10, 45, and 65 μm, respectively, while selenate and methylselenocysteine up to 100 μm have no effect on parasite growth. The effective Se compounds caused the parasites to become shrunken and pyknotic and significantly increased mitochondrial damage against P. falciparum compared to the untreated control. In conclusion, SeO32−, methylseleninic acid, selenomethionine and selenocystine have anti-plasmodial activities that induce apoptosis-like cell death in P. falciparum, and the anti-plasmodial effects of Se seem to be based on its chemical forms. The apoptosis-like cell-death mechanism in P. falciparum can be beneficial to respond to the growing problem of drug resistance.

Chrysin enhances doxorubicin-induced cytotoxicity in human lung epithelial cancer cell lines: the role of glutathione

We hypothesized that flavonoid-induced glutathione (GSH) efflux through multi-drug resistance proteins (MRPs) and subsequent intracellular GSH depletion is a viable mechanism to sensitize cancer cells to chemotherapies. This concept was demonstrated using chrysin (5-25 μM) induced GSH efflux in human non-small cell lung cancer lines exposed to the chemotherapeutic agent, doxorubicin (DOX). Treatment with chrysin resulted in significant and sustained intracellular GSH depletion and the GSH enzyme network in the four cancer cell types was predictive of the severity of chrysin induced intracellular GSH depletion. Gene expression data indicated a positive correlation between basal MRP1, MRP3 and MRP5 expression and total GSH efflux before and after chrysin exposure. Co-treating the cells for 72 h with chrysin (5-30 μM) and DOX (0.025-3.0 μM) significantly enhanced the sensitivity of the cells to DOX as compared to 72-hour DOX alone treatment in all four cell lines. The maximum decrease in the IC(50) values of cells treated with DOX alone compared to co-treatment with chrysin and DOX was 43% in A549 cells, 47% in H157 and H1975 cells and 78% in H460 cells. Chrysin worked synergistically with DOX to induce cancer cell death. This approach could allow for use of lower concentrations and/or sensitize cancer cells to drugs that are typically resistant to therapy.

ABC transporters affect the detection of intracellular oxidants by fluorescent probes

Intracellular production of reactive oxygen species (ROS) plays an important role in the control of cell physiology. For the assessment of intracellular ROS production, a plethora of fluorescent probes is commonly used. Interestingly, chemical structures of these probes imply they could be substrates of plasma membrane efflux pumps, called ABC transporters. This study tested whether the determination of intracellular ROS production and mitochondrial membrane potential by selected fluorescent probes is modulated by the expression and activity of ABC transporters. The sub-clones of the HL-60 cell line over-expressing MDR1, MRP1 and BCRP transporters were employed. ROS production measured by luminol- and L-012-enhaced chemiluminescence and cytochrome c reduction assay showed similar levels of ROS production in all the employed cell lines. It was proved that dihydrorhodamine 123, dihexiloxocarbocyanine iodide, hydroethidine, tetrachloro-tetraethylbenzimidazolocarbo-cyanine iodide and tetramethylrhodamine ethyl ester perchlorate are substrates for MDR1; dichlorodihydrofluoresceine, hydroethidine and tetramethylrhodamine ethyl ester perchlorate are substrates for MRP1; dichlorodihydrofluoresceine, dihydrorhodamine 123, hydroethidine and tetrachloro-tetraethylbenzimidazolocarbo-cyanine iodide are substrates for BCRP. Thus, the determination of intracellular ROS and mitochondrial potential by the selected probes is significantly altered by ABC transporter activities. The activity of these transporters must be considered when employing fluorescent probes for the assessment of ROS production or mitochondrial membrane potential.

Combined use of anticancer drugs and an inhibitor of multiple drug resistance-associated protein-1 increases sensitivity and decreases survival of glioblastoma multiforme cells in vitro

Glioblastoma multiforme (GBM) is a brain tumour characterised by a remarkably high chemoresistance and infiltrating capability. To date, chemotherapy with temozolomide has contributed only poorly to improved survival rates in patients. One of the most important mechanisms of chemoresistance comes about through the activity of certain proteins from the ATP-binding cassette superfamily that extrudes antitumour drugs, or their metabolites, from cells. We identify an increased expression of the multiple drug resistance-associated protein 1 (Mrp1) in glioblastoma multiforme biopsies and in T98G and G44 cell lines. The activity of this transporter was also confirmed by measuring the extrusion of the fluorescent substrate CFDA. The sensitivity of GBM cells was low upon exposure to temozolomide, vincristine and etoposide, with decreases in cell viability of below 20% seen at therapeutic concentrations of these drugs. However, combined exposure to vincristine or etoposide with an inhibitor of Mrp1 efficiently decreased cell viability by up to 80%. We conclude that chemosensitization of cells with inhibitors of Mrp1 activity might be an efficient tool for the treatment of human GBM.

The role of breast cancer stem cells in metastasis and therapeutic implications

Cancer stem cells (CSCs) possess the capacity to self-renew and to generate heterogeneous lineages of cancer cells that comprise tumors. A substantial body of evidence supports a model in which CSCs play a major role in the initiation, maintenance, and clinical outcome of cancers. In contrast, analysis of the role of CSCs in metastasis has been mainly conceptual and speculative. This review summarizes recent data that support the theory of CSCs as the source of metastatic lesions in breast cancer, with a focus on the key role of the microenvironment in the stemness-metastasis link.

A simple and fast microfluidic approach of same-single-cell analysis (SASCA) for the study of multidrug resistance modulation in cancer cells

Due to the cellular heterogeneity in multidrug resistance (MDR) cell populations, positive drug effects on the modulation of MDR can be obscured in conventional methods, especially when only a small number of cells are available. To address cellular variations among different MDR cells, we report a new microfluidic approach to study drug effect on MDR modulation, by investigating drug accumulation of daunorubicin in MDR leukemia cells. We have demonstrated that the new approach of same-single-cell analysis by accumulation (denoted as SASCA-A) is not only superior to different-single-cell analysis, but also has key advantages over our previous approach of same-single-cell analysis. First, SASCA-A is much simpler as it does not require multiple cycles of drug uptake and drug efflux. Second, it is faster, only taking about one fourth of the time used in the previous approach. Third, it provides a more 'identical' and reliable control because it compares the time points just before MDR modulator tests. To help understand the dynamics of drug accumulation in MDR cells, we also developed a mathematical model to describe the kinetics of drug accumulation conducted in individual cells. The SASCA-A method will benefit drug resistance research in minor cell subpopulations (e.g., cancer "stem" cells) because this method requires only a small number of cells in identifying the MDR reversal effect.

Clinical Response of Metastatic Breast Cancer to Multi-targeted Therapeutic Approach: A Single Case Report

The present article describes the ongoing (partial) remission of a female patient (41 years old) from estrogen receptor (ER)-positive/progesterone receptor (PR)-negative metastatic breast cancer in response to a combination treatment directed towards the revitalization of the mitochondrial respiratory chain (oxidative phosphorylation), the suppression of NF-kappaB as a factor triggering the inflammatory response, and chemotherapy with capecitabine. The reduction of tumor mass was evidenced by a continuing decline of CA15-3 and CEA tumor marker serum levels and ¹⁸FDG-PET-CT plus magnetic resonance (MR) imaging. It is concluded that such combination treatment might be a useful option for treating already formed metastases and for providing protection against the formation of metastases in ER positive breast cancer. The findings need to be corroborated by clinical trials. Whether similar results can be expected for other malignant tumor phenotypes relying on glycolysis as the main energy source remains to be elucidated.

[Effect of low doses of x-ray irradiation on the liver detoxication system in rats with transplanted Guerin's carcinoma]

The activity of detoxication enzymes in liver microsomal fraction of preliminary radiation-exposed rats was investigated. It was shown that preliminary organism exposure to radiation reduced cytochrome P450 and glutathione-S-transferase activity in liver microsomal fraction in the latent and logarithmic phases of oncogenesis compared with the unirradiated rats with tumor. Low level of cytochrome P450 activity can be caused by transition of microsomal cytochrome P450 in P420 inactive form. The preliminary radiation does not influence the enzyme activity of liver cytochrome P450 and glutathione-S-transferase on terminal stages of Guerin's carcinoma growth.

A cytotoxic ribonuclease reduces the expression level of P-glycoprotein in multidrug-resistant cell lines

We have previously described a cytotoxic human pancreatic-ribonuclease variant, named PE5, which is able to cleave nuclear RNA, inducing the apoptosis of cancer cells. We have investigated whether PE5 could specifically inhibit the accumulation of P-glycoprotein in multidrug-resistant cells, since P-glycoprotein overexpression is one of the most important mechanisms contributing to the multiple drug resistance phenotype. We show that PE5 is able to reduce the amount of P-glycoprotein in two different multidrug-resistant cell lines, NCI/H460-R and NCI/ADR-RES, while glutathione S-transferase-л is not affected. We also show that onconase, an amphibian ribonuclease that is undergoing phase II/III clinical trials as an antitumor drug, does not affect the expression of these proteins. The reduction of P-glycoprotein accumulation, which has been functionally confirmed by flow cytometry analysis, may be caused by the previously reported underphosphorylation of JNK induced by PE5. We also show that PE5 has synergistic cytotoxicity with doxorubicin on the NCI/ADR-RES multidrug-resistant cell line. In conclusion, PE5 is a cytotoxic ribonuclease that cleaves nuclear RNA and decreases the expression of P-glycoprotein, showing anticancer activity in multidrug-resistant cell lines.

Multiple drug resistance mechanisms in cancer

Multiple drug resistance (multidrug resistance; MDR), a phenomenon whereby human tumours that acquire resistance to one type of therapy are found to be resistant to several other drugs that are often quite different in both structure and mode of action, has been recognised clinically for several decades. An important advance in our understanding of MDR came with the identification of P-glycoprotein and other related transporters that were expressed in some cancer cells and could recognise and catalyse the efflux of diverse anticancer drugs from cells. A second advance came from an understanding of the mechanism of programmed cell death or apoptosis, leading to MDR mediated by increased to resistance to anticancer drug-induced apoptosis. A third advance came with the finding that the proliferation of human tumours was driven by a small population of self-renewing tumour cells, focussing attention on the MDR properties of these so-called tumour stem cells rather than on the cells that comprised the majority of the tumour population. A fourth advance was the delineation of features of the tumour microenvironment, including immunosuppression, which essentially provided tumour stem cells with an MDR phenotype. Most published work on the overcoming of MDR has concentrated on inhibition of drug transporters but the complexity of mechanisms contributing demands a broad strategy for the development of methods to overcome MDR in a clinical setting.

Dihydropyridines and multidrug resistance: previous attempts, present state, and future trends

Multidrug resistance is defined as the resistance of a tumor cell to the cytotoxic action of divergent drugs used in chemotherapy. Dihydropyridines are a class of calcium channel antagonists that were discovered to have a multidrug resistance reversing effect and prompted investigations resulting in the synthesis of hundreds of new derivatives. Most of the investigators tried to achieve two goals: a decrease in Ca²(+) channel-blocking activity and an increase in the multidrug resistance reversing effect. Most of the synthesized compounds failed in the later stages of studies especially in clinical trials because of pharmacokinetic or pharmacodynamic limitations. Therefore, it will be necessary to include new methods, such as combinatorial synthesis, and, more importantly, to apply computational methods based on global structure-activity relationship models that consider all problems. Moreover, some compounds should be synthesized that are effective on several multidrug resistance targets.

Pegylated phosphotidylethanolamine inhibiting P-glycoprotein expression and enhancing retention of doxorubicin in MCF7/ADR cells

The failure of the clinical treatment of cancer patients is often attributed to drug resistance of the tumor to chemotherapeutic agents. P-glycoprotein (P-gp) contributes to drug resistance via adenosine 5'-triphosphate (ATP)-dependent drug efflux pumps and is widely expressed in many human cancers. Up to date, a few of nanomaterials have shown the effects on P-gp function by different ways. To study the mechanism of the increased cytotoxicity of doxorubicin (DOX) by pegylated phosphotidylethanolamine (PEG-PE) in drug-resistant cancer cells, a series of in vitro cell assays were performed, including identification of P-gp function, quantitative studies on uptake and efflux of DOX, inhibitory effects of blank PEG-PE micelles on mRNA and protein levels of P-gp, and intracellular ATP content alteration. Finally, combining MDR-1 RNA interference (siRNA) with DOX encapsulated in PEG-PE micelles (M-DOX) to improve cytotoxicity of DOX was also studied. M-DOX showed fivefold lower the concentration that caused 50% killing tumor cell than that of free DOX in the P-gp-overexpressing MCF-7 breast cancer (MCF-7/ADR) cells. M-DOX enhanced the cellular uptake and retention of DOX in MCF-7/ADR cells. PEG-PE block molecules can inhibit P-gp expression through downregulating MDR-1 gene. Cytotoxicity of M-DOX was further improved by knocking down the MDR-1 gene using siRNA in the multidrug-resistant cells. We conclude that the increased cytotoxicity of DOX encapsulated in PEG-PE micelle is due to the reduced P-gp expression by PEG-PE block molecules, and accordingly enhancing the cellular accumulation of DOX. To overcome drug resistance of tumor cells, the combination of nanotechnology and biotechnology could be an effective strategy such as PEG-PE formed micelles and siRNA.

Role of multidrug resistance protein 2 (MRP2) in chemoresistance and clinical outcome in oesophageal squamous cell carcinoma

BACKGROUND

Although multidrug resistance protein 2 (MRP2) confers chemoresistance in some cancer types, its implication on oesophageal squamous cell carcinoma (ESCC) remains unclear.

METHODS

We evaluated MRP2 expression by immunohistochemistry and RT-PCR using 81 resected specimens from ESCC patients who did or did not receive neo-adjuvant chemotherapy (NACT), including 5-fluorouracil, doxorubicin, and cisplatin (CDDP). Correlation between MRP2 expression and response to chemotherapy was also examined in 42 pre-therapeutic biopsy samples and eight ESCC cell lines.

RESULTS

MRP2-positive immunostaining was more frequently observed in ESCCs with NACT than in those without NACT (27.3 vs 5.4%). The MRP2-positive patients showed poorer prognosis than MRP2-negative patients (5-year survival rate, 25.6 vs 55.7%). Concordantly, ESCC with NACT showed 2.1-fold higher mRNA expression of MRP2 than those without NACT (P=0.0350). In pre-therapeutic biopsy samples of patients with NACT, non-responders showed 2.9-fold higher mRNA expression of MRP2 than responders (P=0.0035). Among the panel of ESCC cell lines, TE14 showed the highest MRP2 mRNA expression along with the strongest resistance to CDDP. Inhibition of MRP2 expression by small-interfering RNA reduced chemoresistance to CDDP.

CONCLUSION

Our data suggested that MRP2 is one of molecules, which regulate the sensitivity to chemotherapy including CDDP in advanced ESCC patients.

Antitumor Agents 291 Expanded B-Ring Modification Study of 6,8,8-Triethyl Desmosdumotin B Analogues as Multidrug-Resistance Selective Agents

Drug usefulnessis frequently obstructed by the incidence of the multidrug resistance (MDR) phenotype and severe adverse effects. Exploiting collateral sensitive(CS)agents (in this case also called MDR-selective agents), which selectively target only MDR cells, is an emerging and novel approach to overcome MDR in cancer treatment. In prior studies, we found that 4'-methyl-6,6,8-triethyldesmosdumotin B (4'-Me-TEDB, 2) is an MDR-selective synthetic flavonoid with significant in vitro anticancer activity against a MDR cell line (KB-Vin) but without activity against the parent cells (KB) as well as other non-MDR tumor cells. Our recent results suggest the absolute MDR-selectivity varies depending on the cell-line system. In order to explore this further and to better understand the critical pharmacophores, we have synthesized nine novel analogues of 2, which contain heteroaromatic as well ascycloalkyl B-rings. The new compounds were evaluated for cytotoxicity to explore the effect of B-ring modifications on MDR-selectivity. All analogues, except 7, 9 and 10, were identified as significant MDR-selective compounds. This observation solidifies the importance of the 5-hydroxy-6,8,8-trialkyl-4H-chromene-4,7(8H)-dione skeleton (AC-ring system) for the pharmacological activity and establishes the B-ring as less critical for the broader spectrum MDR-selectivity. Notably, 3-furanyl (3)and 2-thiophenyl (6)analogues displayed substantial MDR-selectivity with KB/KB-Vin ratios of >12 and 16, respectively. Furthermore, 3 and 6 also exhibited MDR-selectivity in a second set of paired cell lines, the MDR/non-MDR hepatoma-cell system. Interestingly, a cyclohexyl analogue (11) showed moderate inhibition of A549, DU145, and PC-3 cell growth, while the other compounds were inactive. These new findings are discussed in terms of current understanding of mechanism and structure-activity relationship (SAR) of our novel MDR-selective flavonoids.

Antiproliferative and pro-apoptotic effects of quercetin on human pancreatic carcinoma cell lines EPP85-181P and EPP85-181RDB

Polyphenols are present in several edible plants and for many years induce high interest mainly due to their antioxidative and anti-inflammatory influence. At present, numerous studies are conducted on antineoplastic effects of the compounds. One of most effective biopolyphenols involves the flavonol quercetin. Our studies aimed at evaluation of antiproliferative and pro-apoptotic effects of quercetin alone and in combinations with daunorubicin on cells of human pancreatic carcinoma lines. The experiments were conducted on two cell lines, sensitive to daunorubicin EPP85-181P line, and its resistant variant EPP85-181RDB. Effect of studied substances on cell proliferation was detected using sulphorhodamine B (SRB) protein staining method. Apoptotic damage was estimated using comet and TUNEL techniques. Our data demonstrated that quercetin exerted cytotoxic action on cells of the both neoplastic cell lines in concentration-dependent manner. In the case of EPP85-181RDB cell line, quercetin seemed to sensitize resistant cells to daunorubicin. In parallel, the effect of both substances on the sensitive cell line was synergistic. Results of the studies confirmed that quercetin may probably break resistance of neoplastic cells to chemotherapy. On the other side, studied flavonol augmented action of cytostatic drug in case of sensitive tumour cells what suggest, that it might allow to decrease dosage of cytostatic drugs and reduce negative side effects of the treatment.

Apatinib (YN968D1) reverses multidrug resistance by inhibiting the efflux function of multiple ATP-binding cassette transporters

Apatinib, a small-molecule multitargeted tyrosine kinase inhibitor, is in phase III clinical trial for the treatment of patients with non-small-cell lung cancer and gastric cancer in China. In this study, we determined the effect of apatinib on the interaction of specific antineoplastic compounds with P-glycoprotein (ABCB1), multidrug resistance protein 1 (MRP1, ABCC1), and breast cancer resistance protein (BCRP, ABCG2). Our results showed that apatinib significantly enhanced the cytotoxicity of ABCB1 or ABCG2 substrate drugs in KBv200, MCF-7/adr, and HEK293/ABCB1 cells overexpressing ABCB1 and in S1-M1-80, MCF-7/FLV1000, and HEK293/ABCG2-R2 cells overexpressing ABCG2 (wild-type). In contrast, apatinib did not alter the cytotoxicity of specific substrates in the parental cells and cells overexpressing ABCC1. Apatinib significantly increased the intracellular accumulation of rhodamine 123 and doxorubicin in the multidrug resistance (MDR) cells. Furthermore, apatinib significantly inhibited the photoaffinity labeling of both ABCB1 and ABCG2 with [(125)I]iodoarylazidoprazosin in a concentration-dependent manner. The ATPase activity of both ABCB1 and ABCG2 was significantly increased by apatinib. However, apatinib, at a concentration that produced a reversal of MDR, did not significantly alter the ABCB1 or ABCG2 protein or mRNA expression levels or the phosphorylation of AKT and extracellular signal-regulated kinase 1/2 (ERK1/2). Importantly, apatinib significantly enhanced the effect of paclitaxel against the ABCB1-resistant KBv200 cancer cell xenografts in nude mice. In conclusion, apatinib reverses ABCB1- and ABCG2-mediated MDR by inhibiting their transport function, but not by blocking the AKT or ERK1/2 pathway or downregulating ABCB1 or ABCG2 expression. Apatinib may be useful in circumventing MDR to other conventional antineoplastic drugs.

Apatinib (YN968D1) reverses multidrug resistance by inhibiting the efflux function of multiple ATP-binding cassette transporters

Apatinib, a small-molecule multitargeted tyrosine kinase inhibitor, is in phase III clinical trial for the treatment of patients with non-small-cell lung cancer and gastric cancer in China. In this study, we determined the effect of apatinib on the interaction of specific antineoplastic compounds with P-glycoprotein (ABCB1), multidrug resistance protein 1 (MRP1, ABCC1), and breast cancer resistance protein (BCRP, ABCG2). Our results showed that apatinib significantly enhanced the cytotoxicity of ABCB1 or ABCG2 substrate drugs in KBv200, MCF-7/adr, and HEK293/ABCB1 cells overexpressing ABCB1 and in S1-M1-80, MCF-7/FLV1000, and HEK293/ABCG2-R2 cells overexpressing ABCG2 (wild-type). In contrast, apatinib did not alter the cytotoxicity of specific substrates in the parental cells and cells overexpressing ABCC1. Apatinib significantly increased the intracellular accumulation of rhodamine 123 and doxorubicin in the multidrug resistance (MDR) cells. Furthermore, apatinib significantly inhibited the photoaffinity labeling of both ABCB1 and ABCG2 with [(125)I]iodoarylazidoprazosin in a concentration-dependent manner. The ATPase activity of both ABCB1 and ABCG2 was significantly increased by apatinib. However, apatinib, at a concentration that produced a reversal of MDR, did not significantly alter the ABCB1 or ABCG2 protein or mRNA expression levels or the phosphorylation of AKT and extracellular signal-regulated kinase 1/2 (ERK1/2). Importantly, apatinib significantly enhanced the effect of paclitaxel against the ABCB1-resistant KBv200 cancer cell xenografts in nude mice. In conclusion, apatinib reverses ABCB1- and ABCG2-mediated MDR by inhibiting their transport function, but not by blocking the AKT or ERK1/2 pathway or downregulating ABCB1 or ABCG2 expression. Apatinib may be useful in circumventing MDR to other conventional antineoplastic drugs.

Efflux pump inhibitors: a strategy to combat P-glycoprotein and the NorA multidrug resistance pump

Multidrug resistance (MDR) is the cause of an ever-increasing number of problems in the treatment of cancers and bacterial infections. The active efflux of drugs contributes significantly to this phenomenon. This minireview summarizes recent advances in combating MDR, with particular emphasis on natural and synthetic efflux pump inhibitors of P-glycoprotein in resistant tumor cells and of the NorA MDR pump in Staphylococcus aureus.

Papyriferic acid derivatives as reversal agents of multidrug resistance in cancer cells

Forty-one derivatives of papyriferic acid were prepared based on our previous finding that methyl papyriferate (3) showed potent reversing effect on cytotoxicity of colchicine against multidrug resistance (MDR) human cancer cells (KB-C2), and evaluated for their cytotoxicity and effect on reversing P-gp-mediated MDR against KB-C2 cells. 3-O-(Morpholino-beta-oxopropanoyl)-12beta-acetoxy-3alpha,25-dihydroxy-(20S,24R)-epoxydammarane (37) significantly increased the sensitivity of colchicine against KB-C2 cells by 185-fold at 5microg/mL (7.4microM), and the cytotoxicity of colchicine was recovered to nearly that of sensitive (KB) cells. The other several new amide derivatives also exhibited potent reversal activity comparable to or more potent than methyl papyriferate and verapamil.