Increased AP-1 activity in drug resistant human breast cancer MCF-7 cells

Rewiring of the 3D genome during acquisition of carboplatin resistance in a triple-negative breast cancer patient-derived xenograft

Changes in the three-dimensional (3D) structure of the genome are an emerging hallmark of cancer. Cancer-associated copy number variants and single nucleotide polymorphisms promote rewiring of chromatin loops, disruption of topologically associating domains (TADs), active/inactive chromatin state switching, leading to oncogene expression and silencing of tumor suppressors. However, little is known about 3D changes during cancer progression to a chemotherapy-resistant state. We integrated chromatin conformation capture (Hi-C), RNA-seq, and whole-genome sequencing obtained from triple-negative breast cancer patient-derived xenograft primary tumors (UCD52) and carboplatin-resistant samples and found increased short-range (< 2 Mb) interactions, chromatin looping, formation of TAD, chromatin state switching into a more active state, and amplification of ATP-binding cassette transporters. Transcriptome changes suggested the role of long-noncoding RNAs in carboplatin resistance. Rewiring of the 3D genome was associated with TP53, TP63, BATF, FOS-JUN family of transcription factors and led to activation of aggressiveness-, metastasis- and other cancer-related pathways. Integrative analysis highlighted increased ribosome biogenesis and oxidative phosphorylation, suggesting the role of mitochondrial energy metabolism. Our results suggest that 3D genome remodeling may be a key mechanism underlying carboplatin resistance.

Integration of EMT and cellular survival instincts in reprogramming of programmed cell death to anastasis

Apoptosis is a tightly controlled, coordinated cellular event responsible for inducing programmed cell death to rid the body of defective or unfit cells. Inhibition of apoptosis is, therefore, an essential process for cancer cells to harness. Genomic variants in apoptotic-controlling genes are highly prevalent in cancer and have been identified to induce pro-proliferation and pro-survival pathways, rendering cancer cells resistant to apoptosis. Traditional understanding of apoptosis defines it as an irreversible process; however, growing evidence suggests that apoptosis is a reversible process from which cells can escape, even after the activation of its most committed stages. The mechanism invoked to reverse apoptosis has been termed anastasis and poses challenges for the development and utilization of chemotherapeutic agents. Anastasis has also been identified as a mechanism by which cells can recover from apoptotic lesions and revert back to its previous functioning state. In this review, we intend to focus the attention of the reader on the comprehensive role of survival, metastasis, and epithelial mesenchymal transition (EMT), as well as DNA damage repair mechanisms in promoting anastasis. Additionally, we will emphasize the mechanistic consequences of anastasis on drug resistance and recent rational therapeutic approaches designed to combat this resistance.

Epigenetic Regulation of Multidrug Resistance Protein 1 and Breast Cancer Resistance Protein Transporters by Histone Deacetylase Inhibition

Multidrug resistance protein 1 (MDR1, ABCB1, P-glycoprotein) and breast cancer resistance protein (BCRP, ABCG2) are key efflux transporters that mediate the extrusion of drugs and toxicants in cancer cells and healthy tissues, including the liver, kidneys, and the brain. Altering the expression and activity of MDR1 and BCRP influences the disposition, pharmacodynamics, and toxicity of chemicals, including a number of commonly prescribed medications. Histone acetylation is an epigenetic modification that can regulate gene expression by changing the accessibility of the genome to transcriptional regulators and transcriptional machinery. Recently, studies have suggested that pharmacological inhibition of histone deacetylases (HDACs) modulates the expression and function of MDR1 and BCRP transporters as a result of enhanced histone acetylation. This review addresses the ability of HDAC inhibitors to modulate the expression and the function of MDR1 and BCRP transporters and explores the molecular mechanisms by which HDAC inhibition regulates these transporters. While the majority of studies have focused on histone regulation of MDR1 and BCRP in drug-resistant and drug-sensitive cancer cells, emerging data point to similar responses in nonmalignant cells and tissues. Elucidating epigenetic mechanisms regulating MDR1 and BCRP is important to expand our understanding of the basic biology of these two key transporters and subsequent consequences on chemoresistance as well as tissue exposure and responses to drugs and toxicants. SIGNIFICANCE STATEMENT: Histone deacetylase inhibitors alter the expression of key efflux transporters multidrug resistance protein 1 and breast cancer resistance protein in healthy and malignant cells.

Multifactorial Modes of Action of Arsenic Trioxide in Cancer Cells as Analyzed by Classical and Network Pharmacology

Arsenic trioxide is a traditional remedy in Chinese Medicine since ages. Nowadays, it is clinically used to treat acute promyelocytic leukemia (APL) by targeting PML/RARA. However, the drug's activity is broader and the mechanisms of action in other tumor types remain unclear. In this study, we investigated molecular modes of action by classical and network pharmacological approaches. CEM/ADR5000 resistance leukemic cells were similar sensitive to As2O3 as their wild-type counterpart CCRF-CEM (resistance ratio: 1.88). Drug-resistant U87.MG ΔEGFR glioblastoma cells harboring mutated epidermal growth factor receptor were even more sensitive (collateral sensitive) than wild-type U87.MG cells (resistance ratio: 0.33). HCT-116 colon carcinoma p53-/- knockout cells were 7.16-fold resistant toward As2O3 compared to wild-type cells. Forty genes determining cellular responsiveness to As2O3 were identified by microarray and COMPARE analyses in 58 cell lines of the NCI panel. Hierarchical cluster analysis-based heat mapping revealed significant differences between As2O3 sensitive cell lines and resistant cell lines with p-value: 1.86 × 10-5. The genes were subjected to Galaxy Cistrome gene promoter transcription factor analysis to predict the binding of transcription factors. We have exemplarily chosen NF-kB and AP-1, and indeed As2O3 dose-dependently inhibited the promoter activity of these two transcription factors in reporter cell lines. Furthermore, the genes identified here and those published in the literature were assembled and subjected to Ingenuity Pathway Analysis for comprehensive network pharmacological approaches that included all known factors of resistance of tumor cells to As2O3. In addition to pathways related to the anticancer effects of As2O3, several neurological pathways were identified. As arsenic is well-known to exert neurotoxicity, these pathways might account for neurological side effects. In conclusion, the activity of As2O3 is not restricted to acute promyelocytic leukemia. In addition to PML/RARA, numerous other genes belonging to diverse functional classes may also contribute to its cytotoxicity. Network pharmacology is suited to unravel the multifactorial modes of action of As2O3.

MicroRNA 10b promotes abnormal expression of the proto-oncogene c-Jun in metastatic breast cancer cells

MicroRNAs have been shown to act as oncogenes or tumor suppressers via various cellular pathways. Specifically, in breast cancer, upregulation of miR-10b is positively associated with aggressiveness of tumors. However, the mechanism by which miR-10b contributes to cell malignancy is largely unknown. Here we show that at the receiving end of the miR-10b pathway is the proto-oncogene c-Jun, a transcription factor that plays a critical role in stimulation of cell proliferation and tumor progression. c-Jun is known to be translationally activated by loss of cell contacts or restructuring of the cytoskeleton. A comprehensive analysis of miRNA expression exhibited a significant increase in miR-10b expression. This was supported by analysis of breast cancer cells, which showed that loss of E-cadherin in metastatic cells is accompanied by elevation of miR-10b and interestingly, by a marked increase in accumulation of c-Jun. Silencing miR-10b in metastatic breast cancer cells leads to a decline in c-Jun expression, whereas overexpression of miR-10b in HaCaT cells is sufficient to elevate the accumulation of c-Jun. The increase in c-Jun protein accumulation in metastatic cells is not accompanied by an increase in c-Jun mRNA and is not dependent on MAPK activity. Knockdown and overexpression experiments revealed that the increase is mediated by NF1 and RhoC, downstream targets of miR-10b that affect cytoskeletal dynamics through the ROCK pathway. Overall, we show the ability of miR-10b to activate the expression of c-Jun through RhoC and NF1, which represents a novel pathway for promoting migration and invasion of human cancer cells.

Tomentodione M sensitizes multidrug resistant cancer cells by decreasing P-glycoprotein via inhibition of p38 MAPK signaling

In this study, we investigated the mechanism by which tomentodione M (TTM), a novel natural syncarpic acid-conjugated monoterpene, reversed multi-drug resistance (MDR) in cancer cells. TTM increased the cytotoxicity of chemotherapeutic drugs such as docetaxel and doxorubicin in MCF-7/MDR and K562/MDR cells in a dose- and time-dependent manner. TTM reduced colony formation and enhanced apoptosis in docetaxel-treated MCF-7/MDR and K562/MDR cells, and it enhanced intracellular accumulation of doxorubicin and rhodamine 123 in MDR cancer cells by reducing drug efflux mediated by P-gp. TTM decreased expression of both P-gp mRNA and protein by inhibiting p38 MAPK signaling. Similarly, the p38 MAPK inhibitor SB203580 reversed MDR in cancer cells by decreasing P-gp expression. Conversely, p38 MAPK-overexpressing MCF-7 and K562 cells showed higher P-gp expression than controls. These observations indicate that TTM reverses MDR in cancer cells by decreasing P-gp expression via p38 MAPK inhibition.

pH-sensitive micelles for the intracellular co-delivery of curcumin and Pluronic L61 unimers for synergistic reversal effect of multidrug resistance

Pluronic L61 unimers, which are biomacromolecular modulators, and curcumin, a small-molecule modulator, were co-formulated into pH-sensitive micelles to reveal the full synergistic potential of combination drug treatments to reverse multidrug resistance (MDR). Compared to monotherapy, combined therapy significantly improved the cytotoxicity, cellular uptake and apoptotic effects of doxorubicin (DOX) against MCF-7/ADR cells. In mechanistic studies, both L61 and curcumin enhanced the cytotoxic effect by acting on mitochondrial signalling pathways. The compounds selectively accumulated in the mitochondria and disabled the mitochondria by dissipating the mitochondrial membrane potential, decreasing the ATP levels, and releasing cytochrome c, which initiated a cascade of caspase-9 and caspase-3 reactions. Furthermore, both curcumin and L61 down-regulated the expression and function of P-gp in response to drug efflux from the MCF-7/ADR cells. In the MCF-7/ADR tumour-bearing mouse model, intravenous administration of the combined therapy directly targeted the tumour, as revealed by the accumulation of DiR in the tumour site, which led to a significant inhibition of tumour growth without measurable side effects. In conclusion, co-formulation consisting of L61 and curcumin in pH-sensitive micelles induced significant synergistic effects on the reversal of MDR. Therefore, the intracellular co-delivery of various MDR modulators has great potential to reverse MDR in tumours.

MiR-138 indirectly regulates the MDR1 promoter by NF-κB/p65 silencing

MicroRNAs (miRNAs) are known to mediate post-transcriptional gene silencing in the cytoplasm and recent evidence indicates that may also possess nuclear roles in regulating gene expression. A previous study showed that miR-138 is involved in the multidrug resistance of leukemia cells through down-regulation of the drug efflux pump P-glycoprotein (P-gp), the protein encoded by the human multidrug-resistant ABCB1/MDR1 gene. However, the transcriptional regulatory mechanisms responsible remain to be elucidated. To deepen the description of the mechanism of transcriptional gene silencing on the MDR1 promoter, we initially performed a bioinformatics search for potential miR-138 binding sites in the MDR1 gene promoter sequence. Interestingly, we did not find miR-138 binding sites in this region, suggesting an indirect regulation. From six representative transcriptional factors involved in MDR1 gene regulation, an in silico analysis revealed that NF-κB/p65 has a specific binding site for miR-138. The results of luciferase reporter assay, western blot and flow cytometry shown here suggest that miR-138 might modulate the human MDR1 expression by inhibiting NF-κB/p65 as an indirect mechanism of MDR1 regulation. Furthermore, employing the human macrophage-like cell line U937 we observed comparable results with NF-κB/p65 down-regulation and we also observed a significant reduction in the IL-6 and TNF-α mRNA, as well as in their secreted pro-inflammatory cytokines following miR-138 expression, suggesting that canonical NF-κB target genes might also be potential targets for miR-138 in leukemia cells.

Recapitulation of complex transport and action of drugs at the tumor microenvironment using tumor-microenvironment-on-chip

Targeted delivery aims to selectively distribute drugs to targeted tumor tissues but not to healthy tissues. This can address many clinical challenges by maximizing the efficacy but minimizing the toxicity of anti-cancer drugs. However, a complex tumor microenvironment poses various barriers hindering the transport of drugs and drug delivery systems. New tumor models that allow for the systematic study of these complex environments are highly desired to provide reliable test beds to develop drug delivery systems for targeted delivery. Recently, research efforts have yielded new in vitro tumor models, the so called tumor-microenvironment-on-chip, that recapitulate certain characteristics of the tumor microenvironment. These new models show benefits over other conventional tumor models, and have the potential to accelerate drug discovery and enable precision medicine. However, further research is warranted to overcome their limitations and to properly interpret the data obtained from these models. In this article, key features of the in vivo tumor microenvironment that are relevant to drug transport processes for targeted delivery were discussed, and the current status and challenges for developing in vitro transport model systems were reviewed.

Fas signaling promotes chemoresistance in gastrointestinal cancer by up-regulating P-glycoprotein

Fas signaling promotes metastasis of gastrointestinal (GI) cancer cells by inducing epithelial-mesenchymal transition (EMT), and EMT acquisition has been found to cause cancer chemoresistance. Here, we demonstrated that the response to chemotherapy of GI cancer patients with higher expression of FasL was significantly worse than patients with lower expression. Fas-induced activation of the ERK1/2-MAPK pathway decreased the sensitivity of GI cancer cells to chemotherapeutic agents and promoted the expression of P-glycoprotein (P-gp). FasL promoted chemoresistance of GI cancer cell via upregulation of P-gp by increasing β-catenin and decreasing miR-145. β-catenin promoted P-gp gene transcription by binding with P-gp promoter while miR-145 suppressed P-gp expression by interacting with the mRNA 3'UTR of P-gp. Immunostaining and qRT-PCR analysis of human GI cancer samples revealed a positive association among FasL, β-catenin, and P-gp, but a negative correlation between miR-145 and FasL or P-gp. Altogether, our results showed Fas signaling could promote chemoresistance in GI cancer through modulation of P-gp expression by β-catenin and miR-145. Our findings suggest that Fas signaling-based cancer therapies should be administered cautiously, as activation of this pathway may not only lead to apoptosis but also induce chemoresistance.

Autoregulation and heterogeneity in expression of human Cripto-1

Cripto-1 (CR-1) is involved in various processes in embryonic development and cancer. Multiple pathways regulate CR-1 expression. Our present work demonstrates a possible positive feedback circuit where CR-1 induces its own expression. Using U-87 MG cells treated with exogenous CR-1, we show that such induction involves ALK4/SMAD2/3 pathway. Stochasticity in gene expression gives rise to heterogeneity in expression in genetically identical cells. Positive feedback increases such heterogeneity and often gives rise to two subpopulations of cells, having higher and lower expression of a gene. Using flow cytometry, we show that U-87 MG cells have a minuscule subpopulation with detectable expression of CR-1. Induction of CR-1 expression, by exogenous CR-1, increases the size of this CR-1 positive subpopulation. However, even at very high dose, most of the cells remain CR-1 negative. We show that population behavior of CR-1 induction has a signature similar to bimodal expression expected in a transcriptional circuit with positive feedback. We further show that treatment of U-87 MG cells with CR-1 leads to higher expression of drug efflux protein MDR-1 in the CR-1 positive subpopulation, indicating correlated induction of these two proteins. Positive feedback driven heterogeneity in expression of CR-1 may play crucial role in phenotypic diversification of cancer cells.

Modulation of P-glycoprotein efflux pump: induction and activation as a therapeutic strategy

P-glycoprotein (P-gp) is an ATP-dependent efflux pump encoded by the MDR1 gene in humans, known to mediate multidrug resistance of neoplastic cells to cancer therapy. For several decades, P-gp inhibition has drawn many significant research efforts in an attempt to overcome this phenomenon. However, P-gp is also constitutively expressed in normal human epithelial tissues and, due to its broad substrate specificity, to its cellular polarized expression in many excretory and barrier tissues, and to its great efflux capacity, it can play a crucial role in limiting the absorption and distribution of harmful xenobiotics, by decreasing their intracellular accumulation. Such a defense mechanism can be of particular relevance at the intestinal level, by significantly reducing the intestinal absorption of the xenobiotic and, consequently, avoiding its access to the target organs. In this review, the current knowledge on this important efflux pump is summarized, and a new focus is brought on the therapeutic interest of inducing and/or activating P-gp for limiting the toxicity caused by its substrates. Several in vivo and in vitro studies validating the use of such a therapeutic strategy are discussed. An extensive literature search for reported P-gp inducers/activators and for the experimental models used in their characterization was conducted. Those studies demonstrate that effective antidotal pathways can be achieved by efficiently promoting the P-gp-mediated efflux of deleterious xenobiotics, resulting in a significant reduction in their intracellular levels and, consequently, in a significant reduction of their toxicity.

FZD1 activates protein kinase C delta-mediated drug-resistance in multidrug-resistant MES-SA/Dx5 cancer cells

Multidrug-resistant (MDR) cancer is a major clinical problem in chemotherapy of cancer patients. We have noted inappropriate PKCδ hypomethylation and overexpression of genes in the PKCδ/AP-1 pathway in the human uterus sarcoma drug-resistant cell line, MES-SA/Dx5 cells, which also overexpress p-glycoprotein (ABCB1). Recent studies have indicated that FZD1 is overexpressed in both multidrug-resistant cancer cell lines and in clinical tumor samples. These data have led us to hypothesize that the FZD1-mediated PKCδ signal-transduction pathway may play an important role in drug resistance in MES-SA/Dx5 cells. In this work, the PKCδ inhibitor Rottlerin was found to reduce ABCB1 expression and to inhibit the MDR drug pumping ability in the MES-SA/Dx5 cells when compared with the doxorubicin-sensitive parental cell line, MES-SA. PKCδ was up-regulated with concurrent up-regulation of the mRNA levels of the AP-1-related factors, c-JUN and c-FOS. Activation of AP-1 also correlated with up-regulation of the AP-1 downstream genes HGF and EGR1. Furthermore, AP-1 activities were reduced and the AP-1 downstream genes were down-regulated in Rottlerin-treated or PKCδ shRNA-transfected cells. MES-SA/Dx5 cells were resensitized to doxorubicin-induced toxicity by co-treatment with doxorubicin and Rottlerin or PKCδ shRNA. In addition, cell viability and drug pump-out ability were significantly reduced in the FZD1 inhibitor curcumin-treated and FZD1 shRNA-knockdown MES-SA/Dx5 cells, indicating involvement of PKCδ in FZD1-modulated ABCB1 expression pathway. Taken together, our data demonstrate that FZD1 regulates PKCδ, and the PKCδ/AP-1 signalling transduction pathway plays an important role in drug resistance in MES-SA/Dx5 cells.

Reversing multidrug resistance in Caco-2 by silencing MDR1, MRP1, MRP2, and BCL-2/BCL-xL using liposomal antisense oligonucleotides

Multidrug resistance (MDR) is a major impediment to chemotherapy. In the present study, we designed antisense oligonucleotides (ASOs) against MDR1, MDR-associated protein (MRP)1, MRP2, and/or BCL-2/BCL-xL to reverse MDR transporters and induce apoptosis, respectively. The cationic liposomes (100 nm) composed of N-[1-(2,3-dioleyloxy)propyl]-n,n,n-trimethylammonium chloride and dioleoyl phosphotidylethanolamine core surrounded by a polyethylene glycol (PEG) shell were prepared to carry ASOs and/or epirubicin, an antineoplastic agent. We aimed to simultaneously suppress efflux pumps, provoke apoptosis, and enhance the chemosensitivity of human colon adenocarcinoma Caco-2 cells to epirubicin. We evaluated encapsulation efficiency, particle size, cytotoxicity, intracellular accumulation, mRNA levels, cell cycle distribution, and caspase activity of these formulations. We found that PEGylated liposomal ASOs significantly reduced Caco-2 cell viability and thus intensified epirubicin-mediated apoptosis. These formulations also decreased the MDR1 promoter activity levels and enhanced the intracellular retention of epirubicin in Caco-2 cells. Epirubicin and ASOs in PEGylated liposomes remarkably decreased mRNA expression levels of human MDR1, MRP1, MRP2, and BCL-2. The combined treatments all significantly increased the mRNA expressions of p53 and BAX, and activity levels of caspase-3, -8, and -9. The formulation of epirubicin and ASOs targeting both pump resistance of MDR1, MRP1, and MRP2 and nonpump resistance of BCL-2/BCL-xL demonstrated more superior effect to all the other formulations used in this study. Our results provide a novel insight into the mechanisms by which PEGylated liposomal ASOs against both resistance types act as activators to epirubicin-induced apoptosis through suppressing MDR1, MRP1, and MRP2, as well as triggering intrinsic mitochondrial and extrinsic death receptor pathways. The complicated regulation of MDR highlights the necessity for a multifunctional approach using an effective delivery system, such as PEGylated liposomes, to carry epirubicin and ASOs as a potent nanomedicine for improving the clinical efficacy of chemotherapy.

Phosphorylated Sp1 is the regulator of DNA-PKcs and DNA ligase IV transcription of daunorubicin-resistant leukemia cell lines

Multidrug resistance (MDR) is a serious problem faced in the treatment of malignant tumors. In this study, we characterized the expression of non-homologous DNA end joining (NHEJ) components, a major DNA double strand break (DSB) repair mechanism in mammals, in K562 cell and its daunorubicin (DNR)-resistant subclone (K562/DNR). K562/DNR overexpressed major enzymes of NHEJ, DNA-PKcs and DNA ligase IV, and K562/DNR repaired DSB more rapidly than K562 after DNA damage by neocarzinostatin (MDR1-independent radiation-mimetic). Overexpressed DNA-PKcs and DNA ligase IV were also observed in DNR-resistant HL60 (HL60/DNR) cells as compared with parental HL60 cells. Expression level of DNA-PKcs mRNA paralleled its protein level, and the promoter activity of DNA-PKcs of K562/DNR was higher than that of K562, and the 5'-region between -49bp and the first exon was important for its activity. Because this region is GC-rich, we tried to suppress Sp1 family transcription factor using mithramycin A (MMA), a specific Sp1 family inhibitor, and siRNAs for Sp1 and Sp3. Both MMA and siRNAs suppressed DNA-PKcs expression. Higher serine-phosphorylated Sp1 but not total Sp1 of both K562/DNR and HL60/DNR was observed compared with their parental K562 and HL60 cells. DNA ligase IV expression of K562/DNR was also suppressed significantly with Sp1 family protein inhibition. EMSA and ChIP assay confirmed higher binding of Sp1 and Sp3 with DNA-PKcs 5'-promoter region of DNA-PKcs of K562/DNR than that of K562. Thus, the Sp1 family transcription factor affects important NHEJ component expressions in anti-cancer drug-resistant malignant cells, leading to the more aggressive MDR phenotype.

mAPC-GibbsOS: an integrated approach for robust identification of gene regulatory networks

Background

Identification of cooperative gene regulatory network is an important topic for biological study especially in cancer research. Traditional approaches suffer from large noise in gene expression data and false positive connections in motif binding data; they also fail to identify the modularized structure of gene regulatory network. Methods that are capable of revealing underlying modularized structure and robust to noise and false positives are needed to be developed.

Results

We proposed and developed an integrated approach to identify gene regulatory networks, which consists of a novel clustering method (namely motif-guided affinity propagation clustering (mAPC)) and a sampling based method (called Gibbs sampler based on outlier sum statistic (GibbsOS)). mAPC is used in the first step to obtain co-regulated gene modules by clustering genes with a similarity measurement taking into account both gene expression data and binding motif information. This clustering method can reduce the noise effect from microarray data to obtain modularized gene clusters. However, due to many false positives in motif binding data, some genes not regulated by certain transcription factors (TFs) will be falsely clustered with true target genes. To overcome this problem, GibbsOS is applied in the second step to refine each cluster for the identification of true target genes. In order to evaluate the performance of the proposed method, we generated simulation data under different signal-to-noise ratios and false positive ratios to test the method. The experimental results show an improved accuracy in terms of clustering and transcription factor identification. Moreover, an improved performance is demonstrated in target gene identification as compared with GibbsOS. Finally, we applied the proposed method to two breast cancer patient datasets to identify cooperative transcriptional regulatory networks associated with recurrence of breast cancer, as supported by their functional annotations.

Conclusions

We have developed a two-step approach for gene regulatory network identification, featuring an integrated method to identify modularized regulatory structures and refine their target genes subsequently. Simulation studies have shown the robustness of the method against noise in gene expression data and false positives in motif binding data. The proposed method has been applied to two breast cancer gene expression datasets to infer the hidden regulation mechanisms. The experimental results demonstrate the efficacy of the method in identifying key regulatory networks related to the progression and recurrence of breast cancer.

Overcoming paclitaxel resistance in uterine endometrial cancer using a COX-2 inhibitor

Cyclooxygenase (COX)-2 inhibitors have been reported to potentially modulate the resistance of cancer cells to chemotherapeutic drugs by affecting multidrug resistance 1 (MDR1) expression. In the present study, we investigated the association between COX-2 and MDR1 expression in endometrial cancers and evaluated the effects of the COX-2 inhibitor, etodolac, in combination with paclitaxel on paclitaxel-resistant endometrial cancer cells. The relationship between COX-2 and MDR1 mRNA expression was examined by quantitative PCR in 36 endometrial cancer specimens. The paclitaxel-resistant cell line OMC-2P was established from OMC-2 cells. Paclitaxel (1 µg/ml) with or without etodolac (10 µg/ml) was added to OMC-2 and OMC-2P cells, and COX-2 and MDR1 mRNA expression levels were examined. The concentration of prostaglandin E2 (PGE2) in the supernatant of each cell line was examined by enzyme-linked immunosorbent assay. The function of MDR1 was determined by intracellular accumulation of rhodamine 123 using flow cytometry, and the concentration of intracellular paclitaxel was determined by high-performance liquid chromatography. We found a positive relationship between COX-2 and MDR1 mRNA expression in endometrial cancer. Both COX-2 mRNA expression and PGE2 production were elevated in resistant OMC-2P cells when compared to non-resistant OMC-2 cells. Additionally, MDR1 mRNA expression was markedly upregulated in OMC-2P cells. In OMC-2 cells, COX-2 and MDR1 mRNA levels were significantly upregulated by paclitaxel treatment and downregulated by co-administration with etodolac. In OMC-2P cells, COX-2 mRNA expression was also significantly upregulated by paclitaxel treatment and tended to be downregulated by co-administration with etodolac. Moreover, co-administration of paclitaxel and etodolac suppressed the induction of MDR1 mRNA. Rhodamine 123 efflux was increased in OMC-2P cells when compared to the efflux in the OMC-2 cells and was increased in response to paclitaxel treatment. Co-administration of paclitaxel and etodolac in both cell lines resulted in decreased rhodamine 123 efflux. The actual concentration of intracellular paclitaxel in OMC-2P cells was significantly lower than that in OMC-2 cells treated with paclitaxel alone and was significantly increased after co-administration of paclitaxel and etodolac. These findings suggest that paclitaxel resistance may be associated with COX-2 and MDR1 expression in cancer cells. Co-administration of COX-2 inhibitors and paclitaxel may have a key role in modulating or overcoming paclitaxel resistance in endometrial cancers.

Involvement of AP-1 and NF-κB in the up-regulation of P-gp in vinblastine resistant Caco-2 cells

Caco-2 is a widely used cell model in drug absorption and P-glycoprotein (P-gp, MDR1) substrate identification. Long-term vinblastine treatment of Caco-2 cells could increase the expression of P-gp; thus, the vinblastine resistant Caco-2 (Caco-2 vbl) cells can be used as a rapid and sensitive alternative model in identifying P-gp substrates. The mechanism of P-gp induction in this model is not clear; this study was therefore intended to clarify the possible factors involved in P-gp up-regulation in Caco-2 vbl cells. Since vinblastine is the inducer of both activator protein-1 (AP-1) and nuclear factor kappa B (NF-κB), we investigated the role of AP-1 and NF-κB in the regulation of MDR1 gene expression. Our results indicated that the AP-1 and NF-κB luciferase activity was higher in Caco-2 vbl cells than that in Caco-2 cells according to reporter gene assay. The mRNA expression of AP-1 subunit c-Jun and NF-κB was increased in Caco-2 vbl cells. The c-Jun inhibitor SP600125 and NF-κB inhibitor pyrrolidine dithiocarbamate (PDTC) suppressed the expression of MDR1 mRNA in Caco-2 vbl cells. In conclusion, this study provides the evidence that AP-1 and NF-κB are involved in the P-gp induction in Caco-2 vbl cells.

Andrographis paniculata Extract and Andrographolide Modulate the Hepatic Drug Metabolism System and Plasma Tolbutamide Concentrations in Rats

Andrographolide is the most abundant terpenoid of A. paniculata which is used in the treatment of diabetes. In this study, we investigated the effects of A. paniculata extract (APE) and andrographolide on the expression of drug-metabolizing enzymes in rat liver and determined whether modulation of these enzymes changed the pharmacokinetics of tolbutamide. Rats were intragastrically dosed with 2 g/kg/day APE or 50 mg/kg/day andrographolide for 5 days before a dose of 20 mg/kg tolbutamide was given. APE and andrographolide reduced the AUC_0–12 h of tolbutamide by 37% and 18%, respectively, compared with that in controls. The protein and mRNA levels and enzyme activities of CYP2C6/11, CYP1A1/2, and CYP3A1/2 were increased by APE and andrographolide. To evaluate whether APE or andrographolide affected the hypoglycemic action of tolbutamide, high-fat diet-induced obese mice were used and treated in the same manner as the rats. APE and andrographolide increased CYP2C6/11 expression and decreased plasma tolbutamide levels. In a glucose tolerance test, however, the hypoglycemic effect of tolbutamide was not changed by APE or andrographolide. These results suggest that APE and andrographolide accelerate the metabolism rate of tolbutamide through increased expression and activity of drug-metabolizing enzymes. APE and andrographolide, however, do not impair the hypoglycemic effect of tolbutamide.

Differential regulation of c-Jun protein plays an instrumental role in chemoresistance of cancer cells

The chemotherapeutic drug cisplatin (cis-diamminedichloroplatinum(II) (CDDP)) is widely used in the treatment of human cancers. However, the mechanism underlying intrinsic tumor resistance to CDDP remains elusive. Here, we demonstrate that treatment with CDDP resulted in down-regulation of c-Jun expression via caspase-9-dependent cleavage of c-Jun at Asp-65 and MEKK1-mediated ubiquitylation and degradation of c-Jun in CDDP-sensitive cancer cells. In contrast, activation of JNK2 (but not JNK1) phosphorylated and up-regulated the expression of c-Jun in CDDP-resistant cells. Activated c-Jun bound to the promoter regions of the MDR1 gene and promoted the expression of MDR1. Expression of a cleavage-resistant c-Jun mutant (D65A) suppressed CDDP-induced apoptosis of CDDP-sensitive cells, whereas depletion of JNK2, c-Jun, or MDR1 in CDDP-resistant cancer cells promoted apoptosis upon CDDP treatment. In addition, mammary gland tumors induced by polyomavirus middle T antigen in JNK2(-/-) mice were more sensitive to CDDP compared with those in JNK2(+/+) mice. These findings highlight the instrumental role of c-Jun in the resistance of tumors to treatment with CDDP and indicate that c-Jun is a molecular target for improving cancer therapy.

Plk1 phosphorylation of orc2 and hbo1 contributes to gemcitabine resistance in pancreatic cancer

Although gemcitabine is the standard chemotherapeutic drug for treatment of pancreatic cancer, almost all patients eventually develop resistance to this agent. Previous studies identified Polo-like kinase 1 (Plk1) as the mediator of gemcitabine resistance, but the molecular mechanism remains unknown. In this study, we show that Plk1 phosphorylation of Orc2 and Hbo1 mediates the resistance to gemcitabine. We show that the level of Plk1 expression positively correlates with gemcitabine resistance, both in pancreatic cancer cells and xenograft tumors. Overexpression of Plk1 increases gemcitabine resistance, while inhibition of Plk1 sensitizes pancreatic cancer cells to gemcitabine treatment. To validate our findings, we show that inhibition of Plk1 sensitizes tumors to gemcitabine treatment in a mouse xenograft study. Mechanistically, we find that Plk1 phosphorylation of Orc2 maintains DNA replication on gemcitabine treatment. Furthermore, Plk1 phosphorylation of Hbo1 transcriptionally increases cFos expression and consequently elevates its target multidrug resistance 1 (MDR1), which was previously reported to confer chemotherapeutic drug resistance. Knockdown of cFos or MDR1 sensitizes gemcitabine-resistant cells to gemcitabine treatment. Finally, pancreatic cancer cells expressing Plk1-unphosphorylatable mutants of Orc2 or Hbo1 are more sensitive to gemcitabine than cells expressing wild-type Orc2 or Hbo1. In short, our study provides a mechanism for Plk1-mediated gemcitabine resistance, suggesting that Plk1 is a promising target for treatment of gemcitabine-resistant pancreatic cancer.

Modulation of estrogen receptor alpha activity and expression during breast cancer progression

Seventy percent of breast tumors express the estrogen receptor (ER), which is generally considered to predict a better outcome relative to ER-negative tumors, as they often respond to antiestrogen therapies. During cancer progression, mammary tumors can escape from estrogen control, resulting in the acquisition of invasive properties and resistance to treatment. ER expression is a dynamic phenomenon and is finely regulated at numerous levels, including the gene, mRNA, and protein levels. As a consequence, many molecular mechanisms have been implicated in modulating ER activity and estrogen signaling in mammary cancer. In fact, one-third of ER-positive breast cancer cells do not respond to first-line endocrine therapies, and a large subset of relapsing tumors retain ER expression. Increased knowledge of these mechanisms has led to the development of better prognostic methods and targeted therapies for patients; however, additional research is still needed to improve patient survival. In this chapter, we focus on the signaling pathways leading to changes in or loss of ER activity in breast cancer progression.

Transcriptional regulation of hTREX84 in human cancer cells

TREX (transcription/export) is a multiprotein complex that plays a key role in the transcriptional elongation and transport of mRNA from the nucleus to the cytoplasm. We previously reported the purification of the human TREX protein and found that expression of a member of this complex, p84N5 (referred to as hTREX84 or hHPR1), a RB binding protein, correlated with breast tumor size and metastasis. Here we examine the mechanisms of aberrant expression of hTREX84 in breast and ovarian cancer cells and evaluate its role in tumorigenesis. We show that ovarian tumor cells over-express hTREX84 4-fold and 10-fold compared to immortal, non-tumorigenic and primary ovarian surface epithelial cells, respectively. Reduction of hTREX84 levels by small interfering RNA result in inhibition of cellular proliferation and G(2/M) arrest. Even though we observed that hTREX84 expression was induced by treatment with a demethylation agent, 5-aza-2'-deoxycytidine (5-aza-dC), sodium bisulfite DNA sequencing and methylation specific PCR found no evidence of changes in DNA methylation in the CpG islands in the regulator region of hTREX84. We subsequently identify several transcriptional factors, including NF-κB binding sites in the hTREX84 gene promoter and demonstrate by chromatin immunoprecipation (ChIP) and site directed mutagenesis that RelA/p65 binds the NF-kB binding sites and induces hTREX84 expression. Finally, we show by immunohistochemistry (IHC) that RelA/p65 is abundantly expressed in malignant cells that aberrantly express hTREX84 indicating that RelA/p65 might play a pivotal role in regulating hTREX84 expression in cancer. Our results indicate that overexpression of hTREX84 is associated with cancer cell transformation, proliferation and may be regulated by RelA/p65.

Synthesis of a dual functional anti-MDR tumor agent PH II-7 with elucidations of anti-tumor effects and mechanisms

Multidrug resistance mediated by P-glycoprotein in cancer cells has been a major issue that cripples the efficacy of chemotherapy agents. Aimed for improved efficacy against resistant cancer cells, we designed and synthesized 25 oxindole derivatives based on indirubin by structure-activity relationship analysis. The most potent one was named PH II-7, which was effective against 18 cancer cell lines and 5 resistant cell lines in MTT assay. It also significantly inhibited the resistant xenograft tumor growth in mouse model. In cell cycle assay and apoptosis assay conducted with flow cytometry, PH II-7 induced S phase cell cycle arrest and apoptosis even in resistant cells. Consistently revealed by real-time PCR, it modulates the expression of genes related to the cell cycle and apoptosis in these cells, which may contributes to its efficacy against them. By side-chain modification and FITC-labeling of PH II-7, we were able to show with confocal microscopy that not only it was not pumped by P-glycoprotein, it also attenuated the efflux of Adriamycin by P-glycoprotein in MDR tumor cells. Real-time PCR and western blot analysis showed that PH II-7 down-regulated MDR1 gene via protein kinase C alpha (PKCA) pathway, with c-FOS and c-JUN as possible mediators. Taken together, PH II-7 is a dual-functional compound that features both the cytotoxicity against cancer cells and the inhibitory effect on P-gp mediated drug efflux.

Role for Class I histone deacetylases in multidrug resistance

Recent reports have showed that histone deacetylase (HDAC) inhibitor resulted in multidrug resistance (MDR) to other chemotherapeutic agents. However, the molecular mechanisms of Class I HDACs on MDR regulation are poorly understood. In this study, HDAC1 and HDAC2 acted as enhancers to intensify the chemosensitivities of anti-cancer drugs via reducing the expression levels of P-gp, MRP1 and MRP2. Furthermore, the dissociation of HDAC1 and HDAC2 led to transcriptional regulation of P-gp expression via the recruitment of p300, PCAF and NF-Y to the P-gp promoter region, which subsequently increased the level of the active gene marker, hyperacetylated histone H3. In parallel, selective inhibition of HDAC1 and HDAC2 induced the recruitment of p300, PCAF, NF-Y via acetylation of Sp1. Thus, our findings showed HDAC1 and 2 regulated P-gp expression through dynamic changes in chromatin structure and transcription factor association within the promoter region.

Differential chemosensitization of P-glycoprotein overexpressing K562/Adr cells by withaferin A and Siamois polyphenols

Background

Multidrug resistance (MDR) is a major obstacle in cancer treatment and is often the result of overexpression of the drug efflux protein, P-glycoprotein (P-gp), as a consequence of hyperactivation of NFκB, AP1 and Nrf2 transcription factors. In addition to effluxing chemotherapeutic drugs, P-gp also plays a specific role in blocking caspase-dependent apoptotic pathways. One feature that cytotoxic treatments of cancer have in common is activation of the transcription factor NFκB, which regulates inflammation, cell survival and P-gp expression and suppresses the apoptotic potential of chemotherapeutic agents. As such, NFκB inhibitors may promote apoptosis in cancer cells and could be used to overcome resistance to chemotherapeutic agents.

Results

Although the natural withanolide withaferin A and polyphenol quercetin, show comparable inhibition of NFκB target genes (involved in inflammation, angiogenesis, cell cycle, metastasis, anti-apoptosis and multidrug resistance) in doxorubicin-sensitive K562 and -resistant K562/Adr cells, only withaferin A can overcome attenuated caspase activation and apoptosis in K562/Adr cells, whereas quercetin-dependent caspase activation and apoptosis is delayed only. Interestingly, although withaferin A and quercetin treatments both decrease intracellular protein levels of Bcl2, Bim and P-Bad, only withaferin A decreases protein levels of cytoskeletal tubulin, concomitantly with potent PARP cleavage, caspase 3 activation and apoptosis, at least in part via a direct thiol oxidation mechanism.

Conclusions

This demonstrates that different classes of natural NFκB inhibitors can show different chemosensitizing effects in P-gp overexpressing cancer cells with impaired caspase activation and attenuated apoptosis.

Preventing chemoresistance of human breast cancer cell line, MCF-7 with celecoxib

PURPOSE

To investigate the preventive effect of celecoxib, a specific cyclooxygenase-2 (Cox-2) inhibitor, on the development of chemoresistance in breast cancer cell line, MCF-7, and explore the mechanism of the action.

METHODS

Chemoresistance phenotype was established by treating MCF-7 cells with 0.05 μg/ml doxorubicin for 7 days, and then the effect of preventive chemoresistance was investigated by the combination of same dose of doxorubicin with 10 μM celecoxib. 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyl-2H-tetrazolium bromide assay was used to assess cytostatic efficacy of doxorubicin and 50% inhibiting concentration (IC(50)) of MCF-7 cells. RT-PCR was performed to examine mRNA expression of multidrug resistance gene 1 (MDR1) and its transcription factors c-Jun and NF-κB. Western blotting analysis was performed to detect the expression of protein. Flow cytometry (FCM) was applied to analyze the expression and function of P-glycoprotein (P-gp). Electrophoretic gel mobility shift assay (EMSA) was performed to determine the DNA-binding activity of nuclear transcription factors AP-1 and NF-κB.

RESULTS

Compared with sensitive MCF-7 cells, MDR1 and its transcription factors c-Jun and NF-κB were up-regulated at both mRNA level (P < 0.01) and protein level (P < 0.01) by treatment with 0.05 μg/ml doxorubicin for 7 days. After co-incubation with both the same dose of doxorubicin and 10 μM celecoxib for 7 days, both mRNA level and protein level of MDR1, c-Jun and NF-κB up-regulated by doxorubicin were partly reversed (P < 0.01); DNA-binding activity of nuclear transcription factors AP-1 and NF-κB were inhibited; and the function of P-gp was decreased (P < 0.01). When MCF-7 cells were treated with increasing doses of doxorubicin in the presence of 10 μM celecoxib, IC50 value of doxorubicin and doxorubicin plus 10 μM celecoxib was 0.67 ± 0.03 and 0.38 ± 0.04 μg/ml, respectively (P < 0.01).

CONCLUSION

Celecoxib effectively prevents the development of chemoresistance in breast cancer cell line MCF-7 induced by doxorubicin, which was partly involved in inhibiting the expression and DNA-binding activity of nuclear transcription factors AP-1 and NF-κB and downstream expression and function of P-gp. Furthermore, cytostatic efficacy of celecoxib and doxorubicin on MCF-7 cell was synergistic.

Celecoxib inhibits MDR1 expression through COX-2-dependent mechanism in human hepatocellular carcinoma (HepG2) cell line

The role of COX-2 in the regulation of the expression of MDR1, a P-glycoprotein involved in hepatocellular carcinoma cell line, HepG2, was studied in the present investigation. Celecoxib, a selective inhibitor of COX-2, at 25 microM concentration increased the accumulation of doxorubicin in HepG2 cells and enhanced the sensitivity of the cells to doxorubicin by tenfold. The induction of MDR1 expression by PGE2 and its downregulation by celecoxib or by COX-2 knockdown suggests that the enhanced sensitivity of HepG2 cells to doxorubicin by celecoxib is mediated by the downregulation of MDR1 expression, through COX-2-dependent mechanism. Further studies revealed the involvement of AP-1 in the celecoxib-induced downregulation of MDR1 expression. These experimental studies correlated well with in silico predictions and further suggested the inactivation of the signal transduction pathways involving ERK, JNK and p38. The present study thus demonstrates the usefulness of COX-2 intervention in overcoming the drug resistance in HepG2 cells.

Increased p38-MAPK is responsible for chemotherapy resistance in human gastric cancer cells

Background

Chemoresistance is one of the main obstacles to successful cancer therapy and is frequently associated with Multidrug resistance (MDR). Many different mechanisms have been suggested to explain the development of an MDR phenotype in cancer cells. One of the most studied mechanisms is the overexpression of P-glycoprotein (P-gp), which is a product of the MDR1 gene. Tumor cells often acquire the drug-resistance phenotype due to upregulation of the MDR1 gene. Overexpression of MDR1 gene has often been reported in primary gastric adenocarcinoma.

Methods

This study investigated the role of p38-MAPK signal pathway in vincristine-resistant SGC7901/VCR cells. P-gp and MDR1 RNA were detected by Western blot analysis and RT-PCR amplification. Mitgen-activated protein kinases and function of P-gp were demonstrated by Western blot and FACS Aria cytometer analysis. Ap-1 activity and cell apoptosis were detected by Dual-Luciferase Reporter Assay and annexin V-PI dual staining.

Results

The vincristine-resistant SGC7901/VCR cells with increased expression of the multidrug-resistance 1 (MDR1) gene were resistant to P-gp-related drug and P-gp-unrelated drugs. Constitutive increases of phosphorylated p38-MAPK and AP-1 activities were also found in the drug-resistant cells. Inhibition of p38-MAPK by SB202190 reduced activator protein-1 (AP-1) activity and MDR1 expression levels and increased the sensitivity of SGC7901/VCR cells to chemotherapy.

Conclusion

Activation of the p38-MAPK pathway might be responsible for the modulation of P-glycoprotein-mediated and P-glycoprotein-unmediated multidrug resistance in the SGC7901/VCR cell line.

Bovine dialyzable leukocyte extract modulates AP-1 DNA-binding activity and nuclear transcription factor expression in MCF-7 breast cancer cells

BACKGROUND

We have previously demonstrated that bovine dialyzable leukocyte extract (bDLE) induces death through an apoptosis mechanism in MCF-7 breast cancer cells. Depending on the cell type and stimulus, activating protein-1 (AP-1) has been shown to regulate cell proliferation and differentiation, the stress response, apoptosis and survival. It remains unknown whether AP-1 and other transcription factors are mechanisms by which bDLE induces cell death.

METHODS

To determine whether bDLE modulates the AP-1 DNA binding and gene expression, MCF-7 breast cancer cells were treated with bDLE (0, 1, 5, 10 U) for 72 h and evaluated by electrophoretic mobility shift assay, reverse transcriptase-polymerase chain reaction and Western blot assays.

RESULTS

bDLE induced inhibition of cell growth, suppressed the AP-1 DNA-binding activity, decreased c-Jun protein expression and modulated NFATx, NFATc, NFkappaB, c-Jun and c-Fos transcription factor gene expression in MCF-7 breast cancer cells.

DISCUSSION

The present data indicate that bDLE can block the AP-1 DNA-binding activity and expression of several transcriptions factors in breast cancer cells, which will have great potential in improving cancer therapy.

A role for ceramide in driving cancer cell resistance to doxorubicin

Advanced cancers acquire resistance to chemotherapy, and this results in treatment failure. The cellular mechanisms of chemotherapy resistance are not well understood. Here, for the first time, we show that ceramide contributes to cellular resistance to doxorubicin through up-regulating the gene expression of glucosylceramide synthase (GCS). Ceramide, a cellular lipid messenger, modulates doxorubicin-induced cell death. GCS catalyzes ceramide glycosylation, converting ceramide to glucosylceramide; this process hastens ceramide clearance and limits ceramide-induced apoptosis. In the present study, we evaluated the role of the GCS gene in doxorubicin resistance using several paired wild-type and drug-resistant (doxorubicin-selected) cancer cell lines, including breast, ovary, cervical, and colon. GCS was overexpressed in all drug-resistant counterparts, and suppressing GCS overexpression using antisense oligonucleotide restored doxorubicin sensitivity. Characterizing the effect mechanism showed that doxorubicin exposure increased ceramide levels, enhanced GCS expression, and imparted cellular resistance. Exogenous C(6)-ceramide and sphingomyelinase treatments mimicked the influence of doxorubicin on GCS, activating the GCS promoter and up-regulating GCS gene expression. Fumonisin B(1), an inhibitor of ceramide synthesis, significantly suppressed doxorubicin-up-regulated GCS expression. Promoter truncation, point mutation, gel-shift, and protein-DNA ELISA analysis showed that transcription factor Sp1 was essential for ceramide-induced GCS up-regulation. These data indicate that ceramide-governed GCS gene expression drives cellular resistance to doxorubicin.

Up-regulation of ras-GAP genes is reversed by a MEK inhibitor and doxorubicin in v-Ki-ras-transformed NIH/3T3 fibroblasts

Ras-GTPase-activating proteins (Ras-GAPs) have been implicated both as suppressors of Ras and as effectors in regulating cellular activities. To study whether Ras-GAPs have roles in tumor cell survival or not, mRNA levels of ras-related genes were measured in v-Ki-ras-transformed (DT) and the parental NIH/3T3 cells, using real-time PCR. mRNA levels of p120-Gap, Gap1(m), and PIK3CA were increased in DT cells compared with NIH/3T3 cells. p120-Gap and PIK3CA genes were induced by addition of serum or epidermal growth factor to serum-starved DT cells. Three anti-cancer drugs, an ERK kinase (MEK) inhibitor PD98059, a topoisomerase II poison doxorubicin (adriamycin), and a histone deacetylase inhibitor trichostatin A, selectively blocked the overexpression of p120-Gap and Gap1(m) genes in DT cells. These drugs also caused reversion of DT cells to the adherent shape associated with growth arrest. Our results suggest that p120-Gap and Gap1(m) genes provide important biomarkers for cancer therapies.

Methylation-controlled J protein promotes c-Jun degradation to prevent ABCB1 transporter expression

Methylation-controlled J protein (MCJ) is a newly identified member of the DnaJ family of cochaperones. Hypermethylation-mediated transcriptional silencing of the MCJ gene has been associated with increased chemotherapeutic resistance in ovarian cancer. However, the biology and function of MCJ remain unknown. Here we show that MCJ is a type II transmembrane cochaperone localized in the Golgi network and present only in vertebrates. MCJ is expressed in drug-sensitive breast cancer cells but not in multidrug-resistant cells. The inhibition of MCJ expression increases resistance to specific drugs by inducing expression of the ABCB1 drug transporter that prevents intracellular drug accumulation. The induction of ABCB1 gene expression is mediated by increased levels of c-Jun due to an impaired degradation of this transcription factor in the absence of MCJ. Thus, MCJ is required in these cells to prevent c-Jun-mediated expression of ABCB1 and maintain drug response.

Differences in binding of nuclear proteins from P. berghei strains differing by chloroquine resistance to oligonucleotides corresponding to mdr1 gene regulatory elements

Proteins specifically reacting with AP1, MEF1, NF-IL6, and SP1 transcription factor binding sites were detected for the first time in nuclear extract of P. berghei (rodent malaria parasite) using gel retardation assay. P. berghei strains with different chloroquine resistance exhibited appreciable differences in the pattern of nuclear protein binding to the majority of the studied sites, which attests to changes in the plasmodial regulatory system during chloroquine resistance selection.

Modulatory role of verapamil treatment on the cardiac electrophysiological effects of cisapride

The role of transport proteins in the distribution of drugs in various tissues has obvious implications for drug effects. Recent reports indicate that such transporters are present not only in the liver, intestine, or blood−brain barrier but also in the heart. The objective of our study was to determine whether treatment of animals with verapamil, a well-known L-type calcium channel blocker with modulatory properties of membrane transporters, would alter distribution and cardiac electrophysiological effects of an IKrblocker. Male guinea pigs (n = 72) were treated with either saline or verapamil at various doses (1.5 to 15 mg/kg) and for various durations (1 to 7 d). Animals were sacrified 24 h after the last dose of verapamil (or saline), and their hearts were isolated and retroperfused with cisapride, a gastrokinetic drug with IKrblockade properties. In hearts obtained from animals treated with vehicle, 50 nmol/L cisapride prolonged MAPD90by 15 ± 5 ms vs. 36 ± 8 ms in hearts from animals treated with verapamil 15 mg·kg−1·d−1for 5 d (p < 0.01). Treatment effects were dose- and time-dependent. Cardiac myocytes isolated from animals treated with vehicle or verapamil were incubated for 3 h with 100 ng/mL cisapride. Intracellular concentrations of cisapride in cardiac myocytes from animals treated with verapamil were 1.6-fold higher than those measured in myocytes from animals treated with vehicle (p < 0.01). The increase in intracellular concentrations of cisapride and potentiation of cisapride electrophysiological effects suggest that chronic treatment with drugs such as verapamil may modulate drug effects on the QT interval because of an increased access to intracellular binding sites on IKrchannels.

Biologic basis of sequential and combination therapies for hormone-responsive breast cancer

Although pharmacologic therapies that reduce or block estrogen signaling are effective treatments of estrogen receptor (ER)-positive breast cancer, acquired resistance to individual drugs can develop. Furthermore, this approach is ineffective as initial therapy for a subgroup of receptor-positive patients. The mechanisms of drug resistance are not completely understood, but the presence of alternative signaling pathways for activating ER response appears to play a significant role. Cross-talk between signaling pathways can activate ERs when conventional ER pathways are blocked or inactivated. For example, signaling via epidermal growth factor or HER-2 receptors, mitogen-activated protein kinases, phosphatidylinositol 3' kinase/protein kinase B, and vascular endothelial growth factor receptor can lead to estrogen-independent stimulation of ERs and tumor growth. The discovery that alternative pathways are involved in estrogen signaling has prompted development of newer endocrine therapies, such as aromatase inhibitors and pure estrogen antagonists, with distinct mechanisms for interrupting signal transduction. The existence of multiple pathways may explain the effectiveness of follow-up therapy with a different class of endocrine agents after failure of prior endocrine treatment. Because they do not have the partial agonist activity of tamoxifen that is enhanced by the adaptive hypersensitivity process, these alternative endocrine agents may play an increasingly important role in the treatment of ER-positive breast cancer. Although optimal sequencing of these agents has not been determined and is continuing to evolve, current evidence allows rational recommendations to be made. The multiple pathways involved in activating ERs also provide a rationale for combining endocrine and non-endocrine therapies that block different signaling pathways, which may have synergistic and overlapping interactions.

Monitoring the gene expression profiles of doxorubicin-resistant acute myelocytic leukemia cells by DNA microarray analysis

Acquired drug-resistance phenotype is a key factor in the relapse of patients suffering hematological malignancies. In order to investigate the genes involved in drug resistance, a human leukemia cell line that is resistant to doxorubicin, an anthracycline anticancer agent (AML-2/DX100), was selected and its gene expression profile was analyzed using a cDNA microarray. A number of genes were differentially expressed in the AML-2/DX100 cells, compared with the wild type (AML-2/WT). Pro-apoptotic genes such as TNFSF7 and p21 (Cip1/Waf1) were significantly down-regulated, whereas the IKBKB, PCNA, stathmin 1, MCM5, MMP-2 and MRP1 genes, which are involved in anti-apoptotic or cell cycle progression, were over-expressed. The AML-2/DX100 cells were also resistant to other anticancer drugs, including daunorubicin and camptothecin, and the expression levels of the differentially regulated genes such as STMN1, MMP-2 and CTSG, were constantly maintained. This suggests that the deregulated genes obtained from the DNA microarray analysis in a cell line model of drug resistance might contribute to the acquired drug resistance after chronic exposure.

Effect of Vinca alkaloids on ERα levels and Estradiol-induced responses in MCF-7 cells

Vinca alkaloids (VAs) such as Vincristine, Vinblastine and Vinorelbine are antineoplastic drugs that inhibit tubulin polymerisation into microtubules, induce mitotic G2/M arrest, activate c-Jun N-terminal kinase (JNK) and induce apoptosis. Although there are many studies evaluating the effect of VAs on breast cancer patients, until now little was known about how these compounds and estradiol signaling pathways might interfere. In this report, we show for the first time that VAs decreased ERalpha protein levels in the human breast cancer cell line MCF-7; VAs induced a parallel decrease in estrogen receptor mRNA. All the VAs tested inhibited estradiol (E2) mediated transactivation at ERE-driven promoters. E2 inhibited VAs-induced AP1 stimulation in MCF-7, but this inhibition was not observed when E2 is added 24 h in advance of VAs treatment. In contrast to the reported preventing effect over taxol-mediated apoptosis, E2 did not prevent VAs-induced cell death and interestingly, addition of E2 24 hours in advance of VAs treatment resulted in an increase of the number of cells undergoing apoptosis. Similar results were observed when E2 is replaced by other proliferation signals such as EGF. These results demonstrate that in the breast cancer cell-line MCF-7, E2-induced proliferation before VAs treatment enhances the apoptotical response to VAs which might have important implications in clinica.

Vitamin C enhances chemosensitization of esophageal cancer cells in vitro

Chemotherapy is increasingly utilised in multimodal protocols to try and improve outcomes. Cisplatin and 5-fluorouracil (5-Fu) are the mainstay of chemotherapeutic regimens, and an understanding of sensitivity and resistance of esophageal cancer to these agents is of considerable clinical importance. Antioxidants may modulate the response to chemotherapy, and in this study we examined the effect of vitamin C on 5-Fu and cisplatin cytotoxicity and related pathways in the esophageal cancer cell lines OE33 and SKGT-4. The antiproliferative effect of antitumor agents was measured by the MTT assay, and the transcription factors NF-kappaB and AP-1 pathways were assessed by electrophoretic mobility gel shift assay. 5-Fu and cisplatin demonstrated marked morphological changes and decreased cell proliferation. A combination of vitamin C with 5-Fu or cisplatin exerted a significantly enhanced cytotoxic effect compared to both drugs individually. Treatment of esophageal cancer cells with 5-Fu and cisplatin induced NF-kappaB and AP-1 activation. Pretreatment with vitamin C inhibited 5-Fu or cisplatin induced NF-kappaB nuclear translocation and DNA binding activity, but vitamin C had no effect on IkappaB-alpha protein levels. Vitamin C also inhibited 5-Fu- and cisplatin-induced AP-1 activation. Our data demonstrate that vitamin C enhances the antitumor activity of 5-Fu and cisplatin, in part by inhibiting translocation of NF-kappaB and AP-1, and sensitizes cancer cells to drug-induced cell death. The data suggest that vitamin C supplementation may improve the efficacy of chemotherapy for esophageal cancer.