Overcoming drug resistance by regulating nuclear receptors

Modulation of multidrug resistance in cancer cells by chelidonine and Chelidonium majus alkaloids

Cancer cells often develop multidrug resistance (MDR) which is a multidimensional problem involving several mechanisms and targets. This study demonstrates that chelidonine and an alkaloid extract from Chelidonium majus, which contains protoberberine and benzo[c]phenanthridine alkaloids, has the ability to overcome MDR of different cancer cell lines through interaction with ABC-transporters, CYP3A4 and GST, by induction of apoptosis, and cytotoxic effects. Chelidonine and the alkaloid extract inhibited P-gp/MDR1 activity in a concentration-dependent manner in Caco-2 and CEM/ADR5000 and reversed their doxorubicin resistance. In addition, chelidonine and the alkaloid extract inhibited the activity of the drug modifying enzymes CYP3A4 and GST in a dose-dependent manner. The alkaloids induced apoptosis in MDR cells which was accompanied by an activation of caspase-3, -8,-6/9, and phosphatidyl serine (PS) exposure. cDNA arrays were applied to identify differentially expressed genes after treatment with chelidonine and the alkaloid extract. The expression analysis identified a common set of regulated genes related to apoptosis, cell cycle, and drug metabolism. Treatment of Caco-2 cells with 50 μg/ml alkaloid extract and 50 μM chelidonine for up to 48 h resulted in a significant decrease in mRNA levels of P-gp/MDR1, MRP1, BCRP, CYP3A4, GST, and hPXR and in a significant increase in caspase-3 and caspase-8 mRNA. Thus, chelidonine is a promising model compound for overcoming MDR and for enhancing cytotoxicity of chemotherapeutics, especially against leukaemia cells. Its efficacy needs to be confirmed in animal models.

Nuclear receptors PXR and CAR: implications for drug metabolism regulation, pharmacogenomics and beyond

INTRODUCTION

'Orphan' nuclear receptors belong to the nuclear receptor (NR) superfamily of transcriptional factors. Binding of ligands to these receptors results in the recruitment of the co-activators, thereby regulating the expression of cognate target genes.

AREAS COVERED

This review discusses the transcriptional regulation of P450 genes by two major xenobiotic nuclear receptors, pregnane X receptor (PXR) and constitutive androstane receptor (CAR). Additional PXR and CAR target genes include those encoded for UDP-glucuronosyltransferases, glutathione S-transferases, sulfotransferases and drug transporters. The authors discuss the involvement of PXR and CAR in endobiotic metabolism. They also review the polymorphisms of PXR and CAR.

EXPERT OPINION

PXR and CAR are both xenobiotic and endobiotic receptors. A remarkably diverse set of chemicals can activate PXR and CAR. There is significant cross-talk among xenobiotic receptors. Future studies are needed to focus on the polymorphisms of the nuclear receptors and the complex regulatory networks among nuclear receptors. Considerations should be given while designing PXR- or CAR-targeting pharmaceutics to avoid adverse drug effects. In the meantime, due to the diverse functions of PXR and CAR, agonists or antagonists for these receptors may have therapeutic potentials in managing certain diseases and enhancing therapeutic indexes.

Repeated dosing of piperine induced gene expression of P-glycoprotein via stimulated pregnane-X-receptor activity and altered pharmacokinetics of diltiazem in rats

This study investigated the effect of piperine on the gene expression of P-glycoprotein (P-gp) as well as pregnane-X-receptor (PXR) activity and also its implication on the bioavailability of diltiazem, a P-gp substrate. The effect of piperine on the systemic exposure of diltiazem was examined in rats after the intravenous and oral administration of diltiazem with/without 2 week pretreatment with piperine. Compared with the control group given diltiazem (20 mg/kg) alone, the pretreatment with piperine (10 or 20 mg/kg, once daily for 2 weeks) decreased the oral exposure of diltiazem by 36-48% in rats. Consequently, the bioavailability of oral diltiazem was significantly lower (p < 0.05) after the 2 week pretreatment with piperine. The pretreatment with piperine for 2 weeks also reduced the systemic exposure of desacetyldiltiazem, a major active metabolite of diltiazem by approximately 73%, accompanied by a significant decrease in the metabolite-parent ratio. In contrast to the oral pharmacokinetics, piperine did not affect the intravenous pharmacokinetics of diltiazem in rats. Immunoblot analysis indicated that the protein expression level of intestinal P-gp was significantly enhanced after the 2 week pretreatment with piperine in rats. In addition, piperine increased the PXR reporter activity in human hepatoma cells. Taken together, the 2 week pretreatment with piperine significantly induced intestinal P-gp expression in conjunction with stimulated PXR activity and decreased the oral exposure of diltiazem and desacetyldiltiazem in rats.

Increased Nanog expression promotes tumor development and Cisplatin resistance in human esophageal cancer cells

BACKGROUND/AIMS

Nanog plays a key role in stem cell self-renewal and pluripotency differentiation in embryonic stem cells ( ESCs). Recently, some studies reported that abnormal expression of Nanog could be detected in several tumors, indicating that Nanog might be related to tumor development. However, studies on the correlation between Nanog expression and esophageal cancer are sparse.

METHODS

In this study, we established two esophageal cancer cell lines 9706-Nanog and 9706-shNanog which stably expressed Nanog and Nanog-short-hairpin RNA (shRNA) genes.

RESULTS

We found that Nanog expression could promote the proliferation and invasiveness of the cancer cells, and inhibit the apoptosis. We also treated 9706-Nanog, EC9706 and 9706-shNanog cell lines with cisplatin and evaluated the drug sensitivity of the three cell lines. We found that the sensitivity of cisplatin was decreased with increased expression of Nanog. The expression of MDR-1 was also increased in 9706Nanog cells.

CONCLUSIONS

Nanog may play an important role in human esophageal cancer development, and could be used as a therapeutic target in esophageal cancer treatment.

Pregnane xenobiotic receptor in cancer pathogenesis and therapeutic response

Pregnane xenobiotic receptor (PXR) is an orphan nuclear receptor that regulates the metabolism of endobiotics and xenobiotics. PXR is promiscuous and unique in that it is activated by a diverse group of xenochemicals, including therapeutic anticancer drugs and naturally-occurring endocrine disruptors. PXR has been predominantly studied to understand its regulatory role in xenobiotic clearance in liver and intestine via induction of drug metabolizing enzymes and drug transporters. PXR, however, is widely expressed and has functional implications in other normal and malignant tissues, including breast, prostate, ovary, endometrium and bone. The differential expression of PXR and its target genes in cancer tissues has been suggested to determine the prognosis of chemotherapeutic outcome. In addition, the emerging evidence points to the implications of PXR in regulating apoptotic and antiapoptotic as well as growth factor signaling that promote tumor proliferation and metastasis. In this review, we highlight the recent progress made in understanding the role of PXR in cancer, discuss the future directions to further understand the mechanistic role of PXR in cancer, and conclude with the need to identify novel selective PXR modulators.

Role of CAR and PXR in xenobiotic sensing and metabolism

INTRODUCTION

The xenobiotic detoxification system, which protects the human body from external chemicals, comprises drug-metabolizing enzymes and transporters whose expressions are regulated by pregnane X receptor (PXR) and the constitutive androstane receptor (CAR). The progress made in a large number of recent studies calls for a timely review to summarize and highlight these key discoveries.

AREAS COVERED

This review summarizes recent advances in elucidating the roles of PXR and CAR in the xenobiotic detoxification system. It also highlights the progress in understanding the regulation of PXR and CAR activity at the post-translational levels, as well as the structural basis for the regulation of these two xenobiotic sensors.

EXPERT OPINION

Future efforts are needed to discover novel agonists and antagonists with species and isoform selectivity, to systematically understand the regulation of PXR and CAR at multiple levels (transcriptional, post-transcriptional and post-translational levels) in response to xenobiotics exposure, and to solve the structures of the full-length receptors, which will be enabled by improved protein expression and purification techniques and approaches. In addition, more efforts will be needed to validate PXR and CAR as disease-related therapeutic targets and thus expand their roles as master xenobiotic sensors.

Contribution of microRNAs to radio- and chemoresistance of brain tumors and their therapeutic potential

Glioblastomas, particularly high grade brain tumors such as glioblastoma multiforme, are characterized by increased anaplasy, malignancy, proliferation, and invasion. These tumors exhibit high resistance to radiation therapy and treatment with anti-cancer drugs. The radio- and chemoresistance of gliomas is attributed to cancer stem cells (CSCs) that are considered as major contributors for maintenance and propagation of tumor cell mass, cancer malignancy and invasiveness, and tumor cell survival after courses of radiotherapy and medical interventions. MicroRNAs (miRNAs), key post-transcriptional gene regulators, have altered expression profiles in gliomas. Some of miRNAs whose expression is markedly up-regulated in brain tumors are likely to have a pro-oncogenic role through supporting growth, proliferation, migration, and survival of cancer stem and non-stem cells. In contrast, a population of miRNA possessing anti-tumor effects is suppressed in gliomas. In this review, we will consider miRNAs and their influence on radio- and chemoresistance of gliomas. These miRNAs harbor a great therapeutic significance as potent agents in future targeted anti-cancer therapy to sensitize glioma tumor cells and CSCs to cytotoxic effects of radiation exposure and treatment with anti-cancer drugs.

GCS overexpression is associated with multidrug resistance of human HCT-8 colon cancer cells

Purpose

Multidrug resistance is one of the main impediments to the successful treatment of colon cancer. Glucosylceramide synthase (GCS) which is related to multidrug resistance (MDR) can reduce the level of ceramide and can help cells escape from the ceramide-induced cell apoptosis. However, the underlying mechanism is still unclear.

Methods

The cell proliferation and cell toxicity were measured with Cell Counting Kit-8 (CCK-8). The mRNA levels of GCS and MDR1 were detected by semiquantitative reverse transcription-PCR amplification, the protein levels of GCS, caspase-3 and P-gp proteins were indicated by Western blotting. The apoptosis rates of cells were measured with flow cytometry.

Results

The relative mRNA levels of GCS in HCT-8, HCT-8/VCR, HCT-8/VCR- sh-mock and HCT-8/VCR-sh-GCS were 71.4 ± 1.1%, 95.1 ± 1.2%, 98.2 ± 1.5%, and 66.6 ± 2.1% respectively. The mRNA levels of MDR1 were respectively 61.3 ± 1.1%, 90.5 ± 1.4%, 97.6 ± 2.2% and 56.1 ± 1.2%. The IC50 of Cisplatin complexes were respectively 69.070 ± 0.253 μg/ml, 312.050 ± 1.46 μg/ml, 328.741 ± 5.648 μg/ml, 150.792 ± 0.967 μg/ml in HCT-8, HCT-8/VCR, HCT-8/VCR-sh-mock and HCT-8/VCR-sh-GCS. The protein levels of caspase-3 were 34.2 ± o.6%, 93.0 ± 0.7%, 109.09 ± 0.7%, 42.7 ± 1.3% respectively. The apoptosis rates of cells were 8.77 ± 0.14%, 12.75 ± 0.54%, 15.39 ± 0.41% and 8.49 ± 0.23% respectively.

Conclusion

In conclusion, our research indicated that suppression of GCS restores the sensitivity of multidrug resistance colon cancer cells to drug treatment.

Short hairpin RNA targeting Twist1 suppresses cell proliferation and improves chemosensitivity to cisplatin in HeLa human cervical cancer cells

Development of multidrug resistance (MDR) remains a major hurdle to successful cancer chemotherapy and MDR1/P-gp overexpression is believed to be mainly responsible for MDR of tumor cells. Twist1, which is a highly conserved transcription factor that belongs to the family of basic helix-loop-helix proteins, has been shown to be a major regulator of the epithelial-mesenchymal transition (EMT), and therefore promotes carcinoma metastasis. Recently, a novel function of Twist1 was reported to confer radioresistance or chemoresistance in cervical cancer. However, mechanisms of such efficacy are not completely elucidated. In the present study, we firstly analyzed the relationship between Twist1 and MDR1/P-gp expression in human cervical cancer specimens and demonstrated a positive correlation between Twist1 and MDR1/P-gp expression in the same patient. Additionally, we provide the first evidence that silencing of Twist1 by RNAi downregulated MDR1/P-gp expression in HeLa cervical cancer cells, suppressed the cell proliferation, inhibited Rhodamine123 efflux activity of cells and sensitized cells to cisplatin treatment. Collectively, these findings suggest that Twist1-mediated modulation of MDR1/P-gp expression plays an important role in sensitization of cervical cancer cells to cisplatin, and also indicate a novel therapeutic strategy to overcome drug resistance through inactivation of Twist1 expression in cervical cancer.

Chemotherapy dosing schedule influences drug resistance development in ovarian cancer

Drug resistance leads to chemotherapy failure and is responsible for the death of a great majority of patients with metastatic, late-stage ovarian cancer. The present study addressed whether changes in the chemotherapy dosing schedule affect the development, further worsening, or circumvention of drug resistance in chemosensitive and chemoresistant ovarian cancer. Severe combined immunodeficient mice bearing HeyA8 and HeyA8-MDR xenografts were treated with docetaxel intermittently (1×/wk or 3×/wk) or continuously for 21 days. Tumor mRNA expression of genes implicated in docetaxel resistance was measured by quantitative real-time-PCR. Analyzed genes included those encoding for the drug efflux transporters mdr1 and mrp7 and for molecules that interfere with or overcome the effects of docetaxel, including β-tubulinIII, actinin4, stathmin1, bcl2, rpn2, thoredoxin, and akt2. In both models, continuous docetaxel resulted in greater antitumor efficacy than 1×/wk or 3×/wk dosing and did not induce upregulation of any analyzed genes. Once weekly dosing caused upregulation of various drug resistance-related genes, especially in chemoresistant xenografts. More frequent, 3×/wk dosing diminished this effect, although levels of various genes were higher than for continuous chemotherapy. Drug efflux transporter expression was further examined by Western blotting, confirming that intermittent, but not continuous, docetaxel induced significant upregulation. Overall, our results show that the presence and length of treatment-free intervals contribute to the development of drug resistance. Elimination of these intervals by continuous dosing resulted in superior antitumor efficacy and prevented drug resistance induction in chemosensitive and chemoresistant disease. These results encourage the clinical implementation of continuous chemotherapy to overcome and/or prevent drug resistance in newly diagnosed and recurrent, refractory ovarian cancer.