Up-regulation of MDR1 and induction of doxorubicin resistance by histone deacetylase inhibitor depsipeptide (FK228) and ATRA in acute promyelocytic leukemia cells

The Methyltransferases METTL7A and METTL7B Confer Resistance to Thiol-Based Histone Deacetylase Inhibitors

Histone deacetylase inhibitors (HDACi) are part of a growing class of epigenetic therapies used for the treatment of cancer. Although HDACis are effective in the treatment of T-cell lymphomas, treatment of solid tumors with this class of drugs has not been successful. Overexpression of the multidrug resistance protein P-glycoprotein (P-gp), encoded by ABCB1, is known to confer resistance to the HDACi romidepsin in vitro, yet increased ABCB1 expression has not been associated with resistance in patients, suggesting that other mechanisms of resistance arise in the clinic. To identify alternative mechanisms of resistance to romidepsin, we selected MCF-7 breast cancer cells with romidepsin in the presence of the P-gp inhibitor verapamil to reduce the likelihood of P-gp-mediated resistance. The resulting cell line, MCF-7 DpVp300, does not express P-gp and was found to be selectively resistant to romidepsin but not to other HDACis such as belinostat, panobinostat, or vorinostat. RNA-sequencing analysis revealed upregulation of the mRNA coding for the putative methyltransferase, METTL7A, whose paralog, METTL7B, was previously shown to methylate thiol groups on hydrogen sulfide and captopril. As romidepsin has a thiol as the zinc-binding moiety, we hypothesized that METTL7A could inactivate romidepsin and other thiol-based HDACis via methylation of the thiol group. We demonstrate that expression of METTL7A or METTL7B confers resistance to thiol-based HDACis and that both enzymes are capable of methylating thiol-containing HDACis. We thus propose that METTL7A and METTL7B confer resistance to thiol-based HDACis by methylating and inactivating the zinc-binding thiol.

Doxorubicin and other anthracyclines in cancers: Activity, chemoresistance and its overcoming

Anthracyclines have been important and effective treatments against a number of cancers since their discovery. However, their use in therapy has been complicated by severe side effects and toxicity that occur during or after treatment, including cardiotoxicity. The mode of action of anthracyclines is complex, with several mechanisms proposed. It is possible that their high toxicity is due to the large set of processes involved in anthracycline action. The development of resistance is a major barrier to successful treatment when using anthracyclines. This resistance is based on a series of mechanisms that have been studied and addressed in recent years. This work provides an overview of the anthracyclines used in cancer therapy. It discusses their mechanisms of activity, toxicity, and chemoresistance, as well as the approaches used to improve their activity, decrease their toxicity, and overcome resistance.

Multifunctional Protein Hybrid Nanoplatform for Synergetic Photodynamic-Chemotherapy of Malignant Carcinoma by Homologous Targeting Combined with Oxygen Transport

Photodynamic therapy (PDT) under hypoxic conditions and drug resistance in chemotherapy are perplexing problems in anti-tumor treatment. In addition, central nervous system neoplasm-targeted nanoplatforms are urgently required. To address these issues, a new multi-functional protein hybrid nanoplatform is designed, consisting of transferrin (TFR) as the multicategory solid tumor recognizer and hemoglobin for oxygen supply (ODP-TH). This protein hybrid framework encapsulates the photosensitizer protoporphyrin IX (PpIX) and chemotherapeutic agent doxorubicin (Dox), which are attached by a glutathione-responsive disulfide bond. Mechanistically, ODP-TH crosses the blood-brain barrier (BBB) and specifically aggregated in hypoxic tumors via protein homology recognition. Oxygen and encapsulated drugs ultimately promote a therapeutic effect by down-regulating the abundance of multidrug resistance gene 1 (MDR1) and hypoxia-inducible factor-1-α (HIF-1α). The results reveal that ODP-TH achieves oxygen transport and protein homology recognition in the hypoxic tumor occupation. Indeed, compared with traditional photodynamic chemotherapy, ODP-TH achieves a more efficient tumor-inhibiting effect. This study not only overcomes the hypoxia-related inhibition in combination therapy by targeted oxygen transport but also achieves an effective treatment of multiple tumors, such as breast cancer and glioma, providing a new concept for the construction of a promising multi-functional targeted and intensive anti-tumor nanoplatform.

Effect of sodium butyrate on ABC transporters in lung cancer A549 and colorectal cancer HCT116 cells

Histone deacetylase (HDAC) inhibitors and DNA alkylators are effective components of combination chemotherapy. The aim of the present study was to investigate the possible mechanism of their synergism by detecting the effect of HDAC inhibitors on the expression levels of drug transporters that export DNA alkylators. It was demonstrated that the HDAC inhibitor sodium butyrate (NaB) induced the differential expression of multidrug resistant ATP-binding cassette (ABC) transporters in lung cancer and colorectal cancer cells. Specifically, NaB increased the mRNA expression levels of ABC subfamily B member 1 (ABCB1), ABCC10 and ABCC12, and protein expression levels of multidrug resistance-1 (MDR1), multidrug resistance-associated protein 7 (MRP7) and MRP9. Moreover, NaB decreased the expression levels of ABCC1, ABCC2 and ABCC3 mRNAs, as well as those of MRP1, MRP2 and MRP3 proteins. The molecular mechanism underlying this process was subsequently investigated. NaB decreased the expression of HDAC4, but not HDAC1, HDAC2 or HDAC3. In addition, NaB promoted histone H3 acetylation and methylation at lysine 9, as well as MDR1 acetylation, suggesting that acetylation and methylation may be involved in NaB-mediated ABC transporter expression. Thus, the present results indicated that the synergism of the HDAC inhibitors with the DNA alkylating agents may due to the inhibitory effect of MRPs by HDAC inhibitors. The findings also suggested the possibility of antagonistic effects following the combined treatment of HDAC inhibitors with MDR1 ligands.

The SMAC mimetic LCL161 is a direct ABCB1/MDR1-ATPase activity modulator and BIRC5/Survivin expression down-regulator in cancer cells

Upregulation of ABCB1/MDR1 (P-gp) and BIRC5/Survivin promotes multidrug resistance in a variety of human cancers. LCL161 is an anti-cancer DIABLO/SMAC mimetic currently being tested in patients with solid tumors, but the molecular mechanism of action of LCL161 in cancer cells is still incompletely understood. It is still unclear whether LCL161 is therapeutically applicable for patients with ABCB1-overexpressing multidrug resistant tumors. In this study, we found that the potency of LCL161 is not affected by the expression of ABCB1 in KB-TAX50, KB-VIN10, and NTU0.017 cancer cells. Besides, LCL161 is equally potent towards the parental MCF7 breast cancer cells and its BIRC5 overexpressing, hormone therapy resistance subline MCF7-TamC3 in vitro. Mechanistically, we found that LCL161 directly modulates the ABCB1-ATPase activity and inhibits ABCB1 multi-drug efflux activity at low cytotoxic concentrations (i.e. 0.5xIC₅₀ or less). Further analysis revealed that LCL161 also decreases intracellular ATP levels in part through BIRC5 downregulation. Therapeutically, co-treatment with LCL161 at low cytotoxic concentrations restored the sensitivity to the known ABCB1 substrate, paclitaxel, in ABCB1-expressing cancer cells and increased the sensitivity to tamoxifen in MCF7-TamC3 cells. In conclusion, LCL161 has the potential for use in the management of cancer patients with ABCB1 and BIRC5-related drug resistance. The findings of our study provide important information to physicians for designing a more "patient-specific" LCL161 clinical trial program in the future.

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.

Doxorubicin-polyglycerol-nanodiamond conjugates disrupt STAT3/IL-6-mediated reciprocal activation loop between glioblastoma cells and astrocytes

Astrocytes are key stromal components in glioblastoma (GBM) and have complex interactions with the GBM cells (GBC) promoting the survival, progression and therapy resistance of GBM. In this study, we first demonstrated the existence of a reciprocal activation loop mediated by the STAT3/IL-6 signaling between GBC and astrocytes. This loop of reciprocity was found to be initiated by the constitutive activity of STAT3 and downstream expression of IL-6 in the GBC. GBC-derived IL-6 activated STAT3 and thereby upregulated IL-6 expression in the astrocytes. Astrocyte-derived IL-6 acted back on the GBC causing further activation of STAT3 and leading to enhanced downstream events that promote proliferation, migration, invasion and apoptosis resistance of the GBC. Next, we showed that doxorubicin-polyglycerol-nanodiamond conjugates (Nano-DOX), which could be delivered via GBM-associated macrophages, suppressed STAT3 activity in the GBC reducing their IL-6 output to the astrocytes and thereby abolished the astrocytes' feedback activation of the GBC. Moreover, Nano-DOX also suppressed stimulated activation of STAT3 and IL-6 induced by temozolomide, a first-line anti-GBM chemotherapy, resistance to which critically involves STAT3 activation. In conclusion, Nano-DOX could disrupt the STAT3/IL-6-mediated reciprocal activation loop between the GBC and astrocytes. Nano-DOX also provides a novel approach to therapeutic modulation of the GBM microenvironment.

Role of HDACs in normal and malignant hematopoiesis

Normal hematopoiesis requires the accurate orchestration of lineage-specific patterns of gene expression at each stage of development, and epigenetic regulators play a vital role. Disordered epigenetic regulation has emerged as a key mechanism contributing to hematological malignancies. Histone deacetylases (HDACs) are a series of key transcriptional cofactors that regulate gene expression by deacetylation of lysine residues on histone and nonhistone proteins. In normal hematopoiesis, HDACs are widely involved in the development of various lineages. Their functions involve stemness maintenance, lineage commitment determination, cell differentiation and proliferation, etc. Deregulation of HDACs by abnormal expression or activity and oncogenic HDAC-containing transcriptional complexes are involved in hematological malignancies. Currently, HDAC family members are attractive targets for drug design, and a variety of HDAC-based combination strategies have been developed for the treatment of hematological malignancies. Drug resistance and limited therapeutic efficacy are key issues that hinder the clinical applications of HDAC inhibitors (HDACis). In this review, we summarize the current knowledge of how HDACs and HDAC-containing complexes function in normal hematopoiesis and highlight the etiology of HDACs in hematological malignancies. Moreover, the implication and drug resistance of HDACis are also discussed. This review presents an overview of the physiology and pathology of HDACs in the blood system.

APC loss affects DNA damage repair causing doxorubicin resistance in breast cancer cells

Chemoresistance is one of the leading causes of cancer-related deaths in the United States. Triple negative breast cancer (TNBC), a subtype lacking the known breast cancer receptors used for targeted therapy, is reliant on chemotherapy as the standard of care. The Adenomatous Polyposis Coli (APC) tumor suppressor is mutated or hypermethylated in 70% of sporadic breast cancers with APC-deficient tumors resembling the TNBC subtype. Using mammary tumor cells from the ApcMin/+ mouse model crossed to the Polyoma middle T antigen (PyMT) transgenic model, we previously showed that APC loss decreased sensitivity to doxorubicin (DOX). Understanding the molecular basis for chemoresistance is essential for the advancement of novel therapeutic approaches to ultimately improve patient outcomes. Resistance can be caused via different methods, but here we focus on the DNA repair response with DOX treatment. We show that MMTV-PyMT;ApcMin/+ cells have decreased DNA damage following 24 hour DOX treatment compared to MMTV-PyMT;Apc+/+ cells. This decreased damage is first observed 24 hours post-treatment and continues throughout 24 hours of drug recovery. Activation of DNA damage response pathways (ATM, Chk1, and Chk2) are decreased at 24 hours DOX-treatment in MMTV-PyMT;ApcMin/+ cells compared to control cells, but show activation at earlier time points. Using inhibitors that target DNA damage repair kinases (ATM, ATR, and DNA-PK), we showed that ATM and DNA-PK inhibition increased DOX-induced apoptosis in the MMTV-PyMT;ApcMin/+ cells. In the current work, we demonstrated that APC loss imparts resistance through decreased DNA damage response, which can be attenuated through DNA repair inhibition, suggesting the potential clinical use of DNA repair inhibitions as combination therapy.

Effects of histone deacetylase inhibitors on ATP-binding cassette transporters in lung cancer A549 and colorectal cancer HCT116 cells

Histone deacetylase (HDAC) inhibitors and DNA alkylators are effective components used in combination chemotherapy. In the present study, the effects of HDAC inhibitors on the expression of ATP-binding cassette (ABC) transporters were investigated. It was observed that HDAC inhibitors induced the expression of multidrug-resistant ABC transporters differently in lung cancer A549 cells than in colorectal cancer HCT116 cells. In these two cell lines, the HDAC inhibitors suberoylanilide hydroxamic acid (SAHA) and trichostatin A (TSA) significantly increased ABCB1 expression at the mRNA and protein levels, whereas they had no evident effect on ABCG2 protein expression. SAHA and TSA decreased ABCG2 mRNA expression in A549 cells and had no evident effect on ABCG2 mRNA expression in HCT116 cells. Notably, SAHA and TSA increased the mRNA expression levels of ABCC5, ABCC6, ABCC10, ABCC11 and ABCC12, as well as the protein expression levels of ABCC2, ABCC10 and ABCC12. By contrast, these inhibitors decreased the mRNA expression levels of ABCC1, ABCC2, ABCC3 and ABCC4, as well as the expression of ABCC1 and ABCC3 proteins. Furthermore, SAHA and TSA were found to downregulate HDAC3 and HDAC4, but not HDAC1 and HDAC2. Taken together, the results suggested that HDAC inhibitors work synergistically with DNA alkylators, in part, due to the inhibitory effect of these inhibitors on ABCC1 expression, which translocates these alkylators from inside to outside of cancer cells. These results further suggested the possibility of antagonism when HDAC inhibitors are combined with anthracyclines and other ABCB1 drug ligands in chemotherapy.

Brain region-specific regulation of histone acetylation and efflux transporters in mice

Multidrug resistance protein 1 (MDR1) and breast cancer resistance protein (BCRP) protect the brain by restricting the passage of chemicals across the blood-brain barrier. Prior studies have demonstrated the epigenetic regulation of MDR1 and BCRP in cancer cells treated with histone deacetylase (HDAC) inhibitors that enhance histone acetylation and gene transcription. In the present study, we tested the in vivo effects of two HDAC inhibitors, valproic acid (VPA; 400 mg/kg) and apicidin (5 mg/kg), on Mdr1 and Bcrp transporter expression in brain regions of adult male mice injected intraperitoneally daily for 7 days. VPA increased Mdr1 protein expression in the striatum (70%) and Bcrp protein in the midbrain (30%). Apicidin enhanced striatal Mdr1 protein (30%) and hippocampal Bcrp protein (20%). Transporter induction correlated with increased histone H3 acetylation in discrete brain regions. In conclusion, HDAC inhibitors upregulate transporter proteins in vivo, which may be important in regulating regional xenobiotic disposition within the brain.

Increased MDR1 Transporter Expression in Human Brain Endothelial Cells Through Enhanced Histone Acetylation and Activation of Aryl Hydrocarbon Receptor Signaling

Multidrug resistance protein 1 (MDR1, ABCB1, P-glycoprotein) is a critical efflux transporter that extrudes chemicals from the blood-brain barrier (BBB) and limits neuronal exposure to xenobiotics. Prior studies in malignant cells demonstrated that MDR1 expression can be altered by inhibition of histone deacetylases (HDAC), enzymes that modify histone structure and influence transcription factor binding to DNA. Here, we sought to identify the mechanisms responsible for the up-regulation of MDR1 by HDAC inhibitors in human BBB cells. Immortalized human brain capillary endothelial (hCMEC/D3) cells were treated with HDAC inhibitors and assessed for MDR1 expression and function. Of the HDAC inhibitors profiled, valproic acid (VPA), apicidin, and suberoylanilide hydroxamic acid (SAHA) increased MDR1 mRNA and protein levels by 30-200%, which corresponded with reduced intracellular accumulation of the MDR1 substrate rhodamine 123. Interestingly, induction of MDR1 mRNA by HDAC inhibitors mirrored increases in the expression of the aryl hydrocarbon receptor (AHR) and its target gene cytochrome P450 1A1. To explore the role of AHR in HDAC inhibitor-mediated regulation of MDR1, a pharmacological activator (β-naphthoflavone, βNF) and inhibitor (CH-223191, CH) of AHR were tested. The induction of MDR1 in cells treated with SAHA was amplified by βNF and attenuated by CH. Furthermore, SAHA increased the binding of acetylated histone H3K9/K14 and AHR proteins to regions of the MDR1 promoter that contain AHR response elements. In conclusion, HDAC inhibitors up-regulate the expression and activity of the MDR1 transporter in human brain endothelial cells by increasing histone acetylation and facilitating AHR binding at the MDR1 promoter.

PARP inhibitor re‑sensitizes Adriamycin resistant leukemia cells through DNA damage and apoptosis

Resistance to Adriamycin (ADR) is an increasing problem in the treatment of leukemia and the development of novel therapeutic strategies is becoming increasingly important. Olaparib is a poly (adenosine diphosphate-ribose) polymerase (PARP) 1 inhibitor, which has promising antitumor activity in patients with metastatic breast cancer and germline BRCA mutations. Previously published studies have indicated that Olaparib is able to overcome drug resistance in cancer; however, its underlying mechanism of action is yet to be elucidated. The aim of the present study was to explore the mechanism underlying re-sensitization. Annexin V-propidium iodide staining indicated that the percentage of apoptotic ADR resistant cells was markedly increased and the cell cycle was blocked at the G2/M-phase following treatment with ADR combined with Olaparib, when compared with the control group. The alkaline comet assay demonstrated that ADR combined with Olaparib significantly upregulated the induction of the DNA damage response in ADR-resistant cells. Western blot analysis revealed that the protein expression of γ-H2A histone family member X, cleaved PARP, caspase 3 and cleaved caspase 3 was markedly enhanced, while the cell cycle-associated protein cyclin B1 was downregulated in K562/ADR cells following treatment with a combination of ADR and Olaparib. Similar synergistic cytotoxicity was observed in blood mononuclear cells, which were isolated from patients with chemotherapy-resistant leukemia. As Olaparib is available for clinical use, the results of the present study provide a rationale for the development of Olaparib combinational therapies for cases of ADR resistant leukemia.

Doxorubicin-conjugated dexamethasone induced MCF-7 apoptosis without entering the nucleus and able to overcome MDR-1-induced resistance

Background

Doxorubicin (DOX) is the most widely used chemotherapeutic agent that has multimodal cytotoxicity. The main cytotoxic actions of DOX occur in the nucleus. The emergence of drug-resistant cancer cells that have the ability to actively efflux DOX out of the nucleus, and the cytoplasm has led to the search for a more effective derivative of this drug.

Materials and methods

We created a new derivative of DOX that was derived via simple conjugation of the 3' amino group of DOX to the dexamethasone molecule.

Results

Despite having a lower cytotoxic activity in MCF-7 cells, the conjugated product, DexDOX, exerted its actions in a manner that was different to that of DOX. DexDOX rapidly induced MCF-7 cell apoptosis without entering the nucleus. Further analysis showed that Dex-DOX increased cytosolic oxidative stress and did not interfere with the cell cycle. In addition, the conjugated product retained its cytotoxicity in multidrug resistance-1-overexpressing MCF-7 cells that had an approximately 16-fold higher resistance to DOX.

Conclusion

We have synthesized a new derivative of DOX, which has the ability to overcome multidrug resistance-1-induced resistance. This molecule may have potential as a future chemotherapeutic agent.

Entinostat reverses P-glycoprotein activation in snail-overexpressing adenocarcinoma HCC827 cells

Epithelial-to-mesenchymal transition (EMT) in cancer cells facilitates tumor progression by promoting invasion and metastasis. Snail is a transcriptional factor that induces EMT, while P-glycoprotein (P-gp) is an efflux transporter involved in anticancer drug resistance, and P-gp efflux activity is stimulated in Snail-overexpressing lung cancer cells with EMT characteristics. Since the histone deacetylase (HDAC) inhibitor entinostat (Ent) reverses EMT features, our aim in this study was to determine whether Ent also suppresses P-gp activation in Snail-induced cells. First, we confirmed that Ent treatment reduced migration activity, downregulated E-cadherin and upregulated vimentin at the mRNA level in Snail-overexpressing cells, thus inhibiting EMT. Efflux and uptake assays using rhodamine123 (Rho123), a fluorescent P-gp substrate, showed that Ent also inhibited Snail-induced activation of P-gp. Moreover, P-gp activity was more strongly inhibited by Ent in Snail-overexpressing cells than in Mock cells. When we evaluated the uptakes of Rho123 by LLC-PK1 cells and P-gp-overexpressing LLC-GA5COL150 cells, Rho123 accumulation in LLC-GA5COL150 cells was significantly decreased compared with that in LLC-PK1 cells. Coincubation with Ent had no effect on Rho123 accumulation in either of the cell lines. Thus, Ent appears to be an inhibitor, but not a substrate, of P-gp at low concentration. Our results suggest that Ent treatment might suppress not only Snail-induced cancer malignant alteration, but also P-gp-mediated multidrug resistance.

ABCA1 Is Coordinated with ABCB1 in the Arsenic-Resistance of Human Cells

Arsenic is one of the most widespread global environmental toxicants associated with endemic poisoning. ATP-binding cassette (ABC) proteins are transmembrane channels that transport and dispose of lipids and metabolic products across the plasma membrane. The majority of ABC family members (including ABCB1 and ABCC1) are reported to play a role in the development of arsenic and drug resistance in mammals. Previously, we established a human arsenic-resistant ECV-304 (AsRE) cell line and identified ABCA1 as a novel arsenic resistance gene. In the current study, we further investigated the potential contribution of ABCA1, ABCB1, and ABCC1 to arsenic resistance through measurement of survival rates and arsenic accumulation in AsRE cells with RNA interference. The arsenic resistance capacity of ABCC1 was the strongest among the three genes, while those of ABCA1 and ABCB1 were similar. Double or triple gene knockdown of ABCA1, ABCB1, and ABCC1 via RNA interference led to a decrease significant in arsenic resistance when ABCA1/ABCB1 or ABCB1/ABCC1 were simultaneously silenced. Interestingly, no differences were evident between cells with ABCA1/ABCC1 and ABCC1 only knockdown. Our findings suggest that ABCA1 and ABCB1 proteins display similar arsenic resistance capabilities and possibly coordinate to promote arsenic resistance in AsRE cells.

Exosomal miRNA Analysis in Non-small Cell Lung Cancer (NSCLC) Patients' Plasma Through qPCR: A Feasible Liquid Biopsy Tool

The discovery of alterations in the EGFR and ALK genes, amongst others, in NSCLC has driven the development of targeted-drug therapy using selective tyrosine kinase inhibitors (TKIs). To optimize the use of these TKIs, the discovery of new biomarkers for early detection and disease progression is mandatory. These plasma-isolated exosomes can be used as a non-invasive and repeatable way for the detection and follow-up of these biomarkers. One ml of plasma from 12 NSCLC patients, with different mutations and treatments (and 6 healthy donors as controls), were used as exosome sources. After RNAse treatment, in order to degrade circulating miRNAs, the exosomes were isolated with a commercial kit and resuspended in specific buffers for further analysis. The exosomes were characterized by western blotting for ALIX and TSG101 and by transmission electron microscopy (TEM) analysis, the standard techniques to obtain biochemical and dimensional data of these nanovesicles. Total RNA extraction was performed with a high yield commercial kit. Due to the limited miRNA-content in exosomes, we decided to perform retro-transcription PCR using an individual assay for each selected miRNA. A panel of miRNAs (30b, 30c, 103, 122, 195, 203, 221, 222), all correlated with NSCLC disease, were analyzed taking advantage of the remarkable sensitivity and specificity of Real-Time PCR analysis; mir-1228-3p was used as endogenous control and data were processed according to the formula 2(-) (ΔΔct) (13). Control values were used as baseline and results are shown in logarithmic scale.

P-glycoprotein Mediates Postoperative Peritoneal Adhesion Formation by Enhancing Phosphorylation of the Chloride Channel-3

P-glycoprotein (P-gp) is encoded by the multidrug resistance (MDR1) gene and is well studied as a multi-drug resistance transporter. Peritoneal adhesion formation following abdominal surgery remains an important clinical problem. Here, we found that P-gp was highly expressed in human adhesion fibroblasts and promoted peritoneal adhesion formation in a rodent model. Knockdown of P-gp expression by intraperitoneal injection of MDR1-targeted siRNA significantly reduced both the peritoneal adhesion development rate and adhesion grades. Additionally, we found that operative injury up-regulated P-gp expression in peritoneal fibroblasts through the TGF-β1/Smad signaling pathway and histone H3 acetylation. The overexpression of P-gp accelerated migration and proliferation of fibroblasts via volume-activated Cl(-) current and cell volume regulation by enhancing phosphorylation of the chloride channel-3. Therefore, P-gp plays a critical role in postoperative peritoneal adhesion formation and may be a valuable therapeutic target for preventing the formation of peritoneal adhesions.

Elevated expression of MDR1 associated with Line-1 hypomethylation in esophageal squamous cell carcinoma

BACKGROUND

The aim is to discuss the relationship of Line-1 methylation and the MDR1 expression in esophageal squamous cell carcinoma (ESCC).

METHODS

We analyzed the methylation level of Line-1 by quantitative real-time MSP, and the expression of MDR1 by real-time RT-PCR in 310 ESCC and corresponding non-tumor tissues.

RESULTS

We found that the methylation index (MI) of Line-1 decreased from 0.90 in non-tumor tissues toward 0.78 in ESCC. The cumulative survival was significantly shorter in ESCC patients with MI ≤ 0.78 (34 months) than that in patients with MI > 0.78 (43 months). There was a statistical difference between MI ≤ 0.78 and MI > 0.78 cases with these clinicopathologic parameters (age, AJCC stage, differentiation; P = 0.010, P < 0.0001, P = 0.015, respectively). These results implied that Line-1 hypomethylation could be more in ESCC patients with older, advanced tumor and poor differentiation group. Meanwhile, ESCC with demethylation of Line-1 were shown elevated MDR1 expression in tumor (Mean-∆∆Ct = 0.21), but ESCC with hypermethylation of Line-1 were considered to be decreased MDR1 expression in tumor (Mean-∆∆Ct = -0.86).

CONCLUSIONS

Line-1 hypomethylation could be as a biomarker of poor prognosis in ESCC patients. MDR1 gene could be activated via epigenetic mechanisms with demethylation of Line-1 in ESCC, and enhance tumor progression.

Mammalian drug efflux transporters of the ATP binding cassette (ABC) family in multidrug resistance: A review of the past decade

Multidrug resistance (MDR) is a serious phenomenon employed by cancer cells which hampers the success of cancer pharmacotherapy. One of the common mechanisms of MDR is the overexpression of ATP-binding cassette (ABC) efflux transporters in cancer cells such as P-glycoprotein (P-gp/ABCB1), multidrug resistance-associated protein 2 (MRP2/ABCC2), and breast cancer resistance protein (BCRP/ABCG2) that limits the prolonged and effective use of chemotherapeutic drugs. Researchers have found that developing inhibitors of ABC efflux transporters as chemosensitizers could overcome MDR. But the clinical trials have shown that most of these chemosensitizers are merely toxic and only show limited or no benefits to cancer patients, thus new inhibitors are being explored. Recent findings also suggest that efflux pumps of the ABC transporter family are subject to epigenetic gene regulation. In this review, we summarize recent findings of the role of ABC efflux transporters in MDR.

Epigenetics in acute promyelocytic leukaemia pathogenesis and treatment response: a TRAnsition to targeted therapies

Transcriptional deregulation plays a key role in a large array of cancers, and successful targeting of oncogenic transcription factors that sustain diseases has been a holy grail in the field. Acute promyelocytic leukaemia (APL) driven by chimeric transcription factors encoding retinoic acid receptor alpha fusions is the paradigm of targeted cancer therapy, in which the application of all-trans retinoic acid (ATRA) treatments have markedly transformed this highly fatal cancer to a highly manageable disease. The extremely high complete remission rate resulted from targeted therapies using ATRA in combination with arsenic trioxide will likely be able to minimise or even totally eliminate the use of highly toxic chemotherapeutic agents in APL. In this article, we will review the molecular basis and the upcoming challenges of these targeted therapies in APL, and discuss the recent advance in our understanding of epigenetics underlying ATRA response and their potential use to further improve treatment response and overcome resistance.

The modulation of ABC transporter-mediated multidrug resistance in cancer: a review of the past decade

ATP-binding cassette (ABC) transporters represent one of the largest and oldest families of membrane proteins in all extant phyla from prokaryotes to humans, which couple the energy derived from ATP hydrolysis essentially to translocate, among various substrates, toxic compounds across the membrane. The fundamental functions of these multiple transporter proteins include: (1) conserved mechanisms related to nutrition and pathogenesis in bacteria, (2) spore formation in fungi, and (3) signal transduction, protein secretion and antigen presentation in eukaryotes. Moreover, one of the major causes of multidrug resistance (MDR) and chemotherapeutic failure in cancer therapy is believed to be the ABC transporter-mediated active efflux of a multitude of structurally and mechanistically distinct cytotoxic compounds across membranes. It has been postulated that ABC transporter inhibitors known as chemosensitizers may be used in combination with standard chemotherapeutic agents to enhance their therapeutic efficacy. The current paper reviews the advance in the past decade in this important domain of cancer chemoresistance and summarizes the development of new compounds and the re-evaluation of compounds originally designed for other targets as transport inhibitors of ATP-dependent drug efflux pumps.

HDAC inhibitor-induced drug resistance involving ATP-binding cassette transporters (Review)

Histone deacetylase (HDAC) inhibitors are becoming a novel and promising class of antineoplastic agents that have been used for cancer therapy in the clinic. Two HDAC inhibitors, vorinostat and romidepsin, have been approved by the Food and Drug Administration to treat T-cell lymphoma. Nevertheless, similar to common anticancer drugs, HDAC inhibitors have been found to induce multidrug resistance (MDR), which is an obstacle for the success of chemotherapy. The most common cause of MDR is considered to be the increased expression of adenosine triphosphate binding cassette (ABC) transporters. Numerous studies have identified that the upregulation of ABC transporters is often observed following treatment with HDAC inhibitors, particularly the increased expression of P-glycoprotein, which leads to drug efflux, reduces intracellular drug concentration and induces MDR. The present review summarizes the key ABC transporters involved in MDR following various HDAC inhibitor treatments in a range of cancer cell lines and also explored the potential mechanisms that result in MDR, including the effect of nuclear receptors, which are the upstream regulatory factors of ABC transporters.

Repositioning of Tyrosine Kinase Inhibitors as Antagonists of ATP-Binding Cassette Transporters in Anticancer Drug Resistance

The phenomenon of multidrug resistance (MDR) has attenuated the efficacy of anticancer drugs and the possibility of successful cancer chemotherapy. ATP-binding cassette (ABC) transporters play an essential role in mediating MDR in cancer cells by increasing efflux of drugs from cancer cells, hence reducing the intracellular accumulation of chemotherapeutic drugs. Interestingly, small-molecule tyrosine kinase inhibitors (TKIs), such as AST1306, lapatinib, linsitinib, masitinib, motesanib, nilotinib, telatinib and WHI-P154, have been found to have the capability to overcome anticancer drug resistance by inhibiting ABC transporters in recent years. This review will focus on some of the latest and clinical developments with ABC transporters, TKIs and anticancer drug resistance.

A PU.1 suppressive target gene, metallothionein 1G, inhibits retinoic acid-induced NB4 cell differentiation

We recently revealed that myeloid master regulator SPI1/PU.1 directly represses metallothionein (MT) 1G through its epigenetic activity of PU.1, but the functions of MT1G in myeloid differentiation remain unknown. To clarify this, we established MT1G-overexpressing acute promyelocytic leukemia NB4 (NB4MTOE) cells, and investigated whether MT1G functionally contributes to all-trans retinoic acid (ATRA)-induced NB4 cell differentiation. Real-time PCR analyses demonstrated that the inductions of CD11b and CD11c and reductions in myeloperoxidase and c-myc by ATRA were significantly attenuated in NB4MTOE cells. Morphological examination revealed that the percentages of differentiated cells induced by ATRA were reduced in NB4MTOE cells. Since G1 arrest is a hallmark of ATRA-induced NB4 cell differentiation, we observed a decrease in G1 accumulation, as well as decreases in p21WAF1/CIP1 and cyclin D1 inductions, by ATRA in NB4MTOE cells. Nitroblue tetrazolium (NBT) reduction assays revealed that the proportions of NBT-positive cells were decreased in NB4MTOE cells in the presence of ATRA. Microarray analyses showed that the changes in expression of several myeloid differentiation-related genes (GATA2, azurocidin 1, pyrroline-5-carboxylate reductase 1, matrix metallopeptidase -8, S100 calcium-binding protein A12, neutrophil cytosolic factor 2 and oncostatin M) induced by ATRA were disturbed in NB4MTOE cells. Collectively, overexpression of MT1G inhibits the proper differentiation of myeloid cells.

Histone deacetylase inhibitors in glioblastoma: pre-clinical and clinical experience

Epigenetic mechanisms are increasingly recognized as a major factor contributing to pathogenesis of cancer including glioblastoma, the most common and most malignant primary brain tumour in adults. Enzymatic modifications of histone proteins regulating gene expression are being exploited for therapeutic drug targeting. Over the last decade, numerous studies have shown promising results with histone deacetylase (HDAC) inhibitors in various malignancies. This article provides a brief overview of mechanism of anti-cancer effect and pharmacology of HDAC inhibitors and summarizes results from pre-clinical and clinical studies in glioblastoma. It analyses experience with HDAC inhibitors as single agents as well as in combination with targeted agents, cytotoxic chemotherapy and radiotherapy. Hallmark features of glioblastoma, such as uncontrolled cellular proliferation, invasion, angiogenesis and resistance to apoptosis, have been shown to be targeted by HDAC inhibitors in experiments with glioblastoma cell lines. Vorinostat is the most advanced HDAC inhibitor that entered clinical trials in glioblastoma, showing activity in recurrent disease. Multiple phase II trials with vorinostat in combination with targeted agents, temozolomide and radiotherapy are currently recruiting. While the results from pre-clinical studies are encouraging, early clinical trials showed only modest benefit and the value of HDAC inhibitors for clinical practice will need to be confirmed in larger prospective trials. Further research in epigenetic mechanisms driving glioblastoma pathogenesis and identification of molecular subtypes of glioblastoma is needed. This will hopefully lead to better selection of patients who will benefit from treatment with HDAC inhibitors.

Induction of chemoresistance by all-trans retinoic acid via a noncanonical signaling in multiple myeloma cells

Despite the successful application of all-trans retinoic acid (ATRA) in multiple myeloma treatment, ATRA-induced chemoresistance in the myeloma patients is very common in clinic. In this study, we evaluated the effect of ATRA on the expression of apurinic endonuclease/redox factor-1 (Ape/Ref-1) in the U266 and RPMI-8226 myeloma cells to explore the chemoresistance mechanism involved. ATRA treatment induced upregulation of Ape/Ref-1 via a noncanonical signaling pathway, leading to enhanced pro-survival activity counteracting melphalan (an alkylating agent). ATRA rapidly activated p38-MSK (mitogen- and stress activated protein kinase) cascade to phosphorylate cAMP response element-binding protein (CREB). Phosphorylated CREB was recruited to the Ape/Ref-1 promoter to evoke the gene expression. The stimulation of ATRA on Ape/Ref-1 expression was attenuated by either p38-MSK inhibitors or overexpression of dominant-negative MSK1 mutants. Moreover, ATRA-mediated Ape/Ref-1 upregulation was correlated with histone modification and activation of CBP/p300, an important cofactors for CREB transcriptional activity. C646, a competitive CBP/p300 inhibitor, abolished the upregulation of Ape/Ref-1 induced by ATRA. Intriguingly, CBP rather than p300 played a dominant role in the expression of Ape/Ref-1. Hence, our study suggests the existence of a noncanonical mechanism involving p38-MSK-CREB cascade and CBP induction to mediate ATRA-induced Ape/Ref-1 expression and acquired chemoresistance in myeloma cells.

Improved therapeutic effect on malignant glioma with adenoviral suicide gene therapy combined with temozolomide

Malignant gliomas (MGs) are cancers with poor prognosis and limited therapeutic options. Herpes Simplex virus-1 thymidine kinase expressed from adenoviruses with prodrug ganciclovir (TK/GCV) is the best-characterized suicide gene therapy, whereas temozolomide (TMZ) is the first-line chemotherapy for MG. However, the potential of their combination has not been studied thoroughly. The aim of this study was to evaluate the therapeutic response of this combination and to study whether addition of valproic acid (VPA) could benefit the treatment outcome. Efficacies of different treatments were first studied in vitro in BT4C rat MG cells. Therapeutic assessment in vivo was done in an immunocompetent rat MG model for treatment efficacy and toxicity. In vitro, VPA was able to significantly enhance cytotoxicity and increase adenovirus-mediated transduction efficiency up to sevenfold. In vivo, rats receiving TK/GCV+TMZ had notably smaller tumors and enhanced survival (P<0.001) in comparison with control rats. However, VPA was not able to further enhance the treatment response in vivo. Leukocytopenia and thrombocytopenia were the major side effects. We conclude that careful optimization of the treatment schedules and doses of individual therapies are necessary to achieve an optimal therapeutic effect with TK/GCV+TMZ combination. No further in vivo benefit with VPA was observed.

miR-137 regulates the constitutive androstane receptor and modulates doxorubicin sensitivity in parental and doxorubicin-resistant neuroblastoma cells

Chemotherapy is the most common treatment for cancer. However, multidrug resistance (MDR) remains a major obstacle to effective chemotherapy, limiting the efficacy of both conventional chemotherapeutic and novel biologic agents. The constitutive androstane receptor (CAR), a xenosensor, is a key regulator of MDR. It functions in xenobiotic detoxification by regulating the expression of phase I drug-metabolizing enzymes and ATP-binding cassette (ABC) transporters, whose overexpression in cancers and whose role in drug resistance make them potential therapeutic targets for reducing MDR. MicroRNAs (miRNAs) are endogenous negative regulators of gene expression and have been implicated in most cellular processes, including drug resistance. Here, we report the inversely related expression of miR-137 and CAR in parental and doxorubicin-resistant neuroblastoma cells, wherein miR-137 is downregulated in resistant cells. miR-137 overexpression resulted in downregulation of CAR protein and mRNA (via mRNA degradation); it sensitized doxorubicin-resistant cells to doxorubicin (as shown by reduced proliferation, increased apoptosis and increased G2-phase cell cycle arrest) and reduced the in vivo growth rate of neuroblastoma xenografts. We observed similar results in cellular models of hepatocellular and colon cancers, indicating that the doxorubicin-sensitizing effect of miR-137 is not tumor type-specific. Finally, we show for the first time a negative feedback loop whereby miR-137 downregulates CAR expression and CAR downregulates miR-137 expression. Hypermethylation of the miR-137 promoter and negative regulation of miR-137 by CAR contribute in part to reduced miR-137 expression and increased CAR and MDR1 expression in doxorubicin-resistant neuroblastoma cells. These findings demonstrate that miR-137 is a crucial regulator of cancer response to doxorubicin treatment, and they identify miR-137 as a highly promising target to reduce CAR-driven doxorubicin resistance.

Romidepsin (FK228) combined with cisplatin stimulates DNA damage-induced cell death in ovarian cancer

OBJECTIVE

Romidepsin (FK228) was recently approved by the FDA for the treatment of cutaneous and peripheral T cell lymphoma. We have shown in vitro efficacy of FK228 in ovarian cancer. Here, our goal was to evaluate FK228 combined with cisplatin in ovarian cancer in vitro and in vivo.

METHODS

Ovarian cancer cell lines were treated with cisplatin, FK228 or the combination of drugs. Colorimetric assays were used to determine cytotoxicity in vitro. Mice engrafted with 5×10(6) SKOV-3 ovarian cancer cells were treated with cisplatin, FK228 or the combination, and tumor weights and volumes were measured. We assessed molecular markers of proliferation (mib-1), apoptosis (cleaved PARP and cleaved caspase 3) and DNA damage (pH2AX, RAD51 and 53BP1).

RESULTS

FK228 enhanced the cytotoxic effects of cisplatin in ovarian cells compared to vehicle-treated controls or each drug alone. The combination of FK228 and cisplatin-induced apoptosis and activated aberrant DNA damage responses demonstrated by increased expression of pH2AX, RAD51 and 53BP1. Mice treated with FK228, cisplatin and both drugs showed reduced tumor weights and volumes. Drug-treated tumors showed decreased mib-1 and increased cleaved-caspase 3 expression levels. The number and intensity of pH2AX stained cells was greatest in tumors exposed to the combination of FK228 and cisplatin.

CONCLUSION

FK228 causes DNA damage-induced apoptosis and enhances the anti-tumor effects of cisplatin. The DNA damage mark pH2AX is activated by FK228 and cisplatin and may be a useful pharmacodynamic mark of these effects.

Thailandepsins are new small molecule class I HDAC inhibitors with potent cytotoxic activity in ovarian cancer cells: a preclinical study of epigenetic ovarian cancer therapy

Background

New treatment strategies are emerging to target DNA damage response pathways in ovarian cancer. Our group has previously shown that the class I biased HDAC inhibitor romidepsin (FK228) induces DNA damage response and has potent cytotoxic effects in ovarian cancer cells. Here, we investigated newly discovered HDAC inhibitors, thailandepsin A (TDP-A) and thailandepsin B (TDP-B), to determine the effects on cell viability, apoptosis and DNA damage response in ovarian cancer cells.

Methods

FK228, TDP-A and TDP-B were tested in five ovarian cancer cell lines. Cellular viability was measured by 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT) assays. Immunofluorescence assays were used to assess activated caspase 3. Western blots were performed to detect protein expression of PARP cleavage, pH2AX, P-glycoprotein and tubulin acetylation.

Results

Treatment with TDPs decreased cell viability at nanonomolar concentrations in four of the five ovarian cancer cell lines studied. Similar to FK228, both TDP compounds exerted minimal effects on NCI/ADR-RES ovarian cancer cells. Across the four cell lines sensitive to the TDPs, TDP-B consistently had a greater inhibitory effect than TDP-A on cell viability. TDP-B also had relatively greater effects on promoting cell apoptosis and induction of pH2AX (a mark of DNA damage response), than TDP-A. These antitumor effects of TDP-B were of similar magnitude to those induced by an equal concentration of FK228. Similar to FK228, the nanomolar concentrations of the TDPs had little effect on tubulin acetylation (a mark of class II HDAC6 inhibition).

Conclusions

The new small molecule HDAC inhibitors TDP-A and TDP-B are FK228 analogues that suppress cell viability and induce apoptosis at nanomolar drug concentrations. TDP-B showed the most similarity to the biological activity of FK228 with greater cytotoxic effects than TDP-A in vitro. Our results indicate that FK228-like small molecule class I HDAC-biased HDAC inhibitors have therapeutic potential for ovarian cancer.

Drug resistance: still a daunting challenge to the successful treatment of AML

Resistance to chemotherapy remains a challenging issue for patients and their physicians. P-glycoprotein (Pgp, MDR1, ABCB1), as well as a family of structurally and functionally related proteins, are plasma membrane transporters able to efflux a variety of substrates from the cell cytoplasm, including chemotherapeutic agents. The discovery of ABCB1 made available a potential target for pharmacologic down-regulation of efflux-mediated chemotherapy resistance. In patients with acute myeloid leukemia (AML), a neoplasm characterized by proliferation of poorly differentiated myeloid progenitor cells, leukemic cells often express ABCB1 at high levels, which may lead to the development of resistance to chemotherapy. Thus, AML seemed to be a likely cancer for which the addition of drug efflux inhibitors to the chemotherapeutic regimen would improve outcomes in patients. Despite this rational hypothesis, the majority of clinical trials evaluating this strategy have failed to reach a positive endpoint, most recently the Eastern Cooperative Oncology Group E3999 trial. Here we review data suggesting the importance of ABCB1 in AML, address the failure of clinical trials to support a therapeutic strategy aimed at modulating ABCB1-mediated resistance, and consider the type of research that should be conducted in this field going forward.

Epigenetic mechanisms in tumorigenesis, tumor cell heterogeneity and drug resistance

Resistance of cancer cells to chemotherapeutics and emerging targeted drugs is a devastating problem in the treatment of cancer patients. Multiple mechanisms contribute to drug resistance such as increased drug efflux, altered drug metabolism, secondary mutations in drug targets, and activation of downstream or parallel signal transduction pathways. The rapid kinetics, the reversibility of acquired drug resistance and the absence of genetic mutations suggest an epigenetic basis for drug insensitivity. Similar to the cellular variance seen in the human body, epigenetic mechanisms, through reversible histone modifications and DNA methylation patterns, generate a variety of transcriptional states resulting in a dynamic heterogeneous tumor cell population. Consequently, epigenomes favoring survival in the presence of a drug by aberrant transcription of drug transporters, DNA-repair enzymes and pro-apoptotic factors render cytotoxic and targeted drugs ineffective and allow selection of rare drug-resistant tumor cells. Recent advances in charting cancer genomes indeed strongly indicate a role for epigenetic regulators in driving cancer, which may result in the acquisition of additional (epi)genetic modifications leading to drug resistance. These observations have important clinical consequences as they provide an opportunity for "epigenetic drugs" to change reversible drug-resistance-associated epigenomes to prevent or reverse non-responsiveness to anti-cancer drugs.

Molecular pathways: regulation and therapeutic implications of multidrug resistance

Multidrug transporters constitute major mechanisms of MDR in human cancers. The ABCB1 (MDR1) gene encodes a well-characterized transmembrane transporter, termed P-glycoprotein (P-gp), which is expressed in many normal human tissues and cancers. P-gp plays a major role in the distribution and excretion of drugs and is involved in intrinsic and acquired drug resistance of cancers. The regulation of ABCB1 expression is complex and has not been well studied in a clinical setting. In this review, we elucidate molecular signaling and epigenetic interactions that govern ABCB1 expression and the development of MDR in cancer. We focus on acquired expression of ABCB1 that is associated with genomic instability of cancer cells, including mutational events that alter chromatin structures, gene rearrangements, and mutations in tumor suppressor proteins (e.g., mutant p53), which guard the integrity of genome. In addition, epigenetic modifications of the ABCB1 proximal and far upstream promoters by either demethylation of DNA or acetylation of histone H3 play a pivotal role in inducing ABCB1 expression. We describe a molecular network that coordinates genetic and epigenetic events leading to the activation of ABCB1. These mechanistic insights provide additional translational targets and potential strategies to deal with clinical MDR.

Overview of the Classical Histone Deacetylase Enzymes and Histone Deacetylase Inhibitors

The important role of histone deacetylase enzymes in regulating gene expression, cellular proliferation, and survival has made them attractive targets for the development of histone deacetylase inhibitors as anticancer drugs. Suberoylanilide hydroxamic acid (Vorinostat, Zolinza), a structural analogue of the prototypical Trichostatin A, was approved by the US Food and Drug Administration for the treatment of advanced cutaneous T-cell lymphoma in 2006. This was followed by approval of the cyclic peptide, depsipeptide (Romidepsin, Istodax) for the same disease in 2009. Currently numerous histone deacetylase inhibitors are undergoing preclinical and clinical trials for the treatment of hematological and solid malignancies. Most of these studies are focused on combinations of histone deacetylase inhibitors with other therapeutic modalities, particularly conventional chemotherapeutics and radiotherapy. The aim of this paper is to provide an overview of the classical histone deacetylase enzymes and histone deacetylase inhibitors with an emphasis on potential combination therapies.

Screening of deoxyribozyme with high reversal efficiency against multidrug resistance in breast carcinoma cells

Specific inhibition of P-glycoprotein (Pgp) expression, which is encoded by multidrug resistance gene-1 (MDR1), is considered a well-respected strategy to overcome multidrug resistance (MDR). Deoxyribozymes (DRz) are catalytic nucleic acids that could cleave a target RNA in sequence-specific manner. However, it is difficult to select an effective target site for DRz in living cells. In this study, target sites of DRz were screened according to MDR1 mRNA secondary structure by RNA structure analysis software. Twelve target sites on the surface of MDR1 mRNA were selected. Accordingly, 12 DRzs were synthesized and their suppression effect on the MDR phenotype in breast cancer cells was confirmed. The results showed that 4 (DRz 2, 3, 4, 9) of the 12 DRzs could, in a dose-dependent response, significantly suppress MDR1 mRNA expression and restore chemosensitivity in breast cancer cells with MDR phenotype. This was especially true of DRz 3, which targets the 141 site purine-pyrimidine dinucleotide. Compared with antisense oligonucleotide or anti-miR-27a inhibitor, DRz 3 was more efficient in suppressing MDR1 mRNA and Pgp protein expression or inhibiting Pgp function. The chemosensitivity assay also proved DRz 3 to be the best one to reverse the MDR phenotype. The present study suggests that screening targets of DRzs according to MDR1 mRNA secondary structure could be a useful method to obtain workable ones. We provide evidence that DRzs (DRz 2, 3, 4, 9) are highly efficient at reversing the MDR phenotype in breast carcinoma cells and restoring chemosensitivity.

NF-Ya protein delivery as a tool for hematopoietic progenitor cell expansion

The clinical potential of therapeutic quantities of primary hematopoietic cells, either unmodified or altered via genetic modification, has stimulated the search for techniques that allow the production of large numbers of hematopoietic precursors, more primitive progenitors, and perhaps hematopoietic stem cells (HSC) themselves. Modifications of in vitro culture conditions to promote progenitor cell expansion have included combinations of polypeptide cytokines, small molecules, and transcription factors. Here we describe the methods for use of the transcription factor linked to a TAT-based protein transcription domain, in combination with cytokines and serum-free culture condition to stimulate the proliferation of primary cells. Human peripheral blood (PB) CD34(+) cells treated with TAT-NF-Ya fusion protein and grown in vitro for 1 month proliferate four times more than did cells in cultures that contained only cytokines, including increased production of hematopoietic cells of all maturities. These results and techniques should be suitable for multiple applications of ex vivo generation of hematopoietic cells using protein transduction.

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.

NF-Y and the transcriptional activation of CCAAT promoters

The CCAAT box promoter element and NF-Y, the transcription factor (TF) that binds to it, were among the first cis-elements and trans-acting factors identified; their interplay is required for transcriptional activation of a sizeable number of eukaryotic genes. NF-Y consists of three evolutionarily conserved subunits: a dimer of NF-YB and NF-YC which closely resembles a histone, and the "innovative" NF-YA. In this review, we will provide an update on the functional and biological features that make NF-Y a fundamental link between chromatin and transcription. The last 25 years have witnessed a spectacular increase in our knowledge of how genes are regulated: from the identification of cis-acting sequences in promoters and enhancers, and the biochemical characterization of the corresponding TFs, to the merging of chromatin studies with the investigation of enzymatic machines that regulate epigenetic states. Originally identified and studied in yeast and mammals, NF-Y - also termed CBF and CP1 - is composed of three subunits, NF-YA, NF-YB and NF-YC. The complex recognizes the CCAAT pentanucleotide and specific flanking nucleotides with high specificity (Dorn et al., 1997; Hatamochi et al., 1988; Hooft van Huijsduijnen et al, 1987; Kim & Sheffery, 1990). A compelling set of bioinformatics studies clarified that the NF-Y preferred binding site is one of the most frequent promoter elements (Suzuki et al., 2001, 2004; Elkon et al., 2003; Mariño-Ramírez et al., 2004; FitzGerald et al., 2004; Linhart et al., 2005; Zhu et al., 2005; Lee et al., 2007; Abnizova et al., 2007; Grskovic et al., 2007; Halperin et al., 2009; Häkkinen et al., 2011). The same consensus, as determined by mutagenesis and SELEX studies (Bi et al., 1997), was also retrieved in ChIP-on-chip analysis (Testa et al., 2005; Ceribelli et al., 2006; Ceribelli et al., 2008; Reed et al., 2008). Additional structural features of the CCAAT box - position, orientation, presence of multiple Transcriptional Start Sites - were previously reviewed (Dolfini et al., 2009) and will not be considered in detail here.

[Histone deacetylase inhibitors in the treatment of hematological malignancies]

Histone deacetylases inhibitors (HDACi) represent a new epigenetic targeting therapy class, which is widely investigated in fundamental research and clinical trials. They are able to restore and increase tumor suppressor genes expression and to play an anti-tumoral activity through numerous targets, which are distributed all over the main differentiation, proliferation and survival cellular pathways. Their use in hematology led to vorinostat (SAHA) and romidepsin approval by FDA for the treatment of refractory cutaneous T-cell lymphomas. Preclinical and preliminary clinical results show a promising antineoplasic activity in most hematologic malignancies. This review will focus on the HDACi recent developments and current investigations, highlighted by recent communications.

The DNA damage mark pH2AX differentiates the cytotoxic effects of small molecule HDAC inhibitors in ovarian cancer cells

High grade epithelial ovarian cancers are relatively sensitive to DNA damaging platinum-based chemotherapy, suggesting that the dependencies of ovarian tumors on DNA damage response pathways can be harnessed for therapeutic purposes. Our goal was to determine if the DNA damage mark gamma-H2AX phosphorylation (pH2AX) could be used to identify suitable cytotoxic histone deacetylase inhibitors (HDACi) for ovarian cancer treatment. Nineteen chemically diverse HDACi compounds were tested in 7 ovarian cancer cell lines. Fluorescent, biochemical and cell-based assays were performed to assess DNA damage by induction of pH2AX and to measure cell viability and apoptosis. The relationships between pH2AX and the cellular effects of cell viability and apoptosis were calculated. Selected HDACi were tested in combination with cisplatin and other DNA damaging agents to determine if the HDACi improved upon the effects of the DNA damaging agents. The HDACi compounds induced differing levels of pH2AX expression. High levels of pH2AX in HDACi-treated ovarian cancer cells were tightly associated with decreased cell viability and increased apoptosis. Consequently, a ketone-based HDACi was chosen and found to enhance the effects of cisplatin, even in ovarian cancer cells with extreme resistance to DNA damaging drugs. In conclusion, a fluorescent-based assay for pH2AX can be used to determine cellular responses to HDACi in vitro and may be a useful tool to identify potentially more effective HDACi for the treatment of ovarian cancer. In addition, these results lend support to the inclusion of ketone-derived HDACi compounds for future development.

Upregulation of ABCG2 by romidepsin via the aryl hydrocarbon receptor pathway

Histone deacetylase inhibitors (HDACI) are promising anticancer agents and their use in combination with conventional anticancer drugs is currently under investigation. We previously reported cell line-specific upregulation of ABCG2, a multidrug resistance transporter shown to control oral bioavailability and CNS penetration, by the HDACI romidepsin, although the precise mechanism in a particular cell line remains to be determined. The aryl hydrocarbon receptor (AhR) is a ligand-dependent transcription factor that can be activated by numerous environmental contaminants and has been shown to be a client protein of heat shock protein 90 (Hsp90). A xenobiotic response element was defined in the ABCG2 promoter and was shown to mediate AhR signaling. Activated AhR was found to be associated with the ABCG2 promoter only in cell line models that respond to romidepsin with ABCG2 upregulation. Our data suggest that romidepsin acetylated Hsp70 and inhibited the chaperone function of Hsp90, thereby allowing the dissociation of AhR from Hsp90. The dissociation of AhR from Hsp90 may be a prerequisite for the differential upregulation of ABCG2 by romidepsin. Increasing our understanding of the mechanism(s) governing differential upregulation of ABCG2 in response to romidepsin could provide an insight into strategies needed to tackle resistance to HDACIs in cancer therapeutics.

The DAC system and associations with acute leukemias and myelodysplastic syndromes

Imbalances of histone acetyltransferase (HAT) and deacetylase activity (DAC) that result in deregulated gene expression are commonly observed in leukemias. These alterations provide the basis for novel therapeutic approaches that target the epigenetic mechanisms implicated in leukemogenesis. As the acetylation status of histones has been linked to transcriptional regulation of genes involved particularly in differentiation and apoptosis, DAC inhibitors (DACi) have attracted considerable attention for treatment of hematologic malignancies. DACi encompass a structurally diverse family of compounds that are being explored as single agents as well as in combination with chemotherapeutic drugs, small molecule inhibitors of signaling pathways and hypomethylating agents. While DACi have shown clear evidence of activity in acute myeloid leukemia, myelodysplastic syndromes and lymphoid malignancies, their precise role in treatment of these different entities remain to be elucidated. Successful development of these compounds as elements of novel targeted treatment strategies for leukemia will require that clinical studies be performed in conjunction with translational research including efforts to identify predictive biomarkers.

Histone deacetylase (HDAC) inhibitors in recent clinical trials for cancer therapy

Heritable changes in gene expression that are not based upon alterations in the DNA sequence are defined as epigenetics. The most common mechanisms of epigenetic regulation are the methylation of CpG islands within the DNA and the modification of amino acids in the N-terminal histone tails. In the last years, it became evident that the onset of cancer and its progression may not occur only due to genetic mutations but also because of changes in the patterns of epigenetic modifications. In contrast to genetic mutations, which are almost impossible to reverse, epigenetic changes are potentially reversible. This implies that they are amenable to pharmacological interventions. Therefore, a lot of work in recent years has focussed on the development of small molecule enzyme inhibitors like DNA-methyltransferase inhibitors or inhibitors of histone-modifying enzymes. These may reverse misregulated epigenetic states and be implemented in the treatment of cancer or other diseases, e.g., neurological disorders. Today, several epigenetic drugs are already approved by the FDA and the EMEA for cancer treatment and around ten histone deacetylase (HDAC) inhibitors are in clinical development. This review will give an update on recent clinical trials of the HDAC inhibitors used systemically that were reported in 2009 and 2010 and will present an overview of different biomarkers to monitor the biological effects.

TAT-mediated transduction of NF-Ya peptide induces the ex vivo proliferation and engraftment potential of human hematopoietic progenitor cells

Retroviral overexpression of NF-Ya, the regulatory subunit of the transcription factor NF-Y, activates the transcription of multiple genes implicated in hematopoietic stem cell (HSC) self-renewal and differentiation and directs HSCs toward self-renewal. We asked whether TAT-NF-Ya fusion protein could be used to transduce human CD34(+) cells as a safer, more regulated alternative approach to gene therapy. Here we show that externally added recombinant protein was able to enter the cell nucleus and activate HOXB4, a target gene of NF-Ya, using real-time polymerase chain reaction RNA and luciferase-based protein assays. After TAT-NF-Ya transduction, the proliferation of human CD34(+) cells in the presence of myeloid cytokines was increased 4-fold. Moreover, TAT-NF-Ya-treated human primary bone marrow cells showed a 4-fold increase in the percentage of huCD45(+) cells recovered from the bone marrow of sublethally irradiated, transplanted NOD-Scid IL2Rγ(null) mice. These data demonstrate that TAT-peptide therapies are an alternative approach to retroviral stem cell therapies and suggest that NF-Ya peptide delivery should be further evaluated as a tool for HSC/progenitors ex vivo expansion and therapy.

Epigenetic modifiers: basic understanding and clinical development

More than 60 years after the first description of differentiation in cell culture and 40 years after the synthesis of 5-azacytidine, epigenetic therapies have been added to the anticancer armamentarium. DNA methyltransferase (DNMT) inhibitors such as 5-aza-2'-deoxycytidine or 5-azacytidine have been approved in myelodysplastic syndrome (MDS) and acute myelogenous leukemia (AML), whereas the histone deacetylase inhibitors (HDIs) including vorinostat, romidepsin, panobinostat, belinostat, and entinostat have been shown to be active in cutaneous and peripheral T-cell lymphoma. Although the range of malignancies in which monotherapy with DNMT inhibitors or HDIs are effective has been limited to date, the possibility remains that a broader spectrum of activity will be identified as combination studies are completed. Meanwhile, basic science has provided a steadily increasing understanding of the complexity of the epigenome, including the histone code and triggers for aberrant methylation, and their contribution to oncogenesis. As our basic understanding of the epigenetics of cancer increases, the number of potential therapeutic targets will also increase, offering more hope in the quest to treat cancer by normalizing the epigenome. This issue of CCR Focus is dedicated to understanding the clinical and translational aspects of epigenetics research.