Inhibition of hypoxia-inducible factor-1 function enhances the sensitivity of multiple myeloma cells to melphalan

An oxygen-generating metal organic framework nanoplatform as a “synergy motor” for extricating dilemma over photodynamic therapy

Photodynamic therapy (PDT) combined with metal organic frameworks (MOFs) addresses current obstacles.

Targeting hypoxia in solid and haematological malignancies

Tumour hypoxia is a known and extensively researched phenomenon that occurs in both solid and haematological malignancies. As cancer cells proliferate, demand for oxygen can outstrip supply reducing tumour oxygenation. In solid tumours this is contributed to by disorganized blood vessel development. Tumour hypoxia is associated with resistance to treatment, more aggressive disease behaviour and an increased likelihood of metastatic progression. It can be measured using both invasive and non-invasive methods to varying degrees of accuracy. The presence of hypoxia stimulates a complex cellular network of downstream factors including Hypoxia Inducible Factor 1 (HIF1), C-X-C motif chemokine 4 (CXCR4) and Hypoxia‐inducible glycolytic enzyme hexokinase‐2 (HK2) amongst many others. They work by affecting different mechanisms including influencing angiogenesis, treatment resistance, immune surveillance and the ability to metastasize all of which contribute to a more aggressive disease pattern. Tumour hypoxia has been correlated with poorer outcomes and worse prognosis in patients. The correlation between hypoxic microenvironments and poor prognosis has led to an interest in trying to therapeutically target this phenomenon. Various methods have been used to target hypoxic microenvironments. Hypoxia-activated prodrugs (HAPs) are drugs that are only activated within hypoxic environments and these agents have been subject to investigation in several clinical trials. Drugs that target downstream factors of hypoxic environments including HIF inhibitors, mammalian target of rapamycin (mTOR) inhibitors and vascular endothelial growth factor (anti-VEGF) therapies are also in development and being used in combination in clinical trials. Despite promising pre-clinical data, clinical trials of hypoxia targeting strategies have proven challenging. Further understanding of the effect of hypoxia and related molecular mechanisms in human rather than animal models is required to guide novel therapeutic strategies and future trial design. This review will discuss the currently available methods of hypoxia targeting and assessments that may be considered in planning future clinical trials. It will also outline key trials to date in both the solid and haemato-oncology treatment spheres and discuss the limitations that may have impacted on clinical success to date.

Antitumor effect of the selective hypoxia-inducible factor-1 inhibitors echinomycin and PX-478 on uterine fibroids

OBJECTIVE

To investigate the antitumor effects of the selective hypoxia-inducible factor-1 (HIF-1) inhibitors echinomycin and PX-478 on uterine fibroids.

DESIGN

Experimental study using in vitro primary culture systems and an in vivo mouse xenograft model.

SETTING

Academic university center.

PATIENT(S)

Women with uterine fibroids who underwent hysterectomy or myomectomy.

INTERVENTION(S)

Administration of the selective HIF-1 inhibitors echinomycin and PX-478 to the media of the primary cultured uterine fibroid cells and to nonobese diabetic/severe combined immunodeficient mice bearing fibroid xenografts consisting of the primary cultured fibroid cells and type Ⅰ collagen gels beneath the kidney capsule.

MAIN OUTCOME MEASURE(S)

Cell proliferation was measured by Cell Counting Kit-8 assay. Apoptosis was evaluated by terminal deoxynucleotidyl transferase-mediated dUTP nick end labeling assay and by measuring caspase 3 and 7 activities. The xenografts were evaluated by gross appearance, surface area, and histology. The Ki-67 index was measured to evaluate proliferation of the xenografts.

RESULT(S)

Both echinomycin and PX-478 inhibited cell proliferation and induced apoptosis in fibroid cells cultured under hypoxia and normoxia. Enlargement of the fibroid xenografts was significantly attenuated. The Ki-67 index significantly decreased after the administration of the HIF-1 inhibitors in the xenograft model. Eight of 27 xenografts treated with the HIF-1 inhibitors contained calcification and hyalinizing components from 3 days after the grafting to 2 weeks, suggesting that the HIF-inhibitors induce degeneration of the fibroid xenografts.

CONCLUSION(S)

The selective HIF-1 inhibitors echinomycin and PX-478 show antitumor effects against uterine fibroids both in vitro and in vivo. These findings support the potential use of HIF-1 inhibitors for the treatment of uterine fibroids.

Identification of the Cysteine Protease Legumain as a Potential Chronic Hypoxia-Specific Multiple Myeloma Target Gene

Multiple myeloma (MM) is the second most common hematologic malignancy, which is characterized by clonal proliferation of neoplastic plasma cells in the bone marrow. This microenvironment is characterized by low oxygen levels (1–6% O₂), known as hypoxia. For MM cells, hypoxia is a physiologic feature that has been described to promote an aggressive phenotype and to confer drug resistance. However, studies on hypoxia are scarce and show little conformity. Here, we analyzed the mRNA expression of previously determined hypoxia markers to define the temporal adaptation of MM cells to chronic hypoxia. Subsequent analyses of the global proteome in MM cells and the stromal cell line HS-5 revealed hypoxia-dependent regulation of proteins, which directly or indirectly upregulate glycolysis. In addition, chronic hypoxia led to MM-specific regulation of nine distinct proteins. One of these proteins is the cysteine protease legumain (LGMN), the depletion of which led to a significant growth disadvantage of MM cell lines that is enhanced under hypoxia. Thus, herein, we report a methodologic strategy to examine MM cells under physiologic hypoxic conditions in vitro and to decipher and study previously masked hypoxia-specific therapeutic targets such as the cysteine protease LGMN.

Treatment Strategies Considering Micro-Environment and Clonal Evolution in Multiple Myeloma

Simple Summary

Multiple myeloma is an uncurable hematological malignancy, although the prognosis of myeloma patients is getting better using proteasome inhibitors (PIs), immune modulatory drugs (IMiDs), monoclonal antibodies (MoAbs), and cytotoxic agents. Drug resistance makes myeloma difficult to treat and it can be subdivided into two broad categories: de novo and acquired. De novo drug resistance is associated with the bone marrow microenvironment including bone marrow stromal cells, the vascular niche and endosteal niche. Acquired drug resistance is related to clonal evolution and non-genetic diversity. The initial treatment plays the most important role considering de novo and acquired drug resistance and should contain PIs, IMIDs, MoAbs, and autologous stem cell transplantation because these treatments improve the bone marrow microenvironment and might prevent clonal evolution via sustained deep response including minimal residual disease negativity.

Abstract

Multiple myeloma is an uncurable hematological malignancy because of obtained drug resistance. Microenvironment and clonal evolution induce myeloma cells to develop de novo and acquired drug resistance, respectively. Cell adhesion-mediated drug resistance, which is induced by the interaction between myeloma and bone marrow stromal cells, and soluble factor-mediated drug resistance, which is induced by cytokines and growth factors, are two types of de novo drug resistance. The microenvironment, including conditions such as hypoxia, vascular and endosteal niches, contributes toward de novo drug resistance. Clonal evolution was associated with acquired drug resistance and classified as branching, linear, and neutral evolutions. The branching evolution is dependent on the microenvironment and escape of immunological surveillance while the linear and neutral evolution is independent of the microenvironment and associated with aggressive recurrence and poor prognosis. Proteasome inhibitors (PIs), immunomodulatory drugs (IMiDs), monoclonal antibody agents (MoAbs), and autologous stem cell transplantation (ASCT) have improved prognosis of myeloma via improvement of the microenvironment. The initial treatment plays the most important role considering de novo and acquired drug resistance and should contain PIs, IMIDs, MoAb and ASCT. This review summarizes the role of anti-myeloma agents for microenvironment and clonal evolution and treatment strategies to overcome drug resistance.

Targeting the Endothelin-1 Receptors Curtails Tumor Growth and Angiogenesis in Multiple Myeloma

The endothelin-1 (ET-1) receptors were recently found to mediate pro-survival functions in multiple myeloma (MM) cells in response to autocrine ET-1. This study investigated the effectiveness of macitentan, a dual ET-1 receptor antagonist, in MM treatment, and the mechanisms underlying its activities. Macitentan affected significantly MM cell (RPMI-8226, U266, KMS-12-PE) survival and pro-angiogenic cytokine release by down-modulating ET-1-activated MAPK/ERK and HIF-1α pathways, respectively. HIF-1α silencing abrogated the ET-1 mediated induction of genes encoding for pro-angiogenic cytokines such as VEGF-A, IL-8, Adrenomedullin, and ET-1 itself. Upon exposure to macitentan, MM cells cultured in the presence of the hypoxia-mimetic agent CoCl₂, exogenous ET-1, or CoCl₂ plus ET-1, down-regulated HIF-1α and the transcription and release of downstream pro-angiogenic cytokines. Consistently, macitentan limited significantly the basal pro-angiogenic activity of RPMI-8226 cells in chorioallantoic membrane assay. In xenograft mouse models, established by injecting NOG mice either via intra-caudal vein with U266 or subcutaneously with RPMI-8226 cells, macitentan reduced effectively the number of MM cells infiltrating bone marrow, and the size and microvascular density of subcutaneous MM tumors. ET-1 receptors targeting by macitentan represents an effective anti-proliferative and anti-angiogenic therapeutic approach in preclinical settings of MM.

Cyclin D1 targets hexokinase 2 to control aerobic glycolysis in myeloma cells

Cancer cells are characterized by the Warburg effect, a shift from mitochondrial respiration to oxidative glycolysis. We report here the crucial role of cyclin D1 in promoting this effect in a cyclin-dependent kinase (CDK)4/6-independent manner in multiple myeloma (MM) cells. We show that the cyclin D1 oncoprotein targets hexokinase 2 (HK2), a major glycolysis regulator, through two original molecular mechanisms in the cytoplasmic and nuclear compartments. In the cytoplasm, cyclin D1 binds HK2 at the outer mitochondrial membrane, and in the nucleus, it binds hypoxia-inducible factor-1α (HIF1α), which regulates HK2 gene transcription. We also show that high levels of HK2 expression are correlated with shorter event-free survival (EFS) and overall survival (OS) in MM patients. HK2 may therefore be considered as a possible target for antimyeloma therapy.

New role of hypoxia in pathophysiology of multiple myeloma through miR-210

Bone is one of the most common sites of complication in multiple myeloma (MM) progression and bone remodeling gets definitively perturbed during disease progression. Hypoxia and miR-210 play an important role in hematological malignancies. In an attempt to elucidate the specificity of the pathways of hypoxia and miR-210 in suppression of osteoblastic differentiation in MM patients, we examined the effect of miR-210 and hypoxia on expression of important cytokines and genes of myeloma cells. Differentiation of BM-MSCs towards osteoblastic cells in response to microvesicles (MVs) was also investigated. Finally, we proposed a molecular model on how HIF-1α may promote bone lesions in MM patients. To validate the effect of miR-210 and HIF-1α on targeted genes, the shRNA of HIF-1α and off-hsa-miR-210 were transfected into RPMI-8226 cells. BM-MSCs were cultured in osteoblastic inducer and 50 µg/mL of MVs derived from both hypoxic and normoxic myeloma cells. We designed an in vitro study to establish the effects of HIF-1α and miR-210 on the crosstalk between MM and osteoblasts. We here showed that hypoxia-induced miR-210 increased the mRNA expression of VLA-4, CXCR4, IL-6 and TGF-β in myeloma cells. MiR-210 is mandatory for the hypoxia-increased resistance of MM cells to melphalan. Moreover, MVs derived from hypoxic myeloma cells substantially decreased osteoblast differentiation. Considered comprehensively, our findings explain one of the reasons of bone loss that occurs at the sites of MM and a nascent crosstalk model in MM pathogenesis.

Bufalin induces DNA damage response under hypoxic condition in myeloma cells

Hypoxia serves a crucial role in the development of drug resistance in various cancer cells. Therefore, many attempts targeting hypoxia are underway to overcome the drug resistance mediated by hypoxia. This strategy is useful for multiple myeloma (MM) cells, as MM cells reside within the bone marrow, where oxygen concentrations are relatively low. A natural compound library was screened to identify compounds exerting cytotoxicity in MM cells under hypoxic conditions. Bufalin exhibited marked cytotoxicity to MM cells under normoxic and hypoxic conditions. No significant toxicity was observed in lymphocytes obtained from healthy donors. Under normoxic conditions, bufalin induced a DNA double strand break (DSB) response, ROS induction and apoptosis within 24 with a rapid response compared with melphalan. Interestingly, the bufalin-induced DSB response was not impaired by low oxygen concentrations while the DSB response by melphalan was reduced. Furthermore, treatment with bufalin abolished HIF-1α expression under hypoxia, suggesting that bufalin exerts cytotoxicity under hypoxia by regulating HIF-1α. These results indicate that bufalin induces apoptosis in MM cells through DSB under hypoxic conditions by inhibiting HIF-1α, suggesting that bufalin could be useful for eradication of drug-resistant MM cells in the hypoxic microenvironment.

Restoration of the prolyl-hydroxylase domain protein-3 oxygen-sensing mechanism is responsible for regulation of HIF2α expression and induction of sensitivity of myeloma cells to hypoxia-mediated apoptosis

Multiple myeloma (MM) is an incurable disease of malignant plasma B-cells that infiltrate the bone marrow (BM), resulting in bone destruction, anemia, renal impairment and infections. Physiologically, the BM microenvironment is hypoxic and this promotes MM progression and contributes to resistance to chemotherapy. Since aberrant hypoxic responses may result in the selection of more aggressive tumor phenotypes, we hypothesized that targeting the hypoxia-inducible factor (HIF) pathways will be an effective anti-MM therapeutic strategy. We demonstrated that MM cells are resistant to hypoxia-mediated apoptosis in vivo and in vitro, and that constitutive expression of HIF2α contributed to this resistance. Since epigenetic silencing of the prolyl-hydroxylase-domain-3 (PHD3) enzyme responsible for the O2-dependent regulation of HIF2α is frequently observed in MM tumors, we asked if PHD3 plays a role in regulating sensitivity to hypoxia. We found that restoring PHD3 expression using a lentivirus vector or overcoming PHD3 epigenetic silencing using a demethyltransferase inhibitor, 5-Aza-2'-deoxycytidine (5-Aza-dC), rescued O2-dependent regulation of HIF2α and restored sensitivity of MM cells to hypoxia-mediated apoptosis. This provides a rationale for targeting the PHD3-mediated regulation of the adaptive cellular hypoxic response in MM and suggests that targeting the O2-sensing pathway, alone or in combination with other anti-myeloma chemotherapeutics, may have clinical efficacy.

Molecular docking based screening of a simulated HIF-1 protein model for potential inhibitors

Hypoxia inducible factor-1(HIF-1) is a bHLH-family transcription factor that control genes involved in glucolysis, angiogenesis, migration, as well as invasion factors that are important for tumor progression and metastasis. HIF-1, a hetero dimer of HIF-1α and HIF-1β, binds to the hypoxia responsive genes, such as vascular endothelial growth factor (VEGF). It is one the molecular target for angiogenesis. A series of Chalcone - like compounds described that preferentially inhibit HIF-1 dimer, which can interact with amino acids within the active site of the protein. It is of interest model the HIF-1 dimer protein and protein was subjected to molecular dynamics simulations using NAMD 2.9 software with CHARMM27 force field in water and the protein structure was minimized with 25000 steps for 500 ps and simulation with 1000000 steps for 2ns. 2500 compounds were screened from Zinc database through structure based virtual screening with references to Chalcone natural drug compound. The screened compounds were docked into the active site of the protein using AutoDock Vina in PyRx Virtual screening tool. The docking result showed the compounds Zinc04280532, Zinc04280533, Zinc04280469, Zinc04280534, Zinc16405915, Zinc04277060, Zinc04280538, Zinc04582923, Zinc05280554 and Zinc05943723 have high binding affinities then query compound. The lead hit compounds were also testing for toxicity and bioavailability using Osiris and Molinspiration online server. The active site amino acids such as TYR-21, ASN-34, VAL-35, MET-18, LYS-17, SER-36, ARG- 46 and ARG-14 are key role in the inhibitors activity. This is useful in the design of small molecule therapeutics or the treatment of different abnormalities associated with impaired HIF-1α.

Network-based analysis of the molecular mechanisms of multiple myeloma and monoclonal gammopathy of undetermined significance

The present study aimed to reveal the molecular mechanisms of multiple myeloma (MM) and monoclonal gammopathy of undetermined significance (MGUS). This was a secondary study on microarray dataset GSE80608, downloaded from the Gene Expression Omnibus database, which included 10 control samples, 10 MGUS samples and 10 MM samples. Differentially expressed genes (DEGs) were identified between control and MGUS samples, and between control and MM samples. A protein-protein interaction (PPI) network was built for studying the interactions between the DEGs. Kyoto Encyclopedia of Genes and Genomes pathway enrichment analysis was performed for the genes in a gene co-expression network. A microRNA (miRNA/miR)-gene network was built to the evaluate possible the miRNAs and genes involved in the diseases. The present study identified 136 common upregulated DEGs and 165 common downregulated DEGs between MM and MGUS. Pathway enrichment analysis of the genes in the gene co-expression network revealed that the complement and coagulation cascades pathway was significantly enriched for certain complement and coagulation-associated genes. Endothelin-1 (EDN1) was significantly enriched in the hypoxia inducible factor-1 (HIF-1) and tumor necrosis factor signaling pathways. EDN1 was an important node in the PPI network, and a target gene of let-7e, let-7b and miR-19a in the miRNA-gene network. The results of the present study indicate that complement and coagulation-associated genes, the complement and coagulation cascades pathway, EDN1, let-7e, let-7b-5p, miR-19a, and the tumor necrosis factor and HIF-1 signaling pathways may all be implicated in MM and MGUS.

Echinomycin inhibits adipogenesis in 3T3-L1 cells in a HIF-independent manner

Obesity is a risk factor for many diseases including diabetes, cancer, cardiovascular disease, and chronic kidney disease. Obesity is characterized by the expansion of white adipose tissue (WAT). Hypertrophy and hyperplasia of adipocytes cause tissue hypoxia followed by inflammation and fibrosis. Its trigger, preadipocyte differentiation into mature adipocytes, is finely regulated by transcription factors, signal molecules, and cofactors. We found that echinomycin, a potent HIF-1 inhibitor, completely inhibited adipogenesis in 3T3-L1 WAT preadipocytes by affecting the early phase of mitotic clonal expansion. The dose required to exert the effect was surprisingly low and the time was short. Interestingly, its inhibitory effect was independent of HIF-1 pathways. Time-course DNA microarray analysis of drug-treated and untreated preadipocytes extracted a major transcription factor, CCAAT/enhancer-protein β, as a key target of echinomycin. Echinomycin also inhibited adipogenesis and body weight gain in high fat diet mice. These findings highlight a novel role of echinomycin in suppressing adipocyte differentiation and offer a new therapeutic strategy against obesity and diabetes.

Drug metabolism and clearance system in tumor cells of patients with multiple myeloma

Resistance to chemotherapy is a major limitation of cancer treatments with several molecular mechanisms involved, in particular altered local drug metabolism and detoxification process. The role of drug metabolism and clearance system has not been satisfactorily investigated in Multiple Myeloma (MM), a malignant plasma cell cancer for which a majority of patients escapes treatment. The expression of 350 genes encoding for uptake carriers, xenobiotic receptors, phase I and II Drug Metabolizing Enzymes (DMEs) and efflux transporters was interrogated in MM cells (MMCs) of newly-diagnosed patients in relation to their event free survival. MMCs of patients with a favourable outcome have an increased expression of genes coding for xenobiotic receptors (RXRα, LXR, CAR and FXR) and accordingly of their gene targets, influx transporters and phase I/II DMEs. On the contrary, MMCs of patients with unfavourable outcome displayed a global down regulation of genes coding for xenobiotic receptors and the downstream detoxification genes but had a high expression of genes coding for ARNT and Nrf2 pathways and ABC transporters. Altogether, these data suggests ARNT and Nrf2 pathways could be involved in MM primary resistance and that targeting RXRα, PXR, LXR and FXR through agonists could open new perspectives to alleviate or reverse MM drug resistance.

Hypoxia-mediated autophagic flux inhibits silver nanoparticle-triggered apoptosis in human lung cancer cells

Solid tumors are frequently associated with resistance to chemotherapy because the fraction of hypoxic tumor cells is substantial. To understand the underlying mechanism of hypoxia on silver nanoparticle (AgNPs)-induced apoptosis, the expression of hypoxia-inducible factor (HIF)-1α, a hallmark of hypoxia, was measured in the presence and absence of AgNPs. The results showed that HIF-1α expression was upregulated after AgNPs treatment under both hypoxic and normoxic conditions. Cell viability assays showed that AgNPs promoted cell death in cancer cells but not in non-cancer cells, as cancer cells are slightly more acidic than normal cells. However, reactive oxygen species generation induced by AgNPs in lung cancer cells caused high susceptibility to oxidative stress, whereas pre-exposure to hypoxia blocked AgNPs-induced oxidative stress. Notably, HIF-1α inhibited AgNPs-induced mitochondria-mediated apoptosis by regulating autophagic flux through the regulation of ATG5, LC3-II, and p62. Further, cell viability after treatment of cancer cells with AgNPs under hypoxic conditions was lower in HIF-1α siRNA-transfected cells than in control siRNA-transfected cells, indicating that HIF-1α knockdown enhances hypoxia induced decrease in cell viability. Our results suggest that hypoxia-mediated autophagy may be a mechanism for the resistance of AgNPs-induced apoptosis and that strategies targeting HIF-1α may be used for cancer therapy.

Chetomin, targeting HIF-1α/p300 complex, exhibits antitumour activity in multiple myeloma

Background:

Multiple myeloma (MM) is an incurable clonal plasma cell malignancy. The constitutive expression of HIF-1α in MM suggests that inhibition of HIF-1α-mediated transcription represents an interesting target in MM.

Methods:

As p300 is a crucial co-activator of hypoxia-inducible transcription, disrupting the complex HIF-1α/p300 to target HIF activity appears to be an attractive strategy.

Results:

We reported that chetomin, an inhibitor of HIF-1α/p300 interaction, exhibits antitumour activity in human myeloma cell lines and primary MM cells from patients.

Conclusions:

Our data suggest that chetomin may be of clinical value in MM and especially for patients characterised by a high EP300/HIF-1α expression and a poor prognosis.

A DNA-binding Molecule Targeting the Adaptive Hypoxic Response in Multiple Myeloma Has Potent Antitumor Activity

Multiple myeloma is incurable and invariably becomes resistant to chemotherapy. Although the mechanisms remain unclear, hypoxic conditions in the bone marrow have been implicated in contributing to multiple myeloma progression, angiogenesis, and resistance to chemotherapy. These effects occur via adaptive cellular responses mediated by hypoxia-inducible transcription factors (HIF), and targeting HIFs can have anticancer effects in both solid and hematologic malignancies. Here, it was found that in most myeloma cell lines tested, HIF1α, but not HIF2α expression was oxygen dependent, and this could be explained by the differential expression of the regulatory prolyl hydroxylase isoforms. The anti-multiple myeloma effects of a sequence-specific DNA-binding pyrrole-imidazole (Py-Im) polyamide (HIF-PA), which disrupts the HIF heterodimer from binding to its cognate DNA sequences, were also investigated. HIF-PA is cell permeable, localizes to the nuclei, and binds specific regions of DNA with an affinity comparable with that of HIFs. Most of the multiple myeloma cells were resistant to hypoxia-mediated apoptosis, and HIF-PA treatment could overcome this resistance in vitro. Using xenograft models, it was determined that HIF-PA significantly decreased tumor volume and increased hypoxic and apoptotic regions within solid tumor nodules and the growth of myeloma cells engrafted in the bone marrow. This provides a rationale for targeting the adaptive cellular hypoxic response of the O2-dependent activation of HIFα using polyamides.

IMPLICATIONS

Py-Im polyamides target and disrupt the adaptive hypoxic responses in multiple myeloma cells that may have clinical significance as a therapeutic strategy to treat myeloma engrafted in the bone marrow microenvironment.

Hypoxia‑mediated activation of autophagic flux inhibits apoptosis of keratinocytes via blocking tumor necrosis factor‑related apoptosis‑inducing ligand

Tumor necrosis factor‑related apoptosis‑inducing ligand (TRAIL) is toxic against transformed tumor cells. Cornification is the terminal differentiation of keratinocytes and a specific form of programmed cell death caused by TRAIL that occurs in keratinocytes. Apoptosis can also be triggered when TRAIL induces expression of keratinocyte differentiation markers. The present study reported that hypoxia inhibits TRAIL‑induced apoptosis due to autophagic flux. It is well known that hypoxia activates autophagy in keratinocytes and reduces p62 protein levels. The present study demonstrated that hypoxia inhibited TRAIL‑mediated apoptosis and induced autophagic flux in HaCaT cells. In addition, autophagic flux‑inactivating reagents, including 3‑methyladenine and chloroquine, increased the TRAIL sensitivity of HaCaT cells exposed to hypoxia. In conclusion, these results indicated that inactivating autophagy increased TRAIL sensitivity in hypoxic HaCaT cells. Autophagy inhibitors may be beneficial in therapies using TRAIL against skin cancers.

The twisted survivin connection to angiogenesis

Survivin, a member of the inhibitor of apoptosis family of proteins (IAPs) that controls cell division, apoptosis, metastasis and angiogenesis, is overexpressed in essentially all human cancers. As a consequence, the gene/protein is considered an attractive target for cancer treatment. Here, we discuss recent findings related to the regulation of survivin expression and its role in angiogenesis, particularly in the context of hypoxia. We propose a novel role for survivin in cancer, whereby expression of the protein in tumor cells promotes VEGF synthesis, secretion and angiogenesis. Mechanistically, we propose the existence of a positive feed-back loop involving PI3-kinase/Akt activation and enhanced β-Catenin-TCF/LEF-dependent VEGF expression followed by secretion. Finally, we elaborate on the possibility that this mechanism operating in cancer cells may contribute to enhanced tumor vascularization by vasculogenic mimicry together with conventional angiogenesis.

Therapeutic targeting of hypoxia and hypoxia-inducible factor 1 alpha in multiple myeloma

Multiple myeloma (MM) is a clonal B-cell malignancy characterized by accumulation of malignant plasma cells (PCs) within the bone marrow (BM). The PCs are in close contact with stromal cells, which secrete growth factors and cytokines, promoting tumor cell growth and survival. Despite the availability of new drugs with immunomodulatory properties targeting the neoplastic clone and its microenvironment, MM is still an incurable disease, with patients experiencing subsequent phases of remission and relapse, eventually leading to disease resistance and patient death. It is now well established that the MM BM microenvironment is hypoxic, a condition required for the activation of the hypoxia-inducible factor 1 alpha (HIF-1α). It has been shown that HIF-1α is constitutively expressed in MM even in normoxic conditions, suggesting that HIF-1α suppression might be part of a therapeutic strategy. Constitutively activated HIF-1α enhances neovascularization, increases glucose metabolism, and induces the expression of antiapoptotic proteins. HIF-1α is thought to be one of the most important molecular targets in the treatment of cancer, and a variety of chemical inhibitors for HIF-1α have been developed to date. This review examines the role of HIF-1α in MM and recent developments in harnessing the therapeutic potential of HIF-1α inhibition in MM.

Hypoxia-induced chemoresistance in cancer cells: The role of not only HIF-1

BACKGROUND

The aim of this review is to provide the information about molecular basis of hypoxia-induced chemoresistance, focusing on the possibility of diagnostic and therapeutic use.

RESULTS

Hypoxia is a common feature of tumors and represents an independent prognostic factor in many cancers. It is the result of imbalances in the intake and consumption of oxygen caused by abnormal vessels in the tumor and the rapid proliferation of cancer cells. Hypoxia-induced resistance to cisplatin, doxorubicin, etoposide, melphalan, 5-flouoruracil, gemcitabine, and docetaxel has been reported in a number of experiments. Adaptation of tumor cells to hypoxia has important biological effects. The most studied factor responsible for these effects is hypoxia-inducible factor-1 (HIF-1) that significantly contributes to the aggressiveness and chemoresistance of different tumors. The HIF-1 complex, induced by hypoxia, binds to target genes, thereby increasing the expression of many genes. In addition, the expression of hundreds of genes can be also decreased in response to hypoxia in HIF-1 dependent manner, but without the detection of HIF-1 in these genes' promoters. HIF-1 independent mechanisms for drug resistance in hypoxia have been described, however, they are still rarely reported. The first clinical studies focusing on diagnosis of hypoxia and on inhibition of hypoxia-induced changes in cancer cells are starting to yield results.

CONCLUSIONS

The adaptation to hypoxia requires many genetic and biochemical responses that regulate one another. Hypoxia-induced resistance is a very complex field and we still know very little about it. Different approaches to circumvent hypoxia in tumors are under development.

Targeting aerobic glycolysis and HIF-1alpha expression enhance imiquimod-induced apoptosis in cancer cells

Tumor cells rely on aerobic glycolysis to maintain unconstrained cell growth and proliferation. Imiquimod (IMQ), a synthetic Toll-like receptor (TLR) 7/8 ligand, exerts anti-tumor effects directly by inducing cell death in cancer cells and/or indirectly by activating cellular immune responses against tumor cells. However, whether IMQ modulates glucose metabolism pathways remains unclear. In this study, we demonstrated that IMQ can enhance aerobic glycolysis by up-regulating HIF-1α expression at the transcriptional and translational levels via ROS mediated STAT3- and Akt-dependent pathways, independent of TLR7/8 signaling. The genetic silencing of HIF-1α not only repressed IMQ-induced aerobic glycolysis but also sensitized cells to IMQ-induced apoptosis due to faster ATP and Mcl-1 depletion. Moreover, the glucose analog 2-DG and the Hsp90 inhibitor 17-AAG, which destabilizes the HIF-1α protein, synergized with IMQ to induce tumor cell apoptosis in vitro and significantly inhibited tumor growth in vivo. Thus, we hypothesize that the IMQ-induced up-regulation of HIF-1α and aerobic glycolysis is a protective response to the metabolic stress generated by IMQ treatment, and thus, co-treatment with inhibitors of HIF-1α and/or glycolysis may be a useful therapeutic strategy to enhance the anti-tumor effects of IMQ in clinical settings.

Hypoxia inducible factor-1 alpha as a therapeutic target in multiple myeloma

The increasing importance of hypoxia-inducible factor-1α (HIF-1α) in tumorigenesis raises the possibility that agents which specifically inhibit this transcription factor, would provide significant therapeutic benefit. The constitutive expression of HIF-1α in about 35% of Multiple Myeloma (MM) patients suggests HIF-1α suppression might be part of a therapeutic strategy. Accordingly, we explored the effect of EZN-2968, a small 3rd generation antisense oligonucleotide against HIF-1α, in a panel of MM cell lines and primary patients samples. Here, we demonstrated that EZN-2968 is highly specific for HIF-1α mRNA and that exposure of MM cells to EZN-2968 resulted in an efficient and homogeneous loading of the cells showing a long lasting low HIF-1α protein level. In MM cells, HIF-1α suppression induced a permanent cell cycle arrest by prolonging S-phase through cyclin A modulation and in addition it induced a mild apoptotic cell death. Moreover, HIF-1α suppression caused a metabolic shift that leaded to increased production of ATP by oxidative phosphorylation (i.e. Warburg effect reversion), that was confirmed by the observed mitochondrial membrane potential decrease. These results show that HIF-1α is an important player in MM homeostasis and that its inhibition by small antisense oligonucleotides provides a rationale for novel therapeutic strategy to improving MM treatment.

HIF-1α and GLUT1 gene expression is associated with chemoresistance of acute myeloid leukemia

AIMS

Much evidence suggests that increased glucose metabolism in tumor cells might contribute to the development of acquired chemoresistance. However, the molecular mechanisms are not fully clear. Therefore, we investigated a possible correlation of mRNA expression of HIF-1α and GLUT1 with chemoresistance in acute myeloid leukemia (AML).

METHODS

Bone marrow samples were obtained from newly diagnosed and relapsed AML (M3 exclusion) cases. RNA interference with short hairpin RNA (shRNA) was used to stably silence GLUT1 or HIF-1α gene expression in an AML cell line and HIF-1α and GLUT1 mRNA expression was measured by real-time quantitative polymerase chain reaction assay (qPCR).

RESULTS

High levels of HIF-1α and GLUT1 were associated with poor responsiveness to chemotherapy in AML. Down-regulation of the expression of GLUT1 by RNA interference obviously sensitized drug-resistant HL-60/ADR cells to adriamycin (ADR) in vitro, comparable with RNA interference for the HIF-1α gene.

CONCLUSIONS

Our data revealed that over-expression of HIF-1α and GLUT1 might play a role in the chemoresistance of AML. GLUT1 might be a potential target to reverse such drug resistance.

HIF-1α inhibition blocks the cross talk between multiple myeloma plasma cells and tumor microenvironment

Multiple myeloma (MM) is a malignant disorder of post-germinal center B cells, characterized by the clonal proliferation of malignant plasma cells (PCs) within the bone marrow (BM). The reciprocal and complex interactions that take place between the different compartments of BM and the MM cells result in tumor growth, angiogenesis, bone disease, and drug resistance. Given the importance of the BM microenvironment in MM pathogenesis, we investigated the possible involvement of Hypoxia-Inducible transcription Factor-1 alpha (HIF-1α) in the PCs-bone marrow stromal cells interplay. To test this hypothesis, we used EZN-2968, a 3rd generation antisense oligonucleotide against HIF-1α, to inhibit HIF-1α functions. Herein, we provide evidence that the interaction between MM cells and BM stromal cells is drastically reduced upon HIF-1α down-modulation. Notably, we showed that upon exposure to HIF-1α inhibitor, neither the incubation with IL-6 nor the co-culture with BM stromal cells were able to revert the anti-proliferative effect induced by EZN-2968. Moreover, we observed a down-modulation of cytokine-induced signaling cascades and a reduction of MM cells adhesion capability to the extracellular matrix proteins in EZN-2968-treated samples. Taken together, these results strongly support the concept that HIF-1α plays a critical role in the interactions between bone BM cells and PCs in Multiple Myeloma.

The role of hypoxia and exploitation of the hypoxic environment in hematologic malignancies

Tumor hypoxia is a well-described phenomenon during the progression of solid tumors affecting cell signaling pathways and cell metabolism; however, its role in hematologic malignancies has not been given the same attention in the literature. Therefore, this review focuses on the comparative differences between solid and hematologic malignancies with emphasis on the role of hypoxia during tumorigenesis and progression. In addition, contribution of the bone marrow and angiogenic environment are also discussed. Insight is provided into the role of hypoxia in metastatic spread, stemness, and drug resistance in hematologic conditions. Finally, emerging therapeutic strategies such as small-molecule prodrugs and hypoxia-inducible factor (HIF) targeting approaches are outlined to combat hypoxic cells and/or adaptive mechanisms in the treatment of hematologic malignancies.

Overcoming hypoxic-resistance of tumor cells to TRAIL-induced apoptosis through melatonin

A solid tumor is often exposed to hypoxic or anoxic conditions; thus, tumor cell responses to hypoxia are important for tumor progression as well as tumor therapy. Our previous studies indicated that tumor cells are resistant to tumor necrosis factor-related apoptosis-inducing ligand (TRAIL)-induced cell apoptosis under hypoxic conditions. Melatonin inhibits cell proliferation in many cancer types and induces apoptosis in some particular cancer types. Here, we examined the effects of melatonin on hypoxic resistant cells against TRAIL-induced apoptosis and the possible mechanisms of melatonin in the hypoxic response. Melatonin treatment increased TRAIL-induced A549 cell death under hypoxic conditions, although hypoxia inhibited TRAIL-mediated cell apoptosis. In a mechanistic study, hypoxia inducible factor-1α and prolyl-hydroxylase 2 proteins, which increase following exposure to hypoxia, were dose-dependently down-regulated by melatonin treatment. Melatonin also blocked the hypoxic responses that reduced pro-apoptotic proteins and increased anti-apoptotic proteins including Bcl-2 and Bcl-xL. Furthermore, melatonin treatment reduced TRAIL resistance by regulating the mitochondrial transmembrane potential and Bax translocation. Our results first demonstrated that melatonin treatment induces apoptosis in TRAIL-resistant hypoxic tumor cells by diminishing the anti-apoptotic signals mediated by hypoxia and also suggest that melatonin could be a tumor therapeutic tool by combining with other apoptotic ligands including TRAIL, particularly in solid tumor cells exposed to hypoxia.

HIF-1α of bone marrow endothelial cells implies relapse and drug resistance in patients with multiple myeloma and may act as a therapeutic target

PURPOSE

To investigate the role of hypoxia-inducible factor-1α (HIF-1α) in angiogenesis and drug resistance of bone marrow endothelial cells of patients with multiple myeloma.

EXPERIMENTAL DESIGN

HIF-1α mRNA and protein were evaluated in patients with multiple myeloma endothelial cells (MMEC) at diagnosis, at relapse after bortezomib- or lenalidomide-based therapies or on refractory phase to these drugs, at remission; in endothelial cells of patients with monoclonal gammapathies of undetermined significance (MGUS; MGECs), and of those with benign anemia (controls). The effects of HIF-1α inhibition by siRNA or panobinostat (an indirect HIF-1α inhibitor) on the expression of HIF-1α proangiogenic targets, on MMEC angiogenic activities in vitro and in vivo, and on overcoming MMEC resistance to bortezomib and lenalidomide were studied. The overall survival of the patients was also observed.

RESULTS

Compared with the other endothelial cell types, only MMECs from 45% of relapsed/refractory patients showed a normoxic HIF-1α protein stabilization and activation that were induced by reactive oxygen species (ROS). The HIF-1α protein correlated with the expression of its proangiogenic targets. The HIF-1α inhibition by either siRNA or panobinostat impaired the MMECs angiogenesis-related functions both in vitro and in vivo and restored MMEC sensitivity to bortezomib and lenalidomide. Patients with MMECs expressing the HIF-1α protein had shorter overall survival.

CONCLUSIONS

The HIF-1α protein in MMECs may induce angiogenesis and resistance to bortezomib and lenalidomide and may be a plausible target for the antiangiogenic management of patients with well-defined relapsed/refractory multiple myeloma. It may also have prognostic significance.

Effects of hypoxia on human cancer cell line chemosensitivity

Background

Environment inside even a small tumor is characterized by total (anoxia) or partial oxygen deprivation, (hypoxia). It has been shown that radiotherapy and some conventional chemotherapies may be less effective in hypoxia, and therefore it is important to investigate how different drugs act in different microenvironments. In this study we perform a large screening of the effects of 19 clinically used or experimental chemotherapeutic drugs on five different cell lines in conditions of normoxia, hypoxia and anoxia.

Methods

A panel of 19 commercially available drugs: 5-fluorouracil, acriflavine, bortezomib, cisplatin, digitoxin, digoxin, docetaxel, doxorubicin, etoposide, gemcitabine, irinotecan, melphalan, mitomycin c, rapamycin, sorafenib, thalidomide, tirapazamine, topotecan and vincristine were tested for cytotoxic activity on the cancer cell lines A2780 (ovarian), ACHN (renal), MCF-7 (breast), H69 (SCLC) and U-937 (lymphoma). Parallel aliquots of the cells were grown at different oxygen pressures and after 72 hours of drug exposure viability was measured with the fluorometric microculture cytotoxicity assay (FMCA).

Results

Sorafenib, irinotecan and docetaxel were in general more effective in an oxygenated environment, while cisplatin, mitomycin c and tirapazamine were more effective in a low oxygen environment. Surprisingly, hypoxia in H69 and MCF-7 cells mostly rendered higher drug sensitivity. In contrast ACHN appeared more sensitive to hypoxia, giving slower proliferating cells, and consequently, was more resistant to most drugs.

Conclusions

A panel of standard cytotoxic agents was tested against five different human cancer cell lines cultivated at normoxic, hypoxic and anoxic conditions. Results show that impaired chemosensitivity is not universal, in contrast different cell lines behave different and some drugs appear even less effective in normoxia than hypoxia.

Radiation-induced mitotic cell death and glioblastoma radioresistance: a new regulating pathway controlled by integrin-linked kinase, hypoxia-inducible factor 1 alpha and survivin in U87 cells

We have previously shown that integrin-linked kinase (ILK) regulates U87 glioblastoma cell radioresistance by modulating the main radiation-induced cell death mechanism in solid tumours, the mitotic cell death. To decipher the biological pathways involved in these mechanisms, we constructed a U87 glioblastoma cell model expressing an inducible shRNA directed against ILK (U87shILK). We then demonstrated that silencing ILK enhanced radiation-induced centrosome overduplication, leading to radiation-induced mitotic cell death. In this model, ionising radiations induce hypoxia-inducible factor 1 alpha (HIF-1α) stabilisation which is inhibited by silencing ILK. Moreover, silencing HIF-1α in U87 cells reduced the surviving fraction after 2 Gy irradiation by increasing cell sensitivity to radiation-induced mitotic cell death and centrosome amplification. Because it is known that HIF-1α controls survivin expression, we then looked at the ILK silencing effect on survivin expression. We show that survivin expression is decreased in U87shILK cells. Furthermore, treating U87 cells with the specific survivin suppressor YM155 significantly increased the percentage of giant multinucleated cells, centrosomal overduplication and thus U87 cell radiosensitivity. In consequence, we decipher here a new pathway of glioma radioresistance via the regulation of radiation-induced centrosome duplication and therefore mitotic cell death by ILK, HIF-1α and survivin. This work identifies new targets in glioblastoma with the intention of radiosensitising these highly radioresistant tumours.

Inhibition of autophagy with chloroquine is effective in melanoma

BACKGROUND

Cancer cells adapt to the stress resulting from accelerated cell growth and a lack of nutrients by activation of the autophagy pathway. Two proteins that allow cell growth in the face of metabolic stress and hypoxia are hypoxia-inducible factor-1α (HIF-1α) and heat shock protein 90 (Hsp 90). We hypothesize that chloroquine (CQ), an antimalarial drug that inhibits autophagosome function, in combination with either echinomycin, a HIF-1α inhibitor, or 17-dimethylaminoethylamino-17-dimethoxygeldanamycin (17-DMAG), an Hsp 90 inhibitor, will result in cytotoxicity in melanoma.

MATERIALS AND METHODS

Multiple human melanoma cell lines (BRAF wild-type and mutant) were tested in vitro with CQ in combination with echinomycin or 17-DMAG. These treatments were performed in hypoxic (5% O2) and normoxic (18% O2) conditions. Mechanism of action was determined through Western blot of autophagy-associated proteins HIF-1α and Hsp 90.

RESULTS

Chloroquine, echinomycin, and 17-DMAG each induced cytotoxicity in multiple human melanoma cell lines, in both normoxia and hypoxia. Chloroquine combined with echinomycin achieved synergistic cytotoxicity under hypoxic conditions in multiple melanoma cell lines (BRAF wild-type and mutant). Western blot analysis indicated that echinomycin reduced HIF-1α levels, both alone and in combination with CQ. Changes in LC3 flux indicated inhibition of autophagy at the level of the autophagosome by CQ therapy.

CONCLUSIONS

Targeting autophagy with the antimalarial drug CQ may be an effective cancer therapy in melanoma. Sensitivity to chloroquine is independent of BRAF mutational status. Combining CQ with the HIF-1α inhibitor echinomycin improves cytotoxicity in hypoxic conditions.

Understanding the hypoxic niche of multiple myeloma: therapeutic implications and contributions of mouse models

Multiple myeloma (MM) is the second most common hematological malignancy and is characterized by the clonal expansion of plasma cells in the bone marrow. Recently, hypoxia has received increased interest in the context of MM, in both basic and translational research. In this review, we describe the discovery of the hypoxic niche in MM and how it can be targeted therapeutically. We also discuss mouse models that closely mimic human MM, highlighting those that allow preclinical research into new therapies that exploit the hypoxic niche in MM.

Rituximab activates Syk and AKT in CD20-positive B cell lymphoma cells dependent on cell membrane cholesterol levels

The introduction of rituximab, an anti-CD20 monoclonal antibody, has dramatically improved the treatment outcomes of patients with B cell lymphoma. Nevertheless, the clinical response to rituximab varies, and a subpopulation of patients does not respond well to this antibody. Although several molecular events have been shown to be involved in the mechanism of action of rituximab, recent studies have demonstrated that intracellular signaling pathways and the direct effects of rituximab on cell membrane components are responsible for the antilymphoma action of this drug. In the present study, we demonstrated that rituximab activated Syk and Akt, molecules with antiapoptotic functions, in several CD20-positive lymphoma cell lines. Notably, rituximab activated Syk and Akt in all the tested primary lymphoma samples from six patients. Our results show that the cholesterol levels in lymphoma cell membranes have a crucial role in the regulation of Syk and Akt. The depletion of cholesterol from the cell membrane completely blocked rituximab-induced Syk and Akt activation. Simvastatin, an inhibitor of cholesterol synthesis, also abrogated rituximab-mediated Syk and Akt activation. Finally, we report that rituximab inhibited the apoptosis induced by chemotherapeutic drugs, which was observed solely in Akt-activated cells. This work demonstrates for the first time that rituximab paradoxically works to suppress apoptosis under certain conditions in a manner that is dependent on the cell membrane cholesterol level. Our observations provide novel insights and suggest that the cell membrane cholesterol level represents a new biomarker for predicting patient response to rituximab. Furthermore, the modulation of lipid rafts could provide a new strategy for enhancing the antilymphoma action of rituximab.

Hypoxia-inducible factor (HIF)-1α suppression in myeloma cells blocks tumoral growth in vivo inhibiting angiogenesis and bone destruction

Hypoxia-inducible transcription factor-1 (HIF-1α) is overexpressed in multiple myeloma (MM) cells within the hypoxic microenvironment. Herein, we explored the effect of persistent HIF-1α inhibition by a lentivirus short hairpin RNA pool on MM cell growth either in vitro or in vivo and on the transcriptional and pro-angiogenic profiles of MM cells. HIF-1α suppression did not have a significant impact on MM cell proliferation and survival in vitro although, increased the antiproliferative effect of lenalidomide. On the other hand, we found that HIF-1α inhibition in MM cells downregulates the pro-angiogenic genes VEGF, IL8, IL10, CCL2, CCL5 and MMP9. Pro-osteoclastogenic cytokines were also inhibited, such as IL-7 and CCL3/MIP-1α. The effect of HIF-1α inhibition was assessed in vivo in nonobese diabetic/severe combined immunodeficiency mice both in a subcutaneous and an intratibial MM model. HIF-1α inhibition caused a dramatic reduction in the weight and volume of the tumor burden in both mouse models. Moreover, a significant reduction of the number of vessels and vascular endothelial growth factors (VEGFs) immunostaining was observed. Finally, in the intratibial experiments, HIF-1α inhibition significantly blocked bone destruction. Overall, our data indicate that HIF-1α suppression in MM cells significantly blocks MM-induced angiogenesis and reduces MM tumor burden and bone destruction in vivo, supporting HIF-1α as a potential therapeutic target in MM.

Emerging strategies for targeting cell adhesion in multiple myeloma

Multiple myeloma (MM) is an incurable hematological cancer involving proliferation of abnormal plasma cells that infiltrate the bone marrow (BM) and secrete monoclonal antibodies. The disease is clinically characterized by bone lesions, anemia, hypercalcemia, and renal failure. MM is presently treated with conventional therapies like melphalan, doxorubicin, and prednisone; or novel therapies like thalidomide, lenalidomide, and bortezomib; or with procedures like autologous stem cell transplantation. Unfortunately, these therapies fail to eliminate the minimal residual disease that remains persistent within the confines of the BM of MM patients. Mounting evidence indicates that components of the BM-including extracellular matrix, cytokines, chemokines, and growth factors-provide a sanctuary for subpopulations of MM. This co-dependent development of the disease in the context of the BM not only ensures the survival and growth of the plasma cells but contributes to de novo drug resistance. In addition, by fostering homing, angiogenesis, and osteolysis, this crosstalk plays a critical role in the progression of the disease. Not surprisingly then, over the past decade, several strategies have been developed to disrupt this communication between the plasma cells and the BM components including antibodies, peptides, and inhibitors of signaling pathways. Ultimately, the goal is to use these therapies in combination with the existing antimyeloma agents in order to further reduce or abolish minimal residual disease and improve patient outcomes.

Biological aspects of angiogenesis in multiple myeloma

Multiple myeloma (MM) is a hematological malignancy characterized by the aberrant expansion of malignant plasma cells within the bone marrow (BM). One of the hallmarks of this disease is the close interaction between myeloma cells and neighboring cells within the BM. Angiogenesis, through the activation of endothelial cells, plays an essential role in MM biology. In the current review, we describe the angiogenesis process in MM by identifying the interacting cells, the pro- and anti-angiogenic cytokines modulated, and the extracellular matrix degrading proteases liable to participate in the pathophysiology. Finally, we highlight the impact of hypoxia (through hypoxia-inducible factor-1) and constitutive activation of nuclear factor-κB in this tumor-induced neo-vascularization.

Computational modeling on the recognition of the HRE motif by HIF-1: molecular docking and molecular dynamics studies

Hypoxia inducible factor-1 (HIF-1) is a bHLH-family transcription factor that controls genes involved in glycolysis, angiogenesis, migration, as well as invasion factors that are important for tumor progression and metastasis. HIF-1, a heterodimer of HIF-1α and HIF-1β, binds to the hypoxia responsive element (HRE) present in the promoter regions of hypoxia responsive genes, such as vascular endothelial growth factor (VEGF). Neither the structure of free HIF-1 nor that of its complex with HRE is available. Computational modeling of the transcription factor-DNA complex has always been challenging due to their inherent flexibility and large conformational space. The present study aims to model the interaction between the DNA-binding domain of HIF-1 and HRE. Experiments showed that rigid macromolecular docking programs (HEX and GRAMM-X) failed to predict the optimal dimerization of individually modeled HIF-1 subunits. Hence, the HIF-1 heterodimer was modeled based on the phosphate system positive regulatory protein (PHO4) homodimer. The duplex VEGF-DNA segment containing HRE with flanking nucleotides was modeled in the B form and equilibrated via molecular dynamics (MD) simulation. A rigid docking approach was used to predict the crude binding mode of HIF-1 dimer with HRE, in which the putative contacts were found to be present. An MD simulation (5 ns) of the HIF-1-HRE complex in explicit water was performed to account for its flexibility and to optimize its interactions. All of the conserved amino acid residues were found to play roles in the recognition of HRE. The present work, which sheds light on the recognition of HRE by HIF-1, could be beneficial in the design of peptide or small molecule therapeutics that can mimic HIF-1 and bind with the HRE sequence.

The emerging role of hypoxia, HIF-1 and HIF-2 in multiple myeloma

Hypoxia is an imbalance between oxygen supply and demand, which deprives cells or tissues of sufficient oxygen. It is well-established that hypoxia triggers adaptive responses, which contribute to short- and long-term pathologies such as inflammation, cardiovascular disease and cancer. Induced by both microenvironmental hypoxia and genetic mutations, the elevated expression of the hypoxia-inducible transcription factor-1 (HIF-1) and HIF-2 is a key feature of many human cancers and has been shown to promote cellular processes, which facilitate tumor progression. In this review, we discuss the emerging role of hypoxia and the HIFs in the pathogenesis of multiple myeloma (MM), an incurable hematological malignancy of BM PCs, which reside within the hypoxic BM microenvironment. The need for current and future therapeutic interventions to target HIF-1 and HIF-2 in myeloma will also be discussed.

Effects of arsenic trioxide on cell proliferation, apoptosis and HIF-1α expression in human liver cancer HepG2 cells cultured under hypoxic conditions

AIM: To investigate the effects of arsenic trioxide (As₂O₃) on cell proliferation, apoptosis and hypoxia-inducible factor-1α (HIF-1α) expression in human liver cancer HepG2 cells cultured under hypoxic conditions.

METHODS: Hypoxia was induced with cobalt chloride (CoCl₂). After HepG2 cells were incubated with different concentrations of As₂O₃ (1.0, 2.0, 4.0 and 8.0 µmol/L) for 12, 24 and 48 h under hypoxic conditions, cell proliferation was determined by MTT assay, and cell apoptosis was evaluated by Hoechst staining. HepG2 cells were then divided into three groups: normal control group, hypoxia group, and As₂O₃ treatment group. After HepG2 cells were incubated with As₂O₃ at concentrations of 4.0 and 8.0 µmol/L for 48 h under hypoxia, the expression of HIF-1α protein was detected by immunocytochemistry.

RESULTS: As₂O₃ inhibited proliferation but induced apoptosis of HepG2 cells in a dose- and time-dependent manner under both normoxic and hypoxic conditions (both P < 0.01). No significant differences were noted in the reduced proliferation rates of cell proliferation (38.40% vs 37.83%, P > 0.05) and apoptosis rates (45.25% vs 49.28%, P > 0.05) between HepG2 cells treated with 8.0 µmol/L As₂O₃ for 48 h under normoxic and hypoxic conditions. Immunocytochemistry analysis revealed that HIF-1α was weakly expressed in HepG2 cells under normoxia. After hypoxic induction for 48 h, HIF-1α expression was significantly up-regulated (t = 114.37, P < 0.05). The expression of HIF-1α protein gradually decreased with the increase in the concentration of As₂O₃ under hypoxia (F = 347.042, P < 0.01).

CONCLUSION: As₂O₃ can inhibit proliferation but induce apoptosis of HepG2 cells under hypoxia possibly by down-regulating HIF-1α protein expression.

A therapeutic role for targeting c-Myc/Hif-1-dependent signaling pathways

Deregulated c-Myc occurs in approximately 30% of human cancers. Similarly, hypoxia-inducible factor (HIF) is commonly overexpressed in a variety of human malignancies. Under physiologic conditions, HIF inhibits c-Myc activity; however, when deregulated oncogenic c-Myc collaborates with HIF in inducing the expression of VEGF, PDK1 and hexokinase 2. Most of the knowledge of HIF derives from studies investigating a role of HIF under hypoxic conditions, however, HIF-1alpha stabilization is also found in normoxic conditions. Specifically, under hypoxic conditions HIF-1-mediated regulation of oncogenic c-Myc plays a pivotal role in conferring metabolic advantages to tumor cells as well as adaptation to the tumorigenic micromilieu. In addition, our own results show that under normoxic conditions oncogenic c-Myc is required for constitutive high HIF-1 protein levels and activity in Multiple Myeloma (MM) cells, thereby influencing VEGF secretion and angiogenic activity within the bone marrow microenvironment. Further studies are needed to delineate the functional relevance of HIF, MYC, and the HIF-MYC collaboration in MM and other malignancies, also integrating the tumor microenvironment and the cellular context. Importantly, early studies already demonstrate promising preclinical of novel agents, predominantly small molecules, which target c-Myc, HIF or both.

Effects of combined Tan IIA and 5-FU on cell proliferation, apoptosis, and the expression of HIF-1α and mutant P53 in human gastric cancer cell line SGC7901 under hypoxia

AIM: To investigate the effects of combined tanshinone IIA (Tan IIA) and 5-fluorouracil (5-FU) on cell proliferation, apoptosis, and the expressions of hypoxia-inducible factor-1 alpha (HIF-1α) and mutant P53 (mt P53) in human gastric cancer cell line SGC7901 under hypoxia.

METHODS: Hypoxia was induced in SGC7901 cells by cobalt dichloride treatment. SGC7901 cells under hypoxia were treated with different concentrations of Tan IIA in combination with 10.0 mg/L of 5-FU for 24, 48 and 72 hours. Cell proliferation was detected by methyl thiazolyl tetrazolium (MTT) assay. Cell apoptosis was detected by Hoechst staining. The expression of HIF-1α and mt P53 proteins was detected by immunocytochemistry.

RESULTS: Combined Tan IIA and 5-FU significantly inhibited the proliferation of SGC7901 cells (all P < 0.01) in a dose- and time-dependent manner under hypoxia. The reduced proliferation rate of cells incubated with Tan IIA at a concentration of 10 mg/L and 5-FU for 72 hours was 67.46%. Hoechst staining showed that Tan IIA in combination with 5-FU promoted the apoptosis of SGC7901 cells in a dose- and time-dependent manner under hypoxia (all P < 0.01). Immunocytochemical staining revealed that the expression levels of HIF-1α and mt P53 proteins in SGC7901 cells under hypoxia were evidently higher than those in SGC7901 cells under normal conditions (t = 22.786 and 13.914, respectively; both P < 0.01). However, Tan IIA in combination with 5-FU significantly downregulated the expression of HIF-1α and mt P53 proteins in SGC7901 cells under hypoxia (F = 182.234 and 130.062, respectively; both P < 0.01). A significant positive correlation was noted between the expression of HIF-1α and mt P53 in SGC7901 cells (n = 5, r = 0.995, P < 0.01).

CONCLUSION: Tan IIA can significantly enhance 5-FU-mediated growth inhibition and apoptosis induction in SGC7901 cells under hypoxia perhaps by downregulating HIF-1α and mt P53 protein expression.

Inhibition of Notch3 enhances sensitivity to gemcitabine in pancreatic cancer through an inactivation of PI3K/Akt-dependent pathway

Notch3 is one of the four Notch receptors identified in mammal, but its role in human pancreatic cancer remains poorly characterized. In this study, we sought to determine the effect of suppressing Notch3 expression on the chemosensitivity to gemcitabine in human pancreatic cancer cell lines BxPC-3 and PANC-1. RNA interference was used to suppress Notch3 expression. Gemcitabine-induced cytotoxicity was determined by MTT. Cell apoptosis was measured by flow cytometry. Caspase 3 activity was assayed using a Caspase Fluorescent Assay Kit. The effect of Notch3-specific siRNA on PI3K/Akt activity was also quantified. Notch3-specific siRNA suppressed Notch3 expression, and furthermore increased gemcitabine-induced, caspase-mediated apoptosis. The suppression of Notch3 expression decreased the average IC(50) in BxPC-3 and PANC-1 cells treated with gemcitabine. PI3K/Akt activity was decreased by the suppression of Notch3 expression. Taken together, these data demonstrated that Notch3 is a potential therapeutic target for pancreatic cancer, and PI3K/Akt is a key signaling component by which activation of the Notch3 signal transduction pathway protects pancreatic cancer cells from chemotherapy-induced cell death.