Hypoxia signaling and metastatic progression

Disruption of oxygen homeostasis, resulting from an imbalance between O2 supply and demand during malignant proliferation, leads to the development of hypoxic tumor microenvironments that promote the acquisition of aggressive cancer cell phenotypes linked to metastasis and patient mortality. In this review, the mechanistic links between tumor hypoxia and metastatic progression are presented. Current status and perspectives of targeting hypoxia signaling pathways as a strategy to halt cancer cell metastatic activities are emphasized.

Metronomic chemotherapy offsets HIFα induction upon maximum-tolerated dose in metastatic cancers

Conventional maximum-tolerated dose (MTD) chemotherapy relies on periodic, massive cancer cell ablation events followed by treatment-free intermissions, stereotypically resulting in resistance, relapse, and mortality. Furthermore, MTD chemotherapy can promote metastatic dissemination via activation of a transcriptional program dependent on hypoxia-inducible factor (HIF)-1α and (HIF)-2α (hereafter referred to as HIFα). Instead, frequent low-dose metronomic (LDM) chemotherapy displays less adverse effects while preserving significant pre-clinical anticancer activity. Consequently, we hereby compared the effect of MTD or LDM chemotherapy upon HIFα in models of advanced, metastatic colon and breast cancer. Our results revealed that LDM chemotherapy could offset paralog-specific, MTD-dependent HIFα induction in colon cancers disseminating to the liver and lungs, while limiting HIFα and hypoxia in breast cancer lung metastases. Moreover, we assessed the translational significance of HIFα activity in colorectal and breast TCGA/microarray data, by developing two compact, 11-gene transcriptomic signatures allowing the stratification/identification of patients likely to benefit from LDM and/or HIFα-targeting therapies. Altogether, these results suggest LDM chemotherapy as a potential maintenance strategy to stave off HIFα induction within the intra-metastatic tumor microenvironment.

Hypoxia-Dependent Angiogenesis and Lymphangiogenesis in Cancer

Hypoxia (low O₂) is a ubiquitous feature of solid cancers, arising as a mismatch between cellular O₂ supply and consumption. Hypoxia is associated to metastatic disease and mortality owing to its ability to stimulate the formation of blood (angiogenesis) and lymphatic vessels (lymphangiogenesis), thereby allowing cancer cells to escape the unfavorable tumor microenvironment and disseminate into secondary sites. This review outlines molecular mechanisms by which intratumoral hypoxia regulates the expression of motogenic and mitogenic factors that induce angiogenesis and lymphangiogenesis, whilst discussing their implications for metastatic cancers.

Bridging angiogenesis and immune evasion in the hypoxic tumor microenvironment

Hypoxia (low O₂) is a ubiquitous microenvironmental factor promoting cancer progression, metastasis, and mortality, owing to the ability of cancer cells to co-opt physiological angiogenic responses. Notwithstanding, the pathophysiological induction of angiogenesis results in an abnormal tumor vasculature, further aggravating hypoxia in a feedforward loop that limits the efficacy of molecular targeted therapies. Recent studies suggest that, besides their canonical roles, angiogenic factors promote a panoply of immunosuppressive effects in the tumor microenvironment. Therefore, intratumoral hypoxia emerges as a hitherto unrecognized mechanism evolutionarily repurposing angiogenic molecules as (patho)physiological immunomodulators. On the other hand, antiangiogenic therapies could be aimed at impeding both tumor growth and immunotolerance toward cancer cells, a beneficial effect that can be countered if hypoxia signaling pathways are left unchecked, leading to therapeutic failure. This review summarizes evidence supporting the hypothesis that hypoxia acts as a common pathophysiological mechanism of resistance to immunotherapeutic and antiangiogenic agents while proposing potential strategies to curtail resistance and mortality in patients bearing solid malignancies.

Cell-Autonomous Metabolic Reprogramming in Hypoxia

Molecular oxygen (O₂) is a universal electron acceptor that enables ATP synthesis through mitochondrial respiration in all metazoans. Consequently, hypoxia (low O₂) has arisen as an organizing principle for cellular evolution, metabolism, and (patho)biology, eliciting a remarkable panoply of metabolic adaptations that trigger transcriptional, translational, post-translational, and epigenetic responses to determine cellular fitness. In this review we summarize current and emerging cell-autonomous molecular mechanisms that induce hypoxic metabolic reprogramming in health and disease.

Abstract 4499: The oncometabolite fumarate prevents hypoxia-induced ER stress by enhancing the pentose phosphate pathway

Cancer cells co-opt mechanisms of adaptation to hypoxia to minimize energy expenditure and halt proliferation thereby increasing hypoxic tolerance, a major factor contributing to chemo- and radioresistance in patients. The endoplasmic reticulum (ER) kinase PERK is one of the three signaling transducers of the unfolded protein response (UPR) that inhibits mRNA translation via eIF2α phosphorylation to alleviate hypoxia-induced ER stress. We have previously shown that accumulation of fumarate, resulting from loss-of-function (LOF) of the mitochondrial enzyme fumarate hydratase (FH), augments the antioxidant capacity of hypoxic cancer cells through upregulation of the pentose phosphate pathway (PPP). Here, we report for the first time that the fumarate-dependent increase of antioxidants generated by the PPP prevents hypoxic activation of the PERK→eIF2α axis enabling protein synthesis and proliferation leading to an impairment of hypoxic tolerance.

HeLa (cervix), HCT-116 and LS174T (colon) adenocarcinoma cells were transfected with lentiviral vectors encoding for shRNAs targeting FH. Immunoblot assays showed that FH LOF impaired PERK activity under hypoxia thus inactivating eIF2α. Moreover, the ability of fumarate to prevent PERK activation was specific to hypoxia since fumarate did not affect the pharmacological activation of the UPR by thapsigargin, DTT or tunicamycin. A comprehensive analysis utilizing a RT-qPCR array to profile the mRNA expression of 84 UPR genes, showed that FH LOF inhibited the UPR in HCT-116 cells. A similar response was observed in patient-derived UOK262 kidney cancer cells whereby bi-allelic FH mutations resulted in downregulation of 72% of the UPR genes whereas FH re-introduction restored UPR signaling. We employed LS174T mucinous adenocarcinoma cells as a model to assess protein synthesis. Mucin synthesis was not affected in hypoxic FH deficient cells whereas it was abrogated in wild-type cells. Consistent with these results, FH LOF increased 3D spheroid growth and decreased clonogenic potential in HCT-116 and HeLa cells. Pharmacological inhibition of the PPP by 6-aminonicotinamide activated the PERK→eIF2α axis in FH silenced cells thereby suggesting that PPP activation by fumarate is implicated in PERK inhibition. RNAseq data analysis in melanoma, prostate, colon, breast, lung and renal cancers from TCGA cohorts shows a negative correlation between PERK and the PPP enzyme PGLS suggesting that the mechanism hereby delineated occurs in cancer patients.

In conclusion, we show that fumarate impairs PERK→eIF2α UPR signaling in hypoxic cancer cells. Clinical and molecular data show that UPR activation is one of the mechanisms responsible for chemo- and radioresistance in hypoxic tumors. This study suggests that fumarate accumulation (either through extrinsic or FH LOF) represents a novel approach to target hypoxic cancer cells and improve patient prognosis.

Citation Format: Luana Schito, Sergio Rey, Bradly G. Wouters, Marianne Koritzinsky. The oncometabolite fumarate prevents hypoxia-induced ER stress by enhancing the pentose phosphate pathway [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2017; 2017 Apr 1-5; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2017;77(13 Suppl):Abstract nr 4499. doi:10.1158/1538-7445.AM2017-4499

Abstract 4510: ADP- dependent glucokinase controls hypoxic gradients, ex vivo avascular and in vivo tumor growth through modulation of HIF-1α/mTOR signaling

ADP- dependent glucokinase (ADPGK) is an evolutionarily conserved archaeal glycolytic enzyme frequently upregulated in human cancers whose role remains elusive. We have recently discovered that ADPGK contributes to ROS- dependent stabilization of hypoxia- inducible factor (HIF)-1α (and -2α) and hypoxic target gene transactivation in cancer cells. Hereby, we deconvolute the effect of ADPGK loss-of-function (LoF) upon the 3D hypoxic tumor microenvironment, a crucial pathobiological aspect determining therapeutic responses in cancer patients.

ADPGK, HIF-1α and HIF-2α LoF was attained through shRNA- mediated knockdown (>75%) in HCT-116 colon cancer cells. HIF-1α (and -2α) transcriptional activity was measured through RT-qPCR arrays whereas protein levels were assessed by immunoblot. O2 and glucose consumption were measured in 2D with a real-time bioanalyzer (Seahorse). Avascular 3D spheroids and xenografts were used to measure the effect of ADPGK LoF upon tumor growth. Hypoxic gradients in 3D tumor spheroids were quantified using the O2- sensitive nitroimidazole probe EF5 in combination with confocal microscopy and 3D image reconstruction.

RT-qPCR arrays identified a core group of 11 hypoxia- inducible transcripts dependent upon ADPGK expression (CA9, DDIT4, ERO1L, Igfbp3, Scl2a3, Bhlhe40, Bnip3L, Egln1, Fam162a, Pgk1 and PKM), henceforth referred to as ‘ADPGK- dependent HIF-α target signature’ (ADHTS). Comparison of ADHTS transcriptional profiles with HIF-1α or -2α deficient cells showed that ADPGK LoF is not selective for either HIF-α paralog. Since ADHTS contained genes critical for mTOR signaling, glycolytic activity and mitochondrial autophagy, we performed metabolic profiling and found that ADPGK LoF increased O2 consumption in a rapamycin- sensitive manner whilst increasing mitochondrial mass. Moreover, ADPGK LoF enhanced xenograft growth and vascularization associated with decreased protein levels of HIF-2α and the negative mTOR regulator DDIT4. In avascular 3D spheroids, ADPGK LoF increased growth, intra-spheroidal hypoxia and caused steeper hypoxic gradients in parallel to enhanced mTOR→pS6K→p4EBP1 signaling. RNAseq data from colon adenocarcinoma patients (TCGA; n= 382) confirmed that ADPGK expression correlates with ADHTS, HIF-α target gene expression, hypoxia scores and decreased overall survival. Consistent with our preclinical findings, the ADHTS gene signature inversely correlated with an mTOR gene signature in the same dataset.

Our results uncover a hitherto unknown function of ADPGK as a crucial determinant of the degree and distribution of hypoxia within the tumor microenvironment through modulation of HIF-1α→mTOR signaling. Our analysis of TCGA data supports these preclinical findings thereby suggesting that ADPGK is a suitable therapeutic target in patients bearing hypoxic cancers.

Citation Format: Sergio Rey, Luana Schito, Marianne Koritzinsky, Bradly G. Wouters. ADP- dependent glucokinase controls hypoxic gradients, ex vivo avascular and in vivo tumor growth through modulation of HIF-1α/mTOR signaling [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2017; 2017 Apr 1-5; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2017;77(13 Suppl):Abstract nr 4510. doi:10.1158/1538-7445.AM2017-4510

Targeting Hypoxia-Inducible Factors for Antiangiogenic Cancer Therapy

Hypoxia (low O₂) is a pathobiological hallmark of solid cancers, resulting from the imbalance between cellular O₂ consumption and availability. Hypoxic cancer cells (CCs) stimulate blood vessel sprouting (angiogenesis), aimed at restoring O₂ delivery to the expanding tumor masses through the activation of a transcriptional program mediated by hypoxia-inducible factors (HIFs). Here, we review recent data suggesting that the efficacy of antiangiogenic (AA) therapies is limited in some circumstances by HIF-dependent compensatory responses to increased intratumoral hypoxia. In lieu of this evidence, we discuss the potential of targeting HIFs as a strategy to overcome these instances of AA therapy resistance.

A β-galactosidase probe for the detection of cellular senescence by mass cytometry

Enzyme substrates for mass cytometry applications enable new dimensions in multiparametric cellular assays.

Hypoxia-Inducible Factors: Master Regulators of Cancer Progression

Intratumoral hypoxia (reduced O₂ availability) is a common finding in human cancer and leads to increased activity of hypoxia-inducible factors (HIFs), which regulate the expression of genes that contribute to angiogenesis, metabolic reprogramming, extracellular matrix remodeling, epithelial-mesenchymal transition, motility, invasion, metastasis, cancer stem cell maintenance, immune evasion, and resistance to chemotherapy and radiation therapy. Conventional anticancer therapies target well-oxygenated and proliferating cancer cells, whereas there are no approved therapies that target hypoxic cancer cells, despite growing clinical and experimental evidence indicating that intratumoral hypoxia is a critical microenvironmental factor driving cancer progression. In this review, our current understanding of the consequences of HIF activity and the translational potential of targeting HIFs for cancer therapy are discussed.

Abstract 1031: Fumarate hydratase deficiency redirects glucose metabolism of hypoxic cancer cells into the pentose phosphate pathway

Hypoxia is a common feature of all solid cancers and strongly correlated with poor prognosis. As an adaptive response to hypoxia, cancer cells reprogram their metabolism by increasing glycolysis and reductive carboxylation at the expense of mitochondrial respiration, a phenomenon orchestrated by the transcription factor hypoxia inducible factor (HIF) -1. Mutations in the gene encoding for the mitochondrial enzyme fumarate hydratase (FH), found in the hereditary leiomyomatosis and renal cell carcinoma (HLRCC) syndrome, lead to a similar phenotype despite the presence of O2, a phenomenon due to normoxic stabilization of HIF-1 (pseudohypoxia). Here, we report for the first time that FH loss-of-function (LOF) redirects glucose metabolism into the pentose phosphate pathway (PPP) in non-RCC cells subjected to severe hypoxia (O2< .02%). We show that this metabolic shift favors the buildup of biosynthetic precursors supporting hypoxic cell growth and proliferation.

HCT-116 (colon), HeLa (cervix) and H460 (lung) adenocarcinoma cells were transfected with lentiviral vectors encoding for shRNAs targeting FH. Immunoblot analysis showed that FH LOF did not induce pseudohypoxia in these cells. In contrast, HLRCC-derived UOK262 cells showed accumulation of HIF-1 under normoxia which was reversed upon FH re-introduction. A comprehensive analysis utilizing a RT-qPCR array to profile the mRNA expression of 84 HIF-1 target genes, further confirmed that FH LOF did not result in a pseudohypoxic phenotype in HCT-116 cells. An unbiased analysis of 250 metabolites detected by liquid chromatography-tandem mass spectrometry followed by quantitative enrichment analysis, identified glycolysis and the PPP among the most enriched metabolic pathways in hypoxic FH knockdown cells (P< 5×10-8). Since the PPP provides precursors for synthesis of nucleic acids, we analyzed the effect of FH LOF on cell cycle progression and found an inhibition of hypoxia-induced cell cycle arrest in HCT-116 and HeLa cells.

Our study reveals novel insights into the effect of FH loss-of-function in cancer cells and indicates a stark contrast between the pseudohypoxic phenotype described in kidney cancer cell lines obtained from HLRCC patients (i.e, UOK-262) and a HIF- independent mechanism of metabolic rerouting in colon, lung and cervix cancer cell lines. Our data show that FH LOF promotes an anabolic phenotype in hypoxic cancer cells that could be exploited to enhance the therapeutic response targeting this resistant subset of cancer cells.

Citation Format: Luana Schito, Sergio Rey, Judy Pawling, James W. Dennis, Bradly G. Wouters, Marianne Koritzinsky. Fumarate hydratase deficiency redirects glucose metabolism of hypoxic cancer cells into the pentose phosphate pathway. [abstract]. In: Proceedings of the 107th Annual Meeting of the American Association for Cancer Research; 2016 Apr 16-20; New Orleans, LA. Philadelphia (PA): AACR; Cancer Res 2016;76(14 Suppl):Abstract nr 1031.

Abstract 2793: ADP- dependent glucokinase enhances hypoxia- inducible factor-α target gene transactivation through modulation of ROS levels in hypoxic human cancer cells

ADP- dependent glucokinase (ADPGK) is a glycolytic enzyme catalyzing the reaction of glucose→glucose 6-P by using ADP instead of ATP. ADPGK is remarkably conserved across various phyla from archaea to humans. Despite an important role priming glycolysis in conditions of metabolic stress in extremophile organisms, human ADPGK does not contribute to glycolysis. Recent work shows that ADPGK is essential for ROS generation during T-cell activation. Intriguingly, ADPGK protein levels are upregulated across a panel of cancer cell lines and primary tumors. Hereby we hypothesized that the increase of cellular ROS in response to mild (∼1% O2) hypoxia is dependent on ADPGK therefore contributing to the stabilization of hypoxia- inducible factor (HIF)-1α, a central regulator of the transcriptional response of cancer cells to hypoxia.

We achieved ADPGK loss-of-function (LOF) utilizing lentiviral shRNA- mediated knockdown (>75%) in HCT-116 and HT-29 (colon); or H460 (lung) cancer cell lines. Intracellular ROS levels under hypoxia (1% O2) were analyzed by CM-H2DCFDA fluorescence and flow cytometry. Protein levels of HIF-1α (and -2α), and selected HIF-α targets were assessed by immunoblot assays. HIF-1α (and -2α) transcriptional activity was measured through a RT-qPCR array developed in house targeting 84 hypoxia- responsive transcripts in HCT-116 cells exposed to 20, 10, 5, 1, .2 and <.02% O2 for 24 h. Baseline non-hypoxic oxygen consumption and glycolytic activities were measured in real-time with an automated bioanalyzer (Seahorse Biosciences) whereas 3D spheroid growth assays and HCT-116 xenografts were used to assess the effect of ADPGK LOF on tumor mass.

ADPGK LOF decreased ROS and HIF-1α (-and 2α) protein levels in a cell type- and O2- dependent manner in HCT-116, HT-29 and H460 cells. Results from our RT-qPCR array show a blunted transcriptional response to hypoxia with maximal inhibition at .2% O2 (∼15 mmHg). Immunoblots confirmed a striking impairment of CA9 hypoxic induction in addition to a significant decrease of the HIF-α targets IGFBP3, ERO-1α and DDIT4. 3D spheroid assays showed a significant growth rate increase after ADPGK knockdown. Addition of the antioxidant N-Ac-Cysteine during the spheroid formation phase mimicked the effect of ADPGK LOF in control cells whereas it further enhanced cell growth in ADPGK knockdown. However, baseline O2 consumption and glycolysis were not affected. Consistently with results of 3D spheroid assays, we observed enhanced tumor growth of HCT-116 xenografts bearing ADPGK LOF.

Our work uncovers a hitherto unknown function of ADPGK in cancer cells whereby it enhances ROS- dependent HIF-1α (and -2α) hypoxic stabilization and transactivation therefore limiting tumor growth. Further work will be focused on the mitochondrial origin of ADPGK- dependent hypoxic ROS generation as suggested by previous studies in primary T-lymphocytes.

Citation Format: Sergio Rey, Luana Schito, Marianne Koritzinsky, Bradly G. Wouters. ADP- dependent glucokinase enhances hypoxia- inducible factor-α target gene transactivation through modulation of ROS levels in hypoxic human cancer cells. [abstract]. In: Proceedings of the 107th Annual Meeting of the American Association for Cancer Research; 2016 Apr 16-20; New Orleans, LA. Philadelphia (PA): AACR; Cancer Res 2016;76(14 Suppl):Abstract nr 2793.

Modulators of HIF1α and NFkB in Cancer Treatment: Is it a Rational Approach for Controlling Malignant Progression?

HIF1α and NFkB are two transcription factors very frequently activated in tumors and involved in tumor growth, progression, and resistance to chemotherapy. In fact, HIF1α and NFkB together regulate transcription of over a thousand genes that, in turn, control vital cellular processes such as adaptation to the hypoxia, metabolic reprograming, inflammatory reparative response, extracellular matrix digestion, migration and invasion, adhesion, etc. Because of this wide involvement they could control in an integrated manner the origin of the malignant phenotype. Interestingly, hypoxia and inflammation have been sequentially bridged in tumors by the discovery that alarmin receptors genes such as RAGE, P2X7, and some TLRs, are activated by HIF1α; and that, in turn, alarmin receptors strongly activate NFkB and proinflammatory gene expression, evidencing all the hallmarks of the malignant phenotype. Recently, a large number of drugs have been identified that inhibit one or both transcription factors with promising results in terms of controlling tumor progression. In addition, many of these molecules are natural compounds or off-label drugs already used to cure other pathologies. Some of them are undergoing clinical trials and soon they will be used alone or in combination with standard anti-tumoral agents to achieve a better treatment of tumors with reduction of metastasis formation and, more importantly, with a net increase in survival. This review highlights the central role of HIF1α activated in hypoxic regions of the tumor, of NFkB activation and proinflammatory gene expression in transformed cells to understand their progression toward malignancy. Different molecules and strategies to inhibit these transcription factors will be reviewed. Finally, the central role of a new class of deacetylases called Sirtuins in regulating HIF1α and NFkB activity will be outlined.

Hypoxia-inducible factor-dependent breast cancer-mesenchymal stem cell bidirectional signaling promotes metastasis

Metastasis involves critical interactions between cancer and stromal cells. Intratumoral hypoxia promotes metastasis through activation of hypoxia-inducible factors (HIFs). We demonstrate that HIFs mediate paracrine signaling between breast cancer cells (BCCs) and mesenchymal stem cells (MSCs) to promote metastasis. In a mouse orthotopic implantation model, MSCs were recruited to primary breast tumors and promoted BCC metastasis to LNs and lungs in a HIF-dependent manner. Coculture of MSCs with BCCs augmented HIF activity in BCCs. Additionally, coculture induced expression of the chemokine CXCL10 in MSCs and the cognate receptor CXCR3 in BCCs, which was augmented by hypoxia. CXCR3 expression was blocked in cocultures treated with neutralizing antibody against CXCL10. Conversely, CXCL10 expression was blocked in MSCs cocultured with BCCs that did not express CXCR3 or HIFs. MSC coculture did not enhance the metastasis of HIF-deficient BCCs. BCCs and MSCs expressed placental growth factor (PGF) and its cognate receptor VEGFR1, respectively, in a HIF-dependent manner, and CXCL10 expression by MSCs was dependent on PGF expression by BCCs. PGF promoted metastasis of BCCs and also facilitated homing of MSCs to tumors. Thus, HIFs mediate complex and bidirectional paracrine signaling between BCCs and MSCs that stimulates breast cancer metastasis.

Hypoxia-increased RAGE and P2X7R expression regulates tumor cell invasion through phosphorylation of Erk1/2 and Akt and nuclear translocation of NF-{kappa}B

The role of hypoxia in regulating tumor progression is still controversial. Here, we demonstrate that, similarly to what previously observed by us in human prostate and breast tumor samples, hypoxia increases expression of the receptor for advanced glycation end products (RAGE) and the purinergic receptor P2X7 (P2X7R). The role of hypoxia was shown by the fact that hypoxia-inducible factor (HIF)-1α silencing downregulated RAGE and P2X7R protein levels as well as nuclear factor-kappaB (NF-κB) expression. In contrast, NF-κB silencing reduced P2X7R expression without affecting RAGE protein levels or nuclear accumulation of HIF-1α. Treatment of hypoxic tumor cells with HMGB1 and BzATP ligands, respectively, of RAGE and P2X7R, activated a signaling pathway that, through Akt and Erk phosphorylation, determines nuclear accumulation of NF-κB and increases cell invasion. Inhibition of Akt by SH5 and Erk by INH1 prevented both nuclear translocation of NF-κB and cell invasion. Moreover, silencing RAGE and P2X7R abolished nuclear accumulation of NF-κB as well as cell invasion without affecting HIF-1α stabilization. Once in the nucleus, NF-κB would contribute to cell survival and invasion under hypoxia, by maintaining RAGE and P2X7R expression levels and matrix metalloproteinases 2 and 9 synthesis. These results show that, hypoxia can upregulate expression levels of membrane receptors that, by binding extracellular molecules eventually released by necrotic cells, contribute to the increased invasiveness of transformed tumor cells. Moreover, these observations strengthen our working hypothesis that upregulation of damage-associated molecular patterns receptors by HIF-1α represents the crucial event bridging hypoxia and inflammation in obtaining the malignant phenotype.

Role of hypoxia and autophagy in MDA-MB-231 invasiveness

Survival strategies adopted by tumor cells in response to a hypoxic stress include activation of hypoxia-inducible factor 1 (HIF-1) and autophagy. However, the importance and the function of each molecular response is not well defined. In the present study, we investigated invasiveness, migration, matrix metalloproteinases (MMPs) activity, and cell survival of MDA-MB-231 cells under normoxia, hypoxia, and hypoxia/reoxygenation (H/R). Moreover, to assess the importance of hypoxia and autophagy on the parameters studied, cells were either left untreated or treated with Chetomin (a selective inhibitor of HIF-1alpha) or trifluoperazine (TFP, an activator of autophagy). We found that hypoxia and H/R stimulated invasiveness and migration of MDA-MB-231 cells with an increased MMP-2 activity. Chetomin and TFP differently regulated the cellular behavior under the oxygenation conditions studied. In fact, Chetomin was most effective in inhibiting cell invasion, MMPs activity, and cell survival under hypoxia but not normoxia or H/R. By contrast, TFP inhibition of cell invasion, migration, and cell survival was independent from oxygenation conditions. TFP-induced autophagy was inhibited by light chain protein 3 (LC3) silencing or 3-methyladenine (3MA) treatment. In fact, LC3-silenced cells were able to invade in the presence of TFP without any GATE16 processing and p62 degradation. Immunofluorescence assay showed that LC3 silencing inhibited TFP-induced autophagosome formation. However, we also showed that both TPF treatment and LC3 silencing caused cytoskeleton impairments suggesting a possible interaction between LC3 and cytoskeleton components. In conclusion, our study shows that hypoxia and autophagy by acting on common (HIF-1alpha) or separate (MMPs, cytoskeleton) targets differently regulate cell invasion, MMPs activity, and survival.

Up-regulation of pro-inflammatory genes as adaptation to hypoxia in MCF-7 cells and in human mammary invasive carcinoma microenvironment

The role of tumor cells in synthesizing pro-inflammatory molecules is still controversial. Here we report that hypoxic treatment of the MCF-7 human mammary adenocarcinoma cell line induced activation of hypoxia-inducible factor 1alpha (HIF-1alpha) and nuclear factor-kappa B (NF-kappaB). Importantly, hypoxia regulated expression of alarmin receptors such as the receptor for advanced glycation end products (RAGE) and the purinoreceptor (P2X7R), and up-regulated inflammatory response (IR) genes such as the inducible enzymes nitric oxide synthase (NOS2), cycloxygenase (COX2), and the acute-phase protein pentraxin-3 (PTX3). Hypoxia also stimulated chemokine (C-X-C motif) receptor 4 (CXCR4) mRNA synthesis. In fact, the CXCR4 ligand stromal-derived factor-1alpha (SDF-1alpha) increased invasion and migration of hypoxic MCF-7 cells. Inhibition of HIF-1alpha by chetomin and NF-kappaB by parthenolide reduced mRNA and protein expression of the studied molecules and prevented invasion of hypoxic MCF-7 cells. Moreover, solid invasive mammary tumor microenvironment was analyzed after laser-capture microdissection (LCMD) comparing tumor versus host normal tissue. Nuclear translocation of HIF-1alpha and NF-kappaB and up-regulation of IR, CXCR4, estrogen receptor alpha (ERalpha), and epithelial growth factor receptor (EGFR) was observed in tumor but not in host normal tissue in the absence of a local inflammatory leukocyte infiltrate. We conclude that under hypoxic conditions MCF-7 cells acquire a pro-inflammatory phenotype, and that solid human mammary carcinoma evidenced a similar activation of HIF-1alpha, NF-kappaB, and IR genes in malignant tumor cells as compared to the normal host tissues. We suggest a role for IR activation in the malignant progression of transformed cells.

Induction of autophagic cell death by a novel molecule is increased by hypoxia

Adaptation to hypoxia through activation of the hypoxia inducible factor-1 (HIF-1) is crucial for tumor cells survival. Here we describe the antitumoral effects of the new molecule CR 3294 on tumor cells in the presence of hypoxia. Treatment of the breast carcinoma cell line MDA-MB-231 with CR 3294 in 1% O(2) resulted in an in vivo and in vitro inhibition of tumor growth. CR 3294 induced accumulation of autophagosomes in hypoxic MDA-MB-231 cells as assessed by both transmission electron microscopy (TEM) and the autophagic marker LC3-II. TEM analysis revealed the presence of invaginations of the cytoplasm into the nucleus. Autophagosomes were present in such invaginations. Moreover, CR 3294 inhibited both the DNA binding of HIF-1alpha and VEGF mRNA synthesis. Immunoprecipitation and immunofluorescence studies showed an interaction between LC3 and HIF-1alpha. We next detailed the effect of inhibitors and activators of autophagy on both HIF-1alpha and LC3. In particular, 3 methyladenine (3MA) and wortmannin, two macroautophagic inhibitors, prevented both the decrease of HIF-1alpha protein levels and LC3 processing in cells treated with CR 3294. Bafilomycin and leupeptin, inhibitors of lysosomes, prevented HIF-1alpha decrease without affecting LC3 processing. By contrast, treating hypoxic MDA-MB-231 cells with trifluoperazine (TFP) or serum withdrawal (SW), two activators of autophagy, diminished HIF-1alpha levels and stimulated LC3 processing. These results indicate that activation of the autophagic pathway in hypoxic cells by the new molecule CR 3294, as well as by TFP or SW, can have potentially important implications for cancer treatment.