HIF and reactive oxygen species regulate oxidative phosphorylation in cancer

Extracellular vesicles as mediators of stress response in embryo-maternal communication

Introduction: The pivotal role of extracellular vesicles (EVs) in facilitating effective communication between the embryo and maternal cells during the preimplantation stage of pregnancy has been extensively explored. Nonetheless, inquiries persist regarding the alterations in EV cargo from endometrial cells under stress conditions and its potential to elicit specific stress responses in trophoblast cells. Thus, the aim of this study was to elucidate the involvement of EV miRNA miRNAs in transmitting stress signals from maternal cells to trophoblasts. Methods: The receptive endometrial epithelium analogue RL95-2 cells were subjected to stress induction with 200 µM CoCl2 for 24 h before EV isolation. JAr trophoblast spheroids, which serve as embryos, were subjected to treatment with stressed or unstressed EVs derived from RL95-2 cells for 24 h. Transcriptomic alterations in the treated JAr spheroids as well as in the untreated group, as a negative control, were investigated by mRNA sequencing. Furthermore, the changes in EV miRNAs were assessed by sequencing EV samples. Results: A comprehensive analysis comparing the miRNA profiles between stressed and unstressed EVs revealed significant changes in 25 miRNAs. Furthermore, transcriptomic analysis of JAr spheroids treated with stressed RL95-2EVs versus unstressed EVs or the untreated group demonstrated 6 and 27 differentially expressed genes, respectively. Pathway enrichment analysis showed that stressed EVs induce alterations in gene expression in trophoblast cells, which is partially mediated by EV microRNAs. Discussion: Our results suggest that EVs can transfer stress signals from endometrial cells to the embryo. These discoveries shed new light on the mechanism underlying implantation failures under stress conditions. Unraveling the role of EVs in transmitting stress signals, can extend our knowledge to pave the way for targeted interventions to manage stress-related implantation failures.

Czech Footprints in the Bioenergetics Research

Life manifests as growth, movement or heat production that occurs thanks to the energy accepted from the outside environment. The basis of energy transduction attracted the Czech researchers since the beginning of the 20th century. It further accelerated after World War II, when the new Institute of Physiology was established in 1954. When it was found that energy is stored in the form of adenosine triphosphate (ATP) that can be used by numerous reactions as energy source and is produced in the process called oxidative phosphorylation localized in mitochondria, the investigation focused on this cellular organelle. Although the Czech scientists had to overcome various obstacles including Communist party leadership, driven by curiosity, boldness, and enthusiasm, they characterized broad spectrum of mitochondrial properties in different tissues in (patho)physiological conditions in collaboration with many world-known laboratories. The current review summarizes the contribution of the Czech scientists to the bioenergetic and mitochondrial research in the global context. Keywords: Mitochondria, Bioenergetics, Chemiosmotic coupling.

Interactions and Transport of a Bioconjugated Peptide Targeting the Mitomembrane

The Szeto-Schiller (SS) peptides are a subclass of cell-penetrating peptides that can specifically target mitochondria and mediate conditions caused by mitochondrial dysfunction. In this work, we constructed an iron-chelating SS peptide and studied its interaction with a mitochondrial-mimicking membrane using atomistic molecular dynamics (MD) simulations. We report that the peptide/membrane interaction is thermodynamically favorable, and the localization of the peptide to the membrane is driven by electrostatic interactions between the cationic residues and the anionic phospholipid headgroups. The insertion of the peptide into the membrane is driven by hydrophobic interactions between the aromatic side chains in the peptide and the lipid acyl tails. We also probed the translocation of the peptide across the membrane by applying nonequilibrium steered MD simulations and resolved the translocation pathway, free energy profile, and metastable states. We explored four distinct orientations of the peptide along the translocation pathway and found that one orientation was energetically more favorable than the other orientations. We tested a significantly slower pulling velocity on the most thermodynamically favorable system and compared metastable states during peptide translocation. We found that the peptide can optimize hydrophobic interactions with the membrane by having aromatic side chains interacting with the lipid acyl tails instead of forming π-π interactions with each other. The mechanistic insights emerging from our work will potentially facilitate improved peptide design with enhanced activity.

Targeting the Metabolic Paradigms in Cancer and Diabetes

Dysregulated metabolic dynamics are evident in both cancer and diabetes, with metabolic alterations representing a facet of the myriad changes observed in these conditions. This review delves into the commonalities in metabolism between cancer and type 2 diabetes (T2D), focusing specifically on the contrasting roles of oxidative phosphorylation (OXPHOS) and glycolysis as primary energy-generating pathways within cells. Building on earlier research, we explore how a shift towards one pathway over the other serves as a foundational aspect in the development of cancer and T2D. Unlike previous reviews, we posit that this shift may occur in seemingly opposing yet complementary directions, akin to the Yin and Yang concept. These metabolic fluctuations reveal an intricate network of underlying defective signaling pathways, orchestrating the pathogenesis and progression of each disease. The Warburg phenomenon, characterized by the prevalence of aerobic glycolysis over minimal to no OXPHOS, emerges as the predominant metabolic phenotype in cancer. Conversely, in T2D, the prevailing metabolic paradigm has traditionally been perceived in terms of discrete irregularities rather than an OXPHOS-to-glycolysis shift. Throughout T2D pathogenesis, OXPHOS remains consistently heightened due to chronic hyperglycemia or hyperinsulinemia. In advanced insulin resistance and T2D, the metabolic landscape becomes more complex, featuring differential tissue-specific alterations that affect OXPHOS. Recent findings suggest that addressing the metabolic imbalance in both cancer and diabetes could offer an effective treatment strategy. Numerous pharmaceutical and nutritional modalities exhibiting therapeutic effects in both conditions ultimately modulate the OXPHOS-glycolysis axis. Noteworthy nutritional adjuncts, such as alpha-lipoic acid, flavonoids, and glutamine, demonstrate the ability to reprogram metabolism, exerting anti-tumor and anti-diabetic effects. Similarly, pharmacological agents like metformin exhibit therapeutic efficacy in both T2D and cancer. This review discusses the molecular mechanisms underlying these metabolic shifts and explores promising therapeutic strategies aimed at reversing the metabolic imbalance in both disease scenarios.

ISCA2 inhibition decreases HIF and induces ferroptosis in clear cell renal carcinoma

Clear cell renal cell carcinoma (ccRCC), the most common form of kidney cancer, is typically initiated by inactivation of the von Hippel Lindau (VHL) gene, which results in the constitutive activation of the hypoxia inducible factors, HIF-1α and HIF-2α. Using a high throughput screen, we identify novel compounds that decrease HIF-1/2α levels and induce ferroptosis by targeting Iron Sulfur Cluster Assembly 2 (ISCA2), a component of the late mitochondrial Iron Sulfur Cluster (L-ISC) assembly complex. ISCA2 inhibition either pharmacologically or using siRNA decreases HIF-2α protein levels by blocking iron-responsive element (IRE)-dependent translation, and at higher concentrations, also decreases HIF-1α translation through unknown mechanisms. Additionally, ISCA2 inhibition triggers the iron starvation response, resulting in iron/metals overload and death via ferroptosis. ISCA2 levels are decreased in ccRCC compared to normal kidney, and decreased ISCA2 levels are associated with pVHL loss and with sensitivity to ferroptosis induced by ISCA2 inhibition. Strikingly, pharmacological inhibition of ISCA2 using an orally available ISCA2 inhibitor significantly reduced ccRCC xenograft growth in vivo, decreased HIF-α levels and increased lipid peroxidation, suggesting increased ferroptosis in vivo. Thus, the targeting of ISCA2 may be a promising therapeutic strategy to inhibit HIF-1/2α and to induce ferroptosis in pVHL deficient cells.

Histone deacetylase inhibitors inhibit cervical cancer growth through Parkin acetylation-mediated mitophagy

Parkin, an E3 ubiquitin ligase, plays a role in maintaining mitochondrial homeostasis through targeting damaged mitochondria for mitophagy. Accumulating evidence suggests that the acetylation modification of the key mitophagy machinery influences mitophagy level, but the underlying mechanism is poorly understood. Here, our study demonstrated that inhibition of histone deacetylase (HDAC) by treatment of HDACis activates mitophagy through mediating Parkin acetylation, leading to inhibition of cervical cancer cell proliferation. Bioinformatics analysis shows that Parkin expression is inversely correlated with HDAC2 expression in human cervical cancer, indicating the low acetylation level of Parkin. Using mass spectrometry, Parkin is identified to interact with two upstream molecules, acetylase acetyl-CoA acetyltransferase 1 (ACAT1) and deacetylase HDAC2. Under treatment of suberoylanilide hydroxamic acid (SAHA), Parkin is acetylated at lysine residues 129, 220 and 349, located in different domains of Parkin protein. In in vitro experiments, combined mutation of Parkin largely attenuate the interaction of Parkin with PTEN induced putative kinase 1 (PINK1) and the function of Parkin in mitophagy induction and tumor suppression. In tumor xenografts, the expression of mutant Parkin impairs the tumor suppressive effect of Parkin and decreases the anticancer activity of SAHA. Our results reveal an acetylation-dependent regulatory mechanism governing Parkin in mitophagy and cervical carcinogenesis, which offers a new mitophagy modulation strategy for cancer therapy.

Playing the Devil's Advocate: Should We Give a Second Chance to mTOR Inhibition in Renal Clear Cell Carcinoma? - ie Strategies to Revert Resistance to mTOR Inhibitors

In the last decade, the inhibition of the mechanistic target of Rapamycin (mTOR) in renal clear cell carcinoma (RCC) has disappointed the clinician's expectations. Many clinical trials highlighted the low efficacy and unmanageable safety profile of first-generation mTOR inhibitors (Rapalogs), thus limiting their use in the clinical practice only to those patients who already failed several therapy lines. In this review, we analyze the major resistance mechanisms that undermine the efficacy of this class of drugs. Moreover, we describe some of the possible strategies to overcome the mechanisms of resistance and their clinical experimentation, with particular focus on novel mTOR inhibitors and the combinations of mTOR inhibitors and other anti-cancer drugs.

Mechanism of hydrogen on cervical cancer suppression revealed by high‑throughput RNA sequencing

Cervical cancer is considered one of the diseases with the highest mortality among women and with limited treatment options. Hydrogen (H₂) inhalation has been reported to have a variety of tumor-suppressive effects, but the exact mechanism remains unclear. In the present study, HeLa cervical cancer cells and HaCaT keratinocytes treated with H₂, and a HeLa xenograft mouse model subjected to H₂ inhalation were established. TUNEL, Cell Counting Kit-8 and Ki67 staining assays were used to detect cell apoptosis and proliferation. Oxidative stress was determined according to the levels of reactive oxygen species, malondialdehyde and superoxide dismutase. Tumor growth was recorded every 3 days, and the excised tumors were stained with hematoxylin and eosin. High-throughput RNA sequencing and subsequent Gene Ontology (GO) enrichment analysis were performed in HeLa-treated and un-treated HeLa cells. The expression of hypoxia-inducible factor (HIF)-1α and NF-κB p65 was verified by western blotting, immunohistochemistry and reverse transcription-quantitative PCR. The results revealed an increased apoptosis rate, and reduced cell proliferation and oxidative stress in H₂-treated HeLa cells but not in HaCaT cells. Similarly, decreased tumor growth and cell proliferation, and enhanced cell apoptosis were observed in H₂-treated HeLa tumors. RNA sequencing and GO analysis suggest that downregulated HIF1A (HIF-1α mRNA) and RelA (NF-κB p65) levels, and reduced NF-κB signaling were associated with the antitumor effect of H₂. Finally, decreased HIF-1α and NF-κB p65 expression both at the transcriptional and translational levels were observed in H₂-treated HeLa cells and in HeLa-derived tumors. In conclusion, the present study reveals a novel mechanism of H₂ against cervical cancer, which may serve as a potential therapeutic target in clinical practice.

Neuregulin-1 inhibits CoCl2-induced upregulation of excitatory amino acid carrier 1 expression and oxidative stress in SH-SY5Y cells and the hippocampus of mice

Excitatory amino acid carrier 1 (EAAC1) is an important subtype of excitatory amino acid transporters (EAATs) and is the route for neuronal cysteine uptake. CoCl₂ is not only a hypoxia-mimetic reagent but also an oxidative stress inducer. Here, we found that CoCl₂ induced significant EAAC1 overexpression in SH-SY5Y cells and the hippocampus of mice. Transient transfection of EAAC1 reduced CoCl₂-induced cytotoxicity in SH-SY5Y cells. Based on this result, upregulation of EAAC1 expression by CoCl₂ is thought to represent a compensatory response against oxidative stress in an acute hypoxic state. We further demonstrated that pretreatment with Neuregulin-1 (NRG1) rescued CoCl₂-induced upregulation of EAAC1 and tau expression. NRG1 plays a protective role in the CoCl₂-induced accumulation of reactive oxygen species (ROS) and reduction in antioxidative enzyme (SOD and GPx) activity. Moreover, NRG1 attenuated CoCl₂-induced apoptosis and cell death. NRG1 inhibited the CoCl₂-induced release of cleaved caspase-3 and reduction in Bcl-X_L levels. Our novel finding suggests that NRG1 may play a protective role in hypoxia through the inhibition of oxidative stress and thereby maintain normal EAAC1 expression levels.

Insights into the New Cancer Therapy through Redox Homeostasis and Metabolic Shifts

Modest levels of reactive oxygen species (ROS) are necessary for intracellular signaling, cell division, and enzyme activation. These ROS are later eliminated by the body’s antioxidant defense system. High amounts of ROS cause carcinogenesis by altering the signaling pathways associated with metabolism, proliferation, metastasis, and cell survival. Cancer cells exhibit enhanced ATP production and high ROS levels, which allow them to maintain elevated proliferation through metabolic reprograming. In order to prevent further ROS generation, cancer cells rely on more glycolysis to produce ATP and on the pentose phosphate pathway to provide NADPH. Pro-oxidant therapy can induce more ROS generation beyond the physiologic thresholds in cancer cells. Alternatively, antioxidant therapy can protect normal cells by activating cell survival signaling cascades, such as the nuclear factor erythroid 2-related factor 2 (Nrf2)-Kelch-like ECH-associated protein 1 (Keap1) pathway, in response to radio- and chemotherapeutic drugs. Nrf2 is a key regulator that protects cells from oxidative stress. Under normal conditions, Nrf2 is tightly bound to Keap1 and is ubiquitinated and degraded by the proteasome. However, under oxidative stress, or when treated with Nrf2 activators, Nrf2 is liberated from the Nrf2-Keap1 complex, translocated into the nucleus, and bound to the antioxidant response element in association with other factors. This cascade results in the expression of detoxifying enzymes, including NADH-quinone oxidoreductase 1 (NQO1) and heme oxygenase 1. NQO1 and cytochrome b5 reductase can neutralize ROS in the plasma membrane and induce a high NAD⁺/NADH ratio, which then activates SIRT1 and mitochondrial bioenergetics. NQO1 can also stabilize the tumor suppressor p53. Given their roles in cancer pathogenesis, redox homeostasis and the metabolic shift from glycolysis to oxidative phosphorylation (through activation of Nrf2 and NQO1) seem to be good targets for cancer therapy. Therefore, Nrf2 modulation and NQO1 stimulation could be important therapeutic targets for cancer prevention and treatment.

Nitroprusside induces melanoma ferroptosis with serum supplementation and prolongs survival under serum depletion or hypoxia

BACKGROUND

When proliferating tumor cells expand to areas distant from vascular sites, poor diffusion of oxygen and nutrients occur, generating a restrictive hypoxic gradient in which susceptible tumor cells die. The heterogeneous population surviving hypoxia and metabolic starvation include de-differentiated cancer stem cells (CSC), capable of self-renewing tumor-initiating cells (TICs), or those that divide asymmetrically to produce non-tumor-initiating differentiated (NTI-D) cell progeny. Under such restrictive conditions, both populations slowly proliferate, entering quiescence or senescence, when exiting from cell cycle progression. This may drive chemoresistance and tumor recurrence, since most anti-cancer treatments target rapidly proliferating cells.

PURPOSE

Since persistent or additional stress may increase NTI-D cells conversion to TICs, we investigated whether nutrient depletion or hypoxia influence expression of tyrosinase, a crucial enzyme for melanin synthesis, and B16 melanoma survival, when exposed to iron-dependent cell death oxidative stress produced by the Fenton reaction, resembling ferroptosis.

RESULTS

-a) proliferating B16 melanoma with 10% serum-supplementation (10%S) normoxically express hypoxia inducible factor 1α (HIF1α) but lose tyrosinase, in contrast to those transiently exposed to (SF) serum-free medium, in which both HIF1α and tyrosinase are co-expressed; b) in contrast to the resistance to SNP toxicity in (SF) cells with higher tyrosinase expression, those in (10%S) are killed by iron from nitroprusside/ferricyanide (SNP) irrespective of exogenous H₂O₂, in a reaction antagonized by the anti-oxidant and MEK inhibitor UO126; c) Moreover, under transient serum depletion, SNP cooperates with hypoxia (1.5% oxygen), prolonging B16 melanoma (SF) survival; d) the hypoxia mimetic CoCl₂ inhibits proliferation-associated cyclin A, irrespective of SNP, in (10%S) cells or in transiently serum-depleted (SF) cells. However, only in the latter cells, CoCl₂ but not SNP, induce loss of HIF1α and apoptosis-associated PARP cleavage; e) longer term adaptation to survive serum depletion, generates (SS) cells resistant to SNP toxicity, which aerobically co-express HIF1α and tyrosinase. In SS B16 melanoma, exogenous non-toxic 100 μM H₂O₂ super-induces the ratio of tyrosinase to HIF1α. However, co-treatment of SS-B16 cells with SNP plus exogenous H₂O_2, partly increases PARP cleavage by reciprocally decreasing tyrosinase expression.

SIGNIFICANCE

- These results suggest that a phenotypic plasticity in response to depletion of nutrients and/or oxygen, helps decide whether melanoma cells undergo either death by ferroptosis, or resistance to it, when challenged by the same exogenous oxidative stress (iron ± H₂O₂).

Integrated Proteogenomic Characterization of Clear Cell Renal Cell Carcinoma

To elucidate the deregulated functional modules that drive clear cell renal cell carcinoma (ccRCC), we performed comprehensive genomic, epigenomic, transcriptomic, proteomic, and phosphoproteomic characterization of treatment-naive ccRCC and paired normal adjacent tissue samples. Genomic analyses identified a distinct molecular subgroup associated with genomic instability. Integration of proteogenomic measurements uniquely identified protein dysregulation of cellular mechanisms impacted by genomic alterations, including oxidative phosphorylation-related metabolism, protein translation processes, and phospho-signaling modules. To assess the degree of immune infiltration in individual tumors, we identified microenvironment cell signatures that delineated four immune-based ccRCC subtypes characterized by distinct cellular pathways. This study reports a large-scale proteogenomic analysis of ccRCC to discern the functional impact of genomic alterations and provides evidence for rational treatment selection stemming from ccRCC pathobiology.

Targeted Co-delivery of the Iron Chelator Deferoxamine and a HIF1α Inhibitor Impairs Pancreatic Tumor Growth

Rapidly growing cancer cells exhibit a strong dependence on iron for their survival. Thus, iron-removing drugs, iron chelators, have potential applications in cancer treatment. Deferoxamine (DFO) is an efficient iron chelator, but its short circulation half-life and ability to induce hypoxia-inducible factor 1α (HIF1α) overexpression restricts its use as an antitumor agent. In the present study, we first found that a pattern of iron-related protein expression favoring higher intracellular iron closely correlates with shorter overall and relapse-free survival in pancreatic cancer patients. We subsequently found that a combination of DFO and the HIF1α inhibitor, lificiguat (also named YC1), significantly enhanced the antitumor efficacy of DFO in vitro. We then employed transferrin receptor 1 (TFR1) targeting liposomes to codeliver DFO and YC1 to pancreatic tumors in a mouse model. The encapsulation of DFO prolonged its circulation time, improved its accumulation in tumor tissues via the enhanced permeability and retention (EPR) effect, and facilitated efficient uptake by cancer cells, which express high level of TFR1. After entering the tumor cells, the encapsulated DFO and YC1 were released to elicit a synergistic antitumor effect in subcutaneous and orthotopic pancreatic cancer xenografts. In summary, our work overcame two major obstacles in DFO-based cancer treatment through a simple liposome-based drug delivery system. This nanoencapsulation and targeting paradigm lays the foundation for future application of iron chelation in cancer therapy.

Zinc finger E-box-binding homeobox 1 mediates aerobic glycolysis via suppression of sirtuin 3 in pancreatic cancer

AIM

To uncover the roles of tumor-promoting gene ZEB1 in aerobic glycolysis regulation and shed light on the underlying molecular mechanism.

METHODS

Endogenous zinc finger E-box binding homeobox-1 (ZEB1) was silenced using a lentivirus-mediated method, and the impact of ZEB1 and methyl-CpG binding domain protein 1 (MBD1) on aerobic glycolysis was measured using seahorse cellular flux analyzers, reactive oxygen species quantification, and mitochondrial membrane potential measurement. The interaction between ZEB1 and MBD1 was assessed by co-immunoprecipitation and immunofluorescence assays. The impact of ZEB1 and MBD1 interaction on sirtuin 3 (SIRT3) expression was confirmed by quantitative polymerase chain reaction, western blotting, and dual-luciferase and chromatin-immunoprecipitation assays.

RESULTS

ZEB1 was a positive regulator of aerobic glycolysis in pancreatic cancer. ZEB1 transcriptionally silenced expression of SIRT3, a mitochondrial-localized tumor suppressor, through interaction with MBD1.

CONCLUSION

ZEB1 silenced SIRT3 expression via interaction with MBD1 to promote aerobic glycolysis in pancreatic cancer.

VHL-Mediated Regulation of CHCHD4 and Mitochondrial Function

Dysregulated mitochondrial function is associated with the pathology of a wide range of diseases including renal disease and cancer. Thus, investigating regulators of mitochondrial function is of particular interest. Previous work has shown that the von Hippel-Lindau tumor suppressor protein (pVHL) regulates mitochondrial biogenesis and respiratory chain function. pVHL is best known as an E3-ubiquitin ligase for the α-subunit of the hypoxia inducible factor (HIF) family of dimeric transcription factors. In normoxia, pVHL recognizes and binds hydroxylated HIF-α (HIF-1α and HIF-2α), targeting it for ubiquitination and proteasomal degradation. In this way, HIF transcriptional activity is tightly controlled at the level of HIF-α protein stability. At least 80% of clear cell renal carcinomas exhibit inactivation of the VHL gene, which leads to HIF-α protein stabilization and constitutive HIF activation. Constitutive HIF activation in renal carcinoma drives tumor progression and metastasis. Reconstitution of wild-type VHL protein (pVHL) in pVHL-defective renal carcinoma cells not only suppresses HIF activation and tumor growth, but also enhances mitochondrial respiratory chain function via mechanisms that are not fully elucidated. Here, we show that pVHL regulates mitochondrial function when re-expressed in pVHL-defective 786O and RCC10 renal carcinoma cells distinct from its regulation of HIF-α. Expression of CHCHD4, a key component of the disulphide relay system (DRS) involved in mitochondrial protein import within the intermembrane space (IMS) was elevated by pVHL re-expression alongside enhanced expression of respiratory chain subunits of complex I (NDUFB10) and complex IV (mtCO-2 and COX IV). These changes correlated with increased oxygen consumption rate (OCR) and dynamic changes in glucose and glutamine metabolism. Knockdown of HIF-2α also led to increased OCR, and elevated expression of CHCHD4, NDUFB10, and COXIV in 786O cells. Expression of pVHL mutant proteins (R200W, N78S, D126N, and S183L) that constitutively stabilize HIF-α but differentially promote glycolytic metabolism, were also found to differentially promote the pVHL-mediated mitochondrial phenotype. Parallel changes in mitochondrial morphology and the mitochondrial network were observed. Our study reveals a new role for pVHL in regulating CHCHD4 and mitochondrial function in renal carcinoma cells.

Identification of key genes and pathways in human clear cell renal cell carcinoma (ccRCC) by co-expression analysis

Human clear cell renal cell carcinoma (ccRCC) is the most common solid lesion within kidney, and its prognostic is influenced by the progression covering a complex network of gene interactions. In our study, we screened differential expressed genes, and constructed protein-protein interaction (PPI) network and a weighted gene co-expression network to identify key genes and pathways associated with the progression of ccRCC (n = 56). Functional and pathway enrichment analysis demonstrated that upregulated differentially expressed genes (DEGs) were significantly enriched in response to wounding, positive regulation of immune system process, leukocyte activation, immune response and cell activation. Downregulated DEGs were significantly enriched in oxidation reduction, monovalent inorganic cation transport, ion transport, excretion and anion transport. In the PPI network, top 10 hub genes were identified (TOP2A, MYC, ALB, CDK1, VEGFA, MMP9, PTPRC, CASR, EGFR and PTGS2). In co-expression network, 6 ccRCC-related modules were identified. They were associated with immune response, metabolic process, cell cycle regulation, angiogenesis and ion transport. In conclusion, our study illustrated the hub genes and pathways involved in the progress of ccRCC, and further molecular biological experiments are needed to confirm the function of the candidate biomarkers in human ccRCC.

pH-Responsive Aerobic Nanoparticles for Effective Photodynamic Therapy

Rationale: Photodynamic therapy (PDT), an O₂-dependent treatment for inhibition of cancer proliferation, suffers from the low therapeutic effect in clinical application due to the hypoxic microenvironment in tumor cells.

Methods: To overcome this obstacle, a stimuli-responsive drug delivery system with O₂ self-sufficiency for effective PDT was developed. In this study, pH-responsive aerobic nanoparticles were prepared by the electrostatic interaction between the O₂-evolving protein Catalase and Chitosan. Subsequently, the photosensitizer Chlorin e6 (Ce6) was encapsulated in the nanoparticles.

Results: The nanoparticles exhibited high stability in aqueous medium and efficient cellular uptake by tumor cells facilitating their accumulation in tumors by enhanced permeability and retention (EPR) effect. In acidic environment, irradiation caused disassembly of the nanoparticles resulting in the quick release of Catalase and the photosensitizer with continuous formation of cytotoxic singlet oxygen (¹O₂) greatly enhancing the PDT efficacy in hypoxic tumor tissues both in vitro and in vivo biological studies.

Conclusion: Due to the unique O₂ self-sufficiency, the nanoparticles, upon irradiation, exhibited higher anticancer activity than free Ce6 both in vitro and in vivo. Our work has identified a new pH-triggered strategy to overcome hypoxia for effective PDT against cancer cells.

Hypoxia-Inducible Factor 2α Mutation-Related Paragangliomas Classify as Discrete Pseudohypoxic Subcluster

Recently, activating mutations of the hypoxia-inducible factor 2α gene (HIF2A/EPAS1) have been recognized to predispose to multiple paragangliomas (PGLs) and duodenal somatostatinomas associated with polycythemia, and ocular abnormalities. Previously, mutations in the SDHA/B/C/D, SDHAF2, VHL, FH, PHD1, and PHD2 genes have been associated with HIF activation and the development of pseudohypoxic (cluster-1) PGLs. These tumors overlap in terms of tumor location, syndromic presentation, and noradrenergic phenotype to a certain extent. However, they also differ especially by clinical outcome and by presence of other tumors or abnormalities. In the present study, we aimed to establish additional molecular differences between HIF2A and non-HIF2A pseudohypoxic PGLs. RNA expression patterns of HIF2A PGLs (n = 6) from 2 patients were compared with normal adrenal medullas (n = 8) and other hereditary pseudohypoxic PGLs (VHL: n = 13, SDHB: n = 15, and SDHD: n = 14). Unsupervised hierarchical clustering showed that HIF2A PGLs made up a separate cluster from other pseudohypoxic PGLs. Significance analysis of microarray yielded 875 differentially expressed genes between HIF2A and other pseudohypoxic PGLs after normalization to adrenal medulla (false discovery rate 0.01). Prediction analysis of microarray allowed correct classification of all HIF2A samples based on as little as three genes (TRHDE, LRRC63, IGSF10; error rate: 0.02). Genes with the highest expression difference between normal medulla and HIF2A PGLs were selected for confirmatory quantitative reverse transcriptase polymerase chain reaction. In conclusion, HIF2A PGLs show a characteristic expression signature that separates them from non-HIF2A pseudohypoxic PGLs. Unexpectedly, the most significantly differentially expressed genes have not been previously described as HIF target genes.

Screening disrupted molecular functions and pathways associated with clear cell renal cell carcinoma using Gibbs sampling

OBJECTIVE

To explore the disturbed molecular functions and pathways in clear cell renal cell carcinoma (ccRCC) using Gibbs sampling.

METHODS

Gene expression data of ccRCC samples and adjacent non-tumor renal tissues were recruited from public available database. Then, molecular functions of expression changed genes in ccRCC were classed to Gene Ontology (GO) project, and these molecular functions were converted into Markov chains. Markov chain Monte Carlo (MCMC) algorithm was implemented to perform posterior inference and identify probability distributions of molecular functions in Gibbs sampling. Differentially expressed molecular functions were selected under posterior value more than 0.95, and genes with the appeared times in differentially expressed molecular functions ≥5 were defined as pivotal genes. Functional analysis was employed to explore the pathways of pivotal genes and their strongly co-regulated genes.

RESULTS

In this work, we obtained 396 molecular functions, and 13 of them were differentially expressed. Oxidoreductase activity showed the highest posterior value. Gene composition analysis identified 79 pivotal genes, and survival analysis indicated that these pivotal genes could be used as a strong independent predictor of poor prognosis in patients with ccRCC. Pathway analysis identified one pivotal pathway - oxidative phosphorylation.

CONCLUSIONS

We identified the differentially expressed molecular functions and pivotal pathway in ccRCC using Gibbs sampling. The results could be considered as potential signatures for early detection and therapy of ccRCC.

VHL Inactivation in Precancerous Kidney Cells Induces an Inflammatory Response via ER Stress-Activated IRE1 Signaling

Mutations and epigenetic inactivation of the tumor suppressor gene von Hippel-Lindau (VHL) are major causes of clear-cell renal cell carcinoma (ccRCC) that may originate from chronic inflammation. However, the role of VHL loss of function in the development of ccRCC via inflammation remains poorly understood. VHL-mutant cells exhibit metabolic abnormalities that can cause chronic endoplasmic reticulum (ER) stress and unfolded protein response. We hypothesize that unresolved ER stress induces the inflammatory responses observed in ccRCC. ER stress markers including BiP and XBP1s were significantly increased in cultured and primary VHL loss-of-function kidney cells. In epithelial cells, the kinase activity of IRE1α was required for the induction of NF-κB and JNK and for the recruitment of macrophages. IRE1α kinase activity was also important for the development of fibrotic phenotype in conditional Vhlh knockout mice. Our results offer insights into the therapeutic potential against ccRCC development by relieving metabolic stress. Such cancer prevention strategy may be critical for high-risk cohorts such as the familial VHL disease patients. Cancer Res; 77(13); 3406-16. ©2017 AACR.

Mechanisms and applications of the anti-inflammatory effects of photobiomodulation

Photobiomodulation (PBM) also known as low-level level laser therapy is the use of red and near-infrared light to stimulate healing, relieve pain, and reduce inflammation. The primary chromophores have been identified as cytochrome c oxidase in mitochondria, and calcium ion channels (possibly mediated by light absorption by opsins). Secondary effects of photon absorption include increases in ATP, a brief burst of reactive oxygen species, an increase in nitric oxide, and modulation of calcium levels. Tertiary effects include activation of a wide range of transcription factors leading to improved cell survival, increased proliferation and migration, and new protein synthesis. There is a pronounced biphasic dose response whereby low levels of light have stimulating effects, while high levels of light have inhibitory effects. It has been found that PBM can produce ROS in normal cells, but when used in oxidatively stressed cells or in animal models of disease, ROS levels are lowered. PBM is able to up-regulate anti-oxidant defenses and reduce oxidative stress. It was shown that PBM can activate NF-kB in normal quiescent cells, however in activated inflammatory cells, inflammatory markers were decreased. One of the most reproducible effects of PBM is an overall reduction in inflammation, which is particularly important for disorders of the joints, traumatic injuries, lung disorders, and in the brain. PBM has been shown to reduce markers of M1 phenotype in activated macrophages. Many reports have shown reductions in reactive nitrogen species and prostaglandins in various animal models. PBM can reduce inflammation in the brain, abdominal fat, wounds, lungs, spinal cord.

Imperatorin suppresses proliferation and angiogenesis of human colon cancer cell by targeting HIF-1α via the mTOR/p70S6K/4E-BP1 and MAPK pathways

ETHNOPHARMACOLOGICAL RELEVANCE

Angelica dahurica is a commonly used traditional Chinese medicine to treat migraine headache, toothache and cancer. Imperatorin is an active natural furocoumarin component originating from Angelica dahurica and has been shown to exhibit multiple bioeffector functions, including anti-cancer activity. However, the mechanism by which imperatorin inhibits tumor growth is not fully understood.

AIM OF THE STUDY

The aim of this study was to investigate the effectiveness of imperatorin as a treatment of cancer and to identify the underlying mechanisms of its anticancer activity.

MATERIALS AND METHODS

HCT116, HeLa, and Hep3B cells were used in this study. Major assays were promoter-reporter gene assay, MTT, western blot analysis, immunofluorescence assay, reverse transcription-PCR (RT-PCR), flow cytometric analysis, clonogenic assay, EdU labeling and immunofluorescence, xenografted assay, and VEGF ELISA.

RESULTS

We here demonstrated the effect of imperatorin on hypoxia-inducible factor-1 (HIF-1) activation. Imperatorin showed a potent inhibitory activity against HIF-1 activation induced by hypoxia in various human cancer cell lines. This compound markedly decreased the hypoxia-induced accumulation of HIF-1α protein dose-dependently, whereas it did not affect the expressions of HIF-1β and topoisomerase-I (Topo-I). Further analysis revealed that imperatorin inhibited HIF-1α protein synthesis, without affecting the expression level of HIF-1α mRNA or degradation of HIF-1α protein. Moreover, the phosphorylation levels of mammalian target of rapamycin (mTOR), ribosomal protein S6 kinase (p70S6K), eIF4E binding protein-1 (4E-BP1), eukaryotic initiation factor 4E (eIF4E), extracellular signal-regulated kinase-1/2 (ERK1/2), SAPK/JNK and p38 were significantly suppressed by imperatorin. Furthermore, imperatorin prevented hypoxia-induced expression of HIF-1 target genes and flow cytometric analysis indicated that imperatorin induced G1 phase arrest in human colon cancer cell (HCT116). We found that imperatorin administration inhibits tumor growth and blocks tumor angiogenesis in a xenograft tumor model.

CONCLUSIONS

These results show that imperatorin inhibited HIF-1α protein synthesis by downregulating the mTOR/p70S6K/4E-BP1 and MAPK pathways. These conclusions suggest that imperatorin is an effective inhibitor of HIF-1 and provide new perspectives into the mechanism of its anticancer activity.

Tumor-initiating cells of breast and prostate origin show alterations in the expression of genes related to iron metabolism

The importance of iron in the growth and progression of tumors has been widely documented. In this report, we show that tumor-initiating cells (TICs), represented by spheres derived from the MCF7 cell line, exhibit higher intracellular labile iron pool, mitochondrial iron accumulation and are more susceptible to iron chelation. TICs also show activation of the IRP/IRE system, leading to higher iron uptake and decrease in iron storage, suggesting that level of properly assembled cytosolic iron-sulfur clusters (FeS) is reduced. This finding is confirmed by lower enzymatic activity of aconitase and FeS cluster biogenesis enzymes, as well as lower levels of reduced glutathione, implying reduced FeS clusters synthesis/utilization in TICs. Importantly, we have identified specific gene signature related to iron metabolism consisting of genes regulating iron uptake, mitochondrial FeS cluster biogenesis and hypoxic response (ABCB10, ACO1, CYBRD1, EPAS1, GLRX5, HEPH, HFE, IREB2, QSOX1 and TFRC). Principal component analysis based on this signature is able to distinguish TICs from cancer cells in vitro and also Leukemia-initiating cells (LICs) from non-LICs in the mouse model of acute promyelocytic leukemia (APL). Majority of the described changes were also recapitulated in an alternative model represented by MCF7 cells resistant to tamoxifen (TAMR) that exhibit features of TICs. Our findings point to the critical importance of redox balance and iron metabolism-related genes and proteins in the context of cancer and TICs that could be potentially used for cancer diagnostics or therapy.

Deferoxamine Suppresses Collagen Cleavage and Protease, Cytokine, and COL10A1 Expression and Upregulates AMPK and Krebs Cycle Genes in Human Osteoarthritic Cartilage

This study reports the effects of the iron chelator deferoxamine (DFO) on collagen cleavage, inflammation, and chondrocyte hypertrophy in relation to energy metabolism-related gene expression in osteoarthritic (OA) articular cartilage. Full-depth explants of human OA knee articular cartilage from arthroplasty were cultured with exogenous DFO (1–50 μM). Type II collagen cleavage and phospho-adenosine monophosphate-activated protein kinase (pAMPK) concentrations were measured using ELISAs. Gene expression studies employed real-time PCR and included AMPK analyses in PBMCs. In OA explants collagen cleavage was frequently downregulated by 10–50 μM DFO. PCR analysis of 7 OA patient cartilages revealed that 10 μM DFO suppressed expression of MMP-1, MMP-13, IL-1β, and TNFα and a marker of chondrocyte hypertrophy, COL10A1. No changes were observed in the expression of glycolysis-related genes. In contrast, expressions of genes associated with the mitochondrial Krebs cycle (TCA), AMPK, HIF1α, and COL2A1 were upregulated. AMPK gene expression was reduced in OA cartilage and increased in PBMCs from the same patients compared to healthy controls. Our studies demonstrate that DFO is capable of suppressing excessive collagenase-mediated type II collagen cleavage in OA cartilage and reversing phenotypic changes. The concomitant upregulation of proanabolic TCA-related gene expressions points to a potential for availability of energy generating substrates required for matrix repair by end-stage OA chondrocytes. This might normally be prevented by high whole-body energy requirements indicated by elevated AMPK expression in PBMCs of OA patients.

Formation of Neutrophil Extracellular Traps under Low Oxygen Level

Since their discovery, neutrophil extracellular traps (NETs) have been characterized as a fundamental host innate immune defense mechanism. Conversely, excessive NET-release may have a variety of detrimental consequences for the host. A fine balance between NET formation and elimination is necessary to sustain a protective effect during an infectious challenge. Our own recently published data revealed that stabilization of hypoxia-inducible factor 1α (HIF-1α) by the iron chelating HIF-1α-agonist desferoxamine or AKB-4924 enhanced the release of phagocyte extracellular traps. Since HIF-1α is a global regulator of the cellular response to low oxygen, we hypothesized that NET formation may be similarly increased under low oxygen conditions. Hypoxia occurs in tissues during infection or inflammation, mostly due to overconsumption of oxygen by pathogens and recruited immune cells. Therefore, experiments were performed to characterize the formation of NETs under hypoxic oxygen conditions compared to normoxia. Human blood-derived neutrophils were isolated and incubated under normoxic (21%) oxygen level and compared to hypoxic (1%) conditions. Dissolved oxygen levels were monitored in the primary cell culture using a Fibox4-PSt3 measurement system. The formation of NETs was quantified by fluorescence microscopy in response to the known NET-inducer phorbol 12-myristate 13-acetate (PMA) or Staphylococcus (S.) aureus wild-type and a nuclease-deficient mutant. In contrast to our hypothesis, spontaneous NET formation of neutrophils incubated under hypoxia was distinctly reduced compared to control neutrophils incubated under normoxia. Furthermore, neutrophils incubated under hypoxia showed significantly reduced formation of NETs in response to PMA. Gene expression analysis revealed that mRNA level of hif-1α as well as hif-1α target genes was not altered. However, in good correlation to the decreased NET formation under hypoxia, the cholesterol content of the neutrophils was significantly increased under hypoxia. Interestingly, NET formation in response to viable S. aureus wild-type or nuclease-deficient strain was retained under hypoxia. Our results lead to the conclusion that hypoxia is not the ideal tool to analyze HIF-1α in neutrophils. However, the data clearly suggest that neutrophils react differently under hypoxia compared to normoxia and thereby highlight the importance of the usage of physiological relevant oxygen level when studying neutrophil functions.

Perillyl alcohol efficiently scavenges activity of cellular ROS and inhibits the translational expression of hypoxia-inducible factor-1α via mTOR/4E-BP1 signaling pathways

Perillyl alcohol (POH) is a dietary monoterpene present in a variety of plants with a pure or mixed form, and it is one of the very few natural substances with anticancer activity. However, the mechanism by which POH unleashes its anticancer activity in tumor cells remains unclear. We here demonstrated the effect of POH on hypoxia-inducible factor-1α (HIF-1α) activation. POH showed the potent inhibitory activity against HIF-1 activation induced by hypoxia in various human cancer cell lines and efficient scavenging activity of cellular Reactive oxygen species (ROS) by hypoxia in tumor cells. Further analysis revealed that POH inhibited HIF-1α protein synthesis, without affecting the expression level of HIF-1α mRNA or degradation of HIF-1α protein. Moreover, we found that suppression of HIF-1α accumulation by POH correlated with strong de-phosphorylation of mammalian target of rapamycin (mTOR) and eIF4E binding protein-1 (4E-BP1), and eukaryotic initiation factor 4E (eIF4E). These results showed that POH inhibited HIF-1α protein synthesis through the inhibition of mTOR/4E-BP1 signaling pathways. Furthermore, POH increased the expression of p53, p21, induced cell cycle arrest in the G1 phase as well as decreased cyclin D1, c-Myc, and Skp2 expression. In vivo studies further confirmed the inhibitory effect of POH on the expression of HIF-1α proteins, leading to a decrease growth of HCT116 cells in a xenograft tumor model. There results show that POH is an effective inhibitor of HIF-1 and provide new perspectives in to the mechanism of its anticancer activity.

The NET, the trap and the pathogen: neutrophil extracellular traps in cutaneous immunity

Neutrophil extracellular traps (NETs), large chromatin structures casted with various proteins, are externalized by neutrophils upon induction by both self- and non-self-stimuli. It has become clear that NETs are potent triggers of inflammation in autoimmune skin diseases. Moreover, the ability of NETs to trap pathogens suggests a crucial role in innate host defense. However, the outcome of the encounter between pathogens and NETs remains highly controversial. Here, we discuss recent insights into the morphology and formation of NETs, their role in skin inflammation and how NETs might contribute to host protection in skin infection.

Reactive oxygen species, nutrition, hypoxia and diseases: Problems solved?

Within the last twenty years the view on reactive oxygen species (ROS) has changed; they are no longer only considered to be harmful but also necessary for cellular communication and homeostasis in different organisms ranging from bacteria to mammals. In the latter, ROS were shown to modulate diverse physiological processes including the regulation of growth factor signaling, the hypoxic response, inflammation and the immune response. During the last 60–100 years the life style, at least in the Western world, has changed enormously. This became obvious with an increase in caloric intake, decreased energy expenditure as well as the appearance of alcoholism and smoking; These changes were shown to contribute to generation of ROS which are, at least in part, associated with the occurrence of several chronic diseases like adiposity, atherosclerosis, type II diabetes, and cancer. In this review we discuss aspects and problems on the role of intracellular ROS formation and nutrition with the link to diseases and their problematic therapeutical issues.

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Oxidative stress is linked to overnutrition, obesity and associated diseases or cancer.

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Reactive oxygen species (ROS) are crucially involved in modulation of signaling cascades.

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NOX proteins and hypoxia contribute to formation of ROS under different nutrient regimes.

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ROS are powerful post-transcriptional and epigenetic regulators.

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Treatment of obesity with antioxidants requires more, larger, and better monitored clinical trials.

Prognostic significance of mitochondrial oxidative phosphorylation complexes: Therapeutic target in the treatment of retinoblastoma

PURPOSE

Altered energy metabolism plays an important role in the development and progression of cancer. The objective of this study was to elucidate the role of mitochondrial oxidative phosphorylation complexes and their prognostic significance in retinoblastoma (Rb).

METHODS

Immunohistochemistry was performed on 109 primary enucleated retinoblastoma tissues for mitochondrial OXPHOS complexes and their expression was confirmed by western blotting.

RESULTS

Histopathological high risk factors (HRFs) were identified in 42.2% cases. Mitochondrial OXPHOS complexes III, IV and V were expressed in more than 50% of primary retinoblastoma cases each whereas mitochondrial complex I was expressed in only 29/109 (26.60%) cases by immunohistochemistry. Loss of mitochondrial complex I correlated well with poor tumor differentiation and tumor invasion (p < 0.05) whereas expression of mitochondrial complexes III, IV and V was associated with better survival (Kaplan-Meier method).

CONCLUSIONS

This was the first study predicting a relevant role of mitochondrial OXPHOS complexes and highlights the prognostic significance with patient outcome in retinoblastoma. Loss of mitochondrial complex I immunoexpression could prove to be a useful independent prognostic biomarker to identify high risk retinoblastoma patients. Differential expression of these mitochondrial complexes is a novel finding and may be used as an attractive future anticancer target in primary retinoblastoma tumors.

FINANCIAL DISCLOSURE

The author(s) have no proprietary or commercial interest in any materials discussed in this article.

4′,6-dihydroxy-4-methoxyisoaurone inhibits the HIF-1α pathway through inhibition of Akt/mTOR/p70S6K/4E-BP1 phosphorylation

4′,6-Dihydroxy-4-methoxyisoaurone (ISOA) is an isoaurone compound isolated from Trichosanthes kirilowii seeds, which was identified as an inhibitor of tumor growth. However, the mechanism by which ISOA inhibits hypoxia-inducible factor-1 (HIF-1)-mediated tumor growth is not fully understood. We here demonstrated the effect of ISOA on HIF-1 activation. ISOA showed a potent inhibitory activity against HIF-1 activation induced by hypoxia in various human cancer cell lines. This compound markedly decreased the hypoxia-induced accumulation of HIF-1a protein dose-dependently, whereas it did not affect the expressions of HIF-1b and topoisomerase-I (Topo-I). Further analysis revealed that the suppression of HIF-1a accumulation by ISOA was closely correlated with strong dephosphorylation of Akt, mammalian target of rapamycin (mTOR), and its effectors ribosomal protein S6 kinase (p70S6K) and eukaryotic initiation factor 4E-binding protein-1 (4E-BP1), a pathway known to regulate HIF-1a expression at the translational level. Furthermore, ISOA prevented hypoxia-induced expression of HIF-1 target genes and suppresses the invasiveness of tumor cells. Taken together, our results suggested that ISOA is an effective inhibitor of HIF-1 through targeting Akt/mTOR/p70S6K/4E-BP1 pathway, thereby, providing new perspectives into the mechanism of its anticancer activity.

Titanium nanoparticle inhalation induces renal fibrosis in mice via an oxidative stress upregulated transforming growth factor-β pathway

Titanium dioxide nanoparticles (Nano-TiO2) are gradually being used extensively in clinical settings, industry, and daily life. Accumulation studies showed that Nano-TiO2 exposure is able to cause injuries in various animal organs, including the lung, liver, spleen, and kidney. However, it remains unclear whether exposure of Nano-TiO2 by inhalation causes renal fibrosis. Here, we investigated the role of reactive oxygen species (ROS)/reactive nitrogen species (RNS) related signaling molecules in chronic renal damage after Nano-TiO2 inhalation in mice. Mice were treated with Nano-TiO2 (0.1, 0.25, and 0.5 mg/week) or microparticle-TiO2 (0.5 mg/week) by nonsurgical intratracheal instillation for 4 weeks. The results showed that Nano-TiO2 inhalation increased renal pathological changes in a dose-dependent manner. No renal pathological changes were observed in microparticle-TiO2-instilled mice. Nano-TiO2 (0.5 mg/week) possessed the ability to precipitate in the kidneys, determined by transmission electron microscopy and increased serum levels of blood urea nitrogen. The expressions of markers of ROS/RNS and renal fibrosis markers, including nitrotyrosine, inducible nitric oxide synthase, hypoxia inducible factor-1α (HIF-1α), heme oxygenase 1, transforming growth factor-β (TGFβ), and collagen I, determined by immunohistochemical staining were increased in the kidneys. Furthermore, Nano-TiO2-induced renal injury could be mitigated by iNOS inhibitor aminoguanidine and ROS scavenger N-acetylcysteine treatment in transcription level. The in vitro experiments showed that Nano-TiO2 significantly and dose-dependently increased the ROS production and the expressions of HIF-1α and TGFβ in human renal proximal tubular cells, which could be reversed by N-acetylcysteine treatment. Taken together, these results suggest Nano-TiO2 inhalation might induce renal fibrosis through a ROS/RNS-related HIF-1α-upregulated TGF-β signaling pathway.

18F-FAZA PET imaging response tracks the reoxygenation of tumors in mice upon treatment with the mitochondrial complex I inhibitor BAY 87-2243

PURPOSE

We describe a noninvasive PET imaging method that monitors early therapeutic efficacy of BAY 87-2243, a novel small-molecule inhibitor of mitochondrial complex I as a function of hypoxia-inducible factor-1α (HIF1α) activity.

EXPERIMENTAL DESIGN

Four PET tracers [(18)F-FDG, (18)F-Fpp(RGD)2, (18)F-FLT, and (18)F-FAZA] were assessed for uptake into tumor xenografts of drug-responsive (H460, PC3) or drug-resistant (786-0) carcinoma cells. Mice were treated with BAY 87-2243 or vehicle. At each point, RNA from treated and vehicle H460 tumor xenografts (n = 3 each) was isolated and analyzed for target genes.

RESULTS

Significant changes in uptake of (18)F-FAZA, (18)F-FLT, and (18)F-Fpp(RGD)2 (P < 0.01) occurred with BAY 87-2243 treatment with (18)F-FAZA being the most prominent. (18)F-FDG uptake was unaffected. (18)F-FAZA tumor uptake declined by 55% to 70% (1.21% ± 0.10%ID/g to 0.35 ± 0.1%ID/g; n = 6, vehicle vs. treatment) in both H460 (P < 0.001) and PC3 (P < 0.05) xenografts 1 to 3 days after drug administration. (18)F-FAZA uptake in 786-0 xenografts was unaffected. Decline occurred before significant differences in tumor volume, thus suggesting (18)F-FAZA decrease reflected early changes in tumor metabolism. BAY 87-2243 reduced expression of hypoxia-regulated genes CA IX, ANGPTL4, and EGLN-3 by 99%, 93%, and 83%, respectively (P < 0.001 for all), which corresponds with reduced (18)F-FAZA uptake upon drug treatment. Heterogeneous expression of genes associated with glucose metabolism, vessel density, and proliferation was observed.

CONCLUSIONS

Our studies suggest suitability of (18)F-FAZA-PET as an early pharmacodynamic monitor on the efficacy of anticancer agents that target the mitochondrial complex I and intratumor oxygen levels (e.g., BAY 87-2243).

Powerhouse down: Complex II dissociation in the respiratory chain

Complex II of the respiratory chain (RC) recently emerged as a prominent regulator of cell death. In both cancer cells as well as neurodegenerative diseases, mutations in subunits have been found along with other genetic alterations indirectly affecting this complex. Anticancer compounds were developed that target complex II and cause cell death in a tumor-specific way. Our mechanistic understanding of how complex II is activated for cell death induction has recently been made clearer in recent studies, the results of which are covered in this review. This protein assembly is specifically activated for cell death via the dissociation of its SDHA and SDHB subunits from the membrane-anchoring proteins through pH change or mitochondrial Ca(2+) influx. The SDH activity contained in the SDHA/SDHB subcomplex remains intact and then generates, in an uncontrolled fashion, excessive amounts of reactive oxygen species (ROS) for cell death. Future studies on this mitochondrial complex will further elucidate it as a target for cancer treatments and reveal its role as a nexus for many diverse stimuli in cell death signaling.

Celastrol inhibits the HIF-1α pathway by inhibition of mTOR/p70S6K/eIF4E and ERK1/2 phosphorylation in human hepatoma cells

Hypoxia-inducible factor-1 (HIF-1) is the central mediator of cellular responses to low oxygen and vital to many aspects of cancer biology. In a search for HIF-1 inhibitors, we identified celastrol as an inhibitor of HIF-1 activation from Tripterygium wilfordii. In the present study, we demonstrated the effect of celastrol on HIF-1 activation. Celastrol showed a potent inhibitory activity against HIF-1 activation induced by hypoxia in various human cancer cell lines. This compound markedly decreased the hypoxia-induced accumulation of HIF-1α protein dose-dependently, whereas it did not affect the expressions of HIF-1β and topoisomerase-I (topo‑I). Furthermore, celastrol prevented hypoxia-induced expression of HIF-1 target genes for vascular endothelial growth factor (VEGF) and erythropoietin (EPO). Further analysis revealed that celastrol inhibited HIF-1α protein synthesis, without affecting the expression level of HIF-1α mRNA or degradation of HIF-1α protein. Markedly, we found that suppression of HIF-1α accumulation by celastrol correlated with strong dephosphorylation of mammalian target of rapamycin (mTOR) and its effectors, ribosomal protein S6 kinase (p70S6K) and eukaryotic initiation factor 4E (eIF4E) and extracellular signal-regulated kinase (ERK), pathways known to regulate HIF-1α expression at the translational level. In vivo studies further confirmed the inhibitory effect of celastrol on the expression of HIF-1α proteins, leading to a decreased growth of Hep3B cells in a xenograft tumor model. Our data suggested that celastrol is an effective inhibitor of HIF-1 and provide new perspectives into the mechanism of its anticancer activity.

Antioxidants delay clinical signs and systemic effects of ENU induced brain tumors in rats

According to our previous study suggesting that antioxidant properties of phytochemicals in the diet decrease glioma aggressiveness, we used a SUVIMAX-like diet ("Supplementation en VItamines et Minéraux AntioXydants") (enriched with alpha-tocopherol, beta carotene, vitamin C, zinc, and sodium selenite), adapted to rats. The present results showed that each of the antioxidants inhibited growth of glioma cells in vitro. When used in combination for in vivo studies, we showed a highly significant delay in the clinical signs of the disease, but not a statistical significant difference in the incidence of glioma in an Ethyl-nitrosourea (ENU)-model. The SUVIMAX-like diet decreased candidate markers of tumoral aggressiveness and gliomagenesis progression. The mRNA expressions of 2 common markers in human glioma: Mn-SOD (Manganese Superoxide Dismutase) and IGFBP5 (insulin growth factor binding protein) were reduced in the tumors of rats fed the antioxidant diet. In addition, the transcripts of two markers linked to brain tumor proliferation, PDGFRb (platelet-derived growth factor receptor beta) and Ki-67, were also significantly decreased. On the whole, our results suggest a protective role for antioxidants to limit aggressiveness and to some extent, progression of gliomas, in a rat model.

Emerging strategies to overcome the resistance to current mTOR inhibitors in renal cell carcinoma

The mammalian target of rapamycin (mTOR) has emerged as an attractive cancer therapeutic target. Treatment of metastatic renal cell carcinoma (mRCC) has improved significantly with the advent of agents targeting the mTOR pathway, such as temsirolimus and everolimus. Unfortunately, a number of potential mechanisms that may lead to resistance to mTOR inhibitors have been proposed. In this paper, we discuss the mechanisms underlying resistance to mTOR inhibitors, which include the downstream effectors of the phosphoinositide 3-kinase (PI3K)/AKT/mTOR pathway, the activation of hypoxia-inducible factor (HIF), the PIM kinase family, PTEN expression, elevated superoxide levels, stimulation of autophagy, immune cell response and ERK/MAPK, Notch and Aurora signaling pathways. Moreover, we present an updated analysis of clinical trials available on PubMed Central and www.clinicaltrials.gov, which were pertinent to the resistance to rapalogs. The new frontier of inhibiting the mTOR pathway is to identify agents targeting the feedback loops and cross talks with other pathways involved in the acquired resistance to mTOR inhibitors. The true goal will be to identify biomarkers predictive of sensitivity or resistance to efficiently develop novel agents with the aim to avoid toxicities and to better choose the active drug for the right patient.

The role of HIF in cobalt-induced ischemic tolerance

Understanding the endogenous survival pathways induced by ischemic tolerance may yield targets for neuroprotection from stroke. One well-studied pathway reported to be evoked by preconditioning stimuli is the transcription factor HIF (hypoxia-inducible factor). However, whether HIF induction by ischemic insults is neuroprotective or toxic is still unclear. We examined the ability of three prolyl-hydroxylase inhibitors, which induce HIF, to protect hippocampal cultures from oxygen-glucose deprivation. Hippocampal cultures were exposed to ischemic preconditioning or various concentrations of cobalt chloride, deferoxamine (DFO) or dimethyloxylalyglycine (DMOG), prior to lethal oxygen-glucose deprivation (OGD). Cell survival of neurons and astrocytes was determined with dual-label immunocytochemistry. The induction of HIF targets was assessed in mixed as well as astrocyte-enriched cultures. Ischemic preconditioning, as well as low concentrations of cobalt and DFO, enhanced the survival of neurons following OGD. However, DMOG exacerbates OGD-induced neuronal death. At low concentrations, all three prolyl-hydroxylase (PHD) inhibitors increased the survival of astrocytes. Neuroprotective concentrations of cobalt induced the transcription of the cytokine erythropoietin (EPO) in astrocyte cultures. In addition, pretreatment with recombinant human erythropoietin (rH-EPO) also protected neurons from OGD. Our data suggest that HIF-induced EPO, released from astrocytes, protects neurons from OGD. However, the three PHD inhibitors each exhibited different neuroprotective profiles at low concentrations, suggesting that not all PHD inhibitors are created equal. The protective effects at low doses is reminiscent of HIF involvement in ischemic tolerance, in which sub-lethal insults induce HIF pathways resulting in neuroprotection, whereas the high-dose toxicity suggests that over-activation of HIF is not always protective. Therefore, the choice of inhibitor and dose may determine the clinical utility of these compounds. Deferoxamine exhibited little toxicity even at higher doses, and therefore appears a promising candidate for clinical use.

Effects of RNA interference-mediated knock-down of hypoxia-inducible factor-α on respiratory burst activity of the Pacific oyster Crassostrea gigas hemocytes

In mammals, hypoxia-inducible factor-1 α (HIF-1α) is known to play important roles not only in oxygen homeostasis but also in innate immune responses. In this study, to assess the functional role of HIF-α in respiratory burst activity of Crassostrea gigas hemocytes, oysters were injected with HIF-α- or green fluorescent protein (GFP)-targeted-long double-stranded RNAs (dsRNAs), and at 1, 3, and 7 days post-injection, knock-down of C. gigas HIF-α expression and production of reactive oxygen species (ROS) were analyzed. Expression of HIF-α in mantle, gill, and hemocytes of C. gigas was clearly down-regulated by injection of the HIF-α-targeted-long dsRNA, but was not inhibited by the GFP-targeted-long dsRNA, indicating that HIF-α expression was suppressed through sequence-specific and systemic RNA interference (RNAi). Respiratory burst activity of hemocytes was significantly increased by administration of GFP-targeted-long dsRNA. However, knock-down of HIF-α expression led to significant decrease of chemiluminescence (CL) response of C. gigas hemocytes at 3 and 7 days post-administration of HIF-α-targeted-long dsRNA, indicating the critical role of HIF-α in activation of respiratory burst activity of oyster hemocytes.

Mitoplasticity: adaptation biology of the mitochondrion to the cellular redox state in physiology and carcinogenesis

Adaptation and transformation biology of the mitochondrion to redox status is an emerging domain of physiology and pathophysiology. Mitochondrial adaptations occur in response to accidental changes in cellular energy demand or supply while mitochondrial transformations are a part of greater program of cell metamorphosis. The possible role of mitochondrial adaptations and transformations in pathogenesis remains unexplored, and it has become critical to decipher the stimuli and the underlying molecular pathways. Immediate activation of mitochondrial function was described during acute exercise, respiratory chain injury, Endoplasmic Reticulum stress, genotoxic stress, or environmental toxic insults. Delayed adaptations of mitochondrial form, composition, and functions were evidenced for persistent changes in redox status as observed in endurance training, in fibroblasts grown in presence of respiratory chain inhibitors or in absence of glucose, in the smooth muscle of patients with severe asthma, or in the skeletal muscle of patients with a mitochondrial disease. Besides, mitochondrial transformations were observed in the course of human cell differentiation, during immune response activation, or in cells undergoing carcinogenesis. Little is known on the signals and downstream pathways that govern mitochondrial adaptations and transformations. Few adaptative loops, including redox sensors, kinases, and transcription factors were deciphered, but their implication in physiology and pathology remains elusive. Mitoplasticity could play a protective role against aging, diabetes, cancer, or neurodegenerative diseases. Research on adaptation and transformation could allow the design of innovative therapies, notably in cancer.

Autophagy takes place in mutated p53 neuroblastoma cells in response to hypoxia mimetic CoCl(2)

Solid tumors like neuroblastoma exhibit hypoxic areas, which can lead both to cell death or aggressiveness increase. Hypoxia is a known stress able to induce stabilization of p53, implicated in cell fate regulation. Recently, p53 appeared to be involved in autophagy in an opposite manner, depending on its location: when nuclear, it enhanced transcription of pro-autophagic genes whereas when cytoplasmic, it inhibited the autophagic process. Today, we used cobalt chloride, a hypoxia mimetic that inhibits proteasomal HIF-1 degradation and generates reactive oxygen species (ROS). We focused on CoCl2-induced cell death in a DNA-binding mutated p53 neuroblastoma cell line (SKNBE(2c)). An autophagic signaling was evidenced by an increase of Beclin-1, ATG 5-12, and LC3-II expression whereas the p53(mut) presence decreased with CoCl2 time exposure. Activation of the pathway seemed to protect cells from ROS production and, at least in part, from death. The autophagic inhibitors activated the apoptotic signaling and the death was enhanced. To delineate the eventual implication of the p53(mut) in the autophagic process in response to hypoxia, we monitored signaling in p53(WT)SHSY5Y cells, after either shRNA-p53 down-regulation or transcriptional activity inhibition by pifithrin alpha. We did not detect autophagy neither with p53(wt) nor when p53 was lacking whereas such a response was effective with a mutated or inactivated p53. To conclude, mutated p53 in neuroblastoma cells could be linked with the switch between apoptotic response and cell death by autophagy in response to hypoxic mimetic stress.

SCO2 induces p53-mediated apoptosis by Thr845 phosphorylation of ASK-1 and dissociation of the ASK-1-Trx complex

p53 prevents cancer via cell cycle arrest, apoptosis, and the maintenance of genome stability. p53 also regulates energy-generating metabolic pathways such as oxidative phosphorylation (OXPHOS) and glycolysis via transcriptional regulation of SCO2 and TIGAR. SCO2, a cytochrome c oxidase assembly factor, is a metallochaperone which is involved in the biogenesis of cytochrome c oxidase subunit II. Here we have shown that SCO2 functions as an apoptotic protein in tumor xenografts, thus providing an alternative pathway for p53-mediated apoptosis. SCO2 increases the generation of reactive oxygen species (ROS) and induces dissociation of the protein complex between apoptosis signal-regulating kinase 1 (ASK-1) (mitogen-activated protein kinase kinase kinase [MAPKKK]) and its cellular inhibitor, the redox-active protein thioredoxin (Trx). Furthermore, SCO2 induces phosphorylation of ASK-1 at the Thr(845) residue, resulting in the activation of the ASK-1 kinase pathway. The phosphorylation of ASK-1 induces the activation of mitogen-activated protein kinase kinases 4 and 7 (MAP2K4/7) and MAP2K3/6, which switches the c-Jun N-terminal protein kinase (JNK)/p38-dependent apoptotic cascades in cancer cells. Exogenous addition of the SCO2 gene to hypoxic cancer cells and hypoxic tumors induces apoptosis and causes significant regression of tumor xenografts. We have thus discovered a novel apoptotic function of SCO2, which activates the ASK-1 kinase pathway in switching "on" an alternate mode of p53-mediated apoptosis. We propose that SCO2 might possess a novel tumor suppressor function via the ROS-ASK-1 kinase pathway and thus could be an important candidate for anticancer gene therapy.

Oxidative stress and cancer: an overview

Reactive species, which mainly include reactive oxygen species (ROS), are products generated as a consequence of metabolic reactions in the mitochondria of eukaryotic cells. In normal cells, low-level concentrations of these compounds are required for signal transduction before their elimination. However, cancer cells, which exhibit an accelerated metabolism, demand high ROS concentrations to maintain their high proliferation rate. Different ways of developing ROS resistance include the execution of alternative pathways, which can avoid large amounts of ROS accumulation without compromising the energy demand required by cancer cells. Examples of these processes include the guidance of the glycolytic pathway into the pentose phosphate pathway (PPP) and/or the generation of lactate instead of employing aerobic respiration in the mitochondria. Importantly, ROS levels can be used as a thermostat to monitor the damage that cells can bear. The implications for ROS regulation are highly significant for cancer therapy because commonly used radio- and chemotherapeutic drugs influence tumor outcome through ROS modulation. Moreover, the discovery of novel biomarkers that are able to predict the clinical response to pro-oxidant therapies is a crucial challenge to overcome to allow for the personalization of cancer therapies.

Mammalian target of rapamycin regulates neutrophil extracellular trap formation via induction of hypoxia-inducible factor 1 α

Neutrophils are highly specialized innate immune effector cells that evolved for antimicrobial host defense. In response to inflammatory stimuli and pathogens, they form neutrophil extracellular traps (NETs), which capture and kill extracellular microbes. Deficient NET formation predisposes humans to severe infection, but, paradoxically, dysregulated NET formation contributes to inflammatory vascular injury and tissue damage. The molecular pathways and signaling mechanisms that control NET formation remain largely uncharacterized. Using primary human neutrophils and genetically manipulated myeloid leukocytes differentiated to surrogate neutrophils, we found that mammalian target of rapamycin (mTOR) regulates NET formation by posttranscriptional control of expression of hypoxia-inducible factor 1 α (HIF-1α), a critical modulator of antimicrobial defenses. Next-generation RNA sequencing, assays of mRNA and protein expression, and analysis of NET deployment by live cell imaging and quantitative histone release showed that mTOR controls NET formation and translation of HIF-1α mRNA in response to lipopolysaccharide. Pharmacologic and genetic knockdown of HIF-1α expression and activity inhibited NET deployment, and inhibition of mTOR and HIF-1α inhibited NET-mediated extracellular bacterial killing. Our studies define a pathway to NET formation involving 2 master regulators of immune cell function and identify potential points of molecular intervention in strategies to modify NETs in disease.

Rationale for mitochondria-targeting strategies in cancer bioenergetic therapies

In the 1920s, Otto Warburg first hypothesized that mitochondrial impairment is a leading cause of cancer although he recognized the existence of oxidative tumors. Likewise, Weinhouse and others in the 50s found that deficient mitochondrial respiration is not an obligatory feature of cancer and Peter Vaupel suggested in the 1990s that tumor oxygenation rather than OXPHOS capacity was the limiting factor of mitochondrial energy production in cancer. Recent studies now clearly indicate that mitochondria are highly functional in mice tumors and the field of oncobioenergetic identified MYC, Oct1 and RAS as pro-OXPHOS oncogenes. In addition, cancer cells adaptation to aglycemia, metabolic symbiosis between hypoxic and non-hypoxic tumor regions as well the reverse Warburg hypothesis support the crucial role of mitochondria in the survival of a subclass of tumors. Therefore, mitochondria are now considered as potential targets for anti-cancer therapy and tentative strategies including a bioenergetic profile characterization of the tumor and the subsequent adapted bioenergetic modulation could be considered for cancer killing. This article is part of a Directed Issue entitled: Bioenergetic dysfunction, adaptation and therapy.

Metabolic profiling of hypoxic cells revealed a catabolic signature required for cell survival

Hypoxia is one of the features of poorly vascularised areas of solid tumours but cancer cells can survive in these areas despite the low oxygen tension. The adaptation to hypoxia requires both biochemical and genetic responses that culminate in a metabolic rearrangement to counter-balance the decrease in energy supply from mitochondrial respiration. The understanding of metabolic adaptations under hypoxia could reveal novel pathways that, if targeted, would lead to specific death of hypoxic regions. In this study, we developed biochemical and metabolomic analyses to assess the effects of hypoxia on cellular metabolism of HCT116 cancer cell line. We utilized an oxygen fluorescent probe in anaerobic cuvettes to study oxygen consumption rates under hypoxic conditions without the need to re-oxygenate the cells and demonstrated that hypoxic cells can maintain active, though diminished, oxidative phosphorylation even at 1% oxygen. These results were further supported by in situ microscopy analysis of mitochondrial NADH oxidation under hypoxia. We then used metabolomic methodologies, utilizing liquid chromatography–mass spectrometry (LC-MS), to determine the metabolic profile of hypoxic cells. This approach revealed the importance of synchronized and regulated catabolism as a mechanism of adaptation to bioenergetic stress. We then confirmed the presence of autophagy under hypoxic conditions and demonstrated that the inhibition of this catabolic process dramatically reduced the ATP levels in hypoxic cells and stimulated hypoxia-induced cell death. These results suggest that under hypoxia, autophagy is required to support ATP production, in addition to glycolysis, and that the inhibition of autophagy might be used to selectively target hypoxic regions of tumours, the most notoriously resistant areas of solid tumours.