BAY 87-2243, a highly potent and selective inhibitor of hypoxia-induced gene activation has antitumor activities by inhibition of mitochondrial complex I

DNA damage response signaling pathways and targets for radiotherapy sensitization in cancer

Radiotherapy is one of the most common countermeasures for treating a wide range of tumors. However, the radioresistance of cancer cells is still a major limitation for radiotherapy applications. Efforts are continuously ongoing to explore sensitizing targets and develop radiosensitizers for improving the outcomes of radiotherapy. DNA double-strand breaks are the most lethal lesions induced by ionizing radiation and can trigger a series of cellular DNA damage responses (DDRs), including those helping cells recover from radiation injuries, such as the activation of DNA damage sensing and early transduction pathways, cell cycle arrest, and DNA repair. Obviously, these protective DDRs confer tumor radioresistance. Targeting DDR signaling pathways has become an attractive strategy for overcoming tumor radioresistance, and some important advances and breakthroughs have already been achieved in recent years. On the basis of comprehensively reviewing the DDR signal pathways, we provide an update on the novel and promising druggable targets emerging from DDR pathways that can be exploited for radiosensitization. We further discuss recent advances identified from preclinical studies, current clinical trials, and clinical application of chemical inhibitors targeting key DDR proteins, including DNA-PKcs (DNA-dependent protein kinase, catalytic subunit), ATM/ATR (ataxia–telangiectasia mutated and Rad3-related), the MRN (MRE11-RAD50-NBS1) complex, the PARP (poly[ADP-ribose] polymerase) family, MDC1, Wee1, LIG4 (ligase IV), CDK1, BRCA1 (BRCA1 C terminal), CHK1, and HIF-1 (hypoxia-inducible factor-1). Challenges for ionizing radiation-induced signal transduction and targeted therapy are also discussed based on recent achievements in the biological field of radiotherapy.

Anti-VEGF Treatment Enhances CD8+ T-cell Antitumor Activity by Amplifying Hypoxia

Antiangiogenic therapies that target the VEGF pathway have been used clinically to combat cancer for over a decade. Beyond having a direct impact on blood vessel development and tumor perfusion, accumulating evidence indicates that these agents also affect antitumor immune responses. Numerous clinical trials combining antiangiogenic drugs with immunotherapies for the treatment of cancer are ongoing, but a mechanistic understanding of how disruption of tumor angiogenesis may impact immunity is not fully discerned. Here, we reveal that blockade of VEGF-A with a mAb to VEGF augments activation of CD8⁺ T cells within tumors and potentiates their capacity to produce cytokines. We demonstrate that this phenomenon relies on the disruption of VEGFR2 signaling in the tumor microenvironment but does not affect CD8⁺ T cells directly. Instead, the augmented functional capacity of CD8⁺ T cells stems from increased tumor hypoxia that initiates a hypoxia-inducible factor-1α program within CD8⁺ T cells that directly enhances cytokine production. Finally, combinatorial administration of anti-VEGF with an immunotherapeutic antibody, anti-OX40, improved antitumor activity over single-agent treatments. Our findings illustrate that anti-VEGF treatment enhances CD8⁺ T-cell effector function and provides a mechanistic rationale for combining antiangiogenic and immunotherapeutic drugs for cancer treatment.

Fenofibrate-induced mitochondrial dysfunction and metabolic reprogramming reversal: the anti-tumor effects in gastric carcinoma cells mediated by the PPAR pathway

Cancer cells reprogram their metabolism to adapt to fast growth and environmental demands, which differ them from normal cells. Mitochondria are central to the malignant metabolism reprogramming process. Here, we report that PPARα was highly expressed in gastric cancer tissues and negatively correlated with prognosis. Fenofibrate, a common drug used to treat severe hypertriglyceridemia and mixed dyslipidemia, reversed cellular metabolism and mitochondrial dysfunction in gastric cancer cells through PPARα. Our results show that fenofibrate altered glucose and lipid metabolism, inhibited gastric cancer cell proliferation, and promoted apoptosis in gastric cancer cells. We further show that fenofibrate induced mitochondrial reprogramming via CPT1 and the fatty acid oxidation pathway, as well as by activating the AMPK pathway and inhibiting the HK2 pathway. Additionally, fenofibrate inhibited subcutaneous gastric cancer cell tumor growth without obvious toxicity in mice. Collectively, our results indicate that fenofibrate exhibits anti-tumor activity in vitro and in vivo via the mitochondria and metabolic reprogramming, demonstrating that mitochondrial regulation and the normalization of cancer cell metabolism are novel therapeutic strategies for cancer.

Targeting Cell Metabolism as Cancer Therapy

Significance: Cancer cells exhibit altered metabolic pathways to keep up with biosynthetic and reduction-oxidation needs during tumor proliferation and metastasis. The common induction of metabolic pathways during cancer progression, regardless of cancer histio- or genotype, makes cancer metabolism an attractive target for therapeutic exploitation. Recent Advances: Emerging data suggest that these altered pathways may even result in resistance to anticancer therapies. Identifying specific metabolic dependencies that are unique to cancer cells has proved challenging in this field, limiting the therapeutic window for many candidate drug approaches. Critical Issues: Cancer cells display significant metabolic flexibility in nutrient-limited environments, hampering the longevity of suppressing cancer metabolism through any singular approach. Combinatorial "synthetic lethal" approaches may have a better chance for success and promising strategies are reviewed here. The dynamism of the immune system adds a level of complexity, as various immune populations in the tumor microenvironment often share metabolic pathways with cancer, with successive alterations during immune activation and quiescence. Decoding the reprogramming of metabolic pathways within cancer cells and stem cells, as well as examining metabolic symbiosis between components of the tumor microenvironment, would be essential to further meaningful drug development within the tumor's metabolic ecosystem. Future Directions: In this article, we examine evidence for the therapeutic potential of targeting metabolic alterations in cancer, and we discuss the drawbacks and successes that have stimulated this field.

Simvastatin re-sensitizes hepatocellular carcinoma cells to sorafenib by inhibiting HIF-1α/PPAR-γ/PKM2-mediated glycolysis

BACKGROUND

Hepatocellular carcinoma (HCC) is a common primary malignant tumor which usually progresses to an advanced stage because of late diagnosis. Sorafenib (Sora) is a first line medicine for advanced stage HCC; however, it has been faced with enormous resistance. Simvastatin (Sim) is a cholesterol-lowering drug and has been reported to inhibit tumor growth. The present study aims to determine whether Sora and Sim co-treatment can improve Sora resistance in HCC.

METHODS

The HCC cell line LM3 and an established Sora-resistant LM3 cell line (LM3-SR) were used to study the relationship between Sora resistance and aerobic glycolysis. Cell proliferation, apoptosis and glycolysis levels were analyzed by western blotting, flow cytometry analysis and biomedical tests. A xenograft model was also used to examine the effect of Sim in vivo. Detailed mechanistic studies were also undertaken by the use of activators and inhibitors, and lentivirus transfections.

RESULTS

Our results demonstrated that the resistance to Sora was associated with enhanced aerobic glycolysis levels. Furthermore, LM3-SR cells were more sensitive to Sim than LM3 cells, suggesting that combined treatment with both Sora and Sim could enhance the sensitivity of LM3-SR cells to Sora. This finding may be due to the suppression of the HIF-1α/PPAR-γ/PKM2 axis.

CONCLUSIONS

Simvastatin can inhibit the HIF-1α/PPAR-γ/PKM2 axis, by suppressing PKM2-mediated glycolysis, resulting in decreased proliferation and increased apoptosis in HCC cells, and re-sensitizing HCC cells to Sora.

Small molecules targeting HIF-1α pathway for cancer therapy in recent years

Hypoxia is a very important feature of tumors, especially for solid tumors, and it was demonstrated highly relevant with aggressive biology, including anti-apoptosis, vasculogenesis and radiation or chemotherapy resistance. Correlatively, hypoxia-inducible factors 1-α (HIF-1α), which the wildest contribution of hypoxia-inducible factors (HIFs), plays a crucial role in the adaptation of tumor cells to hypoxia via upregulating the transcription of the oncogene and downregulating the transcription of suppressor gene. This review focus on the HIF-1α regulation including hydroxylation and acetylation, growth factors pathway, heat shock proteins(HSPs), and small molecule inhibitors for HIF-1α directly or indirectly.

Mitochondria-driven elimination of cancer and senescent cells

Mitochondria and oxidative phosphorylation (OXPHOS) are emerging as intriguing targets for the efficient elimination of cancer cells. The specificity of this approach is aided by the capacity of non-proliferating non-cancerous cells to withstand oxidative insult induced by OXPHOS inhibition. Recently we discovered that mitochondrial targeting can also be employed to eliminate senescent cells, where it breaks the interplay between OXPHOS and ATP transporters that appear important for the maintenance of mitochondrial morphology and viability in the senescent setting. Hence, mitochondria/OXPHOS directed pharmacological interventions show promise in several clinically-relevant scenarios that call for selective removal of cancer and senescent cells.

Oxidative phosphorylation as a potential therapeutic target for cancer therapy

In contrast to prior belief, cancer cells require oxidative phosphorylation (OXPHOS) to strive, and exacerbated OXPHOS dependency frequently characterizes cancer stem cells, as well as primary or acquired resistance against chemotherapy or tyrosine kinase inhibitors. A growing arsenal of therapeutic agents is being designed to suppress the transfer of mitochondria from stromal to malignant cells, to interfere with mitochondrial biogenesis, to directly inhibit respiratory chain complexes, or to disrupt mitochondrial function in other ways. For the experimental treatment of cancers, OXPHOS inhibitors can be advantageously combined with tyrosine kinase inhibitors, as well as with other strategies to inhibit glycolysis, thereby causing a lethal energy crisis. Unfortunately, most of the preclinical data arguing in favor of OXPHOS inhibition have been obtained in xenograft models, in which human cancer cells are implanted in immunodeficient mice. Future studies on OXPHOS inhibitors should elaborate optimal treatment schedules and combination regimens that stimulate-or at least are compatible with-anticancer immune responses for long-term tumor control.

The lncRNA PVT1 regulates nasopharyngeal carcinoma cell proliferation via activating the KAT2A acetyltransferase and stabilizing HIF-1α

Long noncoding RNAs (lncRNAs) play important roles in regulating the development and progression of many cancers. However, the clinical significance of specific lncRNAs in the context of nasopharyngeal carcinoma (NPC) and the molecular mechanisms by which they regulate this form of cancer remain largely unclear. In this study we found that the lncRNA PVT1 was upregulated in NPC, and that in patients this upregulation was associated with reduced survival. RNA sequencing revealed that PVT1 was responsible for regulating NPC cell proliferation and for controlling a hypoxia-related phenotype in these cells. PVT1 knockdown reduced NPC cell proliferation, colony formation, and tumorigenesis in a subcutaneous mouse xenograft model systems. We further found that PVT1 serves as a scaffold for the chromatin modification factor KAT2A, which mediates histone 3 lysine 9 acetylation (H3K9), recruiting the nuclear receptor binding protein TIF1β to activate NF90 transcription, thereby increasing HIF-1α stability and promoting a malignant phenotype in NPC cells. Overexpression of NF90 or HIF-1α restored the proliferation in cells that had ceased proliferating due to PVT1 or KAT2A depletion. Conversely, overexpression of active KAT2A or TIF1β, but not of KAT2A acetyltransferase activity-deficient mutants or TIF1β isoforms lacking H3K9ac binding sites, promoted a PVT1-mediated increase in NF90 transcription, as well as increased HIF-1α stability and cell proliferation. PVT1 knockdown enhanced the radiosensitization effect in NPC cells via inhibiting binding between H3K9ac and TIF1β in a manner. Taken together, our results demonstrate that PVT1 serves an oncogenic role and plays an important role in radiosensitivity in malignant NPC via activating the KAT2A acetyltransferase and stabilizing HIF-1α.

CHCHD4 regulates tumour proliferation and EMT-related phenotypes, through respiratory chain-mediated metabolism

BACKGROUND

Mitochondrial oxidative phosphorylation (OXPHOS) via the respiratory chain is required for the maintenance of tumour cell proliferation and regulation of epithelial to mesenchymal transition (EMT)-related phenotypes through mechanisms that are not fully understood. The essential mitochondrial import protein coiled-coil helix coiled-coil helix domain-containing protein 4 (CHCHD4) controls respiratory chain complex activity and oxygen consumption, and regulates the growth of tumours in vivo. In this study, we interrogate the importance of CHCHD4-regulated mitochondrial metabolism for tumour cell proliferation and EMT-related phenotypes, and elucidate key pathways involved.

RESULTS

Using in silico analyses of 967 tumour cell lines, and tumours from different cancer patient cohorts, we show that CHCHD4 expression positively correlates with OXPHOS and proliferative pathways including the mTORC1 signalling pathway. We show that CHCHD4 expression significantly correlates with the doubling time of a range of tumour cell lines, and that CHCHD4-mediated tumour cell growth and mTORC1 signalling is coupled to respiratory chain complex I (CI) activity. Using global metabolomics analysis, we show that CHCHD4 regulates amino acid metabolism, and that CHCHD4-mediated tumour cell growth is dependent on glutamine. We show that CHCHD4-mediated tumour cell growth is linked to CI-regulated mTORC1 signalling and amino acid metabolism. Finally, we show that CHCHD4 expression in tumours is inversely correlated with EMT-related gene expression, and that increased CHCHD4 expression in tumour cells modulates EMT-related phenotypes.

CONCLUSIONS

CHCHD4 drives tumour cell growth and activates mTORC1 signalling through its control of respiratory chain mediated metabolism and complex I biology, and also regulates EMT-related phenotypes of tumour cells.

HIF-1α is over-expressed in leukemic cells from TP53-disrupted patients and is a promising therapeutic target in chronic lymphocytic leukemia

In chronic lymphocytic leukemia (CLL), the hypoxia-inducible factor 1 (HIF-1) regulates the response of tumor cells to hypoxia and their protective interactions with the leukemic microenvironment. In this study, we demonstrate that CLL cells from TP53-disrupted (TP53^dis) patients have constitutively higher expression levels of the α-subunit of HIF-1 (HIF-1α) and increased HIF-1 transcriptional activity compared to the wild-type counterpart. In the TP53^dis subset, HIF-1α upregulation is due to reduced expression of the HIF-1α ubiquitin ligase von Hippel-Lindau protein (pVHL). Hypoxia and stromal cells further enhance HIF-1α accumulation, independently of TP53 status. Hypoxia acts through the downmodulation of pVHL and the activation of the PI3K/AKT and RAS/ERK1-2 pathways, whereas stromal cells induce an increased activity of the RAS/ERK1-2, RHOA/RHOA kinase and PI3K/AKT pathways, without affecting pVHL expression. Interestingly, we observed that higher levels of HIF-1A mRNA correlate with a lower susceptibility of leukemic cells to spontaneous apoptosis, and associate with the fludarabine resistance that mainly characterizes TP53^dis tumor cells. The HIF-1α inhibitor BAY87-2243 exerts cytotoxic effects toward leukemic cells, regardless of the TP53 status, and has anti-tumor activity in Em-TCL1 mice. BAY87-2243 also overcomes the constitutive fludarabine resistance of TP53^dis leukemic cells and elicits a strongly synergistic cytotoxic effect in combination with ibrutinib, thus providing preclinical evidence to stimulate further investigation into use as a potential new drug in CLL.

AIF-regulated oxidative phosphorylation supports lung cancer development

Cancer is a major and still increasing cause of death in humans. Most cancer cells have a fundamentally different metabolic profile from that of normal tissue. This shift away from mitochondrial ATP synthesis via oxidative phosphorylation towards a high rate of glycolysis, termed Warburg effect, has long been recognized as a paradigmatic hallmark of cancer, supporting the increased biosynthetic demands of tumor cells. Here we show that deletion of apoptosis-inducing factor (AIF) in a KrasG12D-driven mouse lung cancer model resulted in a marked survival advantage, with delayed tumor onset and decreased malignant progression. Mechanistically, Aif deletion leads to oxidative phosphorylation (OXPHOS) deficiency and a switch in cellular metabolism towards glycolysis in non-transformed pneumocytes and at early stages of tumor development. Paradoxically, although Aif-deficient cells exhibited a metabolic Warburg profile, this bioenergetic change resulted in a growth disadvantage of KrasG12D-driven as well as Kras wild-type lung cancer cells. Cell-autonomous re-expression of both wild-type and mutant AIF (displaying an intact mitochondrial, but abrogated apoptotic function) in Aif-knockout KrasG12D mice restored OXPHOS and reduced animal survival to the same level as AIF wild-type mice. In patients with non-small cell lung cancer, high AIF expression was associated with poor prognosis. These data show that AIF-regulated mitochondrial respiration and OXPHOS drive the progression of lung cancer.

Targeting STAT3 and oxidative phosphorylation in oncogene-addicted tumors

Drug resistance invariably limits the response of oncogene-addicted cancer cells to targeted therapy. The upregulation of signal transducer and activator of transcription 3 (STAT3) has been implicated as a mechanism of drug resistance in a range of oncogene-addicted cancers. However, the development of inhibitors against STAT3 has been fraught with challenges such as poor delivery or lack of specificity. Clinical experience with small molecule STAT3 inhibitors has seen efficacy signals, but this success has been tempered by drug limiting toxicities from off-target adverse events. It has emerged in recent years that, contrary to the Warburg theory, certain tumor types undergo metabolic reprogramming towards oxidative phosphorylation (OXPHOS) to satisfy their energy production. In particular, certain drug-resistant oncogene-addicted tumors have been found to rely on OXPHOS as a mechanism of survival. Multiple cellular signaling pathways converge on STAT3, hence the localization of STAT3 to the mitochondria may provide the link between oncogene-induced signaling pathways and cancer cell metabolism. In this article, we review the role of STAT3 and OXPHOS as targets of novel therapeutic strategies aimed at restoring drug sensitivity in treatment-resistant oncogene-addicted tumor types. Apart from drugs which have been re-purposed as OXPHOS inhibitors for-anti-cancer therapy (e.g., metformin and phenformin), several novel compounds in the drug-development pipeline have demonstrated promising pre-clinical and clinical activity. However, the clinical development of OXPHOS inhibitors remains in its infancy. The further identification of compounds with acceptable toxicity profiles, alongside the discovery of robust companion biomarkers of OXPHOS inhibition, would represent tangible early steps in transforming the therapeutic landscape of cancer cell metabolism.

Inhibition of ERRα Prevents Mitochondrial Pyruvate Uptake Exposing NADPH-Generating Pathways as Targetable Vulnerabilities in Breast Cancer

Most cancer cells exhibit metabolic flexibility, enabling them to withstand fluctuations in intratumoral concentrations of glucose (and other nutrients) and changes in oxygen availability. While these adaptive responses make it difficult to achieve clinically useful anti-tumor responses when targeting a single metabolic pathway, they can also serve as targetable metabolic vulnerabilities that can be therapeutically exploited. Previously, we demonstrated that inhibition of estrogen-related receptor alpha (ERRα) significantly disrupts mitochondrial metabolism and that this results in substantial antitumor activity in animal models of breast cancer. Here we show that ERRα inhibition interferes with pyruvate entry into mitochondria by inhibiting the expression of mitochondrial pyruvate carrier 1 (MPC1). This results in a dramatic increase in the reliance of cells on glutamine oxidation and the pentose phosphate pathway to maintain nicotinamide adenine dinucleotide phosphate (NADPH) homeostasis. In this manner, ERRα inhibition increases the efficacy of glutaminase and glucose-6-phosphate dehydrogenase inhibitors, a finding that has clinical significance.

Hypoxia enhances CD8+ TC2 cell-dependent airway hyperresponsiveness and inflammation through hypoxia-inducible factor 1α

BACKGROUND

CD8+ type 2 cytotoxic T (TC2) cells undergo transcriptional reprogramming to IL-13 production in the presence of IL-4 to become potent, steroid-insensitive, pathogenic effector cells in asthmatic patients and in mice in a model of experimental asthma. However, no studies have described the effects of hypoxia exposure on TC2 cell differentiation.

OBJECTIVE

We determined the effects of hypoxia exposure on IL-13-producing CD8+ TC2 cells.

METHODS

CD8+ transgenic OT-1 cells differentiated with IL-2 and IL-4 (TC2 cells) were exposed to normoxia (21% oxygen) or hypoxia (3% oxygen), and IL-13 production in vitro was monitored. After differentiation under these conditions, cells were adoptively transferred into CD8-deficient mice, and lung allergic responses, including airway hyperresponsiveness to inhaled methacholine, were assessed. The effects of pharmacologic inhibitors of hypoxia-inducible factor (HIF) 1α and HIF-2α were determined, as were responses in HIF-1α-deficient OT-1 cells.

RESULTS

Under hypoxic conditioning, CD8+ TC2 cell differentiation was significantly enhanced, with increased numbers of IL-13+ T cells and increased production of IL-13 in vitro. Adoptive transfer of TC2 cells differentiated under hypoxic conditioning restored lung allergic responses in sensitized and challenged CD8-deficient recipients to a greater degree than seen in recipients of TC2 cells differentiated under normoxic conditioning. Pharmacologic inhibition of HIF-1α or genetic manipulation to reduce HIF-1α expression reduced the hypoxia-enhanced differentiation of TC2 cells, IL-13 production, and the capacity of transferred cells to restore lung allergic responses in vivo. IL-4-dependent, hypoxia-mediated increases in HIF-1α and TC2 cell differentiation were shown to be mediated through activation of Janus kinase 1/3 and GATA-3.

CONCLUSIONS

Hypoxia enhances CD8+ TC2 cell-dependent airway hyperresponsiveness and inflammation through HIF-1α activation. These findings coupled with the known insensitivity of CD8+ T cells to corticosteroids suggests that activation of the IL-4-HIF-1α-IL-13 axis might play a role in the development of steroid-refractory asthma.

The multifaceted effects of metformin on tumor microenvironment

The efficacy of metformin in treating cancer has been extensively investigated since epidemiologic studies associated this anti-diabetic drug with a lower risk of cancer incidence. Since tumors are complex systems, in which cancer cells coexist and interact with several different types of non-malignant cells, it is not surprising that anti-cancer drugs affect not only cancer cells, but also the abundance and functions of cells of the tumor microenvironment. Recent years have seen a wide collection of reports showing how metformin, as well as other complex I inhibitors, may influence cancer progression by modulating the phenotype of non-transformed cells in a tumor. In this review, we particularly focus on the effect of metformin on angiogenesis, cancer-associated fibroblasts, tumor-associated macrophages and cancer immunosuppression.

The miR-873/NDFIP1 axis promotes hepatocellular carcinoma growth and metastasis through the AKT/mTOR-mediated Warburg effect

Hepatocellular carcinoma (HCC) progression depends on cellular metabolic reprogramming as both direct and indirect consequence of oncogenic lesions. However, the underlying mechanisms are still understood poorly. Here, we report that miR-873 promotes Warburg effect in HCC cells by increasing glucose uptake, extracellular acidification rate (ECAR), lactate production, and ATP generation, and decreasing oxygen consumption rate (OCR) in HCC cells. Mechanistically, we show that miR-873 activates the key glycolytic proteins AKT/mTOR via targeting NDFIP1 which triggers metabolic shift. We further demonstrate that enhanced glycolysis is essential for the role of miR-873 to drive HCC progression. By using immunohistochemistry analysis, we show a link between the aberrant expression of miR-873, NDFIP1, and phospho-AKT in clinical HCC samples. We also found that miR-873 was up-regulated by HIF1α, a critical glycolysis-related transcription factor. However, BAY 87-2243, a HIF1α specific inhibitor, blocks miR-873 mediated tumor growth and metastasis in nude mice. Collectively, our data uncover a previously unappreciated function of miR-873 in HCC cell metabolism and tumorigenesis, suggesting that targeting miR-873/NDFIP1 axis could be a potential therapeutic strategy for the treatment of HCC patients.

BAY 87-2243 sensitizes hepatocellular carcinoma Hep3B cells to histone deacetylase inhibitors treatment via GSK-3β activation

Hepatocellular carcinoma (HCC) is associated with some of the highest cancer-associated mortality rates. Histone deacetylase (HDAC) inhibitors anti-HCC activities have been shown to promote Snail-induced metastasis. In the present study, it was shown that BAY 87-2243, a hypoxia-inducible transcription factor-1α inhibitor, could enhance the anti-HCC effects of HDAC inhibitors, including trichostatin A and vorinostat. In addition, BAY 87-2243 plus HDAC inhibitors exhibited synergistic cytotoxicity and induced significant cell death in Hep3B cells. Additionally, BAY 87-2243 combined with HDAC inhibitors-treated Hep3B cells formed fewer and smaller colonies as compared with either the control or single agent-treated cells. Furthermore, glycogen synthase kinase-3β might be involved in the enhanced cell death induced by BAY 87-2243 plus HDAC inhibitors. The present data also indicated that BAY 87-2243 combined with HDAC inhibitors could suppress the migration of Hep3B cells, and BAY 87-2243 could reverse the HDAC inhibitor-induced Snail activation in Hep3B cells. In conclusion, BAY 87-2243 combined with HDAC inhibitors might be an attractive chemotherapy strategy for HCC therapy.

Pard3 suppresses glioma invasion by regulating RhoA through atypical protein kinase C/NF-κB signaling

Partitioning defective protein 3 (Pard3) has been reported to inhibit the progression of numerous human cancer cell types. However, the role of Pard3 in glioma progression remains unclear. In this study, the expression of Pard3 was measured in human gliomas of different grades by both quantitative polymerase chain reaction and Western blotting. The effect of Pard3 on glioma progression was tested using cell counting kit‐8 assays, EdU assays, colony formation assays, cell migration, and invasion assays and tumor xenografts. The effect of Pard3 on Ras homolog family member A (RhoA) protein levels, subcellular localization, and transcriptional activity was measured by immunoblotting and immunofluorescence. Our results indicate that Pard3 functions as a tumor suppressor in gliomas and that the loss of Pard3 protein is strongly associated with a higher grade and poorer outcome. Pard3 overexpression inhibits glioma progression by upregulating RhoA protein levels. However, the level of GTP‐RhoA protein remained unchanged. Further evidence demonstrates that Pard3 regulates RhoA protein levels, subcellular localization and transcriptional activity by activating atypical protein kinase C/NF‐κB signaling. Mouse modeling experiments show that Pard3 overexpression inhibits glioma cell growth in vivo. Taken together, these findings identify RhoA as a novel target of Pard3 in gliomas and substantiate a novel regulatory role for Pard3 in glioma progression. This study reveals that Pard3 plays an inhibitory role in gliomas by regulating RhoA, which reveals a potential benefit for Pard3 activators in the prevention and therapy of gliomas.

CHCHD4 confers metabolic vulnerabilities to tumour cells through its control of the mitochondrial respiratory chain

Background

Tumour cells rely on glycolysis and mitochondrial oxidative phosphorylation (OXPHOS) to survive. Thus, mitochondrial OXPHOS has become an increasingly attractive area for therapeutic exploitation in cancer. However, mitochondria are required for intracellular oxygenation and normal physiological processes, and it remains unclear which mitochondrial molecular mechanisms might provide therapeutic benefit. Previously, we discovered that coiled-coil-helix-coiled-coil-helix domain-containing protein 4 (CHCHD4) is critical for regulating intracellular oxygenation and required for the cellular response to hypoxia (low oxygenation) in tumour cells through molecular mechanisms that we do not yet fully understand. Overexpression of CHCHD4 in human cancers correlates with increased tumour progression and poor patient survival.

Results

Here, we show that elevated CHCHD4 expression provides a proliferative and metabolic advantage to tumour cells in normoxia and hypoxia. Using stable isotope labelling with amino acids in cell culture (SILAC) and analysis of the whole mitochondrial proteome, we show that CHCHD4 dynamically affects the expression of a broad range of mitochondrial respiratory chain subunits from complex I-V, including multiple subunits of complex I (CI) required for complex assembly that are essential for cell survival. We found that loss of CHCHD4 protects tumour cells from respiratory chain inhibition at CI, while elevated CHCHD4 expression in tumour cells leads to significantly increased sensitivity to CI inhibition, in part through the production of mitochondrial reactive oxygen species (ROS).

Conclusions

Our study highlights an important role for CHCHD4 in regulating tumour cell metabolism and reveals that CHCHD4 confers metabolic vulnerabilities to tumour cells through its control of the mitochondrial respiratory chain and CI biology.

Mechanism of the natural product moracin-O derived MO-460 and its targeting protein hnRNPA2B1 on HIF-1α inhibition

Hypoxia-inducible factor-1α (HIF-1α) mediates tumor cell adaptation to hypoxic conditions and is a potentially important anticancer therapeutic target. We previously developed a method for synthesizing a benzofuran-based natural product, (R)-(-)-moracin-O, and obtained a novel potent analog, MO-460 that suppresses the accumulation of HIF-1α in Hep3B cells. However, the molecular target and underlying mechanism of action of MO-460 remained unclear. In the current study, we identified heterogeneous nuclear ribonucleoprotein A2B1 (hnRNPA2B1) as a molecular target of MO-460. MO-460 inhibits the initiation of HIF-1α translation by binding to the C-terminal glycine-rich domain of hnRNPA2B1 and inhibiting its subsequent binding to the 3’-untranslated region of HIF-1α mRNA. Moreover, MO-460 suppresses HIF-1α protein synthesis under hypoxic conditions and induces the accumulation of stress granules. The data provided here suggest that hnRNPA2B1 serves as a crucial molecular target in hypoxia-induced tumor survival and thus offer an avenue for the development of novel anticancer therapies.

A synthetic analog of a chemical found in fruit suppresses tumor growth by targeting an RNA-binding protein (hnRNPA2B1) and preventing the production of a pro-cancer regulatory factor. Nak-Kyun Soung from the Korea Research Institute of Bioscience and Biotechnology, Cheongju, South Korea, and coworkers built on their previous discovery that a compound derived from a medicinal plant metabolite can suppress the activity of hypoxia-inducible factor-1α (HIF-1α). This protein, which is involved in many aspects of cancer biology, is activated in the low-oxygen microenvironments found inside tumors. The researchers show that the compound binds to a protein that helps with the conversion of HIF-1α–encoding RNA transcripts into HIF-1α proteins. Liver cancer cells treated with the compound grew slowly and produced less HIF-1α under both normal and low-oxygen culture conditions, highlighting the potential of this anti-cancer strategy.

Targeting Mitochondria for Treatment of Chemoresistant Ovarian Cancer

Ovarian cancer is the leading cause of death from gynecologic malignancy in the Western world. This is due, in part, to the fact that despite standard treatment of surgery and platinum/paclitaxel most patients recur with ultimately chemoresistant disease. Ovarian cancer is a unique form of solid tumor that develops, metastasizes and recurs in the same space, the abdominal cavity, which becomes a unique microenvironment characterized by ascites, hypoxia and low glucose levels. It is under these conditions that cancer cells adapt and switch to mitochondrial respiration, which becomes crucial to their survival, and therefore an ideal metabolic target for chemoresistant ovarian cancer. Importantly, independent of microenvironmental factors, mitochondria spatial redistribution has been associated to both tumor metastasis and chemoresistance in ovarian cancer while specific sets of genetic mutations have been shown to cause aberrant dependence on mitochondrial pathways in the most aggressive ovarian cancer subtypes. In this review we summarize on targeting mitochondria for treatment of chemoresistant ovarian cancer and current state of understanding of the role of mitochondria respiration in ovarian cancer. We feel this is an important and timely topic given that ovarian cancer remains the deadliest of the gynecological diseases, and that the mitochondrial pathway has recently emerged as critical in sustaining solid tumor progression.

Essential roles of mitochondrial and heme function in lung cancer bioenergetics and tumorigenesis

Contrary to Warburg’s hypothesis, mitochondrial oxidative phosphorylation (OXPHOS) contributes significantly to fueling cancer cells. Several recent studies have demonstrated that radiotherapy-resistant and chemotherapy-resistant cancer cells depend on OXPHOS for survival and progression. Several cancers exhibit an increased risk in association with heme intake. Mitochondria are widely known to carry out oxidative phosphorylation. In addition, mitochondria are also involved in heme synthesis. Heme serves as a prosthetic group for several proteins that constitute the complexes of mitochondrial electron transport chain. Therefore, heme plays a pivotal role in OXPHOS and oxygen consumption. Further, lung cancer cells exhibit heme accumulation and require heme for proliferation and invasion in vitro. Abnormalities in mitochondrial biogenesis and mutations are implicated in cancer. This review delves into mitochondrial OXPHOS and lesser explored area of heme metabolism in lung cancer.

HIF-α factors as potential therapeutic targets in leukemia

INTRODUCTION

Hypoxia-inducible transcription factors have been identified as regulators of adaptive responses to hypoxia. Over the past 20 years, more than 8000 papers have described their increasingly complex role and regulation in cancer. Presently, it is recognized that hypoxia-inducible factors (HIFs) are regulated by oxygen-dependent and oxygen-independent mechanisms in cancer development; the list of their targets has increased to include more than 500 genes involved in most hallmarks of cancer. Areas covered: Most literature describes the function of HIF factors in solid tumors; however, in the past 10 years, evidence has steadily accumulated to indicate that HIFs are implicated in hematological malignancies. This review summarizes our current understanding of the function and regulation of HIF factors in hematopoiesis and leukemia. Moreover, we provide an update on pharmacological inhibitors of this pathway that have shown promising therapeutic effects in clinical trials or leukemia pre-clinical models. Expert opinion: The inhibition of the function of HIF factors may provide an interesting approach for treating leukemia. We posit that before moving into the clinic, we should (i) fully characterize the outcome of HIF inhibition in specific leukemia contexts (ii) test the possibility of combining HIF-targeting strategies with cytotoxic compounds and (iii) consider patient selection to increase therapeutic efficacy.

Warburg effect, lactate dehydrogenase, and radio/chemo-therapy efficacy

The anaerobic metabolism of glucose by cancer cells, even under well-oxygenated conditions, has been documented by Otto Warburg as early as 1927. Micro-environmental hypoxia and intracellular pathways activating the hypoxia-related gene response, shift cancer cell metabolism to anaerobic pathways. In the current review, we focus on a major enzyme involved in anaerobic transformation of pyruvate to lactate, namely lactate dehydrogenase 5 (LDH5). The value of LDH5 as a marker of prognosis of cancer patients, as a predictor of response to radiotherapy (RT) and chemotherapy and, finally, as a major target for cancer treatment and radio-sensitization is reported and discussed. Clinical, translational and experimental data supporting the uniqueness of the LDHA gene and its product LDH5 isoenzyme are summarized and future directions for a metabolic treatment of cancer are highlighted.

Papaverine and its derivatives radiosensitize solid tumors by inhibiting mitochondrial metabolism

Tumor hypoxia reduces the effectiveness of radiation therapy by limiting the biologically effective dose. An acute increase in tumor oxygenation before radiation treatment should therefore significantly improve the tumor cell kill after radiation. Efforts to increase oxygen delivery to the tumor have not shown positive clinical results. Here we show that targeting mitochondrial respiration results in a significant reduction of the tumor cells' demand for oxygen, leading to increased tumor oxygenation and radiation response. We identified an activity of the FDA-approved drug papaverine as an inhibitor of mitochondrial complex I. We also provide genetic evidence that papaverine's complex I inhibition is directly responsible for increased oxygenation and enhanced radiation response. Furthermore, we describe derivatives of papaverine that have the potential to become clinical radiosensitizers with potentially fewer side effects. Importantly, this radiosensitizing strategy will not sensitize well-oxygenated normal tissue, thereby increasing the therapeutic index of radiotherapy.

Preclinical Efficacy of the Novel Monocarboxylate Transporter 1 Inhibitor BAY-8002 and Associated Markers of Resistance

The lactate transporter SLC16A1/monocarboxylate transporter 1 (MCT1) plays a central role in tumor cell energy homeostasis. In a cell-based screen, we identified a novel class of MCT1 inhibitors, including BAY-8002, which potently suppress bidirectional lactate transport. We investigated the antiproliferative activity of BAY-8002 in a panel of 246 cancer cell lines and show that hematopoietic tumor cells, in particular diffuse large B-cell lymphoma cell lines, and subsets of solid tumor models are particularly sensitive to MCT1 inhibition. Associated markers of sensitivity were, among others, lack of MCT4 expression, low pleckstrin homology like domain family A member 2, and high pellino E3 ubiquitin protein ligase 1 expression. The antitumor effect of MCT1 inhibition was less pronounced on tumor xenografts, with tumor stasis being the maximal response. BAY-8002 significantly increased intratumor lactate levels and transiently modulated pyruvate levels. In order to address potential acquired resistance mechanisms to MCT1 inhibition, we generated MCT1 inhibitor-resistant cell lines and show that resistance can occur by upregulation of MCT4 even in the presence of sufficient oxygen, as well as by shifting energy generation toward oxidative phosphorylation. These findings provide insight into novel aspects of tumor response to MCT1 modulation and offer further rationale for patient selection in the clinical development of MCT1 inhibitors. Mol Cancer Ther; 17(11); 2285-96. ©2018 AACR.

Targeting energy metabolism to eliminate cancer cells

Adaptive metabolic responses toward a low oxygen environment are essential to maintain rapid proliferation and are relevant for tumorigenesis. Reprogramming of core metabolism in tumors confers a selective growth advantage such as the ability to evade apoptosis and/or enhance cell proliferation and promotes tumor growth and progression. One of the mechanisms that contributes to tumor growth is the impairment of cancer cell metabolism. In this review, we outline the small-molecule inhibitors identified over the past decade in targeting cancer cell metabolism and the usage of some of these molecules in clinical trials.

An inhibitor of oxidative phosphorylation exploits cancer vulnerability

Metabolic reprograming is an emerging hallmark of tumor biology and an actively pursued opportunity in discovery of oncology drugs. Extensive efforts have focused on therapeutic targeting of glycolysis, whereas drugging mitochondrial oxidative phosphorylation (OXPHOS) has remained largely unexplored, partly owing to an incomplete understanding of tumor contexts in which OXPHOS is essential. Here, we report the discovery of IACS-010759, a clinical-grade small-molecule inhibitor of complex I of the mitochondrial electron transport chain. Treatment with IACS-010759 robustly inhibited proliferation and induced apoptosis in models of brain cancer and acute myeloid leukemia (AML) reliant on OXPHOS, likely owing to a combination of energy depletion and reduced aspartate production that leads to impaired nucleotide biosynthesis. In models of brain cancer and AML, tumor growth was potently inhibited in vivo following IACS-010759 treatment at well-tolerated doses. IACS-010759 is currently being evaluated in phase 1 clinical trials in relapsed/refractory AML and solid tumors.

Oxidative Phosphorylation as an Emerging Target in Cancer Therapy

Cancer cells have upregulated glycolysis compared with normal cells, which has led many to the assumption that oxidative phosphorylation (OXPHOS) is downregulated in all cancers. However, recent studies have shown that OXPHOS can be also upregulated in certain cancers, including leukemias, lymphomas, pancreatic ductal adenocarcinoma, high OXPHOS subtype melanoma, and endometrial carcinoma, and that this can occur even in the face of active glycolysis. OXPHOS inhibitors could therefore be used to target cancer subtypes in which OXPHOS is upregulated and to alleviate therapeutically adverse tumor hypoxia. Several drugs including metformin, atovaquone, and arsenic trioxide are used clinically for non-oncologic indications, but emerging data demonstrate their potential use as OXPHOS inhibitors. We highlight novel applications of OXPHOS inhibitors with a suitable therapeutic index to target cancer cell metabolism. Clin Cancer Res; 24(11); 2482-90. ©2018 AACR.

The Oncojanus Paradigm of Respiratory Complex I

Mitochondrial respiratory function is now recognized as a pivotal player in all the aspects of cancer biology, from tumorigenesis to aggressiveness and chemotherapy resistance. Among the enzymes that compose the respiratory chain, by contributing to energy production, redox equilibrium and oxidative stress, complex I assumes a central role. Complex I defects may arise from mutations in mitochondrial or nuclear DNA, in both structural genes or assembly factors, from alteration of the expression levels of its subunits, or from drug exposure. Since cancer cells have a high-energy demand and require macromolecules for proliferation, it is not surprising that severe complex I defects, caused either by mutations or treatment with specific inhibitors, prevent tumor progression, while contributing to resistance to certain chemotherapeutic agents. On the other hand, enhanced oxidative stress due to mild complex I dysfunction drives an opposite phenotype, as it stimulates cancer cell proliferation and invasiveness. We here review the current knowledge on the contribution of respiratory complex I to cancer biology, highlighting the double-edged role of this metabolic enzyme in tumor progression, metastasis formation, and response to chemotherapy.

Discovery of the novel autophagy inhibitor aumitin that targets mitochondrial complex I

Macroautophagy is a conserved eukaryotic process for degradation of cellular components in response to lack of nutrients. It is involved in the development of diseases, notably cancer and neurological disorders including Parkinson's disease. Small molecule autophagy modulators have proven to be valuable tools to dissect and interrogate this crucial metabolic pathway and are in high demand. Phenotypic screening for autophagy inhibitors led to the discovery of the novel autophagy inhibitor aumitin. Target identification and confirmation revealed that aumitin inhibits mitochondrial respiration by targeting complex I. We show that inhibition of autophagy by impairment of mitochondrial respiration is general for several mitochondrial inhibitors that target different mitochondrial complexes. Our findings highlight the importance of mitochondrial respiration for autophagy regulation.

Inhibition of oxidative phosphorylation suppresses the development of osimertinib resistance in a preclinical model of EGFR-driven lung adenocarcinoma

Metabolic plasticity is an emerging hallmark of cancer, and increased glycolysis is often observed in transformed cells. Small molecule inhibitors that target driver oncogenes can potentially inhibit the glycolytic pathway. Osimertinib (AZD9291) is a novel EGFR tyrosine kinase inhibitor (TKI) that is potent and selective for sensitising (EGFRm) and T790M resistance mutations. Clinical studies have shown osimertinib to be efficacious in patients with EGFRm/ T790M advanced NSCLC who have progressed after EGFR-TKI treatment. However experience with targeted therapies suggests that acquired resistance may emerge. Thus there is a need to characterize resistance mechanisms and to devise ways to prevent, delay or overcome osimertinib resistance. We show here that osimertinib suppresses glycolysis in parental EGFR-mutant lung adenocarcinoma lines, but has not in osimertinib-resistant cell lines. Critically, we show osimertinib treatment induces a strict dependence on mitochondrial oxidative phosphorylation (OxPhos), as OxPhos inhibitors significantly delay the long-term development of osimertinib resistance in osimertinib-sensitive lines. Accordingly, growth conditions which promote a less glycolytic phenotype confer a degree of osimertinib resistance. Our data support a model in which the combination of osimertinib and OxPhos inhibitors can delay or prevent resistance in osimertinib-naïve tumour cells, and represents a novel strategy that warrants further pre-clinical investigation.

Hypoxia regulates TRAIL sensitivity of colorectal cancer cells through mitochondrial autophagy

The capacity of tumor necrosis factor-related apoptosis-inducing ligand (TRAIL) to selectively induce cell death in malignant cells triggered numerous attempts for therapeutic exploitation. In clinical trials, however, TRAIL did not live up to the expectations, as tumors exhibit high rates of TRAIL resistance in vivo. Response to anti-cancer therapy is determined not only by cancer cell intrinsic factors (e.g. oncogenic mutations), but also modulated by extrinsic factors such as the hypoxic tumor microenvironment.Here, we address the effect of hypoxia on pro-apoptotic TRAIL signaling in colorectal cancer cells. We show that oxygen levels modulate susceptibility to TRAIL-induced cell death, which is severely impaired under hypoxia (0.5% O2). Mechanistically, this is attributable to hypoxia-induced mitochondrial autophagy. Loss of mitochondria under hypoxia restricts the availability of mitochondria-derived pro-apoptotic molecules such as second mitochondria-derived activator of caspase (SMAC), thereby disrupting amplification of the apoptotic signal emanating from the TRAIL death receptors and efficiently blocking cell death in type-II cells. Moreover, we identify strategies to overcome TRAIL resistance in low oxygen environments. Counteracting hypoxia-induced loss of endogenous SMAC by exogenous substitution of SMAC mimetics fully restores TRAIL sensitivity in colorectal cancer cells. Alternatively, enforcing a mitochondria-independent type-I mode of cell death by targeting the type-II phenotype gatekeeper X-linked inhibitor of apoptosis protein (XIAP) is equally effective.Together, our results indicate that tumor hypoxia impairs TRAIL efficacy but this limitation can be overcome by combining TRAIL with SMAC mimetics or XIAP-targeting drugs. Our findings may help to exploit the potential of TRAIL in cancer therapy.

MicroRNA-421 regulated by HIF-1α promotes metastasis, inhibits apoptosis, and induces cisplatin resistance by targeting E-cadherin and caspase-3 in gastric cancer

Hypoxia and dysregulation of microRNAs (miRNAs) have been identified as crucial factors in carcinogenesis. However, the potential mechanisms of HIF-1α and miR-421 in gastric cancer have not been well elucidated. In this study, we found that miR-421 was up-regulated by HIF-1α. Overexpression of miR-421 promoted metastasis, inhibited apoptosis, and induced cisplatin resistance in gastric cancer in vivo and in vitro. E-cadherin and caspase-3 were identified as targets of miR-421. Besides, relative mRNA expression of miR-421 was significantly increased in gastric cancer tumor tissues compared with non-tumor tissues in a cohort of gastric cancer specimens (n=107). The expression of miR-421 was higher in advanced gastric cancers compared with localized ones. Moreover, Kaplan–Meier analysis illustrated that those patients with low levels of miR-421 had a significant longer overall survival (p = 0.006) and time to relapse (p = 0.007). Therefore, miR-421 could serve as an important prognostic marker and a potential molecular target for therapy in gastric cancer.

Non-Canonical Mechanisms Regulating Hypoxia-Inducible Factor 1 Alpha in Cancer

Hypoxia-inducible factor 1 alpha (HIF-1α) orchestrates cellular adaptation to low oxygen and nutrient-deprived environment and drives progression to malignancy in human solid cancers. Its canonical regulation involves prolyl hydroxylases (PHDs), which in normoxia induce degradation, whereas in hypoxia allow stabilization of HIF-1α. However, in certain circumstances, HIF-1α regulation goes beyond the actual external oxygen levels and involves PHD-independent mechanisms. Here, we gather and discuss the evidence on the non-canonical HIF-1α regulation, focusing in particular on the consequences of mitochondrial respiratory complexes damage on stabilization of this pleiotropic transcription factor.

Targeting the long noncoding RNA MALAT1 blocks the pro-angiogenic effects of osteosarcoma and suppresses tumour growth

Osteosarcoma (OS), the commonest primary malignant tumour originating from bone, affects a substantial number of people, mostly during adolescent growth, and leads to a very poor prognosis as a result of the high rate of early metastases. Consequently, there is urgent demand for a novel treatment for this disease. There are growing concerns focused on OS-induced pro-angiogenic effects, but to date, the mechanism of OS-induced pro-angiogenesis is still insufficiently well-understood. Long noncoding RNAs (lncRNAs) have attracted increasing interest due to their strong correlation with a variety of diseases and their powerful capacity for epigenetic regulation. Recently, metastasis-associated lung adenocarcinoma transcript 1 (MALAT1), a lncRNA, has been discovered to be closely related to OS progression and hypoxia responses which are associated with angiogenesis. In this study, we confirm that MALAT1 induces pro-angiogenic effects, and demonstrate that the underlying mechanism involves a MALAT1/mechanistic target of rapamycin (mTOR)/hypoxia inducible factor-1α (HIF-1α) loop. With the help of chemically-modified small interfering RNAs targeting MALAT1 (siMALAT1), we confirm that siMALAT could provide a potential strategy to block the abnormally active OS-induced pro-angiogenic effect, and ultimately successfully suppress progression of OS tumours.

Mitochondrial deficiency impairs hypoxic induction of HIF-1 transcriptional activity and retards tumor growth

Mitochondria can be involved in regulating cellular stress response to hypoxia and tumor growth, but little is known about that mechanistic relationship. Here, we show that mitochondrial deficiency severely retards tumor xenograft growth with impairing hypoxic induction of HIF-1 transcriptional activity. Using mtDNA-deficient ρ⁰ cells, we found that HIF-1 pathway activation was comparable in slow-growing ρ⁰ xenografts and rapid-growing parental xenografts. Interestingly, we found that ex vivo ρ⁰ cells derived from ρ⁰ xenografts exhibited slightly increased HIF-1α expression and modest HIF-1 pathway activation regardless of oxygen concentration. Surprisingly, ρ⁰ cells, as well as parental cells treated with oxidative phosphorylation inhibitors, were unable to boost HIF-1 transcriptional activity during hypoxia, although HIF-1α protein levels were ordinarily increased in these cells under hypoxic conditions. These findings indicate that mitochondrial deficiency causes loss of hypoxia-induced HIF-1 transcriptional activity and thereby might lead to a constitutive HIF-1 pathway activation as a cellular adaptation mechanism in tumor microenvironment.

Inhibition of hypoxic response decreases stemness and reduces tumorigenic signaling due to impaired assembly of HIF1 transcription complex in pancreatic cancer

Pancreatic tumors are renowned for their extremely hypoxic centers, resulting in upregulation of a number of hypoxia mediated signaling pathways including cell proliferation, metabolism and cell survival. Previous studies from our laboratory have shown that Minnelide, a water-soluble pro-drug of triptolide (anti-cancer compound), decreases viability of cancer cells in vitro as well as in vivo. However, its mechanism of action remain elusive. In the current study we evaluated the effect of Minnelide, on hypoxia mediated oncogenic signaling as well as stemness in pancreatic cancer. Minnelide has just completed Phase 1 trial against GI cancers and is currently awaiting Phase 2 trials. Our results showed that upon treatment with triptolide, HIF-1α protein accumulated in pancreatic cancer cells even though hypoxic response was decreased in them. Our studies showed even though HIF-1α is accumulated in the treated cells, there was no decrease in HIF-1 binding to hypoxia response elements. However, the HIF-1 transcriptional activity was significantly reduced owing to depletion of co-activator p300 upon treatment with triptolide. Further, treatment with triptolide resulted in a decreased activity of Sp1 and NF-kB the two major oncogenic signaling pathway in pancreatic cancer along with a decreased tumor initiating cell (TIC) population in pancreatic tumor.

The novel hypoxia-inducible factor-1α inhibitor IDF-11774 regulates cancer metabolism, thereby suppressing tumor growth

HIF-1 is associated with poor prognoses and therapeutic resistance in cancer patients. We previously developed a novel hypoxia-inducible factor (HIF)-1 inhibitor, IDF-11774, a clinical candidate for cancer therapy. We also reported that IDF-1174 inhibited HSP70 chaperone activity and suppressed accumulation of HIF-1α. In this study, IDF-11774 inhibited the accumulation of HIF-1α in vitro and in vivo in colorectal carcinoma HCT116 cells under hypoxic conditions. Moreover, IDF-11774 treatment suppressed angiogenesis of cancer cells by reducing the expression of HIF-1 target genes, reduced glucose uptake, thereby sensitizing cells to growth under low glucose conditions, and decreased the extracellular acidification rate (ECAR) and oxygen consumption rate of cancer cells. Metabolic profiling of IDF-11774-treated cells revealed low levels of NAD⁺, NADP⁺, and lactate, as well as of intermediates in glycolysis and the tricarboxylic acid cycle. In addition, we observed elevated AMP and diminished ATP levels, resulting in a high AMP/ATP ratio. The level of AMP-activated protein kinase phosphorylation also increased, leading to inhibition of mTOR signaling in treated cells. In vivo xenograft assays demonstrated that IDF-11774 exhibited substantial anticancer efficacy in mouse models containing KRAS, PTEN, or VHL mutations, which often occur in malignant cancers. Collectively, our data indicate that IDF-11774 suppressed hypoxia-induced HIF-1α accumulation and repressed tumor growth by targeting energy production-related cancer metabolism.

2-Deoxy-d-Glucose Treatment Decreases Anti-inflammatory M2 Macrophage Polarization in Mice with Tumor and Allergic Airway Inflammation

As important effector cells in inflammation, macrophages can be functionally polarized into either inflammatory M1 or alternatively activated anti-inflammatory M2 phenotype depending on surroundings. The key roles of glycolysis in M1 macrophage polarization have been well defined. However, the relationship between glycolysis and M2 polarized macrophages is still poorly understood. Here, we report that 2-deoxy-d-glucose (2-DG), an inhibitor of the glycolytic pathway, markedly inhibited the expressions of Arg, Ym-1, Fizz1, and CD206 molecules, the hall-markers for M2 macrophages, during macrophages were stimulated with interleukin 4. The impacted M2 macrophage polarization by 2-DG is not due to cell death but caused by the impaired cellular glycolysis. Molecular mechanism studies indicate that the effect of 2-DG on M2 polarized macrophages relies on AMPK-Hif-1α-dependent pathways. Importantly, 2-DG treatment significantly decreases anti-inflammatory M2 macrophage polarization and prevents disease progression in a series of mouse models with chitin administration, tumor, and allergic airway inflammation. Thus, the identification of the master role of glycolysis in M2 macrophage polarization offers potential molecular targets for M2 macrophages-mediated diseases. 2-DG therapy may have beneficial effects in patients with tumors or allergic airway inflammation by its negative regulation on M2 macrophage polarization.

Athymic nude mice as an experimental model for cancer treatment

Athymic nude mice, a murine strain bearing spontaneous deletion in the Foxn1 gene that causes deteriorated or absent thymus (which results in inhibited immune system with reduction of number of T cells), represent a widely used model in cancer research having long lasting history as a tool for preclinical testing of drugs. The review describes three models of athymic mice that utilize cancer cell lines to induce tumors. In addition, various methods that can be applied in order to evaluate activity of anticancer agents in these models are shown and discussed. Although each model has certain disadvantages, they are still considered as inevitable instruments in many fields of cancer research, particularly in finding new drugs that would more effectively combat the cancer disease or enhance the use of current chemotherapy. Finally, the review summarizes strengths and weaknesses as well as future perspectives of the athymic nude mice model in cancer research.

Development of Inhibitors Targeting Hypoxia-Inducible Factor 1 and 2 for Cancer Therapy

Hypoxia is frequently observed in solid tumors and also one of the major obstacles for effective cancer therapies. Cancer cells take advantage of their ability to adapt hypoxia to initiate a special transcriptional program that renders them more aggressive biological behaviors. Hypoxia-inducible factors (HIFs) are the key factors that control hypoxia-inducible pathways by regulating the expression of a vast array of genes involved in cancer progression and treatment resistance. HIFs, mainly HIF-1 and -2, have become potential targets for developing novel cancer therapeutics. This article reviews the updated information in tumor HIF pathways, particularly recent advances in the development of HIF inhibitors. These inhibitors interfere with mRNA expression, protein synthesis, protein degradation and dimerization, DNA binding and transcriptional activity of HIF-1 and -2, or both. Despite efforts in the past two decades, no agents directly inhibiting HIFs have been approved for treating cancer patients. By analyzing results of the published reports, we put the perspectives at the end of the article. The therapeutic efficacy of HIF inhibitors may be improved if more efforts are devoted on developing agents that are able to simultaneously target HIF-1 and -2, increasing the penetrating capacity of HIF inhibitors, and selecting suitable patient subpopulations for clinical trials.

Inhibition of monocarboxyate transporter 1 by AZD3965 as a novel therapeutic approach for diffuse large B-cell lymphoma and Burkitt lymphoma

Inhibition of monocarboxylate transporter 1 has been proposed as a therapeutic approach to perturb lactate shuttling in tumor cells that lack monocarboxylate transporter 4. We examined the monocarboxylate transporter 1 inhibitor AZD3965, currently in phase I clinical studies, as a potential therapy for diffuse large B-cell lymphoma and Burkitt lymphoma. Whilst extensive monocarboxylate transporter 1 protein was found in 120 diffuse large B-cell lymphoma and 10 Burkitt lymphoma patients’ tumors, monocarboxylate transporter 4 protein expression was undetectable in 73% of the diffuse large B-cell lymphoma samples and undetectable or negligible in each Burkitt lymphoma sample. AZD3965 treatment led to a rapid accumulation of intracellular lactate in a panel of lymphoma cell lines with low monocarboxylate transporter 4 protein expression and potently inhibited their proliferation. Metabolic changes induced by AZD3965 in lymphoma cells were consistent with a feedback inhibition of glycolysis. A profound cytostatic response was also observed in vivo: daily oral AZD3965 treatment for 24 days inhibited CA46 Burkitt lymphoma growth by 99%. Continuous exposure of CA46 cells to AZD3965 for 7 weeks in vitro resulted in a greater dependency upon oxidative phosphorylation. Combining AZD3965 with an inhibitor of mitochondrial complex I (central to oxidative phosphorylation) induced significant lymphoma cell death in vitro and reduced CA46 disease burden in vivo. These data support clinical examination of AZD3965 in Burkitt lymphoma and diffuse large B-cell lymphoma patients with low tumor monocarboxylate transporter 4 expression and highlight the potential of combination strategies to optimally target the metabolic phenotype of tumors.

Mechanistic Investigations of the Mitochondrial Complex I Inhibitor Rotenone in the Context of Pharmacological and Safety Evaluation

Inhibitors of the mitochondrial respiratory chain complex I are suggested to exert anti-tumor activity on those tumors relying on oxidative metabolism and are therefore of interest to oncology research. Nevertheless, the safety profile of these inhibitors should be thoroughly assessed. Rotenone, a proven complex I inhibitor, has shown anti-carcinogenic activity in several studies. In this context rotenone was used in this study as a tool compound with the aim to identify suitable biomarker candidates and provide enhanced mechanistic insights into the molecular and cellular effects of complex I inhibitors. Rats were treated with 400 ppm rotenone daily for 1, 3 or 14 consecutive days followed by necropsy. Classical clinical endpoints, including hematology, clinical chemistry and histopathology with supporting investigations (FACS-analysis, enzymatic activity assays) were examined as well as gene expression analysis. Through these investigations, we identified liver, bone marrow and bone as target organs amongst approx. 40 organs evaluated at least histopathologically. Our results suggest blood analysis, bone marrow parameters, assessment of lactate in serum and glycogen in liver, and especially gene expression analysis in liver as useful parameters for an experimental model to help to characterize the profile of complex I inhibitors with respect to a tolerable risk-benefit balance.

Functional inhibition of acid sphingomyelinase by Fluphenazine triggers hypoxia-specific tumor cell death

Owing to lagging or insufficient neo-angiogenesis, hypoxia is a feature of most solid tumors. Hypoxic tumor regions contribute to resistance against antiproliferative chemotherapeutics, radiotherapy and immunotherapy. Targeting cells in hypoxic tumor areas is therefore an important strategy for cancer treatment. Most approaches for targeting hypoxic cells focus on the inhibition of hypoxia adaption pathways but only a limited number of compounds with the potential to specifically target hypoxic tumor regions have been identified. By using tumor spheroids in hypoxic conditions as screening system, we identified a set of compounds, including the phenothiazine antipsychotic Fluphenazine, as hits with novel mode of action. Fluphenazine functionally inhibits acid sphingomyelinase and causes cellular sphingomyelin accumulation, which induces cancer cell death specifically in hypoxic tumor spheroids. Moreover, we found that functional inhibition of acid sphingomyelinase leads to overactivation of hypoxia stress-response pathways and that hypoxia-specific cell death is mediated by the stress-responsive transcription factor ATF4. Taken together, the here presented data suggest a novel, yet unexplored mechanism in which induction of sphingolipid stress leads to the overactivation of hypoxia stress-response pathways and thereby promotes their pro-apoptotic tumor-suppressor functions to specifically kill cells in hypoxic tumor areas.

Mitochondrial complex I inhibition triggers a mitophagy-dependent ROS increase leading to necroptosis and ferroptosis in melanoma cells

Inhibition of complex I (CI) of the mitochondrial respiratory chain by BAY 87-2243 (‘BAY') triggers death of BRAF^V600E melanoma cell lines and inhibits in vivo tumor growth. Here we studied the mechanism by which this inhibition induces melanoma cell death. BAY treatment depolarized the mitochondrial membrane potential (Δψ), increased cellular ROS levels, stimulated lipid peroxidation and reduced glutathione levels. These effects were paralleled by increased opening of the mitochondrial permeability transition pore (mPTP) and stimulation of autophagosome formation and mitophagy. BAY-induced cell death was not due to glucose shortage and inhibited by the antioxidant α-tocopherol and the mPTP inhibitor cyclosporin A. Tumor necrosis factor receptor-associated protein 1 (TRAP1) overexpression in BAY-treated cells lowered ROS levels and inhibited mPTP opening and cell death, whereas the latter was potentiated by TRAP1 knockdown. Knockdown of autophagy-related 5 (ATG5) inhibited the BAY-stimulated autophagosome formation, cellular ROS increase and cell death. Knockdown of phosphatase and tensin homolog-induced putative kinase 1 (PINK1) inhibited the BAY-induced Δψ depolarization, mitophagy stimulation, ROS increase and cell death. Dynamin-related protein 1 (Drp1) knockdown induced mitochondrial filamentation and inhibited BAY-induced cell death. The latter was insensitive to the pancaspase inhibitor z-VAD-FMK, but reduced by necroptosis inhibitors (necrostatin-1, necrostatin-1s)) and knockdown of key necroptosis proteins (receptor-interacting serine/threonine-protein kinase 1 (RIPK1) and mixed lineage kinase domain-like (MLKL)). BAY-induced cell death was also reduced by the ferroptosis inhibitor ferrostatin-1 and overexpression of the ferroptosis-inhibiting protein glutathione peroxidase 4 (GPX4). This overexpression also inhibited the BAY-induced ROS increase and lipid peroxidation. Conversely, GPX4 knockdown potentiated BAY-induced cell death. We propose a chain of events in which: (i) CI inhibition induces mPTP opening and Δψ depolarization, that (ii) stimulate autophagosome formation, mitophagy and an associated ROS increase, leading to (iii) activation of combined necroptotic/ferroptotic cell death.

Clinically Evaluated Cancer Drugs Inhibiting Redox Signaling

SIGNIFICANCE

There are a number of redox-active anticancer agents currently in development based on the premise that altered redox homeostasis is necessary for cancer cell's survival. Recent Advances: This review focuses on the relatively few agents that target cellular redox homeostasis to have entered clinical trial as anticancer drugs.

CRITICAL ISSUES

The success rate of redox anticancer drugs has been disappointing compared to other classes of anticancer agents. This is due, in part, to our incomplete understanding of the functions of the redox targets in normal and cancer tissues, leading to off-target toxicities and low therapeutic indexes of the drugs. The field also lags behind in the use biomarkers and other means to select patients who are most likely to respond to redox-targeted therapy.

FUTURE DIRECTIONS

If we wish to derive clinical benefit from agents that attack redox targets, then the future will require a more sophisticated understanding of the role of redox targets in cancer and the increased application of personalized medicine principles for their use. Antioxid. Redox Signal. 26, 262-273.