Hypoxia-mediated drug resistance: novel insights on the functional interaction of HIFs and cell death pathways

Diminished toxicity of C-1748, 4-methyl-9-hydroxyethylamino-1-nitroacridine, compared with its demethyl analog, C-857, corresponds to its resistance to metabolism in HepG2 cells

The narrow "therapeutic window" of anti-tumour therapy may be the result of drug metabolism leading to the activation or detoxification of antitumour agents. The aim of this work is to examine (i) whether the diminished toxicity of a potent antitumour drug, C-1748, 9-(2'-hydroxyethylamino)-4-methyl-1-nitroacridine, compared with its 4-demethyl analogue, C-857, results from the differences between the metabolic pathways for the two compounds and (ii) the impact of reducing and/or hypoxic conditions on studied metabolism. We investigated the metabolites of C-1748 and C-857 formed in rat and human liver microsomes, with human P450 reductase (POR) and in HepG2 cells under normoxia and hypoxia. The elimination rate of C-1748 from POR knockout mice (HRN) was also evaluated. Three products, 1-amino-9-hydroxyethylaminoacridine, 1-aminoacridinone and a compound with an additional 6-membered ring, were identified for C-1748 and C-857 in all studied metabolic systems. The new metabolite was found in HepG2 cells. We showed that metabolic rate and the reactivity of metabolites of C-1748 were considerably lower than those of C-857, in all investigated metabolic models. Compared with metabolism under normoxia, cellular metabolism under hypoxia led to higher levels of 1-aminoacridine and aza-acridine derivatives of both compounds and of the 6-membered ring metabolite of C-1748. In conclusion, the crucial role of hypoxic conditions and the direct involvement of POR in the metabolism of both compounds were demonstrated. Compared with C-857, the low reactivity of C-1748 and the stability of its metabolites are postulated to contribute significantly to the diminished toxicity of this compound observed in animals.

HIF-1α induced by β-elemene protects human osteosarcoma cells from undergoing apoptosis

BACKGROUND

β-Elemene, isolated from more than 50 Chinese herbs and plants, has shown promising anticancer effects against a broad spectrum of tumors, such as lung, breast, prostate, cervical, colon and ovarian carcinomas (Wang et al. in Cell Mol Life Sci 62:881-893, 2005; Li et al. in Cell Mol Life Sci 62:894-904, 2005; J Pharm Pharmacol 62(8):1018-1027, 2010). But it has not reported in osteosarcoma cells. The aim of the present study is to investigate the antitumor effect of β-elemene on human osteosarcoma cancer cells and the molecular mechanism involved.

RESULTS

β-Elemene inhibited the viability of human osteosarcoma cells in a dose-time-dependent manner. The suppression of cell viability was due to the induction of apoptosis. Our study also found that β-elemene treatment upregulated HIF-1α protein, which partially inhibits apoptosis. Knockdown of HIF-1α with small interfering RNA or co-treatment with the HIF-1α inhibitor YC-1 significantly enhanced the antitumor effects of β-elemene.

CONCLUSIONS

Our study first found that β-elemene could increase the expression of HIF-1α through ROS and PI3K/Akt/mTor signaling pathway. And HIF-1α partially prevents human osteosarcoma cells from undergoing apoptosis. The anticancer effects of β-elemene was weakened by HIF-1α. So, we recognize that a combination of β-elemene with HIF-1α inhibitor might be a useful therapeutic option for osteosarcoma.

The role of hypoxia-inducible factor-1α and -2α in androgen insensitive prostate cancer cells

OBJECTIVES

The aim of this study was to investigate the effects of induction and knocking down of hypoxia-inducible factor (HIF)-1α and/or -2α on tumor biology in androgen insensitive prostate cancer cell lines.

MATERIALS AND METHODS

The induction patterns of HIF-1α and -2α after treatment with ZnSO4 were evaluated in PC3 and DU145 cells. Both cell lines were transfected with siRNA targeted against HIF-1α and/or -2α, and the expression patterns of these 2 HIF isoforms were examined. We next performed cell counting Kit-8 (CCK-8) assays and matrigel invasion assays. Potential additive effects of HIF blockade to chemotherapy (docetaxel) or target agents (sunitinib and sorafenib) were examined. In addition, gene expression changes were determined in ZnSO4-treated DU145 cells using Western blotting.

RESULTS

ZnSO4 affected the expression of HIF in a dose-dependent manner. HIF expression was increased within the first 3 hours but then decreased. Cells in which HIF-1α and/or -2α had been knocked down using siRNA showed decreased cell viability. Invasion abilities were increased by ZnSO4 treatment in both cell lines overexpressing HIF. However, invasion potencies were decreased in response to treatment with HIF siRNAs. Blocking HIF prominently augmented the antitumor effects of target agents. The underlying mechanism could be associated with p21, cMET, IGF-1, and GLUT-1.

CONCLUSIONS

Our results demonstrate that HIF-1α and -2α are important for cell proliferation and invasion ability in prostate cancer. Together, our results indicate that combinations of target agents with HIF knockdown may represent a promising strategy for the treatment of prostate cancer.

Microtissue size and hypoxia in HTS with 3D cultures

The three microenvironmental factors that characterize 3D cultures include: first, chemical and/or biochemical composition, second, spatial and temporal dimensions, and third, force and/or substrate physical properties. Although these factors have been studied individually, their interdependence and synergistic interactions have not been well appreciated. We make this case by illustrating how microtissue size (spatial) and hypoxia (chemical) can be used in the formation of physiologically more relevant constructs (or not) for cell-based high-throughput screening (HTS) in drug discovery. We further show how transcriptomic and/or proteomic results from heterogeneously sized microtissues and scaffold architectures that deliberately control hypoxia can misrepresent and represent in vivo conditions, respectively. We offer guidance, depending on HTS objectives, for rational 3D culture platform choice for better emulation of in vivo conditions.

Skin mild hypoxia enhances killing of UVB-damaged keratinocytes through reactive oxygen species-mediated apoptosis requiring Noxa and Bim

The naturally occurring skin hypoxia has emerged as a crucial host factor of the epidermal microenvironment. We wanted to systematically investigate how reduced oxygen availability of the epidermis modulates the response of keratinocytes and melanocytes to noxious ultraviolet B radiation (UVB). We report that the exposure of normal human keratinocytes (NHKs) or melanocytes (NHEMs) to mild hypoxia drastically impacts cell death responses following UVB irradiation. The hypoxic microenvironment favors survival and reduces apoptosis of UVB-irradiated NHEMs and their malignant counterparts (melanoma cells). In contrast, NHKs, but not the transformed keratinocytes, under hypoxic conditions display increased levels of reactive oxygen species (ROS) and are significantly sensitized to UVB-mediated apoptosis as compared to NHKs treated under normoxic conditions. Prolonged exposure of UVB-treated NHKs to hypoxia triggers a sustained and reactive oxygen species-dependent activation of the stress kinases p38(MAPK) and JNKs, which in turn, engage the activation of Noxa and Bim proapoptotic proteins. Combined silencing of Noxa and Bim significantly inhibits UVB-mediated apoptosis under hypoxic conditions, demonstrating that hypoxia results in an amplification of the intrinsic apoptotic pathway. Physiologically occurring skin hypoxia, by facilitating the specific removal of UVB-damaged keratinocytes, may represent a decisive host factor impeding important steps of the photocarcinogenesis process.

Hypoxia-inducible factors: mediators of cancer progression and targets for cancer therapy

Hypoxia-inducible factors (HIFs) mediate adaptive physiological responses to hypoxia. In human cancers that are accessible for O(2) electrode measurements, intratumoral hypoxia is common and severe hypoxia is associated with increased risk of mortality. HIF activity in regions of intratumoral hypoxia mediates angiogenesis, epithelial-mesenchymal transition, stem-cell maintenance, invasion, metastasis, and resistance to radiation therapy and chemotherapy. A growing number of drugs have been identified that inhibit HIF activity by a variety of molecular mechanisms. Because many of these drugs are already FDA-approved for other indications, clinical trials can (and should) be initiated to test the hypothesis that incorporation of HIF inhibitors into current standard-of-care therapy will increase the survival of cancer patients.

The PIM kinases in hematological cancers

The PIM genes represent a family of proto-oncogenes that encode three different serine/threonine protein kinases (PIM1, PIM2 and PIM3) with essential roles in the regulation of signal transduction cascades, which promote cell survival, proliferation and drug resistance. PIM kinases are overexpressed in several hematopoietic tumors and support in vitro and in vivo malignant cell growth and survival, through cell cycle regulation and inhibition of apoptosis. PIM kinases do not have an identified regulatory domain, which means that these proteins are constitutively active once transcribed. They appear to be critical downstream effectors of important oncoproteins and, when overexpressed, can mediate drug resistance to available agents, such as rapamycin. Recent crystallography studies reveal that, unlike other kinases, they possess a hinge region, which creates a unique binding pocket for ATP, offering a target for an increasing number of potent small-molecule PIM kinase inhibitors. Preclinical studies in models of various hematologic cancers indicate that these novel agents show promising activity and some of them are currently being evaluated in a clinical setting. In this review, we profile the PIM kinases as targets for therapeutics in hematologic malignancies.

Targeting DNA damage and repair: embracing the pharmacological era for successful cancer therapy

DNA is under constant assault from genotoxic agents which creates different kinds of DNA damage. The precise replication of the genome and the continuous surveillance of its integrity are critical for survival and the avoidance of carcinogenesis. Cells have evolved an arsenal of repair pathways and cell cycle checkpoints to detect and repair DNA damage. When repair fails, typically cell cycle progression is halted and apoptosis is initiated. Here, we review the different sources and types of DNA damage including DNA replication stress and oxidative stress, the repair pathways that cells utilize to repair damaged DNA, and discuss their biological significance, especially with reference to cancer induction and cancer therapy. We also describe the main methodologies currently used for the detection of DNA damage with their strengths and limitations. We conclude with an outline as to how this information can be used to identify novel pharmacological targets for DNA repair pathways or enhancers of DNA damage to develop improved treatment strategies that will benefit cancer patients.

Autophagy as a mediator of chemotherapy-induced cell death in cancer

Since the 1940s, chemotherapy has been the treatment of choice for metastatic disease. Chemotherapeutic agents target proliferating cells, inducing cell death. For most of the history of chemotherapy, apoptosis was thought to be the only mechanism of drug-induced cell death. More recently, a second type of cell death pathway has emerged: autophagy, also called type II programmed cell death. Autophagy is a tightly regulated process by which selected components of a cell are degraded. It primarily functions as a cell survival adaptive mechanism during stress conditions. However, persistent stress can also promote extensive autophagy, leading to cell death, hence its name. Alterations in the autophagy pathway have been described in cancer cells that suggest a tumor-suppressive function in early tumorigenesis, but a tumor-promoting function in established tumors. Moreover, accumulating data indicate a role for autophagy in chemotherapy-induced cancer cell death. Here, we discuss some of the evidence showing autophagy-dependent cell death induced by anti-neoplastic agents in different cancer models. On the other hand, in some other examples, autophagy dampens treatment efficacy, hence providing a therapeutic target to enhance cancer cell killing. In this paper, we propose a putative mechanism that could reconcile these two opposite observations.