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Hypoxic Radioresistance: Can ROS Be the Key to Overcome It?

ABSTRACT: Radiotherapy is a mainstay treatment for many types of cancer and kills cancer cells via generation of reactive oxygen species (ROS). Incorporating radiation with pharmacological ROS inducers, therefore, has been widely investigated as an approach to enhance aerobic radiosensitization. However, this strategy was overlooked in hypoxic counterpart, one of the most important causes of radiotherapy failure, due to the notion that hypoxic cells are immune to ROS insults because of the shortage of ROS substrate oxygen. Paradoxically, evidence reveals that ROS are produced more in hypoxic than normoxic cells and serve as signaling molecules that render cells adaptive to hypoxia. As a result, hypoxic tumor cells heavily rely on antioxidant systems to sustain the ROS homeostasis. Thereby, they become sensitive to insults that impair the ROS detoxification network, which has been verified in diverse models with or without radiation. Of note, hypoxic radioresistance has been overviewed in different contexts. To the best of our knowledge, this review is the first to systemically summarize the interplay among radiation, hypoxia, and ROS, and to discuss whether perturbation of ROS homeostasis could provide a new avenue to tackle hypoxic radioresistance.

SUBMITTER: Wang H

PROVIDER: S-EPMC6357097 | biostudies-literature | 2019 Jan

REPOSITORIES: biostudies-literature

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Hypoxic Radioresistance: Can ROS Be the Key to Overcome It?

Wang Hui H Jiang Heng H Van De Gucht Melissa M De Ridder Mark M

Cancers 20190118 1

Radiotherapy is a mainstay treatment for many types of cancer and kills cancer cells via generation of reactive oxygen species (ROS). Incorporating radiation with pharmacological ROS inducers, therefore, has been widely investigated as an approach to enhance aerobic radiosensitization. However, this strategy was overlooked in hypoxic counterpart, one of the most important causes of radiotherapy failure, due to the notion that hypoxic cells are immune to ROS insults because of the shortage of ROS ...[more]

PMID: 30669417

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Project description:(1) Background: The sensitivity of head and neck squamous cell carcinoma (HNSCC) to ionizing radiation, among others, is determined by the number of cells with high clonogenic potential and stem-like features. These cellular characteristics are dynamically regulated in response to treatment and may lead to an enrichment of radioresistant cells with a cancer stem cell (CSC) phenotype. Epigenetic mechanisms, particularly DNA and histone methylation, are key regulators of gene-specific transcription and cellular plasticity. Therefore, we hypothesized that specific epigenetic targeting may prevent irradiation-induced plasticity and may sensitize HNSCC cells to radiotherapy. (2) Methods: We compared the DNA methylome and intracellular concentrations of tricarboxylic acid cycle metabolites in radioresistant FaDu and Cal33 cell lines with their parental controls, as well as aldehyde dehydrogenase (ALDH)-positive CSCs with negative controls. Moreover, we conducted a screen of a chemical library targeting enzymes involved in epigenetic regulation in combination with irradiation and analyzed the clonogenic potential, sphere formation, and DNA repair capacity to identify compounds with both radiosensitizing and CSC-targeting potential. (3) Results: We identified the histone demethylase inhibitor GSK-J1, which targets UTX (KDM6A) and JMJD3 (KDM6B), leading to increased H3K27 trimethylation, heterochromatin formation, and gene silencing. The clonogenic survival assay after siRNA-mediated knock-down of both genes radiosensitized Cal33 and SAS cell lines. Moreover, high KDM6A expression in tissue sections of patients with HNSCC was associated with improved locoregional control after primary (n = 137) and post-operative (n = 187) radio/chemotherapy. Conversely, high KDM6B expression was a prognostic factor for reduced overall survival. (4) Conclusions: Within this study, we investigated cellular and molecular mechanisms underlying irradiation-induced cellular plasticity, a key inducer of radioresistance, with a focus on epigenetic alterations. We identified UTX (KDM6A) as a putative prognostic and therapeutic target for HNSCC patients treated with radiotherapy.

Project description:The resistance of hypoxic cells to radiotherapy and chemotherapy is a major problem in the treatment of cancer. Recently, an additional level of Hypoxia Inducible Factor (HIF) dependent transcriptional regulation has emerged involving modulation of a specific set of miRNAs including miR-210. We have recently shown that HIF-1 induction of miR-210 also stabilizes HIF-1 through a positive regulatory loop. We therefore hypothesized that by stabilizing HIF-1 in normoxia, miR-210 may protect cancer cells from radiation. We developed Non-Small Cell Lung Cancer (NSCLC)-derived cell lines (A549 and H1975) stably expressing miR-210 (pmiR-210) or a control miRNA (pmiR-Ctl). MiR-210 expressing cells showed a significant stabilization of HIF-1 associated with mitochondrial defects and a glycolytic phenotype. The cells were subjected to radiation levels ranging from 0 to 10Gy in normoxia and hypoxia. Cells expressing miR-210 in normoxia had the same level of resistance than control cells in hypoxia. pmiR-210 cells under hypoxia showed a low mortality rate due to a decrease in apoptosis and an ability to grow even at 10Gy. We have established that radioresistance was independent of p53 and cell cycle status. In addition, we show here that genomic double strand breaks (DSB) foci disappeared faster in pmiR-210 than in pmiR-Ctl cells, suggesting that miR-210 expression promotes a more efficient DSB repair. Finally, HIF-1 invalidation in pmiR-210 cells (pmiR-210/HIF-1-) abolished radioresistance of cells showing that this mechanism was dependent upon HIF-1. In conclusion, miR-210 appears to be a major component in the radioresistance of hypoxic cancer cells. Given the high stability of most miRNAs, this advantage could even be used by tumor cells in conditions where hypoxia may not be present anymore and strongly suggests that strategies targeting miR-210 would enhance tumor radiosensitization. To identify the set of transcripts targeted by miR-210, we overexpressed has-miR-210 or a control miRNA (ce-miR-67) in human lung adenocarcinoma A549 cells by transduction using lentivirus. The resulting pmiR-67 and pmiR-210 that stably overexpress miR-210 were selected by puromycin. RNA samples were harvested at 2 different times following cell plating (24 hours or 48 hours). Experiments were performed in dye-swap.

Project description:Esophageal squamous cell carcinoma (ESCC), the most frequent esophageal cancer (EC) subtype, entails dismal prognosis. Hypoxia, a common feature of advanced ESCC, is involved in resistance to radiotherapy (RT). RT response in hypoxia might be modulated through epigenetic mechanisms, constituting novel targets to improve patient outcome. Post-translational methylation in histone can be partially modulated by histone lysine demethylases (KDMs), which specifically removes methyl groups in certain lysine residues. KDMs deregulation was associated with tumor aggressiveness and therapy failure. Thus, we sought to unveil the role of Jumonji C domain histone lysine demethylases (JmjC-KDMs) in ESCC radioresistance acquisition. The effectiveness of RT upon ESCC cells under hypoxic conditions was assessed by colony formation assay. KDM3A/KDM6B expression, and respective H3K9me2 and H3K27me3 target marks, were evaluated by RT-qPCR, Western blot, and immunofluorescence. Effect of JmjC-KDM inhibitor IOX1, as well as KDM3A knockdown, in in vitro functional cell behavior and RT response was assessed in ESCC under hypoxic conditions. In vivo effect of combined IOX1 and ionizing radiation treatment was evaluated in ESCC cells using CAM assay. KDM3A, KDM6B, HIF-1α, and CAIX immunoexpression was assessed in primary ESCC and normal esophagus. Herein, we found that hypoxia promoted ESCC radioresistance through increased KDM3A/KDM6B expression, enhancing cell survival and migration and decreasing DNA damage and apoptosis, in vitro. Exposure to IOX1 reverted these features, increasing ESCC radiosensitivity and decreasing ESCC microtumors size, in vivo. KDM3A was upregulated in ESCC tissues compared to the normal esophagus, associating and colocalizing with hypoxic markers (HIF-1α and CAIX). Therefore, KDM3A upregulation in ESCC cell lines and primary tumors associated with hypoxia, playing a critical role in EC aggressiveness and radioresistance. KDM3A targeting, concomitant with conventional RT, constitutes a promising strategy to improve ESCC patients' survival.

Dataset Information

Hypoxic Radioresistance: Can ROS Be the Key to Overcome It?

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Hypoxic Radioresistance: Can ROS Be the Key to Overcome It?

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