Induction Of Radioresistance Research Articles

Elevation of H3K27me3 level contributes to the radioresistance of nasopharyngeal carcinoma by inhibiting OAS1 expression.

Radiotherapy has long been a main treatment option for nasopharyngeal carcinoma (NPC). However, during clinical treatment, NPC is prone to developing radioresistance, resulting in treatment failure. This study aims to examine the role of histone methylation in the induction of radioresistance. It was found that the radioresistance of NPC cells was related to the increase of the level of histone H3 lysine 27 trimethylation (H3K27me3). Treatment of cells with histone methyltransferase inhibitor GSK126 increased the radiosensitivity of NPC cells by triggering Bcl2 apoptosis regulator/BCL2-associated X, apoptosis regulator (Bcl2/BAX) signaling pathway. Bioinformatics analysis indicated that the expression of 2'-5'-oligoadenylate synthetase 1 (OAS1) was reduced in the radioresistant cells but increased in the GSK126-treated cells. Chromatin immunoprecipitation assay confirmed that the decrease of OAS1 expression in radioresistant cells was mainly due to the enrichment of H3K27me3 in its promoter region. Furthermore, downregulation of OAS1 reduced apoptosis due to the inhibition of Bcl2/BAX pathway after irradiation, while OAS1 overexpression increased radiosensitivity. Our findings revealed for the first time that the increase of H3K27me3 level was associated with the decrease of OAS1 expression, leading to the inhibition of apoptosis and ultimately contributing to the radioresistance of NPC cells. Moreover, the histone methyltransferase inhibitor GSK126 could overcome the radioresistance and thus might be a potential therapeutic strategy for NPC.NEW & NOTEWORTHY Our findings revealed for the first time that the increase of H3K27me3 level was associated with the decrease of OAS1 expression, leading to the inhibition of apoptosis and ultimately contributing to the radioresistance of NPC cells. Moreover, we demonstrated that the histone methyltransferase inhibitor GSK126 could be a promising therapeutic strategy for NPC by overcoming radioresistance, providing valuable insights into the clinical treatment of NPC.

Low dose hyper-radiosensitivity in normal human cells

Cells usually have different sensitivity to ionising radiation depending on their phase during the cell cycle, particularly at low-LET radiation. The most sensitive phases in the cell cycle are the M- and G2 phases, where S and G1 are the resistant phases. Low doses of radiation can induce various delayed and non-targeted effects, including bystanders (BE) and hyper-radiosensitivity (HRS), in vitro and in vivo. The region of HRS is thought to be formed by an excessive induction of DNA DSBs, which consequently led to a hyper-activation of the DNA repair mechanisms. Such phenomena result in a modification to the Linear Quadratic (LQ) model to include the out-of-fit dose points. At low doses below 1 Gy of radiation, most mammalian cells have shown HRS, which is frequently followed by an Induced-radioresistance (IRR) phenomenon. To confirm the observations of the HRS and IRR effects and identify their start- and endpoints at low doses of X-ray irradiations, the AG1522 normal human fibroblasts cells were irradiated with a range of selected high- and low doses of 0.2, 0.4, 0.6, 1, 2, 3, 4 and 5 Gy with a specific interest at the doses below 1 Gy. The HRS is pronounced at the dose of 0.2 Gy of X-ray irradiation, followed by the IRR phenomenon as the dose increases up to 0.6 Gy. In the context of radiation protection, these results need to be considered during radiotherapy treatment. The presence of the HRS in the survival curves of normal AG1522 cells after X-irradiation maximises the possible advantage of using such low doses to improve clinical outcomes. These data provide further insight into the radiobiological parameters, highlighting the need to refine existing radiobiological parameters to incorporate such effects and modulate dose distributions.

Targeting radiation-induced upstream stimulatory factor-1 by histone deacetylase inhibitors to reverse radioresistance in prostate cancer.

Ionizing radiation (IR) is a standard modality for the management of solid tumors. Apart from its killing effects, IR can induce pro-survival factors leading to radioresistance of cancer. Mechanistic understanding of radiation resistance is warranted to overcome the pro-survival effects of IR. The aim of this study was to investigate the role of upstream stimulatory factor-1 (USF-1) in the induction of radioresistance in prostate cancer and its targeting by histone deacetylase (HDAC) inhibitors to reverse resistance. This study reports here that USF-1 is a marker for radioresistance in PC-3 cells. Using protein-DNA array analysis, it was documented that DNA binding activity of USF-1 was elevated following IR in PC-3 cells. Novel HDAC inhibitors downregulated USF-1 binding either alone or in combination with IR. A 5Gy dose of IR induced the expression of target genes of USF-1 (human telomerase reverse transcriptase [hTERT], IGF2R, CyclinB1, and Cdk1), however, HDAC inhibitors alone or in combination with IR reduced their expression as measured by real time RT PCR analysis. Furthermore, immunofluorescence analysis revealed that while USF-1 localized primarily in the nucleus following IR, it localized in the cytoplasm when treated with HDAC inhibitors/combination. Maximum effects of modulation of USF-1 expression (overexpression or suppression) were observed on hTERT activity as determined by dual-luciferase reporter assay. To further confirm the role of USF-1 in radioresistance, cell growth was analyzed using the real-time cell electronic sensing (RT-CES) system. This study found that USF-1-transfected cells proliferated faster than the vector-transfected cells with or without treatments with HDAC inhibitors/IR/combination. Colony forming assay also confirmed that USF-1 overexpression led to increased survival following IR. Importantly, colony-forming assay demonstrated that HDAC inhibitors reversed the radioresistance in both PC-3 and DU-145 cells. These studies demonstrate that HDAC inhibitors reverse the radioresistance in prostate cancer through down-modulation of USF-1-mediated transactivation of target genes involved in cell proliferation and cell cycle.

LINC01224/ZNF91 Promote Stem Cell-Like Properties and Drive Radioresistance in Non-Small Cell Lung Cancer

BackgroundRadioresistance is the main reason for the failure of radiotherapy in non-small-cell lung cancer (NSCLC); however, the molecular mechanism of radioresistance is still unclear.MethodsAn RNA-Seq assay was used to screen differentially expressed long non-coding RNAs (lncRNAs) and genes in irradiation-resistant NSCLC cells. RT-PCR and Western blotting assays were performed to analyze the expressions of lncRNAs and genes. The chromosome conformation capture (3C) assay was performed to measure chromatin interactions. Cell cytotoxicity, cell apoptosis, sphere formation and Transwell assays were performed to assess cellular function.ResultsIn this study, it was found that LINC01224 increased during the induction of radioresistance in NSCLC cells. LINC01224 was located within the enhancer of ZNF91, and LINC01224 could affect the transcription of ZNF91 by regulating the long-range interactions between the ZNF91 enhancer and promoter. Moreover, upregulation of LINC01224 and ZNF91 could promote irradiation resistance by regulating the stem cell-like properties of NSCLC cells. In addition, high expression levels of LINC01224 and ZNF91 in tissue samples were associated with radioresistance in NSCLC patients.ConclusionOur findings demonstrated that LINC01224/ZNF91 drove radioresistance regulation by promoting the stem cell-like properties in NSCLC.

The Role and Mechanism of ATM-Mediated Autophagy in the Transition From Hyper-Radiosensitivity to Induced Radioresistance in Lung Cancer Under Low-Dose Radiation.

Objective: This study aimed to investigate the effect of ataxia telangiectasia mutated (ATM)–mediated autophagy on the radiosensitivity of lung cancer cells under low-dose radiation and to further investigate the role of ATM and its specific mechanism in the transition from hyper-radiosensitivity (HRS) to induced radioresistance (IRR).Methods: The changes in the HRS/IRR phenomenon in A549 and H460 cells were verified by colony formation assay. Changes to ATM phosphorylation and cell autophagy in A549 and H460 cells under different low doses of radiation were examined by western blot, polymerase chain reaction (PCR), and electron microscopy. ATM expression was knocked down by short interfering RNA (siRNA) transfection, and ATM-regulated molecules related to autophagy pathways were screened by transcriptome sequencing analysis. The detection results were verified by PCR and western blot. The differential metabolites were screened by transcriptome sequencing and verified by colony formation assay and western blot. The nude mouse xenograft model was used to verify the results of the cell experiments.Results: (1) A549 cells with high expression of ATM showed positive HRS/IRR, whereas H460 cells with low expression of ATM showed negative HRS/IRR. After the expression of ATM decreased, the HRS phenomenon in A549 cells increased, and the radiosensitivity of H460 cells also increased. This phenomenon was associated with the increase in the autophagy-related molecules phosphorylated c-Jun N-terminal kinase (p-JNK) and autophagy/Beclin 1 regulator 1 (AMBRA1). (2) DL-Norvaline, a product of carbon metabolism in cells, inhibited autophagy in A549 cells under low-dose radiation. DL-Norvaline increased the expression levels of ATM, JNK, and AMBRA1 in A549 cells. (3) Mouse experiments confirmed the regulatory role of ATM in autophagy and metabolism and its function in HRS/IRR.Conclusion: ATM may influence autophagy through p-JNK and AMBRA1 to participate in the regulation of the HRS/IRR phenomenon. Autophagy interacts with the cellular carbon metabolite DL-Norvaline to participate in regulating the low-dose radiosensitivity of cells.

Rab1A promotes cancer metastasis and radioresistance through activating GSK-3β/Wnt/β-catenin signaling in nasopharyngeal carcinoma

Many articles have reported that Rab1A was overexpressed in a variety of human cancers and involved in tumor progression and metastasis. However, the biological function and molecular mechanism of Rab1A in nasopharyngeal carcinoma (NPC) remained unknown until now. Here we found that Rab1A overexpression is a common event and was positively associated with distant metastasis and poor prognosis of NPC patients. Functionally, Rab1A depletion inhibited the migration and EMT phenotype of NPC cells, whereas Rab1A overexpression led to the opposite effect. Furthermore, we reveal an important role for Rab1A protein in the induction of radioresistance via regulating homologous recombination (HR) signaling pathway. Mechanistically, Rab1A activated Wnt/β-catenin signaling by inhibiting the activity of GSK-3β via phosphorylation at Ser9. Then Wnt/β-catenin signaling induced NPC cells radioresistance and metastasis through nuclear translocation of β-catenin and transcription upregulation of HR pathway-related and EMT-related genes expression. In general, this study shows that Rab1A may serve as a potential biomarker for predicting prognosis in NPC patients. Targeting Rab1A and Wnt/β-catenin signaling may hold promise to overcome NPC radioresistance.

COMPUTATIONAL MODELING OF LOW DOSE HYPER-RADIOSENSITIVITY AND INDUCED RADIORESISTANCE APPLYING THE PRINCIPLE OF MINIMUM MUTATION LOAD.

Low dose hyper-radiosensitivity (HRS) and induced radioresistance (IRR) can be observed in the dose dependence of survival of many different cell lines. While surviving fraction decreases exponentially in a large-scale view, a local minimum can be found at around 0.5 Gy. Although, there is evidence that the regulation of apoptosis and DNA repair are involved in HRS and IRR, the fundamental causes of the phenomena remain unclear. The objective of the present study is to test whether the principle of minimum mutation load can provide an explanation for both low dose HRS and IRR. For this purpose, a mathematical model was elaborated considering radiation induced mutagenic DNA lesions as well as cell divisions as sources of mutations. It was presumed that cell number is in dynamic equilibrium in the tissue, the number of mutations follows Poisson distribution, and its average is proportional to absorbed dose. For each value of absorbed dose, the minimum number of mutations were computed for different surviving fractions. Then that surviving fraction was plotted that results in the lowest number of mutations. One minimum or multiple minima can be seen in the dose dependence of surviving fractions with reasonable values for the model parameters: spontaneous and radiation induced mutation rate. Although the mechanisms remain unclear, the principle of minimum mutation load provides a potential explanation for low dose HRS and IRR and for the fact that they are mostly observed in cell lines with defected DNA repair.

MicroRNA-125 modulates radioresistance through targeting p21 in cervical cancer.

Cervical cancer (CC) is one of the most common cancers diagnosed in women worldwide, and it is estimated that ~500,000new patients are diagnosed with cervical cancer annually and that ~270,000deaths occur each year. Patients with cervical cancer are treated with different radiotherapy schedules, either alone or with adjuvant chemotherapy. Unfortunately, nearly 50% of all patients with cervical cancer do not respond to standard treatment due to tumor radioresistance. In this scenario, several microRNAs (miRNAs) have been associated with the acquisition of the radioresistance phenotype. The aim of the present study was to evaluate the possible role of miR‑125a in the acquisition of radioresistance in cervical cancer. The expression of miR‑125a was assessed by means of RT‑qPCR in 30cervical cancer samples from patients receiving standard treatment and 3induced radioresistant cervical cancer cell lines. In addition, we employed miR‑125a mimics and inhibitors to evaluate its function in the induction of radioresistance. We showed that miR‑125a was downregulated in patients with cervical cancer who did not respond to standard treatment. Concordantly, radioresistant SiHa, CaSki and HeLa cell lines had low levels of miR‑125a with respect to the sensitive cell lines. Finally, we demonstrated that overexpression of miR‑125a sensitized cervical cancer cells to radiation therapy through the downregulation of CDKN1A. Our data corroborate previously published studies in which it was demonstrated that miRNAs could play a role in the regulation of the process of radioresistance. Additionally, we showed that overexpression of miR‑125a could be used as a radioresistance biomarker in patients with cervical cancer.

Effect of ATM on low-dose hyper-radiosensitivity in A549 cells synchronized at G2 phase

Objective To investigate the low-dose hyper-radiosensitivity (HRS)/induced radioresistance (IRR) in A549 cells synchronized at G2 phase and the role of ATM kinase in the process. Methods Human lung adenocarcinoma cell line A549 was synchronized at G2 phase by aphidicolin. The ATM-specific activator and inhibitor, chloroquine and KU55933, were used to regulate the activity of ATM. The colony formation assay was used to evaluate cell survival. Flow cytometry was used to determine the cell cycle of radiation-exposed A549 cells synchronized at G2 phase. Immunofluorescence was used to observe the dynamics of γ-H2AX fluorescence and evaluate the efficiency of DNA repair in A549 cells synchronized at G2 phase. Western blot was used to detect the expression of phosphorylated ATM (Ser1981) and ATM. Results A549 cells synchronized at G2 phase had substantially enhanced HRS than non-synchronized cells. The dose-induced transition from HRS to IRR was in accordance with the dose-response pattern of early G2/M checkpoint. However, with the same threshold dose, the activation of early checkpoint occurred earlier and lasted longer than normal. The activation of ATM kinase inhibited HRS and enhanced DNA repair, while the inhibition of ATM kinase enhanced HRS and hindered DNA repair. Conclusions ATM kinase-mediated early G2+ M checkpoint is a molecular switch for HRS in synchronized A549 cells. Low-dose irradiation with G2-phase synchronization and ATM inhibitor can enhance the low-dose radiosensitivity. Key words: Low-dose radiation sensitivity/increased radiation resistance; Early G2/M checkpoint; Cell cycle

ATR signaling cooperates with ATM in the mechanism of low dose hypersensitivity induced by carbon ion beam.

Little work has been done on the mechanism of low dose hyper-radiosensitivity (HRS) and later appeared radioresistance (termed induced radioresistance (IRR)) after irradiation with medium and high linear energy transfer (LET) particles. The aim of this study was to find out whether ATR pathway is involved in the mechanism of HRS induced by high LET radiation. GM0639 cells and two ATM deficient/mutant cells, AT5BIVA and AT2KY were irradiated by carbon ion beam. Thymidine block technique was developed to enrich the G2-phase population. Radiation induced early G2/M checkpoint was quantitatively assess with dual-parameter flow cytometry by detecting the cells positive for phospho-histone H3. The involvement of ATR pathway in HRS/IRR response was detected with pretreatment of specific inhibitors prior to carbon ion beam. The link between the early G2/M checkpoint and HRS/IRR under carbon ion beam was first confirmed in GM0639 cells, through the enrichment of cell population in G2-phase or with Aurora kinase inhibitor that attenuates the transition from G2 to M phase. Interestingly, the early G2/M arrest could still be observed in ATM deficient/mutant cells with an effect of ATR signaling, which was discovered to function in an LET-dependent manner, even as low as 0.2Gy for carbon ion radiation. The involvement of ATR pathway in heavy particles induced HRS/IRR was determined with the specific ATR inhibitor in GM0639 cells, which affected the HRS/IRR occurrence similarly as ATM inhibitor. These data demonstrate that ATR pathway may cooperate with ATM in the mechanism of low dose hypersensitivity induced by carbon ion beam.

Hyper-radiosensitivity and induced radioresistance and bystander effects in rodent and human cells as a function of radiation quality.

In the past two decades, a body of experimental evidences in vitro has shown the presence of a plethora of phenomena occurring after low-dose irradiation [including hypersensitivity and induced radioresistance (IRR), adaptive response, bystander effect (BE) and genomic instability], which might imply a non-linear behaviour of cancer risk curves in the low-dose region and question the validity of the linear no-threshold model for cancer risk assessment in such a dose region. In this framework, a systematic investigation have been undertaken on non-linear effects at low doses as a function of different radiation quality and cellular radiosensitivity and in terms of different biological end points. The present article reports the recent results on hyper-radiosensitivity and IRR and BE phenomena, in terms of clonogenic survival in V79 Chinese hamster cells and T98G human glioblastoma cells irradiated with protons and carbon ions with different energy, as a function of dose (and fluence).

The Accomplices of NF-κB Lead to Radioresistance

Ionizing radiation (IR) plays an important role in the treatment of epithelial tumors, such as lung and prostate cancer, by wounding and killing cancer cells. However, IR also activates sophisticated anti-apoptotic transcriptional factors such that cancer cells fail to repair DNA damage and obtain resistance to apoptosis under conditions of radiotherapy. Among these transcription factors, the transcription factor nuclear factor kappa B (NF-κB) is recognized as a key feature for protecting cells from apoptosis in most cell types. Moreover, the induction of radioresistance is mediated by several genes that are regulated by NF- κB. The primary purpose of this review is to introduce the studies of the signaling mechanisms of IR in NF-κB activation, such as ROS/NF-κB, ATM or DNA-PK/MAPKK/ p90rsk, PI3K/AKT/IKK and k-ras/c-raf/ MEKK/ NF-κB pathways. Moreover, we describe how the expression of the target genes (e.g., XIAP, A20, FLIP, Bcl-xL) are induced by NF-κB to regulate the activation of survival signaling pathways and to inhibit apoptotic signaling pathways. In addition, IR activates NF-κB to express cell cycle-specific genes, for example cyclin D1, which is associated with reinforcing radioresistance. We exhibit the signaling pathways that are induced by IR stimulation of NF-κB and illustrate the molecular mechanisms of radioresistance.

The potential use of biogas producing microorganisms in radiation protection

Abstract Radiation induced injury is a limiting factor in radiation related approaches from earth to space. Inductions of a wide spectrum of damages in radiotherapy patients due to unwanted normal tissues irradiation and space radiation related diseases in astronauts have been caused many limitations in cancer treatment and space missions. There are many radiation protection/mitigation approaches including: physical, chemical, biological and physiological methods. Radiation protection using these methods is expensive and also has many problems including acute toxicities and difficulties in their targeting to normal tissues. Based on experimental and hypothetical data, showing that medical/biological gases have many protective effects such as antioxidant, anti-inflammatory, anti-apoptotic, and induction of radioresistance, we hypothesize that similar gases which have been produced by microorganisms (biogases) have those properties and may be used as radiation mitigators/protectors in radiation related approaches such as radiotherapy, radiation accidents and in space missions. Isolation microorganism in safe laboratory conditions in enough amounts, finding non-toxic dose of microorganisms that provide highest radioprotection percent, dose reduction factor (DRF) calculation to compare the radioprotective efficacy of the microorganisms, finding the best targeting techniques to deliver those microorganisms into normal tissues, genetically manipulations of microorganism to achieve the highest amount of biogases with lowest side effects can be done for testing the hypothesis.

MiR-101 sensitizes human nasopharyngeal carcinoma cells to radiation by targeting stathmin 1.

Radioresistance remains a major problem in the treatment of patients suffering from nasopharyngeal carcinoma (NPC). A better understanding of the mechanisms involved in the induction of radioresistance may provide strategies to improve NPC patients’ response to therapy. The present study aimed to investigate the effect of microRNA (miR)-101 on the radioresistance of NPC cells. Analysis of miR-101 expression levels indicated that miR-101 was downregulated in NPC cell lines. Furthermore, ectopic expression of miR-101 suppressed cell proliferation and enhanced radiosensitivity of NPC cells. Stathmin 1 (STMN1) was additionally verified as a direct functional target of miR-101, which was found to be involved in cell viability, radioresistance and radiation-induced autophagy of NPC cells. In conclusions, the results of the present study suggested that the identified miR-101/STMN1 pathway contributed to the elucidation of the mechanisms of radioresistance in human NPC and that it may represent a potential therapeutic target.

Radiobiological Response of Cervical Cancer Cell Line in Low Dose Region: Evidence of Low Dose Hypersensitivity (HRS) and Induced Radioresistance (IRR).

Purpose of the present study was to examine the response of cervical cancer cell line (HeLa cell line) to low dose radiation using clonogenic assay and mathematical modeling of the low dose response by Joiner's induced repair model. Survival of HeLa cells following exposure to single and fractionated low doses of γ (gamma)-ray, 6 MV, and 15 MV photon was measured by clonogenic assay. HeLa cell line demonstrated marked low dose response consisting of an area of HRS and IRR in the dose region of <1 Gy. The two gradients of the low dose region (αs and αr) were distinctly different with a transition dose (Dc) of 0.28-0.40 cGy. HeLa cell line demonstrates marked HRS and IRR with distinct transition dose. This may form the biological basis of the clinical study to investigate the chemo potentiating effect of low dose radiation in cervical cancer.

Involvement of ERK-Nrf-2 Signaling in Ionizing Radiation Induced Cell Death in Normal and Tumor Cells

Prolonged oxidative stress favors tumorigenic environment and inflammation. Oxidative stress may trigger redox adaptation mechanism(s) in tumor cells but not normal cells. This may increase levels of intracellular antioxidants and establish a new redox homeostasis. Nrf-2, a master regulator of battery of antioxidant genes is constitutively activated in many tumor cells. Here we show that, murine T cell lymphoma EL-4 cells show constitutive and inducible radioresistance via activation of Nrf-2/ERK pathway. EL-4 cells contained lower levels of ROS than their normal counterpart murine splenic lymphocytes. In response to radiation, the thiol redox circuits, GSH and thioredoxin were modified in EL-4 cells. Pharmacological inhibitors of ERK and Nrf-2 significantly enhanced radiosensitivity and reduced clonogenic potential of EL-4 cells. Unirradiated lymphoma cells showed nuclear accumulation of Nrf-2, upregulation of its dependent genes and protein levels. Interestingly, MEK inhibitor abrogated its nuclear translocation suggesting role of ERK in basal and radiation induced Nrf-2 activation in tumor cells. Double knockdown of ERK and Nrf-2 resulted in higher sensitivity to radiation induced cell death as compared to individual knockdown cells. Importantly, NF-kB which is reported to be constitutively active in many tumors was not present at basal levels in EL-4 cells and its inhibition did not influence radiosensitivity of EL-4 cells. Thus our results reveal that, tumor cells which are subjected to heightened oxidative stress employ master regulator cellular redox homeostasis Nrf-2 for prevention of radiation induced cell death. Our study reveals the molecular basis of tumor radioresistance and highlights role of Nrf-2 and ERK.

Cell division cycle 25 homolog c effects on low-dose hyper-radiosensitivity and induced radioresistance at elevated dosage in A549 cells

The underlying mechanisms behind both low-dose hyper-radiosensitivity (HRS) and induced radioresistance (IRR), generally occurring at elevated radiation levels, remain unclear; however, elucidation of the relationship between cell cycle division 25 homolog c (Cdc25c) phosphatase and HRS/IRR may provide important insights into this process. Two cell lines with disparate HRS status, A549 and SiHa cells, were selected as cell models for comparison of dose-dependent Cdc25c phosphatase expression subsequent to low-dose irradiation. Knockdown of Cdc25c in A549 cells was mediated by transfection with a pGCsi-RAN-U6neo vector containing hairpin siRNA sequences. S216-phosphorylated Cdc25c protein [p-Cdc25c (Ser216)], cell survival and mitotic ratio were measured by western blot, colony-forming assay and histone H3 phosphorylation analysis. Variant p-Cdc25c (Ser216) expression was observed in the two cell lines after irradiation. The p-Cdc25c (Ser216) expression noted in SiHa cells after administration of 0–1 Gy radiation was similar to the radioresistance model; however, in A549 cells, the dose response for the phosphorylation of the Cdc25c Ser216 residue overlapped the level required to overcome the HRS response. Furthermore, Cdc25c repression prior to low-dose radiation induced more distinct HRS and prevented the development of IRR. The dose required to overcome the HRS response coincided with the effect of early G2-phase checkpoint arrest in A549 cells (approximately 0.3 Gy), and Cdc25c knockdown in A549 cells (approximately 0.5 Gy) corresponded to the phosphorylation of the Cdc25c Ser216 residue. Resultant data confirmed that dose-dependent Cdc25c phosphatase does effectively act as an early G2-phase checkpoint, thus indicating mechanistic importance in the HRS to IRR transition in A549 cells.

P53 -Dependent Adaptive Responses in Human Cells Exposed to Space Radiations

It has been reported that priming irradiation or conditioning irradiation with a low dose of X-rays in the range of 0.02-0.1 Gy induces a p53-dependent adaptive response in mammalian cells. The aim of the present study was to clarify the effect of space radiations on the adaptive response. Two human lymphoblastoid cell lines were used; one cell line bears a wild-type p53 (wtp53) gene, and another cell line bears a mutated p53 (mp53) gene. The cells were frozen during transportation on the space shuttle and while in orbit in the International Space Station freezer for 133 days between November 15, 2008 and March 29, 2009. After the frozen samples were returned to Earth, the cells were cultured for 6 h and then exposed to a challenging X-ray-irradiation (2 Gy). Cellular sensitivity, apoptosis, and chromosome aberrations were scored using dye-exclusion assays, Hoechst33342 staining assays, and chromosomal banding techniques, respectively. In cells exposed to space radiations, adaptive responses such as the induction of radioresistance and the depression of radiation-induced apoptosis and chromosome aberrations were observed in wtp53 cells but not in mp53 cells. These results have confirmed the hypothesis that p53-dependent adaptive responses are apparently induced by space radiations within a specific range of low doses. The cells exhibited this effect owing to space radiations exposure, even though the doses in space were very low.

Enhanced tumor radiosensitivity by a survivin dominant-negative mutant

Radiosensitivity of tumors is due to a complex interaction of various factors, it has been reported that survivin also acts as a constitutive and inducible radioresistance factor in a panel of tumor cells and approaches designed to inhibit survivin expression or function may lead to tumor sensitisation to chemical and physical agents. Previously, we found that the plasmid encoding the phosphorylation-defective mouse survivin threonine 34-->alanine mutant complexed to DOTAP-chol liposome (Lip-mS) can suppress murine primary breast carcinoma. However, little is known regarding the biological effect of Lip-mS combined with radiation. The present study was designed to determine whether Lip-mS could enhance the anti-tumor activity of radiation. The Lewis Lung Carcinoma (LLC) cells treated with a combination of Lip-mS and radiation displayed apparently increased apoptosis compared with those treated with Lip-mS or radiation alone. Mice bearing LLC tumors were treated with intravenous injections of Lip-mS and radiation, the combined treatment significantly reduced mean tumor volume compared with either treatment alone. Moreover, the anti-tumor effect of Lip-mS combined with radiation was greater than their additive effect when compared with the expected effect of the combined treatment. These data suggest that inhibition of survivin using a dominant-negative mutant, survivin T34A, could sensitize LLC cells to radiation efficiently and the synergistic anti-tumor activity may in part result from increasing the apoptosis of tumor cells, inhibiting tumor angiogenesis and inducing a tumor-protective immune response in the combined treatment.

The anti-oxidant capacity of tumour glycolysis

Purpose: In this mini-review data are summarised which provide evidence for the biological and clinical significance of tumour glycolysis and of its relationship to the redox state of cancer cells.Results: Malignant transformation is associated with an overexpression of numerous glycolysis-related genes in the vast majority of human cancers. At the same time, glycolytic activity and glycolysis-linked metabolic milieu are often variable between individual tumours which induces large variations in treatment response and aggressiveness. Currently, there is no genetic or proteomic marker for the prediction of the therapeutic response for individual tumours, but the prognostic value of tumour lactate accumulation for the emergence of metastasis, for patient survival and for radioresistance has been documented in a number of studies.Conclusions: Transactivation of tumour glycolyis appears to generate a chemically reduced milieu associated with an inhibition of ROS (reactive oxygen species) -mediated fixation of DNA damage and induction of radioresistance. Furthermore, highly glycolytic cells enhance the antioxidant defense via glutathione, and pyruvate can be decarboxylated non-enzymatically upon reducing hydrogen peroxide. The summary of data given here emphasises the importance of further research efforts on the link between carbohydrate metabolism and redox state of cancer cells.