Radiation induction of immediate early genes: effectors of the radiation-stress response

Activation of the mevalonate pathway in response to anti-cancer treatments drives glioblastoma recurrences through activation of Rac-1

Glioblastoma is the deadliest adult brain cancer. Under the current standard of care almost all patients succumb to the disease and novel treatments are urgently needed. Dopamine receptor antagonists have been shown to target cancer cell plasticity in GBM and repurposing these FDA-approved drugs in combination with radiation improves the efficacy of radiotherapy in glioma models. In cells surviving this combination treatment the mevalonate pathway is upregulated at the transcriptional and functional level. Here we report that glioblastoma treatments that converge in the immediate early response to radiation through activation of the MAPK cascade universally upregulate the mevalonate pathway and increase stemness of GBM cells through activation of the Rho-GTPase Rac-1. Activation of the mevalonate pathway and Rac-1 is inhibited by statins, which leads to improved survival in mouse models of glioblastoma when combined with radiation and drugs that target the glioma stem cell pool and plasticity of glioma cells.

Co-overexpression of TRAIL and Smac sensitizes MDA-MB-231 cells to radiation through apoptosis depending on mitochondrial pathway

Pro-apoptosis in cancer cells has been proposed as a beneficial therapeutic strategy for potentiating the anticancer effects of radiotherapy. TNF-related apoptosis inducing ligand (TRAIL) and Second mitochondria derived activator of caspase (Smac) can induce cell apoptosis. Herein, we designed a conditionally replicating adenoviral co-overexpression vector of TRAIL and Smac regulated by the Egr1 promoter, in which hTERT, E1A-E1B and E1B55K genes were inserted to achieve enhanced tumor targeting characteristics. After breast cancer MDA-MB-231 cells were infected and irradiated, cellular proliferation and colony formation were measured, apoptotic rate was detected by FCM after AnnexinV-FITC/PI staining. To explore the molecular mechanisms of apoptosis, mRNA and protein levels of TRAIL, Smac, Cytochrome c (Cyt c), death receptor 5 (DR5), caspase-8, -9 and -3 were measured by quantitative real-time PCR, ELISA and Western blot, and caspase-3 activity was detected using caspase-3 activity kits. The results showed that TRAIL and/or Smac overexpression enhanced proliferation inhibition and radio-sensitivity through apoptosis. In addition, the combination of IR and overexpression of TRAIL and/or Smac can activate more apoptosis in tumor cells, and the transcriptional levels and protein expressions of Cyt c, DR5, caspase-8, -9 and -3 had similar regularity with apoptotic changes, indicating the molecular mechanisms of TRAIL and Smac involves the mitochondrial pathway. Our findings may have implications for novel radiotherapy plans for breast tumor treatment.

Amifostine (WR-2721) Mitigates Cognitive Injury Induced by Heavy Ion Radiation in Male Mice and Alters Behavior and Brain Connectivity

The deep space environment contains many risks to astronauts during space missions, such as galactic cosmic rays (GCRs) comprised of naturally occurring heavy ions. Heavy ion radiation is increasingly being used in cancer therapy, including novel regimens involving carbon therapy. Previous investigations involving simulated space radiation have indicated a host of detrimental cognitive and behavioral effects. Therefore, there is an increasing need to counteract these deleterious effects of heavy ion radiation. Here, we assessed the ability of amifostine to mitigate cognitive injury induced by simulated GCRs in C57Bl/6J male and female mice. Six-month-old mice received an intraperitoneal injection of saline, 107 mg/kg, or 214 mg/kg of amifostine 1 h prior to exposure to a simplified five-ion radiation (protons, 28Si, 4He, 16O, and 56Fe) at 500 mGy or sham radiation. Mice were behaviorally tested 2-3 months later. Male mice that received saline and radiation exposure failed to show novel object recognition, which was reversed by both doses of amifostine. Conversely, female mice that received saline and radiation exposure displayed intact object recognition, but those that received amifostine prior to radiation did not. Amifostine and radiation also had distinct effects on males and females in the open field, with amifostine affecting distance moved over time in both sexes, and radiation affecting time spent in the center in females only. Whole-brain analysis of cFos immunoreactivity in male mice indicated that amifostine and radiation altered regional connectivity in areas involved in novel object recognition. These data support that amifostine has potential as a countermeasure against cognitive injury following proton and heavy ion irradiation in males.

Boswellic Acid Synergizes With Low-Level Ionizing Radiation to Modulate Bisphenol Induced-Lung Toxicity in Rats by Inhibiting JNK/ERK/c-Fos Pathway

Bisphenol A (BPA) is a low molecular weight chemical compound that has a deleterious effect on the endocrine system. It was used in plastics manufacturing with injurious effects on different body systems. Occupational exposure to low-level ionizing radiation (<1 Gy) is shown to attenuate an established inflammatory process and therefore enhance cell protection. Therefore, the objective of this study was to investigate the protective effect of boswellic acid (BA) accompanied by whole-body low-dose gamma radiation (γ-R) against BPA-induced lung toxicity in male albino rats. BPA intoxication induced with 500 mg/kg BW. Rats received 50 mg BA/kg BW by gastric gavage concomitant with 0.5 Gy γ-R over 4 weeks. The immunoblotting and biochemical results revealed that BA and/or γ-R inhibited BPA-induced lung toxicity by reducing oxidative damage biomolecules; (MDA and NADPH oxidase gene expression), inflammatory indices (MPO, TNF-α, IL-6, and gene expression of CXCR-4). Moreover, BA and or/γ-R ameliorated the lung inflammation via regulation of the JNK/ERK/c-Fos and Nrf2/ HO-1 signaling pathways. Interestingly, our data demonstrated that BA in synergistic interaction with γ-R is efficacious control against BPA-induced lung injury via anti-oxidant mediated anti-inflammatory activities.

Combining radiotherapy and immunotherapy in definitive treatment of head and neck squamous cell carcinoma: review of current clinical trials

Background Head and neck squamous cell carcinoma (HNSCC) presents as locally advanced disease in a majority of patients and is prone to relapse despite aggressive treatment. Since immune checkpoint inhibitors (ICI) have shown clinically significant efficacy in patients with recurrent/metastatic HNSCC (R/M HNSCC), a plethora of trials are investigating their role in earlier stages of disease. At the same time, preclinical data showed the synergistic role of concurrently administered radiotherapy and ICIs (immunoradiotherapy) and explained several mechanisms behind it. Therefore, this approach is prospectively tested in a neoadjuvant, definitive, or adjuvant setting in non-R/M HNSCC patients. Due to the intricate relationship between host, immunotherapy, chemotherapy, and radiotherapy, each of these approaches has its advantages and disadvantages. In this narrative review we present the biological background of immunoradiotherapy, as well as a rationale for, and possible flaws of, each treatment approach, and provide readers with a critical summary of completed and ongoing trials. Conclusions While immunotherapy with ICIs has already become a standard part of treatment in patients with R/M HNSCC, its efficacy in a non-R/M HNSCC setting is still the subject of extensive clinical testing. Irradiation can overcome some of the cancer's immune evasive manoeuvres and can lead to a synergistic effect with ICIs, with possible additional benefits of concurrent platinum-based chemotherapy. However, the efficacy of this combination is not robust and details in trial design and treatment delivery seem to be of unprecedented importance.

Dual blockade of CD47 and HER2 eliminates radioresistant breast cancer cells

Although the efficacy of cancer radiotherapy (RT) can be enhanced by targeted immunotherapy, the immunosuppressive factors induced by radiation on tumor cells remain to be identified. Here, we report that CD47-mediated anti-phagocytosis is concurrently upregulated with HER2 in radioresistant breast cancer (BC) cells and RT-treated mouse syngeneic BC. Co-expression of both receptors is more frequently detected in recurrent BC patients with poor prognosis. CD47 is upregulated preferentially in HER2-expressing cells, and blocking CD47 or HER2 reduces both receptors with diminished clonogenicity and augmented phagocytosis. CRISPR-mediated CD47 and HER2 dual knockouts not only inhibit clonogenicity but also enhance macrophage-mediated attack. Dual antibody of both receptors synergizes with RT in control of syngeneic mouse breast tumor. These results provide the evidence that aggressive behavior of radioresistant BC is caused by CD47-mediated anti-phagocytosis conjugated with HER2-prompted proliferation. Dual blockade of CD47 and HER2 is suggested to eliminate resistant cancer cells in BC radiotherapy.

Multiple Dynamics in Tumor Microenvironment Under Radiotherapy

The tumor microenvironment (TME) is an evolutionally low-level and embryonically featured tissue comprising heterogenic populations of malignant and stromal cells as well as noncellular components. Under radiotherapy (RT), the major modality for the treatment of malignant diseases [1], TME shows an adaptive response in multiple aspects that affect the efficacy of RT. With the potential clinical benefits, interests in RT combined with immunotherapy (IT) are intensified with a large scale of clinical trials underway for an array of cancer types. A better understanding of the multiple molecular aspects, especially the cross talks of RT-mediated energy reprogramming and immunoregulation in the irradiated TME (ITME), will be necessary for further enhancing the benefit of RT-IT modality. Coming studies should further reveal more mechanistic insights of radiation-induced instant or permanent consequence in tumor and stromal cells. Results from these studies will help to identify critical molecular pathways including cancer stem cell repopulation, metabolic rewiring, and specific communication between radioresistant cancer cells and the infiltrated immune active lymphocytes. In this chapter, we will focus on the following aspects: radiation-repopulated cancer stem cells (CSCs), hypoxia and re-oxygenation, reprogramming metabolism, and radiation-induced immune regulation, in which we summarize the current literature to illustrate an integrated image of the ITME. We hope that the contents in this chapter will be informative for physicians and translational researchers in cancer radiotherapy or immunotherapy.

Histomorphology and immunohistochemical patterns in degenerative disc disease and clinical-radiological correlations: a prospective study

PURPOSE

Degenerative disc disease (DDD) is a common condition causing low-back pain, disability and, eventually, neurological symptoms. This investigation aimed to investigate intervertebral disc DDD-related changes, evaluating histomorphology and cytokines secretion, and their clinical-radiological correlations.

METHODS

This is a monocentric prospective observational study. A cohort of patients who underwent microdiscectomy for DDD, from June 2018 to January 2019, were enrolled. Discs samples were examined for histomorphology, chondrons count, immunohistochemistry for Hif-1α, Nf200 and Egr-1. Demographical and clinical data were also collected.

RESULTS

Twenty patients were finally included. MRI evaluation showed a Modic I alteration in nine patients and a Modic II in 11. The disability grade was low-moderate (ODI score was ≤ 40%) in eight patients and high (ODI score > 40%) in 12. The Modic I was associated with a low-moderate disability in two (22%) patients and to a high disability in seven (88%) (p < 0.01). In Modic I group and in ODI > 40% groups, there were a significative higher mean disability grade 48.4 (± 8.3)%, number of chondrons per section, cells per chondron, Nf200+ nerve fibers and Hif-1α expression, compared with Modic II and ODI ≤ 40% groups, respectively. There were no differences in terms of Egr-1 expression.

CONCLUSIONS

The discs with Modic I MRI signal could represent potential targets for medical treatments, whereas Modic II seems to be a more likely point of no return in a degenerative process. Therefore, further investigations are to better investigate inflammatory pathways and degenerative mechanisms in DDD.

Response to change in the number of visual stimuli in zebrafish:A behavioural and molecular study

Evidence has shown that a variety of vertebrates, including fish, can discriminate collections of visual items on the basis of their numerousness using an evolutionarily conserved system for approximating numerical magnitude (the so-called Approximate Number System, ANS). Here we combine a habituation/dishabituation behavioural task with molecular biology assays to start investigating the neural bases of the ANS in zebrafish. Separate groups of zebrafish underwent a habituation phase with a set of 3 or 9 small red dots, associated with a food reward. The dots changed in size, position and density from trial to trial but maintained their numerousness, and the overall areas of the stimuli was kept constant. During the subsequent dishabituation test, zebrafish faced a change (i) in number (from 3 to 9 or vice versa with the same overall surface), or (ii) in shape (with the same overall surface and number), or (iii) in size (with the same shape and number). A control group of zebrafish was shown the same stimuli as during the habituation. RT-qPCR revealed that the telencephalon and thalamus were characterized by the most consistent modulation of the expression of the immediate early genes c-fos and egr-1 upon change in numerousness; in contrast, the retina and optic tectum responded mainly to changes in stimulus size.

Changes in soil taxonomic and functional diversity resulting from gamma irradiation

Little is known of the effects of ionizing radiation exposure on soil biota. We exposed soil microcosms to weekly bursts of ⁶⁰Co gamma radiation over six weeks, at three levels of exposure (0.1 kGy/hr/wk [low], 1 kGy/hr/wk [medium] and 3 kGy/hr/wk [high]). Soil DNA was extracted, and shotgun metagenomes were sequenced and characterised using MG-RAST. We hypothesized that with increasing radiation exposure there would be a decrease in both taxonomic and functional diversity. While bacterial diversity decreased, diversity of fungi and algae unexpectedly increased, perhaps because of release from competition. Despite the decrease in diversity of bacteria and of biota overall, functional gene diversity of algae, bacteria, fungi and total biota increased. Cycles of radiation exposure may increase the range of gene functional strategies viable in soil, a novel ecological example of the effects of stressors or disturbance events promoting some aspects of diversity. Moreover, repeated density-independent population crashes followed by population expansion may allow lottery effects, promoting coexistence. Radiation exposure produced large overall changes in community composition. Our study suggests several potential novel radiation-tolerant groups: in addition to Deinococcus-Thermus, which reached up to 20% relative abundance in the metagenome, the phyla Chloroflexi (bacteria), Chytridiomycota (fungi) and Nanoarcheota (archaea) may be considered as radiation-tolerant.

c-Fos over-expression promotes radioresistance and predicts poor prognosis in malignant glioma

c-Fos is a major component of activator protein (AP)-1 complex. It has been implicated in cell differentiation, proliferation, angiogenesis, invasion, and metastasis. To investigate the role of c-Fos in glioma radiosensitivity and to understand the underlying molecular mechanisms, we downregulated c-Fos gene expression by lentivirus-mediated shRNA in glioma cell lines and subsequently analyzed the radiosensitivity, DNA damage repair capacity, and cell cycle distribution. Finally, we explored its prognostic value in 41 malignant glioma patients by immunohistochemistry. Our results showed that silencing c-Fos sensitized glioma cells to radiation by increasing radiation-induced DNA double strand breaks (DSBs), disturbing the DNA damage repair process, promoting G2/M cell cycle arrest, and enhancing apoptosis. c-Fos protein overexpression correlated with poor prognosis in malignant glioma patients treated with standard therapy. Our findings provide new insights into the mechanism of radioresistance in malignant glioma and identify c-Fos as a potentially novel therapeutic target for malignant glioma patients.

Demonstration of Tightly Radiation-Controlled Molecular Switch Based on CArG Repeats by In Vivo Molecular Imaging

PURPOSE

Promoters developed for radiogene therapy always show non-negligible transcriptional activities, even when cells are not irradiated. This study developed a tightly radiation-controlled molecular switch based on radiation responsive element (CArG) repeats for in vivo molecular imaging using the Cre/loxP system.

PROCEDURES

Different numbers of CArG repeats were cloned as a basal promoter directly, and its pre- and postirradiation transcriptional activities were analyzed by luciferase assay. Nine CArG repeats (E9) were chosen for use as a radiation-controlled molecular switch for the Cre/loxP system, and the feasibility of the switch in vitro and in vivo was demonstrated by luciferase assay and bioluminescence imaging, respectively.

RESULTS

The E9 promoter, which exhibits extremely low transcriptional activity, showed a 1.8-fold enhancement after irradiation with a clinical dose of 2 Gy. Both in vitro and in vivo results indicated that E9 is relatively inert but sufficient to trigger the Cre/loxP system. The luciferase activity of stable H1299/pSTOP-FLuc cells transfected with pE9-NLSCre and exposed to 2-Gy radiation can reach 44 % of that of the same cells transfected with pCMV-NLSCre and not subjected to irradiation. By contrast, no appreciable difference was observed in reporter gene expression in both H1299/pSTOPFluc cells and tumors transfected with pE4Pcmv-NLSCre before and after irradiation, because the strong basal transcriptional activity of the CMV promoter, which acts as a copartner of E4, masked the response of E4 to radiation.

CONCLUSIONS

Our results provide detailed insight into CArG elements as a radiation-controlled molecular switch that can facilitate the development of radiogene therapy.

Myeloid cell signatures in tumor microenvironment predicts therapeutic response in cancer

Tumor microenvironment (TME) consists of several immune and nonimmune cell populations including tumor cells. For many decades, experimental studies have depicted profound contribution of TME toward cancer progression and metastasis development. Several therapeutic strategies have been tested against TME through preclinical studies and clinical trials. Unfortunately, most of them have shown transient effect, and have largely failed due to aggressive tumor growth and without improving survival. Solid tumors are known to have a strong myeloid component (eg, tumor-associated macrophages) in tumor development. Recent data suggest that therapeutic responses in tumor are characterized by alterations in immune cell signatures, including tumor-associated myeloid cells. Polarized tumor-associated myeloid cells (M1–M2) are critical in impairing therapeutic effect and promoting tumor growth. The present review is intended to compile all the literatures related to the emerging contribution of different populations of myeloid cells in the development of tumor and therapeutic failures. Finally, we have discussed targeting of myeloid cell populations as a combination therapy with chemo-, targeted-, or radiation therapies.

Enhanced EJ Cell Killing of (125)I Radiation by Combining with Cytosine Deaminase Gene Therapy Regulated by Synthetic Radio-Responsive Promoter

Aim: To investigate the enhancing effect of radionuclide therapy by the therapeutic gene placed under the control of radio-responsive promoter.

Methods: The recombinant lentivirus E8-codA-GFP, including a synthetic radiation-sensitive promoter E8, cytosine deaminase (CD) gene, and green fluorescent protein gene, was constructed. The gene expression activated by ¹²⁵I radiation was assessed by observation of green fluorescence. The ability of converting 5-fluorocytosine (5-FC) to 5-fluorourial (5-FU) by CD enzyme was assessed by high-performance liquid chromatography. The viability of the infected cells exposed to ¹²⁵I in the presence of 5-FC was determined by 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT) assay, and the infected cells exposed to ¹²⁵I alone served as negative control and 5-FU as positive control.

Results: The recombinant lentiviral vector was constructed successfully. On exposure of infected cells to ¹²⁵I, green fluorescence can be observed and 5-FU can be detected. MTT assay showed that the survival rate for infected cells treated with ¹²⁵I was lower compared with the ¹²⁵I control group, but higher than the positive control group.

Conclusion: The synthetic promoter E8 can induce the expression of downstream CD gene under ¹²⁵I radiation, and the tumor killing effect of ¹²⁵I can be enhanced by combining CD gene therapy with radiosensitive promoter.

CDK1-Mediated SIRT3 Activation Enhances Mitochondrial Function and Tumor Radioresistance

Tumor adaptive resistance to therapeutic radiation remains a barrier for further improvement of local cancer control. SIRT3, a member of the sirtuin family of NAD(+)-dependent protein deacetylases in mitochondria, promotes metabolic homeostasis through regulation of mitochondrial protein deacetylation and plays a key role in prevention of cell aging. Here, we demonstrate that SIRT3 expression is induced in an array of radiation-treated human tumor cells and their corresponding xenograft tumors, including colon cancer HCT-116, glioblastoma U87, and breast cancer MDA-MB231 cells. SIRT3 transcriptional activation is due to SIRT3 promoter activation controlled by the stress transcription factor NF-κB. Posttranscriptionally, SIRT3 enzymatic activity is further enhanced via Thr150/Ser159 phosphorylation by cyclin B1-CDK1, which is also induced by radiation and relocated to mitochondria together with SIRT3. Cells expressing Thr150Ala/Ser159Ala-mutant SIRT3 show a reduction in mitochondrial protein lysine deacetylation, Δψm, MnSOD activity, and mitochondrial ATP generation. The clonogenicity of Thr150Ala/Ser159Ala-mutant transfectants is lower and significantly decreased under radiation. Tumors harboring Thr150Ala/Ser159Ala-mutant SIRT3 show inhibited growth and increased sensitivity to in vivo local irradiation. These results demonstrate that enhanced SIRT3 transcription and posttranslational modifications in mitochondria contribute to adaptive radioresistance in tumor cells. CDK1-mediated SIRT3 phosphorylation is a potential effective target to sensitize tumor cells to radiotherapy.

Gene expression analysis reveals inhibition of radiation-induced TGFβ-signaling by hyperbaric oxygen therapy in mouse salivary glands

A side effect of radiation therapy in the head and neck region is injury to surrounding healthy tissues such as irreversible impaired function of the salivary glands. Hyperbaric oxygen therapy (HBOT) is clinically used to treat radiation-induced damage but its mechanism of action is largely unknown. In this study, we investigated the molecular pathways that are affected by HBOT in mouse salivary glands two weeks after radiation therapy by microarray analysis. Interestingly, HBOT led to significant attenuation of the radiation-induced expression of a set of genes and upstream regulators that are involved in processes such as fibrosis and tissue regeneration. Our data suggest that the TGFβ-pathway, which is involved in radiation-induced fibrosis and chronic loss of function after radiation therapy, is affected by HBOT. On the longer term, HBOT reduced the expression of the fibrosis-associated factor α-smooth muscle actin in irradiated salivary glands. This study highlights the potential of HBOT to inhibit the TGFβ-pathway in irradiated salivary glands and to restrain consequential radiation induced tissue injury.

Bystander effects as manifestation of intercellular communication of DNA damage and of the cellular oxidative status

It is becoming increasingly clear that cells exposed to ionizing radiation (IR) and other genotoxic agents (targeted cells) can communicate their DNA damage response (DDR) status to cells that have not been directly irradiated (bystander cells). The term radiation-induced bystander effects (RIBE) describes facets of this phenomenon, but its molecular underpinnings are incompletely characterized. Consequences of DDR in bystander cells have been extensively studied and include transformation and mutation induction; micronuclei, chromosome aberration and sister chromatid exchange formation; as well as modulations in gene expression, proliferation and differentiation patterns. A fundamental question arising from such observations is why targeted cells induce DNA damage in non-targeted, bystander cells threatening thus their genomic stability and risking the induction of cancer. Here, we review and synthesize available literature to gather support for a model according to which targeted cells modulate as part of DDR their redox status and use it as a source to generate signals for neighboring cells. Such signals can be either small molecules transported to adjacent non-targeted cells via gap-junction intercellular communication (GJIC), or secreted factors that can reach remote, non-targeted cells by diffusion or through the circulation. We review evidence that such signals can induce in the recipient cell modulations of redox status similar to those seen in the originating targeted cell - occasionally though self-amplifying feedback loops. The resulting increase of oxidative stress in bystander cells induces, often in conjunction with DNA replication, the observed DDR-like responses that are at times strong enough to cause apoptosis. We reason that RIBE reflect the function of intercellular communication mechanisms designed to spread within tissues, or the entire organism, information about DNA damage inflicted to individual, constituent cells. Such responses are thought to protect the organism by enhancing repair in a community of cells and by eliminating severely damaged cells.

Breast cancer adaptive resistance: HER2 and cancer stem cell repopulation in a heterogeneous tumor society

Purpose

The lethal effects of cancer are associated with the enhanced tumor aggressiveness in recurrent and metastatic lesions that show resistant phenotype to anti-cancer therapy, a major barrier to improving overall survival of cancer patients. The presence of heterogeneous populations of cancer cells within a specific tumor including the tumor-initiating cells or so-called cancer stem cells (CSCs) has linked the acquired resistance (AR, or adaptive resistance). Herein, we discuss the CSC-mediated tumor repopulation in AR of breast cancer in this review.

Methods

We emphasize a dynamic feature of gene induction in tumor cells that undergo long-term treatment, and describe a specific HER2-NF-κB-HER2 pro-survival pathway that can be initiated in breast CSCs upon radiation therapy.

Results

Elucidation of HER2-induced pro-survival networks, specifically the force driving tumor repopulation due to radioresistant CSCs during anticancer therapies, will have a significant impact on the generation of new diagnostic and therapeutic targets to control of recurrent and metastatic breast tumors.

Suppression of NF-κB activity by mutant IκBα: A molecular target for radiosensitization of adenoid cystic carcinoma

The constitutive activation of the nuclear factor κB (NF-κB) signaling pathway is involved in oncogenesis, invasive growth, metastasis and induced resistance to radiation and chemotherapy. Selective inhibition of the NF-κB signaling pathway, either by a mutant inhibitor or pharmacological agents, improves the therapeutic efficiency of irradiation. In the present study, the changes in NF-κB expression and the rate of apoptosis were investigated following irradiation of cells of an adenoid cystic carcinoma cell line (ACC-M) in which NF-κB expression had been inhibited by transient transfection with a mutant IκBα plasmid. ACC-M cells were transiently transfected with the mutant IκBα plasmid using Lipofectamine and the expression of this mutant IκBα gene was verified. The presence of the mutant IκBα gene alone did not result in a reduction in cell proliferation. Furthermore, a significant inhibition of translocation and synthesis of NF-κB protein in the transfected cells was observed after irradiation. NF-κB protein was activated by different doses of irradiation in a dose- and time-dependent manner with concordant changes in the radiosensitivity of ACC-M cells. We conclude that the mutant IκBα gene selectively inhibited the NF-κB pathway, which may be a promising method to improve the radiosensitivity of adenoid cystic carcinomas.

The impact of the myeloid response to radiation therapy

Radiation therapy is showing potential as a partner for immunotherapies in preclinical cancer models and early clinical studies. As has been discussed elsewhere, radiation provides debulking, antigen and adjuvant release, and inflammatory targeting of effector cells to the treatment site, thereby assisting multiple critical checkpoints in antitumor adaptive immunity. Adaptive immunity is terminated by inflammatory resolution, an active process which ensures that inflammatory damage is repaired and tissue function is restored. We discuss how radiation therapy similarly triggers inflammation followed by repair, the consequences to adaptive immune responses in the treatment site, and how the myeloid response to radiation may impact immunotherapies designed to improve control of residual cancer cells.

Inference of causal networks from time-varying transcriptome data via sparse coding

Temporal analysis of genome-wide data can provide insights into the underlying mechanism of the biological processes in two ways. First, grouping the temporal data provides a richer, more robust representation of the underlying processes that are co-regulated. The net result is a significant dimensional reduction of the genome-wide array data into a smaller set of vocabularies for bioinformatics analysis. Second, the computed set of time-course vocabularies can be interrogated for a potential causal network that can shed light on the underlying interactions. The method is coupled with an experiment for investigating responses to high doses of ionizing radiation with and without a small priming dose. From a computational perspective, inference of a causal network can rapidly become computationally intractable with the increasing number of variables. Additionally, from a bioinformatics perspective, larger networks always hinder interpretation. Therefore, our method focuses on inferring the simplest network that is computationally tractable and interpretable. The method first reduces the number of temporal variables through consensus clustering to reveal a small set of temporal templates. It then enforces simplicity in the network configuration through the sparsity constraint, which is further regularized by requiring continuity between consecutive time points. We present intermediate results for each computational step, and apply our method to a time-course transcriptome dataset for a cell line receiving a challenge dose of ionizing radiation with and without a prior priming dose. Our analyses indicate that (i) the priming dose increases the diversity of the computed templates (e.g., diversity of transcriptome signatures); thus, increasing the network complexity; (ii) as a result of the priming dose, there are a number of unique templates with delayed and oscillatory profiles; and (iii) radiation-induced stress responses are enriched through pathway and subnetwork studies.

Transcription profile of DNA damage response genes at G₀ lymphocytes exposed to gamma radiation

Ionizing radiation induces a plethora of DNA damages in human cells which may alter the level of mRNA expression. We have analyzed mRNA expression profile of DNA damage response genes involved in G(0)/G(1) check point pathway in whole blood to assess their radio-adaptive response, if any, to gamma radiation. Blood samples were collected from twenty-five random, normal, and healthy male donors with written informed consent and irradiated at doses between 0.1 and 2.0 Gy (0.7 Gy/min). DNA strand breaks were studied using comet assay, whereas DNA double-strand breaks were visualized using γH2AX as a biomarker. Dose response if any, at transcriptional level was studied for all these dose groups at 1 and 5-h post-irradiation. Adaptive response at transcriptional level was studied at three different priming doses (0.1, 0.3, and 0.6 Gy) separately followed by a challenging dose of 2.0 Gy after 4 h. For both the experiments, total RNA was isolated from PBMCs obtained from irradiated whole blood and reverse transcribed to cDNA. The level of mRNA expression of ATM, ATR, GADD45A, CDKN1A, P53, CDK2, MDM2, and Cyclin E was studied using real-time quantitative PCR. A significant dose-dependant increase in the percentage of DNA damage in tail was observed using comet assay. Similarly, increased number of foci was observed at γH2AX with increasing dose. At transcriptional level, a significant dose-dependent up-regulation at GADD45A, CDKN1A, and P53 genes up to 1.0 Gy was observed at 5-h post-irradiation (P ≤ 0.05). Radio-adaptive response at mRNA expression level was observed at CDK2, Cyclin E, and P53, whereas ATM, ATR, GADD45A, MDM2, ATM, and ATR have not shown any radio-adaptive changes in the expression profile. DNA damage response genes involved in G(0)/G(1) checkpoint pathway has important implications in terms of radiosensitivity in vivo and changes in the transcriptional profile might throw some new insights to understand the mechanism of adaptive response.

Adjuvant therapy with agonistic antibodies to CD134 (OX40) increases local control after surgical or radiation therapy of cancer in mice

The tumor recurrence from residual local or micrometastatic disease remains a problem in cancer therapy. In patients with soft tissue sarcoma and the patients with inoperable nonsmall cell lung cancer, local recurrence is common and significant mortality is caused by the subsequent emergence of metastatic disease. Thus, although the aim of the primary therapy is curative, the outcome may be improved by additional targeting of residual microscopic disease. We display in a murine model that surgical removal of a large primary sarcoma results in local recurrence in approximately 50% of animals. Depletion of CD8 T cells results in local recurrence in 100% of animals, indicating that these cells are involved in the control of residual disease. We further show that systemic adjuvant administration of αOX40 at surgery eliminates local recurrences. In this model, αOX40 acts to directly enhance tumor antigen-specific CD8 T-cell proliferation in the lymph node draining the surgical site, and results in increased tumor antigen-specific cytotoxicity in vivo. These results are also corroborated in a murine model of hypofractionated radiation therapy of lung cancer. Administration of αOX40 in combination with radiation significantly extended the survival compared with either agent alone, and resulted in a significant proportion of long-term tumor-free survivors. We conclude that αOX40 increases tumor antigen-specific CD8 T-cell cytotoxic activity resulting in improved endogenous immune control of residual microscopic disease, and we propose that adjuvant αOX40 administration may be a valuable addition to surgical and radiation therapy for cancer.

Dose-rate effects of protons on in vivo activation of nuclear factor-kappa B and cytokines in mouse bone marrow cells

The objective of this study was to determine the kinetics of nuclear factor-kappa B (NF-kappaB) activation and cytokine expression in bone marrow (BM) cells of exposed mice as a function of the dose rate of protons. The cytokines included in this study are pro-inflammatory [i.e., tumor necrosis factor-alpha (TNF-alpha), interleukin-1beta (IL-1beta), and IL-6] and anti-inflammatory cytokines (i.e., IL-4 and IL-10). We gave male BALB/cJ mice a whole-body exposure to 0 (sham-controls) or 1.0 Gy of 100 MeV protons, delivered at 5 or 10 mGy min(-1), the dose and dose rates found during solar particle events in space. As a reference radiation, groups of mice were exposed to 0 (sham-controls) or 1 Gy of (137)Cs gamma rays (10 mGy min(-1)). After irradiation, BM cells were collected at 1.5, 3, 24 h, and 1 month for analyses (five mice per treatment group per harvest time). The results indicated that the in vivo time course of effects induced by a single dose of 1 Gy of 100 MeV protons or (137)Cs gamma rays, delivered at 10 mGy min(-1), was similar. Although statistically significant levels of NF-kappaB activation and pro-inflammatory cytokines in BM cells of exposed mice when compared to those in the corresponding sham controls (Student's t-test, p < 0.05 or <0.01) were induced by either dose rate, these levels varied over time for each protein. Further, only a dose rate of 5 mGy min(-1) induced significant levels of anti-inflammatory cytokines. The results indicate dose-rate effects of protons.

Frequency of background and radiation-induced apoptosis in leukocytes of individuals with alpha-thalassemia variants, assessed by the neutral comet assay

To study effects of ionizing radiation on apoptosis induction in leukocytes of alpha-thalassemia (alpha-thal) variants compared to normal controls, venous blood samples were obtained from 10 healthy volunteers and 30 alpha-thal patients. Different types alpha-thal were diagnosed by multiplex polymerase chain reaction (PCR). Blood samples were irradiated with three Gy gamma rays, used for comet assay, immediately or 48 h after irradiation. Results show that the frequency of background as well as apoptosis in silent alpha-thal carriers, alpha-thal carriers and controls was similar but there was a significant difference between Hb H patients and other groups in the study. The increased apoptosis in Hb H patients might suggest that accumulation of beta-globin and oxidative stresses are effective in causing apoptosis, and cells from these patients are more vulnerable to damage from radiation-induced toxic substances. Therefore, from alpha-thal patients, those with Hb H disease might be considered as radiosensitive in terms of apoptosis formation.

Allylmethylsulfide Down-Regulates X-Ray Irradiation-Induced Nuclear Factor-kappaB Signaling in C57/BL6 Mouse Kidney

Allylmethylsulfide (AMS), a volatile organosulfur derivative from garlic, has been shown to have radioprotective effects in radiation-challenged cell and animal models, but the mechanism of radioprotection is not well understood. To determine the mechanism of radioprotection in an in vivo model, we first verified the antioxidant capacity of AMS using 2,2'-azobis(2-amidinopropane) dihydrochloride-induced human embryonic kidney 293T cells by measuring reactive oxygen species generation, reduced glutathione, protein tyrosine kinase/protein tyrosine phosphatase balance, and nuclear factor-kappaB (NF-kappaB) protein levels. We then investigated the protective effects of AMS (55 and 275 micromol/kg, intraperitoneal treatment) on 15 Gy X-ray-irradiated mouse kidney. The results showed that AMS decreased the free radical-induced lipid peroxidation in mice exposed to X-rays. Moreover, the antioxidative AMS suppressed the activation of NF-kappaB and its dependent genes such as vascular cell adhesion molecule-1, inducible nitric oxide synthase, and cyclooxygenase-2 through inhibition of IkappaBalpha phosphorylation and activation of IkappaB kinase alpha/beta and mitogen-activated protein kinases (MAPKs). Based on these results, AMS may be a useful radioprotective agent by down-regulating the MAPKs and NF-kappaB signaling pathway that can be induced via X-ray irradiation.

Transcriptional control of Flt3 ligand targeted by fluorouracil-induced Egr-1 promoter in hematopoietic damage

BACKGROUND

Ionizing radiation (IR) activate the early growth response-1 (Egr-1) promoter by production of radical oxygen intermediates (ROIs). Egr-EF, an expression vector pCIneo containing Egr-1 promoter cloned upstream of the cDNA for Flt3 ligand, was used to treat hematopoietic damage. 5-fluorouracil, a commonly used chemotherapeutic agent, cause tumor cell death by producing DNA damage and generating ROIs. We therefore hypothesized that clinically employed chemotherapeutic agents that increase ROIs could also be employed to activate Egr-EF in a chemoinducible gene therapy strategy. The goal of this study was to explore the effect of Flt3 Ligand gene transcription regulated by fluorouracil-induced Egr-1 promoter on hematopoietic recovery.

METHODS

Human Flt3 Ligand (FL) cDNA and enhanced green fluorescent protein (EGFP) cDNA were linked together with IRES and inserted into the expression vector pCI-neo under control of the Egr-1 promoter (Egr-EF). The vector was transfected into the HFCL human bone marrow stromal cell line, and these cells were exposed to 5-FU, a chemotherapeutic drug. Expression of FL by HFCL/EF cells after 5-FU treatment was determined with ELISA, western blot and RT-PCR assays. In addition, the effect of FL from HFCL/EF cell culture supernatants on growth of CD34+ cells from cord blood was also studied. HFCL/EF cells were injected into CB-17 combined immunodeficient (SCID) mice with B16 melanoma. 5-FU was given three days after injection of the HFCL/EF cells. In the recipient mice, white blood cell levels in peripheral blood and expression of EGFP and FL in human stromal cells were measured. Tumor volumes in tumor-bearing mice were also measured.

RESULTS

5-FU treatment increased EGFP levels and secreted FL levels in HFCL/EF cells. Supernatants from HFCL/EF cell cultures treated with 5-FU increased CD34+ cell growth significantly. HFCL/EF exhibited an increase in the number of white blood cells after chemotherapy.

CONCLUSION

The data presented here support the use of transcriptional control mediated by chemoinducible gene therapy to reduce hematopoietic injury associated with 5-FU.

Inactivation of AP1 proteins by a nuclear serine protease precedes the onset of radiation-induced fibrosing alveolitis

Radiation-induced lung damage comprises inflammation (alveolitis) as well as disturbed regulation of cell differentiation and proliferation (fibrosis). The transcriptional regulation of this process is poorly understood. One key transcription factor involved in the regulation of proliferation and differentiation is AP1 (activator protein 1). The present study examined changes in the DNA-binding activity of AP1 after irradiation and defined the underlying molecular mechanisms in an animal model. The right lungs of Fischer rats received a single radiation dose of 20 Gy. Lung tissue was tested for AP1 DNA-binding activity, AP1 mRNA, and levels of AP1 proteins as well as for c-Jun specific proteolytic activity. After an initial increase, the AP1 DNA-binding activity was completely lost starting at 5.5 weeks after irradiation, which is 2.5 weeks before the onset of fibrosing alveolitis. This was not caused by reduction of mRNA levels or size. Instead, a selective nuclear cleavage of c-Jun by a serine protease caused the loss of AP1 activity. Considering the central role of AP1 in cell proliferation and differentiation and the strict timely correlation to the onset of the disease, the complete loss of AP1 function is likely to play a critical role in radiation-induced fibrosing alveolitis.

ATM-NF-kappaB connection as a target for tumor radiosensitization

Ionizing radiation (IR) plays a key role in both areas of carcinogenesis and anticancer radiotherapy. The ATM (ataxia-telangiectasia mutated) protein, a sensor to IR and other DNA-damaging agents, activates a wide variety of effectors involved in multiple signaling pathways, cell cycle checkpoints, DNA repair and apoptosis. Accumulated evidence also indicates that the transcription factor NF-kappaB (nuclear factor-kappaB) plays a critical role in cellular protection against a variety of genotoxic agents including IR, and inhibition of NF-kappaB leads to radiosensitization in radioresistant cancer cells. NF-kappaB was found to be defective in cells from patients with A-T (ataxia-telangiectasia) who are highly sensitive to DNA damage induced by IR and UV lights. Cells derived from A-T individuals are hypersensitive to killing by IR. Both ATM and NF-kappaB deficiencies result in increased sensitivity to DNA double strand breaks. Therefore, identification of the molecular linkage between the kinase ATM and NF-kappaB signaling in tumor response to therapeutic IR will lead to a better understanding of cellular response to IR, and will promise novel molecular targets for therapy-associated tumor resistance. This review article focuses on recent findings related to the relationship between ATM and NF-kappaB in response to IR. Also, the association of ATM with the NF-kappaB subunit p65 in adaptive radiation response, recently observed in our lab, is also discussed.

NF-kappa B-mediated adaptive resistance to ionizing radiation

Ionizing radiation (IR) began to be a powerful medical modality soon after Wilhelm Röntgen's discovery of X-rays in 1895. Today, more than 50% of cancer patients receive radiotherapy at some time during the course of their disease. Recent technical developments have significantly increased the precision of dose delivery to the target tumor, making radiotherapy more efficient in cancer treatment. However, tumor cells have been shown to acquire a radioresistance that has been linked to increased recurrence and failure in many patients. The exact mechanisms by which tumor cells develop an adaptive resistance to therapeutic fractional irradiation are unknown, although low-dose IR has been well defined for radioadaptive protection of normal cells. This review will address the radioadaptive response, emphasizing recent studies of molecular-level reactions. A prosurvival signaling network initiated by the transcription factor NF-kappa B, DNA-damage sensor ATM, oncoprotein HER-2, cell cyclin elements (cyclin B1), and mitochondrial functions in radioadaptive resistance is discussed. Further elucidation of the key elements in this prosurvival network may generate novel targets for resensitizing the radioresistant tumor cells.

Ionizing radiation can induce GSK-3beta phosphorylation and NF-kappaB transcriptional transactivation in ATM-deficient fibroblasts

DNA damage by ionizing radiation (IR) can induce activations of both NF-kappaB and p53 through the upstream kinase ataxia telangiectasia mutated (ATM). NF-kappaB activation could also be signaled through two distinct or overlapped pathways; IkappaB kinases (IKKs)-IkappaBalpha and Akt-glycogen synthase kinase-3 (GSK-3). In the present study, however, we show that activation of Akt1 and the subsequent phosphorylation and inactivation of GSK-3beta by IR could also occur in ATM-deficient AT5BIVA cells as well as in normal MRC5CV1 fibroblasts. Similarly, lithium chloride (LiCl) was found to increase the phosphorylation of GSK-3beta independently of ATM. Transfection with either wild-type or kinase dead mutant GSK-3beta to the cells further indicated that phosphorylations of Akt1 and GSK-3beta were closely associated with the transcriptional transactivation of NF-kappaB in response to ionizing radiation. On the other hand, LiCl, having no effect on caspase-3 activation, significantly increased p53 phosphorylation and apoptotic death of the normal MRC5CV1 cells while IR, activating both caspase-3 and p53, profoundly affected AT5BIVA cell death. Hence, our data suggest that although ATM-mediated IKK-IkappaBalpha pathway might be a typical pathway for IR-induced NF-kappaB activation, GSK-3beta phosphorylation could also partially contribute to the transcriptional transactivation of NF-kappaB in an ATM-independent manner and that GSK-3beta phosphorylation could induce ATM-mediated cell apoptosis through the activation of p53.

Dose- and time-dependent changes in gene expression in human glioma cells after low radiation doses

We have used DNA microarrays to identify changes in gene expression in cells of the radioresistant human glioma cell lines T98G and U373 after low radiation doses (0.2-2 Gy). Using Bayesian linear models, we have identified a set of genes that respond to low doses of radiation; furthermore, a hypothesis-driven approach to data analysis has allowed us to identify groups of genes with defined non-linear dose responses. Specifically, one of the cell lines we have examined (T98G) shows increased radiosensitivity at low doses (low-dose hyper-radiosensitivity, HRS); thus we have also assessed sets of genes whose dose response mirrors this survival pattern. We have also investigated a time course for induction of genes over the period when the DNA damage response is expected to occur. We have validated these data using quantitative PCR and also compared genes up-regulated in array data to genes present in the polysomal RNA fraction after irradiation. Several of the radioresponsive genes that we describe code for proteins that may have an impact on the outcome of irradiation in these cells, including RAS homologues and kinases involved in checkpoint signaling, so understanding their differential regulation may suggest new ways of altering radioresistance. From a clinical perspective these data may also suggest novel targets that are specifically up-regulated in gliomas during radiotherapy treatments.

Radiobiological mechanisms in inflammatory diseases of low-dose radiation therapy

PURPOSE

Whereas X-irradiation with high doses is established to exert pro-inflammatory effects, low-dose radiotherapy (LD-RT) with single fractions below 1.0 Gy and a total dose below 12 Gy is clinically well known to exert anti-inflammatory and analgesic effects on several inflammatory diseases and painful degenerative disorders. Experimental studies to confirm the effectiveness, the empirical dose and fractionation schemes, and the underlying radiobiological mechanisms are still fragmentary.

METHOD

The anti-inflammatory efficiency of LD-RT was confirmed in several experimental in vitro and in vivo models.

RESULTS

In vitro studies revealed a variety of mechanisms related to the anti-inflammatory effect, in particular the modulation of cytokine and adhesion molecule expression on activated endothelial cells and leukocytes, and of nitric oxide (NO) production and oxidative burst in activated macrophages and native granulocytes.

CONCLUSION

Inflammatory diseases are the result of complex and pathologically unbalanced multicellular interactions. It is, therefore, reasonable to assume that further molecular pathways and cellular components contribute to the anti-inflammatory effect of LD-RT. This review discusses data and models revealing aspects of the mechanisms underlying the anti-inflammation induced by low doses of X-irradiation and may serve as a basis for systematic analyses, necessary to optimize LD-RT in clinical practice.

Irradiation modulates association of NF-Y with histone-modifying cofactors PCAF and HDAC

Post-irradiation complications including thrombus formation result from increased procoagulant activity of vascular endothelial cells and elevated levels of von Willebrand factor (VWF) contribute to this process. We have previously demonstrated that irradiation induction of the VWF is mediated through interaction of NF-Y transcription factor with its cognate binding site in the VWF promoter. We have also demonstrated that irradiation increases the association of NF-Y with histone acetyltransferase p300/CBP-associated factor (PCAF). We now report that irradiation decreases the association of NF-Y with histone deacetylase 1 (HDAC1). We demonstrate that irradiation-induced changes in association of NF-Y with HDAC1 and PCAF lead to increased PCAF recruitment to the VWF promoter, increased association of acetylated histone H4 with the VWF promoter and subsequently increased transcription. We also demonstrate that this process is correlated to dephosphorylation of HDAC1 and is inhibited by calyculin A, an inhibitor of protein phosphatase1.

The potential of proteasome inhibition in the treatment of colon cancer

Proteasome inhibition is an entirely novel approach to the treatment of malignant disease. By interfering with the ubiquitin-proteasome degradation system, proteasome inhibitors affect numerous cellular processes that are commonly deregulated in cancer cells including gene transcription, cell-cycle regulation, apoptosis, cell migration and DNA repair. This review outlines the physiology of the ubiquitin-proteasome pathway, discusses preclinical and clinical data regarding the activity of proteasome inhibitors against colon cancer and evaluates the rationale for the use of proteasome inhibitors as monotherapy or in combination with other anticancer therapies (i.e., chemotherapy, radiation therapy and other molecular-targeted therapies) in colon cancer.

MAP kinases: Differential activation following in vivo and ex vivo irradiation

Mitogen activated protein kinases (MAPK) play a critical role in controlling cell survival and repopulation following exposure to ionising radiation. Most investigations on these pathways have been done using cultured cells or by ex vivo treatments. The present study was carried out to determine whether the response of MAPKs in mouse lymphocytes differs following in vivo and ex vivo irradiation with 60Co gamma-rays. We observed that ex vivo treatment resulted in a very significant decrease in the activated p44/42 and p38 MAPK as compared to in vivo. However, stress activated protein kinase (SAPK) response showed no significant difference between in vivo and ex vivo treatments. These observations point towards the differences in response elicited when the treatment is given in vivo as compared to in vitro. Therefore the findings reported from in vitro or ex vivo treatments should be treated with caution especially if it has to be clinically applied.

Gene expression changes in peripheral blood cells provide insight into the biological mechanisms associated with regimen-related toxicities in patients being treated for head and neck cancers

Patients treated with radiotherapy are prone to a constellation of local and systemic toxicities including mucositis, xerostomia, fatigue and anorexia. The biological complexities and similarities underlying the development of toxicities have recently been realized. Mucosal barrier injury is one of the best studied, and gene expression patterns, based on animal tissue samples, have added to its understanding. While investigations gene expression based on tissue samples was valuable, its use precludes more generalizable conclusions relative to common pathogenic mechanisms. Additionally, attempting to define the kinetics of changes in gene expression by sequential sampling is pragmatically unrealistic. Our objectives were: 1. to determine if changes in gene expression could be detected during toxicity development using PBM from patients receiving chemoradiation; 2. to characterize the relationship of expressed genes using graph theory and pathway analysis; and 3. to evaluate potential relationships between the expression of particular genes, canonical pathways, and functional networks in explaining the pathogenesis of regimen-related toxicities.

DESIGN

Microarray analysis was performed using PBM-derived cRNA obtained before and 2 weeks after the initiation of chemoradiation in five patients with head and neck cancer who developed documented regimen-related toxicities. We created a database of those genes newly expressed at 2 weeks and evaluated their potential significance relative to toxicity, by canonical pathway analysis, compilation of regional networks around focus genes, and development of a model globalizing the individual functional networks. There was strong concordance between known pathogenic mechanisms of toxicity and the genes, pathways, and networks developed by our data. A role was elicited for unsuspected genes in toxicity development. Our results support the concept that radiation induced toxicities have common underlying mechanisms and demonstrate the utility of PBM as an RNA source for genetic studies. This methodology could be broadly applicable to the study of regimen-related toxicities.

Bystander effect: biological endpoints and microarray analysis

In cell populations exposed to ionizing radiation, the biological effects occur in a much larger proportion of cells than are estimated to be traversed by radiation. It has been suggested that irradiated cells are capable of providing signals to the neighboring unirradiated cells resulting in damage to these cells. This phenomenon is termed the bystander effect. The bystander effect induces persistent, long-term, transmissible changes that result in delayed death and neoplastic transformation. Because the bystander effect is relevant to carcinogenesis, it could have significant implications for risk estimation for radiation exposure. The nature of the bystander effect signal and how it impacts the unirradiated cells remains to be elucidated. Examination of the changes in gene expression could provide clues to understanding the bystander effect and could define the signaling pathways involved in sustaining damage to these cells. The microarray technology serves as a tool to gain insight into the molecular pathways leading to bystander effect. Using medium from irradiated normal human diploid lung fibroblasts as a model system we examined gene expression alterations in bystander cells. The microarray data revealed that the radiation-induced gene expression profile in irradiated cells is different from unirradiated bystander cells suggesting that the pathways leading to biological effects in the bystander cells are different from the directly irradiated cells. The genes known to be responsive to ionizing radiation were observed in irradiated cells. Several genes were upregulated in cells receiving media from irradiated cells. Surprisingly no genes were found to be downregulated in these cells. A number of genes belonging to extracellular signaling, growth factors and several receptors were identified in bystander cells. Interestingly 15 genes involved in the cell communication processes were found to be upregulated. The induction of receptors and the cell communication processes in bystander cells receiving media from irradiated cells supports the active involvement of these processes in inducing bystander effect.

Tumor radiosensitizers--current status of development of various approaches: report of an International Atomic Energy Agency meeting

PURPOSE

The International Atomic Energy Agency (IAEA) held a Technical Meeting of Consultants to (1) discuss a selection of relatively new agents, not those well-established in clinical practice, that operated through a variety of mechanisms to sensitize tumors to radiation and (2) to compare and contrast their tumor efficacy, normal tissue toxicity, and status of development regarding clinical application. The aim was to advise the IAEA as to which developing agent or class of agents would be worth promoting further, by supporting additional laboratory research or clinical trials, with the eventual goal of improving cancer control rates using radiotherapy, in developing countries in particular.

RESULTS

The agents under discussion included a wide, but not complete, range of different types of drugs, and antibodies that interfered with molecules in cell signaling pathways. These were contrasted with new molecular antisense and gene therapy strategies. All the drugs discussed have previously been shown to act as tumor cell radiosensitizers or to kill hypoxic cells present in tumors.

CONCLUSION

Specific recommendations were made for more preclinical studies with certain of the agents and for clinical trials that would be suitable for industrialized countries, as well as trials that were considered more appropriate for developing countries.

Methionine-stress: A pleiotropic approach in enhancing the efficacy of chemotherapy

Malignant cells fail to utilize homocysteine (HCYS) in place of methionine (MET) and they are dependent on exogenous MET for growth. In animals, reduction of plasma MET to <5 microM can be induced by combined dietary restriction of MET and administration of L-methionine-alpha-deamino-gamma-lyase (methioninase). This treatment, termed as MET-stress, inhibits the growth of brain tumor xenografts in athymic mice and enhances the efficacy of DNA alkylating chemotherapeutic agents. The response of tumors to MET-stress depends on their mutational status, however, it always involves inhibition of CDK1 and in most cases the upregulation of p21, p27, GADDs and 14-3-3sigma in response to upregulation of TGF-beta, IRF-1, TNF-alpha, Rb and/or MDA-7 and the downregulation of PI3K, RAS and NF-kappaB. Although inhibition of the cell cycle and mitosis is not necessarily dependent on the tumor's p53 status, the expression of p21, GADD45 and apoptosis related genes (BAX, BCL-2) are regulated by wt-p53, in addition to their regulation by TGF-beta or MDA-7 in mutated p53 tumors. Mutational variability determines the mode of death (mitotic catastrophe versus apoptosis) in tumor cells subjected to MET-stress. The increase of the efficacy of alkylating agents is related to marked inhibition of O6-methylguanine-DNA methyltransferase (MGMT) expression, the induction of cell cycle check points and the inhibition of pro-survival pathways by MET-stress.

Redox-sensitive signaling factors as a novel molecular targets for cancer therapy

Tumor cells undergoing proliferation, de-differentiation and progression depend on a complex set of respiratory pathways to generate the necessary energy. The metabolites from these pathways produce significant oxidative stress and must be buffered to prevent permanent cell damage and cell death. It is now clear that, in order to cope with and defend against the detrimental effects of oxidative stress, a series of redox-sensitive, pro-survival signaling pathways and factors regulate a complex intracellular redox buffering network. This review develops the hypothesis that tumor cells use these redox-sensitive, pro-survival signaling pathways and factors - up-regulated due to increased tumor cell respiration - to evade the damaging and cytotoxic effects of specific anticancer agents. It further suggests that redox-sensitive, signaling factors may be potential novel targets for drug discovery.

The suppression of radiation-induced NF-κB activity by dexamethasone correlates with increased cell death in vivo

In this study, we show that dexamethasone treatment increases ionizing radiation-induced cell death by inducing the inhibitory kappaBalpha (IkappaBalpha) pathway in mice. The effect of dexamethasone on radiation-induced cell death was assessed by changes in total spleen cellularity and bone marrow colony-forming unit-granulocyte-macrophage (CFU-GM) contents after total body irradiation. While in vivo treatment of mice with dexamethasone alone (1 mg/kg/day, for 2 days) failed to elicit cell death in spleen cells, the combined treatment with dexamethasone (1 mg/kg/day, for 2 days) and gamma-rays (1 or 5 Gy) caused a 50-80% reduction in total cellularity in spleen and CFU-GM contents in bone marrow. These results demonstrate that dexamethasone has a synergistic effect on radiation-induced cellular damages in vivo. Immunoblot analysis showed that dexamethasone treatment significantly increases IkappaBalpha expression in the spleens of irradiated mice. In addition, the dexamethasone treatment significantly reduced radiation-induced nuclear translocation of the nucleus factor-kappaB in the spleens of irradiated mice. These results indicate that dexamethasone treatment in vivo may increase radiation-induced cell damages by increasing IkappaBalpha expression in hematopoietic organs such as spleen and bone marrow.

Radiation-induced gene expression profile of human cells deficient in 8-hydroxy-2′-deoxyguanine glycosylase

The human OGG1 gene encodes a DNA glycosylase that is involved in the base excision repair of 8-hydroxy-2'-deoxyguanine (8-OH-dG) from oxidatively damaged DNA. Cellular 8-OH-dG levels accumulate in the absence of this activity and could be deleterious for the cell. To assess the role of 8-oxoguanine glycosylase (OGG1) in the cellular defense mechanism in a specific DNA repair defect background, we set out to determine the expression pattern of base excision repair genes and other cellular genes not involved in the base excision pathway in OGG1-deficient human KG-1 cells after ionizing radiation exposure. KG-1 cells have lost OGG1 activity due to a homozygous mutation of Arg229Gln. Gene expression alterations were monitored at 4, 8, 12 and 24 hr in 2 Gy irradiated cells. Large-scale gene expression profiling was assessed with DNA microarray technology. Gene expression analysis identified a number of ionizing radiation-responsive genes, including several novel genes. There were 2 peaks of radiation-induced gene induction or repression: one at 8 hr and the other at 24 hr. Overall the number of downregulated genes was higher than the number of upregulated genes. The highest number of downregulated genes was at 8 hr postirradiation. Genes corresponding to cellular, physiologic, developmental and extracellular processes were identified. The highest number of radiation-induced genes belonged to the signal transduction category, followed by genes involved in transcription and response to stress. Microarray gene expression data were independently validated by relative quantitative RT-PCR. Surprisingly, none of the genes involved in the base excision repair of radiation-induced DNA damage showed altered expression.

Protective effect of apigenin on radiation-induced chromosomal damage in human lymphocytes

The potential use of flavonoids as a radioprotector is of increasing interest because of their high antioxidant activity and abundance in the diet. The aim of this study is to examine genotoxic and radioprotective effects of one of the most common flavonoids, apigenin, on radiation-induced chromosome aberrations in human lymphocytes. The cytokinesis-block micronucleus (CBMN) assay was used to evaluate such effects of apigenin. Blood samples were collected from two non-smoking healthy male volunteers who had no history of previous exposure to other clastogenic agents. Isolated lymphocytes were cultured. There were two tubes per concentration for all treatments. To evaluate the genotoxicity of apigenin, cells were first treated with different concentrations of apigenin (0, 2.5, 5, 10 and 25 microg/mL) at 24 h after culture initiation, followed by cytochalasin-B (Cyt-B) treatment (3 microg/mL) and cell harvest at 44 and 72 h, respectively. Secondly, to investigate the radioprotective effect, cell cultures were exposed to different concentrations of apigenin as described above for 30 min before being irradiated to 2 Gy of 137Cs gamma rays (at a dose rate of 0.75 Gy/min). In all instances, the frequency of MN was scored in binucleated (BN) cells. The nuclear proliferation index also was calculated. We did not detect an increase in the frequency of MN in non-irradiated human lymphocyte cultures treated with 2.5, 5.0 or 10 microg/mL apigenin; although, we did observe an increase in cultures treated with 25 microg/mL apigenin (the highest concentration of apigenin used in our study). We also observed a significant increase in the frequency of MN in irradiated cells overall; however, the frequency was decreased as the concentration of apigenin increased, suggesting a radioprotective effect. These findings provide a basis for additional studies to help clarify the potential use and benefit of apigenin as a radioprotector.