Protein kinase C mediates x-ray inducibility of nuclear signal transducers EGR1 and JUN

The EGR1/miR-139/NRF2 axis orchestrates radiosensitivity of non-small-cell lung cancer via ferroptosis

Radiotherapy is one of the predominant treatment modalities for almost all kinds of malignant cancers, including non-small cell lung cancer (NSCLC). Increasing evidence shows that ionizing radiation (IR) induces reactive oxygen species (ROS) leading to lipid peroxidation and subsequently ferroptosis of cancer cells. However, cancer cells evolve multiple mechanisms against ROS biology resulting in resistance to ferroptosis and radiotherapy, of which NRF2 signaling is one of the most studied. In the current research, we identified that microRNA-139 (miR-139) could be a novel radiosensitizer for NSCLC by inhibiting NRF2 signaling. We found that miR-139 possessed great potential as a diagnostic biomarker for NSCLC and multiple other types of cancer. Overexpression of miR-139 increased radiosensitivity of NSCLC cells in vitro and in vivo. MiR-139 directly targeted cJUN and KPNA2 to impair NRF2 signaling resulting in enhanced IR-induced lipid peroxidation and cellular ferroptosis. We proved KPNA2 to be a binding partner of NRF2 that involved in nuclear translocation of NRF2. Moreover, we found that IR induced miR-139 expression through transcriptional factor EGR1. EGR1 bound to the promoter region and transactivated miR-139. Overall, our findings elucidated the effect of EGR1/miR-139/NRF2 in IR-induced ferroptosis of NSCLC cells and provided theoretical support for the potential diagnostic biomarkers and therapeutic targets for the disease.

Resveratrol attenuates diabetes-associated cell centrosome amplification via inhibiting the PKCα-p38 to c-myc/c-jun pathway

Type 2 diabetes increases the risk for cancer. Centrosome amplification can initiate tumorigenesis. We have described that type 2 diabetes increases the centrosome amplification of peripheral blood mononuclear cells, with high glucose, insulin, and palmitic acid as the triggers, which suggests that centrosome amplification is a candidate biological mechanism linking diabetes to cancer. In this study, we aimed to further investigate the signaling pathways of the diabetes-associated centrosome amplification and to examine whether and how resveratrol inhibits the centrosome amplification. The results showed that treatment with high glucose, insulin, and palmitic acid, alone or in combination, could increase the protein levels of phospho-protein kinase C alpha (p-PKCα), phospho-p38 mitogen-activated protein kinases (p-p38), c-myc, and c-jun, as well as the mRNA levels of c-myc and c-jun. PKCα inhibitor could inhibit the treatment-induced increase in the protein levels of p-p38, c-myc, and c-jun. Inhibitor or siRNA of p38 was also able to inhibit the treatment-induced increase in the levels of p-p38, c-myc, and c-jun. Meanwhile, knockdown of c-myc or c-jun did not alter the treatment-induced increase in the phosphorylation of PKCα or p38. Importantly, inhibition of the phosphorylation of PKCα or p38 and knockdown of c-myc or c-jun could attenuate the centrosome amplification. In diabetic mice, the levels of p-PKCα, p-p38, c-myc, and c-jun were all increased in the colon tissues. Interestingly, resveratrol, but not metformin, was able to attenuate the treatment-induced increase in the levels of p-PKCα, p-p38, c-myc, and c-jun, as well as the centrosome amplification. In conclusion, our results suggest that PKCα-p38 to c-myc/c-jun is the signaling pathway of the diabetes-associated centrosome amplification, and resveratrol attenuates the centrosome amplification by inhibiting this signaling pathway.

Gene expression profiling of rat livers after continuous whole-body exposure to low-dose rate of gamma rays

PURPOSE

To study gene expression modulation in response to continuous whole-body exposure to low-dose-rate gamma radiation and improve our understanding of the mechanism of this impact at the molecular basis.

MATERIALS AND METHODS

cDNA microarray method with complete pooling of samples was used to study expression changes in the transcriptome profile of livers from rats treated with prolonged low-dose-rate ionizing radiation (IR) relative to that of sham-irradiated rats.

RESULTS

Of the 209 genes that were two-fold-up or down-regulated, 143 were known genes of which 27 were found in previous literatures to be modulated by IR. Remarkably, there were a significant number of differentially expressed genes involved in hepatic lipid metabolism.

CONCLUSION

This study showed changes in transcriptome profile of livers from low-dose irradiated rats when compared with that of sham-irradiated ones. This study will be useful for studying the metabolic changes of human exposed for long term to cosmic ray such as in space and in polar regions.

BET-bromodomain inhibitors modulate epigenetic patterns at the diacylglycerol kinase alpha enhancer associated with radiation-induced fibrosis

BACKGROUND AND PURPOSE

Fibrosis is a frequent adverse effect of radiotherapy and no effective treatments are currently available to prevent or reverse fibrotic disease. We have previously identified altered epigenetic patterns at a gene enhancer of the diacylglycerol kinase alpha (DGKA) locus in normal skin fibroblasts derived from fibrosis patients. An open chromatin pattern related to radiation-inducibility of DGKA is associated with onset of radiation-induced fibrosis. Here, we explore epigenetic modulation of DGKA as a way to mitigate predisposition to fibrosis.

MATERIAL AND METHODS

We studied the effect of the BET-bromodomain inhibitors (JQ1, PFI-1) on DGKA inducibility in primary fibroblasts. Hence, DGKA transcription was additionally induced by the radiomimetic drug bleomycin, and DGKA mRNA expression, histone H3K27 acetylation and downstream markers of profibrotic fibroblast activation after BET-bromodomain inhibition were determined.

RESULTS

BET-bromodomain inhibition suppressed induction of DGKA in bleomycin-treated fibroblasts, reduced H3K27ac at the DGKA enhancer and repressed collagen marker gene expression. Alterations in fibroblast morphology and reduction of collagen deposition were observed.

CONCLUSION

For the DGKA enhancer, we show that BET-bromodomain inhibitors can alter the epigenetic landscape of fibroblasts, thus counteracting profibrotic transcriptional events. Interference with epigenetic patterns of fibrosis predisposition may provide novel preventive therapies that improve radiotherapy.

Intratumoural production of TNFα by bacteria mediates cancer therapy

Systemic administration of the highly potent anticancer therapeutic, tumour necrosis factor alpha (TNFα) induces high levels of toxicity and is responsible for serious side effects. Consequently, tumour targeting is required in order to confine this toxicity within the locality of the tumour. Bacteria have a natural capacity to grow within tumours and deliver therapeutic molecules in a controlled fashion. The non-pathogenic E. coli strain MG1655 was investigated as a tumour targeting system in order to produce TNFα specifically within murine tumours. In vivo bioluminescence imaging studies and ex vivo immunofluorescence analysis demonstrated rapid targeting dynamics and prolonged survival, replication and spread of this bacterial platform within tumours. An engineered TNFα producing construct deployed in mouse models via either intra-tumoural (i.t.) or intravenous (i.v.) administration facilitated robust TNFα production, as evidenced by ELISA of tumour extracts. Tumour growth was impeded in three subcutaneous murine tumour models (CT26 colon, RENCA renal, and TRAMP prostate) as evidenced by tumour volume and survival analyses. A pattern of pro-inflammatory cytokine induction was observed in tumours of treated mice vs. controls. Mice remained healthy throughout experiments. This study indicates the therapeutic efficacy and safety of TNFα expressing bacteria in vivo, highlighting the potential of non-pathogenic bacteria as a platform for restricting the activity of highly potent cancer agents to tumours.

Radiogenic Therapy: Novel Approaches for Enhancing Tumor Radiosensitivity

Radiotherapy (RT) is a well established modality for treating many forms of cancer. However, despite many improvements in treatment planning and delivery, the total radiation dose is often too low for tumor cure, because of the risk of normal tissue damage. Gene therapy provides a new adjunctive strategy to enhance the effectiveness of RT, offering the potential for preferential killing of cancer cells and sparing of normal tissues. This specificity can be achieved at several levels including restricted vector delivery, transcriptional targeting and specificity of the transgene product. This review will focus on those gene therapy strategies that are currently being evaluated in combination with RT, including the use of radiation sensitive promoters to control the timing and location of gene expression specifically within tumors. Therapeutic transgenes chosen for their radiosensitizing properties will also be reviewed, these include:

gene correction therapy, in which normal copies of genes responsible for radiation-induced apoptosis are transfected to compensate for the deletions or mutated variants in tumor cells (p53 is the most widely studied example). enzymes that synergize the radiation effect, by generation of a toxic species from endogenous precursors ( e.g., inducible nitric oxide synthase) or by activation of non toxic prodrugs to toxic species ( e.g., herpes simplex virus thymidine kinase/ganciclovir) within the target tissue. conditionally replicating oncolytic adenoviruses that synergize the radiation effect. membrane transport proteins ( e.g., sodium iodide symporter) to facilitate uptake of cytotoxic radionuclides.

The evidence indicates that many of these approaches are successful for augmenting radiation induced tumor cell killing with clinical trials currently underway.

The Use of Gene Therapy in Cancer Research and Treatment

Gene therapy involves identifying a gene of interest and then manipulating the expression of this gene through a variety of techniques. Here we specifically address gene therapy's role in cancer research. This paper will encompass thoroughly investigated techniques such as cancer vaccines and suicide gene therapy and the latest advancements in and applications of these techniques. It will also cover newer techniques such as Antisense Oligonucleotides and small interfering RNAs and how these technologies are being developed and used. The use of gene therapy continues to expand in cancer research and has an integral role in the advancement of cancer treatment.

Epigenetic regulation of diacylglycerol kinase alpha promotes radiation-induced fibrosis

Radiotherapy is a fundamental part of cancer treatment but its use is limited by the onset of late adverse effects in the normal tissue, especially radiation-induced fibrosis. Since the molecular causes for fibrosis are largely unknown, we analyse if epigenetic regulation might explain inter-individual differences in fibrosis risk. DNA methylation profiling of dermal fibroblasts obtained from breast cancer patients prior to irradiation identifies differences associated with fibrosis. One region is characterized as a differentially methylated enhancer of diacylglycerol kinase alpha (DGKA). Decreased DNA methylation at this enhancer enables recruitment of the profibrotic transcription factor early growth response 1 (EGR1) and facilitates radiation-induced DGKA transcription in cells from patients later developing fibrosis. Conversely, inhibition of DGKA has pronounced effects on diacylglycerol-mediated lipid homeostasis and reduces profibrotic fibroblast activation. Collectively, DGKA is an epigenetically deregulated kinase involved in radiation response and may serve as a marker and therapeutic target for personalized radiotherapy.

Radiotherapy can induce fibrosis in cancer patients, limiting its use in clinical settings. Here, the authors identify a differentially methylated enhancer of the lipid kinase DGKA in fibroblasts from breast cancer patients developing fibrosis after radiotherapy and they show that DGKA inhibition affects lipid homeostasis and reduces pro-fibrotic fibroblast activation.

Silencing Egr1 Attenuates Radiation-Induced Apoptosis in Normal Tissues while Killing Cancer Cells and Delaying Tumor Growth

Normal tissue toxicity reduces the therapeutic index of radiotherapy and decreases the quality of life for cancer survivors. Apoptosis is a key element of the radiation response in normal tissues like the hippocampus and small intestine, resulting in neurocognitive disorders and intestinal malabsorption. The Early Growth Response 1 (Egr1) transcription factor mediates radiation-induced apoptosis by activating the transcription of proapoptosis genes in response to ionizing radiation (IR). Therefore, we hypothesized that the genetic abrogation of Egr1 and the pharmacologic inhibition of its transcriptional activity could attenuate radiation-induced apoptosis in normal tissues. We demonstrated that Egr1-null mice had less apoptosis in the hippocampus and intestine following irradiation as compared with their wild-type littermates. A similar result was achieved using Mithramycin A (MMA) to prevent binding of Egr1 to target promoters in the mouse intestine. Abolishing Egr1 expression using shRNA dampened apoptosis and enhanced the clonogenic survival of irradiated HT22 hippocampal neuronal cells and IEC6 intestinal epithelial cells. Mechanistically, these events involved an abrogation of p53 induction by IR and an increase in the ratio of Bcl-2/Bax expression. In contrast, targeted silencing of Egr1 in two cancer cell lines (GL261 glioma cells and HCT116 colorectal cancer cells) was not radioprotective, since it reduced their growth while also sensitizing them to radiation-induced death. Further, Egr1 depletion delayed the growth of heterotopically implanted GL261 and HCT116 tumors. These results support the potential of silencing Egr1 in order to minimize the normal tissue complications associated with radiotherapy while enhancing tumor control.

Protein kinase C inhibitors sensitize GNAQ mutant uveal melanoma cells to ionizing radiation

PURPOSE

Uveal melanoma (UM) tumors require large doses of radiation therapy (RT) to achieve tumor ablation, which frequently results in damage to adjacent normal tissues, leading to vision-threatening complications. Approximately 50% of UM patients present with activating somatic mutations in the gene encoding for G protein αq-subunit (GNAQ), which lead to constitutive activation of downstream pathways, including protein kinase C (PKC). In this study, we investigated the impact of small-molecule PKC inhibitors bisindolylmaleimide I (BIM) and sotrastaurin (AEB071), combined with ionizing radiation (IR), on survival in melanoma cell lines.

METHODS

Cellular radiosensitivity was determined by using a combination of proliferation, viability, and clonogenic assays. Cell-cycle effects were measured by flow cytometry. Transcriptomic and proteomic profiling were performed by quantitative real-time PCR, reverse-phase protein array analysis, and immunofluorescence.

RESULTS

We found that the PKC inhibitors combined with IR significantly decreased the viability, proliferation, and clonogenic potential of GNAQ(mt), but not GNAQ(wt)/BRAF(mt) cells, compared with IR alone. Combined treatment increased the antiproliferative and proapoptotic effects of IR in GNAQ(mt) cells through delayed DNA-damage resolution and enhanced induction of proteins involved in cell-cycle arrest, cell-growth arrest, and apoptosis.

CONCLUSIONS

Our preclinical results suggest that combined modality treatment may allow for reductions in the total RT dose and/or fraction size, which may lead to better functional organ preservation in the treatment of primary GNAQ(mt) UM. These findings suggest future clinical trials combining PKC inhibitors with RT in GNAQ(mt) UM warrant consideration.

Cavin-3 dictates the balance between ERK and Akt signaling

Cavin-3 is a tumor suppressor protein of unknown function. Using both in vivo and in vitro approaches, we show that cavin-3 dictates the balance between ERK and Akt signaling. Loss of cavin-3 increases Akt signaling at the expense of ERK, while gain of cavin-3 increases ERK signaling at the expense Akt. Cavin-3 facilitates signal transduction to ERK by anchoring caveolae to the membrane skeleton of the plasma membrane via myosin-1c. Caveolae are lipid raft specializations that contain an ERK activation module and loss of the cavin-3 linkage reduces the abundance of caveolae, thereby separating this ERK activation module from signaling receptors. Loss of cavin-3 promotes Akt signaling through suppression of EGR1 and PTEN. The in vitro consequences of the loss of cavin-3 include induction of Warburg metabolism (aerobic glycolysis), accelerated cell proliferation, and resistance to apoptosis. The in vivo consequences of cavin-3 knockout are increased lactate production and cachexia. DOI:http://dx.doi.org/10.7554/eLife.00905.001.

Chapter seven--Cancer treatment with gene therapy and radiation therapy

Radiation therapy methods have evolved remarkably in recent years which have resulted in more effective local tumor control with negligible toxicity of surrounding normal tissues. However, local recurrence and distant metastasis often occur following radiation therapy mostly due to the development of radioresistance through the deregulation of the cell cycle, apoptosis, and inhibition of DNA damage repair mechanisms. Over the last decade, extensive progress in radiotherapy and gene therapy combinatorial approaches has been achieved to overcome resistance of tumor cells to radiation. In this review, we summarize the results from experimental cancer therapy studies on the combination of radiation therapy and gene therapy.

Gamma irradiation and targeted radionuclides enhance the expression of the noradrenaline transporter transgene controlled by the radio-inducible p21(WAF1/CIP1) promoter

The use of radiation-inducible promoters to drive transgene expression offers the possibility of temporal and spatial regulation of gene activation. This study assessed the potential of one such promoter element, p21(WAF1/CIP1) (WAF1), to drive expression of the noradrenaline transporter (NAT) gene, which conveys sensitivity to radioiodinated meta-iodobenzylguanidine (MIBG). An expression vector containing NAT under the control of the radiation-inducible WAF1 promoter (pWAF/NAT) was produced. The non-NAT expressing cell lines UVW (glioma) and HCT116 (colorectal cancer) were transfected with this construct to assess radiation-controlled WAF1 activation of the NAT gene. Transfection of UVW and HCT cells with pWAF/NAT conferred upon them the ability to accumulate [(131)I]MIBG, which led to increased sensitivity to the radiopharmaceutical. Pretreatment of transfected cells with γ radiation or the radiopharmaceuticals [(123)I]MIBG or [(131)I]MIBG induced dose- and time-dependent increases in subsequent [(131)I]MIBG uptake and led to enhanced efficacy of [(131)I]MIBG-mediated cell kill. Gene therapy using WAF1-driven expression of NAT has the potential to expand the use of this therapeutic modality to tumors that lack a radio-targetable feature.

Radiation-inducible silencing of uPA and uPAR in vitro and in vivo in meningioma

Stereospecific radiation treatment offers a distinct opportunity for temporal and spatial regulation of gene expression at tumor sites by means of inducible promoters. To this end, a plasmid, pCArG-U2, was constructed by incorporating nine CArG elements (in tandem) of EGR1 gene upstream to uPA and uPAR siRNA oligonucleotides in a pCi-neo vector. Radiation-induced siRNA expression was detected in a meningioma cell line (IOMM-Lee). Immunoblotting and RT-PCR analyses confirmed downregulation of uPA and uPAR. A similar effect was observed in transfected cells followed by H2O2 treatment. Moreover, pre-treatment of transfected cells with N-acetyl L-cysteine blocked the silencing of uPA and uPAR, which further confirmed the oxidative damage-mediated downregulation. Cell proliferation assays and Western blot analysis for apoptotic molecules confirmed cell death in a radiation-inducible fashion. Migration and matrigel invasion assays also revealed a marked decrease in migration and invasion. Immunocytochemistry showed a marked decrease in uPA and uPAR levels in transfected and irradiated cells. H&E staining revealed a decrease in the pre-established tumor volume among the animals treated with pCArG-U2 and radiation. Immunohistochemistry of the brain sections established with intracranial tumors also revealed a marked decrease in uPA and uPAR in a radiation-inducible fashion. Taken together, our data suggest pCArG-U2 as a suitable candidate for radiation-inducible gene therapy.

Sex and tissue-specific differences in low-dose radiation-induced oncogenic signaling

PURPOSE

The possible adverse health effects of low-dose radiation (LDR) exposure constitute a growing concern. Clinically and environmentally relevant exposures occur predominantly under chronic conditions, notwithstanding that most studies of LDR effects have been performed using a single acute exposure. Sex- and tissue-specificity of the LDR-induced changes have not been considered before. We investigated LDR-related expression patterns in muscle, liver and spleen of male and female mice subjected to acute and chronic LDR exposure. Genes involved in oncogenic signaling were of specific interest, as radiation is a well-known carcinogen.

MATERIALS AND METHODS

We analyzed the expression pattern of genes coding for growth factors and growth-factor receptors, cytoplasmic serine/threonine protein kinases, G-proteins and nuclear DNA-binding proteins, and other important components of oncogenic signaling.

RESULTS

We found sex- and tissue-specific changes in the expression of Ras superfamily members (Nras, Rab2, Rab34, Vav2), protein kinase C (PKC) isoforms (PKCbeta, PKCmu), AP-1 factor components (Jun, JunB and FosB), Wnt signaling pathway members as well as in a variety of other cellular proto-oncogenes and oncogenes. Importantly, Western blot analysis of JunB, PKCmu and Rab2 proteins supported the transcriptomic data.

CONCLUSIONS

Substantially different protein levels were observed in all three tissues (muscle, spleen and liver) of acutely and chronically irradiated female and male animals. Based on the obtained data and available literature, we discuss several possible mechanisms that may contribute to radiation-induced carcinogenesis in various tissues of males and females. From our results we could identify the genes that may serve as sex- and tissue-specific biomarkers of the LDR exposure.

Dysregulation of CXCL9 and reduced tumor growth in Egr-1 deficient mice

BACKGROUND

Early growth response-1 (Egr-1) is an immediate-early transcription factor inducible in the vasculature in response to injury, shear stress, and other stimuli. Mice lacking Egr-1 have a profound deficit in the ability to recover from femoral artery ligation, suggesting a role in neovascularization. Previous studies have shown that manipulating Egr-1 expression can have either positive or negative effects on tumor growth. We hypothesized that Egr-1 knockout mice might exhibit reduced tumor growth, possibly due to a reduced capacity to respond to angiogenic signals from a growing tumor.

RESULTS

We injected 106 Lewis lung carcinoma (LLC1) cells subcutaneously in the flank of wild type and Egr-1 knockout mice. The average mass of tumors from wild type mice at 12 days after implantation was 413 +/- 128 mg, while those from Egr-1-/- mice was 219 +/- 81 mg (p = 0.001, mean +/- SD). However, sectioning the tumors and staining with anti-CD31 antibodies revealed no difference in the vascularity of the tumors and there was no difference in angiogenic growth factor expression. Expression of the chemokine Mig (CXCL9) was increased 2.8-fold in tumors from knockout mice, but no increase was found in serum levels of Mig. Natural killer cells have a 1.7-fold greater prevalence in the CD45+ cells found in tumors from Egr-1-/- mice compared to those from wild type mice. Immunohistochemical staining suggests that Mig expression in the tumors comes from invading macrophages.

CONCLUSION

Mice deficient in Egr-1 exhibit reduced growth of LLC1 tumors, and this phenomenon is associated with overexpression of Mig locally within the tumor. There are no obvious differences in tumor vascularity in the knockout mice. Natural killer cells accumulate in the tumors grown in Egr-1-/- mice, providing a potential mechanism for the reduction in growth.

The radiation-inducible pE9 promoter driving inducible nitric oxide synthase radiosensitizes hypoxic tumour cells to radiation

Driving high-level transgene expression in a tumour-specific manner remains a key requirement in the development of cancer gene therapy. We have previously demonstrated the strong anticancer effects of generating abnormally high levels of intracellular NO(*) following the overexpression of the inducible nitric oxide synthase (iNOS) gene. Much of this work has focused on utilizing exogenously activated promoters, which have been primarily induced using X-ray radiation. Here we further examine the potential of the pE9 promoter, comprising a combination of nine CArG radio-responsive elements, to drive the iNOS transgene. Effects of X-ray irradiation on promoter activity were compared in vitro under normoxic conditions and various degrees of hypoxia. The pE9 promoter generated high-level transgene expression, comparable with that achieved using the constitutively driven cytomegalovirus promoter. Furthermore, the radio-resistance of radiation-induced fibrosarcoma-1 (RIF-1) mouse sarcoma cells exposed to 0.1 and 0.01% O(2) was effectively eliminated following transfection with the pE9/iNOS construct. Significant inhibition of tumour growth was also observed in vivo following direct intratumoural injection of the pE9/iNOS construct compared to empty vector alone (P<0.001) or to a single radiation dose of 10 Gy (P<0.01). The combination of both therapies resulted in a significant 4.25 day growth delay compared to the gene therapy treatment alone (P<0.001). In summary, we have demonstrated the potential of the pE9/iNOS construct for reducing radio-resistance conferred by tumour cell hypoxia in vitro and in vivo, with greater tumour growth delay observed following the treatment with the gene therapy construct as compared with radiotherapy alone.

Role of tumor necrosis factor-alpha and TRAIL in high-dose radiation-induced bystander signaling in lung adenocarcinoma

In the present study, ionizing radiation (IR)-induced bystander effects were investigated in two lung cancer cell lines. A549 cells were found to be more resistant to radiation-conditioned medium (RCM) obtained from A549 cells when compared with the H460 exposed to RCM procured from H460 cells. Significant release of tumor necrosis factor-alpha (TNF-alpha) was observed in A549 cells after IR/RCM exposure, and the survival was reversed with neutralizing antibody against TNF-alpha. In H460 cells, significant release of TNF-related apoptosis-inducing ligand (TRAIL), but not TNF-alpha, was observed in response to IR, RCM exposure, or RCM + 2Gy, and neutralizing antibody against TRAIL diminished clonogenic inhibition. Mechanistically, TNF-alpha present in RCM of A549 was found to mediate nuclear factor-kappaB (NF-kappaB) translocation to nucleus, whereas the soluble TRAIL present in RCM of H460 cells mobilized the nuclear translocation of PAR-4 (a proapoptotic protein). Analysis of IR-inducible early growth response-1 (EGR-1) function showed that EGR-1 was functional in A549 cells but not in H460 cells. A significant decrease in RCM-mediated apoptosis was observed in both A549 cells stably expressing small interfering RNA EGR-1 and EGR-1(-/-) mouse embryonic fibroblast cells. Thus, the high-dose IR-induced bystander responses in A549 may be dependent on the EGR-1 function and its target gene TNF-alpha. These findings show that the reduced bystander response in A549 cells is due to activation of NF-kappaB signaling by TNF-alpha, whereas enhanced response to IR-induced bystander signaling in H460 cells was due to release of TRAIL associated with nuclear translocation of PAR-4.

Enhancing Radiotherapy With Genetically Engineered Viruses

Concurrent radiotherapy and chemotherapy have been used to treat a variety of tumors to improve local control and overall survival. Gene therapy strategies represent a novel means to further improve the therapeutic ratio of ionizing radiation. Cancer gene therapy strategies in clinical trials include the use of replication-defective shuttle vectors to deliver exogenous genes and replication-competent oncolytic viruses. This review focuses on these approaches in the context of radiotherapy and radiochemotherapy. In the shuttle vector approach, exogenous gene products that enhance ionizing radiation–mediated tumor cell destruction have been selected. Moreover, the expression of exogenous genes encoding therapeutic proteins can be regulated through the use of ionizing radiation–enhanced promoters. Also, genetically engineered attenuated replication-competent viruses have been investigated in clinical trials. Preclinical data indicate that ionizing radiation interacts with replication-competent oncolytic viruses to enhance viral replication and tumor destruction. Here, we review the background preclinical and current clinical data utilizing gene therapy with radiotherapy.

alpha- and epsilon-protein kinase C activity during smooth muscle cell apoptosis in response to gamma-radiation

The use of gamma-radiation in treatment of pelvic cancer is associated with injury of healthy surrounding tissues and disorders of intestinal motility; however, the cellular mechanisms involved are unclear. We tested the hypothesis that exposure of visceral smooth muscle cells (SMCs) to gamma-radiation induces apoptosis via activation of specific protein kinase C (PKC) isoforms. Cultured SMCs and slices from guinea pig ileum smooth muscle longitudinal layer (GPISMLL) were exposed to 10 to 50 Gy. Flow cytometry in gamma-radiated SMCs showed increased percentage of cells in the sub-G(0)/G(1) phase, a hallmark of apoptosis. gamma-Radiation-induced reduction in cell survival was partially but significantly alleviated with the PKC inhibitors. Sections of gamma-irradiated GPISMLL showed DNA fragmentation and apoptotic bodies analyzed by the terminal deoxynucleotidyl transferase dUTP nick-end labeling method, whereas the plasma and nuclear membranes were preserved. Confocal microscopy in gamma-radiated SMCs labeled with annexin V-fluorescein showed an increase in apoptotic cells and phosphatidylserine externalization. Contraction of GPISMLL strips in response to KCl and acetylcholine was reduced in tissues exposed to 30 and 50 Gy. gamma-Radiation of GPISMLL caused an increase in PKC activity in the particulate fraction, a decrease in the cytosolic fraction, and increased particulate/cytosolic PKC activity ratio. Western blot analysis revealed significant amounts of alpha- and epsilon-PKC in the cytosolic fraction of control GPISMLL. gamma-Radiation caused an increase in the amount of alpha- and epsilon-PKC in the particulate fraction and a decrease in the cytosolic fraction. Data suggest that gamma-radiation induces apoptosis, growth arrest, and contractile dysfunction in visceral SMCs of GPISMLL via activation and translocation of alpha- and epsilon-PKC isoforms.

Local gene delivery of tumor necrosis factor alpha can impact primary tumor growth and metastases through a host-mediated response

TNFerade is a replication incompetent adenovector designed to express human TNFalpha under control of the Egr-1 radiation and chemotherapy enhanced promoter, and is currently in Phase II/III clinical testing. Data from Phase I clinical testing of TNFerade in a limited set of melanoma patients suggested the potential to impact distal metastases following intratumoral injections of TNFerade. These clinical observations and the multiple potential mechanisms of TNFerade led us to hypothesize local treatment with TNFerade + radiation may impact metastatic disease. We explored this hypothesis in preclinical models using the spontaneously metastatic, syngeneic B16F10 murine melanoma model. Established subcutaneous B16F10 tumors were treated with intratumoral injections of TNFerade and localized 2 Gy fractionated radiation therapy, modeling the clinical treatment regimen. Following 10-14 days of treatment, mice were evaluated for metastases development in the iliac and axillary lymph nodes. Comparisons of metastatic burden to control groups indicated TNFerade +/- radiation suppressed the formation of metastases in the lymph nodes. Additional experiments in TNF receptor knockout mice, where the only possible effects are on tumor cells containing the TNFalpha receptor, indicate TNFerade's local and distal activities are critically dependent on a host-mediated response. These data provide direct preclinical evidence local therapy of a solid tumor with TNFerade can also reduce metastatic disease, in addition to effects on the treated lesion. Furthermore, our finding of a host dependant response(s) for TNFerade at both the treated tumor and on lymph node metastases suggest the potential for broad activity independent of tumor histology.

Epidermal growth factor receptor/angiogenesis dual targeting: preclinical experience

PURPOSE OF REVIEW

This review aims to critically examine the preclinical background regarding the combination of drugs targeting the epidermal growth factor receptor and anti-angiogenic compounds.

RECENT FINDINGS

There are studies exploring the anti-tumor efficacy of dual inhibitors, such as the compound ZD6474, which combines in the same molecule an anti-tyrosine kinase activity against the epidermal growth factor receptor and the vascular endothelial growth factor receptor. In addition, several studies have investigated the anti-tumor effects of combinations of an anti-epidermal growth factor receptor agent and a vascular endothelial growth factor receptor inhibitor. In general, in these studies, supra-additive anti-tumor efficacy was apparent when combining anti-epidermal growth factor receptor and anti-angiogenic treatments. Beneficial effects were also observed when combining this dual targeted therapy with either conventional chemotherapy or irradiation.

SUMMARY

Early clinical trials combining the anti-epidermal growth factor receptor drug erlotinib (Tarceva) and the anti-angiogenic agent bevacizumab (Avastin) show acceptable toxicity and promising anti-tumor activity (lung cancer), which need to be confirmed in randomized trials.

Microarray analysis of differentially expressed genes after exposure of normal human fibroblasts to ionizing radiation from an external source and from DNA-incorporated iodine-125 radionuclide

Exposure of cells to ionizing radiation (IR) produces changes in the expression level of a large number of genes. However, less is known of gene-expression changes caused by local radiation exposure from radionuclides within cells. We studied changes in the genome-wide gene expression induced by decay of 125I incorporated into DNA as [125I]-iododeoxyuridine (125I-IUdR) in normal IMR-90 human lung fibroblasts and compared them with the changes produced by external gamma-radiation delivered at high (HDR) or low (LDR) dose rate. We found that more than 2000 genes were consistently up- or down-regulated following HDR and LDR gamma-radiation. The profiles of differentially expressed genes following HDR and LDR shared about 64% (up) and 74% (down) genes in common, with many genes identified as radiation-responsive for the first time. In contrast, in all only 206 genes changed their expression level in the 125I-IUdR-treated cells, even though the total number of DNA double-strand breaks (DSB) produced by 125I-IUdR exceeded that produced by the gamma-radiation. With few exceptions, the expression levels of 125I-IUdR-responsive genes were also altered following gamma-irradiation. Therefore, nuclear DNA-localized decays of 125I produce 10 times fewer differentially expressed genes than whole-cell exposure to gamma-radiation of comparable dose. These results suggest that the effect of IR on the changes in global gene expression depends on the distribution of energy depositions within the cell. In contrast to cell survival, DNA DSB may not be the major factor modulating changes in gene expression following irradiation.

c-Abl regulates early growth response protein (EGR1) in response to oxidative stress

c-Abl is a tyrosine kinase that can act as a regulator of cell growth and apoptosis in response to stress. Using cell lines expressing c-Abl in an inducible manner, we identified genes whose expression was regulated by c-Abl kinase activity. Microarray analysis indicated that Early Growth Response-1 (EGR1) gene expression is induced by c-Abl kinase activity, which was confirmed at the message and protein levels. Promoter mapping experiments revealed that c-Abl utilizes three distal serum response elements (SREs) in the EGR1 promoter, which are transactivated by mitogen/extracellular receptor kinase (MEK/ERK) signaling. PD 95089, a specific inhibitor of MEK/ERK signaling, attenuated c-Abl-mediated upregulation of EGR1 expression in a dose-dependent manner. Similar results were obtained by using a dominant-negative mutant of mitogen/extracellular kinase. Significantly, hydrogen peroxide-induced EGR1 expression appears to be mediated by c-Abl, as cells expressing dominant negative c-Abl, and c-Abl-/- murine embryonic fibroblasts, are completely defective in hydrogen peroxide-induced EGR1 expression. In addition, c-Abl-induced apoptosis is partially mitigated by EGR1 activity, as cells devoid of EGR1 expression undergo reduced rates of c-Abl-induced apoptosis. Together, these results indicate that c-Abl promotes the induction of EGR1 through the MEK/ERK pathway in regulating apoptotic response to oxidative stress.

Response of endothelial cells to a dual tyrosine kinase receptor inhibition combined with irradiation

Recent studies suggest the possibility of a direct antiangiogenic effect of anti-epidermal growth factor receptor (EGFR) drugs due to the presence of EGFR on endothelial cells. The aim of this study was to analyze the direct effect on endothelial cells of associating EGFR targeting, vascular endothelial growth factor receptor (VEGFR)-2 targeting, and irradiation. We examined both the cytotoxic effects and the effect on molecular markers resulting from the combined action of gefitinib (Iressa; anti-EGFR), ZM317450 [VEGFR tyrosine kinase inhibitor (VTKI); anti-VEGFR-2], and irradiation (radiation therapy) on HMME7 cells, an immortalized microvascular endothelial cell of human origin. The presence of a functional EGFR pathway sensitive to gefitinib was shown in HMME7 cells (gefitinib-induced decrease in phospho-EGFR, phospho-p42/p44, and phospho-Akt). The stimulation of VEGFR-2 pathway led to an increase in Akt phosphorylation that was inhibited by VTKI. Of note, a post-radiation therapy induction of phospho-p42/p44 was observed on HMME7 cells, and this effect was inhibited by a pretreatment with gefitinib. Based on combination indexes (Chou and Talalay analyses), the associations gefitinib-radiation therapy, VTKI-radiation therapy, VTKI-gefitinib, and gefitinib-VTKI-radiation therapy were found to be additive, slightly synergistic, and markedly synergistic, respectively, for the cytotoxicity on HMME7 cells. Among molecular explanatory factors that were examined, the combination gefitinib-radiation therapy totally abolishes DNA-dependent protein kinase expression, and gefitinib attenuates the radiation therapy-induced enhancement of ERCC1 and augments the VTKI-induced CD95 enhancement. The existence of a radiation therapy-dependent neoangiogenesis may be related to the induction of EGFR pathway in endothelial cells, a phenomenon that can be attenuated by anti-EGFR drugs like gefitinib. In complement to the direct antitumor effects of radiation therapy and anti-EGFR drugs, a strong antiangiogenic effect may be obtained with therapeutic strategies combining radiation therapy with EGFR and VEGFR-2 targeting agents.

Involvement of Egr-1 in lens epithelial cell death induced by selenite

Selenite-overdose cataract in young rats may be caused by an initial insult to the lens epithelial cells. Our previous DNA array analysis revealed a significant increase in the expression of mRNA for early growth response protein-1 (Egr-1) in lens epithelial cells after injection of selenite. This suggested that up-regulation of Egr-1 mRNA may be involved in lens epithelial cell death. The purpose of the present experiment was to further clarify the involvement of Egr-1 in lens epithelial cell death induced by selenite. Rat lens epithelial explants were cultured with sodium selenite. Selenite caused epithelial explants to leak LDH into the medium. During LDH leakage, increased expression of mRNA for Egr-1 was observed by RT-PCR. To further test the involvement of Egr-1 in selenite-induced cell death, mouse lens epithelial cell line (alpha-TN4 cells) was treated with antisense oligonucleotide for Egr-1. Antisense oligonucleotide for Egr-1 significantly diminished expression of Egr-1 protein and leakage of LDH. These results suggested that increased activity of Egr-1 may be a factor in lens epithelial cell death induced by selenite.

Analysis of gene-expression profiles after gamma irradiation of normal human fibroblasts

PURPOSE

To understand comprehensive transcriptional profile of normal human fibroblast in response to irradiation.

METHODS AND MATERIALS

To identify genes whose expression is influenced by gamma radiation, we used a cDNA microarray to analyze expression of 23,000 genes in normal human fibroblasts at 7 timepoints (1, 3, 6, 12, 24, 48, and 72 hours) after 5 different doses (0.5, 2, 5, 15, and 50 Gy) of exposure.

RESULTS

Among the genes that showed altered expression patterns, some were already known to be regulated by irradiation, for instance ODC, EGR1, FGF2, PCNA, PKC, and several p53-target genes, including p53DINP1, BTG2, GADD45, and MDM2. The time course of each dose showed that from 350 to 600 genes were affected as to their expression; induction profiles characteristic to each dose were demonstrated. Of the total identified, only 89 genes were up-regulated; the vast majority was down-regulated over the 72-hour time course. We identified 21 genes that were distinctly induced by irradiation; 11 of them were functionally known, and 6 of those were p53-target genes.

CONCLUSIONS

The results underscored the complexity of the transcriptional responses to irradiation, and the data should serve as a basis for global characterization of radiation-regulated genes and pathways.

Current status of tumor radiogenic therapy

Although tumor gene therapy falls behind its clinical use, the combination of irradiation and gene therapy is full of promise in cancer therapy based on traditional radiotherapy, chemotherapy and surgery. We have termed it as radiogenic therapy. This review focuses on the following aspects of radiogenic therapy in recent years: improvement of gene transfer efficiency by irradiation, radiotherapy combined with cytokine gene delivery or enhancement of the immunity of tumor cells by transgene, direct stimulation by radiation to produce cytotoxic agents, increase of tumor cell radiosensitivity in gene therapy by controlling the radiosensitivity genes and adjusting the fraction dose and interval of radiation so as to achieve the optimum antitumor effect while reducing the normal tissue damage, radioprotective gene therapy enhancing radiation tumor killing effect while protecting the normal tissue and organs with transgene using transfer vectors.

Dual responsive promoters to target therapeutic gene expression to radiation-resistant hypoxic tumor cells

PURPOSE

Tumor hypoxia is unequivocally linked to poor radiotherapy outcome. This study aimed to identify enhancer sequences that respond maximally to a combination of radiation and hypoxia for use in genetic radiotherapy approaches.

METHODS AND MATERIALS

The influence of radiation (5 Gy) and hypoxia (1% O2) on reporter-gene expression driven by hypoxia (HRE) and radiation (Egr-1) responsive elements was evaluated in tumor cells grown as monolayers or multicellular spheroids. Hypoxia-inducible factor-1alpha (HIF-1alpha) and HIF-2alpha protein expression was monitored in parallel.

RESULTS

Of the sequences tested, an HRE from the phosphoglycerate kinase-1 gene (PGK-18[5+]) was maximally induced in response to hypoxia plus radiation in all 5 cell lines tested. The additional radiation treatment afforded a significant increase in the induction of PGK-18[5+] compared with hypoxia alone in 3 cell lines. HIF-1alpha/2alpha were induced by radiation but combined hypoxia/radiation treatment did not yield a further increase. The dual responsive nature of HREs was maintained when spheroids were irradiated after delivery of HRE constructs in a replication-deficient adenovirus.

CONCLUSIONS

Hypoxia-responsive enhancer element sequences are dually responsive to combined radiation and hypoxic treatment. Their use in genetic radiotherapy in vivo could maximize expression in the most radio-resistant population at the time of radiation and also exploit microenvironmental changes after radiotherapy to yield additional switch-on.

Administration of ricin induces a severe inflammatory response via nonredundant stimulation of ERK, JNK, and P38 MAPK and provides a mouse model of hemolytic uremic syndrome

Recent interest in the health consequences of ricin as a weapon of terrorism has led us to investigate the effects of ricin on cells in vitro and in mice. Our previous studies showed that depurination of the 28S rRNA by ricin results in the inhibition of translation and the coordinate activation of the stress-activated protein kinases JNK and p38 MAPK. In RAW 264.7 macrophages, ricin induced the activation of ERK, JNK, and p38 MAPK, the accumulation of mRNA encoding tumor necrosis factor (TNF)-alpha, interleukin (IL)-1, the transcription factors c-Fos, c-Jun, and EGR1, and the appearance of TNF-alpha protein in the culture medium. Using specific inhibitors of MAPKs, we demonstrated the nonredundant roles of the individual MAPKs in mediating proinflammatory gene activation in response to ricin. Similarly, the intravenous administration of ricin to mice led to the activation of ERK, JNK, and p38 MAPK in the kidneys, and increases in plasma-borne TNF-alpha, IL-1beta, and IL-6. Ricin-injected mice developed the hallmarks of hemolytic uremic syndrome, including thrombotic microangiopathy, hemolytic anemia, thrombocytopenia, and acute renal failure. Microarray analyses demonstrated a massive proinflammatory transcriptional response in the kidneys, coincidental with the symptoms of hemolytic uremic syndrome. Therapeutic management of the inflammatory response may affect the outcome of intoxication by ricin.

Chemoinducible gene therapy: A strategy to enhance doxorubicin antitumor activity

A replication-defective adenoviral vector, Ad.Egr-TNF.11D, was engineered by ligating the CArG (CC(A/T)6GG) elements of the Egr-1 gene promoter upstream to a cDNA encoding human tumor necrosis factor-α. We report here that Ad.Egr-TNF.11D is activated by the clinically important anticancer agents cisplatin, cyclophosphamide, doxorubicin, 5-fluorouracil, gemcitabine, and paclitaxel. N-acetylcysteine, a free radical scavenger, blocked induction of tumor necrosis factor-α by anticancer agents, supporting a role for reactive oxygen intermediates in activation of the CArG sequences. Importantly, resistance of PC-3 human prostate carcinoma and PROb rat colon carcinoma tumors to doxorubicin in vivo was reversed by combining doxorubicin with Ad.Egr-TNF and resulted in significant antitumor effects. Treatment with Ad.Egr-TNF.11D has been associated with inhibition of tumor angiogenesis. In this context, a significant decrease in tumor microvessel density was observed following combined treatment with doxorubicin and Ad.Egr-TNF.11D as compared with either agent alone. These data show that Ad.Egr-TNF.11D is activated by diverse anticancer drugs.

Radiobiology of radioimmunotherapy: targeting CD20 B-cell antigen in non-Hodgkin's lymphoma

The radiobiology of radioimmunotherapy is an important determinant of both the toxicity and the efficacy associated with the treatment of B-cell non-Hodgkin's lymphoma with radiolabeled anti-CD20 monoclonal antibodies. The properties of the target, CD20, and the mechanisms of action of both the monoclonal antibodies and the associated exponentially decreasing low-dose-rate radiotherapy are described. The radiation dose and dose-rate effects are discussed and related to both the tumor responses and normal organ toxicity. Finally, the use of either unlabeled or radiolabeled anti-CD20 monoclonal antibodies as a component of combined modality therapy (including the sequential or concurrent use of sensitizers) and future directions of the field are discussed.

Catalase-independent early-gene expression in rat brain following acute ethanol exposure

Early-gene expression evoked by acute ethanol treatment was studied in rat brain by quantitative immunocytochemistry, with reference to ethanol metabolism by the enzyme catalase. Colocalization with mu-opioid receptor (MOR) sites was also examined. Ethanol challenges [1, 2.5, and 4 g/kg intraperitoneally (i.p.)] evoked dose-dependent increases in c-Fos expression in several brain regions, but overlap with MOR-rich sites was only partial. Strong inhibition of brain catalase activity (ca. 60%) with 3-amino-1,2,4-triazole (AT, 1 g/kg i.p.) did not alter ethanol-induced c-Fos nor Krox-24 expression in any of the brain regions analyzed. This evidence demonstrates that catalase-mediated metabolism is not a requisite for c-Fos nor Krox-24 induction in rat brain following acute ethanol treatment, and suggests that ethanol is by itself capable of eliciting strong neuronal and circuit-level adaptations in the nervous system.

Mitogen-activated protein kinases: specificity of response to dose of ionizing radiation in liver

Ionizing radiation is known to activate both the cytotoxic stress-activated kinases (SAPK/JNK, p38) and the cytoprotective mitogen-activated protein kinases (MAPKs, ERKs), which send divergent signals to the nucleus. However, all these kinases could not be activated simultaneously and at all the doses. An attempt has been made in this study to establish the dose and temporal response of these kinases with a view to establish the identity of the transcription factors that remain activated because only these will be translated into an effect. The study indicates that the stress-activated kinases (SAPK/JNK and p38) are activated by very low doses (0.1 Gy) of ionizing radiation. An induction of expression of MKK4, precursor to SAPK and p38, was found at lower doses (0.1-0.5 Gy). However, the cytoprotective ERK2 showed a progressive increase in expression with dose, except at 3 Gy where it shows a marginal decline. The stress-activated kinases show an increased expression or activation at early periods, unlike ERK2, which shows a prolonged response to stimuli. This study reveals that in the in vivo condition there is a chronological order of activation of the kinases and a dose-dependent activation. The activations of the cytoplasmic kinases and the transcription factors, Elk-1 and c-Jun, both show prolonged activation and maximum response at high doses.

Apoptosis-modulating agents in combination with radiotherapy-current status and outlook

PURPOSE

To increase the therapeutic efficacy of ionizing radiation or to reduce radiation-mediated side effects, diverse research centers for translational radiation oncology have headed for a specific modulation of defined cellular death pathways. In this regard, several signaling systems have proved to be of high potential value.

RESULTS

It has previously been shown that apoptotic pathways induced by ionizing radiation are distinct from death pathways triggered by death ligands such as tumor necrosis factor-related apoptosis-inducing ligand (TRAIL). The combination of both radiation and TRAIL was highly efficient in vitro and in preclinical mouse models. However, several aspects of normal tissue toxicity have not been solved, and no Phase I data are available yet. A second approach tested in a Phase I trial is based on the observation that synthetic phospholipid derivatives (alkyllysophospholipids and alkylphosphocholines) strongly enhance apoptotic effects by modulating the balance among the mitogenic, anti-apoptotic MAPK, phosphatidylinositol 3'-kinase (PI3K)/Akt, and the pro-apoptotic SAPK/JNK signaling pathways. Furthermore, others have provided evidence that inhibition of anti-apoptotic signals generated by mitogenic stimuli may increase radiation responses. In this context, controversial data are available regarding the influence of a pharmacologic abrogation of MEK1, Erk1/2 signaling on apoptotic sensitivity but no Phase I trials of MEK inhibitors either alone or in combination with radiation have yet been published. However, inhibition of the PI3K/Akt survival pathway using compounds such as the protein kinase C (PKC) inhibitor PKC412 has been shown to induce apoptosis or to increase the apoptotic sensitivity of tumor cells. Therefore, these drugs may be used alone or in combination with radiation to increase tumor control; however, Phase I data are lacking. Several other drugs, including cyclooxygenase-2 inhibitors, betulinic acid, and proteasome inhibitors, have been shown to interact with apoptotic signal transduction. Again, most of the drugs have not been tested in combination with radiation in vivo or-in the case of cyclooxygenase-2 inhibitors-exert pleiotropic effects.

CONCLUSION

Although the examples do not reflect all available strategies, it is clear that several promising approaches targeting defined cell death pathways have been developed and entered into clinical trials. The use of synthetic phospholipid derivatives in a Phase I trial is an important example, proving that basic research in radiation biology finally guides the development of new treatment strategies. This, and other approaches, will hopefully increase tumor control rates and reduce side effects in the future.

Radiobiology of radioimmunotherapy with 90Y ibritumomab tiuxetan (zevalin)

Radioimmunotherapy represents a significant advance over unlabeled immunotherapy for the treatment of patients with B-cell non-Hodgkin's lymphoma. The efficacy of radioimmunotherapeutic agents depends in large part on the basic biological effects associated with their components, monoclonal antibodies and radionuclides, separately and in combination. The radiobiological effects associated with yttrium 90-labeled ibritumomab tiuxetan (Zevalin; Biogen Idec Inc, Cambridge, MA) include the induction of apoptosis and cell-cycle redistribution (eg, arrest of cells in the G(2)/M phase of the cell cycle). Because of dose-rate effects, tumor cells may, in some cases, be more susceptible to the low-dose-rate radiation used in radioimmunotherapy than to the high-dose-rate radiation used in external beam radiotherapy. The efficacy of radioimmunotherapy may potentially be optimized through a variety of approaches, including the use of agents that increase the expression of certain tumor antigens (thus facilitating improved biodistribution of radiolabeled monoclonal antibodies) or that sensitize tumor cells to radiation.

Transcription factors activated in mammalian cells after clinically relevant doses of ionizing radiation

Over the past 15 years, a wealth of information has been published on transcripts and proteins 'induced' (requiring new protein synthesis) in mammalian cells after ionizing radiation (IR) exposure. Many of these studies have also attempted to elucidate the transcription factors that are 'activated' (i.e., not requiring de novo synthesis) in specific cells by IR. Unfortunately, all too often this information has been obtained using supralethal doses of IR, with investigators assuming that induction of these proteins, or activation of corresponding transcription factors, can be 'extrapolated' to low-dose IR exposures. This review focuses on what is known at the molecular level about transcription factors induced at clinically relevant (< or =2 Gy) doses of IR. A review of the literature demonstrates that extrapolation from high doses of IR to low doses of IR is inaccurate for most transcription factors and most IR-inducible transcripts/proteins, and that induction of transactivating proteins at low doses must be empirically derived. The signal transduction pathways stimulated after high versus low doses of IR, which act to transactivate certain transcription factors in the cell, will be discussed. To date, only three transcription factors appear to be responsive (i.e. activated) after physiological doses (doses wherein cells survive or recover) of IR. These are p53, nuclear factor kappa B(NF-kappaB), and the SP1-related retinoblastoma control proteins (RCPs). Clearly, more information on transcription factors and proteins induced in mammalian cells at clinically or environmentally relevant doses of IR is needed to understand the role of these stress responses in cancer susceptibility/resistance and radio-sensitivity/resistance mechanisms.

Biological chemistry of reactive oxygen and nitrogen and radiation-induced signal transduction mechanisms

In the past few years, nuclear DNA damage-sensing mechanisms activated by ionizing radiation have been identified, including ATM/ATR and the DNA-dependent protein kinase. Less is known about sensing mechanisms for cytoplasmic ionization events and how these events influence nuclear processes. Several studies have demonstrated the importance of cytoplasmic signaling pathways in cytoprotection and mutagenesis. For cytoplasmic signaling, radiation-stimulated reactive oxygen species (ROS) and reactive nitrogen species (RNS) are essential activators of these pathways. This review summarizes recent studies on the chemistry of radiation-induced ROS/RNS generation and emphasizes interactions between ROS and RNS and the relative roles of cellular ROS/RNS generators as amplifiers of the initial ionization events. Cellular mechanisms for regulating ROS/RNS levels are discussed. The mechanisms by which cells sense ROS/RNS are examined in terms of how ROS/RNS modify protein structure and function, for example, interactions with metal-thiol clusters, protein tyrosine nitration, protein cysteine oxidation, S-thiolation and S-nitrosylation. We propose that radiation-induced ROS are the initiators and that nitric oxide (NO*) or derivatives are the effectors activating these signal transduction pathways. In responding to cellular ionization events, the cell converts an oxidative signal to a nitrosative one because ROS are too reactive and unspecific in their reactions for regulatory purposes and the cell is equipped to precisely modulate NO* levels.

Changes in expression of transferrin, insulin-like growth factor 1, and interleukin 4 receptors after irradiation of cells of primary malignant brain tumor cell lines

Various immunotoxins have been developed for the treatment of cancer. The toxin is internalized by target cells through cell-surface receptors, and it is essential for these receptors to be expressed for the immunotoxin to have specific anti-tumor activity. Radiation therapy is one of the main treatment modalities for primary malignant brain tumors. The purpose of this study was to determine whether radiation influences the expression of cell-surface receptors. Cells of one human medulloblastoma (Daoy) and two glioblastoma (U373-MG and T98-G) cell lines were tested by exposing the cells to a single dose of 5 Gy gamma rays. Expression of transferrin receptors, type-1 insulin-like growth factor receptors (IGF1R), and interleukin 4 receptors (IL4R) was measured by flow cytometry analysis on unirradiated cells and on cells 3 to 120 h after irradiation. In Daoy cells, the absolute expression index of transferrin receptors increased during the 24 h after irradiation with the greatest change of 26% above control at 9 h. The absolute expression index of IGF1R increased 26.5% above control at 12 h. The absolute expression index of IL4R decreased 9 h after irradiation. In U373-MG cells the absolute expression index of transferrin receptors increased during the 24 h after irradiation, and the greatest increase was 45% above control at 9 h. The absolute expression index of IGF1R increased during the 12 h after irradiation with a maximum increase of 33% above control at 6 h. The absolute expression index of IL4R decreased with time after irradiation. In T98-G cells, the absolute expression index of both transferrin receptors and IL4R decreased after irradiation. The results suggest that the expression of growth factor receptors on brain tumor cells may be influenced by radiation. The effect of ionizing radiation on receptor expression should be considered when administration of targeted toxin is combined with radiation. Similar studies with other growth factor receptors used in targeted toxin therapy are recommended.

Radiosensitization by inhibition of IkappaB-alpha phosphorylation in human glioma cells

To assess the role of nuclear factor kappaB (NFKB) in cellular radiosensitivity, three different IkappaB-alpha (also known as NFKBIA) expression plasmids, i.e., S-IkappaB (mutations at (32, 36)Ser), Y-IkappaB (a mutation at (42)Tyr), and SY-IkappaB, were constructed and introduced into human brain tumor M054 cells. The clones were named as M054-S8, M054-Y2 and M054-SY4, respectively. Compared to the parental cell line, M054-S8 and M054-Y2 cells were more sensitive to X rays while M054-SY4 cells exhibited the greatest sensitivity. After treatment with N-acetyl-Leu-Leu-norleucinal, a proteasome inhibitor, the X-ray sensitivity of M054-S8 and M054-SY4 cells did not change, while that of M054-Y2 cells and the parental cells was enhanced. An increase in X-ray sensitivity accompanied by a decrease in translocation of NFKB to the nucleus in parental cells was observed after treatment with pervanadate, an inhibitor of tyrosine phosphatase, as well as in M054-S8 and M054-SY4 cells. Repair of potentially lethal damage (PLD) was observed in the parental cells but not in the clones. Four hours after irradiation (8 Gy), the expression of TP53 and phospho-p53 ((15)Ser) was induced in the parental cells but not in M054-S8, M054-Y2 or M054-SY4 cells. Our data suggest that inhibition of IkappaB-alpha phosphorylation at serine or tyrosine acts independently in sensitizing cells to X rays. NFKB may play a role in determining radiosensitivity and PLD repair in malignant glioma cells; TP53 may also be involved.

Specific inhibition of Egr-1 prevents mesangial cell hypercellularity in experimental nephritis

BACKGROUND

Mesangial cell proliferation is a frequent finding in glomerulonephritis. In cultured mesangial cells, we demonstrated that inhibition of the zinc finger transcription factor, early growth response gene-1 (Egr-1), by specific antisense oligonucleotides (AS ODN) blocks mesangial cell proliferation. Therefore, we here investigated the effect of Egr-1 inhibition on the course of an experimental mesangioproliferative glomerulonephritis in vivo.

METHODS

On day 3 after induction of anti-Thy-1.1 nephritis, specific glomerular oligonucleotide transfer was achieved by injection of an oligonucleotide/hemagglutinating virus of Japan/liposome mixture into the left renal artery. The right kidney was left untreated.

RESULTS

Induction of nephritis led to a sixfold induction of Egr-1 protein on day 6 of disease. This increase in Egr-1 expression was reduced by 48% in the left kidney by transfer of specific AS ODN. In parallel, the increases in glomerular cellularity, number of mitoses, and glomerular tuft area observed in day 6 nephritic animals were inhibited in the left kidney by 60%, 53%, and 50%, respectively. Changes in the right kidney were not significantly influenced. Likewise, control oligonucleotides showed no effect. Finally, the expression of platelet-derived growth factor-B (PDGF-B), a known target gene of Egr-1, was repressed by transfer of specific AS ODN against Egr-1.

CONCLUSION

We conclude that the transcription factor Egr-1 plays a critical role for mesangial cell proliferation in vivo. Interfering with the induction of Egr-1 or with its target genes could give rise to novel therapeutic principles in mesangioproliferative glomerulonephritis.

Radioprotective effect of FLT3 ligand expression regulated by Egr-1 regulated element on radiation injury of SCID mice

OBJECTIVE

Hematopoietic factors have an important effect on the regulation of hematopoiesis by stimulating the proliferation of hematopoietic progenitor cells. Although the cytokines that stimulate hematopoiesis have also often proved to exert radioprotective effects, no definitive correlation has been found between the expression of these cytokines regulated by radio-inducible genes and their radioprotective effects. In the current experiments, we evaluated the radioprotective effects of the hematopoietic growth factors regulated by a radio-inducible promoter on radiation injury.

METHODS

The human Flt3 (FL) cDNA and enhanced green fluorescent protein (EGFP) cDNA were linked together with the internal ribosome entry site (IRES) and then inserted into the eukaryotic expression vector pCI-neo with the Egr-1 promoter (Egr-GF), and the vector was transduced into bone marrow stromal cell lines HFCL (HFCL/EGF). The level of green fluorescence in HFCL/EGF cells was detected after radiation with flow cytometry. The expression of FL in irradiated HFCL/EGF cells was confirmed with Northern blot and ELISA. The HFCL/EGF and CD34(+) cells from human umbilical cord blood were sequentially transplanted intravenously into sublethally irradiated severe combined immunodeficient (SCID) mice. The numbers of peripheral white blood cells transplanted into recipient mice were detected.

RESULTS

The activity of EGFP in transfected cells was significantly increased after exposure to gamma radiation at 2.0, 2.5, and 5.0 Gy as compared with nontransfected cells. The expression of FL in HFCL/EGF was significantly higher than that of the control groups (HFCL, HFCL/pCI-neo, and HFCL/FG). The level of secreted FL in serum-free supernatants of HFCL/EGF on human CD34(+) cells was higher than that of control groups. In contrast with three control groups (HFCL, HFCL/pCI-neo, and HFCL/GF), HFCL/EGF resulted in a proportional increase in the number of white blood cells at an early stage after radiation.

CONCLUSIONS

We show that radiation enhances the ability of expression of FL in HFCL/EGF to stimulate the proliferation of hematopoietic progenitor cells. These results suggest in vivo use of gene therapy of FL regulated by the Egr-1 promoter protects hematopoiesis from irradiation-induced damage.

Selective gene expression using a DF3/MUC1 promoter in a human esophageal adenocarcinoma model

The efficacy of replication-deficient adenoviral vectors in gene therapy is confined to the number of tumor cells the vector infects. To focus and enhance the therapeutic efficacy, we employed a conditionally replication-competent adenoviral vector with a tissue-specific promoter, DF3/MUC1, in a human esophageal adenocarcinoma model. Our results demonstrate that Ad.DF3.E1A.CMV.TNF (Ad.DF3.TNF) specifically replicates in Bic-1 (DF3-producing cells) and mediates an enhanced biologic effect due to increased TNF-alpha in the same DF3-producing cells. We also show that the increased TNF-alpha interacts with ionizing radiation to produce greater tumor regression and a greater delay in tumor regrowth in Bic-1 (DF3-producing cells) compared to Seg-1 (DF3 non-producers). Tumor cell targeting using conditionally replication-competent adenoviral vectors with tumor-specific promoters to drive viral replication and deliver TNF-alpha provides a novel approach to enhancing tumor radiosensitivity.

Suppression of Egr-1 expression in human oral squamous carcinoma cells by okadaic acid

We examined the expression of early growth response-1 (Egr-1) gene in human oral squamous carcinoma cell lines SCCKN and SCC-25 cells and human osteoblastic cell lines Saos-2 and MG63 cells treated with okadaic acid, a potent inhibitor of protein phosphatases type 1 and type 2A. Western blot analysis revealed that Egr-1 was strongly expressed in SCCKN cells and that okadaic acid decreased the expression of Egr-1 protein in these cells. However, Egr-1 was expressed at lower levels in SCC-25, Saos-2, and MG63 cells and transiently increased with the okadaic acid treatment. Suppression of Egr-1 protein expression in okadaic acid-treated SCCKN cells stemmed from the suppression of the Egr-1 mRNA level, as determined by the RT-RCR method. Formaldehyde-fixed and alcohol-permeabilized cultured SCCKN cells were reacted with the anti-Egr-1 antibody using immunohistochemical methods. Intense fluorescence was observed in the nuclei of the control SCCKN cells interacted with anti-Egr-1 antibody. However, only a weak reaction was observed in the nuclei in SCCKN cells treated with okadaic acid. A gel mobility shift assay showed that treatment of SCCKN cells with okadaic acid suppressed Egr-1 binding to the DIG-labeled Egr-1 consensus oligonucleotide probe. The present results indicate that the alteration of phosphorylation states in SCCKN cells regulates Egr-1 binding to its consensus sequence and its expression at the transcriptional level.

The action of a dietary retinoid on gene expression and cancer induction in electron-irradiated rat skin

Current models of radiation carcinogenesis generally assume that the DNA is damaged in a variety of ways by the radiation and that subsequent cell divisions contribute to the conversion of the damage to heritable mutations. Cancer may seem complex and intractable, but its complexity provides multiple opportunities for preventive interventions. Mitotic inhibitors are among the strongest cancer preventive agents, not only slowing the growth rate of preneoplasias but also increasing the fidelity of DNA repair processes. Ionizing radiation, including electrons, is a strong inducer of cancer in rat skin, and dietary retinoids have shown potent cancer preventive activity in the same system. A non-toxic dietary dose of retinyl acetate altered gene expression levels 24 hours after electron irradiation of rat skin. Of the 8740 genes on an Affymetrix rat expression array, the radiation significantly (5 fold or higher) altered 188, while the retinoid altered 231, including 16 radiation-altered genes that were reversely altered. While radiation strongly affected the expression of stress response, immune/inflammation and nucleic acid metabolism genes, the retinoid most strongly affected proliferation-related genes, including some significant reversals, such as, keratin 14, retinol binding protein, and calcium binding proteins. These results point to reversal of proliferation-relevant genes as a likely basis for the anti-radiogenic effects of dietary retinyl acetate.