Severe, short-duration (0-3 min) heat shocks (50-52 degrees C) inhibit the repair of DNA damage.

PURPOSE: The goal of this study was to determine whether short-duration (15 s-3 min) high-temperature (50 degrees C) heat shocks inhibit the repair of DNA damage. MATERIALS AND METHODS: Cultured HeLa cells were used. DNA damage was measured after UV exposure or X-irradiation. Three methods were used to measure DNA damage: alkaline comet assay with the endonuclease, UVDE, for single strand breaks and UV photoproducts, antibodies specific for cyclo-pyrimidine dimers (CPD) or for 6-4 photoproducts (64PP), and the appearance-resolution of gamma-H2AX foci for DNA double strand breaks. RESULTS: Heat shocks of 15-30 s at 50 degrees C inhibited repair of DNA damage after UV exposure or X-irradiation detected by the alkaline comet assay (after UV) or by persistence of gamma-H2AX foci (after X-rays). The phosphorylation of histone, H2AX, induced by 1 or 4 Gy of X-rays was inhibited in a time-dependent manner after 15-45 s at 52 degrees C. When the excision of UV-induced PP was measured, heat shocks of more than 60 s at 50 degrees C were required to show measurable inhibition. CONCLUSION: Severe (50 degrees C) short-duration (15 s or greater) heat shocks inhibit repair of UV-induced DNA damage. The ability to detect the inhibitory effects of very short, 15-60 s, heat shocks was assay dependent. The comet assay could detect repair inhibition after a 15-s heat shock. Detection of DNA damage by specific antibodies could only detect repair inhibition after 1-3-min heat shocks. Using the gamma-H2AX foci method 30 s at 50 degrees C induced a significant delay in the repair of DNA damage after 1 Gy of X-rays.

Mammalian Rad9 plays a role in telomere stability, S- and G2-phase-specific cell survival, and homologous recombinational repair.

The protein products of several rad checkpoint genes of Schizosaccharomyces pombe (rad1+, rad3+, rad9+, rad17+, rad26+, and hus1+) play crucial roles in sensing changes in DNA structure, and several function in the maintenance of telomeres. When the mammalian homologue of S. pombe Rad9 was inactivated, increases in chromosome end-to-end associations and frequency of telomere loss were observed. This telomere instability correlated with enhanced S- and G2-phase-specific cell killing, delayed kinetics of gamma-H2AX focus appearance and disappearance, and reduced chromosomal repair after ionizing radiation (IR) exposure, suggesting that Rad9 plays a role in cell cycle phase-specific DNA damage repair. Furthermore, mammalian Rad9 interacted with Rad51, and inactivation of mammalian Rad9 also resulted in decreased homologous recombinational (HR) repair, which occurs predominantly in the S and G2 phases of the cell cycle. Together, these findings provide evidence of roles for mammalian Rad9 in telomere stability and HR repair as a mechanism for promoting cell survival after IR exposure.

The heat-induced gamma-H2AX response does not play a role in hyperthermic cell killing.

PURPOSE: The goal of this study was to determine whether the heat-induced formation of gamma-H2AX foci is involved in hyperthermic cell killing. MATERIALS AND METHODS: The heat-induced gamma-H2AX response was determined in cells exhibiting various degrees of heat sensitivity. The panel of cells tested included cells that are transiently thermotolerant, permanently heat resistant, permanently heat sensitive, and permanently resistant to oxidative stress. Cells exposed to non-thermal environmental conditions that lead to protection from, or sensitization to, heat were also tested. The heat sensitivity of cells in which H2AX was knocked out was also ascertained. RESULTS: The protein synthesis independent state of thermotolerance, but not the protein synthesis dependent state of thermotolerance, was found to be involved in the attenuation of the gamma-H2AX response in thermotolerant cells. The initial magnitude of the gamma-H2AX response was found to be the same in all cell lines with altered heat sensitivity. Furthermore, no differences in the resolution of gamma-H2AX foci were found among the cell lines tested. We also found that H2AX knock-out cells were not more heat sensitive. CONCLUSIONS: We conclude that the heat-induced gamma-H2AX response does not play a role in heat-induced cell killing, thereby adding further evidence that the heat-induced gamma-H2AX foci are not due to DNA double strand breaks.

Hyperthermia activates a subset of ataxia-telangiectasia mutated effectors independent of DNA strand breaks and heat shock protein 70 status.

All cells have intricately coupled sensing and signaling mechanisms that regulate the cellular outcome following exposure to genotoxic agents such as ionizing radiation (IR). In the IR-induced signaling pathway, specific protein events, such as ataxia-telangiectasia mutated protein (ATM) activation and histone H2AX phosphorylation (gamma-H2AX), are mechanistically well characterized. How these mechanisms can be altered, especially by clinically relevant agents, is not clear. Here we show that hyperthermia, an effective radiosensitizer, can induce several steps associated with IR signaling in cells. Hyperthermia induces gamma-H2AX foci formation similar to foci formed in response to IR exposure, and heat-induced gamma-H2AX foci formation is dependent on ATM but independent of heat shock protein 70 expression. Hyperthermia also enhanced ATM kinase activity and increased cellular ATM autophosphorylation. The hyperthermia-induced increase in ATM phosphorylation was independent of Mre11 function. Similar to IR, hyperthermia also induced MDC1 foci formation; however, it did not induce all of the characteristic signals associated with irradiation because formation of 53BP1 and SMC1 foci was not observed in heated cells but occurred in irradiated cells. Additionally, induction of chromosomal DNA strand breaks was observed in IR-exposed but not in heated cells. These results indicate that hyperthermia activates signaling pathways that overlap with those activated by IR-induced DNA damage. Moreover, prior activation of ATM or other components of the IR-induced signaling pathway by heat may interfere with the normal IR-induced signaling required for chromosomal DNA double-strand break repair, thus resulting in increased cellular radiosensitivity.

Novel chemical enhancers of heat shock increase thermal radiosensitization through a mitotic catastrophe pathway.

Radiation therapy combined with adjuvant hyperthermia has the potential to provide outstanding local-regional control for refractory disease. However, achieving therapeutic thermal dose can be problematic. In the current investigation, we used a chemistry-driven approach with the goal of designing and synthesizing novel small molecules that could function as thermal radiosensitizers. (Z)-(+/-)-2-(1-Benzenesulfonylindol-3-ylmethylene)-1-azabicyclo[2.2.2]octan-3-ol was identified as a compound that could lower the threshold for Hsf1 activation and thermal sensitivity. Enhanced thermal sensitivity was associated with significant thermal radiosensitization. We established the structural requirements for activity: the presence of an N-benzenesulfonylindole or N-benzylindole moiety linked at the indolic 3-position to a 2-(1-azabicyclo[2.2.2]octan-3-ol) or 2-(1-azabicyclo[2.2.2]octan-3-one) moiety. These small molecules functioned by exploiting the underlying biophysical events responsible for thermal sensitization. Thermal radiosensitization was characterized biochemically and found to include loss of mitochondrial membrane potential, followed by mitotic catastrophe. These studies identified a novel series of small molecules that represent a promising tool for the treatment of recurrent tumors by ionizing radiation.

Ultrasound Hyperthermia Technology for Radiosensitization.

Hyperthermia therapy (HT) raises tissue temperature to 40-45°C for up to 60 min. Hyperthermia is one of the most potent sensitizers of radiation therapy (RT). Ultrasound-mediated HT for radiosensitization has been used clinically since the 1960s. Recently, magnetic resonance-guided high-intensity focused ultrasound (MRgHIFU), which has been approved by the United States Food and Drug Administration for thermal ablation therapy, has been adapted for HT. With emerging clinical trials using MRgHIFU HT for radiosensitization, there is a pressing need to review the ultrasound HT technology. The objective of this review is to overview existing HT technology, summarize available ultrasound HT devices, evaluate clinical studies combining ultrasound HT with RT and discuss challenges and future directions.

The heat-shock factor is not activated in mammalian cells exposed to cellular phone frequency microwaves.

There has been considerable interest in the biological effects of exposure to radiofrequency electromagnetic radiation, given the explosive growth of cellular telephone use, with the possible induction of malignancy being a significant concern. Thus the determination of whether nonthermal effects of radiofrequency electromagnetic radiation contribute to the process leading to malignancy is an important task. One proposed pathway to malignancy involves the induction of the stress response by exposures to cell phone frequency microwaves. The first step in the induction of the stress response is the activation of the DNA-binding activity of the specific transcription factor involved in this response, the heat-shock factor (HSF). The DNA-binding activity of HSF in hamster, mouse and human cells was determined after acute and continuous exposures to frequency domain multiple access (FDMA)- or code domain multiple access (CDMA)-modulated microwaves at low (0.6 W/kg) or high (approximately 5 W/kg) SARs at frequencies used for mobile communication. The DNA-binding activity of HSF was monitored using a gel shift assay; the calibration of this assay indicated that an increase of approximately 10% in the activation of the DNA-binding activity of HSF after a 1 degrees C increase in temperature could be detected. We failed to detect any increase in the DNA-binding ability of HSF in cultured mammalian cells as a consequence of any exposure tested, within the sensitivity of our assay. Our results do not support the notion that the stress response is activated as a consequence of exposure to microwaves of frequencies associated with mobile communication devices.

Valproic acid enhances the efficacy of radiation therapy by protecting normal hippocampal neurons and sensitizing malignant glioblastoma cells.

Neurocognitive deficits are serious sequelae that follow cranial irradiation used to treat patients with medulloblastoma and other brain neoplasms. Cranial irradiation causes apoptosis in the subgranular zone of the hippocampus leading to cognitive deficits. Valproic acid (VPA) treatment protected hippocampal neurons from radiation-induced damage in both cell culture and animal models. Radioprotection was observed in VPA-treated neuronal cells compared to cells treated with radiation alone. This protection is specific to normal neuronal cells and did not extend to cancer cells. In fact, VPA acted as a radiosensitizer in brain cancer cells. VPA treatment induced cell cycle arrest in cancer cells but not in normal neuronal cells. The level of anti-apoptotic protein Bcl-2 was increased and the pro-apoptotic protein Bax was reduced in VPA treated normal cells. VPA inhibited the activities of histone deacetylase (HDAC) and glycogen synthase kinase-3ß (GSK3ß), the latter of which is only inhibited in normal cells. The combination of VPA and radiation was most effective in inhibiting tumor growth in heterotopic brain tumor models. An intracranial orthotopic glioma tumor model was used to evaluate tumor growth by using dynamic contrast-enhanced magnetic resonance (DCE MRI) and mouse survival following treatment with VPA and radiation. VPA, in combination with radiation, significantly delayed tumor growth and improved mouse survival. Overall, VPA protects normal hippocampal neurons and not cancer cells from radiation-induced cytotoxicity both in vitro and in vivo. VPA treatment has the potential for attenuating neurocognitive deficits associated with cranial irradiation while enhancing the efficiency of glioma radiotherapy.

Differential accumulation of U14 snoRNA and hsc70 mRNA in Chinese hamster cells after exposure to various stress conditions.

We have previously characterized the unique organization of the U14 small nucleolar ribonucleic acid (snoRNA) gene in Chinese hamster HA-1 cells. The single copy of the hsc70/U14 gene is the only source for the production of both U14 snoRNA species and hsc70 messenger ribonucleic acid (mRNA) in these cells. Here we report that the accumulations of U14 snoRNA and hsc70 mRNA are different in response to various stress conditions, although both of them are transcribed in a single primary transcript. Heat shock induced an increased accumulation of both U14 snoRNA and hsc70 mRNA. On the other hand, exposure to sodium arsenite or azetidine induced an increased accumulation of hsc70 mRNA, but did not lead to a concomitant increase in the level of U14 snoRNA. Under normal growth conditions, the variations in the levels of U14 snoRNA and hsc70 mRNA, in the different phases of the cell cycle, are correlated. The increased expression of U14 snoRNA and hsc70 mRNA, and the hsc70 protein induced specifically by heat shock suggest that they participate in the repair process of heat-induced damage to macromolecular complexes involved in the synthesis and processing of ribosomal RNA.

Membrane phospholipids, EML4-ALK, and Hsp90 as novel targets in lung cancer treatment.

Approximately one third of patients with non-small cell lung cancer have unresectable stage IIIA or stage IIIB disease; combined cytotoxic chemotherapy and radiation therapy delivered concurrently has been established as the standard treatment for such patients. Despite many clinical trials that tested several different radiochemotherapy combinations, it seems that a plateau of efficiencies at the acceptable risk of complications has been reached. Clinical studies indicate that the improved efficacy of radiochemotherapy is associated with the radiosensitizing effects of chemotherapy. Improvement of outcomes of this combined modality by developing novel radiosensitizers is a viable therapeutic strategy. In addition to causing cell death, ionizing radiation also induces a many-faceted signaling response, which activates numerous prosurvival pathways that lead to enhanced proliferation in the endothelial cells and increased vascularization in tumors. Radiation at doses used in the clinic activates cytoplasmic phospholipase A2, leading to increased production of arachidonic acid and lysophosphatidylcholine. The former is the initial step in the generation of eicosanoids, while the later is the initial step in the formation of lysophosphatidic acid, leading to the activation of inflammatory pathways. The echinoderm microtubule-associated protein-like 4 anaplastic lymphoma kinase (EML4-ALK) is member of the insulin superfamily of receptor tyrosine kinases. The EML4-ALK fusion gene appears unique to lung cancer and signals through extracellular signal regulated kinase and phosphoinositide 3-kinase. Heat shock protein 90 (Hsp90) is often overexpressed and present in an activated multichaperone complex in cancer cells, and it is now regarded as essential for malignant transformation and progression. In this review we focus on radiosensitizing strategies involving the targeting of membrane phospholipids, EML4-ALK, and Hsp90 with specific inhibitors and briefly discuss the combination of radiation with antivascular agents.

Heat-induced perturbations of DNA damage signaling pathways are modulated by molecular chaperones.

Heat is one of the most potent radiosensitizers known. Several randomized trials have shown that hyperthermia is a good adjuvant for radiotherapy at several different cancer sites. However, the mechanism(s) involved in the interaction of heat and radiation that lead to radiosensitization remain to be elucidated. In this report, we have determined that heat induces perturbations in some of the earliest events in the cellular response to DNA damage induced by ionizing radiation. We studied the effect of heat on the formation of complexes containing gamma-H2AX/MDC1/53BP1 in heated-irradiated cells. We found that the formation of this complex was delayed in heated-irradiated cells, in a heat but not radiation dose-dependent manner. The length of the heat-induced delay of complex formation was attenuated in thermotolerant and heat radiosensitization-resistant cells. The length of the delay of gamma-H2AX/MDC1/53BP1 complex formation correlated with the magnitude of heat radiosensitization and was modulated by the molecular chaperone Hsc70. Heat radiosensitization was attenuated in 53BP1-null cells, implying that the delay of the formation of the gamma-H2AX/MDC1/53BP1 complex plays a role in heat radiosensitization. Heat also induced a delay of events in the DNA damage response that are downstream from 53BP1. Our results support the notion that heat-induced perturbations in the earliest events of the cellular response to ionizing radiation-induced DNA damage play a role in heat radiosensitization.

Alterations in heat-induced radiosensitization accompanied by nuclear structure alterations in Chinese hamster cells.

This paper examined heat-induced radiosensitization in two Chinese hamster heat-resistant cell lines, HR-1 and OC-14, that were isolated from the same wild-type HA-1 cell line. It found a reduction of the magnitude of heat-induced radiosensitization after exposure to 43 degrees C in both HR-1 and OC-14 cells and a similar reduction after exposure to 45 degrees C in HR-1 cells, but not in OC-14 cells. The effect of heat exposure on a class of ionizing radiation-induced DNA damage that inhibits the ability of nuclear DNA to undergo super-coiling changes was also studied using the fluorescent halo assay in these three cell lines. Wild type cells exposed to either 43 or 45 degrees C before irradiation had a DNA rewinding ability that was intermediate between control and unheated cells, a phenomenon previously described as a masking effect. This masking effect was significantly reduced in HR-1 cells exposed to either 43 or 45 degrees C or in OC-14 cells exposed to 43 degrees C under conditions that heat-induced radiosensitization was reduced. In contrast, the masking effect was not altered in OC-14 cells exposed to 45 degrees C, conditions under which heat-induced radiosensitization was similar to that observed in wild-type HA-1 cells. These results suggest that a reduction in the masking effect is associated with a reduction of the magnitude of heat-induced radiosensitization in the HR-1 and OC-14 heat-resistant cell lines. The reduction of the masking effect in the cell lines resistant to heat-induced radiosensitization was associated with neither a reduction in the magnitude of the heat-induced increase in total nuclear protein content nor major differences in the protein profiles of the nucleoids isolated from heated cells.

Indomethacin and ibuprofen induce Hsc70 nuclear localization and activation of the heat shock response in HeLa cells.

It has been established that non-steroidal anti-inflammatory drugs (NSAIDs), such as sodium salicylate, sulindac, ibuprofen, and indomethacin, induce anti-inflammatory and anti-proliferative effects independent of cyclooxygenase. These cyclooxygenase-independent pharmacodynamic effects appear to regulate several signaling pathways involving proliferation, apoptosis, and heat shock response. However, the mechanisms of these actions remain an area of ongoing investigation. Hsc70 is a cytoplasmic chaperone protein involved in folding and trafficking of client proteins to different subcellular compartments, plays roles in signal transduction and apoptosis processes, and translocates to the nucleus following exposure to heat shock. Since NSAIDs induce some aspects of the heat shock response, we hypothesized that they may also induce Hsc70 nuclear translocation. Western immunoblotting and indirect cellular immunofluorescence showed that indomethacin and ibuprofen induce Hsc70 nuclear translocation at concentrations previously shown to induce HSF DNA-binding activity. Chemical inhibition of both p38(MAPK) and Erk42/44 had no effect on localization patterns. In addition, while indomethacin has been shown to behave as an oxidative stressor, the radical scavenging agent, N-acetyl cysteine, did not inhibit nuclear translocation. These results indicate that induction of the heat shock response by NSAIDs occurs at concentrations fivefold greater than those required to inhibit cyclooxygenase activity, suggesting a cyclooxygenase-independent mechanism, and in the presence or absence of kinase inhibitors and a free radical scavenger, suggesting independence of Erk42/44 or p38(MAPK) activities and intracellular oxidoreductive state.