Heat shock proteins, thermotolerance, and their relevance to clinical hyperthermia

Pulsed high-power microwaves do not impair the functions of skin normal and cancer cells in vitro: A short-term biological evaluation

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Pulsed high power microwave (MW) at a frequency 3.5 GHz was generated.

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MW did not induce cell death in skin fibroblast normal cells and melanoma cells.

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MW did not alter the morphology of melanoma cells.

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Gene expression related to ATP synthesis and proliferation can get altered by MW.

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MW selectively stimulated viability and proliferation of only melanoma cells.

Over the past few decades, microwave (MW) radiation has been widely used, and its biological effects have been extensively investigated. However, the effect of MW radiation on human skin biology is not well understood. We study the effects of pulsed high-power microwaves (HPMs) on melanoma (G361 and SK-Mel-31) and normal human dermal fibroblast (NHDF) cells. A pulsed power generator (Chundoong) was used to generate pulsed HPMs (dominant frequency: 3.5 GHz). For treatment 1, 5, 15, and 45 shots are given to cells in which the electromagnetic energy of 0.6 J was delivered to the cells at each trigger shot. Cell viability, proliferation rate, apoptosis, cell death, metabolic activity, and oxygen-free radical regulation were evaluated after the MW exposure at low and high doses. MW exposure increased the viabilities and proliferation rates of both melanoma cell lines in a dose-dependent manner, while no significant effects on the fibroblast cells were observed. We found an elevated level of ATP and mitochondrial activity in melanoma cells. Also, it was observed that MW exposure did not affect cell death in melanoma and fibroblast cells. A polymerase chain reaction analysis indicated that the MWs induced dose-dependent proliferation markers without affecting the cell cycle and apoptotic genes in the melanoma cells. Our findings show the differential effects of the MW radiation on the melanoma cells, compared to those on the fibroblast cells.

Millimeter-wave pulsed heating in vitro: cell mortality and heat shock response

Millimeter wave (MMW)-induced heating represents a promising alternative for non-invasive hyperthermia of superficial skin cancer, such as melanoma. Pulsed MMW-induced heating of tumors allows for reaching high peak temperatures without overheating surrounding tissues. Herein, for the first time, we evaluate apoptotic and heat shock responses of melanoma cells exposed in vitro to continuous (CW) or pulsed-wave (PW) amplitude-modulated MMW at 58.4 GHz with the same average temperature rise. Using an ad hoc exposure system, we generated 90 min pulse train with 1.5 s pulse duration, period of 20 s, amplitude of 10 °C, and steady-state temperature at the level of cells of 49.2 °C. The activation of Caspase-3 and phosphorylation of HSP27 were investigated using fluorescence microscopy to monitor the spatial variation of cellular response. Our results demonstrate that, under the considered exposure conditions, Caspase-3 activation was almost 5 times greater following PW exposure compared to CW. The relationship between the PW-induced cellular response and SAR-dependent temperature rise was non-linear. Phosphorylation of HSP27 was 58% stronger for PW compared to CW. It exhibits a plateau for the peak temperature ranging from 47.7 to 49.2 °C. Our results provide an insight into understanding of the cellular response to MMW-induced pulsed heating.

Bismuth embedded silica nanoparticles loaded with autophagy suppressant to promote photothermal therapy

An unpredicted side effect of photothermal therapy (PTT) is agitated by hyperthermia which results in damage to healthy tissue. Developing PTT platforms, enabling effective tumor ablation under mild irradiation conditions, is of wide interest, but challenging. Here, we investigated bismuth crystals embedded silica (Bi@SiO₂) nanoparticles, loaded with an autophagy inhibitor (chloroquine, CQ). It was found that SiO₂ effectively prevented the oxidization of Bi nanocrystals in the physiological environment and could serve as a scatter layer to improve NIR absorption, enabling a high photothermal conversion efficiency (~43%) and excellent photostability. Furthermore, the findings indicated that CQ molecules, delivered intracellularly by the particles, significantly weakened the degradation of autolysosomes by lysosome within the tumor cells, thus inducing suppression effect to autophagy and resistance to photothermia. Both in vitro and in vivo anti-tumor effects were consequently promoted owing to the combined effects enabled by Bi@SiO₂-CQ nanoparticles under mild NIR irradiation conditions. This study demonstrates a potential new PTT platform with superior therapeutic efficacy.

Biomodal Tumor-Targeted and Redox-Responsive Bi2 Se3 Hollow Nanocubes for MSOT/CT Imaging Guided Synergistic Low-Temperature Photothermal Radiotherapy

Hyperthemia (>50 °C) induced heating damage of nearby normal organs and inflammatory diseases are the main challenges for photothermal therapy (PTT) of cancers. To overcome this limitation, a redox-responsive biomodal tumor-targeted nanoplatform is synthesized, which can achieve multispectral optoacoustic tomography/X-ray computed tomography imaging-guided low-temperature photothermal-radio combined therapy (PTT RT). In this study, Bi₂ Se₃ hollow nanocubes (HNCs) are first fabricated based on a mild cation exchange way and Kirkendall effect and then modified with hyaluronic acid (HA) through redox-cleavable linkage (-s-s-), thus enabling the HNC to target cancer cells overexpressing CD-44 and control the cargo release profile. Finally, gambogic acid (GA), a type of heat-shock protein (HSP) inhibitor, which is vital to cells resisting heating-caused damage is loaded, into Bi₂ Se₃ HNC. Such HNC-s-s-HA/GA under a mild NIR laser irradiation can induce efficient cancer cell apoptosis, achieving PTT under relatively low temperature (≈43 °C) with remarkable cancer cell damage efficiency. Furthermore, enhanced radiotherapy (RT) can also be experienced without depth limitation based on RT sensitizer Bi₂ Se₃ HNC. This research designs a facile way to synthesize Bi₂ Se₃ HNC-s-s-HA/GA possessing theranostic functionality and cancer cells-specific GSH, but also shows a low-temperature PTT RT method to cure tumors in a minimally invasive and highly efficient way.

Removal of DNA adducts

DNA adducts are associated with a number of diseases, including cancer. Based on a recent report by our group, the aim of this study was to test the hypothesis that DNA adducts can be removed by means of one or more of the following three intervention programmes: intermittent whole-body hyperthermia; detoxification; and cell repair. The number of DNA adducts and total DNA adduct concentrations were measured in 104 patients who underwent one or more of the three intervention programmes. DNA adduct assessments were carried out on extracted genomic DNA by gas-liquid chromatography, with any DNA adducts found being localised using DNA microarrays. The baseline median number of DNA adducts was 2. The follow-up median number of adducts was highly significantly lower at 0 (p < 0.000000000000003). The mean total DNA adduct concentration at baseline was 9.308 ng/mL, and highly significantly lower at follow-up at 1.553 ng/mL (p < 0.000000000000006). Of the three intervention programmes, only the intermittent whole-body hyperthermia was associated with a significant reduction in DNA adducts. This study offers support for the hypothesis that DNA adducts can be removed by intermittent whole-body hyperthermia. The intermittent hyperthermia used involved infrared-A (wavelength 700-1400 nm, or, equivalently, a frequency of 215-430 THz) being preferentially delivered to the whole body, apart from the head, for up to one hour per session, with gradual core body temperature elevation usually occurring during the first 20-30 min. These results may offer an explanation at the molecular level for other reported clinical benefits of intermittent whole-body hyperthermia.

Energy-Converting Nanomedicine

Serious side effects to surrounding normal tissues and unsatisfactory therapeutic efficacy hamper the further clinic applications of conventional cancer-therapeutic strategies, such as chemotherapy and surgery. The fast development of nanotechnology provides unprecedented superiorities for cancer therapeutics. Externally activatable therapeutic modalities mediated by nanomaterials, relying on highly effective energy transformation to release therapeutic elements/effects (cytotoxic reactive oxygen species, thermal effect, photoelectric effect, Compton effect, cavitation effect, mechanical effect or chemotherapeutic drug) for cancer therapies, categorized and termed as "energy-converting nanomedicine," have arouse considerable concern due to their noninvasiveness, desirable tissue-penetration depth, and accurate modulation of therapeutic dose. This review summarizes the recent advances in the engineering of intelligent functional nanotherapeutics for energy-converting nanomedicine, including photo-based, radiation-based, ultrasound-based, magnetic field-based, microwave-based, electric field-based, and radiofrequency-based nanomedicines, which are enabled by external stimuli (light, radiation, ultrasound, magnetic field, microwave, electric field, and radiofrequency). Furthermore, biosafety issues of energy-converting nanomedicine related to future clinical translation are also addressed. Finally, the potential challenges and prospects of energy-converting nanomedicine for future clinical translation are discussed.

Efficient Near Infrared Light Triggered Nitric Oxide Release Nanocomposites for Sensitizing Mild Photothermal Therapy

Mild photothermal therapy (PTT), as a new anticancer therapeutic strategy, faces big challenges of limited therapeutic accuracy and side-effects due to uneven heat distribution. Here, near infrared triggered nitric oxide (NO) release nanocomposites based on bismuth sulfide (Bi2S3) nanoparticles and bis-N-nitroso compounds (BNN) are constructed for NO-enhanced mild photothermal therapy. Upon 808 nm irradiation, the high photothermal conversion efficiency and on-demand NO release are realized simultaneously. Due to the unique properties of NO, enhanced antitumor efficacy of mild PTT based on BNN-Bi2S3 nanocomposites is achieved in vitro and in vivo. Mechanism studies reveal that the exogenous NO from BNN-Bi2S3 could not only impair the autophagic self-repairing ability of tumor cells in situ, but also diffuse to the surrounding cells to enhance the therapeutic effect. This work points out a strategy to overcome the difficulties in mild PTT, and has potentials for further exploitation of NO-sensitized synergistic cancer therapy.

Combining Bulk Temperature and Nanoheating Enables Advanced Magnetic Fluid Hyperthermia Efficacy on Pancreatic Tumor Cells

Many efforts are made worldwide to establish magnetic fluid hyperthermia (MFH) as a treatment for organ-confined tumors. However, translation to clinical application hardly succeeds as it still lacks of understanding the mechanisms determining MFH cytotoxic effects. Here, we investigate the intracellular MFH efficacy with respect to different parameters and assess the intracellular cytotoxic effects in detail. For this, MiaPaCa-2 human pancreatic tumor cells and L929 murine fibroblasts were loaded with iron-oxide magnetic nanoparticles (MNP) and exposed to MFH for either 30 min or 90 min. The resulting cytotoxic effects were assessed via clonogenic assay. Our results demonstrate that cell damage depends not only on the obvious parameters bulk temperature and duration of treatment, but most importantly on cell type and thermal energy deposited per cell during MFH treatment. Tumor cell death of 95% was achieved by depositing an intracellular total thermal energy with about 50% margin to damage of healthy cells. This is attributed to combined intracellular nanoheating and extracellular bulk heating. Tumor cell damage of up to 86% was observed for MFH treatment without perceptible bulk temperature rise. Effective heating decreased by up to 65% after MNP were internalized inside cells.

Regulation of heat shock protein 70 (Hsp70) levels in the bdelloid rotifer Rotaria rotatoria under temperature stress

The bdelloid rotifer is an important component of freshwater zooplankton, exhibiting the features of parthenogenesis and anhydrobiotic capability. Heat shock proteins (Hsps), acting as molecular chaperones, are a highly conserved, ubiquitously expressed family of stress response proteins. In this study, the thermal optimums for heat-shock response and the levels of Hsp70 in Rotaria rotatoria (bdelloid rotifer) under different stress conditions were evaluated using survival assays and western blotting with fluorescent detection. The results showed that: (1) The survivorship in R. rotatoria were 100% throughout the temperature range of 12°C to 40°C, and the population growth rate reached its culmination at 28°C, suggesting the retardation of growth and reproduction at the other temperatures; (2) While stressed under 40°C, the levels of Hsp70 in R. rotatoria increased significantly over time, correlating with the duration of the stress; (3) As responses to different temperatures, the synthesis of Hsp70 could be induced significantly in R. rotatoria under both of high (40°C) and low (16°C) temperatures; (4) After removal of the thermal stress and recovery at 28°C, the levels of Hsp70 continued to rise for a period of time, peaked at 12 h, and then slowly declined with the extension of recovery duration, until there is no significant difference of Hsp70 levels. Summarily, with the fluctuations of stress duration and temperature, the rotifers could adapt to the environments sensitively by regulating the synthesis of Hsp70.

1D Coordination Polymer Nanofibers for Low-Temperature Photothermal Therapy

Near-infrared (NIR)-light-triggered photothermal therapy (PTT) usually requires hyperthermia to >50 °C for effective tumor ablation, which can potentially induce inflammatory disease and heating damage of normal organs nearby, while tumor lesions without sufficient heating (e.g., the internal part) may survive after treatment. Achieving effective tumor killing under relatively low temperatures is thus critical toward successful clinical use of PTT. Herein, we design a simple strategy to fabricate poly(ethylene glycol) (PEG)-modified one-dimensional nanoscale coordination polymers (1D-NCPs) with intrinsic biodegradability, large surface area, pH-responsive behaviors, and versatile theranostic functions. With NCPs consisting of Mn2+/indocyanine green (ICG) as the example, Mn-ICG@pHis-PEG display efficient pH-responsive tumor retention after systemic administration and then load Gambogic acid (GA), a natural inhibitor of heat-shock protein 90 (Hsp90) that plays an essential role for cells to resist heating-induced damage. Such Mn-ICG@pHis-PEG/GA under a mild NIR-triggered heating is able to induce effective apoptosis of tumor cells, realizing low-temperature PTT (~43 °C) with excellent tumor destruction efficacy. This work not only develops a facile approach to fabricate PEGylated 1D-NCPs with tumor-specific pH responsiveness and theranostic functionalities, but also presents a unique low-temperature PTT strategy to kill cancer in a highly effective and minimally invasive manner.

Overcoming the Heat Endurance of Tumor Cells by Interfering with the Anaerobic Glycolysis Metabolism for Improved Photothermal Therapy

In this study, we developed a general method to decorate plasmonic gold nanorods (GNRs) with a CD44-targeting functional polymer, containing a hyaluronic acid (HA)-targeting moiety and a small molecule Glut1 inhibitor of diclofenac (DC), to obtain GNR/HA-DC. This nanosystem exhibited the superiority of selectively sensitizing tumor cells for photothermal therapy (PTT) by inhibiting anaerobic glycolysis. Upon specifically targeting CD44, sequentially time-dependent DC release could be achieved by the trigger of hyaluronidase (HAase), which abundantly existed in tumor tissues. The released DC depleted the Glut1 level in tumor cells and induced a cascade effect on cellular metabolism by inhibiting glucose uptake, blocking glycolysis, decreasing ATP levels, hampering heat shock protein (HSP) expression, and ultimately leaving malignant cells out from the protection of HSPs to stress (e.g., heat), and then tumor cells were more easy to kill. Owing to the sensitization effect of GNR/HA-DC, CD44 overexpressed tumor cells could be significantly damaged by PTT with an enhanced therapeutic efficiency in vitro and in vivo.

Laser-Triggered Small Interfering RNA Releasing Gold Nanoshells against Heat Shock Protein for Sensitized Photothermal Therapy

The resistance of cancer cells to photothermal therapy is closely related to the overexpression of heat shock proteins (HSPs), which are abnormally upregulated when cells are under lethal stresses. Common strategies that use small molecule inhibitors against HSPs to enhance hyperthermia effect lack spatial and temporal control of drug release, leading to unavoidable systemic toxicity. Herein, a versatile photothermal platform is developed which is composed of a hollow gold nanoshell core densely packed with small interfering RNAs against heat shock protein 70 (Hsp70). Upon near infrared light irradiation, the small interfering RNAs can detach from gold surface specifically and escape from endosomes for Hsp70 silencing. Meanwhile, the temperature increases for hyperthermia therapy due to the high photothermal efficiency of the nanoshells. Efficient downregulation of Hsp70 after light activation is achieved in vitro and in vivo. Ultimately, the light-controlled dual functional nanosystem, with the effects of Hsp70 silencing and temperature elevation, results in sensitized photothermal therapy in nude mice model under mild temperature. This strategy smartly combines the localized photothermal therapy with controlled Hsp70 silencing, and has great potential for clinical translation with a simple and easily controlled structure.

Selectively Sensitizing Malignant Cells to Photothermal Therapy Using a CD44-Targeting Heat Shock Protein 72 Depletion Nanosystem

Selectively enhance the therapeutic efficacy to malignancy is one of the most important issues for photothermal therapy (PTT). However, most solid tumors, such as triple negative breast cancer (TNBC), do not have identifiable surface markers to distinguish themselves from normal cells, thus it is challenging to selectively identify and eliminate those malignances by PTT. In this report, we hypothesized that, by targeting CD44 (one TNBC-overexpressed surface molecule) and depleting heat shock protein 72 (HSP72, one malignancy-specific-overexpressed thermotolerance-related chaperone) subsequently, the TNBC could be selectively sensitized to PTT and improve the accuracy of treatment. To this end, a rationally designed nanosystem gold nanostar (GNS)/siRNA against HSP72 (siHSP72)/hyaluronic acid (HA) was successfully constructed using a layer-by-layer method. Hydrodynamic diameter and zeta potential analysis demonstrated the formation of GNS/siHSP72/HA having a particle size of 73.2 ± 3.8 nm and a negative surface charge of -18.3 ± 1.6 mV. The CD44-targeting ability of GNS/siHSP72/HA was confirmed by the flow cytometer, confocal microscopic imaging, and competitive binding analysis. The HSP72 silencing efficacy of GNS/siHSP72/HA was ∼95% in complete culture medium. By targeting CD44 and depleting HSP72 sequentially, GNS/siHSP72/HA could selectively sensitize TNBC cells to hyperthermia and enhance the therapeutic efficacy to TNBC with minimal side effect both in vitro and in vivo. Other advantages of GNS/siHSP72/HA included easy synthesis, robust siRNA loading capacity, endosome/lysosome escaping ability, high photothermal conversion efficacy and superior hemo- and biocompatibility.

Network analysis of genes involved in the enhancement of hyperthermia sensitivity by the knockdown of BAG3 in human oral squamous cell carcinoma cells

BCL2-associated athanogene 3 (BAG3), a co-chaperone of the heat shock 70 kDa protein (HSPA) family of proteins, is a cytoprotective protein that acts against various stresses, including heat stress. The aim of the present study was to identify gene networks involved in the enhancement of hyperthermia (HT) sensitivity by the knockdown (KD) of BAG3 in human oral squamous cell carcinoma (OSCC) cells. Although a marked elevation in the protein expression of BAG3 was detected in human the OSCC HSC-3 cells exposed to HT at 44˚C for 90 min, its expression was almost completely suppressed in the cells transfected with small interfering RNA against BAG3 (siBAG) under normal and HT conditions. The silencing of BAG3 also enhanced the cell death that was increased in the HSC-3 cells by exposure to HT. Global gene expression analysis revealed many genes that were differentially expressed by >2-fold in the cells exposed to HT and transfected with siBAG. Moreover, Ingenuity® pathways analysis demonstrated two unique gene networks, designated as Pro-cell death and Anti-cell death, which were obtained from upregulated genes and were mainly associated with the biological functions of induction and the prevention of cell death, respectively. Of note, the expression levels of genes in the Pro-cell death and Anti-cell death gene networks were significantly elevated and reduced in the HT + BAG3-KD group compared to those in the HT control group, respectively. These results provide further insight into the molecular mechanisms involved in the enhancement of HT sensitivity by the silencing of BAG3 in human OSCC cells.

Regional hyperthermia combined with chemotherapy in paediatric, adolescent and young adult patients: current and future perspectives

Here we evaluate the current status of clinical research on regional hyperthermia (RHT) in combination with chemotherapy or radiation therapy in paediatric oncology.Data were identified in searches of MEDLINE, Current Contents, PubMed, and references from relevant articles using medical subject headings including hyperthermia, cancer, paediatric oncology, children, radiation therapy and chemotherapy. Currently, only two RHT centres exist in Europe which treat children. Clinical RHT research in paediatric oncology has as yet been limited to children with sarcomas and germ cell tumours that respond poorly to or recur after chemotherapy. RHT is a safe and effective treatment delivering local thermic effects, which may also stimulate immunological processes via heat-shock protein reactions. RHT is used chiefly in children and adolescents with sarcomas or germ cell tumours located in the abdomino-pelvic region, chest wall or extremities to improve operability or render the tumour operable. It could potentially be combined with radiation therapy in a post-operative R1 setting where more radical surgery is not possible or combined with chemotherapy instead of radiation therapy in cases where the necessary radiation dose is impossible to achieve or would have mutilating consequences. RHT might also be an option for chemotherapy intensification in the neoadjuvant first-line treatment setting for children and adolescents, as was recently reflected in the promising long-term outcome data in adults with high-risk soft tissue sarcomas (EORTC 62961/ESHO trial).The limited data available indicate that combining RHT with chemotherapy is a promising option to treat germ cell tumours and, potentially, sarcomas. RHT may also be beneficial in first-line therapy in children, adolescents and young adults. The research should focus on optimising necessary technical demands and then initiate several clinical trials incorporating RHT into interdisciplinary treatment of children, adolescents and young adults that include translational research components exploring potential immunological mechanisms of action.

Cytoprotective effects of cerium and selenium nanoparticles on heat-shocked human dermal fibroblasts: an in vitro evaluation

It is a widely accepted fact that environmental factors affect cells by modulating the components of subcellular compartments and altering metabolic enzymes. Factors (such as oxidative stress and heat-shock-induced proteins and heat shock factors, which upregulate stress-response related genes to protect affected cells) are commonly altered during changes in environmental conditions. Studies by our group and others have shown that nanoparticles (NPs) are able to efficiently attenuate oxidative stress by penetrating into specific tissues or organs. Such findings warrant further investigation on the effects of NPs on heat-shock-induced stress, specifically in cells in the presence or absence (pretreated) of NPs. Here, we examined the cytoprotective effects of two different NPs (cerium and selenium) on heat-induced cell death for a model cell using dermal fibroblasts. We report for the first time that both ceria and selenium NPs (at 500 µg/mL) possess stress-relieving behavior on fibroblasts undergoing heat shock. Such results indicate the need to further develop these NPs as a novel treatment for heat shock.

Insights into the role of heat shock protein 72 to whole-body heat acclimation in humans

Heat acclimation results in systemic and cellular adaptions that reduce the negative effect of heat and, consequently, the risk of heat illness. Although the classical changes observed with heat acclimation lead to increased tolerance to exercise in the heat by reducing heat storage (reflected in reduced core and skin temperatures) and increasing whole-body capacity for heat dissipation (greater plasma volume, sweat output, and skin blood flow), it appears that heat acclimation also induces changes at the cellular level that might increase tolerance of the whole organism to a higher core temperature for the development of fatigue. Thermotolerance is a process that involves increased resilience to an otherwise lethal heat stress that follows a sublethal exposure to heat. Thermotolerance is believed to be the result of increased content of heat shock proteins (Hsp), specially a member of the 70 kDa family, Hsp72 kDa. In humans, we and others have reported that heat acclimation increases intracellular Hsp72 levels. This increase in intracellular Hsp72 could improve whole-body organism thermotolerance by maintaining intestinal epithelial tight junction barriers, by increasing resistance to gut-associated endotoxin translocation, or by reducing the inflammatory response. In this review, we will initially provide an overview of the physiological adaptations induced by heat acclimation and emphasize the main cellular changes that occur with heat acclimation associated with intracellular accumulation of Hsp72. Finally, we will present an argument for a role of whole-body heat acclimation in augmenting cellular thermotolerance, which may protect vital organs from deleterious effects of heat stress in humans.

Effects of hyperthermia on DNA repair pathways: one treatment to inhibit them all

The currently available arsenal of anticancer modalities includes many DNA damaging agents that can kill malignant cells. However, efficient DNA repair mechanisms protect both healthy and cancer cells against the effects of treatment and contribute to the development of drug resistance. Therefore, anti-cancer treatments based on inflicting DNA damage can benefit from inhibition of DNA repair. Hyperthermia – treatment at elevated temperature – considerably affects DNA repair, among other cellular processes, and can thus sensitize (cancer) cells to DNA damaging agents. This effect has been known and clinically applied for many decades, but how heat inhibits DNA repair and which pathways are targeted has not been fully elucidated. In this review we attempt to summarize the known effects of hyperthermia on DNA repair pathways relevant in clinical treatment of cancer. Furthermore, we outline the relationships between the effects of heat on DNA repair and sensitization of cells to various DNA damaging agents.

Amphetamine- and methamphetamine-induced hyperthermia: Implications of the effects produced in brain vasculature and peripheral organs to forebrain neurotoxicity

The adverse effects of amphetamine- (AMPH) and methamphetamine- (METH) induced hyperthermia on vasculature, peripheral organs and peripheral immune system are discussed. Hyperthermia alone does not produce amphetamine-like neurotoxicity but AMPH and METH exposures that do not produce hyperthermia (≥40°C) are minimally neurotoxic. Hyperthermia likely enhances AMPH and METH neurotoxicity directly through disruption of protein function, ion channels and enhanced ROS production. Forebrain neurotoxicity can also be indirectly influenced through the effects of AMPH- and METH- induced hyperthermia on vasculature. The hyperthermia and the hypertension produced by high doses amphetamines are a primary cause of transient breakdowns in the blood-brain barrier (BBB) resulting in concomitant regional neurodegeneration and neuroinflammation in laboratory animals. This BBB breakdown can occur in the amygdala, thalamus, striatum, sensory and motor cortex and hippocampus. Under these conditions, repetitive seizures greatly enhance neurodegeneration in hippocampus, thalamus and amygdala. Even when the BBB is less disrupted, AMPH- or METH- induced hyperthermia effects on brain vasculature may play a role in neurotoxicity. In this case, striatal and cortical vascular function are adversely affected, and even greater ROS, immune and damage responses are seen in the meninges and cortical surface vasculature. Finally, muscle and liver damage and elevated cytokines in blood can result when amphetamines produce hyperthermia. Proteins, from damaged muscle may activate the peripheral immune system and exacerbate liver damage. Liver damage can further increase cytokine levels, immune system activation and increase ammonia levels. These effects could potentially enhance vascular damage and neurotoxicity.

In vivo applications of magnetic nanoparticle hyperthermia

Hyperthermia is considered to be a promising tool for the treatment of tumours. Intensive research activities reveal a distinct impact not only on the cellular level but also on tumour physiology which favours the combination with the classical oncologic modalities radio- and chemotherapy. Different techniques have been established so far. Among them, magnetic hyperthermia exploits the intrinsic magnetic properties of iron oxide nanoparticles (magnetite and maghemite) which induce heating during the exposure to an alternating magnetic field. Beyond the advantage that heating is generated within the tumour and not from outside the body, the amounts of magnetic material and their intratumoral distribution patterns are key factors determining the therapeutic outcome. They can be influenced by the use of different application routes, which will be discussed in this paper.

Near-infrared dye loaded polymeric nanoparticles for cancer imaging and therapy and cellular response after laser-induced heating

BACKGROUND

In the past decade, researchers have focused on developing new biomaterials for cancer therapy that combine imaging and therapeutic agents. In our study, we use a new biocompatible and biodegradable polymer, termed poly(glycerol malate co-dodecanedioate) (PGMD), for the synthesis of nanoparticles (NPs) and loading of near-infrared (NIR) dyes. IR820 was chosen for the purpose of imaging and hyperthermia (HT). HT is currently used in clinical trials for cancer therapy in combination with radiotherapy and chemotherapy. One of the potential problems of HT is that it can up-regulate hypoxia-inducible factor-1 (HIF-1) expression and enhance vascular endothelial growth factor (VEGF) secretion.

RESULTS

We explored cellular response after rapid, short-term and low thermal dose laser-IR820-PGMD NPs (laser/NPs) induced-heating, and compared it to slow, long-term and high thermal dose heating by a cell incubator. The expression levels of the reactive oxygen species (ROS), HIF-1 and VEGF following the two different modes of heating. The cytotoxicity of NPs after laser/NP HT resulted in higher cell killing compared to incubator HT. The ROS level was highly elevated under incubator HT, but remained at the baseline level under the laser/NP HT. Our results show that elevated ROS expression inside the cells could result in the promotion of HIF-1 expression after incubator induced-HT. The VEGF secretion was also significantly enhanced compared to laser/NP HT, possibly due to the promotion of HIF-1. In vitro cell imaging and in vivo healthy mice imaging showed that IR820-PGMD NPs can be used for optical imaging.

CONCLUSION

IR820-PGMD NPs were developed and used for both imaging and therapy purposes. Rapid and short-term laser/NP HT, with a low thermal dose, does not up-regulate HIF-1 and VEGF expression, whereas slow and long term incubator HT, with a high thermal dose, enhances the expression of both transcription factors.

Protein misfolding, aggregation, and autophagy after brain ischemia

Ischemic brain injury is a common disorder linked to a variety of diseases. Significant progress has been made in our understanding of the underlying mechanisms. Previous studies show that protein misfolding, aggregation, and multiple organelle damage are major pathological events in postischemic neurons. The autophagy pathway is the chief route for bulk degradation of protein aggregates and damaged organelles. The latest studies suggest that impairment of autophagy contributes to abnormal protein aggregation and organelle damages after brain ischemia. This article reviews recent studies of protein misfolding, aggregation, and impairment of autophagy after brain ischemia.

Magnetically triggered dual functional nanoparticles for resistance-free apoptotic hyperthermia

Overcoming resistance: Heat-treated cancer cells possess a protective mechanism for resistance and survival. Resistance-free apoptosis-inducing magnetic nanoparticles (RAINs) successfully promote hyperthermic apoptosis, obstructing cell survival by triggering two functional units of heat generation and the release of geldanamycin (GM) for heat shock protein (Hsp) inhibition under an alternating magnetic field (AMF).

Heat stress and sudden infant death syndrome--stress gene expression after exposure to moderate heat stress

The aim of the present study was to investigate stress gene expression in cultured primary fibroblasts established from Achilles tendons collected during autopsies from sudden infant death syndrome (SIDS) cases, and age-matched controls (infants dying in a traumatic event). Expression of 4 stress responsive genes, HSPA1B, HSPD1, HMOX1, and SOD2, was studied by quantitative reverse transcriptase PCR analysis of RNA purified from cells cultured under standard or various thermal stress conditions. The expression of all 4 genes was highly influenced by thermal stress in both SIDS and control cells. High interpersonal variance found in the SIDS group indicated that they represented a more heterogeneous group than controls. The SIDS group responded to thermal stress with a higher expression of the HSPA1B and HSPD1 genes compared to the control group, whereas no significant difference was observed in the expression of SOD2 and HMOX1 between the two groups. The differences were related to the heat shock treatment as none of the genes were expressed significantly different in SIDS at base levels at 37 °C. SOD2 and HMOX1 were up regulated in both groups, for SOD2 though the expression was lower in SIDS at all time points measured, and may be less related to heat stress. Being found dead in the prone position (a known risk factor for SIDS) was related to a lower HSPA1B up-regulation in SIDS compared to SIDS found on their side or back. The study demonstrates the potential usefulness of gene expression studies using cultured fibroblasts established from deceased individuals as a tool for molecular and pathological investigations in forensic and biomedical sciences.

Impact of hyperthermic intraperitoneal chemotherapy on Hsp27 protein expression in serum of patients with peritoneal carcinomatosis

Despite the strong rationale for combining cytoreductive surgery (CRS) with hyperthermic intraperitoneal chemotherapy (HIPEC) in patients with peritoneal carcinomatosis, thermotolerance and chemoresistance might result from heat shock protein overexpression. The aim of the present study was thus to determine whether the heat shock protein 27 (Hsp27), a potential factor in resistance to treatment, could have a higher level in serum from patients under this combined therapy. Patients receiving CRS plus HIPEC for peritoneal carcinomatosis (group 1), patients with cancer or a history of cancer undergoing abdominal surgery (group 2), and patients without malignancies undergoing abdominal surgery (group 3) were included. Hsp27 serum levels were determined before and at different times following CRS and HIPEC using enzyme-linked immunosorbent assay. In group 1 (n = 25), the high Hsp27 levels, observed at the end of surgery compared with before (p < 0.0001), decreased during HIPEC, but remained significantly higher than before surgery (p < 0.0005). In groups 2 (n = 11) and 3 (n = 15), surgery did not significantly increase Hsp27 levels. A targeted molecular strategy, inhibiting Hsp27 expression in tumor tissue, could significantly reduce resistance to the combined CRS plus HIPEC treatment. This approach should be further assessed in a clinical phase I trial.

Targeting heat shock transcription factor 1 for novel hyperthermia therapy (review)

Hyperthermia (HT) has shown promising antitumor effects against various types of malignant tumors, and its pleiotropic effects support its combined use with radiotherapy and/or chemotherapy. However, HT is rendered less effective by the acquisition of thermoresistance in tumors, which arises through the elevation of heat shock proteins (HSPs) or other tumor responses. In mammals, the induction of HSPs is principally regulated at the transcriptional level by the activation of heat shock transcription factor 1 (HSF1). This transactivator has been shown to be abundantly expressed in a wide variety of tumors in humans. In addition, HSF1 participates in the initiation, proliferation and maintenance of tumors. Of note, HSF1 silencing has been shown to prevent the progression of tumors and to enhance their sensitivity to HT. Here, we review the physiological and pathological roles of HSF1 in cancer cells, and discuss its potential as a therapeutic target for HT therapy.

New insight into hyperthermic intraperitoneal chemotherapy: induction of oxidative stress dramatically enhanced tumor killing in in vitro and in vivo models

BACKGROUND

The aim of hyperthermic intraperitoneal chemotherapy (HIPEC) is to eradicate microscopic residual tumor after radical surgical tumor excision in patients with peritoneal carcinomatosis. The common use of antineoplastic agents such as mitomycin C, doxorubicin, or oxaliplatin with hyperthermia fails to eradicate tumors in a significant subset of patients, and alternative approaches to target chemoresistant cells are needed. The induction of reactive oxygen species (ROS) by inhibiting the critical detoxification enzyme superoxide dismutase (SOD) during hyperthermia is an appealing approach to induce death of residual cancer cells.

METHODS

Human and murine colon cancer cell lines were subjected to mild hyperthermia (40-42°C), and treated with chemotherapy, similar to clinical protocols. ROS were induced by the SOD inhibitor diethyldithiocarbamate (DDC), a metabolite of the drug disulfiram. In mice, peritoneal carcinomatosis use C57Bl/6 was induced in C57Bl/6 by intraperitoneal injection of syngenic tumor cells (MC38).

RESULTS

Hyperthermia alone failed to kill cells but induced intracellular ROS and activated protective mechanisms. Chemotherapy conferred inconsistent cytotoxicity depending on the cell line and dose. In contrast, induction of ROS by DDC consistently activated apoptotic pathways, with increased cell death in combination with mild hyperthermia. In vivo, combined treatment with DDC and hyperthermia significantly delayed tumor progression in tumor-bearing mice. In addition, hyperthermic combined treatment with chemotherapy and DDC significantly improved animal survival compared with chemotherapy alone.

CONCLUSIONS

Addition of DDC improves the efficacy of existing HIPEC protocols in a safe way and may open the door to a more effective, multimodal HIPEC.

Prions in yeast

The concept of a prion as an infectious self-propagating protein isoform was initially proposed to explain certain mammalian diseases. It is now clear that yeast also has heritable elements transmitted via protein. Indeed, the "protein only" model of prion transmission was first proven using a yeast prion. Typically, known prions are ordered cross-β aggregates (amyloids). Recently, there has been an explosion in the number of recognized prions in yeast. Yeast continues to lead the way in understanding cellular control of prion propagation, prion structure, mechanisms of de novo prion formation, specificity of prion transmission, and the biological roles of prions. This review summarizes what has been learned from yeast prions.

Constitutive overexpression of HSP-70 in thermal resistant tumor cells does not alter sensitivity to porphyrin-, chlorin-, or purpurin-mediated PDT

Cellular expression of the 70 kDa heat shock protein (HSP-70) is observed following hyperthermia and is correlated with transient resistance to subsequent heating. Photodynamic therapy (PDT) mediated oxidative stress can also induce transcriptional and translational expression of a variety of genes including HSP-70. However, PDT-mediated HSP-70 expression can vary as a function of photosensitizer type and incubation conditions. In the current study we used three clinically relevant photosensitizers, a porphyrin (Photofrin), a purpurin (SnET2), and a chlorin (NPe6), to examine PDT-mediated HSP-70 expression profiles and photosensitivity characteristics in parental radiation-induced fibrosarcoma cells (RIF-1) and in thermal resistant RIF-1 clones. We observed that in vitro PDT treatments using either SnET2 or NPe6 induced HSP-70 expression but that comparable PDT treatments using Photofrin did not result in increased HSP-70 levels. We also observed that PDT sensitivity in parental and heat-resistant cell clones were similar for each photosensitizer while thermal sensitivity was significantly reduced in the RIF clones which constitutively overexpressed HSP-70. These results indicate that definable differences can exist in the molecular pathways induced by PDT for different photosensitizers. Our results also demonstrate that constitutive overexpression of HSP-70 does not modulate PDT photosensitivity regardless of whether PDT treatments induce HSP-70 expression. We conclude that HSP-70 expression does not play a significant role in cellular PDT photosensitivity.

Biological applications of magnetic nanoparticles

In this review an overview about biological applications of magnetic colloidal nanoparticles will be given, which comprises their synthesis, characterization, and in vitro and in vivo applications. The potential future role of magnetic nanoparticles compared to other functional nanoparticles will be discussed by highlighting the possibility of integration with other nanostructures and with existing biotechnology as well as by pointing out the specific properties of magnetic colloids. Current limitations in the fabrication process and issues related with the outcome of the particles in the body will be also pointed out in order to address the remaining challenges for an extended application of magnetic nanoparticles in medicine.

Non-invasive, quantitative monitoring of hyperthermia-induced EGFR activation in xenograft tumours

PURPOSE

To examine the molecular mechanism of cellular EGFR activation during hyperthermia treatment.

MATERIALS AND METHODS

EGR activities in tumour cells were quantified through the use of a recently developed split-luciferase-based EGFR reporter system which allowed us to monitor EGFR activation in vitro as well as in vivo in a non-invasive manner.

RESULTS

We found that hyperthermia treatment of MDA-MB231 breast cancer cells resulted in a strong induction of EGFR activity in tissue culture as well as in xenograft tumours. Furthermore, we found that this induction is mediated by the heat shock protein Hsp90. Administration of the specific Hsp90 inhibitor geldanamycin as well as RNAi directed against HSP90 effectively inhibited EGFR activation, suggesting an essential role for Hsp90 in hyperthermia-induced EGFR activation. In addition, cells treated with geldanamycin were sensitised to heat treatment, suggesting that adding Hsp90 inhibitors to hyperthermia regimens might have a beneficial effect for cancer treatment.

CONCLUSIONS

Our bioluminescent imaging reporter provided a powerful tool to examine hyperthermia-induced EGFR activation in vitro as well as in vivo. Hsp90 was found to be a key factor mediating heat-induced EGFR activation in tumour cells.

Thermal boost combined with interstitial brachytherapy in breast conserving therapy - Assessment of early toxicity

BACKGROUND

Hyperthermia (HT) causes a direct damage to cancerous cells and/or sensitize them to radiotherapy with usually minimal injury to normal tissues. Adjuvant HT is probably one of the most effective radiation sensitizers known and works best when delivered simultaneously with radiation. In breast conserving therapy, irradiation has to minimize the risk of local relapse within the treated breast, especially in an area of a tumor bed. Brachytherapy boost reduces 5-year local recurrence rate to mean 5,5%, so there still some place for further improvement. The investigated therapeutic option is an adjuvant single session of local HT (thermal boost) preceding standard CT-based multicatheter interstitial HDR brachytherapy boost in order to increase the probability of local cure.

AIM

To report the short-term results in regard to early toxicity of high-dose-rate (HDR) brachytherapy (BT) boost with or without interstitial microwave hyperthermia (MV HT) for early breast cancer patients treated with breast conserving therapy (BCT).

MATERIALS AND METHODS

Between February 2006 and December 2007, 57 stage IA-IIIA breast cancer patients received a 10 Gy HDR BT boost after conservative surgery and 42.5-50 Gy whole breast irradiation (WBI) ± adjuvant chemotherapy. 32 patients (56.1%) were treated with additional pre-BT single session of interstitial MW HT to a tumor bed (multi-catheter technique). Reference temperature was 43 °C and therapeutic time (TT) was 1 h. Incidence, severity and duration of radiodermatitis, skin oedema and skin erythema in groups with (I) or without HT (II) were assessed, significant p-value ≤ 0.05.

RESULTS

Median follow-up was 40 months. Local control was 100% and distant metastasis free survival was 91.1%. HT sessions (median): reference temperature 42.2 °C, therapeutic time (TT) 61.4 min, total thermal dose 42 min and a gap between HT and BT 30 min. Radiodermatitis grades I and II occurred in 24 and 6 patients, respectively, differences between groups I and II were not significant. Skin oedema and erythema occurred in 48 (85.7%) and 36 (64.3%) cases, respectively, and were equally distributed between the groups. The incidence and duration of skin oedema differed between the subgroups treated with different fractionation protocols of WBI, p = 0.006. Skin oedema was present up to 12 months. No difference in pattern of oedema regression between groups I and II was observed, p = 0.933.

CONCLUSION

Additional thermal boost preceding standard HDR BT boost has a potential of further improvement in breast cancer local control in BCT. Pre-BT hyperthermia did not increase early toxicity in patients treated with BCT and was well tolerated. All side effects of combined treatment were transient and were present for up to 12 months. The increase in incidence of skin oedema was related to hypofractionated protocols of WBI. The study has to be randomized and continued on a larger group of breast cancer patients to verify the potential of local control improvement and to assess the profile of late toxicity.

Involvement of DNA-PK and ATM in radiation- and heat-induced DNA damage recognition and apoptotic cell death

Exposure to ionizing radiation and hyperthermia results in important biological consequences, e.g. cell death, chromosomal aberrations, mutations, and DNA strand breaks. There is good evidence that the nucleus, specifically cellular DNA, is the principal target for radiation-induced cell lethality. DNA double-strand breaks (DSBs) are considered to be the most serious type of DNA damage induced by ionizing radiation. On the other hand, verifiable mechanisms which can lead to heat-induced cell death are damage to the plasma membrane and/or inactivation of heat-labile proteins caused by protein denaturation and subsequent aggregation. Recently, several reports have suggested that DSBs can be induced after hyperthermia because heat-induced phosphorylated histone H2AX (γ-H2AX) foci formation can be observed in several mammalian cell lines. In mammalian cells, DSBs are repaired primarily through two distinct and complementary mechanisms: non-homologous end joining (NHEJ), and homologous recombination (HR) or homology-directed repair (HDR). DNA-dependent protein kinase (DNA-PK) and ataxia-telangiectasia mutated (ATM) are key players in the initiation of DSB repair and phosphorylate and/or activate many substrates, including themselves. These phosphorylated substrates have important roles in the functioning of cell cycle checkpoints and in cell death, as well as in DSB repair. Apoptotic cell death is a crucial cell suicide mechanism during development and in the defense of homeostasis. If DSBs are unrepaired or misrepaired, apoptosis is a very important system which can protect an organism against carcinogenesis. This paper reviews recently obtained results and current topics concerning the role of DNA-PK and ATM in heat- or radiation-induced apoptotic cell death.

Biomedical Nanomagnetics: A Spin Through Possibilities in Imaging, Diagnostics, and Therapy

Biomedical nanomagnetics is a multidisciplinary area of research in science, engineering and medicine with broad applications in imaging, diagnostics and therapy. Recent developments offer exciting possibilities in personalized medicine provided a truly integrated approach, combining chemistry, materials science, physics, engineering, biology and medicine, is implemented. Emphasizing this perspective, here we address important issues for the rapid development of the field, i.e., magnetic behavior at the nanoscale with emphasis on the relaxation dynamics, synthesis and surface functionalization of nanoparticles and core-shell structures, biocompatibility and toxicity studies, biological constraints and opportunities, and in vivo and in vitro applications. Specifically, we discuss targeted drug delivery and triggered release, novel contrast agents for magnetic resonance imaging, cancer therapy using magnetic fluid hyperthermia, in vitro diagnostics and the emerging magnetic particle imaging technique, that is quantitative and sensitive enough to compete with established imaging methods. In addition, the physics of self-assembly, which is fundamental to both biology and the future development of nanoscience, is illustrated with magnetic nanoparticles. It is shown that various competing energies associated with self-assembly converge on the nanometer length scale and different assemblies can be tailored by varying particle size and size distribution. Throughout this paper, while we discuss our recent research in the broad context of the multidisciplinary literature, we hope to bridge the gap between related work in physics/chemistry/engineering and biology/medicine and, at the same time, present the essential concepts in the individual disciplines. This approach is essential as biomedical nanomagnetics moves into the next phase of innovative translational research with emphasis on development of quantitative in vivo imaging, targeted and triggered drug release, and image guided therapy including validation of delivery and therapy response.

Hyperthermia classic article commentary: 'Re-induction of hsp70 synthesis: an assay for thermotolerance' by Gloria C. Li and Johnson Y. Mak, International Journal of Hyperthermia 1989;5:389-403

Of the many heat shock proteins (HSPs), hsp70 appears to correlate best with heat resistance, either permanent or transient. We have investigated various approaches to quantify the concentration of hsp70, and examined the relationship between hsp70 and cells' thermal sensitivity during the development and decay of thermotolerance in model systems. Specifically, experiments were performed to determine the possibility of using the rate of synthesis of hsp70 after a second test heat shock to predict the kinetics of thermotolerance in tumor cells in vitro and in animal tumor models. We found that the cells' ability to re-initiate hsp70 synthesis in response to the test heat shock inversely correlated with retained thermotolerance. These data suggest the level of hsp70 in thermotolerant cells regulates the rate of synthesis of additional hsp70 in response to the subsequent heat challenge. Furthermore, the results showed that the rate of re-induction of hsp70 synthesis after a test heat shock can be used as a rapid measure of retained thermotolerance. This study suggests an approach for quantifying the level of retained thermotolerance during fractionated hyperthermia.

Combined effects of laser-ICG photothermotherapy and doxorubicin chemotherapy on ovarian cancer cells

Doxorubicin (DOX) is an anthracycline antibiotic widely used in cancer chemotherapy. Its use is limited by cardiac toxicity and drug resistance. Hyperthermia can aid the functionality of DOX, but current hyperthermia delivery methods are hard to apply selectively and locally. The slow temperature increase associated with the external heating may lead to thermal tolerance in cancer cells. The FDA approved dye indocynine green (ICG) has been demonstrated to absorb near-infrared (NIR) light at 808 nm (ideal for tissue penetration) and emit the energy as heat, making it an ideal agent for localized hyperthermia with a rapid rate of temperature increase. The purpose of this study was to investigate the in vitro cytotoxic effect of combined chemotherapy and hyperthermia to a DOX resistant ovarian cancer cell line (SKOV-3). The effect of two different heating methods, ICG induced rapid rate heating and an incubator induced slow rate heating, were compared. All the experiments were conducted in 96-well plates. Cells were subjected to different concentrations of DOX and 60 min 43 degrees C incubation or 5 microM of ICG with 1 min 808 nm NIR laser. SRB assay was used to measure cell proliferation. ICG itself without laser irradiation was not toxic to SKOV-3 cells. The two types of hyperthermia individually produced similar cytotoxicity. DOX by itself was toxic with an IC(50) value of about 5 microM. Hyperthermia in combination with DOX achieved significantly greater cell killing/growth inhibition at all DOX concentrations compared to DOX alone. A subadditive cytotoxic effect was observed by combining DOX and 60 min 43 degrees C incubation which lead to a lowered DOX IC(50) value of about 1 microM. This value was even lower with 1 min laser-ICG photothermotherapy (0.1 microM) and, though not statistically significant, a synergistic effect may exist between DOX and laser-ICG photothermotherapy. The rate of heating may have an effect on chemotherapy-hyperthermia interaction. In conclusion, the combination of photothermal therapy and chemotherapy may provide a valuable tool for cancer treatment with minimized side effect.

Characterization of a recombinant adenovirus vector encoding heat-inducible feline interleukin-12 for use in hyperthermia-induced gene-therapy

Interleukin-12 (IL-12) is a pro-inflammatory cytokine that has shown great promise as a therapeutic agent in experimental models of infectious disease and cancer. However, it is also a highly toxic molecule and for that reason has not been accepted readily into the clinic. A replication-deficient adenoviral vector was designed to deliver the feline interleukin-12 gene into tumour cells. The interleukin-12 gene has been placed under control of a heat inducible promoter, human heat shock promoter 70b, with the intent of spatially and temporally controlling the expression of IL-12, thus limiting its toxicity. In vitro, the transfection efficiency of the adenoviral vector, the effect of multiplicity of infection and the production of biologically active feline IL-12 were studied in the infected cells in response to a range of temperatures. This adenoviral vector will be a useful tool to examine the effects of intra-tumoural IL-12 delivery in a spontaneously occurring feline soft tissue sarcoma model.

Induction of radiation resistance by a heat shock protein inhibitor, KNK437, in human glioblastoma cells

PURPOSE

We examined the effects of a heat shock protein (hsp) inhibitor, N-formyl-3, 4-methylenedioxy-gamma-butyrolactam (KNK437), on the radiosensitivity of human glioblastoma cells (A-172).

MATERIALS AND METHODS

Effects of KNK437 on radiosensitivity and cell cycle regulation were examined using colony formation assays, flow cytometry analysis and Western blot analysis. KNK437 was added to the culture medium 1 h before X-ray irradiation at 50, 100 or 300 microM final concentration.

RESULTS

KNK437 induced the resistance of A-172 cells and human squamous cell carcinoma cells (SAS) to X-rays. Flow cytometry analysis showed that KNK437 alone efficiently induced A-172 cells to enter G2/M phase. Though A-172 cells irradiated with X-rays at 6 Gy showed no clear change in the cell cycle, the irradiated cells were induced to enter G2/M phase when they had been pre-treated with KNK437. By Western blot analysis, p53, 14-3-3sigma and cell division cycle 2 (cdc2) proteins that function in G2 arrest were observed to be persistently accumulated or phosphorylated in KNK437-treated cells, regardless of X-ray irradiation.

CONCLUSIONS

These results show that KNK437 causes cells to be resistant to radiation, and that this might be correlated with maintenance of G2 arrest in the cell cycle regulation.