Skin sensitization by misonidazole: a demonstration of uniform mild hypoxia

A reliable set of reference genes to normalize oxygen-dependent cytoglobin gene expression levels in melanoma

Cytoglobin (CYGB) is a ubiquitously expressed protein with a protective role against oxidative stress, fibrosis and tumor growth, shown to be transcriptionally regulated under hypoxic conditions. Hypoxia-inducible CYGB expression is observed in several cancer cell lines and particularly in various melanoma-derived cell lines. However, reliable detection of hypoxia-inducible mRNA levels by qPCR depends on the critical choice of suitable reference genes for accurate normalization. Limited evidence exists to support selection of the commonly used reference genes in hypoxic models of melanoma. This study aimed to select the optimal reference genes to study CYGB expression levels in melanoma cell lines exposed to hypoxic conditions (0.2% O₂) and to the HIF prolyl hydroxylase inhibitor roxadustat (FG-4592). The expression levels of candidate genes were assessed by qPCR and the stability of genes was evaluated using the geNorm and NormFinder algorithms. Our results display that B2M and YWHAZ represent the most optimal reference genes to reliably quantify hypoxia-inducible CYGB expression in melanoma cell lines. We further validate hypoxia-inducible CYGB expression on protein level and by using CYGB promoter-driven luciferase reporter assays in melanoma cell lines.

Redox Active Antimicrobial Peptides in Controlling Growth of Microorganisms at Body Barriers

Epithelia in the skin, gut and other environmentally exposed organs display a variety of mechanisms to control microbial communities and limit potential pathogenic microbial invasion. Naturally occurring antimicrobial proteins/peptides and their synthetic derivatives (here collectively referred to as AMPs) reinforce the antimicrobial barrier function of epithelial cells. Understanding how these AMPs are functionally regulated may be important for new therapeutic approaches to combat microbial infections. Some AMPs are subject to redox-dependent regulation. This review aims to: (i) explore cysteine-based redox active AMPs in skin and intestine; (ii) discuss casual links between various redox environments of these barrier tissues and the ability of AMPs to control cutaneous and intestinal microbes; (iii) highlight how bacteria, through intrinsic mechanisms, can influence the bactericidal potential of redox-sensitive AMPs.

The Impact of Hypoxia on Neutrophil Degranulation and Consequences for the Host

Neutrophils are key effector cells of innate immunity, rapidly recruited to defend the host against invading pathogens. Neutrophils may kill pathogens intracellularly, following phagocytosis, or extracellularly, by degranulation and the release of neutrophil extracellular traps; all of these microbicidal strategies require the deployment of cytotoxic proteins and proteases, packaged during neutrophil development within cytoplasmic granules. Neutrophils operate in infected and inflamed tissues, which can be profoundly hypoxic. Neutrophilic infiltration of hypoxic tissues characterises a myriad of acute and chronic infectious and inflammatory diseases, and as well as potentially protecting the host from pathogens, neutrophil granule products have been implicated in causing collateral tissue damage in these scenarios. This review discusses the evidence for the enhanced secretion of destructive neutrophil granule contents observed in hypoxic environments and the potential mechanisms for this heightened granule exocytosis, highlighting implications for the host. Understanding the dichotomy of the beneficial and detrimental consequences of neutrophil degranulation in hypoxic environments is crucial to inform potential neutrophil-directed therapeutics in order to limit persistent, excessive, or inappropriate inflammation.

A systems approach reveals distinct metabolic strategies among the NCI-60 cancer cell lines

The metabolic phenotype of cancer cells is reflected by the metabolites they consume and by the byproducts they release. Here, we use quantitative, extracellular metabolomic data of the NCI-60 panel and a novel computational method to generate 120 condition-specific cancer cell line metabolic models. These condition-specific cancer models used distinct metabolic strategies to generate energy and cofactors. The analysis of the models' capability to deal with environmental perturbations revealed three oxotypes, differing in the range of allowable oxygen uptake rates. Interestingly, models based on metabolomic profiles of melanoma cells were distinguished from other models through their low oxygen uptake rates, which were associated with a glycolytic phenotype. A subset of the melanoma cell models required reductive carboxylation. The analysis of protein and RNA expression levels from the Human Protein Atlas showed that IDH2, which was an essential gene in the melanoma models, but not IDH1 protein, was detected in normal skin cell types and melanoma. Moreover, the von Hippel-Lindau tumor suppressor (VHL) protein, whose loss is associated with non-hypoxic HIF-stabilization, reductive carboxylation, and promotion of glycolysis, was uniformly absent in melanoma. Thus, the experimental data supported the predicted role of IDH2 and the absence of VHL protein supported the glycolytic and low oxygen phenotype predicted for melanoma. Taken together, our approach of integrating extracellular metabolomic data with metabolic modeling and the combination of different network interrogation methods allowed insights into the metabolism of cells.

Hypoxic regulation of neutrophil function and consequences for Staphylococcus aureus infection

Staphylococcal infection and neutrophilic inflammation can act in concert to establish a profoundly hypoxic environment. In this review we summarise how neutrophils and Staphylococcus aureus are adapted to function under hypoxic conditions, with a particular focus on the impaired ability of hypoxic neutrophils to effect Staphylococcus aureus killing.

Clinical development of new drug-radiotherapy combinations

In countries with the best cancer outcomes, approximately 60% of patients receive radiotherapy as part of their treatment, which is one of the most cost-effective cancer treatments. Notably, around 40% of cancer cures include the use of radiotherapy, either as a single modality or combined with other treatments. Radiotherapy can provide enormous benefit to patients with cancer. In the past decade, significant technical advances, such as image-guided radiotherapy, intensity-modulated radiotherapy, stereotactic radiotherapy, and proton therapy enable higher doses of radiotherapy to be delivered to the tumour with significantly lower doses to normal surrounding tissues. However, apart from the combination of traditional cytotoxic chemotherapy with radiotherapy, little progress has been made in identifying and defining optimal targeted therapy and radiotherapy combinations to improve the efficacy of cancer treatment. The National Cancer Research Institute Clinical and Translational Radiotherapy Research Working Group (CTRad) formed a Joint Working Group with representatives from academia, industry, patient groups and regulatory bodies to address this lack of progress and to publish recommendations for future clinical research. Herein, we highlight the Working Group's consensus recommendations to increase the number of novel drugs being successfully registered in combination with radiotherapy to improve clinical outcomes for patients with cancer.

Hypoxia upregulates neutrophil degranulation and potential for tissue injury

Background

The inflamed bronchial mucosal surface is a profoundly hypoxic environment. Neutrophilic airway inflammation and neutrophil-derived proteases have been linked to disease progression in conditions such as COPD and cystic fibrosis, but the effects of hypoxia on potentially harmful neutrophil functional responses such as degranulation are unknown.

Methods and results

Following exposure to hypoxia (0.8% oxygen, 3 kPa for 4 h), neutrophils stimulated with inflammatory agonists (granulocyte-macrophage colony stimulating factor or platelet-activating factor and formylated peptide) displayed a markedly augmented (twofold to sixfold) release of azurophilic (neutrophil elastase, myeloperoxidase), specific (lactoferrin) and gelatinase (matrix metalloproteinase-9) granule contents. Neutrophil supernatants derived under hypoxic but not normoxic conditions induced extensive airway epithelial cell detachment and death, which was prevented by coincubation with the antiprotease α-1 antitrypsin; both normoxic and hypoxic supernatants impaired ciliary function. Surprisingly, the hypoxic upregulation of neutrophil degranulation was not dependent on hypoxia-inducible factor (HIF), nor was it fully reversed by inhibition of phospholipase C signalling. Hypoxia augmented the resting and cytokine-stimulated phosphorylation of AKT, and inhibition of phosphoinositide 3-kinase (PI3K)γ (but not other PI3K isoforms) prevented the hypoxic upregulation of neutrophil elastase release.

Conclusion

Hypoxia augments neutrophil degranulation and confers enhanced potential for damage to respiratory airway epithelial cells in a HIF-independent but PI3Kγ-dependent fashion.

Hypoxia‑mediated activation of autophagic flux inhibits apoptosis of keratinocytes via blocking tumor necrosis factor‑related apoptosis‑inducing ligand

Tumor necrosis factor‑related apoptosis‑inducing ligand (TRAIL) is toxic against transformed tumor cells. Cornification is the terminal differentiation of keratinocytes and a specific form of programmed cell death caused by TRAIL that occurs in keratinocytes. Apoptosis can also be triggered when TRAIL induces expression of keratinocyte differentiation markers. The present study reported that hypoxia inhibits TRAIL‑induced apoptosis due to autophagic flux. It is well known that hypoxia activates autophagy in keratinocytes and reduces p62 protein levels. The present study demonstrated that hypoxia inhibited TRAIL‑mediated apoptosis and induced autophagic flux in HaCaT cells. In addition, autophagic flux‑inactivating reagents, including 3‑methyladenine and chloroquine, increased the TRAIL sensitivity of HaCaT cells exposed to hypoxia. In conclusion, these results indicated that inactivating autophagy increased TRAIL sensitivity in hypoxic HaCaT cells. Autophagy inhibitors may be beneficial in therapies using TRAIL against skin cancers.

Interplay between Candida albicans and the antimicrobial peptide armory

Antimicrobial peptides (AMPs) are key elements of innate immunity, which can directly kill multiple bacterial, viral, and fungal pathogens. The medically important fungus Candida albicans colonizes different host niches as part of the normal human microbiota. Proliferation of C. albicans is regulated through a complex balance of host immune defense mechanisms and fungal responses. Expression of AMPs against pathogenic fungi is differentially regulated and initiated by interactions of a variety of fungal pathogen-associated molecular patterns (PAMPs) with pattern recognition receptors (PRRs) on human cells. Inflammatory signaling and other environmental stimuli are also essential to control fungal proliferation and to prevent parasitism. To persist in the host, C. albicans has developed a three-phase AMP evasion strategy, including secretion of peptide effectors, AMP efflux pumps, and regulation of signaling pathways. These mechanisms prevent C. albicans from the antifungal activity of the major AMP classes, including cathelicidins, histatins, and defensins leading to a basal resistance. This minireview summarizes human AMP attack and C. albicans resistance mechanisms and current developments in the use of AMPs as antifungal agents.

Design of optimized hypoxia-activated prodrugs using pharmacokinetic/pharmacodynamic modeling

Hypoxia contributes to resistance of tumors to some cytotoxic drugs and to radiotherapy, but can in principle be exploited with hypoxia-activated prodrugs (HAP). HAP in clinical development fall into two broad groups. Class I HAP (like the benzotriazine N-oxides tirapazamine and SN30000), are activated under relatively mild hypoxia. In contrast, Class II HAP (such as the nitro compounds PR-104A or TH-302) are maximally activated only under extreme hypoxia, but their active metabolites (effectors) diffuse to cells at intermediate O2 and thus also eliminate moderately hypoxic cells. Here, we use a spatially resolved pharmacokinetic/pharmacodynamic (SR-PK/PD) model to compare these two strategies and to identify the features required in an optimal Class II HAP. The model uses a Green's function approach to calculate spatial and longitudinal gradients of O2, prodrug, and effector concentrations, and resulting killing in a digitized 3D tumor microregion to estimate activity as monotherapy and in combination with radiotherapy. An analogous model for a normal tissue with mild hypoxia and short intervessel distances (based on a cremaster muscle microvessel network) was used to estimate tumor selectivity of cell killing. This showed that Class II HAP offer advantages over Class I including higher tumor selectivity and greater freedom to vary prodrug diffusibility and rate of metabolic activation. The model suggests that the largest gains in class II HAP antitumor activity could be realized by optimizing effector stability and prodrug activation rates. We also use the model to show that diffusion of effector into blood vessels is unlikely to materially increase systemic exposure for realistic tumor burdens and effector clearances. However, we show that the tumor selectivity achievable by hypoxia-dependent prodrug activation alone is limited if dose-limiting normal tissues are even mildly hypoxic.

Epidermal deletion of HIF-2α stimulates wound closure

Wound closure requires a complex series of micro-environmentally influenced events. A key aspect of wound closure is the migration of keratinocytes across the open wound. It has been found previously that the response to hypoxia via the HIF-1α transcription factor is a key feature of wound closure. The need for hypoxic response is likely due to interrupted wound vasculature, as well as infection, and in this work we investigated the need for a highly related hypoxic response transcription factor, HIF-2α. This factor was deleted tissue specifically in mice, and the resulting mice were found to have an accelerated rate of wound closure. This is correlated with a reduced bacterial load and inflammatory response in these mice. This indicates that manipulating or reducing the HIF-2α response in keratinocytes could be a useful means to accelerate wound healing and tissue repair.

Stromal fibroblasts synergize with hypoxic oxidative stress to enhance melanoma aggressiveness

On the basis of recent advances indicating a key role of microenvironment for tumor progression, we investigated the role of fibroblasts, macrophages and hypoxia, for primary melanoma aggressiveness. Our data indicate a key role of hypoxia in stromal reactivity, acting on both myofibroblasts and machrophages differentiation. Hypoxic myofibroblasts are more active than macrophages in inducing melanoma invasiveness and exploit their oxidative stress due to hypoxia to secrete soluble factors favouring melanoma invasion and chemotaxis. We underscore the key role of microenviroment on melanoma malignancy, highlighting reactive fibroblasts, intratumoral hypoxia and oxidative stress as promising targets for melanoma antimetastatic strategies.

Metronidazole radical anion formation studied by means of electrochemical impedance spectroscopy

Radiosensitizers belong to the most important class of the cancerostatic drugs. The electrochemical transfer of the first electron to the cytotoxic radiosensitizer Metronidazole (MET) and MET radical anion formation in aprotic medium was studied by means of electrochemical impedance spectroscopy. The heterogeneous electron transfer rate constant for the first reduction of MET (radical anion production) k0 for the redox couple was determined. Similarly, the diffusion coefficient of MET in dimethylformamide was also calculated by impedance measurements using expression for Warburg coefficient and Warburg plot. Moreover, the equivalent circuit for the redox couple MET/MET•– was proposed and its parameters were evaluated using a non-linear least square fitting. Our results, from the electrochemical point of view, also confirm the suitability of MET for the effective treatment of selected types of the cancer.

Loss of epidermal hypoxia-inducible factor-1α accelerates epidermal aging and affects re-epithelialization in human and mouse

In mouse and human skin, HIF-1α is constitutively expressed in the epidermis, mainly in the basal layer. HIF-1α has been shown to have crucial systemic functions: regulation of kidney erythropoietin production in mice with constitutive HIF-1α epidermal deletion, and hypervascularity following epidermal HIF-1α overexpression. However, its local role in keratinocyte physiology has not been clearly defined. To address the function of HIF-1α in the epidermis, we used the mouse model of HIF-1α knockout targeted to keratinocytes (K14-Cre/Hif1a(flox/flox)). These mice had a delayed skin phenotype characterized by skin atrophy and pruritic inflammation, partly mediated by basement membrane disturbances involving laminin-332 (Ln-332) and integrins. We also investigated the relevance of results of studies in mice to human skin using reconstructed epidermis and showed that HIF-1α knockdown in human keratinocytes impairs the formation of a viable reconstructed epidermis. A diminution of keratinocyte growth potential, following HIF-1α silencing, was associated with a decreased expression of Ln-322 and α6 integrin and β1 integrin. Overall, these results indicate a role of HIF-1α in skin homeostasis especially during epidermal aging.

HIF-1α in epidermis: oxygen sensing, cutaneous angiogenesis, cancer, and non-cancer disorders

Besides lung, postnatal human epidermis is the only epithelium in direct contact with atmospheric oxygen. Skin epidermal oxygenation occurs mostly through atmospheric oxygen rather than tissue vasculature, resulting in a mildly hypoxic microenvironment that favors increased expression of hypoxia-inducible factor-1α (HIF-1α). Considering the wide spectrum of biological processes, such as angiogenesis, inflammation, bioenergetics, proliferation, motility, and apoptosis, that are regulated by this transcription factor, its high expression level in the epidermis might be important to HIF-1α in skin physiology and pathophysiology. Here, we review the role of HIF-1α in cutaneous angiogenesis, skin tumorigenesis, and several skin disorders.

Impedance study of hypoxic cells radiosensitizer etanidazole radical anion in water

Electrochemical transfer of the first electron to cytotoxic radiosensitizer etanidazole (ETN) and ETN radical anion formation in the alkaline buffered aqueous solution were studied by means of electrochemical impedance spectroscopy (EIS). The heterogeneous electron transfer rate constant for the first reduction of ETN (radical anion production), k0, was calculated. The value of k0 from EIS measurements and the previously obtained value of so-called E71 potential indicate that ETN, compared with other possible chemical radiosensitizers, requires lower energy to accept the first electron during the metabolic pathway. However, the necessity of the alkaline pH may decrease the ability of ETN to act as hypoxic radiosensitizer in the human body.

Expression and function of hypoxia inducible factor-1 alpha in human melanoma under non-hypoxic conditions

Background

Hypoxia inducible factor-1 alpha (HIF-1α) protein is rapidly degraded under normoxic conditions. When oxygen tensions fall HIF-1α protein stabilizes and transactivates genes involved in adaptation to hypoxic conditions. We have examined the normoxic expression of HIF-1α RNA and protein in normal human melanocytes and a series of human melanoma cell lines isolated from radial growth phase (RGP), vertical growth phase (VGP) and metastatic (MET) melanomas.

Results

HIF-1α mRNA and protein was increased in RGP vs melanocytes, VGP vs RGP and MET vs VGP melanoma cell lines. We also detected expression of a HIF-1α mRNA splice variant that lacks part of the oxygen-dependent regulation domain in WM1366 and WM9 melanoma cells. Over-expression of HIF-1α and its splice variant in the RGP cell line SbCl2 resulted in a small increase in soft agar colony formation and a large increase in matrigel invasion relative to control transfected cells. Knockdown of HIF-1α expression by siRNA in the MET WM9 melanoma cell line resulted in a large decrease in both soft agar colony formation and matrigel invasion relative to cells treated with non-specific siRNA. There is a high level of ERK1/2 phosphorylation in WM9 cells, indicating an activated Ras-Raf-MEK-ERK1/2 MAPK pathway. Treatment of WM9 cells with 30 μM U0126 MEK inhibitor, decreased ERK1/2 phosphorylation and resulted in a decrease in HIF-1α expression. However, a 24 h treatment with 10 μM U0126 totally eliminated Erk1/2 phosphorylation, but did not change HIF-1alpha levels. Furthermore, siRNA knockdown of MEK siRNA did not change HIF-1alpha levels.

Conclusion

We speculate that metabolic products of U0126 decrease HIF-1alpha expression through "off target" effects. Overall our data suggest that increased HIF-1α expression under normoxic conditions contributes to some of the malignant phenotypes exhibited by human melanoma cells. The expanded role of HIF-1α in melanoma biology increases its importance as a therapeutic target.

Oxygen deprivation inhibits basal keratinocyte proliferation in a model of human skin and induces regio-specific changes in the distribution of epidermal adherens junction proteins, aquaporin-3, and glycogen

It is generally accepted that hypoxia and recovery from oxygen deprivation contribute to the breakdown and ulceration of human skin. The effects of these stresses on proliferation, differentiation and expression of cell-cell adhesion molecules were investigated for the first time in an organotypic model of human skin. Fully stratified tissues were exposed to a time course of oxygen deprivation and subsequent reoxygenation. Regional changes in keratinocyte morphology, glycogen stores and cellular junctions were observed, with more differentiated layers of the epidermis exhibiting the first evidence of oxygen deprivation. Cellular swelling within the granular layer was concurrent with aquaporin-3 depletion. The keratinocyte adherens junction proteins E-cadherin and beta-catenin were dramatically decreased in a regio-specific manner throughout the epidermis following oxygen deprivation. In contrast, P-cadherin and the desmosomal proteins desmoplakin and desmoglein-1 were refractory to oxygen deprivation. Relative to normoxic controls, hypoxic tissues exhibited increased mRNA levels of the transcriptional repressor Slug; however, mRNA levels of the related transcriptional factor Snail were unaffected. All cellular and molecular changes were reversible upon reoxygenation. These results show that oxygen deprivation and reoxygenation exert differential effects on epidermal adhesion proteins and suggest a novel role for cadherins, beta-catenin, and Slug in hypoxia-induced junctional changes occurring in stratified squamous epithelium.

Hypoxia, melanocytes and melanoma - survival and tumor development in the permissive microenvironment of the skin

The tissue microenvironment plays a critical role in cell survival and growth and can contribute to cell transformation and tumor development. Cellular interactions with the stroma and with other cells provide key signals that control cellular arrest or division, survival or death, and entrance or exit from a quiescent state. Together, these decisions are essential for maintenance of tissue homeostasis. Tissue oxygenation is an important component of the microenvironment that can acutely alter the behavior of a cell through the direct regulation of genes involved in cell survival, apoptosis, glucose metabolism, and angiogenesis. Loss of tissue homeostasis due to, for example, oncogene activation leads to the disruption of these signals and eventually can lead to cell transformation and tumor development. Here we review the role of tissue oxygenation, and in particular physiologic skin hypoxia, on cell survival and senescence and how it contributes to melanocyte transformation and melanoma development.

Critical role of HIF-1alpha in keratinocyte defense against bacterial infection

Skin, the first barrier against invading microorganisms, is hypoxic, even under baseline conditions. The transcription factor hypoxia-inducible factor-1alpha (HIF-1alpha, the principal regulator of cellular adaptation to low oxygen, is strongly expressed in skin epithelium. HIF-1alpha is now understood to play a key role in the bactericidal capacity of phagocytic cells such as macrophages and neutrophils. In the skin, keratinocytes provide a direct antibacterial activity through production of antimicrobial peptides, including cathelicidin. Here, we generate mice with a keratinocyte-specific deletion of HIF-1alpha and examine effects on intrinsic skin immunity. Keratinocyte HIF-1alpha is seen to provide protection against necrotic skin lesions produced by the pathogen group A Streptococcus. RNA interference studies reveal that HIF-1alpha regulation of keratinocyte cathelicidin production is critical to their antibacterial function.

Understanding signaling cascades in melanoma

Understanding regulatory pathways involved in melanoma development and progression has advanced significantly in recent years. It is now appreciated that melanoma is the result of complex changes in multiple signaling pathways that affect growth control, metabolism, motility and the ability to escape cell death programs. Here we review the major signaling pathways currently known to be deregulated in melanoma with an implication to its development and progression. Among these pathways are Ras, B-Raf, MEK, PTEN, phosphatidylinositol-3 kinase (PI3Ks) and Akt which are constitutively activated in a significant number of melanoma tumors, in most cases due to genomic change. Other pathways discussed in this review include the [Janus kinase/signal transducer and activator of transcription (JAK/STAT), transforming growth factor-beta pathways which are also activated in melanoma, although the underlying mechanism is not yet clear. As a paradigm for remodeled signaling pathways, melanoma also offers a unique opportunity for targeted drug development.

Microenvironmental influences in melanoma progression

An often overlooked facet of tumor biology research is the involvement of the surrounding tumor microenvironment. Increasing evidence is being presented to support a major role for stromal components in all stages of tumorigenesis including initiation, progression, and metastasis. Melanoma serves as a model for studying cellular and stromal interactions within the tumor microenvironment due to the array of cell types localized to these lesions. Here, we discuss the both the molecular mechanisms, as well as the extracellular and contextual input that contribute to melanoma progression. Special emphasis is given to the assorted cell types and their interactions with the extracellular matrix and adjacent cells. Melanoma progression also initiates development of intralesional hypoxic regions; the relative significance of hypoxia in disease is also addressed. Lastly, a number of laboratories are currently developing innovative strategies to study melanoma within a microenvironmental platform. These promising model systems and their potential for closing current gaps in knowledge of disease are reviewed. The development of such models holds translational value that cannot be achieved with most current systems.

Chemical radiosensitizers for use in radiotherapy

Radiosensitizers are intended to enhance tumour cell killing while having much less effect on normal tissues. Some drugs target different physiological characteristics of the tumour, particularly hypoxia associated with radioresistance. Oxygen is the definitive hypoxic cell radiosensitizer, the large differential radiosensitivity of oxic vs hypoxic cells being an attractive factor. The combination of nicotinamide to reduce acute hypoxia with normobaric carbogen breathing is showing clinical promise. 'Electron-affinic' chemicals that react with DNA free radicals have the potential for universal activity to combat hypoxia-associated radioresistance; a nitroimidazole, nimorazole, is clinically effective at tolerable doses. Hypoxia-specific cytotoxins, such as tirapazamine, are valuable adjuncts to radiotherapy. Nitric oxide is a potent hypoxic cell radiosensitizer; variations in endogenous levels might have prognostic significance, and routes to deliver nitric oxide specifically to tumours are being developed. In principle, many drugs can be delivered selectively to hypoxic tumours using either reductase enzymes or radiation-produced free radicals to activate drug release from electron-affinic prodrugs. A redox-active agent based on a gadolinium chelate is being evaluated clinically. Pyrimidines substituted with bromine or iodine are incorporated into DNA and enhance free radical damage; fluoropyrimidines act by different mechanisms. A wide variety of drugs that influence the nature or repair of DNA damage are being evaluated in conjunction with radiation; it is often difficult to define the mechanisms underlying chemoradiation regimens. Drugs being evaluated include topoisomerase inhibitors (e.g. camptothecin, topotecan), and the hypoxia-activated anthraquinone AQ4N; alkylating agents include temozolomide. Drugs involved in DNA repair pathways being investigated include the potent poly(ADP ribose)polymerase inhibitor, AG14,361. Proteins involved in cell signalling, such as the Ras family, are attractive targets linked to radioresistance, as are epidermal growth factor receptors and linked kinases (drugs including vandetanib [ZD6,474], cetuximab and gefitinib), and cyclooxygenase-2 (celecoxib). The suppression of radioprotective thiols seems to offer more potential with alkylating agents than with radiotherapy, although it remains a strategy worthy of exploration.

HIF1alpha delays premature senescence through the activation of MIF

Premature senescence in vitro has been attributed to oxidative stress leading to a DNA damage response. In the absence of oxidative damage that occurs at atmospheric oxygen levels, proliferation of untransformed cells continues for extended periods of time. We have investigated the role of the hypoxia-inducible factor 1alpha (HIF1alpha) transcription factor in preventing senescence in aerobic and hypoxic conditions. Using embryonic fibroblasts from a conditional HIF1alpha knockout mouse, we found that loss of HIF1alpha under aerobic conditions significantly accelerated the onset of cellular senescence, and decreased proliferation under hypoxia. Furthermore, we identify the macrophage migration inhibitory factor (MIF) as a crucial effector of HIF1alpha that delays senescence. Inhibition of MIF phenocopies loss of HIF1alpha. Our findings highlight a novel role for HIF1alpha under aerobic conditions, and identify MIF as a target responsible for this function.

Oxygen levels in normal and previously irradiated human skin as assessed by EF5 binding

The oxygen status of skin is a controversial topic. Skin is radiosensitive, suggesting it is well-oxygenated. However, it can be further sensitized with nitroimidazole drugs, implying that it is partially hypoxic. Skin oxygen levels are difficult to measure with either electrodes or the hypoxia-monitoring agent (3)H-misonidazole. For the latter, binding has previously been reported to be high in murine skin, but this could be attributed to either non-oxygen-dependent variations in nitroreductase activity, drug metabolism, and/or actual oxygen gradients. We obtained tumor and skin from patients given EF5, a 2-nitroimidazole tissue hypoxia monitor. We performed immunohistochemical studies using highly specific monoclonal antibodies for the hypoxia-dependent production of EF5 tissue adducts. Some tissue sections were counterstained using either Ki67 for proliferation or CD31 for vessels. We found that the human dermis is well-oxygenated, the epidermis is modestly hypoxic and portions of some sebaceous glands and hair follicles are moderately to severely hypoxic. Normal and irradiated skin had similar oxygenation patterns. Control studies demonstrated that these observations are not due to tissue variations in nitroreductase activity. The importance of the highly heterogeneous distribution of oxygen in skin requires further study, but recent investigations suggest that skin hypoxia may have important clinical ramifications including mediating cellular transformation.

The hypoxic microenvironment of the skin contributes to Akt-mediated melanocyte transformation

Constitutive activation of Akt characterizes a high percentage of human melanomas and represents a poor prognostic factor of the disease. We show that Akt transforms melanocytes only in a hypoxic environment, which is found in normal skin. The synergy between Akt and hypoxia is HIF1alpha mediated. Inhibition of HIF1alpha decreases Akt transformation capacity in hypoxia and tumor growth in vivo, while overexpression of HIF1alpha allows anchorage-independent growth in normoxia and development of more aggressive tumors. Finally, we show that mTOR activity is necessary to maintain the transformed phenotype by sustaining HIF1alpha activity. Taken together, these findings demonstrate that Akt hyperactivation and HIF1alpha induction by normally occurring hypoxia in the skin significantly contribute to melanoma development.

Radiobiological rationale and patient selection for high-LET radiation in cancer therapy

The rationale for introducing ion beams in cancer therapy is the high level of physical selectivity that can be achieved with ions, equal or even better than with proton beams or modern photon techniques, as well as the potential advantage of high-LET radiations for some tumour types and sites. The radiobiological arguments for high-LET radiation in cancer therapy are reviewed: reduction of OER in the case of hypoxic and poorly-reoxygenating tumours, and the lesser importance of repair phenomena which are a problem in controlling repair-proficient photon-resistant tumours. Fast neutrons were the first type of high-LET radiation used clinically, and were often applied under suboptimal technical conditions. Nevertheless, useful clinical information was derived from the neutron experience. A greater benefit from neutrons than from conventional radiotherapy was found for several tumour sites. The present discussion is limited to the results for salivary gland tumours and prostatic adenocarcinoma. Based on the fast neutron experience, radiobiological arguments, and the added benefit of excellent physical selectivity of ion beams, the potential clinical indications for high-LET ions are discussed: hypoxic, slowly growing and well-differentiated photon-resistant tumours. One of the main remaining issues is the selection of individual patients for high- or low-LET radiation. Since the physical selectivity of ions now matches that obtained with other techniques, the selection of patients will be based only on the radiobiological characteristics of the tumour.

Radiosensitisation in normal tissues with oxygen, carbogen or nicotinamide: therapeutic gain comparisons for fractionated x-ray schedules

METHODS

Radiosensitisation with oxygen, carbogen or nicotinamide alone and oxygen or carbogen combined with nicotinamide was compared in early and late responding normal tissues in rodents. X-ray treatments were delivered as single doses or fractionated schedules of 2 fractions in 1 day, 2, 12 and 36 fractions in an overall time of 12 days and 10 fractions in 5 or 12 days. Acute skin reactions, survival of intestinal crypts, breathing rate, reduction in the packed red-cell volume and clearance of 51Cr-EDTA were used as assays of epidermal, gut, lung and renal damage.

RESULTS

Relative to air-breathing mice, carbogen or oxygen produced a small, and not always significant, increase in sensitivity (enhancement ratios < or = 1.15) in gut, lung and kidneys; however, in skin a dose enhancement of 1.2-1.3 was observed. The effect of nicotinamide in air, carbogen or oxygen was studied only in lung and gut. The drug produced variable but generally significant increases in radiosensitisation ( < or = 1.26) in all three gases. Relative to treatments in air, enhancement ratios for nicotinamide alone were usually slightly higher than those observed when either carbogen or oxygen were administered without the drug. With all three modifiers (i.e. oxygen, carbogen, nicotinamide alone or for the drug-gas combinations) there was no significant change in the enhancement ratios observed as the number of radiation dose fractions was varied.

CONCLUSIONS

Comparisons with fractionated X-ray studies done previously in rodent tumours indicate that a therapeutic benefit, relative to lung, gut and renal damage, would be observed with oxygen or carbogen alone but not with nicotinamide alone. The greatest gain would be achieved with the combination of carbogen and nicotinamide, with which a benefit was observed even relative to epidermal damage. These results indicate that some decrease in normal tissue tolerance could be observed when using these modifiers in clinical radiotherapy and, although small, the appropriate dose reductions should be considered; caution should be exercised especially when carbogen and nicotinamide are used in conjunction with the more radical accelerated schedules.

Radiosensitization of mouse skin by oxygen and depletion of glutathione

PURPOSE

To determine the oxygen enhancement ratio (OER) and shape of the oxygen sensitization curve of mouse foot skin, the extent to which glutathione (GSH) depletion radiosensitized skin, and the dependence of such sensitization on the ambient oxygen tension.

METHODS AND MATERIALS

The feet of WHT mice were irradiated with single doses of 240 kVp x-rays while mice were exposed to carbogen or gases with oxygen/nitrogen mixtures containing 8-100% O2. The anoxic response was obtained by occluding the blood supply to the leg of anesthetized mice with a tourniquet, surrounding the foot with nitrogen, and allowing the mice to breathe 10% O2. Further experiments were performed to assess the efficacy of this method to obtain an anoxic response. Radiosensitivity of skin was assessed using the acute skin-reaction assay. Glutathione levels were modified using two schedules of DL-buthionine sulphoximine (BSO) and diethylmaleate (DEM), which were considered to produce extensive and intermediate levels of GSH depletion in the skin of the foot during irradiation.

RESULTS

Carbogen caused the greatest radiosensitization of skin, with a reproducible enhancement of 2.2 relative to the anoxic response. The OER of 2.2 is lower than other reports for mouse skin. This may indicate that the extremes of oxygenation were not produced, although there was no direct evidence for this. When skin radiosensitivity was plotted against the logarithm of the oxygen tension in the ambient gas, a sigmoid curve with a K value of 17-21% O2 in the ambient gas was obtained. Depletion of GSH caused minimal radiosensitization when skin was irradiated under anoxic or well-oxygenated conditions. Radiosensitization by GSH depletion was maximal at intermediate oxygen tensions of 10-21% O2 in the ambient gas. Increasing the extent of GSH depletion led to increasing radiosensitization, with sensitization enhancement ratios of 1.2 and 1.1, respectively, for extensive and intermediate levels of GSH depletion. In mice exposed to 100% O2, a significant component of skin radiosensitivity was due to diffusion of oxygen directly through the skin. Pentobarbitone anesthesia radiosensitized skin in mice exposed to 100% O2 by a factor of 1.2, but did not further sensitize skin in mice exposed to carbogen.

CONCLUSIONS

Glutathione levels and the local oxygen tension at the time of irradiation were important determinants of mouse foot skin radiosensitivity. The extent to which GSH levels altered the radiosensitivity of skin was critically dependent on the local oxygen tension. These results have significant implications for potential clinical application of GSH depletion.

Clinical pharmacokinetic study and sensitive effect of AK-2123

PURPOSE

The pharmacokinetic parameters of a radiosensitizer, AK-2123 given to 10 lung cancer patients are represented and its sensitizing effect is evaluated.

METHODS AND MATERIALS

Ten patients with lung cancer: eight males, two females. The diagnosis was confirmed radiologically and pathologically. Seven patients were diagnosed with squamous cell cancer, two had adenocarcinoma, and one had nonsquamous cell lung cancer. AK-2123 was administered orally twice a week. The total dose per patient was 12.8-15.75 g. Radiotherapy was delivered 3 h after AK-2123 administration, 2 Gy per fraction. Blood samples were taken from the ear at 1, 3, 6, 9, 12, and 24 h after AK-2123 administration. The concentration of AK-2123 in plasma was measured by HPLC.

RESULTS AND CONCLUSIONS

The Cm (maximum concentration of AK-2123 averaging from 10 patients) was 27.75 micrograms/mL, ranging 22.62-39.97 micrograms/mL, Tm (the time of getting Cm) 3 h. The data of the drug fitted a two-compartment open model. The mean parameteds of these cases were: rate constant K12 0.1658, K21 0.0671, Ke 0.0254, h-1; apparent volumes of distribution V1 18.6154, V2 51.2317, L; biological half life T1(2)a 1.0863, T1(2) alpha 2.7546, T1(2) beta 35.2064 h. The response to the treatment: CR four cases, PR four cases, NC two cases. So, AK-2123 may be a promising radiosensitizer.

Pharmacokinetics of varying doses of nicotinamide and tumour radiosensitisation with carbogen and nicotinamide: clinical considerations

Plasma concentrations, after administration of varying doses of nicotinamide, were measured in CBA male mice using a newly-developed high performance liquid chromatography assay. In all dose groups, peak levels were observed within the first 15 min after an i.p. administration of 0.1, 0.2, 0.3 or 0.5 mg g-1 of nicotinamide. There was a clear dose-dependent increase in plasma concentration with increasing dose, with almost a five-fold lower concentration (1.0 vs 4.9 mumol ml-1) achieved with a dose of 0.1 mg g-1 compared with 0.5 mg g-1, respectively. The half-life of nicotinamide increased from 1.4 h to 2.2 h over the dose range (P < 0.01). Comparisons with previous pharmacokinetic data in humans show that clinically-relevant oral doses of 6 and 9 g in humans give plasma levels slightly higher than those achieved at 1 h with doses of 0.1 to 0.2 mg g-1 in mice. Tumour radiosensitisation with carbogen alone, and with carbogen combined with varying doses of nicotinamide (0.05 to 0.5 mg g-1), was investigated using a 10-fraction in 5 days X-ray schedule. Relative to air-breathing mice, a statistically significant increase in sensitisation was observed with both a local tumour control and with an in vivo/in vitro excision assay (P < or = 0.007). With the local control assay, a trend was observed towards lower enhancement ratios (ERs) with decreasing nicotinamide dose (from 1.85 to 1.55); carbogen alone was almost as effective as when combined with 0.1 mg g-1 of nicotinamide. With the excision assay, ERs for carbogen combined with nicotinamide increased with decreased levels of cell survival. At a surviving fraction of 0.02, enhancement ratios of 1.39-1.48 were obtained for carbogen plus 0.1 to 0.3 mg g-1 of nicotinamide. These were lower than those seen with the two higher doses of 0.4 to 0.5 mg g-1 (ERs = 1.63-1.69).

Modification of radioresponse of sublethally irradiated mouse jejunum by misonidazole

The radiation-induced changes in a critically radiosensitive tissue, jejunum of BALB/c mice and their modification by a hypoxic cell sensitizer, misonidazole (MISO), were studied. Adult mice were exposed to 1.5, 3.0 and 5.0 Gy of 60Co gamma radiation 30 min after MISO injection and quantitative studies in jejunal cross sections were carried out at different post-treatment times from 3 h to 28 d. Radiation-induced damage to the jejunal mucosa was dose-dependent and reached a maximum on day 1 post-treatment in all the groups. MISO pretreated animals did not exhibit any change in the crypt survival or crypt and villous cellularity compared to the radiation alone group. However, there was a significant suppression of mitotic activity by MISO at early intervals after irradiation. This reduction in mitosis in the drug pretreated animals appeared to affect the rate of recovery from radiation damage, which was slower and prolonged compared with that in the radiation alone group.

Interaction of misonidazole, hyperthermia, and irradiation in a C3H mammary carcinoma and its surrounding skin in vivo

The interaction of irradiation, Misonidazole (MISO), and hyperthermia was studied in a C3H mouse mammary carcinoma and its surrounding skin in vivo. MISO (0.5-1.0 mg/g) was injected 30 min before irradiation. Hyperthermia (41.5 degrees-43.5 degrees C for 60 min) was given either simultaneously, 0.5 hr, or 4 hr after X rays. The results were evaluated as the radiation dose to achieve tumor control (TCD50) or moist desquamation of the skin (DD50) in half of the treated animals. A therapeutic gain was found when the enhancement in tumors were greater than that found in skin. The combination of simultaneous heat and irradiation caused great enhancement in radiation response, but with no therapeutic gain. A slightly lower enhancement of the damage in both tissues was found with a 30 min interval between irradiation and hyperthermia, whereas heat 4 hr after X rays gave a small, but significant therapeutic gain. MISO significantly enhanced the response in tumors but not in skin. Combined trimodality treatment with MISO, irradiation, and hyperthermia resulted in enhancement ratios up to 15, dependent on temperature, radiation-heat interval, and to a lesser extent the MISO dose. The enhancement was for all schedules most pronounced in the tumors, resulting in an improved therapeutic effect. The combination of MISO and hyperthermia may be a valuable addition to radiotherapy, especially if heat and irradiation can be applied with close interval and with one of the modalities given selectively to the tumor.

Response of the mouse mediastinum to single and fractionated X-rays

The acute oesophageal response, after localized mediastinal irradiation in unanaesthetized mice, was assessed with a sequential, non-invasive and clinically orientated assay. Changes in body weight, after single and fractionated X-ray doses (8 fractions in 8 or 15 days and 4 fractions in 4 or 13 days), were recorded and the nadir of weight loss for each regime was used as the end-point. In our studies, quantal and non-quantal analyses of the weight loss data gave good dose-response relationships. The shapes of the dose-effect curves for single doses, 4F/4 days and 8F/8 days showed a remarkable degree of radioresistance, which became less apparent when the overall time was increased to 13 and 15 days for 4 and 8 fractions, respectively. The alpha/beta values (7-17 Gy) are within the range found for other acutely responding normal tissues. Histopathological changes were also assessed and the structural changes observed in the oesophageal epithelium, after a single dose of 34 Gy or after 46 Gy given as 3F/6 days, correlated with the gross changes observed in body weight.

Radioprotection of normal tissues of the mouse by hypoxic breathing

Hypoxic breathing during irradiation has been advocated as a therapeutic modality, to increase the efficacy of radiotherapy. In this form of treatment, the total and daily X-ray dose is increased by a factor of 1.25, on the assumption that all normal tissues in the beam will be protected to a similar extent by breathing gas containing a reduced oxygen concentration (usually 10%). To test this concept, we have determined the effect of varying the inspired oxygen tension on the radiosensitivity of 3 normal tissues in the mouse (kidney, jejunum and skin), and have compared these results with data from the literature for mouse lung. Reduction of the inspired oxygen tension from 21% (air) to 7-8% led to much greater radioprotection of skin (protection factor 1.37) than of lung (1.09). Protection factors for jejunum and kidney were 1.16 and 1.36 respectively. The results show that the extent of radioprotection afforded by hypoxic breathing is tissue dependent, and that great care must be taken clinically in choosing the increased radiation dose to be used in conjunction with hypoxic breathing.

The effect of mixed fractionation with X rays and neutrons on tumour growth delay and skin reactions in mice

We have compared the effects of mixed fractionation schedules with X rays and neutrons on growth delay of a murine tumour and skin reactions in mice. The schedules were five daily fractions of X rays, neutrons or mixtures (NNXXX, XXXNN or NXXXN). For clamped tumours or skin all three mixed schedules had the same effect. In contrast, for unclamped tumours giving the neutrons first (NNXXX) was more effective than the other two mixed schedules. This represented a true therapeutic gain and implies that if neutrons are used clinically as only part of a course of fractionated radiotherapy, they should be given at the beginning rather than at the end of treatment.

Single-dose relative biological effectiveness and toxicity studies under conditions of hypothermia and hyperbaric oxygen

An approach to using hyperbaric oxygen with radiation in a clinical situation has been described in the preceding paper in this issue. To ascertain whether there might be a change in the relative biological effectiveness of radiation on normal mammalian tissue treated under conditions of hypothermia and hyperbaric oxygen, the acute reaction to radiation of pig skin was studied. A single dose enhancement ratio at the erythema reaction level of 1.4 +/- 0.08 was obtained when compared with irradiation at normal body temperature in air. We studied also a series of antioxidant enzymes in rat liver and lung after exposure to hypothermia and hyperbaric oxygen. Enzyme changes were such as to combat oxygen toxicity which might develop as a result of the pre-treatment.

Reactions of tumors and normal tissues in mice to irradiation in the presence and absence of a perfluorochemical emulsion

The effect of pre-treatment with the perfluorochemical emulsion, Fluosol-DA, on the radiation response of normal tissues and EMT6 mammary tumors in BALB/c mice was examined. Pre-treating tumor-bearing mice with .015 ml/g of Fluosol and 30 min of carbogen (95% O2/5% CO2) increased the number of tumor cells killed by irradiation with doses of 2.5-20 Gy; the change in the radiation dose-response curve was consistent with a reduction in the hypoxic fraction. Fluosol did not alter the response of tumors in air-breathing or N2-asphyxiated mice and carbogen alone did not alter the radiation response of this tumor significantly. Carbogen treatments 5-60 min in duration produced similar enhancements of tumor radiosensitivity in Fluosol-treated animals. Pre-treatment with Fluosol plus carbogen also increased the number of tumor cells killed by a fractionated regimen of four 2.5 Gy fractions given over 2 days. Pre-treatment with Fluosol-DA plus carbogen, therefore, increased the antineoplastic effects of radiotherapy in both single-dose and multi-fraction radiation regimens. In contrast, Fluosol did not increase the effect of radiation on the partially committed (CFU-GM) or pluripotent (CFU-S) stem cells of the bone marrow or on the CFU-GM of the spleen. The radiation response of the skin was only slightly enhanced by pre-treatment with Fluosol plus carbogen. These data show that treatment of mice with perfluorochemical emulsions plus carbogen can produce therapeutic gain by improving the radiation response of solid tumors, without producing an equivalent increase in the radiation response of potentially dose-limiting normal tissues. These findings encourage further evaluations of these agents as adjuncts to clinical radiotherapy.

An investigation of changes in relative biological effectiveness (RBE) with depth for X ray beams generated between 100 and 250 kVp using the mouse foot as biological test system

For the early mouse foot skin reactions an increase in RBE relative to 60Co has been found for the irradiations with X ray beams generated between 100 and 250 kVp at both the surface and depth, respectively. In most cases, the RBE of the late skin reactions for irradiations at the surface and at depth are significantly lower than those for the early reactions. The clinical implications of these results, the effect of a possible hypoxic fraction of cells in the skin, and the choice of a "standard" radiation modality for radiobiological experiments are discussed.

Reaction of the vascular system in the trachea of the rabbit exposed to fractionated irradiation with and without the addition of misonidazole

As the radiation field used in the radiation therapy of malignancies in the thoracic cavity often exposes the trachea to ionizing irradiation, it is important to ascertain the effects of radiation on this tissue either as a single therapy or in combination with radiosensitizers. In the study reported here the vascular area in the subepithelial layer of the trachea has been calculated in 160 rabbits treated in four ways: (1) 10 rabbits received no treatment and served as controls; (2) 50 rabbits were given 100 mg misonidazole daily on consecutive days, with the individual total dose ranging from 100 to 1000 mg; (3) 50 rabbits were treated with misonidazole in the same way, but were also exposed to radiation (2 Gy/F) at 15-30 min later; (4) 50 rabbits received only fractionated radiation (2 Gy/F). The total radiation dose in the irradiated animals ranged from 2 to 20 Gy. In the treated groups, an oedema was observed in both the ciliary cell layer and in the subepithelial area. In the group given only irradiation, this oedema was dose-dependent, but no such dose-dependency was observed in the two groups treated with misonidazole. The vascular area in the groups treated with misonidazole was significantly increased as compared with the group given only irradiation and the control group; this was valid both with and without correction for the oedema. There was a significant correlation between the oedema and the vascular area in the groups treated with misonidazole, which was not found in the group irradiated without the drug.

Scanning electron microscopy and transmission electron microscopy of the ciliated cells of the trachea of the rabbit treated with misonidazole alone and in combination with ionizing radiation

The trachea is often located in the treatment volume when irradiating malignant tumours in the thorax. In order to evaluate possible synergism between misonidazole and irradiation on this tissue, the following studies were made. Fifty rabbits were treated with daily injections of 100 mg misonidazole given i.p. on consecutive days from 1 to 10 days. Morphological investigations of the trachea were made with scanning electron microscopy (SEM), transmission electron microscopy (TEM) and light microscopy (LM). Physiological examinations were performed with recording of the ciliary beat frequency. The results were compared with those from a group of 100 rabbits given misonidazole in a similar manner and exposed to irradiation (2 Gy) 15-30 min after each injection. Ten rabbits were used as controls. The results are compared to the effect of fractionated irradiation alone with 2 Gy/day. Fractionated irradiation of the ciliary epithelium in the trachea of the rabbit has shown dose-dependent physiological and morphological effects. Misonidazole potentiates these effects of radiation with a more pronounced change of the ciliary beat frequency and an increased metabolic activity as could be visualized on TEM. The combination of drug and irradiation also induced a hyperplasia of the ciliary epithelium. Misonidazole itself had no effect on the ciliary beat frequency, but caused a hypoplasia of the ciliary epithelium.

Enhancement of misonidazole radiosensitization by buthionine sulphoximine

The influence of glutathione (GSH) depletion on the radiation response and on the radiosensitizing efficiency of misonidazole (miso) has been studied in two types of mouse tumour and in mouse skin. Buthionine sulphoximine (BSO) has been administered in a variety of regimes, leading to a maximal depletion of GSH to 37% of control values in one tumour (CA MT) and 61% in the other (SA FA). Pretreatment with BSO did not alter the radiosensitivity of either tumour when treated with X-rays. It had a slight effect on the sensitizing efficiency of miso, corresponding to a factor less than three, which was detectable only at the highest X-ray doses used. No enhancement of miso efficiency was seen with 5 daily fractions. Prolonged administration of BSO resulted in a slight radiosensitization of mouse skin. When combined with miso the effect was very small and was only detectable at high X-ray doses. BSO however produced a marked enhancement of the acute toxicity of miso, as judged by lethality after large single doses.