New criteria for efficient Raman and Brillouin amplification of laser beams in plasma

Raman or Brillouin amplification of a laser beam in plasma has long been seen as a way to reach multi-PW powers in compact laser systems. However, no significant plasma-based Raman amplification of a laser pulse beyond 0.1 TW has been achieved in nearly 20 years, and only one report of Brillouin amplification beyond 1 TW. In this paper, we reveal novel non-linear criteria for the initial seed pulse that will finally open the door to efficient Raman and Brillouin amplification to petawatt powers and Joule-level energies. We show that the triple product of the coupling constant [Formula: see text], seed pulse duration [Formula: see text] and seed pulse amplitude a for the Raman seed pulse (or [Formula: see text] for Brillouin) must exceed a specific minimum threshold for efficient amplification. We also analyze the plasma-based Raman and Brillouin amplification experiments to date, and show that the seed pulses used in nearly all experiments are well below our new threshold, which explains the poor efficiency obtained in them. Finally, we analyze a recent Brillouin amplification experiment that used increased seed pulse power to obtain Joule-level amplification, and find excellent agreement with our theory.

Metabolic targeting of HIF-dependent glycolysis reduces lactate, increases oxygen consumption and enhances response to high-dose single-fraction radiotherapy in hypoxic solid tumors

Background

A high rate of glycolysis leading to elevated lactate content has been linked to poor clinical outcomes in patients with head and neck and cervical cancer treated with radiotherapy. Although the biological explanation for this relationship between lactate and treatment response remains unclear, there is a continued interest in evaluating strategies of targeting metabolism to enhance the effectiveness of radiotherapy. The goal of this study was to investigate the effect of metabolic-targeting through HIF-1α inhibition and the associated changes in glycolysis, oxygen consumption and response on the efficacy of high-dose single-fraction radiotherapy (HD-SFRT).

Methods

HIF-1α wild-type and HIF-1α knockdown FaDu and ME180 xenograft tumors were grown in the hind leg of mice that were placed in an environmental chamber and exposed to different oxygen conditions (air-breathing and hypoxia). Ex vivo bioluminescence microscopy was used to measure lactate and ATP levels and the hypoxic fraction was measured using EF5 immunohistochemical staining. The oxygen consumption rate (OCR) in each cell line in response to in vitro hypoxia was measured using an extracellular flux analyzer. Tumor growth delay in vivo was measured following HD-SFRT irradiation of 20 Gy.

Results

Targeting HIF-1α reduced lactate content, and increased both oxygen consumption and hypoxic fraction in these tumors after exposure to short-term continuous hypoxia. Tumors with intact HIF-1α subjected to HD-SFRT immediately following hypoxia exposure were less responsive to treatment than tumors without functional HIF-1α, and tumors irradiated under air breathing conditions regardless of HIF-1α status.

Conclusions

Blocking the HIF1 response during transient hypoxic stress increased hypoxia, reduced lactate levels and enhanced response to HD-SFRT. This strategy of combining hypofractionated radiotherapy with metabolic reprogramming to inhibit anaerobic metabolism may increase the efficacy of HD-SFRT through increased oxygen consumption and complementary killing of radiosensitive and hypoxic, radioresistant cells.

Electronic supplementary material

The online version of this article (doi:10.1186/s12885-017-3402-6) contains supplementary material, which is available to authorized users.

Fire and water: Tumor cell adaptation to metabolic conditions

Lorenz Poellinger was a leader in understanding the effects of altered microenvironmental conditions in tumor biology and in normal physiology. His work examining the effects of hypoxia and the HIF transcription factors has expanded our understanding of the role of the microenvironment in affecting the behaviour of both normal and malignant cells. Furthermore, his work provides a model for understanding the adaptive responses to other metabolic stress conditions. By investigating the molecular mechanisms responsible for the adaptive responses to metabolic stress in normal physiological situations, across pathological conditions, and in different model organisms, his work shows the power of combining data from different model systems and physiological contexts. In cancers, it has become clear that in order to evolve to become an aggressive malignant disease, tumor cells must acquire the capacity to tolerate a host of abnormal and stressful metabolic conditions. This metabolic stress can be thought of as a fire that tumor cells must douse with enough water to survive, and may offer opportunities to exploit smoldering vulnerabilities in order to eradicate malignant cells.

An Alternative Sugar Fuels AML

Although altered glucose metabolism is a well-studied feature of malignant cells, little is known about the direct metabolism of fructose. In this issue of Cancer Cell, Chen et al. report that AML cells consume fructose and use it to maintain viability, especially when glucose is scarce.

Mutant IDH1 Downregulates ATM and Alters DNA Repair and Sensitivity to DNA Damage Independent of TET2

Mutations in the isocitrate dehydrogenase-1 gene (IDH1) are common drivers of acute myeloid leukemia (AML) but their mechanism is not fully understood. It is thought that IDH1 mutants act by inhibiting TET2 to alter DNA methylation, but there are significant unexplained clinical differences between IDH1- and TET2-mutant diseases. We have discovered that mice expressing endogenous mutant IDH1 have reduced numbers of hematopoietic stem cells (HSCs), in contrast to Tet2 knockout (TET2-KO) mice. Mutant IDH1 downregulates the DNA damage (DD) sensor ATM by altering histone methylation, leading to impaired DNA repair, increased sensitivity to DD, and reduced HSC self-renewal, independent of TET2. ATM expression is also decreased in human IDH1-mutated AML. These findings may have implications for treatment of IDH-mutant leukemia.

PINK1 Is a Negative Regulator of Growth and the Warburg Effect in Glioblastoma

Proliferating cancer cells are characterized by high rates of glycolysis, lactate production, and altered mitochondrial metabolism. This metabolic reprogramming provides important metabolites for proliferation of tumor cells, including glioblastoma. These biological processes, however, generate oxidative stress that must be balanced through detoxification of reactive oxygen species (ROS). Using an unbiased retroviral loss-of-function screen in nontransformed human astrocytes, we demonstrate that mitochondrial PTEN-induced kinase 1 (PINK1) is a regulator of the Warburg effect and negative regulator of glioblastoma growth. We report that loss of PINK1 contributes to the Warburg effect through ROS-dependent stabilization of hypoxia-inducible factor-1A and reduced pyruvate kinase muscle isozyme 2 activity, both key regulators of aerobic glycolysis. Mechanistically, PINK1 suppresses ROS and tumor growth through FOXO3a, a master regulator of oxidative stress and superoxide dismutase 2. These findings highlight the importance of PINK1 and ROS balance in normal and tumor cells. PINK1 loss was observed in a significant number of human brain tumors including glioblastoma (n > 900) and correlated with poor patient survival. PINK1 overexpression attenuates in vivo glioblastoma growth in orthotopic mouse xenograft models and a transgenic glioblastoma model in Drosophila Cancer Res; 76(16); 4708-19. ©2016 AACR.

Lung Cancer Resets the Liver's Metabolic Clock

The impact of a tumor on distant organs is not well characterized but may be important for understanding immune interactions and the process of metastasis. Masri and colleagues (2016) now identify an interesting effect of lung tumor development on circadian regulation of liver metabolism.

Drivers of the Warburg phenotype

The Warburg effect was first described by Otto Warburg in the 1920s and describes the preferential conversion of glucose to lactate as opposed to its metabolism through the citric acid cycle to fuel oxidative phosphorylation in the mitochondria, even in the presence of oxygen. This phenotype is a common feature of malignant cells and is also observed in some highly proliferative normal tissues. The selective advantage provided by this phenotype is not entirely clear. Adopting this metabolic state may allow tumor cells to balance their need for ATP, biosynthetic precursor molecules, and reducing power in order to respond to growth and proliferation signals and may provide a selective advantage in the hypoxic and acidic microenvironments that are often a feature of solid tumors. Oncogenic signaling pathways and responses to the local microenvironment combine to produce this metabolic phenotype via a number of molecular mechanisms. A better understanding of these mechanisms in both tumor and normal tissues and a more complete understanding of how the Warburg effect interacts with the rest of the tumor metabolic network should provide opportunities for novel clinical intervention.

Backward wave cyclotron-maser emission in the auroral magnetosphere

In this Letter, we present theory and particle-in-cell simulations describing cyclotron radio emission from Earth's auroral region and similar phenomena in other astrophysical environments. In particular, we find that the radiation, generated by a down-going electron horseshoe distribution is due to a backward-wave cyclotron-maser emission process. The backward wave nature of the radiation contributes to upward refraction of the radiation that is also enhanced by a density inhomogeneity. We also show that the radiation is preferentially amplified along the auroral oval rather than transversely. The results are in agreement with recent Cluster observations.

Oncogenic isocitrate dehydrogenase mutations: mechanisms, models, and clinical opportunities

Heterozygous mutations in catalytic arginine residues of isocitrate dehydrogenases 1 and 2 (IDH1 and IDH2) are common in glioma, acute myeloid leukemia, chondrosarcoma, cholangiocarcinoma, and angioimmunoblastic T-cell lymphoma. The mutant enzymes acquire a neomorphic activity that converts α-ketoglutarate (α-KG) to D-2-hydroxyglutarate (D2HG), a rare metabolite. In cells and tissues expressing mutant IDH, D2HG concentrations are highly elevated. D2HG may act as an "oncometabolite" by inhibiting a class of α-KG-dependent enzymes involved in epigenetic regulation, collagen synthesis, and cell signaling. Knock-in mouse models of IDH1 mutations have shed light on these mechanisms and will provide valuable animal models for further investigation.

D-2-hydroxyglutarate produced by mutant IDH1 perturbs collagen maturation and basement membrane function

Isocitrate dehydrogenase-1 (IDH1) R132 mutations occur in glioma, but their physiological significance is unknown. Here we describe the generation and characterization of brain-specific Idh1 R132H conditional knock-in (KI) mice. Idh1 mutation results in hemorrhage and perinatal lethality. Surprisingly, intracellular reactive oxygen species (ROS) are attenuated in Idh1-KI brain cells despite an apparent increase in the NADP(+)/NADPH ratio. Idh1-KI cells also show high levels of D-2-hydroxyglutarate (D2HG) that are associated with inhibited prolyl-hydroxylation of hypoxia-inducible transcription factor-1α (Hif1α) and up-regulated Hif1α target gene transcription. Intriguingly, D2HG also blocks prolyl-hydroxylation of collagen, causing a defect in collagen protein maturation. An endoplasmic reticulum (ER) stress response induced by the accumulation of immature collagens may account for the embryonic lethality of these mutants. Importantly, D2HG-mediated impairment of collagen maturation also led to basement membrane (BM) aberrations that could play a part in glioma progression. Our study presents strong in vivo evidence that the D2HG produced by the mutant Idh1 enzyme is responsible for the above effects.

Cancer cell metabolism

Although the generation of a distinctive metabolic profile is a well-known aspect of cancer, the significance of these adaptations and their potential for exploitation for anticancer therapy has not been fully appreciated until recently. Many oncogenic changes known to affect intracellular signaling pathways play an active role in mediating these metabolic changes, which, in turn, function to support cancer cell growth and replication. In this chapter, we discuss the most current findings in cancer cell metabolism in terms of their impact on tumor cell growth as well as their potential for identifying new targets for therapeutic intervention.

Production of picosecond, kilojoule, and petawatt laser pulses via Raman amplification of nanosecond pulses

Raman amplification in plasma has been promoted as a means of compressing picosecond optical laser pulses to femtosecond duration to explore the intensity frontier. Here we show for the first time that it can be used, with equal success, to compress laser pulses from nanosecond to picosecond duration. Simulations show up to 60% energy transfer from pump pulse to probe pulse, implying that multikilojoule ultraviolet petawatt laser pulses can be produced using this scheme. This has important consequences for the demonstration of fast-ignition inertial confinement fusion.

Regulation of cancer cell metabolism

Interest in the topic of tumour metabolism has waxed and waned over the past century of cancer research. The early observations of Warburg and his contemporaries established that there are fundamental differences in the central metabolic pathways operating in malignant tissue. However, the initial hypotheses that were based on these observations proved inadequate to explain tumorigenesis, and the oncogene revolution pushed tumour metabolism to the margins of cancer research. In recent years, interest has been renewed as it has become clear that many of the signalling pathways that are affected by genetic mutations and the tumour microenvironment have a profound effect on core metabolism, making this topic once again one of the most intense areas of research in cancer biology.

Abstract 5452: Cancer-associated metabolite 2-hydroxyglutarate accumulates in AML with IDH1/2 mutations

Mutations in isocitrate dehydrogenase 1 and 2 (IDH1/2), are present in most gliomas and secondary glioblastomas, but are rare in other neoplasms. IDH1/2 mutations are heterozygous, and affect a single arginine residue. Recently, IDH1 mutations were identified in 8% of acute myelogenous leukemia (AML) patients. Our previous study revealed that IDH1 mutations cause a gain of function, resulting in the production and accumulation of 2-hydroxyglutarate (2-HG). Genotyping of 145 AML biopsies identified 11 IDH1 R132 mutant samples. Liquid chromatography-mass spectrometry metabolite screening revealed increased 2-HG levels in IDH1 R132 mutant cells and sera, and uncovered two IDH2 R172K mutations. IDH1/2 mutations were associated with normal karyotypes. Recombinant IDH1 R132C and IDH2 R172K proteins catalyze the novel NADPH -dependent reduction of alpha-ketoglutarate (a-KG) to 2-HG. The IDH1 R132C mutation commonly found in AML reduces the affinity for isocitrate, and increases the affinity for NADPH and a-KG. This prevents the oxidative decarboxylation of isocitrate to a-KG, and facilitates the conversion of a-KG to 2-HG. IDH1/2 mutations confer an enzymatic gain of function that dramatically increases 2-HG in AML. This provides an explanation for the heterozygous acquisition of these mutations during tumorigenesis. 2-HG is a tractable metabolic biomarker of mutant IDH1/2 enzyme activity.

Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 101st Annual Meeting of the American Association for Cancer Research; 2010 Apr 17-21; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2010;70(8 Suppl):Abstract nr 5452.

Cancer-associated metabolite 2-hydroxyglutarate accumulates in acute myelogenous leukemia with isocitrate dehydrogenase 1 and 2 mutations

Mutations in isocitrate dehydrogenase 1 and 2 (IDH1/2), are present in most gliomas and secondary glioblastomas, but are rare in other neoplasms. IDH1/2 mutations are heterozygous, and affect a single arginine residue. Recently, IDH1 mutations were identified in 8% of acute myelogenous leukemia (AML) patients. A glioma study revealed that IDH1 mutations cause a gain-of-function, resulting in the production and accumulation of 2-hydroxyglutarate (2-HG). Genotyping of 145 AML biopsies identified 11 IDH1 R132 mutant samples. Liquid chromatography-mass spectrometry metabolite screening revealed increased 2-HG levels in IDH1 R132 mutant cells and sera, and uncovered two IDH2 R172K mutations. IDH1/2 mutations were associated with normal karyotypes. Recombinant IDH1 R132C and IDH2 R172K proteins catalyze the novel nicotinamide adenine dinucleotide phosphate (NADPH)–dependent reduction of α-ketoglutarate (α-KG) to 2-HG. The IDH1 R132C mutation commonly found in AML reduces the affinity for isocitrate, and increases the affinity for NADPH and α-KG. This prevents the oxidative decarboxylation of isocitrate to α-KG, and facilitates the conversion of α-KG to 2-HG. IDH1/2 mutations confer an enzymatic gain of function that dramatically increases 2-HG in AML. This provides an explanation for the heterozygous acquisition of these mutations during tumorigenesis. 2-HG is a tractable metabolic biomarker of mutant IDH1/2 enzyme activity.

Pharmacologically increased tumor hypoxia can be measured by 18F-Fluoroazomycin arabinoside positron emission tomography and enhances tumor response to hypoxic cytotoxin PR-104

PURPOSE

Solid tumors contain microenvironmental regions of hypoxia that present a barrier to traditional radiotherapy and chemotherapy, and this work describes a novel approach to circumvent hypoxia. We propose to overcome hypoxia by augmenting the effectiveness of drugs that are designed to specifically kill hypoxic tumor cells.

EXPERIMENTAL DESIGN

We have constructed RKO colorectal tumor cells that express a small RNA hairpin that specifically knocks down the hypoxia-inducible factor 1a (HIF1a) transcription factor. We have used these cells in vitro to determine the effect of HIF1 on cellular sensitivity to the hypoxic cytotoxin PR-104, and its role in cellular oxygen consumption in response to the pyruvate dehydrogenase kinase inhibitor dichloroacetate (DCA). We have further used these cells in vivo in xenografted tumors to determine the role of HIF1 in regulating tumor hypoxia in response to DCA using (18)F-fluoroazomycin arabinoside positron emission tomography, and its role in regulating tumor sensitivity to the combination of DCA and PR-104.

RESULTS

HIF1 does not affect cellular sensitivity to PR-104 in vitro. DCA transiently increases cellular oxygen consumption in vitro and increases the extent of tumor hypoxia in vivo as measured with (18)F-fluoroazomycin arabinoside positron emission tomography. Furthermore, we show that DCA-dependent alterations in hypoxia increase the antitumor activity of the next-generation hypoxic cytotoxin PR-104.

CONCLUSIONS

DCA interferes with the HIF-dependent "adaptive response," which limits mitochondrial oxygen consumption. This approach transiently increases tumor hypoxia and represents an important method to improve antitumor efficacy of hypoxia-targeted agents, without increasing toxicity to oxygenated normal tissue.

Dust-acoustic shock waves due to strong correlation among arbitrarily charged dust

The nonlinear propagation of the dust-acoustic (DA) waves in a strongly coupled dusty plasma containing strongly correlated arbitrarily (positively or negatively) charged dust and weakly correlated Boltzmann electrons and ions has been investigated by employing the generalized hydrodynamic model and the reductive perturbation method. It has been shown that the strong correlation among the charged dust is a source of dissipation and is responsible for the formation of the DA shock waves in such a strongly coupled dusty plasma. It has also been found that the DA shock waves with positive (negative) potential are formed for positively (negatively) charged dust. The basic features of such DA shock waves have been identified. It has been suggested that a laboratory experiment be performed to test the theory presented here.

Cyclotron maser radiation from an inhomogeneous plasma

Cyclotron maser radiation is important in both laboratory devices such as gyrotrons and in space physics applications to phenomena such as auroral kilometric radiation. To understand the behavior, especially in the latter case where there is generally a localized region of instability, requires an understanding of how such instabilities behave in an inhomogeneous plasma. Here we consider, for simplicity, a simple ring distribution of electrons in either a step function variation of magnetic field or a continuous gradient. In each case we show that there can exist localized regions of instability from which waves, growing in time, can be radiated outwards.

Metabolic targeting of hypoxia and HIF1 in solid tumors can enhance cytotoxic chemotherapy

Solid tumors frequently contain large regions with low oxygen concentrations (hypoxia). The hypoxic microenvironment induces adaptive changes to tumor cell metabolism, and this alteration can further distort the local microenvironment. The net result of these tumor-specific changes is a microenvironment that inhibits many standard cytotoxic anticancer therapies and predicts for a poor clinical outcome. Pharmacologic targeting of the unique metabolism of solid tumors could alter the tumor microenvironment to provide more favorable conditions for anti-tumor therapy. Here, we describe a strategy in which the mitochondrial metabolism of tumor cells is increased by pharmacologic inhibition of hypoxia-inducible factor 1 (HIF1) or its target gene pyruvate dehydrogenase kinase 1 (PDK1). This acute increase in oxygen consumption leads to a corresponding decrease in tumor oxygenation. Whereas decreased oxygenation could reduce the effectiveness of some traditional therapies, we show that it dramatically increases the effectiveness of a hypoxia-specific cytotoxin. This treatment strategy should provide a high degree of tumor specificity for increasing the effectiveness of hypoxic cytotoxins, as it depends on the activation of HIF1 and the presence of hypoxia, conditions that are present only in the tumor, and not the normal tissue.

HIF-1 mediates adaptation to hypoxia by actively downregulating mitochondrial oxygen consumption

The HIF-1 transcription factor drives hypoxic gene expression changes that are thought to be adaptive for cells exposed to a reduced-oxygen environment. For example, HIF-1 induces the expression of glycolytic genes. It is presumed that increased glycolysis is necessary to produce energy when low oxygen will not support oxidative phosphorylation at the mitochondria. However, we find that while HIF-1 stimulates glycolysis, it also actively represses mitochondrial function and oxygen consumption by inducing pyruvate dehydrogenase kinase 1 (PDK1). PDK1 phosphorylates and inhibits pyruvate dehydrogenase from using pyruvate to fuel the mitochondrial TCA cycle. This causes a drop in mitochondrial oxygen consumption and results in a relative increase in intracellular oxygen tension. We show by genetic means that HIF-1-dependent block to oxygen utilization results in increased oxygen availability, decreased cell death when total oxygen is limiting, and reduced cell death in response to the hypoxic cytotoxin tirapazamine.

Efficiency and energy spread in laser-wakefield acceleration

The theoretical limits on efficiency and energy spread of the laser-wakefield accelerator are investigated using a one-dimensional model. Modifications, both of the wakefield due to the electron bunch, and of the laser pulse shape due to the varying permittivity of the plasma, are described self-consistently. It is found that a short laser pulse gives a higher efficiency than a long laser pulse with the same initial energy. Energy spread can be minimized by optimizing bunch length and bunch charge such that the variation of the accelerating force along the length of the bunch is minimized. An inherent trade-off between energy spread and efficiency exists.

A fluorescent orthotopic model of metastatic cervical carcinoma

Currently, there is no mouse model of cervical cancer that allows for the study of the later stages of the disease, including metastasis. We report here the development of an orthotopic model of human cervical carcinoma in which tumor fragments are surgically implanted into the cervix of SCID mice. The human cervical carcinoma cell lines used in this study (CaSki, ME-180, and SiHa) have been engineered to stably express the fluorescent proteins enhanced green fluorescent protein (EGFP) or DsRed2, allowing for in vivo optical monitoring of tumor growth and metastasis. The cervical implants develop into large intraperitoneal masses involving the entire reproductive tract, with little local invasion of other abdominal structures. These tumors metastasize initially to local lymph nodes and later to lung, a pattern consistent with the clinical course of the disease. It was found that the use of the DsRed2 protein as a fluorescent marker has distinct advantages over EGFP due to the wavelength of its emission spectrum (575-625 nm vs 500-550 nm). Tissue penetration of light at this wavelength is greater, and the auto-fluorescence of mouse tissues is less intense, resulting in an enhanced signal to noise ratio compared to results obtained with EGFP. This model should allow for a more relevant investigation of the factors that affect the metastasis of cervical carcinoma and presents an opportunity to evaluate potential therapeutic strategies designed to prevent the spread of disease.

Acute hypoxia enhances spontaneous lymph node metastasis in an orthotopic murine model of human cervical carcinoma

An orthotopic mouse model of cervical carcinoma has been used to investigate the relationship between acute (cyclic) hypoxia and spontaneous lymph node metastasis in vivo. The human cervical carcinoma cell line ME-180 was stably transfected to express the fluorescent protein DsRed2, which allowed the in vivo optical monitoring of tumor growth and metastasis by fluorescent microscopy. The surgically implanted primary tumors metastasize initially to local lymph nodes and later to lung, a pattern consistent with the clinical course of the disease. The effect of acute hypoxia on the growth and spread of these tumors was examined by exposing tumor-bearing mice to treatment consisting of exposure to 12 cycles of 10 min 7% O(2) followed by 10 min air (total 4 h) daily during tumor growth. After 21 days, the tumors were excised, lymph node and lung metastases were quantified, and the hypoxic fraction and relative vascular area of the primary tumors were assessed by immunohistochemical staining for the hypoxic marker drug EF5 [2-(2-nitro-1H-imidazole-1-yl)-N-(2,2,3,3,3-pentafluoropropyl) acetamide] and the vascular marker CD31, respectively. In untreated mice, the primary tumor size was directly correlated with lymph node metastatic burden. The acute hypoxia treatment resulted in a significant decrease in the size of the primary tumors at the time of excision. However, the mice in the acute hypoxia group had an increased number of positive lymph nodes (2-4) as compared with control mice (1-3). Lung metastasis was not affected. The acute hypoxia treatment also decreased the relative vascular area in the primary tumors but did not affect the hypoxic fraction. These results suggest that fluctuating oxygenation in cervical carcinoma tumors may reduce tumor growth rate, but it may also enhance the ability of tumor cells to metastasize to local lymph nodes.

Molecular mechanisms of tumor invasion and metastasis: an integrated view

As tumors progress to increased malignancy, cells within them develop the ability to invade into surrounding normal tissues and through tissue boundaries to form new growths (metastases) at sites distinct from the primary tumor. The molecular mechanisms involved in this process are incompletely understood but those associated with cell-cell and cell-matrix adhesion, with the degradation of extracellular matrix, and with the initiation and maintenance of early growth at the new site are generally accepted to be critical. This article discusses current knowledge of molecular events involved in these various processes. The potential role of adhesion molecules (eg. integrins and cadherins) has undergone a major transition over the last ten years, as it has become apparent that such molecules play a major role in signaling from outside to inside a cell, thereby controlling how a cell is able (or not) to sense and interact with its local environment. Similarly the roles of proteolytic enzymes and their inhibitors (eg. matrix metalloproteinases and TIMPs) have also expanded as it has become apparent that they not only have the abilities to break down the components of the extracellular matrix but also are involved in the release of factors which can affect the growth of the tumor cells positively or negatively. Recent work has highlighted the importance of the later, post-extravasational stages of metastasis, where adhesion and proteolysis are now known to play a role along with other processes such as apoptosis, dormancy, growth factor-receptor interactions and signal transduction. Recent work has also demonstrated that not only the immediate cellular microenvironment, in terms of specific cell-cell and cell-matrix interactions, but also the extended cellular microenvironment, in terms of vascular insufficiency and hypoxia in the primary tumor, can modify cellular gene expression and enhance metastasis. Mechanisms of metastasis appear to involve a complex array of genetic and epigenetic changes many of which appear to be specific both for different types of tumors and for different sites of metastasis. Our improved understanding of the expanded roles of the individual molecules involved has resulted in a mechanistic blurring of the previously described discrete stages of the metastatic process.

Role of parallel flow in the improved mode on the STOR-M tokamak

A novel feature of the H-mode induced by compact torus injection on the STOR-M tokamak is observed. There is almost no change in the radial electric field profiles during and after the L-H transition. The usual hypothesis of the E x B shear stabilization mechanism is therefore unlikely to play a role in this transition. A new mechanism of the stabilization of microinstabilities by parallel flow is suggested as the plausible cause for the transition to this improved regime.

Acute (cyclic) hypoxia enhances spontaneous metastasis of KHT murine tumors

Hypoxia exists in most human and rodent solid tumors and has been shown to correlate with poor survival in carcinoma of the cervix, carcinoma of the head and neck, and soft tissue sarcoma. It exists both chronically, due to the poorly organized vasculature of solid tumors, and acutely, due to fluctuations in blood flow. It has been found that tumors that are more hypoxic are more likely to metastasize in humans and in rodent models, and it has been demonstrated that exposure of tumor cells to hypoxia in vitro can transiently enhance their metastatic potential when they are reinjected i.v. into mice. The purpose of the present study was to determine whether experimentally imposed hypoxic stress in vivo, either chronic or acute, affects the process of spontaneous metastasis in tumor-bearing mice. We exposed mice bearing KHT tumors to low oxygen conditions (5-7% O(2) breathing) daily during tumor growth in an attempt to induce additional chronic (2 h/day) and acute (12 x 10 min/day) hypoxia in their tumors. By monitoring tumor pO(2) levels over the course of treatment, we demonstrated that these treatments produce acute and chronic hypoxia within the tumor tissue. The acute but not the chronic hypoxia treatment significantly increased the number of spontaneous microscopic lung metastases in the mice by a factor of about 2, and the results suggest that this effect was due to the changes induced in the primary tumor. This study describes a novel method for studying the effects of hypoxia in solid tumors and demonstrates that acute and chronic hypoxia can have different effects on tumor cell behavior in vivo.

Knee magnetic resonance imaging in childhood chronic monarthritis

OBJECTIVE

To describe the usefulness of magnetic resonance imaging (MRI) of the knee in the evaluation of chronic monarthritis of uncertain cause in childhood.

METHODS

We retrospectively reviewed 21 children referred to our clinic with a putative diagnosis of chronic inflammatory monarthritis of the knee who had MRI performed between May 1993 and June 1997. The median age was 13 years (range 2-17) and 11 were girls.

RESULTS

The clinical diagnosis prior to MRI assessment was inflammatory arthritis in 16 patients, and a primary noninflammatory cause in 5. MRI was done in the patients with presumptive inflammatory arthritis when there were atypical symptoms, signs, or radiographs (n = 14), or when they failed to respond to therapy (n = 2). In the patients with a presumptive noninflammatory diagnosis, MRI was performed to clarify the diagnosis. Twelve children (57%) had MRI evidence of a noninflammatory diagnosis. In 4 children (19%) the MRI study indicated the presence of arthritis, and in 5 children (24%) the MRI studies were normal. The noninflammatory diagnoses included: lipoma arborescens (n = 1), vascular malformation [intraarticular (n = 1), extraarticular (n = 1)], synovial chondromatosis (n = 2), partial anterior cruciate ligament tear (n = 2), traumatic bone contusion (n = 2), possible meniscal tear (n = 1), osteochondritis dissecans (n = 1), and a soft tissue mass of uncertain significance in the suprapatellar pouch (n = 1).

CONCLUSION

Inflammatory arthritis is usually diagnosed by clinical assessment alone. Uncommonly, when a single joint is involved, and atypical features are identified by a pediatric rheumatologist, other causes of chronic pain and swelling need to be excluded. In this selected patient population, MRI is a useful tool either to confirm the presence of inflammatory arthritis or to investigate a wide range of pathology that can mimic knee joint arthritis.

Congenital-infantile fibrosarcoma: magnetic resonance imaging findings

Congenital-infantile, fibrosarcoma is a rare tumour presenting at birth or in the neonatal period. Few such tumours have been reported, and imaging details in particular are scant. The authors describe two neonates with congenital-infantile fibrosarcoma, the first case involving the right thigh and extending into the pelvis, and the second involving the calf and the ankle. In both cases magnetic resonance imaging (MRI) demonstrated well-demarcated, low-signal-intensity soft-tissue masses with t1-weighting and inhomogeneous, high-signal-intensity masses with T2-weighting. MRI was superior to other imaging modalities in the assessment of soft-tissue involvement and proved especially useful in planning therapy and monitoring chemotherapeutic response.

Osteosarcoma in a 19-month-old girl

Osteosarcoma develops only rarely in patients under 6 years of age. The authors describe a 19-month-old girl who presented with proximal humeral metaphyseal osteosarcoma. To the authors' knowledge, this report represents the youngest patient with this bone lesion.

An unusual case of mixed sclerosing bone dystrophy presenting with morning stiffness and joint swelling in childhood: a case report

We describe a case of a 16 year old native Indian girl with pain, morning stiffness and foot swelling who had radiographic changes consistent with mixed sclerosing bone dystrophy (MSBD) combined with fibrous dysplasia.

Atlantoaxial subluxation in children with seronegative enthesopathy and arthropathy syndrome: 2 case reports and a review of the literature

We describe 2 HLA-B27 positive children with seronegative enthesopathy and arthropathy (SEA) syndrome who developed spontaneous (nontraumatic) atlantoaxial subluxation early in their disease course. Neither child had evidence of spinal cord compression but both had progressive atlantoaxial subluxation in spite of conservative treatment. Both underwent elective posterior cervical (C1-C2) fusion.

Obstructive lung disease in children after allogeneic bone marrow transplantation: evaluation with high-resolution CT

OBJECTIVE

Obstructive lung disease is a major complication of bone marrow transplantation related to graft-versus-host disease. The purpose of this study was to determine the usefulness of high-resolution CT to evaluate obstructive lung disease occurring in children after bone marrow transplantation.

MATERIALS AND METHODS

Ten high-resolution CT scans of the lungs were obtained in seven children who developed chronic obstructive lung disease after bone marrow transplantation. All seven patients had chronic graft-versus-host disease. Spirometry, the gold standard test, confirmed airflow obstruction in each case, five prior to high-resolution CT. Two patients were too young to have spirometry until 10 and 15 months respectively after successful high-resolution CT. Selected images from these studies were randomized with similar images from five control subjects and reviewed blindly. All images from scans in patients with obstructive lung disease were analyzed retrospectively for parenchymal hypoattenuation, bronchial dilatation, bronchial wall thickening, and abnormal parenchymal opacity. Expiratory air-trapping was assessed on cine high-resolution CT done in four cases.

RESULTS

Three blinded observers each correctly identified all five controls among 15 high-resolution CT examinations. No scan from a patient with obstructive lung disease was considered normal. Areas of parenchymal hypoattenuation affected 35 of 35 lobes of the lung. Expiratory air-trapping was shown by cine high-resolution CT. Subsegmental or segmental bronchial dilatation was seen in 23 of 25 lobes in five patients. Bronchial wall thickening was not a prominent feature. Increasing abnormality was demonstrated in three patients on follow-up high-resolution CT. The high-resolution CT abnormalities were similar to those reported in patients with bronchiolitis obliterans.

CONCLUSION

High-resolution CT of the lungs can show extensive abnormality in children who develop chronic obstructive lung disease after bone marrow transplantation. High-resolution CT is a useful noninvasive technique in the evaluation of this disease.

Comparison of stimulable phosphor technology and conventional screen-film technology in pediatric scoliosis

One hundred consecutive patients being investigated for scoliosis were studied using a double cassette containing a conventional film screen and a stimulable phosphor plate. The images were separated, randomised and scored thrice by three radiologists for anatomic structure visualisation. The exposure to the plate and film and repeat rate were measured. Scoliosis angles were comparable on both sets of images, however, visualisation of vertebrae, vertebral end plates, pedicles, spinous processes and other structures were significantly improved (p < 0.0001). Intra- and inter-observer reliability was high with good intraclass correlation. There was a 40% potential exposure reduction, and retakes were decreased from 3 to 0%. We conclude that stimulable phosphor images give better anatomic structure visualisation with potential radiation exposure reduction and lower repeat rate.