Metabolic changes during carcinogenesis: Potential impact on invasiveness

Successful adaptation to varying microenvironmental constraints plays a crucial role during carcinogenesis. We develop a hybrid cellular automation approach to investigate the cell–microenvironmental interactions that mediate somatic evolution of cancer cells. This allows investigation of the hypothesis that regions of premalignant lesions develop a substrate-limited environment as proliferation carries cells away from blood vessels which remain separated by the intact basement membrane. We find that selective forces in tumoural regions furthest from the blood supply act to favour cells whose metabolism is best suited to respond to local changes in oxygen, glucose and pH levels. The model predicts three phases of somatic evolution. Initially, cell survival and proliferation is limited due to diminished oxygen levels. This promotes adaptation to a second phase of growth dominated by cells with constitutively up-regulated glycolysis, less reliant on oxygen for ATP production. Increased glycolysis induces acidification of the local environment, limiting proliferation and inducing cell death through necrosis and apoptosis. This promotes a third phase of cellular evolution, with emergence of phenotypes resistant to acid-induced toxicity. This emergent cellular phenotype has a significant proliferative advantage because it will consistently acidify the local environment in a way that is toxic to its competitors but harmless to itself. The model's results suggest this sequence is essential in the transition from self-limited premalignant growth to invasive cancer, and, therefore, that this transition may be delayed or prevented through novel strategies directed towards interrupting the hypoxia–glycolysis–acidosis cycle

Reducing the hypoxic fraction of a tumour model by growth in low glucose.

The question of whether growth under low glucose conditions leads to a reduced amount of cell hypoxia was investigated using an in vitro tumour analogue, the sandwich system. In this multicellular system, the interplay between diffusion and consumption of oxygen and nutrients results in spatial gradients of these environmental factors. Gradients in the environment lead to biological heterogeneity within the cell population. A necrotic centre, surrounded by a viable cell border, subsequently develops. Cells adjacent to the necrotic centre in sandwiches are hypoxic and are in an environment somewhat analogous to that of cells adjacent to necrotic regions in solid tumours. Using sandwiches of the 9L and V79 cell lines, the effects of growth under low glucose conditions on the degree of hypoxia in regions adjacent to the necrotic centre were investigated. Per-cell binding of 3H-misonidazole, assessed by autoradiography, was used as an indicator of oxygen deprivation. It was found that the extent of the hypoxic region and the severity of hypoxia were considerably reduced by growing sandwiches in a glucose concentration of 0.6 mM rather than 6.5 mM. This reduction was found in conjunction with a smaller viable border; it occurred despite the fact that the average per-cell oxygen consumption is higher in the low glucose sandwiches. The data are qualitatively consistent with a joint oxygen-glucose deprivation model for cell necrosis

Mathematical modelling of tumour acidity

Acid-mediated tumour invasion is receiving increasing experimental and clinical attention. Previous models proposed to describe this phenomenon failed to capture key properties of the system, such as the existence of the benign steady state, or predicted incorrectly the size of the inter-tissue gap. Here we show that taking proper account of quiescence ameliorates these drawbacks as well as revealing novel behaviour. The simplicity of the model allows us to fully identify the key parameters controlling different aspects of behaviour

Detecting 6 MV X-rays using an organic photovoltaic device

An organic photovoltaic (OPV) device has been used in conjunction with a flexible inorganic phosphor to produce a radiation tolerant, efficient and linear detector for 6 MV Xrays. The OPVs were based on a blend of poly(3-hexylthiophene-2,5-diyl) (P3HT) and phenyl-C61-butyric acid methyl ester (PCBM). We show that the devices have a sensitivity an order of magnitude higher than a commercial silicon detector used as a reference. Exposure to 360 Grays of radiation resulted in a small (2%) degradation in performance demonstrating that these detectors have the potential to be used as flexible, real-time, in vivo dosimeters for oncology treatments. (C) 2009 Elsevier B.V. All rights reserved

A study of some factors influencing intestinal function in calves

Culture filtrates prepared from a strain of Escherichia coli associated with calf diarrhoea were shown to produce fluid accumulation in ligated segments of calf intestine. No activity could be demonstrated in vitro in the other experimental systems in which these culture filtrates were tested. The material was therefore examined using Thiry-Vella loops prepared in calves.Thiry-Vella loops were found to be a useful test preparation for the study of enterotoxin activity, and were used to examine the effect of enterotoxio extracts on net fluid, electrolyte and glucose absorption. It was found that a significant shift towards secretion of fluid, sodium, bicarbonate and chloride occurred in each case in which they were examined. Potassium was not consistently affected, and glucose absorption was unchanged.The effects of enterotoxin on unidirectional fluxes of water and sodium were studied using isotopic labels. It was found that the net effect on water movement resulted from an increase in exsorption. However, the net effect on sodium movement was mainly the result of decreased insorption. It was suggested that this indicated a complex mechanism for enterotoxin activity.Culture filtrates prepared from strains of E.coli isolated from diarrhoeic but non-septicaemic calves provoked a greater volume of fluid exudate than did filtrates from strains in septicaemic or healthy animals. It was suggested that enterotoxin production may be a graded phenomenon, and moreover, may be commonly encountered in organisms associated with diarrhoea in calves.Using Thiry-Vella loops as a test preparation, it was shown that enterotoxic activity was distinct from bacterial endotoxin, and that the activity was dialysable using Visking tubing. Ultrafiltration showed that most of the activity was contained in the 1000 to 10,000 molecular weight fraction. The material was stable when heated at 100°C, but showed partial loss of activity when heated at 121°C for two hours.Evidence of systemic absorption of enterotoxin was obtained in one animal, but could not be confirmed in another. Attempts to inhibit enterotoxin activity with drugs were not successful.Mucosal lactase was assayed in material from healthy calves and from calves which had died after scouring. Lactase activity was shown to be depressed in the latter group. Normal calves were shown to be able to digest at least twice the normal lactose intake before changes were seen in faeces weight and dry matter, but despite this, lactose tolerance tests showed that there was a significant regression of peak blood glucose rise on faecal dry-matter content. It was therefore suggested that scouring calves may be unable to fully utilise dietary lactose. No effect of enterotoxin on lactase activity could be demonstrated