Distribution of nutrients in the spheroid and de-oxygenation during growth.

<p>(<b>a</b>) Central cut-section through an <i>in silico</i> EMT6 tumour spheroid after 12 days of growth. Normoxic cells (pO₂ > 2.5%) in blue, cells below 2.5% pO₂ in purple, below 0.5% in red and necrotic cells in grey. Slice thickness is 40 μm. Compare to the <i>in vitro</i> immunodetection of pimonidazole in hypoxic cells in the peri-necrotic regions of a tumour spheroids (T47D after 10–14 days of growth) in Fig 3a in [<a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0133357#pone.0133357.ref080" target="_blank">80</a>] (bar size in both images 50 μm). (<b>b</b>) Lateral concentration profiles of glucose and oxygen. The higher reach of survival-promoting glucose will lead to the formation of an anoxic region (between grey and brown dashed line). Hypoxic cells will be found in low-oxygen regions (between red and grey dashed line) and normoxic cells beyond the red dashed line. Compare also reference [<a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0133357#pone.0133357.ref001" target="_blank">1</a>]. (<b>c</b>) Central cut-section of 40 μm thickness through an <i>in silico</i> EMT6 tumour with oxygen-dependent staining after 2, 6.5, 8.3, 9.5 and 10.2 days of growth. Cell staining corresponds to the line color in graph (d) (green cells are above 7.8%pO₂). (<b>d</b>) Development of cell populations below defined oxygen concentrations in the spheroid as visualised in (c).