Profiles of the functions , , and .

<p>Thresholds of necroxia, hypoxia and normoxia are marked as , and , respectively.</p

Model simulations of intracellular GSH concentration (a), pH (b), and oxygen tension (c) changing with time in DTX-treated and non-treated tumors, combined with WT or HIF-1<i>α</i> KO macrophages.

<p>Model simulations of intracellular GSH concentration (a), pH (b), and oxygen tension (c) changing with time in DTX-treated and non-treated tumors, combined with WT or HIF-1<i>α</i> KO macrophages.</p

Variables and units of the model.

<p>Variables and units of the model.</p

Simulations of intracellular ROS concentration (first row) and tumor growth (second row) with different levels of GSH depletion in tumors with wild-type macrophages (left column) and HIF-1<i>α</i> KO macrophages (right column).

<p>Red: no depletion (); Green: moderate depletion (); Blue: severe depletion (). (a–b): ROS levels (<i>µ</i>M) against time (days); (c–d): the corresponding tumor volume (cm³).</p

Experiments and simulations of intracellular GSH concentration ([GSH]) in tumors with wild-type, HIF-1<i>α</i>- and HIF-2<i>α</i>-deficient macrophages (WT, HIF-1<i>α</i> KO, and HIF-2<i>α</i> KO).

<p>Horizontal axis represents time (in days) and vertical axis scales [GSH] in units of Molar. (a): Experimental data of [GSH] with error bars. Red: WT; Blue: HIF-1<i>α</i> KO; Green: HIF-2<i>α</i> KO. (b) – (d): Comparison of experiments (dots with error bars) and numerical simulations (dash curves) of [GSH] for tumors with WT, HIF-1<i>α</i>, and HIF-2<i>α</i> KO macrophages, respectively.</p

Schematic diagram of the roles of ROS, GSH, and hydrogen ions in cancer cell growth and tumor angiogenesis.

<p>(i) ROS is a major by-product of aerobic metabolism and plays a dual role in cancer cell life-cycle: below a certain threshold, increasing amounts of ROS promotes cell proliferation through pathways of extracellular-signal-regulated kinases (ERKs) and cell survival factors such as Akt. However, ROS leads to cell apoptosis when its concentration is over the toxic threshold. Additionally, ROS may play a function in up-regulating HIF-1 expression, which in turn results in increasing the production of angiogenesis factor VEGF. (ii) GSH (glutathione) is the most abundant antioxidant produced by cancer cells to protect themselves from oxidative stress; it can remove ROS (mostly ) with the help of enzyme . (iii) Large amount of hydrogen ions are produced as a consequence of glucose metabolism, and are pumped out by abnormally expressed proton transporters. There is evidence indicating that acidic extracellular environment induces VEGF production through the ERK/MAPK signaling pathway.</p

Experiments and simulations of tumor volume with wild-type, HIF-1<i>α</i>- and HIF-2<i>α</i>-deficient macrophages (WT, HIF-1<i>α</i> KO, and HIF-2<i>α</i> KO).

<p>Horizontal axis represents time (in days) and vertical axis scales tumor volume (in units of cm³). (a): Experimental data of tumor volumes with error bars (standard deviations). Red: WT; Blue: HIF-1<i>α</i> KO; Green: HIF-2<i>α</i> KO. (b)-(d): Comparison of experiments (dots with error bars) and numerical simulations (dash curves) for tumor volumes with WT, HIF1-<i>α</i>, and HIF-2<i>α</i> KO macrophages, respectively.</p

Experiments and simulations of oxygen tension of tumors with wild-type, HIF-1<i>α</i>- and HIF-2<i>α</i>-deficient macrophages (WT, HIF-1<i>α</i> KO and HIF-2<i>α</i> KO).

<p>(a): Experimental data of oxygen tension (mmHg) against time (days). Red: WT; Blue: HIF-1<i>α</i> KO; Green: HIF-2<i>α</i> KO; (b): Same experiments aligned with tumor volumes (dots) and the correspondingly fitted curves; (c): Numerical simulations of oxygen tension against time; (d): Numerical simulations of oxygen tension aligned with tumor volumes.</p

Simulations of intracellular ROS concentration and tumor growth with severe GSH depletion () at different time in tumors with wild-type macrophages.

<p>Red: GSH depletion at the beginning; Green: GSH depletion starts from the ninth day; Blue: GSH depletion from the fourteenth day. (a) ROS levels (<i>µ</i>M) against time (days); (b) the corresponding tumor volume (cm³).</p

Comparison of simulations (colored curves) with the experiments from <b>Figure 10</b> (dots with error bars) for DTX effectiveness in tumors with wild-type, HIF-1<i>α</i>-, and HIF-2<i>α</i>-deficient macrophages (WT, HIF-1<i>α</i> KO and HIF-2<i>α</i> KO) in (a) – (c), respectively.

<p>Tumor volumes are normalized in the same way as in <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0107511#pone-0107511-g010" target="_blank">Figure 10</a>.</p