Imaging the Impact of Nox4 in Cycling Hypoxia-mediated U87 Glioblastoma Invasion and Infiltration

We determined the impact of the cycling hypoxia tumor microenvironment on tumor cell invasion and infiltration in U87 human glioblastoma cells and investigated the underlying mechanisms using molecular bio-techniques and imaging. The invasive phenotype of U87 cells and xenografts exposed to experimentally imposed cycling hypoxic stress in vitro and in vivo was determined by the matrigel invasion assay in vitro and dual optical reporter gene imaging in vivo. RNAi-knockdown technology was utilized to study the role of the NADPH oxidase subunit 4 (Nox4) on cycling hypoxia-mediated tumor invasion. Cycling hypoxic stress significantly promoted tumor invasion in vitro and in vivo. However, Nox4 knockdown inhibited this effect. Nox4-generated reactive oxygen species (ROS) are required for cycling hypoxia-induced invasive potential in U87 cells through the activation of NF-kappa B- and ERK-mediated stimulation of MMP-9. Cycling hypoxia-induced ROS via Nox4 should be considered for therapeutic targeting of tumor cell invasion and infiltration in glioblastoma.