TMIC-16NOX GENERATED REACTIVE OXYGEN SPECIES PROMOTES GLIOBLASTOMA GROWTH AND SURVIVAL THROUGH INACTIVATION OF PTEN

Abstract

TMIC-16. NOX GENERATED REACTIVE OXYGEN SPECIES PROMOTES GLIOBLASTOMA GROWTH AND SURVIVAL THROUGH INACTIVATION OF PTEN Kirsten Ludwig and Harley Kornblum; University of California, Los Angeles, Los Angeles, CA, USA PTEN is inactivated in 40% of glioblastoma (GBM), however almost all GBM’s have increased Akt activity, regardless of PTEN status. Treatment with exogenous reactive oxygen species (ROS) inactivates PTEN through oxidation, suggesting that a similar event may occur in the hypoxic tumor environment. Recent data indicate that low levels of ROS are required for cell maintenance and stem cell renewal while moderate increases may promote tumorigenesis. Much of the endogenous ROS is produced by NADPH oxidase (NOX), amembraneboundcomplexofproteins,activatedunderhypoxic conditions. This raises the possibility that the tumor microenvironment may inactivate PTEN through means other than mutation or deletion. We investigated the role of NOX generated ROS in primary cultures of patient-derived GBM cells across the spectrum of GBM subtypes. Endogenous ROS levels correlated with proliferation; those with higher ROS had higher proliferation rates. Placement of cells in low oxygen levels (1%) enhanced proliferation, an effect that was reversed by treatment with antioxidants and the NOX inhibitor Apocynin, supporting the hypothesis that NOX-induced ROS promotes GBM growth. The effects of hypoxia-induced NOX activation were dependent upon PTEN, as PTEN knockdown or PTEN null cells exhibited no enhanced growthwhenplaced inhypoxicconditions.Furthermore,pharmacologicblockade of AKT prevented enhanced growth in hypoxia. A role for PTEN was further demonstrated by the finding that it was oxidatively inactivated in GBM cells grown under hypoxic conditions. Finally, pharmacological inhibition of NOX rescued radiation-induced activation of Akt resulting in increased radio-sensitivity. Taken together, these data support the hypothesis that the relativelyhypoxic tumorenvironment activatesNOX, resulting in functional inactivation of PTEN andenhanced GBMproliferation andsurvival. Thesefindings represent a novel opportunity for therapeutic intervention in a subset of GBM. Neuro-Oncology 17:v221–v225, 2015. doi:10.1093/neuonc/nov236.16 Published by Oxford University Press on behalf of the Society for Neuro-Oncology 2015.