Abstract:
Targeting cancers; that exhibit amino acid auxotrophy, such as glioblastoma multiforme, through starvation of amino acids is becoming a promising therapy. The efficiency of this targeted therapy is based on the idea of killing cancer cells without damaging normal cells that are capable of synthesizing specific amino acids being targeted. In this study, we examine the mechanism of HuArgI (Co)-PEG5000-induced cell death in both partially and completely auxotrophic GBM cell lines. Our results first showed a significant increase in HuArgI (Co)-PEG5000 treated cells for both U251 and A172 in autophagosome formation; suggesting activation of autophagy in response to arginine deprivation. Secondly, the results also showed in both U251 and A172 cells, an increase in the percentage of the survival of cells co-treated with HuArgI (Co)-PEG5000 and chloroquine; indicating that autophagy is contributing to cell death at late time points in GBM cells.
Moreover, only U251 cells showed an overexpression in Argininosuccinate Synthetase-1 (ASS-1); the main key player in L-arginine biosynthesis, in case of arginine deprivation and the rescue was detected upon addition of exogenous L-citrulline.
Addition of N-acetyl-cysteine (NAC); being a reactive oxygen species (ROS) scavenger, led to a significant decrease in the cytotoxicity of arginine deprivation to U251 and A172 cells, indicating that ROS generation reversed the cytotoxicity of arginine deprivation to GBM cells. Finally, we have also shown that in U251 cells the autophagosome formation; thus, death by autophagy is mediated by ROS generation.
Taken together, ROS plays an essential role in the mechanism of autophagy activation in some arginine deprived GBM cells, where we have ROS-induced autophagy.
