The Novel Phloroglucinol PMT7 Kills Glycolytic Cancer Cells by Blocking Autophagy and Sensitizing to Nutrient Stress

The switch from oxidative phosphorylation to glycolytic metabolism results in cells that generate fewer reactive oxygen species (ROS) and are resistant to the intrinsic induction of apoptosis. As a consequence, glycolytic cancer cells are resistant to radiation and chemotherapeutic agents that rely on production of ROS or intrinsic apoptosis. Further, the level of glycolysis correlates with tumor invasion, making glycolytic cancer cells an important target for new therapy development. We have synthesized a novel redox-active quinone phloroglucinol derivative, PMT7. Toxicity of PMT7 was in part due to loss of mitochondrial membrane potential in treated cells with subsequent loss of mitochondrial metabolic activity. Mitochondrial gene knockout rho 0 cells, a model of highly glycolytic cancers, were only half as sensitive as the corresponding wild-type cells and metabolic pathways downstream of MET were unaffected in rho 0 cells. However, PMT7 toxicity was also due to a block in autophagy. Both wild-type and rho 0 cells were susceptible to autophagy blockade, and the resistance of rho 0 cells to PMT7 could be overcome by serum deprivation, a situation where autophagy becomes necessary for survival. The stress response class III deacetylase SIRT1 was not significantly involved in PMT7 toxicity, suggesting that unlike other chemotherapeutic drugs, SIRT1-mediated stress and survival responses were not induced by PMT7. The dependence on autophagy or other scavenging pathways makes glycolytic cancer cells vulnerable. This can be exploited by induction of energetic stress to specifically sensitize glycolytic cells to other stresses such as nutrient deprivation or potentially chemotherapy. J. Cell. Biochem. 112: 1869-1879, 2011. (C) 2011 Wiley-Liss, Inc.