274 - Targeting of Mutant KRAS Driven Tumors by a Novel Small Molecule is Associated with ROS-Driven Mitophagy and Changes in Mitochondrial Morphology

Abstract

Since its discovery in human cancers, mutant RAS remains as one of the most common genetic lesions found in many cancers such as lung, pancreatic and colorectal carcinoma. Given its widespread occurrence in cancer, mutant RAS is an unequivocal therapeutic target in malignancies and remains a subject of intense interest hitherto. Nevertheless, no successful RAS inhibitor has been identified despite the many years of unwavering effort. We recently reported the death-inducing activity of a small-molecule compound, C1, which is capable of triggering ROS-dependent autophagy-associated cell death. Using heterozygous mutant KRAS expressing HCT116 cells as well as wildtype (WT) KRAS expressing HT29, we showed that C1 selectively targets mutant KRAS expressing cells while sparing cells expressing WT KRAS. Importantly, scavenging of reactive oxygen species (ROS) as well as genetic knockdown and pharmacological inhibition of mutant KRAS and AKT suppressed C1-induced reactive oxygen species (ROS) production and restored clonogenic survival of HCT116 cells. These findings indicate that C1-induced cell death in mutant KRAS expressing cells is dependent on a paradoxical activation of mutant KRAS, downstream AKT and increased of intracellular ROS level. Nevertheless, the subsequent death-inducing pathway that stems from the increase of intracellular ROS is still poorly understood. Given the increasing evidence showing the inextricability between ROS and mitochondrial dynamics, we examined the protein machinery regulating mitochondrial morphology. Preliminary data suggests an increase in mitochondrial fission activity as indicated by increased translocation of DRP1 from cytosol to mitochondria and auto-cleavage of OPA1. In addition, we have also observed increased accumulation of LC3-II at the mitochondria indicating the presence of mitophagy. As oxidative stress is an important mediator of mitophagy, we speculate that increased mitochondrial fission activity may be an important step to ROS-induced mitophagy and subsequent cell death.