Glutamine deficiency promotes stemness and chemoresistance in tumor cells through DRP1-induced mitochondrial fragmentation

Glutamine is essential for maintaining the TCA cycle in cancer cells yet they undergo glutamine starvation in the core of tumors. Cancer stem cells (CSCs), responsible for tumor recurrence are often found in the nutrient limiting cores. Our study uncovers the molecular basis and cellular links between glutamine deprivation and stemness in the cancer cells. We showed that glutamine is dispensable for the survival of ovarian and colon cancer cells while it is required for their proliferation. Glutamine starvation leads to the metabolic reprogramming in tumor cells with enhanced glycolysis and unaltered oxidative phosphorylation. Production of reactive oxygen species (ROS) in glutamine limiting condition induces MAPK-ERK1/2 signaling pathway to phosphorylate dynamin-related protein-1(DRP1) at Ser616. Moreover, p-DRP1 promotes mitochondrial fragmentation and enhances numbers of CD44 and CD117/CD45 positive CSCs. Besides the established features of cancer stem cells, glutamine deprivation induces perinuclear localization of fragmented mitochondria and reduction in proliferation rate which are usually observed in CSCs. Treatment with glutaminase inhibitor (L-DON) mimics the effects of glutamine starvation without altering cell survival in in vitro as well as in in vivo model. Interestingly, the combinatorial treatment of L-DON with DRP1 inhibitor (MDiVi-1) reduces the stem cell population in tumor tissue in mouse model. Collectively our data suggest that glutamine deficiency in the core of tumors can increase the cancer stem cell population and the combination therapy with MDiVi-1 and L-DON is a useful approach to reduce CSCs population in tumor.