Abstract 4793: The M2 isoform of pyruvate kinase (PKM2) contributes to leukemia stem cell persistence by maintaining oxidative homeostasis and promoting glycolysis

Abstract

Abstract Selective expression of PKM2 and its unique ability to switch between states of enzymatic activity are exploited by proliferating cells; limiting the generation of pyruvate available for oxidative phosphorylation and in turn providing a robust store of glucose carbons for the generation of daughter cells. Tumor cells rely on PKM2 to maintain a similar metabolic state that provides a growth advantage even in the presence of oxygen–a phenomenon known as aerobic glycolysis. It is the inactive non-tetramer of PKM2 that not only contributes to the build up of biosynthetic precursors but also limits the production of mitochondrial reactive oxygen species (ROS) and even scavenges ROS directly (Anastasiou et al. 2011). ROS is important for the maintenance of normal hematopoietic stem cells (HSCs) as well as their malignant counter parts, leukemia stem cells (LSCs) (Ito et al. 2004). Both HSCs and LSCs have been characterized as having low levels of endogenous ROS and decreased rates of oxidative metabolism (Lagadinou et al. 2013). In acute myeloid leukemia (AML), therapy has been limited by the persistence of LSCs that endure chemotherapy and recapitulate disease. Since HSCs rely mainly on glucose metabolism in the hypoxic bone marrow (Suda et al. 2011), we hypothesize that PKM2 may be important in LSC maintenance by influencing cellular redox state. We found using western blot analysis that primitive CD34+ AML cells show no significant difference in total PKM2 levels relative to more mature CD34- cells. However, we found CD34+ cells had significantly increased levels of phosphorylated PKM2 at Tyr105, which has been reported to promote the less active non-tetramer (Hitosugi et al. 2009). Importantly, fluorometric assays measuring PKM2 activity in AML cells separated by CD34 expression revealed decreased PKM2 activity in CD34+ cells compared to CD34-. These data suggest that LSCs may require even lower PKM2 activity than more mature proliferating AML cells to limit the accumulation of damaging ROS while remaining primed for proliferation with a reservoir of biomass. As LSCs give rise to more mature malignant blasts that are exposed to oxygen in the periphery, aberrant growth signaling as well as exposure to inflammatory cytokines antagonize apoptosis and continue to promote aerobic glycolysis (Bauer et al. 2004) for sustained growth. To determine the role of proliferation signals on PKM2, we stimulated primary AML cells with interleukin-6 and found a significant increase in PKM2 nuclear localization, suggesting that its transcriptional activity also contributes to the proliferation of leukemia. Our data suggests that influencing the metabolic state of AML cells by altering PKM2 activity using small molecules could be a novel way to disrupt LSC homeostasis while also impairing growth in more differentiated AML cells for therapy. Citation Format: Eric M. Sturgill, Monica L. Guzman. The M2 isoform of pyruvate kinase (PKM2) contributes to leukemia stem cell persistence by maintaining oxidative homeostasis and promoting glycolysis. [abstract]. In: Proceedings of the 105th Annual Meeting of the American Association for Cancer Research; 2014 Apr 5-9; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2014;74(19 Suppl):Abstract nr 4793. doi:10.1158/1538-7445.AM2014-4793