Abstract 145: Pharmacologic inhibition of SIAH2 stabilizes DYRK2 and inhibits survival and self-renewal in chronic myeloid leukemia (CML) leukemic stem cells

Leukemia stem cells (LSCs) are a rare population able to sustain and recapitulate leukemia through a poorly understood mechanism of self-renewal. Because more than half of patients relapse after the cessation of TKI therapy, it is clear that a cure is not possible with TKIs alone, and LSC-specific drugs are urgently needed to simultaneously eliminate bulk leukemia with TKIs and LSCs. Here we report that KLF4 promotes disease progression in chronic myeloid leukemia (CML) by repressing an inhibitory mechanism in LSCs that can be activated with small molecules. Deletion of the Klf4 gene severely abrogated maintenance of BCR-ABL(p210)-induced CML by impairing survival and self-renewal in LSCs whereas increased self-renewal was observed in hematopoietic stem cells during serial transplantation. Mechanistically, KLF4 represses the Dyrk2 gene and thus loss-of-KLF4 resulted in elevated levels of the DYRK2 kinase in LSCs, which was associated with p53-mediated apoptosis and inhibition of self-renewal through depletion of c-Myc protein. Supporting this model, stabilization of DYRK2 protein, by inhibiting the ubiquitin E3 ligase SIAH2 with vitamin K3, promoted apoptosis in a panel of CML cell lines (K562, KU-812, and KCL-22) by inducing DYRK2 expression. Knocking out the DYRK2 gene in K562 cells by Cas9/CRISPR abrogated cytotoxicity induced by vitamin K3 and the presence of p53 significantly lowered IC50. In vivo treatment of CML mice diminished the number of LSCs evaluated in secondary transplants. In humans, vitamin K3 induced apoptosis in bone marrow cells from CML patients but not in healthy individuals by inducing DYRK2, p53 phosphorylation, and c-Myc depletion; furthermore, vitamin K3 abrogated capacity of CD34 + cells to generate colonies in methylcellulose only in CML. Altogether, our results suggest that DYRK2 is a molecular checkpoint controlling both p53 and c-Myc mediated regulation of survival and self-renewal in CML LSCs that can be activated pharmacologically. Citation Format: Chun Shik Park, Ye Shen, Andrew Lewis, Koramit Suppipat, Monica Puppi, Julie Tomolonis, Taylor Chen, Paul Pang, Toni-Ann Mistretta, Leyuan Ma, Michael Green, Rachel Rau, Daniel Lacorazza. Pharmacologic inhibition of SIAH2 stabilizes DYRK2 and inhibits survival and self-renewal in chronic myeloid leukemia (CML) leukemic stem cells [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2018; 2018 Apr 14-18; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2018;78(13 Suppl):Abstract nr 145.