PP2A-activating Drugs Enhance FLT3 Inhibitor Efficacy through AKT Inhibition–Dependent GSK-3β–Mediated c-Myc and Pim-1 Proteasomal Degradation
Abstract
Fms-like tyrosine-like kinase 3 internal tandem duplication (FLT3-ITD) is present in acute myeloid leukemia (AML) in 30% of patients and is associated with short disease-free survival. FLT3 inhibitor efficacy is limited and transient but may be enhanced by multitargeting of FLT3-ITD signaling pathways. FLT3-ITD drives both STAT5-dependent transcription of oncogenic Pim-1 kinase and inactivation of the tumor-suppressor protein phosphatase 2A (PP2A), and FLT3-ITD, Pim-1, and PP2A all regulate the c-Myc oncogene. We studied mechanisms of action of cotreatment of FLT3-ITD–expressing cells with FLT3 inhibitors and PP2A-activating drugs (PADs), which are in development. PADs, including FTY720 and DT-061, enhanced FLT3 inhibitor growth suppression and apoptosis induction in FLT3-ITD–expressing cell lines and primary AML cells in vitro and MV4-11 growth suppression in vivo. PAD and FLT3 inhibitor cotreatment independently downregulated c-Myc and Pim-1 protein through enhanced proteasomal degradation. c-Myc and Pim-1 downregulation was preceded by AKT inactivation, did not occur in cells expressing myristoylated (constitutively active) AKT1, and could be induced by AKT inhibition. AKT inactivation resulted in activation of GSK-3β, and GSK-3β inhibition blocked downregulation of both c-Myc and Pim-1 by PAD and FLT3 inhibitor cotreatment. GSK-3β activation increased c-Myc proteasomal degradation through c-Myc phosphorylation on T58; infection with c-Myc with T58A substitution, preventing phosphorylation, blocked downregulation of c-Myc by PAD and FLT3 inhibitor cotreatment. GSK-3β also phosphorylated Pim-1L/Pim-1S on S95/S4. Thus, PADs enhance efficacy of FLT3 inhibitors in FLT3-ITD–expressing cells through a novel mechanism involving AKT inhibition–dependent GSK-3β–mediated increased c-Myc and Pim-1 proteasomal degradation.
Document Details
- Document Type
- Pub Defense Publication
- Publication Date
- Feb 10, 2021
- Source ID
- 10.1158/1535-7163.mct-20-0663
Entities
People
- Christopher M. Bailey
- Danilo Perrotti
- Goutham Narla
- Jaya Sangodkar
- Jonelle K. Lee
- Maria R. Baer
- Mario Scarpa
- Prerna Singh
- Rena G. Lapidus
- Sandrine Niyongere
- Shivani Kapoor
- Yin Wang
Organizations
- National Heart, Lung, and Blood Institute
- National Institutes of Health
- United States Department of Veterans Affairs
- University of Maryland
- University of Maryland School of Medicine
- University of Michigan