Submitted July 15, 2008
Accepted November 30, 2008
BH3-only protein Bim more critical than Puma in tyrosine kinase inhibitor-induced apoptosis of human leukemic cells and transduced hematopoietic progenitors carrying oncogenic FLT3
Amanda Nordigarden, Maria Kraft, Pernilla Eliasson, Verena Labi, Eric W-F Lam, Andreas Villunger, and Jan-Ingvar Jonsson*
Department of Clinical and Experimental Medicine, Linkoping University, Linkoping, Sweden
Division of Developmental Immunology, Biocenter, Innsbruck Medical University, Innsbruck, Austria
Cancer Research-UK Labs, Department of Oncology, Imperial College London, Hammersmith Hospital Campus, London, United Kingdom
* Corresponding author; email: jan-ingvar.jonsson{at}liu.se.
Constitutively activating internal tandem duplications (ITD) of FLT3 are the most common mutations in acute myeloid leukemia (AML) and correlate with poor prognosis. Receptor tyrosine kinase inhibitors targeting FLT3 have developed as attractive treatment options. Because relapses occur after initial responses, identification of FLT3-ITD-mediated signaling events are important to facilitate novel therapeutic interventions. Here, we have determined the growth-inhibitory and proapototic mechanisms of two small molecule inhibitors of FLT3, AG1295 or PKC412, in hematopoietic progenitor cells, human leukemic cell lines, and primary AML cells expressing FLT3-ITD. Inactivation of the PI3-kinase pathway, but not of Ras-MAP kinase signaling, was essential to elicit cytotoxic responses. Both compounds induced upregulation of proapoptotic BH3-only proteins Bim and Puma, and subsequent cell death. However, only silencing of Bim, or its direct transcriptional activator FOXO3a, abrogated apoptosis efficiently. Similar findings were made in bone marrow cells from gene-targeted mice lacking Bim and/or Puma infected with FLT3-ITD and treated with inhibitor, where loss of Puma only provided transient protection from apoptosis but loss of Bim preserved clonal survival upon FLT3-ITD-inhibition.
