Core binding factor (CBF) leukemias, those with translocations or inversions that affect transcription factor genes RUNX1 or CBFB, account for approximately 24% of adult acute myeloid leukemia (AML) and 25% of pediatric acute lymphocytic leukemia. Our section has been developing clinically relevant transgenic mouse models to study human CBF leukemia. We previously generated mice that express the human CBFB-MYH11 fusion gene, which is one of the most common causes of AML. During the last several years we have been generating transgenic mice that harbor CBFB-MYH11 and other common mutations in AML, such as activating mutations of KIT and internal tandem duplication of FLT3 (FLT3-ITD), to demonstrate and analyze their cooperation during leukemogenesis. In the past year we generated data demonstrating cooperation between CBFB-MYH11 and the mutated KIT gene for leukemogenesis in a mouse model. KIT mutations are among the most common secondary mutations in CBF AML and are associated with poor prognosis. It is therefore important to verify that KIT mutations cooperate with CBFB-MYH11 for leukemogenesis. In this study, we transduced wild type (WT) and conditional Cbfb-MYH11 knockin (KI) mouse bone marrow (BM) cells with KIT D816V/Y mutations, and the transduced cells were then transplanted to adult healthy recipient mice. We found that 60% and 80% of mice transplanted with KI BM cells expressing D816V or D816Y KIT, respectively, died from leukemia within 9 months, while no control mice did. Results from limiting dilution transplantations indicate higher frequencies of leukemia initiating cells in KIT-induced leukemia. Signaling pathway analysis revealed that p44/42 MAPK and Stat3, but not AKT and Stat5, were strongly phosphorylated in the leukemia cells. Finally, leukemia cells carrying KIT D816 mutations were sensitive to the kinase inhibitor PKC412. Our data provide clear evidence for cooperation between mutated KIT and CBFB-MYH11 during leukemogenesis. These findings were published recently (Zhao et al., Blood 119:1511-21, 2012). Current treatments for CBF leukemias are associated with significant morbidity and mortality, with a 5-year survival rate of approximately 50%. We hypothesize that the interaction between RUNX1 and CBFβ, the proteins encoded by RUNX1 and CBFB respectively, is critical for CBF leukemia and can be targeted for drug development. We developed high-throughput screen methods to quantify the RUNX1-CBFβinteraction and screened a library collection of 243,398 compounds. Ro5-3335, a benzodiazepine identified from the screen, was able to interact with RUNX1 and CBFβdirectly, repress RUNX1/CBFB-dependent transactivation in reporter assays, and repress runx1-dependent hematopoiesis in zebrafish embryos. Ro5-3335 preferentially killed human CBF leukemia cell lines, rescued pre-leukemic phenotype in a RUNX1-ETO (another CBF fusion gene in leukemia) transgenic zebrafish, and reduced leukemia burden in a mouse CBFB-MYH11 leukemia model. Our data thus confirmed that RUNX1-CBFβinteraction can be targeted for leukemia treatment and we have identified a promising lead compound for this purpose. These results have been published recently (Cunningham et al., Proc Natl Acad Sci USA 109:14592-7, 2012). A new direction of the lab is the development of human induced pluripotent stem cells (iPSCs) to model human disease. The utility of iPSCs as models to study diseases and as sources for cell therapy depends on the integrity of their genomes. Despite recent publications of DNA sequence variations in the iPSCs, the true scope of such changes for the entire genome is not clear. We conducted the first whole-genome sequencing of three human iPSC lines, which were derived from two cell types of an adult donor by episomal vectors. The vector sequence was not detected in the genomes of the deeply sequenced iPSC lines. We identified 1058-1808 heterozygous single nucleotide variants (SNVs), but no copy number variants, in each iPSC line. Six to twelve of these SNVs were within coding regions in each iPSC line, but 50% of them are synonymous changes and the remaining are not selectively enriched for known genes associated with cancers or other diseases. Our data thus suggest that episome-mediated reprogramming is not inherently mutagenic during iPSC induction. These findings have been published earlier this year (Cheng et al., Cell Stem Cell, 10:337-44, 2012).
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