Session: 602. Myeloid Oncogenesis: Basic: Poster II
Hematology Disease Topics & Pathways:
Research, Fundamental Science, Acute Myeloid Malignancies, AML, Diseases, Myeloid Malignancies, Biological Processes, Study Population, pathogenesis, Animal model
Methods: We crossed inducible Mx1-Cre+ CBFB56M mice with 2 separate cohesin models: mice with a heterozygous germline deletion of Smc3 (Smc3+/-) or mice with inducible deletion of one allele of Rad21 (Rad21+/fl). Following induction with 3 doses of polyinosinic:polycytidylic acid (pIpC) Mx1-Cre+ CBFB56M mice (CBFBΔ) develop AML [Kuo, Cancer Cell 2006]. We injected Mx1-Cre+ CBFB56M mice with and without cohesin gene deletions and CBFB+ controls with 3 doses of pIpC at 3-4 weeks of age and monitored for leukemia development for up to 1 year via monthly complete blood cell counts and peripheral blood immunophenotyping. We humanely euthanized moribund mice and harvested hematologic organs for further analyses.
Results: Over 90% of Mx1-Cre+ CBFBΔ mice developed leukemia regardless of cohesin mutation status whereas no leukemia occurred in CBFB+ controls. Median survival was 15.9 weeks in Mx1-Cre+ CBFBΔ mice, 13.8 weeks in Mx1-Cre+ CBFBΔ Smc3+/- mice, and 19.6 weeks in Mx1-Cre+ CBFBΔ Rad21+/Δ mice (Figure 1; p = 0.11). There was no difference in blood parameters between CBFBΔ groups and all mice with leukemia demonstrated splenomegaly with variable hepatomegaly. Leukemia immunophenotyping was similar between groups with loss of mature myeloid markers CD11b and Ly-6G/C, variable expression of CD71, and high expression of immature myeloid marker CD117. Both LSK cell (Lin-Sca1+CD117+) and myeloid progenitor (Lin-Sca1-CD117+) populations were increased in leukemic mice compared to controls. Mx1-Cre+ CBFBΔ Smc3+/- mice had a significantly lower percentage of myeloid progenitors compared to Mx1-Cre+ CBFBΔ mice (Figure 2). Additional experiments including limiting dilution transplants and high-throughput sequencing are ongoing.
Conclusions: Haploinsufficiency of cohesin genes Smc3 and Rad21 do not prevent leukemia development in a mouse model of inv(16) AML. While loss of Smc3 reduced myeloid progenitors, loss of cohesin genes did not alter disease latency, clinical features, or immunophenotype of inv(16) AML. The reason for lack of cohesin mutations in patients with inv(16) AML is thus unclear. It is possible that the effects of cohesin mutations are redundant with CBFβ-SMMHC, thus there is no selective pressure for acquisition of a cohesin mutation in inv(16) AML. It is also plausible that experimental factors influenced our results. Mutation order can impact leukemogenesis, and it is possible the mutation order used in our study may not reflect the order of acquisition in patients. Finally, there may be other aspects of the chromosomal inversion independent of CBFβ-SMMHC expression that impact cohesin function in inv(16) AML that are not recapitulated in this study. In conclusion, our work suggests that intact cohesin function is not required for the development of inv(16) AML.
Disclosures: Rau: AbbVie Pharmaceuticals: Other: Spouse is employee and stock holder; Servier Pharmaceuticals: Consultancy, Membership on an entity's Board of Directors or advisory committees; Jazz Pharmaceuticals: Consultancy, Membership on an entity's Board of Directors or advisory committees.
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