Graduation Date

Spring 5-4-2019

Document Type

Dissertation

Degree Name

Doctor of Philosophy (PhD)

Programs

Biochemistry & Molecular Biology

First Advisor

R. Katherine Hyde, Ph.D.

Abstract

Inversion of chromosome 16 [inv(16)] acute myeloid leukemia (AML) generates a fusion gene CBFB-MYH11. Approximately half of inv(16) AML patients eventually relapse mainly due to the existence of leukemia stem cells (LSCs). Previous work using a Cbfb-MYH11 knockin mouse model showed that the LSCs are enriched within CSF2RB- population. Another gene upregulated by Cbfb-MYH11 encodes the cytokine receptor IL1RL1. Using Cbfb-MYH11 knockin mice, we showed that LSCs exist in multiple sub-populations defined by their immunophenotype, and IL1RL1 is expressed by cell populations with high LSC activity. We also found that treatment of IL-33, the ligand for IL1RL1, promoted cell survival in vitro. Our results imply that therapeutic approaches based on a single cell surface molecule antigen may not work against the entire, diverse population of LSCs.

The CBFB-MYH11 fusion gene is expressed in all LSCs but not in normal cells. Thus, targeting CBFB-MYH11 may have potential as a therapeutic strategy. Here, we used a new knockin mouse model allowing for deletion of Cbfb-MYH11 after leukemic transformation and demonstrated that the loss of the Cbfb-MYH11 caused apoptosis and decreased colony-forming ability in vitro. By transducing leukemia cells from Cbfb-MYH11 knockin mice with doxycycline inducible short hairpin RNA (shRNA) targeting MYH11 and transplanting into recipient mice. We found that Cbfb-MYH11 knockdown significantly reduced the leukemic burden in vivo. Thus, our data indicates that Cbfb-MYH11 is required for the survival of inv(16) leukemia cells.

Given the role of Cbfb-MYH11 in leukemia cell survival, it is important to develop targeted therapies to inhibit the fusion gene activity. In collaboration with Dr. David Oupicky’s laboratory, we tested a polymeric CXCR4 antagonist (PCX) which can deliver short interfering RNA (siRNA). We found that PCX exerts a cytotoxic effect in leukemia cells and successfully delivered siRNAs into leukemia cells, as well as caused apoptosis. Our results imply that using PCX to deliver siRNAs targeting key genes is a potential strategy for the treatment of AML. Overall, our results provide insights into promising molecular therapeutic agents for treating AML patients in the future.

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