Acute myeloid leukemia (AML) is a fatal disease that is characterized by a rapid expansion of myeloid leukemic blasts with impaired differentiation that accumulate in the bone marrow. The prognosis for AML is generally poor, with a five-year overall survival of around 20% in patients over 60 years old. Current AML treatment strategies, including chemotherapy and hemapoietic stem cell trasplantation, commonly fail to eradicate all leukemia cells. Thus, demand is strong for new therapeutic strategies in AML. We have in this thesis investigated differential expression patterns of cell surface proteins on AML cells and their responsiveness to external signals as a strategy to identify novel AML dependencies.
In article I, we identified Toll-like receptor 1 (TLR1) and TLR2 as being more highly expressed on immature primary human AML cells than on their normal counterparts. Stimulation with the TLR1/TLR2 agonist Pam3CSK4 induced p38 MAPK-dependent apoptosis and NFκB-dependent differentiation of AML cells. Normal hematopoietic stem and progenitor cells were less affected by Pam3CSK4 stimulation. In vivo Pam3CSK4 treatment decreased the leukemia burden in mice. In addition, transplantation of ex vivo Pam3CSK4-stimulated mouse and human AML cells resulted in a prolonged survival of mice relative to controls.
In articles II-IV, we applied high-throughput screening methods to identify novel vulnerabilities in AML. An in vivo pooled shRNA-screen identified CD97 as important for AML cell survival in article II. CD97 suppression resulted in decreased self-renewal and increased apoptosis of AML cells. In addition, mice transplanted with leukemia cells with CD97 silenced survived longer. We found that CD97 was upregluated on a fraction of primary human AML patient samples, especially on NPM1-mutated AML cells.
In article III, we assessed the effect of 114 cytokines on a mixture of murine fluorescently-labeled AML cells and normal cKit+ BM cells. IL4 was identified as a leukemia-selective negative regulator. IL4 stimulation caused decreased proliferation and induced apoptosis of murine and human leukemia cells. IL4 treatment of mice reduced leukemia burden, resulting in a prolonged survival.
In article IV, we combined arrayed molecular barcoding of AML cells with an ex vivo cytokine screen of 114 cytokines to allow for a competitive in vivo read-out of leukemia stem cell activity. We identified TNFSF13 as a positive regulator of AML-initiating cells and found that TNFSF13 is released from normal myeloid cells.
In conclusion, we have in this thesis identified novel AML vulnerabilities, which micht translate into new therapeutic oppertunities. The thesis also contributes to our understanding of AML biology.