Abstract 4668: Therapeutic efficacy of aryl hydrocarbon receptor agonist in acute myeloid leukemia

Background The presence of leukemic stem cells (LSCs) is known to be a major cause of treatment failure and recurrence in acute myeloid leukemia (AML) patients. Therefore, it is important to develop a treatment method of targeting LSCs. Based on several research, aryl hydrocarbon receptor (AhR) antagonist, StemRegenin 1 (SR1), supports LSC activity. Thus, we speculated that the AhR agonist with the opposite of SR1 could trigger LSC differentiation which may result in the anti-cancer effects. We also hypothesize that the combination of the AhR agonist and ASP2215 targeting FMS-like tyrosine kinase 3(FLT3) mutation, which is known to be present at the LSC level shows the augmented effect on cancer therapy. Here we show the biological significance of AhR and its contribution to leukemic cells, and the therapeutic applicability of this approach. Methods and Results The effects of AhR agonists of 6-formylindolo[3,2-b]carbazole(FICZ), and (2′Z)-Indirubin, and AhR antagonist, SR1 were tested on AML cell lines (MV4-11, MOLM14, HL60, NB4, KG-1) using western blot and flow cytometry. AhR modulation was confirmed by changes in AhR and CYP1B1 protein expression levels at 24hours. . When AML cells were exposed to FICZ for 72hours, surface markers for myeloid differentiation, increased significantly. Mononuclear cells isolated from AML patients’ leukapheresis blood samples(n=5) were cultured with stem culture medium containing growth factors with agonists or antagonist of AhR to determine the effect on LSC differentiation and stem-ness. The cell surface markers Lin-CD34+CD38- represent the stem/progenitor cell fraction were analyzed by FACS, FICZ and indirubin reduces this cell proportion by 2.4-fold 1.8-fold respectively compared to the control. In addition, multipotential progenitors-like LSCs(Lin- CD34+CD38-CD90-CD45RA-) and lymphoid-primed multipotential progenitors-like LSCs (Lin- CD34+CD38-CD90-CD45RA+) was reduced by 2.8 and 2.6-fold in the FICZ treatment group and 1.8 and 2.2-fold in the Indirubin treatment group, respectively. Colony formation assay was performed to verify the effect of AhR modulating on LSC function. FICZ and indirubin reduced the stem-ness of cultured leukemic cells compared with control and SR1. We investigated whether the AhR agonist, FICZ, has an anti-leukemia effect through a cell viability assay. As a single agent, FICZ did not affect AML cells. However, FICZ improves the cytotoxicity of ASP2215, a potent FLT3 inhibitor, in FLT3 mutant A