Abstract 4668: Therapeutic efficacy of aryl hydrocarbon receptor agonist in acute myeloid leukemia
Authors: Han Hee Joo , Shin Dong-Yeop , Yoon Sung-Soo 
Published: August 2019

Abstract
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 AML cells. And more, the combination enhances the effect of ASP2215 on cancer cell signaling pathways AKT-mTOR and MEK-ERK.
Conclusion
We found that FICZ, an AhR agonist not only results in the LSCs differentiation, but also enhances the inhibitory effect of ASP2215 on cancer cell survival through the AKT-mTOR and MEK-ERK signaling. This cross-talk has the multiple meaning on cancer therapy in that it can simultaneously target cancer cells as well as LSCs.
Citation Format: Hee Joo Han, Dong-Yeop Shin, Sung-Soo Yoon. Therapeutic efficacy of aryl hydrocarbon receptor agonist in acute myeloid leukemia [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2019; 2019 Mar 29-Apr 3; Atlanta, GA. Philadelphia (PA): AACR; Cancer Res 2019;79(13 Suppl):Abstract nr 4668.