Acute myeloid leukemia (AML) is characterized by a differentiation block resulting in accumulation of immature myeloid cells. Differentiation therapy, e.g. with all-trans retinoic acid (ATRA) has become a part of standard treatment for the acute promyelocytic leukemia variant of AML. Other agents like cytokines and HDAC inhibitors were shown to enhance differentiation of AML cells, which results in apoptosis induction or re-sensitization to ATRA. However, a differentiation therapy resulting in the restoration of antigen presenting function of AML cells would be a more desirable asset, since such cells will be able to induce or enhance immune response against residual malignant AML cells.

Here, we analyzed the impact of 4SC-202 alone and in combination with different cytokines on differentiation of AML cell lines THP-1, HL-60 and MOLM-13 (AML-M4, -M2, and -M5 class, respectively). Myeloid lineage markers CD11b, CD86, CD14 and HLA-DR were analyzed by flow cytometry and quantitative PCR. Cytokine production was measured using Luminex multiplex system. Furthermore, chromatin immunoprecipitation (ChIP) was performed to assess the direct impact of 4SC-202 on promoter histone acetylation of differentiation genes.

4SC-202 is an orally available clinical stage epigenetic small molecule inhibitor which specifically targets histone deacetylases HDAC class I isoenzymes 1-3 as well as the lysine-specific demethylase LSD1 (KDM1A). 4SC-202 treatment of AML cell lines resulted in a dose-dependent increase of myeloid differentiation genes CD86 and ITGAM (=CD11b) on mRNA and protein level. On the chromatin level, 4SC-202 correspondently induced an upregulation of chromatin activation marks like acetylation of histone H3 lysine 9 and 27 (H3K9ac, H3K27ac) at the promoters of these genes. Interestingly, reference compounds like ATRA, bexarotene, GM-CSF and TNF-α were not as efficacious as 4SC-202 in the induction of differentiation markers in AML cells, whereas IFN-γ strongly induced MHC class II molecules HLA-DR and myeloid lineage marker CD14. Finally, the combination of 4SC-202 and IFN-γ resulted in a strong and complementary induction of differentiation and APC markers CD11b, CD14, CD86 and HLA-DR resulting in a CD86high/HLA-DRhigh phenotype which was able to produce pro-inflammatory cytokines.

In summary, we demonstrate that 4SC-202 induces differentiation of AML cells of different subtypes and thus provide promising preclinical data for applying this novel epigenetic modulator for differentiation therapy of AML. Moreover, the mature APC phenotype induced by the combination of 4SC-202 and IFN-γ may further suggest an application in consolidation treatment of AML to enhance or even elicit a tumor-specific T-cell response against residual malignant AML cells preventing AML recurrence.

Citation Format: Anne Catherine Bretz, Ulrike Parnitzke, Kerstin Kronthaler, Svetlana Hamm. Combination of 4SC-202 and IFN-γ restores mature APC phenotype in AML cells [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2017; 2017 Apr 1-5; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2017;77(13 Suppl):Abstract nr 3088. doi:10.1158/1538-7445.AM2017-3088