PB1808: EPIGENETIC INHIBITOR SCREEN TO IDENTIFY THERAPEUTIC CANDIDATES FOR MNX1-OVEREXPRESSING AML

Topic: 3. Acute myeloid leukemia - Biology & Translational Research Background: Acute myeloid leukemia (AML) is an aggressive hematological malignancy resulting from a block in the differentiation of myeloid progenitors and activation of growth promoting genes. In clinics, hypomethylating agents (HMA) such as 5-azacitidine (AZA) or 2-deoxy-5-azacytidine (decitabine) are routinely used to treat patients with AML. Chromosomal rearrangements in AML can lead to aberrant activation of an oncogene by juxtaposition with an activating enhancer, a phenomenon known as enhancer hijacking. However, there is currently no therapeutic agent known to specifically target oncogenic enhancers in AML. Aims: To find an epigenetic inhibitor which abrogates enhancer hijacking leading to oncogenic overexpression of MNX1 (motor neuron and pancreas homeobox 1) in a subset of AML cases. Methods: 174 different epigenetic inhibitors were screened in the AML cell line GDM-1, which carries a translocation t(6;7) and overexpresses MNX1 due to hijacking of an enhancer from the MYB locus on chromosome 6. Candidate inhibitors were identified by cell viability assays. Western blot, real-time quantitative polymerase chain reaction (RT-qPCR) and microRNA (miRNA) sequencing were then applied to analyze changes of MNX1 and miRNA expression, respectively. Results: Top hits included compounds targeting DNMT, BET, KDM6A/6B, P300/CBP proteins and domains found in the SWI/SNF complex. Treatment with the HMA, decitabine (DAC), resulted in significant reduction of MNX1 expression at both RNA and protein level. DAC treatment induced activation of cancer testis antigens (CTAs), long terminal repeats (LTRs). Hypomethylation after DAC treatment will be confirmed through MiSeq of LINE-1. To investigate the mechanism of DAC-dependent MNX1 downregulation, we performed high throughput sequencing of microRNA (miRNA). However, we could not detect upregulated miRNAs upon DAC treatment precluding the contribution of miRNAs on MNX1 downregulation. Summary/Conclusion: We screened 174 epigenetic inhibitors in the AML cell line GDM-1 and showed that DAC treatment significantly reduces MNX1 expression, which is activated by enhancer hijacking. The contribution of activated miRNAs targeting MNX1 and DAC treatment mediated disruption of the topologically associated domain, which allows the enhancer-promoter interaction, are investigated as possible mechanisms for MNX1 expression. Further candidate compound validation will make use of a GDM-1 derivative control cell line without t(6;7) translocation but with ectopic MNX1 expression. Epigenetic inhibitor screening will be repeated in this isogenic cell line. The epigenetic inhibitor, which will not lead to reduction in cell viability of the isogenic line but result in a significant reduction in cell viability of wild type GDM1, will be identified as the inhibitor that disrupts the enhancer-promoter interactions driving oncogenic MNX1 overexpression. This inhibitor may offer clinical benefit in other MNX1-dependent AMLs with enhancer hijacking events.Keywords: Acute myeloid leukemia, decitabine, Epigenetic, Screening