Unlocking the curative potential of ATRA in non-APL AML: Identification of the mechanisms underlying repression of retinoic acid receptor activity by aberrant lysine modification.

• Applicant: Tino Schenk, Ph.D.
• Subject Area: Hematology, Oncology ; Cell Biology
• Term: since 2015
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 274481353

Survival rates of patients with acute myeloid leukemia (AML) are still unacceptably low. The lack of alternatives to conventional chemotherapy and bone marrow transplantation causes significant morbidity especially among elderly patients. Differentiation therapy represents a more specific and less toxic therapy option. The potential of forced differentiation as therapy is demonstrated by the discovery of all-trans-retinoic acid (ATRA) for the targeted treatment of acute promyelocytic leukemia (APL). However, most other AML subtypes (non-APL AML) are resistant to ATRA. We identified the lysine demethylase LSD1 and the acetyltransferase GCN5 to block ATRA induced differentiation in non-APL AML cells. Combination treatment with ATRA and inhibitors against LSD1 and GCN5 triggered myeloid differentiation in vitro and in vivo.The underlying mechanisms by which LSD1 and GCN5 block the response to ATRA and induction of myeloid differentiation are yet to be fully understood.The goal of this research proposal is to elucidate the interplay of the acetyltransferase GCN5 and the lysine demethylase LSD1 in the dysregulation of the myeloid transcription factors GFI1 and CEBPA and how these processes cause resistance to retinoic acid receptor (RAR)-driven differentiation in AML. First, we will evaluate if GCN5 acts as a downstream regulator of LSD1-mediated stabilization of GFI1/CoREST via repression of CEBPA, controlling myeloid gene expression in an MLL-independent manner. Second, we are going to map direct and indirect RAR target genes in AML and determine if they are directly or indirectly controlled by GFI1/CoREST and CEBPA, regulating the response to ATRA and other retinoids in AML.Third, we will define and target components of the LSD1/GCN5-regulatory pathway, as CEBPA mutations and aberrant activation of RAR-gamma, that prevent an efficient response to the ATRA/LSD1i/GCN5i combination treatment in primary material of different AML subtypes. Together, these experiments will reveal how LSD1 and GCN5 regulate the chromatin-binding of crucial myeloid transcription factors, preventing differentiation of AML. Moreover, the first ever use of UV Laser ChIP-seq in combination with classic ChIP-seq for the detection of transcription factor binding sites will not only enhance the quantity and quality of the detected sites but also allow to distinguish between direct and indirect transcription factor binding. In combination with genome wide gene expression data this will make it possible for the first time to study different functions of directly and indirectly bound factors – a largely unexplored field.Finally, analysis of the treatment response of primary AML samples in combination with their gene expression pattern will reveal signatures that can be used to predict which patients can benefit from differentiation therapy with ATRA, LSD1 and GCN5 inhibitors.

• DFG Programme: Research Grants