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Epigenetic therapy as a novel approach for GFI136N-associated AML

ABSTRACT: Acute myeloid leukemia (AML) is characterized by accumulation of myeloid blast cells in the bone marrow. Despite all efforts, prognosis of AML patients remains poor, warranting new therapeutic approaches. A single nucleotide polymorphism of growth factor independence 1 (GFI1), a hematopoietic transcription factor, generates a protein with an asparagine (GFI136N) instead of a serine at position 36 (GFI136S), which we have previously reported to be associated with de novo AML in humans. Using knock-in mouse strains, in which the endogenous murine Gfi1 coding sequences are substituted by human GFI136N or GFI136S, we found that GFI136N shortened latency and increased incidence of AML in three different, well-established murine models of AML. On a molecular level, the presence of GFI136N was associated with increased acetylation of histone H3 at lysine 9 (H3K9) at Gfi1 target genes in both murine and human samples, contributing to AML development. Since in GFI136N containing leukemic cells Gfi1 target genes have hyperacetylated H3K9, the treatment strategy currently used with histone deacetylases inhibitors (HDACis) might not be beneficial. We show that treatment with an HDACi impeded growth of murine and human cells homozygous for GFI136S, but had a limited effect on cells expressing GFI136N. In contrast, treatment with a histone acetyltransferase inhibitor (HATi) specifically targeted GFI136N-expressing malignant cells while sparing non-malignant cells. These results establish, as a proof of principle, how epigenetic changes in GFI136N-induced AML can be exploited to treat AML and implicate HATi as a new, more effective potential therapeutic strategy for GFI136N AML patients.

ORGANISM(S): Mus musculus

PROVIDER: GSE77073 | GEO | 2016/12/31

SECONDARY ACCESSION(S): PRJNA309396

REPOSITORIES: GEO

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Project description:MDS is characterized by a disturbed function of the myeloid lineage of the hematopoietic system that may transform to AML, a malignant disease of the myeloid compartment. Epigenetic and genetic aberrations contribute to the initiation and progression of MDS/AML. GFI1 is a transcriptional repressor, which regulates expression of its target genes by, among other approaches, recruiting HDACs to its target genes to remove histone 3 lysine 9 (H3K9) acetylation, a marker for active gene expression. Low levels of GFI1 expression and deletion of one GFI1 allele contribute to MDS/AML development in human patients and are associated with a specific gene expression signature and inferior prognosis. To explore the mechanism behind this, we used a mouse strain, which expresses GFI1 only at 5-10% of the normal level (GFI1-Knock-down (KD)). Knock-down of GFI1 or loss of one murine Gfi1 allele reduced latency and increased incidence of AML in different murine models of human MDS/AML development. On the epigenetic level, KD of Gfi1 lead to increased amount of H3K9 acetylation, resulting in increased expression of genes involved in AML development. On a translational level both murine as well as human AML cells with low expression of GFI1 are resistant to standard epigenetic therapy. We show that treatment with histone acetyltransferase inhibitors might be a novel treatment approach for low Gfi1-expressing blast cells. GFI1 has a dose dependent role in myeloid malignancies and is a biomarker for therapeutic intervention. We used microarrays to detail the global programme of gene expression in bone marrow cells of Nup98HoxD13 leucemic mice and identified distinct classes of up-regulated genes during this process. Bone marrow cells of leukemic mice (from KI & KD Nup98HoxD13 mice) were collected for RNA extraction and hybridization on Affymetrix microarrays. We sought to obtain homogeneous populations of leukemic cell population, so we took samples of mice which had the same age.

Project description:Transcriptional repressor Growth factor independence 1 (GFI1) is a key regulator of haematopoiesis. We previously established that the germline variant GFI1-36N promotes acute myeloid leukemia (AML) development, however the mechanism is not full elucidated. Here using multi-omics approach, we show GFI1-36N expression impedes DNA repair in leukemic cells. We demonstrate the presence of GFI1-36N is associated with increased frequency of chromosomal aberrations and mutational burden in murine and human AML cells. In particular, GFI1-36N modulates DNA repair pathways, O6-methylguanine-DNA-methyltransferase (MGMT) and homologous recombination repair (HR). Mechanistically, GFI1-36N exhibits impaired binding to Ndrg1 promoter element compared to GFI1-36S (wild type), causing decreased NDRG1 levels consequently leading to suppression of MGMT expression, imprinted at the transcriptome and proteome, thus leaving the AML cells vulnerable to DNA damaging agents. Targeting MGMT via temozolomide and HR via olaparib caused specifically extensive lethality in in vitro and ex vivo human and AML samples expressing GFI1-36N. Whereas the effects were insignificant on non-malignant GFI1-36S or GFI1-36N cells. Further, mice transplanted with GFI1-36N leukemic cells treated with combination of temozolomide and olaparib had a significantly longer AML-free survival than mice transplanted with GFI1-36S leukemic cells. In summary, we show that GFI1-36N disturbs DNA repair activity via NDRG1-MGMT axis and thus provides critical insights into novel therapeutic option for AML presented with GFI1-36N variant. Key Points Presence of GFI1-36N impedes Homologous DNA and MGMT DNA repair selectively in AML cells via the NDRG1-MGMT axis. Use of temozolomide and olaparib allows selectively targeting GFI1-36N leukemic cells. Introduction Gfi1 is a transcription factor which regulates the development of haematopoietic cells as well as neuronal and intestinal epithelial cells 1-5. We reported that a variant of GFI1, denominated GFI1-36N (characterized by an exchange of serine to asparagine at position 36), has a prevalence of 5-7% in a healthy control population but is found at an increased frequency of 10-15% among MDS and AML patients 6,7. The expression of germline variant GFI1-36N predisposes the carriers to develop de novo AML and MDS and correlates with a poor prognosis 6,7. Recently, we and other showed that malignant cells with GFI1-36N variant have increased H3K9-acetylation at target genes resulting in higher expression of genes required for cell survival and proliferation 8. GFI1 exerts its repressive role by recruiting histone-modifying enzymes (deacetylases HDAC1-3, demethylase LSD1, methyl transferase G9a) and regulates the accessibility of DNA to its target genes such as Hoxa9, Pbx1, Meis1, CSF1 and CSFR1 9-15. We also showed that GFI1 regulates apoptosis through its regulation of p53 in lymphoblastic leukemia 16 and we have demonstrated that GFI1 facilitates DNA repair 17. However, it is not known how these activities are affected in the GFI1-36N variant and whether the ability of GFI1 to regulate DNA repair pathways is maintained and how this might affect the development of myeloid malignancies. In this study, we leveraged multi-omics profiling to gain mechanistic insights into the molecular architecture that drives leukemia in the presence of GFI1-36N. We provide evidence that GFI1-36N interferes with DNA in leukemic myeloid cells, which leads to a higher frequency of genetic aberrations in MDS/AML cells. We also show that GFI1-36N myeloid leukemic cells are more sensitive to targeting MGMT and HR repair deficient cells, which opens a new selective therapeutic window to treat AML/MDS.

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Epigenetic therapy as a novel approach for GFI136N-associated AML

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