DNMT3A mutation in AML

Acute myeloid leukemia (AML) is caused by the accumulation of genetic mutations in undifferentiated myeloid precursors, resulting in impaired hematopoiesis and bone marrow failure. One of the common aberration in AML is mutation in the epigenetic modifying gene DNA methyltransferase 3A ( DNMT3A ). DNMT3A is a de novo DNA methyltransferase that has recently gained relevance because of its frequent mutation in a large variety of immature and mature hematologic neoplasms. DNMT3A mutations are early events during cancer development and seem to confer poor prognosis to AML patients making this gene an attractive target for new therapies.

The occurrence of DNMT3A mutation in pre-leukemic cells (pre-LSCs) explains a particular attention to DNMT3A. Much evidence confirmed that early mutations transform stem cells into pre-LSCs. Later, cooperating mutations would arise in cells that already contain the initiating mutations, resulting that pre-LSCs undergo clonal evolution leadingto AML. Last studies have exposed a complex architecture of leukemia, where several genetically diverse subclones coexist with the dominant primary clone. We and other groups have shown that clonal genetic diversity, complex structure of gene crosstalk, multiple mutations, and extensive sub-clonal changes are common for AML.

DNMT3A mutation is a specific alteration with distinct biological properties. It was shown that DNMT3A mutations are present in T-cells and B-cells in diagnostic samples of AML and in T-cells several years later. The evidence from our study confirmed this data. The presence of DNMT3A in both B-and T-cells leadto assumption that mutation had occurred in an early pre-LSCs prior to the acquisition of other genetic events, and could be resistant to chemotherapy.

Recent studies using sequencing of adults without hematological malignancies have identified premalignant genetic changes in leukemia-associated genes, most commonly in DNMT3A, TET2 , and ASXL1. This can suggest the significant role of these mutations in early phase of leukemia development.

We and other groups have demonstrated that pre-LSCs with DNMT3A mutations persist in CR. The loss of correlation between DNMT3A and others mutations in CR after standard chemotherapy could be explained by the presence of mutations in different leukemic subclones. Additionally, we have shown disappearance of DNMT3A mutation in patients with complete donor chimerism after allogeneic stem cell transplantation. This data suggests the removal of leukemic stem cells after transplantation and indicate the importance of this therapy for high risk AML patients.

Induction therapy leads to achieving complete remission (CR) in 52 % to 72 % of AML patients. Although potentially curative therapy (eg, new agents, target therapy) is now available for many patients, about 50 % have relapse after CR. There are many various clonal pathways to relapse, including the addition of novel mutations in pre-LSC and LSC. Recent progress in understanding the pathogenesis of leukemia relapse has revealed many dysregulated molecular pathways that could provide a rational basis for the development of novel targeted therapies.

Recently, the prognostic value of DNMT3A activities via alterations in methylation patterns that have a clear effect on the activity of genespecific promoters was demonstrated. DNMT3A mutations may cause irregular DNA methylation patterns and transcriptional expression levels in genes known to be involved in acute myeloid leukemia pathogenesis. Changes of enzymatic activity affect normal methylation patterns in AML specific genes. Moreover, it was shown that alternative splicing of DNMT3A have epigenetic and functional effects. Specific variant of DNMT3A have a distinct epigenetic effects.

In addition to changes in methylation, specific mutations in epigenetic modifiers sufficiently disrupt interactions with their regulatory components or bindings factors, which could be restored pharmacologically. The ability to rationally direct such changes will require an understanding of mutations in epigenetic regulators. In the last years, DNMT3A and its potentially pathway partners are extensively studied. It was shown that symmetric methylation of histone H4 arginine 3 (H4R3me2s) by the protein arginine methyltransferase (PRMT5) is required for subsequent DNA methylation. The histone-binding protein Cooperator of PRMT5 (COPRS) guides PRMT5. H4R3me2s serves as a direct bindingtarget for the DNMT3A. Furthermore, GFI1 (Growth Factor Independent 1) is one of the targets of PRMT5 in complex processes of epigenetic regulation. We analyzed expression level of DNMT3A, DNMT3B, PRMT5, and GFI1 genes in AML patients and found significant correlation in expression levels of above genes. Moreover, AML patients are characterized by upregulation of DNMT3A, DNMT3B, and PRMT5 genes expression. However, within the AML cohort patients with DNMT3A mutation presented with lower expression of these genes compared to other AML cases. This could be caused by the inactivating mutation. Additionally, our data demonstrate that not only mutations in DNMT3A but also its expression level correlates with outcome of AML.