DNA methylation as a pathogenic event and as a therapeutic target in AML.

DNA methylation and its influence on gene expression are key in understanding cancer pathogenesis. Even though it is becoming clear that DNA methylation strongly interacts with other components of the epigenetic machinery such as histone modifications, aberrant DNA methylation can still be regarded as a crucial hallmark of cancer by itself. In Acute Myeloid Leukemia (AML), aberrations of DNA methylation also rank among the most frequent alterations observed. Recent studies revealed that specific patterns of DNA methylation characterize AML and help to distinguish AML subtypes. The contribution of this epigenetic dysregulation to leukemogenesis in AML is currently unclear. However, interactions between mutated transcription factors and epigenetic networks have already been shown to be partially responsible for leukemic transformation, for e.g. in acute promyelocytic leukemia (APL). Also, direct mutations in the epigenetic master regulators EZH2 and DNMT3A were recently identified in AML and in diseases leading to secondary leukemia. These findings strengthen the view that dysregulated epigenetic networks can induce AML. Correspondingly, epigenetic therapies e.g. hypomethylating drugs show significant activity in AML. While benefit is observed in many patients, DNA hypomethylating therapy by itself is not curative. Furthermore, it is not clear whether the drugs' effects are solely epigenetic in nature since in vitro studies suggest different mechanisms of action. Current clinical trials aim to improve efficacy of DNA hypomethylating drugs for e.g. by combination with standard AML chemotherapy. Taken together, targeting the epigenetic machinery seems to be the way towards more effective therapies in AML.