Abstract 5382: A DNMT3A-independent hypomethylator phenotype is a unifying epigenetic signature of AML with good risk cytogenetics
Authors: Kelly Andrew D. , Madzo Jozef , Madireddi Priyanka , Kropf Patricia , Good Charly R. , Jelinek Jaroslav , Issa Jean-Pierre J. 
Published: July 2017

Background: Acute myeloid leukemia (AML) causes the most leukemia-related deaths in the United States, and has frequent mutations in epigenetic regulators, including DNMT3A, IDH, and TET2. Such aberrations have been proposed to transform the epigenetic state in cancer, often involving DNA hypomethylation, however, the genomic specificity, causes, and clinical consequences of such methylation changes in AML remain unclear.

Methods: We queried genome-wide CpG methylation using The Cancer Genome Atlas (TCGA) AML samples (n=194) run on Illumina 450k arrays. We used RNA-seq data to study gene expression changes associated with hypomethylator phenotypes (HP). Analysis was done using R.

Results: Genome-wide analysis of CpG sites that are highly methylated in normal blood, and variably methylated in AML (β-value standard deviation in AML &gt; 0.2; average β-value in normal blood &gt; 0.8) revealed two distinct HPs by hierarchical clustering: Good-risk (GR) HP which included favorable cytogenetics, and DNMT-HP, which was enriched for DNMT3A mutations. We refined DNA methylation signatures of each HP cluster by differential methylation analysis and re-classified patients accordingly. Strikingly, all patients with t(8;21), inv(16), or t(15;17) belonged to the GR-HP+ group, suggesting that a common epigenetic thread connects these otherwise disparate genetic aberrations. From a clinical perspective GR-HP+ patients were younger than GR-HP- patients, and had significantly longer overall survival (median OS, years: GR-HP+ = Not reached; GR-HP- = 1.00; P &lt; 0.001). In contrast, DNMT-HP+ cases were statistically equivalent to DNMT-HP- except for an enrichment for higher WBC counts, including no difference in survival (median OS, years: DNMT-HP+ = 0.92; DNMT-HP- = 1.34; P = 0.27). From an epigenetic perspective the two HP clusters harbored distinct DNA methylation changes; although both favored hypomethylation within non-CpG islands relative to CpG islands, the enrichment was more pronounced for DNMT-HP (Odds ratio: hypomethylated CpG islands/hypomethylated non-CpG islands, GR-HP = 0.64; DNMT-HP = 0.18). Genetic analysis revealed that GR-HP+ leukemia had wild-type IDH, DNMT3A, and NPM1 genes. In contrast, DNMT-HP+ AML had significantly more FLT3, NPM1, and DNMT3A mutations compared to DNMT-HP- patients. RNA-seq revealed significant up-regulation of genes in both HP phenotypes (216, and 150 genes for GR-HP and DNMT-HP, respectively at FDR &lt; 0.01 and FC &gt; 2). Pathway analysis of these genes revealed enrichments for ion channels and the complement pathway in DNMT-HP, and for nervous system and developmental genes in GR-HP.

Conclusions: Our data suggest that two HPs exist in AML with unique epigenetic and transcriptomic signatures. The striking association between GR-HP and different favorable cytogenetic changes suggests that a common set of epigenetic features may contribute to improved survival in these patients.

Citation Format: Andrew D. Kelly, Jozef Madzo, Priyanka Madireddi, Patricia Kropf, Charly R. Good, Jaroslav Jelinek, Jean-Pierre J. Issa. A DNMT3A-independent hypomethylator phenotype is a unifying epigenetic signature of AML with good risk cytogenetics [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2017; 2017 Apr 1-5; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2017;77(13 Suppl):Abstract nr 5382. doi:10.1158/1538-7445.AM2017-5382