Mutations Of Genes Regulating DNA Methylation Are Common In MLL Partial Tandem Duplication AML and DNMT3A Mutations Are Associated With Adverse Outcome

Abnormalities of genes regulating DNA methylation have been described in acute myeloid leukemia (AML). MLL protein is a transcriptional regulator and governs proper hematopoiesis through its histone methyltransferase activity. AML with partial tandem duplication of MLL (MLL-PTD) was associated with an unfavorable prognosis. The cooperating roles of MLL-PTD with other mutated genes regulating DNA methylation have not been comprehensively studied in AML. We aimed to determine the prevalence and clinical impact of mutations of DNA methylation regulators in AML with MLL-PTD.

Bone marrow samples from 98 AML patients with MLL-PTD were analyzed for gene mutations of TET2, DNMT3A, IDH1 and IDH2. MLL-PTD was screened by RT-PCR and confirmed by real-time quantitative PCR assays. The mutational analysis was performed with PCR assays followed by direct sequencing for TET2 (whole coding exons 3–11) and IDH1/2 (hotspots exon 4). For the detection of DNMT3A mutations, the PCR products amplified for entire coding exons 2 to 23 were first screened with denaturing high-performance liquid chromatography followed by direct sequencing for the abnormal profiles.

The frequency of TET2, IDH1, IDH2 and DNMT3A mutations in AML patients with MLL-PTD was 17.0% (16/94), 10.2% (10/98), 18.4% (18/98), and 31.6% (31/98), respectively. Taken together, 61.1% of patients with MLL-PTD had at least one mutated gene of DNA methylation regulators. TET2, IDH1 and IDH2 mutations were mutually exclusive with each other whereas DNMT3A mutations frequently co-existed with other DNA methylation modifiers:TET2 (n=8), IDH1 (n=5) and IDH2 (n=4). No differences were observed between the mutation status of the DNA methylation modifiers and clinico-hematologic features of patients with MLL-PTD except that TET2 (P=0.012) and DNMT3A (P=0.024) mutations were associated with older age. Of the 55 MLL-PTD patients who received standard chemotherapy, IDH2 mutation was associated with a lower complete remission rate (25.0% vs 67.8%, P=0.018), while DNMT3A mutations conferred an inferior event-free survival (0.0 vs 6.8 months, P=0.027) and overall survival (6.0 vs 11.5 months, P=0.032). In multivariate analysis, older age (P=0.008) and DNMT3A mutations (P=0.049) were independent adverse factors for overall survival. The crosstalk between MLL-PTD and genes involving DNA methylation in the leukemogenesis of AML warrants further investigation.

Gene mutations involving DNA methylation frequently co-existed in AML patients with MLL-PTD, especially DNMT3A mutations which conferred a poor outcome. Our study demonstrated the importance of genetic alterations involving DNA methylation in the pathogenesis of MLL-PTD AML and provided potential epigenetic-targeted therapy.

The work was supported by NHRI-EX93-9011SL, NSC95-2314-B-195-001, NSC96-2314-B-195-006-MY3, NSC97-2314-B-182-011-MY3 and MMH-E-101-09.

No relevant conflicts of interest to declare.