Assessment of ATRX expression in patients with myelodysplastic syndromes treated with decitabine

Abstract

Treatment with one of the DNA methyltransferase inhibitors (DNMTIs, “hypomethylating agents”), azacitidine or decitabine, is now considered standard care for patients with higherrisk myelodysplastic syndromes (MDS) (1) – especially since results were released from the AZA-001 trial (2), which demonstrated a 9-month survival advantage with azacitidine therapy compared to supportive care. However, many patients with MDS do not respond to treatment with DNMTIs as they are currently used, and adverse events are common. It is desirable to be able to predict a priori which patients are most likely to benefit from DNMTI therapy, in order to spare patients unlikely to respond from the risks and cost of treatment, but there are currently no well-established molecular methods for DNMTI response prediction.(3) ATRX is an X-encoded chromatin-associated protein with an evolutionarily conserved Nterminal DNA methyltransferase (DNMT3-like) domain.(4) Germline mutations in ATRX cause a mental retardation-dysmorphology syndrome often associated with mild alpha thalassemia, which gave the gene its name (ATR-X syndrome: alpha thalassemia, retardation, X-linked) (5); in contrast, somatic point mutations in ATRX have been linked to acquired alpha thalassemia arising in the context of MDS, which may be present in as many as 8% of patients. (6-8) Germline mutations in ATRX are associated with widespread and diverse DNA methylation abnormalities across the genome.(9) Recent evidence suggests that the ATRX protein also has an important role in chromosome dynamics during mitosis, as ATRX-depleted cells exhibit defective sister chromatid cohesion and congression at the metaphase plate, as well as abnormal chromosome alignment. (10,11) Circumstantial evidence for a role of ATRX in neoplasia is increasing. In an array-based gene expression profiling study of 42 children with acute myeloid leukemia (AML) associated with somatic FLT3 mutations, the expression ratio of the transcription factor RUNX3 (formerly AML2) to ATRX predicted event-free survival (EFS).(12) In a subsequent study of 132 adults with de novo AML by another investigative group, low ATRX expression correlated with highrisk karyotype and poor clinical outcome.(13) Altered ATRX expression levels have also been reported in gene expression profiling experiments using prostate cancer primary cells (14), esophageal squamous cell carcinoma cell lines (15), chronic lymphocytic leukemia primary cells (Neil Kay, personal communication October 2007), and irradiated breast cancer cell lines (16).