Abstract
Background. In human neoplasia, aberrant methylation of CpG islands leads to gene silencing, and has an essential role in tumorigenesis through down regulation of tumor suppressor genes. A phase III randomized study comparing a DNA methyltransferase inhibitor; decitabine (DAC) versus supportive care has been completed recently in myelodysplastic syndrome (MDS) patients. The purpose of our study was to determine the prognostic significance of CpG islands methylation in these patients, to test the significance of methylation events in predicting drug response, and to explore the correlation between modulation of DNA methylation and response to DAC.
Methods. DNA was extracted from blood and bone marrow of 89 patients before treatment (baseline) and also from a subset of 34 patients at multiple time-points and modified by bisulfite. In this study, we selected 24 CpG islands based on previous studies and ongoing efforts to identify methylated genes by MCA/RDA. For 14 genes, very low levels of methylation were detected in an initial group of 20 MDS patients, and we excluded them from further study. We then analyzed the methylation status of a total of 10 genes in all the samples. Bisulfite-PCR followed by Pyrosequencing was used to analyze DNA methylation levels of each gene. For statistical analysis, methylation levels of each gene were normalized by a Z score method, and each patient was assigned a methylation “score” based on the sum of Z scores for all genes, or a selected group of genes. Samples before and after treatment were available for 20 patients on supportive care (SC) and 14 patients on DAC, and methylation levles at each time point were averaged across the 10 genes.
Results. Methylation frequencies of RIL, PGRA, PGRB, Olig2, p15, CDH13, NPM2, ECAD, NOR1 and ER ranged from 7% to 70% in MDS patients at baseline. Methylation levels of all these genes were significantly linked, suggesting concurrent methylation affected by CpG Island Methylator Phenotype (CIMP). There was no association between methylation by Z scores with age, IPSS, or cytogenetics. There was no correlation between baseline methylation and response to DAC therapy. By univariate analysis, methylation was significantly associated with both shortened overall survival and progression-free survival. In multivariate analysis, IPSS score and methylation were independent predictors of progression free survival, and methylation was the only independent predictor of overall survival. Methylation changes were then analyzed for correlation with response in 34 patients (Decitabine arm: 2 CR, 3 PR, 4HI, 4 SD, 1 PD; supportive care arm: 2 HI, 6 SD, 12 PD) at multiple time-points. At the latest available time-point (>4 months at therapy), methylation decreased by 11.2% in patients in DAC but increased by 20.1% in patients in SC. A greater decrease was observed in patients with CR or PR (40.6+/− 15.7%) compared to HI (9.8+/− 13.2%). Methylation increased by 15.4% in patients with SD and 27.2% in patients with PD.
Conclusions. Concordant methylation of multiple genes suggests the existence of a CpG island methylator phenotype in MDS. This methylation was associated with poor prognosis and risk of leukemia transformation. Decitabine therapy was associated with reduced methylation over time, which was associated with clinical responses.
The Methylation of SDC2 and TFPI2 Defined Three Methylator Phenotypes of Colorectal Cancer
