Abstract 190: p53 target gene expression, DNA hypomethylation, and clinical response in MDS patients undergoing decitabine therapy

Proceedings: AACR 101st Annual Meeting 2010‐‐ Apr 17‐21, 2010; Washington, DC The myelodysplastic syndromes (MDS) are a heterogeneous group of blood disorders characterized by peripheral cytopenias, a cellular bone marrow with dysplasia and increased intramedullary apoptosis, and are associated with risk of progression to acute myelogenous leukemia (AML). MDS are often fatal due to complications from cytopenias and/or progression to AML. DNA methyltransferase inhibitors (DNMTi), including 5-azacytidine and 5-aza-2’-deoxycytidine (decitabine) have recently assumed a major role in the clinical management of MDS, and are two of only three FDA-approved treatments for these disorders. The mechanistic basis for the activity of DNMTi in MDS is unclear. We recently reported that decitabine treatment induces the expression of p53-inducible ribonucleotide reductase p53R2/RRM2B in tumor cell lines and MDS patient bone marrow (Link et al., Cancer Research 68; 9358-9366, 2008). Importantly, p53R2 induction was independent of DNA hypomethylation at its promoter region, and the level of p53R2 induction correlated with clinical response in a cohort of 13 patients. These data suggest that important pharmacodynamic responses to DNMTi may be associated with DNA damage and/or p53 activation. To better understand the overall nature of the molecular responses occurring in the bone marrow of MDS patients treated with decitabine, in the current study we examined a variety of pharmacodynamic endpoints including: p53 target gene expression, global DNA methylation, tumor antigen gene expression and methylation, and tumor suppressor gene expression. Specifically, we measured the expression of three classical p53 target genes (p21, GADD45-α, NOXA), LINE-1 repetitive element methylation, the expression and methylation of cancer-germline (CG) antigens including MAGE-A1, NY-ESO-1, XAGE-1, and CTCFL/BORIS, and the expression of the tumor suppressor genes (TSGs) p15INK4b and PDLIM4. Our data reveal that decitabine treatment causes robust induction of p53 target genes in MDS patient bone marrow, which coincides with LINE-1 hypomethylation and clinical responses. In contrast, while CG antigen genes showed some evidence for DNA hypomethylation post-therapy, this did not coincide with CG antigen gene induction. Surprisingly, TSGs were also not induced by decitabine therapy in MDS patient bone marrow. Ongoing studies seek to define p53 mutational status in MDS patients and to determine how this relates to p53 target gene induction and/or clinical response. In summary, our data reveal a connection between p53 target gene activation, global DNA hypomethylation, and clinical response in MDS patients undergoing decitabine therapy. Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 101st Annual Meeting of the American Association for Cancer Research; 2010 Apr 17-21; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2010;70(8 Suppl):Abstract nr 190.