Epigenetic Regulation of Lipid Signalling Pathways In Low-Risk MDS Patients During Azacitidine Treatment

Abstract 233

Azacitidine, a DNA methyltransferase inhibitor currently used for the treatment of higher-risk myelodysplastic syndromes (MDS) patients, was shown to delay the evolution into acute myeloid leukemia (AML) and prolong overall survival (Fenaux P et al, Lancet Oncol 2009). In addition, azacitidine has recently been shown to potentially be a feasible and effective treatment even for patients with lower-risk MDS (Musto P et al, Cancer 2010). Lipid signalling pathways are involved in many important biological processes, such as cell growth, differentiation and apoptosis and play a role in the progression of MDS towards AML (Follo MY et al, J Cell Biochem 2010). Moreover, we recently demonstrated that phosphoinositide-phospholipase C beta1 (PI-PLCbeta1) promoter gene is hyper-methylated in higher-risk MDS and that azacitidine treatment can induce an increase in the level of PI-PLCbeta1 splicing variants as well as a down-regulation of activated Akt (Follo MY et al, Leukemia 2008; Follo MY et al, PNAS 2009). In fact, responding patients showed an increase in PI-PLCbeta1 expression in correlation with the therapeutic response, whereas their PI-PLCbeta1 promoter methylation was reduced. Furthermore, the decrease of promoter methylation anticipated the hematologic response, since the variations in PI-PLCbeta1 gene expression were observed prior to the clinical outcome. Stemming from these data, we further investigated the role of inositide signalling pathways during the epigenetic therapy, focusing on the effect of azacitidine on lipid signal transduction pathways in lower-risk MDS patients. The study included 25 patients (IPSS risk: low or intermediate-1) treated with azacitidine (75mg/m² subcutaneous daily for 5 consecutive days every 28 days, for a total of 8 courses). For each patient we followed the effect of azacitidine in correlation to both PI-PLCbeta1 promoter methylation and gene expression, as well as the molecular profile of key molecules involved in the regulation of methylation processes, such as histone deacetylases (HDACs), methyl-CpG binding domain proteins (MBDs), and transcription factors correlated to hematopoietic stem cell differentiation and proliferation. Our results show that 8/25 (34%) of our lower-risk MDS patients, showing hematologic improvements after azacitidine therapy, had a significant increase in PI-PLCbeta1 expression, as compared with the amount of the pre-treatment period, thus confirming the involvement of this molecule in the response to demethylating agents. As for the remaining patients, mainly showing a stable disease, we observed slight increases or almost constant levels of PI-PLCbeta1 expression. Moreover, ongoing analyses are trying to disclose whether lower-risk MDS patients responding to azacitidine show a specific molecular epigenetic profile during the regulation of methylation processes. Taken together, our data suggest a correlation between azacitidine treatment and PI-PLCbeta1 signalling even in lower-risk MDS, thus hinting at a role for PI-PLCbeta1 in the evaluation of patients likely to respond to azacitidine and paving the way for the development of innovative therapeutic strategies in lower-risk MDS patients.