PI-PLCBETA1 GENE METHYLATION AND EXPRESSION AS A RELIABLE AND DYNAMIC MARKER OF CLINICAL RESPONSE TO 5-AZACYTIDINE IN PATIENTS WITH LOW-RISK MYELODYSPLASTIC SYNDROMES

Hypomethylating agents, such as 5-Azacytidine (AZA), significantly modified the therapeutic approach to MDS, primarily in older patients with higher risk disease for whom intensive chemotherapy and allogeneic stem cell transplantation are not an option. In low-risk MDS, 5- AZA aims to reduce transfusion dependency, improve quality of life and hopefully the survival, but it is still unclear if this therapeutic approach would be cost-effective. At a molecular level, the mechanisms underlying the effect of epigenetic therapy are not completely understood, although it is well known that DNA methyltransferase inhibitors can induce the expression of Phosphoinositide-Phospholipase C (PIPLC) beta1 in high-risk MDS. Here, we prospectively investigated the efficacy and safety of AZA in low-risk MDS patients. AZA was administered at a lower intensity schedule, that is 75 mg/sqm/day subcutaneous for 5 days every 28, for a total of 8 cycles, and response was assessed at the 4th and 8th cycle of AZA. Moreover, PI-PLCbeta1 promoter methylation and gene expression levels were quantified before and after each cycle of 5-AZA. The study included 32 patients, and 26 cases completed 8 cycles of AZA. ORR was 47% (15/32) on intention to treat and 58% (15/26) for patients completing the treatment program. In this latter group, 5 (19%) cases achieved CR and 10 (38%) had HI, according to the IWG criteria. Interestingly, three patients have maintained their HI after 37, 34 and 33 months without other treatments. At a molecular level, although baseline PI-PLCbeta1 levels were not correlated to clinical response, 5d-AZA induced a statistically significant decrease in PI-PLCbeta1 promoter methylation in 14/15 responders, which corresponded to a significant increase in PI-PLCbeta1 mRNA. In 9/14 (64%) responsive patients, the first molecular increase in PI-PLCbeta1 level was observed between the 3rd and 4th cycle, therefore anticipating the clinical evaluation. In addition, 8 cases showed a loss of the response after the end of therapy (8th cycle) and these cases displayed a significant reduction of PI-PLCbeta1 levels, below the pre-treatment values, already before the clinical loss of the response. Taken together, our results show that 5d-AZA is safe and effective in a proportion of low risk MDS patients. PI-PLCbeta1 gene expression is a reliable and dynamic marker of response that can be useful to optimize AZA therapy.