Role of Nuclear Inositide Signalling and microRNA Signature in Myelodysplastic Syndromes during Azacitidine and Lenalidomide Therapy

Phosphoinositide-specific phospholipase C (PI-PLC) gamma1 is involved in erythroid differentiation, via activation of the Akt/PI-PLCgamma1 pathway, and its increase has been associated with erythropoiesis in MDS cells. On the other hand, PI-PLCbeta1 is a nuclear inositide-dependent enzyme implicated in the regulation of hematopoietic differentiation. Interestingly, PI-PLCbeta1 increase plays an important predictive role in the response of MDS cells to epigenetic therapy. Indeed, PI-PLCbeta1 promoter is specifically hypomethylated by azacitidine, a demethylating agent that is clinically used in MDS to improve patients' overall survival and delay the AML evolution. Moreover, azacitidine is currently studied in combination with lenalidomide, to sustain both myeloid and erythroid lineages and balance MDS cell proliferation and differentiation. However, the molecular effects of this combination therapy on inositide signalling pathways and microRNA expression are still unclear.

This study included 44 patients diagnosed with high-risk MDS who were given azacitidine and lenalidomide. Patients were considered clinically evaluable after at least 6 cycles of treatment. Molecular analyses were performed at baseline and during the therapy. At first, Real-Time PCR and immunocytochemical experiments were performed to determine PI-PLCbeta1 and PI-PLCgamma1 expression. Then, we also carried out cell cycle analyses and studied both PI-PLCbeta1 methylation status and the expression of erythroid-specific molecules, i.e. Globin genes. On the other hand, to further investigate the effect of the combination therapy on epigenetic mechanisms, we analyzed microRNA expression at baseline and during the treatment. In particular, we started by comparing the 4^th cycle of the therapy to baseline, and in case of significant differences, for responder patients, we carried out microRNA profiling at the 8^th cycle of the therapy or during the follow-up.

Our study included 44 patients, but only 28 subjects were clinically evaluable, with an overall response rate of 78.6% (22/28 cases). At a molecular level, a significant increase of PI-PLCbeta1 expression was associated with a favourable clinical response to the combination therapy. Moreover, responder cases also showed an increased expression of Beta-Globin and PI-PLCgamma1, hinting at a specific contribution of lenalidomide on erythroid activation. On the other hand, the frequent demethylation of PI-PLCbeta1 promoter in responder cases could be specifically linked to azacitidine. Furthermore, MDS cells treated with azacitidine and lenalidomide not only showed an increased G0/G1 phase of cell cycle, but also microRNA expression was affected. In fact, responder and non responder cases showed a specific molecular pattern of microRNAs and, interestingly, some of these microRNAs can target or are strictly associated with inositide signalling pathways.

Our results show that the combination of azacitidine and lenalidomide in high-risk MDS patients can be important to induce PI-PLCbeta1, and possibly PI-PLCgamma1. These enzymes can regulate cell cycle, myeloid and erythroid differentiation, thus improving peripheral cytopenia. On the other hand, a specific microRNA signature is important to make a molecular distinction between responder and non responder cases, so that their expression or interactions, possibly with PI-PLCs or other nuclear inositides, can be important to disclose new mechanisms in MDS pathogenesis and identify new predictive markers for the assessment of the response to azacitidine and lenalidomide therapy.