DIFFERENTIAL EFFECT OF LENALIDOMIDE ON INDUCTION OF INOSITIDE-DEPENDENT ERYTHROPOIESIS AND CELL CYCLE IN MYELODYSPLASTIC SYNDROMES

Introduction. Erythropoiesis is associated with the activation of specific inositide-dependent signalling pathways, such as Akt/PLCgamma1. On the other hand, Akt can also be associated with cell cycle and differentiation in MDS, via activation of mTOR pathway. Lenalidomide is currently used in the treatment of del(5q) low-risk MDS patients, to compensate and counteract the MDS ineffective erythropoiesis and selectively inhibit cell cycle in del(5q) cells. The exact molecular mechanisms underlying the effect of Lenalidomide in del(5q) and non-del(5q) MDS cells are still unclear, even though it is clear that Leanlidomide can target signalling molecules playing a role in the maintenance of the balance between apoptosis, proliferation and differentiation, such as Akt. Methods.We studied 6 patients diagnosed with del(5q) Low-Risk MDS (IPSS: Low or Int-1) who were given Lenalidomide. We also analyzed the effect of Lenalidomide on two cell lines: Namalwa CSN.70, bearing a del(5q) karyotype, and U937, with a normal 5q chromosome. In particular, we quantified the expression of several genes implicated in inositide signalling, such as Akt, mTOR and PI-PLCgamma1, as well as Cyclins and Globin genes, in order to assess the effect of Lenalidomide on cell cycle and erythropoiesis. Results. In our case series, 4 out of 6del(5q) Low-Risk MDS patients responded to Lenalidomide and showed an activation of erythropoiesis, in that Beta-Globin levels increased. Moreover, these subjects also displayed a specific phosphorylation of Akt only in non-del(5q) cells, as assessed by co-localization experiments. As for the other 2 cases, patients early discontinued Lenalidomide for adverse events, and for these patients a clinical assessment of Lenalidomide effect was not possible. As for cell lines, our findings hint at a specific activation of cell cycle and erythropoiesis only in U937 cells, whereas cell cycle, but not erythropoiesis, was selectively inhibited in Namalwa CSN.70 cell line, so that in these cells proliferation is slower than in non-del(5q) cells. Conclusions. In our case series, as well as in cell lines, erythropoiesis activation is associated with a response to Lenalidomide, with an induction of Akt/PLCgamma1. Moreover, only in non-del(5q) cells, a normal proliferation is allowed, given that in del(5q) cells our analyses show a cell cycle arrest and an inhibition of Akt/mTOR pathway. Therefore, our data support the hypothesis of a specific activation of both inositide-dependent proliferation and erythroid differentiation pathways in response to Lenalidomide treatment in non-del(5q) cells, whereas in the del(5q) cell clone there is a cell cycle arrest and a slower erythroid differentiation. Taken together, these results point to a specific activation of signalling pathways during Lenalidomide administration and possibly pave the way to a larger investigation aiming to assess the role of these pathways during the therapy.