Clonal Effect Of Lenalidomide On Akt Activation In Low-Risk MDS Patients With Del(5q)

Lenalidomide is an immunomodulating drug currently used in the treatment of del(5q) low-risk MDS patients, where it can suppress the del(5q) clone and restore a normal erythropoiesis. The exact molecular mechanisms underlying the effect of Lenalidomide in del(5q) MDS are not completely clear, although Akt phosphorylation is inhibited in Lenalidomide-sensitive del(5q) cell lines (Gandhi et al, 2006). On the other hand, the activation of the Akt/mTOR pathway has been demonstrated in CD34+ cells from high-risk MDS (Follo et al, 2007), which show alterations on stem cell proliferation, differentiation and apoptosis. These processes are important also in low-risk MDS, that usually show a stable disease but can evolve towards a worse clinical status, characterized by an increased cell proliferation.

In this study we firstly investigated the effect of Lenalidomide in 6 patients with del(5q) MDS (IPSS: Low or Int-1). Given the limited number of cells, we analyzed bone marrow total mononuclear cells. As for Akt phosphorylation, we analyzed its localization along with RPS14, in order to specifically detect the del(5q) clone. On the other hand, by Real-Time PCR analyses, we assessed the expression of Globin genes, to evaluate the effect of the drug on erythropoiesis. In addition, we analyzed the effect of Lenalidomide on two cell lines with a different 5q status, one bearing a normal 5q chromosome and one showing the 5q deletion, to further investigate the effect of this drug on cell cycle, erythroid differentiation and inositide signalling pathways.

Clinically, 4/6 del(5q) MDS patients showed a favourable response to Lenalidomide. At a molecular level, these cases showed an activation of erythropoiesis, in that Beta-Globin levels increased, as compared with baseline. Moreover, these subjects also displayed a specific phosphorylation of Akt. Interestingly, Akt resulted to be specifically activated in cells not showing the 5q deletion, whereas it was down-regulated in del(5q) cells. The two non responder patients early discontinued Lenalidomide for adverse events, and for these patients neither a clinical assessment of Lenalidomide effect, nor a molecular analysis, were possible. As for cell lines, ongoing analyses are showing that Lenalidomide specifically inhibits the growth of the del(5q) clone, blocking cells in G1 phase. On the other hand, Akt phosphorylation specifically increases in cells with a normal 5q chromosome.

Taken together, our data show a specific activation of erythropoiesis in del(5q) low-risk MDS patients responding to Lenalidomide. In addition, our results indicate that Akt is specifically phosphorylated in normal cells without the del(5q), leading to hypothesize that Lenalidomide has a double effect: it can induce apoptosis in clonal del(5q) cells, but it also supports the proliferation and erythroid differentiation of normal cells, as also described in non-del(5q) MDS (Ebert et al, 2008). Therefore, our findings might contribute to elucidate the molecular mechanisms of Lenalidomide and possibly pave the way for the development of innovative therapeutic targeted strategies in MDS.