Nemorosone blocks proliferation and induces apoptosis in leukemia cells.

Objective: This work is aimed at characterizing nemorosone, isolated from Clusia rosea, as a potential antileukemic agent. In addition, we analyzed its influence on hematopoiesis in a mouse model. Materials and methods: The isolation of nemorosone was carried out employing the RP-HPLC (reversed phase high-performance liquid chromatography) technique. Cytotoxicity was assessed in human leukemia cell lines including parental and chemotherapy-refractory sublines based on the MTT compound. Its effects on the cell cycle were analyzed using FACS (fluorescence-activated cell sorting) and Western blot techniques. Studies on the drug-induced early apoptotic process were carried out by means of fluorescence microscopy. Major signal transducers and the enzymatic inhibition of immunoprecipitated Akt/PKB were detected by Western blot. Hematopoiesis was analyzed in NMRI nu/nu mice after chronic nemorosone treatment, measuring hematological parameters by conventional laboratory techniques. Results: Nemorosone proved cytotoxic in both parental and chemoresistant leukemia cell lines with IC 50 values between 2.10 and 3.10 μg/ml. No cross-resistances could be detected. Cell cycle studies showed apoptosis induction accompanied by an increase in the G0/G1 population in both cell lines studied, whereas a significant decrease in the S-phase was found in Jurkat cells. Nemorosone induced a down-regulation of cyclins A, B1, D1, and E as well as a dephosphorylation of cdc2. Major signal transduction elements such as ERK1/2 and p38 MAPK, as well as important oncoproteins such as c-Myb and BCR/ABL were also found down-regulated. The enzymatic activity of immunoprecipitated Akt/PKB was substantially inhibited in vitro. Moreover, sub-chronic nemorosone treatment induced reversible monocytosis and thrombocytosis in the mouse model examined. Conclusions: Here, we demonstrate for the first time that nemorosone exerts cytotoxicity in leukemia cells, partly by targeting the Akt/PKB signal transducer, affecting protein levels and cell cycle progression. Finally, in vivo studies suggest that nemorosone significantly affects hematopoiesis in mice.