Perifosine induces protective autophagy and upregulation of ATG5 in human chronic myelogenous leukemia cells in vitro

Aim: The efficacy of the Akt inhibitor perifosine against chronic myeloid leukemia (CML) cells and its mechanisms of action are unknown. In this study, the cytotoxic effects of perifosine on CML and acute myeloid leukemia (AML) cell lines were compared to elucidate the mechanisms underlying the differences. Methods: Human AML cell lines Kasumi-1 and HL-60, and the CML cell line K562 were used. Cell viability was quantitated using MU assay. Apoptosis was determined using Annexin V-FITC/propidium iodide and Hoechst staining, which were followed by flow cytometry and fluorescence microscopy analysis, respectively. Caspase pathway activation and the expression of autophagy-related genes were examined using Western blot. Autophagy was studied using electron microscopy, the acridine orange staining method, and GFP-LC3 was examined with fluorescence microscopy. Results: In contrast to AML cell lines, the CML cell lines K562 and K562/G (an imatinib-insensitive CML cell line) were resistant to perifosine (2.5-20 pmol/L) in respect to inhibiting cell growth and inducing apoptosis. Perifosine (2.5, 5, and 10 pmol/L) inhibited Akt and its phosphorylation in AML cells, but not in CML cells. Treatment with perifosine (20 pmol/L) resulted in autophagy in CML cells as shown by the increased formation of acidic vesicular organelles and the accumulation of LC3-1I. Treatment of CML cells with perifosine (5, 10, and 20 pmol/L) dose-dependently upregulated AGT5, but not Beclin 1 at the protein level. Furthermore, inhibition of autophagy by chloroquine (40 nmol/L) significantly suppressed the cell growth and induced apoptosis in CML cells treated with perifosine (20 pmol/L). Conclusion: Our results show that CML cell lines were resistant to the Akt inhibitor perifosine in vitro, which is due to perifosine-induced protective autophagy and upregulation of ATG5.