Myelodysplastic syndrome (MDS) represents a heterogenous group of clonal stem cell disorders with qualitative and quantitative abnormalities of blood cells and a high probability of evolving to acute leukemia. Intensive induction chemotherapy in order to reduce the malignant clone and reconstruct normal hematopoiesis is a classic therapy for MDS, especially high risk MDS. Homoharringtonine (HHT), one of the alkaloids from a Chinese natural plant, Cephalotaxus, incombination with cytarabine (A-rac) (HA chemotherapy) has been used successfully in the treatment of MDS. It has been recently reported that the effect of HA chemotherapy could be enhanced by granulocyte colony stimulating factor (G-CSF) (HAG chemotherapy). But the mechanism underlying the enhanced effectiveness in HAG remains unknown. We investigated the effect and mechanism of HAG chemotherapy on the apoptosis and chemotaxis in MDS cell line MUTZ-1. Cells were divided into HA group (HHT + Ara-C) and HAG group (treated with G-CSF before HA). Growth inhibition was measured by MTT method and 50% inhibiting concentration (IC50) was calculated. Cell cycle and apoptosis were measured by flow cytometry. Mitochondria membrane electric potential was determined by confocal microscopy. The mRNA expression of the chemokine receptor CXCR4 and the cysteinyl leukotriene receptor Cys-LT1 were detected by RT-PCR. The protein expression of Cys-LT1 and signaling molecular in MUTZ-1 cells was detected by western blot. The chemotaxsis of MUTZ-1 cells was detected by transwell migration assay. We found that the percentage of apoptotic MUTZ-1 cells increased and the mitochondria membrane electric potential in the cells decreased significantly more in HAG group than in HA group. The percentage in S phase of the cell cycle increased after exposure to G-CSF for 4 hours, and at its peak after 6 hours. Cys-LT1 mRNA and protein expression and chemotactic migration increased more in HAG group than in HA group, while no significant change was observed in CXCR4 expression. G-CSF activated both mitogen activated protein kinase kinase (MEK1/2) and extracellular signal-regulated kinase (ERK1/2). Chemotactic migration was partly blocked by the MEK1/2 inhibitor U0126. These results indicated that G-CSF priming before HA chemotherapy increased apoptosis and chemotaxis in MDS cell line MUTZ-1, and MEK/ERK signaling pathway is involved in G-CSF-induced chemotaxis.

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