OBJECTIVETo investigate the effects and mechanisms of the combination of homoharringtonine (HHT) with arsenic trioxide(AsO) on human myeloid cell line U937 in vitro.

METHODSMTT method was used to determine the antiproliferating effect of different concentrations of HHT, AsOand their combination on U937 cells; the flow cytometry with Annexin-V-FITC/PI double staining was used to determine the apoptosis-induced effect of HHT and AsOalone or their combination; Western blot method was used to detect the protein expression of P-Akt,P-Akt,BCL-XL, BID,MCL-1,P-MCL-1 and so on.

RESULTSHHT and AsOcould significantly inhibit proliferation of U937 cells and induce their apoptosis. The combination of these 2 drugs could significantly enhance the early apoptosis of U937 cells. After combination of these 2 drugs was used, the protein expressions of P-Akt,P-Akt,MCL-1,P-MCL-1 and BCL-XL were obviously down-regulated, but the expression of BID protein did not change.

CONCLUSIONThe combination treatment of HHT and AsOcan synergistically inhibit the growth of U937 cells through inhibition of PI3K/Akt signal way and MCL-1 protein.