OBJECTIVETo investigate the effect of valproic acid on the expression of P27(Kip1) and P170 and drug resistance of leukemia HL60/HT cell line and explore its possible mechanisms.

METHODSHL-60/HT cells were derived from HL-60 cells induced by harringtonine (HT) in gradient concentrations. The inhibitory effect of valproic acid on the proliferation of HL-60 and HL-60/HT cells was evaluated by MTT assay, and the P27(Kip1) expression, P170 expression and cell cycle of the cells were analyzed with flow cytometry.

RESULTSThe multidrug-resistant HL-60/HT was acquired, which showed a stable drug-resistant index with increased IC(50) of HT, VCR, DNR and Ara-c by 9.30, 5.20, 4.91 and 3.65 folds, respectively, as compared with those of HL60 cells. The expression of P27(Kip1) in HL-60/HT cells was significantly lower but P170 expression significantly higher than that of HL-60 cells and normal mononuclear cells (P<0.05). The expressions of P27(Kip1) and P170 showed no significant difference between normal mononuclear cells and HL-60 cells. The growth inhibition rate of VPA combined with Ara-C was significantly higher than that of valproic acid or Ara-C alone in HL-60/HT cells and HL-60 cells (q=1.37 and 1.51, respectively). HL-60/HT and HL-60 cells cultured in the presence of VPA resulted in a significant increase in the expression of P27(Kip1) and the G(1)-phase cells (P<0.05), but the expression of P170 underwent no significant changes (P>0.05).

CONCLUSIONHL-60/HT cells have lower P27(Kip1) expression compared with HL-60 cells. Valproic acid can inhibit the growth of HL-60/HT cells and enhance their Ara-C sensitivity possibly by increasing P27(Kip1) expression and causing cell cycle arrest in G(1) phase.