OBJECTIVETo investigate the effect of bortezomib (Bor) alone and in combination with arabinoside (Ara-C) on proliferation and apoptosis of leukemia cell line K562.

METHODSK562 cells were treated with 20 nmol/L Bor and 0.2 microg/ml Ara-C alone and in combination for 48 h. MTT was used to study the inhibitory effects on cell growth and the apoptosis rate was analysed by flow cytometry. After K562 cells treated with 20 nmol/L Bor or 0.2 microg/ml Ara-C for 6 h, the activity of NF-kappaB was analyzed by SP immunohistochemistry and cell cycle by flow cytometry.

RESULTSThe inhibition and apoptosis rates of K562 cells in combination groups were higher than those in the two single treatment groups (P < 0.01), especially in the combined treatment group in which K562 cells were treated first with Ara-C for 6 h then with Bor combined,the inhibition and apoptosis rates were the highest [(81.5 +/- 4.0)% and (29.2 +/- 3.1)%, respectively] (P < 0.01). In the other two combined groups in which the cells were treated with Bor for 6 h then with Ara-C combined, or treated with the two drugs simultaneously, the inhibition and apoptosis rates were (54.1 +/- 4.2)% and (18.7 +/- 3.5)%, and (66.2 +/- 2.8)% and (21.1 +/- 2.2)%, respectively. Treatment of K562 cells with 20 nmol/L Bor for 6 h, the activity of NF-kappaB was decreased significantly, and the cells were apparently arrested in G(2)/M phase, and treatment with 0.2 microg/ml Ara-C in the same manner, the activity of NF-kappaB was increased significantly, and the cells were apparently arrested in G(1) phase.

CONCLUSIONSBor can effectively inhibit K562 cell proliferation, and induced its apoptosis. This effect was enhanced significantly when in combination with Ara-C. Pretreatment of K562 cells with Ara-C lead to the increased activity of NF-kappaB and the fraction of G(1) phase cells.