Objective      To investigate the synergistic effect of cantharidin analog LB1

a novel inhibitor of protein phosphatase 2A

with doxorubicin (DOX) on human HepG2 hepatocellular carcinoma cells.       Methods      In vitro cell viability analysis was applied to detect the effect of different doses of LB1 and the synergistic effect of LB1 with DOX on HepG2 cells. The in vivo synergistic effect of LB1 with DOX was further examined in HepG2 tumor xenografts in athymic nude mice by immunohistochemical assay. Tumor growth and mouse weight were measured after the treatment.       Results      The effect of LB1 on the growth of HepG2 cells was associated with the doses of administration. Low doses of LB1 (10  mol/L) promoted cell viability

while high doses of LB1 (10  mol/L) induced the mitotic catastrophe and apoptosis of HepG2 cells. The in vivo experiment results showed that the growth inhibition rate of HepG2 cells was 57% for DOX alone

and increased significantly to 77% for LB1 and DOX combination. LB1 significantly enhanced the effect of DOX on tumor growth inhibition in both cultured HepG2 in vitro and mouse xenografts in vivo without apparent toxicity (P0.05).       Conclusion      LB1 can enhance the effect of doxorubicin in the chemotherapy against hepatocellular carcinoma cells.