In vitro and in vivo antitumor activity of the proteasome inhibitor MLN2238 in hepatocellular carcinoma cells

Hepatocellular carcinoma (HCC) is one of the common malignancies and an increasing cause of cancer death. The traditional surgery, chemotherapy and radiation therapy increased the 5-year survival in patients with HCC only by 6%. Therefore, there is the need to develop new therapeutic strategies. MLN2238 is a orally bioavailable proteasome inhibitor with anti-cancer activity in different tumor types. In the present study, Here, we report that MLN2238 reduced cell viability in a time- and dose-dependent manner in HCC cells. Flow cytometry analyses indicated that MLN2238 induced G2/M cell cycle arrest and cellular apoptosis in HCC cells. The cell cycle arrest caused by MLN2238 was associated with increases in the expression levels of p21 and p27. At the molecular level, induction of apoptosis by MLN2238 was confirmed by activation of caspase-3 and PARP degradation. In addition, MLN2238 induced production of reactive oxygen species (ROS) and DNA damage. Furthermore, MLN2238 treatment induced expression of anti-apoptotic protein Mcl-1 in HCC cells. To demonstrate that Mcl-1 induction contributed to the MLN2238 resistance, expression of Mcl-1 was silenced through the use of specific siRNA. Mcl-1 knockdown sensitized HCC cells to MLN2238 treatment. These results were further confirmed by using a novel pharmacological inhibitor of Mcl-1, A1210477, in combination with MLN2238. The combination of A1210477 and MLN2238 determined synergistic antitumor effects in HCC cells. Finally, in vivo MLN2238 inhibited tumor growth of HCC cells in xenograft models. Our results provide a rational basis for the use of MLN2238 in HCC treatment.