Urokinase-type Plasminogen Activator Is a Therapeutic Target for Overcoming Sorafenib Resistance in Hepatoma Cells.

BACKGROUND/AIM: Sorafenib is a multikinase inhibitor approved as a first-line therapy for hepatocellular carcinoma. This study examined the sorafenib resistance mechanism. MATERIALS AND METHODS: Hepatoma HepG2 cells were exposed to sorafenib, and the biological activity of the conditioned media was analyzed using cell proliferation/apoptosis assays, multiplex immunoassays, ELISA, and western blot analyses. The effect of urokinase-type plasminogen activator (uPA) inhibitors or siRNA-mediated gene silencing was examined in culture experiments and a mouse xenograft tumor model. RESULTS: Sorafenib increased uPA secretion, which was abrogated by an Akt inhibitor. The growth-inhibitory effect of sorafenib was significantly enhanced by the uPA inhibitors UK122 and amiloride. Sorafenib-induced apoptosis was increased 2.4-fold in uPA siRNA-transduced cells (p<0.05). Combined therapy with sorafenib and amiloride significantly decreased tumor volumes [mean volume: 759 mm3 (sorafenib) vs. 283 mm3 (sorafenib plus amiloride), p<0.05]. CONCLUSION: uPA may play a critical role in sorafenib resistance.

Valproic acid overcomes transforming growth factor-ß-mediated sorafenib resistance in hepatocellular carcinoma.

Sorafenib is a multi-kinase inhibitor approved for hepatocellular carcinoma, but rarely causes tumor regression in patients with chronic liver diseases. To investigate whether growth factor-mediated signaling is involved in sorafenib resistance, HepG2 and PLC/PRF/5 hepatoma cells were exposed to epidermal growth factor (EGF), hepatocyte growth factor (HGF) or transforming growth factor-ß (TGF-ß) prior to treatment with sorafenib. Furthermore, to identify an effective combination treatment with sorafenib, growth factor-sensitized cells were treated with sorafenib alone or in combination with celecoxib, lovastatin or valproic acid (VPA). Trypan blue staining and Annexin V assays showed that the cytotoxic effect of sorafenib was inhibited by 15-54% in cells sensitized to TGF-ß (P<0.05). Western blotting analysis showed that TGF-ß significantly activated extracellular signal-regulated kinase (ERK)-mediated AKT signaling, and sorafenib failed to suppress both ERK and AKT in TGF-ß-sensitized cells. The decreased anti-tumor effect of sorafenib was rescued by chemical inhibition of ERK and AKT. When TGF-ß-sensitized cells were treated with sorafenib plus VPA, the levels of phosphorylated ERK and AKT were considerably suppressed and the numbers of dead cells were increased by 3.7-5.7-fold compared with those exposed to sorafenib alone (P<0.05). Moreover, low dose sorafenib-induced cell migration was effectively suppressed by combination treatment with sorafenib and VPA. Collectively, TGF-ß/ERK/AKT signaling might play a critical role in sorafenib resistance in hepatoma cells, and combination treatment with VPA may be effective against this drug resistance.

Blockade of ataxia telangiectasia mutated sensitizes hepatoma cell lines to sorafenib by interfering with Akt signaling.

Sorafenib is a multi-kinase inhibitor applicable to hepatocellular carcinoma (HCC), but its limited therapeutic effects are a major problem to be solved. Here, we show that blockade of ataxia telangiectasia mutated (ATM) improves the antitumor effects of sorafenib. When hepatoma cell lines HepG2 and PLC/PRF/5 were treated with sorafenib plus ATM small inhibitory RNAs, ATM inhibitor KU55933 or caffeine, Akt signaling was suppressed and the cytotoxic effects were significantly potentiated. Moreover, ATM inhibition effectively suppressed the sorafenib-induced cell migration. Taken together, manipulation of ATM activity might be a useful strategy for improving sorafenib treatment of HCC.