No abstract

Sorafenib is the standard first-line systemic drug for advanced hepatocellular carcinoma (HCC), but the acquired resistance to sorafenib results in limited benefits. Activation of Akt is thought to be responsible for mediating the acquired resistance to sorafenib. The present study aims to examine the underlying mechanism and seek potential strategies to reverse this resistance. Two sorafenib-resistant HCC cell lines, which had been established from human HCC HepG2 and Huh7 cells, were refractory to sorafenib-induced growth inhibition and apoptosis in vitro and in vivo. Sustained exposure to sorafenib activated Akt via the feedback loop of mTOR but independent of protein phosphatase 2A in HCC cells. Autophagy participated in the resistance to sorafenib as inhibition of autophagy reduced the sensitivity of sorafenib-resistant HCC cells to sorafenib, whereas activation of autophagy by rapamycin had the opposite effect. However, rapamycin did not show a synergistic effect with sorafenib to inhibit cell proliferation, while it also activated Akt via a feedback mechanism in sorafenib-resistant HCC cells. Inhibition of Akt reversed the acquired resistance to sorafenib by switching autophagy from a cytoprotective role to a death-promoting mechanism in the sorafenib-resistant HCC cells. Akt inhibition by GDC0068 synergized with sorafenib to suppress the growth of sorafenib-resistant HCC tumors that possessed the sorafenib-resistant feature in vivo. The results have provided evidence for clinical investigation of GDC0068, a novel ATP-competitive pan-Akt inhibitor, as the second-line treatment after the failure of sorafenib-medicated molecular targeted therapy for advanced HCC. Mol Cancer Ther; 13(6); 1589-98. Ó2014 AACR.

Sorafenib resistance remains a major obstacle for the effective treatments of hepatocellular carcinoma (HCC). Recent studies indicate that activated Akt contributes to the acquired resistance to sorafenib, and miR-21 dysregulates phosphatase and tensin homolog (PTEN), which inhibits Akt activation. Sorafenib-resistant HCC cells were shown to be refractory to sorafenib-induced growth inhibition and apoptosis. Akt and its downstream factors were highly activated and/or upregulated in sorafenib-resistant cells. Inhibition of autophagy decreased the sensitivity of sorafenib-resistant cells to sorafenib, while its induction had the opposite effect. Differential screening of miRNAs showed higher levels of miR-21 in sorafenib-resistant HCC cells. Exposure of HCC cells to sorafenib led to an increase in miR-21 expression, a decrease in PTEN expression and sequential Akt activation. Transfection of miR-21 mimics in HCC cells restored sorafenib resistance by inhibiting autophagy. Anti-miR-21 oligonucleotides re-sensitized sorafenib-resistant cells by promoting autophagy. Inhibition of miR-21 enhances the efficacy of sorafenib in treating sorafenib-resistant HCC tumors in vivo. We conclude that miR-21 participates in the acquired resistance of sorafenib by suppresing autophagy through the Akt/PTEN pathway. MiR-21 could serve as a therapeutic target for overcoming sorafenib resistance in the treatment of HCC.

It is intriguing that some pan-caspase inhibitors such as zVAD-fmk (zVAD) are capable of inducing necrotic cell death in a selected group of cells. As earlier reports from our laboratory have ruled out the original notion that zVAD-induced necrosis in mouse fibrosarcoma L929 cells was autophagic cell death, the main objective of this study was thus to determine the underlying mechanism of this form of cell death. In this study, we provided clear evidence that zVAD-induced necroptosis in L929 cells and such cell death is dependent on autocrine production of tumor necrosis factor-a (TNFa) at the transcriptional level. More importantly, we identified that activating protein-1 (AP-1), but not nuclear factor j-B, is the transcription factor controlling zVADinduced TNFa transcription. Moreover, zVAD is able to activate AP-1 through activation of two upstream mitogen-activated kinases (MAPKs), c-Jun N-terminal kinase and extracellular signal-regulated kinase. Finally, we found that protein kinase C is the important upstream signaling molecule in mediating zVAD-induced activation of MAPKs and AP-1, and subsequent autocrine production of TNFa and cell death. Data from this study reveal the molecular mechanisms underlying zVAD-induced necroptosis, an important form of programmed necrotic cell death with increasing understanding of its biological significance in health and diseases.