Torin2 overcomes sorafenib resistance via suppressing mTORC2-AKT-BAD pathway in hepatocellular carcinoma cells.

Background: Sorafenib is an oral multi-kinase inhibitor that was approved by the US Food and Drug Administration for the treatment of patients with advanced hepatocellular carcinoma (HCC). However, resistance to sorafenib is an urgent problem to be resolved to improve the therapeutic efficacy of sorafenib. As the activation of AKT/mTOR played a pivotal role in sorafenib resistance, we evaluated the effect of a dual mTOR complex 1/2 inhibitor Torin2 on overcoming the sorafenib resistance in HCC cells.

Methods: The sorafenib-resistant Huh7 and Hep3B cell lines were established from their parental cell lines. The synergistic effect of sorafenib and Torin2 on these cells was measured by cell viability assay and quantified using the Chou-Talalay method. Apoptosis induced by the combination of sorafenib and Torin2 and the alteration in the specific signaling pathways of interest were detected by Western blotting.

Results: Sorafenib treatment inversely inhibited AKT in parental but activated AKT in sorafenib-resistant Huh7 and Hep3B HCC cells, which underscores the significance of AKT activation. Torin2 and sorafenib synergistically suppressed the viability of sorafenib-resistant cells via apoptosis induction. Torin2 successfully suppressed the sorafenib-activated mTORC2-AKT axis, leading to the dephosphorylation of Ser136 in BAD protein, and increased the expression of total BAD, which contributed to the apoptosis in sorafenib-resistant HCC cells.

Conclusions: In this study, Torin2 and sorafenib showed synergistic cytostatic capacity in sorafenib-resistant HCC cells, via the suppression of mTORC2-AKT-BAD pathway. Our results suggest a novel strategy of drug combination for overcoming sorafenib resistance in HCC.