Effect of GSK-3 inhibition in vitro and in vivo on antitumor effect of sorafenib in renal cell carcinoma (RCC).

Abstract

4617 Background: Sorafenib is a multikinase inhibitor which has been approved as the first-line treatment of advanced and/or metastaticrenal cell carcinoma (RCC). Sorafenib suppresses tumor growth directly by affecting tumor cells and indirectly by targeting tumor vasculature and angiogenesis. While the detailed molecular mechanisms of its action in RCC are still unclear, combining sorafenib with other signal transduction inhibitors may improve its activity and provide additional benefits to patients with RCC. Recently we showed that glycogen synthase kinase 3 (GSK-3) might be a potential new therapeutic target for RCC and targeting GSK-3 is an effective way to directly induce apoptosis in RCC, which is resistant to apoptosis-triggering treatment modalities (Br J Cancer. 101:2005-14, 2009). Methods: Here we examined effects of sorafenib on human RCC cell lines in vitro and in vivo by tumor xenograft mouse model as a single agent or in combination with a GSK-3 small molecule inhibitor AR-A014418. Protein expression and phosphorylation states were analyzed by Western blots. GSK-3 expression in cells was also confirmed by Q-RT-PCR (using TaqMan technology). Cell viability in vitro was examined by MTS assay. Morphological and biochemical features of apoptosis were detected with standard methods. Results: We detected that sorafenib induced growth inhibition of human RCC cell lines in vitro in a time (24-96 hours) and dose (2.5-10μ M) dependent manner as well as in vivo xenograft tumors in mice (30 mg/kg). Sorafenib treatment triggered apoptosis demonstrated by PARP cleavage which was more prominent with higher doses. However, in vitro sorafenib upregulated total GSK-3 expression and almost completely depleted inactive GSK3 pool as shown by diminished phosphorylation at Ser9. GSK-3 pharmacological inhibition with AR-A014418 (25 μ M, 30 mg/kg) potentiated sorafenib antitumor activity both in vitro and in vivo. Conclusions: Our results confirmed the direct antitumor effect of sorafenib in RCC andrevealed GSK-3 activation as one of potential consequence of sorafenib treatment. Targeting GSK-3 may synergize with sorafenib and this combination treatment might be a potential new approach for RCC. No significant financial relationships to disclose.