The multikinase inhibitor Sorafenib induces apoptosis and sensitises endometrial cancer cells to TRAIL by different mechanisms

Sorafenib induces apoptosis and enhances Tumour Necrosis Factor-Related Apoptosis-Inducing Ligand (TRAIL)-induced cell killing of tumoural cells. We have investigated the effects of the multikinase inhibitor Sorafenib alone or in combination with TRAIL and agonistic Fas antibodies on endometrial carcinoma cells. We have also focused on the search of the differential molecular mechanisms by which Sorafenib induces cell death and the ones involved in sensitisation to TRAIL. In the present study, we show that Sorafenib induces apoptosis of both endometrial cancer cell lines and human primary cultures and sensitises these cells to TRAIL and agonistic Fas antibodies (aFas)-induced apoptosis. However, Raf/MEK/ERK inhibition by Sorafenib was not responsible for Sorafenib cell death or TRAIL sensitisation of endometrial cancer cells. Sorafenib treatment correlated with a downregulation of both FLICE-Inhibitory Protein (FLIP) and myeloid cell leukaemia-1 (Mcl-1), caused by a proteasomal degradation of both proteins. We evaluated the contribution of FLIP and Mcl-1 downregulation in apoptosis triggered by Sorafenib alone or Sorafenib plus TRAIL. Interestingly, cell death caused by Sorafenib was mediated by downregulation of Mcl-1, but not by FLIP. In contrast, we found that Sorafenib sensitisation of endometrial carcinoma cells to TRAIL- and Fas-induced apoptosis was dependent on FLIP but not on Mcl-1 downregulation. Altogether, we discern the dual mechanisms by which Sorafenib causes cell death from those involved in death receptor sensitisation.