BRD4 inhibition sensitizes renal cell carcinoma cells to the PI3K/mTOR dual inhibitor VS-5584

Activation of the PI3K/AKT/mTOR pathway promotes the progression of renal cell carcinoma (RCC). This study tested the anti-RCC cell activity of the PI3K/mTOR dual inhibitor, VS-5584. We show that VS-5584 inhibited PI3K/AKT/mTORC1/2 activation in established (786-O and A498 lines) and primary RCC cells, thereby suppressing cell survival, proliferation, migration and cell cycle progression. VS-5584 induced significant apoptosis in RCC cells. A daily single oral dose of VS-5584 (20 mg/kg) significantly inhibited 786-O tumor growth in vivo. VS-5584 treatment of 786-O tumor xenografts and RCC cells resulted in feedback upregulation of bromodomain-containing protein 4 (BRD4). Furthermore, BRD4 inhibition (by JQ1 and CPI203), knockdown or complete knockout potentiated VS-5584-induced RCC cell death and apoptosis. Conversely, forced overexpression of BRD4 attenuated the cytotoxicity of VS-5584 in 786-O cells. Collectively, VS-5584 potently inhibits RCC cell proliferation and survival. Its anti-tumor activity is further enhanced by the targeted inhibition of BRD4.