SIRT1 and cancer: EX527 also suppressed efflux of Rho 123 and consequently increased the intracellular level of fluorescence, and combined treatment of EX527 and AUY922 suppressed further the efflux of Rho 123 in MCF7-MDR and CEM/VBL100 cells, while AUY922 did not show any effect on Rho 123 efflux at a concentration used, indicating that SIRT1 inhibition could suppress the resistance of MDR cancer cells to AUY922 as well as 17-AAG through suppression of P-gp-mediated efflux.