For LNCaP cells, they were treated DMSO (control), Rad001 (0.37 μM), ATO (11.19 μM), and their combination, for 24 hrs. For PC3 cells, they were treated DMSO (control), Rad001 (0.35 μM), ATO (12.00 μM), and their combination, for 24 hrs. (A) Trypan blue (TB) analysis of the LNCaP and PC3 cells treated alone or in combination group. Two drugs resulted in more reduction of the cell viability than single treat. Two-way T-test results P < 0.05 between the two groups. (B) Increased levels of cleaved Caspase-3/PARP were detected in LNCaP and PC3 cells with 24 hrs of Rad001 and ATO. What's more, higher activities of Caspase-3/7 were observed in LNCaP and PC3 cells with 24 hrs treatment of Rad001 and ATO combination (P < 0.05 between the two groups). (C) Flow cytometry analysis of apoptosis with Annexin-V and 7-AAD staining. Right (top and bottom) is Annexin-V positive cells. A significant increase of percentage of apoptotic cell was observed with Rad001 and ATO combination treatment (P < 0.05).