Figure 2. The toxic interaction between PDE5 inhibitors and chemotherapy is blocked by overexpression of BCL-XL or c-FLIP-s. (A) DAOY cells were treated with zVAD, LEHD, or IETD (all 50 μM) followed by drugs and viability determined by trypan blue exclusion (n = 3, ± SEM). (B–E) HOSS1, D283, and DAOY cells were infected with empty vector adenovirus (CMV) or three other viruses to express dominant negative caspase 9 (dn casp 9), BCL-XL, and c-FLIP-s respectively. Thirty-six hours after infection cells were treated with drugs and viability determined by trypan blue exclusion (n = 3, ± SEM) ^#P < 0.05 less than corresponding value in CMV control. (F) DAOY cells were transfected with scrambled siRNA (siSCR) or siRNA molecules to knock down expression of CD95 or FADD (siCD95, siFADD). Thirty-six hours after infection cells were treated with drugs and viability determined by trypan blue exclusion (n = 3, ± SEM) ^#P < 0.05 less than corresponding value in siSCR control.