FADD and leukemia: Although at 12 hours there is activation of Caspase-8, leukemia cells that are dominant negative for the Fas-Associated Death Domain (FADD) (DN FADD Jurkat), a critical component of the extrinsic pathway and activation of Caspase-8, were still very sensitive to PST and PST analogs compared to corresponding leukemia cells with functional FADD (Supplemental Fig. 3c).