CASP3 and cancer: However, a central role for caspase activation in mediating the anticancer actions of DDAs is indicated by the observations that (1) the caspase inhibitor Q-VD-OPH reverses many of the biochemical and biological responses to DDAs, with the exception of the DDA-mediated ER stress response (Fig. 5c), and (2) mouse tumor studies demonstrate strong DDA induction of caspase 3 cleavage by DDAs in cancer cells in vivo, but not in the surrounding normal tissues (Fig. 4e).