Apoptosis Activator 2 is a cell-permeable indoledione compound that activates caspases in a cytochrome c-dependent manner and induces apoptosis in tumor cells by promoting the oligomerization of Apaf-1 into the mature apoptosome. Its cytotoxicity is selective towards tumor cells (IC50 < 10 µM for Jurkat, Molt-4, and CCRF-CEM). Apoptosis Activator 2 shows little or no effect on non-tumor cells or cells that are deficient in caspase-3 or Apaf-1 (IC50 > 40 µM). Through the induction of apoptosis, Apoptosis Activator 2 notably induces caspase-3 activation, PARP cleavage and DNA fragmentation. Moreover, this induction of apoptosis only occurs in tumor cell lines (such as breast, lung, colon, and epidermal cancer cell lines).