Preliminary cytotoxicity tests of 9a after 72 hours of treatment versus MDA-MB-231 (a breast cancer cell line that has repeatedly been used to test Smac-mimetics/XIAP inhibitors), HL60 (known to be Smac-mimetic sensitive), and PC-3 cells (as an example of Smac-mimetic refractory cells), were addressed [14]. The gene discussed is XIAP; the disease is breast cancer.