A molecular modeling approach with the BIR3 domain of XIAP has demonstrated that some natural molecules such as embeline, eriopodol A, gibbilimbol B, and erioquinol, can bind to the BIR3 domain of XIAP in the same binding site of Smac (the endogenous antagonist of XIAP) and promote apoptosis in different types of human cancer cells [32,33]. The gene discussed is XIAP; the disease is cancer.