ABT-737 is a small molecule BH3 mimetic inhibitor of the anti-apoptotic members of the BCL-2 family, selective for BCL-2, BCL-XL, and BCL-W (EC50=78.7, 30.3, and 197.8nM, respectively). Developed by Abbvie, it failed in clinical trials due to toxicity issues, but was proven efficacious with various radiation therapies in triggering apoptosis in cancer cells and xenografts.