A small-molecule inhibitor of the anti-apoptotic proteins Bcl-2, Bcl-X(L) and Bcl-w. In vitro, ABT-737 binds Bcl-xL, Bcl-2 and Bcl-w with comparable high affinity, while it has over 1000-fold lower affinities for Bcl-B, Bfl-1 and Mcl-1. Displays wide range of single-agent activity against acute lymphoblastic leukemia (ALL) cell lines and xenografts.