A BH3 mimetic that selectively inhibits Bcl-2 (Ki 3-fold less avidly to the related family proteins, Bcl-xL and Bcl-W (Kis = 48 and 245 nM, respectively); inhibits the growth of Bcl-2-dependent cell lines and in vivo tumor xenografts and demonstrates antileukemic activity in patients with refractory chronic lymphocytic leukemia