Bcl-2-IN-4, an orally active and selective inhibitor of Bcl-2, demonstrates potent efficacy with an IC50 value of 1.5 nM and exhibits more than 200-fold selectivity over Bcl-xL (IC50 of 411 nM). Additionally, it effectively inhibits the proliferation of RS4;11 cells, achieving an IC50 of 2.7 nM.