The BCL-2 proteins BCL-2, BCL-XL, BCL-W, MCL-1, and A1 are antiapoptotic proteins that sequester the apoptotic effectors BAX and BAK. Proapoptotic proteins BIM, BID, PUMA antagonize the function of all BCL-2 proteins, whereas BAD specifically antagonizes BCL-2, BCL-XL and BCL-W while NOXA antagonizes MCL-1 and A1. The small molecule BH-3 mimetic GX15-070 and AT-101 are pan-BCL-2 inhibitors, in contrast to ABT-737/ABT-263, which specifically inhibits BCL-2, BCL-XL and BCL-W but not MCL-1 and A1.