ABT-199/GDC-0199 is a small molecule drug in co-development by Abbvie and Genentech for the selective inhibition of BCL-2, a key regulator of cellular apoptosis. BCL-2, part of the larger BCL-2 family, is responsible for the sequestration of pro-apoptotic proteins along the mitochondrial membrane. Displacement of these proteins from BCL-2 in cancerous cells may prime these cells for apoptosis.