AT-101 is the R-(-) enantiomer of Gossypol that acts as an inhibitor of the antiapoptotic Bcl proteins (Bcl-2, Bcl-XL, Bcl-W, and Mcl-1) and an inducer of the pro-apoptotic proteins noxa and puma. It induces apoptosis in drug-resistant multiple myeloma cell lines. Apoptosis is activated by the mitochondrial pathway.