The first BH3 mimetic tested in clinical trial of AML was obatoclax, which was thought to inhibit Bcl-2 and other antiapoptotic proteins (Bcl-xL, Bcl-w, Bcl-b, A1, and Mcl-1) (Fig. 2b).74 In preclinical studies, obatoclax was shown to inhibit cell growth and induce apoptosis in both AML cell lines and primary patient samples75 and was able to potentiate the cytotoxic effect of cytarabine in AML cells.76 A phase I study of obatoclax included patients with myelodysplasia or refractory leukemia, including AML, ALL, and CLL. This evidence concerns the gene MCL1 and acute myeloid leukemia.