A Bcl2-BH4 domain antagonist (Ki 3.3 nM) selective for Bcl-2 over Bcl-xL Mcl-1 A1/Bfl-1 and Bcl-2 lacking the BH4 domain (Kis 500 500 500 and 654.8 nM respectively) binds to BH1- BH2- or BH3 domain-deficient Bcl-2 (Kis 12.4 7.6 and 23.4 nM respectively) induces Bax activation in HT cells which lack endogenous Bcl-2 and in HT cells overexpressing Bcl-2 indicating a context-specific Bcl-2-independent mechanism of cell death is cytotoxic against a panel of NSCLC and SCLC cell lines (IC50s 0.2-1.73 UM) reduces tumor growth and induces tumoral caspase-3 activation in an H460 lung cancer mouse xenograft model at 10 20 and 30 mg/kg