Multi-targeting therapy is an emerging strategy of drug discovery to improve therapeutic efficacy, safety and resistance profiles. In this study, we monitored the binding of a potent MDM2 inhibitor Nutlin-3 with anti-apoptotic Bcl-2 family proteins using NMR spectroscopy. Our results showed the universal binding of Nutlin-3 with diverse anti-apoptotic Bcl-2 family proteins. Taken together with the binding data for Nutlin-3 analogs, the structural model of the Bcl-X-L/Nutlin-3 complex showed that the binding mode of Nutlin-3 resembles that of the Bcl-X-L/Bcl-2 inhibitors, suggesting the molecular mechanism of transcription-independent mitochondrial apoptosis by Nutlin-3. Finally, our structural comparison provides structural insights into the dual-targeting mechanism of how Nutlin-3 can bind to two different target proteins, MDM2 and anti-apoptotic Bcl-2 family proteins in a similar manner. (C) 2012 Elsevier Inc. All rights reserved.