BH3I-1, while inhibiting its reported target Bcl-2/Bim and Bcl-xL/Bim, shows significant inhibition of both the p53/hDM2 and p300/Hif-1α interactions. This surprising promiscuity, displays by a well studied compound leads to further interrogate the p53/hDM2 interaction utilizing a standard fluorescence polarization (FP) assay with purified protein. The results from the FP assay validates the split-luciferase screen and demonstrates that BH3I-1 has a K _d =5.3 μM against the p53/mDM2 pair, which is comparable to its low micromolar potency reported for the BH3 family of receptors. BH3I-1 inhibits interaction between the BH3 domain and Bcl-xL. NMR analyses reveal that BH3I-1 targets the BH3-binding pocket of Bcl-xL with a K _i of 7.8±0.9 μM.