In Vitro: G5 is capable of activating an apoptosome-independent apoptotic pathway. It targets the ubiquitinproteasome system by inhibiting the ubiquitin isopeptidases. G5 induces a rather unique apoptotic pathway, which includes a Bcl-2-dependent but apoptosome-independent mitochondrial pathway with upregulation of the BH3-only protein Noxa, stabilization of the inhibitor of apoptosis antagonist Smac, but also the involvement of the death receptor pathway. G5 is a potent apoptotic inducer showing IC50s of 1.76 and 1.6 μM in E1A and E1A/C9DN cells, respectively.