Quantifiable analysis of cellular pathway inhibition of a Nedd8-activating enzyme inhibitor, MLN4924, using AlphaScreen.

Abstract Cellular effects of a Nedd8-activating enzyme (NAE) inhibitor, MLN4924, using the AlphaScreen format were explored. MLN4924 acts as a substrate-assisted inhibitor of NAE by forming a tight binding Nedd8–MLN4924 adduct. The inhibited enzyme can no longer transfer Nedd8 downstream to modify and activate the E3 cullin–RING ligases. This results in the stabilization of proteins regulated by the proteasome, leading to cell death. These studies monitored the endogenous cellular changes to NAE∼Nedd8 thioester, the formation of the Nedd8–MLN4924 adduct, and the reduction in the Cul1–Nedd8. Lysates derived from MLN4924-treated HCT116 cells showed that whereas the β-subunit of NAE remained constant, reductions of both NAE∼Nedd8 thioester and Cul1–Nedd8 levels occurred with a concomitant rise of the adduct. Moreover, the formation of the Nedd8–MLN4924 adduct was approximately stoichiometric with the concentration of NAEβ. Higher density 384-well cell-based assays illustrated the kinetics of enzyme inactivation across a wider range of MLN4924 concentrations, showing a rapid loss of NAE∼Nedd8 thioester and Cul1–Nedd8. The reduction of NAE∼Nedd8 thioester precedes the loss of Cul1–Nedd8 at twice the rate. Finally, these results clearly demonstrate the utility of the homogeneous assay for quantitative assessment of these endogenous cellular components in a 384-well plate in response to inhibition of NAE by MLN4924.