Unhooking the Hook: Optimization of the Aurora A Targeting PROTAC JB170 to CCT400028, an In Vitro Degrader Chemical Probe

Proteolysis TArgeting Chimeras (PROTACs) can be used to target both the catalytic and noncatalytic functions of a protein, which can be particularly beneficial for proteins with important scaffolding functions like Aurora A. However, instability, poor selectivity profiles, and the hook effect often limit the applicability of PROTACs as chemical probes. In this study, we report the development of CCT400028, a second-generation alisertib-derived Aurora A PROTAC. The hook effect was removed through rational optimization of the CRBN-targeting warhead to decrease affinity for cereblon, which, combined with improved stability to hydrolysis, expands the range of concentrations and duration at which maximal degradation can be achieved. Potent Aurora A degradation was shown in three pediatric tumor cell lines, as well as excellent selectivity and on-target mechanism of action. CCT400028 and a matched inactive control analogue fulfill the criteria for a degrader chemical probe for studying Aurora A degradation in vitro.