Evaluation of Cereblon-Directing Warheads for the Development of Orally Bioavailable PROTACs

PROTACs usually occupy physicochemical space outside the one defined by classical drug-like molecules, which often presents considerable challenges in their optimization and development for oral administration. We have previously reported phenyl glutarimide (PG)-based BET PROTAC SJ995973, with improved overall in vitro degradation and antiproliferative activities compared to its direct thalidomide-based analogue dBET1, but similarly poor in vivo pharmacokinetic profile. To further demonstrate the PG utility, we describe here optimization efforts that led to the discovery of an orally bioavailable BET-PROTAC SJ44236 (8), and results of a comprehensive in vitro/vivo comparative study with analogues containing alternative CRBN-directing warheads. Our study highlights the importance of considering warhead modifications when optimizing PROTACs for oral delivery.