Discovery of Potent, Selective, and In Vivo Efficacious AKT Kinase Protein Degraders via Structure–Activity Relationship Studies

We recently reported a potent, selective,
and in vivo efficacious
AKT degrader, MS21, which is a von Hippel–Lindau (VHL)-recruiting
proteolysis targeting chimera (PROTAC) based on the AKT inhibitor
AZD5363. However, no structure–activity relationship (SAR)
studies that resulted in this discovery have been reported. Herein,
we present our SAR studies that led to the discovery of MS21, another
VHL-recruiting AKT degrader, MS143 (compound 20) with
similar potency as MS21, and a novel cereblon (CRBN)-recruiting PROTAC,
MS5033 (compound 35). Compounds 20 and 35 induced rapid and robust AKT degradation in a concentration-
and time-dependent manner via hijacking the ubiquitin-proteasome system.
Compound 20 suppressed cell growth more effectively than
AZD5363 in multiple cancer cell lines. Furthermore, 20 and 35 displayed good plasma exposure levels in mice
and are suitable for in vivo efficacy studies. Lastly, compound 20 effectively suppressed tumor growth in vivo in a xenograft
model without apparent toxicity.