Development of selective FGFR1 degraders using a Rapid synthesis of proteolysis targeting Chimera (Rapid-TAC) platform.

Proteolysis Targeting Chimera (PROTAC) has emerged as a novel therapeutic strategy. The major bottleneck for the development of PROTACs is the need to screen multiple parameters to create an effective degrader. It often involves the synthesis of dozens to hundreds of compounds one by one through a tedious process. We have developed a two-stage approach that allows for the rapid synthesis of PROTACs (Rapid-TAC) using preassembled building blocks to screen multiple parameters simultaneously. We herein report the application of this method to the development of PROTACs for FGFR, a challenging membrane protein target. In the first stage, we prepared 24 potential PROTACs quickly from a hydrazide-containing FGFR inhibitor and our previously reported VHL and CRBN ligand library bearing various linkers and an aldehyde functional group. These 24 PROTACs were then directly used for screening in cellular assay for protein degradation. Multiple hits were identified from the initial screening. We then prepared the corresponding stable analogues by replacing the hydrolytic labile acylhydrazone motif with an amide in the second stage. Among them, PROTAC LG1188 was identified as a potent and selective FGFR1 degrader.