Discovery of Potent Dual PROTAC Degraders Targeting BET-Kinase To Overcome FLT3 Inhibitor Resistance

FMS-like tyrosine kinase 3 (FLT3) is a validated therapeutic target in acute myeloid leukemia (AML). However, numerous single-agent FLT3 or multitarget inhibitors fail to achieve complete and sustained suppression of FLT3 signaling due to the development of drug resistance. Herein, we report the design, synthesis, and evaluation of a novel series of dual BET-kinase degraders targeting FLT3, JAK2, and BRD4. Optimization led to 13e, which efficiently degraded FLT3, JAK2, and BRD4 in MV4;11 cells with DC₅₀ values of 5.23, 0.678, and 1.17 nM, respectively. Mechanistic studies confirmed cereblon- and proteasome-dependent degradation. 13e significantly inhibited MV4;11 cell proliferation and demonstrated promising antitumor activity in an MV4;11 xenograft model. Additionally, 13e showed enhanced antiproliferative activity against FLT3 mutant-transformed Ba/F3 cells, indicating its potential to overcome resistance. Collectively, 13e represents a highly promising FLT3/JAK2/BRD4 degrader with potent antileukemic activity and the ability to overcome resistance associated with current FLT3 inhibitors.