Discovery of potent indole-2-one-based BRD4 PROTACs for the treatment of acute myeloid leukemia.

Bromodomain-containing protein 4 (BRD4) represents a significant therapeutic target in acute myeloid leukemia (AML). However, the clinical efficacy of BRD4 inhibitors is often compromised by side effects. In response to this challenge, we designed and synthesized a series of PROTACs derived from our recently reported BRD4 inhibitor, Y47 (an indole-2-one derivative). Among these compounds, the representative derivative, P6, demonstrated a capacity to effectively inhibit the proliferation of MV-4-11 cells, with an IC of 0.64 ± 0.02 μM. Notably, P6 exhibited low cytotoxicity toward the normal WI-38 cell line, with an IC exceeding 100 μM, and showed significant degradation activity against BRD4, yielding a DC of 1.11 ± 0.07 μM and a degradation percentage of 74.8 %. Furthermore, compound P6 facilitated the degradation of BRD4 in a concentration- and time-dependent manner. Molecular modeling, including docking and dynamics simulations, indicated that P6 engages key amino acids (Asn433, Tyr98, Arg107, Ser111, and His115) within both the BRD4 and VHL proteins, resulting in the formation of a stable ternary complex. Preliminary mechanistic investigations revealed that P6 could downregulate c-Myc expression and induce apoptosis through the upregulation of apoptosis-associated proteins, specifically BAD and BAX. Moreover, assessments of drug-like properties indicated that compound P6 possesses favorable hepatic microsomal metabolic stability (t = 49.5 min; Cl = 0.028 mL/min/mg), and it exhibited a high safety profile in vivo. Collectively, these findings suggest that compound P6 holds promise as a potential BRD4 degrader for further exploration and development.