Discovery of a potent BRD4 PROTAC and evaluation of its bioactivity in breast cancer cell lines.

Proteolysis targeting chimeras (PROTACs) targeting bromodomain-containing protein 4 (BRD4) proved to be powerful BRD4 degraders, which showed superiority in vitro and in vivo anti-tumor activity in many cancer models. Referring to the design of ARV-825, ARV-771 and MZ1, two novel BRD4 PROTACs were rationally designed and prepared via connecting the pan-BET selective bromodomain inhibitor JQ1 and two universal E3 ligase ligands targeting Von Hippel-Lindau (VHL) and cereblon (CRBN), namely VHL-JQ1 and CRBN-JQ1. Comparable to the degradation potency of ARV-825, ARV-771, and MZ1, both BRD4 PROTACs demonstrated potent BRD4 degradation efficacy. VHL-JQ1 showed superior antitumor activity against triple-negative breast cancer (TNBC) cell lines across multiple cellular processes, including cell proliferation suppression, migration and invasion inhibition, cell cycle arrest, and apoptosis induction. In addition, RNA-seq analysis revealed both shared and distinct gene expression profiles between BRD4 PROTAC-treated and JQ1-treated cells. Notably, VHL-JQ1 induced more pronounced mRNA expression changes compared to CRBN-JQ1 and JQ1. KRAS and NOTCH signaling pathways might be involved in the transcriptomic differences induced by BRD4 PROTACs and JQ1 treatment. Furthermore, combination therapy studies revealed that VHL-Q1 exhibited antagonistic effects when combined with paclitaxel, while demonstrating synergistic effects with cisplatin in TNBC treatment. Overall, our findings highlight VHL-JQ1 as a promising chemical probe for investigating BRD4 biological functions and a potential therapeutic candidate for TNBC treatment.