Dual BRD4/AKT inhibition overcomes c-MYC-driven resistance in metastatic castration-resistant prostate cancer

Metastatic castration-resistant prostate cancer (mCRPC) represents the terminal and most challenging stage of prostate cancer progression, characterized by limited therapeutic options and poor prognosis. Although AKT inhibitors have been explored as a potential treatment strategy for mCRPC, their efficacy as monotherapy is often constrained by the rapid development of resistance. Emerging evidence indicates that this acquired resistance is frequently associated with the elevated expression of the c-MYC oncogene. Bromodomain and extraterminal (BET) inhibitors, such as those targeting BRD4, can disrupt the interaction between BRD4 and chromatin, thereby attenuating c-Myc-driven oncogenic signaling. To address this dual-pathway challenge, we designed and synthesized a novel series of dual BRD4/AKT inhibitors. Through structure-activity relationship analyses, compound 21d was identified as a potent dual inhibitor, exhibiting activity against both BRD4 and AKT1 with IC₅₀ values of 66.12 ± 7.69 nM and 143.81 ± 12.21 nM, respectively. In vitro, 21d effectively modulated key downstream effectors of both AKT1 and BRD4, leading to significant suppression of mCRPC cell proliferation, migration, and colony formation. Mechanistically, 21d induced G0/G1 phase cell-cycle arrest by downregulating phosphorylated RB (p-RB), cyclin E1, and CDK2. Concurrently, 21d elevated the protein levels of the autophagy marker LC3B, promoting apoptosis in 22Rv1 cells. In vivo, 21d demonstrated a favorable pharmacokinetic profile and markedly inhibited tumor growth in an mCRPC xenograft mouse model, achieving a tumor growth inhibition (TGI) rate of 62.0%. Collectively, our findings establish 21d as the first-in-class dual BRD4/AKT inhibitor, offering a promising therapeutic strategy to overcome c-Myc-associated resistance in mCRPC.