Quercetin Inhibits AKT Ser473 Phosphorylation and Disrupts AKT–Androgen Receptor Signaling in Castration-Resistant Prostate Cancer Cells

The progression of prostate cancer to castration-resistant disease (CRPC) remains a clinical challenge in which oxidative stress intersects with the PI3K/AKT–androgen receptor (AR) axis. Quercetin (QRC) is a redox-active dietary flavonol, yet its mechanistic impact on CRPC is incompletely defined. Here, we tested whether QRC suppresses AR output by directly modulating AKT. C4-2B and 22Rv1 CRPC cell lines were treated with increasing QRC concentrations, with or without enzalutamide (Enz). Proliferation and viability were monitored by IncuCyte imaging and SYTOX Green incorporation. AKT phosphorylation (S473), AR phosphorylation (S210/213), AR abundance and localization, and prostate-specific antigen (PSA) secretion were assessed by immunoblotting, immunofluorescence, and dot blot, respectively. Docking and molecular dynamic simulations were performed to identify and evaluate a putative QRC-binding site on AKT. QRC produced a dose-dependent cytostatic effect (IC50 24.37 μM in C4-2B; 21.54 μM in 22Rv1) without marked cell death, reduced pAKT(S473) by up to 80%, decreased pAR(S210/213), and diminished nuclear AR and PSA secretion. Simulations suggested a putative druggable allosteric pocket in the AKT1 N-lobe, with G159 emerging as a potential anchor residue. Enz cotreatment with QRC did not produce additive effects, consistent with a model in which QRC acts upstream of ligand-driven AR activation and thereby limits the incremental benefit of AR antagonism under these conditions. These data support QRC as an AKT–AR axis modulator in CRPC and provide a target engagement framework beyond simple ROS scavenging.