Abstract
BACKGROUND: Castration-resistant prostate cancer (CRPC) is a deadly disease that in addition to being resistant to androgen deprivation often exhibits also resistant to androgen receptor (AR)-antagonists. Supraphysiological androgen levels (SAL) are used in the bipolar androgen therapy in clinical phase trials to inhibit CRPC. METHODS: Co-immunoprecipitation, immunofluorescence, growth and cell senescence assays, mouse xenografted CRPC, AR target gene analyses of organs, analyses of RNA-seq, ChIP-seq and patient-derived xenografts, qRT-PCR, 3D tumor spheroids, knockdown experiments. RESULTS: Both AR-antagonists and -agonist at SAL induce cellular senescence despite acting oppositely on AR transcriptional activity. Here, we identified two common growth inhibitory pathways induced by SAL and AR-antagonists. Using the novel AR-antagonist compound 28 (C28), that inhibits also those AR mutants mediating therapy resistance, represses growth including CRPC tumor spheroids and mouse xenografted tumors. Mechanistically, C28 reduces phosphorylation of AR at serine 81 and HSP27 required for AR transcriptional activity and enhances AR-p130 interaction. Notably, increased p130 levels were also detected by SAL treatment leading to activation of DREAM complex signaling and induction of cellular senescence indicating that both AR-agonist and -antagonist use the same pathway for growth repression. Inhibition of DYRK1A, a key kinase to activate DREAM complex, blocks C28- and SAL-induced cellular senescence. Both C28 and SAL also induces the atypical cyclin G2 (CCNG2), which also mediates cellular senescence. Induction of CCNG2 is confirmed in CRPC tumor spheroids and xenograft tumors of treated mice. The second-generation AR-antagonist Darolutamide (Dar) also activates DREAM complex and CCNG2. CONCLUSION: Taken together, these findings suggest the identification of two common and independently acting pathways induced by AR-antagonists and SAL, used in bipolar androgen therapy, to mediate growth inhibition and induction of cellular senescence in CRPC.