ABSTRACT: Bone metastasis is a leading cause of death in prostate cancer (PC) patients. Although androgen‐deprivation therapy (ADT) combined with novel androgen‐targeted agents constitutes the cornerstone of systemic treatment, its efficacy is limited. We investigated the adrenal contribution in promoting progression of castration-resistant PC (CRPC) within bone using a preclinical intratibial xenograft model (VCaP, 22Rv1, and LNCaP cells). Mice underwent orchiectomy (ORX) to mimic ADT, with or without adrenalectomy (ORX+ADX) to eliminate adrenal contribution. A significant increase in bone mineral density (BMD) was observed in tumor-grafted tibiae in ORX-treated mice compared to controls (p<0.001), indicating a strong tumor-induced sclerotic response. In contrast, ORX+ADX reduced tumor take rate by approximately 50% and decreased tumor-induced BMD by over 80% (p<0.001). Transcriptomic analysis revealed that ADX downregulated tumor-induced transcripts in bone by over 90%, including osteogenic (Lox, Sparcl1, Bmp2, Postn, Col1a1) and pro-angiogenic (Bmper, Pecam-1, Esam) signatures. Additionally, BMP, PI3K/Akt and ERK1/2 signaling pathways were associated with the tumor-induced bone response. Both high serum progesterone and intratumoral levels of dihydrotestosterone (DHT) were associated with the sclerotic bone phenotype. ADX markedly reduced intratumoral DHT and downregulated glycolytic genes (HK2, PFK2, LDHA) and secretory proteins expressed by the tumor, including Stanniocalcin 2, potentially mediating paracrine effects in the sclerotic bone response. Altogether, these findings highlight the critical role of adrenal- dependent androgen synthesis, particularly via progesterone, in driving the sclerotic CRPC in bone. Our findings suggest that a comprehensive blockade of adrenal contribution is essential to prevent the sclerotic bone response associated with CRPC.
