Osteoblasts Generate Testosterone From DHEA and Activate Androgen Signaling in Prostate Cancer Cells.

Bone metastasis is a complication of prostate cancer in up to 90% of men afflicted with advanced disease. Therapies that reduce androgen exposure remain at the forefront of treatment. However, most prostate cancers transition to a state whereby reducing testicular androgen action becomes ineffective. A common mechanism of this transition is intratumoral production of testosterone (T) using the adrenal androgen precursor dehydroepiandrosterone (DHEA) through enzymatic conversion by 3ß- and 17ß-hydroxysteroid dehydrogenases (3ßHSD and 17ßHSD). Given the ability of prostate cancer to form blastic metastases in bone, we hypothesized that osteoblasts might be a source of androgen synthesis. RNA expression analyses of murine osteoblasts and human bone confirmed that at least one 3ßHSD and 17ßHSD enzyme isoform was expressed, suggesting that osteoblasts are capable of generating androgens from adrenal DHEA. Murine osteoblasts were treated with 100 nM and 1 µM DHEA or vehicle control. Conditioned media from these osteoblasts were assayed for intermediate and active androgens by liquid chromatography-tandem mass spectrometry. As DHEA was consumed, the androgen intermediates androstenediol and androstenedione were generated and subsequently converted to T. Conditioned media of DHEA-treated osteoblasts increased androgen receptor (AR) signaling, prostate-specific antigen (PSA) production, and cell numbers of the androgen-sensitive prostate cancer cell lines C4-2B and LNCaP. DHEA did not induce AR signaling in osteoblasts despite AR expression in this cell type. We describe an unreported function of osteoblasts as a source of T that is especially relevant during androgen-responsive metastatic prostate cancer invasion into bone. © 2021 American Society for Bone and Mineral Research (ASBMR). This article has been contributed to by US Government employees and their work is in the public domain in the USA.

Castration Determines the Efficacy of ETAR Blockade in a Mouse Model of Prostate Cancer Bone Metastasis.

Bone metastasis is a painful complication of advanced prostate cancer. Endothelin-1 is a tumor-secreted factor that plays a central role in osteoblast activation and the osteosclerotic response of prostate cancer metastatic to bone. Antagonists that block the activation of the endothelin A receptor (ETAR), located on osteoblasts, reduce osteoblastic bone lesions in animal models of bone metastasis. However, ETAR antagonists demonstrated limited efficacy in clinical trials of men with advanced prostate cancer who also received standard androgen deprivation therapy (ADT). Previous data from our group suggested that, in a mouse model, ETAR antagonists might only be efficacious when androgen signaling in the osteoblast is lowered beyond the ability of standard ADT. This notion was tested in a mouse model of prostate cancer bone metastasis. Castrated and sham-operated male athymic nude mice underwent intracardiac inoculation of the ARCaPM castration-resistant prostate cancer cell line. The mice were then treated with either the ETAR antagonist zibotentan or a vehicle control to generate four experimental groups: vehicle+sham (Veh+Sham), vehicle+castrate (Veh+Castr), zibotentan+sham (Zibo+Sham), and zibotentan+castrate (Zibo+Castr). The mice were monitored radiographically for the development of skeletal lesions. The Zibo+Castr group had significantly longer survival and a single incidental lesion. Mice in the Zibo+Sham group had the shortest survival and the largest number of skeletal lesions. Survival and skeletal lesions of the Veh+Sham and Veh+Castr groups were intermediate compared with the zibotentan-treated groups. We report a complex interaction between ETAR and androgen signaling, whereby ETAR blockade was most efficacious when combined with complete androgen deprivation.

Dural Cells Release Factors Which Promote Cancer Cell Malignancy and Induce Immunosuppressive Markers in Bone Marrow Myeloid Cells.

BACKGROUND: Thirty per cent of cancer patients develop spine metastases with a substantial number leading to spinal cord compression and neurological deficits. Many demonstrate a propensity toward metastasis to the posterior third of the vertebral body. The dura, the outer layer of the meninges, lies in intimate contact with the posterior border of the vertebral body and has been shown to influence adjacent bone. The effects of the dura on bone marrow and cancer cells have not been examined. Understanding the biology of spinal metastasis will provide insights into mechanisms of cancer growth and allow for new treatment strategies. OBJECTIVE: To examine the extent to which dura influences bone marrow/tumor cell metastatic characteristics. METHODS: Dura conditioned media (DCM) from primary dura was examined for the ability to stimulate tumor cell proliferation/invasion and to alter bone marrow cell populations. RNA sequencing of dural fibroblasts was performed to examine expression of cytokines and growth factors. RESULTS: DCM induced a significant increase in invasion and proliferation of multiple tumor cell lines, and of patient-derived primary spinal metastatic cells. DCM also increased the proliferation of bone marrow myeloid cells, inducing expression of immunosuppressive markers. RNA sequencing of dural fibroblasts demonstrated abundant expression of cytokines and growth factors involved in cancer/immune pathways. CONCLUSION: Factors released by primary dural cells induce proliferation of tumor cells and alter bone marrow to create a fertile environment for tumor growth. The dura therefore may play an important role in the increased incidence of metastases to adjacent bone.