Bone stroma-derived cells change coregulators recruitment to androgen receptor and decrease cell proliferation in androgen-sensitive and castration-resistant prostate cancer cells

Osteoclasts directly influence castration-resistant prostate cancer cells

Metastasis to bone is the leading cause of death from prostate cancer. Interaction between tumor cells and bone cells can promote progression and influence tumor phenotype. It is known that prostate cancer cells support osteoclast differentiation, and degradation of bone matrix by osteoclasts releases growth factors stimulating tumor cell proliferation and invasion. In the present study osteolytic (PC-3) and osteoblastic (LNCaP-19) castration-resistant prostate cancer (CRPC) cells were co-cultured with mature osteoclasts or their precursor cells (RAW 264.7) to characterize direct effects of mature osteoclasts on CRPC cells. Osteoclasts increased proliferation and decrease apoptosis of CRPC cells as assessed with flow cytometry. RNA sequencing revealed that osteolytic CRPC cells were more responsive to osteoclast stimulation regarding gene expression, but the overall induced expression patterns were similar between the prostate cancer cell lines. Genes related to DNA repair were upregulated by osteoclasts, while genes related to endoplasmic reticulum stress-induced apoptosis and cholesterol synthesis were downregulated. The results of this study shows that osteoclasts directly influence CRPC cells, increasing proliferation, decreasing apoptosis, and affecting gene expression pathways that can affect sensitivity to DNA damage and endoplasmic reticulum function. This suggests targeting of osteoclasts to be a possible way to affect efficacy of other drugs by combination regimens in treating prostate cancer metastases.

Cellular specificity of androgen receptor, coregulators, and pioneer factors in prostate cancer

Androgen signalling, through the transcription factor androgen receptor (AR), is vital to all stages of prostate development and most prostate cancer progression. AR signalling controls differentiation, morphogenesis, and function of the prostate. It also drives proliferation and survival in prostate cancer cells as the tumour progresses; given this importance, it is the main therapeutic target for disseminated disease. AR is also essential in the surrounding stroma, for the embryonic development of the prostate and controlling epithelial glandular development. Stromal AR is also important in cancer initiation, regulating paracrine factors that excite cancer cell proliferation, but lower stromal AR expression correlates with shorter time to progression/worse outcomes. The profile of AR target genes is different between benign and cancerous epithelial cells, between castrate-resistant prostate cancer cells and treatment-naïve cancer cells, between metastatic and primary cancer cells, and between epithelial cells and fibroblasts. This is also true of AR DNA-binding profiles. Potentially regulating the cellular specificity of AR binding and action are pioneer factors and coregulators, which control and influence the ability of AR to bind to chromatin and regulate gene expression. The expression of these factors differs between benign and cancerous cells, as well as throughout disease progression. The expression profile is also different between fibroblast and mesenchymal cell types. The functional importance of coregulators and pioneer factors in androgen signalling makes them attractive therapeutic targets, but given the contextual expression of these factors, it is essential to understand their roles in different cancerous and cell-lineage states.

Clinical relevance of androgen receptor alterations in prostate cancer

Prostate cancer (PC) remains a leading cause of cancer-related deaths among men worldwide, despite continuously improved treatment strategies. Patients with metastatic disease are treated by androgen deprivation therapy (ADT) that with time results in the development of castration-resistant prostate cancer (CRPC) usually established as metastases within bone tissue. The androgen receptor (AR) transcription factor is the main driver of CRPC development and of acquired resistance to drugs given for treatment of CRPC, while a minority of patients have CRPC that is non-AR driven. Molecular mechanisms behind epithelial AR reactivation in CRPC include AR gene amplification and overexpression, AR mutations, expression of constitutively active AR variants, intra-tumoural and adrenal androgen synthesis and promiscuous AR activation by other factors. This review will summarize AR alterations of clinical relevance for patients with CRPC, with focus on constitutively active AR variants, their possible association with AR amplification and structural rearrangements as well as their ability to predict patient resistance to AR targeting drugs. The review will also discuss AR signalling in the tumour microenvironment and its possible relevance for metastatic growth and therapy.