Advanced prostate cancers that progress to tumor metastases are often considered incurable or difficult to treat. The etiology of prostate cancers is multi-factorial. Among other factors, de-regulation of calcium signals in prostate tumor cells mediates several pathological dysfunctions associated with tumor progression. Calcium plays a relevant role on tumor cell death, proliferation, motility-invasion and tumor metastasis. Calcium controls molecular factors and signaling pathways involved in the development of prostate cancer and its progression. Such factors and pathways include calcium channels and calcium-binding proteins. Nevertheless, the involvement of calcium signaling on prostate cancer predisposition for bone tropism has been relatively unexplored. In this regard, a diversity of mechanisms triggers transient accumulation of intracellular calcium in prostate cancer cells, potentially favoring bone metastases development. New therapies for the treatment of prostate cancer include compounds characterized by potent and specific actions that target calcium channels/transporters or pumps. These novel drugs for prostate cancer treatment encompass calcium-ATPase inhibitors, voltage-gated calcium channel inhibitors, transient receptor potential (TRP) channel regulators or Orai inhibitors. This review details the latest results that have evaluated the relationship between calcium signaling and progression of prostate cancer, as well as potential therapies aiming to modulate calcium signaling in prostate tumor progression.

Bone metastases are common in advanced prostate cancer patients, but mechanisms by which specific pro-metastatic skeletal niches are formed before tumor cell homing are unclear. We aimed to analyze the effects of proteins secreted by primary prostate tumors on the bone microenvironment before the settlement and propagation of metastases. Here, using an in vivo pre-metastatic prostate cancer model based on the implantation of prostate adenocarcinoma TRAMP-C1 cells in immunocompetent C57BL/6 mice, we identify MINDIN as a prostate tumor secreted protein that induces bone microstructural and bone remodeling gene expression changes before tumor cell homing. Associated with these changes, increased tumor cell adhesion to the endosteum ex vivo and to osteoblasts in vitro was observed. Furthermore, MINDIN promoted osteoblast proliferation and mineralization and monocyte expression of osteoclast markers. β-catenin signaling pathway revealed to mediate MINDIN actions on osteoblast gene expression but failed to affect MINDIN-induced adhesion to prostate tumor cells or monocyte differentiation to osteoclasts. Our study evidences that MINDIN secretion by primary prostate tumors creates a favorable bone environment for tumor cell homing before metastatic spread.

Advanced prostate cancer cells preferentially metastasize to bone by acquiring a bone phenotype that allows metastatic cells to thrive in the skeletal environment. Identification of factors that promote the expression of ectopic bone genes—process known as osteomimicry—leading to tumor progression is crucial to prevent and treat metastatic prostate cancer and prolong life expectancy for patients. Here, we identify the extracelular matrix protein mindin in the secretome of prostate adenocarcinoma cells and show that mindin overexpression in human and mouse TRAMP-C1-induced prostate tumors correlates with upregulated levels of bone-related genes in the tumorigenic prostate tissues. Moreover, mindin silencing decreased osteomimicry in adenocarcinoma cells and in the prostate tumor mice model, as well as reduced tumor cell proliferation, migration and adhesion to bone cells. Inhibition of the extracellular signal-regulated kinase 1/2 (ERK 1/2) phosphorylation decreased the proliferative, migratory and pro-adhesion actions of mindin on prostate tumor cells. In addition, conditioned media obtained by crosstalk stimulation of either osteocytes or osteoblasts with the secretome of TRAMP-C1 cells promoted osteomimicry in prostate tumor cells; an effect inhibited by mindin silencing of TRAMP-C1 cells. In vivo, tibiae of primary tumor-bearing mice overexpressed the pro-angiogenic and pro-metastattic factor vascular endothelial growth factor receptor 2 (VEGFR2) in a mindin-dependent manner. Our findings indicate that mindin is a novel regulator of osteomimicry in prostate tumors and potentially mediates tumor-bone cell crosstalk, suggesting its promising role as a target to inhibit bone metastases.

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Objective: To analyze the effect of the secrets of solid organotropic tumors towards bone in osteogenic, osteoblastic and osteocytic lineage cells, in the expression of genes related to bone metabolism. Material and method: We characterize the changes in gene expression by quantitative real-time PCR of the OPG/RANKL axis, as well as other genes related to osteoblastic differentiation such as Runx2 and osteocalcin, induced by the conditioned means of prostate tumor cells, breast and melanoma in pre MC3T3-E1 osteoblasts and murine MLO-Y4 osteocytes or in human osteoblasts, as appropriate by species. Results: Stimulation of osteocitic cells with conditioned means of melanoma or prostate adenocarcinoma cells induced an increase in OPG and RANKL gene expression, with the OPG/RANKL ratio being increased. Only the secretome of prostate adenocarcinoma cells altered the expression of Runx2 in osteocytes. Conditioned media of breast cancer cells only modified the expression of RANKL in osteoblast cells, with a decrease in OPG/RANKL ratio. Conclusion: Soluble tumor factors have osteocitic cells as their cellular target, favoring the induction of a pre-metastatic bone niche by modifying the OPG/RANKL ratio in the bone environment, and, thus, the progression of bone organotropic tumors such as melanoma and prostatic adenocarcinomas.