Testosterone Replacement versus Placebo Bone and Bone Marrow in Castrated Mice. Mus musculus

Metastatic prostate cancer is commonly localized in bone and treated with androgen ablation, which is initially highly effective, but eventually results in resistant cancer cells. The decreased dependence on androgen is associated with activation of the androgen receptor (AR) via other growth factor receptor pathways. The current study analyzed global gene expression in bone from castrated and sham operated C57BL/6 mice to identify factors that may be responsible for androgen signaling. Androgen suppression by castration increased the expression of 159 genes with insulin-like growth factor binding protein 5 (IGFBP5) being the most consistently increased. IGFBP5 protein was detected by immune histochemistry in osteoblasts, bone marrow stromal cells and endothelial cells. In vitro treatment of marrow stromal cells with charcoal-stripped serum increased IGFBP5 mRNA expression approximately 25-fold and was reversed by androgen supplementation. Endogenous IGFBP5 was incorporated into extracellular matrix. In addition, treatment of extracellular matrices with exogenous IGFBP5 and IGF-1 or IGF-2 enhanced the growth of immortalized human prostate cells. These results suggest that androgen ablative therapy may increase IGFBP5 in the marrow microenvironment, thereby providing support for the development of therapy resistance prostate cancer cells. Keywords: Bone Marrow Environment, Androgen Suppression, IGFBP5, prostate cancer Overall design: Femural, tibial and humeral bones were collected from paired castrated C57BL/6 mice received Testosterone or placebo pellets (12.5 mg 60 day slow release, Innovative Research of America, Sarasota, FL) for 4 weeks. Each timepoint includes three replicates (mouse pairs) and cy dye labeling is alternated between experiment and control to account for dye effect. Testosterone Replacement is the experimental channel and Placebo Control is the control channel.