Prostate cancer is the most common cancer in men, and bone is the preferred site for metastasis. Current treatment options for metastasised prostate cancer are not curative since conventional therapies (hormone, chemo-, and radiation therapy) seem relatively ineffective in targeting prostate cancer cells with stem/progenitor-like characteristics (CSCs). It is becoming increasing clear that the generation of CSCs may be linked to the acquisition of an invasive phenotype via epithelial-to-mesenchymal transition (EMT). Previously we found that bone morphogenetic protein 7 (BMP7) inhibited EMT and bone metastasis formation but the effect of BMP7 on prostate CSCs has remained largely elusive. In this study, we show that BMP7 is the most potent inducer (180×) of BMP reporter signalling of all tested BMPs (BMP2, BMP4, BMP6, BMP2/7, and BMP4/7). In clonogenic assays, BMP7 (2 nM) reduced the formation of holoclones (colonies enriched for CSCs) of PC-3 and PC-3M-Pro4 prostate cancer cells. While TGFβ pretreatment increased, BMP7 pretreatment reduced migration, and inhibited proliferation at later time points. Interestingly, when PC-3M-Pro4 cells were FACS-sorted for high aldehyde dehydrogenase (ALDH) enzymatic activity, BMP7 was shown to differentially inhibit clonogenic capability of the CSC subpopulation (ALDH-hi vs ALDH-lo). In vivo, intravascular injection of red-fluorescent prostate cancer cells in zebrafish with a GFP+ vasculature a model of dissemination and metastasis- led to rapid dissemination, extravasation, and metastatic colonisation of distant sites. Strikingly, BMP7 pretreatment (2 nM) of PC-3M-Pro4/mCherry cells inhibited extravasation and reduced formation of distant metastases at 1 and 3 days post inoculation respectively. Furthermore, BMP7 pretreatment increased the metastasis-free survival (62.5% vs 100% in vehicle) and reduced the number of distant metastases in a model of intracardiac injection of PC-3M-Pro4/Luciferase cells in nude mice allowing for real-time cell-tracking. In conclusion, we have shown that BMP7 targets the CSC subpopulation in human prostate cancer leading to impaired formation of distant metastasis.
Disclosure: The authors declared no competing interests. This study was supported by the Netherlands Organization for Scientific Research (NWO, VENI-grant, 916.131.10).