In an effort to determine whether the primary

In an effort to determine whether the primary tumour might be responsible for “fertilising” the bone “soil” ready for the cancer “seed”, we recently found that a hypoxic gene signature, and more specifically the secreted enzyme lysyl oxidase (LOX) was closely associated with bone metastasis, specifically in estrogen receptor negative (ER-) breast cancer patients. We further investigated the role of LOX in bone metastasis in vivo and found that tumour-bearing mice showed increased bone loss and the formation of focal osteolytic lesions over time. Whilst this would not be too surprising an observation in a mouse that has overt bone metastases – we found these changes occurred from as little as 2-weeks post tumour implantation (when no metastases are present) and that they could be recapitulated by injection of cell-free conditioned medium (secreted factors) from cancer pppa manufacturer into mice. These changes were LOX-dependent, as cancer cells expressing shLOX injected into mice showed significantly less osteolytic lesions. Our data clearly showed that early osteolytic lesions are formed in the absence of tumour cells by hypoxia-induced tumour-secreted factors. Mechanistically these macroscopic changes, which would directly alter the physical, biochemical and biomechanical properties of bone ECM, were as a result of LOX modulating bone homeostasis leading to unbalanced coupling in favour of bone degradation and the formation of pre-metastatic osteolytic lesions. The physiological consequence of these ECM changes were increased metastatic burden in the bone, with micro-CT analysis revealing a positive correlation between lesion number and tumour burden. This demonstrated that LOX-mediated pre-metastatic changes to bone ECM led to the generation of pre-metastatic niches within the bone microenvironment that support colonisation of circulating tumour cells and the formation of overt bone metastases [13]. Furthermore, LOX may well be a useful marker for predicting the likelihood of metastases to the bone in ER- breast cancer patients and identifying these patients for early adjuvant bisphosphonate treatment. Similarly, in the future anti-LOX therapy, may prevent secondary bone cancer form occurring. Interestingly, a recent meta-analysis from the Early Breast Cancer Trialists’ Collaborative Group recently confirmed that adjuvant bisphosphonates reduce the rate of breast cancer recurrence in the bone and improve breast cancer survival, albeit with definite benefit only in women who were postmenopausal when treatment began [14]. For more information on this see our recently published Cancer Research Review [15]. Increasing evidence for the role of the LOX family of proteins in other cancers that metastasise to bone, specifically prostate cancer, has recently been provided. Caley and colleagues demonstrated that the tumour-associated collagen receptor Endo180 and the crosslinking of collagen by stromal-derived LOX controls tumour cell movement and as such is a potential target for limiting metastatic progression in prostate cancer [16]. In another study by Alsulaiman and colleagues whose initial aim was to provide evidence to support previous work that suggests LOX pro-peptide (LOX-PP), an 18KDa pro-peptide that is formed as Pro-LOX is processed by procollagen C-proteinases to yield the mature LOX enzyme, acts as a tumour suppressor. However, unexpectedly they found that LOX-PP was able to stimulate osteoblast differentiation as well as osteoclast formation and differentiation either in the presence or absence of exogenously added RANKL and M-SCF. Intramedullary injections of PC3 cells expressing LOX-PP showed increased osteoclast resorption and bone destruction in vivo, whilst the effect to enhance the development of osteoblastic lesions in the DU145 cells expressing LOX-PP was absent in their model [17]. This apparent paradox, that the effects of LOX-PP in all soft tissue tumour studies so far have demonstrated a beneficial outcome, whilst in mineralized tissue, LOX-PP shifts the balance towards a destructive, pro-cancerous effect could be due to the very unique properties of bone ECM. Delineating the differences between the effects of the same protein on different ECM will have beneficial therapeutic value for both types of cancer.