The Involvement of P2X7R Signalling in LOX Mediated Formation of a Pre-Metastatic Niche in Bone

Metastasis to bone seriously complicates treatment of cancer, resulting in an incurable and debilitating condition which can greatly decrease quality of life as a result of excessive bone destruction. Recent research has identified tumour secreted LOX as a contributor to cancer induced bone loss, by generating osteolytic lesions prior to cancer cell arrival, thus contributing to pre-metastatic niche formation, and enhancing metastatic cell recruitment and survival in bone. Previous research has also observed that LOX accumulates at areas of pressure, and is hypoxically regulated, highlighting a potential involvement with P2X7R, which contributes significantly to cancer cell survival and osteoclastic resorption of bone. This thesis builds on these observations by investigating the involvement of LOX and P2X7R in pre-metastatic modification of bone in a syngeneic BALB/c mouse/4T1 murine breast cancer model. Analysis of µCT data from the tibia of tumour bearing mice revealed significantly reduced bone destruction upon knockdown of LOX in the tumour, or knockout of P2X7R in the mouse, confirming an interaction. These observations were repeated in cancer cell free mice, receiving injections of conditioned medium from 4T1 cells grown in vitro, confirming that bone destruction and osteolytic lesion formation are the result of secreted factors from the primary tumour, and can occur prior to cancer cell arrival at the bone. The effect of mechanical loading upon LOX/P2X7R modification of pre-metastatic bone was also investigated by subjecting tumour bearing mice to non-invasive axial loading of the right hindlimb. Mechanical loading was found to have a mixed effect on bone, driving thickening of cortical and trabecular bone, but also osteolytic lesion formation. P2X7R contributed to bone response to loading, while tumour-secreted LOX had no effect. Taken together, mechanical loading and P2X7R inhibition were found to effectively combat tumour induced bone loss, identifying novel targets for future treatments of metastatic bone disease.