• The frequency of osteolytic bone metastasis is determined by conditions of the soil, not the number of seeds; evidence from in vivo models of breast and prostate cancer.

      Wang, N; Reeves, Kimberley J; Brown, H; Fowles, A; Docherty, F; Ottewell, P; Croucher, P; Holen, I; Eaton, C; The Mellanby Centre for Bone Research, Department of Human Metabolism, Medical School, University of Sheffield, Beech Hill Road, Sheffield, S10 2RX (2015)
      While both preclinical and clinical studies suggest that the frequency of growing skeletal metastases is elevated in individuals with higher bone turnover, it is unclear whether this is a result of increased numbers of tumour cells arriving in active sites or of higher numbers of tumour cells being induced to divide by the bone micro-environment. Here we have investigated how the differences in bone turnover affect seeding of tumour cells and/or development of overt osteolytic bone metastasis using in vivo models of hormone-independent breast and prostate cancer.
    • Mitotic quiescence, but not unique "stemness," marks the phenotype of bone metastasis-initiating cells in prostate cancer.

      Wang, N; Docherty, F; Brown, H; Reeves, Kimberley J; Fowles, A; Lawson, M; Ottewell, P; Holen, I; Croucher, P; Eaton, C; et al. (2015-04-17)
      This study aimed to identify subpopulations of prostate cancer cells that are responsible for the initiation of bone metastases. Using rapidly dividing human prostate cancer cell lines, we identified mitotically quiescent subpopulations (<1%), which we compared with the rapidly dividing populations for patterns of gene expression and for their ability to migrate to the skeletons of athymic mice. The study used 2-photon microscopy to map the presence/distribution of fluorescently labeled, quiescent cells and luciferase expression to determine the presence of growing bone metastases. We showed that the mitotically quiescent cells were very significantly more tumorigenic in forming bone metastases than fast-growing cells (55 vs. 15%) and had a unique gene expression profile. The quiescent cells were not uniquely stem cell like, with no expression of CD133 but had the same level expression of other putative prostate stem cell markers (CD44 and integrins α2/β1), when compared to the rapidly proliferating population. In addition, mitotic quiescence was associated with very high levels of C-X-C chemokine receptor type 4 (CXCR4) production. Inhibition of CXCR4 activity altered the homing of quiescent tumor cells to bone. Our studies suggest that mitotic dormancy is a unique phenotype that facilitates tumor cell colonization of the skeleton in prostate cancer.-Wang, N., Docherty, F., Brown, H. K., Reeves, K., Fowles, A., Lawson, M., Ottewell, P. D., Holen, I., Croucher, P. I., Eaton, C. L. Mitotic quiescence, but not unique "stemness," marks the phenotype of bone metastasis-initiating cells in prostate cancer.
    • Prostate cancer cells preferentially home to osteoblast-rich areas in the early stages of bone metastasis: evidence from in vivo models.

      Wang, N; Docherty, F; Brown, H; Reeves, Kimberley J; Fowles, A; Ottewell, P; Dear, T; Holen, I; Croucher, P; Eaton, C; et al. (2014-12)
      It has been suggested that metastasis-initiating cells gain a foothold in bone by homing to a metastastatic microenvironment (or "niche"). Whereas the precise nature of this niche remains to be established, it is likely to contain bone cell populations including osteoblasts and osteoclasts. In the mouse tibia, the distribution of osteoblasts on endocortical bone surfaces is non-uniform, and we hypothesize that studying co-localization of individual tumor cells with resident cell populations will reveal the identity of critical cellular components of the niche. In this study, we have mapped the distribution of three human prostate cancer cell lines (PC3-NW1, LN-CaP, and C4 2B4) colonizing the tibiae of athymic mice following intracardiac injection and evaluated their interaction with potential metastatic niches. Prostate cancer cells labeled with the fluorescent cell membrane dye (Vybrant DiD) were found by two-photon microscopy to be engrafted in the tibiae in close proximity (∼40 µm) to bone surfaces and 70% more cancer cells were detected in the lateral compared to the medial endocortical bone regions. This was associated with a 5-fold higher number of osteoblasts and 7-fold higher bone formation rate on the lateral endocortical bone surface compared to the medial side. By disrupting cellular interactions mediated by the chemokine (C-X-C motif) receptor 4 (CXCR4)/chemokine ligand 12 (CXCL12) axis with the CXCR4 inhibitor AMD3100, the preferential homing pattern of prostate cancer cells to osteoblast-rich bone surfaces was disrupted. In this study, we map the location of prostate cancer cells that home to endocortical regions in bone and our data demonstrate that homing of prostate cancer cells is associated with the presence and activity of osteoblast lineage cells, and suggest that therapies targeting osteoblast niches should be considered to prevent development of incurable prostate cancer bone metastases. © 2014 American Society for Bone and Mineral Research.