Yoshihiro Morinaga

Suppression of interleukin-11-mediated bone resorption by cyclooxygenases inhibitors.

We previously found that human melanoma (A375M) and human breast cancer (MDA‐MB‐231) cells formed osteolytic bone metastasis in vivo. These cancer cells produced interleukin‐11 (IL‐11) by themselves and stimulated its production from osteoblasts. Interleukin‐11 could increase the number of osteoclasts and raise the calcium concentration in the medium of neonatal murine calvaria organ culture, indicating bone resorption in vitro. Therefore, IL‐11 could play an important role in the promotion of osteolysis at the site of bone metastasis. In the present study, we used the calvaria culture system to try to clarify the mechanisms of IL‐11–mediated bone resorption. The murine calvaria expressed both the specificity‐determining α subunit and the signal–transducing β subunit (gp130) of the IL‐11 receptor. When IL‐11 was added to the calvaria culture, the concentrations of prostaglandin E2 (PGE2) was elevated. Pretreatment of calvaria with cyclooxygenases inhibitors (e.g., indomethacin, NS‐398, and dexamethasone) suppressed the production of PGE2 and the bone resorption induced by IL‐11. Addition of exogenous PGE2 overcame the inhibitory effect of cyclooxygenases inhibitors and promoted bone resorption. These results indicate that IL‐11 promotes bone resorption through a PGE2 synthesis–dependent mechanism and that cyclooxygenases inhibitors could be interesting drugs to suppress IL‐11–mediated osteolytic bone metastasis of cancer cells. J. Cell. Physiol. 175:247–254, 1998.

Stimulation of interleukin‐11 production from osteoblast‐like cells by transforming growth factor‐β and tumor cell factors

Bone is one of the most common sites of metastasis in melanoma and breast cancer cells. Human melanoma (A375M) and human breast cancer (MDA‐MB‐231) cells form osteolytic bone metastasis in vivo when these tumor cells are injected into the left ventricles of BALB/c nude mice. These tumor cells promote bone resorption in the in vitro neonatal murine calvaria organ culture system by indirectly stimulating the production of a bone resorption‐inducing factor (or factors) from human osteoblast‐like cells. This secreted factor was identified as interleukin‐11 (IL‐11). Although many cytokines and hormones were associated with IL‐11 production from osteoblasts, transforming growth factor‐β (TGF‐β) was found to be involved in the promotion of IL‐11 production from osteoblasts, because the addition of a neutralizing anti‐TGF‐β antibody decreased the production of IL‐11. However, these tumor cells did not produce TGF‐β by themselves. We found that they enhanced IL‐11 production by activating latent TGF‐β produced from osteoblast‐like cells. Our results indicate that metastatic tumor cells induce osteolysis by activating TGF‐β, which leads IL‐11 production from osteoblasts to promote bone resorption. Int. J. Cancer 71:422‐428, 1997.

Production of interleukin-11 in bone-derived endothelial cells and its role in the formation of osteolytic bone metastasis

The interactions of the cells in the bone microenvironment play important roles in bone remodeling. Osteoblasts are involved in the bone remodeling through the production of soluble factors that regulate proliferation and differentiation of osteoclasts and through cell–cell interactions. Histological studies have suggested that endothelial cells are also associated with some osteolytic bone diseases. However, it is still unclear how endothelial cells contribute to bone resorption. We established bone-derived endothelial cells (BDECs) to study their roles in bone remodeling. The established BDECs promoted bone resorption in a murine neonatal calvaria organ culture system by secreting a soluble bone resorption-inducing factor(s) when stimulated by several inflammatory cytokines. This bone resorption-inducing factor was identified as interleukin-11 (IL-11). IL-11 is known to enhance bone resorption by promoting osteoclastogenesis and by suppressing the activity of osteoblasts. The production of IL-11 in BDECs was also promoted by conditioned medium of human melanoma A375M cells. Because A375M cells formed osteolytic bone metastasis in vivo, BDECs might be involved in pathological osteolysis by producing IL-11. These results suggest that endothelial cells in bone play important roles in the promotion of bone resorption by secreting IL-11 in physiological and pathological conditions.

H-31 human breast cancer cells stimulate type I collagenase production in osteoblast-like cells and induce bone resorption.

Bone is one of the most common sites of metastasis in breast cancer. For metastasis to occur in bone, tumor cells must induce osteolysis by osteoclasts. Degradation of the osteoid layer by type I collagenase is a necessary process before osteolysis can occur because the psteoid layer hinders osteoclasts from adhering to bone. In this study, we investigated the function of H-31 human breast cancer cells in inducing type I collagenase production and in enhancing bone resorption. H-31 cells did not themselves produce type I collagenase whereas MG-63 human osteoblast-like cells and MC3T3-E1 mouse osteoblast cells constantly produced type I collagenase. When these osteoblast-like cells were cocultured with H-31 cells, type I collagenase production was enhanced. The same enhancement occurred when the conditioned medium of H-31 cells was added to the osteoblast-like cells. The activity of this type I collagenase was inhibited by EDTA and minocyclin, an inhibitor of matrix metalloproteinases, hence it was identified as matrix metalloproteinase-1 (MMP-1). H-31 cells exhibited chemotactic migration towards collagen; therefore, collagen degraded by MMP-1 may play an important role in the localisation of breast cancer cells like H-31 to bone. In an organ culture system using newborn mouse calvaria, the conditioned medium of H-31 cells increased the concentration of calcium in the medium, and this effect was inhibited by minocyclin, indicating that bone resorption occurred in this system. Based on these observations, we speculate that type I collagenase produced by osteoblast cells in response to breast cancer cells (exemplified by H-31) may facilitate degradation of the osteoid layer and the homing of breast cancer cells to bone. This can lead to osteolysis by osteoclasts, a crucial event for bone metastasis.