ABSTRACT
Melanoma is commonly associated with multi-organ metastasis, and bone is a frequent metastatic site for melanoma. However, the mechanism responsible for such melanoma-induced bone metastasis is still poorly understood. In the present study, the intracardiac inoculation of leukemia inhibitory factor (LIF)-producing human melanoma-derived cells (SEKI) developed osteolytic bone destruction in male BALB/cA-nu/nu nude mice. To elucidate the role of LIF in melanoma-induced osteolysis, cells were prepared in which the expression of LIF was reduced using a siRNA technique from the parent SEKI cells. Osteoclastogenesis was induced in the co-culture of LIF and/or SEKI cells with osteoblastic stromal cells in vitro, whereas the LIF-reduced SEKI cells did not induce osteoclastogenesis. The intracardiac inoculation of LIF-reduced SEKI cells resulted in a significant reduction in the incidence and number of bone metastasis in comparison to those in the mice inoculated with the parent SEKI cells. The expression of LIF was found in seven of nine human melanoma-derived cell lines, suggesting that LIF expression is a universal event in melanoma. These findings suggest that a potential role for LIF in the melanoma-induced bone metastasis possibly through the stimulation of osteoclastogenesis. LIF might therefore be a potentially effective drug target in the treatment of bone metastasis in melanoma.
Subject(s)
Bone Neoplasms/metabolism , Leukemia Inhibitory Factor/physiology , Melanoma, Experimental/metabolism , Osteoclasts/metabolism , Osteolysis/pathology , Animals , Bone Neoplasms/secondary , Cell Line, Tumor , Humans , Male , Melanoma, Experimental/pathology , Mice , Mice, Inbred BALB C , Mice, Nude , Osteoclasts/pathology , Osteolysis/metabolismABSTRACT
We have previously demonstrated that parathyroid hormone-related protein (PTHrP) is a cachexia inducer, but it is still not known what PTHrP effects on target tissues induce the cachexia. Therefore, we examined the effects of anti-PTHrP antibody and osteoprotegerin (OPG) on PTHrP-producing tumor-induced cachexia. Nude mice bearing PTHrP-producing human lung cancer cells (HARA-B) exhibited cachexia with hypercalcemia 3-4 weeks after inoculation, accompanied by losses in body, adipose tissue, and muscle weight. OPG ameliorated hypercalcemia, as did neutralization of PTHrP with antibody; and it increased both body and adipose tissue weights. These increases in body and adipose tissue weight, however, were significantly less than those in mice treated with anti-PTHrP antibody. Simultaneous administration of OPG and anti-PTHrP antibody caused significant increases in body, adipose tissue, and muscle weight, along with an immediate decrease in blood ionized calcium levels. The increase in body weight was similar to that observed in mice treated with anti-PTHrP antibody alone, and the decrease in the blood ionized calcium levels was significantly greater than that in mice treated with OPG or anti-PTHrP antibody alone. These results suggest that an effect of PTHrP on target tissues other than hypercalcemia is involved in the development of cachexia. Expression of cachexia-inducing proinflammatory cytokines (interleukin-6 and leukemia inhibitory factor) is stimulated by PTHrP. This might be a mechanism by which PTHrP produces tumor-induced cachexia. It is also suggested that OPG and anti-PTHrP antibody synergistically act to ameliorate hypercalcemia, although the mechanism responsible for this is unclear.
