Interleukin 1-Dependent and -Independent Mouse Melanoma Metastases

Abstract

The adhesion of cancer cells to the endothelial lining of blood vessels, which is important for metastasis, is promoted by the action of interleukin 1 (IL-1) and other cytokines. IL-1-producing melanoma cells were used to induce metastases in mice to test whether melanoma metastasis--wherever it occurs--depends on the action of IL-1. We used the following experimental designs in this study: 1) Male C57BL/6J mice were inoculated in the left cardiac ventricle with 5 x 10(4) murine B16 melanoma cells, and no treatment was given (control animals). 2) Mice received an intraperitoneal injection of either saline (control animals) or recombinant human IL-1 receptor antagonist (rHuIL-1Ra) 2 hours before the injection of cancer cells; thereafter, they received an additional injection of saline or rHuIL-1Ra daily for 20 days. 3) Mice received an intravenous injection of either saline or rHuIL-1Ra; 15 minutes later, mice that received saline were given either a second injection of saline (control animals) or an injection of bacterial lipopolysaccharide (LPS) to stimulate host IL-1 production and endothelial cell activation. The mice that received rHuIL-1Ra were also given an injection of LPS at this time. Six hours later, all mice were inoculated with cancer cells, followed by no further treatment. In all experiments, the mice were killed 20 days after the injection of cancer cells, and metastases were counted in multiple organs and bones. Metastasis incidence values (relating to the frequency that a given site was positive for metastasis) and metastasis development index values (relating to the extent of metastasis at a given site) were calculated. A hierarchical cluster analysis was performed to determine whether groups of organs exhibited characteristic changes in their metastasis development index values in response to the three treatments given (i.e., rHuIL-1Ra, LPS, or rHuIL-1Ra plus LPS). Reported P values are two-sided. Treatment with rHuIL-1Ra alone significantly (P<.05) reduced the occurrence of metastasis in the bone marrow, spleen, liver, lung, pancreas, skeletal muscle, adrenal gland, and heart, indicating that host- and/or melanoma-derived IL-1 promoted metastasis in these organs; treatment with rHuIL-1Ra had no effect on metastasis in the kidney, testis, brain, skin, and gastrointestinal tract, suggesting that metastasis in these latter organs was IL-1 independent. Treatment with LPS alone significantly (P<.05) enhanced metastasis in the same organs for which rHuIL-1Ra treatment reduced metastasis, except for the heart and the adrenal gland. Treatment with rHuIL-1Ra 15 minutes before LPS treatment abrogated the LPS-mediated enhancement of metastasis. Two independent organ groups for which IL-1 promoted melanoma metastasis were identified in the cluster analysis.