Interleukin-6 (IL-6), one of the proinflammatory cytokines, is considered to be one of the factors associated with poor prognosis of patients with renal cell carcinoma (RCC). Suppressor of cytokine signalling-3 (SOCS3) is rapidly up-regulated by IL-6 and a negative regulator of cytokine signalling. SOCS3 not only suppresses cytokine-mediated JAK/STAT signalling, but also sustains MAPK pathways. In our study, among the RCC cell lines, IL-6 mRNA expression was the highest in the 786-O cells, which also showed the highest level of SOCS3 mRNA expression under the condition of interferon stimulation. In contrast, ACHN cells had the lowest expression of both IL-6 and SOCS3 mRNA under the same condition. Our study is undertaken to evaluate the effect of humanised antihuman IL-6 receptor (IL-6R) antibody, which completely neutralises IL-6 activity, in RCC cell proliferation and its effect on signalling pathways. IL-6R antibody, tocilizumab, significantly suppressed cell proliferation in 786-O cells with interferon stimulation. Western blot analysis revealed that the tocilizumab enhanced the interferon-induced phosphorylation of STAT1 and inhibited SOCS3 expression and the phosphorylation of both STAT3 and ERK. In contrast, the IL-6 inhibited STAT1 phosphorylation, enhanced STAT3 phosphorylation and accelerated cell proliferation in ACHN cells. The in vivo effects of combination therapy with tocilizumab and interferon showed significant suppression of 786-O tumour growth in a xenograft model. Morphological observation of the tumours revealed the apoptosis, invasion of inflammatory cells and fibrosis. These findings suggest that combination therapy using an antihuman IL-6R antibody with interferon may represent a novel therapeutic approach for the treatment of RCC.
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