Interleukin 6 (IL-6) facilitates the differentiation of B cells to immunoglobulin-secreting cells and is reported to be a proliferative factor in some tumors. In this study, we examined IL-6 production in non-small cell lung carcinoma (NSCLC) and the proliferation of tumor cells following IL-6 treatment in vitro and in vivo. We analyzed the expression of IL-6 mRNA and protein in a series of 15 human lung cancer cell lines (four adenocarcinomas, five squamous cell carcinomas, two large cell carcinomas, and four small cell carcinomas) by reverse transcriptase polymerase chain reaction (RT-PCR) and enzyme-linked immunosorbent assay (ELISA). We established an IL-6-producing cell line (ABC-1#IL-6) by transfecting a human IL-6 cDNA into a human non-IL-6-producing NSCLC cell line (ABC-1). These two cell lines were used to determine tumor cell proliferation both in vivo and in vitro in order to clarify the effect of IL-6 on tumor growth and metastasis. Athymic nude mice, SCID mice, and BALB/c mice were subcutaneously inoculated with these two cell lines, and body weight, tumor growth, and tumor doubling time were measured. The presence of IL-6 and tumor-infiltrating lymphocytes (TILs) within tumor tissues was examined by immunohistochemical staining.
Results: Eight of 15 (53%) lung cancer cell lines expressed both IL-6 mRNA and protein. Tumor lesions of both cell lines developed in nude and SCID mice, although no such lesions of either cell lines developed in BALB/c mice. The tumor doubling time in nude and SCID mice was 2.97+/-1.22 days and 2.45+/-1.32 days, respectively, in mice inoculated with the cell line ABC-1#IL-6. These doubling times were statistically significantly shorter than those evident in mice inoculated with the control original ABC-1 cell line (nude, p=0.0337; SCID, p=0.0119; unpaired t-test). The rates of cell proliferation in vitro of the ABC-1#IL-6 and original ABC-1 cells lines were comparable ( p=0.1441, unpaired t-test). Immunohistochemical staining revealed strong IL-6 expression in tumors derived from the IL-6-producing cell line but not in tumors derived from the original ABC-1 cell line (both in nude and SCID mice).
Conclusion: 53% of lung cancer cell lines produce IL-6 mRNA and protein. Although IL-6 itself does not influence tumor cell proliferation in vitro, an association between IL-6 expression and tumor proliferation was found in vivo in nude and SCID mice. An anti-IL-6 reagent could provide a novel therapeutic strategy in patients with IL-6-producing lung tumors.