Adaptive upregulation of EGFR limits attenuation of tumor growth by neutralizing IL-6 antibodies with implications for combined therapy in ovarian cancer

Excess production of the pro-inflammatory interleukin IL-6 has both local and systemic tumor-promoting activity in many cancers, including ovarian cancer. However, treatment of advanced ovarian cancer patients with a neutralizing IL-6 antibody yielded little efficacy in a previous Phase II clinical trial. Here we report results that may explain this outcome, based on the finding that neutralizing antibodies to IL-6 and STAT3 inhibition are sufficient to up-regulate the EGFR pathway in high-grade serous and other ovarian cancer cells. Cell treatment with the EGFR inhibitor gefitinib abolished upregulation of the EGFR pathway. Combining neutralizing IL-6 antibodies and gefitinib inhibited malignant cell growth in 2D and 3D culture. We found that ErbB-1 was localized predominantly in the nucleus of ovarian cancer cells examined, contrasting with plasma membrane localization in lung cancer cells. Treatment with anti-IL-6, gefitinib or their combination all led to partial restoration
of ErbB-1 on the plasma membrane. In vivo experiments confirmed the effects of IL-6 inhibition on the EGFR pathway and the enhanced activity of a combination of anti-IL-6 antibodies and gefitinib on malignant cell growth. Taken together, our results offer a preclinical rationale to combine anti-IL-6 and gefitinib to treat patients with advanced stage ovarian cancer.