Overriding TKI resistance of renal cell carcinoma by combination therapy with IL-6 receptor blockade

// Kei Ishibashi 1, 2 , Tobias Haber 2 , Ines Breuksch 3 , Susanne Gebhard 3 , Takashi Sugino 4 , Hitoshi Kubo 5 , Junya Hata 1 , Tomoyuki Koguchi 1 , Michihiro Yabe 1 , Masao Kataoka 1 , Soichiro Ogawa 1 , Hiroyuki Hiraki 1 , Tomohiko Yanagida 1 , Nobuhiro Haga 1 , Joachim W. Thuroff 2 , Dirk Prawitt 6, * , Walburgis Brenner 2, 3, * and Yoshiyuki Kojima 1, * 1 Department of Urology, Fukushima Medical University, Fukushima, Japan 2 Department of Urology, Johannes Gutenberg University Medical Center, Mainz, Germany 3 Department of Gynecology and Obstetrics, Johannes Gutenberg University Medical Center, Mainz, Germany 4 Department of Pathology, Shizuoka Cancer Center, Shizuoka, Japan 5 Advanced Clinical Research Center, Fukushima Medical University, Fukushima, Japan 6 Center for Pediatrics and Adolescent Medicine, Johannes Gutenberg University Medical Center, Mainz, Germany * These authors contributed equally to this work Correspondence to: Walburgis Brenner, email: brenner@uni-mainz.de Kei Ishibashi, email: keikun@fmu.ac.jp Keywords: renal cell carcinoma, tyrosine kinase inhibitor, resistance, IL-6, tocilizumab Received: March 01, 2017      Accepted: July 12, 2017      Published: July 21, 2017 ABSTRACT Metastatic renal cell carcinoma (RCC) is a tumor entity with poor prognosis due to limited therapy options. Tyrosine kinase inhibitors (TKI) represent the standard of care for RCCs, however a significant proportion of RCC patients develop resistance to this therapy. Interleukin-6 (IL-6) is considered to be associated with poor prognosis in RCCs. We therefore hypothesized that TKI resistance and IL-6 secretion are causally connected. We first analyzed IL-6 expression after TKI treatment in RCC cells and RCC tumor specimens. Cell proliferation and signal transduction activity were then quantified after co-treatment with tocilizumab, an IL-6R inhibitor, in vitro and in vivo . 786-O RCC cells secrete high IL-6 levels after low dose stimulation with the TKIs sorafenib, sunitinib and pazopanib, inducing activation of AKT-mTOR pathway, NFκB, HIF-2α and VEGF expression. Tocilizumab neutralizes the AKT-mTOR pathway activation and results in reduced proliferation. Using a mouse xenograft model we can show that a combination therapy with tocilizumab and low dosage of sorafenib suppresses 786-O tumor growth, reduces AKT-mTOR pathway and inhibits angiogenesis in vivo more efficient than sorafenib alone. Furthermore FDG-PET imaging detected early decrease of maximum standardized uptake values prior to extended central necrosis. Our findings suggest that a combination therapy of IL-6R inhibitors and TKIs may represent a novel therapeutic approach for RCC treatment.