Ovarian
clear cell adenocarcinoma (OCCA) is characterized by a particularly poor response to conventional
chemotherapy and a short overall survival time in women with established disease. The development of targeted treatments for OCCA relies on a better understanding of its molecular characteristics.
IL6 is strongly expressed in OCCA and may therefore provide a novel therapeutic target. Here we use CRISPR/Cas9 and conditional short hairpin interfering
RNA to perform loss-of-function studies in human OCCA cell lines to explore the requirement for
IL6 in vitro and in vivo. While reduction of
IL6 expression exerted limited effects in vitro, its attenuation significantly impaired
tumor growth and neovascularization in vivo. In contrast to typical signaling via STAT3,
IL6 in OCCA signaled via a noncanonical pathway involving gp130, Src, and the Hippo pathway
protein YAP. A high-throughput
combination drug screen identified agents that enhanced cell killing following reduction of
IL6 signaling. Intersection of screen hits obtained from two cell lines and orthogonal approaches to attenuation of
IL6 yielded AKT and EGFR inhibitors as enhancers of the inhibitory monoclonal
IL6 receptor antibody
tocilizumab. This study defines for the first time the requirements for, and mechanisms of, signaling by
IL6 in human OCCA cell lines and identifies potential combinatory therapeutic approaches. Given the molecular diversity of OCCA, further in vitro and in vivo studies are warranted to determine whether such approaches will overcome the limited efficacy of
tocilizumab observed in
ovarian cancer to date. SIGNIFICANCE: This study defines the requirements for and mechanisms of noncanonical signaling by
IL6 in human ovarian
clear cell adenocarcinoma cell lines and identifies combinatory therapeutic approaches to be explored clinically.