The NF-kB pathway promotes survival of cancer cells. My research in ovarian cancer began with characterizing the activation state and biological relevance of NF-kB in this disease. The NF-kB family of transcription factors is ubiquitously expressed. NF-kB signaling has been implicated in ovarian cancer, but the significance and mechanism of NF-kB signaling in ovarian cancer is unknown. There is precedent to propose that NF-kB is a critical signaling mechanism in cancer. I initially hypothesized that the NF-kB pathway is over-activated in ovarian cancers with more aggressive behavior. The NF-kB pathway was implicated in ovarian cancer proliferation and cytokine secretion in vitro, and contributed to chemoresistance of ovarian cancer cell lines. I therefore sought to determine the expression patterns and prognostic associations of NF-kB pathway proteins in primary ovarian cancer tissues. I demonstrated that overexpression of the NF-kB subunit p50 at diagnosis conveyed poor outcome in these patients. The biological relevance of NF-kB in ovarian cancer was established in my laboratory. Having demonstrated the coordinate presence of NF-kB machinery in ovarian cancers, I sought to modulate its activity. Inhibitors of NF-kB (IkBs) are tagged for degradation through the proteasome upon specific inducible phosphorylation by IkB kinases (IKKs). Therefore, targeted inhibition of IKKs could isolate NF-kB as a mechanism for ovarian cancer pathogenesis. A subset of ovarian cancer cell lines was affected by inhibition of IKKb in properties of growth, adhesion, invasion and cytokine secretion. I developed a gene expression signature of IKKb signaling in ovarian cancer using both pharmacologic and genetic manipulation of IKKb. This signature gave insight into the results of NF-kB in ovarian cancer, based on known functions of the ovarian cancer-specific target genes, and allowed me to probe established ovarian cancer databases in order to estimate the relative impact of NF-kB signaling on the survival of women with ovarian cancer. Higher NF-kB activity conveyed a worse outcome, suggesting that modulation of IKKb might benefit patients whose tumors showed elevated target gene expression. A key discovery from this work was the tissue specificity of NF-kB signaling. The 9-gene signature experimentally defined in ovarian cancer was completely different from the 11 genes I previously identified in multiple myeloma. The overall goal of this project is to dissect the molecular structure of NF-kB signaling in ovarian cancer, with the intent to develop biomarkers of dependence on NF-kB, and novel points of therapeutic intervention. In FY 2013 we published a study identifying IKKepsilon as instrumental in the metastasis and invasion of ovarian cancer. We also completed two shRNA library screens, one in combination with an inhibitor of IKKbeta, and another in combination with shRNA against IKKepsilon. These studies identified novel interactions between the NF-kB pathway in ovarian cancer. In combination with IKKbeta, we found caspase 8 to be cooperative in protecting the cells from necroptosis. In combination with IKKepsilon, we discovered that CHEK1 protected the cells from catastrophic DNA damage by stalling the cell cycle driven by IKKepsilon. From a therapeutic standpoint, we have completed a phase 2 clinical trial using the SMAC mimetic birinapant in women with relapsed and refractory ovarian cancer. This drug targets cIAP1 for degradation, and thus interrupts NF-kB signaling and triggers apoptosis. We are analyzing blood, serum, and tumor biopsies from patients on this clinical trial to identify changes in NF-kB and apoptosis activation states.
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