Our previous studies from an ongoing project have demonstrated that DDX3 may activate the P-catenin/ZEB1 axis via the PI3K/AKT signaling pathway to promote tumor invasion in colorectal cancer. In addition, DDX3 may increase the expression of KRAS, HIF-1a, and YAP1 and ROS generation to promote tumor invasion. Patients with high DDX3-expressing tumors exhibited poorer prognosis and unfavorable response to 5-FU-based chemotherapy than those with low DDX3-expressing tumors. KRAS mutation is commonly used to predict anti-EGFR monoclonal antibody cetuximab (CTX) response. However, not all KRAS-mutated and -WT patients exhibited unfavorable and favorable response to CTX. Our preliminary data showed that high DDX3-expressing cells exhibited higher CTX resistance than low DDX3-expressing colon cancer cells, regardless of KRAS status. We therefore hypothesized that DDX3 may act as an adjuvant biomarker to predict CTX resistance. In this three-year proposal, we will identify which signaling pathway(s) or gene expression(s) could be responsible for DDX3-mediated CTX resistance. To this end, in the first-year, we will examine: (i) Whether the feedback loop of DDX3-KRAS-ROS-HIF-1a could contribute to DDX3-mediated CTX resistance? (2) Whether a persistent increase in HIF-1a expression by the feedback loop could be responsible for DDX3-mediated CTX resistance? (3) Whether different mechanistic actions of DDX3-mediated CTX resistance could occur between KRAS-mutated and -WT cells? (4) Whether different inhibitors could be used to overcome DDX3-mediated CTX resistance between KRAS-mutated and -WT cells? In the second-year, we will examine: (1) Whether HIF-1a or ROS scavenger could overcome DDX3-mediated CTX resistance in KRAS-mutated and -WT cells? (2) Whether the ROS-HIF-1 a-YAP 1 cascade could be responsible for DDX3-mediated CTX resistance in KRAS-mutated and -WT cells? (3) Whether an increase in YAP1 expression by DDX3-mediated HIF-1a could simultaneously occur in KRAS-mutated and -WT cells? (4) Whether YAP1 could confer DDX3-mediated CTX resistance via activating the PI3K/AKT signaling pathway due to decreased PTEN expression? (5) An apoptotic protein array will perform to identify which apoptosis-related gene(s) could be responsible for DDX3-mediated CTX resistance. In the third-year, we will perform three preclinical therapeutic animal models (subcutaneous, tail-vein injection, and orthotopic colorectal cancer) to establish a combination therapy to overcome DDX3-mediated CTX resistance. Combining CTX with HIF-1a inhibitors, AKT inhibitors, or MEK/ERK inhibitor will treat with three animal models to verify which combination therapy could have more effective to suppress tumor burden induced by DDX3-overexpressing KRAS-mutated and -WT stable clones. The expression of DDX3, HIF-1a, p-ERK, p-AKT, YAP1, and apoptosis-related proteins in tumor burden of mice will be evaluated by immunohistochemistry. The results obtained from the three-year project will be helpful to understand whether DDX3 could act as an adjuvant biomarker to predict CTX resistance in colorectal cancer. The valuable combination therapy obtained from animal models may support to further conduct clinical trials in colorectal cancer patients who harbored high DDX3-expressing tumor.
|Effective start/end date||8/1/16 → 7/31/17|