Lung cancer is the most common malignancy worldwide and is a focus for developing targeted therapies due to its refractory nature to current treatment. We identified a RNA helicase, DDX3, which is overexpressed in many cancer types including lung cancer and is associated with lower survival in lung cancer patients. We designed a first‐in‐class small molecule inhibitor, RK‐33, which binds to DDX3 and abrogates its activity. Inhibition of DDX3 by RK‐33 caused G1 cell cycle arrest, induced apoptosis, and promoted radiation sensitization in DDX3‐overexpressing cells. Importantly, RK‐33 in combination with radiation induced tumor regression in multiple mouse models of lung cancer. Mechanistically, loss of DDX3 function either by shRNA or by RK‐33 impaired Wnt signaling through disruption of the DDX3–β‐catenin axis and inhibited non‐homologous end joining—the major DNA repair pathway in mammalian somatic cells. Overall, inhibition of DDX3 by RK‐33 promotes tumor regression, thus providing a compelling argument to develop DDX3 inhibitors for lung cancer therapy.

Aims DDX3 is an RNA helicase that has antiapoptotic properties, and promotes proliferation and transformation. In addition, DDX3 was shown to be a direct downstream target of HIF-1α (the master regulatory of the hypoxia response) in breast cancer cell lines. However, the relation between DDX3 and hypoxia has not been addressed in human tumors. In this paper, we studied the relation between DDX3 and the hypoxic responsive proteins in human breast cancer. Methods and Results DDX3 expression was investigated by immunohistochemistry in breast cancer in comparison with hypoxia related proteins HIF-1α, GLUT1, CAIX, EGFR, HER2, Akt1, FOXO4, p53, ERα, COMMD1, FER kinase, PIN1, E-cadherin, p21, p27, Transferrin receptor, FOXO3A, c-Met and Notch1. DDX3 was overexpressed in 127 of 366 breast cancer patients, and was correlated with overexpression of HIF-1α and its downstream genes CAIX and GLUT1. Moreover, DDX3 expression correlated with hypoxia-related proteins EGFR, HER2, FOXO4, ERα and c-Met in a HIF-1α dependent fashion, and with COMMD1, FER kinase, Akt1, E-cadherin, TfR and FOXO3A independent of HIF-1α. Conclusions In invasive breast cancer, expression of DDX3 was correlated with overexpression of HIF-1α and many other hypoxia related proteins, pointing to a distinct role for DDX3 under hypoxic conditions and supporting the oncogenic role of DDX3 which could have clinical implication for current development of DDX3 inhibitors.

Purpose: Accurately predicting treatment response in metastatic colorectal cancer (mCRC) is critical to avoid unnecessary toxicity and improve patient outcomes. Patient-derived organoids (PDO) are promising models, but larger prospective studies are needed to confirm their predictive value. Experimental Design: Patients with mCRC underwent a metastatic biopsy for PDO establishment, before starting new systemic treatment. Predictors of PDO establishment were identified. PDOs were incubated with a seven-drug panel, including the patient’s treatment, to determine drug sensitivity as measured by CyQUANT cell viability [area under the nonfitted “curve” of the raw viability or growth rate inhibition values (AUC and GRAUC) and concentration that gives half-maximal viability or GR inhibition (IC50 and GR50)]. Patient response was measured by size change of biopsied and all target lesions. The diagnostic performance was evaluated by positive predictive value, negative predictive value, and area under the ROC curve. Additionally, the association between PDO response and survival was assessed. Results: A total of 232 patients were included, and 205 biopsies were obtained. PDO establishment success increased from 22% to 75%, yielding 52% overall. Male sex, increased lactate dehydrogenase, biopsy in academic hospitals, optimized culture conditions, and experience were related to PDO establishment success. In this interim analysis, focused on oxaliplatin-based doublet chemotherapy, 42 PDOs were screened. PDO drug sensitivity significantly correlated with the response of the biopsied lesion (R = 0.41–0.49, P < 0.011) and all target lesions (R = 0.54–0.60, P < 0.001) for all treatments combined. The 5-fluorouracil and oxaliplatin PDO screens demonstrated high predictive accuracy (positive predictive value: 0.78; negative predictive value: 0.80; area under the ROC curve: 0.78–0.88) and were associated with progression-free survival and overall survival (P = 0.016 and 0.049). Conclusions: We identified predictors for successful mCRC PDO establishment and validated that PDOs can accurately predict patient outcomes during systemic treatment, specifically with 5-fluorouracil and oxaliplatin.

DEAD box protein, DDX3, is aberrantly expressed in breast cancer cells ranging from weakly invasive to aggressive phenotypes and functions as an important regulator of cancer cell growth and survival. Here, we demonstrate that hypoxia inducible factor-1α is a transcriptional activator of DDX3 in breast cancer cells. Within the promoter region of the human DDX3 gene, we identified three putative hypoxia inducible factor-1 responsive elements. By luciferase reporter assays in combination with mutated hypoxia inducible factor-1 responsive elements, we determined that the hypoxia inducible factor-1 responsive element at position -153 relative to the translation start site is essential for transcriptional activation of DDX3 under hypoxic conditions. We also demonstrated that hypoxia inducible factor-1 binds to the DDX3 promoter and that the binding is specific, as revealed by siRNA against hypoxia inducible factor-1 and chromatin immunoprecipitation assays. Thus, the activation of DDX3 expression during hypoxia is due to the direct binding of hypoxia inducible factor-1 to hypoxia responsive elements in the DDX3 promoter. In addition, we observed a significant overlap in the protein expression pattern of hypoxia inducible factor-1α and DDX3 in MDA-MB-231 xenograft tumors. Taken together, our results demonstrate, for the first time, the role of DDX3 as a hypoxia-inducible gene that exhibits enhanced expression through the interaction of hypoxia inducible factor-1 with hypoxia inducible factor-1 responsive elements in its promoter region.