Ethacrynic Acid Exhibits Selective Toxicity to Chronic Lymphocytic Leukemia Cells by Inhibition of the Wnt/β-Catenin Pathway

BACKGROUND Aberrant activation of Wnt/beta-catenin signaling promotes the development of several cancers. It has been demonstrated that the Wnt signaling pathway is activated in chronic lymphocytic leukemia (CLL) cells, and that uncontrolled Wnt/beta-catenin signaling may contribute to the defect in apoptosis that characterizes this malignancy. Thus, the Wnt signaling pathway is an attractive candidate for developing targeted therapies for CLL. METHODOLOGY/PRINCIPAL FINDINGS The diuretic agent ethacrynic acid (EA) was identified as a Wnt inhibitor using a cell-based Wnt reporter assay. In vitro assays further confirmed the inhibitory effect of EA on Wnt/beta-catenin signaling. Cell viability assays showed that EA selectively induced cell death in primary CLL cells. Exposure of CLL cells to EA decreased the expression of Wnt/beta-catenin target genes, including LEF-1, cyclin D1 and fibronectin. Immune co-precipitation experiments demonstrated that EA could directly bind to LEF-1 protein and destabilize the LEF-1/beta-catenin complex. N-acetyl-L-cysteine (NAC), which can react with the alpha, beta-unsaturated ketone in EA, but not other anti-oxidants, prevented the drug's inhibition of Wnt/beta-catenin activation and its ability to induce apoptosis in CLL cells. CONCLUSIONS/SIGNIFICANCE Our studies indicate that EA selectively suppresses CLL survival due to inhibition of Wnt/beta-catenin signaling. Antagonizing Wnt signaling in CLL with EA or related drugs may represent an effective treatment of this disease.