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Research on existing drugs often discovers novel mechanisms of their action and leads to the expansion of their therapeutic scope and subsequent remarketing. The Wnt signaling pathway is of the immediate therapeutic relevance, as it plays critical roles in cancer development and progression. However, drugs which disrupt this pathway are unavailable despite the high demand. Here we report an attempt to identify antagonists of the Wnt-FZD interaction among the library of the FDA-approved drugs. We performed an in silico screening which brought up several potential antagonists of the ligand-receptor interaction. 14 of these substances were tested using the TopFlash luciferase reporter assay and four of them identified as active and specific inhibitors of the Wnt3a-induced signaling. However, further analysis through GTP-binding and β-catenin stabilization assays showed that the compounds do not target the Wnt-FZD pair, but inhibit the signaling at downstream levels. We further describe the previously unknown inhibitory activity of an anti-leprosy drug clofazimine in the Wnt pathway and provide data demonstrating its efficiency in suppressing growth of Wnt-dependent triple-negative breast cancer cells. These data provide a basis for further investigations of the efficiency of clofazimine in treatment of Wnt-dependent cancers. © 2013 Elsevier Inc.

Research on existing drugs often discovers novel mechanisms of their action and leads to the expansion of their therapeutic scope and subsequent remarketing. The Wnt signaling pathway is of the immediate therapeutic relevance, as it plays critical roles in cancer development and progression. However, drugs which disrupt this pathway are unavailable despite the high demand. Here we report an attempt to identify antagonists of the Wnt-FZD interaction among the library of the FDA-approved drugs. We performed an in silico screening which brought up several potential antagonists of the ligand-receptor interaction. 14 of these substances were tested using the TopFlash luciferase reporter assay and four of them identified as active and specific inhibitors of the Wnt3a-induced signaling. However, further analysis through GTP-binding and β-catenin stabilization assays showed that the compounds do not target the Wnt-FZD pair, but inhibit the signaling at downstream levels. We further describe the previously unknown inhibitory activity of an anti-leprosy drug clofazimine in the Wnt pathway and provide data demonstrating its efficiency in suppressing growth of Wnt-dependent triple-negative breast cancer cells. These data provide a basis for further investigations of the efficiency of clofazimine in treatment of Wnt-dependent cancers. © 2013 Elsevier Inc.