Aberrant activation of the Wnt/β-catenin signaling pathway has been implicated in oncogenesis and cancer progression. Accordingly, disruption of this pathway offers an opportunity for effective cancer therapy. Our group and several others have found one such compound, curcumin (5-hydroxy-1, 7-bis-(4-hydroxy-3-methoxy-phenyl)-hepta-1, 4, 6-triene-3-one), a dietary pigment found in spice tumeric, to be an effective antagonist of the Wnt/β-catenin pathway. However, clinical application of curcumin as effective Wnt antagonist is much limited by its low bioavailability due to poor absorption and rapid metabolism. The objective of this study is thus to design, synthesize and screen 5 series of analogues to identify crucial motifs leading to improved potency and selectivity as Wnt inhibitors, as well as those with enhanced bioavailability. Here, a panel of 35 compounds comprising of diarylheptanoids, diarylpentanoids, dibenzylidene-cyclohexanones, dibenzylidene-cyclopentanones and chalcones were designed based on these reasons: (1) Natural derivatives of curcumin, which differs only by the substitutions on both rings, were reported to suppress β-catenin/Tcf transcription, thus regioisomers of diarylheptanoids were included to study the role of substitution patterns; (2) The dienone moiety of diarylpentanoids, dibenzylidene-cyclohexanones and dibenzylidene-cyclopentanones were metabolically more stable then the diene-dienone of diarylheptanoids; (3) Chalcones were included to study the effects of removing structural symmetry. Screening for Wnt-inhibitory activity was performed in HEK293 human embryonic kidney, activated with Wnt3a conditioned-medium, using a reporter gene containing four copies of the Tcf-binding sites (TOPGlow). A total of 16 compounds were found to be more potent than curcumin in inhibiting the downstream transcriptional activity of β-catenin/Tcf complex. Among these, dibenzylidene-cyclohexanones and dibenzylidene-cyclopentanones were the most promising Wnt antagonists, with EC50 values in the low micromolar ranges. Specifically, members with 4-hydroxyl and 3-hydroxyl-4-methoxy substitutions on both rings, with EC50 ranges between 0.1-1 μM, were over 20 times more potent than curcumin (EC50 20 μM). These compounds had limited cytotoxicity (>80% cell survival) at their EC50, as demonstrated using the MTS cell viability assays. Collectively, our findings suggest that conformation restrictions around the dienone moiety as well as the introduction of suitable alkoxyl and hydroxyl substitutions on the aromatic rings drastically enhanced Wnt-inhibitory activity. As such, the dibenzylidene-cyclohexanones and dibenzylidene-cyclopentanones templates are promising scaffolds for structural optimization and investigations are on-going to provide better insight of structural-activity relationships and the design of more potent and specific Wnt antagonist.
Note: This abstract was not presented at the AACR 101st Annual Meeting 2010 because the presenter was unable to attend.
Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 101st Annual Meeting of the American Association for Cancer Research; 2010 Apr 17-21; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2010;70(8 Suppl):Abstract nr 755.
