Discovery of 2-(isoxazol-5-yl)phenyl 3,4-dihydroxybenzoate as a potential inhibitor for the Wnt/β-catenin pathway

Carnosic acid could disrupt the β-catenin/BCL9 protein-protein interaction and inhibit β-catenin dependent transcription, thereby reduce the incidence of colorectal cancer induced by abnormal activation of Wnt/β-catenin signalling pathway. However, its activity was weak (IC50 for SW480: 28.2 ± 2.05 μM) and total synthesis was difficult. During the structural simplification of natural products, S0 was revealed to be the basic pharmacophore of carnosic acid. Subsequent structural optimization of S0 led to the discovery of S11 as a possible anticancer agent with prominent proliferation inhibition effect (IC50 for SW480: 9.56 ± 0.91 μM) and best selectivity index (SI = 3.0) against Wnt hyperactive cancer cells. Futher mechanism investigation through TOP/FOP dual luciferase reporter assay, immunofluorescence, co-immunoprecipitation, microscale thermophoresis, downstream oncoprotein expression and cell apoptosis showed that compound S11 could significantly inhibit the proliferation of SW480 cells via obvioudsly decreasing the nucleus translocation of β-catenin and effectively disrupting β-catenin/BCL9 protein-protein interaction. Additionally, cell migration, molecule docking, in vitro stability and solubility assays were also conducted. Overall, S11 was worthy of in-depth study as a potential inhibitor for the Wnt/β-catenin pathway and its discovery also proved that the structural simplification of natural products was still one of the effective methods to find new lead compounds or candidate drugs.