Background and Purpose Salinomycin is a well‐known inhibitor of human cancer stem cells ( CSCs ). However, the molecular mechanism(s) by which salinomycin targets colorectal CSCs is poorly understood. Here, we have investigated underlying antitumour mechanisms of salinomycin in colorectal cancer cells and three tumour models. Experimental Approach The inhibitory effect of salinomycin on the Wnt/β‐catenin pathway was analysed with the SuperTopFlash reporter system. The mRNA expression of Wnt target genes was evaluated with real‐time PCR. Effects of salinomycin on β‐catenin/TCF4E interaction were examined using co‐immunoprecipitation and an in vitro GST pull‐down assay. Cell proliferation was determined by BrdU incorporation and soft agar colony formation assay. The stemness of the cells was assessed by sphere formation assay. Antitumour effects of salinomycin on colorectal cancers was evaluated with colorectal CSC xenografts, APC min/+ transgenic mice, and patient‐derived colorectal tumour xenografts. Key Results Salinomycin blocked β‐catenin/TCF4E complex formation in colorectal cancer cells and in an in vitro GST pull‐down assay, thus decreasing expression of Wnt target genes. Salinomycin also suppressed the transcriptional activity mediated by β‐catenin/LEF1 or β‐catenin/TCF4E complex and exhibited an inhibitory effect on the sphere formation, proliferation, and anchorage‐independent growth of colorectal cancer cells. In colorectal tumour xenografts and APC min/+ transgenic mice, administration of salinomycin significantly reduced tumour growth and the expression of CSC‐related Wnt target genes including LGR5. Conclusions and Implications Our study suggested that salinomycin could suppress the growth of colorectal cancer by disrupting the β‐catenin/TCF complex and thus may be a promising agent for colorectal cancer treatment.

The increasing emergence of infectious diseases associated with multidrug-resistant Gram-positive pathogens has raised the urgent need to develop novel antibiotics. GA (15:1) is a natural product derived from Ginkgo biloba and possesses a wide range of bioactivities, including antimicrobial activity.

BackgroundCK1 is involved in regulating Wnt/β-catenin signaling and represents a promising target for the treatment of breast cancer. A purine derivative longdaysin has recently been identified as a novel modulator of cellular circadian rhythms through targeting the protein kinases CK1δ, CK1α, and ERK2. However, the antitumor activity of longdaysin and its underlying mechanisms remain unclear.MethodsThe inhibitory effect of longdaysin on Wnt/β-catenin signaling was investigated using the SuperTOPFlash reporter system. The levels of phosphorylated LRP6, total LRP6, DVL2, active β-catenin, and total β-catenin were examined by Western blot. The expression of Wnt target genes was determined using real-time PCR. The ability of colony formation of breast cancer cells was measured by colony formation assay. The effects of longdaysin on cancer cell migration and invasion were assessed using transwell assays. The effect of longdaysin on cancer stem cells was tested by sphere formation assay. The in vivo antitumor effect of longdaysin was evaluated using MDA-MB-231 breast cancer xenografts.ResultsLongdaysin suppressed Wnt/β-catenin signaling through inhibition of CK1δ and CK1ε in HEK293T cells. In breast cancer Hs578T and MDA-MB-231 cells, micromolar concentrations of longdaysin attenuated the phosphorylation of LRP6 and DVL2 and reduced the expression of active β-catenin and total β-catenin, leading to the downregulation of Wnt target genes Axin2, DKK1, LEF1, and Survivin. Furthermore, longdaysin inhibited the colony formation, migration, invasion, and sphere formation of breast cancer cells. In MDA-MB-231 breast cancer xenografts, treatment with longdaysin suppressed tumor growth in association with inhibition of Wnt/β-catenin signaling.ConclusionLongdaysin is a novel inhibitor of the Wnt/β-catenin signaling pathway. It exerts antitumor effect through blocking CK1δ/ε-dependent Wnt signaling.