A reporter gene system for screening inhibitors of Wnt signaling pathway

Cepharanthine suppresses APC-mutant colorectal cancers by down-regulating the expression of β-catenin

The aberrant activation of the Wnt/β-catenin signaling pathway is closely associated with the development of various carcinomas, especially colorectal cancers (CRCs), where adenomatous colorectal polyposis (APC) mutations are the most frequently observed, which limits the anti-tumor efficiency of inhibitors targeting the upstream of Wnt/β-catenin pathway. The anti-tumor activity of the naturally occurring alkaloid cepharanthine (CEP) extracted from the plant Stephania cepharantha Hayata has been reported in various types of tumors. We previously observed that its derivatives inhibited the Wnt/β-catenin signaling in liver cancer; however, the specific mechanism remains unknown. In this study, we confirmed CEP can effectively inhibit APC-mutant CRC cell lines (SW480, SW620, LoVo) through disturbing of the Wnt/β-catenin signaling and elucidated the underlying mechanisms. Here, we demonstrate that CEP attenuates the Wnt/β-catenin signaling by decreasing the β-catenin, subsequently impeding the proliferation of APC-mutant CRCs. Moreover, CEP induced β-catenin transcription inhibition rather than the instability of β-catenin protein and mRNA contributes to reduction of β-catenin. Taken together, our findings identify CEP as the first β-catenin transcriptional inhibitor in the modulation of Wnt/β-catenin signaling and indicate CEP as a potential therapeutic option for the treatment of APC-mutated CRCs.

Novel PORCN inhibitor WHN-88 targets Wnt/β-catenin pathway and prevents the growth of Wnt-driven cancers

Wnt/β-catenin signaling pathway is a classical and crucial oncogenic pathway in many carcinomas, and Porcupine (PORCN) is an O-acyltransferase, which is indispensable and highly specific for catalyzing palmitoylation of Wnt ligands and facilitating their secretion and biofunction. Targeting PORCN provides a promising approach to specifically cure Wnt-driven cancers from the root. In this study, we designed series of pyridonyl acetamide compounds, and discovered a novel PORCN inhibitor WHN-88 with a unique di-iodinated pyridone structural fragment, which is significantly different from the reported inhibitors. We demonstrated that WHN-88 effectively abolished palmitoylation of Wnt ligands and prevented their secretion and the subsequent Wnt/β-catenin signaling transduction. Further experiments showed that, at well-tolerated doses, WHN-88 remarkably suppressed the spontaneous occurrence and growth of MMTV-Wnt1 murine breast tumors. Consistently, WHN-88 also notably restrained the progress of xenografted Wnt-driven human tumors, including PA-1 teratocarcinoma with high autocrine Wnt signaling and Aspc-1 pancreatic carcinoma with Wnt-sensitizing RNF43 mutation. Additionally, we disclosed that WHN-88 inhibited cancer cell stemness obviously. Together, we verified WHN-88 is a novel PORCN inhibitor with potent efficacy against the Wnt-driven cancers. Our findings enriched the structural types of PORCN inhibitors, and facilitated the development and application of PORCN inhibiting therapy in clinic.

Physalis peruviana-Derived 4β-Hydroxywithanolide E, a Novel Antagonist of Wnt Signaling, Inhibits Colorectal Cancer In Vitro and In Vivo

Deregulation of the Wnt signaling pathway leads to colorectal cancer progression. Natural dietary compounds serve as promising candidates for development as chemopreventive agents by suppressing the Wnt/β-catenin signaling pathway. Physalis peruviana-derived 4βHWE showed a significant inhibitory activity with a calculated IC₅₀ of 0.09 μΜ in a screening of novel inhibitors of Wnt signaling with the dual-luciferase reporter assay. This study investigated the anti-tumor effect of 4βHWE and the potential Wnt signaling inhibitory mechanism. Both the western blot analysis and immunofluorescence assay showed that 4βHWE promoted the phosphorylation and degradation of β-catenin and the subsequent inhibition of its nuclear translocation to attenuate the endogenous Wnt target gene expression in colorectal cancer (CRC) cells. The cell viability assay indicated that 4βHWE preferentially inhibited the proliferation of CRC compared with CCD-841-CoN, a normal human colonic epithelial cell line. 4βHWE-mediated G0/G1 cell cycle arrest and apoptosis induction contributed to the suppression of the proliferation of CRC in the cell cycle and Annexin V-FITC/Propidium Iodide apoptosis analysis. Moreover, in vivo, 4βHWE dramatically inhibited tumor growth in HCT116 xenografts by attenuating the Wnt/β-catenin signaling pathway. In conclusion, our study suggested that 4βHWE could be of potential use in anti-tumor agent development as a novel Wnt signaling inhibitor.

USP7 inhibitor P5091 inhibits Wnt signaling and colorectal tumor growth

Aberrant activation of Wnt/β-catenin signaling is closely associated with the development of various human cancers, especially colorectal cancers (CRC). The ubiquitin proteasome system (UPS) is essential in the regulation of Wnt signaling and inhibitors targeting the UPS could have great potential in CRC therapy. Ubiquitin-specific protease 7 (USP7), a deubiquitinating enzyme, plays a significant role in neoplastic diseases due to its well-known function of regulating the MDM2-p53 complex. Inspired by our recent study identifying the positive role of USP7 in the Wnt signaling, we report here that USP7 is overexpressed in colorectal carcinoma cell lines and tissues, which is closely related with the poor prognosis. USP7 knockdown inhibits the proliferation of CRC cells with different p53 status, and USP7 inhibition by its inhibitor P5091 attenuates the activity of Wnt signaling via enhanced ubiquitination and the subsequent degradation of β-catenin. In vitro, P5091 inhibited the proliferation and induced apoptosis of CRC cells. P5091 also suppressed in vivo tumor growth in the HCT116 xenograft mouse model, which is consistently associated with reduced expression of β-catenin and Wnt target genes. In conclusion, our preclinical study indicated that USP7 could be a potential drug target and its inhibitor P5091 deserves further development as anticancer agent for Wnt hyper-activated CRC therapy.

Bisleuconothine A, a bisindole alkaloid, inhibits colorectal cancer cell in vitro and in vivo targeting Wnt signaling

Wnt signaling pathway is aberrantly activated in a variety of cancers, especially in colorectal cancer and small molecule antagonists of Wnt/β-catenin signaling are attractive candidates for developing effective therapeutics. In the present study, we identified Bisleuconothine A, a bisindole alkaloid with an eburnane-aspidosperma type skeleton, as a novel and selective Wnt signaling inhibitor by using a cell-based luciferase assay system. Our study found that Bisleuconothine A down-regulated the endogenous Wnt target gene expression through promoting phosphorylation of β-catenin and the subsequent inhibition of its nuclear translocation in HCT116 and SW480 colorectal cancer cells. In vitro, Bisleuconothine A inhibited cell proliferation through induction of apoptosis by increasing the cleavage of caspases in HCT116 and SW480 colorectal cancer cells. Moreover, in vivo, Bisleuconothine A dramatically suppressed tumor growth in HCT116 Xenograft. And further analysis showed that Bisleuconothine A suppressed the Wnt target gene expression in HCT116 Xenograft, which was associated with up-regulation of β-catenin phosphorylation and subsequent Wnt signaling inhibition. Taken together, our study indicated that bisindole alkaloids could be included as a new chemotype of small-molecule Wnt signaling inhibitors, and have great potential to be further developed for anti-tumor agents.

A Group of ent-Kaurane Diterpenoids Inhibit Hedgehog Signaling and Induce Cilia Elongation

The Hedgehog (Hh) signaling pathway plays important roles in the tumorigenesis of multiple cancers and is a key target for drug discovery. In a screen of natural products extracted from Chinese herbs, we identified eight ent-Kaurane diterpenoids and two triterpene dilactones as novel Hh pathway antagonists. Epistatic analyses suggest that these compounds likely act at the level or downstream of Smoothened (Smo) and upstream of Suppressor of Fused (Sufu). The ent-Kauranoid-treated cells showed elongated cilia, suppressed Smo trafficking to cilia, and mitotic defects, while the triterpene dilactones had no effect on the cilia and ciliary Smo. These ent-Kaurane diterpenoids provide new prototypes of Hh inhibitors, and are valuable probes for deciphering the mechanisms of Smo ciliary transport and ciliogenesis.

Novel β-carbolines against colorectal cancer cell growth via inhibition of Wnt/β-catenin signaling

Wnt signaling pathway is aberrantly activated in a variety of cancers, especially in colorectal cancer (CRC), because of mutations in the genes encoding adenomatous polyposis coli (APC), β-catenin and Axin. Small-molecule antagonists of Wnt/β-catenin signaling are attractive candidates for developing effective therapeutics for CRC. In this study, we have identified a novel Wnt signaling inhibitor, isopropyl 9-ethyl-1- (naphthalen-1-yl)-9H-pyrido[3,4-b]indole-3- carboxylate (Z86). Z86 inhibited Wnt reporter activities and the expression of endogenous Wnt signaling target genes in mammalian cells and antagonized the second axis formation of Xenopus embryos induced by Wnt8. We showed that Z86 treatment inhibits GSK3β (Ser9) phosphorylation, leading to its overactivation and promoting the phosphorylation and degradation of β-catenin. In vitro, Z86 selectively inhibited the growth of CRC cells with constitutive Wnt signaling and caused obvious G1-phase arrest of the cell cycle. Notably, in a nude mouse model, Z86 inhibited dramatically the xenografted tumor growth of CRC. Daily intraperitoneal injection of Z86 at 5 mg/kg resulted in >70% reduction in the tumor weight of HCT116 cell origin that was associated with decreased GSK3β (Ser9) phosphorylation and increased β-catenin phosphorylation. Taken together, our findings provide a novel promising chemotype for CRC therapeutics development targeting the canonical Wnt signaling.

Cycloartane Glycosides from the Roots of Cimicifuga foetida with Wnt Signaling Pathway Inhibitory Activity

Four new 9,19-cycloartane triterpenoids, cimilactone E (1), cimilactone F (2), 2'-O-(E)-butenoyl-23-epi-26-deoxyactein (3), and 2',12β-O-diacetylcimiracemonol-3-O-β-d-xylopyranoside (4), together with four known constituents (5-8) were isolated from the roots of Cimicifuga foetida. The new structures were elucidated by extensive spectroscopic analysis. In addition, compounds 7 and 8 showed significant Wnt signaling pathway inhibitory activity, with IC50 values of 3.33 and 13.34 μM, respectively, using the luciferase reporter gene assay.

Biflavone Ginkgetin, a Novel Wnt Inhibitor, Suppresses the Growth of Medulloblastoma

Medulloblastoma (MB) is a form of malignant brain tumor that predominantly arises in infants and children, of which approximately 25 % is due to upregulation of canonical Wnt pathway with mainly mutations in CTNNB1. Therefore, Wnt inhibitors could offer rational therapeutic strategies and chemoprevention for this malignant cancer. In our present study, we undertook a screening for antagonists of Wnt signaling from 600 natural compounds, and identified Ginkgetin, a biflavone isolated from Cephalotaxus fortunei var. alpina. Ginkgetin inhibited Wnt pathway with an IC50 value around 5.92 μM and structure-activity relationship analysis suggested the methoxy group in Ginkgetin as a functional group. Biflavone Ginkgetin showed obvious cytotoxicity in Daoy and D283 MB cells. Cell cycle analysis by flow cytometry showed that Ginkgetin induced efficiently G2/M phase arrest in Daoy cells. Further mechanism studies showed that Ginkgetin reduced the expression of Wnt target genes, including Axin2, cyclinD1 and survivin in MB cells. The phosphorylation level of β-catenin also decreased in a time- and concentration-dependent manner. Collectively, our data suggest that Ginkgetin is a novel inhibitor of Wnt signaling, and as such warrants further exploration as a promising anti-medulloblastoma candidate.

Two Natural ent-kauranoids as Novel Wnt Signaling Inhibitors

Constitutively active Wnt signaling frequently occurs in most colon cancers. Therefore, inhibitors of Wnt signaling pathway could provide rational therapeutic effects for colorectal malignancy. Within this paper, we identified two inhibitors of Wnt signaling pathway, rabdoternin B and maoecrystal I from a natural ent-kauranoid library by a dual-luciferase reporter gene assay. The two compounds inhibited Wnt signaling pathway in a concentration-dependent manner and exhibited selective cytotoxicity toward a number of colon carcinoma cell lines SW480, HCT116, and HT29, with only weak cytotoxicity towards the normal colonic epithelial cell line CCD-841-CoN. Rabdoternin B and maoecrystal I treatment induced G2/M phase arrest efficiently in SW480 cells as revealed by flow cytometry analysis. A further study found that maoecrystal I decreased the expression of Wnt signaling target genes, including c-myc, cyclin D1, survivin and Axin2 in colon cancer cells. Collectively our data suggests that rabdoternin B and maoecrystal I are novel inhibitors of canonical Wnt signaling pathway and may possess potentials for colon cancer therapy.