Two Natural ent-kauranoids as Novel Wnt Signaling Inhibitors

Therapeutic Potential of Naturally Occurring Small Molecules to Target the Wnt/β-Catenin Signaling Pathway in Colorectal Cancer

Simple Summary

Colorectal cancer (CRC) is an emerging public health problem and the second leading cause of death worldwide, with a significant socioeconomic impact in several countries. The 5-year survival rate is only 12% due to the lack of early diagnosis and resistance to available treatments, and the canonical Wnt signaling pathway is involved in this process. This review underlines the importance of understanding the fundamental roles of this pathway in physiological and pathological contexts and analyzes the use of naturally occurring small molecules that inhibits the Wnt/β-catenin pathway in experimental models of CRC. We also discuss the progress and challenges of moving these small molecules off the laboratory bench into the clinical platform.

Abstract

Colorectal cancer (CRC) ranks second in the number of cancer deaths worldwide, mainly due to late diagnoses, which restrict treatment in the potentially curable stages and decrease patient survival. The treatment of CRC involves surgery to remove the tumor tissue, in addition to radiotherapy and systemic chemotherapy sessions. However, almost half of patients are resistant to these treatments, especially in metastatic cases, where the 5-year survival rate is only 12%. This factor may be related to the intratumoral heterogeneity, tumor microenvironment (TME), and the presence of cancer stem cells (CSCs), which is impossible to resolve with the standard approaches currently available in clinical practice. CSCs are APC-deficient, and the search for alternative therapeutic agents such as small molecules from natural sources is a promising strategy, as these substances have several antitumor properties. Many of those interfere with the regulation of signaling pathways at the central core of CRC development, such as the Wnt/β-catenin, which plays a crucial role in the cell proliferation and stemness in the tumor. This review will discuss the use of naturally occurring small molecules inhibiting the Wnt/β-catenin pathway in experimental CRC models over the past decade, highlighting the molecular targets in the Wnt/β-catenin pathway and the mechanisms through which these molecules perform their antitumor activities.

Mechanistic Pathways and Molecular Targets of Plant-Derived Anticancer ent-Kaurane Diterpenes

Since the first discovery in 1961, more than 1300 ent-kaurane diterpenoids have been isolated and identified from different plant sources, mainly the genus Isodon. Chemically, they consist of a perhydrophenanthrene subunit and a cyclopentane ring. A large number of reports describe the anticancer potential and mechanism of action of ent-kaurane compounds in a series of cancer cell lines. Oridonin is one of the prime anticancer ent-kaurane diterpenoids that is currently in a phase-I clinical trial in China. In this review, we have extensively summarized the anticancer activities of ent-kaurane diterpenoids according to their plant sources, mechanistic pathways, and biological targets. Literature analysis found that anticancer effect of ent-kauranes are mainly mediated through regulation of apoptosis, cell cycle arrest, autophagy, and metastasis. Induction of apoptosis is associated with modulation of BCL-2, BAX, PARP, cytochrome c, and cleaved caspase-3, -8, and -9, while cell cycle arrest is controlled by cyclin D1, c-Myc, p21, p53, and CDK-2 and -4. The most common metastatic target proteins of ent-kauranes are MMP-2, MMP-9, VEGF, and VEGFR whereas LC-II and mTOR are key regulators to induce autophagy.

Umbelliprenin isolated from Ferula sinkiangensis inhibits tumor growth and migration through the disturbance of Wnt signaling pathway in gastric cancer

The traditional herb medicine Ferula sinkiangensis K. M. Shen (F. sinkiangensis) has been used to treat stomach disorders in Xinjiang District for centuries. Umbelliprenin is the effective component isolated from F. sinkiangensis which is particularly found in plants of the family Ferula. We previously reported the promising effects of Umbelliprenin against gastric cancer cells, but its anti-migration effect remained unknown. Here we investigated the anti-migration effect and mechanism of Umbelliprenin in human gastric cancer cells. In SRB assay, Umbelliprenin showed cytotoxic activities in the gastric cancer cell lines AGS and BGC-823 in a dose-and-time-dependent manner, while it showed lower cytotoxic activity in the normal gastric epithelium cell line GES-1. During transwell, scratch and colony assays, the migration of tumor cells was inhibited by Umbelliprenin treatment. In gelatin zymography assay, Umbelliprenin could inhibit the expression of MMP2 and MMP9 in tumor cells The expression levels of the Wnt-associated signaling pathway proteins were analyzed with western blots, and the results showed that Umbelliprenin decreased the expression levels of proteins of the Wnt signalling pathway, such as Wnt-2, β-catenin, GSK-3β, p-GSK-3β, Survivin and c-myc. The translocation of β-catenin to the nucleus was also inhibited by Umbelliprenin treatment. In TCF reporter assay, the transcriptional activity of T-cell factor/lymphoid enhancer factor (TCF/LEF) was decreased after Umbelliprenin treatment. The in vivo results suggested that Umbelliprenin induced little to no harm in the lung, heart and kidney. Overall, these data provided evidence that Umbelliprenin may inhibit the growth, invasion and migration of gastric cancer cells by disturbing the Wnt signaling pathway.

Wnt/β-catenin signaling pathway is involved in regulating the migration by an effective natural compound brucine in LoVo cells

BACKGROUND

Colorectal cancer remains the third most common malignancies and migration is one of the main factors for its high mortality rate. Brucine, a natural plant alkaloid, has been proved to possess a variety of pharmacological functions including anti-tumor activities.

PURPOSE

The aim of this study was to investigate the inhibitory effect of brucine on the colorectal cancer and the underlying mechanism.

METHODS

In this study, colony formation assay and transwell assay were used to investigate the effect of brucine on LoVo cells viability and migration. Immunofluorescence assay, western blot assay and Gelatin zymography assay were used to study the mechanism of brucine. Xenograft model in nude mice was induced to investigate the in vivo effect of brucine on LoVo cells.

RESULTS

Brucine could significantly decrease the viability, inhibit the colony formation and induce the apoptosis of LoVo cells. Brucine could also suppress the migration of LoVo cells in a dose-dependent manner. Western blot analysis elucidated that the inhibition of migration was associated with the decreasing expression of matrix metalloproteinases including MMP2, MMP3 and MMP9. Moreover, we found that treatment of brucine could downregulate the expression of Frizzled-8, Wnt5a, APC and GSNK1A1, and increase the expression of AXIN1. Meanwhile, brucine also decreased the phosphorylation level of LRP5/6 and GSK3β, and increased the level of p-β-catenin. Xenografted model in nude mice study also revealed that oral administration of brucine could inhibit the growth and migration of LoVo cells by activating the expression of AXIN1 and p-β-catenin.

CONCLUSION

Brucine could suppress the migration of the colorectal cancer in vitro and in vivo and the effect was associated with the inhibition of the Wnt/β-catenin signaling pathway.

Wnt Drug Discovery: Weaving Through the Screens, Patents and Clinical Trials

The Wnt signaling pathway is intricately involved in many aspects of development and is the root cause of an increasing number of diseases. For example, colorectal cancer is the second leading cause of death in the industrialized world and aberration of Wnt signaling within the colonic stem cell is the cause of more than 90% of these cancers. Despite our advances in successfully targeting other pathways, such as Human Epidermal Growth Factor Receptor 2 (HER2), there are no clinically relevant therapies available for Wnt-related diseases. Here, we investigated where research activities are focused with respect to Wnt signaling modulators by searching the United States Patent and Trade Office (USPTO) for patents and patent applications related to Wnt modulators and compared this to clinical trials focusing on Wnt modulation. We found that while the transition of intellectual property surrounding the Wnt ligand-receptor interface to clinical trials is robust, this is not true for specific inhibitors of β-catenin, which is constitutively active in many cancers. Considering the ubiquitous use of the synthetic T-cell Factor/Lymphoid Enhancer Factor (TCF/Lef) reporter system and its success in identifying novel modulators in vitro, we speculate that this model of drug discovery does not capture the complexity of in vivo Wnt signaling that may be required if we are to successfully target the Wnt pathway in the clinic. Notwithstanding, increasingly more complex models are being developed, which may not be high throughput, but more pragmatic in our pursuit to control Wnt signaling.

A network-based analysis of colon cancer splicing changes reveals a tumorigenesis-favoring regulatory pathway emanating from ELK1

Splicing aberrations are prominent drivers of cancer, yet the regulatory pathways controlling them are mostly unknown. Here we develop a method that integrates physical interaction, gene expression, and alternative splicing data to construct the largest map of transcriptomic and proteomic interactions leading to cancerous splicing aberrations defined to date, and identify driver pathways therein. We apply our method to colon adenocarcinoma and non-small-cell lung carcinoma. By focusing on colon cancer, we reveal a novel tumor-favoring regulatory pathway involving the induction of the transcription factor MYC by the transcription factor ELK1, as well as the subsequent induction of the alternative splicing factor PTBP1 by both. We show that PTBP1 promotes specific RAC1,NUMB, and PKM splicing isoforms that are major triggers of colon tumorigenesis. By testing the pathway's activity in patient tumor samples, we find ELK1,MYC, and PTBP1 to be overexpressed in conjunction with oncogenic KRAS mutations, and show that these mutations increase ELK1 levels via the RAS-MAPK pathway. We thus illuminate, for the first time, a full regulatory pathway connecting prevalent cancerous mutations to functional tumor-inducing splicing aberrations. Our results demonstrate our method is applicable to different cancers to reveal regulatory pathways promoting splicing aberrations.

Small-molecule inhibitors of Wnt signaling pathway: towards novel anticancer therapeutics

BACKGROUND

The Wnt signaling pathway involves secreted glycoproteins that bind to the Frizzled family receptors to activate intracellular signal transduction events that regulate cell proliferation, apoptosis, cell migration and many critical aspects of developmental biology.

DISCUSSION

Aberrant Wnt signaling underlies a wide range of pathologies in humans including tumor initiation, tumor growth, cell senescence, cell death, differentiation and metastasis. The inhibition of Wnt signaling offers a novel approach for anticancer therapeutics.

CONCLUSION

Focusing on recent developments, we reviewed the small-molecule inhibitors targeting various components of Wnt signaling pathways and the progress from the discovery of lead compounds to highly potent inhibitors with significant therapeutic potential.

Epigenetic mechanisms in cancer: push and pull between kneaded erasers and fate writers

Research concerning the epigenome over the years has systematically and sequentially shown substantial development and we have moved from global inhibition of modifications of the epigenome toward identification and targeted therapy against tumor-specific epigenetic mechanisms. In accordance with this approach, several drugs with epigenetically modulating activity have received considerable attention and appreciation, and recently emerging scientific evidence is uncovering details of their mode of action. High-throughput technologies have considerably improved our existing understanding of tumor suppressors, oncogenes, and signaling pathways that are key drivers of cancer. In this review, we summarize the general epigenetic mechanisms in cancer, including: the post-translational modification of DNA methyltransferase and its mediated inactivation of Ras association domain family 1 isoform A, Sonic hedgehog signaling, Wnt signaling, Notch signaling, transforming growth factor signaling, and natural products with epigenetic modification ability. Moreover, we introduce the importance of nanomedicine for delivery of natural products with modulating ability to epigenetic machinery in cancer cells. Such in-depth and comprehensive knowledge regarding epigenetic dysregulation will be helpful in the upcoming era of molecular genomic pathology for both detection and treatment of cancer. Epigenetic information will also be helpful when nanotherapy is used for epigenetic modification.

Targeting the Wnt pathway in human cancers: therapeutic targeting with a focus on OMP-54F28

The Wnt signaling pathways are a group of signal transduction pathways that play an important role in cell fate specification, cell proliferation and cell migration. Aberrant signaling in these pathways has been implicated in the development and progression of multiple cancers by allowing increased proliferation, angiogenesis, survival and metastasis. Activation of the Wnt pathway also contributes to the tumorigenicity of cancer stem cells (CSCs). Therefore, inhibiting this pathway has been a recent focus of cancer research with multiple targetable candidates in development. OMP-54F28 is a fusion protein that combines the cysteine-rich domain of frizzled family receptor 8 (Fzd8) with the immunoglobulin Fc domain that competes with the native Fzd8 receptor for its ligands and antagonizes Wnt signaling. Preclinical models with OMP-54F28 have shown reduced tumor growth and decreased CSC frequency as a single agent and in combination with other chemotherapeutic agents. Due to these findings, a phase 1a study is nearing completion with OMP-54F28 in advanced solid tumors and 3 phase 1b studies have been opened with OMP-54F28 in combination with standard-of-care chemotherapy backbones in ovarian, pancreatic and hepatocellular cancers. This article will review the Wnt signaling pathway, preclinical data on OMP-54F28 and other Wnt pathway inhibitors and ongoing clinical trials.