An RNAi-based chemical genetic screen identifies three small-molecule inhibitors of the Wnt/wingless signaling pathway. Proc Natl Acad Sci U S A. 2011;108:5954-5963. [PMID: 21393571 DOI: 10.1073/pnas.1017496108]

Inhibition of oncogenic Wnt signaling through direct targeting of β-catenin

Aberrant activation of signaling by the Wnt pathway is strongly implicated in the onset and progression of numerous types of cancer. Owing to the persistent dependence of these tumors on Wnt signaling for growth and survival, inhibition of this pathway is considered an attractive mechanism-based therapeutic approach. Oncogenic activation of Wnt signaling can ensue from a variety of distinct aberrations in the signaling pathway, but most share the common feature of causing increased cellular levels of β-catenin by interfering with its constitutive degradation. β-Catenin serves as a central hub in Wnt signaling by engaging in crucial protein-protein interactions with both negative and positive effectors of the pathway. Direct interference with these protein-protein interactions is a biologically compelling approach toward suppression of β-catenin hyperactivity, but such interactions have proven intransigent with respect to small-molecule targeting. Hence β-catenin remains an elusive target for translational cancer therapy. Here we report the discovery of a hydrocarbon-stapled peptide that directly targets β-catenin and interferes with its ability to serve as a transcriptional coactivator for T-cell factor (TCF) proteins, the downstream transcriptional regulators of the Wnt pathway.

High-throughput screening strategies for targeted identification of therapeutic compounds in colorectal cancer

Recent advancements in understanding the role of both genetics and molecular pathways in the formation and progression of colorectal cancer have allowed the identification of factors that may be targeted for drug discovery. During the past decade, various approaches have been developed to target specific steps or components of these pathways in order to prevent the development and progression of colorectal cancer and to treat this disease. The innovation and optimization of high-throughput screening methods, as well as the recent emphasis from the NIH on translational sciences, have enabled rapid progress in drug discovery in many fields, including colorectal cancer. Here we present a summary of the recent efforts of targeted high-throughput drug discovery directed at pathways affected in colorectal cancer.

Wnt/β-catenin signalling in prostate cancer

The Wnts are secreted cysteine-rich glycoproteins that have important roles in the developing embryo as well as in tissue homeostasis in adults. Dysregulation of Wnt signalling can lead to several types of cancer, including prostate cancer. A hallmark of the signalling pathway is the stabilization of the transcriptional co-activator β-catenin, which not only regulates expression of many genes implicated in cancer but is also an essential component of cadherin cell adhesion complexes. β-catenin regulates gene expression by binding members of the T-cell-specific transcription factor/lymphoid enhancer-binding factor 1 (TCF/LEF-1) family of transcription factors. In addition, β-catenin associates with the androgen receptor, a key regulator of prostate growth that drives prostate cancer progression. Wnt/β-catenin signalling can be controlled by secreted Wnt antagonists, many of which are downregulated in cancer. Activation of the Wnt/β-catenin pathway has effects on prostate cell proliferation, differentiation and the epithelial-mesenchymal transition, which is thought to regulate the invasive behaviour of tumour cells. However, whether targeting Wnt/β-catenin signalling is a good therapeutic option for prostate cancer remains unclear.

Drugging Wnt signalling in cancer

Aberrant regulation of the Wnt signalling pathway has emerged as a prevalent theme in cancer biology. This chapter summarizes the research that provides a proof of concept for inhibiting Wnt signalling in cancer, the potential means by which this could be achieved, and some recent advances towards this goal. A brief discussion of molecular diagnostics and possible safety concerns is also provided.

Embryonic signaling pathways and rhabdomyosarcoma: contributions to cancer development and opportunities for therapeutic targeting

Rhabdomyosarcoma is the most common soft tissue sarcoma of childhood and adolescence, accounting for approximately 7% of childhood cancers. Current therapies include nonspecific cytotoxic chemotherapy regimens, radiation therapy, and surgery; however, these multimodality strategies are unsuccessful in the majority of patients with high-risk disease. It is generally believed that these tumors represent arrested or aberrant skeletal muscle development, and, accordingly, developmental signaling pathways critical to myogenesis such as Notch, WNT, and Hedgehog may represent new therapeutic targets. In this paper, we summarize the current preclinical studies linking these embryonic pathways to rhabdomyosarcoma tumorigenesis and provide support for the investigation of targeted therapies in this embryonic cancer.

Wnt signalling in smooth muscle cells and its role in cardiovascular disorders

Vascular smooth muscle cells (SMCs) are the major cell type within blood vessels. SMCs exhibit low rates of proliferation, migration, and apoptosis in normal blood vessels. However, increased SMC proliferation, migration, and apoptosis rates radically alter the composition and structure of the blood vessel wall and contribute to cardiovascular diseases, such as atherosclerosis, and restenosis that occur after coronary artery vein grafting and stent implantation. Consequently, therapies that modulate SMC proliferation, migration, and apoptosis may be useful for treating cardiovascular diseases. The family of Wnt proteins, which were first identified in the wingless drosophila, has a well-established role in embryogenesis and development. It is now emerging that Wnt proteins also regulate SMC proliferation, migration, and survival. In this review article, we discuss recently emerging research that has revealed that Wnt proteins are important regulators of SMC behaviour via activation of β-catenin-dependent and β-catenin-independent Wnt signalling pathways.

Selective small molecule inhibition of poly(ADP-ribose) glycohydrolase (PARG)

The poly(ADP-ribose) (PAR) post-translational modification is essential for diverse cellular functions, including regulation of transcription, response to DNA damage, and mitosis. Cellular PAR is predominantly synthesized by the enzyme poly(ADP-ribose) polymerase-1 (PARP-1). PARP-1 is a critical node in the DNA damage response pathway, and multiple potent PARP-1 inhibitors have been described, some of which show considerable promise in the clinic for the treatment of certain cancers. Cellular PAR is efficiently degraded by poly(ADP-ribose) glycohydrolase (PARG), an enzyme for which no potent, readily accessible, and specific inhibitors exist. Herein we report the discovery of small molecules that effectively inhibit PARG in vitro and in cellular lysates. These potent PARG inhibitors can be produced in two chemical steps from commercial starting materials and have complete specificity for PARG over the other known PAR glycohydrolase (ADP-ribosylhydrolase 3, ARH3) and over PARP-1 and thus will be useful tools for studying the biochemistry of PAR signaling.

Wnt signaling from membrane to nucleus: β-catenin caught in a loop

β-catenin is the central nuclear effector of the Wnt signaling pathway, and regulates other cellular processes including cell adhesion. Wnt stimulation of cells culminates in the nuclear translocation of β-catenin and transcriptional activation of target genes that function during both normal and malignant development. Constitutive activation of the Wnt pathway leads to inappropriate nuclear accumulation of β-catenin and gene transactivation, an important step in cancer progression. This has generated interest in the mechanisms regulating β-catenin nuclear accumulation and retention. Here we discuss recent advances in understanding feedback loops that trap β-catenin in the nucleus and provide potential insights into Wnt signaling and the development of anti-cancer drugs.

β-catenin signaling: a novel mediator of fibrosis and potential therapeutic target

PURPOSE OF REVIEW

The Wnt/β-catenin signaling pathway plays a critical role in development and adult tissue homeostasis. Recent investigations implicate Wnt/β-catenin signaling in abnormal wound repair and fibrogenesis. The purpose of this review is to highlight recent key studies that support a role for Wnt/β-catenin signaling in fibrosis.

RECENT FINDINGS

Studies of patients with fibrotic diseases have demonstrated changes in components of the Wnt/β-catenin pathway. In animal models, perturbations in Wnt/β-catenin signaling appear to aggravate or ameliorate markers of injury and fibrosis in a variety of different tissues. Studies also suggest that fibroblasts from different tissue sources may have markedly divergent responses to Wnt/β-catenin signaling. Cross-talk between Wnt/β-catenin and transforming growth factor-β pathways is complex and context-dependent, and may promote fibrogenesis through coregulation of fibrogenic gene targets. High throughput screening has identified several novel chemical inhibitors of Wnt/β-catenin signaling that may be of therapeutic potential.

SUMMARY

Wnt/β-catenin signaling appears important in normal wound healing and its sustained activation is associated with fibrogenesis. The mechanism by which Wnt/β-catenin signaling may modify the response to injury is cell-type and context-dependent. Better understanding of this signaling pathway may provide a promising new therapeutic approach for human fibrotic diseases.

β-catenin signaling: a novel mediator of fibrosis and potential therapeutic target

PURPOSE OF REVIEW

The Wnt/β-catenin signaling pathway plays a critical role in development and adult tissue homeostasis. Recent investigations implicate Wnt/β-catenin signaling in abnormal wound repair and fibrogenesis. The purpose of this review is to highlight recent key studies that support a role for Wnt/β-catenin signaling in fibrosis.

RECENT FINDINGS

Studies of patients with fibrotic diseases have demonstrated changes in components of the Wnt/β-catenin pathway. In animal models, perturbations in Wnt/β-catenin signaling appear to aggravate or ameliorate markers of injury and fibrosis in a variety of different tissues. Studies also suggest that fibroblasts from different tissue sources may have markedly divergent responses to Wnt/β-catenin signaling. Cross-talk between Wnt/β-catenin and transforming growth factor-β pathways is complex and context-dependent, and may promote fibrogenesis through coregulation of fibrogenic gene targets. High throughput screening has identified several novel chemical inhibitors of Wnt/β-catenin signaling that may be of therapeutic potential.

SUMMARY

Wnt/β-catenin signaling appears important in normal wound healing and its sustained activation is associated with fibrogenesis. The mechanism by which Wnt/β-catenin signaling may modify the response to injury is cell-type and context-dependent. Better understanding of this signaling pathway may provide a promising new therapeutic approach for human fibrotic diseases.

Wnt inhibition correlates with human embryonic stem cell cardiomyogenesis: a structure-activity relationship study based on inhibitors for the Wnt response

Human embryonic stem cell-based high-content screening of 550 known signal transduction modulators showed that one "lead" (1, a recently described inhibitor of the proteolytic degradation of Axin) stimulated cardiomyogenesis. Because Axin controls canonical Wnt signaling, we conducted an investigation to determine whether the cardiogenic activity of 1 is Wnt-dependent, and we developed a structure-activity relationship to optimize the cardiogenic properties of 1. We prepared analogues with a range of potencies (low nanomolar to inactive) for Wnt/β-catenin inhibition and for cardiogenic induction. Both functional activities correlated positively (r(2) = 0.72). The optimal compounds induced cardiogenesis 1.5-fold greater than 1 at 30-fold lower concentrations. In contrast, no correlation was observed for cardiogenesis and modulation of transforming growth factor β (TGFβ)/Smad signaling that prominently influences cardiogenesis. Taken together, these data show that Wnt signaling inhibition is essential for cardiogenic activity and that the pathway can be targeted for the design of druglike cardiogenic molecules.

RNAi screening: new approaches, understandings, and organisms

RNA interference (RNAi) leads to sequence-specific knockdown of gene function. The approach can be used in large-scale screens to interrogate function in various model organisms and an increasing number of other species. Genome-scale RNAi screens are routinely performed in cultured or primary cells or in vivo in organisms such as C. elegans. High-throughput RNAi screening is benefitting from the development of sophisticated new instrumentation and software tools for collecting and analyzing data, including high-content image data. The results of large-scale RNAi screens have already proved useful, leading to new understandings of gene function relevant to topics such as infection, cancer, obesity, and aging. Nevertheless, important caveats apply and should be taken into consideration when developing or interpreting RNAi screens. Some level of false discovery is inherent to high-throughput approaches and specific to RNAi screens, false discovery due to off-target effects (OTEs) of RNAi reagents remains a problem. The need to improve our ability to use RNAi to elucidate gene function at large scale and in additional systems continues to be addressed through improved RNAi library design, development of innovative computational and analysis tools and other approaches.

Chemical genetics and drug screening in Drosophila cancer models

Drug candidates often fail in preclinical and clinical testing because of reasons of efficacy and/or safety. It would be time- and cost-efficient to have screening models that reduce the rate of such false positive candidates that appear promising at first but fail later. In this regard, it would be particularly useful to have a rapid and inexpensive whole animal model that can pre-select hits from high-throughput screens but before testing in costly rodent assays. Drosophila melanogaster has emerged as a potential whole animal model for drug screening. Of particular interest have been drugs that must act in the context of multi-cellularity such as those for neurological disorders and cancer. A recent review provides a comprehensive summary of drug screening in Drosophila, but with an emphasis on neurodegenerative disorders. Here, we review Drosophila screens in the literature aimed at cancer therapeutics.

Industry Update: The latest developments in therapeutic delivery

The present Industry Update covers the period 16 March to 15 April 2011, with information sourced from company press releases, media newswires, regulatory agencies and relevant patent offices. There was considerable activity in the area of ‘Business development’; however for reasons of brevity, only those, which in my view, are most relevant are included. Cephalon continues to build its business through acquisitions, in this case the privately held company Gemin X, which has a promising portfolio of targeted cancer therapeutics. SuperGen and Astex Therapeutics have agreed a merger from which Astex Pharmaceuticals will emerge as a stronger commercial entity with critical mass that may find itself a prospective acquisition in the future. Pfizer have agreed to off-load Capsugel to KKR at a cost of US$2.375 billion in cash. A significant number of licensing deals have also taken place, a notable number involving large Japanese pharmaceutical companies. A rash of product approvals occurred both in the EU and the USA following the pre- and post-christmas lull, and positive top-line results from two Phase III multiple sclerosis trials involving laquinimod and dimethyl fumarate, were of particular interest. An exciting range of journal publications also appeared relating to potential therapeutic targets or targeting strategies including the LNA-based compounds developed by Santaris Pharma, identification of inhibitors of the Wnt signaling pathway, and the synthesis and evaluation of the multimodal porphysome nanovesicles.