Discovery of Selective Small-Molecule Inhibitors for the β-Catenin/T-Cell Factor Protein-Protein Interaction through the Optimization of the Acyl Hydrazone Moiety

Discovery of Novel 1-Phenylpiperidine Urea-Containing Derivatives Inhibiting β-Catenin/BCL9 Interaction and Exerting Antitumor Efficacy through the Activation of Antigen Presentation of cDC1 Cells

Aberrant activation of the Wnt/β-catenin signaling is associated with tumor development, and blocking β-catenin/BCL9 is a novel strategy for oncogenic Wnt/β-catenin signaling. Herein, we presented two novel β-catenin variations and exposed conformational dynamics in several β-catenin crystal structures at the BCL9 binding site. Furthermore, we identified a class of novel urea-containing compounds targeting β-catenin/BCL9 interaction. Notably, the binding modalities of inhibitors were greatly affected by the conformational dynamics of β-catenin. Among them, 28 had a strong affinity for β-catenin (Kd = 82 nM), the most potent inhibitor reported. In addition, 13 and 35 not only activate T cells but also promote the antigen presentation of cDC1, showing robust antitumor efficacy in the CT26 model. Collectively, our study demonstrated a series of potent small-molecule inhibitors targeting β-catenin/BCL9, which can enhance antigen presentation and activate cDC1 cells, delivering a potential strategy for boosting innate and adaptive immunity to overcome immunotherapy resistance.

Wnt/β-catenin signaling pathway in carcinogenesis and cancer therapy

The Wnt/β-catenin signaling pathway plays a crucial role in various physiological processes, encompassing development, tissue homeostasis, and cell proliferation. Under normal physiological conditions, the Wnt/β-catenin signaling pathway is meticulously regulated. However, aberrant activation of this pathway and downstream target genes can occur due to mutations in key components of the Wnt/β-catenin pathway, epigenetic modifications, and crosstalk with other signaling pathways. Consequently, these dysregulations contribute significantly to tumor initiation and progression. Therapies targeting the Wnt/β-catenin signaling transduction have exhibited promising prospects and potential for tumor treatment. An increasing number of medications targeting this pathway are continuously being developed and validated. This comprehensive review aims to summarize the latest advances in our understanding of the role played by the Wnt/β-catenin signaling pathway in carcinogenesis and targeted therapy, providing valuable insights into acknowledging current opportunities and challenges associated with targeting this signaling pathway in cancer research and treatment.

Design, synthesis, and biological evaluation of novel 8-substituted quercetin derivatives targeting the β‑catenin/B-cell lymphoma 9 interaction

The β-catenin/B-cell lymphoma 9 (BCL9) protein-protein interaction (PPI) is a potential target for aberrantly active Wnt/β-catenin signaling which actively participates in initiating and progressing of many cancers. Herein, we discovered novel 8-substituted quercetin derivatives with potential inhibitory activities targeting β-catenin/BCL9 PPI. Among all the derivatives, compound B4 displayed the most promising PPI inhibitory activity with an IC50 value of 2.25 μM in a competitive fluorescence polarization assay and a KD value of 1.44 μM for the β-catenin protein. Furthermore, B4 selectively inhibited the growth of colorectal cancer (CRC) cells, suppressed the transactivation of Wnt signaling, and downregulated the expression of oncogenic Wnt target gene. Especially, B4 showed potent anti-CRC activity in vivo with the tumor growth inhibition (TGI) of 75.99 % and regulated the tumor immune microenvironment.

β-catenin inhibitors in cancer therapeutics: intricacies and way forward

β-catenin is an evolutionary conserved, quintessential, multifaceted protein that plays vital roles in cellular homeostasis, embryonic development, organogenesis, stem cell maintenance, cell proliferation, migration, differentiation, apoptosis, and pathogenesis of various human diseases including cancer. β-catenin manifests both signaling and adhesive features. It acts as a pivotal player in intracellular signaling as a component of versatile WNT signaling cascade involved in embryonic development, homeostasis as well as in carcinogenesis. It is also involved in Ca2+ dependent cell adhesion via interaction with E-cadherin at the adherens junctions. Aberrant β-catenin expression and its nuclear accumulation promote the transcription of various oncogenes including c-Myc and cyclinD1, thereby contributing to tumor initiation, development, and progression. β-catenin's expression is closely regulated at various levels including its stability, sub-cellular localization, as well as transcriptional activity. Understanding the molecular mechanisms of regulation of β-catenin and its atypical expression will provide researchers not only the novel insights into the pathogenesis and progression of cancer but also will help in deciphering new therapeutic avenues. In the present review, we have summarized the dual functions of β-catenin, its role in signaling, associated mutations as well as its role in carcinogenesis and tumor progression of various cancers. Additionally, we have discussed the challenges associated with targeting β-catenin molecule with the presently available drugs and suggested the possible way forward in designing new therapeutic alternatives against this oncogene.

Pterostilbene-Isothiocyanate Inhibits Proliferation of Human MG-63 Osteosarcoma Cells via Abrogating β-Catenin/TCF-4 Interaction-A Mechanistic Insight

Osteosarcoma, a highly metastasizing bone neoplasm, is a leading cause of death and disability in children and adolescents worldwide. Osteosarcoma is only suboptimally responsive to surgery and radio- and chemotherapy, that too with adverse side effects. Hence, there is a necessary need for safer alternative therapeutic approaches. This study evaluated the anticancer effects of the semi-synthetic compound, pterostilbene-isothiocyanate (PTER-ITC), on human osteosarcoma MG-63 cells through cytotoxicity, wound-healing, and transwell-migration assays. Results showed that PTER-ITC specifically inhibited the survival, proliferation, and migration of osteosarcoma cells. PTER-ITC induced apoptosis in MG-63 cells by disrupting mitochondrial membrane potential, as evident from the outcomes of different cytological staining. The antimetastatic potential of PTER-ITC was evaluated through immunostaining, RT-qPCR, and immunoblotting. In silico (molecular docking and dynamic simulation) and, subsequently, biochemical [co-immunoprecipitation (Co-IP) and luciferase reporter] assays deciphered the underlying mode-of-action of this compound. PTER-ITC increased E-cadherin and reduced N-cadherin levels, thereby facilitating the reversal of epithelial-mesenchymal transition (EMT). It also modulated the expressions of proliferative cell nuclear antigen (PCNA), caspase-3, poly [ADP-ribose] polymerase (PARP-1) and matrix metalloproteinase-2/9 (MMPs-2/9) at transcriptional and translational levels. PTER-ITC interfered with the β-catenin/transcription factor-4 (TCF-4) interaction in silico by occupying the β-catenin binding site on TCF-4, confirmed by their reduced physical interactions (Co-IP assay). This inhibited transcriptional activation of TCF-4 by β-catenin (as shown by luciferase reporter assay). In conclusion, PTER-ITC exhibited potent anticancer effects in vitro against human osteosarcoma cells by abrogating the β-catenin/TCF-4 interaction. Altogether, this study suggests that PTER-ITC may be regarded as a new approach for osteosarcoma treatment.

Recent advances in anticancer peptoids

Since most tumors become resistant to drugs in a gradual and irreversible manner, making treatment less effective over time, anticancer drugs require continuous development. Peptoids are a class of peptidomimetics that can be easily synthesized and optimized. They exhibit a number of unique characteristics, including protease resistance, non-immunogenicity, do not interfere with peptide functionality and skeleton polarity, and can adopt different conformations. They have been studied for their efficacy in different cancer therapies, and can be considered as a promising alternative molecular category for the development of anticancer drugs. Herein, we discuss the extensive recent advances in peptoids and peptoid hybrids in the treatment of cancers such as prostate, breast, lung, and other ones, in the hope of providing a reference for the further development of peptoid anticancer drugs.

Design, synthesis and biological evaluation of quercetin derivatives as novel β-catenin/B-cell lymphoma 9 protein-protein interaction inhibitors

The β-catenin/B-cell lymphoma 9 (BCL9) protein-protein interaction (PPI) is a potential target for the suppression of hyperactive Wnt/β-catenin signaling that is vigorously involved in cancer initiation and development. Herein, we first described quercetin and its derivatives had potential inhibitory effects on β-catenin/BCL9 PPI. The most potent compound, quercetin-3'-O-(4-methylpiperazine-1-yl) propyl (C1), directly binded with β-catenin and disrupted the β-catenin/BCL9 interaction in both the protein level and the cellular context. C1 also effectively inhibited colorectal cancer in vitro and showed better selectivity in inhibiting hyperactive Wnt/β-catenin signaling cells like CT26 and HCT116. And we further confirmed that C1 could inhibit CT26 tumor growth in vivo and regulate the tumor immune microenvironment. This study provides a good chemical probe to explore β-catenin-related biology and a drug-like quercetin derivative as novel β-catenin/BCL9 PPI inhibitors for further drug development.

Medicinal Chemistry Strategies for the Development of Inhibitors Disrupting β-Catenin's Interactions with Its Nuclear Partners

Dysregulation of the Wnt/β-catenin signaling pathway is strongly associated with various aspects of cancer, including tumor initiation, proliferation, and metastasis as well as antitumor immunity, and presents a promising opportunity for cancer therapy. Wnt/β-catenin signaling activation increases nuclear dephosphorylated β-catenin levels, resulting in β-catenin binding to TCF and additional cotranscription factors, such as BCL9, CBP, and p300. Therefore, directly disrupting β-catenin's interactions with these nuclear partners holds promise for the effective and selective suppression of the aberrant activation of Wnt/β-catenin signaling. Herein, we summarize recent advances in biochemical techniques and medicinal chemistry strategies used to identify potent peptide-based and small-molecule inhibitors that directly disrupt β-catenin's interactions with its nuclear binding partners. We discuss the challenges involved in developing drug-like inhibitors that target the interactions of β-catenin and its nuclear binding partner into therapeutic agents.

Emerging Direct Targeting β-Catenin Agents

Aberrant accumulation of β-catenin in the cell nucleus as a result of deregulation of the Wnt/β-catenin pathway is found in various types of cancer. Direct β-catenin targeting agents are being researched despite obstacles; however, specific β-catenin drugs for clinical treatments have not been approved so far. We focused on direct β-catenin targeting of potential therapeutic value as anticancer agents. This review provides recent advances on small molecule β-catenin agents. Structure-activity relationships and biological activities of reported inhibitors are discussed. This work provides useful knowledge in the discovery of β-catenin agents.

Targeting the interaction of β-catenin and TCF/LEF transcription factors to inhibit oncogenic Wnt signaling

The Wnt/β-catenin signaling pathway is crucially involved in embryonic development, stem cell maintenance and tissue renewal. Hyperactivation of this pathway is associated with the development and progression of various types of cancers. The transcriptional coactivator β-catenin represents a pivotal component of the pathway and its interaction with transcription factors of the TCF/LEF family is central to pathway activation. Inhibition of this crucial protein-protein interaction via direct targeting of β-catenin is considered a promising strategy for the inactivation of oncogenic Wnt signaling. This review summarizes advances in the development of Wnt antagonists that have been shown to directly bind β-catenin.

A novel survivin dimerization inhibitor without a labile hydrazone linker induces spontaneous apoptosis and synergizes with docetaxel in prostate cancer cells

Survivin, a member of the inhibitor of apoptosis protein family, exists as a homodimer and is aberrantly upregulated in a wide spectrum of cancers. It was thought to be an ideal target due to its lack of expression in most adult normal tissues and importance in cancer cell survival. However, it has been challenging to target survivin due to its "undruggable" nature. We previously attempted to target its dimerization domain with a hypothesis that inhibiting survivin dimerization would promote its degradation in proteasome, which led to identification of a lead small-molecule inhibitor, LQZ-7F. LQZ-7F consists of a flat tetracyclic aromatic core with labile hydrazone linking a 1,2,5-oxadiazole moiety. In this study, we tested the hypothesis that LQZ-7F could be developed as a prodrug because the labile hydrazone linker could be hydrolyzed, releasing the tetracyclic aromatic core. To this end, we synthesized the tetracyclic aromatic core (LQZ-7F1) using reported procedure and tested LQZ-7F1 for its biological activities. Here we show that LQZ-7F1 has a significantly improved potency with submicromolar IC_50's and induces spontaneous apoptosis in prostate cancer cells. It also more effectively inhibits survivin dimerization and induces survivin degradation in a proteasome-dependent manner than LQZ-7F. We also show that the combination of LQZ-7F1 and docetaxel have strong synergism in inhibiting prostate cancer cell survival. Together, we conclude that the hydrazone linker with the oxadiazole tail is dispensable for survivin inhibition and the survivin dimerization inhibitor, LQZ-7F, may be developed as a prodrug for prostate cancer treatment and to overcome docetaxel resistance.

Biophysical Survey of Small-Molecule β-Catenin Inhibitors: A Cautionary Tale

The canonical Wingless-related integration site signaling pathway plays a critical role in human physiology, and its dysregulation can lead to an array of diseases. β-Catenin is a multifunctional protein within this pathway and an attractive yet challenging therapeutic target, most notably in oncology. This has stimulated the search for potent small-molecule inhibitors binding directly to the β-catenin surface to inhibit its protein–protein interactions and downstream signaling. Here, we provide an account of the claimed (and some putative) small-molecule ligands of β-catenin from the literature. Through in silico analysis, we show that most of these molecules contain promiscuous chemical substructures notorious for interfering with screening assays. Finally, and in line with this analysis, we demonstrate using orthogonal biophysical techniques that none of the examined small molecules bind at the surface of β-catenin. While shedding doubts on their reported mode of action, this study also reaffirms β-catenin as a prominent target in drug discovery.

Discovery of 1-Benzoyl 4-Phenoxypiperidines as Small-Molecule Inhibitors of the β-Catenin/B-Cell Lymphoma 9 Protein-Protein Interaction

Structure-based design and optimization were performed to develop small-molecule β-catenin/B-cell lymphoma 9 (BCL9) inhibitors and improve their inhibitory activities. Compound ZL3138 with a novel 1-benzoyl 4-phenoxypiperidine scaffold was discovered to disrupt the β-catenin/BCL9 protein-protein interaction (PPI) with a K_i of 0.96 μM in AlphaScreen competitive inhibition assays and displayed good selectivity for β-catenin/BCL9 over β-catenin/E-cadherin PPIs. The binding mode of new inhibitors was characterized by structure-activity relationship and site-directed mutagenesis studies. Protein pull-down assays indicate that this series of compounds directly binds with β-catenin. Cellular target engagement and co-immunoprecipitation experiments demonstrate that ZL3138 binds with β-catenin and disrupts the β-catenin/BCL9 interaction without affecting the β-catenin/E-cadherin interaction in living cells. Further cell-based studies show that ZL3138 selectively suppresses transactivation of Wnt/β-catenin signaling, regulates transcription and expression of Wnt target genes, and inhibits the growth of Wnt/β-catenin-dependent cancer cells.

Recent advances in β-catenin/BCL9 protein-protein interaction inhibitors

Wnt/β-catenin signaling is crucial both in normal embryonic development and throughout the life of an organism. Moreover, aberrant Wnt signaling has been associated with various diseases, especially cancer and fibrosis. Recent research suggests that direct targeting of the β-catenin/BCL9 protein-protein interaction (PPI) is a promising strategy to block the Wnt pathway. Progress in understanding the cocrystalline complex and mechanism of action of the β-catenin/BCL9 interaction facilitates the discovery process of its inhibitors, but only a few inhibitors have been reported. In this review, the discovery and development of β-catenin/BCL9 PPI inhibitors in the areas of drug design, structure-activity relationships and biological and biochemical properties are summarized. In addition, perspectives for the future development of β-catenin/BCL9 PPI inhibitors are explored.

Small-Molecule Inhibitors Targeting the Canonical WNT Signaling Pathway for the Treatment of Cancer

Canonical WNT signaling is an important developmental pathway that has attracted increased attention for anticancer drug discovery. From the production and secretion of WNT ligands, their binding to membrane receptors, and the β-catenin destruction complex to the expansive β-catenin transcriptional complex, multiple components have been investigated as drug targets to modulate WNT signaling. Significant progress in developing WNT inhibitors such as porcupine inhibitors, tankyrase inhibitors, β-catenin/coactivators, protein-protein interaction inhibitors, casein kinase modulators, DVL inhibitors, and dCTPP1 inhibitors has been made, with several candidates (e.g., LGK-974, PRI-724, and ETC-159) in human clinical trials. Herein we summarize recent progress in the drug discovery and development of small-molecule inhibitors targeting the canonical WNT pathway, focusing on their specific target proteins, in vitro and in vivo activities, physicochemical properties, and therapeutic potential. The relevant opportunities and challenges toward maintaining the balance between efficacy and toxicity in effectively targeting this pathway are also highlighted.

Furazans in Medicinal Chemistry

Incorporation of heterocycles into drug molecules can enhance physical properties and biological activity. A variety of heterocyclic groups is available to medicinal chemists, many of which have been reviewed in detail elsewhere. Oxadiazoles are a class of heterocycle containing one oxygen and two nitrogen atoms, available in three isomeric forms. While the 1,2,4- and 1,3,4-oxadiazoles have seen widespread application in medicinal chemistry, 1,2,5-oxadiazoles (furazans) are less common. This Review provides a summary of the application of furazan-containing molecules in medicinal chemistry and drug development programs from analysis of both patent and academic literature. Emphasis is placed on programs that reached clinical or preclinical stages of development. The examples provided herein describe the pharmacology and biological activity of furazan derivatives with comparative data provided where possible for other heterocyclic groups and pharmacophores commonly used in medicinal chemistry.

Direct targeting of β-catenin in the Wnt signaling pathway: Current progress and perspectives

Aberrant activation of the Wnt/β-catenin signaling circuit is associated with cancer recurrence and relapse, cancer invasion and metastasis, and cancer immune evasion. Direct targeting of β-catenin, the central hub in this signaling pathway, is a promising strategy to suppress the hyperactive β-catenin signaling but has proven to be highly challenging. Substantial efforts have been made to discover compounds that bind with β-catenin, block β-catenin-mediated protein-protein interactions, and suppress β-catenin signaling. Herein, we characterize potential small-molecule binding sites in β-catenin, summarize bioactive small molecules that directly target β-catenin, and review structure-based inhibitor optimization, structure-activity relationship, and biological activities of reported inhibitors. This knowledge will benefit future inhibitor development and β-catenin-related drug discovery.

A perspective on medicinal chemistry approaches towards adenomatous polyposis coli and Wnt signal based colorectal cancer inhibitors

Colorectal cancer (CRC) is one of the major causes of carcinogenic mortality in numbers only after lung and breast cancers. The mutations in adenomatous polyposis coli (APC) gene leads to formation of colorectal polyps in the colonic region and which develop as a malignant tumour upon coalition with patient related risk factors. The protein-protein interaction (PPI) of APC with Asef (A Rac specific guanine nucleotide exchange factor) overwhelms the patient's conditions by rapidly spreading in the entire colorectal region. Most mutations in APC gene occur in mutated cluster region (MCR), where it specifically binds with the cytosolic β-catenin to regulate the Wnt signalling pathway required for CRC cell adhesion, invasion, progression, differentiation and stemness in initial cell cycle phages. The current broad spectrum perspective is attempted to elaborate the sources of identification, development of selective APC inhibitors by targeting emopamil-binding protein (EBP) & dehydrocholesterol reductase-7 & 24 (DHCR-7 & 24); APC-Asef, β-catenin/APC, Wnt/β-catenin, β-catenin/TCF4 PPI inhibitors with other vital Wnt signal cellular proteins and APC/Pol-β interface of colorectal cancer. In this context, this perspective would serve as a platform for design of new medicinal agents by targeting cellular essential components which could accelerate anti-colorectal potential candidates.

Targeting the Wnt/β-catenin signaling pathway in cancer

The aberrant Wnt/β-catenin signaling pathway facilitates cancer stem cell renewal, cell proliferation and differentiation, thus exerting crucial roles in tumorigenesis and therapy response. Accumulated investigations highlight the therapeutic potential of agents targeting Wnt/β-catenin signaling in cancer. Wnt ligand/ receptor interface, β-catenin destruction complex and TCF/β-catenin transcription complex are key components of the cascade and have been targeted with interventions in preclinical and clinical evaluations. This scoping review aims at outlining the latest progress on the current approaches and perspectives of Wnt/β-catenin signaling pathway targeted therapy in various cancer types. Better understanding of the updates on the inhibitors, antagonists and activators of Wnt/β-catenin pathway rationalizes innovative strategies for personalized cancer treatment. Further investigations are warranted to confirm precise and secure targeted agents and achieve optimal use with clinical benefits in malignant diseases.

Synthesis of Heteroannulated Indolopyrazines through Domino N-H Palladium-Catalyzed/Metal-Free Oxidative C-H Bond Activation

A convenient approach to [1,2,5]oxadiazolo[3',4':5,6]pyrazino[2,3-b]indoles and their heteroannulated analogues bearing various aryl substituents in the backbone has been developed. This synthetic protocol is based on Pd-catalyzed Buchwald-Hartwig and subsequent annulation by intramolecular oxidative cyclodehydrogenation. The photophysical properties for new polycycles have been measured.

Discovery of chemical probes that suppress Wnt/β-catenin signaling through high-throughput screening

Aberrant activation of the Wnt/β‐catenin signaling pathway has been observed in a wide range of human tumors. Deregulation of the pathway is closely linked to various aspects of human carcinogenesis such as cell viability, regulation of cell cycle, epithelial‐mesenchymal transition, and maintenance of stemness. In addition, recent studies have disclosed the involvement of Wnt signaling in immune evasion of tumor cells. The accumulation of β‐catenin in the nucleus is a common feature of cancer cells carrying defects in the pathway, which leads to the continuous activation of T‐cell factor (TCF)/LEF transcription factors. Consequently, a genetic program is switched on, leading to the uncontrolled growth, prolonged survival, and acquisition of mesenchymal phenotype. As β‐catenin/TCF serves as a signaling hub for the pathway, β‐catenin/TCF‐dependent transcriptional activity is a relevant readout of the pathway. To date, a wide variety of synthetic TCF/LEF reporters has been developed, and high‐throughput screening (HTS) using these reporters has made significant contributions to the discovery of Wnt inhibitors. Indeed, HTS led to the identification of chemical probes targeting porcupine, a membrane bound O‐acyltransferase, and CREB‐binding protein, a transcriptional coactivator. This review focuses on various screening strategies for the discovery of Wnt inhibitors and their mode of action to help the creation of new concepts for assay/screening methods.

An engineered antibody fragment targeting mutant β-catenin via major histocompatibility complex I neoantigen presentation

Mutations in CTNNB1, the gene encoding β-catenin, are common in colon and liver cancers, the most frequent mutation affecting Ser-45 in β-catenin. Peptides derived from WT β-catenin have previously been shown to be presented on the cell surface as part of major histocompatibility complex (MHC) class I, suggesting an opportunity for targeting this common driver gene mutation with antibody-based therapies. Here, crystal structures of both the WT and S45F mutant peptide bound to HLA-A*03:01 at 2.20 and 2.45 Å resolutions, respectively, confirmed the accessibility of the phenylalanine residue for antibody recognition. Phage display was then used to identify single-chain variable fragment clones that selectively bind the S45F mutant peptide presented in HLA-A*03:01 and have minimal WT or other off-target binding. Following the initial characterization of five clones, we selected a single clone, E10, for further investigation. We developed a computational model of the binding of E10 to the mutant peptide-bound HLA-A3, incorporating data from affinity maturation as initial validation. In the future, our model may be used to design clones with maintained specificity and higher affinity. Such derivatives could be adapted into either cell-based (CAR-T) or protein-based (bispecific T-cell engagers) therapies to target cancer cells harboring the S45F mutation in CTNNB1.

Targeting transcription factor TCF4 by γ-Mangostin, a natural xanthone

Given that colon cancer is the third most common cancer in incidence and cause of death in the United States, and current treatment modalities are insufficient, there is a need to develop novel agents. Towards this, here we focus on γ-Mangostin, a bioactive compound present in the Mangosteen (Garcinia mangostana) fruit. γ-Mangostin suppressed proliferation and colony formation, and induced cell cycle arrest and apoptosis of colon cancer cell lines. Further, γ-Mangostin inhibited colonosphere formation. Molecular docking and CETSA (Cellular thermal shift assay) binding assays demonstrated that γ-Mangostin interacts with transcription factor TCF4 (T-Cell Factor 4) at the β-catenin binding domain with the binding energy of -5.5 Kcal/mol. Moreover, γ-Mangostin treatment decreased TCF4 expression and reduced TCF reporter activity. The compound also suppressed the expression of Wnt signaling target proteins cyclin D1 and c-Myc, and stem cell markers such as LGR5, DCLK1 and CD44. To determine the effect of γ-Mangostin on tumor growth in vivo, we administered nude mice harboring HCT116 tumor xenografts with 5 mg/Kg of γ-Mangostin intraperitoneally for 21 days. γ-Mangostin treatment significantly suppressed tumor growth, with notably lowered tumor volume and weight. In addition, western blot analysis revealed a significant decrease in the expression of TCF4 and its downstream targets such as cyclin D1 and c-Myc. Together, these data suggest that γ-Mangostin inhibits colon cancer growth through targeting TCF4. γ-Mangostin may be a potential therapeutic agent for colon cancer.

Optimization of Peptidomimetics as Selective Inhibitors for the β-Catenin/T-Cell Factor Protein-Protein Interaction

The β-catenin/T-cell factor (Tcf) protein-protein interaction (PPI) plays a critical role in the β-catenin signaling pathway which is hyperactivated in many cancers and fibroses. Based on compound 1, which was designed to target the Tcf4 G¹³ANDE¹⁷ binding site of β-catenin, extensive structure-activity relationship studies have been conducted. As a result, compounds 53 and 57 were found to disrupt the β-catenin/Tcf PPI with the K_i values of 0.64 and 0.44 μM, respectively, and exhibit good selectivity for β-catenin/Tcf over β-catenin/E-cadherin and β-catenin/adenomatous polyposis coli (APC) PPIs. The 3-(4,5-dimethylthiazol-2-yl)-5-(3-carboxymethoxyphenyl)-2-(4-sulfophenyl)-2 H-tetrazolium (MTS) cell viability assays revealed that 56, the ethyl ester of 53, was more potent than 53 in inhibiting viability of most of the Wnt/β-catenin hyperactive cancer cells. Further cell-based studies indicated that 56 disrupted the β-catenin/Tcf PPI without affecting the β-catenin/E-cadherin and β-catenin/APC PPIs, suppressed transactivation of Wnt/β-catenin signaling in dose-dependent manners, and inhibited migration and invasiveness of Wnt/β-catenin-dependent cancer cells.

TRIB3 Interacts With β-Catenin and TCF4 to Increase Stem Cell Features of Colorectal Cancer Stem Cells and Tumorigenesis

BACKGROUND & AIMS

Activation of Wnt signaling to β-catenin contributes to the development of colorectal cancer (CRC). Expression of tribbles pseudo-kinase 3 (TRIB3) is increased in some colorectal tumors and associated with poor outcome. We investigated whether increased TRIB3 expression promotes stem cell features of CRC cells and tumor progression by interacting with the Wnt signaling pathway.

METHODS

We performed studies with C57BL/6J-Apc^Min/J mice injected with an adeno-associated virus vector that expresses a small hairpin RNA against Trib3 mRNA (Apc^Min/J-Trib3^KD) or a control vector (Apc^Min/J-Ctrl). We created BALB/c mice that overexpress TRIB3 from an adeno-associated virus vector and mice with small hairpin RNA-mediated knockdown of β-catenin. The mice were given azoxymethane followed by dextran sodium sulfate to induce colitis-associated cancer. Intestinal tissues were collected and analyzed by histology, gene expression profiling, immunohistochemistry, and immunofluorescence. Leucine-rich repeat-containing G-protein-coupled receptor 5 (LGR5)-positive (LGR5^Pos) and LGR5-negative (LGR5^Neg) HCT-8 CRC cells, with or without knockdown or transgenic expression of TRIB3, were sorted and analyzed in sphere-formation assays. We derived organoids from human and mouse colorectal tumors to analyze the function of TRIB3 and test the effect of a peptide inhibitor. Wnt signaling to β-catenin was analyzed in dual luciferase reporter, chromatin precipitation, immunofluorescence, and immunoblot assays. Proteins that interact with TRIB3 were identified by immunoprecipitation. CRC cell lines were grown in nude mice as xenograft tumors.

RESULTS

At 10 weeks of age, more than half the Apc^Min/J-Ctrl mice developed intestinal high-grade epithelial neoplasia, whereas Apc^Min/J-Trib3^KD mice had no intestinal polyps and normal histology. Colon tissues from Apc^Min/J-Trib3^KD mice expressed lower levels of genes regulated by β-catenin and genes associated with cancer stem cells. Mice with overexpression of Trib3 developed more tumors after administration of azoxymethane and dextran sodium sulfate than BALB/c mice. Mice with knockdown of β-catenin had a lower tumor burden after administration of azoxymethane and dextran sodium sulfate, regardless of Trib3 overexpression. Intestinal tissues from mice with overexpression of Trib3 and knockdown of β-catenin did not have activation of Wnt signaling or expression of genes regulated by β-catenin. LGR5^Pos cells sorted from HCT-8 cells expressed higher levels of TRIB3 than LGR5^Neg cells. CRC cells that overexpressed TRIB3 had higher levels of transcription by β-catenin and formed larger spheroids than control CRC cells; knockdown of β-catenin prevented the larger organoid size caused by TRIB3 overexpression. TRIB3 interacted physically with β-catenin and transcription factor 4 (TCF4). TRIB3 overexpression increased, and TRIB3 knockdown decreased, recruitment of TCF4 and β-catenin to the promoter region of genes regulated by Wnt. Activated β-catenin increased expression of TRIB3, indicating a positive-feedback loop. A peptide (P2-T3A6) that bound β-catenin disrupted its interaction with TRIB3 and TCF4. In primary CRC cells and HCT-8 cells, P2-T3A6 decreased expression of genes regulated by β-catenin and genes associated with cancer stem cells and decreased cell viability and migration. Injection of C57BL/6J-Apc^Min/J mice with P2-T3A6 decreased the number and size of tumor nodules and colon expression of genes regulated by β-catenin. P2-T3A6 increased 5-fluorouracil-induced death of CRC cells and survival times of mice with xenograft tumors.

CONCLUSION

TRIB3 interacts with β-catenin and TCF4 in intestine cells to increase expression of genes associated with cancer stem cells. Knockdown of TRIB3 decreases colon neoplasia in mice, migration of CRC cells, and their growth as xenograft tumors in mice. Strategies to block TRIB3 activity might be developed for treatment of CRC.

Polynitro-1,2,4-triazole-functionalized azo-furazans as high-performance and insensitive energetic materials

Polynitro-1,2,4-triazoles were introduced into the azo-furazan backbones to boost their energetic performance and to simultaneously keep these compounds from exhibiting hazardous sensitivity.

Physicochemical and Ion-Sensing Properties of Benzofurazan-Appended Calix[4]arene in Solution and on Gold Nanoparticles: Spectroscopy, Microscopy, and DFT Computations in Support of the Species of Recognition

A calix[4]arene conjugate (L) functionalized at the lower rim with a benzofurazan fluorophore (NBD) and at the upper rim with a thioether moiety has been synthesized and characterized by ¹H NMR, ¹³C NMR, and mass spectrometry techniques. Both the absorption and emission spectral data for L in different solvents exhibited progressive changes with an increase in polarity. Ion recognition studies were performed by absorption and fluorescence spectroscopy using 10 different metal ions. Among these, Hg²⁺ exhibited greater changes in these spectra, whereas Cu²⁺ showed only significant changes and all other ions showed no change in the spectral features. Although the Hg²⁺ has dominant influence on the spectral features and provides a detection limit of 56.0 ± 0.6 ppb, the selectivity was hampered because of the presence of the derivatizations present on both the rims of L for ion interaction in solution. Therefore, L was immobilized onto gold nanoparticles (AuNP_L's) so that the upper rim derivatizations anchor onto the gold surface through Au-S interactions, and this leaves out only the lower rim NBD derivatization for interaction with ions selectively. The AuNP_L's were characterized by transmission electron microscopy, scanning electron microscopy, energy-dispersive X-ray spectroscopy, and X-ray photoelectron spectroscopy (XPS) analyses. The surface characteristics were analyzed by contact angle measurements. The AuNP_L's exhibit greater selectivity and enhanced sensitivity for Hg²⁺ ions with a lowest detection limit of 48.0 ± 0.8 ppb. The immobilization of L onto AuNPs was reflected in the corresponding fluorescence lifetime values, and the addition of Hg²⁺ to either L or AuNP_L showed fluorescence quenching. The reversible recognition of Hg²⁺ by L was demonstrated by titrating L or AuNP_L with Hg²⁺ followed by tetra-butyl ammonium iodide for several cycles. The structural features of Hg²⁺-bound species were demonstrated by density functional theory computations and were supported by the XPS data. The Hg²⁺ induces aggregated fibrillar morphology into supramolecular L, as demonstrated by microscopy when Hg²⁺ was added either to L or to AuNP_L, supporting aggregation-caused quenching.

Design of Peptoid-peptide Macrocycles to Inhibit the β-catenin TCF Interaction in Prostate Cancer

New chemical inhibitors of protein-protein interactions are needed to propel advances in molecular pharmacology. Peptoids are peptidomimetic oligomers with the capability to inhibit protein-protein interactions by mimicking protein secondary structure motifs. Here we report the in silico design of a macrocycle primarily composed of peptoid subunits that targets the β-catenin:TCF interaction. The β-catenin:TCF interaction plays a critical role in the Wnt signaling pathway which is over-activated in multiple cancers, including prostate cancer. Using the Rosetta suite of protein design algorithms, we evaluate how different macrocycle structures can bind a pocket on β-catenin that associates with TCF. The in silico designed macrocycles are screened in vitro using luciferase reporters to identify promising compounds. The most active macrocycle inhibits both Wnt and AR-signaling in prostate cancer cell lines, and markedly diminishes their proliferation. In vivo potential is demonstrated through a zebrafish model, in which Wnt signaling is potently inhibited.

Design and Synthesis of Bioisosteres of Acylhydrazones as Stable Inhibitors of the Aspartic Protease Endothiapepsin

Acylhydrazone‐based dynamic combinatorial chemistry (DCC) is a powerful strategy for the rapid identification of novel hits. Even though acylhydrazones are important structural motifs in medicinal chemistry, their further progression in development may be hampered by major instability and potential toxicity under physiological conditions. It is therefore of paramount importance to identify stable replacements for acylhydrazone linkers. Herein, we present the first report on the design and synthesis of stable bioisosteres of acylhydrazone‐based inhibitors of the aspartic protease endothiapepsin as a follow‐up to a DCC study. The most successful bioisostere is equipotent, bears an amide linker, and we confirmed its binding mode by X‐ray crystallography. Having some validated bioisosteres of acylhydrazones readily available might accelerate hit‐to‐lead optimization in future acylhydrazone‐based DCC projects.

Inhibitors of protein-protein interactions (PPIs): an analysis of scaffold choices and buried surface area

Protein-protein interactions (PPI) were once considered 'undruggable', but clinical successes, driven by advanced methods in drug discovery, have challenged that notion. Here, we review the last three years of literature on PPI inhibitors to understand what is working and why. From the 66 recently reported PPI inhibitors, we found that the average molecular weight was significantly greater than 500Da, but that this trend was driven, in large part, by the contribution of peptide-based compounds. Despite differences in average molecular weight, we found that compounds based on small molecules or peptides were almost equally likely to be potent inhibitors (K_D<1μM). Finally, we found PPIs with buried surface area (BSA) less than 2000Ų were more likely to be inhibited by small molecules, while PPIs with larger BSA values were typically inhibited by peptides. PPIs with BSA values over 4000Ų seemed to create a particular challenge, especially for orthosteric small molecules. Thus, it seems important to choose the inhibitor scaffold based on the properties of the target interaction. Moreover, this survey suggests a (more nuanced) conclusion to the question of whether PPIs are good drug targets; namely, that some PPIs are readily 'druggable' given the right choice of scaffold, while others still seem to deserve the 'undruggable' moniker.

A Small Molecule Inhibitor of the β-Catenin-TCF4 Interaction Suppresses Colorectal Cancer Growth In Vitro and In Vivo

Colorectal cancer is associated with aberrant activation of the Wnt pathway. β-Catenin plays essential roles in the Wnt pathway by interacting with T-cell factor 4 (TCF4) to transcribe oncogenes. We synthesized a small molecule, referred to as HI-B1, and evaluated signaling changes and biological consequences induced by the compound. HI-B1 inhibited β-catenin/TCF4 luciferase activity and preferentially caused apoptosis of cancer cells in which the survival is dependent on β-catenin. The formation of the β-catenin/TCF4 complex was disrupted by HI-B1 due to the direct interaction of HI-B1 with β-catenin. Colon cancer patient-derived xenograft (PDX) studies showed that a tumor with higher levels of β-catenin expression was more sensitive to HI-B1 treatment, compared to a tumor with lower expression levels of β-catenin. The different sensitivities of PDX tumors to HI-B1 were dependent on the β-catenin expression level and potentially could be further exploited for biomarker development and therapeutic applications against colon cancer.

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HI-B1 is a synthesized compound identified as a β-catenin inhibitor suppressing the β-catenin-TCF4 protein interaction.

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HI-B1 preferentially causes apoptosis in β-catenin-dependent cancer cells.

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A colon cancer PDX mouse model with a high level of β-catenin is sensitive to HI-B1.

β-catenin is an important protein that facilitates colon cancer. Shin et al. synthesized and identified HI-B1 as a direct β-catenin inhibitor. HI-B1 disrupted formation of the β-catenin-TCF4 protein complex. HI-B1 preferentially caused apoptosis of cancer cells in which the survival is dependent on β-catenin. In a comparison of two colon cancer PDX models with different β-catenin levels, they showed that β-catenin-high PDX is more sensitive to HI-B1 treatment than β-catenin-low PDX. HI-B1 could thus be further developed as a colon cancer drug, and β-catenin expression levels might be a predictive biomarker for colon cancer therapy using β-catenin inhibitors.

The regulation of β-catenin activity and function in cancer: therapeutic opportunities

Wnt/β-catenin signaling is an evolutionarily conserved and versatile pathway that is known to be involved in embryonic development, tissue homeostasis and a wide variety of human diseases. Aberrant activation of this pathway gives rise to the accumulation of β-catenin in the nucleus and promotes the transcription of many oncogenes such as c-Myc and CyclinD-1. As a result, it contributes to carcinogenesis and tumor progression of several cancers, including colon cancer, hepatocellular carcinoma, pancreatic cancer, lung cancer and ovarian cancer. β-Catenin is a pivotal component of the Wnt signaling pathway and it is tightly regulated at three hierarchical levels: protein stability, subcellular localization and transcriptional activity. Uncovering the regulatory mechanisms of β-catenin will provide new insights into the pathogenesis of cancer and other diseases, as well as new therapeutic strategies against these diseases. In this review we dissect the concrete regulatory mechanisms of β-catenin from three aspects mentioned above. Then we focus on the role of β-catenin in cancer initiation, progression, dormancy, immunity and cancer stem cell maintenance. At last, we summarize the recent progress in the development of agents for the pharmacological modulation of β-catenin activity in cancer therapy.

Structure-Based Target-Specific Screening Leads to Small-Molecule CaMKII Inhibitors

Target-specific scoring methods are more commonly used to identify small-molecule inhibitors among compounds docked to a target of interest. Top candidates that emerge from these methods have rarely been tested for activity and specificity across a family of proteins. In this study we docked a chemical library into CaMKIIδ, a member of the Ca2+ /calmodulin (CaM)-dependent protein kinase (CaMK) family, and re-scored the resulting protein-compound structures using Support Vector Machine SPecific (SVMSP), a target-specific method that we developed previously. Among the 35 selected candidates, three hits were identified, such as quinazoline compound 1 (KIN-1; N4-[7-chloro-2-[(E)-styryl]quinazolin-4-yl]-N1,N1-diethylpentane-1,4-diamine), which was found to inhibit CaMKIIδ kinase activity at single-digit micromolar IC50 . Activity across the kinome was assessed by profiling analogues of 1, namely 6 (KIN-236; N4-[7-chloro-2-[(E)-2-(2-chloro-4,5-dimethoxyphenyl)vinyl]quinazolin-4-yl]-N1,N1-diethylpentane-1,4-diamine), and an analogue of hit compound 2 (KIN-15; 2-[4-[(E)-[(5-bromobenzofuran-2-carbonyl)hydrazono]methyl]-2-chloro-6-methoxyphenoxy]acetic acid), namely 14 (KIN-332; N-[(E)-[4-(2-anilino-2-oxoethoxy)-3-chlorophenyl]methyleneamino]benzofuran-2-carboxamide), against 337 kinases. Interestingly, for compound 6, CaMKIIδ and homologue CaMKIIγ were among the top ten targets. Among the top 25 targets of 6, IC50 values ranged from 5 to 22 μm. Compound 14 was found to be not specific toward CaMKII kinases, but it does inhibit two kinases with sub-micromolar IC50 values among the top 25. Derivatives of 1 were tested against several kinases including several members of the CaMK family. These data afforded a limited structure-activity relationship study. Molecular dynamics simulations with explicit solvent followed by end-point MM-GBSA free-energy calculations revealed strong engagement of specific residues within the ATP binding pocket, and also changes in the dynamics as a result of binding. This work suggests that target-specific scoring approaches such as SVMSP may hold promise for the identification of small-molecule kinase inhibitors that exhibit some level of specificity toward the target of interest across a large number of proteins.

Discovery of small molecule inhibitors of the Wnt/β-catenin signaling pathway by targeting β-catenin/Tcf4 interactions

The Wnt/β-catenin signaling pathway typically shows aberrant activation in various cancer cells, especially colorectal cancer cells. This signaling pathway regulates the expression of a variety of tumor-related proteins, including c-myc and cyclin D1, and plays essential roles in tumorigenesis and in the development of many cancers. Small molecules that block the interactions between β-catenin and Tcf4, a downstream stage of activation of the Wnt/β-catenin signaling pathway, could efficiently cut off this signal transduction and thereby act as a novel class of anticancer drugs. This paper reviews the currently reported inhibitors that target β-catenin/Tcf4 interactions, focusing on the discovery approaches taken in the design of these inhibitors and their bioactivities. A brief perspective is then shared on the future discovery and development of this class of inhibitors. Impact statement This mini-review summarized the current knowledge of inhibitors of interactions of beta-catenin/Tcf4 published to date according to their discovery approaches, and discussed their in vitro and in vivo activities, selectivities, and pharmacokinetic properties. Several reviews presently available now in this field describe modulators of the Wnt/beta-catenin pathway, but are generally focused on the bioactivities of these inhibitors. By contrast, this review focused on the drug discovery approaches taken in identifying these types of inhibitors and provided our perspective on further strategies for future drug discoveries. This review also integrated many recently published and important works on highly selective inhibitors as well as rational drug design. We believe that the findings and strategies summarized in this review have broad implications and will be of interest throughout the biochemical and pharmaceutical research community.

Continuous Flow α-Arylation of N,N-Dialkylhydrazones under Visible-Light Photoredox Catalysis

The first direct α-arylation of aldehyde-derived N,N-dialkylhydrazones with electron deficient aryl and heteroaryl cyanides under visible-light photoredox catalysis has been developed. Structurally complex α,α'-diaryl-N,N-cycloalkylhydrazones were obtained in moderate yields by repetition of the direct arylation protocol. A continuous-flow procedure for the preparation of α-aryl-N,N-dialkylhydrazones on a multigram scale has also been established.

A Versatile Method to Determine the Cellular Bioavailability of Small-Molecule Inhibitors

The determination of the cellular bioavailability of small-molecule inhibitors is a critical step for interpreting cell-based data and guiding inhibitor optimization. Herein, a HPLC-MS based protocol was developed to determine inhibitor cellular bioavailability. This generalizable protocol allows determination of the accurate intracellular concentrations and characterization of various properties of inhibitors including the extra- and intracellular stability, the dose- and time-dependence of the intracellular concentrations, the cell permeability, and the nonspecific binding with the cell culture plates, the extracellular matrices, and the cell membrane. The inhibitors of the protein-protein interactions, bromodomains, and the β-catenin/B-cell lymphoma 9 (BCL9) interaction were used to examine the protocol, and the cellular bioavailability of the inhibitors in cancer cells was determined. High nonspecific binding and low cellular uptake were observed for two bromodomain inhibitors. The two β-catenin/BCL9 inhibitors had low nonspecific binding but different cellular uptake. These inhibitors exhibited different stability kinetics in cells.

Developing drugs that target the Wnt pathway: recent approaches in cancer and neurodegenerative diseases

INTRODUCTION

Wnt/β-catenin signaling is an evolutionarily conserved pathway that has a crucial role in embryonic and adult life. Dysregulation of Wnt/β-catenin pathway has been associated with various diseases, including cancer and neurodegenerative disorders, including Parkinson's disease (PD). Several molecular components of the signaling have been proposed as innovative targets for cancer therapy, and very recently, some of them have been also evaluated as potential therapeutic targets for PD. Areas covered: This review focuses on the role of Wnt/β-catenin pathway in the pathogenensis of cancer and PD, examining some recent therapeutic approaches that are ongoing in preclinical and clinical studies. The possibilities that this signaling offers for diagnosis and prognosis of neoplastic diseases, and the concerns of targeting this pathway are also discussed. Expert opinion: Despite the stimulating results obtained in preclinical studies on cancer and other disease models, the clinical experience with Wnt modulators is still in its infancy, and is mainly restricted to anticancer therapy. Even with concerns of the safety of drugs targeting Wnt signaling, the attention of researchers worldwide is increasing to this issue in terms of their therapeutic potential for diseases such as PD, for which no cure exists.

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.

Rational design of selective small-molecule inhibitors for β-catenin/B-cell lymphoma 9 protein-protein interactions

Selective inhibition of α-helix-mediated protein-protein interactions (PPIs) with small organic molecules provides great potential for the discovery of chemical probes and therapeutic agents. Protein Data Bank data mining using the HippDB database indicated that (1) the side chains of hydrophobic projecting hot spots at positions i, i + 3, and i + 7 of an α-helix had few orientations when interacting with the second protein and (2) the hot spot pockets of PPI complexes had different sizes, shapes, and chemical groups when interacting with the same hydrophobic projecting hot spots of α-helix. On the basis of these observations, a small organic molecule, 4'-fluoro-N-phenyl-[1,1'-biphenyl]-3-carboxamide, was designed as a generic scaffold that itself directly mimics the binding mode of the side chains of hydrophobic projecting hot spots at positions i, i + 3, and i + 7 of an α-helix. Convenient decoration of this generic scaffold led to the selective disruption of α-helix-mediated PPIs. A series of small-molecule inhibitors selective for β-catenin/B-cell lymphoma 9 (BCL9) over β-catenin/cadherin PPIs was designed and synthesized. The binding mode of new inhibitors was characterized by site-directed mutagenesis and structure-activity relationship studies. This new class of inhibitors can selectively disrupt β-catenin/BCL9 over β-catenin/cadherin PPIs, suppress the transactivation of canonical Wnt signaling, downregulate the expression of Wnt target genes, and inhibit the growth of Wnt/β-catenin-dependent cancer cells.

Fluorescence anisotropy (polarization): from drug screening to precision medicine

INTRODUCTION

Fluorescence anisotropy (FA) is one of the major established methods accepted by industry and regulatory agencies for understanding the mechanisms of drug action and selecting drug candidates utilizing a high-throughput format.

AREAS COVERED

This review covers the basics of FA and complementary methods, such as fluorescence lifetime anisotropy and their roles in the drug discovery process. The authors highlight the factors affecting FA readouts, fluorophore selection and instrumentation. Furthermore, the authors describe the recent development of a successful, commercially valuable FA assay for long QT syndrome drug toxicity to illustrate the role that FA can play in the early stages of drug discovery.

EXPERT OPINION

Despite the success in drug discovery, the FA-based technique experiences competitive pressure from other homogeneous assays. That being said, FA is an established yet rapidly developing technique, recognized by academic institutions, the pharmaceutical industry and regulatory agencies across the globe. The technical problems encountered in working with small molecules in homogeneous assays are largely solved, and new challenges come from more complex biological molecules and nanoparticles. With that, FA will remain one of the major work-horse techniques leading to precision (personalized) medicine.