Hh signaling inhibitors from Vitex negundo; naturally occurring inhibitors of the GLI1-DNA complex

Beyond cyclopamine: Targeting Hedgehog signaling for cancer intervention

Hedgehog (Hh) signaling plays a significant role in embryogenesis and several physiological processes, such as wound healing and organ homeostasis. In a pathological setting, it is associated with oncogenesis and is responsible for disease progression and poor clinical outcomes. Hedgehog signaling mediates downstream actions via Glioma Associated Oncogene Homolog (GLI) transcription factors. Inhibiting Hh signaling is an important oncological strategy in which inhibitors of the ligands SMO or GLI have been looked at. This review briefly narrates the Hh ligands, signal transduction, the target genes involved and comprehensively describes the numerous inhibitors that have been evaluated for use in various neoplastic settings.

Evaluation of the toxicity of Caralluma europaea (C.E) extracts and their effects on apoptosis and chemoresistance in pancreatic cancer cells

Pancreatic adenocarcinoma is a disease with no effective treatment. Chemo-resistance contributes to the dismal prognosis for patients diagnosed with the disease. This study aims to evaluate the toxicity and the effect of Caralluma europaea (C.E) extracts on cancer cell survival, apoptosis, chemo-resistance, and pro-cancer pathways, in pancreatic cancer. The acute and subacute toxicities of C.E extracts were evaluated. The cytotoxic effect on pancreatic cancer cell survival and apoptosis was determined by MTT assay and DNA fragmentation. The expression of cancer stemness markers was measured using Western blot. A molecular docking was used to test the possible effects of C.E compounds in inhibiting the Hedgehog and activating caspase-3. The hydroethanolic extract's DL50 was over 5000 mg/kg. During the subacute toxicity, only saponins extract showed some hepatic toxicity signs. Cells treated with C.E extracts combined with gemcitabine revealed an additive anti-survival activity. C.E extracts sensitized resistant MIA-PaCa-2 to gemcitabine treatment. Most of the C.E extracts downregulated the expression of cancer stemness-associated genes. Luteolin-7-O-glucoside presented the highest docking Gscore on human Smoothened. Isorhamnetin-3-O-rutinoside induced apoptosis via activation of caspase-3. C.E extracts can be considered safe in inhibiting pancreatic cancer cell survival, inducing apoptosis, and sensitizing cells to chemotherapy via Hedgehog inhibition and caspase-3 activation.Communicated by Ramaswamy H. Sarma.

Traditional uses, phytochemistry, and pharmacology of genus Vitex (Lamiaceae)

Vitex, the genus of the family Lamiaceae, comprises of about 230 species mostly distributed in the warm regions of Europe and temperate regions of Asia. Several Vitex species have been used as folk medicine in different countries for the treatment of various kinds of diseases and ailments. The main aim of this review is to collect and analyze the scientific information available about the Vitex species regarding their chemical constituents and pharmacological activities. The phytochemical investigation of various Vitex species has resulted in the isolation of about 556 chemical constituents belong to various chemical category viz. iridoids, diterpenoids, triterpenoids, flavonoids, lignans, sesquiterpenoids, monoterpenoids, ecdysteroids, and others. The crude extracts of different Vitex species as well as pure phytochemicals exhibited a wide spectrum of in-vitro and in-vivo pharmacological activities. In the present review, the scientific literature data on the ethnopharmacological, phytochemical, and pharmacological investigations on the genus Vitex are summarized. More attention should be given in future research to evaluate the pharmacological potential with detailed mechanism of actions for the pure compounds, extracts of plants from this genus. Moreover, their clinical study is needed to justify their use in modern medicine and to further exploring this genus for new drug discovery.

Targeting the GLI family of transcription factors for the development of anti-cancer drugs

INTRODUCTION

GLI1 is a transcription factor that has been identified as a downstream effector for multiple tumorigenic signaling pathways. These include the Hedgehog, RAS-RAF-MEK-ERK, and PI3K-AKT-mTOR pathways, which have all been separately validated as individual anti-cancer drug targets. The identification of GLI1 as a key transcriptional regulator for each of these pathways highlights its promise as a therapeutic target. Small molecule GLI1 inhibitors are potentially efficacious against human malignancies arising from multiple oncogenic mechanisms.

AREAS COVERED

This review provides an overview of the key oncogenic cellular pathways that regulate GLI1 transcriptional activity. It also provides a detailed account of small molecule GLI1 inhibitors that are currently under development as potential anti-cancer chemotherapeutics.

EXPERT OPINION

Interest in developing inhibitors of GLI1-mediated transcription has significantly increased as its role in multiple oncogenic signaling pathways has been elucidated. To date, it has proven difficult to directly target GLI1 with small molecules, and the majority of compounds that inhibit GLI1 activity function through indirect mechanisms. To date, no direct-acting GLI1 inhibitor has entered clinical trials. The identification and development of new scaffolds that can bind and directly inhibit GLI1 are essential to further advance this class of chemotherapeutics.

Design of Hedgehog pathway inhibitors for cancer treatment

Hedgehog (Hh) signaling is involved in the initiation and progression of various cancers and is essential for embryonic and postnatal development. This pathway remains in the quiescent state in adult tissues but gets activated upon inflammation and injuries. Inhibition of Hh signaling pathway using natural and synthetic compounds has provided an attractive approach for treating cancer and inflammatory diseases. While the majority of Hh pathway inhibitors target the transmembrane protein Smoothened (SMO), some small molecules that target the signaling cascade downstream of SMO are of particular interest. Substantial efforts are being made to develop new molecules targeting various components of the Hh signaling pathway. Here, we have discussed the discovery of small molecules as Hh inhibitors from the diverse chemical background. Also, some of the recently identified natural products have been included as a separate section. Extensive structure-activity relationship (SAR) of each chemical class is the focus of this review. Also, clinically advanced molecules are discussed from the last 5 to 7 years. Nanomedicine-based delivery approaches for Hh pathway inhibitors are also discussed concisely.

Vitex negundo and its medicinal value

Natural products are rich in several potent bioactive compounds, targeting complex network of proteins involved in various diseases. Vitex negundo (VN), commonly known as "chaste tree", is an ethnobotanically important plant with enormous medicinal properties. Different species of Vitex vary in chemical composition, thus producing different phytochemicals. Several bioactive compounds have been extracted from leaves, seeds, roots in form of volatile oils, flavonoids, lignans, iridoids, terpenes, and steroids. These bioactive compounds exhibit anti-inflammatory, antioxidant, antidiabetic, anticancer, antimicrobial. VN is typically known for its role in the modulation of cellular events like apoptosis, cell cycle, motility of sperms, polycystic ovary disease, and menstrual cycle. VN, reportedly, perturbs many cancer-signaling pathways involving p-p38, p-ERK1/2, and p-JNK in LPS-elicited cells, N-terminal kinase (JNK), COX-1 pathways, MAPK, NF-κB, tumor necrosis factor α (TNF-α), Akt, mTOR, vascular endothelial growth factor, hypoxia-inducible factor (HIF-1α). Several bioactive compounds obtained from VN have been commercialized and others are under investigation. This is the first review presenting up-to-date information about the VN, its bioactive constituents and their mode of action.

GLI1 Inhibitors Identified by Target Protein Oriented Natural Products Isolation (TPO-NAPI) with Hedgehog Inhibition

This report describes the development of a target-protein-oriented natural-products-isolation (TPO-NAPI) method for Hedgehog inhibitors and the direct GLI1 inhibitor, 5'- O-methyl-3-hydroxyflemingin A (3), which inhibited hedgehog (Hh) signal transduction and diminished characteristics of cancer stem cells. Eight natural products (including three newly described products) that directly bind to GLI1 were rapidly obtained via the TPO-NAPI method developed using GLI1 protein-immobilized beads. 5'- O-Methyl-3-hydroxyflemingin A (3) inhibited Hh signaling (IC₅₀ 7.3 μM), leading to decreasing production of the Hh target proteins BCL2, PTCH1, and BMI1. 5'- O-Methyl-3-hydroxyflemingin A (3) was cytotoxic to Hh-related cancer cells. CD experiments revealed that 5'- O-methyl-3-hydroxyflemingin A (3) directly bound GLI1 ( K_d = 7.7 μM). Moreover, 5'- O-methyl-3-hydroxyflemingin A (3) diminished cancer stem cell characters of Huh7 such as sphere formation and production of the cancer stem cell marker EpCAM. These results suggest that Hh inhibitors can efficiently suppress the activity of cancer stem cells.

Role of GLI Transcription Factors in Pathogenesis and Their Potential as New Therapeutic Targets

GLI transcription factors have important roles in intracellular signaling cascade, acting as the main mediators of the HH-GLI signaling pathway. This is one of the major developmental pathways, regulated both canonically and non-canonically. Deregulation of the pathway during development leads to a number of developmental malformations, depending on the deregulated pathway component. The HH-GLI pathway is mostly inactive in the adult organism but retains its function in stem cells. Aberrant activation in adult cells leads to carcinogenesis through overactivation of several tightly regulated cellular processes such as proliferation, angiogenesis, EMT. Targeting GLI transcription factors has recently become a major focus of potential therapeutic protocols.

Strategies to target the Hedgehog signaling pathway for cancer therapy

Hedgehog (Hh) signaling is an essential pathway in the human body, and plays a major role in embryo development and tissue patterning. Constitutive activation of the Hh signaling pathway through sporadic mutations or other mechanisms is explicitly associated with cancer development and progression in various solid malignancies. Therefore, targeted inhibition of the Hh signaling pathway has emerged as an attractive and validated therapeutic strategy for the treatment of a wide range of cancers. Vismodegib, a first-in-class Hh signaling pathway inhibitor was approved by the US Food and Drug Administration in 2012, and sonidegib, another potent Hh pathway inhibitor, received FDA's approval in 2015 as a new treatment of locally advanced or metastatic basal cell carcinoma. The clinical success of vismodegib and sonidegib provided strong support for the development of Hh signaling pathway inhibitors via targeting the smoothened (Smo) receptor. Moreover, Hh signaling pathway inhibitors aimed to target proteins, which are downstream or upstream of Smo, have also been pursued based on the identification of additional therapeutic benefits. Recently, much progress has been made in Hh singling and inhibitors of this pathway. Herein, medicinal chemistry strategies, especially the structural optimization process of different classes of Hh inhibitors, are comprehensively summarized. Further therapeutic potentials and challenges are also discussed.

Regulation of Hedgehog Signaling in Cancer by Natural and Dietary Compounds

The aberrant Hedgehog (Hh) signaling induced by mutations or overexpression of the signaling mediators has been implicated in cancer, associated with processes including inflammation, tumor cell growth, invasion, and metastasis, as well as cancer stemness. Small molecules targeting the regulatory components of the Hh signaling pathway, especially Smoothened (Smo), have been developed for the treatment of cancer. However, acquired resistance to a Smo inhibitor vismodegib observed in clinical trials suggests that other Hh signaling components need to be explored as potential anticancer targets. Natural and dietary compounds provide a resource for the development of potent agents affecting intracellular signaling cascades, and numerous studies have been conducted to evaluate the efficacy of natural products in targeting the Hh signaling pathway. In this review, we summarize the role of Hh signaling in tumorigenesis, discuss results from recent studies investigating the effect of natural products and dietary components on Hh signaling in cancer, and provide insight on novel small molecules as potential Hh signaling inhibitors.

A Review on the Terpenes from Genus Vitex

The genus Vitex, which belongs to the Verbenaceae family, includes approximately 250 species. Some species of the genus Vitex have traditionally been used for the treatment of headaches, ophthalmodynia, coughs, asthma, premenopausal syndrome, etc. Chemical investigations indicate that the characteristic constituents of the genus Vitex are terpenes, and 210 of these compounds, including monoterpenoids, sesquiterpenoids, diterpenoids and triterpenoids, have been obtained from 12 species. Pharmacological studies had shown that these terpenes possess anti-inflammatory, antitumor, antibacterial, antioxidant activities, and so on. In this paper, the identity of these terpenes and their pharmacological effects are reviewed, which can provide references for further research regarding the chemistry and utilization of the Vitex species.

Evaluation of WO2014207069 A1: Multitarget Hedgehog pathway inhibitors and uses thereof

In recent years, the involvement of the Hedgehog (Hh) signaling pathway in various human diseases and dysfunctions has been clearly demonstrated. Smoothened (Smo), one of the upstream signal transducers, has been the most druggable target of the Hh pathway. However, the emergence of resistance to Smo inhibitors and the identification of Smo-independent activation of the Hh pathway led to the need to find new chemical entities able to interfere with downstream components, such as Gli. For this purpose, two different computational approaches have been applied to a small-sized library of natural compounds. As a result, an isoflavone derivative that showed ability to inhibit both Smo and Gli1 has been identified; namely, Glabrescione B. A new synthetic approach has been planned for this compound and its derivatives. Biological evaluation demonstrated the mechanism of action and showed a promising preclinical profile.

Hedgehog inhibitors from Withania somnifera

The hedgehog (Hh) signaling pathway performs an important role in embryonic development and in cellular proliferation and differentiation. However, aberrant activation of the Hh signaling pathway is associated with tumorigenesis. Hh signal inhibition was evaluated using a cell-based assay system that targets GLI1-mediated transcription. Activity-guided isolation of the Withania somnifera MeOH extract led to the isolation of six compounds: withaferin A (1) and its derivatives (2-6). Compounds 1 and 2 showed strong inhibition of Hh/GLI1-mediated transcriptional activity with IC50 values of 0.5 and 0.6 μM, respectively. Compounds 1, 2, 3, and 6 were cytotoxic toward human pancreatic (PANC-1), prostate (DU145) and breast (MCF7) cancer cells. Furthermore, 1 also inhibited GLI1-DNA complex formation in EMSA.

Hedgehog/GLI-mediated transcriptional activity inhibitors from Crinum asiaticum

The inhibition of the hedgehog (Hh) signaling pathway has emerged as an attractive anti-cancer strategy. As part of our continuing search for natural inhibitors of the Hh/GLI1 signaling pathway, we isolated three alkaloids (1-3) from Crinum asiaticum. Compounds 1 and 3 showed potent Hh/GLI1-mediated transcriptional inhibitory activity and exhibited cytotoxicity against human pancreatic (PANC1) and prostate (DU145) cancer cells. Our data revealed that compounds 1 and 3 clearly inhibited the Hh signaling pathway by down-regulating the expression of GLI-related proteins (PTCH and BCL2) in DU145 cells.

Targeting GLI proteins in human cancer by small molecules (WO2014116651 A1): a patent evaluation

The invention reviewed in this patent evaluation is the synthesis and application of small molecule inhibitors of Gli transcriptional activity as potential anticancer agents. The oncogenic nature of Gli proteins has been traditionally associated with the hedgehog (Hh) signaling pathway; however, the recent identification of aberrant Gli activation unrelated to Hh signaling has prompted drug discovery efforts directly targeting Gli proteins. The central core of the compounds described in this patent (WO2014116651 A1) is structurally analogous to the pyrazoline scaffold previously disclosed by these inventors. Data describing the inhibitory activity of these compounds against the Hh pathway in vitro and in Hh-dependent in vivo models of human cancer are not provided. For this patent disclosure, the inventors primarily focus on the anticancer properties of their compounds in lung and lung-related malignancies. The compounds are moderately active in these models, but they do not exhibit the overall preclinical profile generally required for advancement into clinical trials.

Physalin H from Solanum nigrum as an Hh signaling inhibitor blocks GLI1-DNA-complex formation

Hedgehog (Hh) signaling plays an important role in embryonic development, cell maintenance and cell proliferation. Moreover, Hh signaling contributes to the growth of cancer cells. Physalins are highly oxidized natural products with a complex structure. Physalins (1–7) were isolated from Solanum nigrum (Solanaceae) collected in Bangladesh by using our cell-based assay. The isolated physalins included the previously reported Hh inhibitors 5 and 6. Compounds 1 and 4 showed strong inhibition of GLI1 transcriptional activity, and exhibited cytotoxicity against cancer cell lines with an aberrant activation of Hh signaling. Compound 1 inhibited the production of the Hh-related proteins patched (PTCH) and BCL2. Analysis of the structures of different physalins showed that the left part of the physalins was important for Hh inhibitory activity. Interestingly, physalin H (1) disrupted GLI1 binding to its DNA binding domain, while the weak inhibitor physalin G (2) did not show inhibition of GLI1-DNA complex formation.