Identification of a novel Smoothened antagonist that potently suppresses Hedgehog signaling

Expression Pattern of Sonic Hedgehog, Patched and Smoothened in Clear Cell Renal Carcinoma

Clear cell renal cell carcinoma (ccRCC) is the deadliest neoplasm of the urinary tract, and we are still far from completely understanding ccRCC development and treatment. The renal tissue paraffin blocks (20) of patients with ccRCC were collected at the University Hospital in Split from 2019 to 2020, and tissue sections were stained with patched (PTCH), anti-smoothened (SMO) and anti-Sonic Hedgehog (SHH) antibodies. SHH was highly expressed (31.9%) in grade 1 tumour, it being higher than all other grades and the control (p < 0.001-p < 0.0001). The trend of a linear decrease in the expression of SHH was observed with the progression of the tumour grade (p < 0.0001). PTCH expression was significantly lower in grades 1 and 2 in comparison to the control (p < 0.01) and grade 4 (p < 0.0001). A significant increase in the expression of SMO was found in grade 4 compared to all other grades (p < 0.0001) and the control (p < 0.001). The strong expression of SHH was observed in carcinoma cells of the G1 stage with a diffuse staining pattern (>50% of neoplastic cells). Stroma and/or inflammatory infiltrate display no staining and no expression of SHH in G1 and G2, while mild focal staining (10-50% of neoplastic cells) was observed in G3 and G4. Patients with high PTCH and low SMO expression had significant time survival differences (p = 0.0005 and p = 0.029, respectively). Therefore, high levels of PTCH and low levels of SMO expression are important markers of better survival rates in ccRCC patients.

A Potent Antagonist of Smoothened in Hedgehog Signaling for Epilepsy

Epilepsy is one of the common encephalopathies caused by sudden abnormal discharges of neurons in the brain. About 30% of patients with epilepsy are insensitive and refractory to existing antiseizure medications. The sonic hedgehog signaling pathway is essential to the development and homeostasis of brain. Aberrant sonic hedgehog signaling is increased in refractory epileptic lesions and may involve the etiology of epilepsy. Thus, new inhibitors of Smoothened, a key signal transducer of this signaling pathway are urgently need for refractory epilepsy. We have established a high-throughput screening platform and discovered several active small molecules targeting Smoothened including TT22. Here we show that the novel Smoothened inhibitor TT22 could block the translocation of βarrestin2-GFP to Smoothened, reduce the accumulation of Smoothened on primary cilia, displace Bodipy-cyclopamine binding to Smoothened, and inhibit the expression of downstream Gli transcription factor. Moreover, TT22 inhibits the abnormal seizure-like activity in neurons. Furthermore, we demonstrated that FDA-approved Smoothened inhibitor GDC-0449 and LDE-225 are able to inhibit abnormal seizure-like activity in neurons. Thus, our study suggests that targeting the sonic hedgehog signaling with new small-molecule Smoothened inhibitors might provide a potential new therapeutic avenue for refractory epilepsy.

The Role of the Hedgehog Pathway in Cholangiocarcinoma

Simple Summary

Cholangiocarcinoma (CCA) is one of the most refractory malignancies with a high mortality rate. Among all the pathways involved in CCA development, emerging evidence highlights Hedgehog (HH) signaling as a substantial player in CCA-genesis and development. The pro-tumoral function of HH provides potential therapeutic implications, and recently the use of HH inhibitors has paved the way for clinical application in various solid tumors. Targeting HH members, namely Hedgehog ligands, SMO transmembrane protein and GLI transcription factors may thus confer therapeutic options for the improvement of CCA treatment outcome.

Abstract

Cholangiocarcinoma (CCA) is a poorly treatable type of cancer and, along with hepatocellular carcinoma (HCC), is the predominant type of primitive liver cancer in adults. The lack of understanding of CCA biology has slowed down the identification of novel targets and the development of effective treatments. While tumors share some general characteristics, detailed knowledge of specific features is essential for the development of effectively tailored therapeutic approaches. The Hedgehog (HH) signaling cascade regulates stemness biology, embryonal development, tissue homeostasis, and cell proliferation and differentiation. Its aberrant activation has been associated with a variety of solid and hematological human malignancies. Several HH-inhibiting compounds have been indeed developed as potential anticancer agents in different types of tumors, with Smoothened and GLI inhibitors showing the most promising results. Beside its well-established function in other tumors, findings regarding the HH signaling in CCA are still controversial. Here we will give an overview of the most important clinical and molecular features of cholangiocarcinoma, and we will discuss the available evidence of the crosstalk between the HH signaling pathway and the cholangiocarcinoma cell biology.

The oxysterome and its receptors as pharmacological targets in inflammatory diseases

Oxysterols have gained attention over the last decades and are now considered as fully fledged bioactive lipids. The study of their levels in several conditions, including atherosclerosis, obesity and neurodegenerative diseases, led to a better understanding of their involvement in (patho)physiological processes such as inflammation and immunity. For instance, the characterization of the cholesterol-7α,25-dihydroxycholesterol/GPR183 axis and its implication in immunity represents an important step in the oxysterome study. Besides this axis, others were identified as important in several inflammatory pathologies (such as colitis, lung inflammation and atherosclerosis). However, the oxysterome is a complex system notably due to a redundancy of metabolic enzymes and a wide range of receptors. Indeed, deciphering oxysterol roles and identifying the potential receptor(s) involved in a given pathology remain challenging. Oxysterol properties are very diverse, but most of them could be connected by a common component: inflammation. Here, we review the implication of oxysterol receptors in inflammatory diseases.

Identification of a potent antagonist of smoothened in hedgehog signaling

Background

Hedgehog signaling is essential to the regulation of embryonic development, tissue homeostasis, and stem cell self-renewal, making it a prime target for developing cancer therapeutics. Given the close link between aberrant Hedgehog signaling and cancers, many small molecular compounds have been developed to inhibit Smoothened, a key signal transducer of this pathway, for treating cancer and several such compounds have been approved by the United States Food and Drug Administration (GDC-0449 and LDE-225). However, acquired drug resistance has emerged as an important obstacle to the effective use of these first generation Hedgehog pathway blockers. Thus, new Smoothened inhibitors that can overcome such resistance is an urgent need going forward.

Results

We established the Smoothened/βarrestin2-GFP high-throughput screening platform based on the mechanistic discovery of Hedgehog signaling pathway, and discovered several active small molecules targeting Smoothened including 0025A. Here we show that 0025A can block the translocation of βarrestin2-GFP to Smoothened, displace Bodipy-cyclopamine binding to wild-type Smoothened or mutant Smoothened-D473H, reduce the accumulation of Smo on primary cilia and the expression of Gli upon Hedgehog stimulation. In addition, we show that 0025A can effectively suppress hair follicle morphogenesis and hair growth in mice.

Conclusions

Our results demonstrate that 0025A is a potent antagonist targeting Smoothened wild-type and mutant receptors in the Hedgehog signaling pathway and may provide a new therapy for refractory cancers.

Nilotinib, an approved leukemia drug, inhibits smoothened signaling in Hedgehog-dependent medulloblastoma

Dysregulation of the seven-transmembrane (7TM) receptor Smoothened (SMO) and other components of the Hedgehog (Hh) signaling pathway contributes to the development of cancers including basal cell carcinoma (BCC) and medulloblastoma (MB). However, SMO-specific antagonists produced mixed results in clinical trials, marked by limited efficacy and high rate of acquired resistance in tumors. Here we discovered that Nilotinib, an approved inhibitor of several kinases, possesses an anti-Hh activity, at clinically achievable concentrations, due to direct binding to SMO and inhibition of SMO signaling. Nilotinib was more efficacious than the SMO-specific antagonist Vismodegib in inhibiting growth of two Hh-dependent MB cell lines. It also reduced tumor growth in subcutaneous MB mouse xenograft model. These results indicate that in addition to its known activity against several tyrosine-kinase-mediated proliferative pathways, Nilotinib is a direct inhibitor of the Hh pathway. The newly discovered extension of Nilotinib's target profile holds promise for the treatment of Hh-dependent cancers.

Targeting the Oncoprotein Smoothened by Small Molecules: Focus on Novel Acylguanidine Derivatives as Potent Smoothened Inhibitors

Hedgehog-GLI (HH) signaling was originally identified as a critical morphogenetic pathway in embryonic development. Since its discovery, a multitude of studies have reported that HH signaling also plays key roles in a variety of cancer types and in maintaining tumor-initiating cells. Smoothened (SMO) is the main transducer of HH signaling, and in the last few years, it has emerged as a promising therapeutic target for anticancer therapy. Although vismodegib and sonidegib have demonstrated effectiveness for the treatment of basal cell carcinoma (BCC), their clinical use has been hampered by severe side effects, low selectivity against cancer stem cells, and the onset of mutation-driven drug resistance. Moreover, SMO antagonists are not effective in cancers where HH activation is due to mutations of pathway components downstream of SMO, or in the case of noncanonical, SMO-independent activation of the GLI transcription factors, the final mediators of HH signaling. Here, we review the current and rapidly expanding field of SMO small-molecule inhibitors in experimental and clinical settings, focusing on a class of acylguanidine derivatives. We also discuss various aspects of SMO, including mechanisms of resistance to SMO antagonists.

Overcoming the emerging drug resistance of smoothened: an overview of small-molecule SMO antagonists with antiresistance activity

Hedgehog (HH) signaling pathway plays vital roles in controlling embryonic cell fate and homeostatic, and becomes dormant in mature individuals, aberrant activation of HH signaling pathway is involved in a number of human cancers. Smoothened (SMO), a vital transducer of HH signaling pathway, attracts significant attentions in HH signaling pathway-related cancer therapy. The approval of SMO antagonists vismodegib proves that SMO is a promising therapeutic target, and a number of SMO antagonists are reported since then. However, high incidence of tumor recurrence with the clinical application of vismodegib urges exploring of novel drugs with antiresistance profiles. This review provides an overview of SMO mutations reported in the literature, crystal structures of SMO, as well as reported antagonists with antiresistance profiles.

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.

Design, Synthesis, and Structure-Activity Relationship of Tetrahydropyrido[4,3-d]pyrimidine Derivatives as Potent Smoothened Antagonists with in Vivo Activity

Medulloblastoma is one of the most prevalent brain tumors in children. Aberrant hedgehog (Hh) pathway signaling is thought to be involved in the initiation and development of medulloblastoma. Vismodegib, the first FDA-approved cancer therapy based on inhibition of aberrant hedgehog signaling, targets smoothened (Smo), a G-protein coupled receptor (GPCR) central to the Hh pathway. Although vismodegib exhibits promising therapeutic efficacy in tumor treatment, concerns have been raised from its nonlinear pharmacokinetic (PK) profiles at high doses partly due to low aqueous solubility. Many patients experience adverse events such as muscle spasms and weight loss. In addition, drug resistance often arises among tumor cells during treatment with vismodegib. There is clearly an urgent need to explore novel Smo antagonists with improved potency and efficacy. Through a scaffold hopping strategy, we have identified a series of novel tetrahydropyrido[4,3-d]pyrimidine derivatives, which exhibited effective inhibition of Hh signaling. Among them, compound 24 is three times more potent than vismodegib in the NIH3T3-GRE-Luc reporter gene assay. Compound 24 has a lower melting point and much greater solubility compared with vismodegib, resulting in linear PK profiles when dosed orally at 10, 30, and 100 mg/kg in rats. Furthermore, compound 24 showed excellent PK profiles with a 72% oral bioavailability in beagle dogs. Compound 24 demonstrated overall favorable in vitro safety profiles with respect to CYP isoform and hERG inhibition. Finally, compound 24 led to significant regression of subcutaneous tumor generated by primary Ptch1-deficient medulloblastoma cells in SCID mouse. In conclusion, tetrahydropyrido[4,3-d]pyrimidine derivatives represent a novel set of Smo inhibitors that could potentially be utilized to treat medulloblastoma and other Hh pathway related malignancies.

Dual MET and SMO Negative Modulators Overcome Resistance to EGFR Inhibitors in Human Nonsmall Cell Lung Cancer

Tyrosine kinase inhibitors (TKIs) of the EGF receptor (EGFR) have provided a significant improvement in the disease outcome of nonsmall cell lung cancer (NSCLC). Unfortunately, resistance to these agents frequently occurs, and it is often related to the activation of the Hedgehog (Hh) and MET signaling cascades driving the epithelial-to-mesenchymal transition (EMT). Because the concomitant inhibition of both Hh and MET pathways restores the sensitivity to anti-EGFR drugs, here we aimed at discovering the first compounds that block simultaneously MET and SMO. By using an "in silico drug repurposing" approach and by validating our predictions both in vitro and in vivo, we identified a set of compounds with the desired dual inhibitory activity and enhanced antiproliferative activity on EGFR TKI-resistant NSCLC. The identification of the known MET TKIs, glesatinib and foretinib, as negative modulators of the Hh pathway, widens their application in the context of NSCLC.

Treatment response in the PIVENS trial is associated with decreased Hedgehog pathway activity

Hedgehog (Hh) ligand production by ballooned hepatocytes drives nonalcoholic steatohepatitis (NASH) progression in mice. The NIDDK-sponsored PIVENS trial (NCT00063622) showed that vitamin E (VitE) improved NASH. We investigated whether VitE treatment and improvement in NASH were associated with changes in Hh pathway activity. Immunohistochemistry (IHC) was performed on both pre- and posttreatment liver biopsies of 59 PIVENS patients randomized to VitE (n = 30) or placebo (n = 29). Sonic Hh (Shh) ligand-producing cells and Shh-responsive cells were quantified. The latter was accomplished by triple IHC for gli2+ (marker of Hh signaling), sox-9 (progenitor marker), and α-smooth muscle actin (α-SMA; myofibroblast marker). Ballooned hepatocytes were quantified by keratin 8/18 and ubiquitin (K8/18/Ub) staining. IHC results were correlated with primary clinical and histologic PIVENS data. Pretreatment clinical, histologic, and IHC parameters did not differ significantly in the two treatment groups. Regardless of treatment arm, the number of Shh+ hepatocytes correlated with K8/18/Ub foci (r(2) = 0.47, P < 0.001) and aspartate aminotransferase (AST) (r(2) = 0.15, P = 0.002). Treatment-related changes in the numbers of Shh+ hepatocytes correlated with changes in serum AST (partial r(2) = 0.75, P < 0.0001), hepatocyte ballooning (P = 0.004), the ductular reaction (i.e., numbers of gli2+/sox9+ cells; P = 0.03 and α-SMA+ cells; P = 0.10), and fibrosis stage (P = 0.02). Treatment response was associated with a greater decrease in Shh+ hepatocytes than nonresponse (P = 0.007). The VitE group demonstrated a greater reduction in K8/18/Ub+ foci (P < 0.08) and Shh+ hepatocytes (P < 0.05) than the placebo group, effects that became more significant after correction for baseline differences and multiple linear regression analysis.

CONCLUSION

During PIVENS, treatment response correlated with loss of Shh+ hepatocytes and improvement in Hh-regulated processes that promote NASH progression.