The hedgehog processing pathway is required for NSCLC growth and survival

Targeting the Hedgehog pathway with novel Gli1 hydrophobic tagging degraders

The Hedgehog/Glioma-associated oncogene (Hh/Gli) signaling pathway plays an essential role in embryonic development and tissue homeostasis. Aberrant regulation of this pathway has been linked to various human malignancies. Gli1, the downstream transcription factor of the Hh pathway, is the ultimate effector of the canonical Hh pathway and has been identified as a common regulator of several tumorigenic pathways prevalent in Hh-independent cancers. Thus Gli1 represents a unique and promising drug target for a wide range of cancers. However, the identification and development of small molecules that directly target Gli1 protein have progressed slowly, due to an insufficient efficacy and selectivity. Herein, we developed novel small-molecule Gli1 degraders based on the hydrophobic tagging (HyT) strategy. The Gli1 HyT degrader 8e potently inhibited the proliferation of Gli1-overexpressed HT29 colorectal cancer cells, induced Gli1 degradation with a DC50 value of 5.4 μM in HT29 and achieved 70% degradation at 7.5 μM in MEFPTCH1-/- and MEFSUFU-/-cell lines, via proteasome pathway. Compared to the canonical Hh antagonist Vismodegib, 8e exhibited much stronger potency in suppressing the mRNA expression of Hh target genes in Hh-overactivated MEFPTCH1-/- and Vismodegib resistant MEFSUFU-/- cells. Our study provides small molecule Gli1 degraders effectively interfering with both canonical and noncanonical Hh signaling and overcoming current Smoothened (SMO) antagonists resistance, which might pave a new avenue for developing therapeutic modalities targeting Hh/Gli1 signaling pathway.

Hedgehog pathway and its inhibitors in chronic obstructive pulmonary disease (COPD)

COPD affects millions of people and is now ranked as the third leading cause of death worldwide. This largely untreatable chronic airway disease results in irreversible destruction of lung architecture. The small lung hypothesis is now supported by epidemiological, physiological and clinical studies. Accordingly, the early and severe COPD phenotype carries the most dreadful prognosis and finds its roots during lung growth. Pathophysiological mechanisms remain poorly understood and implicate individual susceptibility (genetics), a large part of environmental factors (viral infections, tobacco consumption, air pollution) and the combined effects of those triggers on gene expression. Genetic susceptibility is most likely involved as the disease is severe and starts early in life. The latter observation led to the identification of Mendelian inheritance via disease-causing variants of SERPINA1 - known as the basis for alpha-1 anti-trypsin deficiency, and TERT. In the last two decades multiple genome wide association studies (GWAS) identified many single nucleotide polymorphisms (SNPs) associated with COPD. High significance SNPs are located in 4q31 near HHIP which encodes an evolutionarily highly conserved physiological inhibitor of the Hedgehog signaling pathway (HH). HHIP is critical to several in utero developmental lung processes. It is also implicated in homeostasis, injury response, epithelial-mesenchymal transition and tumor resistance to apoptosis. A few studies have reported decreased HHIP RNA and protein levels in human adult COPD lungs. HHIP^+/- murine models led to emphysema. HH pathway inhibitors, such as vismodegib and sonidegib, are already validated in oncology, whereas other drugs have evidenced in vitro effects. Targeting the Hedgehog pathway could lead to a new therapeutic avenue in COPD. In this review, we focused on the early and severe COPD phenotype and the small lung hypothesis by exploring genetic susceptibility traits that are potentially treatable, thus summarizing promising therapeutics for the future.

Casein Kinase 1D Encodes a Novel Drug Target in Hedgehog-GLI-Driven Cancers and Tumor-Initiating Cells Resistant to SMO Inhibition

Simple Summary

Uncontrolled activation of hedgehog (HH)—GLI signaling contributes to the development of several human malignancies. Targeted inhibition of the HH—GLI signaling cascade with small-molecule inhibitors can reduce cancer growth, but patient relapse is very common due to the development of drug resistance. Therefore, a high unmet medical need exists for new drug targets and inhibitors to achieve efficient and durable responses. In the current study, we identified CSNK1D as a novel drug target in the HH—GLI signaling pathway. Genetic and pharmacological inhibition of CSNK1D activity leads to suppression of oncogenic HH—GLI signaling, even in cancer cells in which already approved HH inhibitors are no longer effective due to resistance mechanisms. Inhibition of CSNK1D function reduces the malignant properties of so-called tumor-initiating cells, thereby limiting cancer growth and presumably metastasis. The results of this study form the basis for the development of efficient CSNK1D inhibitors for the therapy of HH—GLI-associated cancers.

Abstract

(1) Background: Aberrant activation of the hedgehog (HH)—GLI pathway in stem-like tumor-initiating cells (TIC) is a frequent oncogenic driver signal in various human malignancies. Remarkable efficacy of anti-HH therapeutics led to the approval of HH inhibitors targeting the key pathway effector smoothened (SMO) in basal cell carcinoma and acute myeloid leukemia. However, frequent development of drug resistance and severe adverse effects of SMO inhibitors pose major challenges that require alternative treatment strategies targeting HH—GLI in TIC downstream of SMO. We therefore investigated members of the casein kinase 1 (CSNK1) family as novel drug targets in HH—GLI-driven malignancies. (2) Methods: We genetically and pharmacologically inhibited CSNK1D in HH-dependent cancer cells displaying either sensitivity or resistance to SMO inhibitors. To address the role of CSNK1D in oncogenic HH signaling and tumor growth and initiation, we quantitatively analyzed HH target gene expression, performed genetic and chemical perturbations of CSNK1D activity, and monitored the oncogenic transformation of TIC in vitro and in vivo using 3D clonogenic tumor spheroid assays and xenograft models. (3) Results: We show that CSNK1D plays a critical role in controlling oncogenic GLI activity downstream of SMO. We provide evidence that inhibition of CSNK1D interferes with oncogenic HH signaling in both SMO inhibitor-sensitive and -resistant tumor settings. Furthermore, genetic and pharmacologic perturbation of CSNK1D decreases the clonogenic growth of GLI-dependent TIC in vitro and in vivo. (4) Conclusions: Pharmacologic targeting of CSNK1D represents a novel therapeutic approach for the treatment of both SMO inhibitor-sensitive and -resistant tumors.

CRKL is a critical target of Hh-GLI2 pathway in lung adenocarcinoma

Lung adenocarcinoma (LUAD) is one of the important components of non-small-cell lung cancer (NSCLC) and leads to many deaths every year. During the initiation and progression of the LUAD, the Hh-GLI2 pathway plays critical roles. Several components of this pathway have been shown to be amplified or overexpressed in LUAD, providing this pathway as an attractive target for therapeutics. However, a gap in our understanding of the Hh-GLI2 pathway is the identity of transcriptional targets of GLI2 that drive LUAD tumorigenesis. Here, we show that the oncogene CRKL is a direct target of GLI2. GLI2 turns on CRKL transcription through binding its second intron. Furthermore, CRKL is an essential mediator for GLI2-driven proliferation and migration of LUAD cells. Depletion of CRKL blunts Hh-GLI2 pathway-mediated cell proliferation and invasion. Lastly, we find that CRKL knockout cells are more sensitive to EGFR-TKI and chemotherapeutics. Taken together, our work here identifies a specific target for Hh-related malignancies and provides CRKL as a promising therapeutic target for LUAD.

Palmitoylation of Hedgehog proteins by Hedgehog acyltransferase: roles in signalling and disease

Hedgehog acyltransferase (Hhat), a member of the membrane-bound O-acyltransferase (MBOAT) family, catalyses the covalent attachment of palmitate to the N-terminus of Hedgehog proteins. Palmitoylation is a post-translational modification essential for Hedgehog signalling. This review explores the mechanisms involved in Hhat acyltransferase enzymatic activity, similarities and differences between Hhat and other MBOAT enzymes, and the role of palmitoylation in Hedgehog signalling. In vitro and cell-based assays for Hhat activity have been developed, and residues within Hhat and Hedgehog essential for palmitoylation have been identified. In cells, Hhat promotes the transfer of palmitoyl-CoA from the cytoplasmic to the luminal side of the endoplasmic reticulum membrane, where Shh palmitoylation occurs. Palmitoylation is required for efficient delivery of secreted Hedgehog to its receptor Patched1, as well as for the deactivation of Patched1, which initiates the downstream Hedgehog signalling pathway. While Hhat loss is lethal during embryogenesis, mutations in Hhat have been linked to disease states or abnormalities in mice and humans. In adults, aberrant re-expression of Hedgehog ligands promotes tumorigenesis in an Hhat-dependent manner in a variety of different cancers, including pancreatic, breast and lung. Targeting hedgehog palmitoylation by inhibition of Hhat is thus a promising, potential intervention in human disease.

HEDGEHOG/GLI Modulates the PRR11-SKA2 Bidirectional Transcription Unit in Lung Squamous Cell Carcinomas

We previously demonstrated that proline-rich protein 11 (PRR11) and spindle and kinetochore associated 2 (SKA2) constituted a head-to-head gene pair driven by a prototypical bidirectional promoter. This gene pair synergistically promoted the development of non-small cell lung cancer. However, the signaling pathways leading to the ectopic expression of this gene pair remains obscure. In the present study, we first analyzed the lung squamous cell carcinoma (LSCC) relevant RNA sequencing data from The Cancer Genome Atlas (TCGA) database using the correlation analysis of gene expression and gene set enrichment analysis (GSEA), which revealed that the PRR11-SKA2 correlated gene list highly resembled the Hedgehog (Hh) pathway activation-related gene set. Subsequently, GLI1/2 inhibitor GANT-61 or GLI1/2-siRNA inhibited the Hh pathway of LSCC cells, concomitantly decreasing the expression levels of PRR11 and SKA2. Furthermore, the mRNA expression profile of LSCC cells treated with GANT-61 was detected using RNA sequencing, displaying 397 differentially expressed genes (203 upregulated genes and 194 downregulated genes). Out of them, one gene set, including BIRC5, NCAPG, CCNB2, and BUB1, was involved in cell division and interacted with both PRR11 and SKA2. These genes were verified as the downregulated genes via RT-PCR and their high expression significantly correlated with the shorter overall survival of LSCC patients. Taken together, our results indicate that GLI1/2 mediates the expression of the PRR11-SKA2-centric gene set that serves as an unfavorable prognostic indicator for LSCC patients, potentializing new combinatorial diagnostic and therapeutic strategies in LSCC.

NRF2 and Primary Cilia: An Emerging Partnership

When not dividing, many cell types target their centrosome to the plasma membrane, where it nucleates assembly of a primary cilium, an antenna-like signaling structure consisting of nine concentric microtubule pairs surrounded by membrane. Primary cilia play important pathophysiological roles in many tissues, their dysfunction being associated with cancer and ciliopathies, a diverse group of congenital human diseases. Several recent studies have unveiled functional connections between primary cilia and NRF2 (nuclear factor erythroid 2-related factor 2), the master transcription factor orchestrating cytoprotective responses to oxidative and other cellular stresses. These NRF2-cilia relationships are reciprocal: primary cilia, by promoting autophagy, downregulate NRF2 activity. In turn, NRF2 transcriptionally regulates genes involved in ciliogenesis and Hedgehog (Hh) signaling, a cilia-dependent pathway with major roles in embryogenesis, stem cell function and tumorigenesis. Nevertheless, while we found that NRF2 stimulates ciliogenesis and Hh signaling, a more recent study reported that NRF2 negatively affects these processes. Herein, we review the available evidence linking NRF2 to primary cilia, suggest possible explanations to reconcile seemingly contradictory data, and discuss what the emerging interplay between primary cilia and NRF2 may mean for human health and disease.

Regulating autophagy facilitated therapeutic efficacy of the sonic Hedgehog pathway inhibition on lung adenocarcinoma through GLI2 suppression and ROS production

Lung adenocarcinoma (LUAD), which comprises over 50% of all cases of non-small-cell lung cancer, has a poor prognosis and requires novel therapeutic approaches. The sonic Hedgehog (Shh) pathway, which plays a crucial role in differentiation, proliferation, and survival of cancer cells, is likely to be activated in LUADs, suggesting the Shh pathway as a potential therapeutic target for LUAD treatment. In this study, we reported that vismodegib, an inhibitor of the Shh pathway, only elicited minor antitumor efficacy in A549 and NCI-H1975 LUAD cells as well as in the xenograft tumors, with overexpressed GLI2 and increased autophagic activity. The aberrant autophagy in LUAD cells was further confirmed by the three main stages of autophagic flux, including the formation of autophagosomes, the fusion of autophagosomes with lysosomes, and degradation of autophagosomes in lysosomes. Furthermore, inhibition of autophagy by siRNA against ATG5 or ATG7 rescued the sensitivity of A549 and NCI-H1975 LUAD cells to vismodegib in vitro. Meanwhile, administration of the pharmaceutical inhibitor of autophagy, chloroquine, contributed to the enhanced anti-LUAD efficacy of vismodegib in vivo, probably through overproduction of ROS, acceleration of apoptosis, and suppression of GLI2 in LUAD tissues. In summary, our research revealed that downregulating autophagy facilitated the anti-LUAD efficacy of the Shh pathway suppression, thus highlighting a potential approach for LUAD therapy via simultaneously targeting the Shh signaling and autophagy pathway.

TSPAN8 promotes cancer cell stemness via activation of sonic Hedgehog signaling

Cancer stem cells (CSCs) represent a major source of treatment resistance and tumor progression. However, regulation of CSCs stemness is not entirely understood. Here, we report that TSPAN8 expression is upregulated in breast CSCs, promotes the expression of the stemness gene NANOG, OCT4, and ALDHA1, and correlates with therapeutic resistance. Mechanistically, TSPAN8 interacts with PTCH1 and inhibits the degradation of the SHH/PTCH1 complex through recruitment of deubiquitinating enzyme ATXN3. This results in the translocation of SMO to cilia, downstream gene expression, resistance of CSCs to chemotherapeutic agents, and enhances tumor formation in mice. Accordingly, expression levels of TSPAN8, PTCH1, SHH, and ATXN3 are positively correlated in human breast cancer specimens, and high TSPAN8 and ATXN3 expression levels correlate with poor prognosis. These findings reveal a molecular basis of TSPAN8-enhanced Sonic Hedgehog signaling and highlight a role for TSPAN8 in promoting cancer stemness.

Tetraspanin 8 (TSPAN8) has been implicated in a number of different tumours, but the underlying mechanisms remain unclear. Here, in breast cancer the authors highlight a role for TSPAN8 in promoting tumorigenesis through the activation of Hedgehog signalling.

Inhibition of the Hedgehog pathway in lung cancer

Inhibitors of the hedgehog pathway are effective in patients with basal cell carcinoma and a subgroup of patients with medulloblastoma with active hedgehog signaling. Despite preclinical work suggesting otherwise, clinical trials in solid tumors of epithelial origin have not shown added benefit with these drugs. Here, we review the preclinical and clinical data of hedgehog pathway inhibition in the most common histologic types of lung cancer. We focus on highlighting areas of uncertainty, where further research might define a niche for hedgehog pathway inhibition in patients with lung cancer.

HERC4 exerts an anti-tumor role through destabilizing the oncoprotein Smo

The GPCR-like transmembrane protein Smoothened (Smo) is an indispensable transducer in Hedgehog (Hh) pathway, its hyperactivation leads to several human cancers, including non-small cell lung cancer (NSCLC). The mechanism governing Smo stability still remains elusive. Here, we perform a modifier screening in Drosophila, and find that the E3 ligase dHerc4 degrades dSmo. Depletion of dherc4 increases dSmo protein and activates Hh pathway. In addition, we reveal that HERC4 is downregulated in NSCLC samples, negative correlating with Smo. HERC4 interacts with Smo reciprocally in NSCLC cells. Finally, we show that knockdown of herc4 activates Hh pathway and promotes NSCLC cell proliferation. Taken together, our studies have demonstrated that HERC4 acts as a tumor suppressor via destabilizing the oncoprotein Smo, and provided HERC4 as a promising therapeutic target for NSCLC treatment.

A CK1α Activator Penetrates the Brain and Shows Efficacy Against Drug-resistant Metastatic Medulloblastoma

PURPOSE

Although most children with medulloblastoma are cured of their disease, Sonic Hedgehog (SHH) subgroup medulloblastoma driven by TRP53 mutations is essentially lethal. Casein kinase 1α (CK1α) phosphorylates and destabilizes GLI transcription factors, thereby inhibiting the key effectors of SHH signaling. We therefore tested a second-generation CK1α activator against TRP53-mutant, MYCN-amplified medulloblastoma.

EXPERIMENTAL DESIGN

The ability of this CK1α activator to block SHH signaling was determined in vitro using GLI reporter cells, granular precursor primary cultures, and PATCHED1 (PTCH1)-mutant sphere cultures. While in vivo efficacy was tested using 2 different medulloblastoma mouse models: PTCH1 and ND2:SMOA1. Finally, the clinical relevance of CK1α activators was demonstrated using a TRP53-mutant, MYCN-amplified patient-derived xenograft.

RESULTS

SSTC3 inhibited SHH activity in vitro, acting downstream of the vismodegib target SMOOTHENED (SMO), and reduced the viability of sphere cultures derived from SHH medulloblastoma. SSTC3 accumulated in the brain, inhibited growth of SHH medulloblastoma tumors, and blocked metastases in a genetically engineered vismodegib-resistant mouse model of SHH medulloblastoma. Importantly, SSTC3 attenuated growth and metastasis of orthotopic patient-derived TRP53-mutant, MYCN-amplified, SHH subgroup medulloblastoma xenografts, increasing overall survival.

CONCLUSIONS

Using a newly described small-molecule, SSTC3, we show that CK1a activators could address a significant unmet clinical need for patients with SMO inhibitor-resistant medulloblastoma, including those harboring mutations in TRP53.

MiR-520b promotes the progression of non-small cell lung cancer through activating Hedgehog pathway

Although the non-small cell lung cancer (NSCLC) is one of the most malignant tumours worldwide, the mechanisms controlling NSCLC tumourigenesis remain unclear. Here, we find that the expression of miR-520b is up-regulated in NSCLC samples. Further studies have revealed that miR-520b promotes the proliferation and metastasis of NSCLC cells. In addition, miR-520b activates Hedgehog (Hh) pathway. Inhibitor of Hh pathway could relieve the oncogenic effect of miR-520b upon NSCLC cells. Mechanistically, we demonstrate that miR-520b directly targets SPOP 3'-UTR and decreases SPOP expression, culminating in GLI2/3 stabilization and Hh pathway hyperactivation. Collectively, our findings unveil that miR-520b promotes NSCLC tumourigenesis through SPOP-GLI2/3 axis and provide miR-520b as a potential diagnostic biomarker and therapeutic target for NSCLC.

Widespread Expression of Hedgehog Pathway Components in a Large Panel of Human Tumor Cells and Inhibition of Tumor Growth by GANT61: Implications for Cancer Therapy

The sonic Hedgehog/GLI signaling pathway (HH) is critical for maintaining tissue polarity in development and contributes to tumor stemness. Transcription factors GLI1–3 are the downstream effectors of HH and activate oncogenic targets. To explore the completeness of the expression of HH components in tumor cells, we performed a screen for all HH proteins in a wide spectrum of 56 tumor cell lines of various origin using Western blot analysis. Generally, all HH proteins were expressed. Important factors GLI1 and GLI2 were always expressed, only exceptionally one of them was lowered, suggesting the functionality of HH in all tumors tested. We determined the effect of a GLI inhibitor GANT61 on proliferation in 16 chosen cell lines. More than half of tumor cells were sensitive to GANT61 to various extents. GANT61 killed the sensitive cells through apoptosis. The inhibition of reporter activity containing 12xGLI consensus sites by GANT61 and cyclopamine roughly correlated with cell proliferation influenced by GANT61. Our results recognize the sensitivity of tumor cell types to GANT61 in cell culture and support a critical role for GLI factors in tumor progression through restraining apoptosis. The use of GANT61 in combined targeted therapy of sensitive tumors, such as melanomas, seems to be immensely helpful.

Genome-wide association study evaluating single-nucleotide polymorphisms and outcomes in patients with advanced stage serous ovarian or primary peritoneal cancer: An NRG Oncology/Gynecologic Oncology Group study

OBJECTIVE

This study evaluated single nucleotide polymorphisms (SNPs) associated with progression free (PFS) and overall survival (OS) in patients with advanced stage serous EOC.

METHODS

Patients enrolled in GOG-172 and 182 who provided specimens for translational research and consent were included. Germline DNA was evaluated with the Illumina's HumanOMNI1-Quad beadchips and scanned using Illumina's iScan optical imaging system. SNPs with allele frequency>0.05 and genotyping rate>0.98 were included. Analysis of SNPs for PFS and OS was done using Cox regression. Statistical significance was determined using Bonferroni corrected p-values with genomic control adjustment.

RESULTS

The initial GWAS analysis included 1,124,677 markers in 396 patients. To obtain the final data set, quality control checks were performed and limited to serous tumors and self-identified Caucasian race. In total 636,555 SNPs and 289 patients passed all the filters. The pre-specified statistical level of significance was 7.855e-08. No SNPs met this criteria for PFS or OS, however, two SNPs were close to significance (rs10899426 p-2.144e-08) (rs6256 p-9.774e-07) for PFS and 2 different SNPs were identified (rs295315 p-7.536e-07; rs17693104 p-7.734e-07) which were close to significance for OS.

CONCLUSIONS

Using the pre-specified level of significance of 1×10-08, we did not identify any SNPs of statistical significance for OS or PFS, however several were close. The SNP's identified in this GWAS study will require validation and these preliminary findings may lead to identification of novel pathways and biomarkers.

GLI1 Blockade Potentiates the Antitumor Activity of PI3K Antagonists in Lung Squamous Cell Carcinoma

Lung squamous cell carcinoma (SCC), strongly associated with smoking, is treated primarily with traditional cytotoxic chemotherapy due to a lack of FDA-approved targeted agents available. Here, we identify the Hedgehog pathway transcription factor GLI1 as a critical driver of lung SCC. Analysis of human lung cancer datasets showed that GLI1 mRNA was highly expressed in human lung SCC and portended a poor prognosis. Inhibition of GLI1 in human lung SCC cell lines suppressed tumor cell clonogenicity and proliferation in culture and in vivo Addition of SHH ligand, SMO antagonists, or other Hedgehog pathway agonists did not affect GLI1 expression in lung SCC cells. However, GLI1 expression was modulated by either inhibition or activation of the PI3K and MAPK pathways. Furthermore, in vivo growth of SCC harboring amplifications of the PI3K gene PIK3CA was attenuated by antagonizing GLI1 and PI3K. Thus, a combinatorial therapeutic strategy that targets the PI3K-mTOR pathway and GLI1 may lead to effective outcomes for PI3K pathway-dependent cancers, in contrast to recent results of human trials with single-agent PI3K antagonists. Cancer Res; 77(16); 4448-59. ©2017 AACR.

Palmitoylation of proteins in cancer

Post-translational modification of proteins by attachment of palmitate serves as a mechanism to regulate protein localization and function in both normal and malignant cells. Given the essential role that palmitoylation plays in cancer cell signaling, approaches that target palmitoylated proteins and palmitoyl acyltransferases (PATs) have the potential for therapeutic intervention in cancer. Highlighted here are recent advances in understanding the importance of protein palmitoylation in tumorigenic pathways. A new study has uncovered palmitoylation sites within the epidermal growth factor receptor that regulate receptor trafficking, signaling and sensitivity to tyrosine kinase inhibitors. Global data analysis from nearly 150 cancer studies reveals genomic alterations in several PATs that may account for their ability to function as tumor suppressors or oncogenes. Selective inhibitors have recently been developed that target hedgehog acyltransferase (Hhat) and Porcupine (Porcn), the acyltransferases that modify hedgehog and Wnt proteins, respectively. These inhibitors, coupled with targeted knockdown of Hhat and Porcn, reveal the essential functions of fatty acylation of secreted morphogens in a wide variety of human tumors.

Noncanonical GLI1 signaling promotes stemness features and in vivo growth in lung adenocarcinoma

Aberrant Hedgehog/GLI signaling has been implicated in a diverse spectrum of human cancers, but its role in lung adenocarcinoma (LAC) is still under debate. We show that the downstream effector of the Hedgehog pathway, GLI1, is expressed in 76% of LACs, but in roughly half of these tumors, the canonical pathway activator, Smoothened, is expressed at low levels, possibly owing to epigenetic silencing. In LAC cells including the cancer stem cell compartment, we show that GLI1 is activated noncanonically by MAPK/ERK signaling. Different mechanisms can trigger the MAPK/ERK/GLI1 cascade including KRAS mutation and stimulation of NRP2 by VEGF produced by the cancer cells themselves in an autocrine loop or by stromal cells as paracrine cross talk. Suppression of GLI1, by silencing or drug-mediated, inhibits LAC cells proliferation, attenuates their stemness and increases their susceptibility to apoptosis in vitro and in vivo. These findings provide insight into the growth of LACs and point to GLI1 as a downstream effector for oncogenic pathways. Thus, strategies involving direct inhibition of GLI1 may be useful in the treatment of LACs.

Gli1 expression in cancer stem-like cells predicts poor prognosis in patients with lung squamous cell carcinoma

PURPOSE

Glioma-associated oncogene homolog 1 (Gli1) is involved in cancer stem cell (CSC) maintenance in various tumors; however, its expression and clinical significance in lung squamous cell carcinoma (LSCC) has not been reported. In this study, we aimed to reveal the clinical significance of Gli1 in LSCC and investigate the potential of Gli1 as a CSC marker by comparing its expression with that of other stemness-related genes in LSCC.

METHODS

We assessed the expressions of Gli1, LSD1, CD44, Sox9 and Sox2 by immunohistochemistry in the tissue specimens obtained from 101 patients with LSCC. The relationship of Gli1 expression with clinicopathological parameters and cell-cycle regulating genes was investigated.

RESULTS

Gli1 expression was significantly correlated with T stage (P<0.001), lymph node metastasis (P=0.002), and clinical stage (P=0.005) of LSCC. The Kaplan-Meier survival analysis revealed that the expression of Gli1 in LSCC was all significantly associated with poor overall survival (OS: P=0.005). Cox regression analysis further confirmed that Gli1 is a prognostic marker of unfavorable clinical outcome of LSCC. Gli1 expression was significantly correlated with the expression of stemness-related genes such as LSD1 (P=0.009) and CD44 (P<0.001), but not with those of Sox2 and Sox9. However, Gli1 expression was associated with the expression of hypoxia-inducible factors1α (HIF1α; P<0.001) and Cyclin D1 (P=0.002), respectively. In additionally, microvessel density (MVD) was significantly higher in Gli1-positive LSCC than in the negative LSCC (P=0.026).

CONCLUSIONS

Our results suggest that Gli1 may be a potential LSCC stem cell marker and an independent indicator of poor prognosis for patients with LSCC.

A Phase I Study of FOLFIRINOX Plus IPI-926, a Hedgehog Pathway Inhibitor, for Advanced Pancreatic Adenocarcinoma

OBJECTIVES

In mouse models of pancreatic cancer, IPI-926, an oral Hedgehog inhibitor, increases chemotherapy delivery by depleting tumor-associated stroma. This multicenter phase Ib study evaluated IPI-926 in combination with FOLFIRINOX (5-fluorouracil, leucovorin, irinotecan, oxaliplatin) in patients with advanced pancreatic cancer.

METHODS

Patients were treated with once-daily IPI-926 plus FOLFIRINOX. A 3 + 3 dose escalation design was used, with cohort expansion at the maximum tolerated dose. A subset of patients underwent perfusion computed tomography to assess changes in tumor perfusion.

RESULTS

The maximum tolerated dose was identified 1 dose level below standard FOLFIRINOX. Common treatment-related adverse events included liver function test abnormalities, neuropathy, nausea/vomiting, and diarrhea. Objective response rate was high (67%), and patients receiving IPI-926 maintenance showed further declines in CA19-9 levels even after FOLFIRINOX discontinuation. Treatment did not result in consistent increases in tumor perfusion. The study closed early when a separate phase II trial of IPI-926 plus gemcitabine indicated detrimental effects of this combination.

CONCLUSIONS

This is the first study to demonstrate the feasibility of using FOLFIRINOX as the chemotherapeutic backbone in a clinical trial design. Although robust antitumor activity and acceptable safety were observed with the addition of IPI-926 to this regimen, future development of Hedgehog inhibitors in pancreatic cancer seems unlikely.

Arsenic trioxide inhibits cancer stem-like cells via down-regulation of Gli1 in lung cancer

Cancer stem cells (CSCs) are responsible for the tumorigenesis and recurrence, so targeting CSCs is a potential effective method to cure cancers. Activated Hedgehog signaling pathway has been proved to be implicated in the maintenance of self-renewal of CSCs, and arsenic trioxide (As2O3) has been reported to inhibit Gli1, a key transcription factor of Hedgehog pathway. In this study, we evaluated whether As2O3 has inhibitory effects on cancer stem-like cells (CSLCs) in lung cancer and further explored the possible mechanism. CCK8 assay and colony formation assay were performed to demonstrate the ability of As2O3 to inhibit the growth of NCI-H460 and NCI-H446 cells, which represented non-small cell lung cancer (NSCLC) and small cell lung cancer (SCLC), respectively. Tumor sphere formation assay was carried out to evaluate the effects of As2O3 on stem cell-like subpopulations. The expression of stem cell biomarkers CD133 and stem cell transcription factors such as Sox2 and Oct4 were detected. Moreover, the effects of As2O3 on expression of Gli1 and its target genes were observed. We found that As2O3 inhibited the cell proliferation and reduced the colony formation ability. Importantly, As2O3 decreased the formation of tumor spheres. The expression of stem cell biomarker CD133 and stem cell transcription factors such as Sox2 and Oct4 were markedly reduced by As2O3 treatment. Furthermore, As2O3 decreased the expression of Gli1, N-myc and GAS1. Our results suggested that As2O3 is a promising agent to inhibit CSLCs in lung cancer. In addition, the mechanism of CSLCs inhibition might involve Gli1 down-regulation.

Survivin, a novel target of the Hedgehog/GLI signaling pathway in human tumor cells

Survivin, an important antiapoptotic protein, is expressed in tumors, whereas in normal tissues the expression of this protein is extremely low, defining a role for survivin as a cancer gene. Survivin exhibits multifunctional activity in tumor cells. However, why survivin expression is sharply and invariably restricted to tumor tissue remains unclear. Here, we identified 11 putative consensus binding sites for GLI transcription factors in the survivin promoter and characterized the promoter activity. Inhibitors of the Hedgehog/GLI pathway, cyclopamine and GANT61, decreased the promoter activity in reporter assays. ΔNGLI2 (which lacks the repressor domain) was the most potent vector in activating the survivin promoter–reporter. Moreover, GANT61, a GLI1/2 inhibitor, repressed endogenous survivin protein and mRNA expression in most cells across a large panel of tumor cell lines. Chromatin immunoprecipitation showed GLI2 binding to the survivin promoter. The ectopic GLI2-evoked expression of endogenous survivin was observed in normal human fibroblasts. GANT61 decreased survivin level in nude mice tumors, mimicking the activity of GANT61 in cultured cells. The immunohistochemistry and double immunofluorescence of human tumors revealed a correlation between the tissue regions showing high GLI2 and survivin positivity. Thus, these results demonstrated that survivin is a classical transcriptional target of GLI2, a Hedgehog pathway signaling effector. This potentially reflects the high expression of survivin in human tumor cells. As the Hedgehog pathway is upregulated in virtually all types of cancer cells, these findings substantially contribute to the explanation of uniform survivin expression in tumors as a potential target for the development of a more effective treatment of cancers through the inhibition of GLI2 to restrain survivin activity.

Click chemistry armed enzyme-linked immunosorbent assay to measure palmitoylation by hedgehog acyltransferase

Hedgehog signaling is critical for correct embryogenesis and tissue development. However, on maturation, signaling is also found to be aberrantly activated in many cancers. Palmitoylation of the secreted signaling protein sonic hedgehog (Shh) by the enzyme hedgehog acyltransferase (Hhat) is required for functional signaling. To quantify this important posttranslational modification, many in vitro Shh palmitoylation assays employ radiolabeled fatty acids, which have limitations in terms of cost and safety. Here we present a click chemistry armed enzyme-linked immunosorbent assay (click-ELISA) for assessment of Hhat activity through acylation of biotinylated Shh peptide with an alkyne-tagged palmitoyl-CoA (coenzyme A) analogue. Click chemistry functionalization of the alkyne tag with azido-FLAG peptide allows analysis through an ELISA protocol and colorimetric readout. This assay format identified the detergent n-dodecyl β-d-maltopyranoside as an improved solubilizing agent for Hhat activity. Quantification of the potency of RU-SKI small molecule Hhat inhibitors by click-ELISA indicated IC50 values in the low- or sub-micromolar range. A stopped assay format was also employed that allows measurement of Hhat kinetic parameters where saturating substrate concentrations exceed the binding capacity of the streptavidin-coated plate. Therefore, click-ELISA represents a nonradioactive method for assessing protein palmitoylation in vitro that is readily expandable to other classes of protein lipidation.

Hedgehog Acyltransferase as a target in estrogen receptor positive, HER2 amplified, and tamoxifen resistant breast cancer cells

Background

Hedgehog acyltransferase (Hhat) catalyzes the transfer of the fatty acid palmitate onto Sonic Hedgehog (Shh), a modification that is essential for Shh signaling activity. The Shh signaling pathway has been implicated in the progression of breast cancer.

Methods

To determine the functional significance of Hhat expression in breast cancer, we used a panel of breast cancer cell lines that included estrogen receptor (ER) positive, HER2 amplified, triple negative, and tamoxifen resistant cells. We monitored both anchorage dependent and independent proliferation of these cells following depletion of Hhat with lentiviral shRNA and inhibition of Hhat activity with RU-SKI 43, a small molecule inhibitor of Hhat.

Results

Depletion of Hhat decreased anchorage-dependent and anchorage-independent proliferation of ER positive, but not triple negative, breast cancer cells. Treatment with RU-SKI 43 also reduced ER positive cell proliferation, whereas a structurally related, inactive compound had no effect. Overexpression of Hhat in ER positive cells not only rescued the growth defect in the presence of RU-SKI 43 but also resulted in increased cell proliferation in the absence of drug. Furthermore, depletion or inhibition of Hhat reduced proliferation of HER2 amplified as well as tamoxifen resistant cells. Inhibition of Smoothened had no effect on proliferation, indicating that canonical Shh signaling was not operative. Moreover, Hhat regulated the proliferation of both Shh responsive and non-responsive ER positive cells, suggesting a Shh independent function for Hhat.

Conclusions

These data suggest that Hhat plays a critical role in ER positive, HER2 amplified, and hormone resistant breast cancer proliferation and highlights the potential promise of Hhat inhibitors for therapeutic benefit in breast cancer.

Electronic supplementary material

The online version of this article (doi:10.1186/s12943-015-0345-x) contains supplementary material, which is available to authorized users.

Topological analysis of Hedgehog acyltransferase, a multipalmitoylated transmembrane protein

Hedgehog proteins are secreted morphogens that play critical roles in development and disease. During maturation of the proteins through the secretory pathway, they are modified by the addition of N-terminal palmitic acid and C-terminal cholesterol moieties, both of which are critical for their correct function and localization. Hedgehog acyltransferase (HHAT) is the enzyme in the endoplasmic reticulum that palmitoylates Hedgehog proteins, is a member of a small subfamily of membrane-bound O-acyltransferase proteins that acylate secreted proteins, and is an important drug target in cancer. However, little is known about HHAT structure and mode of function. We show that HHAT is comprised of ten transmembrane domains and two reentrant loops with the critical His and Asp residues on opposite sides of the endoplasmic reticulum membrane. We further show that HHAT is palmitoylated on multiple cytosolic cysteines that maintain protein structure within the membrane. Finally, we provide evidence that mutation of the conserved His residue in the hypothesized catalytic domain results in a complete loss of HHAT palmitoylation, providing novel insights into how the protein may function in vivo.

The Hedgehog pathway: role in cell differentiation, polarity and proliferation

Hedgehog (Hh) is first described as a genetic mutation that has "spiked" phenotype in the cuticles of Drosophila in later 1970s. Since then, Hh signaling has been implicated in regulation of differentiation, proliferation, tissue polarity, stem cell population and carcinogenesis. The first link of Hh signaling to cancer was established through discovery of genetic mutations of Hh receptor gene PTCH1 being responsible for Gorlin syndrome in 1996. It was later shown that Hh signaling is associated with many types of cancer, including skin, leukemia, lung, brain and gastrointestinal cancers. Another important milestone for the Hh research field is the FDA approval for the clinical use of Hh inhibitor Erivedge/Vismodegib for treatment of locally advanced and metastatic basal cell carcinomas. However, recent clinical trials of Hh signaling inhibitors in pancreatic, colon and ovarian cancer all failed, indicating a real need for further understanding of Hh signaling in cancer. In this review, we will summarize recent progress in the Hh signaling mechanism and its role in human cancer.

Hedgehog acyltransferase as a target in pancreatic ductal adenocarcinoma

Sonic Hedgehog (Shh) is abnormally expressed in pancreatic cancer and is associated with disease onset and progression. Inhibition of Shh signaling is thus an attractive clinical target for therapeutic intervention. Most efforts to block Shh signaling have focused on inhibitors of Smoothened, which target the canonical Shh signaling pathway. These approaches have met with limited success, in part due to development of resistance-conferring mutations and contributions from non-canonical signaling pathways. Here, we show that Hedgehog acyltransferase (Hhat), the enzyme responsible for the attachment of palmitate onto Shh, is a novel target for inhibition of Shh signaling in pancreatic cancer cells. Depletion of Hhat with lentivirally delivered small hairpin RNA decreased both anchorage-dependent and independent proliferation of human pancreatic cancer cells. In vivo, Hhat knockdown led to reduction of tumor growth in a mouse xenograft model of pancreatic cancer. RU-SKI 43, a small molecule inhibitor of Hhat recently developed by our group, reduced pancreatic cancer cell proliferation and Gli-1 activation through Smoothened-independent non-canonical signaling. In addition, RU-SKI 43 treatment inhibited two key proliferative pathways regulated by Akt and mTOR. This work demonstrates that Hhat has a critical role in pancreatic cancer and that a small molecule inhibitor of Hhat can successfully block pancreatic cancer cell proliferation. It also highlights the importance of developing optimized Hhat inhibitors to be used as therapeutics in pancreatic cancer, as well as in other malignancies characterized by Shh overexpression.

Membrane topology of hedgehog acyltransferase

Hedgehog acyltransferase (Hhat) is a multipass transmembrane enzyme that mediates the covalent attachment of the 16-carbon fatty acid palmitate to the N-terminal cysteine of Sonic Hedgehog (Shh). Palmitoylation of Shh by Hhat is critical for short and long range signaling. Knowledge of the topological organization of Hhat transmembrane helices would enhance our understanding of Hhat-mediated Shh palmitoylation. Bioinformatics analysis of transmembrane domains within human Hhat using 10 different algorithms resulted in highly consistent predictions in the C-terminal, but not in the N-terminal, region of Hhat. To empirically determine the topology of Hhat, we designed and exploited Hhat constructs containing either terminal or 12 different internal epitope tags. We used selective permeabilization coupled with immunofluorescence as well as a protease protection assay to demonstrate that Hhat contains 10 transmembrane domains and 2 re-entrant loops. The invariant His and highly conserved Asp residues within the membrane-bound O-acyltransferase (MBOAT) homology domain are segregated on opposite sides of the endoplasmic reticulum membrane. The localization of His-379 on the lumenal membrane surface is consistent with a role for this invariant residue in catalysis. Analysis of the activity and stability of the Hhat constructs revealed that the C-terminal MBOAT domain is especially sensitive to manipulation. Moreover, there was remarkable similarity in the overall topological organization of Hhat and ghrelin O-acyltransferase, another MBOAT family member. Knowledge of the topological organization of Hhat could serve as an important tool for further design of selective Hhat inhibitors.

Expression of the GLI family genes is associated with tumor progression in advanced lung adenocarcinoma

BACKGROUND

The hedgehog (Hh) signaling pathway is aberrantly activated in various cancers. Expression of the GLI family of genes, which encode for transcriptional factors of the Hh pathway, has not been fully assessed in clinical samples of advanced lung adenocarcinoma. In this study, we retrospectively evaluated the expression of the GLI family of genes in advanced stage lung adenocarcinoma samples and determined their relation to patient survival.

METHODS

The levels of GLI1, GLI2, and GLI3 mRNA expression were measured by quantitative real-time polymerase chain reaction in surgically obtained tissue samples from stage II-IV lung adenocarcinoma patients (n = 102). Pairwise comparisons between all three GLI mRNA expression were performed, and after dichotomizing the patients into low and high expression groups according to each GLI mRNA expression level, survival curves were calculated and multivariate analyses were conducted.

RESULTS

Significant positive correlation was found between GLI1 and GLI3 mRNA expression (P <0.001). Tumors with higher expression (upper 15%) of GLI1 or GLI3 mRNA were associated with poor survival in stage II-IV (5-year overall survival rates: GLI1 mRNA low, 41.7% vs. high, 20.0%, P = 0.0074; GLI3 mRNA low, 43.1% vs. high, 13.3%, P = 0.0062) and stage III-IV (5-year overall survival rates: GLI1 mRNA low, 34.0% vs. high, 0%, P = 0.0012; GLI3 mRNA low, 33.4% vs. high, 7.7%, P = 0.057) lung adenocarcinoma patients. GLI2 mRNA expression did not appear to have great clinical significance. Multivariate analysis revealed higher GLI1 mRNA expression as an independent factor for unfavorable patient survival (P = 0.0030, hazard ratio = 3.1, 95% confidence interval = 1.5-6.2), as well as tumor differentiation and stage.

CONCLUSIONS

Expression of GLI1 and GLI3 mRNA was strongly correlated, and their overexpression, especially that of GLI1, was found to be predictive of aggressive tumor behavior. This study indicates that the Hh pathway may be a key oncogenic signaling network in tumor pathogenesis and, thus, a potential therapeutic target in advanced lung adenocarcinoma.

Attenuation of hedgehog acyltransferase-catalyzed sonic Hedgehog palmitoylation causes reduced signaling, proliferation and invasiveness of human carcinoma cells

Overexpression of Hedgehog family proteins contributes to the aetiology of many cancers. To be highly active, Hedgehog proteins must be palmitoylated at their N-terminus by the MBOAT family multispanning membrane enzyme Hedgehog acyltransferase (Hhat). In a pancreatic ductal adenocarcinoma (PDAC) cell line PANC-1 and transfected HEK293a cells Hhat localized to the endoplasmic reticulum. siRNA knockdown showed that Hhat is required for Sonic hedgehog (Shh) palmitoylation, for its assembly into high molecular weight extracellular complexes and for functional activity. Hhat knockdown inhibited Hh autocrine and juxtacrine signaling, and inhibited PDAC cell growth and invasiveness in vitro. In addition, Hhat knockdown in a HEK293a cell line constitutively expressing Shh and A549 human non-small cell lung cancer cells inhibited their ability to signal in a juxtacrine/paracrine fashion to the reporter cell lines C3H10T1/2 and Shh-Light2. Our data identify Hhat as a key player in Hh-dependent signaling and tumour cell transformed behaviour.

"Atypical" regulation of Hedgehog-dependent cancers

Growing evidence indicates targeting PKCι may be effective in treating Hedgehog-dependent cancers. In this issue of Cancer Cell, Justilien and colleagues present the surprising finding that PKCι promotes Hedgehog ligand production and lung squamous cell carcinoma growth through SOX2, rather than the canonical transcription factor GLI.

The PRKCI and SOX2 oncogenes are coamplified and cooperate to activate Hedgehog signaling in lung squamous cell carcinoma

We report that two oncogenes coamplified on chromosome 3q26, PRKCI and SOX2, cooperate to drive a stem-like phenotype in lung squamous cell carcinoma (LSCC). Protein kinase Cι (PKCι) phosphorylates SOX2, a master transcriptional regulator of stemness, and recruits it to the promoter of Hedgehog (Hh) acyltransferase (HHAT) that catalyzes the rate-limiting step in Hh ligand production. PKCι-mediated SOX2 phosphorylation is required for HHAT promoter occupancy, HHAT expression, and maintenance of a stem-like phenotype. Primary LSCC tumors coordinately overexpress PKCι, SOX2, and HHAT and require PKCι-SOX2-HHAT signaling to maintain a stem-like phenotype. Thus, PKCι and SOX2 are genetically, biochemically, and functionally linked in LSCC, and together they drive tumorigenesis by establishing a cell-autonomous Hh signaling axis.

Targeting hedgehog signaling in cancer: research and clinical developments

Since its first description in Drosophila by Drs Nusslein-Volhard and Wieschaus in 1980, hedgehog (Hh) signaling has been implicated in regulation of cell differentiation, proliferation, tissue polarity, stem cell maintenance, and carcinogenesis. The first link of Hh signaling to cancer was established through studies of Gorlin syndrome in 1996 by two independent teams. Later, it was shown that Hh signaling may be involved in many types of cancer, including skin, leukemia, lung, brain, and gastrointestinal cancers. In early 2012, the US Food and Drug Administration approved the clinical use of Hh inhibitor Erivedge/vismodegib for treatment of locally advanced and metastatic basal cell carcinomas. With further investigation, it is possible to see more clinical applications of Hh signaling inhibitors. In this review, we will summarize major advances in the last 3 years in our understanding of Hh signaling activation in human cancer, and recent developments in preclinical and clinical studies using Hh signaling inhibitors.

Targeting of the Hedgehog signal transduction pathway suppresses survival of malignant pleural mesothelioma cells in vitro

OBJECTIVE

The present study sought to determine whether the Hedgehog (Hh) pathway is active and regulates the cell growth of cultured malignant pleural mesothelioma (MPM) cells and to evaluate the efficacy of pathway blockade using smoothened (SMO) antagonists (SMO inhibitor GDC-0449 or the antifungal drug itraconazole [ITRA]) or Gli inhibitors (GANT61 or the antileukemia drug arsenic trioxide [ATO]) in suppressing MPM viability.

METHODS

Selective knockdown of SMO to inhibit Hh signaling was achieved by small interfering RNA in 3 representative MPM cells. The growth inhibitory effect of GDC-0449, ITRA, GANT61, and ATO was evaluated in 8 MPM lines, with cell viability quantified using the 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT) assay. Cell death was determined by annexinV/propidium iodide staining and flow cytometry.

RESULTS

SMO small interfering RNA mediated a two- to more than fivefold reduction of SMO and Gli1 gene expression as determined by real-time quantitative reverse-transcriptase polymerase chain reaction, indicating significant Hh pathway blockade. This was associated with significantly reduced cell viability (34% ± 7% to 61% ± 14% of nontarget small interfering RNA controls; P = .0024 to P = .043). Treating MPM cells with Hh inhibitors resulted in a 1.5- to 4-fold reduction of Gli1 expression. These 4 Hh antagonists strongly suppressed MPM cell viability. More importantly, ITRA, ATO, GANT61 induced significant apoptosis in the representative MPM cells.

CONCLUSIONS

Hh signaling is active in MPM and regulates cell viability. ATO and ITRA were as effective as the prototypic SMO inhibitor GDC-0449 and the Gli inhibitor GANT61 in suppressing Hh signaling in MPM cells. Pharmaceutical agents Food and Drug Administration-approved for other indications but recently found to have anti-Hh activity, such as ATO or ITRA, could be repurposed to treat MPM.