Clinical experience with Hedgehog pathway inhibitors

Medulloblastomics: the end of the beginning

The division of medulloblastoma into different subgroups by microarray expression profiling has dramatically changed our perspective of this malignant childhood brain tumour. Now, the availability of next-generation sequencing and complementary high-density genomic technologies has unmasked novel driver mutations in each medulloblastoma subgroup. The implications of these findings for the management of patients are readily apparent, pinpointing previously unappreciated diagnostic and therapeutic targets. In this Review, we summarize the 'explosion' of data emerging from the application of modern genomics to medulloblastoma, and in particular the recurrent targets of mutation in medulloblastoma subgroups. These data are currently making their way into clinical trials as we seek to integrate conventional and molecularly targeted therapies.

Salinomycin as a drug for targeting human cancer stem cells

Cancer stem cells (CSCs) represent a subpopulation of tumor cells that possess self-renewal and tumor initiation capacity and the ability to give rise to the heterogenous lineages of malignant cells that comprise a tumor. CSCs possess multiple intrinsic mechanisms of resistance to chemotherapeutic drugs, novel tumor-targeted drugs, and radiation therapy, allowing them to survive standard cancer therapies and to initiate tumor recurrence and metastasis. Various molecular complexes and pathways that confer resistance and survival of CSCs, including expression of ATP-binding cassette (ABC) drug transporters, activation of the Wnt/β-catenin, Hedgehog, Notch and PI3K/Akt/mTOR signaling pathways, and acquisition of epithelial-mesenchymal transition (EMT), have been identified recently. Salinomycin, a polyether ionophore antibiotic isolated from Streptomyces albus, has been shown to kill CSCs in different types of human cancers, most likely by interfering with ABC drug transporters, the Wnt/β-catenin signaling pathway, and other CSC pathways. Promising results from preclinical trials in human xenograft mice and a few clinical pilote studies reveal that salinomycin is able to effectively eliminate CSCs and to induce partial clinical regression of heavily pretreated and therapy-resistant cancers. The ability of salinomycin to kill both CSCs and therapy-resistant cancer cells may define the compound as a novel and an effective anticancer drug.

WIP1 phosphatase modulates the Hedgehog signaling by enhancing GLI1 function

The Hedgehog-GLI (HH-GLI) signaling plays a critical role in controlling growth and tissue patterning during embryogenesis and is implicated in a variety of human malignancies, including those of the skin. Phosphorylation events have been shown to regulate the activity of the GLI transcription factors, the final effectors of the HH-GLI signaling pathway. Here, we show that WIP1 (or PPM1D), an oncogenic phosphatase amplified/overexpressed in several types of human cancer, is a positive modulator of the HH signaling. Mechanistically, WIP1 enhances the function of GLI1 by increasing its transcriptional activity, nuclear localization and protein stability, but not of GLI2 nor GLI3. We also find that WIP1 and GLI1 are in a complex. Modulation of the transcriptional activity of GLI1 by WIP1 depends on the latter's phosphatase activity and, remarkably, does not require p53, a known WIP1 target. Functionally, we find that WIP1 is required for melanoma and breast cancer cell proliferation and self-renewal in vitro and melanoma xenograft growth induced by activation of the HH signaling. Pharmacological blockade of the HH pathway with the SMOOTHENED antagonist cyclopamine acts synergistically with inhibition of WIP1 in reducing growth of melanoma and breast cancer cells in vitro. Overall, our data uncover a role for WIP1 in modulating the activity of GLI1 and in sustaining cancer cell growth and cancer stem cell self-renewal induced by activation of the HH pathway. These findings open a novel therapeutic approach for human melanomas and, possibly, other cancer types expressing WIP1 and with activated HH pathway.

A randomized phase II trial of vismodegib versus placebo with FOLFOX or FOLFIRI and bevacizumab in patients with previously untreated metastatic colorectal cancer

PURPOSE

Vismodegib, a Hedgehog pathway inhibitor, has preclinical activity in colorectal cancer (CRC) models. This trial assessed the efficacy, safety, and pharmacokinetics of adding vismodegib to first-line treatment for metastatic CRC (mCRC).

EXPERIMENTAL DESIGN

Patients were randomized to receive vismodegib (150 mg/day orally) or placebo, in combination with FOLFOX or FOLFIRI chemotherapy plus bevacizumab (5 mg/kg) every 2 weeks until disease progression or intolerable toxicity. The primary endpoint was progression-free survival (PFS). Key secondary objectives included evaluation of predictive biomarkers and pharmacokinetic drug interactions.

RESULTS

A total of 199 patients with mCRC were treated on protocol (124 FOLFOX, 75 FOLFIRI). The median PFS hazard ratio (HR) for vismodegib treatment compared with placebo was 1.25 (90% CI: 0.89-1.76; P = 0.28). The overall response rates for placebo-treated and vismodegib-treated patients were 51% (90% CI: 43-60) and 46% (90% CI: 37-55), respectively. No vismodegib-associated benefit was observed in combination with either FOLFOX or FOLFIRI. Increased tumor tissue Hedgehog expression did not predict clinical benefit. Grade 3 to 5 adverse events reported for more than 5% of patients that occurred more frequently in the vismodegib-treated group were fatigue, nausea, asthenia, mucositis, peripheral sensory neuropathy, weight loss, decreased appetite, and dehydration. Vismodegib did not alter the pharmacokinetics of FOLFOX, FOLFIRI, or bevacizumab.

CONCLUSIONS

Vismodegib does not add to the efficacy of standard therapy for mCRC. Compared with placebo, treatment intensity was lower for all regimen components in vismodegib-treated patients, suggesting that combined toxicity may have contributed to lack of efficacy.

A phase II, randomized, placebo-controlled study of vismodegib as maintenance therapy in patients with ovarian cancer in second or third complete remission

PURPOSE

Hedgehog pathway inhibition has been suggested as a potential maintenance treatment approach in ovarian cancer through disruption of tumor-stromal interactions. Vismodegib is an orally available Hedgehog pathway inhibitor with clinical activity in advanced basal cell carcinoma and medulloblastoma. This phase II, randomized, double-blind, placebo-controlled trial was designed to provide a preliminary estimate of efficacy in patients with ovarian cancer in second or third complete remission (CR).

EXPERIMENTAL DESIGN

Patients with recurrent epithelial ovarian, fallopian tube, or primary peritoneal cancer in second or third CR were randomized 1:1 to vismodegib (GDC-0449; 150 mg daily) or placebo three to 14 weeks after completing chemotherapy. Treatment continued until radiographic progression or toxicity. The primary endpoint was investigator-assessed progression-free survival (PFS).

RESULTS

One hundred four patients were randomized to vismodegib (n = 52) or placebo (n = 52); median PFS was 7.5 months and 5.8 months, respectively [HR 0.79; 95% confidence interval (CI), 0.46-1.35]. The HR was 0.66 (95% CI, 0.36-1.20) for second CR patients (n = 84) and 1.79 (95% CI, 0.50-6.48) for third CR patients (n = 20). The most common adverse events in the vismodegib arm were dysgeusia/ageusia, muscle spasms, and alopecia. Grade 3/4 adverse events occurred in 12 patients (23.1%) with vismodegib and six (11.5%) with placebo. Hedgehog expression was detected in 13.5% of archival tissues.

CONCLUSIONS

In this study, the sought magnitude of increase in PFS was not achieved for vismodegib maintenance versus placebo in patients with ovarian cancer in second or third CR. The frequency of Hedgehog ligand expression was lower than expected.

Identification of a novel Smoothened antagonist that potently suppresses Hedgehog signaling

The Hedgehog signaling pathway plays an essential role in embryo development and adult tissue homeostasis, in regulating stem cells and is abnormally activated in many cancers. Given the importance of this signaling pathway, we developed a novel and versatile high-throughput, cell-based screening platform using confocal imaging, based on the role of β-arrestin in Hedgehog signal transduction, that can identify agonists or antagonist of the pathway by a simple change to the screening protocol. Here we report the use of this assay in the antagonist mode to identify novel antagonists of Smoothened, including a compound (A8) with low nanomolar activity against wild-type Smo also capable of binding the Smo point mutant D473H associated with clinical resistance in medulloblastoma. Our data validate this novel screening approach in the further development of A8 and related congeners to treat Hedgehog related diseases, including the treatment of basal cell carcinoma and medulloblastoma.

Response to inhibition of smoothened in diverse epithelial cancer cells that lack smoothened or patched 1 mutations

Hedgehog (HH) pathway Smoothened (Smo) inhibitors are active against Gorlin syndrome-associated basal cell carcinoma (BCC) and medulloblastoma where Patched (Ptch) mutations occur. We interrogated 705 epithelial cancer cell lines for growth response to the Smo inhibitor cyclopamine and for expressed HH pathway-regulated species in a linked genetic database. Ptch and Smo mutations that respectively conferred Smo inhibitor response or resistance were undetected. Previous studies revealed HH pathway activation in lung cancers. Therefore, findings were validated using lung cancer cell lines, transgenic and transplantable murine lung cancer models, and human normal-malignant lung tissue arrays in addition to testing other Smo inhibitors. Cyclopamine sensitivity most significantly correlated with high cyclin E (P=0.000009) and low insulin-like growth factor binding protein 6 (IGFBP6) (P=0.000004) levels. Gli family members were associated with response. Cyclopamine resistance occurred with high GILZ (P=0.002) expression. Newer Smo inhibitors exhibited a pattern of sensitivity similar to cyclopamine. Gain of cyclin E or loss of IGFBP6 in lung cancer cells significantly increased Smo inhibitor response. Cyclin E-driven transgenic lung cancers expressed a gene profile implicating HH pathway activation. Cyclopamine treatment significantly reduced proliferation of murine and human lung cancers. Smo inhibition reduced lung cancer formation in a syngeneic mouse model. In human normal-malignant lung tissue arrays cyclin E, IGFBP6, Gli1 and GILZ were each differentially expressed. Together, these findings indicate that Smo inhibitors should be considered in cancers beyond those with activating HH pathway mutations. This includes tumors that express genes indicating basal HH pathway activation.

Regulation of DNA damage following termination of Hedgehog (HH) survival signaling at the level of the GLI genes in human colon cancer

Transcriptional regulation of the Hedgehog (HH) signaling response is mediated by GLI genes (GLI1, GLI2) downstream of SMO, that are also activated by oncogenic signaling pathways. We have demonstrated the importance of targeting GLI downstream of SMO in the induction of cell death in human colon carcinoma cells. In HT29 cells inhibition of GLI1/GLI2 by the small molecule inhibitor GANT61 induced DNA double strand breaks (DSBs) and activation of ATM, MDC1 and NBS1; γH2AX and MDC1, NBS1 and MDC1 co-localized in nuclear foci. Early activation of ATM was decreased by 24 hr, when p-NBS1^Ser343, activated by ATM, was significantly reduced in cell extracts. Bound γH2AX was detected in isolated chromatin fractions or nuclei during DNA damage but not during DNA repair. MDC1 was tightly bound to chromatin at 32 hr as cells accumulated in early S-phase prior to becoming subG1, and during DNA repair. Limited binding of NBS1 was detected at all times during DNA damage but was strongly bound during DNA repair. Transient overexpression of NBS1 protected HT29 cells from GANT61-induced cell death, while knockdown of H2AX by H2AXshRNA delayed DNA damage signaling. Data demonstrate following GLI1/GLI2 inhibition: 1) induction of DNA damage in cells that are also resistant to SMO inhibitors, 2) dynamic interactions between γH2AX, MDC1 and NBS1 in single cell nuclei and in isolated chromatin fractions, 3) expression and chromatin binding properties of key mediator proteins that mark DNA damage or DNA repair, and 4) the importance of NBS1 in the DNA damage response mechanism.

Triparanol suppresses human tumor growth in vitro and in vivo

Despite the improved contemporary multidisciplinary regimens treating cancer, majority of cancer patients still suffer from adverse effects and relapse, therefore posing a significant challenge to uncover more efficacious molecular therapeutics targeting signaling pathways central to tumorigenesis. Here, our study have demonstrated that Triparanol, a cholesterol synthesis inhibitor, can block proliferation and induce apoptosis in multiple human cancer cells including lung, breast, liver, pancreatic, prostate cancer and melanoma cells, and growth inhibition can be rescued by exogenous addition of cholesterol. Remarkably, we have proved Triparanol can significantly repress Hedgehog pathway signaling in these human cancer cells. Furthermore, study in a mouse xenograft model of human lung cancer has validated that Triparanol can impede tumor growth in vivo. We have therefore uncovered Triparanol as potential new cancer therapeutic in treating multiple types of human cancers with deregulated Hedgehog signaling.

The utility of hedgehog signaling pathway inhibition for cancer

The Hedgehog (Hh) signaling pathway has been implicated in tumor initiation and metastasis across different malignancies. Major mechanisms by which the Hh pathway is aberrantly activated can be attributed to mutations of members of Hh pathway or excessive/inappropriate expression of Hh pathway ligands. The Hh signaling pathway also affects the regulation of cancer stem cells, leading to their capabilities in tumor formation, disease progression, and metastasis. Preliminary results of early phase clinical trials of Hh inhibitors administered as monotherapy demonstrated promising results in patients with basal cell carcinoma and medulloblastoma, but clinically meaningful anticancer efficacy across other tumor types seems to be lacking. Additionally, cases of resistance have been already observed. Mutations of SMO, activation of Hh pathway components downstream to SMO, and upregulation of alternative signaling pathways are possible mechanisms of resistance development. Determination of effective Hh inhibitor-based combination regimens and development of correlative biomarkers relevant to this pathway should remain as clear priorities for future research.

Platforms for high-throughput screening of Wnt/Frizzled antagonists

Signaling cascades initiated by Wnt lipoglycoproteins and their receptors of the Frizzled family regulate many aspects of animal development and physiology. Improper activation of this signaling promotes carcinogenic transformation and metastasis. Development of agents blocking the Wnt-Frizzled signaling is of prime interest for drug discovery. Despite certain progress no such agents are as yet brought to the market or even to clinical trials. One reason for these delays might be the use of suboptimal readout assays. In this article we overview existing and developing assay platforms to screen for Wnt-Frizzled antagonists. Among those, G protein-activating assays built on the emerging GPCR properties of Frizzleds are highlighted.

Diindolylmethane-mediated Gli1 protein suppression induces anoikis in ovarian cancer cells in vitro and blocks tumor formation ability in vivo

Anoikis is a cell death that occurs due to detachment of a cell from the extracellular matrix (ECM). Resistance to anoikis is a primary feature of a cell that undergoes metastasis. In this study for the first time, we demonstrated the potential role of Gli1 in anoikis resistance. Treatment of various ovarian cancer cells by different concentrations of diindolylmethane (DIM), an active ingredient of cruciferous vegetables, reduced the anoikis resistance in a concentration-dependent manner. Reduction in anoikis resistance was associated with a decrease in the expression of Gli1 and an increase in the cleavage of poly(ADP-ribose) polymerase (PARP). Sonic hedgehog (Shh) treatment not only increased the expression of Gli1, but also blocked anoikis induced by DIM and abrogated the change in the expression of Gli1 and cleaved PARP by DIM. To confirm the role of Gli1, hedgehog inhibitor cyclopamine, Gli1 siRNA and Gli1(-/-) mouse embryonic fibroblasts (MEFs) were used. Cyclopamine treatment alone significantly reduced anoikis resistance in A2780 and OVCAR-429 cells. Cyclopamine-mediated reduction in anoikis resistance was associated with reduced expression of Gli1 and induction of cleaved PARP. Shh treatment blocked cyclopamine-induced anoikis. Silencing Gli1 expression induced anoikis and cleavage of PARP in A2780 and OVCAR-429 cells. Furthermore, Gli1(-/-) MEFs were more sensitive to anoikis compared with Gli1(+/+) MEFs. Our in vivo studies established that DIM- or cyclopamine-treated ovarian cancer cells under suspension culture conditions drastically lost their ability of tumor formation in vivo in mice. Taken together, our results establish that Gli1 is a critical player in anoikis resistance in ovarian cancer.

Extrinsic aging: UV-mediated skin carcinogenesis

Age-associated skin lesions linked to UV radiation (UVR) include actinic keratosis, non-melanoma skin cancer-such as basal cell carcinoma and squamous cell carcinoma-lentigo senilis and lentigo maligna. Their incidence is increasing worldwide, mainly due to exaggerated UV exposure and to an aging population. Early diagnosis and therapy of pre-malignant cutaneous lesions is crucial for the secondary prophylaxis of invasive and highly aggressive skin cancers. Combined efforts to increase public awareness, patient education about self-examination, prophylactic modalities, such as consistent and sufficient UV protection, and rigorous follow-up of high-risk groups are of highest importance.

The hedgehog processing pathway is required for NSCLC growth and survival

Considerable interest has been generated from the results of recent clinical trials using smoothened (SMO) antagonists to inhibit the growth of hedgehog (HH) signaling-dependent tumors. This interest is tempered by the discovery of SMO mutations mediating resistance, underscoring the rationale for developing therapeutic strategies that interrupt HH signaling at levels distinct from those inhibiting SMO function. Here, we demonstrate that HH-dependent non-small cell lung carcinoma (NSCLC) growth is sensitive to blockade of the HH pathway upstream of SMO, at the level of HH ligand processing. Individually, the use of different lentivirally delivered shRNA constructs targeting two functionally distinct HH-processing proteins, skinny hedgehog (SKN) or dispatched-1 (DISP-1), in NSCLC cell lines produced similar decreases in cell proliferation and increased cell death. Further, providing either an exogenous source of processed HH or a SMO agonist reverses these effects. The attenuation of HH processing, by knocking down either of these gene products, also abrogated tumor growth in mouse xenografts. Finally, we extended these findings to primary clinical specimens, showing that SKN is frequently overexpressed in NSCLC and that higher DISP-1 expression is associated with an unfavorable clinical outcome. Our results show a critical role for HH processing in HH-dependent tumors, identifies two potential druggable targets in the HH pathway, and suggest that similar therapeutic strategies could be explored to treat patients harboring HH ligand-dependent cancers.

Cetuximab in refractory skin cancer treatment

Objectives: Non-melanoma skin cancer is the most common malignancy in US, with an annual incidence of in excess of 1.5 million cases. In the majority of cases, locoregional treatment is curative and systemic therapy is not indicated. Platinum-based chemotherapy regimens have been used most commonly in refractory cases. The use of cetuximab, a monoclonal antibody targeting epidermal growth factor receptor [EGFR], has been reported for skin cancer treatment. This current study evaluated eight cases of locally advanced and refractory basal cell or squamous cell cancers which were treated with cetuximab.

Methods: This is a retrospective study on eight patients who had received cetuximab for treatment of cutaneous carcinoma since 2007 at Southern Illinois University School of Medicine (SIU-SOM) Medical Oncology clinic.

Results: Three of the four patients with basal cell carcinoma and two of the four patients with squamous cell carcinoma maintained remission on treatment.. The main side effect was acneiform rash which required termination of treatment for one patient and dose reduction in another.

Conclusion: The study indicates that cetuximab may have a beneficial role for patients with non-melanoma cutaneous carcinomas that are refractory to standard therapy.

Hedgehog inhibitor decreases chemosensitivity to 5-fluorouracil and gemcitabine under hypoxic conditions in pancreatic cancer

Pancreatic cancer is one of the deadliest types of cancer. Previously, we showed that hypoxia increases invasiveness through upregulation of Smoothened (Smo) transcription in pancreatic ductal adenocarcinoma (PDAC) cells. Here, we first evaluated whether hypoxia-induced increase in Smo contributes to the proliferation of PDAC cells. We showed that Smo, but not Gli1, inhibition decreases proliferation significantly under hypoxic conditions. To further investigate the effects of Smo on PDAC growth, cell cycle analysis was carried out. Inhibition of Smo under hypoxia led to G(0) /G(1) arrest and decreased S phase. As 5-fluorouracil (5-FU) and gemcitabine, which are first-line drugs for pancreatic cancer, are sensitive to S phase, we then evaluated whether cyclopamine-induced decreased S phase under hypoxia affected the chemosensitivity of 5-FU and gemcitabine in PDAC cells. Cyclopamine treatment under hypoxia significantly decreased chemosensitivity to 5-FU and gemcitabine under hypoxia in both in vitro and in vivo models. In contrast, cis-diamminedichloroplatinum, which is cell cycle-independent, showed significant synergistic effects. These results suggest that hypoxia-induced increase of Smo directly contributes to the proliferation of PDAC cells through a hedgehog/Gli1-independent pathway, and that decreased S phase due to the use of Smo inhibitor under hypoxia leads to chemoresistance in S phase-sensitive anticancer drugs. Our results could be very important clinically because a clinical trial using Smo inhibitors and chemotherapy drugs will begin in the near future.

Medulloblastoma/Primitive neuroectodermal tumor and germ cell tumors: the uncommon but potentially curable primary brain tumors

This article presents an overview of medulloblastomas, central nervous system primitive neuroectodermal tumors, and germ cell tumors for the practicing oncologist. Discussion includes the definition of these tumors, histopathologic findings, molecular and genetic characteristics, prognoses, and evolution of treatment.

Cancer drug pan-resistance: pumps, cancer stem cells, quiescence, epithelial to mesenchymal transition, blocked cell death pathways, persisters or what?

Although chemotherapy of tumours has scored successes, drug resistance remains the major cause of death of cancer patients. Initial treatment often leaves residual disease, from which the tumour regrows. Eventually, most tumours become resistant to all available chemotherapy. I call this pan-resistance to distinguish it from multi-drug resistance, usually describing resistance caused by upregulation of drug transporters, such as P-glycoprotein. In this review, I discuss mechanisms proposed to explain both residual disease and pan-resistance. Although plausible explanations are at hand for residual disease, pan-resistance is still a mystery. My conclusion is that it is time for a major effort to solve this mystery using the new genetically modified mouse tumour models that produce real tumours resembling cancer in human patients.

The activity of Gli transcription factors is essential for Kras-induced pancreatic tumorigenesis

Pancreatic ductal adenocarcinoma (PDAC), one of the most aggressive human malignancies, is thought to be initiated by KRAS activation. Here we find that transcriptional activation mediated by the Gli family of transcription factors, although dispensable for pancreatic development, is required for Kras-induced proliferation and survival in primary pancreatic epithelial cells in culture and for Kras-driven pancreatic intraepithelial neoplasia and PDAC formation in vivo. Further, ectopic Gli1 activation in the mouse pancreas accelerates Kras-driven tumor formation, underscoring the importance of Gli transcription factors in pancreatic tumorigenesis. Interestingly, we demonstrate Gli-regulated I-kappa-B kinase epsilon (IKBKE) and NF-κB activity in pancreatic cancer cells and show that this activity is a critical downstream mediator for Gli-dependent PDAC cell transformation and survival. Together, these studies demonstrate the requirement for Gli in Kras-dependent pancreatic epithelial transformation, suggest a mechanism of Gli-NF-κB oncogenic activation, and provide genetic evidence supporting the therapeutic targeting of Gli activity in pancreatic cancer.

Biological and clinical heterogeneity of MYCN-amplified medulloblastoma

Focal high-level amplifications of MYC (or MYCC) define a subset of high-risk medulloblastoma patients. However, the prognostic role of MYCN oncogene amplification remains unresolved. We aimed to evaluate the prognostic value of this alteration alone and in combination with biological modifiers in 67 pediatric medulloblastomas with MYCN amplification (MYCN-MB). Twenty-one MYCN-MB were examined using gene expression profiling and array-CGH, whereas for 46 tumors immunohistochemical analysis and FISH were performed. All 67 tumors were further subjected to mutational analyses. We compared molecular, clinical, and prognostic characteristics both within biological MYCN-MB groups and with non-amplified tumors. Transcriptomic analysis revealed SHH-driven tumorigenesis in a subset of MYCN-MBs indicating a biological dichotomy of MYCN-MB. Activation of SHH was accompanied by variant-specific cytogenetic aberrations including deletion of 9q in SHH tumors. Non-SHH MB were associated with gain of 7q and isochromosome 17q/17q gain. Among clinically relevant variables, SHH subtype and 10q loss for non-SHH tumors comprised the most powerful markers of favorable prognosis in MYCN-MB. In conclusion, we demonstrate considerable heterogeneity within MYCN-MB in terms of genetics, tumor biology, and clinical outcome. Thus, assessment of disease group and 10q copy-number status may improve risk stratification of this group and may delineate MYCN-MB with the same dismal prognosis as MYC amplified tumors. Furthermore, based on the enrichment of MYCN and GLI2 amplifications in SHH-driven medulloblastoma, amplification of these downstream signaling intermediates should be taken into account before a patient is enrolled into a clinical trial using a smoothened inhibitor.

Rapid, reliable, and reproducible molecular sub-grouping of clinical medulloblastoma samples

The diagnosis of medulloblastoma likely encompasses several distinct entities, with recent evidence for the existence of at least four unique molecular subgroups that exhibit distinct genetic, transcriptional, demographic, and clinical features. Assignment of molecular subgroup through routine profiling of high-quality RNA on expression microarrays is likely impractical in the clinical setting. The planning and execution of medulloblastoma clinical trials that stratify by subgroup, or which are targeted to a specific subgroup requires technologies that can be economically, rapidly, reliably, and reproducibly applied to formalin-fixed paraffin embedded (FFPE) specimens. In the current study, we have developed an assay that accurately measures the expression level of 22 medulloblastoma subgroup-specific signature genes (CodeSet) using nanoString nCounter Technology. Comparison of the nanoString assay with Affymetrix expression array data on a training series of 101 medulloblastomas of known subgroup demonstrated a high concordance (Pearson correlation r = 0.86). The assay was validated on a second set of 130 non-overlapping medulloblastomas of known subgroup, correctly assigning 98% (127/130) of tumors to the appropriate subgroup. Reproducibility was demonstrated by repeating the assay in three independent laboratories in Canada, the United States, and Switzerland. Finally, the nanoString assay could confidently predict subgroup in 88% of recent FFPE cases, of which 100% had accurate subgroup assignment. We present an assay based on nanoString technology that is capable of rapidly, reliably, and reproducibly assigning clinical FFPE medulloblastoma samples to their molecular subgroup, and which is highly suited for future medulloblastoma clinical trials.

Gli inhibitor GANT61 causes apoptosis in myeloid leukemia cells and acts in synergy with rapamycin

Aberrant reactivation of Gli signaling has been described in a wide variety of human cancers and rapamycin can down-regulate Gli pathway in some solid tumors. In this study, we attempt to define the cytotoxic effect of Gli inhibitor on AML cells. And the regulation action of rapamycin on Gli in AML cells also has been assessed. Gli inhibitor GANT61 caused growth arrest and apoptosis in AML cells. Rapamycin decreased not only the Gli protein and mRNA expressions but also expression of the Gli-luciferase reporter in AML cells. Synergism effect between GANT61 and rapamycin was found in Kasumi-1, HL-60 and U937 cell lines. The results suggest that aberrant Gli activation is a feature of some myeloid leukemic cells and Gli activiation can be down-regulated by rapamycin.

The molecular classification of medulloblastoma: driving the next generation clinical trials

PURPOSE OF REVIEW

Most children diagnosed with cancer today are expected to be cured. Medulloblastoma, the most common pediatric malignant brain tumor, is an example of a disease that has benefitted from advances in diagnostic imaging, surgical techniques, radiation therapy and combination chemotherapy over the past decades. It was an incurable disease 50 years ago, but approximately 70% of children with medulloblastoma are now cured of their disease. However, the pace of increasing the cure rate has slowed over the past 2 decades, and we have likely reached the maximal benefit that can be achieved with cytotoxic therapy and clinical risk stratification. Long-term toxicity of therapy also remains significant. To increase cure rates and decrease long-term toxicity, there is great interest in incorporating biologic 'targeted' therapy into treatment of medulloblastoma, but this will require a paradigm shift in how we classify and study disease.

RECENT FINDINGS

Using genome-based high-throughput analytic techniques, several groups have independently reported methods of molecular classification of medulloblastoma within the past year. This has resulted in a working consensus to view medulloblastoma as four molecular subtypes, including wingless-type murine mammary tumor virus integration site (WNT) pathway subtype, Sonic Hedgehog pathway subtype and two less well defined subtypes (groups C and D).

SUMMARY

Novel classification and risk stratification based on biologic subtypes of disease will form the basis of further study in medulloblastoma and identify specific subtypes that warrant greater research focus.

The GLI genes as the molecular switch in disrupting Hedgehog signaling in colon cancer

The Hedgehog (HH) signaling pathway leads to activation of GLI, which transcriptionally regulate target genes. Regulated HH signaling activity is critical during embryogenesis while aberrantly activated HH signaling is evident in a variety of human cancers. Canonical HH signaling engages the transmembrane receptor Patched (PTCH) and the signaling intermediate Smoothened (SMO) to activate GLI1 and GLI2. In addition GLI1 and GLI2 are activated by non-canonical oncogenic signaling pathways to further drive HH-dependent survival. We have demonstrated in human colon carcinoma cells that inhibition of the RAS/RAF pathway by U0126 decreases p-ERK protein expression and also inhibits GLI-luciferase activity and GLI1 mRNA and protein levels. Of importance is the demonstration that targeting of SMO (using cyclopamine) has minimal effect on cell survival in comparison to the inhibition of GLI (using GANT61), which induced extensive cell death in 7/7 human colon carcinoma cell lines. Genetic inhibition of the function of GLI1 and GLI2 by transient transfection of the C-terminus deleted repressor GLI3R, reduced proliferation and induced cleavage of caspase-3 and cell death in HT29 cells, similar to the effects of GANT61. Mechanistically, downstream of GLI1 and GLI2 inhibition, γH2AX (a marker of DNA double strand breaks) expression was upregulated, and γH2AX nuclear foci were demonstrated in cells that expressed GLI3R. Activation of the ATM/Chk2 axis with co-localization of γH2AX and p-Chk2 nuclear foci were demonstrated following GLI1/GLI2 inhibition. GANT61 induced cellular accumulation at G1/S and early S with no further progression before cells became subG1, while cDNA microarray gene profiling demonstrated downregulation of genes involved in DNA replication, the DNA damage response, and DNA repair, mechanisms that are currently being pursued. These studies highlight the importance of targeting the GLI genes downstream of SMO for terminating HH-dependent survival, suggesting that GLI may constitute a molecular switch that determines the balance between cell survival and cell death in human colon carcinoma.

The epigenetics of brain tumors

Glioblastoma, medulloblastoma, and ependymoma represent molecularly and clinically diverse forms of adult and pediatric brain tumors. While each tumor displays genetic, transcriptional, and cytogenetic heterogeneity, the epigenome of these tumors has only recently emerged as a major field of interest. Here, we describe advances in our understanding of the epigenetics of brain tumors, focusing on DNA methylation, histone modifications, and microRNA deregulation which contribute to the pathogenesis of these diseases.

The role of cancer-associated myofibroblasts in intrahepatic cholangiocarcinoma

Intrahepatic cholangiocarcinoma is typically characterized by a dense desmoplastic stroma, of which cancer-associated myofibroblasts (which express α-smooth muscle actin), are a major cellular component. These stromal myofibroblasts have a crucial role in accelerating the progression of intrahepatic cholangiocarcinoma and in promoting resistance to therapy through interactive autocrine and paracrine signaling pathways that promote malignant cell proliferation, migration, invasiveness, apoptosis resistance and/or epithelial-mesenchymal transition. These changes correlate with aggressive tumor behavior. Hypoxic desmoplasia and aberrant Hedgehog signaling between stromal myofibroblastic cells and cholangiocarcinoma cells are also critical modulators of intrahepatic cholangiocarcinoma progression and therapy resistance. A novel strategy has been developed to achieve improved therapeutic outcomes in patients with advanced intrahepatic cholangiocarcinoma, based on targeting of multiple interactive pathways between cancer-associated myofibroblasts and intrahepatic cholangiocarcinoma cells that are associated with disease progression and poor survival. Unique organotypic cell culture and orthotopic rat models of cholangiocarcinoma progression are well suited to the rapid preclinical testing of this potentially paradigm-shifting strategy.

The role of cancer-associated myofibroblasts in intrahepatic cholangiocarcinoma

Intrahepatic cholangiocarcinoma is typically characterized by a dense desmoplastic stroma, of which cancer-associated myofibroblasts (which express α-smooth muscle actin), are a major cellular component. These stromal myofibroblasts have a crucial role in accelerating the progression of intrahepatic cholangiocarcinoma and in promoting resistance to therapy through interactive autocrine and paracrine signaling pathways that promote malignant cell proliferation, migration, invasiveness, apoptosis resistance and/or epithelial-mesenchymal transition. These changes correlate with aggressive tumor behavior. Hypoxic desmoplasia and aberrant Hedgehog signaling between stromal myofibroblastic cells and cholangiocarcinoma cells are also critical modulators of intrahepatic cholangiocarcinoma progression and therapy resistance. A novel strategy has been developed to achieve improved therapeutic outcomes in patients with advanced intrahepatic cholangiocarcinoma, based on targeting of multiple interactive pathways between cancer-associated myofibroblasts and intrahepatic cholangiocarcinoma cells that are associated with disease progression and poor survival. Unique organotypic cell culture and orthotopic rat models of cholangiocarcinoma progression are well suited to the rapid preclinical testing of this potentially paradigm-shifting strategy.

Investigational Notch and Hedgehog inhibitors--therapies for cardiovascular disease

INTRODUCTION

During the past decade, a variety of Notch and Hedgehog pathway inhibitors have been developed for the treatment of several cancers. An emerging paradigm suggests that these same gene regulatory networks are often recapitulated in the context of cardiovascular disease and may now offer an attractive target for therapeutic intervention.

AREAS COVERED

This article briefly reviews the profile of Notch and Hedgehog inhibitors that have reached the preclinic and clinic for cancer treatment and discusses the clinical issues surrounding targeted use of these inhibitors in the treatment of vascular disorders.

EXPERT OPINION

Preclinical and clinical data using pan-Notch inhibitors (γ-secretase inhibitors) and selective antibodies to preferentially target notch receptors and ligands have proven successful but concerns remain over normal organ homeostasis and significant pathology in multiple organs. By contrast, the Hedgehog-based drug pipeline is rich with more than a dozen Smoothened (SMO) inhibitors at various stages of development. Overall, refined strategies will be necessary to harness these pathways safely as a powerful tool to disrupt angiogenesis and vascular proliferative phenomena without causing prohibitive side effects already seen with cancer models and patients.

Direct in vivo evidence for tumor propagation by glioblastoma cancer stem cells

High-grade gliomas (World Health Organization grade III anaplastic astrocytoma and grade IV glioblastoma multiforme), the most prevalent primary malignant brain tumors, display a cellular hierarchy with self-renewing, tumorigenic cancer stem cells (CSCs) at the apex. While the CSC hypothesis has been an attractive model to describe many aspects of tumor behavior, it remains controversial due to unresolved issues including the use of ex vivo analyses with differential growth conditions. A CSC population has been confirmed in malignant gliomas by preferential tumor formation from cells directly isolated from patient biopsy specimens. However, direct comparison of multiple tumor cell populations with analysis of the resulting phenotypes of each population within a representative tumor environment has not been clearly described. To directly test the relative tumorigenic potential of CSCs and non-stem tumor cells in the same microenvironment, we interrogated matched tumor populations purified from a primary human tumor transplanted into a xenograft mouse model and monitored competitive in vivo tumor growth studies using serial in vivo intravital microscopy. While CSCs were a small minority of the initial transplanted cancer cell population, the CSCs, not the non-stem tumor cells, drove tumor formation and yielded tumors displaying a cellular hierarchy. In the resulting tumors, a fraction of the initial transplanted CSCs maintained expression of stem cell and proliferation markers, which were significantly higher compared to the non-stem tumor cell population and demonstrated that CSCs generated cellular heterogeneity within the tumor. These head-to-head comparisons between matched CSCs and non-stem tumor cells provide the first functional evidence using live imaging that in the same microenvironment, CSCs more than non-stem tumor cells are responsible for tumor propagation, confirming the functional definition of a CSC.

The hedgehog receptor patched is involved in cholesterol transport

Background

Sonic hedgehog (Shh) signaling plays a crucial role in growth and patterning during embryonic development, and also in stem cell maintenance and tissue regeneration in adults. Aberrant Shh pathway activation is involved in the development of many tumors, and one of the most affected Shh signaling steps found in these tumors is the regulation of the signaling receptor Smoothened by the Shh receptor Patched. In the present work, we investigated Patched activity and the mechanism by which Patched inhibits Smoothened.

Methodology/Principal Findings

Using the well-known Shh-responding cell line of mouse fibroblasts NIH 3T3, we first observed that enhancement of the intracellular cholesterol concentration induces Smoothened enrichment in the plasma membrane, which is a crucial step for the signaling activation. We found that binding of Shh protein to its receptor Patched, which involves Patched internalization, increases the intracellular concentration of cholesterol and decreases the efflux of a fluorescent cholesterol derivative (BODIPY-cholesterol) from these cells. Treatment of fibroblasts with cyclopamine, an antagonist of Shh signaling, inhibits Patched expression and reduces BODIPY-cholesterol efflux, while treatment with the Shh pathway agonist SAG enhances Patched protein expression and BODIPY-cholesterol efflux. We also show that over-expression of human Patched in the yeast S. cerevisiae results in a significant boost of BODIPY-cholesterol efflux. Furthermore, we demonstrate that purified Patched binds to cholesterol, and that the interaction of Shh with Patched inhibits the binding of Patched to cholesterol.

Conclusion/Significance

Our results suggest that Patched may contribute to cholesterol efflux from cells, and to modulation of the intracellular cholesterol concentration. This activity is likely responsible for the inhibition of the enrichment of Smoothened in the plasma membrane, which is an important step in Shh pathway activation.

Hedgehog signaling pathway as a therapeutic target in various types of cancer

Hedgehog (Hh) signaling is an important factor in growth and patterning during embryonic development. A mutation in Patched, Smoothened or Gli1, which regulate the Hh signaling pathway, might lead to the onset of glioblastoma, basal cell carcinoma, medulloblastoma and rhabdomyosarcoma. Recently, Hh signaling has been reported to be activated in a ligand-dependent manner, contributing to carcinogenesis and cancer progression. Hedgehog signaling is reactivated in various types of cancer, and this contributes to cancer progression by facilitating proliferation, invasion and cell survival. Moreover, Hh signaling is associated with several other signaling pathways that contribute to cancer progression. These observations indicate that controlling Hh signaling might become a target for novel molecular targeting therapy.

Gli proteins in development and disease

Gli zinc-finger proteins are transcription factors involved in the intracellular signal transduction controlled by the Hedgehog family of secreted molecules. They are frequently mutated in human congenital malformations, and their abnormal regulation leads to tumorigenesis. Genetic studies in several model systems indicate that their activity is tightly regulated by Hedgehog signaling through various posttranslational modifications, including phosphorylation, ubiquitin-mediated degradation, and proteolytic processing, as well as through nucleocytoplasmic shuttling. In vertebrate cells, primary cilia are required for the sensing of Hedgehog pathway activity and involved in the processing and activation of Gli proteins. Two evolutionarily conserved Hedgehog pathway components, Suppressor of fused and Kif7, are core intracellular regulators of mammalian Gli proteins. Recent studies revealed that Gli proteins are also regulated transcriptionally and posttranslationally through noncanonical mechanisms independent of Hedgehog signaling. In this review, we describe the regulation of Gli proteins during development and discuss possible mechanisms for their abnormal activation during tumorigenesis.

Hedgehog signaling: networking to nurture a promalignant tumor microenvironment

In addition to its role in embryonic development, the Hedgehog pathway has been shown to be an active participant in cancer development, progression, and metastasis. Although this pathway is activated by autocrine signaling by Hedgehog ligands, it can also initiate paracrine signaling with cells in the microenvironment. This creates a network of Hedgehog signaling that determines the malignant behavior of the tumor cells. As a result of paracrine signal transmission, the effects of Hedgehog signaling most profoundly influence the stromal cells that constitute the tumor microenvironment. The stromal cells in turn produce factors that nurture the tumor. Thus, such a resonating cross-talk can amplify Hedgehog signaling, resulting in molecular chatter that overall promotes tumor progression. Inhibitors of Hedgehog signaling have been the subject of intense research. Several of these inhibitors are currently being evaluated in clinical trials. Here, we review the role of the Hedgehog pathway in the signature characteristics of cancer cells that determine tumor development, progression, and metastasis. This review condenses the latest findings on the signaling pathways that are activated and/or regulated by molecules generated from Hedgehog signaling in cancer and cites promising clinical interventions. Finally, we discuss future directions for identifying the appropriate patients for therapy, developing reliable markers of efficacy of treatment, and combating resistance to Hedgehog pathway inhibitors.

Hedgehog fights back: mechanisms of acquired resistance against Smoothened antagonists

Acquired resistance to targeted therapies threatens the value of these otherwise very promising agents. The recent description of resistance to the Hedgehog pathway inhibitor vismodegib (GDC-0449) in a medulloblastoma patient who had a dramatic initial response has spurred efforts to understand potential mechanisms of drug resistance. Elucidating these mechanisms will play a significant role in informing strategies to overcome this meaningful limitation.

Cytotoxic T lymphocytes efficiently recognize human colon cancer stem-like cells

Cancer stem-like cells (CSCs) and tumor-initiating cells (TICs) are a small population of cancer cells that share three properties: tumor initiating ability, self-renewal, and differentiation. These properties suggest that CSCs/TICs are essential for tumor maintenance, recurrence, and distant metastasis. Here, we show that cytotoxic T lymphocytes (CTLs) specific for the tumor-associated antigen CEP55 can efficiently recognize colon CSCs/TICs both in vitro and in vivo. Using Hoechst 33342 dye staining, we isolated CSCs/TICs as side population (SP) cells from colon cancer cell lines SW480, HT29, and HCT15. The SP cells expressed high levels of the stem cell markers SOX2, POU5F1, LGR5, and ALDH1A1 and showed resistance to chemotherapeutic agents such as irinotecan or etoposide.To evaluate the susceptibility of SP cells to CTLs, we used CTL clone 41, which is specific for the CEP55-derived antigenic peptide Cep55/c10orf3_193 (10) (VYVKGLLAKI). The SP cells expressed HLA class I and CEP55 at the same level as the main population cells. The SP cells were susceptible to CTL clone 41 at the same level as main population cells. Furthermore, adoptive transfer of CTL clone 41 inhibited tumor growth of SW480 SP cells in vivo. These observations suggest that Cep55/c10orf3_193(10) peptide-based cancer vaccine therapy or adoptive cell transfer of the CTL clone is a possible approach for targeting chemotherapy-resistant colon CSCs/TICs.

A novel synthetic smoothened antagonist transiently inhibits pancreatic adenocarcinoma xenografts in a mouse model

BACKGROUND

Hedgehog (Hh) signaling is over-activated in several solid tumors where it plays a central role in cell growth, stroma recruitment and tumor progression. In the Hh signaling pathway, the Smoothened (SMO) receptor comprises a primary drug target with experimental small molecule SMO antagonists currently being evaluated in clinical trials.

PRINCIPAL FINDINGS

Using Shh-Light II (Shh-L2) and alkaline phosphatase (AP) based screening formats on a "focused diversity" library we identified a novel small molecule inhibitor of the Hh pathway, MS-0022 (2-bromo-N-(4-(8-methylimidazo[1,2-a]pyridin-2-yl)phenyl)benzamide). MS-0022 showed effective Hh signaling pathway inhibition at the level of SMO in the low nM range, and Hh pathway inhibition downstream of Suppressor of fused (SUFU) in the low µM range. MS-0022 reduced growth in the tumor cell lines PANC-1, SUIT-2, PC-3 and FEMX in vitro. MS-0022 treatment led to a transient delay of tumor growth that correlated with a reduction of stromal Gli1 levels in SUIT-2 xenografts in vivo.

SIGNIFICANCE

We document the in vitro and in vivo efficacy and bioavailability of a novel small molecule SMO antagonist, MS-0022. Although MS-0022 primarily interferes with Hh signaling at the level of SMO, it also has a downstream inhibitory effect and leads to a stronger reduction of growth in several tumor cell lines when compared to related SMO antagonists.

Stem cell biology and drug discovery

There are many reasons to be interested in stem cells, one of the most prominent being their potential use in finding better drugs to treat human disease. This article focuses on how this may be implemented. Recent advances in the production of reprogrammed adult cells and their regulated differentiation to disease-relevant cells are presented, and diseases that have been modeled using these methods are discussed. Remaining difficulties are highlighted, as are new therapeutic insights that have emerged.

Adult medulloblastoma comprises three major molecular variants

PURPOSE

Medulloblastoma is a rare primary brain tumor in adults, whereas it constitutes the most common malignant brain tumor in children. Integrated genomics approaches revealed at least four distinct disease variants in children. The aim of this study was to investigate molecular subtypes and their prognostic implication in a large cohort of adult medulloblastomas as the biology in this age group remains poorly understood.

PATIENTS AND METHODS

We combined transcriptome and DNA copy number analyses for 28 adult medulloblastomas. Statistical and bioinformatic tools were applied to discover distinct molecular variants. Clinical and molecular characteristics of each biologic subtype were validated using immunohistochemistry on a tissue microarray derived from an independent patient cohort of adult medulloblastomas (n = 103).

RESULTS

Gene expression profiles revealed three distinct molecular variants with stable subtype separation using the 300 most varying transcripts. Distinct demographics, genetics, transcriptome, and prognosis were noted for each subtype of adult medulloblastoma. Immunohistochemistry revealed aberrant activation of the sonic hedgehog (SHH) pathway in over half of adult medulloblastomas constituting a promising molecular therapeutic target. In contrast, subtype C tumors, which comprise a robust subtype in childhood medulloblastoma are only exceptionally seen in adult cohorts. Notably, adult subtype D and Wnt/wingless tumors were associated with worse prognosis than pediatric cohorts, whereas survival for SHH tumors was similar for both age groups.

CONCLUSION

The transcriptome of adult medulloblastomas differs considerably from pediatric counterparts, both in terms of tumor biology and prognostic impact. Therefore, age-specific classification is required and must be adapted for use in clinical trials of adult medulloblastoma.

The Hedgehog's tale: developing strategies for targeting cancer

Research into basic developmental biology has frequently yielded insights into cancer biology. This is particularly true for the Hedgehog (HH) pathway. Activating mutations in the HH pathway cause a subset of sporadic and familial, skin (basal cell carcinoma) and brain (medulloblastoma) tumours. Furthermore, the growth of many human tumours is supported by HH pathway activity in stromal cells. Naturally occurring and synthetic inhibitors of HH signalling show great promise in animal models and in early clinical studies. However, it remains unclear how many cancers will ultimately benefit from these new, molecularly targeted therapies.

Cancer stem cells: characteristics and their potential role for new therapeutic strategies

With the cancer stem cell (CSC) hypothesis many questions regarding cancer development and drug resistance can be answered more coherently than with the traditional model based on clonal evolution. CSCs are a small subset of cancer cells within the tumour that show stem cell characteristics like self-renewal, the capability to develop into multiple lineages and the potential to proliferate extensively, and are characterised by a typical profile of different markers like CD44 and CD133. In the CSC model, the role of embryonic pathways like Wnt, Hedgehog and Notch is of special interest. This review presents current scientific knowledge on this topic and discusses the potential role of CSC in the resistance against chemotherapy or radiation and presents challenging options for therapeutic interventions.

Mechanisms and functions of Hedgehog signalling across the metazoa

Hedgehog proteins constitute one of a small number of families of secreted signals that have a central role in the development of metazoans. Genetic analyses in flies, fish and mice have uncovered the major components of the pathway that transduces Hedgehog signals, and recent genome sequence projects have provided clues about its evolutionary origins. In this Review we provide an updated overview of the mechanisms and functions of this signalling pathway, highlighting the conserved and divergent features of the pathway, as well as some of the common themes in its deployment that have emerged from recent studies.

Glioma-associated oncogene family zinc finger 1 expression and metastasis in patients with head and neck squamous cell carcinoma treated with radiation therapy (RTOG 9003)

PURPOSE

Glioma-associated oncogene family zinc finger 1 (GLI1) expression was assessed to determine a potential role of hedgehog (Hh) signaling in head and neck squamous cell carcinoma (HNSCC). Additional proteins known to be modulated by Hh signaling, including beta-catenin (CTNNB1) and epidermal growth factor receptor (EGFR), were also assessed to determine the correlation among these distinct signaling pathways.

PATIENTS AND METHODS

Nuclear GLI1 and CTNNB1 expression levels were determined in tumors from patients enrolled on Radiation Therapy Oncology Group (RTOG) 9003, a radiation fractionation trial. The results were also correlated with previously determined EGFR expression. The expression levels were evaluated in relation to three end points: time to metastasis (TTM), time to disease progression (TDP), and overall survival (OS).

RESULTS

Among 1,068 eligible patients, data on GLI1, CTNNB1, and EGFR were available in 339, 164, and 300 patients, respectively. Although CTNNB1 expression did not differentiate prognosis, GLI1 was associated with poorer outcomes, adjusted for age, TNM stages, and Karnofsky performance score, and the significant influence persisted in a multivariable analysis (quartile 4 [Q4] v Q1 to Q3: TTM hazard ratio [HR], 2.7; 95% CI, 1.5 to 4.9; TDP HR, 1.6; 95% CI, 1.1 to 2.5; OS HR, 1.9; 95% CI, 1.4 to 2.7). The significance of GLI1 persisted in a multivariable analysis that included EGFR expression levels.

CONCLUSION

These data suggest that Hh signaling may play an important role in metastasis and that GLI1 could serve as a marker in HNSCC, but the regulatory mechanisms and oncogenic significance need further investigation. Risk classification based on this analysis needs a validation in independent cohorts.