Inhibition of the hedgehog pathway in advanced basal-cell carcinoma

Immunolocalization of glioma-associated oncogene homolog 1 in non melanoma skin cancer

Glioma-associated oncogene homolog (GLI)1 is involved in controlling cell proliferation and angiogenesis. The aim of this work was to explore its possible role in non-melanoma skin cancer pathogenesis through its immunohistochemical (IHC) expression in skin biopsies of these diseases and correlating this expression with the clinico-pathological parameters of the studied cases. Seventy-six cutaneous specimens were studied; 30 cases with basal cell carcinoma (BCC), 30 cases with squamous cell carcinoma (SCC) and 16 normal skin samples, from age- and gender-matched subjects, as a control group. GLI1 was expressed in all BCC cases and in 60% of SCC cases. All SCC cases showed cytoplasmic, while 70% of BCC cases showed nucleocytoplasmic immunoreactivity. It was over expressed in BCC and SCC compared to normal skin (p = 0.01 and 0.0006, respectively). Higher Histo (H) score in BCC cases was significantly associated with female gender (p = 0.04), multiple lesions, desmoplastic stromal reaction and stromal angiogenesis (p < 0.001 for all). Higher H score in SCC cases was significantly associated with scalp location, nodular type, recurrent lesions, high tumor grade, lymphovascular invasion (p = 0.004 for all), inflammatory stromal reaction (p = 0.01), lymph node involvement and absence of calcification (p = 0.001 for both). In conclusion, GLI1 may play a role in BCC pathogenesis through its role in cell proliferation, migration, and angiogenesis. Its upregulation and cytoplasmic localization in SCC may suggest that its role in tumor pathogenesis is through mechanisms other than Hedgehog pathway activation. Further studies are needed to clarify the exact molecular basis of its oncogenic action.

Hedgehog signaling pathway: a novel target for cancer therapy: vismodegib, a promising therapeutic option in treatment of basal cell carcinomas

The Hedgehog signaling pathway is one of the major regulators of cell growth and differentiation during embryogenesis and early development. It is mostly quiescent in adults but inappropriate mutation or deregulation of the pathway is involved in the development of cancers. Therefore; recently it has been recognized as a novel therapeutic target in cancers. Basal cell carcinomas (BCC) and medulloblastomas are the two most common cancers identified with mutations in components of the hedgehog pathway. The discovery of targeted Hedgehog pathway inhibitors has shown promising results in clinical trials, several of which are still undergoing clinical evaluation. Vismodegib (GDC-0449), an oral hedgehog signaling pathway inhibitor has reached the farthest in clinical development. Initial clinical trials in basal cell carcinoma and medulloblastoma have shown good efficacy and safety and hence were approved by U.S. FDA for use in advanced basal cell carcinomas. This review highlights the molecular basis and the current knowledge of hedgehog pathway activation in different types of human cancers as well as the present and future prospects of the novel drug vismodegib.

Challenges and new horizons in the management of advanced basal cell carcinoma: a UK perspective

Basal cell carcinoma (BCC) is a common malignancy with a good prognosis in the majority of cases. However, some BCC patients develop a more advanced disease that poses significant management challenges. Such cases include locally advanced, recurrent or metastatic BCC, or tumours that occur in anatomical sites where surgical treatment would result in significant deformity. Until recently, treatment options for these patients have been limited, but increased understanding of the molecular basis of BCC has enabled potential therapies, such as hedgehog signalling pathway inhibitors, to be developed. A clear definition of advanced BCC as a distinct disease entity and formal management guidelines have not previously been published, presumably because of the rarity, heterogeneity and lack of treatment options available for the disease. Here we provide a UK perspective from a multidisciplinary group of experts involved in the treatment of complex cases of BCC, addressing the key challenges associated with the perceived definition and management of the disease. With new treatments on the horizon, we further propose a definition for advanced BCC that may be used as a guide for healthcare professionals involved in disease diagnosis and management.

Strategies for modern biomarker and drug development in oncology

Technological advancements in the molecular characterization of cancers have enabled researchers to identify an increasing number of key molecular drivers of cancer progression. These discoveries have led to multiple novel anticancer therapeutics, and clinical benefit in selected patient populations. Despite this, the identification of clinically relevant predictive biomarkers of response continues to lag behind. In this review, we discuss strategies for the molecular characterization of cancers and the importance of biomarkers for the development of novel antitumor therapeutics. We also review critical successes and failures in oncology, and detail the lessons learnt, which may aid in the acceleration of anticancer drug development and biomarker discovery.

Gorlin syndrome (nevoid basal cell carcinoma syndrome): update and literature review

Gorlin syndrome, also called nevoid basal cell carcinoma syndrome, is an autosomal dominant neurocutaneous disease characterized by developmental anomalies such as palmar pits and rib anomaly, and tumorigenesis such as medulloblastoma and basal cell carcinoma. This syndrome is mainly caused by a mutation of PTCH1, a human homologue of Drosophila patched, including frameshift, missense, or nonsense mutations. Genotype-phenotype correlation has not been established. PTCH1 is a member of hedgehog signaling, which is a highly conserved pathway in vertebrates, composed of hedgehog, SMO, and GLI proteins as well as PTCH1. Given that hedgehog signaling regulates cell growth and development, disorder of this pathway gives rise to not only developmental anomalies but also diverse tumors such as those seen in Gorlin syndrome. We recently reported, for the first time, a nationwide survey of Gorlin syndrome in Japan, noting that the frequency was 1/235,800 in the Japanese population, and that the frequency of basal cell carcinomas was significantly lower in Japan than in the USA and Europe, suggesting that ethnicity and genetic background contribute to these differences. Given that many clinical trials using newly discovered molecular inhibitors are still ongoing, these agents should become the new therapeutic options for hedgehog pathway-dependent tumors in patients with or without Gorlin syndrome.

Smoothened (SMO) receptor mutations dictate resistance to vismodegib in basal cell carcinoma

Basal cell carcinomas (BCCs) and a subset of medulloblastomas are characterized by loss-of-function mutations in the tumor suppressor gene, PTCH1. PTCH1 normally functions by repressing the activity of the Smoothened (SMO) receptor. Inactivating PTCH1 mutations result in constitutive Hedgehog pathway activity through uncontrolled SMO signaling. Targeting this pathway with vismodegib, a novel SMO inhibitor, results in impressive tumor regression in patients harboring genetic defects in this pathway. However, a secondary mutation in SMO has been reported in medulloblastoma patients following relapse on vismodegib to date. This mutation preserves pathway activity, but appears to confer resistance by interfering with drug binding. Here we report for the first time on the molecular mechanisms of resistance to vismodegib in two BCC cases. The first case, showing progression after 2 months of continuous vismodegib (primary resistance), exhibited the new SMO G497W mutation. The second case, showing a complete clinical response after 5 months of treatment and a subsequent progression after 11 months on vismodegib (secondary resistance), exhibited a PTCH1 nonsense mutation in both the pre- and the post-treatment specimens, and the SMO D473Y mutation in the post-treatment specimens only. In silico analysis demonstrated that SMO(G497W) undergoes a conformational rearrangement resulting in a partial obstruction of the protein drug entry site, whereas the SMO D473Y mutation induces a direct effect on the binding site geometry leading to a total disruption of a stabilizing hydrogen bond network. Thus, the G497W and D473Y SMO mutations may represent two different mechanisms leading to primary and secondary resistance to vismodegib, respectively.

Targeting EGFR and sonic hedgehog pathways for locally advanced eyelid and periocular carcinomas

For patients with metastatic or locally advanced eyelid and periocular carcinoma not amenable to surgical excision, targeted therapies have shown efficacy with better tolerability compared to cytotoxic chemotherapy. Overexpression of epithelial growth factor receptor was found in squamous cell carcinomas. Vismodegib targets the mutation in the hedgehog pathway identified in basal cell carcinoma and basal cell nevus syndrome. Targeted therapies provide a novel and potentially effective treatment alternative for patients with eyelid carcinoma not amendable for surgery, including those with metastatic, locally advanced disease, advanced age, and significant comorbidities. High cost, need for long-term treatment, and toxicity are relative limitations.

An old friend with new skills: Imiquimod as novel inhibitor of Hedgehog signaling in basal cell carcinoma

Deregulated Hedgehog (HH)/GLI signaling plays an etiologic role in the initiation, progression and maintenance of many cancers. Small molecule targeting of HH signaling by inhibiting the essential pathway effector Smoothened (SMO) has proven exceptionally efficient for the treatment of advanced and metastatic basal cell carcinoma. That said, severe side effects, limited response rates, SMO-independent GLI signaling and rapid development of drug resistance limit the therapeutic success of SMO antagonists, urgently calling for the identification of alternative and additional strategies repressing oncogenic HH signaling. In this perspective article we highlight recent findings showing that the Toll-like receptor-7/8 (TLR7/8) agonist imiquimod (IMQ), an immune modulator approved for the treatment of basal cell carcinoma, can also act as a potent cell autonomous inhibitor of oncogenic HH signaling. Surprisingly, IMQ reduces HH signal strength independent of TLR signaling, via adenosine receptor (ADORA)/Adenylate cyclase (AC)/Protein kinase A (PKA) activation. We here highlight the molecular mechanisms of IMQ-mediated repression of HH/GLI and discuss the possible benefits as well as challenges of using ADORA agonists for the treatment of HH-associated cancer.

Targeting the hedgehog-glioma-associated oncogene homolog pathway inhibits bleomycin-induced lung fibrosis in mice

Idiopathic pulmonary fibrosis has been associated with the reactivation of developmental pathways, notably the Hedgehog-Glioma-associated oncogene homolog (GLI) pathway. In this study, we determined whether the Hedgehog pathway was activated in bleomycin-induced lung injury in mice, and whether targeting the Hedgehog-Gli pathway could decrease bleomycin-induced lung fibrosis. After intratracheal injection of bleomycin on Day 0, C57Bl6 mice received GDC-0449 (an inhibitor of Smoothened, the transducer of the pathway), or 2,2'-[[Dihydro-2-(4-pyridinyl)-1,3(2H,4H)-pyrimidinediyl]bis(methylene)]bis[N,N dimethylbenzenamine (GANT61; an inhibitor of GLI transcription factors in the nucleus), from Day 7 to Day 13. At Day 14, whole-lung homogenates were obtained for morphological analysis, assessment of cell apoptosis and proliferation, collagen quantification, and evaluation of profibrotic (transforming growth factor-β, connective tissue growth factor, plasminogen activator inhibitor 1, vascular endothelial growth factor-A) and proinflammatory mediators (IL-1β) expression. We showed that the Hedgehog pathway was activated in bleomycin-induced lung fibrosis on Day 14 after injury, with an increased lung expression of the ligand, Sonic Hedgehog, and with increased messenger RNA expression and nuclear localization of GLI1 and GLI2. Inhibition of Smoothened with GDC-0449 did not influence the development of bleomycin-induced lung fibrosis. By contrast, the inhibition of GLI activity with GANT61 decreased lung fibrosis and lung collagen accumulation, and promoted an antifibrotic and anti-inflammatory environment. Our results identify the hedgehog-Gli pathway as a profibrotic pathway in experimental fibrosis. Inhibition of the Hedgehog-Gli pathway at the level of GLI transcriptional activity could be a therapeutic option in fibrotic lung diseases.

Context-dependent signal integration by the GLI code: the oncogenic load, pathways, modifiers and implications for cancer therapy

Canonical Hedgehog (HH) signaling leads to the regulation of the GLI code: the sum of all positive and negative functions of all GLI proteins. In humans, the three GLI factors encode context-dependent activities with GLI1 being mostly an activator and GLI3 often a repressor. Modulation of GLI activity occurs at multiple levels, including by co-factors and by direct modification of GLI structure. Surprisingly, the GLI proteins, and thus the GLI code, is also regulated by multiple inputs beyond HH signaling. In normal development and homeostasis these include a multitude of signaling pathways that regulate proto-oncogenes, which boost positive GLI function, as well as tumor suppressors, which restrict positive GLI activity. In cancer, the acquisition of oncogenic mutations and the loss of tumor suppressors - the oncogenic load - regulates the GLI code toward progressively more activating states. The fine and reversible balance of GLI activating GLI(A) and GLI repressing GLI(R) states is lost in cancer. Here, the acquisition of GLI(A) levels above a given threshold is predicted to lead to advanced malignant stages. In this review we highlight the concepts of the GLI code, the oncogenic load, the context-dependency of GLI action, and different modes of signaling integration such as that of HH and EGF. Targeting the GLI code directly or indirectly promises therapeutic benefits beyond the direct blockade of individual pathways.

Elevated International Normalized Ratio in a patient concurrently using warfarin and vismodegib

PURPOSE

A case report of a sharp rise in International Normalized Ratio (INR) values during a patient's concomitant use of warfarin and the antineoplastic agent vismodegib is presented.

SUMMARY

About three weeks after he was prescribed vismodegib for skin cancer, a 78-year-old Caucasian man whose INR had been stable during nine months of warfarin use was found to have a critical INR value (9.5) during a visit to a pharmacy anticoagulation clinic. After clinic interventions including brief suspensions of warfarin therapy and an incremental 36% decrease in the weekly dose, the patient's INR returned to a high-normal value over the next few weeks, and treatment with warfarin was resumed. One week later, the man was admitted to the emergency department for altered mental status and loss of consciousness, which were thought to be unrelated to anticoagulation therapy. The patient died in the hospital shortly thereafter of unknown causes. At the time of death, laboratory values were stable, the most recent INR was 1.8, and the patient was hemodynamically stable and on a non-intensive care ward. Assessment with the Drug Interaction Probability Scale indicated a probable interaction between warfarin and vismodegib. Since its introduction in 2012, vismodegib has been implicated as a possible factor in seven reports of patient deaths.

CONCLUSION

Concurrent use of vismodegib and warfarin was deemed the probable cause of acute INR elevation in this case, suggesting the need for close monitoring of INR values in patients receiving this combination of drugs.

Sonic hedgehog signaling in Basal cell nevus syndrome

The hedgehog (Hh) signaling pathway is considered to be a major signal transduction pathway during embryonic development, but it usually shuts down after birth. Aberrant Sonic hedgehog (Shh) activation during adulthood leads to neoplastic growth. Basal cell carcinoma (BCC) of the skin is driven by this pathway. Here, we summarize information related to the pathogenesis of this neoplasm, discuss pathways that crosstalk with Shh signaling, and the importance of the primary cilium in this neoplastic process. The identification of the basic/translational components of Shh signaling has led to the discovery of potential mechanism-driven druggable targets and subsequent clinical trials have confirmed their remarkable efficacy in treating BCCs, particularly in patients with nevoid BCC syndrome (NBCCS), an autosomal dominant disorder in which patients inherit a germline mutation in the tumor-suppressor gene Patched (Ptch). Patients with NBCCS develop dozens to hundreds of BCCs due to derepression of the downstream G-protein-coupled receptor Smoothened (SMO). Ptch mutations permit transposition of SMO to the primary cilium followed by enhanced expression of transcription factors Glis that drive cell proliferation and tumor growth. Clinical trials with the SMO inhibitor, vismodegib, showed remarkable efficacy in patients with NBCCS, which finally led to its FDA approval in 2012.

Zfx facilitates tumorigenesis caused by activation of the Hedgehog pathway

The Hedgehog (Hh) signaling pathway regulates normal development and cell proliferation in metazoan organisms, but its aberrant activation can promote tumorigenesis. Hh-induced tumors arise from various tissues and they may be indolent or aggressive, as is the case with skin basal cell carcinoma (BCC) or cerebellar medulloblastoma, respectively. Little is known about common cell-intrinsic factors that control the development of such diverse Hh-dependent tumors. Transcription factor Zfx is required for the self-renewal of hematopoietic and embryonic stem cells, as well as for the propagation of acute myeloid and T-lymphoblastic leukemias. We report here that Zfx facilitates the development of experimental BCC and medulloblastoma in mice initiated by deletion of the Hh inhibitory receptor Ptch1. Simultaneous deletion of Zfx along with Ptch1 prevented BCC formation and delayed medulloblastoma development. In contrast, Zfx was dispensable for tumorigenesis in a mouse model of glioblastoma. We used genome-wide expression and chromatin-binding analysis in a human medulloblastoma cell line to characterize direct, evolutionarily conserved targets of Zfx, identifying Dis3L and Ube2j1 as two targets required for the growth of the human medulloblastoma cells. Our results establish Zfx as a common cell-intrinsic regulator of diverse Hh-induced tumors, with implications for the definition of new therapeutic targets in these malignancies.

Potential smoothened inhibitor from traditional Chinese medicine against the disease of diabetes, obesity, and cancer

Nowadays, obesity becomes a serious global problem, which can induce a series of diseases such as type 2 diabetes mellitus, cancer, cardiovascular disease, metabolic syndrome, and stoke. For the mechanisms of diseases, the hedgehog signaling pathway plays an important role in body patterning during embryogenesis. For this reason, smoothened homologue (Smo) protein had been indicated as the drug target. In addition, the small-molecule Smo inhibitor had also been used in oncology clinical trials. To improve drug development of TCM compounds, we aim to investigate the potent lead compounds as Smo inhibitor from the TCM compounds in TCM Database@Taiwan. The top three TCM compounds, precatorine, labiatic acid, and 2,2′-[benzene-1,4-diylbis(methanediyloxybenzene-4,1-diyl)]bis(oxoacetic acid), have displayed higher potent binding affinities than the positive control, LY2940680, in the docking simulation. After MD simulations, which can optimize the result of docking simulation and validate the stability of H-bonds between each ligand and Smo protein under dynamic conditions, top three TCM compounds maintain most of interactions with Smo protein, which keep the ligand binding stable in the binding domain. Hence, we propose precatorine, labiatic acid, and 2,2′-[benzene-1,4-diylbis(methanediyloxybenzene-4,1-diyl)]bis(oxoacetic acid) as potential lead compounds for further study in drug development process with the Smo protein.

[Skin adnexal tumors with follicular differentiation]

Skin adnexal tumors with predominantly follicular differentiation represent a clinicopathological heterogeneous group of neoplasms and are classified according to the cytologically achieved differentiation of the follicular compartment. Given the complex structure of non-neoplastic hair follicles it is not surprising to find varying differentiations in neoplasms and there are overlapping clinicopathological features between the established entities. The use of immunohistochemical staining has only a limited value in the diagnosis of follicular neoplasms.

Optimal management of skin cancer in immunosuppressed patients

Skin cancer is the most common malignancy in humans with basal cell carcinoma representing the majority of cases in the general population. The prevalence of skin cancer is increased amongst immunosuppressed patients such as those with lymphoproliferative disorders including non-Hodgkin lymphoma and chronic lymphocytic leukemia or those with iatrogenic immunosuppression following organ transplantation. In addition, these patients experience greater morbidity and mortality associated with skin cancers. The most common skin cancer in immunosuppressed patients is squamous cell carcinoma, which often presents with more aggressive features and has a greater rate of metastasis. This article reviews the risk factors, etiology, clinical presentation, and prevalence of skin cancer amongst immunosuppressed patients, including organ transplant, lymphoproliferative disorders, autoimmune disorders, and human immunodeficiency virus. We also provide a comprehensive review of treatment guidelines for immunosuppressed patients with cutaneous malignancy. Surgical therapy is the cornerstone of treatment; however, we also discuss pharmacologic treatment options, lifestyle modifications, and revision of immunosuppressive regimens.

Current and future systemic treatment options in metastatic pancreatic cancer

Although pancreatic adenocarcinoma is the fourth leading cause of cancer death, only modest improvement has been observed in the past two decades, single agent gemcitabine has been the only standard treatment in patients with advanced disease. Recently newer agents such as nab-paclitaxel, nimotuzumab and regimens such as FOLFIRINOX have been shown to have promising activity being superior to gemcitabine as a single agent. With better understanding of tumour biology coupled with the improvements in targeted and immunotherapies, there is increasing expectation for better response rates and extended survival in pancreatic cancer.

Pediatric medulloblastoma - update on molecular classification driving targeted therapies

As advances in the molecular and genetic profiling of pediatric medulloblastoma evolve, associations with prognosis and treatment are found (prognostic and predictive biomarkers) and research is directed at molecular therapies. Medulloblastoma typically affects young patients, where the implications of any treatment on the developing brain must be carefully considered. The aim of this article is to provide a clear comprehensible update on the role molecular profiling and subgroups in pediatric medulloblastoma as it is likely to contribute significantly toward prognostication. Knowledge of this classification is of particular interest because there are new molecular therapies targeting the Shh subgroup of medulloblastomas.

Cholestatic hepatic injury associated with vismodegib, aspirin, and naproxen use: a case study and review of vismodegib safety

BACKGROUND

Vismodegib is a novel hedgehog pathway inhibitor approved to treat advanced and metastatic basal cell carcinoma (BCC) in the United States. Several studies have demonstrated efficacy for treatment of new and existing BCC in both basal cell nevus syndrome (BCNS) and non-BCNS patients. However, severe and numerous adverse events are associated with vismodegib use. Therefore, we have also examined all of the currently published clinical trials and tabulated the available adverse events for review. The most frequently reported adverse events include muscle spasms (53.4%), dysgeusia/ageusia (49.3%), alopecia (38.8%), fatigue (32.0%), nausea (28.4%), weight loss (24.2%), and decreased appetite (16.5%).

CASE STUDY

We report a case of a previously healthy 72-year-old male with a history of innumerable BCCs who developed severe nausea, jaundice, and cholestasis with significantly elevated BUN, creatinine, and liver enzymes one month after starting vismodegib. The patient began using over-the-counter nonsteroidal anti-inflammatory drugs (NSAIDs) to treat severe, vismodegib-induced myalgia. No other new medications were started. Our patient had no history of liver disease.

CONCLUSIONS

Herein, we describe a potential serious adverse effect associated with vismodegib use. Whether the illness is directly attributable to the medication or the result of drug-drug interactions between vismodegib and NSAIDs, practitioners should be aware of the possibility of hepatic injury in patients on vismodegib. Furthermore, patients need to be informed of the potential risks of vismodegib and should be monitored closely to ensure that life-threatening complications of treatment are avoided.

Structural basis for Smoothened receptor modulation and chemoresistance to anticancer drugs

The Smoothened receptor (SMO) mediates signal transduction in the hedgehog pathway, which is implicated in normal development and carcinogenesis. SMO antagonists can suppress the growth of some tumours; however, mutations at SMO have been found to abolish their antitumour effects, a phenomenon known as chemoresistance. Here we report three crystal structures of human SMO bound to the antagonists SANT1 and Anta XV, and the agonist, SAG1.5, at 2.6-2.8 Å resolution. The long and narrow cavity in the transmembrane domain of SMO harbours multiple ligand binding sites, where SANT1 binds at a deeper site as compared with other ligands. Distinct interactions at D473(6.54f) elucidated the structural basis for the differential effects of chemoresistance mutations on SMO antagonists. The agonist SAG1.5 induces a conformational rearrangement of the binding pocket residues, which could contribute to SMO activation. Collectively, these studies reveal the structural basis for the modulation of SMO by small molecules.

Clinical benefit assessment of vismodegib therapy in patients with advanced basal cell carcinoma

PURPOSE

Vismodegib was approved for the treatment of advanced basal cell carcinoma (aBCC) based on the pivotal ERIVANCE BCC study. The primary endpoint (objective response rate [ORR]) was assessed 9 months after the last patient was enrolled. To confirm the clinical benefit of vismodegib, an additional analysis was performed 12 months after the primary analysis.

MATERIALS AND METHODS

ERIVANCE BCC was a multicenter, nonrandomized, two-cohort study of 104 patients with histologically confirmed aBCC. Patients received 150 mg oral vismodegib daily until disease progression, intolerable toxicity, or withdrawal. An independent review panel comprising three expert clinicians reviewed patient photographs individually and as a consensus panel to evaluate baseline disease severity and clinical benefit after vismodegib treatment in 71 patients with locally advanced BCC (laBCC).

RESULTS

Sixty-three patients were efficacy evaluable; baseline and postprogression photographs for 61 were available for review. Baseline disease severity was judged as 5 or 4 (very severe or moderately severe) in 71.4%. Clinical benefit was observed in 76.2% (significant: 65.1%; some: 11.1%). Interpanelist agreement (maximum difference ≤1 point among panelists' scores in 65.1% and 87.3% of patients for clinical benefit and baseline disease severity, respectively) and correlation between individual and panel reviews were strong. Clinical benefit scores showed good concordance with the protocol-specified ORR obtained by an independent review facility and with investigator-assessed response.

CONCLUSION

Clinical benefit assessed by independent review based on expert clinical judgment provides strong evidence that treatment with vismodegib results in clinically meaningful and durable responses in patients with laBCC.

Structural insights into the role of the Smoothened cysteine-rich domain in Hedgehog signalling

Smoothened (Smo) is a member of the Frizzled (FzD) class of G-protein-coupled receptors (GPCRs), and functions as the key transducer in the Hedgehog (Hh) signalling pathway. Smo has an extracellular cysteine-rich domain (CRD), indispensable for its function and downstream Hh signalling. Despite its essential role, the functional contribution of the CRD to Smo signalling has not been clearly elucidated. However, given that the FzD CRD binds to the endogenous Wnt ligand, it has been proposed that the Smo CRD may bind its own endogenous ligand. Here we present the NMR solution structure of the Drosophila Smo CRD, and describe interactions between the glucocorticoid budesonide (Bud) and the Smo CRDs from both Drosophila and human. Our results highlight a function of the Smo CRD, demonstrating its role in binding to small-molecule modulators.

Activating FGFR2-RAS-BRAF mutations in ameloblastoma

PURPOSE

Ameloblastoma is an odontogenic neoplasm whose overall mutational landscape has not been well characterized. We sought to characterize pathogenic mutations in ameloblastoma and their clinical and functional significance with an emphasis on the mitogen-activated protein kinase (MAPK) pathway.

EXPERIMENTAL DESIGN

A total of 84 ameloblastomas and 40 non-ameloblastoma odontogenic tumors were evaluated with a combination of BRAF V600E allele-specific PCR, VE1 immunohistochemistry, the Ion AmpliSeq Cancer Hotspot Panel, and Sanger sequencing. Efficacy of a BRAF inhibitor was evaluated in an ameloblastoma-derived cell line.

RESULTS

Somatic, activating, and mutually exclusive RAS-BRAF and FGFR2 mutations were identified in 88% of cases. Somatic mutations in SMO, CTNNB1, PIK3CA, and SMARCB1 were also identified. BRAF V600E was the most common mutation, found in 62% of ameloblastomas and in ameloblastic fibromas/fibrodentinomas but not in other odontogenic tumors. This mutation was associated with a younger age of onset, whereas BRAF wild-type cases arose more frequently in the maxilla and showed earlier recurrences. One hundred percent concordance was observed between VE1 immunohistochemistry and molecular detection of BRAF V600E mutations. Ameloblastoma cells demonstrated constitutive MAPK pathway activation in vitro. Proliferation and MAPK activation were potently inhibited by the BRAF inhibitor vemurafenib.

CONCLUSIONS

Our findings suggest that activating FGFR2-RAS-BRAF mutations play a critical role in the pathogenesis of most cases of ameloblastoma. Somatic mutations in SMO, CTNNB1, PIK3CA, and SMARCB1 may function as secondary mutations. BRAF V600E mutations have both diagnostic and prognostic implications. In vitro response of ameloblastoma to a BRAF inhibitor suggests a potential role for targeted therapy.

Advanced treatment for basal cell carcinomas

Basal cell carcinomas (BCCs) are very common epithelial cancers that depend on the Hedgehog pathway for tumor growth. Traditional therapies such as surgical excision are effective for most patients with sporadic BCC; however, better treatment options are needed for cosmetically sensitive or advanced and metastatic BCC. The first approved Hedgehog antagonist targeting the membrane receptor Smoothened, vismodegib, shows remarkable effectiveness on both syndromic and nonsyndromic BCCs. However, drug-resistant tumors frequently develop, illustrating the need for the development of next-generation Hedgehog antagonists targeting pathway components downstream from Smoothened. In this article, we will summarize available BCC treatment options and discuss the development of next-generation antagonists.

Epigenetic targeting of Hedgehog pathway transcriptional output through BET bromodomain inhibition

Hedgehog signaling drives oncogenesis in several cancers and strategies targeting this pathway have been developed, most notably through inhibition of Smoothened. However, resistance to Smoothened inhibitors occurs via genetic changes of Smoothened or other downstream Hedgehog components. Here, we overcome these resistance mechanisms by modulating GLI transcription via inhibition of BET bromodomain proteins. We show the BET bromodomain protein, BRD4, regulates GLI transcription downstream of SMO and SUFU and chromatin immunoprecipitation studies reveal BRD4 directly occupies GLI1 and GLI2 promoters, with a substantial decrease in engagement of these sites upon treatment with JQ1, a small molecule inhibitor targeting BRD4. Globally, genes associated with medulloblastoma-specific GLI1 binding sites are downregulated in response to JQ1 treatment, supporting direct regulation of GLI activity by BRD4. Notably, patient- and GEMM-derived Hedgehog-driven tumors (basal cell carcinoma, medulloblastoma and atypical teratoid/rhabdoid tumor) respond to JQ1 even when harboring genetic lesions rendering them resistant to Smoothened antagonists.

Hedgehog signaling pathway and cancer therapeutics: progress to date

The Hedgehog (Hh) pathway is a developmental signaling pathway involved in numerous developmental processes, including determination of cell fate, patterning, proliferation, survival, and differentiation. While this pathway is silenced in most adult tissues, aberrant activation of it has been documented in a variety of malignancies. In cancers such as basal cell carcinoma (BCC), ligand-independent mechanisms lead to constitutive Hh pathway activation through mutations in components of the pathway, including patched-1 (PTCH1) or smoothened (SMO). On the contrary, numerous other solid and hematologic tumors have been shown to harbor ligand-dependent activation of the Hh pathway by autocrine or paracrine mechanisms. Given that aberrant Hh pathway signaling has been seen in a number of malignancies, this pathway has been an attractive target for drug development. While the best-characterized approach is to target the SMO receptor, other rational approaches for inhibiting the Hh pathway include inhibiting downstream components or directly binding Hh ligands. In January of 2012, vismodegib, a SMO antagonist, became the first agent to target the Hh pathway to receive approval by the United States Food and Drug Administration (FDA) after this agent showed remarkable activity in phase I and II trials for the treatment of BCC. Despite promising preclinical studies with Hh pathway inhibitors in other malignancies that have suggested a potential role for these agents, attempts to translate this potential to clinical benefit has been disappointing. Future efforts will require further careful interpretation and analysis to determine the potential determinants and predictors of efficacy. Currently, several phase I and II trials evaluating Hh inhibitors in a variety of tumor settings are underway.

Noninvasive monitoring of basal cell carcinomas treated with systemic hedgehog inhibitors: pseudocysts as a sign of tumor regression

BACKGROUND

Oral hedgehog inhibitors (HHIs) have shown significant efficacy in the treatment of basal cell carcinoma (BCC). The evaluation of tumor regression has been performed using clinical photography and radiographic scans. Noninvasive imaging techniques, such as reflectance confocal microscopy (RCM) and high-definition optical coherence tomography (HD-OCT), have been shown to be valuable in detecting BCC in the skin.

OBJECTIVE

We monitored HHI-treated BCC using RCM and HD-OCT in vivo and correlated morphologic changes seen on imaging to changes in traditional histopathology.

METHODS

Six BCCs in 5 patients receiving HHIs (vismodegib or sonidegib) were examined by RCM and HD-OCT before and during treatment. Characteristic features were compared to histopathologic findings, including immunohistochemical analysis.

RESULTS

Characteristic features of BCC in RCM and HD-OCT decreased or disappeared completely during HHI treatment. Half of the clinically complete responding tumors still featured tumor residue. Pseudocystic structures ("empty" tumor nests in imaging) and widespread fibrosis (coarse bright fibers) were new findings and could be confirmed by histopathology.

LIMITATIONS

Our study was limited by the number of tumor samples and imaging timepoints.

CONCLUSION

Using RCM and HD-OCT, HHI-induced regression of BCC can be visualized noninvasively in the skin. The formation of pseudocysts and fibrosis were characteristic signs of BCC response to HHIs.

Hedgehog inhibition reduces angiogenesis by downregulation of tumoral VEGF-A expression in hepatocellular carcinoma

BACKGROUND

Dysregulation and activation of Hedgehog (Hh) signalling may contribute to tumorigenesis, angiogenesis, and metastatic seeding in several solid tumours.

OBJECTIVE

We investigated the impact of Hh inhibition on tumour growth and angiogenesis using in-vitro and in-vivo models of hepatocellular carcinoma (HCC).

METHODS

The effect of the Hh pathway inhibitor GDC-0449 on tumour growth was investigated using an orthotopic rat model. Effects on angiogenesis were determined by immunohistochemical staining of von Willebrand factor antigen and by assessing the mRNA expression of several angiogenic factors. In vitro, HCC cell lines were treated with GDC-0449 and evaluated for viability and expression of vascular endothelial growth factor (VEGF). Endothelial cells were evaluated for viability, migration, and tube formation.

RESULTS

In the orthotopic HCC model, GDC-0449 significantly decreased tumoral VEGF expression which was accompanied by a significant reduction of microvessel density and tumour growth. In HCC cells, GDC-0449 had no effect on cell growth but significantly reduced target gene regulation and VEGF expression while having no direct effect on endothelial cell viability, migration, and tube formation.

CONCLUSIONS

Hh inhibition with GDC-0449 downregulates tumoral VEGF production in vitro and reduces tumoral VEGF expression, angiogenesis, and tumour growth in an orthotopic HCC model.

Direct functional consequences of ZRS enhancer mutation combine with secondary long range SHH signalling effects to cause preaxial polydactyly

Sonic hedgehog (SHH) plays a central role in patterning numerous embryonic tissues including, classically, the developing limb bud where it controls digit number and identity. This study utilises the polydactylous Silkie (Slk) chicken breed, which carries a mutation in the long range limb-specific regulatory element of SHH, the ZRS. Using allele specific SHH expression analysis combined with quantitative protein analysis, we measure allele specific changes in SHH mRNA and concentration of SHH protein over time. This confirms that the Slk ZRS enhancer mutation causes increased SHH expression in the posterior leg mesenchyme. Secondary consequences of this increased SHH signalling include increased FGF pathway signalling and growth as predicted by the SHH/GREM1/FGF feedback loop and the Growth/Morphogen models. Manipulation of Hedgehog, FGF signalling and growth demonstrate that anterior-ectopic expression of SHH and induction of preaxial polydactyly is induced secondary to increased SHH signalling and Hedgehog-dependent growth directed from the posterior limb. We predict that increased long range SHH signalling acts in combination with changes in activation of SHH transcription from the Slk ZRS allele. Through analysis of the temporal dynamics of anterior SHH induction we predict a gene regulatory network which may contribute to activation of anterior SHH expression from the Slk ZRS.

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Overexpression of posterior SHH in the limb bud can cause preaxial polydactyly.

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Increased activation of SHH/GREM/FGF feedback and growth induces Slk preaxial polydactyly.

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Autoregulated expression of SHH can occur within 1.5–2 h in the limb bud.

Discovery and preclinical development of vismodegib

INTRODUCTION

Vismodegib is the first Hedgehog (Hh) pathway inhibitor approved in the US for the treatment of adults with metastatic or locally advanced basal cell carcinoma (BCC). It was approved by the US FDA on 30 January 2012, and by the European Commission on 12 July 2013, for the treatment of adult patients with symptomatic metastatic BCC, or locally advanced BCC inappropriate for surgery or radiotherapy. Vismodegib selectively inhibits the Hh signaling pathway, binding to and inhibiting a critical signal-transducing component of the pathway, Smoothened (SMO). Vismodegib was discovered by Genentech, Inc., under a collaboration agreement with Curis, Inc.

AREAS COVERED

This article reviews the development of vismodegib from its discovery, preclinical pharmacology and validation to the clinical pharmacokinetics and validation in Phase I and II clinical investigations. We also provide a survey of other Hh pathway inhibitors in clinical development.

EXPERT OPINION

The authors' experience in target-based drug discovery suggests that vismodegib's path to the clinic deserves some reflection to identify key steps that have contributed to its success. Targeting the Hh pathway with vismodegib blocks the abberant signaling caused by mutational inactivation of the negative regulator PTCH1 or mutational activation of SMO. Vismodegib gives physicians a treatment option for patients with locally advanced or metastatic BCC for whom surgery or radiation is not recommended.

A rare case of endobronchial and lung metastasis in basal cell carcinoma

Basal cell carcinoma (BCC) is the most common skin cancer, but rarely metastasizes. This article describes diagnosis and treatment of an extremely rare case of BCC metastasizing to the lung and endobronchial tissue.

Hedgehog signaling and radiation induced liver injury: a delicate balance

Radiation-induced liver disease (RILD) is a major limitation of radiation therapy (RT) for the treatment of liver cancer. Emerging data indicate that hedgehog (Hh) signaling plays a central role in liver fibrosis and regeneration after liver injury. Here, we review the potential role of Hh signaling in RILD and propose the temporary use of Hh inhibition during liver RT to radiosensitize HCC tumor cells and inhibit their progression, while blocking the initiation of the radiation-induced fibrotic response in the surrounding normal liver.

Activation of liver X receptors inhibits hedgehog signaling, clonogenic growth, and self-renewal in multiple myeloma

The Hedgehog (Hh) signaling pathway is aberrantly activated in a wide variety of human cancers, and recent clinical studies have demonstrated that pathway inhibitors are effective in advanced basal cell carcinoma (BCC). The majority of these agents have been designed to target SMOOTHENED (SMO), a transmembrane regulator of Hh signaling, but subsequent mutations in SMO have been found to generate drug resistance. In other cancers, oncogenic events that bypass SMO may activate canonical Hh signaling, and SMO antagonists have not demonstrated significant activity in several diseases. Therefore, alternative strategies targeting the Hh pathway downstream of SMO may have clinical utility. Liver X receptors (LXR) regulate cholesterol and fatty acid homeostasis, and LXR activation can inhibit the Hh pathway in normal mouse embryonic fibroblasts. We examined the effects of LXR activation on Hh signaling in human multiple myeloma cells and found that LXR agonists inhibited Hh pathway activity and clonogenic tumor growth in vitro. LXR activation also inhibited putative multiple myeloma cancer stem cells in vivo leading to the loss of tumor initiating and self-renewal potential. Finally, Hh signaling was inhibited downstream of SMO, suggesting that LXR agonists may represent a novel strategy to target pathogenic Hh signaling as well as treat multiple myeloma.

Emerging drugs and combination strategies for basal cell carcinoma

INTRODUCTION

Basal cell carcinoma (BCC) is a malignancy that is driven by an activated Hedgehog (Hh) pathway. Smoothened inhibitors are a new promising treatment option for patients with locally advanced or metastatic BCC or basal cell nevus syndrome. But long-term data are still limited, the optimal treatment duration is not yet defined and there are already documented cases with acquired resistance.

AREAS COVERED

Treatment modalities with Hh inhibitors, side effects and potential pharmacological combination options are discussed. The current literature, including PubMed, Cochrane database and registered trials on ClinicalTrials.gov, was searched.

EXPERT OPINION

BCCs typically regress during therapy with Hh inhibitors. Muscle toxicity, dysgeusia and hair loss can be considered as on target adverse reactions. Muscle toxicity is the dose-limiting toxicity of sonidegib. It was not seen with vismodegib because of its high binding to plasma protein α-1-acid glycoprotein. Sonidegib is different and shows a clear dose-toxicity relationship, which allows to address the question of whether there is a dose dependency of regression rate, cure rate and progression-free survival. In addition, basic research has offered strategies to enhance efficacy by the combination with other molecules, such as EGFR inhibitors, MEK inhibitors or immunotherapy.

Cancer stem cells: progress and challenges in lung cancer

The identification of a subpopulation of tumor cells with stem cell-like characteristics first in hematological malignancies and later in solid tumors has emerged into a novel field of cancer research. It has been proposed that this aberrant population of cells now called "cancer stem cells" (CSCs) drives tumor initiation, progression, metastasis, recurrence, and drug resistance. CSCs have been shown to have the capacity of self-renewal and multipotency. Adopting strategies from the field of stem cell research has aided in identification, localization, and targeting of CSCs in many tumors. Despite the huge progress in other solid tumors such as brain, breast, and colon cancers no substantial advancements have been made in lung cancer. This is most likely due to the current rudimentary understanding of lung stem cell hierarchy and heterogeneous nature of lung disease. In this review, we will discuss the most recent findings related to identification of normal lung stem cells and CSCs, pathways involved in regulating the development of CSCs, and the importance of the stem cell niche in development and maintenance of CSCs. Additionally, we will examine the development and feasibility of novel CSC-targeted therapeutic strategies aimed at eradicating lung CSCs.

Arsenic trioxide induces differentiation of CD133+ hepatocellular carcinoma cells and prolongs posthepatectomy survival by targeting GLI1 expression in a mouse model

BACKGROUND

Cancer stem cells (CSCs) play a key role in the posthepatectomy recurrence of hepatocellular carcinoma (HCC). CD133+ HCC cells exhibit liver CSC-like properties, and CSC differentiation-inducing therapy may lead these cells to lose their self-renewal ability and may induce terminal differentiation, which may in turn allow their malignant potential to be controlled. Because arsenic trioxide (As₂O₃) increases remission rates and prolongs survival among patients with acute promyelocytic leukemia by inducing differentiation and apoptosis of leukemic cells, we hypothesized that As₂O₃ might also inhibit HCC recurrence and prolong survival time after hepatectomy by inducing differentiation of HCC CSCs.

METHODS

We evaluated the As₂O₃ induced differentiation of human HCC CSCs and its mechanism in vitro, and we investigated the effects of treatment with As₂O₃ on recurrence rates and median survival in a mouse xenograft model.

RESULTS

We found that As₂O₃ induced HCC CSC differentiation by down-regulating the expression of CD133 and some stemness genes, thus inhibiting the cells' self-renewal ability and tumorigenic capacity without inhibiting their proliferation in vitro. In vivo experiments indicated that As₂O₃ decreased recurrence rates after radical resection and prolonged survival in a mouse model. As₂O₃, which shows no apparent toxicity, may induce HCC CSC differentiation by down-regulating the expression of GLI1.

CONCLUSIONS

We found that As₂O₃ induced HCC CSC differentiation, inhibited recurrence, and prolonged survival after hepatectomy by targeting GLI1expression. Our results suggest that the clinical safety and utility of As₂O₃ should be further evaluated.