A paracrine requirement for hedgehog signalling in cancer

Primary Cilium in Cancer Hallmarks

The primary cilium is a solitary, nonmotile and transitory appendage that is present in virtually all mammalian cells. Our knowledge of its ultrastructure and function is the result of more than fifty years of research that has dramatically changed our perspectives on the primary cilium. The mutual regulation between ciliogenesis and the cell cycle is now well-recognized, as well as the function of the primary cilium as a cellular "antenna" for perceiving external stimuli, such as light, odorants, and fluids. By displaying receptors and signaling molecules, the primary cilium is also a key coordinator of signaling pathways that converts extracellular cues into cellular responses. Given its critical tasks, any defects in primary cilium formation or function lead to a wide spectrum of diseases collectively called "ciliopathies". An emerging role of primary cilium is in the regulation of cancer development. In this review, we seek to describe the current knowledge about the influence of the primary cilium in cancer progression, with a focus on some of the events that cancers need to face to sustain survival and growth in hypoxic microenvironment: the cancer hallmarks.

Global gene expression of histologically normal primary skin cells from BCNS subjects reveals "single-hit" effects that are influenced by rapamycin

Studies of dominantly heritable cancers enabled insights about tumor progression. BCNS is a dominantly inherited disorder that is characterized by developmental abnormalities and postnatal neoplasms, principally BCCs. We performed an exploratory gene expression profiling of primary cell cultures derived from clinically unaffected skin biopsies of BCNS gene-carriers (PTCH1^+/-) and normal individuals. PCA and HC of untreated keratinocytes or fibroblasts failed to clearly distinguish BCNS samples from controls. These results are presumably due to the common suppression of canonical HH signaling in vitro. We then used a relaxed threshold (p-value <0.05, no FDR cut-off; FC 1.3) that identified a total of 585 and 857 genes differentially expressed in BCNS keratinocytes and fibroblasts samples, respectively. A GSEA identified pancreatic β cell hallmark and mTOR signaling genes in BCNS keratinocytes, whereas analyses of BCNS fibroblasts identified gene signatures regulating pluripotency of stem cells, including WNT pathway. Significantly, rapamycin treatment (FDR<0.05), affected a total of 1411 and 4959 genes in BCNS keratinocytes and BCNS fibroblasts, respectively. In contrast, rapamycin treatment affected a total of 3214 and 4797 genes in normal keratinocytes and normal fibroblasts, respectively. The differential response of BCNS cells to rapamycin involved 599 and 1463 unique probe sets in keratinocytes and fibroblasts, respectively. An IPA of these genes in the presence of rapamycin pointed to hepatic fibrosis/stellate cell activation, and HIPPO signaling in BCNS keratinocytes, whereas mitochondrial dysfunction and AGRN expression were uniquely enriched in BCNS fibroblasts. The gene expression changes seen here are likely involved in the etiology of BCCs and they may represent biomarkers/targets for early intervention.

Gli Proteins: Regulation in Development and Cancer

Gli proteins are transcriptional effectors of the Hedgehog signaling pathway. They play key roles in the development of many organs and tissues, and are deregulated in birth defects and cancer. We review the molecular mechanisms of Gli protein regulation in mammals, with special emphasis on posttranslational modifications and intracellular transport. We also discuss how Gli proteins interact with co-activators and co-repressors to fine-tune the expression of Hedgehog target genes. Finally, we provide an overview of the regulation of developmental processes and tissue regeneration by Gli proteins and discuss how these proteins are involved in cancer progression, both through canonical regulation via the Hedgehog pathway and through cross-talk with other signaling pathways.

Misactivation of Hedgehog signaling causes inherited and sporadic cancers

The Hedgehog pathway is critical for the development of diverse organs. Misactivation of the Hedgehog pathway can cause developmental abnormalities and cancers, including medulloblastoma, the most common pediatric brain tumor, and basal cell carcinoma, the most common cancer in the United States. Here, we review how basic, translational, and clinical studies of the Hedgehog pathway have helped reveal how cells communicate, how intercellular communication controls development, how signaling goes awry to cause cancer, and how to use targeted molecular agents to treat both inherited and sporadic cancers.

Novel-smoothened inhibitors for therapeutic targeting of naïve and drug-resistant hedgehog pathway-driven cancers

The G protein-coupled receptor (GPCR) smoothened (SMO) is a key signaling component of the sonic hedgehog (Hh) pathway and a clinically validated target for cancer treatment. The FDA-approved SMO inhibitors GDC-0449/Vismodegib and LDE225/Sonidegib demonstrated clinical antitumor efficacy. Nevertheless, relatively high percentage of treated patients would eventually develop acquired cross resistance to both drugs. Here, based on published structure and activity of GDC-0449 inhibitor class, we replaced its amide core with benzimidazole which retained bulk of the SMO-targeting activity as measured in our Hh/SMO/Gli1-reporter system. Synthesis and screening of multiple series of benzimidazole derivatives identified HH-1, HH-13, and HH-20 with potent target suppression (IC₅₀: <0.1 μmol/L) in the reporter assays. In NIH3T3 cells stimulated with a secreted Hh (SHH), these inhibitors dose dependently reduced mRNA and protein expression of the endogenous pathway components PTCH-1, Gli1, and cyclin D1 resulting in growth inhibition via G₀/G₁ arrest. Mechanistically, the SMO-targeted growth inhibition involved downregulation of mTOR signaling inputs and readouts consistent with diminished mTORC1/mTORC2 functions and apoptosis. In mice, as with GDC-0449, orally administered HH inhibitors blocked paracrine activation of stromal Hh pathway in Calu-6 tumor microenvironment and attenuated growth of PTCH^+/-/P53^-/- medulloblastoma allograft tumors. Furthermore, HH-13 and HH-20 potently targeted the drug-resistant smoothened SMO-D473H (IC₅₀: <0.2 μmol/L) compared to the poor inhibition by GDC-0449 (IC₅₀: >60 μmol/L). These results identify HH-13 and HH-20 as potent inhibitors capable of targeting naïve and drug-resistant Hh/SMO-driven cancers. The current leads may be optimized to improve pharmaceutical property for potential development of new therapy for treatment of Hh pathway-driven cancers.

Stromal biology and therapy in pancreatic cancer: ready for clinical translation?

Pancreatic ductal adenocarcinoma (PDA) is notoriously aggressive and hard to treat. The tumour microenvironment (TME) in PDA is highly dynamic and has been found to promote tumour progression, metastasis niche formation and therapeutic resistance. Intensive research of recent years has revealed an incredible heterogeneity and complexity of the different components of the TME, including cancer-associated fibroblasts, immune cells, extracellular matrix components, tumour vessels and nerves. It has been hypothesised that paracrine interactions between neoplastic epithelial cells and TME compartments may result in either tumour-promoting or tumour-restraining consequences. A better preclinical understanding of such complex and dynamic network systems is required to develop more powerful treatment strategies for patients. Scientific activity and the number of compelling findings has virtually exploded during recent years. Here, we provide an update of the most recent findings in this area and discuss their translational and clinical implications for basic scientists and clinicians alike.

M2 macrophage-derived IL6 mediates resistance of breast cancer cells to hedgehog inhibition

Hedgehog (Hh) pathway hyperactivation has been observed in various tumors, including breast cancer, and Hh pathway inhibitors have demonstrated antitumor activity in breast cancer. The tumor microenvironment (TME) has been shown to play an important role in modulating cancer cell drug sensitivity, but the TME response to Hh pathway inhibitors is unclear. In the current study, we observed increased TME infiltration of macrophages in breast cancer tissue, and specifically, M2 polarized macrophages after neoadjuvant chemotherapy. Furthermore, we observed an enhanced tolerance to Hh pathway inhibitors in MDA-MB-231 cells after co-culturing with M2 macrophages. In addition, we demonstrated that Hh pathway inhibition significantly induced IL6 expression, and validated that the tolerance to Hh pathway inhibitors was IL6-dependent. This study demonstrates a role of macrophages in Hh pathway inhibition resistance and a role of macrophage-derived IL6 in this resistance of breast cancer cells to Hh inhibition. These data indicate that antagonizing IL6 together with Hh pathway inhibitors may be a novel therapeutic strategy for breast cancer.

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

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

From Friend to Enemy: Dissecting the Functional Alteration of Immunoregulatory Components during Pancreatic Tumorigenesis

Pancreatic ductal adenocarcinoma (PDAC) is a lethal disease with a 5-year survival rate of approximately 8%. More than 80% of patients are diagnosed at an unresectable stage due to metastases or local extension. Immune system reactivation in patients by immunotherapy may eliminate tumor cells and is a new strategy for cancer treatment. The anti-CTLA-4 antibody ipilimumab and anti-PD-1 antibodies pembrolizumab and nivolumab have been approved for cancer therapy in different countries. However, the results of immunotherapy on PDAC are unsatisfactory. The low response rate may be due to poor immunogenicity with low tumor mutational burden in pancreatic cancer cells and desmoplasia that prevents the accumulation of immune cells in tumors. The immunosuppressive tumor microenvironment in PDAC is important in tumor progression and treatment resistance. Switching from an immune tolerance to immune activation status is crucial to overcome the inability of self-defense in cancer. Therefore, thoroughly elucidation of the roles of various immune-related factors, tumor microenvironment, and tumor cells in the development of PDAC may provide appropriate direction to target inflammatory pathway activation as a new therapeutic strategy for preventing and treating this cancer.

Epithelial-Stromal Interactions in Pancreatic Cancer

Pancreatic cancer is characterized by an extensive fibroinflammatory reaction that includes immune cells, fibroblasts, extracellular matrix, vascular and lymphatic vessels, and nerves. Overwhelming evidence indicates that the pancreatic cancer microenvironment regulates cancer initiation, progression, and maintenance. Pancreatic cancer treatment has progressed little over the past several decades, and the prognosis remains one of the worst for any cancer. The contribution of the microenvironment to carcinogenesis is a key area of research, offering new potential targets for treating the disease. Here, we explore the composition of the pancreatic cancer stroma, discuss the network of interactions between different components, and describe recent attempts to target the stroma therapeutically. We also discuss current areas of active research related to the tumor microenvironment.

Hedgehog Signaling in Cancer: A Prospective Therapeutic Target for Eradicating Cancer Stem Cells

The Hedgehog (Hh) pathway is a signaling cascade that plays a crucial role in many fundamental processes, including embryonic development and tissue homeostasis. Moreover, emerging evidence has suggested that aberrant activation of Hh is associated with neoplastic transformations, malignant tumors, and drug resistance of a multitude of cancers. At the molecular level, it has been shown that Hh signaling drives the progression of cancers by regulating cancer cell proliferation, malignancy, metastasis, and the expansion of cancer stem cells (CSCs). Thus, a comprehensive understanding of Hh signaling during tumorigenesis and development of chemoresistance is necessary in order to identify potential therapeutic strategies to target various human cancers and their relapse. In this review, we discuss the molecular basis of the Hh signaling pathway and its abnormal activation in several types of human cancers. We also highlight the clinical development of Hh signaling inhibitors for cancer therapy as well as CSC-targeted therapy.

Disruption of stromal hedgehog signaling initiates RNF5-mediated proteasomal degradation of PTEN and accelerates pancreatic tumor growth

Disrupting paracrine Hedgehog signaling in pancreatic cancer stroma through genetic deletion of fibroblast Smoothened leads to proteasomal degradation of fibroblast PTEN and accelerates tumor growth.

The contribution of the tumor microenvironment to pancreatic ductal adenocarcinoma (PDAC) development is currently unclear. We therefore examined the consequences of disrupting paracrine Hedgehog (HH) signaling in PDAC stroma. Herein, we show that ablation of the key HH signaling gene Smoothened (Smo) in stromal fibroblasts led to increased proliferation of pancreatic tumor cells. Furthermore, Smo deletion resulted in proteasomal degradation of the tumor suppressor PTEN and activation of oncogenic protein kinase B (AKT) in fibroblasts. An unbiased proteomic screen identified RNF5 as a novel E3 ubiquitin ligase responsible for degradation of phosphatase and tensin homolog (PTEN) in Smo-null fibroblasts. Ring Finger Protein 5 (Rnf5) knockdown or pharmacological inhibition of glycogen synthase kinase 3β (GSKβ), the kinase that marks PTEN for ubiquitination, rescued PTEN levels and reversed the oncogenic phenotype, identifying a new node of PTEN regulation. In PDAC patients, low stromal PTEN correlated with reduced overall survival. Mechanistically, PTEN loss decreased hydraulic permeability of the extracellular matrix, which was reversed by hyaluronidase treatment. These results define non-cell autonomous tumor-promoting mechanisms activated by disruption of the HH/PTEN axis and identifies new targets for restoring stromal tumor-suppressive functions.

Stromal Modulation Reverses Primary Resistance to Immune Checkpoint Blockade in Pancreatic Cancer

Pancreatic ductal adenocarcinoma (PDAC) remains one of the most difficult cancers to treat. It is refractory to most existing therapies, including immunotherapies, due to the presence of an excessive desmoplastic stroma, which restricts penetration of drugs and cytotoxic CD8⁺ T cells. Stromal modulation has shown promising results in the enhancement of immune checkpoint blockade treatment in PDAC. We demonstrate here effective stromal modulation by a polymeric micelle-based nanoformulation to codeliver a sonic hedgehog inhibitor (cyclopamine, abbreviated as CPA) and a cytotoxic chemotherapy drug (paclitaxel, abbreviated as PTX). The formulation, M-CPA/PTX, modulated the PDAC stroma by increasing the intratumoral vasculature density, which then promoted the tumor infiltration by cytotoxic CD8⁺ T cells without depletion of tumor-restraining α-smooth muscle action-positive fibroblasts and type I collage in the stroma. The combination of M-CPA/PTX and the PD-1 checkpoint blockade significantly prolonged animal survival in an orthotopic murine PDAC model as well as a genetically engineered mouse model of PDAC. The superior antitumor efficacy was mediated by enhanced tumor infiltration of CD8⁺ T cells without concomitant infiltration of suppressive regulatory T cells or myeloid-derived suppressor cells and by the coordinated action of PTX and interferon-gamma. Our results demonstrate that stroma-modulating nanoformulations are a promising approach to potentiate immune checkpoint blockade therapy of pancreatic cancer.

Macrophages and Fibroblasts, Key Players in Cancer Chemoresistance

Chemotherapy is routinely used in cancer treatment to eliminate primary and metastatic tumor cells. However, tumors often display or develop resistance to chemotherapy. Mechanisms of chemoresistance can be either tumor cell autonomous or mediated by the tumor surrounding non-malignant cells, also known as stromal cells, which include fibroblasts, immune cells, and cells from the vasculature. Therapies targeting cancer cells have shown limited effectiveness in tumors characterized by a rich tumor stroma. Tumor-associated macrophages (TAMs) and cancer-associated fibroblasts (CAFs) are the most abundant non-cancerous cells in the tumor stroma and have emerged as key players in cancer progression, metastasis and resistance to therapies. This review describes the recent advances in our understanding of how CAFs and TAMs confer chemoresistance to tumor cells and discusses the therapeutic opportunities of combining anti-tumor with anti-stromal therapies. The continued elucidation of the mechanisms by which TAMs and CAFs mediate resistance to therapies will allow the development of improved combination treatments for cancer patients.

Gain-of-function Shh mutants activate Smo cell-autonomously independent of Ptch1/2 function

Sonic Hedgehog (Shh) signaling is characterized by non-cell autonomy; cells expressing Shh do not respond to the ligand. Here, we identify several Shh mutations that can activate the Hedgehog (Hh) pathway cell-autonomously. Cell-autonomous pathway activation requires the extracellular cysteine rich domain of Smoothened, but is otherwise independent of the Shh receptors Patched1 and -2. Many of the Shh mutants that gain activity fail to undergo auto processing resulting in the perdurance of the Shh pro-peptide, a form of Shh that is sufficient to activate the Hh response cell-autonomously. Our results demonstrate that Shh is capable of activating the Hh pathway via Smoothened, independently of Patched1/2, and that it harbors an intrinsic mechanism that prevents cell-autonomous activation of the Shh response.

GLI3 knockdown decreases stemness, cell proliferation and invasion in oral squamous cell carcinoma

Oral squamous cell carcinoma (OSCC) is an extremely aggressive disease associated with a poor prognosis. Previous studies have established that cancer stem cells (CSCs) actively participate in OSCC development, progression and resistance to conventional treatments. Furthermore, CSCs frequently exhibit a deregulated expression of normal stem cell signalling pathways, thereby acquiring their distinctive abilities, of which self-renewal is an example. In this study, we examined the effects of GLI3 knockdown in OSCC, as well as the differentially expressed genes in CSC-like cells (CSCLCs) expressing high (CD44^high) or low (CD44^low) levels of CD44. The prognostic value of GLI3 in OSCC was also evaluated. The OSCC cell lines were sorted based on CD44 expression; gene expression was evaluated using a PCR array. Following this, we examined the effects of GLI3 knockdown on CD44 and ESA expression, colony and sphere formation capability, stem-related gene expression, proliferation and invasion. The overexpression of genes related to the Notch, transforming growth factor (TGF)β, FGF, Hedgehog, Wnt and pluripotency maintenance pathways was observed in the CD44^high cells. GLI3 knockdown was associated with a significant decrease in different CSCLC fractions, spheres and colonies in addition to the downregulation of the CD44, Octamer-binding transcription factor 4 (OCT4; also known as POU5F1) and BMI1 genes. This downregulation was accompanied by an increase in the expression of the Involucrin (IVL) and S100A9 genes. Cellular proliferation and invasion were inhibited following GLI3 knockdown. In OSCC samples, a high GLI3 expression was associated with tumour size but not with prognosis. On the whole, the findings of this study demonstrate for the first time, at least to the best of our knowledge, that GLI3 contributes to OSCC stemness and malignant behaviour. These findings suggest the potential for the development of novel therapies, either in isolation or in combination with other drugs, based on CSCs in OSCC.

Overexpression of Gremlin 1 by sonic hedgehog signaling promotes pancreatic cancer progression

Sonic hedgehog (SHH) signaling is an important promotor of desmoplasia, a critical feature in pancreatic cancer stromal reactions involving the activation of pancreatic stellate cells (PSCs). Gremlin 1 is widely overexpressed in cancer-associated stromal cells, including activated PSCs. In embryonic development, SHH is a potent regulator of Gremlin 1 through an interaction network. This subtle mechanism in the cancer microenvironment remains to be fully elucidated. The present study investigated the association between Gremlin 1 and SHH, and the effect of Gremlin 1 in pancreatic cancer. The expression of Gremlin 1 in different specimens was measured using immunohistochemistry. The correlations among clinico-pathological features and levels of Gremlin 1 were evaluated. Primary human PSCs and pancreatic cancer cell lines were exposed to SHH, cyclopamine, GLI family zinc finger-1 (Gli-1) small interfering RNA (siRNA), and Gremlin 1 siRNA to examine their associations and effects using an MTT assay, reverse transcription-quantitative polymerase chain reaction analysis, western blot analysis, and migration or invasion assays. The results revealed the overexpression of Gremlin 1 in pancreatic cancer tissues, mainly in the stroma. The levels of Gremlin 1 were significantly correlated with survival rate and pT status. In addition, following activation of the PSCs, the expression levels of Gremlin 1 increased substantially. SHH acts as a potent promoter of the expression of Gremlin 1, and cyclopamine and Gli-1 siRNA modulated this effect. In a screen of pancreatic cancer cell lines, AsPC-1 and BxPC-3 cells expressed high levels of Gremlin 1, but only AsPC-1 cells exhibited a high expression level of SHH. The results of the indirect co-culture experiment suggested that paracrine SHH from the AsPC-1 cells induced the expression of Gremlin 1 in the PSCs. Furthermore, Gremlin 1 siRNA negatively regulated the proliferation and migration of PSCs, and the proliferation, invasion and epithelial-mesenchymal transition of AsPC-1 and BxPC-3 cells. Based on the data from the present study, it was concluded that an abnormal expression level of Gremlin 1 in pancreatic cancer was induced by SHH signaling, and that the overexpression of Gremlin 1 enabled pancreatic cancer progression.

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

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

PKCι and YAP1 are crucial in promoting pancreatic tumorigenesis

Pancreatic ductal adenocarcinoma (PDAC) is a fatal malignant disease with 5-year survival rate of less than 6%. Activating mutations of Kras (mu-Kras) are often detected in most of PDAC patients. Although it has been known that oncogenic Kras is the driver of pancreatic cancer initiation and development, the underlying mechanisms by which mu-Kras promotes PDAC remain poorly understood. Here, we identify that PKCι is one of the crucial factors for supporting the survival of pancreatic cancer cells expressing mu-Kras. Our study demonstrates that after the knockdown of PKCι, the expression of the transcriptional co-activator YAP1 is decreased, which hinders the expression of the downstream target gene Mcl-1, and subsequently sensitizes pancreatic cancer MiaPaCa and PANC-1 cells experssing mu-Kras to apoptosis. In comparison, the suppression of PKCι has little impact on the viability of non-neoplastic pancreatic HPDE6-C7 cells. Moreover, the transient overexpression of oncogenic Kras in HPDE6-C7 elevates the expression of PKCι and YAP1 concomitantly. The upregulated YAP1 in HPDE6-C7/ mu-Kras cells is abolished once PKCι is suppressed, suggesting the linear relationship among mu-Kras, PKCι and YAP1. This phenomenon is further proven by the co-upregulation of PKCι and YAP1 in HPDE6-C7 cells stably transfected with mu-Kras. Taken together, our findings suggest that PKCι acts through promoting YAP1 function to promote the survival of pancreatic cancer cells expressing mu-Kras. It appears that targeting PKCι-YAP1 signaling is a feasible strategy for developing new therapeutics for treating pancreatic cancer patients.

Targeting the Multidrug Transporter Ptch1 Potentiates Chemotherapy Efficiency

One of the crucial challenges in the clinical management of cancer is resistance to chemotherapeutics. Multidrug resistance (MDR) has been intensively studied, and one of the most prominent mechanisms underlying MDR is overexpression of adenosine triphosphate (ATP)-binding cassette (ABC) transporters. Despite research efforts to develop compounds that inhibit the efflux activity of ABC transporters and thereby increase classical chemotherapy efficacy, to date, the Food and Drug Administration (FDA) has not approved the use of any ABC transporter inhibitors due to toxicity issues. Hedgehog signaling is aberrantly activated in many cancers, and has been shown to be involved in chemotherapy resistance. Recent studies showed that the Hedgehog receptor Ptch1, which is over-expressed in many recurrent and metastatic cancers, is a multidrug transporter and it contributes to the efflux of chemotherapeutic agents such as doxorubicin, and to chemotherapy resistance. Remarkably, Ptch1 uses the proton motive force to efflux drugs, in contrast to ABC transporters, which use ATP hydrolysis. Indeed, the “reversed pH gradient” that characterizes cancer cells, allows Ptch1 to function as an efflux pump specifically in cancer cells. This makes Ptch1 a particularly attractive therapeutic target for cancers expressing Ptch1, such as lung, breast, prostate, ovary, colon, brain, adrenocortical carcinoma, and melanoma. Screening of chemical libraries have identified several molecules that are able to enhance the cytotoxic effect of different chemotherapeutic agents by inhibiting Ptch1 drug efflux activity in different cancer cell lines that endogenously over-express Ptch1. In vivo proof of concept has been performed in mice where combining one of these compounds with doxorubicin prevented the development of xenografted adrenocortical carcinoma tumors more efficiently than doxorubicin alone, and without obvious undesirable side effects. Therefore, the use of a Ptch1 drug efflux inhibitor in combination with classical or targeted therapy could be a promising therapeutic option for Ptch1-expressing cancers.

Itraconazole perturbs colorectal cancer dormancy through SUFU-mediated WNT inhibition

Cancer cell dormancy is an important source of treatment failure. We studied the molecular characteristics and functional behaviour of dormant colorectal cancer cells finding them to be a differentiated yet plastic population. Organoid drug screening identified itraconazole perturbs dormancy through non-canonical hedgehog signalling effects on the WNT pathway.

SOX2 regulation by hedgehog signaling controls adult lingual epithelium homeostasis

Adult tongue epithelium is continuously renewed from epithelial progenitor cells, a process that requires hedgehog (HH) signaling. In mice, pharmacological inhibition of the HH pathway causes taste bud loss within a few weeks. Previously, we demonstrated that sonic hedgehog (SHH) overexpression in lingual progenitors induces ectopic taste buds with locally increased SOX2 expression, suggesting that taste bud differentiation depends on SOX2 downstream of HH. To test this, we inhibited HH signaling in mice and observed a rapid decline in Sox2 and SOX2-GFP expression in taste epithelium. Upon conditional deletion of Sox2, differentiation of both taste and non-taste epithelial cells was blocked, and progenitor cell number increased. In contrast to basally restricted proliferation in controls, dividing cells were overabundant and spread to suprabasal epithelial layers in mutants. SOX2 loss in progenitors also led non-cell-autonomously to taste cell apoptosis, dramatically shortening taste cell lifespans. Finally, in tongues with conditional Sox2 deletion and SHH overexpression, ectopic and endogenous taste buds were not detectable; instead, progenitor hyperproliferation expanded throughout the lingual epithelium. In summary, we show that SOX2 functions downstream of HH signaling to regulate lingual epithelium homeostasis.

Non-Canonical Hedgehog Signaling Is a Positive Regulator of the WNT Pathway and Is Required for the Survival of Colon Cancer Stem Cells

Colon cancer is a heterogeneous tumor driven by a subpopulation of cancer stem cells (CSCs). To study CSCs in colon cancer, we used limiting dilution spheroid and serial xenotransplantation assays to functionally define the frequency of CSCs in a panel of patient-derived cancer organoids. These studies demonstrated cancer organoids to be enriched for CSCs, which varied in frequency between tumors. Whole-transcriptome analysis identified WNT and Hedgehog signaling components to be enhanced in CSC-enriched tumors and in aldehyde dehydrogenase (ALDH)-positive CSCs. Canonical GLI-dependent Hedgehog signaling is a negative regulator of WNT signaling in normal intestine and intestinal tumors. Here, we show that Hedgehog signaling in colon CSCs is autocrine SHH-dependent, non-canonical PTCH1 dependent, and GLI independent. In addition, using small-molecule inhibitors and RNAi against SHH-palmitoylating Hedgehog acyltransferase (HHAT), we demonstrate that non-canonical Hedgehog signaling is a positive regulator of WNT signaling and required for colon CSC survival.

Pharmacokinetics and biodistribution of polymeric micelles containing miRNA and small-molecule drug in orthotopic pancreatic tumor-bearing mice

Rationale: Successful treatment of pancreatic cancer remains a challenge due to desmoplasia and prevalence of KRAS mutation. While hedgehog (Hh) ligand levels are upregulated in pancreatic cancer cells and contribute to desmoplasia, there is significant downregulation of tumor suppressor let-7b, which targets mutant KRAS, C-MYC and several other genes involved in pancreatic cancer progression, invasion, and metastasis. We recently explored combination therapy of GDC-0449 (Hh inhibitor) and let-7b mimic using poly(ethylene glycol)-block-poly(2-methyl-2-carboxyl-propylene carbonate-graft-dodecanol-graft-tetraethylenepentamine) (PEG-b-PCC-g-DC-g-TEPA) micelles in pancreatic tumor mouse model. Here, our objective was to determine the biodistribution (BD), pharmacokinetics (PK), therapeutic efficacy and toxicity of this micellar formulation. Methods: We determined the PK of micelles encapsulating Cy5.5-let-7b and GDC-0449 following intravenous injection in orthotopic pancreatic tumor-bearing NSG mice at doses of 2 mg/kg and 10 mg/kg, respectively. Mice were scanned for fluorescence by IVIS to determine the biodistribution of Cy5.5-let-7b at the whole-body level, and its concentration in plasma and major organs was determined by measuring fluorescence using a fluorimeter and by real-time RT-PCR. GDC-0449 concentration was determined by LC/MS/MS. Therapeutic efficacy and toxicity of the micellar formulation of let-7b and GDC-0449 was also determined after two weeks of treatment. Results: The use of a micellar formulation markedly prolonged the elimination half-life (t_{1/2, e}) of Cy5.5-let-7b in plasma from 0.49 ± 0.19 h to 2.65 ± 0.46 h and increased the area-under-the-curve (AUC _0-∞ ) by 7-fold, while t_1/2,e and AUC _0-∞ of GDC-0449 were increased by 1.78-fold and 3.2-fold, respectively. The micelles significantly decreased the clearance of both encapsulated let-7b mimic and GDC-0449 compared to the emulsion formulation. Compared to the emulsion counterpart, the micellar formulation elevated the delivery of Cy5.5-let-7b and GDC-0449 to the orthotopic pancreatic tumor tissue by 7.8- and 4.2-fold, respectively. Furthermore, there was a significant reduction in tumor volume and negligible systemic toxicity as evident by hematological parameters and histological evaluation. Conclusion: PEG-b-PCC-g-DC-g-TEPA micelles carrying GDC-0449 and let-7b mimic have great potential to improve drug delivery for pancreatic cancer treatment.

Tumor cross-talk networks promote growth and support immune evasion in pancreatic cancer

In the event of an injury, normal tissues exit quiescent homeostasis and rapidly engage a complex stromal and immune program. These tissue repair responses are hijacked and become dysregulated in carcinogenesis to form a growth-supportive tumor microenvironment. In pancreatic ductal adenocarcinoma (PDA), which remains one of the deadliest major cancers, the microenvironment is a key driver of tumor maintenance that impedes many avenues of therapy. In this review, we outline recent efforts made to uncover the microenvironmental cross-talk mechanisms that support pancreatic cancer cells, and we detail the strategies that have been undertaken to help overcome these barriers.

Patched-2 functions to limit Patched-1 deficient skin cancer growth

Purpose

Basal cell carcinoma (BCC) is one of the most common skin cancers, and is typically driven by an aberrantly activated Hedgehog (Hh) pathway. The Hh pathway is regulated by interactions between the Patched-1 (Ptch1) and Smoothened (Smo) receptors. Smo is an activating receptor and is subject to inhibition by Ptch1. Following ligand binding to Ptch1, its inhibitory action is relieved and pathway activation occurs. This receptor interaction is pivotal to restraining uncontrolled cellular growth. Both receptors have been found to be frequently mutated in BCCs. Ptch2 is a Ptch1 paralog that exhibits overlapping functions in both normal development and tissue homeostasis. As yet, its contribution to cancer growth is poorly defined. Here we set out to assess how Ptch2 inhibits BCC growth.

Methods

We used several in vitro readouts for transcriptional and chemotactic Hh signaling in BCC-derived ASZ001 cells, and a novel xenograft model to assess in vivo BCC tumor growth. Gene editing by TALEN was used to untangle the different Ptch2-dependent responses to its ligand sonic hedgehog (Shh).

Results

We first defined the signaling competence of Ptch2 in Ptch1-deficient ASZ001 cells in vitro, and found that Ptch2 ligand binding drives their migration rather than eliciting a transcriptional response. We found that subsequent targeting of Ptch2 abrogated the chemotaxic effect. Next, we tested the contribution of Ptch2 to in vivo tumor growth using a xenograft model and found that reduced Ptch function results in increased tumor growth, but that selective pressure appatently acts against complete Ptch2 ablation.

Conclusions

We conclude that like Ptch1, Ptch2 exerts a tumor-suppressive function in BCC cells, and that after targeting of both paralogs, ligand-independent activation of the Hh pathway contributes to tumor growth.

Electronic supplementary material

The online version of this article (10.1007/s13402-018-0381-9) contains supplementary material, which is available to authorized users.

Time-dependent contribution of BMP, FGF, IGF, and HH signaling to the proliferation of mesenchymal stroma cells during chondrogenesis

Early loss of up to 50% of cells is common for in vitro chondrogenesis of mesenchymal stromal cells (MSC) in pellet culture, reducing the efficacy and the tissue yield for cartilage engineering. Enhanced proliferation could compensate for this unwanted effect, but relevant signaling pathways remain largely unknown. The aim of this study was to identify the contribution of bone morphogenetic protein (BMP), fibroblast growth factor (FGF), insulin-like growth factor (IGF), and hedgehog (HH) signaling toward cell proliferation during chondrogenesis and investigate whether a further mitogenic stimulation is possible and promising. Human MSC were subjected to chondrogenesis in the presence or absence of pathway inhibitors or activators up to Day 14 or from Days 14 to 28, before proliferation, DNA and proteoglycan content were quantified. [3H]-thymidine incorporation revealed arrest of proliferation on Day 3, after which cell division was reinitiated. Although BMP signaling was essential for proliferation throughout chondrogenesis, IGF signaling was relevant only up to Day 14. In contrast, FGF and HH signaling drove proliferation only from Day 14 onward. Early BMP4, IGF-1, or FGF18 treatment neither prevented early cell loss nor allowed further mitogenic stimulation. However, application of the HH-agonist purmorphamine from Day 14 increased proliferation 1.44-fold (p < 0.05) and late BMP4-application enhanced the DNA and proteoglycan content, with significant effects on tissue yield. Conclusively, a differential and phase-dependent contribution of the four pathways toward proliferation was uncovered and BMP4 treatment was promising to enhance tissue yield. Culture forms less prone to size limitations by nutrient/oxygen gradients and a focus on early apoptosis prevention may be considered as the next steps to further enhance chondrocyte formation from MSC.

Hedgehog inhibition mediates radiation sensitivity in mouse xenograft models of human esophageal adenocarcinoma

Background

The Hedgehog (Hh) signaling pathway is active in esophageal adenocarcinoma (EAC). We used a patient-derived murine xenograft (PDX) model of EAC to evaluate tumour response to conventional treatment with radiation/chemoradiation with or without Hh inhibition. Our goal was to determine the potential radioresistance effects of Hh signaling and radiosensitization by Hh inhibitors.

Methods

PDX models were treated with radiation, chemotherapy or combined chemoradiation. Tumour response was measured by growth delay. Hh transcript levels (qRT-PCR) were compared among frozen tumours from treated and control mice. 5E1, a monoclonal SHH antibody, or LDE225, a clinical SMO inhibitor (Novartis®) inhibited Hh signaling.

Results

Precision irradiation significantly delayed xenograft tumour growth in all 7 PDX models. Combined chemoradiation further delayed growth relative to either modality alone in three of six PDX models. Following irradiation, two of three PDX models demonstrated sustained up-regulation of Hh transcripts. Combined LDE225 and radiation, and 5E1 alone delayed growth relative to either treatment alone in a Hh-responsive PDX model, but not in a non-responsive model.

Conclusion

Hh signaling mediates the radiation response in some EAC PDX models, and inhibition of this pathway may augment the efficacy of radiation in tumours that are Hh dependent.

Acetyl-CoA carboxylase inhibitors attenuate WNT and Hedgehog signaling and suppress pancreatic tumor growth

Acetyl-CoA carboxylase (ACC) is the rate-limiting enzyme in de novo fatty acid synthesis, and its ACC1 isoform is overexpressed in pancreatic and various other cancers. The activity of many oncogenic signaling molecules, including WNT and Hedgehog (HH), is post-translationally modified by lipidation. Here, we report that inhibition of ACC by a small molecule inhibitor, BAY ACC002, blocked WNT3A lipidation, secretion, and signaling. In pancreatic cancer cells, where WNT and HH are key oncogenic drivers, ACC inhibition simultaneously suppressed WNT and HH signaling, and led to anti-proliferative effects. Treatment with ACC inhibitors blocked tumor growth and converted the poorly differentiated histological phenotype to epithelial phenotype in multiple cell line-based and patient-derived pancreatic cancer xenograft models. Together, our data highlight the potential utility of ACC inhibitors for pancreatic cancer treatment, and provide novel insight into the link between upregulated de novo fatty acid synthesis in cancer cells, protein lipidation, and oncogenic signaling.

Calcium and Nuclear Signaling in Prostate Cancer

Recently, there have been a number of developments in the fields of calcium and nuclear signaling that point to new avenues for a more effective diagnosis and treatment of prostate cancer. An example is the discovery of new classes of molecules involved in calcium-regulated nuclear import and nuclear calcium signaling, from the G protein-coupled receptor (GPCR) and myosin families. This review surveys the new state of the calcium and nuclear signaling fields with the aim of identifying the unifying themes that hold out promise in the context of the problems presented by prostate cancer. Genomic perturbations, kinase cascades, developmental pathways, and channels and transporters are covered, with an emphasis on nuclear transport and functions. Special attention is paid to the molecular mechanisms behind prostate cancer progression to the malignant forms and the unfavorable response to anti-androgen treatment. The survey leads to some new hypotheses that connect heretofore disparate results and may present a translational interest.

Stroma - A Double-Edged Sword in Pancreatic Cancer: A Lesson From Targeting Stroma in Pancreatic Cancer With Hedgehog Signaling Inhibitors

Pancreatic cancer is a uniformly lethal malignancy with an abundant dense desmoplastic stroma. Because of its dense stroma, conventional drugs were considered to not penetrate this physical barrier, and this caused a systemic drug resistance. Thus, abolishing this barrier with targeted agents is considered to improve the efficiency of chemotherapeutic treatment. The Hedgehog (Hh) signaling pathway is a critical regulator of pancreas development and plays diversified roles in pancreatic cancer stroma and neoplastic cells. Increasing Hh expression in neoplastic cells added desmoplastic stroma accumulation in orthotopic tumors, and Hh inhibitors that target the stroma have an ability to prolong the overall survival of Pdx-1-Cre/KrasG12D/p53R172H mice models via deleting the stromal components and increasing vascularity in pancreatic tumor. However, the failure of translation from bench to bedside indicate the complexity of the relationship between Hh signaling and desmoplastic stroma, and more insights into the complex relationships between Hh signaling pathway and stroma, even tumor cells, might help redesign Hh-targeted therapy. In this review, we discuss the possible mechanism of translation of Hh inhibitor in the clinic from pathology to molecular mechanism.

Cyclopamine treatment disrupts extracellular matrix and alleviates solid stress to improve nanomedicine delivery for pancreatic cancer

As one of the most intractable tumours, pancreatic ductal adenocarcinoma (PDA) has a dense extracellular matrix (ECM) which could increase solid stress within tumours to compress tumour vessels, reduce tumour perfusion and compromise nanomedicine delivery for PDA. Thus, alleviating solid stress represents a potential therapeutic target for PDA treatment. In this study, cyclopamine, a special inhibitor of the hedgehog signalling pathway which contributes a lot to ECM formation of PDA, was exploited to alleviate solid stress and improve nanomedicine delivery to PDA. Results demonstrated that cyclopamine successfully disrupted ECM and lowered solid stress within PDA, which increased functional tumour vessels and resulted in enhanced tumour perfusion as well as improved tumour nanomedicine delivery in PDA-bearing animal models. Therefore, solid stress within PDA represents a new therapeutic target for PDA treatment.

Do anti-stroma therapies improve extrinsic resistance to increase the efficacy of gemcitabine in pancreatic cancer?

Pancreatic ductal adenocarcinoma (PDAC) is among the most devastating human malignancies, with approximately 20-30% of PDAC patients receiving the surgical resection with curative intent. Although many studies have focused on finding ideal "drug chaperones" that facilitate and/or potentiate the effects of gemcitabine (GEM) in pancreatic cancer, a significant benefit in overall survival could not be demonstrated for any of these combination therapies in PDAC. Given that pancreatic cancer is characterized by desmoplasia and the dual biological roles of stroma in pancreatic cancer, we reassess the importance of stroma in GEM-based therapeutic approaches in light of current findings. This review is focused on understanding the role of stromal components in the extrinsic resistance to GEM and whether anti-stroma therapies have a positive effect on the GEM delivery. This work contributes to the development of novel and promising combination GEM-based regimens that have achieved significant survival benefits for the patients with pancreatic cancer.

Biomimetic nanoparticles delivered hedgehog pathway inhibitor to modify tumour microenvironment and improved chemotherapy for pancreatic carcinoma

The unique tumour microenvironment (TM) of pancreatic ductal adenocarcinoma (PDA) including highly desmoplastic ECM and low tumour perfusion supports a considerable barrier for effective delivery of nanomedicines. Effectively modulating PDA microenvironment to enhance tumour drug delivery represents a pinpoint in the field of PDA treatment. In this study, it was the first time that biomimetic nanoparticles, which were designed in the form of erythrocyte membrane-camouflaged PLGA nanoparticles (MNP), were utilized for PDA microenvironment modulation. Cyclopamine (CYC), an inhibitor of Hedgehog pathway that contributed a lot to desmoplastic ECM of PDA, was selected as the model drug and successfully encapsulated into MNP. Advantages of CYC-loaded MNP (CMNP) included favourable biocompatibility, long circulation time, and powerful TM modulation effect. CMNP could effectively deliver CYC to the tumour site, disrupt tumour ECM, increase functional vessels, and improve tumour perfusion significantly. The combination treatment with CMNP and PTX-loaded MNP (PMNP) successfully improved PTX delivery to tumour, resulting in remarkable tumour growth inhibition in vivo. Therefore, biomimetic nanoparticles provide a new strategy for modulating PDA TM and will have great potential to improve the therapeutic effects of nanomedicines for PDA patients.

Endoplasmic reticulum chaperone glucose-regulated protein 78 in gastric cancer: An emerging biomarker

The endoplasmic reticulum (ER) is the principal organelle responsible for the synthesis, initial post-translational modification, folding, export and secretion of proteins. It is also responsible for the maintenance of cellular homeostasis. In response to cellular stress conditions including glucose deprivation, hypoxia and changes in calcium homeostasis, ER stress machinery is activated and triggers the unfolded protein response, resulting in the restoration of homeostasis or activation of cell death. Glucose-regulated protein 78 (GRP78), a molecular chaperone, may be induced by ER stress at the transcriptional and translational level. A number of studies have demonstrated that GRP78 serves an important role in tumor cell proliferation, metastasis, angiogenesis and drug-resistance. The present review systematically describes the association between GRP78 expression and gastric cancer pathogenesis, and emphasizes that GRP78 is a novel diagnostic and therapeutic biomarker of gastric cancer.

Preclinical characterization of therapeutic antibodies targeted at the carboxy-terminus of Sonic hedgehog

The Sonic Hedgehog (Shh) signaling pathway has been implicated in the development and tumor progression of a number of human cancers. Using synthetic peptide mimics to mount an immune response, we generated a mouse mAb to the carboxy (C)-terminus of the Shh protein and characterized its preclinical antitumor effects. In vitro screening guided selection of the best candidate for mAb scale-up production and therapeutic development. C-term anti-Shh, Ab 1C11-2G4 was selected based on ELISA screens, Western blotting, and flow cytometric analyses. Purified Ab 1C11-2G4 was shown to recognize and bind both Shh peptide mimics and cell surface Shh. Administration of Ab 1C11-2G4 not only reduced cell viability in 7 cancer cell lines but also significantly inhibitted tumor growth in a xenograft model of A549 lung cancer cells. Ex vivo analyses of xenograft tumors revealed a reduction in Shh signal transduction and apoptosis in 2G4-treated mice. Collectively, our results provide early demonstration of the antitumor utility of antibodies specific for the C-terminal region of Shh, and support continued development to evaluate their potential efficacy in cancers in which Shh activity is elevated.

SMO Inhibition Modulates Cellular Plasticity and Invasiveness in Colorectal Cancer

HIGHLIGHTS Preliminary results of this work were presented at the 2016 Academic Surgical Congress, Jacksonville (FL), February 2-4 2016 (Original title: Selective Smo-Inhibition Interferes With Cellular Energetic Metabolism In Colorectal Cancer)This study was funded by "Sapienza-University of Rome" (Funds for young researchers) and "AIRC" (Italian Association for Cancer Research)Hedgehog inhibitor was kindly provided by Genentech, Inc.®. Colon Cancer (CC) is the fourth most frequently diagnosed tumor and the second leading cause of death in the USA. Abnormalities of Hedgehog pathway have been demonstrated in several types of human cancers, however the role of Hedgehog (Hh) in CC remain controversial. In this study, we analyzed the association between increased mRNA expression of GLI1 and GLI2, two Hh target genes, and CC survival and recurrence by gene expression microarray from a cohort of 382 CC patients. We found that patients with increased expression of GLI1 showed a statistically significant reduction in survival. In order to demonstrate a causal role of Hh pathway activation in the pathogenesis of CC, we treated HCT 116, SW480 and SW620 CC cells lines with GDC-0449, a pharmacological inhibitor of Smoothened (SMO). Treatment with GDC-0449 markedly reduced expression of Hh target genes GLI1, PTCH1, HIP1, MUC5AC, thus indicating that this pathway is constitutively active in CC cell lines. Moreover, GDC-0449 partially reduced cell proliferation, which was associated with upregulation of p21 and downregulation of CycD1. Finally, treatment with the same drug reduced migration and three-dimensional invasion, which were associated with downregulation of Snail1, the EMT master gene, and with induction of the epithelial markers Cytokeratin-18 and E-cadherin. These results were confirmed by SMO genetic silencing. Notably, treatment with 5E1, a Sonic Hedgehog-specific mAb, markedly reduced the expression of Hedgehog target genes, as well as inhibited cell proliferation and mediated reversion toward an epithelial phenotype. This suggests the existence of a Hedgehog autocrine signaling loop affecting cell plasticity and fostering cell proliferation and migration/invasion in CC cell lines. These discoveries encourage future investigations to better characterize the role of Hedgehog in cellular plasticity and invasion during the different steps of CC pathogenesis.

Transcriptional deregulation underlying the pathogenesis of small cell lung cancer

The discovery of recurrent alterations in genes encoding transcription regulators and chromatin modifiers is one of the most important recent developments in the study of the small cell lung cancer (SCLC) genome. With advances in models and analytical methods, the field of SCLC biology has seen remarkable progress in understanding the deregulated transcription networks linked to the tumor development and malignant progression. This review will discuss recent discoveries on the roles of RB and P53 family of tumor suppressors and MYC family of oncogenes in tumor initiation and development. It will also describe the roles of lineage-specific factors in neuroendocrine (NE) cell differentiation and homeostasis and the roles of epigenetic alterations driven by changes in NFIB and chromatin modifiers in malignant progression and chemoresistance. These recent findings have led to a model of transcriptional network in which multiple pathways converge on regulatory regions of crucial genes linked to tumor development. Validation of this model and characterization of target genes will provide critical insights into the biology of SCLC and novel strategies for tumor intervention.

Veratramine modulates AP-1-dependent gene transcription by directly binding to programmable DNA

Because the transcription factor activator protein-1 (AP-1) regulates a variety of protein-encoding genes, it is a participant in many cellular functions, including proliferation, transformation, epithelial mesenchymal transition (EMT), and apoptosis. Inhibitors targeting AP-1 have potential use in the treatment of cancer and other inflammatory diseases. Here, we identify veratramine as a potent natural modulator of AP-1, which selectively binds to a specific site (TRE 5'-TGACTCA-3') of the AP-1 target DNA sequence and regulates AP-1-dependent gene transcription without interfering with cystosolic signaling cascades that might lead to AP-1 activation. Moreover, RNA-seq experiments demonstrate that veratramine does not act on the Hedgehog signaling pathway in contrast to its analogue, cyclopamine, and likely does not harbor the same teratogenicity and toxicity. Additionally, veratramine effectively suppresses EGF-induced AP-1 transactivation and transformation of JB6 P+ cells. Finally, we demonstrate that veratramine inhibits solar-ultraviolet-induced AP-1 activation in mice. The identification of veratramine and new findings in its specific regulation of AP-1 down stream genes pave ways to discovering and designing regulators to regulate transcription factor.

GANT-61 and GDC-0449 induce apoptosis of prostate cancer stem cells through a GLI-dependent mechanism

Aberrant reactivation of the Sonic Hedgehog (SHH) signaling pathway promotes prostate cancer (PC) growth and progression by regulating cancer-related genes through its downstream effectors GLI1 and GLI2. Therefore, targeting the SHH-GLI pathway provides an alternative approach to avoid cancer progression. The aim of this study was to delineate the underlying molecular mechanisms by which GDC-0449 (a SMO receptor inhibitor) and GANT-61 (a GLI transcription factor inhibitor) regulate cellular proliferation and self-renewal in human PC stem cells (ProCSCs). Inhibition of the SHH signaling pathway by GANT-61 induced apoptosis with more efficacy than by GDC-0449 in ProCSCs and PC cell lines. GLI1 and GLI2 expression, promoter-binding activity and GLI-responsive luciferase reporter activity were all decreased with either GDC-0449 or GANT-61 treatment. Expression of Fas, DR4, DR5, and cleavage of caspase-3 and PARP were increased, whereas levels of PDGFR-α and Bcl-2 were reduced. Double knockout of GLI1 and GLI2 using shRNA abolished the effects observed with either GDC-0449 or GANT-61 treatment. Collectively, our results showed that GANT-61 and GDC-0449 induced ProCSC apoptosis by directly or indirectly inhibiting the activities of the GLI family transcription factors, may enhance the efficacy of PC treatment.

Strategies to target the Hedgehog signaling pathway for cancer therapy

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

Vismodegib

Vismodegib (GDC-0449, Erivedge^®) is a small molecule antagonist of the hedgehog (Hh) pathway that binds to smoothened (SMO) and leads to inhibition of an aberrant activation of the Hh pathway. Dysregulated Hh signaling results in uncontrolled proliferation in basal cell carcinoma (BCC) and has also been found present in medulloblastoma, and many other cancers such as those of gastrointestinal tract, brain, lung, breast, and prostate. In January 2012, vismodegib became the first agent to target the Hh pathway to receive approval by the United States Food and Drug Administration (FDA) and in July 2013 approval by the European Medicines Agency (EMA) followed for the treatment of adult patients with symptomatic metastatic BCC, or locally advanced BCC inappropriate for surgery or radiotherapy. The role of vismodegib in other malignancies than BCC has still to be investigated.

Carcinogenicity assessment of the Hedgehog pathway inhibitor, vismodegib in Tg.rasH2 mice and Sprague-Dawley rats

Vismodegib (also known as GDC-0449) is a novel small molecule inhibitor of the Hedgehog (Hh) signaling pathway currently approved for the treatment of metastatic or locally advanced basal cell carcinoma (BCC) in humans. Its tumorigenic potential was assessed in dedicated carcinogenicity studies in rasH2 transgenic (Tg.rasH2) mice and Sprague Dawley (SD) rats. Tumorigenicity potential of vismodegib was identified in rats only and was limited to benign hair follicle tumors, including pilomatricomas and keratoacanthomas at exposures of ≥0.1-fold and ≥0.6-fold, respectively, of the steady-state exposure (AUC_0-24h) of the recommended human dose. No malignant tumors were identified in either species. Overall, the totality of pharmacology and nonclinical safety data (lack of genotoxicity, in vitro secondary pharmacological binding, and immunoregulatory effects, and limited effects on the endocrine system) suggests that the development of the benign hair follicle tumors may be related to pharmacologically-mediated disruption of hair follicle morphogenesis, although the exact mechanism of tumorigenesis is unclear. Hair follicle tumors have not been reported in vismodegib-treated patients. The relevance of this finding in rats to patients is uncertain.

Complex roles of the stroma in the intrinsic resistance to gemcitabine in pancreatic cancer: where we are and where we are going

Pancreatic ductal adenocarcinoma (PDAC) is among the most devastating human malignancies. The poor clinical outcome in PDAC is partly attributed to a growth-permissive tumor microenvironment. In the PDAC microenvironment, the stroma is characterized by the development of extensive fibrosis, with stromal components outnumbering pancreatic cancer cells. Each of the components within the stroma has a distinct role in conferring chemoresistance to PDAC, and intrinsic chemoresistance has further worsened this pessimistic prognosis. The nucleoside analog gemcitabine (GEM) is usually the recommended first-line chemotherapeutic agent for PDAC patients and is given alone or in combination with other agents. The mechanisms of intrinsic resistance to GEM are an active area of ongoing research. This review highlights the important role the complex structure of stroma in PDAC plays in the intrinsic resistance to GEM and discusses whether antistroma therapy improves the efficacy of GEM. The addition of antistroma therapy combined with GEM is expected to be a novel therapeutic strategy with significant survival benefits for PDAC patients.

Cancer stem cells and differentiation therapy

Cancer stem cells can generate tumors from only a small number of cells, whereas differentiated cancer cells cannot. The prominent feature of cancer stem cells is its ability to self-renew and differentiate into multiple types of cancer cells. Cancer stem cells have several distinct tumorigenic abilities, including stem cell signal transduction, tumorigenicity, metastasis, and resistance to anticancer drugs, which are regulated by genetic or epigenetic changes. Like normal adult stem cells involved in various developmental processes and tissue homeostasis, cancer stem cells maintain their self-renewal capacity by activating multiple stem cell signaling pathways and inhibiting differentiation signaling pathways during cancer initiation and progression. Recently, many studies have focused on targeting cancer stem cells to eradicate malignancies by regulating stem cell signaling pathways, and products of some of these strategies are in preclinical and clinical trials. In this review, we describe the crucial features of cancer stem cells related to tumor relapse and drug resistance, as well as the new therapeutic strategy to target cancer stem cells named "differentiation therapy."

Targeted molecular ablation of cancer stem cells for curing gastrointestinal cancers

Abundance of the ATPase-binding cassette (ABC) transporters and deranged self-renewal pathways characterize the presence of cancer stem cells (CSCs) in gastrointestinal cancers (GI cancers), which play crucial roles in tumorigenesis, chemotherapy resistance, tumor recurrence, and cancer metastasis. Therefore, in order to ensure high cure rates, chemoquiescence, CSCs should be ablated. Recent advances in either understanding CSCs or biomarker identification enable scientists to develop techniques for ablating CSCs and clinicians to provide cancer cure, especially in GI cancers characterized by inflammation-driven carcinogenesis. Areas covered: A novel approach to ablate CSCs in GI cancers, including esophageal, gastric, and colon cancers, is introduced along with explored underlying molecular mechanisms. Expert commentary: Though CSC ablation is still in the empirical stages and not in clinical practice, several strategies for ablating CSCs in GI cancers had been published, proton-pump inhibitors (PPIs) that regulate the membrane-bound ABC transporters, which underlie drug resistance; chloroquine (CQ) that inhibits autophagy, which is responsible for tumor survival; Hedgehog/Wnt/Notch inhibitors that influence the underlying stem-cell growth, and some natural products including Korean red ginseng, cancer-preventive kimchi, Artemisia extract, EGCG from green tea, and walnut extracts.

GDC-0449 improves the antitumor activity of nano-doxorubicin in pancreatic cancer in a fibroblast-enriched microenvironment

Pancreatic cancer is one of the most lethal human cancers that currently does not have effective therapies. Novel treatments including nanomedicines and combination therapies are thus urgently needed for these types of deadly diseases. A key feature of pancreatic cancer is its tumor protective dense stroma, which is generated by cancer-associated fibroblasts (CAFs). The interaction between CAFs and pancreatic cancer cells abnormally activates sonic hedgehog (SHH) signaling and facilitates tumor growth, metastasis, and drug resistance. Here, we report that the commercial SHH inhibitor GDC-0449 reverses fibroblast-induced resistance to doxorubicin in Smoothened (SMO)-positive pancreatic cancer cells by downregulating SHH signaling proteins. Importantly, the synergistic combination of GDC-0449 with PEG-PCL-Dox exhibited potent antitumor efficacy in a BxPC-3 tumor xenograft model, whereas single treatments did not significantly inhibit tumor growth. Our findings reveal a potential treatment strategy for fibroblast-enriched pancreatic cancer.

LSD1 protects against hippocampal and cortical neurodegeneration

To investigate the mechanisms that maintain differentiated cells, here we inducibly delete the histone demethylase LSD1/KDM1A in adult mice. Loss of LSD1 leads to paralysis, along with widespread hippocampus and cortex neurodegeneration, and learning and memory defects. We focus on the hippocampus neuronal cell death, as well as the potential link between LSD1 and human neurodegenerative disease and find that loss of LSD1 induces transcription changes in common neurodegeneration pathways, along with the re-activation of stem cell genes, in the degenerating hippocampus. These data implicate LSD1 in the prevention of neurodegeneration via the inhibition of inappropriate transcription. Surprisingly, we also find that transcriptional changes in the hippocampus are similar to Alzheimer’s disease (AD) and frontotemporal dementia (FTD) cases, and LSD1 is specifically mislocalized to pathological protein aggregates in these cases. These data raise the possibility that pathological aggregation could compromise the function of LSD1 in AD and FTD.

“LSD1 is a histone demethylase that plays many roles during development. Here, the authors provide evidence that loss of LSD1 in adult mice leads to paralysis and neurodegeneration in the hippocampus and cortex and suggest a potential link between LSD1 and human neurodegenerative disease.