Hh Signaling In Cancer Research Articles

Hedgehog Signaling in Colorectal Cancer: All in the Stroma?

Hedgehog (Hh) signaling regulates intestinal development and homeostasis. The role of Hh signaling in cancer has been studied for many years; however, its role in colorectal cancer (CRC) remains controversial. It has become increasingly clear that the “canonical” Hh pathway, in which ligand binding to the receptor PTCH1 initiates a signaling cascade that culminates in the activation of the GLI transcription factors, is mainly organized in a paracrine manner, both in the healthy colon and in CRC. Such canonical Hh signals largely act as tumor suppressors. In addition, stromal Hh signaling has complex immunomodulatory effects in the intestine with a potential impact on carcinogenesis. In contrast, non-canonical Hh activation may have tumor-promoting roles in a subset of CRC tumor cells. In this review, we attempt to summarize the current knowledge of the Hh pathway in CRC, with a focus on the tumor-suppressive role of canonical Hh signaling in the stroma. Despite discouraging results from clinical trials using Hh inhibitors in CRC and other solid cancers, we argue that a more granular understanding of Hh signaling might allow the exploitation of this key morphogenic pathway for cancer therapy in the future.

Hedgehog Signaling Pathway and Autophagy in Cancer.

Hedgehog (Hh) pathway controls complex developmental processes in vertebrates. Abnormal activation of Hh pathway is responsible for tumorigenesis and maintenance of multiple cancers, and thus addressing this represents promising therapeutic opportunities. In recent years, two Hh inhibitors have been approved for basal cell carcinoma (BCC) treatment and show extraordinary clinical outcomes. Meanwhile, a series of novel agents are being developed for the treatment of several cancers, including lung cancer, leukemia, and pancreatic cancer. Unfortunately, Hh inhibition fails to show satisfactory benefits in these cancer types compared with the success stories in BCC, highlighting the need for better understanding of Hh signaling in cancer. Autophagy, a conserved biological process for cellular component elimination, plays critical roles in the initiation, progression, and drug resistance of cancer, and therefore, implied potential to be targeted. Recent evidence demonstrated that Hh signaling interplays with autophagy in multiple cancers. Importantly, modulating this crosstalk exhibited noteworthy capability to sensitize primary and drug-resistant cancer cells to Hh inhibitors, representing an emerging opportunity to reboot the efficacy of Hh inhibition in those insensitive tumors, and to tackle drug resistance challenges. This review will highlight recent advances of Hh pathway and autophagy in cancers, and focus on their crosstalk and the implied therapeutic opportunities.

Abstract 4128: Loss of p53 and Rb enhances ligand-dependent hedgehog signaling in development and cancer

Abstract The evolutionary conserved Hedgehog (Hh) signaling pathway plays fundamental morphogenic and mitogenic roles in tissue development and homeostasis, as well as in the initiation and progression of various cancers. Signaling is driven by the binding of Sonic hedgehog (Shh) ligand to the receptor Patched (Ptch1), to initiate primary cilia dependent Smoothened (Smo)-Gli activation. Although mutations in Hh pathway components are described in some cancers, the majority of Hh tumors exhibit ligand-dependent Hh signaling, where Hh ligand is produced by the stroma and/or tumor cells to maintain pathway activation and self-renewal. Here, we have utilized various Hh-dependent developmental models to better understand the tumorigenic mechanisms of Hh ligand-dependent signaling in cancer. During cerebellar development, Shh is secreted from cerebellar purkinje cells for rapid expansion of the cerebellar granule cell precursor (GCP) population in the external granule layer (EGL). Inactivation of Shh in purkinje cells (Pcp2Cre;Shhfl/fl) leads to reduced GCP proliferation, premature eradication of the EGL and reduced cerebellar size. In contrast, Shh overexpression by purkinje cells (Pcp2Cre;ShhTg) results in increased GCP expansion, a sustained EGL and increased cerebellar size. Indeed, signs of remnant EGL persist into adulthood, similar to the pre-neoplastic lesions observed in Ptch1+/- mice, believed to be the origin of SHH medulloblastoma. During skeletal development, Indian hedgehog secreted from pre-hypertrophic chondroblasts is required for osteoblast progenitor specification from multipotent mesenchymal stem cells. Sustained Hh signaling in osteoblast precursors (OsxCre;SmoM2 or OsxCre;ShhTg) results in reduced ossification of the calvaria, maxilla and mandible, reduced long bone width, and reduced expression of mature osteoblast markers. Together, these models implicate sustained Hh expression in the maintenance of an immature cell state at the expense of differentiation. Moreover, in a mouse model of osteosarcoma, inactivation of Smo (OsxCre;p53fl/fl;Rbfl/fl;Smofl/fl) abolished the malignant phenotype of OsxCre;p53fl/fl;Rbfl/fl mice, leading to benign osteoid osteoma consistent with osteoblast differentiation. Increased Hh signaling in cancers with prevalent p53 and Rb mutations led us to investigate a role for p53 and Rb in Hh ligand-dependent signaling. Genetic inactivation of p53 and/or Rb in the developing mouse neural tube resulted in expansion of the Hh-dependent Nkx2.2 ventral domain, consistent with a Hh gain of function phenotype. Similarly, siRNA knockdown of p53 and/or Rb in mouse mesenchymal stem cell line C3H10T1/2 markedly increased Hh-dependent osteoblast specification in response to Hh ligand. Taken together, we propose that p53 and Rb mutations enhance ligand-dependent Hh pathway activation that maintains cells in a primitive state and promotes tumorigenesis. Citation Format: Catherine R. Cochrane, Anette Szczepny, Samantha W. Jayasekara, Vijesh Vaghjiani, D. Watkins, Jason E. Cain. Loss of p53 and Rb enhances ligand-dependent hedgehog signaling in development and cancer [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2018; 2018 Apr 14-18; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2018;78(13 Suppl):Abstract nr 4128.

Regulation of Hedgehog Signaling in Cancer by Natural and Dietary Compounds.

The aberrant Hedgehog (Hh) signaling induced by mutations or overexpression of the signaling mediators has been implicated in cancer, associated with processes including inflammation, tumor cell growth, invasion, and metastasis, as well as cancer stemness. Small molecules targeting the regulatory components of the Hh signaling pathway, especially Smoothened (Smo), have been developed for the treatment of cancer. However, acquired resistance to a Smo inhibitor vismodegib observed in clinical trials suggests that other Hh signaling components need to be explored as potential anticancer targets. Natural and dietary compounds provide a resource for the development of potent agents affecting intracellular signaling cascades, and numerous studies have been conducted to evaluate the efficacy of natural products in targeting the Hh signaling pathway. In this review, we summarize the role of Hh signaling in tumorigenesis, discuss results from recent studies investigating the effect of natural products and dietary components on Hh signaling in cancer, and provide insight on novel small molecules as potential Hh signaling inhibitors.

Abstract C89: The small molecule inhibitor 4SC-202 controls aberrant HH signaling in cancer

Abstract Introduction: 4SC-202, a clinical stage inhibitor of LSD1 and HDAC1, 2 and 3 was investigated to identify its unique mechanism to target cancer cells by controlling aberrant Hedgehog signaling. Experiments: 4SC-202 is an oral available epigenetic modulator exhibiting a combined inhibition of the lysine specific demethylase LSD1 (KDM1A) and histone deacetylases HDAC1, 2 and 3. 4SC-202's impact on Hedgehog signaling activity was tested in a SMO-dependent setting and in a SMO-independent setting. Therefore, Hedgehog signaling in DAOY cells was either activated by addition of sHH or Smoothened agonist or by stable depletion of SUFU for instrinsic, SMO-independent signaling. Pathway activity was determined by the expression of the effector protein GLI and primary target genes. SMO-independent Hedgehog signaling can be driven as well by growth factors like TGF-ß as demonstrated for the pancreatic cancer cell line PANC1. Therefore, 4SC-202's impact on spheroid formation and protein expression was tested in PANC1 cells. Results: Compared to HDAC inhibitors like Vorinostat, LSD1 inhibitors like OGL-002 and Hedgehog inhibitors targeting SMO like Vismodegib, 4SC-202 was able to inhibit canonical as well as non-canonical GLI-driven Hedgehog signaling. Additionally, 4SC-202 was able to prevent spheroid formation of pancreatic cancer cells and inhibit TGF-ß driven signaling in PANC1 cells. Conclusion: Aberrant activity of the Hedgehog signaling pathway has been implicated in the development, progression and relapse of different cancer entities. Especially the interaction of tumor cells and the microenvironment is driven by SMO-independent Hedgehog signals and therefore Hedgehog inhibitors targeting SMO like Vismodegib were not able to demonstrate clinical benefit in SMO-independent Hedgehog driven cancer types like PDAC. The unique feature of 4SC-202 to control both SMO-dependent and SMO-independent HH signaling provides the opportunity to demonstrate activity in Hedgehog driven entities in further clinical investigations. 4SC-202 was safe and well tolerated in a phase I clinical trial (TOPAS) in patients with advanced hematological diseases. With a disease control rate of 83%, one partial responder treated for 8 months and one complete responder treated for 28 months, patients benefited from 4SC-202 treatment and hints of activity could be demonstrated. Citation Format: Hella Kohlhof, Wolfgang Gruber, Daniel Vitt, Fritz Aberger, Tanja Prenzel. The small molecule inhibitor 4SC-202 controls aberrant HH signaling in cancer. [abstract]. In: Proceedings of the AACR-NCI-EORTC International Conference: Molecular Targets and Cancer Therapeutics; 2015 Nov 5-9; Boston, MA. Philadelphia (PA): AACR; Mol Cancer Ther 2015;14(12 Suppl 2):Abstract nr C89.

Non-Canonical Hh Signaling in Cancer-Current Understanding and Future Directions.

As a major regulatory pathway for embryonic development and tissue patterning, hedgehog signaling is not active in most adult tissues, but is reactivated in a number of human cancer types. A major milestone in hedgehog signaling in cancer is the Food and Drug Administration (FDA) approval of a smoothened inhibitor Vismodegib for treatment of basal cell carcinomas. Vismodegib can block ligand-mediated hedgehog signaling, but numerous additional clinical trials have failed to show significant improvements in cancer patients. Amounting evidence indicate that ligand-independent hedgehog signaling plays an essential role in cancer. Ligand-independent hedgehog signaling, also named non-canonical hedgehog signaling, generally is not sensitive to smoothened inhibitors. What we know about non-canonical hedgehog signaling in cancer, and how should we prevent its activation? In this review, we will summarize recent development of non-canonical hedgehog signaling in cancer, and will discuss potential ways to prevent this type of hedgehog signaling.

Targeting the Hedgehog signaling pathway in cancer: beyond Smoothened.

An essential role for Hedgehog (Hh) signaling in human cancer has been established beyond doubt. At present, targeting Hh signaling has mainly been investigated with SMO inhibitors. Unfortunately, resistance against currently used SMO inhibitors has already been observed in basal cell carcinoma (BCC) patients. Therefore, the use of Hh inhibitors targeting the signaling cascade more downstream of SMO could represent a more promising strategy. Furthermore, besides the classical canonical way of Hh signaling activation, non-canonical activation of the GLI transcription factors by multiple important signaling pathways (e.g. MAPK, PI3K, TGFβ) has also been described, pinpointing the importance of targeting the transcription factors GLI1/2. The most promising agent in this context is probably the GLI1/2 inhibitor GANT61 which has been investigated preclinically in numerous tumor types in the last few years. In this review, the emerging role of Hh signaling in cancer is critically evaluated focusing on the potential of targeting Hh signaling more downstream of SMO, i.e. at the level of the GLI transcription factors. Furthermore, the working mechanism and therapeutic potential of the most extensively studied GLI inhibitor in human cancer, i.e. GANT61, is discussed in detail. In conclusion, GANT61 appears to be highly effective against human cancer cells and in xenograft mouse models, targeting almost all of the classical hallmarks of cancer and could hence represent a promising treatment option for human cancer.

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

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

Lateral transport of Smoothened from the plasma membrane to the membrane of the cilium

The function of primary cilia depends critically on the localization of specific proteins in the ciliary membrane. A major challenge in the field is to understand protein trafficking to cilia. The Hedgehog (Hh) pathway protein Smoothened (Smo), a 7-pass transmembrane protein, moves to cilia when a ligand is received. Using microscopy-based pulse-chase analysis, we find that Smo moves through a lateral transport pathway from the plasma membrane to the ciliary membrane. Lateral movement, either via diffusion or active transport, is quite distinct from currently studied pathways of ciliary protein transport in mammals, which emphasize directed trafficking of Golgi-derived vesicles to the base of the cilium. We anticipate that this alternative route will be used by other signaling proteins that function at cilia. The path taken by Smo may allow novel strategies for modulation of Hh signaling in cancer and regeneration.