Indispensable role of Notch ligand-dependent signaling in the proliferation and stem cell niche maintenance of APC-deficient intestinal tumors. Biochem Biophys Res Commun. 2017;482:1296-1303. [PMID: 27939883 DOI: 10.1016/j.bbrc.2016.12.031]

Notch receptor/ligand diversity: contribution to colorectal cancer stem cell heterogeneity

Cancer cell heterogeneity is a key contributor to therapeutic failure and post-treatment recurrence. Targeting cell subpopulations responsible for chemoresistance and recurrence seems to be an attractive approach to improve treatment outcome in cancer patients. However, this remains challenging due to the complexity and incomplete characterization of tumor cell subpopulations. The heterogeneity of cells exhibiting stemness-related features, such as self-renewal and chemoresistance, fuels this complexity. Notch signaling is a known regulator of cancer stem cell (CSC) features in colorectal cancer (CRC), though the effects of its heterogenous signaling on CRC cell stemness are only just emerging. In this review, we discuss how Notch ligand-receptor specificity contributes to regulating stemness, self-renewal, chemoresistance and cancer stem cells heterogeneity in CRC.

Subversion of Niche-Signalling Pathways in Colorectal Cancer: What Makes and Breaks the Intestinal Stem Cell

The intestinal epithelium fulfils pleiotropic functions in nutrient uptake, waste elimination, and immune surveillance while also forming a barrier against luminal toxins and gut-resident microbiota. Incessantly barraged by extraneous stresses, the intestine must continuously replenish its epithelial lining and regenerate the full gamut of specialized cell types that underpin its functions. Homeostatic remodelling is orchestrated by the intestinal stem cell (ISC) niche: a convergence of epithelial- and stromal-derived cues, which maintains ISCs in a multipotent state. Following demise of homeostatic ISCs post injury, plasticity is pervasive among multiple populations of reserve stem-like cells, lineage-committed progenitors, and/or fully differentiated cell types, all of which can contribute to regeneration and repair. Failure to restore the epithelial barrier risks seepage of toxic luminal contents, resulting in inflammation and likely predisposing to tumour formation. Here, we explore how homeostatic niche-signalling pathways are subverted in tumorigenesis, enabling ISCs to gain autonomy from niche restraints ("ISC emancipation") and transform into cancer stem cells capable of driving tumour initiation, progression, and therapy resistance. We further consider the implications of the pervasive plasticity of the intestinal epithelium for the trajectory of colorectal cancer, the emergence of distinct molecular subtypes, the propensity to metastasize, and the development of effective therapeutic strategies.

The Relevance of Notch Signaling in Cancer Progression

The Notch signaling pathway controls normal embryonic development and tissue homeostasis of many cell types. It regulates cell proliferation, fate, differentiation, and cell death by short-range signaling between nearby cells that come in contact. The Notch pathway has also been critically involved in the pathobiology of a variety of malignancies, regulating cancer initiation and development, as well as early stages of cancer progression, by adjusting conserved cellular programs. Fibroblasts, an essential for tumor growth component of stroma, have also been affected by Notch regulation. Sequencing Notch gene mutations have been identified in a number of human tumors, revealing information on the progression of specific cancer types, such as ovarian cancer and melanoma, immune-associated tumors such as myeloid neoplasms, but especially in lymphocytic leukemia. Activation of the Notch can be either oncogenic or it may contain growth-suppressive functions, acting as a tumor suppressor in other hematopoietic cells, hepatocytes, skin, and pancreatic epithelium.

Shaping of the Tumor Microenvironment by Notch Signaling

The tumor microenvironment (TME) has become a major concern of cancer research both from a basic and a therapeutic point of view. Understanding the effect of a signaling pathway-and thus the effect of its targeting-in every aspect of the microenvironment is a prerequisite to predict and analyze the effect of a therapy. The Notch signaling pathway is involved in every component of the TME as well as in the interaction between the different parts of the TME. This review aims at describing how Notch signaling is impacting the TME and the consequences this may have when modulating Notch signaling in a therapeutic perspective.

Targeting cancer stem cells in drug discovery: Current state and future perspectives

In recent decades, cancer stem cells (CSCs) have been increasingly identified in many malignancies. CSC-related signaling pathways and their functions provide new strategies for treating cancer. The aberrant activation of related signaling pathways (e.g., Wnt, Notch, and Hedgehog pathways) has been linked to multiple types of malignant tumors, which makes these pathways attractive targets for cancer therapy. CSCs display many characteristic features, such as self-renewal, differentiation, high tumorigenicity, and drug resistance. Therefore, there is an urgent need to develop new therapeutic strategies to target these pathways to control stem cell replication, survival, and differentiation. Notable crosstalk occurs among different signaling pathways and potentially leads to compensatory escape. Therefore, multitarget inhibitors will be one of the main methods to overcome the drug resistance of CSCs. Many small molecule inhibitors of components of signaling pathways in CSCs have entered clinical trials, and some inhibitors, such as vismodegib, sonidegib, and glasdegib, have been approved. Tumor cells are susceptible to sonidegib and vismodegib resistance due to mutations in the Smo protein. The signal transducers and activators of transcription 3 (STAT3) inhibitor BBI608 is being evaluated in a phase III trial for a variety of cancers. Structural derivatives of BBI608 are the main focus of STAT3 inhibitor development, which is another strategy for CSC therapy. In addition to the potential pharmacological inhibitors targeting CSC-related signaling pathways, other methods of targeting CSCs are available, such as nano-drug delivery systems, mitochondrion targeting, autophagy, hyperthermia, immunotherapy, and CSC microenvironment targeting. In addition, we summarize the latest advances in the clinical development of agents targeting CSC-related signaling pathways and other methods of targeting CSCs.

Notch Signaling in the Tumor Microenvironment

The Notch signaling pathway regulates many aspects of cancer biology. Most attention has been given to its role in the transformed cell. However, it is now clear that cancer progression and metastasis depend on the bidirectional interactions between cancer cells and their environment, forming the tumor microenvironment (TME). These interactions are mediated and constantly evolve through paracrine and juxtacrine signaling. In this review, we discuss how Notch signaling takes an important part in regulating the crosstalk between the different compartments of the TME. We also address the consequences of the Notch-TME involvement from a therapeutic perspective.

LGR5 promotes epithelial ovarian cancer proliferation, metastasis, and epithelial-mesenchymal transition through the Notch1 signaling pathway

Leucine-rich repeat-containing G protein-coupled receptor 5 (LGR5) plays a vital role in the development of malignant tumors; however, its biological role and underlying mechanism in epithelial ovarian cancer (EOC) remain unclear. In this study, we aimed to investigate the biological function and clinical significance of LGR5 in human EOC. We evaluated LGR5 expression in EOC cell lines and tissues from ovarian cancer patients by qPCR, Western blotting, and immunohistochemical analysis. Cell proliferation, colony formation, transwell invasion assay, and scratch-wound assays were conducted to evaluate the expansion and invasion abilities of EOC cells. Tumor xenograft experiments were performed in female BALB/c athymic nude mice to test cell proliferation in vivo. Western blot analysis was performed to confirm the expression of epithelial-to-mesenchymal transition (EMT) signature proteins and their association with Notch1 signaling. The results demonstrated that LGR5 was overexpressed in EOC tissues and cell lines. Aberrant expression of LGR5 was significantly associated with patient age (P = 0.006), tumor histologic type (P < 0.001), and distant metastasis (P = 0.025). Consistent with these findings, suppression of LGR5 expression led to decreased proliferation and metastasis of EOC cell lines. Furthermore, LGR5 could induce EMT and regulate the Notch1 signaling pathway. Taken together,LGR5 may have an important role in the promotion of tumorigenesis and metastasis of EOC and is a potential therapeutic target for EOC management.

Colorectal cancer: genetic abnormalities, tumor progression, tumor heterogeneity, clonal evolution and tumor-initiating cells

Colon cancer is the third most common cancer worldwide. Most colorectal cancer occurrences are sporadic, not related to genetic predisposition or family history; however, 20-30% of patients with colorectal cancer have a family history of colorectal cancer and 5% of these tumors arise in the setting of a Mendelian inheritance syndrome. In many patients, the development of a colorectal cancer is preceded by a benign neoplastic lesion: either an adenomatous polyp or a serrated polyp. Studies carried out in the last years have characterized the main molecular alterations occurring in colorectal cancers, showing that the tumor of each patient displays from two to eight driver mutations. The ensemble of molecular studies, including gene expression studies, has led to two proposed classifications of colorectal cancers, with the identification of four/five non-overlapping groups. The homeostasis of the rapidly renewing intestinal epithelium is ensured by few stem cells present at the level of the base of intestinal crypts. Various experimental evidence suggests that colorectal cancers may derive from the malignant transformation of intestinal stem cells or of intestinal cells that acquire stem cell properties following malignant transformation. Colon cancer stem cells seem to be involved in tumor chemoresistance, radioresistance and relapse.

Progress in research of cancer stem cells

Cancer stem cells are a class of malignant cancer cells characterized by self-renewal, high tumorigenicity, differentiation potential, and drug resistance. They not only retain the characteristics of normal stem cells, but also possess their unique features. The study of cancer stem cells can help us develop new strategies for targeted therapy of cancer. In this paper, we will discuss the definition of cancer stem cells, their surface markers, detection methods, and separation methods.

Data showing proliferation and differentiation of intestinal epithelial cells under targeted depletion of Notch ligands in mouse intestine

The data on the immunohistochemical analysis of conditional Notch ligand knockout mice is presented. Targeted deletion of Jag1, Dll1, Dll4, or Dll1 plus Dll4 in Lgr5^+ve cells was induced by a Cre-mediated gene recombination, and differentiation or proliferation of the intestinal epithelial cells was examined by immunohistochemistry. These data are the extension of the data presented and discussed in the paper entitled "Indispensable role of non-canonical Notch signaling in the proliferation of Apc-deficient intestinal tumors" (Nakata et al., Submitted for publication) [1].