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-Secretase Inhibitors, and Cancer TherapyDepartments of Gynecology, Oncology, and Pathology, Johns Hopkins Medical Institutions, Baltimore, Maryland
Requests for reprints: Tian-Li Wang, Johns Hopkins Medical Institutions, Cancer Research Building-II, Room 306, 1550 Orleans Street, Baltimore, Maryland 21231. Phone: 410-502-7774; Fax: 410-502-7943; E-mail: tlw{at}jhmi.edu.
| Abstract |
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-secretase inhibitors prevent the generation of the oncogenic (intracellular) domain of Notch molecules and suppress the Notch activity. This review article summarizes the biological roles of Notch molecules in cancer development with special emphasis on the promise and challenges in applying
-secretase inhibitors as a new line of targeted therapeutic agents. [Cancer Res 2007;67(5):187982] | Background |
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-secretase (also called tumor necrosis factor-
converting enzyme) and
-secretase (Fig. 1A
). The released intracellular Notch-IC then translocates into the nucleus where it modulates gene expression primarily by binding to a ubiquitous transcription factor, CBF1, suppressor of hairless, Lag-1 (CSL). This binding recruits transcription activators to the CSL complex and converts it from a transcriptional repressor into an activator, which turns on several downstream effectors. The physiologic functions of Notch signaling are multifaceted, including maintenance of stem cells, specification of cell fate, and regulation of differentiation in development as well as in oncogenesis (2, 3).
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10% of T-ALL cases and activating point mutations of Notch1 are present in
50% of T-ALL cases (5, 6). Constitutive activation of nuclear factor-
B and formation of T-cell leukemia/lymphoma were observed in a Notch-IC transgenic mouse model (7), which indicates a causal role of Notch activation in T-ALL development. In nonsmall cell lung cancer, chromosomal translocation (15;19) has been identified in a subset of tumors, and the translocation is thought to elevate Notch3 transcription in tumors (8). In ovarian cancer, Notch3 gene amplification was found to occur in
19% of tumors, and overexpression of Notch3 was found in more than half of the ovarian serous carcinomas (9). Similarly, Notch signaling activation has been shown in the development of breast cancer. In animal models, constitutively active Notch4 expression causes mammary tumors in mice (10) and Notch1-activating mutations contribute to the development of T-ALL. A recent study further shows that overexpression of activated Notch1 and Notch3 in transgenic mice blocks mammary gland development and induces mouse breast tumors (11). Overexpression of Notch3 is sufficient to induce choroid plexus tumor formation in a mouse model, suggesting a role of Notch3 in the development of certain types of brain tumors (12).
-Secretase as a Key Mediator of Notch Signaling
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-secretase at the extracellular surface, which leads to liberation of the extracellular fragment, and then by intramembranous cleavage mediated by
-secretase. Notch-IC is then released from the inner surface of cell membrane and is translocated into nucleus where it activates transcription of the target genes. The proteolytic events in Notch signaling activation are comparable with the processes involving amyloid precursor protein (APP) cleavage (Fig. 1B), in which sequential cleavages by ß-secretase and
-secretase release the amyloid ß-peptide (the precursor of amyloid plaques found in the brain of Alzheimer's disease).
-Secretase is a large protease complex and is composed of a catalytic subunit (presenilin-1 or presenilin-2) and accessory subunits (Pen-2, Aph1, and nicastrin). All these subunits contain transmembrane domains and thus they are membrane proteins. The pivotal role of
-secretase in the Notch activation cascade has been well shown in an elegant knockin experiment, showing that introduction of a single point mutation near the transmembrane cleavage site in Notch1 molecules results in an embryonic lethality in mice, which is similar to the effects observed in Notch1 knockout (15). Furthermore, the presenilin-1deficient and presenilin-1/presenilin-2 double knockout mice had a marked decrease in Notch-IC generation (16, 17).
Over the past decades, inhibitors for
-secretase have been actively investigated for their potential to block the generation of Aß peptide that is associated with Alzheimer's disease (18). Because
-secretase inhibitors are also able to prevent Notch receptor activation, several forms of
-secretase inhibitors have been tested for antitumor effects. First, an original
-secretase inhibitor, IL-X (cbz-IL-CHO), was shown to have Notch1-dependent antineoplastic activity in Ras-transformed fibroblasts. More recently, tripeptide
-secretase inhibitor (z-Leu-leu-Nle-CHO) was reported to suppress tumor growth in cell lines and/or xenografts in mice from melanoma and Kaposi sarcoma (19). Treatment with dipeptide
-secretase inhibitor N-[N-(3,5-difluorophenacetyl)-L-alanyl]-S-phenylglycine t-butyl ester (DAPT) also resulted in a marked reduction in medulloblastoma growth and induced G0-G1 cell cycle arrest and apoptosis in a T-ALL animal model (20, 21). Another
-secretase inhibitor, dibenzazepine, has been shown to inhibit epithelial cell proliferation and induce goblet cell differentiation in intestinal adenomas in Apc/ (min) mice (22). More recently, functional inactivation of Notch3 either by tripeptide
-secretase inhibitor or Notch3-specific small interfering RNA results in suppression of cell proliferation and induction of apoptosis in the tumor cell lines that overexpressed Notch3 but not in those with minimal amounts of Notch3 expression (9). Futhermore, a phase I clinical trial for a Notch inhibitor, MK0752 (developed by Merck, Whitehouse Station, NJ), has been launched for relapsed or refractory T-ALL patients and advanced breast cancers.1 As discussed above, Notch signaling and APP metabolism are triggered by the similar proteolytic process; it is foreseeable that
-secretase inhibitors that are currently tested in clinical trials for Alzheimer's disease may be applicable to treat neoplastic diseases, especially those tumors known to harbor constitutive Notch activation. Besides the evidence of
-secretase inhibitors in directly inactivating Notch signaling on cancer cells,
-secretase inhibitors may also suppress angiogenesis in solid tumors by interfering in the cross-talk between the tumor and vasculature through the Notch signaling (23).
The exciting studies summarized above strongly suggest a potential clinical application of
-secretase inhibitors in cancer therapeutics. However, one of the major challenges on the way toward this goal is the untoward side effects associated with the inhibitors, especially the cytotoxicity in the gastrointestinal tract (24), which can be exacerbated by conventional chemotherapeutic drugs. Therefore, balancing efficacy and toxicity of
-secretase inhibitors must be considered in future clinical applications. The possible mechanisms underlying the unwanted cytotoxicity are multifactorial. First, Notch signaling pathway is known to widely participate in cellular physiology in normal tissues, including hematopoiesis and maintenance of arterial smooth muscle (25); therefore, it is plausible that inactivation of
-secretase may lead to dysfunction of vital organs. Second, it is likely that
-secretase inhibitors do not exclusively target the Notch signaling pathways. This is because
-secretase has many substrates in addition to Notch receptors, such as several Notch ligands, ErbB4, syndecan (an extracellular matrix), and CD44 (1). Additionally,
-secretase inhibitors may target proteases other than
-secretase. As proteases participate in a wide variety of cellular functions,
-secretase inhibitors may have other widespread adverse effects in vivo. Some of the concerns of the nonselectivity of the inhibitors will be addressed based on the results of the ongoing clinical trials. Nevertheless, it may prove possible to identify a therapeutic window, in which partial inhibition of
-secretase is sufficient to suppress Notch signaling in cancer cells, whereas the dosage will not significantly affect the functions in normal tissues. It is thought that the differential killing between cancer and normal cells can be exaggerated in treating those tumors with constitutive Notch activation, in which cancer cells are "addicted" to the Notch signaling.
| Implications and Future Directions |
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-secretase complex, the molecular switch for Notch signaling activation. Recently, there has been an increased enthusiasm in targeting this pathway using
-secretase inhibitors for new cancer therapeutics because accumulating preclinical studies have shown that
-secretase inhibitors hold promise as a new target-based therapy for those tumors with Notch activation. However, before Notch-based therapy becomes a reality, future studies should primarily focus on the issues of target specificity and address the possible side effects that may affect cancer patients who receive this new treatment regimen. Furthermore, the clinical promise of
-secretase inhibitors in cancer therapeutics depends on careful correlation studies between the molecular genetic alterations in the Notch gene (e.g., mutations and gene amplification) and clinical response to
-secretase inhibitors. To maximize the therapeutic effects (together with conventional therapeutics) and minimize the adverse side effects in cancer patients, it is essential to show the "tumor dependency" of Notch activation experimentally and clinically. Despite several challenges on the way, it is expected that in the coming years, there will be substantial efforts in identifying new specific
-secretase inhibitors and in opening new clinical trials to test the potential of this new line of cancer therapeutic agents. | Acknowledgments |
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We thank Jook Park for the editorial assistance.
| Footnotes |
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Received 10/25/06. Revised 12/21/06. Accepted 1/ 5/07.
| References |
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B and T-cell leukemia/lymphoma in Notch3 transgenic mice. EMBO J 2000;19:333748.[CrossRef][Medline]
-secretase-like protease mediates release of Notch intracellular domain. Nature 1999;398:51822.[CrossRef][Medline]
Secretase inhibitor blocks Notch activation and induces apoptosis in Kaposi's sarcoma tumor cells. Oncogene 2005;24:633344.[Medline]
-secretase inhibition turns proliferative cells in intestinal crypts and adenomas into goblet cells. Nature 2005;435:95963.[CrossRef][Medline]
-Secretase inhibitors for Alzheimer's disease: balancing efficacy and toxicity. Drugs R D 2006;7:8797.[CrossRef][Medline]This article has been cited by other articles:
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A. L. Radke, L. E. Reynolds, R. C. N. Melo, A. M. Dvorak, P. F. Weller, and L. A. Spencer Mature human eosinophils express functional Notch ligands mediating eosinophil autocrine regulation Blood, March 26, 2009; 113(13): 3092 - 3101. [Abstract] [Full Text] [PDF] |
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A. Magnifico, L. Albano, S. Campaner, D. Delia, F. Castiglioni, P. Gasparini, G. Sozzi, E. Fontanella, S. Menard, and E. Tagliabue Tumor-Initiating Cells of HER2-Positive Carcinoma Cell Lines Express the Highest Oncoprotein Levels and Are Sensitive to Trastuzumab Clin. Cancer Res., March 15, 2009; 15(6): 2010 - 2021. [Abstract] [Full Text] [PDF] |
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R. D. Meng, C. C. Shelton, Y.-M. Li, L.-X. Qin, D. Notterman, P. B. Paty, and G. K. Schwartz {gamma}-Secretase Inhibitors Abrogate Oxaliplatin-Induced Activation of the Notch-1 Signaling Pathway in Colon Cancer Cells Resulting in Enhanced Chemosensitivity Cancer Res., January 15, 2009; 69(2): 573 - 582. [Abstract] [Full Text] [PDF] |
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C. S. Park, O. S. Kim, S.-M. Yun, S. A. Jo, I. Jo, and Y. H. Koh Presenilin 1/{gamma}-Secretase Is Associated with Cadmium-Induced E-Cadherin Cleavage and COX-2 Gene Expression in T47D Breast Cancer Cells Toxicol. Sci., December 1, 2008; 106(2): 413 - 422. [Abstract] [Full Text] [PDF] |
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J. T. Park, I.-M. Shih, and T.-L. Wang Identification of Pbx1, a Potential Oncogene, as a Notch3 Target Gene in Ovarian Cancer Cancer Res., November 1, 2008; 68(21): 8852 - 8860. [Abstract] [Full Text] [PDF] |
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J.-H. Choi, J. T. Park, B. Davidson, P. J. Morin, I.-M. Shih, and T.-L. Wang Jagged-1 and Notch3 Juxtacrine Loop Regulates Ovarian Tumor Growth and Adhesion Cancer Res., July 15, 2008; 68(14): 5716 - 5723. [Abstract] [Full Text] [PDF] |
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C. W. Lee, C. M. Raskett, I. Prudovsky, and D. C. Altieri Molecular Dependence of Estrogen Receptor-Negative Breast Cancer on a Notch-Survivin Signaling Axis Cancer Res., July 1, 2008; 68(13): 5273 - 5281. [Abstract] [Full Text] [PDF] |
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D.-H. Nam, H.-M. Jeon, S. Kim, M. H. Kim, Y.-J. Lee, M. S. Lee, H. Kim, K. M. Joo, D.-S. Lee, J. E. Price, et al. Activation of Notch Signaling in a Xenograft Model of Brain Metastasis Clin. Cancer Res., July 1, 2008; 14(13): 4059 - 4066. [Abstract] [Full Text] [PDF] |
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S. R. Moore, D. L. Persons, J. A. Sosman, D. Bobadilla, V. Bedell, D. D. Smith, S. R. Wolman, R. J. Tuthill, J. Moon, V. K. Sondak, et al. Detection of Copy Number Alterations in Metastatic Melanoma by a DNA Fluorescence In situ Hybridization Probe Panel and Array Comparative Genomic Hybridization: A Southwest Oncology Group Study (S9431) Clin. Cancer Res., May 15, 2008; 14(10): 2927 - 2935. [Abstract] [Full Text] [PDF] |
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C. F. O'Neill, S. Urs, C. Cinelli, A. Lincoln, R. J. Nadeau, R. Leon, J. Toher, C. Mouta-Bellum, R. E. Friesel, and L. Liaw Notch2 Signaling Induces Apoptosis and Inhibits Human MDA-MB-231 Xenograft Growth Am. J. Pathol., September 1, 2007; 171(3): 1023 - 1036. [Abstract] [Full Text] [PDF] |
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C. C. Lynch, T. Vargo-Gogola, M. D. Martin, B. Fingleton, H. C. Crawford, and L. M. Matrisian Matrix Metalloproteinase 7 Mediates Mammary Epithelial Cell Tumorigenesis through the ErbB4 Receptor Cancer Res., July 15, 2007; 67(14): 6760 - 6767. [Abstract] [Full Text] [PDF] |
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G. C. Prendergast AACR Cancer Reviews Online: A new resource for cancer researchers Cancer Reviews Online Content, April 1, 2007; 2007(1): 1 - 2. [Full Text] [PDF] |
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