Notch pathway inhibition depletes stem-like cells and blocks engraftment in embryonal brain tumors

• Published in: Cancer research (Chicago, Ill.) Vol. 66; no. 15; pp. 7445 - 7452
• Main Authors: XING FAN, MATSUI, William, KHAKI, Leila, STEAMS, Duncan, JIONG CHUN, LI, Yue-Ming, EBERHART, Charles G
• Format: Journal Article
• Language: English
• Published: Philadelphia, PA American Association for Cancer Research 01-08-2006
• Subjects: Amyloid Precursor Protein Secretases; Animals; Apoptosis - drug effects; Apoptosis - physiology; Aspartic Acid Endopeptidases; Biological and medical sciences; Brain Neoplasms - metabolism; Brain Neoplasms - pathology; Brain Neoplasms - prevention & control; Cell Differentiation - physiology; Cell Growth Processes - physiology; Cell Line, Tumor; Endopeptidases - metabolism; Humans; Intermediate Filament Proteins - metabolism; Medical sciences; Medulloblastoma - metabolism; Medulloblastoma - pathology; Medulloblastoma - prevention & control; Mice; Neoplastic Stem Cells - metabolism; Neoplastic Stem Cells - pathology; Nerve Tissue Proteins - metabolism; Nestin; Neurology; Neurons - pathology; Protease Inhibitors - pharmacology; Receptors, Notch - antagonists & inhibitors; Signal Transduction - drug effects; Transplantation, Heterologous; Tumors of the nervous system. Phacomatoses; Intracranial; Signal transduction; Nervous system diseases; Notch receptor; Stem cell; Central nervous system disease; Engraftment; Inhibitor; Malignant tumor; Intracranial tumor; Cerebral disorder; Embryonal carcinoma
• ISSN: 0008-5472; 1538-7445
• DOI: 10.1158/0008-5472.can-06-0858

The Notch signaling pathway is required in both nonneoplastic neural stem cells and embryonal brain tumors, such as medulloblastoma, which are derived from such cells. We investigated the effects of Notch pathway inhibition on medulloblastoma growth using pharmacologic inhibitors of gamma-secretase. Notch blockade suppressed expression of the pathway target Hes1 and caused cell cycle exit, apoptosis, and differentiation in medulloblastoma cell lines. Interestingly, viable populations of better-differentiated cells continued to grow when Notch activation was inhibited but were unable to efficiently form soft-agar colonies or tumor xenografts, suggesting that a cell fraction required for tumor propagation had been depleted. It has recently been hypothesized that a small population of stem-like cells within brain tumors is required for the long-term propagation of neoplastic growth and that CD133 expression and Hoechst dye exclusion (side population) can be used to prospectively identify such tumor-forming cells. We found that Notch blockade reduced the CD133-positive cell fraction almost 5-fold and totally abolished the side population, suggesting that the loss of tumor-forming capacity could be due to the depletion of stem-like cells. Notch signaling levels were higher in the stem-like cell fraction, providing a potential mechanism for their increased sensitivity to inhibition of this pathway. We also observed that apoptotic rates following Notch blockade were almost 10-fold higher in primitive nestin-positive cells as compared with nestin-negative ones. Stem-like cells in brain tumors thus seem to be selectively vulnerable to agents inhibiting the Notch pathway.