SVZ-nested GBM-initiating cells are resistant to radiotherapy treatment, due to mesenchymal activation by SVZ-released CXCL12.
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1
University of Liège - CHU of Liège, Giga - Neuroscience, Belgium
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2
CHU of Liège, Department of Neurosurgery, Belgium
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3
CHU of Liège, Department of Neurology, Belgium
Summary
This study shows that Glioblastoma (GBM) cells which migrate from the tumor mass to the Subventricular Zone (SVZ) acquire stem features. This acquisition is in fact induced by a chemokine, CXCL12, which is essentially founded in SVZ. CXCL12 is able to induce a transition from an epithelial state to a mesenchymal state, known as Epithelio-Mesenchymal Transition (EMT), via its receptor CXCR4. We finally showed that this transition is associated to radioresistance and that radiosensitization of GBM cells, nested in the SVZ, could be induced by AMD 3100, an antagonist of CXCR4.
Introduction
Patients with glioblastoma multiforme (GBM) have an overall median survival of 15 months despite multimodal therapy, due to systematic relapses. We previously demonstrated that GBM-initiating cells (GIC) are able to escape the tumor mass and specifically colonize the sub-ventricular zone (SVZ – one of the two neurogenic zone in adult brain, including in humans) after experimental striatal xenotransplantation. We also demonstrated that this specific and oriented migration of GIC is a consequence of the release of the CXCL12 cytokine by SVZ and that GIC expressed CXCR4, the CXCL12 receptor. Using the same approach, we demonstrated in vivo a higher survival rate of SVZ-nested GIC after irradiation and investigated the pathway implied.
Materials and Methods
We collected conditioned media (CM) of the SVZ from nude mice and from one human brain. We used three human GBM primary cultures and one human GBM cell line for in vitro radiotherapy tests, with or without exposition to SVZ-CM or human recombinant CXCL12. We performed Western Blot and quantitative RT-PCR after stimulation of human GBM primary culture and cell line by CXCL12, with or without the use of AMD 3100, the antagonist of CXCR4. Finally, we tested in vivo a potential radiosensitization of SVZ-nested GBM cells by AMD 3100.
Results
Exposition to human and mice SVZ-CM and to CXCL12, present in SVZ-CM, induces radioresistance in vitro, quantified by clonogenic assays, γH2AX and 53bp1 immunostainings. The use of CXCL12 blocking antibodies in SVZ-CM sensitizes GBM cells to irradiation in vitro. We report here that CXCL12 promotes in vitro the mesenchymal activation of GBM cells quantified by N-cadherin and vimentin expression. In vivo, SVZ-nested GBM cells exhibit also those mesenchymal markers. Finally, we showed in vivo the radiosensitization of SVZ-nested GBM cells by a concomitant AMD3100 administration.
Conclusion
Mesenchymal activation of GICs, mediated by CXCL12 of the SVZ, promotes their resistance to radiotherapy. Therefore, we propose that a modulation of the CXCL12 signalization could be useful during radiotherapy in order to decrease the risk of the deadly GBM relapses.
Résumé en Français :
Le glioblastome est une tumeur dans laquelle on trouve des cellules mobiles et résistantes à la radiothérapie ce qui permet leur diffusion hors de la tumeur.
Dans ce travail, nous montrons que ces cellules acquièrent cette radiorésistance par une transition vers un stade de cellules souches générées par une chemokine* la CXCL12. Cette chemokine est produite par les cellules épithéliales voisines. Pour exercer sa fonction la CXCL12 doit interagir avec un récepteur présent sur les cellules du glioblastome, le CXCR4. Nous avons aussi montré qu’en faisant agir un antagoniste qui blocque le récepteur CXCR4, les cellules perdent cette radio-résistance et redeviennent sensibles à la radiothérapie.
*Chemokine : facteur de différentiation de cellules, permet lnotamment l’acquisition par la cellule stimulée de mobilité
Samenvatting in het Nederlands:
De gliobastoom of glioom is een tumor waarin radiotherapie-resistente mobiele cellen aanwezig zijn, waardoor ze ook buiten de tumor verspreid worden. In dit werk tonen we aan dat deze cellen resistent worden voor radiotherapie door omvorming naar een stadium van stamcellen die gegenereerd worden door een chemokine*: CXCL12. Dit chemokine wordt geproduceerd door de nabije epitheelcellen (dekweefsel). Om te functioneren moet de CXCL12 in interactie treden met een receptor aanwezig in het glioom, het CXCR4. We toonden ook aan dat het activeren van een antagonist die de CXCR4 blokkeert, de cellen hun radiotherapieresistentie verliezen, en opnieuw reageren op de radiotherapie.
* Chemokine is een factor die cellen differentieert, en die de gestimuleerde molecule mobiel maakt.
Keywords:
Glioblastoma stem cells,
radioresistance,
Epithelio-Mesenchymal Transition,
CXCL12,
suventricular zone
Conference:
6th Belgian Brain Congress, MONS, Belgium, 8 Oct - 8 Oct, 2016.
Presentation Type:
Poster Presentation
Topic:
Brain and brain diseases: between heredity and environment
Citation:
Lombard
A,
Goffart
N,
Dedobbeleer
M,
Willems
E,
Martin
D and
Rogister
B
(2016). SVZ-nested GBM-initiating cells are resistant to radiotherapy treatment, due to mesenchymal activation by SVZ-released CXCL12..
Conference Abstract:
6th Belgian Brain Congress.
doi: 10.3389/conf.fnagi.2016.03.00091
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Received:
24 Aug 2016;
Published Online:
24 Aug 2016.
*
Correspondence:
MD, PhD. Arnaud Lombard, University of Liège - CHU of Liège, Giga - Neuroscience, Liège, Belgium, alombard@student.ulg.ac.be