Controlled release microspheres loaded with BMP7 suppress primary tumors from human glioblastoma.

Pilar González-Gómez,Marcos Garcia-Fuentes,Maria De La Fuente,Cristina Zahonero,Pilar Sánchez-Gómez,Aurelio Hernández-Laín,Jose Crecente-Campo,Helena Mira

doi:10.18632/oncotarget.3459

Abstract

Glioblastoma tumor initiating cells are believed to be the main drivers behind tumor recurrence, and therefore therapies that specifically manage this population are of great medical interest. In a previous work, we synthesized controlled release microspheres optimized for intracranial delivery of BMP7, and showed that these devices are able to stop the in vitro growth of a glioma cell line. Towards the translational development of this technology, we now explore these microspheres in further detail and characterize the mechanism of action and the in vivo therapeutic potential using tumor models relevant for the clinical setting: human primary glioblastoma cell lines. Our results show that BMP7 can stop the proliferation and block the self-renewal capacity of those primary cell lines that express the receptor BMPR1B. BMP7 was encapsulated in poly (lactic-co-glycolic acid) microspheres in the form of a complex with heparin and Tetronic, and the formulation provided effective release for several weeks, a process controlled by carrier degradation. Data from xenografts confirmed reduced and delayed tumor formation for animals treated with BMP7-loaded microspheres. This effect was coincident with the activation of the canonical BMP signaling pathway. Importantly, tumors treated with BMP7-loaded microspheres also showed downregulation of several markers that may be related to a malignant stem cell-like phenotype: CD133(+), Olig2, and GFAPδ. We also observed that tumors treated with BMP7-loaded microspheres showed enhanced expression of cell cycle inhibitors and reduced expression of the proliferation marker PCNA. In summary, BMP7-loaded controlled release microspheres are able to inhibit GBM growth and reduce malignancy markers. We envisage that this kind of selective therapy for tumor initiating cells could have a synergistic effect in combination with conventional cytoreductive therapy (chemo-, radiotherapy) or with immunotherapy.

Highlights

A glioblastoma (GBM) is a highly aggressive brain tumor characterized by its lack of response to conventional chemo, radio, and immunotherapies.Recent studies suggest that recurrence of GBM may be due to the therapeutic resistance of a subpopulation of undifferentiated GBM tumor-initiating cells (GBMTICs)
GBM1–8 primary cell lines grow in suspension as non-adherent spheres and proliferate in serum-free media supplemented with Epidermal Growth Factor (EGF) and basic Fibroblast Growth Factor (bFGF) (Figure 1A)
We found that BMPR2 and BMPR1A were expressed in all the GBM-TICs, albeit at different levels

Summary

Introduction

A glioblastoma (GBM) is a highly aggressive brain tumor characterized by its lack of response to conventional chemo-, radio-, and immunotherapies.Recent studies suggest that recurrence of GBM may be due to the therapeutic resistance of a subpopulation of undifferentiated GBM tumor-initiating cells (GBMTICs). BMPs signal via specific serine/ threonine kinase receptors on the cell surface known as bone morphogenetic protein receptors (BMPRs). Both type-I and -II BMPRs are required for signal transduction. Previous studies have shown that treatment of GBM-TICs with BMP4 or BMP7 triggers Smad-mediated signaling, leading to the inhibition of cell proliferation, the induction of differentiation and a reduction of tumor formation in immunodeficient mice [4, 6, 7]. In a minority of GBMs displaying epigenetic silencing of the type I receptor BMPRIB, BMPs fail to induce differentiation but instead support the proliferation of GBM-TICs, thereby promoting tumorigenesis [8]

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