Evolution of Experimental Models in the Study of Glioblastoma: Toward Finding Efficient Treatments

Abstract

Glioblastoma (GBM) is the most common form of brain tumor characterized by its resistance to conventional therapies, including temozolomide, the most widely used chemotherapeutic agent in the treatment of GBM. Within the tumor, the presence of glioma stem cells (GSC) seems to be the reason for drug resistance. The discovery of GSC has boosted the search for new experimental models to study GBM, which allow the development of new GBM treatments targeting these cells. In here, we describe different strategies currently in use to study GBM. Initial GBM investigations were focused in the development of xenograft assays. Thereafter, techniques advanced to dissociate tumor cells into single-cell suspensions, which generate aggregates referred to as neurospheres, thus facilitating their selective expansion. Concomitantly, the finding of genes involved in the initiation and progression of GBM tumors, led to the generation of mice models for the GBM. The latest advances have been the use of GBM organoids or 3D-bioprinted mini-brains. 3D bio-printing mimics tissue cytoarchitecture by combining different types of cells interacting with each other and with extracellular matrix components. These in vivo models faithfully replicate human diseases in which the effect of new drugs can easily be tested. Based on recent data from human glioblastoma, this review critically evaluates the different experimental models used in the study of GB, including cell cultures, mouse models, brain organoids, and 3D bioprinting focusing in the advantages and disadvantages of each approach to understand the mechanisms involved in the progression and treatment response of this devastating disease.

Keywords: 3D bioprinting; brain organoids; cell cultures of glioma cells; glioma stem cells; mouse models of glioblastoma.

Figure 1

Drawing summary of classical models currently in use to study GBM. Tumor samples resected from patients upon surgery are used to (A) generate immortalized cell lines that can be maintained in time; (B) select GSC by culturing these cells as neurospheres under floating conditions; (C) produce xenograft models by transplanting either cultured isolated cells or tumor tissue; (D) perform genomic analysis to select candidate genes to produce genetically modified mice models of GBM; (E) canine models are good model for the study of GBM based on their analogies with human GBM.

Figure 2

Drawing summary of novel models currently in use to study GBM. (A) 3D Cultures of cells embedded in Matrigel have been key techniques in the development of brain organoids; (B) growth of 3D structures using microfluidic systems replicates the changing microenvironment surrounding GBM in the human brain; (C) GBM cells can be grafted in vitro in human brain slices grown as organotypic cultures replicating the natural environment of a GBM tumor; (D) culture GBM organoids by either using glioma cells or by inserting GSC into brain organoids; (E) bio-print GBM 3D-spheroids using extracellular matrix materials and other cell types.