CEREBRAL ORGANOIDS AS A MODEL FOR GLIOBLASTOMA MULTIFORME

Abstract

Glioblastoma multiforme (GBM) is a highly lethal and elusive cancer. While many in vitro and in vivo models have been developed to recapitulate the factors that contribute to its invasive behavior, they suffer from drawbacks related to genetic variability, expense and scope. Technologies utilizing human pluripotent stem cells can now generate organoids which can recapitulate the relative complexity the cytoarchitecture and microenvironment of human brain tissue. In conjunction with protocols which effectively induce GBM tumors within these "cerebral organoids", such approaches represent an unprecedented model to investigate GBM invasion and its effect on the brain ECM. This review focuses on methods of brain organoid development, protocols for inducing GBM, the relevant findings on invasion and microenvironmental changes, and discusses their limitations and potential future direction.

Keywords: brain organoid; cerebral organoid; glioblastoma; glioblastoma invasion; glioma.

Figure 1:

Layering structure of 3D brain organoid generated by serum-free floating culture of embryoid body-like aggregates with quick aggregations followed by incorporation of ECM elements. Neuronal layers appear in which earlier-born neurons were situated below later-born neurons. Legend presents cell types and other elements found in the tissue. Adapted from Kelava et al., 2016 [38].

Figure 2:

Morphological similarity of cerebral organoids grown in vitro (bottom) compared to in vivo development of the human brain during gestation (top). The top bar depicts the general progression of morphological changes to the developing brain in vivo. The middle bar is a qualitative representation of degree to which organoid development in vitro is like the native brain development in vivo. The bottom bar and accompanying graphics give an overview of the cerebral organoid protocol and development in vitro. Adapted from Kelava et al., 2016 [38].

Figure 3:

Overview of the process for obtaining GBM induced cerebral organoids. The top row depicts an abbreviated process for organoid formation. Below show alternative methods of tumor induction either by co-culture with patient-derived primary tumor stem cells (left) or by genetic engineering techniques (left) adapted from Ogawa et al., Linkous et al., and Lancaster et al. [20, 32, 33]

Figure 4:

Selected results from studies using cerebral organoids to model GBM. (A) Example of tumor growth in a cerebral organoid by induction using genetic engineering techniques. In this case, an HRas cassette with tdTomato fluorescent marker is used to disrupt the TP53 domain by homologous recombination facilitated by CRISPR-Cas9. Immunofluorescent images depict tumor invasion over the course of 13 weeks. Image at the right is a close-up of the invasive front. Adapted from Ogawa et al., 2018. [33] (B) Tumor formation by 1-week co-culture with GFP-expressing GSCs. Scale bare is 400 μm. Adapted from Linkous et al. [32] (C) Tumor infiltration of different patient-derived GSC lines 1 week after introduction into organoid demonstrates that invasive profiles are highly variable from patient to patient. Adapted from Linkous et al., 2019. [32] (D & E) Immunofluorescence images of CA-IX (carbonic anhydrase marker presented by cells in response to low-oxygen conditions) in cerebral organoid tissue. Adapted from Hubert et al. [37]