A novel and generalizable organotypic slice platform to evaluate stem cell potential for targeting pediatric brain tumors

Abstract

Brain tumors are now the leading cause of cancer-related deaths in children under age 15. Malignant gliomas are, for all practical purposes, incurable and new therapeutic approaches are desperately needed. One emerging strategy is to use the tumor tracking capacity inherent in many stem cell populations to deliver therapeutic agents to the brain cancer cells. Current limitations of the stem cell therapy strategy include that stem cells are treated as a single entity and lack of uniform technology is adopted for selection of clinically relevant sub-populations of stem cells. Specifically, therapeutic success relies on the selection of a clinically competent stem cell population based on their capacity of targeting brain tumors. A novel and generalizable organotypic slice platform to evaluate stem cell potential for targeting pediatric brain tumors is proposed to fill the gap in the current work flow of stem cell-based therapy. The organotypic slice platform has advantages of being mimic in vivo model, easier to manipulate to optimize parameters than in vivo models such as rodents and primates. This model serves as a framework to address the discrepancy between anticipated in vivo results and actual in vivo results, a critical barrier to timely progress in the field of the use of stem cells for the treatment of neurological disorders.

Figure 1

A workflow chart for development of stem cell sub-populations capable of targeting brain tumors for clinical application. CR: Chemokine receptor; HST: High throughput screening; MMPs: Metal metalloproteases; 3D: Three-dimensional culture. Dash line: Current workflow. Solid line: our proposed workflows.

Figure 2

Schematic diagram for model systems of studying brain stem cells including in vitro, ex vivo and in vivo.

Figure 3

Stem cells showing tropism for malignant tumor cells implanted on rodent organotypic slice model. An organotypic slice is derived from a central nervous system tissue of an organism, indicating that the central nervous system tissue is sliced at a boundary such that an endogenous fiber tract of the central nervous system tissue is intact, through which the stem cell migrate toward the CNS tumor. Scheme is based on [15].

Figure 4

Model of SDF-1-mediated signal transduction for targeting of stem cells toward brain tumor. Brain tumors release SDF-1 gradient into the tumor microenvironment. Binding SDF-1 to its receptor expressed in stem cells triggers the signal transduction pathways that lead to cytoskeletons reorganization, which drives stem cell migration toward brain tumor microenvironment. CXCR-4: chemokine (C-X-C motif) receptor 4, a.k.a., SDF-1 receptor or CD184; SDF-1: stromal cell-derived factor-1 (chemokine), a.k.a., CXCL12 (see [37]).

Figure 5

Rat brain organotypic slice can support stem cell survival and migration toward human tumor cells. A: Part of rat brain slice showing the implantation site (arrow) of GFP labeled neural stem cells (NSC) (phase contrast, 4×). B: Same field as (A) under fluorescence illumination showing the implanted cells (arrow). C: As early as 1 hour of implantation, NSC migrated out of the initial site toward a remotely implanted brain tumor site (not shown); D Live imaging of NSC 30 days after implantation indicating that NSC survived at least 30 days on the slice (40×).