Abstract 409: Analysis of invasion patterns in an induced cancer stem cell model of malignant brain tumor
Authors: Sampetrean Oltea , Saga Isako , Onishi Nobuyuki , Sugihara Eiji , Saya Hideyuki 
Published: February 2011

Background: The invasive phenotype of malignant brain tumors is a major cause for their recurrence and resistance to therapy. It has been suggested that tumor cells recapitulate the migration patterns of glial progenitors. However, it is still unclear which cells acquire a migratory potential, at which stage they acquire it and whether and how invasion patterns change during tumorigenesis and treatment. The present study aims to define the characteristics of infiltrating cells and the patterns of invasion of genetically-induced brain tumor-initiating cells (BTICs) in the syngeneic mouse adult brain.

Methods: We have established a mouse malignant brain tumor model by overexpressing RASV12 in neural stem cells/multipotent progenitor stem cells derived from the subventricular zone of mice with a homozygous deletion of the Ink4a/ARF locus. Orthotopic implantation of these BTICs into 6-week-old wild type mice resulted in formation of highly invasive, hypervascular, serially transplantable glioblastoma-like tumors with a 100% penetrance and a 5-week median survival. Fifteen mice were sacrificed at one-week intervals (n=3) and fixed brain sections were analyzed for onset and direction of cell migration. A second series of 10 mice were sacrificed at two-day intervals (n=2), and the live brains were sliced, cultured and motility and infiltration patterns were analyzed by timelapse microscopy, cell tracking and 3D reconstruction.

Results: Pathological analysis revealed that cellular migration was detectable at one week post-injection, with both movement along fiber tracts, as well as perivascular trajectories. During the later stages of tumorigenesis, invasive foci were located mostly around blood vessels and the invasive front coincided with VEGFR and HO-1 expression.

Timelapse microscopy confirmed motility of tumor cells as early as two days post- injection. Movement along blood vessels was quick and directed away from the tumor, while intraparenchymal movement was more saltatory, with repeated extension and retraction of leading processes, pausing and turning. Cells which exited the tumor early sometimes tested several routes before taking one and then exhibited a to-and-fro movement, creating paths for other cells. Motility was not affected by cell number and cells from secondary and tertiary tumors retained the infiltrative characteristics. Furthermore, co-injection of dsRed-labeled nestin-positive and GFP-labeled GFAP-positive tumor cells showed that differentiation status seems to affect infiltration patterns more than motility in itself.

Conclusion: Our results show that invasion is one of the earliest events in tumorigenesis. Moreover, the once established infiltration paths might facilitate further invasion at later stages. We therefore suggest that, to efficiently prevent recurrence, migration should be considered as a therapeutic target from the time of diagnosis.

Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 101st Annual Meeting of the American Association for Cancer Research; 2010 Apr 17-21; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2010;70(8 Suppl):Abstract nr 409.