Abstract 2364: Identification of therapy resistant pediatric brain tumor cells that have extraordinary survival and tumorigenic capabilities: The ultimate seed cells that drives the growth of autopsied tumor cells in mouse brains

Brain tumors are a leading cause of cancer related death in children. Little is known about the biology of recurrent or refractory pediatric CNS tumors, particularly those that are inoperable, such as hypothalamic or brainstem tumors. Since autopsy may be the only opportunity to obtain tumor tissue for inoperable or recurrent tumors, we have obtained postmortem tissue for the purpose of developing orthotopic xenografts. We hypothesized that a small fraction of tumor cells would survive the postmortem period of extreme hypoxia and starvation, maintain their tumorigenic capacity, leading to tumor formation in an appropriate in vivo microenvironment; and that these tumor cells may represent the ultimate seed cells that drive tumor recurrence and treatment failure. To identify this subpopulation of TREST cells, i.e. therapy resistant with extraordinary survival and tumorigenic capabilities, we collected 11 postmortem tumor samples, including 3 recurrent medulloblastomas (MBs),1 glioblastoma multiforme (GBM) and 7 diffuse intrinsic pontine glioma (DIPG), 5-72 hrs (mean 32 hrs) after the time of death. We examined tumor cell viability and their capacity of growth in vitro (neurospheres in serum-free medium and proliferation in FBS-based DMEM), analyzed the content of putative cancer stem cells, and determined their tumor forming capability in vivo in mouse brains. Our results showed that a small fraction (5-10%) of viable tumor cells exists in all the autopsied tumors, although most of them failed to proliferate in vitro. More importantly, we found that injection of unfractionated tumor cells into mouse brains resulted in the formation of xenograft tumors in 2 of 3 MBs (66.6%), 1/1 GBM and 5 of 7 DIPGs (71%). One of the medulloblastomas and the GBM model have been serially passaged in mouse brains 6 times, and two of the DIPGs in mouse brainstems 3 times. These tumors replicated the histopathological phenotypes of the corresponding patient tumors demonstrating diffuse invasion. Using a series of putative cancer stem cell markers (CD133, CD15, CD24/CD44, CD57 and CD117), we showed that CD133+ and CD15+ cells were enriched in the xenograft tumors. In conclusion, we have demonstrated that a small fraction of tumor cells, some of which expressed putative CSC markers, can survive a lengthy period of postmortem hypoxia/anoxia and starvation and maintain tumorigenic capabilities in mouse brains. Detailed analysis of these TREST cells, particularly with our unique panel of orthotopic xenograft mouse models, should provide novel insights about their biology and future development of new therapies specifically targeting the recurrent/late stage brain tumors. Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 103rd Annual Meeting of the American Association for Cancer Research; 2012 Mar 31-Apr 4; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2012;72(8 Suppl):Abstract nr 2364. doi:1538-7445.AM2012-2364