TMOD-18. THREE-DIMENSIONAL MICROTUMORS IN PHYSIOLOGIC MICROENVIRONMENTS MAINTAIN BRAIN TUMOR INITIATING CELLS

Abstract

Elucidation of mechanisms of brain tumor initiating cell (BTIC) maintenance and therapeutic resistance offers great promise for development of novel anti-tumor treatments. Current leading studies rely on BTIC isolation from patient-derived xenografts followed by propagation as neurospheres. As this process is expensive and time-consuming, we determined if three-dimensional microtumors were an alternative in vitro method for modeling tumor growth via BITC maintenance and/or enrichment. Brain tumor cells were grown as neurospheres or as microtumors produced using a human-derived biomatrix HuBiogelTM and maintained with physiologically relevant microenvironments. Percentages of BITCs were then determined based on cell surface marker expression (CD133), label retention (carboxyfluorescein succinimidyl ester; CFSE), and tumorsphere formation capacity. Our data demonstrate that expansion of brain tumor cells as hypoxic and nutrient restricted microtumors significantly increased the percentage of both CD133+ and CFSE+ cells. For example, fifteen percent of all brain tumor cells from a xenograft propagated as microtumors were CD133+, whereas only one percent of neurosphere cultured cells expressed the BTIC marker. Relative to CD133, CFSE was retained in a higher percentage of cells, but CFSE+ cells were still increased in the microtumor condition in comparison to neurospheres. We further demonstrate that BTIC-marker positive cells isolated from microtumors maintain neurosphere formation capacity in the in vitro limiting dilution assay and tumorigenic potential in vivo. These data demonstrate that microtumors can be a useful three-dimensional biological model for the study of BTIC maintenance and targeting.