Cells Isolated from Residual Intracranial Tumors after Treatment Express iPSC Genes and Possess Neural Lineage Differentiation Plasticity

Background: The goal of this study is to identify and characterize treatment resistant tumor initiating cells (TRTICs) using orthotopic xenografts. Methods: TRTICs were enriched from GBM cell lines using mouse xenografts treated with fractionated doses of radiation and temozolomide. TRTICs were characterized by neurosphere clonogenicity and self-renewal, serial xenotransplantation, differentiation potential, and mRNA & miRNA transcriptomic profiling. We use an unbiased approach to identify antigens encoding TRTIC and glioma stem cells (GSC) populations. Co-culture experiments of TRTIC and differentiated cells were conducted to evaluate the reliance of TRTIC differentiation on the secretome of differentiated cells. Findings: TRTICs acquire stem-like gene expression signatures and increased side population staining resulting from the activation of multi-drug resistance genes. Genetic and functional characterization of TRTICs shows a striking resemblance with GSCs. TRTICs can differentiate towards specific progeny in the neural stem cell lineage. TRTIC-derived tumors display all the histological hallmarks of glioblastoma (GBM) and exhibit a miRNA-transcript and mRNA-transcriptomic profile associated with aggressiveness. We report that CD24 /CD44 antigens encode TRTICs and patient-derived GSCs. Interestingly, co-culture experiments with TRTICs and differentiated cells indicated that the regulation of TRTIC differentiation could rely on the secretome in the tumor niche. Interpretation: Radiation and temozolomide treatment enriches for a population of cells that have increased iPSC gene expression. As few as 500 cells produced aggressive intracranial tumors resembling patient GBM. CD24 /CD44 antigens are increased in TRTICs and patient-derived GSCs. The enrichment for TRTICs may result in part from the secretome of differentiated cells. Funding Statement: NIH/NCI 1RC2CA148190, 1RO1CA108633, 1R01CA188228, and The Ohio State University Comprehensive Cancer Center. Declaration of Interests: The authors declare no potential conflicts of interests. Ethics Approval Statement: Study methodology used the Institutional guidelines and approved protocols IACUC (2009A012&-R1), IBC (2009R0169), and IRB (2009C0065 & 2014C0115).