Figure 6. Mutant Idh1 alters progression of Tp53-deleted tumors and changes tumor biology.

(a) Kaplan-Meier survival of E18.5-treated animals. Tp53-deleted animals develop brain tumors and the presence of mutant Idh1 alters progression of tumor development (Nestin-CreER^T2, n=6; Nestin-CreER^T2; Idh1^LSL:R132H/WT, n=7; Nestin-CreER^T2; Idh1^LSL:R132H/WT; Tp53^fl/fl, n=16; Nestin-CreER^T2; Tp53^fl/fl, n=12) (b) Histological comparisons between tumors that developed in Nestin-CreER^T2; Idh1^LSL:R132H/WT; Tp53^fl/fl (n=2) (top row) and Nestin-CreER^T2; Tp53^fl/fl (n=2) (bottom row). H&E staining shows the presence of giant cells (red arrowheads) in the mutant Idh1 cohort. Nearly 100% of tumor cells stained positive for Olig2 in Idh1 mutant tumors compared to 20%–60% in Tp53-deleted tumors. An IDH1-R132H-specific antibody shows the presence of Idh1 mutant cells in both non-tumor brain tissue as well as tumor tissue from tumor-bearing Nestin-CreER^T2; Idh1^LSL:R132H/WT; Tp53^fl/fl animals. This is in contrast to tumors from Nestin-CreER^T2; Tp53^fl/fl animals which show no IDH1-R132H-positive staining. (c) Data was extracted from the TCGA dataset for lower-grade gliomas. Olig2 expression was assessed in IDH1 mutant (n=416) and IDH1 wildtype (n=118) human glioma samples. Data shows a significant increase in Olig2 expression among the IDH1 mutant gliomas (p<0.05). (d) Global methylation was assessed in tumor-derived cell lines that developed in Nestin-CreER^T2; Tp53^fl/fl and Nestin-CreER^T2; Idh1^LSL:R132H/WT; Tp53^fl/fl animals. (e) The methylation status of the second promoter of mouse Bcat1 was assessed in aforementioned mouse brain tumor-derived cell lines. Greater promoter methylation is observed in the Nestin-CreER^T2; Idh1^LSL:R132H/WT; Tp53^fl/fl compared to the Nestin-CreER^T2; Tp53^fl/fl lines. Percent of the loci that is methylated and unmethylated is shown.