Abstract 3182: A human neural stem cell glial brain tumor model identifies the relative contribution of different oncogenic elements to malignant transformation

Diffuse intrinsic pontine glioma (DIPG) is an invasive malignancy of the brainstem that accounts for greater than 80% of pediatric brainstem gliomas. In the past 40 years, there have been no significant advances in DIPG treatments and survival, so it remains a leading cause of death from pediatric brain tumors. Nearly 80% of DIPG harbor a point mutation in H3F3A or HIST1H3B, and the presence of this H3.3K27M mutation is inversely correlated with reduced OS, suggesting that epigenetic dysregulation is a key driver to cause the pathogenesis of DIPG. However, it is unclear how the H3.3K27M mutation and the other common alterations in DIPG contribute to tumorigenicity in human neural stem cells. To address the relative contributions of different oncogenic elements to DIPG, we sought to add common DIPG elements in a stepwise fashion to human neural stem cells derived from the developing hindbrain. We chose oncogenic elements that are known to present in DIPG, including the stem cell factor BMI1, mutant (R248W) p53, H3.3K27M, constitutively active AKT (representing the activation of mTOR detected in the vast majority of DIPG) and hTERT. We found that the combination of the stem cell factor BMI1 along with mutant (R248W) p53 and hTERT could immortalize neural stem cells, but was insufficient to form orthotopic xenograft tumors when placed in the pons of immunodeficient mice. Addition of activated AKT led to aggressive tumor formation, with a glial phenotype as evidenced by robust GFAP expression and absence of synaptophysin expression. All mice bearing these four genetic alterations succumbed to their tumors within 100 days of implantation. We found that introduction of H3.3K27M mutation reduces the level of tri-methylation of H3.3KK27 to that seen in patient-derived DIPG cell lines. Furthermore, we found that H3.3KK27 mutation introduction increases expression of LIN28B, a stem cell factor, which is also found in patient-derived DIPGs. Our previous study showing that LIN28A, another family member of LIN28 proteins, regulates invasion and tumorigenicity in adult high-grade gliomas suggests that H3.3K27M mutation might facilitate invasiveness of DIPG through LIN28B and its downstream effectors HMGA2, SNAI1, and SLUG. In summary, we have developed a human hindbrain neural stem cell DIPG model that has both accurate cell of origin and genetic defects including H3.3K27M mutation. Our models allow for assessment of the relative contribution to transformation of each genetic element in a stepwise fashion in the likely cell of origin of this deadly tumor. Citation Format: Youngran Park, Ping An, Dacheng Ding, Charles G. Eberhart, Eric H. Raabe. A human neural stem cell glial brain tumor model identifies the relative contribution of different oncogenic elements to malignant transformation [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2018; 2018 Apr 14-18; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2018;78(13 Suppl):Abstract nr 3182.