Abstract 71: Investigating the sexually dimorphic susceptibility to brain cancer in a glioblastoma model system

Proceedings: AACR Annual Meeting 2014; April 5-9, 2014; San Diego, CA Background: Clinical studies have shown that brain cancers including Glioblastoma Multiforme (GBM) and several subtypes of medulloblastomas, occur more frequently in males than in females worldwide. The reason for this sex disparity is poorly understood. Sex differences in brain tumor rates exist not only in adults but also in the pediatric population. In children, brain tumor incidence peaks at approximately 4 years of age when the levels of circulating sex hormones are equivalently low in both boys and girls. This suggested to us that cell-intrinsic sex differences may play a role in the oncogenesis of brain tumors. The current study examines the contribution of cell intrinsic sexual dimorphism in oncogenic pathways to the sex differences in brain cancers. Methods: We analyzed 3 publicly accessible gene expression databases containing over 600 GBM patient specimens to determine whether sex differences are present in a molecular subtype specific fashion. We were able to assign sex to each patient based on the Y-chromosome gene expression, and found that male prevalence exists consistently in both proneural and mesenchymal subgroups of GBMs. Mesenchymal GBM is frequently associated with inactivation of two tumor suppressors Neurofibromin 1 (NF1) and TP53. Therefore, to model the impact of sex on the oncogenesis of glioblastoma, we established a step-wise transformation system by using murine astrocytes with ablation of Nf1. The Nf1-/- astrocytes were further engineered to lose p53 function by over-expression of dominant-negative p53 (DNp53). These Nf1-/-;DNp53 astrocytes were either treated with epidermal growth factor (EGF) in vitro, or implanted into immunodeficient mice. Results: Over-expression of DNp53 in Nf1-/- astrocytes enhanced the growth rate in both male and female astrocytes, but with a much greater increase in male cultures. In addition, EGF treatment resulted in in vitro transformation of male but not female, Nf1-/-;DNp53 astrocytes. In line with these results, limiting dilution analyses demonstrated that there is a much higher stem cell frequency in male than in female Nf1-/-;DN-p53 cells. Implants of Nf1-/-;DN-p53 cells into nude mice led to a male predominant pattern of tumor growth. Survival analyses on the nude mice with intracranial implants of the Nf1-/-;DNp53 cells showed a sex-dependent survival pattern with 100% death in mice bearing male Nf1-/-;DNp53 cells vs. 36% death in mice carrying the female counterparts. Conclusions: We established a model system that allows us to model the impact of sex on gliomagenesis. By employing Nf1-/-;DNp53 mouse astrocytes, we were able to demonstrate that male astrocytes are more susceptible to malignant transformation both in vitro and in vivo. Furthermore, our tumor formation data suggest that it is the cell-intrinsic sex differences rather than circulating sex hormones that may determine the sex disparity in glioma rates in patients. Citation Format: Tao Sun, Nicole M. Warrington, Jingqin Luo, Michael Brooks, Sonika Dahiya, Steven C. Snyder, Rajarshi Sengupta, Joshua B. Rubin. Investigating the sexually dimorphic susceptibility to brain cancer in a glioblastoma model system. [abstract]. In: Proceedings of the 105th Annual Meeting of the American Association for Cancer Research; 2014 Apr 5-9; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2014;74(19 Suppl):Abstract nr 71. doi:10.1158/1538-7445.AM2014-71