Caren Stuebe

 Introduction. Glioblastoma multiforme (GBM) is the most common and aggressive primary brain tumor.¹ GBM is characterized as a grade IV glioma diagnosed with imaging and biopsy.^2,3 With standard of care treatment of  maximal surgical resection, radiation, and temozolomide chemotherapy, median survival is 12-14.6 months.^1,2,3,4 Of note is the higher incidence and worse survival of GBM in men than in women, with an incidence ratio of 1.6:1, and a 5-year survival rate of 6.8% versus 8.3%, respectively.^4,5 TP53 mutations are common in GBM, and loss of TP53 has been shown to increase the susceptibility of males astrocytes to malignancy more than females, indicating a potential sex-based GBM treatment target.⁴ Methods. The CRISPR-IUE Glioma Model was used with knockout Nf1 and TP53 genes in mice. GBM tumors were verified by inspection and histopathology.⁷ Growth of GBM astrocytes null for Nf1 and TP53 genes, and mRNA expression of Rb regulators TP16, TP21, and TP27, was measured in basal and experimental stress conditions (serum deprivation, cyclin dependent kinase inhibitors (CDKis), and chemotherapy). Using CRISPR/Cas9, each CDKi was abrogated alone and in combination to determine the role of these CDKis in protecting female GBM astrocytes from tumorigenesis.⁷ The interaction of TP16 and TP21 with TP53 was measured by serially passaging human skin fibroblast HFSN1 cells and assessing protein levels via immunoblotting. The levels of TP16 downstream effector miRNAs miR-141 and miR-146b-5p were assessed in knockout TP16 and control plasmid via qRT-PCR.⁸ Results. Combined loss of Nf1 and TP53 accelerated tumorigenesis in male mice.⁷ Female GBM astrocytes underwent nearly complete growth arrest under serum deprivation and etoposide treatment while male GBM astrocytes continued to proliferate. Male GBM astrocytes were more susceptible to CDKi cytotoxicity.⁷ Serum deprivation resulted in an elevation of TP16 levels in female GBM astrocytes.⁷ Etoposide treatment increased TP21 mRNA levels more significantly in female GBM astrocytes.⁷ The combination of TP16 and TP21 loss increased in vivo female cell tumorigenesis to male levels.⁷ TP16 positively regulated TP53 expression by inhibiting MDM2 through tumor suppressor miRNAs.⁸ Conclusions. Loss of TP53 accelerated tumorigenesis in male GBM models. Under stress conditions, female GBM models exhibited a compensatory protective effect against tumorigenesis through upregulation of CDK inhibitors TP16 and TP21. Further research on the sex-based differences of TP53 and CDKis in GBM pathogenesis, with a focus on mechanism, whether sex hormone-based or cellular, is warranted to determine their potential as targets in sex-based GBM treatment.

1.  Nizamutdinov D, Stock EM, Dandashi JA, et al. Prognostication of Survival Outcomes in Patients Diagnosed with Glioblastoma. World Neurosurgery. 2018;109. doi:10.1016/j.wneu.2017.09.104.
2. Alexander BM, Cloughesy TF. Adult Glioblastoma. Journal of Clinical Oncology. 2017;35(21).
3. Sasmita AO, Wong YP, Ling APK. Biomarkers and therapeutic advances in glioblastoma multiforme. Asia-Pacific Journal of Clinical Oncology. 2017;14(1):40-51. doi:10.1111/ajco.12756.
4. Yang W, Warrington NM, Taylor SJ, et al. Sex differences in GBM revealed by analysis of patient imaging, transcriptome, and survival data. Science Translational Medicine. 2019;11(473). doi:10.1101/232744.
5. Tian M, Ma W, Chen Y, et al. Impact of gender on the survival of patients with glioblastoma. Bioscience Reports. 2018;38(6). doi:10.1042/bsr20180752.
6. Bao D, Cheng C, Lan X, et al. Regulation of p53^wtglioma cell proliferation by androgen receptor-mediated inhibition of small VCP/p97-interacting protein expression. Oncotarget. 2017;8(14). doi:10.18632/oncotarget.15509.
7. Kfoury N, Sun T, Yu K, et al. Cooperative p16 and p21 action protects female astrocytes from transformation. Acta Neuropathologica Communications. 2018;6(1). doi:10.1186/s40478-018-0513-5.
8. Al-Khalaf HH, Aboussekhra A. p16 Controls p53 Protein Expression Through miR-dependent Destabilization of MDM2. Molecular Cancer Research. 2018;16(8):1299-1308. doi:10.1158/1541-7786.mcr-18-0017.