E-Poster Presentation 33rd Lorne Cancer Conference 2021

A novel orthotopic patient-derived xenograft model of radiation-induced glioma following medulloblastoma (#109)

Jacqueline P. Whitehouse 1 2 , Meegan Howlett 1 2 , Hilary Hii 1 , Chelsea Mayoh 3 4 , Marie Wong 3 4 , Paulette Barahona 3 , Pamela Ajuyah 3 , Christine L. White 5 6 , Molly K. Buntine 5 6 , Jason M. Dyke 2 7 , Sharon Lee 8 , Santosh Valvi 1 2 8 , Jason Stanley 1 2 , Clara Andradas Arias 1 2 , Brooke Carline 1 , Mani Kuchibhotla 1 , Paul G. Ekert 3 4 9 10 , Mark J. Cowley 3 4 , Nick G. Gottardo 1 2 8 , Raelene Endersby 1 2
  1. Telethon Kids Institute, Nedlands, WA, Australia
  2. University of Western Australia, Nedlands, WA, Australia
  3. Children's Cancer Institute, Kensington, NSW, Australia
  4. University of New South Wales, Kensington, NSW, Australia
  5. Hudson Institute of Medical Research, Clayton, Victoria , Australia
  6. Monash University, Melbourne, Victoria, Australia
  7. PathWest Laboratory Medicine, Perth, WA, Australia
  8. Perth Children's Hospital, Nedlands, WA, Australia
  9. Murdoch Children’s Research Institute, Parkville, Victoria, Australia
  10. Peter MacCallum Cancer Centre, Melbourne, Victoria, Australia

Radiation-induced glioma (RIG) is a highly aggressive brain cancer arising as a consequence of radiation therapy. We report a case of RIG that arose in the brain stem following treatment for paediatric medulloblastoma, and the development and characterisation of a matched orthotopic patient-derived xenograft (PDX) model (TK-RIG915). Patient and PDX tumours were analysed using DNA methylation profiling, whole genome sequencing (WGS) and RNA sequencing. While initially thought to be a diffuse intrinsic pontine glioma (DIPG) based on disease location, results from methylation profiling and WGS were not consistent with this diagnosis. Furthermore, clustering analyses based on RNA expression suggested the tumours were distinct from primary DIPG. Additional gene expression analysis demonstrated concordance with a published RIG expression profile. Multiple genetic alterations that enhance PI3K/AKT and Ras/Raf/MEK/ERK signalling were discovered in TK-RIG915 including an activating mutation in PIK3CA, upregulation of PDGFRA and AKT2, inactivating mutations in NF1, and a gain-of-function mutation in PTPN11. Additionally, deletion of CDKN2A/B, increased IDH1 expression, and decreased ARID1A expression were observed. Detection of phosphorylated S6 and ERK via immunohistochemistry confirmed PI3K pathway and ERK activation. Here, we report one of the first PDX models for RIG, which recapitulates the patient disease and is molecularly distinct from primary brain stem glioma. Genetic interrogation of this model has enabled the identification of potential therapeutic vulnerabilities in this currently incurable disease.