Xenotransplantation of pediatric low grade gliomas confirms the enrichment of V600E mutation and preservation of deletion in a novel orthotopic xenograft mouse model of progressive pleomorphic xanthoastrocytoma.

To identify cellular and molecular changes that driver pediatric low grade glioma (PLGG) progression, we analyzed putative cancer stem cells (CSCs) and evaluated key biological changes in a novel and progressive patient-derived orthotopic xenograft (PDOX) mouse model. Flow cytometric analysis of 22 PLGGs detected CD133 (<1.5%) and CD15 (20.7 ± 28.9%) cells, and direct intra-cranial implantation of 25 PLGGs led to the development of 1 PDOX model from a grade II pleomorphic xanthoastrocytoma (PXA). While CSC levels did not correlate with patient tumor progression, neurosphere formation and tumorigenicity, the PDOX model, IC-3635PXA, reproduced key histological features of the original tumor. Similar to the patient tumor that progressed and recurred, IC-3635PXA also progressed during serial subtransplantations (4 passages), exhibiting increased tumor take rate, elevated proliferation, loss of mature glial marker (GFAP), accumulation of GFAP/Vimentin cells, enhanced local invasion, distant perivascular migration, and prominent reactive gliosis in normal mouse brains. Molecularly, xenograft cells with homozygous deletion of shifted from disomy chromosome 9 to trisomy chromosome 9; and V600E mutation allele frequency increased (from 28% in patient tumor to 67% in passage III xenografts). drug screening identified 2/7 V600E inhibitors and 2/9 inhibitors that suppressed cell proliferation. In summary, we showed that PLGG tumorigenicity was low despite the presence of putative CSCs, and our data supported GFAP/Vimentin cells, homozygous deletion in trisomy chromosome 9 cells, and mutation as candidate drivers of tumor progression in the PXA xenografts.