Isolation and characterization of tumorspheres from a recurrent pineoblastoma patient: Feasibility of a patient-derived xenograft

The existence of tumorspheres (TSs) might confer treatment resistance to pineoblastoma (PB). The existence of PB TSs with cellular immortalization potential has not yet been reported. We developed a procedure for isolating TSs from recurrent PB (rPB) and tested whether their properties made them suitable for use as a patient-derived xenograft (PDX). Immunocytochemical staining, RT-PCR and quantitative real-time PCR showed that, among stemness proteins, CD133, musashi and podoplanin were expressed at elevated levels in rPB TSs, but nestin was not. rPB TSs cultured under neuro-glial differentiation conditions expressed TUBB3, but not GFAP, MBP or NeuN. Unlike glioblastoma TSs, rPB TSs showed no clear evidence of invasion in 3D invasion assay or increased expression of genes associated with epithelialmesenchymal transition. An orthotopic xenograft showed that tumor xenografts replicated the histopathological features of the patient tumor and expressed similar genome profiles, as determined by short tandem repeat genotyping. These data demonstrate the isolation and the characterization of rPB TSs for the first time. Using an orthotopic xenograft, we showed that rPB TSs could replicate the patient tumor, demonstrating their potential as a PDX for precision medicine.